Pharmacological targeting of HDAC/BET pathway enhances 5-FU efficacy in esophageal squamous cancer cells.

5-Fluorouracil (5-FU) remains the most commonly used first-line chemotherapeutic agent for the treatment of esophageal cancer (EC), but its therapeutic efficacy is unsatisfactory. In this study, we found that 5% of ESCC cells survived the treatment with high doses of 5-FU for 5 days. Compared to the parental cells, the rapidly acquired drug-tolerant persister (DTP) cells showed enhanced expression of those genes associated with stemness and epithelial-mesenchymal transition. Once 5-FU was removed, the regrown cells regained their sensitivity to 5-FU. Additionally, the transcriptomic profiles analysis showed that the parental and the regrown cells had very similar gene expression profile, while DTP cells showed distinct changes. Significant changes in histone deacetylation pathway were observed in DTP cells. Knockdown of HDAC2/6/9 and BRD4 markedly reduced the formation of DTP cells. We screened our drug library and found that HDAC4/5/6/7 inhibitor TMP269 and BRD2/3/4 inhibitor ABBV-744 showed potent synergistic cytotoxic effects with 5-FU in the parental ESCC cells. Our team then synthesized a new HDAC inhibitor YFF-702 and BET inhibitor C-34, which showed synergistic effects with 5-FU in the parental ESCC cells. Moreover, ABBV-744 and YFF-702 showed synergistic cytotoxic effects with 5-FU in DTP cells. Animal experiments further demonstrated that YFF-702 significantly improved the efficacy of 5-FU in an in vivo tumor model. This current research demonstrates that combining HDAC/BET inhibition with 5-FU may be a promising therapeutic strategy for ESCC patients by targeting 5-FU indued DTP cells.