New Inhibitors of Neuronal Nitric Oxide Synthase for the Treatment of Melanoma.

In 2024, an estimated 100,640 new cases of invasive melanoma were diagnosed in the U.S., with 9290 deaths. Our previous studies revealed that neuronal nitric oxide synthase (nNOS) derived nitric oxide plays a critical role in melanoma progression, making nNOS inhibition a promising strategy. High structural similarity among NOS isoforms requires careful design of nNOS inhibitors to avoid off-target effects. Our previous lead, HH044, demonstrated potent antimelanoma activity but exhibited only moderate nNOS selectivity. Here, we utilized a structure-based approach to design nNOS inhibitors that promote interactions with human nNOS-specific residue His342. Compound 9 exhibited inhibition of both human (Ki = 1.7 nM) and rat nNOS (Ki = 2.3 nM), with 5654-fold selectivity over human eNOS and 250-fold selectivity over iNOS. X-ray crystallography and molecular modeling revealed a novel SAR, forming the basis for nNOS inhibition and providing a foundation for further innovative design of nNOS inhibitors for melanoma treatment.