title: Suppression of PDGF-induced PI3 kinase activity by imatinib promotes adipogenesis and adiponectin secretion.
abstract: Improved glucose and lipid metabolism is a unique side effect of imatinib therapy in some chronic myeloid leukaemia (CML) patients. We recently reported that plasma levels of adiponectin, an important regulator of insulin sensitivity, are elevated following imatinib therapy in CML patients, which could account for these improved metabolic outcomes. Adiponectin is secreted exclusively from adipocytes, suggesting that imatinib modulates adiponectin levels directly, by transcriptional upregulation of adiponectin in pre-existing adipocytes, and/or indirectly, by stimulating adipogenesis. In this report, we have demonstrated that imatinib promotes adipogenic differentiation of human mesenchymal stromal cells (MSCs), which in turn secrete high-molecular-weight adiponectin. Conversely, imatinib does not stimulate adiponectin secretion from mature adipocytes. We hypothesise that inhibition of PDGFRα (PDGFRA) and PDGFRβ (PDGFRB) is the mechanism by which imatinib promotes adipogenesis. Supporting this, functional blocking antibodies to PDGFR promote adipogenesis and adiponectin secretion in MSC cultures. We have shown that imatinib is a potent inhibitor of PDGF-induced PI3 kinase activation and, using a PI3 kinase p110α-specific inhibitor (PIK-75), we have demonstrated that suppression of this pathway recapitulates the effects of imatinib on MSC differentiation. Furthermore, using mitogens that activate the PI3 kinase pathway, or MSCs expressing constitutively activated Akt, we have shown that activation of the PI3 kinase pathway negates the pro-adipogenic effects of imatinib. Taken together, our results suggest that imatinib increases plasma adiponectin levels by promoting adipogenesis through the suppression of PI3 kinase signalling downstream of PDGFR.
authors.affiliation: Myeloma Research Laboratory, Bone and Cancer Research Laboratories, Department of Haematology, Institute of Medical and Veterinary Science, Centre for Cancer Biology, SA Pathology, GPO Box 14, Adelaide, South Australia 5000, Australia.
authors.forename: Stephen
authors.initials: S
authors.lastname: Fitter
authors.forename: Kate
authors.initials: K
authors.lastname: Vandyke
authors.forename: Stan
authors.initials: S
authors.lastname: Gronthos
authors.forename: Andrew C W
authors.initials: AC
authors.lastname: Zannettino
mesh_terms: D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism; D050156:Adipogenesis / Q000187:drug effects*; D052242:Adiponectin / Q000737:chemistry / Q000378:metabolism*; D001549:Benzamides; D002454:Cell Differentiation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D006835:Hydrazones / Q000378:metabolism; D000068877:Imatinib Mesylate; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D008934:Mitogens / Q000494:pharmacology; D008970:Molecular Weight; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010879:Piperazines / Q000494:pharmacology*; D010982:Platelet-Derived Growth Factor / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011743:Pyrimidines / Q000494:pharmacology*; D017479:Receptors, Platelet-Derived Growth Factor / Q000037:antagonists & inhibitors; D013449:Sulfonamides / Q000378:metabolism
chemical_list: D052242:Adiponectin; D001549:Benzamides; D006835:Hydrazones; D008934:Mitogens; C549211:PIK 75; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010879:Piperazines; D010982:Platelet-Derived Growth Factor; D047428:Protein Kinase Inhibitors; D011743:Pyrimidines; D013449:Sulfonamides; D000068877:Imatinib Mesylate; D017479:Receptors, Platelet-Derived Growth Factor; D051057:Proto-Oncogene Proteins c-akt