<PAGE>

                                                  CONFIDENTIAL TREATMENT REQUEST

                                                                     EXHIBIT 4.4



* 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 (PACLITAXEL)


         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
paclitaxel 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;


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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 paclitaxel (GMP grade) 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
paclitaxel required. In the event that Company cannot or does not provide
Clayton with the required quantities of paclitaxel, 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


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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
(Paclitaxel) 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 paclitaxel and all
analogues thereof 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 paclitaxel itself.
Clayton, at its sole expense, may conduct research on paclitaxel analogues
(hereafter "Analogue(s)") either during or after the term of this Agreement. If
comparative xenograft model studies of any Analogue(s) demonstrate equivalency
to paclitaxel, 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 Analogue(s) that are the subject of Clayton's
or RDF's notice to Company. Absent such a timely election by Company, the
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 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 Analogue(s) up to the date of
Company's written election, said sum to be calculated as follows:

                           i.       [  *  ]; and

                           ii.      [  *  ].


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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


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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.

         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


                                      -6-
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                                                  CONFIDENTIAL TREATMENT REQUEST

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:

                  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


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                                                  CONFIDENTIAL TREATMENT REQUEST

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.

         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]


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


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                                                  CONFIDENTIAL TREATMENT REQUEST

                                    EXHIBIT A

                                FIELD OF INTEREST

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


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                                                  CONFIDENTIAL TREATMENT REQUEST

                                    EXHIBIT B

                                    WORK PLAN



                                      [ * ]


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                                                  CONFIDENTIAL TREATMENT REQUEST

                                    EXHIBIT C

                              FUNDING REQUIREMENTS


                                       [ * ]


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