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Blood, 23 April 2009, Vol. 113, No. 17, pp. 4027-4037.
Prepublished online as a Blood First Edition Paper on December 18, 2008; DOI 10.1182/blood-2008-09-179796.
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LYMPHOID NEOPLASIA
Identification of a potent natural triterpenoid inhibitor of proteosome chymotrypsin-like activity and NF- B with antimyeloma activity in vitro and in vivo
Rodger E. Tiedemann1,
Jessica Schmidt1,
Jonathan J. Keats1,
Chang-Xin Shi1,
Yuan Xiao Zhu1,
Stephen E. Palmer1,
Xinliang Mao2,3,
Aaron D. Schimmer2,3, and
A. Keith Stewart1
1 Division of Hematology and Oncology, Comprehensive Cancer Center, Mayo Clinic, Scottsdale, AZ;
2 The Princess Margaret Hospital and The Ontario Cancer Institute, Toronto, ON; and
3 The Sinai-McLaughlin Assay and Robotic Technologies Facility, Mount Sinai Hospital, Toronto, ON
As multiple myeloma tumors universally dysregulate cyclin D genes we conducted high-throughput chemical library screens for compounds that induce suppression of cyclin D2 promoter transcription. The top-ranked compound was a natural triterpenoid, pristimerin. Strikingly, the early transcriptional response of cells treated with pristimerin closely resembles cellular responses elicited by proteosome inhibitors, with rapid induction of heat shock proteins, activating transcription factor 3 (ATF3), and CHOP. Enzymatic assays and immunoblotting confirm that pristimerin rapidly (< 90 minutes) and specifically inhibits chymotrypsin-like proteosome activity at low concentrations (< 100 nM) and causes accumulation of cellular ubiquitinated proteins. Notably, cytotoxic triterpenoids including pristimerin inhibit NF- B activation via inhibition of IKK or IKKβ, whereas proteosome inhibitors instead suppress NF-B function by impairing degradation of ubiquitinated IB. By inhibiting both IKK and the proteosome, pristimerin causes overt suppression of constitutive NF-B activity in myeloma cells that may mediate its suppression of cyclin D. Multiple myeloma is exquisitely sensitive to proteosome or NF-B pathway inhibition. Consistent with this, pristimerin is potently and selectively lethal to primary myeloma cells (IC50 < 100 nM), inhibits xenografted plasmacytoma tumors in mice, and is synergistically cytotoxic with bortezomib—providing the rationale for pharmaceutical development of triterpenoid dual-function proteosome/NF-B inhibitors as therapeutics for human multiple myeloma and related malignancies.
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