Residues 17 and 18 in nef of SIVmac239 were changed from RQ to YE to create a translated sequence of SRPSGDLYERLLRARGETYGRLLGEVEDGYSQSP from residues 10-43. The YXXL motifs in this context match very well with consensus sequences for SH2 binding domains and are similar to ones present in nef of the acutely lethal pathogen SIVpbj14. The YE variant of SIVmac239, unlike SIVmac239 but like SIVpbj14, replicated well in resting peripheral blood mononuclear cell cultures, caused extensive T lymphocyte activation, and produced an acute disease in rhesus and pigtailed monkeys characterized by severe diarrhea, rash, and extensive lymphoid proliferation in the gastrointestinal tract. The YEnef gene transformed NIH 3T3 cells in culture. Both 239nef and YEnef were found to associate with src in cotransfected COS cells, and both 60 kDa src and 34 kDa nef were phosphorylated at tyrosine in these cells. The extent of tyrosine phosphorylation of 239nef was considerably less than that of YEnef in these assays. These findings identify an important determinant of the SIVpbj14 phenotype, and they provide evidence of a role for nef in signal transduction and cellular activation.

Elesclomol (formerly STA-4783) is a novel small molecule undergoing clinical evaluation in a pivotal phase III melanoma trial (SYMMETRY). In a phase II randomized, double-blinded, controlled, multi-center trial in 81 patients with stage IV metastatic melanoma, treatment with elesclomol plus paclitaxel showed a statistically significant doubling of progression-free survival time compared with treatment with paclitaxel alone. Although elesclomol displays significant therapeutic activity in the clinic, the mechanism underlying its anticancer activity has not been defined previously. Here, we show that elesclomol induces apoptosis in cancer cells through the induction of oxidative stress. Treatment of cancer cells in vitro with elesclomol resulted in the rapid generation of reactive oxygen species (ROS) and the induction of a transcriptional gene profile characteristic of an oxidative stress response. Inhibition of oxidative stress by the antioxidant N-acetylcysteine blocked the induction of gene transcription by elesclomol. In addition, N-acetylcysteine blocked drug-induced apoptosis, indicating that ROS generation is the primary mechanism responsible for the proapoptotic activity of elesclomol. Excessive ROS production and elevated levels of oxidative stress are critical biochemical alterations that contribute to cancer cell growth. Thus, the induction of oxidative stress by elesclomol exploits this unique characteristic of cancer cells by increasing ROS levels beyond a threshold that triggers cell death.

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.

Objective Mutations of the receptor tyrosine kinase Kit occur in several human and canine cancers. While Kit inhibitors have activity in the clinical setting, they possess variable efficacy against particular forms of mutant Kit and drug resistance often develops over time. Inhibitors of heat shock protein 90 (HSP90), a chaperone for which Kit is a client protein, have demonstrated activity against human cancers and evidence suggests they downregulate several mutated and imatinib-resistant forms of Kit. The purpose of this study was to evaluate a novel HSP90 inhibitor, STA-9090, against wild-type (WT) and mutant Kit in canine bone marrow–derived cultured mast cells (BMCMCs), malignant mast cell lines, and fresh malignant mast cells. Materials and Methods BMCMCs, cell lines, and fresh malignant mast cells were treated with STA-9090, 17-AAG, and SU11654 and evaluated for loss in cell viability, cell death, alterations in HSP90 and Kit expression/signaling, and Kit mutation. STA-9090 activity was tested in a canine mastocytoma xenograft model. Results Treatment of BMCMCs, cell lines, and fresh malignant cells with STA-9090 induced growth inhibition, apoptosis that was caspase-3/7–dependent, and downregulation of phospho/total Kit and Akt, but not extracellular signal-regulated kinase (ERK) or phosphoinositide-3 kinase (PI-3K). Loss of Kit cell-surface expression was also observed. Furthermore, STA-9090 exhibited superior activity to 17-AAG and SU11654, and was effective against malignant mast cells expressing either WT or mutant Kit. Lastly, STA-9090 inhibited tumor growth in a canine mastocytoma mouse xenograft model. Conclusions STA-9090 exhibits broad activity against mast cells expressing WT or mutant Kit, suggesting it may be an effective agent in the clinical setting against mast cell malignancies.

Overall benefits of EGFR‐TKIs are limited because these treatments are largely only for adenocarcinoma (ADC) with EGFR activating mutation. The treatments also usually lead to development of resistances. We have established a panel of patient‐derived xenografts (PDXs) from treatment naïve Asian NSCLC patients, including those containing “classic” EGFR activating mutations. Some of these EGFR‐mutated PDXs do not respond to erlotinib: LU1868 containing L858R/T790M mutations, and LU0858 having L858R mutation as well as c‐MET gene amplification, both squamous cell carcinoma (SCC). Treatment of LU0858 with crizotinib, a small molecule inhibitor for ALK and c‐MET, inhibited tumor growth and c‐MET activity. Combination of erlotinib and crizotinib caused complete response, indicating the activation of both EGFR and c‐MET promote its growth/survival. LU2503 and LU1901, both with wild‐type EGFR and c‐MET gene amplification, showed complete response to crizotinib alone, suggesting that c‐MET gene amplification, not EGFR signaling, is the main oncogenic driver. Interestingly, LU1868 with the EGFR L858R/T790M, but without c‐met amplification, had a complete response to cetuximab. Our data offer novel practical approaches to overcome the two most common resistances to EGFR‐TKIs seen in the clinic using marketed target therapies.

A T-lymphoid cell line termed 221 was derived from a rhesus monkey infected with herpesvirus saimiri. Growth of 221 cells was dependent on the addition of interleukin-2 (IL-2) to the culture medium. In the absence of IL-2, 221 cells arrested in G 0 -G 1 but did not die. Simian immunodeficiency virus (SIV) replicated efficiently in IL-2-stimulated 221 cells whether or not the nef gene was present. In the absence of IL-2, nef-containing SIV replicated 8 to 100 times more efficiently in 221 cells than did the same virus lacking nef. nef-containing virus preferentially stimulated the production of IL-2 from 221 cells. HIV-1 nef and v-ras genes, but not the c-ras gene, were shown to substitute functionally for SIV nef when tested as recombinant viruses in this assay system. These results demonstrate a role for natural nef in causing lymphoid cell activation, and they provide a system for delineating the biochemical mechanisms responsible for this activation.

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When residues 17 and 18 in nef of simian immunodeficiency virus strain SIVmac239 were changed from RQ to YE, the resultant virus was able to replicate in peripheral blood mononuclear cell cultures without prior lymphocyte activation and without the addition of exogenous interleukin-2, caused extensive lymphocyte activation in these cultures, and produced an acute disease in rhesus and pigtail macaques (Z.