Document:

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                                                                     Exhibit 4.2

                             SUBSCRIPTION AGREEMENT

         This Subscription Agreement is made this 1st day of December, 1999,
by and between SUPERGEN, INC., a Delaware corporation ("SuperGen"), and AVI
BIOPHARMA, INC., an Oregon corporation ("AVI"), in connection with the
subscription by SuperGen for 1,000,000 shares of the common stock of AVI (the
"AVI Securities"), par value .0001, for a price of Five Dollars ($5.00) per
share.

         1.       SUBSCRIPTION.  SuperGen subscribes for the AVI Securities.

                  1.1 CASH CONSIDERATION. At closing, SuperGen shall pay to
AVI the amount of Two Million Five Hundred Dollars ($2,500,000) in
immediately available funds.

                  1.2 STOCK CONSIDERATION. At closing, SuperGen shall deliver
to AVI 100,000 shares of the common stock of SuperGen, .001 par value,
registered in the name of AVI (the "SuperGen Securities"), which shares shall
be deemed to have a value of Two Million Five Hundred Thousand Dollars
($2,500,000).

         2.       REPRESENTATIONS OF SUPERGEN.

                  2.1 INVESTMENT INTENT. SuperGen represents and warrants to AVI
that SuperGen is purchasing the AVI Securities for SuperGen's own account and
investment and not with a view to, or for sale in connection with, any
distribution, and that SuperGen can withstand the loss of SuperGen's entire
investment and has no need for liquidity in the investment the Securities
represent.

                  2.2 QUALIFIED INVESTOR. SuperGen warrants and represents to
AVI that SuperGen is an accredited investor within the meaning of Regulation
501, as promulgated under the Securities Act of 1933, as amended, and warrants
that all information there presented is materially accurate.

                  2.3 INVESTMENT EXPERIENCE. SuperGen is experienced in
evaluating and investing in companies in the development stage, and has such
knowledge and experience in financial or business matters that it is capable of
evaluating the merits and risks of the investment in the AVI Securities.

                  2.4 AUTHORIZATION. The execution, delivery and performance of
this Agreement by SuperGen does not (i) require the consent, approval or
authorization of any governmental or regulatory authority having jurisdiction
and (ii) will not violate any applicable law, judgment, order, injunction,
decree, rule, regulation or ruling of any governmental authority applicable to
SuperGen.

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                  2.5 AUTHORITY TO EXECUTE AGREEMENT. SuperGen has full power
and authority and legal right to make this Agreement and to incur and perform
its obligations hereunder and the performance by SuperGen of this Agreement has
been duly authorized by all necessary action of SuperGen.

                  2.6 ACCESS TO INFORMATION. SuperGen represents and warrants
that SuperGen and its Board of Directors has received copies of AVI's filings
under the Securities and Exchange Act of 1934, as amended, including, without
limitation, the risk factors they contain; SuperGen further understands that
forward-looking statements in such filings are not warranted and must be
regarded as highly speculative and uncertain. SuperGen has had such opportunity
to ask questions and to examine the operations of AVI as SuperGen wishes, and
has availed themselves of such opportunity as SuperGen deems appropriate.

                  2.7 RESTRICTED SECURITIES, LEGEND. SuperGen understands that
the AVI Securities have not been registered under the Securities Act of 1933, as
amended, in reliance upon an exemption from registration. Such exemption depends
upon, among other things, the bona fide nature of SuperGen's investment intent
stated in this Subscription Agreement. SuperGen understands that the AVI
Securities must be held indefinitely, unless the Securities subsequently are
registered under the Securities Act of 1933 or unless an exemption from
registration is otherwise available. SuperGen understands that AVI is not
obligated to register the Securities, except as hereafter provided. SuperGen
agrees that the AVI Securities may not be offered, sold, transferred, pledged,
or otherwise disposed of in the absence of an effective registration statement
under the Securities Act of 1933 and applicable state securities laws or an
opinion of counsel acceptable to AVI that such registration is not required.
SuperGen understands that the documentation representing the Securities will be
imprinted with substantially the following legend:

         THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED
         UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE "ACT"), OR APPLICABLE
         STATE SECURITIES LAWS. THE SHARES HAVE BEEN ACQUIRED WITHOUT A VIEW TO
         DISTRIBUTION AND MAY NOT BE OFFERED, SOLD, TRANSFERRED, PLEDGED OR
         HYPOTHECATED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT FOR
         THE SHARES UNDER THE ACT AND UNDER ANY APPLICABLE SECURITIES LAWS, OR
         AN OPINION OF COUNSEL FOR THE HOLDER (CONCURRED IN BY LEGAL COUNSEL FOR
         THE CORPORATION) THAT SUCH REGISTRATION IS NOT REQUIRED AS TO SUCH
         OFFER OR SALE. THE STOCK TRANSFER AGENT HAS BEEN ORDERED TO EFFECTUATE
         TRANSFERS OF THIS CERTIFICATE ONLY IN ACCORDANCE WITH THE ABOVE
         INSTRUCTION.

