ARONEX PHARMACEUTICALS INC
8-K, 1999-06-04
PHARMACEUTICAL PREPARATIONS
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                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                      ------------------------------------


                                    FORM 8-K

             Current Report Filed Pursuant to Section 13 or 15(d) of
                       the Securities Exchange Act of 1934


                                 Date of Report
                 (Date of earliest event reported): May 21, 1999


                          ARONEX PHARMACEUTICALS, INC.
             (Exact name of registrant as specified in its charter)

<TABLE>
<S>                                            <C>                               <C>

               Delaware                                0-20111                                76-0196535
    (State or other jurisdiction of            (Commission File Number)          (I.R.S. Employer Identification No.)
    incorporation or organization)
</TABLE>

                          8707 Technology Forest Place
                         The Woodlands, Texas 77381-1191

                              (Address of principal
                                executive offices
                                  and zip code)

                                 (281) 367-1666

                         (Registrant's telephone number,
                              including area code)

                      ------------------------------------











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<PAGE>



ITEM 5. OTHER EVENTS

         On May 21, 1999, Aronex  Pharmaceuticals,  Inc. (the "Company") entered
into an  Amendment  No. 4 to License  and  Development  Agreement  with  Genzyme
Corporation  ("Genzyme")  to convert a $2.5  million  payment  into a three-year
convertible  note  bearing  interest  at 10%  annum.  The $2.5  million  payment
obligation to Genzyme was triggered on March 29, 1999 when the Company  regained
the worldwide  commercial  rights of  ATRAGEN(R),  an injectable  formulation of
all-trans-retinoic  acid (ATRA or tretinoin),  from Genzyme.  In connection with
the  Amendment,  the Company  entered  into a 10%  Convertible  Note  payable to
Genzyme for $2.5 million.  Genzyme has the right to convert the principal of the
Note into shares of common stock of the Company at a conversion  price of $4.35.
Additionally,  Genzyme was given a Common Stock Purchase Warrant entitling it to
purchase  50,000  shares of the Company's  common stock at an exercise  price of
$4.00 per share over a five-year term.
<TABLE>
<CAPTION>

ITEM 7.  EXHIBITS
<S>     <C>                         <C>

         Exhibit 10.1      --       Amendment No. 4 to License and Development Agreement dated
                                    May 21, 1999 by and between Aronex Pharmaceuticals, Inc. and
                                    Genzyme Corporation.

         Exhibit 10.2      --       10% Convertible Note dated May 21, 1999 by Aronex
                                    Pharmaceuticals, Inc. made payable to Genzyme Corporation for $2.5
                                    million.

         Exhibit 10.3      --       Common Stock Purchase Warrant for 50,000 shares of Common
                                    Stock of Aronex Pharmaceuticals, Inc. issued in the name of
                                    Genzyme Corporation.


</TABLE>






                                       -2-

<PAGE>



                                   SIGNATURES

         Pursuant to the  requirements  of the Securities  Exchange Act of 1934,
the  Registrant  has duly  caused  this report to be signed on its behalf by the
undersigned hereunto duly authorized.


                                         ARONEX PHARMACEUTICALS, INC.

Date: May 27, 1998

                                         By: /s/  Terance A. Murnane
                                             -------------------------
                                                  Ternace A. Murnane
                                                  Controller and Secretary


                                       -3-



                                                               Exhibit 10.1


                                 AMENDMENT NO. 4
                                       TO
                        LICENSE AND DEVELOPMENT AGREEMENT


         This  Amendment  No.  4 to  License  and  Development  Agreement  (this
"Amendment") is made as of the 21st day of May, 1999 (the  "Effective  Date") by
and between Aronex Pharmaceuticals, Inc., a Delaware corporation ("Aronex"), and
Genzyme Corporation, a Massachusetts corporation ("Genzyme").  Capitalized terms
used without  definition in this Amendment shall have the meanings given to such
terms in the Development Agreement (as defined below).

                                    RECITALS

         WHEREAS, Aronex (f/k/a Argus Pharmaceuticals, Inc.) and Genzyme entered
into  a  License  and  Development   Agreement  dated  September  10,  1993  (as
subsequently  amended by amendments dated September 8, 1995,  September 10, 1996
and March 27, 1997, the  "Development  Agreement")  relating to the development,
license,   manufacture,   marketing  and  sale  of  pharmaceutical  compositions
incorporating "AR-623" (also known as "Atragen(TM)");

         WHEREAS, Genzyme has elected to terminate its Option and relinquish its
rights thereunder, effective as of March 24, 1999 (the "Election");

         WHEREAS,  as a result of the  Election by Genzyme,  Aronex is obligated
pursuant to Section 2.4 of the  Development  Agreement to pay Genzyme the sum of
$2,000,000 (the "Repayment  Amount") on or before April 24, 1999, which has been
extended to the  Effective  Date,  plus an  additional  amount of $500,000  (the
"Minimum Royalty Amount") of minimum royalty payments by April 24, 2000; and

         WHEREAS,  Aronex and Genzyme desire to amend the Development  Agreement
(i) to restructure the Repayment  Amount and the Minimum Royalty Amount owing by
Aronex as a result of such Election under Section 2.4 thereof into a convertible
note to be issued to  Genzyme  by  Aronex,  (ii) to issue  Genzyme a warrant  to
purchase 50,000 shares of Aronex Common Stock, and (iii) to provide Genzyme with
registration  rights with  respect to shares it may receive upon  conversion  of
such convertible note as well as shares issuable upon exercise of the warrant;

         NOW,  THEREFORE,  in  consideration  of the  foregoing  and the  mutual
covenants contained herein, Aronex and Genzyme agree as follows:




                                       -4-

<PAGE>



         1.  RESTRUCTURING OF REPAYMENT  AMOUNT AND MINIMUM ROYALTY AMOUNT.
The  parties  agree that the  Repayment  Amount and the Minimum  Royalty  Amount
required  to be paid by Aronex to Genzyme as a result of the  Election  shall be
due and payable  pursuant  to the terms of a  three-year  Convertible  Note from
Aronex in the form of Exhibit 2.4(a) hereto. Such Convertible Note shall provide
for  interest of 10% per annum,  to be payable in  semi-annual  payments and the
principal  amount  thereof  to be due on  the  expiration  of  three  years.  In
addition, part or all of the principal of the Convertible Note may be converted,
at Genzyme's election, into shares of Common Stock of Aronex at a purchase price
of $4.35 per share,  at any time and from time to time,  prior to the  repayment
thereof. As a result, Section 2.4 of the Development Agreement is hereby amended
by adding the following paragraph at the end thereof:

         "Notwithstanding   anything  contained  in  this  Section  2.4  to  the
         contrary,  the obligation of Aronex to pay (i) $2,000,000 within thirty
         days of the Option  Expiration  Date and (ii) $500,000  minimum royalty
         within the first twelve months following the due date of the $2,000,000
         amount,  is hereby canceled and terminated in exchange for the issuance
         by Aronex  and  delivery  to  Genzyme  of (i) a  Convertible  Note (the
         "Convertible  Note") in the principal  amount of $2,500,000 in the form
         attached  hereto as  Exhibit  2.4(a) and (ii) a Common  Stock  Purchase
         Warrant (the  "Warrant") to purchase  50,000 shares of the Common Stock
         of  Aronex,  par value  $.001  per share  (the  "Common  Stock"),  at a
         purchase  price of $4.00  per  share in the  form  attached  hereto  as
         Exhibit 2.4(b)."

         2.       REGISTRATION RIGHTS.

         The following  section shall be added to the  Development  Agreement as
Section 11 thereof:

         "11.     Registration Rights.

          (a)  Shelf Registration.  Within sixty days from the receipt of notice
               from  Genzyme of its  interest to either  exercise the Warrant or
               convert  a portion  of the  principal  amount of the  Convertible
               Note, Aronex shall use its reasonable best efforts to prepare for
               filing  with  the   Securities  and  Exchange   Commission   (the
               "Commission"),  and  cause to be  declared  effective,  a "shelf"
               registration  statement  (the "Shelf  Registration")  pursuant to
               Rule 415  under  the  Securities  Act of 1933,  as  amended  (the
               "Securities Act"),  providing for the sale by the Stockholder (as
               hereafter  defined)  of the  Registrable  Shares (as  hereinafter
               defined).  Aronex  agrees to use its  reasonable  best efforts to
               keep such Shelf Registration  continuously effective for a period
               ending  on the  earliest  of (a)  the  tenth  anniversary  of the
               effective date of such Shelf Registration,  (b) the date on which
               all Registrable Shares covered thereby have been sold thereunder,
               or (c) the date upon  which all  Registrable  Shares  are  freely
               transferable  without  restriction  under the Securities Act. For
               the purpose of this Section 11, "reasonable best efforts"

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<PAGE>


               shall mean the best efforts of Aronex  consistent  with sound and
               reasonable business practices and judgment.  "Registrable Shares"
               means any shares of Common Stock issuable upon  conversion of the
               Convertible  Note,  (ii) any shares of Common Stock issuable upon
               exercise  of the  Warrant,  and (iii) any other  shares of Common
               Stock issued in respect of the shares  referred to in (i) or (ii)
               (because  of  stock  splits,   stock   dividends,   subdivisions,
               combinations,  reclassifications,  recapitalizations,  or similar
               events),  provided,  however, that any such shares shall cease to
               be Registrable Shares when such shares become eligible for resale
               under Rule  144(k) of the  Securities  Act by persons who are not
               affiliates of Aronex or upon (a) any transfer that results in the
               purchaser   of  such  shares   receiving   shares  that  are  not
               "restricted securities" within the meaning of Rule 144 or (b) any
               transfer to a person or entity that,  by virtue of Section  11(g)
               hereof is not  entitled  to the rights set forth in this  Section
               11.  "Stockholder"  means  Genzyme and any persons or entities to
               whom the rights granted under this Section 11 are  transferred in
               accordance with Section 11(g).

