Abstract B024: Investigating a novel KIF18A inhibitor ATX020 in chromosomally instable ovarian cancer

Abstract High-grade serous ovarian cancer (HGSOC) is the most common subtype of ovarian cancer (∼80%) and is one of the most lethal gynecological malignancies in the United States. HGSOC is characterized by universal mutations in the TP53 gene and defects in DNA repair pathways, contributing to high incidence of chromosomal instability (CIN). CIN refers to an ongoing process involving the gain or loss of parts of chromosomes, leading to chromosomal mis-segregation, aneuploidy, and copy number variations (CNV). CINhigh cancers display a greater dependency on KIF18A, an essential cytoskeletal motor protein for cell division, in contrast to normal somatic cells. Therefore, KIF18A represents a promising target for therapeutic interventions in CINhigh cancers. We investigated the use of a novel KIF18A inhibitor (KIF18Ai), ATX020, for selectively targeting CINhigh HGSOC cells. Our approach involved advanced techniques such as RNA sequencing (RNA-seq), siRNA-based gene silencing, cell cycle analysis, and immunofluorescence. We utilized DEPMAP and flow cytometric analysis to categorize ovarian cancer cell lines according to their aneuploidy score (AS) and ploidy to investigate their response to ATX020. Cell growth inhibition studies demonstrated a correlation between AS/ploidy levels and sensitivity to ATX020 in a panel of HGSOC cells including PEO4, OVCAR3, OVCAR8 and A2780. Assessments of cell viability, cell cycle analysis, phospho-histone H3 expression, clonogenic assays, and invasion assays indicated that the growth inhibition observed over 72 hours was primarily due to the toxic effects of ATX020 on tumorigenicity and mitotic arrest. Mechanistically, ATX020 exerts its toxic effects by inhibiting the plus-end movement of KIF18A on spindle fibers, which increases the inter-kinetochore (Inter-KT) distance and induces adverse effects such as chromosomal mis-segregation, aneuploidy, and double-strand DNA damage. We also observed that KIF18Ai-resistant cells (A2780, PEO4) showed inhibited KIF18A plus-end movement and increased inter-KT distance but did not exhibit the accompanying toxic effects. In summary, our findings indicate that ATX020 inhibits CINhigh HGSOC cells primarily by inducing mitotic arrest, causing DNA damage, and reducing tumorigenicity. This effect is facilitated by ATX020's ability to inhibit the plus-end directed movement of KIF18A along spindle fibers, which is detrimental to CINhigh cells that rely on KIF18A for normal mitotic divisions. Further mechanistic investigation is ongoing. Citation Format: Jayakumar R. Nair, Maureen M. Lynes, Laura Ghisolfi, Serena J. Silver, Jung-Min Lee. Investigating a novel KIF18A inhibitor ATX020 in chromosomally instable ovarian cancer abstract. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Ovarian Cancer Research; 2025 Sep 19-21; Denver, CO. Philadelphia (PA): AACR; Cancer Res 2025;85 (18Suppl): Abstract nr B024.