Role of α1-Acid Glycoprotein in Therapeutic Antifibrotic Effects of Imatinib with Macrolides in Mice

Rationale: Imatinib is an inhibitor of platelet-derived growth factor receptors. We have reported that treatment with imatinib inhibited bleomycin-induced pulmonary fibrosis in mice. However, late treatment with imatinib had no effect.Objectives: To clarify why imatinib had no antifibrotic effect when its administration was delayed, we focused on α1-acid glycoprotein (AGP), because it was reported to bind imatinib and mediate drug resistance.Methods: The concentration of AGP in serum of mice and patients with idiopathic pulmonary fibrosis was measured by radial immunodiffusion testing. The effects of AGP in vitro were evaluated by assaying the growth of lung fibroblasts. We examined the combined effects of erythromycin (EM) or clarithromycin (CAM) on bleomycin-induced pulmonary fibrosis in mice.Measurements and Main Results: Addition of AGP abrogated imatinib-mediated inhibition of the growth of fibroblasts. However, treatment with EM or CAM restored the growth-inhibitory effects of imatinib. The elevated...