         3.       REPRESENTATIONS OF AVI.

                  3.1 INVESTMENT INTENT. AVI represents and warrants to SuperGen
that AVI is purchasing the SuperGen Securities for AVI's own account and
investment and not with a view

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to, or for sale in connection with, any distribution, and that AVI can withstand
the loss of AVI's entire investment and has no need for liquidity in the
investment the Securities represent.

                  3.2 QUALIFIED INVESTOR. AVI warrants and represents to
SuperGen that AVI is an accredited investor within the meaning of Regulation
501, as promulgated under the Securities Act of 1933, as amended, and warrants
that all information there presented is materially accurate.

                  3.3 INVESTMENT EXPERIENCE. AVI is experienced in evaluating
and investing in companies in the development stage, and has such knowledge and
experience in financial or business matters that it is capable of evaluating the
merits and risks of the investment in the SuperGen Securities.

                  3.4 AUTHORIZATION. The execution, delivery and performance of
this Agreement by AVI does not (i) require the consent, approval or
authorization of any governmental or regulatory authority having jurisdiction
and (ii) will not violate any applicable law, judgment, order, injunction,
decree, rule, regulation or ruling of any governmental authority applicable to
AVI.

                  3.5 AUTHORITY TO EXECUTE AGREEMENT. AVI has full power and
authority and legal right to make this Agreement and to incur and perform its
obligations hereunder and the performance by AVI of this Agreement has been duly
authorized by all necessary action of AVI.

                  3.6 ACCESS TO INFORMATION. AVI represents and warrants that
AVI and its Board of Directors has received copies of SuperGen's filings under
the Securities and Exchange Act of 1934, as amended, including, without
limitation, the risk factors they contain; AVI further understands that
forward-looking statements in such filings are not warranted and must be
regarded as highly speculative and uncertain. AVI has had such opportunity to
ask questions and to examine the operations of SuperGen as AVI wishes, and has
availed themselves of such opportunity as AVI deems appropriate.

                  3.7 RESTRICTED SECURITIES, LEGEND. AVI understands that the
SuperGen Securities have not been registered under the Securities Act of 1933,
as amended, in reliance upon an exemption from registration. Such exemption
depends upon, among other things, the bona fide nature of AVI's investment
intent stated in this Subscription Agreement. AVI understands that the SuperGen
Securities must be held indefinitely, unless the Securities subsequently are
registered under the Securities Act of 1933 or unless an exemption from
registration is otherwise available. AVI understands that SuperGen is not
obligated to register the Securities, except as hereafter provided. AVI agrees
that the SuperGen Securities may not be offered, sold, transferred, pledged, or
otherwise disposed of in the absence of an effective registration statement
under the Securities Act of 1933 and applicable state securities laws or an
opinion of counsel acceptable to SuperGen that such registration is not
required. SuperGen understands that the documentation representing the
Securities will be imprinted with substantially the following legend:

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         THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED
         UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE "ACT"), OR APPLICABLE
         STATE SECURITIES LAWS. THE SHARES HAVE BEEN ACQUIRED WITHOUT A VIEW TO
         DISTRIBUTION AND MAY NOT BE OFFERED, SOLD, TRANSFERRED, PLEDGED OR
         HYPOTHECATED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT FOR
         THE SHARES UNDER THE ACT AND UNDER ANY APPLICABLE SECURITIES LAWS, OR
         AN OPINION OF COUNSEL FOR THE HOLDER (CONCURRED IN BY LEGAL COUNSEL FOR
         THE CORPORATION) THAT SUCH REGISTRATION IS NOT REQUIRED AS TO SUCH
         OFFER OR SALE. THE STOCK TRANSFER AGENT HAS BEEN ORDERED TO EFFECTUATE
         TRANSFERS OF THIS CERTIFICATE ONLY IN ACCORDANCE WITH THE ABOVE
         INSTRUCTION.

         4. CLOSING. The closing of the transaction contemplated hereunder shall
take place at a place and time mutually agreed by SuperGen and AVI not more than
fifteen (15) days after the date hereof.

