Abstract #4677: NVP-BEP795 and NVP-BEP800: Novel, fragment derived orally bioavailable small molecule Hsp90 inhibitors with potent antitumor activity

Heat shock protein 90 (Hsp90) is a ubiquitously expressed molecular chaperone with ATPase activity involved in the conformational maturation and stability of key signalling molecules involved in cell proliferation, survival and transformation. Through its ability to modulate multiple pathways involved in oncogenesis, Hsp90 has generated considerable interest as a therapeutic target. The most advanced Hsp90 inhibitor, tanespimycin (KOS-953, 17-AAG), is from the benzoquinone ansamycin class of inhibitors which demonstrated promising activity in human xenograft models and is now undergoing Phase III clinical evaluation for multiple myeloma. Several non-ansamycin Hsp90 inhibitors are currently progressing through Phase I clinical trials. Both NVP-BEP795 and NVP-BEP800 are novel, orally active Hsp90 inhibitor discovered through a combination of fragment based and in silico screening, and developed using SBDD. They potently bind to purified Hsp90 with IC₅₀ values of 58nM and 56nM respectively and exhibit selectivity of around 8-fold for NVP-BEP795 and 90-100 fold for NVP-BEP800 vs. Grp94 and TRAP-1. Inhibition of Hsp90 translates into proliferative inhibition of a wide variety of human tumour cell lines with GI₅₀ values in the range 43-1050nM for both compounds. Treatment of cell lines with NVP-BEP800 resulted in dissociation of p23/Hsp90, Hsp70 induction and client protein degradation - all hallmarks of Hsp90 inhibition. Exposure of cell lines to NVP-BEP800 resulted in both G1 and G2/M arrest as well as apoptosis. In a panel of breast tumour lines, NVP-BEP800 exhibited good potency with an average GI₅₀ of 160nM. Treatment of these breast cell lines with NVP-BEP800 resulted in Her2 degradation and Hsp70 upregulation, characteristic markers of an Hsp90 inhibitor mode of action. Following NVP-BEP800 treatment, cells responded through induction of both apoptotic and non-apoptotic forms of cell death as well as cytostasis. The propensity of a particularly cell line to apoptose could not be correlated with either client protein expression or expression of other factors known to modulate cell death responses. Pharmacokinetic analysis of the free base of NVP-BEP800 in mice resulted in reasonable bioavailability with a %F of 23%. In the BT474 Her2^+ve, daily oral dosing of both NVP-BEP795 and NVP-BEP800 at doses as low as 30mg/kg resulted in significant tumour regression without overt compound toxicity. Overall, we demonstrate that both NVP-BEP795 and NVP-BEP800 are potent, orally bioavailable small molecule inhibitors of Hsp90 with potent in vivo anti-tumour effects warranting further development.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 4677.