Coulter Pharmaceutical Reports Clinical Data From a Phase I/II Investigational Trial of High-Dose Bexxar in Combination With Chemotherapy for Non-Hodgkin's Lymphoma.

PALO ALTO, Calif.--(BW HealthWire)--May 18, 1998--

Data Presented at American Society of Clinical Oncology (ASCO)

Coulter Pharmaceutical (NASDAQ: CLTR) today announced preliminary data from an investigational clinical trial with high doses of Bexxar(TM) (iodine I 131 tositumomab) in combination with chemotherapy and stem cell transplantation in non-Hodgkin's lymphoma (NHL) patients.

The data, presented by Oliver Press, M.D., Ph.D., professor of Medicine in the Division of Medical Oncology at the University of Washington Medical Center and member of the Fred Hutchinson Cancer Research Center, at the 34th Annual ASCO meeting, demonstrated that Bexxar, a radiolabeled monoclonal antibody, has the potential to be safely and effectively combined with chemotherapy and autologous stem cell transplantation to treat patients with relapsed NHL.

Clinical Trial Results

This Phase I/II trial enrolled 43 relapsed NHL patients in which 28 of 43 patients (65 percent) had low grade and 15 of 43 patients (35 percent) had intermediate or high grade NHL. Of the 42 evaluable patients, 31 of 42 patients (74 percent) are progression-free after a median follow-up of 1.5 years. All patients experienced myelosuppression by design with the high dose combination regimen of chemotherapy and Bexxar(TM) (at a level approximately four to ten times the mean standard dose of Bexxar(TM) ). Other dose-limiting toxicities included pulmonary and gastrointestinal toxicities.

Each patient was administered a combination regimen consisting of high-dose Bexxar(TM) (iodine I 131 tositumomab) (20-27 Gy from 318-840 mCi) and high-dose chemotherapy which was used to ablate the patients' bone marrow prior to transplantation in an effort to eradicate residual tumor cells in the body. Following myeloablation, the bone marrow was replenished through autologous stem cell transplantation. The goal of this dose-escalating study was to define the maximally tolerated dose of high-dose Bexxar(TM) in combination with high-dose chemotherapy and to define the response rates and toxicities associated with this regimen.

"The purpose of this study was to investigate whether combining high-dose Bexxar(TM) with chemotherapy before stem cell transplantation was a safe and effective method to treat relapsed NHL patients," said Dr. Press. "Currently, for cancer patients who are in need of a bone marrow transplant, the conventional preparation is total body irradiation as well as chemotherapy. This approach, while necessary, is successful in less than half the patients using conventional irradiation and chemotherapy. It is our belief that utilizing Bexxar(TM), a more targeted and site-specific approach, instead of total body irradiation, may increase both the efficacy and safety profile of transplantation."

Dr. Press continued, "While our results are preliminary, we have observed that a majority of patients respond to this regimen, with manageable toxicities at dose levels below 25 Gy to normal organs, and that this protocol is worthy of further study. Additionally, we believe this protocol may be effective in treating intermediate-grade NHL patients."

Dr. Press is also evaluating high-dose Bexxar(TM) as a single agent in conjunction with bone marrow transplantation. In this trial, 14 out of 29 patients (48 percent) remain in remission for up to 8.5 years following Bexxar(TM)/bone marrow transplant treatment.

Background on Bexxar and NHL

Bexxar(TM) (iodine I 131 tositumomab), which is an antibody conjugated to iodine-131, attaches to the CD20 antigen found only on the surface of B-cells, both non-Hodgkin's lymphoma B-cells and some normal B-cells. Coulter believes that through this targeted approach, the tumor cells receive a greater concentration of the therapeutic radiation from Bexxar(TM) relative to normal tissues.

NHL is a form of cancer that affects the blood and lymph tissues. NHL currently is the sixth leading cause of death among cancers in the United States and has the second fastest growing mortality rate. According to statistics from the National Cancer Institute, approximately 270,000 people are afflicted with NHL in the United States alone. Of the total, the company estimates that approximately 140,000 people have low-grade or transformed low-grade disease. There are approximately 54,000 new cases of NHL diagnosed each year.

Coulter Pharmaceutical, Inc. is engaged in the development of novel drugs and therapies for the treatment of people with cancer. The company currently is developing a family of cancer therapeutics based upon two drug development programs: therapeutic antibodies and targeted oncologics. The company's most advanced investigational biologic product candidate is Bexxar(TM) (iodine I 131 tositumomab), a monoclonal antibody conjugated to a radioisotope. The company intends to file a BLA for Bexxar by the end of 1998. Initial efforts in the targeted oncologics program are focused on the development of a tumor-activated peptide pro-drug version of doxorubicin to potentially treat certain solid tumor cancers.

Except for the historical information contained herein, the matters discussed in this news release are forward-looking statements 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 Annual Report on Form 10-K for the year ended December 31, 1997.

CONTACT: Coulter Pharmaceutical Inc.

Sylvia Wheeler, 650/842-7306

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Noonan/Russo Communications, Inc.

Neil Cohen, 212/696-4455

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