         5. EXCLUSIVE RIGHT TO NEGOTIATE. SuperGen and AVI presently are
negotiating the terms and conditions of a definitive agreement wherein SuperGen
shall enjoy the rights to market and sell AVICINE, AVI's anti-cancer therapeutic
vaccine. For and in consideration of this Subscription, SuperGen and AVI agree
that between the date of this Subscription Agreement and the earlier of (a)
termination of negotiations with respect to the Definitive Agreement by mutual
agreement of SuperGen and AVI, or (b) February 28, 2000, AVI shall not, and
shall use its best efforts to insure that its directors, officers and advisors
do not, directly or indirectly, institute, pursue or enter into any discussions,
negotiations, or agreements (whether preliminary or definitive) with any person
or entity other than SuperGen contemplating or providing for the marketing and
sale of AVICINE by any party other than SuperGen. In addition, AVI shall suspend
and not resume during such time period any discussions or negotiations described
above which were initiated prior to the execution of this Subscription
Agreement. AVI further agrees that any definitive agreement entered into between
SuperGen and AVI to market and sell AVICINE, contemplated by this section, shall
include provisions, mutually agreed by the parties, whereby SuperGen shall enjoy
a first option on AVI's portfolio of anti-cancer therapeutic products.

         6.       REGISTRATION RIGHTS.

                  6.1 REGISTRATION OF AVI SECURITIES. At the closing, AVI shall
enter into a Registration Rights Agreement with SuperGen providing Super Gen
"piggyback" registration rights with respect to the AVI Securities but providing
further for the registration of the AVI Securities not later than ninety (90)
days after the closing date hereof.

                  6.2 REGISTRATION OF SUPERGEN. At the closing, SuperGen shall
enter into a Registration Rights agreement with AVI providing AVI "piggyback"
registration rights with

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respect to the SuperGen Securities but providing further for the registration of
the SuperGen Securities not later than ninety (90) days after the closing date
hereof.

      7.       OTHER MATTERS.

                  7.1 SEVERABILITY. Each clause of this agreement is severable.
If any clause is ruled void or unenforceable, the balance of the agreement shall
nonetheless remain in effect.

                  7.2 NON-WAIVER. A waiver of one or more breaches of any clause
of this agreement shall not act to waive any other breach, whether of the same
or different clauses.

                  7.3 GOVERNING LAW, JURISDICTION. This agreement is governed by
the laws of the state of Oregon, and is enforceable only in the state or federal
courts located in Oregon, in which both parties consent to jurisdiction.

                  7.4 ATTORNEYS' FEES. The prevailing party in any suit, action,
arbitration, or appeal filed or held concerning this agreement shall be entitled
to reasonable attorneys' fees.

                  7.5 AMENDMENTS. This agreement may be modified only in writing
signed by the original parties hereto, their successors, or by their authorized
representatives.

         IN WITNESS WHEREOF, the parties have heretofore signed this
Subscription Agreement.

SUPERGEN, INC., a Delaware corporation            AVI BIOPHARMA, INC. an Oregon
                                                  corporation

By: /s/ Joseph Rubinfeld                          By: /s/ Alan Timmins
    --------------------                              ----------------

Title: Chief Executive Officer & President        Title: Chief Operating Officer
                                                  & Chief Financial Officer

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                      AMENDMENT 1 TO SUBSCRIPTION AGREEMENT

This amendment to Section 1 of the Subscription agreement is an addition to the
terms previously agreed to.

1.3      RE-EXCHANGE OF CASH CONSIDERATION. SuperGen and AVI each have the
         right, but not the obligation, to demand a re-exchange of AVI's 500,000
         shares and SuperGen's $2.5 million in cash if an arrangement, under the
         general terms of the Letter of Intent between the two companies, is not
         agreed to by the date contemplated therein. This right shall last for
         30 days from the termination date of the Letter of Intent and will be
         completed within 180 days of such date.

IN WITNESS WHEREOF, the parties have heretofore signed this Amendment.

AVI BIOPHARMA, INC., an Oregon corporation

By:      /s/ Alan Timmins
         ----------------

Title:   Chief Operating Officer & Chief Financial Officer

SUPERGEN, INC., a Delaware corporation

By:      /s/ Joseph Rubinfeld
         --------------------

Title:   Chief Executive Officer & President

<PAGE>

                       AMENDMENT TO SUBSCRIPTION AGREEMENT
         This Amendment (the "AMENDMENT") is made as of December 15, 1999 by and
between SuperGen, Inc., a Delaware corporation ("SUPERGEN") and AVI BioPharma,
Inc., an Oregon corporation ("AVI").

