Repurposing screen identifies Amlodipine as an inducer of PD-L1 degradation and antitumor immunity

Cancer cell expression of PD-L1 leads to T cells exhaustion by transducing co-inhibitory signal, and further understanding the regulation of PD-L1 in cancer cells may provide additional therapeutic strategies. Here by drug repurposing screen, we identified amlodipine as a potent inhibitor of PD-L1 expression in cancer cells. Further survey of calcium-associated pathways revealed calpain-dependent stabilization of the PD-L1 protein. Intracellular calcium delivered an operational signal to calpain-dependent Beclin-1 cleavage, blocking autophagic degradation of PD-L1 accumulated on recycling endosome (RE). Blocking calcium flux by amlodipine depleted PD-L1 expression and increased CD8+ T-cell infiltration in tumor tissues but not in myocardium, causing dose-dependent tumor suppression in vivo. Rescuing PD-L1 expression eliminated the effects of amlodipine, suggesting the PD-L1-dependent effect of amlodipine. These results reveal a calcium-dependent mechanism controlling PD-L1 degradation, and highlight calcium flux blockade as a potential strategy for combinatorial immunotherapy.