Inhibition of autophagy enhances the sensitivity of ciclopirox olamine in human chronic myelogenous leukemia K562 cells

Hematological malignancies, such as leukemia and multiple myeloma, are heterogeneous blood diseases that affect blood, lymphoid and other related tissues. Ciclopirox olamine (CPX), which is an antifungal agent, was identified as a promising anti-cancer candidate drug recently, especially in hematologic malignancy. However, CPX resistance in hematologic malignancy and the underlying molecular mechanisms are largely unknown. Our present study found that different leukemia cells exhibited different apoptotic responses to CPX. CPX effectively induced mitochondrial-mediated apoptosis in adult acute myeloid leukemia OCI-AML2 cells. However, in human chronic myelogenous leukemia K562 cells, CPX induced little apoptosis. Further study showed that CPX inhibited autophagy in OCI-AML2 cells, but induced autophagy in K562 cells. Notably, compared with CPX alone, the combination of CPX with the autophagy inhibitor chloroquine (CQ) or Bafilomycin A1 (Baf-A1) significantly enhanced pro-apoptotic activity of CPX, suggesting that CPX-induced autophagy is cytoprotective in K562 cells. Mechanism study showed that CPX induced autophagy by activating AMP-activated protein kinase (AMPK)/Unc-51 like autophagy activating kinase 1 (ULK1) signaling. Ectopic expression of dominant negative AMPKα or pharmacological inhibition of AMPK with its inhibitor compound C partially prevented from CPX inducing autophagy and re-sensitized K562 cells to CPX-induced apoptosis. Taken together, our present study demonstrates that AMPK-ULK1-mediated autophagy protects human chronic myelogenous leukemia K562 cells from CPX-induced apoptosis. To improve the clinical therapeutic efficacy of CPX in chronic myelogenous leukemia, the combination therapy of CQ and CPX might be a worthwhile alternative option.