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

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 inhibitioninduced 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 sphingolipid and a potent GSK-3 activator. We found that either PDMP or silence of GCS increased Bcr-Abl inhibitioninduced GSK-3 activation and apoptosis. Furthermore, PDMP sensitized the most clinical problematic drug-resistant CML T315I mutant to Bcr-Abl inhibitor GNF2-, 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