Glioblastoma (GBM) is the most common and lethal primary brain tumor and remains incurable. This is in part due to the cellular heterogeneity within these tumors, which includes a subpopulation of treatment-resistant cells called cancer stem-like cells (CSC). We previously identified that the anaphase-promoting complex/cylosome (APC/C), a key cell-cycle regulator and tumor suppressor, had attenuated ligase activity in CSCs. Here, we assessed the mechanism of reduced activity, as well as the efficacy of pharmacologically targeting the APC/C in CSCs. We identified hyperphosphorylation of CDH1, but not pseudosubstrate inhibition by early mitotic inhibitor 1 (EMI1), as a major mechanism driving attenuated APC/C CDH1 activity in the G 1 -phase of the cell cycle in CSCs. Small-molecule inhibition of the APC/C reduced viability of both CSCs and nonstem tumor cells (NSTCs), with the combination of proTAME and apcin having the biggest impact. Combinatorial drug treatment also led to the greatest mitotic arrest and chromosomal abnormalities.Implications: Our findings demonstrate how the activity of the APC/C CDH1 tumor suppressor is reduced in CSCs and also validates small-molecule inhibition of the APC/C as a promising therapeutic target for the treatment of GBM.

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Purpose: Advanced/metastatic forms of clear cell Renal Cell Carcinomas (ccRCCs) have limited therapeutic options. Genome-wide genetic screens have identified cellular dependencies in many cancers. Using the Broad Institute/Novartis’ combined shRNA dataset, and cross-validation with the CRISPR/Cas9 DepMap (21Q3) dataset, we sought therapeutically actionable dependencies in kidney lineage cancers. Experimental Design: We identified preferential genetic dependencies in kidney cancer cells versus other lineages. BCL2L1, which encodes the BCL-XL anti-apoptotic protein, scored as the top actionable dependency. We validated this finding using genetic and pharmacological tools in a panel of ccRCC cell lines. Select BCL-XL-dependent (versus independent) cell lines were then transcriptionally profiled to identify biomarkers and mechanistic drivers of BCL-XL dependence. Cell-based studies (in vitro and in vivo) and clinical validations were used to address physiological relevance. Results: Inactivation of BCL-XL, but not BCL-2, led to fitness defects in renal cancer cells, and sensitized them to chemotherapeutics. Transcriptomic profiling identified a ‘BCL-XL dependency’ signature, including an elevated mesenchymal gene signature. A mesenchymal state was both necessary and sufficient to confer increased BCL-XL dependence. The ‘BCL-XL dependency’ signature was observed in ~30% of human ccRCCs, which were also associated with worse clinical outcomes. Finally, an orally bioavailable BCL-XL inhibitor, A-1331852, showed anti-tumor efficacy in vivo. Conclusions: Our studies uncovered an unexpected link between cell state and BCL-XL dependence in ccRCC. Therapeutic agents that specifically target BCL-XL are available. Our work justifies testing the utility of BCL-XL blockade to target, likely, a clinically aggressive subset of human kidney cancers.