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| |  FLT-3 Ligand Induces Tumor Regression and Anti-Tumor Responses SEATTLE, June 2, 1997 -- The results of a new study demonstrating that Flt-3 ligand may have a role in cancer treatment are published in the June 1 issue of the journal Nature Medicine. In the study, Flt-3 ligand, which helps increase stem cells and dendritic cells, was administered to mice challenged with progressively growing tumors. The results showed complete regression of those tumors in a significant proportion of the mice and a decrease in tumor growth rate in the remainder. "We knew that dendritic cells were important in treating cancer, but the scarcity of these cells has hampered the feasibility of using them to induce immune responses to tumor cells," said David Lynch, Ph.D., author of the paper and a senior staff scientist at Immunex Corporation, makers of the drug. "However, the findings that Flt-3 ligand stimulates the production of large numbers of dendritic cells led us to investigate its potential in treating cancer. The results are both surprising and gratifying." Treatment with daily injections of Flt-3 ligand for 19 days caused complete regression of tumors in 38 percent of mice challenged with chemically-induced skin tumors, called fibrosarcomas. Flt-3 ligand injections also caused a significant decrease in the rate of tumor growth in the mice not experiencing complete regression. Five weeks after tumor challenge, mean tumor size in treated mice was less than one-third the size in controls (approximately 60mm2 vs 185mm2, respectively). The beneficial effects of Flt-3 ligand administration were dependent on both the dose of Flt-3 ligand used per treatment and the number of treatments. The study also demonstrated that administration of Flt-3 ligand to mice with tumors established as much as seven days prior to treatment, resulted in complete regression of a high proportion of the tumors. Treatment that began 10 to 14 days after tumors were established showed a low proportion of complete tumor rejection, but a significant decrease in tumor growth was observed compared to controls. "These results demonstrate that Flt-3 ligand may prove to be an important cytokine in the generation of effective anti-tumor immune responses in vivo and in the treatment of cancer," said Doug Williams, Ph.D. and Immunex senior vice president, discovery research. "We have just begun the first human clinical study to test the effects of Flt-3 ligand on the generation of anti-tumor immune responses." Flt-3 ligand is a cytokine growth factor that helps to increase numbers of vital immune system cells including stem cells and dendritic cells. Dendritic cells are relatively rare cells that play a crucial role in processing and presenting antigens to the immune system. The presentation of antigens by dendritic cells is a critical step in initiating effective immune responses not only to pathogens, but to cancer cells as well. Immunex is also conducting Phase I/II clinical trials of Flt-3 ligand in healthy human volunteers for mobilization of stem cells. Blood stem cells are increasingly used to replace white blood cells damaged by aggressive cancer treatments. The results of one of these trials demonstrated that Flt-3 ligand was safe when given to healthy volunteers. Immunex Corporation is a biopharmaceutical company dedicated to developing immune system science to protect human health. The company's products offer hope to patients with cancer, inflammatory and infectious disease. American Home Products Corporation owns a majority interest in Immunex Corporation. AHPC is one of the world's largest research-based pharmaceutical and health care products companies and is a leading developer, manufacturer and marketer of prescription drugs and over-the-counter medications. It is also a leader in vaccines, biotechnology, agricultural products, animal health care and medical devices.
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