Autophagy controls everolimus (RAD001) activity in mantle cell lymphoma.

Mantle cell lymphoma (MCL) is an aggressive neoplasm, which lacks effective therapy. The mechanistic target of rapamycin (MTOR) kinase inhibitor everolimus (RAD001) has shown activity in preclinical and clinical models of MCL, despite the fact that its mechanism of action has not been fully elucidated. We found that everolimus activity in MCL cells is closely linked to AKT phosphorylation status, and that the prevention of AKT rephosphorylation upon everolimus treatment by means of a selective AKT inhibitor, greatly enhances everolimus activity. Furthermore, our data show that an accumulation of autophagic vacuoles correlates with a lack of efficacy of dual AKT-MTOR targeting and that the complete therapeutic potential of this strategy can be restored by ATG gene selective knockdown or secondary inhibition of autolysosome formation by hydroxychloroquine. We thus demonstrated for the first time that the use of an autophagy inhibitor can overcome resistance to the combination of MTOR and AKT inhibitors in MCL cell lines and primary samples, demonstrating the prosurvival role of autophagy in AKT-MTOR compromised cells, and pointing out some potential opportunities using this triple combinational strategy in hematological malignancies.