<PAGE>

                                                                  EXHIBIT 4.6

                          REGISTRATION RIGHTS AGREEMENT

                  This Registration Rights Agreement (the "Agreement") is made
and entered into as of this 27th day of September, 2000 by and between Supergen,
Inc., a Delaware corporation (the "Company"), and the "Seller" named in that
ASSET PURCHASE AGREEMENT of February 18, 2000 by and between the Company and the
Seller (the "Purchase Agreement").

                  The parties hereby agree as follows:

                  1.   CERTAIN DEFINITIONS.

                  As used in this Agreement, the following terms shall have the
following meanings:

                  "COMMON STOCK" shall mean the Company's Common Stock, par
value $0.001 per share.

                  "SELLER" shall mean AMUR Pharmaceuticals, Inc. and any
affiliate or transferee of Seller who is a subsequent holder of any Warrants or
Registrable Securities [pursuant to the terms of the Purchase Agreement and the
Warrants ("permitted transferee")].

                  "PROSPECTUS" shall mean the prospectus included in any
Registration Statement, as amended or supplemented by any prospectus supplement,
with respect to the terms of the offering of any portion of the Registrable
Securities covered by such Registration Statement and by all other amendments
and supplements to the prospectus, including post-effective amendments and all
material incorporated by reference in such prospectus.

                  "REGISTER," "REGISTERED" and "REGISTRATION" refer to a
registration made by preparing and filing a registration statement or similar
document in compliance with the 1933 Act (as defined below), and the declaration
or ordering of effectiveness of such registration statement or document.

                  "REGISTRABLE SECURITIES" shall mean the shares of Common Stock
issued to the Seller and issuable to the Seller upon exercise of the Warrants,
all pursuant to the Purchase Agreement, and any other securities issued or
issuable with respect to or in exchange for Registrable Securities, provided,
however, that shares of Common Stock, or other securities shall only be treated
as Registrable Securities if and so long as they have not been (A) sold to or
through a broker or dealer or underwriter in a public distribution or a public
securities transaction, whether in a registered offering, Rule 144 or otherwise,
or (B) sold or are, in the opinion of counsel for the Company, available for
sale in a single transaction exempt from the registration and prospectus
delivery requirements of the 1933 Act pursuant to Rule 144(k) so that all
transfer restrictions and restrictive legends with respect thereto are removed
upon the consummation of such sale.

<PAGE>

                  "REGISTRATION STATEMENT" shall mean any registration statement
filed under the 1933 Act of the Company that covers the resale of any of the
Registrable Securities pursuant to the provisions of this Agreement, amendments
and supplements to such Registration Statement, including post-effective
amendments, all exhibits and all material incorporated by reference in such
Registration Statement.

                  "SEC" means the U.S. Securities and Exchange Commission.

                  "1933 ACT" means the Securities Act of 1933, as amended, and
the rules and regulations promulgated thereunder.

                  "1934 ACT" means the Securities Exchange Act of 1934, as
amended, and the rules and regulations promulgated thereunder.

                  "WARRANTS" mean the warrants to purchase shares of Common
Stock issued to the Seller pursuant to the Purchase Agreement, the form of which
is attached to the Purchase Agreement as Exhibit 2.2.

                  2.   REGISTRATION.

                       (a)   REGISTRATION STATEMENTS.

                             (i)   REGISTRABLE SECURITIES. Promptly following
the closing of the purchase and sale of Common Stock and issuance of Warrants
contemplated by the Purchase Agreement (the "Closing Date") (but no later than
forty-five (45) days after the Closing Date), the Company shall prepare and file
with the SEC one Registration Statement on Form S-3 (or, if Form S-3 is not then
available to the Company, on such form of registration statement as is then
available to effect a registration for resale of the Registrable Securities,
subject to the Seller's consent) covering the resale of the Registrable
Securities in an amount equal to the number of shares of Common Stock issued to
the Seller on the Closing Date plus the number of shares of Common Stock
necessary to permit the exercise in full of the Warrants. Such Registration
Statement also shall cover, to the extent allowable under the 1933 Act and the
Rules promulgated thereunder (including Rule 416), such indeterminate number of
additional shares of Common Stock resulting from stock splits, stock dividends
or similar transactions with respect to the Registrable Securities. The
Registration Statement (and each amendment or supplement thereto, and each
request for acceleration of effectiveness thereof) shall be provided in
accordance with Section 3(c) to the Seller prior to its filing or other
submission.

