Cells in the solid tumor microenvironment are frequently exposed to hypoxic conditions, necessitating molecular adaptations for survival. Of particular importance are transcriptional changes mediated by heterodimeric Hypoxia-Inducible Factor (HIF) proteins that consist of an oxygen-regulated α monomer (either HIF-1α, -2α, and -3α) coupled to a constitutively expressed β monomer (HIF-1β/ARNT). In normal oxygen conditions, HIF-2α is degraded following ubiquitination by the von Hippel-Lindau (pVHL) E3-ubiquitin ligase complex. Exposure to hypoxia, VHL mutation, or epigenetic silencing of pVHL leads to HIF-2α stabilization and transcription of pro-tumorigenic gene sets in both cancer and non-cancer cells. Inhibition of HIF-2α has been shown clinically to be an effective strategy to mitigate tumor growth, particularly in patients suffering from VHL disease or clear cell renal cell carcinoma (ccRCC), a cancer that has a particularly high prevalence of pVHL dysfunction. Applying a pharmacophore mapping and structure-based design approach, we identified a novel and potent small molecule HIF-2α inhibitor, AB521. AB521 avidly binds the HIF-2α PAS-B domain, preventing HIF-2α-mediated gene transcription. AB521 is characterized by a favorable preclinical pharmacokinetic profile and is projected to be suitable for once-daily dosing in humans. When delivered orally in mice, AB521 significantly regressed established 786-O xenograft tumors and decreased pharmacodynamic markers associated with HIF-2α in a dose-dependent manner. In vitro, AB521 potently inhibited HIF-2α-specific luciferase reporter transcription under high-serum conditions, VEGF protein secretion, colony formation in soft agar, and did not exhibit off-target cytotoxicity in 786-O cells. AB521 selectively inhibited HIF-2α-, but not HIF-1α-, mediated gene expression in hypoxic Hep3B hepatocellular carcinoma cells. AB521 also inhibited the transcriptional activity of endogenous HIF-2α in relevant human primary cell types, including endothelial cells and pro-tumorigenic M2-polarized macrophages. Importantly, inhibiting HIF-2α did not impact functionality of activated hypoxic human T cells, suggesting that AB521 would be favorable combination partner for I-O therapeutic agents. Indeed, expression of CD73, the primary enzyme responsible for synthesis of the immunosuppressive metabolite adenosine, was highly correlated with hypoxic signatures across several indications in publicly available bioinformatic datasets, suggesting combinations with adenosine pathway antagonists in ccRCC and beyond. In summary, AB521 is a novel and selective HIF-2α inhibitor with potent anti-tumor activity. Clinical evaluation of this molecule is expected to begin in the latter part of 2021.

Citation Format: Kelsey E. Sivick Gauthier, Dana Piovesan, Soonweng Cho, Kenneth V. Lawson, Patrick G. Schweickert, Alejandra Lopez, Suan Liu, Timothy Park, Artur Mailyan, Jeremy T. A. Fournier, Joel W. Beatty, Samuel L. Drew, Jarek Kalisiak, Balint Gal, Guillaume Mata, Zhang Wang, Brandon R. Rosen, Clayton Hardman, Matthaw P. Epplin, Kai Yu, Karl T. Haelsig, Lixia Jin, Elaine Ginn, Jennie Au, Cesar A. Meleza, Joel Tencer, Amber Pham, Hyock J. Kwon, Stephen W. Young, Manmohan Leleti, Jay P. Powers, Matthew J. Walters. AB521 potently and selectively inhibits pro-tumorigenic gene transcription by Hypoxia-Inducible Factor (HIF)-2α in vitro and in vivo [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P206.