PT  - JOURNAL ARTICLE
AU  - Chang, Chuan-Hsin
AU  - Drechsel, Derek A.
AU  - Kitson, Russell R. A.
AU  - Siegel, David
AU  - You, Qiang
AU  - Backos, Donald S.
AU  - Ju, Cynthia
AU  - Moody, Christopher J.
AU  - Ross, David
TI  - 19-Substituted Benzoquinone Ansamycin Heat Shock Protein-90 Inhibitors: Biological Activity and Decreased Off-Target Toxicity
AID  - 10.1124/mol.113.090654
DP  - 2014 Jun 01
TA  - Molecular Pharmacology
PG  - 849--857
VI  - 85
IP  - 6
4099  - http://molpharm.aspetjournals.org/content/85/6/849.short
4100  - http://molpharm.aspetjournals.org/content/85/6/849.full
SO  - Mol Pharmacol2014 Jun 01; 85
AB  - The benzoquinone ansamycins (BQAs) are a valuable class of antitumor agents that serve as inhibitors of heat shock protein (Hsp)-90. However, clinical use of BQAs has resulted in off-target toxicities, including concerns of hepatotoxicity. Mechanisms underlying the toxicity of quinones include their ability to redox cycle and/or arylate cellular nucleophiles. We have therefore designed 19-substituted BQAs to prevent glutathione conjugation and nonspecific interactions with protein thiols to minimize off-target effects and reduce hepatotoxicity. 19-Phenyl– and 19-methyl–substituted versions of geldanamycin and its derivatives, 17-allylamino-17-demethoxygeldanamycin and 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17-DMAG), did not react with glutathione, whereas marked reactivity was observed using parent BQAs. Importantly, although 17-DMAG induced cell death in primary and cultured mouse hepatocytes, 19-phenyl and 19-methyl DMAG showed reduced toxicity, validating the overall approach. Furthermore, our data suggest that arylation reactions, rather than redox cycling, are a major mechanism contributing to BQA hepatotoxicity. 19-Phenyl BQAs inhibited purified Hsp90 in a NAD(P)H:quinone oxidoreductase 1 (NQO1)–dependent manner, demonstrating increased efficacy of the hydroquinone ansamycin relative to its parent quinone. Molecular modeling supported increased stability of the hydroquinone form of 19-phenyl-DMAG in the active site of human Hsp90. In human breast cancer cells, 19-phenyl BQAs induced growth inhibition also dependent upon metabolism via NQO1 with decreased expression of client proteins and compensatory induction of Hsp70. These data demonstrate that 19-substituted BQAs are unreactive with thiols, display reduced hepatotoxicity, and retain Hsp90 and growth-inhibitory activity in human breast cancer cells, although with diminished potency relative to parent BQAs.