Although several microtubule-targeting drugs are in clinical use, there remains a need to identify novel agents that can overcome the limitations of current therapies, including acquired and innate drug resistance and undesired side effects. In this study, we show that ELR510444 has potent microtubuledisrupting activity, causing a loss of cellular microtubules and the formation of aberrant mitotic spindles and leading to mitotic arrest and apoptosis of cancer cells. ELR510444 potently inhibited cell proliferation with an IC 50 value of 30.9 nM in MDA-MB-231 cells, inhibited the rate and extent of purified tubulin assembly, and displaced colchicine from tubulin, indicating that the drug directly interacts with tubulin at the colchicine-binding site. ELR510444 is not a substrate for the P-glycoprotein drug transporter and retains activity in ␤III-tubulin-overexpressing cell lines, suggesting that it circumvents both clinically relevant mechanisms of drug resistance to this class of agents. Our data show a close correlation between the concentration of ELR510444 required for inhibition of cellular proliferation and that required to cause significant loss of cellular microtubule density, consistent with its activity as a microtubule depolymerizer. ELR510444 also shows potent antitumor activity in the MDA-MB-231 xenograft model with at least a 2-fold therapeutic window. Studies in tumor endothelial cells show that a low concentration of ELR510444 (30 nM) rapidly alters endothelial cell shape, similar to the effect of the vascular disrupting agent combretastatin A4. These results suggest that ELR510444 is a novel microtubule-disrupting agent with potential antivascular effects and in vivo antitumor efficacy.

BackgroundHypoxia-inducible factor (HIF) is an attractive therapeutic target for renal cell carcinoma (RCC) as its high expression due to the loss of von Hippel-Lindau (VHL) promotes RCC progression. Considering this, we hypothesized that ELR510444, a novel orally available small molecule inhibitor of HIF activity, would reduce angiogenesis and possess significant activity in RCC. The mechanism of action and therapeutic efficacy of ELR510444 were investigated in in vitro and in vivo models of RCC.Principal FindingsELR510444 decreased HIF-1α and HIF-2α levels, reduced RCC cell viability and clonogenic survival, and induced apoptosis. VHL-deficient RCC cells were more sensitive to ELR510444-mediated apoptosis and restoration of VHL promoted drug resistance. Higher concentrations of ELR51044 promoted apoptosis independently of VHL status, possibly due to the microtubule destabilizing properties of this agent. ELR510444 significantly reduced tumor burden in the 786-O and A498 RCC xenograft models. These effects were associated with increased necrosis and apoptosis and inhibition of angiogenesis.ConclusionsELR510444 is a promising new HIF inhibitor that reduced RCC cell viability, induced apoptosis, and diminished tumor burden in RCC xenograft models. ELR510444 also destabilized microtubules suggesting that it possesses vascular disrupting and anti-angiogenic properties. Further investigation of ELR510444 for the therapy of RCC is warranted.

Inhibitors of hypoxia-inducible factor 1 (HIF-1) represent promising anticancer therapeutics. We have identified a series of potent toluidinesulfonamide HIF-1 inhibitors. However, the series was threatened by a potential liability to inhibit CYP2C9 which could cause dangerous drug-drug interactions when being coadministered with other drugs. We used structure-activity data from the PubChem database to develop a topomer CoMFA model that guided the design of novel sulfonamides with high selectivity for HIF-1 over CYP2C9 inhibition.

The HIF signaling pathway is a crucial way in which tumors can circumvent the constraints of regions of low oxygen (hypoxia) to induce angiogenesis and maintain proliferation. The oxygen regulated subunit of the transcription factor hypoxia-inducible factor 1 (HIF1), HIF1αlpha, is a positive factor in tumor growth and its expression has been correlated with poor patient prognosis in a number of settings. We here present in vitro and in vivo data for a novel series of orally available small-molecule HIF signaling modulators that show nanomolar inhibition of the HIF signaling pathway in addition to potent anti-proliferative activity against a large number of cell lines derived from solid and blood tumors (EC50 in the range 1-100nM). Phenotypically, the compounds elicit an initial G2/M arrest, followed by the induction of caspase-3/7 and the onset of apoptosis. The in vitro results also translate into in vivo animal models. The lead compounds from the series show efficacy in tumor xenograft mouse models, with dose-dependent tumor growth inhibition of 60-70% after oral dosing (MDA-MB-231 xenograft). Structural optimisation has additionally allowed us to improve the PK and physicochemical characteristics of the compounds, with a lead candidate currently in formal pre-clinical development with the aim of entering a Phase 1 clinical trial in multiple myeloma at the end of 2010. In conclusion, we believe that the development towards clinical Proof-of-Concept of this new class of dual-mechanism inhibitors of HIF signaling and cell proliferation presents a promising new option for cancer therapeutics. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-294.

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