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                                                                 EXHIBIT 10.24

                                                       OSI Pharmaceuticals, Inc.
                                                58 South Service Road, Suite 110
                                                              Melville, NY 11747
                                                   T 631.962.2000 F 631.752.3880
                                                                    www.osip.com

[(OSI)(TM) PHARMACEUTICALS LOGO)]

January 11, 2004

                                                             VIA FEDERAL EXPRESS

Sean A. McCarthy, D.Phil.
Vice President, Business Development
Structural GenomiX, Inc.
10505 Roselle Street
San Diego, CA  92121

Re:      Collaboration Agreement dated August 1, 2003 between Structural
         GenomiX, Inc. and OSI Pharmaceuticals, Inc.

Dear Sean:

This letter confirms acceptance by Structural GenomiX of an amendment to Section
2.8(b) of the above-referenced Collaboration Agreement whereby effective
immediately, OSI Pharmaceuticals shall have the option to increase its
membership on the Joint Steering Committee (JSC) to three (3) representatives,
one of whom shall be a non-voting representative.

Please indicate your agreement by signing two copies and returning one copy to
my attention at OSI Pharmaceuticals, Inc.

Regards,

/s/ Barbara A. Sawitsky

Barbara A. Sawitsky
Director, Corporate Development

Agreed and Accepted:

STRUCTURAL GENOMIX, INC.

Name:         /s/Herbert G. Mutter
     ----------------------------------------

Title:        Vice President, Finance
      ---------------------------------------

Date:         2/26/04
     ----------------------------------------

Copy:      N. Gibson
           L. Arnold
           A. Castelhano
           N. Pegg<PAGE>

                                                                   EXHIBIT 10.25

                                           *** TEXT OMITTED AND FILED SEPARATELY
                                    PURSUANT TO A CONFIDENTIAL TREATMENT REQUEST
                                            UNDER 17 C.F.R. SECTION 200.80(b)(4)
                                               AND RULE 406 UNDER THE SECURITIES
                                                         ACT OF 1933, AS AMENDED

                             AMENDMENT TO AGREEMENT

      THIS AMENDMENT TO AGREEMENT (the "Amendment") is made and entered into
effective this 1st day of February, 2005 (the "Amendment Effective Date"), by
and between STRUCTURAL GENOMIX, INC., a corporation organized and existing under
the laws of the State of Delaware and having its principal place of business
located at 10505 Roselle Street, San Diego, CA 92121 ("SGX") and OSI
PHARMACEUTICALS, INC., and its Affiliates, a Delaware corporation, with
executive offices at 58 South Service Road, Melville, New York 11747 ("OSIP").
OSIP and SGX may be referred to herein as a "Party" or, collectively, as
"Parties".

                                    RECITALS

      A. OSIP and SGX have entered into a Collaboration Agreement (the
"Agreement") effective August 1, 2003, under which the Parties have agreed to
conduct a collaborative research program.

      B. The Parties desire to amend the terms of the Agreement as provided in
this Amendment.

      NOW, THEREFORE, the Parties agree as follows:

1.    AMENDMENT OF THE AGREEMENT

      The Parties hereby agree to amend the terms of the Agreement as provided
below, effective as of the Amendment Effective Date. To the extent that the
Agreement is explicitly amended by this Amendment, the terms of the Amendment
will control where the terms of the Agreement are contrary to or conflict with
the following provisions. Where the Agreement is not explicitly amended, the
terms of the Agreement will remain in force. Capitalized terms used in this
Amendment that are not otherwise defined herein shall have the same meanings as
such terms are defined in the Agreement.

      1.1 AMEND SECTION 1.14. Section 1.14 of the Agreement is hereby amended to
add the words "an OSIP Target that has demonstrated biologic or enzymatic
activity or" after the word "express".

      1.2 AMEND SECTION 2.2. Section 2.2 of the Agreement is hereby amended by
deleting the words "[...***...] ([...***...])" and replacing them with
"[...***...] ([...***...])".

      1.3 AMEND SECTION 2.6. Section 2.6 is hereby amended to delete the words
"[...***...] ([...***...]) and replace with "[...***...] ([...***...]) to
[...***...] ([...***...]) and delete the words "[...***...] ([...***...])" and
replace them with "[...***...] ([...***...])".

      1.4 AMEND SECTION 3.1 Section 3.1 of the Agreement is hereby amended to
add the following sentence: "within thirty (30) days after February 1, 2005,
OSIP will pay to SGX an extension payment of one hundred thousand dollars
($100,000)."

                                             ***CONFIDENTIAL TREATMENT REQUESTED

                                       1.
<PAGE>

      1.5 AMEND SECTION 3.2. Section 3.2 of the Agreement is hereby deleted in
its entirety and replaced with the following: "Research Funding. For the period
from the Effective Date through to January 31, 2005, OSIP will pay SGX research
funding of $60,000 per month, and for the period from February 1, 2005 through
to the end of the Term of the Collaboration, OSIP will pay SGX research funding
of $[...***...] per month, in each case payable quarterly in advance.

