Abstract 2064: Novel HIF-2α targeted RNAi therapeutic for renal cell carcinoma
Authors: Wong So , Cheng Weijun , Wakefield Darren , Almeida Aaron , Blokhin Andrei , Hamilton Holly , Subbotin Vladimir , Hegge Julia , Neal Zane , Zhang Guofeng , Rozema David , Lewis David , Kanner Steven 
Published: July 2016

Background: Targeted therapy including VEGF and mTOR pathway inhibitors has dramatically transformed treatment options and outcomes for patients with metastatic clear cell renal cell carcinoma (ccRCC). However, alternate treatments are needed as resistance to these initially promising agents occurs frequently. RNAi interference (RNAi), an innate gene silencing mechanism, has been explored as a new class of therapeutics where conventional treatments are lacking or have failed. The challenge in leveraging this promising approach has been efficient delivery of an RNAi trigger (siRNA) to target tissue. Over 90% of ccRCC tumors express a mutant inactive form of the von Hippel-Landau protein (pVHL), an E3 ubiquitin ligase that promotes target protein degradation. Strong evidence supports the observation that pVHL functional loss leads to the accumulation of the transcription factor hypoxia-inducible factor 2α (HIF-2α), a tumorigenic driver of ccRCC.

Methods: We have developed a targeted delivery platform called Dynamic Polyconjugte™ (DPC) as an RNAi-based therapeutic targeting HIF-2α for advanced ccRCC. The ccRCC-specific DPC (ITG-DPC) comprises a membrane active polymer to promote RNAi trigger endosomal release, a ligand that binds to αV-containing integrin receptors expressed on tumor cells, reversible masking to prevent polymer activity before reaching the endosomal compartment, and a potent and specific RNAi trigger to HIF-2α. The modular nature of this delivery platform allows for flexibility to optimize each functional component independently. The ligand-dependent delivery of ITG-DPC was first evaluated in cultured tumor cells and then confirmed in ccRCC tumors established in nude mice using fluorescently-labeled ITG-DPC and confocal microscopy. To validate silencing of HIF-2α as an effective therapeutic approach, an inducible shRNA to HIF-2α was expressed in ccRCC tumors established in mice that significantly silenced HIF-2α gene expression and induced tumor regression.

Results: Bi-weekly injection of ITG-DPC into nude mice with established orthotopic A498 ccRCC tumors resulted in &gt;80% knockdown of HIF-2α mRNA and significant tumor growth inhibition. Histological examination of tumor sections showed substantial cell killing and destruction of tumor architecture. Down-regulation of HIF-2α regulated pathways genes including VEGF-A, and the corresponding reduction in tumor-associated CD31 positive neovascularization, corroborated on-target effects of HIF-2α gene silencing.

Conclusion: Targeted delivery of a HIF-2α specific RNAi-based-therapeutic has the potential to radically impact the late-stage ccRCC treatment paradigm.

Citation Format: So Wong, Weijun Cheng, Darren Wakefield, Aaron Almeida, Andrei Blokhin, Holly Hamilton, Vladimir Subbotin, Julia Hegge, Zane Neal, Guofeng Zhang, David Rozema, David Lewis, Steven Kanner. Novel HIF-2α targeted RNAi therapeutic for renal cell carcinoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2064.