title: Targeting glucosylceramide synthase sensitizes imatinib-resistant chronic myeloid leukemia cells via endogenous ceramide accumulation.
abstract: OBJECTIVE
  Drug resistance presents a major obstacle for the treatment of some patients with chronic myeloid leukemia (CML). Pro-apoptotic ceramide mediates imatinib-induced apoptosis, and metabolism of ceramide by glucosylceramide synthase (GCS) activity, converting ceramide to glucosyl ceramide, might contribute to imatinib resistance. In this study, we investigated the role of ceramide metabolism by GCS in the regulation of imatinib-induced apoptosis in drug-sensitive and drug-resistant K562 and K562/IMA-0.2 and K562/IMA-1 human CML cells, which exhibit about 2.3- and 19-fold imatinib resistance, respectively.
  
  
  METHODS
  Cytotoxic effects of PDMP and imatinib were determined by XTT cell proliferation assay. Expression levels of GCS were determined by RT-PCR and western blot. Intracellular ceramide levels were determined by LC-MS. Cell viability analyses was conducted by Trypan blue dye exclusion assay. Cell cycle and apoptosis analyses were examined by flow cytometry.
  
  
  RESULTS
  We first showed that mRNA and protein levels of GCS are increased in drug-resistant K562/IMA as compared to sensitive K562 cells. Next, forced expression of GCS in sensitive K562 cells conferred resistance to imatinib-induced apoptosis. In reciprocal experiments, targeting GCS using its known inhibitor, PDMP, enhanced ceramide accumulation and increased cell death in response to imatinib in K562/IMA cells.
  
  
  CONCLUSIONS
  Our data suggest the involvement of GCS in resistance to imatinib-induced apoptosis, and that targeting GCS by PDMP increased imatinib-induced cell death in drug-sensitive and drug-resistant K562 cells via enhancing ceramide accumulation.
authors.affiliation: Department of Molecular Biology and Genetics, Izmir Institute of Technology, Faculty of Science, Gulbahce Campus, 35430, Urla, Izmir, Turkey. yusufbaran@iyte.edu.tr
authors.forename: Yusuf
authors.initials: Y
authors.lastname: Baran
authors.forename: Jacek
authors.initials: J
authors.lastname: Bielawski
authors.forename: Ufuk
authors.initials: U
authors.lastname: Gunduz
authors.forename: Besim
authors.initials: B
authors.lastname: Ogretmen
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001549:Benzamides; D002453:Cell Cycle / Q000187:drug effects; D002518:Ceramides / Q000378:metabolism*; D019008:Drug Resistance, Neoplasm; D005964:Glucosyltransferases / Q000037:antagonists & inhibitors* / Q000502:physiology; D006801:Humans; D000068877:Imatinib Mesylate; D020014:K562 Cells; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D009025:Morpholines / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology*; D011743:Pyrimidines / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D001549:Benzamides; D002518:Ceramides; D009025:Morpholines; D010879:Piperazines; D011743:Pyrimidines; C033110:RV 538; D000068877:Imatinib Mesylate; D005964:Glucosyltransferases; C023246:ceramide glucosyltransferase