     (b)  Registration Procedures.  In connection with Aronex's obligations with
          respect to the Shelf  Registration,  Aronex  shall use its  reasonable
          best efforts to effect the  registration in furtherance of the sale of
          the  Registrable  Shares in  accordance  with the  intended  method or
          methods of distribution  thereof described in the Shelf  Registration.
          In  connection  therewith,   Aronex  shall,  as  promptly  as  may  be
          practicable:

                    (i)  prepare  and file with the  Commission  a  registration
               statement with respect to the Registrable  Shares on any form for
               which  Aronex then  qualifies  or which  counsel for Aronex shall
               deem  appropriate  and  which  form  shall be  available  for the
               disposition  of the  Registrable  Shares in  accordance  with the
               intended method or methods of disposition thereof;

                    (ii) prepare and file with the  Commission  such  amendments
               and supplements to such registration statement and the prospectus
               used in  connection  therewith  as may be  necessary to keep such
               registration   statement  effective  for  the  applicable  period
               specified  in  Section  11(a)  above  or  as  may  be  reasonably
               requested  by  Stockholder  in order to  incorporate  information
               concerning  Stockholder or its intended  method of  distribution,
               and otherwise to comply with the provisions of the Securities Act
               with respect to the disposition of all securities covered by such
               registration statement.

                    (iii) furnish to  Stockholder,  prior to the filing  thereof
               with the Commission,  a copy of such  registration  statement and
               each  amendment  thereof  and  each  supplement,  if any,  to the
               prospectus included therein and Aronex shall use its




                                       -6-

<PAGE>



                  reasonable best efforts to reflect in each such document, when
                  so filed with the Commission, such comments as Stockholder may
                  reasonably propose;

                           (iv)   furnish   to   Stockholder   a  copy  of  such
                  registration statement,  each amendment and supplement thereto
                  (in each case including all exhibits thereto but excluding all
                  documents    incorporated   by   reference    therein   unless
                  specifically so requested by Stockholder)  and such reasonable
                  number  of  copies  of  the   prospectus   included   in  such
                  registration statement (including each preliminary prospectus)
                  as Stockholder may reasonably request;

                           (v)  use  reasonable  best  efforts  to  register  or
                  qualify the  Registrable  Shares  under such other  securities
                  laws or blue sky  laws of such  jurisdictions  as  Stockholder
                  shall reasonably request, and take any and all such actions as
                  may be reasonably necessary or advisable to enable Stockholder
                  to consummate the  disposition in such  jurisdictions  of such
                  Registrable Shares;

                           (vi)   notify   Stockholder,   at  any  time  when  a
                  prospectus  relating thereto is required to be delivered under
                  the  Securities  Act within the period that Aronex is required
                  to keep the registration statement effective, of the happening
                  of any event as a result of which the  prospectus  included in
                  such  registration  statement (as then in effect)  contains an
                  untrue  statement  of a  material  fact or omits to state  any
                  material  fact  required to be stated  therein or necessary to
                  make  the  statements  therein  not  misleading  and  promptly
                  prepare,  file with the Commission  and furnish  Stockholder a
                  reasonable number of copies of a supplement to or an amendment
                  of such  prospectus  as may be necessary so that as thereafter
                  declared to the  purchasers  of such shares,  such  prospectus
                  shall not include an entire  statement  of a material  fact or
                  omit to state any material fact required to be stated  therein
                  or necessary to make the statements therein not misleading.

                           (vii) advise  Stockholder,  promptly after  receiving
                  notice thereof,  of any stop order issued or threatened by the
                  Commission  and use its  reasonable  best  efforts to take all
                  actions  required to prevent the entry of such stop order,  or
                  to remove it if entered; and

                           (viii) use its  reasonable  best efforts to cause all
                  Registrable Shares included in such registration  statement to
                  be listed, by the date of the first sale of Registrable Shares
                  pursuant to such  registration  statement,  on each securities
                  exchange or market on which the Common Stock of Aronex is then
                  listed or proposed to be listed.

                           (ix)  shall  (a)  make   reasonably   available   for
                  inspection by  Stockholder,  and any  attorney,  accountant or
                  other agent retained by Stockholder all relevant financial and
                  other records, pertinent corporate documents and properties of
                  Aronex and (b) cause Aronex's officers, directors,  employees,
                  accountants and auditors to supply all



                                       -7-

<PAGE>



                  relevant  information  reasonably  requested by Stockholder or
                  any such attorney, accountant or agent in connection with such
                  registration  statement,  in each  case  as may be  reasonably
                  necessary  to enable  such  persons  to  conduct a  reasonable
                  investigation   within  the  meaning  of  Section  11  of  the
                  Securities Act.

                           (x) shall use its reasonable best efforts to take all
                  other  steps   necessary   effect  the   registration  of  the
                  Registrable Shares contemplated hereby.

         (c)      Expenses.  All expenses incident to Aronex's performance of or
                  compliance  with the  provisions  of this  Section  11 will be
                  borne by Aronex.  Notwithstanding  the foregoing,  Stockholder
                  shall  pay  any  and  all  underwriting  fees,   discounts  or
                  commissions attributable to the sale of Registrable Shares.

         (d)   Indemnification.

               (i)  Upon the  registration  of  Registrable  Shares  pursuant to
                    Section 11 hereof,  Aronex  shall,  and it hereby agrees to,
                    indemnify and hold harmless, to the extent permitted by law,
                    Stockholder, its officers and directors, each underwriter of
                    such  Registrable  Shares,  if  any,  and  each  person  who
                    controls such person  (within the meaning of the  Securities
                    Act) against all losses,  claims,  damages,  liabilities and
                    expenses (including reasonable attorneys' fees and expenses)
                    to  which  Stockholder,   its  officers,   directors,   each
                    underwriter, or such controlling persons may become subject,
                    insofar as such losses,  claims,  damages,  liabilities  and
                    expenses (or actions in respect thereof) arise out of or are
                    based upon any untrue  statement or alleged untrue statement
                    of  material  fact   contained  in  any  such   registration
                    statement,   any   prospectus  or   preliminary   prospectus
                    contained therein or any amendment or supplement thereto, or
                    any omission or alleged omission to state therein a material
                    fact required to be stated  therein or necessary to make the
                    statements  therein  not  misleading,   and  will  reimburse
                    Stockholder, each such underwriter and each such controlling
                    person for any legal or other expenses  reasonably  incurred
                    by them in connection  with  investigating  or defending any
                    such loss, claim,  damage,  liability or action;  except (A)
                    insofar as the same arise out of or are based upon an untrue
                    statement or omission or alleged omission so made based upon
                    information   furnished  by   Stockholder,   underwriter  or
                    controlling  person in writing  specifically for use in such
                    registration  statement or  prospectus or (B) insofar as the
                    same  are  caused  by  Stockholder's  or such  underwriter's
                    failure to deliver a copy of such registration  statement or
                    prospectus or any  amendments or  supplements  thereto after
                    Aronex has furnished  Stockholder or such underwriter with a
                    sufficient number of copies of the same.