                                   BACKGROUND
         A. SuperGen and AVI entered into a Subscription Agreement dated as of
December 1, 1999 (the "SUBSCRIPTION AGREEMENT") providing for SuperGen to pay
AVI $2.5 million in cash (the "CASH CONSIDERATION") and issue to AVI 100,000
shares of SuperGen common stock in exchange for 1,000,000 shares of AVI common
stock and the exclusive right from the date of the Subscription Agreement until
February 28, 2000 to negotiate an agreement for SuperGen to market and sell
Avicine and have a right of first option with respect to AVI's portfolio of
anti-cancer therapeutic compounds.
         B. Pursuant to Section 7.5 of the Subscription Agreement, SuperGen and
AVI previously amended the Subscription Agreement and desire to further amend
the Subscription Agreement to clarify the conditions under which there may be a
redemption of 500,000 shares of AVI common stock. Unless defined in this
Amendment, all capitalized terms shall have the meanings set forth in the
Subscription Agreement.
         NOW, THEREFORE, SuperGen and AVI agree as follows:
         Section 1.3 of the Agreement shall be deleted and replaced in its
entirety by the following:
         1.3 REDEMPTION. In the event that by February 28, 2000 (the "EXPIRATION
DATE") SuperGen and AVI have not entered into a definitive agreement for
SuperGen to market and sell Avicine and for SuperGen to have a right of first
option with respect to AVI's portfolio of anti-cancer therapeutic compounds, all
on substantially the terms as set forth in the letter of intent attached to this
Amendment, SuperGen and AVI shall each have the right, but not the obligation,
to request in writing a redemption of 500,000 shares of AVI common stock in
exchange for return to SuperGen of the Cash Consideration (the "REDEMPTION").
                  (a) NOTICE PERIOD. For a period of 30 calendar days following
the Expiration Date (the "NOTICE PERIOD"), SuperGen and AVI may each deliver
written notice to the other of their desire to cause the Redemption.
                  (b) EXCHANGE DATE. The Redemption shall occur on a date (the
"REDEMPTION DATE") no later than 180 calendar days after the Expiration Date.
                  (c) DELIVERY. AVI shall deliver to SuperGen the full amount of
the Cash Consideration, along with any interest earned thereon, and SuperGen
shall deliver 500,000 shares of AVI common stock on the Redemption Date.
                  (d) SECURITY. To ensure AVI's obligations under this Section
1.3, AVI shall establish an account for the receipt of the Cash Consideration.
The account will be owned by AVI and will require the signature of an officer of
AVI and an officer of SuperGen before any funds can be disbursed from this
account. Once established, there will be no changes of any nature whatsoever to
the account without the written consent of an officer from both SuperGen and
AVI. SuperGen agrees to terminate this security arrangement promptly after the
earlier of (i) the expiration of the Notice Period (if a Redemption was not
requested) or (ii) AVI's full performance of its obligations under the
Redemption provisions of Section 1.3.

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         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed as of the day and year first above written.

                                    SUPERGEN, INC.

                                    By: /s/ Joseph Rubinfeld
                                        --------------------
                                         Joseph Rubinfeld
                                         Chief Executive Officer and President

                                    AVI BIOPHARMA, INC.

                                    By: /s/ Alan P. Timmins
                                        -------------------
                                         Alan P. Timmins
                                         Chief Operating Officer and
                                         Chief Financial Officer<PAGE>

                                                  CONFIDENTIAL TREATMENT REQUEST

                                                                     EXHIBIT 4.3

* Portions denoted with an asterisk have been omitted and filed separately with
the Securities and Exchange Commission pursuant to a request for confidential
treatment.

                        RESEARCH AGREEMENT (CAMPTOTHECIN)

         This Research Agreement (the "Agreement"), effective as of the 15th day
of November, 1999 (the "Effective Date"), is between CLAYTON FOUNDATION FOR
RESEARCH, a Texas nonprofit corporation having its office at One Riverway, Suite
1560, Houston, Texas 77056 ("Clayton"); RESEARCH DEVELOPMENT FOUNDATION, a
Nevada nonprofit corporation having its office at 402 North Division Street,
Carson City, Nevada 89703 ("RDF"); and SUPERGEN, INC., a Delaware corporation
having an office at Two Annabel Lane, Suite 220, San Ramon, California 94583
("Company").

