The Integrin Inhibitor Cilengitide and Bleomycin-Induced Pulmonary Fibrosis Cilengitide and Bleomycin-Induced Pulmonary Fibrosis

Purpose Fibroproliferation and excess deposition of extracellular matrix (ECM) are the pathologic hallmarks of idiopathic pulmonary fibrosis (IPF), a chronic progressive disorder with high mortality and suboptimal treatment options. Although the etiologic mechanisms responsible for the development and progression of IPF remain unclear, cell-ECM interactions and growth factors are considered important. Cilengitide is a cyclic RGD pentapeptide with anti-angiogenic activity that targets alpha v beta 3, alpha v beta 5 and alpha 5 beta 1, integrins known to mediate cell-ECM interactions and activate the pro-fibrotic growth factor Transforming Growth Factor beta (TGF-beta). Methods Cilengitide was studied in vitro with the use of NIH/3T3 cells and primary lung fibroblasts, and in vivo in the well-characterized bleomycin-induced lung injury model. The extent of ECM deposition was determined by RT-PCR, Western blot, histologic analysis and hydroxyproline assay of lung tissue. Bronchoalveolar lavage analysis was used to determine cell counts. Results Cilengitide treatment of cultured fibroblasts showed decreased adhesion to vitronectin and fibronectin, both integrin-dependent events. Cilengitide also inhibited TGF-beta-induced fibronectin gene expression and reduced the accumulation of mRNAs and protein for fibronectin and collagen type I. Both preventive and treatment effects of daily injections of cilengitide (20 mg/kg) failed to inhibit the development of pulmonary fibrosis as determined by histological analysis (Ashcroft scoring), bronchoalveolar lavage (BAL) fluid cell counts, and hydroxyproline content. Conclusions Overall, our data suggest that, despite its in vitro activity in fibroblasts, daily injections of cilengitide (20 mg/kg) did not inhibit the development of or ameliorate bleomycin-induced pulmonary fibrosis in mice.