                                       -8-

<PAGE>



               (ii) In connection  with any  registration  statement under which
                    Registrable  Shares are registered  under the Securities Act
                    and   pursuant  to  which   Stockholder   offers  and  sells
                    Registrable Shares,  Stockholder shall, and it hereby agrees
                    to, indemnify and hold harmless,  to the extent permitted by
                    law, each of Aronex,  its officers and  directors,  and each
                    person  who  controls  Aronex  (within  the  meaning  of the
                    Securities  Act) and,  if the  offering  is an  underwritten
                    offering,  the  underwriters,  against all  losses,  claims,
                    damages,  liabilities  and  expenses  (including  reasonable
                    attorneys' fees and expenses) to which Aronex,  its officers
                    and  directors,  underwriters,  or  controlling  persons may
                    become  subject,  insofar as such losses,  claims,  damages,
                    liabilities  and  expenses  (or actions in respect  thereof)
                    arise  out of or are  based  upon any  untrue  statement  or
                    alleged  untrue  statement of material fact contained in any
                    such registration  statement,  any prospectus or preliminary
                    prospectus  contained therein or any amendment or supplement
                    thereto,  or any  omission  or  alleged  omission  to  state
                    therein a material  fact  required  to be stated  therein or
                    necessary to make the statements  therein not misleading and
                    will  reimburse  Aronex  and each  such  officer,  director,
                    underwriter  and  controlling  person for any legal or other
                    expenses  reasonably  incurred  by them in  connection  with
                    investigating  or defending  any such loss,  claim,  damage,
                    liability or action, insofar as (A) the same arise out of or
                    are based upon any untrue  statement  or omission or alleged
                    omission  so  made  based  upon  information   furnished  by
                    Stockholder,  or an  underwriter  or  controlling  person of
                    Stockholder,   in  writing  specifically  for  use  in  such
                    registration  statement  or  prospectus  or (B) the same are
                    caused by  Stockholder's  or such  underwriter's  failure to
                    deliver a copy of such registration  statement or prospectus
                    or any  amendments or  supplements  thereto after Aronex has
                    furnished  Stockholder or such underwriter with a sufficient
                    number of copies of the same and provided, further, that the
                    liability  of  Stockholder  under  this  Section 11 shall be
                    limited to the proportion of any such loss,  claim,  damage,
                    liability or expense which is equal to the  proportion  that
                    the public  offering  price of  Registrable  Shares  sold by
                    Stockholder under such  registration  statement bears to the
                    total  public   offering  price  of  all   securities   sold
                    thereunder,  but not to exceed  the  amount of the  proceeds
                    received  by  Stockholder  from the sale of the  Registrable
                    Shares covered by such registration statement.

               (iii)Any person  entitled to  indemnification  hereunder will (A)
                    give prompt  notice to the  indemnifying  party of any claim
                    with  respect  to which it  seeks  indemnification  (but the
                    failure  to give such  notice  will not  affect the right to
                    indemnification hereunder,  unless the indemnifying party is
                    materially  prejudiced  by such  failure)  and (B) unless in
                    such indemnified  party's reasonable  judgment a conflict of
                    interest may exist between such indemnified and indemnifying
                    parties with respect to such claim, permit such indemnifying
                    party to assume  the  defense  of such  claim  with  counsel
                    selected



                                       -9-

<PAGE>



                    by the indemnifying party and reasonably satisfactory to the
                    indemnified  party.  If such  defense is not  assumed by the
                    indemnifying  party  or if  the  indemnifying  party  is not
                    permitted to assume such  defense  then (x) the  indemnified
                    party shall select counsel, which counsel must be reasonably
                    satisfactory   to  the   indemnifying   party  and  (y)  the
                    indemnifying  party will not be subject to any liability for
                    any settlement  made without its consent (which consent will
                    not be unreasonably  withheld).  No indemnifying  party will
                    consent  to  entry  of  any   judgment  or  enter  into  any
                    settlement which does not include as an  unconditional  term
                    thereof  the giving by the  claimant  or  plaintiff  to such
                    indemnified party of a release from all liability in respect
                    of such claim or litigation.  An  indemnifying  party who is
                    not entitled  to, or elects not to,  assume the defense of a
                    claim will not be  obligated to pay the fees and expenses of
                    more than one counsel for all  parties  indemnified  by such
                    indemnifying party with respect to such claim, unless in the
                    reasonably  judgment of any indemnified  party a conflict of
                    interest may exist  between such  indemnified  party and any
                    other  of such  indemnified  parties  with  respect  to such
                    claim,  in  which  case  the  indemnifying  party  shall  be
                    obligated  to pay the fees and  expenses  of one  additional
                    counsel,   who  must  be  reasonably   satisfactory  to  the
                    indemnifying party.

               (iv) Each  party  hereto  agrees  that,  if for  any  reason  the
                    indemnification  provisions contemplated by Section 11(d)(i)
                    or 11(d)(ii) are  unavailable  or are  insufficient  to hold
                    harmless  an  indemnified  party in respect  of any  losses,
                    claims,  damages,  liabilities  or  expenses  (or actions in
                    respect thereof) referred to therein, then each indemnifying
                    party shall contribute to the amount paid or payable by such
                    indemnified  party  as a  result  of  such  losses,  claims,
                    damages,  liabilities  or  expenses  (or  actions in respect
                    thereof) in such proportion as is appropriate to reflect the
                    relative fault of the indemnifying party and the indemnified
                    party   as   well   as   any   other   relevant    equitable
                    considerations.  The  relative  fault  of such  indemnifying
                    party and indemnified party shall be determined by reference
                    to, among other things, whether the untrue or alleged untrue
                    statement of a material fact or omission or alleged omission
                    to state a material fact relates to information  supplied by
                    such  indemnifying  party  or  indemnified  party,  and  the
                    parties' relative intent,  knowledge,  access to information
                    and  opportunity  to correct or prevent  such  statement  or
                    omission. The parties hereto agree that it would not be just
                    and  equitable  if  contribution  pursuant  to this  Section
                    11(d)(iv) were  determined by pro rata  allocation  (even if
                    Stockholder or any  underwriters or all of them were treated
                    as one entity for such  purpose)  or by any other  method of
                    allocation  which does not take into  account the  equitable
                    considerations  referred to in this  Section  11(d)(iv).  No
                    person  guilty of fraudulent  misrepresentation  (within the
                    meaning of Section 11(f) of the Securities Act)



                                      -10-

<PAGE>



                    shall be  entitled to  contribution  from any person who was
                    not guilty of such fraudulent misrepresentation.

               (v)  The  indemnification  and contribution  obligations and each
                    other provision set forth in this Section 11(d) shall remain
                    in full force and  effect  regardless  of any  investigation
                    made by or on behalf of Aronex, Stockholder,  any officer or
                    employee  of Aronex or  Stockholder,  any  underwriter,  any
                    officer or employee of such underwriter,  or any controlling
                    person  of  any of  the  foregoing  and  shall  survive  the
                    transfer  and   registration   of   Registrable   Shares  by
                    Stockholder.

          (e)  Rule  144  Reporting.   With  a  view  to  making   available  to
               Stockholder   the  benefits  of  Rule  144   promulgated  by  the
               Commission  under the  Securities  Act,  Aronex agrees to use its
               reasonable best efforts to:

               (i)  make and  keep  adequate  current  public  information  with
                    respect to Aronex available, as those terms are used in Rule
                    144 under the Securities Act;

               (ii) file with the  Commission in a timely manner all reports and
                    other documents  required of Aronex under the Securities Act
                    and the  Securities  Exchange  Act of 1934,  as amended (the
                    "Exchange Act"); and

               (iii)furnish  to  Stockholder  promptly  upon  request  a written
                    statement by Aronex as to its compliance  with the reporting
                    requirements of Rule 144 and the Exchange Act, a copy of the
                    most recent annual or quarterly  report of Aronex,  and such
                    other  reports and  documents of Aronex as  Stockholder  may
                    reasonably  request in order to permit  Stockholder to avail
                    itself of any rule or regulation of the Commission  allowing
                    Stockholder   to  sell  its   Registrable   Shares   without
                    registration.

          (f)  Amendments  and Waivers.  Any provision of this Section 11 may be
               amended or waived  if, but only if, in the case of an  amendment,
               such  amendment  is in  writing  and  is  signed  by  Aronex  and
               Stockholder.  No  failure  or delay by Aronex or  Stockholder  in
               exercising any right, power or privilege  hereunder shall operate
               as a waiver  thereof,  nor shall any single or  partial  exercise
               thereof  preclude  any other or further  exercise  thereof or the
               exercise of any other right, power or privilege.

          (g)  Transfers of Certain Rights.

                  (i) The rights  granted to  Stockholder  under this Section 11
may be transferred or succeeded to only by (i) an affiliate of Stockholder, (ii)
a person or entity that acquires substantially all of the assets of Stockholder,
or  (iii)  any  other  person  or  entity  that  acquires  at  least  25% of the
Registrable Shares; provided, however, that Aronex is given written notice prior
to or



                                      -11-

<PAGE>



promptly  following such transfer stating the name and address of the transferee
and  identifying  the  securities  with  respect to which such  rights are being
assigned.  Such notice shall include or be accompanied by a written  undertaking
by the transferee to comply with the obligations  imposed on Stockholders  under
this Section 11.

                  (ii) A transferee to whom rights are  transferred  pursuant to
this  Section  11(g) may not again  transfer  such rights to any other person or
entity, other than as provided in Section 11(g)(i) above."

     3.  NO  OTHER  AMENDMENTS.  Except  as  specifically  amended  hereby,  the
Development Agreement shall continue in full force and effect.

         IN WITNESS  WHEREOF the parties  hereto have executed this Amendment in
one or more copies effective as of the Effective Date.

                                        ARONEX PHARMACEUTICALS, INC.


                                        By:    /s/ Geoffrey F. Cox
                                               ---------------------------------
                                        Name:  Geoffrey F. Cox
                                               ---------------------------------
                                        Title: Chairman of the Board & Chief
                                                 Executive Officer
                                               ---------------------------------

                                        GENZYME CORPORATION

                                        By:    /s/ Richard Douglas
                                               ---------------------------------
                                        Name:  Richard Douglas
                                               ---------------------------------
                                        Title: Senior Vice President,
                                                 Corporate Development
                                               ---------------------------------





                                      -12-




                                                                Exhibit 10.2

No. ___                                                         May 21, 1999


                          ARONEX PHARMACEUTICALS, INC.

