SNX2112, a synthetic heat shock protein 90 inhibitor, has potent antitumor activity against HER kinase-dependent cancers

Purpose: The heat shock protein 90 (Hsp90) chaperone plays an important role in transformation by regulating the conformational maturation and stability of oncogenic kinases and transcription factors. Ansamycins, such as 17-(allylamino)-17-demethoxygeldanmycin (17-AAG), inhibit Hsp90 function; induce the degradation of Hsp90 client proteins such as HER2, and have shown activity in early clinical trials. However, the utility of these drugs has been limited by their hepatotoxicity, poor solubility, and poorly tolerated formulations. Experimental Design: We determined the pharmacodynamic and antitumor properties of a novel, synthetic Hsp90 inhibitor, SNX-2112, in cell culture and xenograft models of HER kinase-dependent cancers. Results: We show in a panel of tumor cell lines that SNX-2112 and its prodrug SNX-5542 are Hsp90 inhibitors with properties and potency similar to that of 17-AAG, including: degradation of HER2, mutant epidermal growth factor receptor, and other client proteins, inhibition of extracellular signal-regulated kinase and Akt activation, and induction of a Rb-dependent G(1) arrest with subsequent apoptosis. SNX-5542 can be administered to mice orally on a daily schedule. Following oral administration, SNX-5542 is rapidly converted to SNX-2112, which accumulates in tumors relative to normal tissues. A single dose of SNX-5542 causes HER2 degradation and inhibits its downstream signaling for up to 24 h, and daily dosing results in regression of HER2-dependent xenografts. SNX-5542 also shows greater activity than 17-AAG in a non small cell lung cancer xenograft model expressing mutant EGFR. Conclusions: These results suggest that Hsp90 inhibition with SNX-2112 (delivered as a prodrug) may represent a promising therapeutic strategy for tumors whose growth and survival is dependent on Hsp90 clients.