No abstract

Targeted inhibition of the molecular chaperone Hsp90 results in the simultaneous blockade of multiple oncogenic signaling pathways and has, thus, emerged as an attractive strategy for the development of novel cancer therapeutics. Ganetespib (formerly known as STA-9090) is a unique resorcinolic triazolone inhibitor of Hsp90 that is currently in clinical trials for a number of human cancers. In the present study, we showed that ganetespib exhibits potent in vitro cytotoxicity in a range of solid and hematologic tumor cell lines, including those that express mutated kinases that confer resistance to small-molecule tyrosine kinase inhibitors. Ganetespib treatment rapidly induced the degradation of known Hsp90 client proteins, displayed superior potency to the ansamycin inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG), and exhibited sustained activity even with short exposure times. In vivo, ganetespib showed potent antitumor efficacy in solid and hematologic xenograft models of oncogene addiction, as evidenced by significant growth inhibition and/or regressions. Notably, evaluation of the microregional activity of ganetespib in tumor xenografts showed that ganetespib was efficiently distributed throughout tumor tissue, including hypoxic regions >150 mm from the microvasculature, to inhibit proliferation and induce apoptosis. Importantly, ganetespib showed no evidence of cardiac or liver toxicity. Taken together, this preclinical activity profile indicates that ganetespib may have broad application for a variety of human malignancies, and with select mechanistic and safety advantages over other first-and second-generation Hsp90 inhibitors. Mol Cancer Ther; 11(2); 475-84. Ó2011 AACR.

Elesclomol is a first-in-class investigational drug currently undergoing clinical evaluation as a novel cancer therapeutic. The potent antitumor activity of the compound results from the elevation of reactive oxygen species (ROS) and oxidative stress to levels incompatible with cellular survival. However, the molecular target(s) and mechanism by which elesclomol generates ROS and subsequent cell death were previously undefined. The cellular cytotoxicity of elesclomol in the yeast S. cerevisiae appears to occur by a mechanism similar, if not identical, to that in cancer cells. Accordingly, here we used a powerful and validated technology only available in yeast that provides critical insights into the mechanism of action, targets and processes that are disrupted by drug treatment. Using this approach we show that elesclomol does not work through a specific cellular protein target. Instead, it targets a biologically coherent set of processes occurring in the mitochondrion. Specifically, the results indicate that elesclomol, driven by its redox chemistry, interacts with the electron transport chain (ETC) to generate high levels of ROS within the organelle and consequently cell death. Additional experiments in melanoma cells involving drug treatments or cells lacking ETC function confirm that the drug works similarly in human cancer cells. This deeper understanding of elesclomol's mode of action has important implications for the therapeutic application of the drug, including providing a rationale for biomarker-based stratification of patients likely to respond in the clinical setting.

Mutant KRAS is a feature of more than 25% of non-small cell lung cancers (NSCLC) and represents one of the most prevalent oncogenic drivers in this disease. NSCLC tumors with oncogenic KRAS respond poorly to current therapies, necessitating the pursuit of new treatment strategies. Targeted inhibition of the molecular chaperone Hsp90 results in the coordinated blockade of multiple oncogenic signaling pathways in tumor cells and has thus emerged as an attractive avenue for therapeutic intervention in human malignancies. Here, we examined the activity of ganetespib, a small-molecule inhibitor of Hsp90 currently in clinical trials for NSCLCs in a panel of lung cancer cell lines harboring a diverse spectrum of KRAS mutations. In vitro, ganetespib was potently cytotoxic in all lines, with concomitant destabilization of KRAS signaling effectors. Combinations of low-dose ganetespib with MEK or PI3K/mTOR inhibitors resulted in superior cytotoxic activity than single agents alone in a subset of mutant KRAS cells, and the antitumor efficacy of ganetespib was potentiated by cotreatment with the PI3K/mTOR inhibitor BEZ235 in A549 xenografts in vivo. At the molecular level, ganetespib suppressed activating feedback signaling loops that occurred in response to MEK and PI3K/mTOR inhibition, although this activity was not the sole determinant of combinatorial benefit. In addition, ganetespib sensitized mutant KRAS NSCLC cells to standard-of-care chemotherapeutics of the antimitotic, topoisomerase inhibitor, and alkylating agent classes. Taken together, these data underscore the promise of ganetespib as a single-agent or combination treatment in KRAS-driven lung tumors. Mol Cancer Ther; 11(12); 2633-43. Ó2012 AACR.

IntroductionAn array of chronic inflammatory diseases, including Crohn disease, psoriasis, rheumatoid arthritis, and multiple sclerosis, cause widespread and severe health problems. These and other immune diseases can be considered to have a predominantly T helper cell type 1 (Th1) bias. Although injectable biologic treatments such as antibodies and soluble protein that block TNF-␣ have provided significant clinical benefit, there is still a high unmet medical need, particularly for a safe targeted drug that can be taken orally.Interleukin-12 (IL-12) is a heterodimeric cytokine (p70) composed of 2 independently regulated protein subunits, p35 and p40. IL-12 plays a central role in the immune response by bridging innate resistance and antigen-specific adaptive immunity. 1 It is produced from phagocytic cells and antigen-presenting cells, in particular macrophages and dendritic cells, upon stimulation with bacteria, bacterial products such as lipopolysaccharide (LPS), and intracellular parasites. 2,3 The well-documented biologic functions of IL-12 are the induction of interferon-␥ (IFN-␥) expression from T and natural killer (NK) cells 4,5 and the differentiation of naive T cells toward a Th1-cell type. 6,7 IL-12 also appears to be critical in the expansion and maintenance of the Th1 phenotype. [8][9][10] IL-23, a more recently discovered member of the IL-12 family, also promotes Th1 response, but has distinct functions from IL-12. IL-23 is required for the generation of effector memory T cells. 11 IL-23 is also needed for the generation of IL-17-producing T cells, which play a significant role in the inflammatory response. 12 Through these activities, IL-23 plays a critical role in chronic inflammatory diseases.Although the inflammatory effector function of Th1 is essential for the clearance of intracellular pathogens, the excessive production of proinflammatory cytokines leads to serious tissue damage typical of organ-specific autoimmunity, 13,14 including type 1 diabetes, 15 multiple sclerosis, 16,17 rheumatoid arthritis, 18,19 inflammatory bowel disease, 20 psoriasis, 21 and sepsis. 22 IL-12/IL-23 has been validated as an attractive clinical target by a number of studies. Mice lacking the gene encoding the p40 subunit shared by IL-12 and IL-23 or lacking the IL-23-specific subunit p19 have proven the integral role of IL-12/IL-23 to the pathogenesis of these disorders, implying that blockade of the cytokines could be effective in the treatment of a variety of autoimmune diseases. 21,[23][24][25][26][27][28] Monoclonal antibodies to the IL-12/23 p40 subunit have been shown to be effective in human clinical trials in patients with Crohn disease and psoriasis. 29,30 While antibodies against IL-12/IL-23 could provide significant medical benefit, a small-molecule IL-12/IL-23 inhibitor that could be administered orally would be highly desirable. Although some compounds weakly or nonselectively inhibit IL-12, there are no potent and selective small-molecule IL-12 inhibitors. To find an effective inhibitor against the...