A Mesenchymal Tumor Cell State Confers Increased Dependency on the BCL-XL Anti-apoptotic Protein in Kidney Cancer

Genome-wide genetic screens have identified cellular dependencies in many cancers. Using the Broad Institutes Achilles shRNA screening dataset, we mined for targetable dependencies by cell lineage. Our studies identified a strong dependency on BCL2L1, which encodes the BCL-XL anti-apoptotic protein, in a subset of kidney cancer cells. Genetic and pharmacological inactivation of BCL-XL, but not the related anti-apoptotic proteins BCL-2, led to fitness defects in renal cancer cells, and also sensitized them to chemotherapeutics. Neither BCL-XL levels (absolute or normalized to BCL-2) nor the status of the VHL gene, which is frequently mutated in kidney cancer, predicted BCL-XL dependence. Transcriptional profiling, however, identified a BCL-XL dependency mRNA signature, which included elevated mesenchymal gene expression in BCL-XL dependent cells. Promoting mesenchymal transition increased BCL-XL dependence; whereas, conversion to a more differentiated state overcame BCL-XL dependence in kidney cancer cells. The BCL-XL dependency mRNA signature was observed in almost a third of human clear cell Renal Cell Carcinomas (ccRCCs), which were also associated with worse clinical outcomes. Finally, an orally bioavailable BCL-XL inhibitor, A-1331852, showed anti-tumor efficacy in vivo. Altogether, our studies uncovered an unexpected link between cancer cell state and dependence on the anti-apoptotic BCL-XL protein and justify further testing on BCL-XL blockade as a potential way to target a clinically aggressive subset of human kidney cancers. One Sentence SummaryCell state, but not pVHL and/or HIF status, defines the dependency of kidney cancer cells on the BCL-XL anti-apoptotic protein.