Abstract B090: Partially open conformation of the G323E mutated HIF-2α PASB domain captured by X-ray crystallography

Abstract

Abstract Under hypoxic conditions, vital cell processes such as angiogenesis, erythropoiesis, cell proliferation and metabolism are regulated by a group of transcription factors known as hypoxia-inducible factors (HIFs). These proteins belong to the helix-loop-helix family of transcription factors and require heterodimerization to function. Constitutively expressed HIF-1β protein forms a heterodimer with one of the oxygen-labile counterparts: HIF-1α, HIF-2α, or HIF-3α. The HIF-αs are degraded under normoxic conditions via ubiquitination by the von Hippel Lindau (VHL) E3 ubiquitin ligase and become available for dimerization under either hypoxia or VHL dysfunction. Certain cancer types take advantage of this HIF-regulated transcription for survival and growth, as exemplified by VHL-deficient clear cell renal cell carcinoma (ccRCC). Inhibitors aimed at disruption of the HIF-1β:HIF-2α heterodimer have been advanced into clinical development, including belzutifan (approved by the Food and Drug Administration for adult patients with VHL disease who require therapy for RCC among other indications) and AB521 (Arcus Biosciences). This class of small molecules functions by binding to and causing a conformational change in the internal cavity of the PasB domain of HIF-2α. A mutation within this internal cavity, G323E, was reported in a patient undergoing treatment with HIF-2α inhibitor. This mutation restored the ability of HIF-1β to heterodimerize with HIF-2α in presence of the inhibitor. To better understand this potential resistance mechanism and how the G323E mutation affects inhibitor binding, we used X-ray crystallography to examine the structure of the mutant HIF-2α PasB domain in complex with a novel small molecule inhibitor active in vitro against the G323E mutant form. We report a co-crystal structure that reveals a partially disordered open conformation of the HIF-2α PasB domain. This structure strengthens existing hypotheses regarding the route of compound entry into the HIF-2α PasB cavity and lays the foundation for structure-based design of HIF-2α PasB G323E-active inhibitors. Citation Format: Steven Shia, Ian Malgapo, Jeffrey Chen, Amber Pham, Cesar A Meleza, Lunda Shen, Mariya Morar, Kenneth V Lawson, Kelsey E Sivick Gauthier, Hyock J Kwon. Partially open conformation of the G323E mutated HIF-2α PASB domain captured by X-ray crystallography [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B090.