                                   WITNESSETH:

         WHEREAS, Clayton is a nonprofit organization exempt from taxation under
Section 501(c)(3) of the Internal Revenue Code of 1986, as amended (the "Code");

         WHEREAS, RDF is a nonprofit organization exempt from taxation under
Section 501(c)(3) of the Code that is assigned title to inventions, discoveries
and know-how arising out of Clayton's research for patenting and licensing;

         WHEREAS, Company is interested in research in the field described in
Exhibit A hereto (the "Field of Interest");

         WHEREAS, Clayton has ongoing research involving cancer therapy wherein
camptothecin and analogues thereof, including, but not limited to,
9-nitro-camptothecin and analogues thereof, are delivered in liposomes to the
respiratory tract via aqueous aerosol droplets, at Baylor College of Medicine
("Institution") under the direction of Vernon Knight, M.D. ("Scientist"), at
least some of which is directed to the Field of Interest;

         WHEREAS, Company will provide funding to Clayton for its use in the
conduct of further research at Institution under the direction of Scientist, all
as described herein;

                                      -1-

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                                                  CONFIDENTIAL TREATMENT REQUEST

         WHEREAS, Clayton will assign to RDF any inventions, discoveries and
know-how arising out of such research; and

         WHEREAS, RDF will, subject to the terms and conditions hereof, grant to
Company an exclusive license to any inventions or discoveries arising out of the
research funded hereunder;

         NOW THEREFORE, in consideration of the above premises and the mutual
covenants and agreements herein, the parties agree as follows:

         1. SUPPLY OF RESEARCH MATERIAL. Company will provide to Scientist at no
cost such quantities of 9-nitro-camptothecin (GMP grade) (hereafter "9-NC") as
Clayton and Scientist will need to conduct the research contemplated hereunder.
Clayton, through Scientist, will notify Company reasonably in advance of its
needs for and quantities of 9-NC required. In the event that Company cannot or
does not provide Clayton with the required quantities of 9-NC, Clayton may
purchase such quantities, and Company will promptly reimburse Clayton for the
cost thereof by cash payment. Such cost shall not reduce the amounts that
Company agrees to pay Clayton otherwise pursuant to this Agreement.

         2. RESEARCH. Clayton will conduct research at Institution under the
direction of Scientist in accordance with the work plan set forth in Exhibit B
hereto. Such work plan may be modified or changed from time to time by written
agreement of Clayton and Company.

         3. FUNDING. Company will provide funding to be used for the performance
of this research as set forth in Exhibit C hereto.

         4. REPORTING. Clayton will keep Company informed of the progress of the
research conducted hereunder. Clayton agrees to make periodic informal verbal
reports to a designated representative or representatives of Company, to respond
to reasonable inquiries of Company regarding the status of the research, to
promptly disclose to Company the existence of any discoveries or inventions
which are made in the conduct of the research hereunder, and to provide to
Company a detailed written report to be prepared annually or at the conclusion
of the research.

         5. INVENTIONS/PATENTS. Any discoveries or inventions which are
conceived or reduced to practice during the term of this Agreement and which
directly result from the performance of the research hereunder, as well as any
patent applications and patents therefor, shall be owned by RDF but shall be
subject to Company's license as set forth below. RDF shall have the right in the
first instance to elect to prepare, file, prosecute and maintain patent
applications for such inventions and, if it declines to do so, Company shall
have the right to do so. Neither Company nor RDF

                                      -2-

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                                                  CONFIDENTIAL TREATMENT REQUEST

will forego or abandon such patenting efforts without first notifying the other
party of its intent and allowing such other party the opportunity to pursue
patenting at the latter's sole expense and responsibility.

         6.       a. LICENSE. Any discoveries or inventions hereunder shall be
deemed to be "Proprietary Property" as defined in the License Agreement
(Camptothecin) of November 15, 1999, between RDF and Company (the "License
Agreement"), which License Agreement is incorporated herein by reference for all
purposes. Thus such discoveries and inventions automatically shall be licensed
exclusively to Company in the Field of Use as defined in the License Agreement
under the terms and conditions set forth therein. At the appropriate time, the
parties agree to amend Exhibit 1 of the License Agreement to include discoveries
and inventions hereunder as Proprietary Property for purposes of the License
Agreement.

