Abstract
ARL-17477 is a selective neuronal nitric oxide synthase (NOS1) inhibitor that has been used in many preclinical studies since its initial discovery in the 1990s. In the present study, we demonstrate that ARL-17477 exhibits a NOS1-independent pharmacological activity that involves inhibition of the autophagy-lysosomal system and prevents cancer growth in vitro and in vivo. Initially, we screened a chemical compound library for potential anticancer agents, and identified ARL-17477 with micromolar anticancer activity against a wide spectrum of cancers, preferentially affecting cancer stem-like cells and KRAS-mutant cancer cells. Interestingly, ARL-17477 also affected NOS1-knockout cells, suggesting the existence of a NOS1-independent anticancer mechanism. Analysis of cell signals and death markers revealed that LC3B-II, p62, and GABARAP-II protein levels were significantly increased by ARL-17477. Furthermore, ARL-17477 had a chemical structure similar to that of chloroquine, suggesting the inhibition of autophagic flux at the level of lysosomal fusion as an underlying anticancer mechanism. Consistently, ARL-17477 induced lysosomal membrane permeabilization, impaired protein aggregate clearance, and activated transcription factor EB and lysosomal biogenesis. Furthermore, in vivo ARL-17477 inhibited the tumor growth of KRAS-mutant cancer. Thus, ARL-17477 is a dual inhibitor of NOS1 and the autophagy-lysosomal system that could potentially be used as a cancer therapeutic.