Systemic sclerosis (SSc) is systemic autoimmune disease that is characterized by microangiopathy with progressive loss of capillaries, sparse inflammation and an overproduction of extracellular matrix proteins by SSc fibroblasts leading to tissue fibrosis. IM is a tyrosine kinase inhibitor that is widely used for the treatment of CML and GIST tumors and that targets selectively abl and PDGF receptor. We have demonstrated recently, the IM inhibits potently the productions of extracellular matrix by SSc fibroblasts and prevents experimental dermal fibrosis. The aim of the present study was to exclude that the antifibrotic effects of SSc are accompanied by antiangiogenic side-effects, which might augment vascular disease in SSc.

EC were incubated with IM in concentrations from 0.01 to 1.0 μg/ml IM, which corresponds to physiologically relevant doses. The expression of VEGF was analyzed in microvascular EC after incubation with IM. IM did not alter the expression of mRNA of VEGF as analyzed by real-time PCR. Cell viability was analyzed by caspase3 assays and by annexin V/ propidium iodide staining. IM did not increase the percentage of PI-positive and annexin V–positive cells. Consistently, the activity of caspase3 did not increase upon incubation of EC with IM. IM also did not alter the rate of proliferating cells or metabolic capacity of EC as assessed with the MTT assay neither after 24 h nor after long term incubation for 4 d. Cell migration was analyzed by scratch and migration assay. IM did not reduce the migratory capacity of EC. IM did also not alter the ability of endothelial cells to form tubes upon stimulation with VEGF as analyzed by capillary morphogenesis assay. The mouse model of bleomycin-induced dermal fibrosis was used to assess the effect of IM on markers of endothelial apoptosis in vivo. Consistent with the in vitro data, no differences in the number of apoptotic endothelial cells was observed in vivo with TUNEL assay.

IM does not inhibit proliferation, migration or tube forming in endothelial cells or induce apoptosis in vitro or in vivo, suggesting that IM has no direct inhibitory effects on endothelial cells.