Effects of the Second Generation Tyrosin Kinase Inhibitors on Osteogenic Differentiation.

Abstract 3386

It has been demonstrated that long term treatment of CML patients with Imatinib (IM) is associated with altered bone and mineral metabolism. The mechanisms that are responsible for this effect are not fully understood but an inhibition of the PDGF-Rβ (Platelet Derived Growth Factor- Receptor beta) axis has been documented. In order to evaluate if stimulation of osteoblastogenesis is a common feature of other tyrosine kinase inhibitors (TKIs) approved for the treatment of patients with CML, we evaluated the osteoblatic differentiation of Mesenchymal Stem Cells derived from adult bone marrow donors (BM-MSCs) after in vitro treatment with Dasatinib (DA), Nilotinib (NI) or Bosutinib (BO). BM-MSCs were induced to differentiate in osteoblastic cells by treatment with osteogenic medium (OM) with or without DA, NI or BO. BM-MSCs was induced to differentiate in osteoblastic cells by treatmet with osteogenic medium (0.2 mM ascorbic acid, 0.1 μ m dexamethasone and 10 mM β-glycerophosphate, OM) with or without DA 2nM, BO 5nM or NI 100nM. After 21 days of treatment, in the cultures treated with DA e NI for 21 days we have observed a significant increase of extracellular mineralization and of osteogenic markers such as bone morphogenetic protein (BMP2) (p<0.005), osteocalcin (OCN) (p<0.002), and Runx2/cfba1, (p<0.002) measured by real time PCR. OPG/RANKL ratio (measured by ELISA) was also increased in surnatant of cultures treated with DA and NI (p<0.002). All these phenomena were not observed when BO was added to the cultures.

In conclusion, we show that besides IM, other TKIs such as DA and NI, but not BO, increase osteogenic markers in hBM-MSCs. Since BO differs from the other TKIs because of its low affinity to PDGF-R, these experiments suggest that inhibition of PDGF-R is a major pathway in the induction of osteoblastogenesis by TKIs. In addition, a perturbation of bone metabolism induced by TKi may interfere with physiological growth and have negative consequences in children and adolescents. In this subset of patients, treatment with BO could became the first choice because we have demonstrated that this drug does not affect osteoblastogenesis.