                              10% CONVERTIBLE NOTE

                  THE  SECURITIES  REPRESENTED  BY  THIS  INSTRUMENT  HAVE  BEEN
ACQUIRED FOR INVESTMENT AND HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF
1933, AS AMENDED,  OR THE  SECURITIES  LAWS OF ANY STATE OR OTHER  JURISDICTION.
WITHOUT  SUCH   REGISTRATION,   SUCH  SECURITIES  MAY  NOT  BE  SOLD,   PLEDGED,
HYPOTHECATED   OR  OTHERWISE   TRANSFERRED,   EXCEPT  UPON  DELIVERY  TO  ARONEX
PHARMACEUTICALS,   INC.   ("COMPANY")  OF  AN  OPINION  OF  COUNSEL   REASONABLY
SATISFACTORY TO THE COMPANY THAT REGISTRATION IS NOT REQUIRED FOR SUCH TRANSFER,
OR SUBMISSION TO THE COMPANY OF SUCH OTHER  EVIDENCE AS MAY BE  SATISFACTORY  TO
THE COMPANY TO THE EFFECT THAT ANY SUCH  TRANSFER  SHALL NOT BE IN  VIOLATION OF
THE  SECURITIES  ACT OF 1933,  AS AMENDED,  OR ANY  APPLICABLE  STATE OR FOREIGN
SECURITIES LAWS OR ANY RULE OR REGULATION PROMULGATED THEREUNDER.

                  Aronex   Pharmaceuticals,   Inc.,   a   Delaware   corporation
("Company"),  for value received, hereby promises to pay to Genzyme Corporation,
or registered assigns, the principal amount of Two Million Five Hundred Thousand
and No/100 Dollars  ($2,500,000.00) on May 21, 2002, (the "Due Date") except for
any portion of the principal  amount of this Convertible Note which is converted
to shares of Common Stock of the Company  pursuant to the terms of Section 1, at
the office of the Company in The Woodlands,  Texas. Interest shall accrue and be
payable  from  the  date of  issuance  of this  Convertible  Note on the  unpaid
principal   balance  at  a  rate  of  ten  percent  (10%)  per  annum,   payable
semi-annually  on each September 30 and March 30 following the issuance  hereof.
Except as otherwise provided herein, all sums of past-due principal and interest
shall bear  interest at a rate equal to 12% or at the  maximum  rate of interest
permitted  by  applicable  law, if lower.  Payment  shall be made prior to 12:00
noon, Boston, Massachusetts time, on the Due Date. When due, by wire transfer of
immediately  available  funds and  shall be in coin or  currency  of the  United
States of America  which at the time of payment is legal  tender for the payment
of public and private debts.

                  This Convertible Note may not be prepaid by the Company at any
time, in whole or in part.

                  The  following  is a statement of rights of the holder of this
Convertible  Note and the conditions to which this  Convertible Note is subject,
to which the holder hereof, by the acceptance of this Convertible Note, assents:


                                      -13-

<PAGE>



                  2. Optional  Conversion Rights. The holder of this Convertible
Note  shall  have the  right to  convert  at any  time  during  the term of this
Convertible  Note part or all of the  principal  amount  hereof,  together  with
accrued  interest  thereon,  into  shares of Common  Stock of the  Company  (the
"Conversion  Shares")  at a price  per  share  equal to $4.35  (the  "Conversion
Price")  subject  to  adjustment  as  provided  in Section 9. Such right must be
exercised by written  notice  given by the holder to the  Company,  which notice
shall specify that portion of the principal  amount and accrued  interest  which
the holder  elects to  convert  and the name of the person or entity for which a
stock certificate  should be issued.  Any such notice given by a holder shall be
final and  irrevocable,  and  conversion  shall occur at the time such notice is
received by the Company with respect to that  portion of this  Convertible  Note
which the holder has  elected to  convert.  The  Company  shall  deliver a stock
certificate  to the holder  within  five  business  days  following  the date of
conversion  with  respect to that number of  Conversion  Shares of Common  Stock
acquired by the holder pursuant to the terms hereof,  and the Company shall have
no further  obligation to pay any principal amount of or accrued interest on the
portion of this Convertible Note which was so converted by the holder.

                  3. Collection  Fees. In the event of default  hereunder and if
this  Convertible  Note is placed in the hands of any  attorney  for  collection
(whether or not suit is filed), or if this Convertible Note is collected by suit
or legal proceedings or through  bankruptcy  proceedings,  the Company agrees to
pay in addition to all sums then due hereon,  including  principal and interest,
all reasonable attorney's fees.

                  4. Registered  Owner;  Transfer.  The Company and any agent of
the Company may treat the person or entity  identified in the initial  paragraph
of this  Convertible  Note as the  absolute  owner  hereof  for the  purpose  of
receiving payment of, or on account of, the principal or interest due hereon and
for all other  purposes,  and  neither  the  Company nor any such agent shall be
affected  by notice to the  contrary.  Subject  to  compliance  with  applicable
federal and state securities laws, this Convertible Note is transferable only on
the books of the  Company  (at its  offices  or agency to be  maintained  in The
Woodlands, Texas) by the registered holder in person or by attorney on surrender
of this Convertible Note properly endorsed.

                  5. No Recourse Against  Individuals.  This Convertible Note is
the obligation of the Company only, and no recourse shall be had for the payment
hereof or the interest hereon against any incorporator, shareholder, director or
officer  as such  (whether  past,  present  or  future)  of the  Company  or any
successor entity whether by virtue of any  constitution,  statute or rule of law
or equity, or by the enforcement of any assessment of penalty, or otherwise, all
such  liability of the  incorporators,  shareholders,  directors and officers as
such being expressly  waived and released by the holder hereof by the acceptance
of this Convertible Note.

                  6. Amendments and Waivers. The holder of this Convertible Note
may waive or otherwise consent to the amendment of any of the provisions hereof.

                  7. Maximum Rate of Interest. Notwithstanding any provisions to
the  contrary in this  Convertible  Note,  or in any of the  documents  relating
hereto,  in no event shall this Convertible  Note or such documents  require the
payment or permit the collecting of interest in



                                      -14-

<PAGE>



excess of the maximum amount permitted by the laws of the State of Texas. If any
such  excess  interest  is  contracted  for,  charged  or  received  under  this
Convertible Note or under the terms of any of the documents  relating hereto, or
in the event the maturity of the indebtedness evidenced by this Convertible Note
is  accelerated  in whole or in part,  or in the  event  that all or part of the
principal or interest of this Convertible  Note shall be prepaid,  so that under
any of such  circumstances  the amount of interest  contracted  for,  charged or
received  under this  Convertible  Note or under any of the  documents  relating
hereto, on the amount of principal actually  outstanding from time to time under
this Convertible Note, shall exceed the maximum amount of interest  permitted by
the laws of the State of Texas,  then in any such  event (a) the  provisions  of
this paragraph  shall govern and control,  (b) neither the Company nor any other
person or entity  now or  hereafter  liable  for the  payment  hereof,  shall be
obligated to pay the amount of such  interest to the extent that it is in excess
of the maximum  amount of interest  permitted by the laws of the State of Texas,
(c) any such excess which may have been  collected  shall be either applied as a
credit  against  the then  unpaid  principal  amount  hereof or  refunded to the
Company, at the holder's option, and (d) the effective rate of interest shall be
automatically  reduced to the maximum lawful rate of interest  allowed under the
laws of the State of Texas as now or hereafter  construed  by the courts  having
jurisdiction  thereof.  It is further  agreed  that  without  limitation  of the
foregoing,  all calculations of the rate of interest  contracted for, charged or
received under this  Convertible  Note or under such other  documents  which are
made for the purpose of determining whether such rate exceeds the maximum lawful
rate of  interest,  shall be made,  to the extent  permitted  by the laws of the
State of Texas, by amortizing,  prorating,  allocating and spreading  during the
period  of the  full  stated  term of the  indebtedness  evidenced  hereby,  all
interest at any time  contracted  for,  charged or received  from the Company or
otherwise by the holder or holders hereof in connection with such indebtedness.

                  8. Restrictions on Transferability.  This Convertible Note and
the  Conversion  Shares which may be acquired upon  conversion  hereof have been
acquired for investment and have not been registered under the Securities Act of
1933, as amended,  or the  securities  laws of any state or other  jurisdiction.
Without  such   registration,   such  securities  may  not  be  sold,   pledged,
hypothecated or otherwise transferred, except upon delivery to the Company of an
opinion of counsel satisfactory to the Company that registration is not required
for such transfer, or submission to the Company of such other evidence as may be
reasonably  satisfactory  to the  Company to the effect  that any such  transfer
shall not be in  violation of the  Securities  Act of 1933,  as amended,  or any
applicable  state  or  foreign   securities  laws  or  any  rule  or  regulation
promulgated   thereunder.   Notwithstanding   the  above,  the  holder  of  this
Convertible Note has been provided certain  registration  rights with respect to
the Conversion  Shares which may be acquired upon conversion  hereof pursuant to
the Amendment No. 4 to License and  Development  Agreement of even date herewith
between  the  Company  and  such  holder  (the  "Fourth   Amendment  to  License
Agreement").

