Veliparib (ABT-888), a PARP Inhibitor Potentiates the Cytotoxic Activity of 5-Fluorouracil by Inhibiting MMR Pathway through Deregulation of MSH6 in Colorectal Cancer Stem Cells

5-Fluorouracil (5-FU) caused DNA damage and ABT-888 enhanced the accumulation of the DNA lesions by inhibiting the mismatch repair repair pathway in 5-FU-pre-treated MMR-proficient-CRC-CSCs. This resulted in S-phase arrest, induction of apoptosis, and finally CSCs death.