The benzoquinone ansamycin Hsp90 inhibitors 17-AAG and 17-DMAG are in Phase II trials but their use is limited by hepatotoxicity. In the last grant period we found that the active forms of the BQA Hsp90 inhibitors were their hydroquinone metabolites generated by the quinone reductase NQO1 rather than the parent quinones. We defined the molecular determinants of hepatotoxicity of BQA Hsp90 inhibitors and have focused on the development of entirely novel 19-substituted BQAs (19BQAs) which are metabolized by NQO1 to active hydroquinone ansamycin Hsp90 inhibitors. 19BQAs were rationally designed in our labs (DR and CJM) specifically to prevent off-target interactions with glutathione and protein thiols and to be markedly less toxic than the current BQA derivatives in clinical trials. Preliminary data validates the underlying rationale and shows that 19BQAs do not interact with cellular thiols and are not toxic in mouse hepatocyte systems. In this proposal, we will focus on testing the hypothesis that 19BQAs are potent Hsp90 inhibitors that have markedly less toxicity than their parent quinones using both in-vitro and in-vivo approaches. We will finalize the structure-activity relationship for 19BQAs in the geldanamycin, 17-AAG and 17-DMAG series and characterize their structure and binding to purified Hsp90 using X-ray and NMR analysis. Cellular studies will define a) the Hsp90 and growth inhibitory effects of 19BQAs in both human breast and pancreatic tumor cells b) metabolism of 19BQAs to their hydroquinones by NQO1 using isogenic breast and pancreatic tumor cell lines differing only in NQO1 and c) the effects of 19 BQAs on association of Hsp90 with co-chaperones which modulate Hsp90 function and deliver key client proteins essential for growth to Hsp90. The hepatotoxicity of 19BQAs in both mouse and human hepatocyte systems will be characterized and together with data from studies in tumor cell systems will allow us to advance compounds with the greatest therapeutic index to in-vivo testing in xenograft and explant systems where the use of an integrated PK-PD model will address the in-vivo therapeutic selectivity of 19BQAs. Using a mechanistic approach, these studies will validate the potential of an entirely novel class of Hsp90 inhibitors designed to be markedly less hepatotoxic than the BQA Hsp90 inhibitors currently in clinical trials.

Public Health Relevance

The benzoquinone ansamycin Hsp90 inhibitors 17-AAG and 17-DMAG are in Phase II trials but their use is limited by hepatotoxicity. We have designed novel benzoquinone ansamycin Hsp90 inhibitors to limit their off target effects and specifically their hepatotoxicity. Preliminary data validates this approach and we will define the Hsp90 inhibitory activity of this novel class of molecules, their biology, lack of hepatotoxicity and therapeutic activity in pre-clinical models of breast and pancreatic cancer.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
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Drug Discovery and Molecular Pharmacology Study Section (DMP)
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Forry, Suzanne L
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University of Colorado Denver
Schools of Pharmacy
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Ross, David; Siegel, David (2017) Functions of NQO1 in Cellular Protection and CoQ10 Metabolism and its Potential Role as a Redox Sensitive Molecular Switch. Front Physiol 8:595
Xiong, Rui; Zhou, Wenbo; Siegel, David et al. (2015) A Novel Hsp90 Inhibitor Activates Compensatory Heat Shock Protein Responses and Autophagy and Alleviates Mutant A53T ?-Synuclein Toxicity. Mol Pharmacol 88:1045-54
Chang, Chuan-Hsin; Drechsel, Derek A; Kitson, Russell R A et al. (2014) 19-substituted benzoquinone ansamycin heat shock protein-90 inhibitors: biological activity and decreased off-target toxicity. Mol Pharmacol 85:849-57
Kitson, Russell R A; Chang, Chuan-Hsin; Xiong, Rui et al. (2013) Synthesis of 19-substituted geldanamycins with altered conformations and their binding to heat shock protein Hsp90. Nat Chem 5:307-14
Siegel, David; Yan, Chao; Ross, David (2012) NAD(P)H:quinone oxidoreductase 1 (NQO1) in the sensitivity and resistance to antitumor quinones. Biochem Pharmacol 83:1033-40
Reigan, Philip; Siegel, David; Guo, Wenchang et al. (2011) A mechanistic and structural analysis of the inhibition of the 90-kDa heat shock protein by the benzoquinone and hydroquinone ansamycins. Mol Pharmacol 79:823-32
Siegel, David; Shieh, Biehuoy; Yan, Chao et al. (2011) Role for NAD(P)H:quinone oxidoreductase 1 and manganese-dependent superoxide dismutase in 17-(allylamino)-17-demethoxygeldanamycin-induced heat shock protein 90 inhibition in pancreatic cancer cells. J Pharmacol Exp Ther 336:874-80
Guo, Wenchang; Siegel, David; Ross, David (2008) Stability of the Hsp90 inhibitor 17AAG hydroquinone and prevention of metal-catalyzed oxidation. J Pharm Sci 97:5147-57
Yan, Chao; Kepa, Jadwiga K; Siegel, David et al. (2008) Dissecting the role of multiple reductases in bioactivation and cytotoxicity of the antitumor agent 2,5-diaziridinyl-3-(hydroxymethyl)-6-methyl-1,4-benzoquinone (RH1). Mol Pharmacol 74:1657-65
Guo, Wenchang; Reigan, Philip; Siegel, David et al. (2008) Enzymatic reduction and glutathione conjugation of benzoquinone ansamycin heat shock protein 90 inhibitors: relevance for toxicity and mechanism of action. Drug Metab Dispos 36:2050-7

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