A novel, selective, orally active, potent small molecule inhibitor of Hsp90

Abstract

13067 Background: The preclinical and clinical data evaluating derivatives of the natural product geldanamycin, including 17-AAG and 17-DMAG, reveal that inhibition of the molecular chaperone HSP90 results in multiple anti-tumor effects. SNX-5422 and SNX-5542 are potent, novel, highly specific, water soluble and orally active small molecule inhibitors of Hsp90. Here we describe the preclinical efficacy and toxicity evaluation of these compounds. Methods: The PK profile of SNX-5422 and SNX-5542 was determined following oral and iv dosing in mice and rats. HT29 xenografts were performed oral doses of SNX-5542 on a schedule of Q2DX3,2 for 2 weeks or 17-DMAG on the previously reported regimen of bid×5,2 for 2 weeks, with tumor progression and body weight monitored. Plasma, tumor and other tissues were harvested for evaluation of HSP70 induction and levels of HSP90 client proteins. Rats were treated with varying oral doses on a schedule of Q2DX3,2 for two weeks. Clinical observations were noted and standard hematology and clinical chemistry parameters were monitored. Results: SNX-5542 exhibited 37% oral BA in rats and >75% in mice, with t½ >7h in each species. SNX-5542 was well tolerated in normal and tumor-bearing mice at 300 mg/m2 Q2DX3,2 for 2 weeks, 0.9% weight gain. 17-DMAG at 30 mg/m2 bid×5,2 for 2 weeks caused 3.3% body weight loss. At these doses, SNX-5542 exhibited 78% median tumor growth inhibition of HT29 tumors while 17-DMAG exhibited 23% inhibition. Mechanistic indicators of HSP90 inhibition correlated with efficacy across multiple dosing levels. At 120 mg/m2 Q2DX3,2 for 2 weeks SNX-5422 was well tolerated in rats, with no significant effect on any clinical, hematology or clinical chemistry parameter with the exception of a slight increase in blood urea nitrogen levels. Histopathological evaluation of liver, thymus, spleen and kidneys revealed no significant treatment-related effects. At 120 mg/m2 Q2DX3,2 for 13 days SNX-5422 does not exhibit any of the toxicities reported for 17-DMAG (bidX5,2 for 8 days at 24 mg/m2). Conclusions: SNX small-molecule HSP90 inhibitors have favorable pharmacokinetic profiles, oral bioavailability, tolerability and superior anti-tumor activity compared to the natural product derivative 17-DMAG. [Table: see text]