                       (b)   EXPENSES. The Company will pay all expenses
associated with each registration, including the Seller's reasonable expenses in
connection with the registration but excluding discounts, commissions, fees of
underwriters, selling brokers, dealer managers or similar securities industry
professionals.

                       (c)   EFFECTIVENESS.

                                       2
<PAGE>


                             (i)   The Company shall use its best efforts to
have each Registration Statement declared effective as soon as practicable.

                             (ii)  For not more than twenty-five (25)
consecutive trading days or for a total of not more than thirty-five (35)
trading days in any twelve (12) month period, the Company may delay the
disclosure of material non-public information concerning the Company, by
terminating or suspending effectiveness of any registration contemplated by this
Section containing such information, the disclosure of which at the time is not,
in the good faith opinion of the Company, in the best interests of the Company
(an "Allowed Delay"); provided, that the Company shall promptly (a) notify the
Seller in writing of the existence of (but in no event, without the prior
written consent of the Seller, shall the Company disclose to such Seller any of
the facts or circumstances regarding) material non-public information giving
rise to an Allowed Delay, and (b) advise the Seller in writing to cease all
sales under the Registration Statement until the end of the Allowed Delay.

                        (d)   UNDERWRITTEN OFFERING. If any offering by the
Seller pursuant to a Registration Statement pursuant to Section 2(a) hereof
involves a firm commitment underwritten offering, the Company shall have the
right to select an investment banker and manager to administer the offering,
which investment banker or manager shall be reasonably satisfactory to the
Seller.

                  3.    COMPANY OBLIGATIONS. The Company will use its best
efforts to effect the registration of the Registrable Securities in accordance
with the terms hereof, and pursuant thereto the Company will, as expeditiously
as possible:

                        (a)   use its best efforts to cause such Registration
Statement to become effective and to remain continuously effective for a period
that will terminate upon the earlier of the date on which all Registrable
Securities covered by such Registration Statement, as amended from time to time,
have been sold (the "Registration Period");

                        (b)   prepare and file with the SEC such amendments and
post-effective amendments to the Registration Statement and the Prospectus as
may be necessary to keep the Registration Statement effective for the period
specified in Section 3(a) and to comply with the provisions of the 1933 Act and
the 1934 Act with respect to the distribution of all Registrable Securities;
provided that, at least five (5) business days prior to the filing of a
Registration Statement or Prospectus, or any amendments or supplements thereto,
the Company will furnish to the Seller copies of all documents proposed to be
filed, which documents will be subject to the comments of the Seller;

                        (c)   furnish to the Seller and their legal counsel (i)
promptly after the same is prepared and publicly distributed, filed with the
SEC, or received by the Company, one copy of any Registration Statement and any
amendment thereto, each preliminary prospectus and Prospectus and each amendment
or supplement thereto, and each letter written by or on behalf of the Company to
the SEC or the staff of the SEC, and each item of correspondence from the SEC or
the staff of the SEC, in each case relating to such Registration Statement
(other than any portion of any thereof which contains information for which the
Company has sought

                                       3
<PAGE>

confidential treatment), and (ii) such number of copies of a Prospectus,
including a preliminary prospectus, and all amendments and supplements thereto
and such other documents as each Seller may reasonably request in order to
facilitate the disposition of the Registrable Securities owned by such Seller;

                        (d)   in the event the Company selects an underwriter
for the offering, the Company shall enter into and perform its reasonable
obligations under an underwriting agreement, in usual and customary form,
including, without limitation, customary indemnification and contribution
obligations, with the underwriter of such offering;

