Glucosylceramide synthase inhibitor PDMP sensitizes chronic myeloid leukemia T315I mutant to Bcr‐Abl inhibitor and cooperatively induces glycogen synthase kinase‐3‐regulated apoptosis

ABSTRACT Inactivation of glycogen synthase kinase (GSK)‐3 has been implicated in cancer progression. Previously, we showed an abundance of inactive GSK‐3 in the human chronic myeloid leukemia (CML) cell line. CML is a hematopoietic malignancy caused by an oncogenic Bcr‐Abl tyrosine kinase. In Bcr‐Abl signaling, the role of GSK‐3 is not well defined. Here, we report that enforced expression of constitutively active GSK‐3 reduced proliferation and increased Bcr‐Abl inhibition‐induced apoptosis by nearly 1‐fold. Bcr‐Abl inhibition activated GSK‐3 and GSK‐3‐dependent apoptosis. Inactivation of GSK‐3 by Bcr‐Abl activity is, therefore, confirmed. To reactivate GSK‐3, we used glucosylceramide synthase (GCS) inhibitor PDMP to accumulate endogenous ceramide, a tumor‐suppressor sphingo‐lipid and a potent GSK‐3 activator. We found that either PDMP or silence of GCS increased Bcr‐Abl inhibition‐induced GSK‐3 activation and apoptosis. Furthermore, PDMP sensitized the most clinical problematic drug‐resistant CML T315I mutant to Bcr‐Abl inhibitor GNF‐2‐, imatinib‐, or nilotinib‐induced apoptosis by >5‐fold. Combining PDMP and GNF‐2 eliminated transplanted‐CML‐T315I‐mutants in vivo and dose dependently sensitized primary cells from CML T315I patients to GNF‐2‐induced proliferation inhibition and apoptosis. The synergistic efficacy was Bcr‐Abl restricted and correlated to increased intracellular ceramide levels and acted through GSK‐3‐mediated apoptosis. This study suggests a feasible novel anti‐CML strategy by accumulating endogenous ceramide to reactivate GSK‐3 and abrogate drug resistance.—Huang, W.‐C., Tsai, C.‐C., Chen, C.‐L., Chen, T.‐Y., Chen, Y.‐P., Lin, Y.‐S., Lu, P.‐J., Lin, C.‐M., Wang, S.‐W., Tsao, C.‐W., Wang, C.‐Y., Cheng, Y.‐L., Hsieh, C.‐Y., Tseng, P.‐C., Lin, C.‐F. Glucosylceramide synthase inhibitor PDMP sensitizes chronic myeloid leukemia T315I mutant to Bcr‐Abl inhibitor and cooperatively induces glycogen synthase kinase‐3‐regulated apoptosis. FASEB J. 25, 3661–3673 (2011). www.fasebj.org