Abstract #4678: Preclinical anti-myeloma activity of the novel Hsp90 ATPase inhibitor NVP-BEP800

Inhibitors of heat shock protein of 90 kD (Hsp90) molecular chaperone ATPase activity are currently under intense preclinical and clinical evaluation for their use as anti-neoplastic agents. Because multiple myeloma (MM) has a propensity for relapse, Hsp90 inhibition, which leads to simultaneous breakdown of several growth and survival pathways, may offer additional treatment options. We have characterised the effects of a novel Hsp90 inhibitor (NVP-BEP800) on MM cell lines and primary MM cells. Western analyses and intracellular staining of several pathway components were employed to monitor levels of Hsp90 client proteins and signaling inhibition. Annexin V staining was used to establish kill curves. Alamar Blue assays served to analyse simultaneous exposure of MM cells to NVP-BEP800, standard of care and other agents (potentially) relevant to myeloma treatment (single-ray, constant ratio combination analysis according to the principle of Chou & Talalay). Exposure of MM cell lines (n=9) to NVP-BEP800 generally led to significant apoptotic responses (EC50: 80-300 nM, EC90: 130-1000 nM), although EC90 was not reached in 3 MM cell lines (U266, RPMI-8226 and KMS-12-BM). Similarly, the majority of primary MM cells was sensitive to treatment with the compound (n=37; all tested in coculture with bone marrow stromal cells (BMSCs)). After exposure to 500 nM NVP-BEP800 for 3 days 21/37 samples retained less than 25% surviving cells. In 9 of the samples tested less than 50% apoptosis was recorded. These non-sensitive samples were similar in their (un)responsiveness to nonmalignant peripheral blood mononuclear cells (n=10), while BMSCs remained unaffected at even higher concentrations of NVP-BEP800. Treatment with the Hsp90 inhibitor induced strong upregulation of Hsp70 in both MM cell lines and in primary tumour samples, and led to significant decreases in the levels of activated STAT3 and ERK1,2 in primary MM cells cocultured with BMSCs. Other pathways affected included those involving Akt and NF-kappaB. Combinations of NVP-BEP800 with either melphalan, doxorubicin, bortezomib or SAHA in MM cell lines AMO-1 and KMS-12-BM were synergistic for melphalan, largely additive for doxorubicin and slightly antagonistic for bortezomib and SAHA. In conclusion, the preclinical effects of NVP-BEP800 on MM cells confirm its molecular mode of action as an Hsp90 inhibitor and its potential utility to specifically target malignant cells in a majority of MM patients.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 4678.