CHK1 inhibition by prexasertib sensitizes cisplatin-resistant malignant tumor cells via checkpoint abrogation and STAT1-driven PD-L1 upregulation.

Malignant tumors such as rhabdomyosarcoma, head and neck squamous cell carcinoma, and cervical cancer exhibit resistance to conventional therapies, underscoring the urgent need for novel treatment strategies. Checkpoint kinase 1 (CHK1), a central regulator of the DNA damage response and cell cycle progression, is frequently overexpressed in these malignancies and represents a promising therapeutic target. In this study, we evaluated the antineoplastic efficacy of the CHK1 inhibitor Prexasertib across multiple tumor models. Prexasertib inhibited CHK1 activity, induced DNA double-strand breaks (DSBs) and pronounced cell cycle dysregulation, resulting in significant suppression of tumor cell proliferation and survival. It enhanced the cytotoxicity of cisplatin and effectively reversed resistance in a newly established cisplatin-resistant FaDu/DDP cell line. Mechanistically, Prexasertib abrogated S and G2/M phase checkpoints and was accompanied by STAT1 activation and PD-L1 induction in a cell type-dependent manner. Co-treatment with interferon-γ further amplified PD-L1 and γH2A.X expression, highlighting a link between CHK1 inhibition, DNA damage, and immune checkpoint modulation. These findings suggest that Prexasertib not only enhances the cytotoxic effects of cisplatin but also influences immune signaling, providing a mechanistic rationale for future exploration of combined DNA damage response inhibition with immune checkpoint blockade.