                        (e)   if required by the underwriter, or if any Seller
is described in the Registration Statement as an underwriter, the Company shall
furnish, on the effective date of the Registration Statement, on the date that
Registrable Securities are delivered to an underwriter for sale in connection
with the Registration Statement and at periodic intervals thereafter from time
to time on request, (i) an opinion, dated as of such date, from independent
legal counsel representing the Company for purposes of such Registration
Statement, in form, scope and substance as is customarily given in an
underwritten public offering, addressed to the underwriter and the Seller and
(ii) a letter, dated such date, from the Company's independent certified public
accountants in form and substance as is customarily given by independent
certified public accountants to underwriters in an underwritten public offering,
addressed to the underwriter and the Seller;

                        (f)   make effort to prevent the issuance of any stop
order or other suspension of effectiveness and, if such order is issued, obtain
the withdrawal of any such order at the earliest possible moment;

                        (g)   furnish to each Seller at least five (5) copies of
the Registration Statement and any post-effective amendment thereto, including
financial statements and schedules;

                        (h)   prior to any public offering of Registrable
Securities, use its reasonable best efforts to register or qualify or cooperate
with the Seller and their counsel in connection with the registration or
qualification of such Registrable Securities for offer and sale under the
securities or blue sky laws of all United States jurisdictions and do any and
all other reasonable acts or things necessary or advisable to enable the
distribution in such jurisdictions of the Registrable Securities covered by the
Registration Statement;

                        (i)   use its reasonable best efforts to maintain its
listing on each securities exchange, interdealer quotation system or other
market on which similar securities issued by the Company are then listed;

                        (j)   immediately notify the Seller, at any time when a
Prospectus relating to the Registrable Securities is required to be delivered
under the Securities Act, upon discovery that, or upon the happening of any
event as a result of which, the Prospectus included in such Registration
Statement, as then in effect, includes an untrue statement of a material fact or
omits to state any material fact required to be stated therein or necessary to
make the

                                       4
<PAGE>

statements therein not misleading in the light of the circumstances then
existing, and at the request of any such holder, promptly prepare and furnish to
such holder a reasonable number of copies of a supplement to or an amendment of
such Prospectus as may be necessary so that, as thereafter delivered to the
purchasers of such Registrable Securities such Prospectus shall not include an
untrue statement of a material fact or omit to state a material fact required to
be stated therein or necessary to make the statements therein not misleading in
the light of the circumstances then existing; and

                        (k)   otherwise use its best efforts to comply with all
applicable rules and regulations of the SEC under the 1933 Act and the 1934 Act,
take such other actions as may be reasonably necessary to facilitate the
registration of the Registrable Securities.

                   4.   DUE DILIGENCE REVIEW. The Company shall make available,
during normal business hours, for inspection and review by the Seller, advisors
to and representatives of the Seller (who may or may not be affiliated with the
Seller and who are reasonably acceptable to the Company), any underwriter
participating in any disposition of Common Stock on behalf of the Seller
pursuant to the Registration Statement or amendments or supplements thereto or
any blue sky, NASD or other filing, all SEC Documents and other filings with the
SEC as may be reasonably necessary for the purpose of such review, and cause the
Company's officers, directors and employees, within a reasonable time period, to
supply all such information reasonably requested by the Seller or any such
representative, advisor or underwriter in connection with such Registration
Statement (including, without limitation, in response to all questions and other
inquiries reasonably made or submitted by any of them), prior to and from time
to time after the filing and effectiveness of the Registration Statement for the
sole purpose of enabling the Seller and such representatives, advisors and
underwriters and their respective accountants and attorneys to conduct initial
and ongoing due diligence with respect to the Company and the accuracy of the
Registration Statement.

                  The Company shall not disclose nonpublic information to the
Seller, advisors to or representatives of the Seller unless prior to disclosure
of such information the Company identifies such information as being nonpublic
information and provides the Seller, such advisors and representatives with the
opportunity to accept or refuse to accept such nonpublic information for review.
The Company may, as a condition to disclosing any nonpublic information
hereunder, require the Seller, their advisors and representatives to enter into
a confidentiality agreement (including an agreement with such advisors and
representatives prohibiting them from trading in Common Stock during such period
of time as they are in possession of nonpublic information) in form reasonably
satisfactory to the Company and the Seller.