                  b. ANALOGUE RESEARCH; ELECTION. While all analogues of
camptothecin are included in the Field of Use granted to Company pursuant to the
License Agreement, the Work Plan (Exhibit B) contemplates that the research
pursuant to this Agreement will be limited to the 9-NC analogue of camptothecin.
Clayton, at its sole expense, may conduct research on camptothecin analogues
other than 9-NC (hereafter "Other Analogue(s)") either during or after the term
of this Agreement. If comparative xenograft model studies of any Other
Analogue(s) demonstrate equivalency to 9-NC, Clayton or RDF may so notify
Company in writing. Within thirty (30) days from the date of such notice,
Company shall inform Clayton or RDF in writing whether it elects to enter into a
research agreement with Clayton and fund research with respect to the Other
Analogue(s) that are the subject of Clayton's or RDF's notice to Company. Absent
such a timely election by Company, the Other Analogue(s) subject of Clayton's or
RDF's notice to Company shall thereafter be deemed excluded from the Field of
Use of Exhibit 1A of the License Agreement. In the event that Company elects to
fund research with respect to the Other Analogue(s) that are subject of
Clayton's or RDF's notice to Company, the parties shall in good faith negotiate
a research agreement with mutually agreeable terms, and Company will pay to
Clayton (i) the amount that Company and Clayton agree upon for conduct of the
research, and (ii) a sum to reimburse Clayton for its research costs with
respect to each of the Other Analogue(s) up to the date of Company's written
election, said sum to be calculated as follows:

                           i.       [  *  ]; and

                           ii.      [  *  ].

                                      -3-

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                                                  CONFIDENTIAL TREATMENT REQUEST

         7. TERM; TERMINATION OF AGREEMENT. Anything herein to the contrary
notwithstanding, this Agreement and the transactions contemplated by this
Agreement shall terminate on November 15, 2001; provided that the term hereof
may be extended by mutual consent in writing of Clayton and Company; and
provided further that this Agreement may otherwise be terminated at any time as
follows:

                  a. MUTUAL CONSENT.  By mutual consent in writing of Clayton
and Company.

                  b. COMPANY'S FAILURE TO MEET ITS OBLIGATIONS HEREUNDER. By
Clayton by written notice to Company if Company fails to carry out its
obligations under the terms of this Agreement or under the terms of other legal
agreements between Company and either RDF or Clayton, and does not cure any such
failure within thirty (30) days after notice thereof from Clayton.

                  c. RDF OR CLAYTON'S FAILURE TO MEET OBLIGATIONS HEREUNDER. By
Company by written notice to RDF if RDF or Clayton fail to carry out their
obligations under the terms of this Agreement and do not cure any such failure
within thirty (30) days after notice thereof from Company.

          8. EFFECT OF TERMINATION. In the event that this Agreement shall be
terminated, all further obligations of the parties under this Agreement shall
terminate without further liability of any party to another; provided, however,
that the confidentiality obligations of the parties contained in Section 17
hereof, Company's license under discoveries and inventions prior to termination
pursuant to Section 6 a., and the analogue research and election pursuant to
Section 6 b., shall survive any such termination. Notwithstanding the foregoing,
a termination shall not relieve any party of any liability for a breach of, or
for any misrepresentation under, this Agreement or be deemed to constitute a
waiver of any available remedy (including specific performance if available) for
any such breach or misrepresentation.

         9. AMENDMENTS; WAIVERS. This Agreement and any schedule or exhibit
attached hereto may be amended only by agreement in writing of all parties. No
waiver of any provision nor consent to any exception to the terms of this
Agreement or any agreement contemplated hereby shall be effective unless in
writing and signed by the party to be bound and then only to the specific
purpose, extent and instance so provided.

         10. SCHEDULES; EXHIBITS; INTEGRATION. Each schedule and exhibit
delivered pursuant to the terms of this Agreement shall be in writing and shall
constitute a part of this Agreement, although schedules need not be attached to
each copy of this Agreement. This Agreement, together with such schedules and
exhibits, and the

                                      -4-

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                                                  CONFIDENTIAL TREATMENT REQUEST

License Agreement constitute the entire agreement among the parties pertaining
to the subject matter hereof and supersede all prior agreements and
understandings of the parties in connection therewith.

         11. BEST EFFORTS; FURTHER ASSURANCES. Each party shall use its best
efforts to cause all conditions to its and the other parties' obligations
hereunder to be timely satisfied and to perform and fulfill all obligations on
its part to be performed and fulfilled under this Agreement, to the end that the
transactions contemplated by this Agreement shall be effected substantially in
accordance with its terms as soon as reasonably practicable. The parties shall
cooperate with each other in such actions.

         12. GOVERNING LAW. Except as otherwise expressly provided, this
Agreement and the legal relations between the parties shall be governed by and
construed in accordance with the laws of the State of Nevada applicable to
contracts made and performed in such State and without regard to conflicts of
law doctrines, and jurisdiction and venue for any dispute regarding this
Agreement will be in such State.

