The tyrosine kinase inhibitor dasatinib dysregulates bone remodeling through inhibition of osteoclasts in vivo.

Dasatinib is a potent tyrosine kinase inhibitor that is used to treat chronic myeloid leukemia in patients resistant or intolerant to imatinib mesylate. While designed to inhibit Abl and Src kinases, dasatinib shows multitarget effects, including inhibition of the macrophage colony-stimulating factor (M-CSF) receptor c-fms. We have shown previously that dasatinib abrogates osteoclast formation and activity in vitro owing, in part, to its specificity for c-fms. In this study we examined whether dasatinib could significantly alter bone volume in a model of physiologic bone turnover. Sprague-Dawley rats were administered dasatinib (5 mg/kg/day) or vehicle by gavage or zoledronic acid (ZOL; 100 microg/kg/6 weeks) subcutaneously. Following 4, 8, and 12 weeks of treatment, serum biochemical, bone morphometric, and histologic analyses were performed. Whole-body bone mineral density and tibial cortical thickness where unchanged in the dasatinib- or ZOL-treated animals relative to controls. However, micro-computed tomographic (microCT) analysis of cancellous bone at the proximal tibias showed that trabecular volume (BV/TV) and thickness (Tb.Th) were increased in dasatinib-treated animals at levels comparable with those of the ZOL-treated group. These changes were associated with a decrease in osteoclast numbers (N.Oc/B.Pm) and surface (Oc.S/BS) and decreased serum levels of the osteoclast marker c-terminal collagen crosslinks (CTX-1). Mineral apposition rate (MAR), bone-formation rate (BFR), and levels of the serum osteoblast markers osteocalcin and N-terminal propeptide of type I procollagen (P1NP) were not altered significantly in the dasatinib-treated animals relative to controls. These studies show that dasatinib increases trabecular bone volume at least in part by inhibiting osteoclast activity, suggesting that dasatinib therapy may result in dysregulated bone remodeling.