                  Nothing herein shall require the Company to disclose nonpublic
information to the Seller or their advisors or representatives, and the Company
represents that it does not disseminate nonpublic information to any Seller who
purchase stock in the Company in a public offering, to money managers or to
securities analysts, provided, however, that notwithstanding anything herein to
the contrary, the Company will, as hereinabove provided, immediately notify the
advisors and representatives of the Seller and underwriters, of any event or the
existence of any circumstance (without any obligation to disclose the specific
event or circumstance) of

                                       5
<PAGE>

which it becomes aware, constituting nonpublic information (whether or not
requested of the Company specifically or generally during the course of due
diligence by and such persons or entities), which, if not disclosed in the
Prospectus included in the Registration Statement, would cause such Prospectus
to include a material misstatement or to omit a material fact required to be
stated therein in order to make the statements therein, in light of the
circumstances in which they were made, not misleading. Nothing contained in this
Section 4 shall be construed to mean that such persons or entities other than
the Seller (without the written consent of the Seller prior to disclosure of
such information) may not obtain nonpublic information in the course of
conducting due diligence in accordance with the terms of this Agreement and the
Purchase Agreement; provided, however, that in no event shall the Seller's
advisors or representatives disclose to the Seller the nature of the specific
event or circumstances constituting any nonpublic information discovered by such
advisors or representatives in the course of their due diligence without the
written consent of the Seller prior to disclosure of such information. The
Seller' advisors or representatives shall make complete disclosure to the
Seller' independent counsel of all events or circumstances constituting
nonpublic information discovered by such advisors or representatives in the
course of their due diligence upon which such advisors or representatives form
the opinion that the Registration Statement contains an untrue statement of a
material fact or omits a material fact required to be stated in the Registration
Statement or necessary to make the statements contained therein, in the light of
the circumstances in which they were made, not misleading. Upon receipt of such
disclosure, the Seller's independent counsel shall consult with the Company's
independent counsel in order to address the concern raised as to the existence
of a material misstatement or omission and to discuss appropriate disclosure
with respect thereto; provided, however, that such consultation shall not
constitute the advice of the Company's independent counsel to the Seller as to
the accuracy of the Registration Statement and related Prospectus. In the event
after such consultation the Seller' independent counsel reasonably believes that
the Registration Statement contains an untrue statement or a material fact or
omits a material fact required to be stated in the Registration Statement or
necessary to make the statements contained therein, in light of the
circumstances in which they were made, not misleading, (a) the Company shall
file with the SEC an amendment to the Registration Statement responsive to such
alleged untrue statement or omission and provide the Seller, as promptly as
practicable, with copies of the Registration Statement and related Prospectus,
as so amended, or (b) if the Company disputes the existence of any such material
misstatement or omission, (i) the Company's independent counsel shall provide
the Seller's independent counsel with an opinion stating that nothing has come
to their attention that would lead them to believe that the Registration
Statement or the related Prospectus, as of the date of such opinion, contains an
untrue statement of a material fact or omits a material fact required to be
stated in the Registration Statement or the related Prospectus or necessary to
make the statements contained therein, in light of the circumstances in which
they were made, not misleading and (ii) in the event the dispute relates to the
adequacy of financial disclosure and the Seller shall reasonably request, the
Company's independent auditors shall provide to the Company a letter outlining
the performance of such "agreed upon procedures" as shall be reasonably
requested by the Seller and the Company shall provide the Seller with a copy of
such letter.

                                       6
<PAGE>

                   5.   OBLIGATIONS OF THE SELLER.

                        (a)   Each Seller shall furnish in writing to the
Company such information regarding itself, the Registrable Securities held by it
and the intended method of disposition of the Registrable Securities held by it,
as shall be reasonably required to effect the registration of such Registrable
Securities and shall execute such documents in connection with such registration
as the Company may reasonably request. At least fifteen (15) business days prior
to the first anticipated filing date of any Registration Statement, the Company
shall notify each Seller of the information the Company requires from such
Seller if such Seller elects to have any of the Registrable Securities included
in the Registration Statement. A Seller shall provide such information to the
Company at least seven (7) business days prior to the first anticipated filing
date of such Registration Statement if such Seller elects to have any of the
Registrable Securities included in the Registration Statement.

