Combination therapy with WEE1 inhibition and trifluridine/tipiracil against esophageal squamous cell carcinoma.

Despite advanced therapeutics, esophageal squamous cell carcinoma (ESCC) remains one of the deadliest cancers. Here, we propose a novel therapeutic strategy based on synthetic lethality combining trifluridine/tipiracil and MK1775 (WEE1 inhibitor) as a treatment for ESCC. This study demonstrates that trifluridine induces single-strand DNA damage in ESCC cells, as evidenced by phosphorylated replication protein 32. The DNA damage response includes cyclin-dependent kinase 1 (CDK1) (Tyr15) phosphorylation as CDK1 inhibition and a decrease of the proportion of phospho-histone H3 (p-hH3)-positive cells, indicating cell cycle arrest at the G2 phase before mitosis entry. The WEE1 inhibitor remarkedly suppressed CDK1 phosphorylation (Try15) and reactivated CDK1, and also increased the proportion of p-hH3-positive cells, which indicates an increase of the number of cells into mitosis. Trifluridine combined with a WEE1 inhibitor increased trifluridine-mediated DNA damage, namely DNA double-strand breaks, as shown by increased γ-H2AX expression. Moreover, the combination treatment with trifluridine/tipiracil and a WEE1 inhibitor significantly suppressed tumor growth of ESCC-derived xenograft models. Hence, our novel combination treatment with trifluridine/tipiracil and a WEE1 inhibitor is considered a candidate treatment strategy for ESCC.

Synthetic Lethality with Trifluridine/Tipiracil and Checkpoint Kinase 1 Inhibitor for Esophageal Squamous Cell Carcinoma.

Esophageal squamous cell carcinoma (ESCC) is a disease characterized by a high mutation rate of the TP53 gene, which plays pivotal roles in the DNA damage response (DDR) and is regulated by checkpoint kinase (CHK) 2. CHK1 is another key DDR-related protein, and its selective inhibition is suggested to be particularly sensitive to TP53-mutated cancers, because a loss of both pathways (CHK1 and/or CHK2-p53) is lethal due to the serious impairment of DDR. Such a therapeutic strategy is termed synthetic lethality. Here, we propose a novel therapeutic strategy based on synthetic lethality combining trifluridine/tipiracil and prexasertib (CHK1 inhibitor) as a treatment for ESCC. Trifluridine is a key component of the antitumor drug combination with trifluridine/tipiracil (an inhibitor of trifluridine degradation), also known as TAS-102. In this study, we demonstrate that trifluridine increases CHK1 phosphorylation in ESCC cells combined with a reduction of the S-phase ratio as well as the induction of ssDNA damage. Because CHK1 phosphorylation is considered to be induced as DDR for trifluridine-mediated DNA damage, we examined the effects of CHK1 inhibition on trifluridine treatment. Consequently, CHK1 inhibition by short hairpin RNA or treatment with the CHK1 inhibitor, prexasertib, markedly enhanced trifluridine-mediated DNA damage, represented by an increase of γH2AX expression. Moreover, the combination of trifluridine/tipiracil and CHK1 inhibition significantly suppressed tumor growth of ESCC-derived xenograft tumors. Furthermore, the combination of trifluridine and prexasertib enhanced radiosensitivity both in vitro and in vivo Thus, the combination of trifluridine/tipiracil and a CHK1 inhibitor exhibits effective antitumor effects, suggesting a novel therapeutic strategy for ESCC.