                  9. Default;  Acceleration.  An Event of Default  exists if the
Company fails to pay interest  within five days following the date due; fails to
pay principal  within three days  following  the date due;  fails to perform any
other  obligations  within  twenty days of notice;  is subject to a voluntary or
involuntary  bankruptcy proceeding and such involuntary proceeding is not stayed
or  dismissed  within sixty days;  if a default by the Company  exists under the
Development   Agreement  between  the  Company  and  Genzyme  Corporation  dated
September 10, 1993, as amended, or the

                                      -15-

<PAGE>



Common Stock  Purchase  Warrant of even date  herewith  issued by the Company to
Genzyme  Corporation  pursuant  to  the  Amendment  No.  4 to  such  Development
Agreement,  which default,  in either case, has not been remedied by the Company
prior to the expiration of any applicable  grace period;  or if the Common Stock
of the  Company is no longer  listed for trading on The Nasdaq  Stock  Market or
other  national  securities  exchange.  In the event of any  default  under this
Convertible  Note by the  Company,  provided  there is no  agreement  for waiver
thereof or the Company has not cured such  default,  then,  at the option of the
holder of the Convertible  Note, the Convertible Note shall thereupon become and
be due and payable, without any other presentment,  demand, protest or notice of
any kind, all of which are hereby expressly waived.

                  10.      Adjustment of Conversion Price.

         (a) The  Conversion  Price and the number of Conversion  Shares and the
number or amount of any other  securities and property as  hereinafter  provided
into  which  this  Convertible  Note  may be  convertible  shall be  subject  to
adjustment  from  time to time  effective  upon  each  occurrence  of any of the
following events.

         (b) If the Company  shall  declare or pay any dividend  with respect to
its Common Stock  payable in shares of Common Stock,  subdivide the  outstanding
Common  Stock  into a greater  number of shares of Common  Stock,  or reduce the
number of shares of Common  Stock  outstanding  (by stock split,  reverse  stock
split,  reclassification  or otherwise  than by  repurchase of its Common Stock)
(any of such events being  hereinafter  called a "Stock Split"),  the Conversion
Price  and  number  of  Conversion  Shares  issuable  upon  conversion  of  this
Convertible  Note shall be  appropriately  adjusted  so as to entitle the holder
hereof  to  receive  upon  conversion  of this  Convertible  Note,  for the same
aggregate  consideration  provided  herein,  the same number of shares of Common
Stock (plus cash in lieu of fractional shares) as the holder would have received
as a result of such Stock Split had such holder  converted this Convertible Note
in full immediately prior to such Stock Split.

         (c) If the Company shall merge or consolidate  with or into one or more
corporations or partnerships and the Company is the sole surviving  corporation,
or the Company shall adopt a plan of recapitalization or reorganization in which
the Common  Stock is exchanged  for or changed  into  another  class of stock or
other security or property of the Company,  the holder of this  Convertible Note
shall, for the same aggregate  consideration  provided herein,  be entitled upon
conversion of this  Convertible  Note to receive in lieu of the number of shares
of  Common  Stock  as  to  which  this   Convertible  Note  would  otherwise  be
convertible, the number of shares of Common Stock or other securities (plus cash
in lieu of  fractional  shares) or property to which such holder would have been
entitled   pursuant  to  the  terms  of  the   agreement   or  plan  of  merger,
consolidation, recapitalization or reorganization had such holder converted this
Convertible  Note in full  immediately  prior  to  such  merger,  consolidation,
recapitalization or reorganization.

         (d) If the Company is merged or  consolidated  with or into one or more
corporations or partnerships under circumstances in which the Company is not the
sole  surviving  corporation,  or if the Company sells or otherwise  disposes of
substantially all its assets, and in connection with any

                                      -16-

<PAGE>



such merger,  consolidation or sale the holders of Common Stock receive stock or
other  securities   convertible  into  equity  of  the  surviving  or  acquiring
corporations  or entities,  or other  securities or property after the effective
date of such merger,  consolidation  or sale,  as the case may be, the holder of
this  Convertible  Note shall,  for the same  aggregate  consideration  provided
herein, be entitled upon conversion of this Convertible Note to receive, in lieu
of the shares of Common Stock as to which this  Convertible Note would otherwise
be convertible,  shares of such stock or other  securities (plus cash in lieu of
fractional shares) or property as the holder of this Convertible Note would have
received  pursuant  to the terms of the merger,  consolidation  or sale had such
holder converted this Convertible Note in full immediately prior to such merger,
consolidation  or sale.  In the  event of any  consolidation,  merger or sale as
described in this Section 9(d),  provision shall be made in connection therewith
for the  surviving  or  acquiring  corporations  or  partnerships  to assume all
obligations and duties of the Company hereunder or to issue a substitute note in
lieu of this  Convertible  Note with all such  changes  and  adjustments  in the
number or kind of shares of stock or securities or property  thereafter  subject
to this  Convertible  Note or in the  Conversion  Price as shall be  required in
connection with this Section 9(d).

         (e) If the  Company,  at any time after the date  hereof and before the
Due Date,  shall issue or sell or fix a record date for the  issuance of rights,
options,  warrants or convertible or  exchangeable  securities to all holders of
Common  Stock  entitling  them to  subscribe  for or purchase  Common  Stock (or
securities  convertible  into  Common  Stock) at a price per share (or  having a
conversion price per share),  that together with the value of any  consideration
paid for any such  rights,  options,  warrants or  convertible  or  exchangeable
securities  (as  determined  in good  faith  by the  Board of  Directors  of the
Company) is less than the fair market value of a share of Common Stock as of the
date of such issuance or sale or on such record date;  then,  immediately  after
the date of such issuance or sale or on such record date,  the holder shall have
the right to receive,  upon the same terms as the holders of Common  Stock,  the
kind and amount of rights,  options,  warrants or  convertible  or  exchangeable
securities  receivable in such  offerings by a holder of the number of shares of
Common Stock that the holder would have been entitled to receive upon conversion
of this  Convertible Note pursuant to Section 1 hereof had such Convertible Note
been  converted  immediately  before  such  issuance or the record date for such
issuance.

         (f) If (other than in  dissolution  or  liquidation)  securities of the
Company  (other than shares of Common Stock or securities  issued  pursuant to a
shareholder rights or similar plan) or assets are issued by way of a dividend on
outstanding  shares of Common Stock, then the Conversion Price shall be adjusted
so that it shall equal the price  determined by multiplying the Conversion Price
by a fraction, the numerator of which shall be the last sale price of the Common
Stock on such record date less the then fair market value as  determined  by the
Board of  Directors  of the company of the portion of the  securities  or assets
distributed  applicable to one share of Common  Stock,  and the  denominator  of
which shall be such last sale price.  Such  adjustment  shall  become  effective
immediately  prior to the opening of business on the day  following  such record
date.

         (g) If the Company  (other than in connection  with a sale described in
Section 9(d)) proposes to liquidate and dissolve,  the Company shall give notice
thereof as provided in Section  10(b) hereof and shall permit the holder of this
Convertible Note to convert any unconverted

                                      -17-

<PAGE>



portion hereof at any time within the 10 day period  following  delivery of such
notice,  if such holder should elect to do so, and  participate as a stockholder
of the Company in connection with such dissolution.

         (h)      Whenever any adjustment is made as provided in any provision
                  of this Section 9:

                           (i) the  Company  shall  compute the  adjustments  in
                  accordance with this Section 9 and shall prepare a certificate
                  signed by an officer of the Company setting forth the adjusted
                  number  of  shares  or  other   securities   or  property  and
                  Conversion  Price,  as  applicable,  and showing in reasonable
                  detail the facts upon which such adjustment is based, and such
                  certificate  shall  forthwith be filed with the Company or its
                  designee; and

                           (ii) a notice  setting  forth the adjusted  number of
                  shares or other  securities  or  property  and the  Conversion
                  Price, as applicable, shall forthwith be required, and as soon
                  as  practicable  after it is  prepared,  such notice  shall be
                  delivered  by the  Company  to the  holder  of  record of this
                  Convertible Note.

         (i) If at any time, as a result of any adjustment made pursuant to this
Section  9, the holder of this  Convertible  Note shall  become  entitled,  upon
exercise  hereof,  to receive any shares other than shares of Common Stock or to
receive any other  securities,  the number of such other shares or securities so
receivable  upon  conversion  of this  Convertible  Note  shall  be  subject  to
adjustment  from time to time in a manner and on terms as nearly  equivalent  as
practicable  to the  provisions  contained in this Section 9 with respect to the
Common Stock.