                        (b)   Each Seller, by its acceptance of the Registrable
Securities agrees to cooperate with the Company as reasonably requested by the
Company in connection with the preparation and filing of a Registration
Statement hereunder, unless such Seller has notified the Company in writing of
its election to exclude all of its Registrable Securities from the Registration
Statement, in which case the Seller shall be deemed to have waived its rights to
have Registrable Securities registered under this Agreement.

                        (c)   In the event the Company at an Seller's request,
determines to engage the services of an underwriter, such Seller agrees to enter
into and perform its obligations under an underwriting agreement, in usual and
customary form, including, without limitation, customary indemnification and
contribution obligations, with the managing underwriter of such offering and
take such other actions as are reasonably required in order to expedite or
facilitate the dispositions of the Registrable Securities.

                        (d)   Each Seller agrees that, upon receipt of any
notice from the Company of the happening of any event rendering a Registration
Statement no longer effective, such Seller will immediately discontinue
disposition of Registrable Securities pursuant to the Registration Statement
covering such Registrable Securities until the Seller's receipt of the copies of
the supplemented or amended prospectus filed with the SEC and declared effective
and, if so directed by the Company, the Seller shall deliver to the Company (at
the expense of the Company) or destroy (and deliver to the Company a certificate
of destruction) all copies in the Seller's possession of the prospectus covering
the Registrable Securities current at the time of receipt of such notice.

                        (e)   No Seller may participate in any third party
underwritten registration hereunder unless it (i) agrees to sell the Registrable
Securities on the basis provided in any underwriting arrangements in usual and
customary form entered into by the Company, (ii) completes and executes all
questionnaires, powers of attorney, indemnities, underwriting agreements and
other documents reasonably required under the terms of such underwriting
arrangements, and (iii) agrees to pay its pro rata share of all underwriting
discounts and commissions and any expenses in excess of those payable by the
Company pursuant to the terms of this Agreement.

                                       7
<PAGE>

                   6.   INDEMNIFICATION.

                        (a)   INDEMNIFICATION BY COMPANY. The Company agrees to
indemnify and hold harmless, to the fullest extent permitted by law the Seller,
each of its officers, directors, partners and employees and each person who
controls the Seller (within the meaning of the 1933 Act) against all losses,
claims, damages, liabilities, costs (including, without limitation, reasonable
attorney's fees) and expenses imposed on such person caused by (i) any untrue or
alleged untrue statement of a material fact contained in any Registration
Statement, Prospectus or any preliminary prospectus 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, except insofar as the same are based upon any
information furnished in writing to the Company by such Seller, expressly for
use therein, or (ii) any violation by the Company of any federal, state or
common law, rule or regulation applicable to the Company in connection with any
Registration Statement, Prospectus or any preliminary prospectus, or any
amendment or supplement thereto, and shall reimburse in accordance with
subparagraph (c) below, each of the foregoing persons for any legal and any
other expenses reasonably incurred in connection with investigating or defending
any such claims. The foregoing is subject to the condition that, insofar as the
foregoing indemnities relate to any untrue statement, alleged untrue statement,
omission or alleged omission made in any preliminary prospectus or Prospectus
that is eliminated or remedied in any Prospectus or amendment or supplement
thereto, the above indemnity obligations of the Company shall not inure to the
benefit of any indemnified party if a copy of such corrected Prospectus or
amendment or supplement thereto had been made available to such indemnified
party and was not sent or given by such indemnified party at or prior to the
time such action was required of such indemnified party by the 1933 Act and if
delivery of such Prospectus or amendment or supplement thereto would have
eliminated (or been a sufficient defense to) any liability of such indemnified
party with respect to such statement or omission. Indemnity under this Section
6(a) shall remain in full force and effect regardless of any investigation made
by or on behalf of any indemnified party and shall survive the permitted
transfer of the Registrable Securities.