      1.6 AMEND SECTION 3.3. Section 3.3 of the Agreement is hereby amended to
delete the words: "; or an aggregate of [...***...] ([...***...]) milestones
during the Term of the Collaboration (i.e. $[...***...])" and replace them with
the following: "; or for more than [...***...] ([...***...]) milestones during
the period from February 1, 2005 through the end of the Term of the
Collaboration (i.e.$ [...***...]), unless otherwise agreed by the Parties."

      1.7 AMEND EXHIBIT A. Exhibit A of the Agreement will be amended by adding
the attached Exhibit A-1.

      1.8 AMEND EXHIBIT B. Exhibit B of the Agreement is deleted in its entirety
and replaced with the Exhibit B attached hereto.

2.    MISCELLANEOUS

      2.1 FULL FORCE AND EFFECT. This Amendment amends the terms of the
Agreement and is deemed incorporated into, and governed by all other terms of,
the Agreement. The provisions of the Agreement, as amended by this Amendment,
remain in full force and effect.

      2.2 COUNTERPARTS. This Amendment 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.

      IN WITNESS WHEREOF, the Parties have executed this Amendment in duplicate
originals by their authorized officers as of the date and year first above
written.

                                      OSI PHARMACEUTICALS, INC.

                                      By: /s/ [Illegible]
                                          --------------------------------------

                                      Title:  Vice President - Research

                                      STRUCTURAL GENOMIX, INC.

                                      By: /s/ M. Grey
                                         ---------------------------------------

                                      Title:  President and CEO

                                       2.   ***CONFIDENTIAL TREATMENT REQUESTED
<PAGE>

                                   EXHIBIT A-1

                              SGX-OSI COLLABORATION
                             RESEARCH PLAN EXTENSION

With an extension of the collaboration, SGX will undertake the following
programs of experimental work:

1. Continue to provide structures of [...***...], and [...***...] as needed and
as long as compounds are supplied,

2. Continue research experiments on purification and crystallization of
[...***...] with the goal of solving a crystal structure. Further experiments
involving [...***...] can follow if [...***...] from [...***...] or [...***...],

3. Additional research experiments will be performed to identify constructs and
crystallization conditions that yield a crystallographic structure of
[...***...] in a [...***...].

Assuming that [...***...] and [...***...] continue as active targets, an
additional two targets will also be activated by the JSC. Upon finalization of
the contract amendment, [...***...], [...***...] and [...***...] on these
targets will commence immediately with the goal of [...***...]. As needed during
the term of the amendment, other targets may be nominated and approved by the
JSC.

POTENTIAL TARGETS

      -     [...***...]
            [...***...] will be made based on [...***...] of [...***...], and
            [...***...] to [...***...] will be used for the [...***...], since
            protein for all [...***...] of [...***...] have been [...***...] in
            [...***...]. If we [...***...], we may [...***...] and [...***...]
            the [...***...] will be tested in [...***...] and, in parallel,
            [...***...] to [...***...] followed by [...***...] to
            [...***...] the [...***...] such as [...***...] or
            [...***...] will be included in [...***...], as well as [...***...].
            The [...***...] of the [...***...] will be [...***...] at
            [...***...] prior to [...***...]

      -     [...***...]
            [...***...] will be [...***...] in [...***...] will be included
            during [...***...], and an [...***...] included in [...***...]
            and/or [...***...] will be evaluated. If [...***...] from such
            [...***...] using [...***...] will be [...***...] will be
            [...***...] in [...***...] and, in parallel, subjected to
            [...***...]to optimize the [...***...]

                                       3.    ***CONFIDENTIAL TREATMENT REQUESTED
<PAGE>

      -     [...***...]

            [...***...] will be attempted in [...***...] as a [...***...], with
            and without [...***...] will be evaluated, if necessary. [...***...]
            will start after the [...***...] and the [...***...] and [...***...]
            will be deleted. If needed, [...***...] will be [...***...].
            [...***...] will advise on the [...***...] to support [...***...]
            and [...***...] can also be started in parallel if [...***...] or
            [...***...] from [...***...] is a [...***...]

OTHER POTENTIAL TARGETS

      -     [...***...]
      -     [...***...]
      -     [...***...]
      -     [...***...]

                                       4.    ***CONFIDENTIAL TREATMENT REQUESTED
<PAGE>

                            EXHIBIT B - OSIP TARGETS

Initial [...***...] targets:
[...***...]

Targets [...***...]:
[...***...]

Targets [...***...]:
[...***...]

ADDITIONAL TARGETS TO BE ADDED FROM TIME TO TIME AS AGREED UPON BY THE JSC.

                                       5.    ***CONFIDENTIAL TREATMENT REQUESTED

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