Nitric oxide-dependent stabilization of vimentin confers chemoresistance in ovarian cancer

High-grade serous ovarian carcinoma (HGSC) is often diagnosed at an advanced stage and is characterized by an immunosuppressive tumor microenvironment that facilitates disease progression, therapeutic resistance, and poor survival. We recently demonstrated that nitric oxide (NO) blockade enhances the response of metaplastic breast cancer to PI3K inhibition and taxane therapy by reducing S-nitrosylation-mediated activation of the JNK/c-Jun pathway, thereby promoting tumor differentiation, suppressing stemness, and improving survival in patient-derived xenograft models. Here, we demonstrate that inducible nitric oxide synthase (iNOS) is constitutively expressed in HGSC and that pharmacologic inhibition of NO signaling with the pan-NOS inhibitor NG-monomethyl-L-arginine (L-NMMA) enhances cisplatin efficacy by reprogramming the tumor microenvironment. By targeting NO signaling with either L-NMMA or through CRISPR-Cas9-mediated iNOS knockout and iNOS small interfering RNA (siRNA), we impaired epithelial-to-mesenchymal transition (EMT) by inhibiting NO-mediated stabilizing effects on vimentin in both in vitro and in vivo models. Mechanistically, L-NMMA-mediated inhibition of iNOS signaling reduced S-nitrosylation, accelerated vimentin ubiquitination, and promoted its proteasome-dependent degradation. These findings identify iNOS-mediated S-nitrosylation as a key regulator of vimentin stability and EMT and suggest that therapeutic inhibition of NO signaling may increase cisplatin sensitivity in HGSC and improve patient outcomes.