                        (b)   INDEMNIFICATION BY HOLDER. In connection with any
registration pursuant to the terms of this Agreement, each Seller will furnish
to the Company in writing such information as the Company reasonably requests
concerning the holders of Registrable Securities or the proposed manner of
distribution for use in connection with any Registration Statement or Prospectus
and agrees, severally but not jointly, to indemnify and hold harmless, to the
fullest extent permitted by law, the Company, its directors, officers,
employees, stockholders and each person who controls the Company (within the
meaning of the 1933 Act) against any losses, claims, damages, liabilities and
expense (including reasonable attorney's fees) resulting from any untrue
statement or alleged untrue statement of a material fact or any omission or
alleged omission of a material fact required to be stated in the Registration
Statement or Prospectus or preliminary prospectus or amendment or supplement
thereto or necessary to make the statements therein not misleading, to the
extent, but only to the extent that such untrue statement or omission is
contained in any information furnished in writing by such Seller to the Company
specifically for inclusion in such Registration Statement or Prospectus or
amendment or supplement thereto and that such information was substantially
relied upon by the Company in

                                       8
<PAGE>

preparation of the Registration Statement or Prospectus or any amendment or
supplement thereto. In no event shall the liability of an Seller be greater in
amount than the dollar amount of the proceeds (net of all the amount of any
damages such holder has otherwise been required to pay by reason of such untrue
statement or omission) received by such Seller upon the sale of the Registrable
Securities included in the Registration Statement giving rise to such
indemnification obligation.

                        (c)   CONDUCT OF INDEMNIFICATION PROCEEDINGS. Any person
entitled to indemnification hereunder shall (i) give prompt notice to the
indemnifying party of any claim with respect to which it seeks indemnification
and (ii) permit such indemnifying party to assume the defense of such claim with
counsel reasonably satisfactory to the indemnified party; PROVIDED that any
person entitled to indemnification hereunder shall have the right to employ
separate counsel and to participate in the defense of such claim, but the fees
and expenses of such counsel shall be at the expense of such person unless (a)
the indemnifying party has agreed to pay such fees or expenses, or (b) the
indemnifying party shall have failed to assume the defense of such claim and
employ counsel reasonably satisfactory to such person or (c) in the reasonable
judgment of any such person, based upon written advice of its counsel, a
conflict of interest exists between such person and the indemnifying party with
respect to such claims (in which case, if the person notifies the indemnifying
party in writing that such person elects to employ separate counsel at the
expense of the indemnifying party, the indemnifying party shall not have the
right to assume the defense of such claim on behalf of such person); and
PROVIDED, FURTHER, that the failure of any indemnified party to give notice as
provided herein shall not relieve the indemnifying party of its obligations
hereunder, except to the extent that such failure to give notice shall
materially adversely affect the indemnifying party in the defense of any such
claim or litigation. It is understood that the indemnifying party shall not, in
connection with any proceeding in the same jurisdiction, be liable for fees or
expenses of more than one separate firm of attorneys at any time for all such
indemnified parties. No indemnifying party will, except with the consent of the
indemnified party, consent to entry of any judgment or enter into any settlement
that 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.

                        (d)   CONTRIBUTION. If for any reason the
indemnification provided for in the preceding paragraphs (a) and (b) is
unavailable to an indemnified party or insufficient to hold it harmless, other
than as expressly specified therein, then the indemnifying party shall
contribute to the amount paid or payable by the indemnified party as a result of
such loss, claim, damage or liability in such proportion as is appropriate to
reflect the relative fault of the indemnified party and the indemnifying party,
as well as any other relevant equitable considerations. No person guilty of
fraudulent misrepresentation within the meaning of Section 11(f) of the 1933 Act
shall be entitled to contribution from any person not guilty of such fraudulent
misrepresentation. In no event shall the contribution obligation of a holder of
Registrable Securities be greater in amount than the dollar amount of the
proceeds (net of the amount of any damages such holder has otherwise been
required to pay by reason of such untrue or alleged untrue statement or omission
or alleged omission) received by it upon the sale of the Registrable Securities
giving rise to such contribution obligation.