         13. NO ASSIGNMENT. Neither this Agreement nor any rights or obligations
under it are assignable without the prior written consent of the other parties
hereto.

         14. HEADINGS. The descriptive headings of the sections and subsections
of this Agreement are for convenience only and do not constitute a part of this
Agreement.

         15. COUNTERPARTS. This Agreement and any amendment hereto or any other
agreement (or document) delivered pursuant hereto may be executed in one or more
counterparts and by different parties in separate counterparts. All of such
counterparts shall constitute one and the same agreement (or other document) and
shall become effective (unless otherwise provided therein) when one or more
counterparts have been signed by each party and delivered to the other parties.

                                      -5-

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                                                  CONFIDENTIAL TREATMENT REQUEST

         16.      PUBLICITY / PUBLICATIONS.

                  a. Clayton and Company shall coordinate all publicity relating
to the transactions contemplated by this Agreement. No party hereto shall issue
any press release, publicity statement or other public notice relating to this
Agreement, or the transactions contemplated by this Agreement, without the prior
consent of both Clayton and Company, except to the extent otherwise required by
applicable law. Unless required by law, without prior written consent from the
other party, a party shall not use for purposes of sales, advertising,
marketing, marking of goods, promotion to investors, press releases or other
publicity, etc.: (i) the name of (or any other information which would identify)
the other party or any corporation which is controlled by the same persons who
control such other party ("Other Corporation"); (ii) the names of trustees,
directors, officers, or employees of such other party or an Other Corporation;
or (iii) any trademarks (or adaptations thereof) of such other party or an Other
Corporation.

                  b. Each party is prepared to assist the other parties in
seeking patent or copyright protection for proprietary property owned by the
others. In this regard, no publication of the subject matter and/or results of
the research conducted hereunder shall be made by any party without giving the
other parties sixty (60) days notice in advance thereof so that patent
applications can be filed before such publication, if appropriate.

                                      -6-

<PAGE>

                                                  CONFIDENTIAL TREATMENT REQUEST

         17. CONFIDENTIALITY. All proprietary property and information disclosed
by any party (or its representatives) whether before or after the date hereof,
in connection with the transactions contemplated by, or the discussions and
negotiations preceding, this Agreement to any other party (or its
representatives) shall be kept confidential by such other party and its
representatives and, unless waived in writing by the other parties, shall not be
used by any such persons other than as contemplated by this Agreement, except
that such restrictions shall not apply to: (i) information which, at the time of
disclosure, is in the public domain or which, after disclosure, becomes part of
the public domain through no fault of the receiving party; (ii) information
which the receiving party can show was in its possession at the time of
disclosure and which was not acquired, directly or indirectly, from the
disclosing party; (iii) information which was lawfully obtained or received from
a third party, other than the disclosing party, having the legal right to
transmit same; or (iv) the disclosure of such information is essential for the
commercial exploitation of the Proprietary Property under this Agreement,
provided that such information is disclosed subject to a secrecy agreement. If
this Agreement is terminated in accordance with its terms, each party shall use
all reasonable efforts to return upon written request from any other party all
documents (and reproductions thereof) received by it or its representatives from
such other party (and, in the case of reproductions, all such reproductions made
by the receiving party) that include information not within the exceptions
contained in the first sentence of this Section 17, unless the recipients
provide assurances reasonably satisfactory to the requesting party that such
documents have been destroyed; provided, however, that one copy of any such
documentation may be retained by the receiving party for the sole purpose of
monitoring compliance with this Agreement.

         18. PARTIES IN INTEREST. This Agreement shall be binding upon and inure
to the benefit of each party, and nothing in this Agreement, express or implied,
is intended to confer upon any other person any rights or remedies of any nature
whatsoever under or by reason of this Agreement. Nothing in this Agreement is
intended to relieve or discharge the obligation of any third person to (or to
confer any right of subrogation or action over against) any party to this
Agreement.

         19. NOTICES. Any notice or other communication hereunder must be given
in writing and (a) delivered in person, (b) transmitted by telex, telefax or
other telecommunications mechanism, (c) mailed by certified or registered mail,
postage prepaid, receipt requested, or (d) sent by overnight delivery with
charges prepaid and receipt acknowledged, as follows:

                                      -7-

<PAGE>

                                                  CONFIDENTIAL TREATMENT REQUEST

                  If to Clayton, addressed to:
                  Clayton Foundation for Research
                  One Riverway, Suite 1440
                  Houston, Texas  77056
                     Attn:  C. W. Wellen, President
                     cc:  James F. Weiler, Esq., Vice President

                  If to RDF, addressed to:

                  Research Development Foundation
                  c/o Andrew MacKenzie, Esq.
                  402 North Division Street
                  Carson City, Nevada 89703
                     Attn:  C. W. Wellen, President
                     cc:  James F. Weiler, Esq.

