Trifluridine to enhance cytotoxicity by DNA mismatch repair deficiency and subsequent MBD4 frameshift mutation in colorectal cancer.

Abstract

608 Background: TAS-102 is composed of trifluridine (FTD) and tipiracil hydrochloride and was shown to prolong survival of patients with refractory metastatic colorectal cancer (CRC). FTD is the active antitumor component of TAS102 and its metabolite TF-TTP chemically resembles 5FU-derived metabolite FdUTP in that both of them are misincorporated into DNA and lead to cytotoxicity. Several groups have reported that stage II-III colorectal cancer patients with tumors that lost DNA mismatch repair (MMR) function do not derive a benefit from 5-FU based chemotherapy. Although FTD is reported to be misincorporated into DNA, it is not known if MMR deficient CRC cells have chemoresistance for FTD. Methods: We first utilized human colorectal cancer cell lines HCT-116 (hMLH1-deficient cells) and HCT116+ch3 (hMLH1-retained cells), and compared cytotoxicity for FTD by clonogenic assay. To further analyze if 5FU refractory CRC cells have chemosensitivity for FTD, we established 5FU refractory HCT116 cells by continuous 5FU treatment for 10 month and analyzed cytotoxicity for FTD. Finally we constructed an expression plasmid of truncated DNA grycosylase MBD4, (MBD4tru) by frameshift mutation with MMR deficiency and stably transfected the construct into HCT116 CRC cells and selected HCT116MBD4tru cell clones. The HCT116MBD4tru cells were treated with FTD and analyzed for cytotoxicity by clonogenic assay. Results: In hMLH1-deficient cells, the number of colony was reduced by FTD treatment to a same degree of hMLH1-proficient cells whereas the number of colony by 5FU treatment is higher in hMLH1-deficitent cells than hMLH1-retained cells (p< 0.05). In 5FU refractory cells, treatment of FTD showed cytotoxicity to the same degree of non-5FU refractory cells. Interestingly, HCT116MBD4tru cells led to cytotoxicity with a higher sensitivity than control cells (p< 0.05). Conclusions: FTD induces cytotoxisity independently of MMR status as well as under 5FU refractory condition, and MBD4 frameshift mutation by MMR deficiency enhances FTD sensitivity. These results suggest that FTD may be useful for patients with MSI-H/MBD4 mutant CRC as well as for those with 5FU refractory CRC.