To: keokalani'nui who wrote (925 ) 2/27/2002 10:59:55 PM From: keokalani'nui Respond to of 3044 Proteasome Inhibitor PS-341, a Potential Therapeutic Agent for Adult T-Cell Leukemia Chalet Tan and Thomas A. Waldmann1 Metabolism Branch, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland 20892-1374 Nuclear factor B (NF-B) plays a major role in the pathogenesis of human T-cell lymphotrophic virus I-associated malignancy. Proteasome inhibitors provide a rational approach to control constitutively activated NF-B in human T-cell lymphotrophic virus I-infected T cells. We report that the proteasome inhibitor PS-341 decreased NF-B DNA binding activity by preventing degradation of IB. In our murine model of adult T-cell leukemia, PS-341 used alone did not yield prolongation of the survival of tumor-bearing mice. However, when combined with the current clinically approved drug humanized anti-Tac, therapy with PS-341 was associated with a complete remission in a proportion of treated animals, whereas only a partial response was observed in animals treated with humanized anti-Tac alone. 2/15 Cancer Research And from feb The Oncologist: Development of the Proteasome Inhibitor PS-341 Julian Adams Millennium Pharmaceuticals, Inc., Cambridge, Massachusetts, USA Correspondence: Julian Adams, Ph.D., Millennium Pharmaceuticals, Inc., 75 Sidney Street, Cambridge, Massachusetts 02139, USA. Telephone: 617-551-3674; Fax: 617-679-7370; e-mail: jadams@mpi.com Over the last decade, the critical role of the proteasome in cell-cycle regulation has become increasingly apparent. The proteasome, a multicatalytic protease present in all eukaryotic cells, is the primary component of the protein degradation pathway of the cell. By degrading regulatory proteins (or their inhibitors), the proteasome serves as a central conduit for many cellular regulatory signals and, thus, is a novel target for therapeutic drugs. PS-341 is a small molecule that is a potent and selective inhibitor of the proteasome. In vitro and mouse xenograft studies of PS-341 have shown antitumor activity in a variety of tumor types, including myeloma, chronic lymphocytic leukemia, prostate cancer, pancreatic cancer, and colon cancer, among others. Although PS-341 rapidly leaves the vascular compartment, a novel pharmacodynamic assay has shown that inhibition of proteasome—the biologic target—is dose dependent and reversible. These studies provided the rationale for a twice-weekly dosing schedule employed in ongoing clinical studies. Phase I trials in a variety of tumor types have shown PS-341 to be well tolerated, and phase II trials in several hematologic malignancies and solid tumor types are now in progress. Efficacy and safety data from the most advanced of these, a phase II multicenter trial in myeloma, will be available in early 2002.theoncologist.alphamedpress.org