Preliminary and Updated Results of Four ZEVALIN Studies Presented at ASCO

Business Editors & Health/Medical Writers

(BW HealthWire) — IDEC Pharmaceuticals Corporation (Nasdaq:IDPH) today announced that preliminary and updated results of four studies of ZEVALIN(TM) (ibritumomab tiuxetan, IDEC-Y2B8) were presented at the 36th Annual Meeting of the American Society of Clinical Oncology (ASCO). ZEVALIN is an investigational radioimmunotherapy in late stages of development as a treatment for certain non-Hodgkin’s lymphomas (NHL).
“The interim ZEVALIN clinical findings and safety profile are favorable, even in patients who are resistant to chemotherapy,” said Christine A. White, M.D., IDEC Pharmaceuticals’ senior director of oncology and hematology and an author of all four presentations. “In addition, these preliminary data indicate that ZEVALIN’s dose may be standardized, based on patient body weight and baseline platelet count — without need for complex and time-consuming dosimetry.”

Biodistribution and Dosimetry of ZEVALIN

Gregory A Wiseman, M.D., of the Mayo Clinic, Rochester, MN, delivered a poster presentation discussing the biodistribution and dosimetry of ZEVALIN in 179 patients with relapsed or refractory B-cell NHL.
Each patient was treated with a standard dose of ZEVALIN at 0.4 mCi/kg, or 0.3 mCi/kg of yttrium-90 if they entered the study with reduced platelet count (100,000-149,000/mm3). In addition, each patient prior to therapy received ZEVALIN labeled with a tracer dose of indium-111, which allows the physician using dosimetry to predict the biodistribution of the yttrium-labeled radiotherapeutic agent.
Dr. Wiseman concluded, “Based on dosimetry measurements we can predict that patients would receive radiation-absorbed doses to normal organs and bone marrow well within a safe range for this population of 179 patients. In fact, toxicity upon treatment was primarily hematologic and transient with no dysfunction of major organs. Tumor response rates were very favorable.”

ZEVALIN in Chemotherapy-Resistant Patients

Thomas E. Witzig, M.D., of the Mayo Clinic gave a poster presentation of interim results of 90 patients from a prospectively randomized, controlled Phase III trial comparing ZEVALIN radioimmunotherapy to a standard course of Rituxan (four weekly doses of 375 mg/m2). The data were analyzed to assess the ability of prior chemotherapy response to predict response to ZEVALIN.
Patients in the analysis were designated chemotherapy-refractory if they had no response to their most recent chemotherapy regimen or a response with time-to-progression of less than six months. Using these criteria, 56 percent of patients were chemotherapy-refractory. The response rate to ZEVALIN was 77 percent for chemotherapy-refractory versus 81 percent for chemotherapy-sensitive patients (p=0.49).
Dr. Witzig concluded, “These interim results suggest that ZEVALIN may find especially important applications in treatment of patients who have become refractory or unresponsive to chemotherapy. Final conclusions await completion of the study.”

ZEVALIN Safety Profile

Leo I. Gordon, M.D., of the Division of Hematology/Oncology at Northwestern University Medical School and the Robert H. Lurie Cancer Center, Northwestern University, Chicago, IL, gave a poster presentation analyzing infection risk associated with ZEVALIN therapy in 210 patients. The data were analyzed for immunological effects as well as clinical events.
Treatment with the ZEVALIN regimen leads to prompt depletion of cancerous and normal B cells. Circulating B cells are undetectable for the first 12 weeks with normal B-cell recovery beginning the sixth month following therapy. The patients’ own circulating antibodies remain within the normal range following therapy.
Approximately 32 percent of ZEVALIN-treated patients experienced Grade 4 neutropenia (neutrophil count below 500/mm3). Clinical infections of moderate or greater severity occurred in 21 percent of patients. Sixteen of 210 patients were hospitalized, primarily due to infections; there were no deaths from infections.
Dr. Gordon concluded, “A full course of ZEVALIN therapy can be completed within eight days, compared to four to six months for standard chemotherapy. Moreover, neutropenia, treatment with growth factors and hospitalizations for infections are not unusual for patients undergoing chemotherapy.”

