Background: Multiple myeloma (MM) is tumor of long-lived bone marrow plasma cells. Nearly 40% of MM tumors have immunoglobulin heavy chain (IgH) translocations involving recurrent chromosomal loci: such as 11q13 (Cyclin D1), 6q21 (Cyclin D3), 4p16 (FGFR3 and MMSET), and 16q23 (c-Maf), resulting in aberrant expression of each gene. The heat shock protein 90 (Hsp90) plays an important role in chaperoning client proteins that regulate cell growth and survival, and has recently been found overexpressed in MM. Here, we report the molecular and biological effects of a novel Hsp90 inhibitor of non-ansamycin, non-purine analog class, KW-2478, in human MM cell lines having various IgH translocations. This drug is currently undergoing clinical evaluation in a phase I trial in patients with haematological malignancies including MM. Methods: The effects of KW-2478 on time dependency of cell growth, apoptosis induction, and the changes in Hsp90 client proteins in MM cell lines (KMS-11, OPM-2, NCI-H929, RPMI-8226, and U266) were studied. In addition, the effects on Cyclin D1, FGFR3, and c-Maf proteins encoded by the partner genes in IgH translocations were also examined. The in vivo anti-tumor activity of KW-2478 was evaluated in a subcutaneously (s.c.) inoculated xenograft model in two dosing schedules. Results: KW-2478 clearly inhibited cancer cell growth in all cell lines, with GI50 values from 120 to 390 nM in MM cell lines. The growth inhibitory activity against OPM-2 and NCI-H929 cells was shown to be time-dependent, and the potent growth inhibitory activity was observed after 12 hours of drug treatment. Exposure of KW-2478 to MM cell lines resulted in the degradation of well-known Hsp90 client proteins (IGF-1R\#946; and c-Raf-1) as well as the decrease of IgH translocation products (Cyclin D1, FGFR3, and c-Maf). KW-2478 also induced PARP cleavage and dephosphorylated signalling molecules in KMS-11, OPM-2, and NCI-H929 cells. Moreover, CDK9, a key transcriptional regulator of protein kinase, was also depleted by treatment of KW-2478 in all cells. In the NCI-H929 s.c. inoculated model, anti-tumor activity of KW-2478 in qd×5 schedule was more potent than that in biw×2 schedule, which correlated with the reduction of serum M protein concentrations. Conclusions: The novel Hsp90 inhibitor KW-2478 showed more potent anti-myeloma activity both in vitro and in vivo by consecutive drug treatment and administration. Moreover, this drug induced significant reductions in major IgH translocation products, associated with the depletion of CDK9. It is indicated that CDK9 might play a critical role in transcriptional regulation of the partner genes in IgH translocations. Inhibition of CDK9 by KW-2478 could serve as useful pharmacological effects. KW-2478 could be a potent therapeutic agent against transcriptional CDK-activating human malignancies in addition to MM.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 4686.

100th AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO

American Association for Cancer Research
2009