                  If to Company, addressed to:

                  SuperGen, Inc.
                  Two Annabel Lane, Suite 220
                  San Ramon, California 94583
                     Attn:  Simeon Wrenn, Ph.D., Vice President
                     cc:  Ms. Lucy Chang, Director, Planning and Legal Affairs

or to such other address or to such other person as the party shall have last
designated by such notice to the other party. Each such notice or other
communication shall be effective (i) if given by mail, three (3) days after such
communication is deposited in the mails with postage prepaid, addressed as
aforesaid, or (ii) if given by telecommunication or any other means, when
actually received at such address.

         20. EXPENSES. Each party shall pay its own expenses incident to the
negotiation, preparation and performance of this Agreement and the transactions
contemplated hereby, including but not limited to the fees, expenses and
disbursements of their respective accountants and counsel.

         21. REMEDIES; WAIVER. All rights and remedies existing under this
Agreement and any related agreements or documents are cumulative to and not
exclusive of, any rights or remedies otherwise available under applicable law.
No failure on the part of any party to exercise or delay in exercising any right
hereunder shall be deemed a waiver thereof, nor shall any single or partial
exercise preclude any further or other exercise of such or any other right.

                                      -8-

<PAGE>

                                                  CONFIDENTIAL TREATMENT REQUEST

         22. ATTORNEY FEES. In the event of any action for the breach of this
Agreement or misrepresentation by any party, the prevailing party shall be
entitled to reasonable attorney's fees, costs and expenses incurred in such
action.

         23. SEVERABILITY. If any provision of this Agreement is determined to
be invalid, illegal or unenforceable by any governmental entity, the remaining
provisions of this Agreement to the extent permitted by law shall remain in full
force and effect; provided that the essential terms and conditions of this
Agreement remain valid, binding and enforceable and provided that the economic
and legal substance of the transactions contemplated is not affected in any
manner materially adverse to any party. In the event of any such determination,
the parties agree to negotiate in good faith to modify this Agreement to fulfill
as closely as possible the original intents and purposes hereof. To the extent
permitted by law, the parties hereby to the same extent waive any provision of
law that renders any provision hereof prohibited or unenforceable in any
respect.

                  [Remainder of page intentionally left blank]

                                      -9-

<PAGE>

                                                  CONFIDENTIAL TREATMENT REQUEST

         IN WITNESS WHEREOF, each of the parties hereto has caused this
Agreement to be executed by its duly authorized officers effective as of the
date and year first above written.

                                             CLAYTON FOUNDATION FOR RESEARCH

                                             By:      /s/  C. W. Wellen
                                                      ----------------------

                                             Name:    C. W. Wellen
                                                      ----------------------

                                             Title:   President
                                                      ----------------------

                                             Date:    December  3, 1999
                                                      ----------------------

                                             RESEARCH DEVELOPMENT FOUNDATION

                                             By:      /s/ Andrew MacKenzie
                                                      ----------------------

                                             Name:    Andrew MacKenzie
                                                      ----------------------

                                             Title:   Vice President
                                                      ----------------------

                                             Date:    December 7, 1999
                                                      ----------------------

SCIENTIST                                    SUPERGEN, INC.

Agreed to and Accepted:
                                             By:      /s/  Dr. Joseph Rubinfeld
                                                      -------------------------

                                             Name:    Dr. Joseph Rubinfeld
                                                      -------------------------
/s/ Vernon Knight
---------------------------------
Vernon Knight, M.D. ("Scientist")            Title:   President & CEO
                                                      -------------------------

                                             Date:    December 1, 1999
                                                      -------------------------

                                      -10-

<PAGE>

                                                  CONFIDENTIAL TREATMENT REQUEST

                                    EXHIBIT A

                                FIELD OF INTEREST

         Cancer therapy in humans wherein 9-nitro-camptothecin is delivered in
liposomes, lipid complexes, or other liposome particles, to the respiratory
tract via aqueous aerosol droplets.

                                      -11-

<PAGE>

                                                  CONFIDENTIAL TREATMENT REQUEST

                                    EXHIBIT B

                                    WORK PLAN

                                      [ * ]

                                      -12-

<PAGE>

                                                  CONFIDENTIAL TREATMENT REQUEST

                                    EXHIBIT C

                              FUNDING REQUIREMENTS

                                      [ * ]

                                      -13-

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