DHX9 inhibition enhances paclitaxel sensitivity by inducing mitotic failure in ovarian and endometrial cancers

Recurrent high-grade serous ovarian carcinoma (HGSOC) and endometrial Cancer (EC) remain major clinical challenges with limited effective treatment options. DHX9, a DNA/RNA helicase essential for genomic stability, has not yet been explored as a therapeutic target in gynecologic cancers. Here, we show that a selective DHX9 inhibitor (DHX9i) suppresses proliferation in a subset of HGSOC and EC cell lines by inducing DNA damage, chromosomal instability, and mitotic failure. This effect was independent of microsatellite instability status and prior resistance to platinum or PARP inhibitors. Genomic analysis indicated that DHX9i resistance was unlikely to be driven by single-gene mutations but was instead associated with copy-number alterations in mitotic spindle and microtubule-regulating genes in both HGSOC and EC. Transcriptomic profiling further revealed consistent alteration of microtubule- and spindle-associated pathways in DHX9i-resistant models following DHX9i treatment. Mechanistically, DHX9i induced mitotic defects in DHX9i-sensitive models, while resistant lines maintained mitotic integrity. Given the convergence of resistance-associated features on microtubule-related pathways, we combined DHX9i with the microtubule-stabilizing agent paclitaxel to enhance mitotic stress. This combination triggered mitotic disruption and enhanced cytotoxicity in DHX9i-resistant cells. In vivo, the combination led to sustained tumor regression and prolonged survival in both DHX9i-sensitive and -resistant models without notable toxicity. Overall, our findings define genomic, transcriptomic, and phenotypic characteristics associated with differential response to DHX9i and support clinical evaluation of DHX9i-paclitaxel combination as a therapeutic strategy in recurrent gynecologic cancers.