IITZ-01, a novel potent lysosomotropic autophagy inhibitor, has single-agent antitumor efficacy in triple-negative breast cancer in vitro and in vivo

Autophagy is a homeostatic process that recycles damaged organelles and long-lived proteins by delivering them in double-membrane vesicles to lysosomes for degradation. Autophagy has a prominent role in survival, proliferation, and resistance of tumors in metabolic and chemotherapeutic stress conditions. Clinical trials with chloroquine-a known autophagy inhibitor-were unable to achieve complete autophagy inhibition in vivo, warranting the search for more potent autophagy inhibitors. In a process of exploring the mechanism of action of previously identified cytotoxic s-triazine analogs, we discovered that both IITZ-01 and IITZ-02 act as potent autophagy inhibitors. Treatment with these compounds resulted in the vacuolated appearance of cells due to their specific accumulation in lysosomes. In addition, these basic compounds also deacidify lysosomes as evidenced by the decrease in lysotracker red staining and inhibit maturation of lysosomal enzymes leading to lysosomal dysfunction. IITZ-01 and IITZ-02 enhance autophagosome accumulation but inhibit autophagosomal degradation by impairing lysosomal function, finally resulting in the inhibition of autophagy. Interestingly, compound IITZ-01 exhibited more than 10-fold potent autophagy inhibition along with 12- to 20-fold better cytotoxic action than CQ. IITZ-01 and IITZ-02 also abolished mitochondrial membrane potential and triggered apoptosis through the mitochondria-mediated pathway. Furthermore, IITZ-01 and IITZ-02 displayed potent antitumor action in vivo through autophagy inhibition and apoptosis induction in MDA-MB-231 breast cancer xenograft model with IITZ-01 exhibiting superior anticancer efficacy. Overall, these data demonstrate that IITZ-01 is potent autophagy inhibitor with single-agent anticancer activity and awaits further preclinical development as potential anticancer therapeutic.