Clear cell Renal Cell Carcinoma (ccRCC) is characterized by VHL inactivation1,2. Because no other gene is mutated as frequently, and VHL mutations are truncal3, VHL inactivation is regarded as the governing event4. VHL loss activates HIF-2, and constitutive HIF-2 restores tumorigenesis in VHL-reconstituted ccRCC cells5. HIF-2 is implicated in angiogenesis and multiple other processes6–9, but angiogenesis is the main target of drugs like sunitinib10. HIF-2, a transcription factor, has been regarded as undruggable11. A structure-based design approach identified a selective HIF-2 antagonist (PT2399) that we evaluate using a tumorgraft (TG)/PDX platform12,13. PT2399 dissociated HIF-2 (an obligatory heterodimer [HIF-2α/HIF-1β])14 in human ccRCC suppressing tumorigenesis in 56% (10/18) lines. PT2399 had greater activity than sunitinib, was active in sunitinib-progressing tumors, and was better tolerated. Unexpectedly, some VHL-mutant ccRCCs were resistant. Resistance occurred despite HIF-2 dissociation in tumors and evidence of Hif-2 inhibition in the mouse as determined by suppression of circulating erythropoietin, a HIF-2 target15 and possible pharmacodynamic marker. We identified a HIF-2-dependent gene signature in sensitive tumors. Illustrating drug specificity, gene expression was largely unaffected by PT2399 in resistant tumors. Sensitive tumors exhibited a distinguishing gene expression signature, and generally higher HIF-2α levels. Prolonged PT2399 treatment led to resistance. We identified a binding site and second site suppressor mutation in HIF-2α and HIF-1β respectively. Both mutations preserved HIF-2 dimers despite treatment with PT2399. Finally, an extensively pretreated patient with a sensitive TG had disease control for >11 months with the close analogue PT2385. We validate HIF-2 as a target in ccRCC, show that some ccRCC are, unexpectedly, HIF-2 independent, and set the stage for biomarker-driven clinical trials.

Purpose: The Ras-Raf-mitogen-activated protein kinase kinase (MEK) pathway is overactive in many human cancers and is thus a target for novel therapeutics. We have developed a highly potent and selective inhibitor of MEK1/2. The purpose of these studies has been to show the biological efficacy of ARRY-142886 (AZD6244) in enzymatic, cellular, and animal models. Experimental Design: The ability of ARRY-142886 to inhibit purified MEK1 as well as other kinases was evaluated. Its effects on extracellular signal-regulated kinase (ERK) phosphorylation and proliferation in several cell lines were also determined. Finally, the inhibitor was tested in HT-29 (colorectal) and BxPC3 (pancreatic) xenograft tumor models. Results: The IC 50 of ARRY-142886 was determined to be 14 nmol/L against purified MEK1. This activity is not competitive with ATP, which is consistent with the high specificity of compound for MEK1/2. Basal and epidermal growth factor^induced ERK1/2 phosphorylation was inhibited in several cell lines as well as 12-O-tetradecanoylphorbol-13-acetate^induced ERK1/2 phosphorylation in isolated peripheral blood mononuclear cells.Treatment with ARRY-142886 resulted in the growth inhibition of several cell lines containing B-Raf and Ras mutations but had no effect on a normal fibroblast cell line.When dosed orally, ARRY-142886 was capable of inhibiting both ERK1/ 2 phosphorylation and growth of HT-29 xenograft tumors in nude mice. Tumor regressions were also seen in a BxPC3 xenograft model. In addition, tumors remained responsive to growth inhibition after a 7-day dosing holiday. Conclusions: ARRY-142886 is a potent and selective MEK1/2 inhibitor that is highly active in both in vitro and in vivo tumor models. This compound is currently being investigated in clinical studies.Excessive growth factor signaling leads to unregulated growth that can contribute to the pathogenesis of human cancer. The signaling cascade is initiated by the binding of peptide growth factors to their tyrosine kinase receptors at the plasma membrane. The receptor kinases are activated and through the recruitment of the growth factor receptor binding protein 2/son of sevenless complex to autophosphorylated sites on the receptors, the G protein Ras is induced to its active GTP-bound state. Ras recruits the serine/threonine kinase Raf to the plasma membrane, where it is then able to phosphorylate and activate mitogen-activated protein kinase kinases (MEK) 1 and 2, which are dual specificity protein kinases that phosphorylate serine/ threonine and tyrosine residues. The MEK kinases in turn phosphorylate and activate their only currently known substrates, extracellular signal-regulated kinases (ERK) 1 and 2. ERK1/2 proteins translocate to the nucleus where they phosphorylate and activate effector proteins and transcription factors, resulting in diverse cellular responses, including proliferation.The overexpression and/or mutation of epidermal growth factor (EGF) receptor (EGFR), erbB2, platelet-derived growth factor receptor, RET, and othe...

Clear cell renal cell carcinoma (ccRCC), the most common form of kidney cancer, is usually linked to inactivation of the pVHL tumor suppressor protein and consequent accumulation of the HIF2α transcription factor 1. Here we show that a small molecule (PT2399) that directly inhibits HIF2α causes tumor regression in preclinical models of primary and metastatic pVHL-defective ccRCC in an on-target fashion. pVHL-defective ccRCC cell lines display unexpectedly variable sensitivity to PT2399, however, suggesting the need for predictive biomarkers.

More than 90% of clear cell renal cell carcinomas (ccRCC) exhibit inactivation of the von Hippel-Lindau (pVHL) tumor suppressor, establishing it as the major underlying cause of this malignancy. pVHL inactivation results in stabilization of the hypoxia-inducible transcription factors, HIF1a and HIF2a, leading to expression of a genetic program essential for the initiation and progression of ccRCC. Herein, we describe the potent, selective, and orally active small-molecule inhibitor PT2385 as a specific antagonist of HIF2a that allosterically blocks its dimerization with the

Purpose The von Hippel-Lindau tumor suppressor is inactivated in the majority of clear cell renal cell carcinomas (ccRCCs), leading to inappropriate stabilization of hypoxia-inducible factor-2α (HIF-2α). PT2385 is a first-in-class HIF-2α antagonist. Objectives of this first-in-human study were to characterize the safety, pharmacokinetics, pharmacodynamics, and efficacy, and to identify the recommended phase II dose (RP2D) of PT2385. Patients and Methods Eligible patients had locally advanced or metastatic ccRCC that had progressed during one or more prior regimens that included a vascular endothelial growth factor inhibitor. PT2385 was administered orally at twice-per-day doses of 100 to 1,800 mg, according to a 3 + 3 dose-escalation design, followed by an expansion phase at the RP2D. Results The dose-escalation and expansion phases enrolled 26 and 25 patients, respectively. Patients were heavily pretreated, with a median of four (range, one to seven) prior therapies. No dose-limiting toxicity was observed at any dose. On the basis of safety, pharmacokinetic, and pharmacodynamic profiling, the RP2D was defined as 800 mg twice per day. PT2385 was well tolerated, with anemia (grade 1 to 2, 35%; grade 3, 10%), peripheral edema (grade 1 to 2, 37%; grade 3, 2%), and fatigue (grade 1 to 2, 37%; no grade 3 or 4) being the most common treatment-emergent adverse events. No patients discontinued treatment because of adverse events. Complete response, partial response, and stable disease as best response were achieved by 2%, 12%, and 52% of patients, respectively. At data cutoff, eight patients remained in the study, with 13 patients in the study for ≥ 1 year. Conclusion PT2385 has a favorable safety profile and is active in patients with heavily pretreated ccRCC, validating direct HIF-2α antagonism for the treatment of patients with ccRCC.