This Article Full Text Full Text (PDF) Supplementary Data Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Demo, S. D. Articles by Bennett, M. K. Search for Related Content PubMed PubMed Citation Articles by Demo, S. D. Articles by Bennett, M. K.

Antitumor Activity of PR-171, a Novel Irreversible Inhibitor of the Proteasome

Proteolix, Inc., South San Francisco, California

Requests for reprints: Mark K. Bennett, Proteolix, Inc., South San Francisco, CA 94080. E-mail: mkbennett{at}proteolix.com.

Clinical studies with bortezomib have validated the proteasome as a therapeutic target for the treatment of multiple myeloma and non-Hodgkin's lymphoma. However, significant toxicities have restricted the intensity of bortezomib dosing. Here we describe the antitumor activity of PR-171, a novel epoxyketone-based irreversible proteasome inhibitor that is currently in clinical development. In comparison to bortezomib, PR-171 exhibits equal potency but greater selectivity for the chymotrypsin-like activity of the proteasome. In cell culture, PR-171 is more cytotoxic than bortezomib following brief treatments that mimic the in vivo pharmacokinetics of both molecules. Hematologic tumor cells exhibit the greatest sensitivity to brief exposure, whereas solid tumor cells and nontransformed cell types are less sensitive to such treatments. Cellular consequences of PR-171 treatment include the accumulation of proteasome substrates and induction of cell cycle arrest and/or apoptosis. Administration of PR-171 to animals results in the dose-dependent inhibition of the chymotrypsin-like proteasome activity in all tissues examined with the exception of the brain. PR-171 is well tolerated when administered for either 2 or 5 consecutive days at doses resulting in >80% proteasome inhibition in blood and most tissues. In human tumor xenograft models, PR-171 mediates an antitumor response that is both dose and schedule dependent. The antitumor efficacy of PR-171 delivered on 2 consecutive days is stronger than that of bortezomib administered on its clinical dosing schedule. These studies show the tolerability, efficacy, and dosing flexibility of PR-171 and provide validation for the clinical testing of PR-171 in the treatment of hematologic malignancies using dose-intensive schedules. [Cancer Res 2007;67(13):6383–91]

This article has been cited by other articles:

				L. Paoluzzi, M. Gonen, J. R. Gardner, J. Mastrella, D. Yang, J. Holmlund, M. Sorensen, L. Leopold, K. Manova, G. Marcucci, et al. Targeting Bcl-2 family members with the BH3 mimetic AT-101 markedly enhances the therapeutic effects of chemotherapeutic agents in in vitro and in vivo models of B-cell lymphoma Blood, June 1, 2008; 111(11): 5350 - 5358. [Abstract] [Full Text] [PDF]

				R. Z. Orlowski and D. J. Kuhn Proteasome Inhibitors in Cancer Therapy: Lessons from the First Decade Clin. Cancer Res., March 15, 2008; 14(6): 1649 - 1657. [Abstract] [Full Text] [PDF]

				D. Chauhan, A. Singh, M. Brahmandam, K. Podar, T. Hideshima, P. Richardson, N. Munshi, M. A. Palladino, and K. C. Anderson Combination of proteasome inhibitors bortezomib and NPI-0052 trigger in vivo synergistic cytotoxicity in multiple myeloma Blood, February 1, 2008; 111(3): 1654 - 1664. [Abstract] [Full Text] [PDF]