Fig. 6: Effect of decitabine on SLFN11 expression.

A Effect of decitabine on SLFN11 expression. Cell lines BCX-010CL, HCC-1937, HCC-1143, and MDA-MB-157 were treated with decitabine at 1 µM for 3 days. SLFN11 and TROP2 proteins in cell lysates were detected by immunoblotting. B, C Effect of decitabine on cell sensitivity to SN-38 (B) and SG (C). These breast cancer cell lines were treated with the indicated agents at concentrations in serial dilutions, with or without decitabine co-treatment for 3 days. IC50s of individual agents and combination index were calculated. D Effect of ZEB1 knockdown on SLFN11 expression in BCX-010CL cells. Cells with or without ZEB1 knockdown were treated with decitabine at 1 µM for 3 days, followed by immunoblotting for SLFN11. E Mechanism of decitabine action. In tumor cells, decitabine decreases promoter methylation of the TACSTD2 gene by inhibiting DNA methyltransferase 1 (DNMT1), activating expression of TACSTD2/TROP2. On cell membrane, TROP2 protein binds to TROP2 ADC drug sacituzumab govitecan (SG). After internalization, SG is proteolytically cleaved in lysosome to release payload SN-38. SN-38 then moves into nucleus where it inhibits topoisomerase 1 (TOP1), leading to DNA damage, cell cycle arrest, and cell death. Decitabine also increases SLFN11 expression which further strengthens the chemocytoxic effect of SN-38 in the tumor cells.