Clear cell renal cell carcinoma (CC-RCC) is the most lethal of all genitourinary cancers. The functional loss of the von Hippel-Lindau (VHL) gene occurs in 90% of CC-RCC, driving cancer progression. The objective of this study was to identify chemical compounds that are synthetically lethal with VHL deficiency in CC-RCC. An annotated chemical library, the library of pharmacologically active compounds (LOPAC), was screened in parallel on VHL-deficient RCC4 cells and RCC4VHL cells with re-introduced VHL. The ROCK inhibitor, Y-27632, was identified and validated for selective targeting of VHL-deficient CC-RCC in multiple genetic backgrounds by clonogenic assays. Downregulation of ROCK1 by small interfering RNA (siRNA) selectively reduced the colony forming ability of VHL-deficient CC-RCC, thus mimicking the effect of Y-27632 treatment, whereas downregulation of ROCK2 had no effect. In addition, three other ROCK inhibitors, RKI 1447, GSK 429286, AT13148 selectively targeted VHL-deficient CC-RCC. Importantly, we found that mammalian target of rapamycin (mTOR) inhibitor Everolimus synergized with ROCK inhibitor RKI 1447 in targeting VHL-deficient cells. Accordingly, AT13148, an AGC kinase inhibitor blocking S6 kinase (S6K, downstream target of mTOR) in addition to ROCK1&2, showed the most strong synthetic lethality effect out of all ROCK inhibitors tested. CC-RCC treatment with ROCK inhibitors is cytotoxic and cytostatic based on bromodeoxyuridine (BrdU) assay, propidium iodide (PI) staining and growth curves, and blocks cell migration based on transwell assay. On the one hand, knockdown of hypoxia-inducible factor (HIF) β in the VHL-deficient CC-RCC had a protective effect against Y-27632 treatment, mimicking VHL reintroduction. On the other hand, CC-RCCVHL cells were sensitized to Y-27632 treatment in hypoxia (2% O2). These results suggest that synthetic lethality between ROCK inhibition and VHL deficiency is dependent on HIF activation. Moreover, HIF1α or HIF2α overexpression in CC-RCCVHL cells is sufficient to sensitize them to ROCK inhibition. Finally, Y-27632 treatment inhibited growth of subcutaneous 786-OT1 CC-RCC tumors in mice. Thus, ROCK inhibitors represent potential therapeutics for VHL-deficient CC-RCC.

Citation Format: Jordan M. Thompson, Quy H. Nguyen, Manpreet Singh, Matthew W. Pavesic, Irina Nesterenko, Luke J. Nelson, Alicia Liao, Olga V. Razorenova. Rho-associated kinase 1 inhibition is synthetically lethal with von Hippel-Lindau deficiency in clear cell renal cell carcinoma [abstract]. In: Proceedings of the AACR Precision Medicine Series: Opportunities and Challenges of Exploiting Synthetic Lethality in Cancer; Jan 4-7, 2017; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2017;16(10 Suppl):Abstract nr PR15.