Unraveling a New Therapeutic Potential of Imatinib Mesylate

Evidence suggests that bone marrow (BM) cells may give rise to a significant proportion of smooth muscle cells (SMCs) that contribute to intimal hyperplasia after vascular injury; however, the molecular pathways involved and the timeline of these events remain poorly characterized. We hypothesized that the stem cell factor (SCF)/c-Kit tyrosine kinase signaling pathway is critical to neointimal formation by BM-derived progenitors. Wire-induced femoral artery injury in mice reconstituted with wild-type BM cells expressing yellow fluorescent protein was performed, which revealed that 66 12% of the SMCs ( -smooth muscle actin–positive [ SMA ] cells) in the neointima were from BM. To characterize the role of the SCF/c-Kit pathway, we used c-Kit deficient W/W and SCF-deficient Steel–Dickie mice. Strikingly, vascular injury in these mice resulted in almost a complete inhibition of neointimal formation, whereas wild-type BM reconstitution of c-Kit mutant mice led to neointimal formation in a similar fashion as wild-type animals, as did chronic administration of SCF in matrix metalloproteinase-9–deficient mice, a model of soluble SCF deficiency. Pharmacological antagonism of the SCF/c-Kit pathway with imatinib mesylate (Gleevec) or ACK2 (c-Kit antibody) also resulted in a marked reduction in intimal hyperplasia. Vascular injury resulted in the local upregulation of SCF expression. c-Kit progenitor cells (PCs) homed to the injured vascular wall and differentiated into SMA cells. Vascular injury also caused an increase in circulating SCF levels which promoted CD34 PC mobilization, a response that was blunted in mutant and imatinib mesylate–treated mice. In vitro, SCF promoted adhesion of BM PCs to fibronectin. Additionally, anti-SCF antibodies inhibited adhesion of BM PCs to activated SMCs and diminished SMC differentiation. These data indicate that SCF/c-Kit signaling plays a pivotal role in the development of neointima by BM-derived PCs and that the inhibition of this pathway may serve as a novel therapeutic target to limit aberrant vascular remodeling. (Circ Res. 2006;99:0-0.)