Targeting renal cell carcinoma with a HIF-2 antagonist

Abstract

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.

HIF2α-Targeted RNAi Therapeutic Inhibits Clear Cell Renal Cell Carcinoma

“…In these studies, the HIF2a antagonists showed antitumor activity in several tumor cell line xenograft mouse models and patient-derived xenograft (PDX) models. Early clinical data showed a patient treated with the HIF2a antagonist PT2385 remained free of progression for more than 11 months (20). These encouraging results lend validation towards developing novel therapeutics that target the pVHL/HIF2a pathway.…”

“…In general, transcription factors such as HIF2a have generally been considered undruggable therapeutic targets (47). Recently, several reports described the antitumor effects of a small-molecule HIF2a antagonist that binds to a hydrophobic binding pocket discovered in HIF2a PAS-B domain (16,(20)(21)(22). Although these studies showed encouraging results that validated HIF2a as a therapeutic target, certain limitations are apparent.…”

“…Although these studies showed encouraging results that validated HIF2a as a therapeutic target, certain limitations are apparent. These included preexisting drug-resistant mutations, posttreatment mutations discovered surrounding the binding pocket of this small molecule, and the dependence of some tumors on cellular pathways other than VHL-HIF (20)(21)(22).…”

“…These encouraging results lend validation towards developing novel therapeutics that target the pVHL/HIF2a pathway. However, these studies also uncovered several preclinical mouse models that are not responsive to these HIF2a antagonists (20,21). In some models, the lack of antitumor activity was attributed to missense mutations that resulted in amino acid substitutions surrounding the binding pocket of HIF2a antagonists (20,21).…”

“…Accordingly, potential new therapies targeting HIF2a function, including in this study, are being explored. Recently, preclinical and limited early clinical results using small-molecule inhibitors targeting HIF2a were reported (16,(20)(21)(22). In these studies, the HIF2a antagonists showed antitumor activity in several tumor cell line xenograft mouse models and patient-derived xenograft (PDX) models.…”