Identifying Synthetic Lethal Interactions in VHL-Deficient CC-RCC

Clear Cell Renal Cell Carcinoma (CC-RCC) is a devastating disease in its metastatic manifestation with a 5-year survival rate of 11.7%. The loss of the tumor suppressor von Hippel-Lindau (VHL) has been shown to drive the initiation and progression of CC-RCC. Since most of the currently approved FDA therapies act on a patient’s endothelial cells to reduce angiogenesis, instead of directly on the tumor, new targeted therapies are needed to treat this disease. One method for identifying targeted and tumor specific therapies is by identifying synthetic lethal interactions with the most common mutations in the cancer.We conducted an annotated chemical library screen in a CC-RCC cell line with and without VHL re-expressed and identified seven potential synthetic lethal interactions. Validation of these potential hits confirmed that inhibition of Rho Kinase (ROCK) 1 is synthetically lethal with VHL loss in CC-RCC. We then confirmed the interaction both genetically via siRNA knockdown and with multiple ROCK inhibitors. The synthetic lethality interaction effect between ROCK1 inhibition and VHL loss is dependent on the overactivation of HIFs that occurs upon VHL loss. Furthermore, treatment with the ROCK inhibitor Y-27632 inhibited tumor growth in vivo in a subcutaneous xenograft model using 786-O CC-RCC cells. While ROCK inhibitors have great potential to become CC-RCC therapeutics, with the exception of Fasudil approved in Japan and China for treating cerebral vasospasm and pulmonary hypertension, the existing inhibitors are currently limited to topical applications for glaucoma. Statins, HMG CoA Reductase inhibitors, can disrupt the Rho/ROCK pathway at doses administered for treating hypercholesterolemia. We have confirmed the synthetic lethal effect of statin treatment in VHL-deficient CC-RCC. The effect is cytostatic at low nanomolar doses and becomes cytotoxic as the dose is increased into the low micromolar. The addition of both Mevalonate and Geranylgeranyl pyrophosphate (GGPP) can fully rescue the effect. Increasing ROCK activity with arachidonic acid only partially rescues the effect suggesting that statins act through more synthetic lethal partners beyond the Rho/ROCK pathway. In vivo, treatment with Fluvastatin decreased tumor initiation and caused tumor regression in established tumors in subcutaneous xenograft models using 786-O CC-RCC cells. Combined, these studies identify ROCK inhibitors and HMG CoA Reductase inhibitors as promising new therapies for treating VHL-deficient CC-RCC and the biomarkers (VHL/HIF pathway) by which patients can be stratified for clinical trials