CRISPR screening identifies synergy between BET and mTOR inhibitors in cholangiocarcinoma through impaired serine glycine one carbon metabolism [RNA-seq]

Patients with cholangiocarcinoma have poor clinical outcomes due to late diagnoses, poor prognoses, and limited treatment strategies. To identify novel drug combinations for this disease, we have conducted a genome-wide CRISPR screen anchored on the bromodomain and extraterminal domain (BET) PROTAC degrader ARV-825, from which we identified anti-cancer synergy when combined with genetic ablation of members of the mTOR pathway. This combination effect was validated using multiple pharmacological BET and mTOR inhibitors, accompanied by increased levels of apoptosis and cell cycle arrest. In a xenograft model, combined BET degradation and mTOR inhibition induced tumor regression. Mechanistically, the two inhibitor classes converged on H3K27ac-marked epigenetic suppression of the serine glycine one carbon (SGOC) metabolism pathway, including the key regulators PHGDH and PSAT1. Knockdown of PSAT1 was sufficient to replicate synergy with single agent inhibition of either BET or mTOR. Our results tied together epigenetic regulation, metabolism, and apoptosis induction as key therapeutic targets for further exploration in this underserved disease. Overall design: Compare RNA from each group (vehicle, BETp, mTORi, and BETp + mTORi) of CCA cell lines (SNU1079 and SSP25) with 48h of drug treatment