Abstract 372: ARNT2 and AhR promote resistance to HIF2a inhibitor belzutifan.

Abstract Introduction: The von Hippel-Lindau (VHL) tumor suppressor gene is inactivated in all VHL disease-associated tumors and in more than 90% of sporadic renal cell carcinomas and central nervous system hemangioblastomas. VHL-depleted cells constitutively express high levels of the oncogenic transcription factors Hypoxia-Inducible Factors (HIF1a and HIF2a). HIF2a belongs to the family of bHLH-PAS proteins, it is a sensor of hypoxia and forms nuclear obligatory heterodimers with several adaptor bHLH-PAS protein. HIF-ARNT heterodimers bind HRE sequences in the promoters of hypoxia inducible genes. Belzutifan, a first in class oral medication, disrupt the interaction of HIF2a with ARNT (HIF1b) and suppresses HIF2a target genes expression that drive VHL tumor growth. De novo and acquired resistance to this medication has been detected. Experimental procedures: Here we show that the nuclear levels of the bHLH-PAS protein ARNT2 contribute to the sensitivity or resistance of RCC to belzutifan. Knock down or knock out of ARNT2 in human cancer cell lines renders the cells resistant to belzutifan, while overexpression of exogenous ARNT2 increases the sensitivity of the cells to the anti-proliferative effect of belzutifan in vitro. Belzutifan disrupts preferentially the ARNT-HIF2a but not the ARNT2-HIF2a heterodimers and its effect depends on levels of ARNT-HIF2a. The global gene expression from bulk RNA sequencing in ARNT2 knock out cells clustered with HIF2a overexpression cells in PCA plot analysis and significantly induced detoxification signaling that functionally involved in AhR (Aryl hydrocarbon Receptor) sensor protein. Treatment of cells with belzutifan or an AhR ligand re-arranges these programs based on the nuclear levels of sensor and adaptor molecules. We show that belzutifan and/or AhR agonist, FICZ treatment increased AhR-Luc activity and CYP1A1 expression, which is a target gene of AhR, and affected to the sensitivity to belzutifan. Summary: Our data suggest that strategies to increase ARNT2 cellular levels may help in combating de novo or acquired resistance to belzutifan. Citation Format: Dongkook Min, Sunil Poudel, Robert Morris, Irene Mitsiades, Monica Perez, Eric Zaniewski, Toshi Shioda, Esther Rheinbay, Mo Motamedi, Wilhelm Haas, Othon Iliopoulos. ARNT2 and AhR promote resistance to HIF2a inhibitor belzutifan abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 372.