ZEVALIN Depletes Peripheral Blood BCL-2 Positive Cells

James L. Murray, M. D., of M. D. Anderson Cancer Center, Houston, TX, gave a poster presentation of interim results of a subset of 74 ZEVALIN-treated patients who had their peripheral blood evaluated by PCR analysis for the bcl-2 translocation, a chromosomal marker found in approximately 85 percent of patients with follicular NHL. Using PCR analysis, bcl-2 positive malignant cells can be detected down to a limit of one malignant cell among 100,000 normal cells. Fifty-six of the 74 ZEVALIN patients (76 percent) were positive at baseline.
Clearance of pre-existing bcl-2 from the circulation of ZEVALIN-treated patients was a good predictor of anti-tumor response — 84 percent of these patients responded to therapy. Patients without clearance of bcl-2 from the circulation were less likely (20 percent) to respond to ZEVALIN therapy. Time-to-progression of disease was similarly longer in patients responding to therapy who also cleared bcl-2 positive cells from the circulation.
Dr. Murray concluded, “ZEVALIN therapy appears to be well tolerated and clinically active in the treatment of relapsed or refractory, low grade, follicular or transformed B-cell NHL and, unlike typical courses of chemotherapy, has the ability to clear circulating bcl-2 positive cells.”
ZEVALIN is a monoclonal antibody that targets the CD20 antigen and is stably linked to the radioisotope yttrium-90. In December 1999, an interim analysis of a multi-center, randomized controlled study was presented at the American Society of Hematology conference indicating that ZEVALIN can be dosed based on clinical factors including patient body weight and baseline platelet count without need for complex and time-consuming dosimetry. This interim analysis showed an overall response rate (ORR) of 80 percent for the ZEVALIN group compared to ORR of 44 percent for the Rituxan group. Final results await completion of these studies.
IDEC Pharmaceuticals focuses on the commercialization and development of targeted therapies for the treatment of cancer and autoimmune diseases. IDEC’s antibody products act chiefly through immune system mechanisms, exerting their effect by binding to specific, readily targeted immune cells in the patient’s blood or lymphatic systems.
IDEC Pharmaceuticals’ news releases are available at no charge through Business Wire’s News on Demand Plus. For a menu of IDEC’s current news releases and quarterly reports or to retrieve a specific release, call (888) 329-2309. On the Internet check the News Center at IDEC’s website: .

The statements made in this press release contain certain forward-looking statements that involve a number of risks and uncertainties. Actual events or results may differ from IDEC’s expectations. For example, achievement of product development milestone events and future product sales, the timing, success and cost of product launches and clinical studies, the timing, acceptability and review periods of regulatory filings, the timing of and ability to obtain regulatory approval of products, the level of manufacturing performance and performance of our suppliers, and the risk factors listed from time to time in IDEC’s SEC filings, including but not limited to its Annual Report on Form 10-K for the year ended December 31, 1999 and Form 10-Q for the quarter ended March 31, 2000, may affect the actual results achieved by IDEC. These forward-looking statements represent the company’s judgment as of the date of this release. The company disclaims, however, any intent or obligation to update these forward-looking statements.

IDEC Pharmaceuticals and Rituxan are registered U.S. trademarks of the company. ZEVALIN is a trademark of the company. IDEC’s headquarters is located at 3030 Callan Road, San Diego, CA 92121.

IDEC Pharmaceuticals’ press releases are available at no charge through Business Wire’s News on Demand Plus. For a menu of IDEC’s current press releases and quarterly reports or to retrieve a specific release, call 888/329-2309. On the Internet, check the News Center at IDEC’s website http// .