         10.      Special Agreements of the Company.

         (a) The Company covenants and agrees that it will reserve and set apart
and have at all times a number of shares of authorized but unissued Common Stock
then  deliverable  upon the  conversion  of this  Convertible  Note or any other
rights or privileges  provided for herein sufficient to enable it at any time to
fulfill  all  its  obligations  hereunder;  and if at any  time  the  number  of
authorized but unissued shares of Common Stock shall not be sufficient to effect
the conversion of this  Convertible Note at the Conversion Price then in effect,
the Company will take such corporate action as may, in the reasonable opinion of
its counsel,  be necessary to increase its authorized shares but unissued shares
of  Common  Stock to such  number  of  shares  as shall be  sufficient  for such
purposes.

         (b)      In case the Company proposes

                  (i)    to pay  any  dividend  upon  the  Common  Stock  or
                         make any distribution or offer any subscription or
                         other rights to the holders of Common Stock, or

                  (ii)   to  effect  any  capital  reorganization  or
                         reclassification  of  capital  stock  of the
                         Company,


                                      -18-

<PAGE>




                 (iii)   to effect the consolidation, merger, sale of all or
                         substantially all of the assets, liquidation,
                         dissolution or winding up of the Company,

                 (iv)    to effect a rights offering to its stockholders, or

                  (v)    to   conduct  a   self-tender   offer  or  other
                         repurchase  of  outstanding  shares of Company  Common
                         Stock, other than in connection with  repurchases from
                         employees upon termination of their employment,

then the Company shall cause notice of any such  intended  action to be given to
the holder of this Convertible Note not less than 15 nor more than 60 days prior
to the date on which the transfer  books of the Company  shall close or a record
be taken for such  dividend  or  distribution,  or the date  when  such  capital
reorganization,  reclassification,  consolidation,  merger,  sale,  liquidation,
dissolution or winding up shall be effected, or the date of such other event, as
the case may be.

         11. Notices.  Any notice or other document  required or permitted to be
given or  delivered to the holder of this  Convertible  Note shall be in writing
and sent (a) by telecopy if the sender on the same day sends a  confirming  copy
of such notice by a recognized overnight delivery service (charges prepaid),  or
(b) by  registered  or certified  mail with return  receipt  requested  (postage
prepaid)  or  (c) by a  recognized  overnight  delivery  service  (with  charges
prepaid).

                  (i) if to the Company, at Aronex Pharmaceuticals, Inc., 8707
         Technology Forest Drive, The Woodlands, Texas 77381, Telecopy No.:
         (281) 367-1676, or such other address as it shall have specified to
         the holder of this Convertible Note in writing; or

                  (ii) if to a holder,  at its address set forth below,  or such
         other address as it shall have specified to the Company in writing.

Notices  given under this  Section 11 shall be deemed  given only when  actually
received.

                  12.  Governing Law. This Convertible Note shall be governed by
and  construed in  accordance  with the laws of the State of  Delaware,  without
reference to the conflicts of law principles thereof.




                                      -19-

<PAGE>



                  IN WITNESS  WHEREOF,  the Company has caused this  Convertible
Note to be duly executed as of the 21st day of May, 1999.


                                       ARONEX PHARMACEUTICALS, INC.


                                       By:   /s/ Geoffrey F. Cox
                                             ----------------------------------
                                       Name: Geoffrey F. Cox
                                             ----------------------------------
                                       Title: Chairman of the Board & Chief
                                              Executive Officer
                                             ----------------------------------




                                      -20-



                                                                  Exhibit 10.3

NEITHER THIS WARRANT NOR THE SECURITIES  ISSUABLE UPON EXERCISE HEREOF HAVE BEEN
REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES  ACT"),
OR THE  SECURITIES  LAWS  OF ANY  STATE.  SUCH  SECURITIES  MAY  NOT BE  SOLD OR
OTHERWISE  DISPOSED OF UNLESS  PURSUANT TO A REGISTERED  OFFERING OR BY TRANSFER
EXEMPT  FROM  REGISTRATION   UNDER  THE  SECURITIES  ACT  AND  APPLICABLE  STATE
SECURITIES LAWS.

                          ARONEX PHARMACEUTICALS, INC.

                          Common Stock Purchase Warrant
No. ___                                                          50,000 Shares

         This  certifies  that,  for  value  received,  Genzyme  Corporation  or
registered  assigns  (the  "holder"),  upon due  exercise  of this  Warrant,  is
entitled to purchase from Aronex  Pharmaceuticals,  Inc., a Delaware corporation
(the  "Company"),  at any time on or after May 21, 1999 (the  "Initial  Exercise
Date"),  and before the close of business on May 21,  2004,  or if not a trading
date on the New York  Stock  Exchange,  the next  following  trading  date  (the
"Expiration  Date"),  all or any part of  50,000  fully  paid and  nonassessable
Shares (the "Warrant  Shares") of the Common Stock,  par value $0.001 per share,
of the Company  ("Common  Stock"),  at a purchase  price of $4.00 per share (the
"Purchase  Price"),  both the  Purchase  Price and the number of Warrant  Shares
issuable upon  exercise of this Warrant being subject to possible  adjustment as
provided below.

         This Warrant is hereinafter called the "Warrant." The holder hereof and
all  subsequent  holders of this  Warrant  shall be  entitled  to all rights and
benefits  provided to the holder or holders hereof pursuant to the terms of this
Warrant.

         SECTION 1. EXERCISE OF WARRANT.  (a) The holder of this Warrant may, at
any time on or after the Initial  Exercise Date and on or before the  Expiration
Date,  exercise  this Warrant in whole at any time or in part (but not less than
10,000 Warrant  Shares) from time to time for the purchase of the Warrant Shares
or other  securities  which such holder is then  entitled to purchase  hereunder
("Warrant  Securities") at the Purchase Price (as hereinafter defined). In order
to exercise this Warrant in whole or in part, the holder hereof shall deliver to
the  Company (i) a written  notice of such  holder's  election to exercise  this
Warrant,  which  notice  shall  specify  the  number  of  Warrant  Shares  to be
purchased,  (ii) payment of the aggregate  purchase  price of the Warrant Shares
being  purchased by  certified or bank  cashier's  check,  unless  pursuant to a
Cashless  Exercise as described in subsection (b) below, and (iii) this Warrant.
Upon receipt thereof, the Company shall, as promptly as practicable,  execute or
cause to be executed and deliver to such holder a  certificate  or  certificates
representing  the aggregate  number of Warrant Shares (or if  applicable,  other
Warrant  Securities)   specified  in  said  notice.  The  stock  certificate  or
certificates  so delivered  shall be in the  denomination  of 100 shares each or
such  other  denominations  as may be  specified  in said  notice  and  shall be
registered  in the name of such holder or such other name as shall be designated
in said notice.




                                      -21-

<PAGE>



         No fractional Warrant Shares are to be issued upon the exercise of this
Warrant,  but the Company shall pay a cash adjustment in respect of any fraction
of a share which  would  otherwise  be  issuable in an amount  equal to the same
fraction of the Current  Market Price (as defined  below) of the Common Stock on
the day of exercise,  as reasonably  determined by the Company.  If this Warrant
shall  have been  exercised  only in part,  the  Company  shall,  at the time of
delivery  of said  certificate  or  certificates,  deliver to such  holder a new
Warrant  evidencing the rights of such holder to purchase the remaining  Warrant
Shares called for by this Warrant, which new Warrant shall in all other respects
be identical with this Warrant,  or, at the request of such holder,  appropriate
notation  may be made on this  Warrant  and same  returned to such  holder.  The
Company  shall pay all expenses,  taxes and other charges  payable in connection
with the preparation,  execution and delivery of share  certificates  under this
Section,  except that, if such share certificates are requested to be registered
in a name or names  other  than the name of the  holder of this  Warrant,  funds
sufficient  to pay all stock  transfer  taxes  which  shall be payable  upon the
execution  and delivery of such share  certificates  shall be paid by the holder
hereof at the time of delivering the notice of exercise mentioned above.

         The Company  represents,  warrants  and agrees that all Warrant  Shares
issuable  upon any  exercise of this  Warrant in  accordance  herewith  shall be
validly authorized and issued, fully paid and nonassessable.

         This Warrant  shall not entitle the holder  hereof to any of the rights
of a stockholder of the Company prior to exercise in the manner herein provided.

