EXHIBIT 3

                    STOCK PURCHASE AGREEMENT AMENDMENT NO. 1

         This Stock Purchase Agreement Amendment No. 1 (this "Amendment") dated
as of July 15, 2003, is entered into by and among Estate of Gordon A. Cain (the
"Estate"), RCM Financial Services, L.P., a Delaware limited partnership
("Financial Services"), and Cogene Biotech Ventures, L.P., a Delaware limited
partnership ("Cogene Biotech" and, together with Financial Services, the
"Purchasers"). All capitalized terms not defined in this Amendment shall have
the meanings set forth in that certain Stock Purchase Agreement dated as of July
10, 2003 by and among the Purchasers and the Estate (the "Purchase Agreement").

         Whereas, the Purchase Agreement contemplates that pursuant to Section
6(a) thereof that it may be amended by the written agreement of the Purchasers
and the Estate; and

         Whereas, the Purchasers and the Estate each desire to provide for
amendments to the Purchase Agreement in accordance with the following
provisions.

         Now, Therefore, in consideration of the premises and other good and
valuable consideration, the parties hereto agree as follows:

         1. Section 1(f) of the Purchase Agreement is hereby amended and
restated so as to read in its entirety as follows:

                   "If on or before February 1, 2004 (such date, as it may be
                  extended by written agreement of the Purchasers and the
                  Estate, the "Termination Date") the Demand Registration
                  Statement is not declared effective by the Securities and
                  Exchange Commission, or, if on or before the Termination Date,
                  Financial Services has not paid to the Estate the amount
                  described in Section 1(a)(ii), or, if on or before the
                  Termination Date, Cogene has not paid to the Estate the amount
                  described in Section 1(b)(ii), then on the third business day
                  occurring after the Termination Date (such day, or such other
                  day as may be agreed upon by the Purchasers and the Estate,
                  the "Subsequent Closing Date"), (i) the Estate shall pay to
                  Financial Services, in immediately available funds by wire
                  transfer to a bank account designated in writing by Financial
                  Services, cash in the amount of $3,268,000, (ii) Financial
                  Services shall deliver to the Estate a stock certificate
                  representing 3,440,000 of the Shares, together with stock
                  powers and signature guarantees in form and substance
                  satisfactory to the Estate, (iii) Financial Services' payment
                  obligation to the Estate under Section 1(a)(ii) hereof shall
                  terminate, (iv) the Estate shall pay to Cogene Biotech, in
                  immediately available funds by wire transfer to a bank account
                  designated in writing by Cogene Biotech, cash in the amount of
                  $817,000, (v) Cogene Biotech shall deliver to the Estate a
                  stock certificate representing 860,000 of the Shares, together
                  with stock powers and signature guarantees in the form and
                  substance satisfactory to the Estate, (vi) Cogene Biotech's
                  payment





                  obligation to the Estate under Section 1(b)(ii) hereof shall
                  terminate, (vii) the Purchasers shall assign and transfer to
                  the Estate the rights transferred to them under Section 4(a),
                  (viii) the Estate shall assume the obligations of the
                  Purchasers under the Registration Rights Agreement, and (ix)
                  the Purchasers and the Estate shall comply with the notice and
                  assumption requirements of Section 9 of the Registration
                  Rights Agreement. The Purchasers shall pay all stamp and other
                  transfer taxes, if any, that may be payable in respect of the
                  sale and delivery of such shares to the Estate on the
                  Subsequent Closing Date."

         2. Each reference to the Purchase Agreement in the Purchase Agreement,
this Amendment and all agreements, documents and notices executed in connection
with the Purchase Agreement shall, unless the context otherwise requires, mean
the Purchase Agreement as amended by this Amendment.

         3. The Purchase Agreement, as amended hereby, is in all respects
ratified, approved and confirmed.

         4. This Amendment may be executed in any number of counterparts, all of
which together make and shall constitute one and the same instrument and any of
the parties hereto may execute this Amendment by signing any such counterpart.

         5. This Amendment and the legal relations between the parties shall be
governed by and construed in accordance with the laws of the State of Delaware,
without regard to the principles of conflicts of law thereof.

                         [Signatures on following page]



                                      -2-


         IN WITNESS WHEREOF, the parties hereto have hereunto set their hands as
of the day and year first above written.

                                           RCM FINANCIAL SERVICES, L.P.

                                           By: RCM Financial Services GP, Inc.,
                                               its General Partner

                                           By: /s/ M. Robert Dussler
                                              ---------------------------------
                                           Name: M. Robert Dussler
                                           Title: Vice President


                                           COGENE BIOTECH VENTURES, L.P.

                                           By: Cogene Biotech Ventures GP, LLC,
                                               its General Partner


                                           By: /s/ M. Robert Dussler
                                              ---------------------------------
                                           Name: M. Robert Dussler
                                           Title: Vice President


                                           ESTATE OF GORDON A. CAIN


                                           By: /s/ James D. Weaver
                                              ---------------------------------
                                           Name: James D. Weaver
                                           Title: Independent Executor