Discovery of KPT-6566 as STAG1/2 Inhibitor sensitizing PARP and NHEJ Inhibitors to suppress tumor cells growth in vitro

Stromal antigen 1 and 2 (STAG1 and STAG2) are two mutually exclusive components of the cohesin complex that is crucial for centromeric and telomeric cohesion. Beyond its structural role, STAG2 also plays a pivotal role in homologous recombination (HR) repair and has emerged as a promising therapeutic target in cancer treatment. Here, we employed a fluorescence polarization (FP)-based high-throughput screening and identified KPT-6566 as a dual inhibitor of STAG1 and STAG2. Biochemical and biophysical analyses demonstrated that KPT-6566 directly binds to STAG1 and STAG2, disrupting their interactions with SCC1 and double-stranded DNA. A metaphase chromosome spread assay showed that KPT-6566 causes premature chromosome separation and induces chromosome damages in HeLa cells. Furthermore, KPT-6566 also impairs DNA damage repair, leading to the accumulation of double-strand breaks and cell apoptosis. Finally, KPT-6566 can sensitize HeLa and HepG2 cells to PARP inhibitor Olaparib and the NHEJ inhibitor UMI-77, exhibiting a synergistic effect in suppressing cell proliferation. Our findings highlight the potential of STAG1/2 as promising therapeutic targets in cancer treatment, particularly when they are targeted in combination with other DNA damage response inhibitors.