         (b)  Notwithstanding  anything in subsection  (a) to the contrary,  the
holder of this  Warrant may elect to exercise  this Warrant in part (but not for
less  than  10,000  Warrant  Shares)  or in  whole,  at any time on or after the
Initial  Exercise Date and on or before the Expiration Date, by the surrender of
this Warrant (with the cashless  exercise form at the end hereof duly  executed)
(a  "Cashless  Exercise")  at the  address  set forth in Section 6 hereof.  Such
presentation  and surrender shall be deemed a waiver of the holder's  obligation
to pay the Purchase Price, or the proportionate  part thereof if this Warrant is
exercised  in part.  In the  event of a  Cashless  Exercise,  the  Holder  shall
exchange its Warrant for that number of Warrant Shares or Warrant Securities, as
the case may be, subject to such Cashless Exercise multiplied by a fraction, the
numerator of which shall be the difference between the then Current Market Price
per  share  of the  Common  Stock  and the per  share  Purchase  Price,  and the
denominator  of which shall be the then  Current  Market  Price per share of the
Common Stock. For purposes of any computation  under this  subsection,  the then
Current  Market  Price shall be based on the  trading day prior to the  Cashless
Exercise.  "Current  Market  Price" shall be deemed to be the last sale price of
the  Common  Stock on the  trading  day  prior to such  date or, in case no such
reported  sales take place on such day, the average of the last reported bid and
asked  prices of the Common  Stock on such day, in either case on the  principal
national securities exchange on which the Common Stock is admitted to trading or
listed,  or if not  listed or  admitted  to trading  on any such  exchange,  the
representative closing bid price of the Common Stock as reported by the National
Association of Securities Dealers,  Inc. Automated Quotations System ("NASDAQ"),
or other similar organization if NASDAQ is no longer reporting such information,
or, if the Common Stock is not reported on NASDAQ,  the high per share bid price
for the Common Stock in the over-

                                      -22-
<PAGE>



the-counter  market as  reported  by the  National  Quotation  Bureau or similar
organization,  or if not so available, the fair market value of the Common Stock
as determined in good faith by the Board of Directors.

         SECTION 2. TRANSFER,  DIVISION AND COMBINATION.  The Company shall keep
at its  principal  executive  office a  register  for the  registration  of, and
registration of transfers of, the Warrants.  The name and address of each holder
of one or more Warrants,  each transfer thereof and the name and address of each
transferee of one or more Warrants shall be registered in such  register.  Prior
to due  presentment for  registration of transfer,  the person in whose name any
Warrants shall be registered shall be deemed and treated as the owner and holder
thereof for all purposes  hereof,  and the Company  shall not be affected by any
notice or knowledge to the  contrary.  The Company shall give to any holder of a
Warrant promptly upon request therefor, a complete and correct copy of the names
and addresses of all registered holders of Warrants.

         Subject to the  provisions of Section 3, upon  surrender of any Warrant
at the principal executive office of the Company for registration of transfer or
exchange  (and in the case of a surrender  for  registration  of transfer,  duly
endorsed or accompanied by a written instrument of transfer duly executed by the
registered holder of such Warrant or his attorney duly authorized in writing and
accompanied  by the address for notices of each  transferee  of such  Warrant or
part thereof),  the Company shall execute and deliver, at the Company's expense,
one or more new  Warrants  (as  requested  by the holder  thereof)  in  exchange
therefor,  exercisable  for an aggregate  number of Warrant  Shares equal to the
number of shares for which the surrendered  Warrant is exercisable and issued to
such person or persons as such  holder may  request,  which  Warrant or Warrants
shall in all other respects be identical with this Warrant.

         Upon receipt by the Company of evidence  reasonably  satisfactory to it
of the  ownership  of and the loss,  theft,  destruction  or  mutilation  of any
Warrant,  and (a) in the  case of  loss,  theft  or  destruction,  of  indemnity
reasonably  satisfactory  to it (provided that if the holder of such Warrant is,
or is a nominee for, an original holder,  such person's own unsecured  agreement
of  indemnity  shall  be  deemed  to be  satisfactory),  or (b) in the  case  of
mutilation,  upon  surrender and  cancellation  thereof,  the Company at its own
expense shall execute and deliver,  in lieu thereof,  a new Warrant identical in
all respects to such lost, stolen, destroyed or mutilated Warrant.

         SECTION 3. COMPLIANCE WITH SECURITIES ACT; RESTRICTIONS ON TRANSFER AND
SALE.  (a) Each  certificate  for Warrant  Shares (or other Warrant  Securities)
initially  issued upon the  exercise of this  Warrant and each  certificate  for
Warrant Shares (or other Warrant Securities) issued to subsequent transferees of
any such  certificate  shall (unless  otherwise  permitted by this Section 3) be
stamped or otherwise imprinted with legend in substantially the following form:

         "THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT
         BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED
         (THE "SECURITIES ACT") OR THE SECURITIES LAWS OF ANY STATE.
         SUCH SECURITIES MAY NOT BE SOLD OR OTHERWISE DISPOSED OF
         UNLESS PURSUANT TO A REGISTERED OFFERING OR BY TRANSFER



                                      -23-

<PAGE>



         EXEMPT FROM REGISTRATION UNDER THE SECURITIES ACT AND
         APPLICABLE STATE SECURITIES LAWS."

         (b) The  holder  understands  that  Warrant  Shares  (or other  Warrant
Securities)  which may be acquired by it upon  exercise of this Warrant shall be
entitled to certain  registration  rights provided for in the Amendment No. 4 to
the License and  Development  Agreement  of even date  herewith  relating to the
issuance of this Warrant between the Company and the holder.

         SECTION 4. ADJUSTMENT OF PURCHASE PRICE.

         (a) The Purchase  Price and the number of Warrant Shares and the number
or amount of any other securities and property as hereinafter provided for which
this Warrant may be exercisable shall be subject to adjustment from time to time
effective upon each occurrence of any of the following events.

         (b) If the Company  shall  declare or pay any dividend  with respect to
its Common Stock  payable in shares of Common Stock,  subdivide the  outstanding
Common  Stock  into a greater  number of shares of Common  Stock,  or reduce the
number of shares of Common  Stock  outstanding  (by stock split,  reverse  stock
split,  reclassification  or otherwise  than by  repurchase of its Common Stock)
(any of such events  being  hereinafter  called a "Stock  Split"),  the Purchase
Price and number of Warrant Shares  issuable upon exercise of this Warrant shall
be  appropriately  adjusted so as to entitle the holder  hereof to receive  upon
exercise of this Warrant, for the same aggregate  consideration provided herein,
the same  number  of shares of Common  Stock  (plus  cash in lieu of  fractional
shares) as the holder  would have  received  as a result of such Stock Split had
such  holder  exercised  this  Warrant in full  immediately  prior to such Stock
Split.

         (c) If the Company shall merge or consolidate  with or into one or more
corporations or partnerships and the Company is the sole surviving  corporation,
or the Company shall adopt a plan of recapitalization or reorganization in which
the Common  Stock is exchanged  for or changed  into  another  class of stock or
other security or property of the Company, the holder of this Warrant shall, for
the same aggregate  consideration  provided herein, be entitled upon exercise of
this  Warrant to  receive in lieu of the number of shares of Common  Stock as to
which this  Warrant  would  otherwise  be  exercisable,  the number of shares of
Common Stock or other  securities  (plus cash in lieu of  fractional  shares) or
property to which such holder would have been entitled  pursuant to the terms of
the   agreement   or  plan  of  merger,   consolidation,   recapitalization   or
reorganization  had such holder exercised this Warrant in full immediately prior
to such merger, consolidation, recapitalization or reorganization.

         (d) If the Company is merged or  consolidated  with or into one or more
corporations or partnerships under circumstances in which the Company is not the
sole  surviving  corporation,  or if the Company sells or otherwise  disposes of
substantially  all  its  assets,   and  in  connection  with  any  such  merger,
consolidation  or sale  the  holders  of  Common  Stock  receive  stock or other
securities convertible into equity of the surviving or acquiring corporations or
entities,  or other  securities  or property  after the  effective  date of such
merger, consolidation or sale, as the case may be, the holder



                                      -24-

<PAGE>



of this Warrant shall, for the same aggregate  consideration provided herein, be
entitled  upon  exercise of this  Warrant to  receive,  in lieu of the shares of
Common Stock as to which this Warrant would otherwise be exercisable,  shares of
such  stock or other  securities  (plus  cash in lieu of  fractional  shares) or
property as the holder of this Warrant would have received pursuant to the terms
of the merger,  consolidation  or sale had such holder exercised this Warrant in
full  immediately  prior to such merger,  consolidation or sale. In the event of
any consolidation,  merger or sale as described in this Section 4(d),  provision
shall  be  made  in   connection   therewith  for  the  surviving  or  acquiring
corporations or partnerships to assume all obligations and duties of the Company
hereunder or to issue substitute  warrants in lieu of this Warrant with all such
changes and  adjustments  in the number or kind of shares of stock or securities
or property thereafter subject to this Warrant or in the Purchase Price as shall
be required in connection with this Section 4(d).

         (e) If the  Company,  at any time after the date  hereof and before the
Expiration  Date,  shall issue or sell or fix a record date for the  issuance of
rights,  options,  warrants or  convertible  or  exchangeable  securities to all
holders of Common Stock entitling them to subscribe for or purchase Common Stock
(or securities  convertible into Common Stock) at a price per share (or having a
conversion price per share),  that together with the value of any  consideration
paid for any such  rights,  options,  warrants or  convertible  or  exchangeable
securities  (as  determined  in good  faith  by the  Board of  Directors  of the
Company) is less than the fair market value of a share of Common Stock as of the
date of such issuance or sale or on such record date;  then,  immediately  after
the date of such issuance or sale or on such record date,  the holder shall have
the right to receive,  upon the same terms as the holders of Common  Stock,  the
kind and amount of rights,  options,  warrants or  convertible  or  exchangeable
securities  receivable  in such  offering by a holder of the number of shares of
Common Stock that the holder would have been  entitled to receive upon  exercise
of this Warrant  pursuant to Section 1 hereof had such  Warrant  been  exercised
immediately before such issuance or the record date for such issuance.

