ABSTRACT
DNA replication stress is a predominant cause of genome instability, a driver of tumorigenesis and malignant progression. Nucleoside analog-type chemotherapeutic drugs introduce DNA damage and exacerbate DNA replication stress in tumor cells. However, the mechanisms underlying tumor cytotoxicity triggered by the drugs are not fully understood. Here, we show that the fluorinated thymidine analog trifluridine (FTD), an active component of the chemotherapeutic drug trifluridine/tipiracil, delayed DNA synthesis by human replicative DNA polymerases. FTD acted as an inefficient deoxyribonucleotide triphosphate source (FTD triphosphate) and as an obstacle base (trifluorothymine) in the template DNA strand. At the cellular level, FTD decreased thymidine triphosphate in the dNTP pool and induced FTD triphosphate accumulation, resulting in replication fork stalling caused by FTD incorporation into DNA. DNA lesions involving single-stranded DNA were generated as a result of replication fork stalling, and the p53-p21 pathway was activated. Although FTD suppressed tumor cell growth irrespective of p53 status, tumor cell fate diverged at the G2/M phase transition according to p53 status; tumor cells with wild-type p53 underwent cellular senescence via mitosis skip, whereas tumor cells that lost wild-type p53 underwent apoptotic cell death via aberrant late mitosis with severely impaired separation of sister chromatids. These results suggest that DNA replication stress induced by a nucleoside analog-type chemotherapeutic drug triggers tumor cytotoxicity by determining tumor cell fate according to p53 status.
Significance This study identified a unique type of DNA replication stress induced by trifluridine, which directs tumor cell fate either toward cellular senescence or apoptotic cell death according to p53 status.
Footnotes
Financial Support: This study was supported in part by grants-in-aid from the Ministry of Education, Culture, Sports, Science, and Technology of Japan (to H.K., JSPS KAKENHI grant number 17H03598 and 18K19478) and by commercial grants of Shinnihon Foundation of Advanced Medical Treatment Research (to M.I.).
Disclosure of Potential Conflicts of Interest: Y.K., and T.W. are employees of Taiho Pharmaceutical Co. Ltd.; M.I., and H.K. are staff of the Joint Research Department funded by Taiho Pharmaceutical Co. Ltd. in Kyushu University. Y.M. received research funding from Taiho Pharmaceutical Co. Ltd. Other authors declare that they have no competing interests.
