HIF2 Inactivation and Tumor Suppression with a Tumor-Directed RNA-Silencing Drug in Mice and Humans
Purpose: Hypoxia-inducible factor 2α (HIF2α) is a key driver of kidney cancer. Using a belzutifan analogue (PT2399), we previously demonstrated in tumorgrafts (TGs) that approximately 50% of clear cell renal cell carcinomas (ccRCC) are HIF2α dependent. However, prolonged treatment led to resistance mutations, which we also identified in patients. In this study, we evaluated a tumor-directed, systemically delivered siRNA therapeutic (siHIF2) designed to target both wild-type and resistance-mutant HIF2α.
Experimental Design: Leveraging our validated TG platform, we conducted pharmacokinetic and pharmacodynamic analyses to assess drug uptake, HIF2α silencing, target gene suppression, and antitumor activity. Orthogonal RNA-sequencing of siHIF2- and PT2399-treated tumors was performed to characterize the HIF2α transcriptome. Studies were extended to a TG line derived from a biopsy obtained during a phase I clinical trial (NCT04169711) of siHIF2, as well as to the corresponding patient—an extensively pretreated individual with rapidly progressive ccRCC and paraneoplastic polycythemia, consistent with HIF2α dependence.
Results: siHIF2 was efficiently taken up by ccRCC TGs, robustly depleted HIF2α, and suppressed orthogonally defined downstream pathways, including Myc and novel E2F signaling, leading to downregulation of cell cycle genes and inhibition of tumor growth. In the patient-derived TG, effects mirrored those observed in the patient: HIF2α silencing in tumor biopsies, decreased circulating erythropoietin, suppression of polycythemia, and induction of a partial tumor response.
Conclusions: This work represents, to our knowledge, the first demonstration of functional inactivation of an oncoprotein and tumor suppression using a systemic, tumor-directed RNA-silencing drug. The findings provide proof-of-principle for HIF2α inhibition via RNA-targeting therapeutics in ccRCC and establish a framework for the development of tumor-directed RNA-based cancer therapies.