         (f) If (other than in  dissolution  or  liquidation)  securities of the
Company  (other than shares of Common Stock or securities  issued  pursuant to a
shareholder rights or similar plan) or assets are issued by way of a dividend on
outstanding shares of Common Stock, then the Purchase Price shall be adjusted so
that it shall equal the price  determined by multiplying the Purchase Price by a
fraction,  the  numerator  of which  shall be the last sale  price of the Common
Stock on such record date less the then fair market value as  determined  by the
Board of  Directors  of the Company of the portion of the  securities  or assets
distributed  applicable to one share of Common  Stock,  and the  denominator  of
which shall be such last sale price.  Such  adjustment  shall  become  effective
immediately  prior to the opening of business on the day  following  such record
date.

         (g) If the Company  (other than in connection  with a sale described in
Section 4(d)) proposes to liquidate and dissolve,  the Company shall give notice
thereof as provided in Section  5(b) hereof and shall  permit the holder of this
Warrant to exercise any unexercised portion hereof at any time within the 10 day
period following  delivery of such notice, if such holder should elect to do so,
and  participate  as a  stockholder  of the  Company  in  connection  with  such
dissolution.

         (h) Whenever any adjustment is made as provided in any provision of
this Section 4:



                                      -25-

<PAGE>



                           (i) the  Company  shall  compute the  adjustments  in
                  accordance with this Section 4 and shall prepare a certificate
                  signed by an officer of the Company setting forth the adjusted
                  number of shares or other  securities or property and Purchase
                  Price,  as  applicable,  and showing in reasonable  detail the
                  facts  upon  which  such   adjustment   is  based,   and  such
                  certificate  shall  forthwith be filed with the Company or its
                  designee; and

                           (ii) a notice  setting  forth the adjusted  number of
                  shares or other securities or property and the Purchase Price,
                  as  applicable,  shall  forthwith be required,  and as soon as
                  practicable  after  it  is  prepared,  such  notice  shall  be
                  delivered  by the  Company  to the  holder  of  record of each
                  Warrant.

         (i) If at any time, as a result of any adjustment made pursuant to this
Section 4, the holder of this  Warrant  shall  become  entitled,  upon  exercise
hereof,  to receive any shares  other than shares of Common  Stock or to receive
any  other  securities,  the  number  of such  other  shares  or  securities  so
receivable  upon exercise of this Warrant  shall be subject to  adjustment  from
time to time in a manner and on terms as nearly equivalent as practicable to the
provisions contained in this Section 4 with respect to the Common Stock.

         SECTION 5.  SPECIAL AGREEMENTS OF THE COMPANY.

         (a) The Company covenants and agrees that it will reserve and set apart
and have at all times a number of shares of authorized but unissued Common Stock
(and,  if  applicable,  other  Warrant  Securities)  then  deliverable  upon the
exercise of the Warrants or any other rights or privileges  provided for therein
sufficient to enable it at any time to fulfill all its  obligations  thereunder;
and if at any time the number of authorized but unissued  shares of Common Stock
shall not be  sufficient  to effect the exercise of this Warrant at the Purchase
Price then in effect, the Company will take such corporate action as may, in the
reasonable  opinion of its counsel,  be  necessary  to increase  its  authorized
shares but unissued  shares of Common Stock (and, if  applicable,  other Warrant
Securities) to such number of shares as shall be sufficient for such purposes.

         (b)      In case the Company proposes

                    (i)       to pay any dividend  upon the Common Stock or make
                              any  distribution  or offer  any  subscription  or
                              other rights to the holders of Common Stock, or


                    (ii)      to   effect   any   capital    reorganization   or
                              reclassification of capital stock of the Company,

                    (iii)     to effect the consolidation,  merger,  sale of all
                              or substantially  all of the assets,  liquidation,
                              dissolution or winding up of the Company,

                    (iv)      to effect a rights  offering to its  stockholders,
                              or



                                      -26-

<PAGE>



                    (v)       to conduct a self-tender offer or other repurchase
                              of  outstanding  shares of Company  Common  Stock,
                              other than in  connection  with  repurchases  from
                              employees upon termination of their employment,

then the Company shall cause notice of any such  intended  action to be given to
each holder of the  Warrants not less than 15 nor more than 60 days prior to the
date on which the transfer books of the Company shall close or a record be taken
for such dividend or distribution, or the date when such capital reorganization,
reclassification,  consolidation,  merger,  sale,  liquidation,  dissolution  or
winding up shall be effected,  or the date of such other event,  as the case may
be.

         Section 6. Notices.  Any notice or other document required or permitted
to be given or  delivered to holders of Warrants and holders of Common Stock (or
other  Warrant  Securities)  shall be in writing and sent (a) by telecopy if the
sender on the same day sends a  confirming  copy of such notice by a  recognized
overnight delivery service (charges prepaid),  or (b) by registered or certified
mail with return  receipt  requested  (postage  prepaid) or (c) by a  recognized
overnight delivery service (with charges prepaid).

          (i)       if to the Company,  at Aronex  Pharmaceuticals,  Inc.,  8707
                    Technology   Forest  Drive,  The  Woodlands,   Texas  77381,
                    Telecopy No.:  (281)  367-1676,  or such other address as it
                    shall have  specified to the holders of Warrants in writing;
                    or

          (ii)      if to a holder,  at its  address  set forth  below,  or such
                    other  address as it shall have  specified to the Company in
                    writing.

Notices  given  under this  Section 6 shall be deemed  given only when  actually
received.

          SECTION 7.  AMENDMENT.  This  Warrant may not be amended,  modified or
otherwise altered in any respect except by the written consent of the registered
holder of this Warrant and the Company.

          SECTION 8. SUCCESSORS AND ASSIGNS.  This Warrant shall be binding upon
and inure to the benefit of the Company and the holder of this Warrant and their
respective successors and permitted assigns.

          SECTION 9.  GOVERNING  LAW.  This  Warrant  shall be  governed  by and
construed  in  accordance  with  the  laws of the  State  of  Delaware,  without
reference to the conflicts of law principles thereof.


                                      -27-

<PAGE>




                  IN WITNESS WHEREOF,  the Company has caused this Warrant to be
signed in its name by its duly authorized officers and accepted by the holder of
this Warrant this 21st day of May, 1999.


Attest:                                             ARONEX PHARMACEUTICALS, INC.

By:   /s/ Terance A. Murnane                          By: /s/ Geoffrey F. Cox
    -------------------------------                      -----------------------
Name:     Terance A. Murnane                        Name: Geoffrey F. Cox
    -------------------------------                      -----------------------
Title:   Secretary                                  Title: Chairman of the Board
    -------------------------------                    & Chief Executive Officer
                                                       -------------------------

Holder:

 /s/ Richard Douglas
- --------------------
Address for Notices:

- --------------------

- --------------------

- --------------------







                                      -28-

<PAGE>



                                  SUBSCRIPTION

                  The   undersigned,   ___________________,   pursuant   to  the
provisions of the foregoing Warrant, hereby agrees to subscribe for and purchase
____________________  shares of the Common Stock,  par value $.001 per share, of
Aronex Pharmaceuticals, Inc. covered by said Warrant, and makes payment therefor
in full at the price per share provided by said Warrant.

Dated:__________________                    Signature:____________________

Signature Guarantee:                        Address:______________________

________________________                    Social Security No. _____________


                                CASHLESS EXERCISE

                  The   undersigned   ___________________,   pursuant   to   the
provisions of the foregoing  Warrant,  hereby elects to exchange its Warrant for
___________________ shares of Common Stock, par value $.001 per share, of Aronex
Pharmaceuticals,  Inc.  pursuant  to the  Cashless  Exercise  provisions  of the
Warrant.

Dated:__________________                      Signature:____________________

Signature Guarantee:                          Address:______________________


________________________                      Social Security No.:_____________


                                   ASSIGNMENT

                  FOR VALUE RECEIVED  _______________  hereby sells, assigns and
transfers unto ____________________ (SS#_________________) the foregoing Warrant
and all rights evidenced  thereby,  and does irrevocably  constitute and appoint
_____________________, attorney, to transfer said Warrant on the books of Aronex
Pharmaceuticals, Inc.


Dated:__________________                         Signature:____________________

Signature Guarantee:                             Address:______________________


________________________




                                      -29-

<PAGE>


                               PARTIAL ASSIGNMENT

                  FOR  VALUE   RECEIVED   _______________   hereby  assigns  and
transfers unto ____________________  (SS#________________) the right to purchase
_______  shares of the  Common  Stock,  par value  $.001  per  share,  of Aronex
Pharmaceuticals, Inc. covered by the foregoing Warrant, and a proportionate part
of  said  Warrant  and  the  rights  evidenced  thereby,  and  does  irrevocably
constitute and appoint ____________________,  attorney, to transfer that part of
said Warrant on the books of Aronex Pharmaceuticals, Inc.

Dated:_______________                             Signature:____________________

Signature Guarantee:                              Address:______________________


_____________________






                                      -30-



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