News

CAMBRIDGE, Mass., May 20, 2002 /PRNewswire-FirstCall via COMTEX/ -- ImmunoGen, Inc. (Nasdaq: IMGN) and British Biotech plc (LSE: BBG, Nasdaq: BBIOY) today announced the presentation of safety and pharmacokinetic data from the first human clinical trial of the Tumor-Activated Prodrug (TAP) product, huN901-DM1/BB-10901. Early evidence of biologic activity was also reported.

BB-10901 is a conjugate of the cytotoxic maytansinoid drug, DM1, with the humanized monoclonal antibody, huN901. The drug is designed to selectively kill certain types of cancer cells including those found in small-cell lung cancer tumors.

The ongoing Phase I study is in patients with advanced small-cell lung cancer and other solid tumors potentially targeted by the drug. The study is designed to evaluate the pharmacokinetics and maximum tolerated dose of BB- 10901 when administered as a single infusion once a week. Once the maximum tolerated dose has been established, an additional forty patients will be treated in the Phase II portion of the study at that dosage.

The data were presented yesterday by the study's Principal Investigator, Frank V. Fossella, M.D., of the Houston-based University of Texas M. D. Anderson Cancer Center. The presentation was at the 2002 meeting of the American Society of Clinical Oncology (ASCO) currently taking place in Orlando, Florida.

To date, twenty-three patients have been enrolled in the study. Of these, eleven had relapsed after responding to earlier chemotherapy treatment, nine had shown no response to previous chemotherapy and three patients with neuroendocrine tumors had received no prior treatment. Patients have been recruited in cohorts of four and have been dosed with the drug once a week for four weeks, followed by two weeks off treatment. Dosing has been completed at the 5, 10, 20 and 40 mg/m2 levels and patient recruitment and dosing at the fifth level of 60 mg/m2 is continuing.

Repeated cycles of BB-10901 at doses up to and including 40 mg/m2 have been well tolerated. No dose-limiting toxicity has been found at these levels, nor has there been any evidence to date of hematologic or cardiac toxicity. At the 60 mg/m2 dosage level, two patients experienced dose-limiting events, but it is unclear if these were drug-related. Pharmacokinetic analysis has found the agent to have a half-life of approximately one day at the 40 mg/m2 dose level.

One patient had a transient partial response (>50% tumor reduction) at the 40 mg/m2 dosage level. Another patient had a minor response (>35% tumor reduction) at the 60 mg/m2 dosage level. Two additional patients had disease stabilization.

Later this year, British Biotech plans to initiate a second phase I study of BB-10901 to evaluate the effects of the drug when given on a more frequent dosing regimen. This follows the grant last month of a Clinical Trials Exemption (CTX) by the U.K.'s Medicines Control Agency for this study. More information will be announced when the study begins.

British Biotech acquired rights to develop and commercialize BB-10901 for Europe and Japan under an agreement with ImmunoGen in May 2000. ImmunoGen retained commercialization rights for the U.S. and the rest of the world.

About ImmunoGen, Inc.

ImmunoGen, Inc. develops innovative biopharmaceuticals for the treatment of cancer. The Company's TAP technology couples highly potent cytotoxic agents with tumor-targeting antibodies to create effective new treatments for cancer with minimal damage to normal tissue. Two TAP products developed by ImmunoGen are in clinical trials -- huN901-DM1/BB-10901 and cantuzumab mertansine; the latter is licensed to GlaxoSmithKline. Several companies are advancing TAP products comprised of ImmunoGen's TAP technology and the partner's antibody - Genentech (Trastuzumab-DM1), Millennium (MLN591DM1) and Boehringer Ingelheim (bivatuzumab mertansine). ImmunoGen also has multi-target agreements with Genentech, Abgenix, and Millennium that can potentially yield additional TAP products.

About British Biotech plc

British Biotech is a biopharmaceuticals company that aims to develop and commercialize specialist drugs for serious illnesses. It currently has four products in patient trials, supplemented by three focused and innovative laboratory research programs. Cash reserves of more than 50 million pounds sterling and recognized expertise in research and clinical development provide the resources to advance these programs and the basis for the creation of lasting shareholder value.

For ImmunoGen, Inc.

This press release includes forward-looking statements based on management's current expectations. Factors that could cause future results to differ materially from such expectations include, but are not limited to: the success of the Company's research strategy; the applicability of the discoveries made therein; the difficulties inherent in the development of pharmaceuticals, including uncertainties as to the timing and results of preclinical studies; delayed achievements of milestones; reliance on collaborators; uncertainty as to whether the Company's potential products will succeed in entering human clinical trials and uncertainty as to the results of such trials; uncertainty as to whether adequate reimbursement for these products will exist from the government, private healthcare insurers and third-party payors; the uncertainties as to the extent of future government regulation of the pharmaceutical business; and other factors described in ImmunoGen's periodic filings with the Securities and Exchange Commission.

For British Biotech plc

This news release contains forward-looking statements that reflect the Company's current expectations regarding future events. Forward-looking statements involve risks and uncertainties. Actual events could differ materially from those projected herein and depend on a number of factors including the success of the Company's research strategies, the applicability of the discoveries made therein, the successful and timely completion of clinical studies and the uncertainties related to the regulatory process.

SOURCE ImmunoGen, Inc.

CONTACT: Carol Hausner, Senior Director, Investor Relations and Corporate Communications, +1-617-995-2500, info@immunogen.com; or Dr Elliot Goldstein, Chief Executive Officer, or Tony Weir, Finance Director both of British Biotech plc, 01865 781166; or Pete Holmberg (Media) or Rx Communications Group, LLC, +1-917-322-2164, pholmberg@rxir.com; or Duke Coffey (Media) of GA Kraut, +1-212-696-5600; or John Olsen of Hogarth Partnership, 020 7357 9477