Coulter Pharmaceutical Acquires Rights to Potent Anti-Cancer Compounds.

Business Editors and Health/Medical Writers

SOUTH SAN FRANCISCO, Calif.--(BW HealthWire)--Sept. 21, 2000

Coulter Pharmaceutical, Inc. (Nasdaq:CLTR) today announced that it has acquired rights to a class of ultra-potent anti-cancer compounds from Kyowa Hakko Kogyo Co., Ltd. of Japan. Coulter intends to enhance the potency of these agents by incorporating them into Coulter's proprietary tumor activated prodrug (TAP) and tumor specific targeting (TST) technologies. The resulting drug candidates will be designed to target the potent anti-cancer power of these agents directly to tumor cells to maximize efficacy while minimizing side-effects to normal tissues.

The ultra-potent compounds, Duocarmycin B2 and KW-2189, have been shown to be 1,000 times more potent than standard chemotherapy drugs and work by directly attacking the DNA of cancer cells, causing cell death. They represent a new class of chemotherapeutics which may be added to the armamentarium available to oncologists. Drug candidates using these compounds have already been created by Coulter and have shown significant activity against multi-drug resistant human tumor cell lines. The company is currently conducting studies to support human clinical trials.

"We are pleased to enter into this agreement with Kyowa Hakko Kogyo, the discoverer of the Duocarmycin class of ultra-potent compounds and a leader in their development," said Michael F. Bigham, president and chief executive officer of Coulter. "These newly acquired compounds are extremely potent anti-cancer agents which can be delivered directly to tumors using our proprietary tumor targeting technologies."

Under the terms of the agreement, Coulter acquired exclusive worldwide rights to all uses of the ultra-potent agents. Detailed financial terms of the agreement were not disclosed but include an upfront payment to Kyowa Hakko Kogyo with future payments committed for certain development milestones and royalties upon commercialization.

Coulter is developing its tumor activated prodrug (TAP) technology to enhance the specificity of chemotherapeutic agents for tumor cells. TAP prodrugs are designed to remain stable in circulation until being activated preferentially at the tumor site. As a result, relatively larger quantities of cytotoxic agents are expected to reach and enter malignant cells compared to normal cells. This approach is designed to permit an increase in maximum tolerated dosages, potentially overcoming drug resistance in some cancer cells. In addition to TAP, the company is also developing tumor specific targeting (TST) technologies including peptides, non-peptides and internalizing antibodies. These targeting approaches are designed to bind the TST compound selectively to tumor target cells. Upon binding, the TST compound is internalized into the cell and the ultra potent payload is released from the targeting entity. Once released, the ultra potent drug acts on its intracellular target and kills the tumor cell.

Coulter Pharmaceutical, Inc. is engaged in the development of novel drugs and therapies for the treatment of cancer and autoimmune diseases. The company currently is developing a family of therapeutics based upon two drug development programs: therapeutic antibodies and targeted oncologics. The company's most advanced product candidate is Bexxar(TM), a monoclonal antibody conjugated to a radioisotope. The company's therapeutic antibodies program also includes an interferon receptor antagonist. Initial efforts in the targeted oncologics program are based on tumor activated prodrug (TAP) and tumor-specific targeting (TST) technologies. For more company information, visit Coulter Pharmaceutical's web site at http://www.coulterpharm.com.

Except for the historical information contained herein, the matters discussed in this news release are forward-looking statements for Coulter Pharmaceutical, Inc. that involve risks and uncertainties, including uncertainties related to product development, uncertainties related to the need for regulatory and other government approvals, dependence on proprietary technology, uncertainty of market acceptance of Bexxar(TM) or the company's other product candidates and other risks detailed from time to time in the company's filings with the Securities and Exchange Commission (SEC). In particular, see "Risk Factors" in the company's Registration Statement on Form S-3 filed August 30, 2000, and Annual Report on Form 10-K for the year ended December 31, 1999.