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Semin Oncol. 2001 Dec;28(6):613-9.

Proteasome inhibition in cancer: development of PS-341.

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Millennium Pharmaceuticals, Inc., 75 Sydney Street, Cambridge, MA 02139, USA.


The 26S proteasome regulates protein turnover in eukaryotic cells. This is relevant in human cancer because the cell cycle, tumor growth, and survival are governed by a large repertoire of intracellular proteins that are regulated by the ubiquitin-mediated proteasome degradative pathway. In the development of new antitumor agents whose mechanisms are distinct from currently available therapies, we have discovered a potent, selective inhibitor of the proteasome: PS-341, a dipeptide boronic acid. Compared with normal cells, cancer cells--and specifically myeloma--treated with PS-341 are differentially sensitive to proteasome inhibition and apoptosis. A unique feature of PS-341 involves the inhibition of nuclear factor (NF)-kappaB activation through stabilization of the inhibitor protein IkappaB. Myeloma cells depend on NF-kappaB-mediated transcription of cytokine growth factor interleukin-6, angiogenesis through vascular endothelial growth factor, and the cell adhesion molecule VCAM-1 for adherence of the plasma cells to the stromal tissue in bone marrow. At low nanomolar concentrations, PS-341 is highly effective in abrogating the transcription of these genes, which are under the direct regulation of NF-kappaB. Moreover, PS-341 appears to synergize with dexamethasone in myeloma cell culture, which may prove to be of additional benefit clinically. The safety profile in phase I trials of PS-341 in patients with cancer appears encouraging. Because proteasome inhibition with PS-341 results in potent antitumor activity in vitro, PS-341 may offer a promising new approach to treating otherwise fatal malignancy.

[Indexed for MEDLINE]

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