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Br J Haematol. 2011 Jan;152(2):155-63. doi: 10.1111/j.1365-2141.2010.08491.x. Epub 2010 Nov 29.

PR-924, a selective inhibitor of the immunoproteasome subunit LMP-7, blocks multiple myeloma cell growth both in vitro and in vivo.

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Jerome Lipper Multiple Myeloma Center, Department of Medical Oncology, Dana Farber Cancer Institute, Harvard Medical School, Boston, MA, USA.


PR-924 is an LMP-7-selective tripeptide epoxyketone proteasome inhibitor that covalently modifies proteasomal N-terminal threonine active sites. In the present study, we show that PR-924 inhibits growth and triggers apoptosis in multiple myeloma (MM) cell lines and primary patient MM cells, without significantly affecting normal peripheral blood mononuclear cells. PR-924-induced apoptosis in MM cells is associated with activation of caspase-3, caspase-8, caspase-9, BID, PARP and cytochrome-c release. In vivo administration of PR-924 inhibits tumour growth in human plasmacytoma xenografts. Results from SCID-hu model show a significant reduction in the shIL-6R levels in mice treated with PR-924 versus vehicle-control. PR-924 treatment was well tolerated as evidenced by the lack of weight loss. Importantly, treatment of tumour-bearing mice with PR-924, but not vehicle alone, prolonged survival. Our preclinical findings therefore validate immunoproteasome LMP-7 subunit as a novel therapeutic target in MM.

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