Dual inhibition of REV-ERBβ and autophagy as a novel pharmacological approach to induce cytotoxicity in cancer cells

REV-ERBα and REV-ERBβ nuclear receptors regulate several physiological processes, including circadian rhythm and metabolism. A previous study reported the REV-ERBα gene to be co-overexpressed with ERBB2 in breast Cancer cell lines. Surprisingly, we found that several tumor types, including a number of breast Cancer cell lines, predominantly express the REV-ERBβ variant. This pattern was independent of ERBB2 and ER status, and opposite to that of non-cancer mammary epithelial HMEC cells, in which REV-ERBα was the major variant. Consistent with this molecular profile, REV-ERB target genes in both circadian and metabolic pathways were derepressed upon silencing of REV-ERBβ, but not REV-ERBα. Strikingly, we found that REV-ERBβ is a determinant of sensitivity to chloroquine, a clinically relevant lysosomotropic agent that suppresses Autophagy. The cytoprotective function of REV-ERBβ appears to operate downstream of Autophagy blockade. Through compound screening, we identified ARN5187, a novel lysosomotropic REV-ERBβ ligand with a dual inhibitory activity toward REV-ERB-mediated transcriptional regulation and Autophagy. Remarkably, although ARN5187 and chloroquine share similar lysosomotropic potency and have a similar effect on Autophagy inhibition, ARN5187 is significantly more cytotoxic. Collectively, our results reveal that dual inhibition of REV-ERBβ and Autophagy is an effective strategy for eliciting cytotoxicity in Cancer cells. Furthermore, our discovery of a novel inhibitor compound of both REV-ERB and Autophagy may provide a scaffold for the discovery of new multifunctional Anticancer agents.