Epidermal growth factor receptor tyrosine kinase inhibition augments a murine model of pulmonary fibrosis.

The inappropriate regeneration of sequentially injured epithelium is an important process leading to pulmonary fibrosis. Previous studies have shown that the epithelial expression of epidermal growth factor receptor (EGFR) is increased in fibrotic lung tissue, compared with normal lung tissue, suggesting that EGFR-mediated signaling is involved in epithelial regeneration in fibrotic lung diseases. We examined the effect of EGFR inhibition using ZD1839, a selective EGFR tyrosine kinase inhibitor (TKI), on bleomycin-induced pulmonary fibrosis in mice. ICR mice were administered a single intratracheal injection of bleomycin (5 units/kg) on day 1. ZD1839 (200 mg/kg) or vehicle alone were administered p.o. 1 h before this injection and on days 1-5 each week for 3 weeks. Lung tissue was harvested on day 21. Lung histology and collagen analysis performed on day 21 showed more severe fibrosis in the mice receiving both bleomycin and the EGFR-TKI than in the mice receiving bleomycin and the vehicle. An immunohistochemistry analysis showed that phosphorylated EGFR and proliferation cell nuclear antigen were highly expressed by the regenerated epithelial cells in the mice treated with bleomycin and the vehicle. In contrast, the expression of these antigens was attenuated in the mice treated with bleomycin and the EGFR-TKI. In vitro studies also demonstrated that the addition of ZD1839 at a concentration of < or =1 microM suppressed the proliferation of type II-like epithelial cells (A549) but not that of lung fibroblasts (IMR90). These results suggest that the inhibition of EGFR phosphorylation augments bleomycin-induced pulmonary fibrosis by reducing regenerative epithelial proliferation. Our data suggest that EGFR-TKIs should be used with caution in cancer patients with pulmonary fibrosis.