                                       9
<PAGE>

                   7.   MISCELLANEOUS.

                        (a)   AMENDMENTS AND WAIVERS. This Agreement may be
amended only by a writing signed by the Company and the holders of a majority of
the Registrable Securities. The Company may take any action herein prohibited,
or omit to perform any act herein required to be performed by it, only if the
Company shall have obtained the written consent to such amendment, action or
omission to act, of each Seller.

                        (b)   NOTICES. All notices and other communications
provided for or permitted hereunder shall be made as set forth below:


                        To the Seller:
                        Ms. Sandi Yurichuk
                        President
                        AMUR Pharmaceuticals, Inc.
                        227 Lyndhurst Ave.
                        Belmont, CA   94002

                        To the Company:
                        Dr. Joseph Rubinfeld
                        President
                        SuperGen, Inc.
                        Two Annabel Lane
                        Suite 220
                        San Ramon, CA  94583

                        (c)   ASSIGNMENTS AND TRANSFERS BY SELLER. This
Agreement and all the rights and obligations of the Seller hereunder may not be
assigned or transferred to any transferee or assignee except to an affiliate or
permitted transferee of a Seller who is a subsequent holder of any Registrable
Securities, provided that such affiliate or permitted transferee holds at least
25,000 Registrable Securities upon completion of such assignment or transfer.

                        (d)   ASSIGNMENTS AND TRANSFERS BY THE COMPANY. This
Agreement may not be assigned by the Company without the prior written consent
of each Seller, except that without the prior written consent of the Seller, but
after notice duly given, the Company shall assign its rights and delegate its
duties hereunder to any successor-in-interest corporation, and such
successor-in-interest shall assume such rights and duties, in the event of a
merger or consolidation of the Company with or into another corporation or the
sale of all or substantially all of the Company's assets.

                        (e)   BENEFITS OF THE AGREEMENT. The terms and
conditions of this Agreement shall inure to the benefit of and be binding upon
the respective permitted successors and assigns of the parties. Nothing in this
Agreement, express or implied, is intended to confer upon any party other than
the parties hereto or their respective successors and assigns any rights,

                                       10
<PAGE>

remedies, obligations, or liabilities under or by reason of this Agreement,
except as expressly provided in this Agreement.

                        (f)   COUNTERPARTS. This Agreement may be executed in
two or more counterparts, each of which shall be deemed an original, but all of
which together shall constitute one and the same instrument.

                        (g)   TITLES AND SUBTITLES. The titles and subtitles
used in this Agreement are used for convenience only and are not to be
considered in construing or interpreting this Agreement.

                        (h)   SEVERABILITY. If one or more provisions of this
Agreement are held to be unenforceable under applicable law, such provision
shall be excluded from this Agreement and the balance of this Agreement shall be
interpreted as if such provision were so excluded and shall be enforceable in
accordance with its terms to the fullest extent permitted by law.

                        (i)   FURTHER ASSURANCES. The parties shall execute and
deliver all such further instruments and documents and take all such other
actions as may reasonably be required to carry out the transactions contemplated
hereby and to evidence the fulfillment of the agreements herein contained.

                        (j)   ENTIRE AGREEMENT. This Agreement is intended by
the parties as a final expression of their agreement and intended to be a
complete and exclusive statement of the agreement and understanding of the
parties hereto in respect of the subject matter contained herein. This Agreement
supersedes all prior agreements and understandings between the parties with
respect to such subject matter.

                        (k)   APPLICABLE LAW. This Agreement shall be governed
by, and construed in accordance with, the laws of the State of Delaware without
regard to principles of conflicts of law.



                                       11
<PAGE>


                  IN WITNESS WHEREOF, the parties have executed this Agreement
as of the date first written above.

The Company:                                   SUPERGEN, INC.


                                               By: /s/ Joseph Rubinfeld
                                                   --------------------
                                               Name: Joseph Rubinfeld, Ph.D.
                                               Title: President and CEO


The Seller:                                    AMUR PHARMACEUTICALS, INC.


                                               By: /s/ Sandi Yurichuk
                                                   --------------------
                                               Name: Sandi Yurichuk
                                               Title: President



                                       12