Imatinib mesylate and AMN107 inhibit PDGF-signaling in orbital fibroblasts: A potential treatment for Graves' ophthalmopathy
PURPOSE. Excessive orbital fibroblast proliferation and hyaluronan production are characteristic of Graves' ophthalmopathy (GO) and are driven by local mediators. Imatinib mesylate and AMN107 are tyrosine kinase inhibitors that inhibit fibroblast proliferation and collagen production in lungs and skin. This study was conducted to determine whether imatinib mesylate and AMN107 inhibit orbital fibroblast proliferation and hyaluronan production induced by PDGF-BB and TGF-β1and whether expression of the genes PDGF-B and TGF-B1(growth factors suggested to play a role in GO) are increased in GO orbital tissues. METHODS. PDGF-B and TGF-B1mRNA levels were determined in orbital tissues of 13 patients with GO and 5 control patients. Orbital fibroblasts were cultured from eight patients with GO and three control patients and the effect of imatinib mesylate and AMN107 on PDGF-BB and TGF-β1-induced orbital fibroblast proliferation, signaling cascades, hyaluronan synthase (HAS) gene expression and hyaluronan production were determined. RESULTS. PDGF-B and TGF-B1mRNA levels were significantly increased in GO orbital tissues. Imatinib mesylate and AMN107 inhibited PDGF-BB-induced orbital fibroblast proliferation, HAS induction and hyaluronan production by blocking PDGFreceptor phosphorylation. TGF-β1induced HAS expression and hyaluronan production. This induction was not inhibited by imatinib mesylate or AMN107, due to the inability of TGF-β1to activate c-Abl kinase activity in orbital fibroblasts. CONCLUSIONS. Imatinib mesylate and AMN107 inhibit orbital fibroblast proliferation and hyaluronan production induced by PDGF-BB; a factor highly expressed in orbital tissue from patients with GO. The drugs, however, had no effect on TGF-β1-induced HAS expression and hyaluronan production. Nevertheless, imatinib mesylate and AMN107 should be considered as treatment candidates for GO.