Aulosirazole Stimulates FOXO3a Nuclear Translocation to Regulate Apoptosis and Cell Cycle Progression in High-Grade Serous Ovarian Cancer (HGSOC) Cells .

Ovarian cancer, the fifth leading cause of cancer-related mortality in women, is the most lethal gynecological malignancy globally. Within various ovarian cancer subtypes, high-grade serous ovarian cancer (HGSOC) is the most prevalent and there is frequent emergence of chemoresistance. Aulosirazole, an isothiazolonaphthoquinone alkaloid, isolated from the cyanobacterium Nostoc sp. UIC 10771, demonstrated cytotoxic activity against OVCAR3 cells (IC50 = 301 {plus minus} 80 nM). Using immunocytochemistry, OVCAR3 cells treated with aulosirazole demonstrated increased concentrations of pAKT and pJNK with subsequent accumulation of FOXO3a in the nucleus. The combination of aulosirazole with AKT inhibitors resulted in the most nuclear accumulation of FOXO3a Aulosirazole induced apoptosis based on cleavage of PARP, Annexin V staining, and induction of caspase 3/7 activity in OVCAR3, OVCAR5 and OVCAR8. The expression of downstream targets of FOXO3a, including BCL2 and PUMA, significantly increased following aulosirazole treatment. Aulosirazole upregulated the FOXO3a target, p21, and increased cell cycle arrest in the G0/G1 phase. The downregulation of FOXO3a by shRNA reduced the cytotoxicity after aulosirazole treatment by threefold IC50 (949 {plus minus} 16 nM) and eliminated its ability to regulate downstream targets of FOXO3a. These findings underscore FOXO3a as a critical mediator of aulosirazole-induced cytotoxicity. Additionally, aulosirazole was able to decrease migration and invasion while increasing cell death in 3D tumor spheroids. However, in vivo OVCAR8 tumor burden was not significantly reduced by aulosirazole using an intraperitoneal tumor model. Given the mechanism of action of aulosirazole, this class of alkaloids represents promising lead compounds to develop treatments against FOXO3a-downregulated cancers. Significance Statement Aulosirazole, an isothiazolonaphthoquinone alkaloid, exhibits potent cytotoxic effects against HGSOC by promoting FOXO3a nuclear accumulation and modulating downstream targets. These findings highlight the potential of aulosirazole as a promising therapeutic intervention for cancers characterized by FOXO3a downregulation.