Effects of the fibroblast activation protein inhibitor, PT100, in a murine model of pulmonary fibrosis.

Bleomycin (BLM) induced lung injury is detectable in C57BL/6 mice using magnetic resonance imaging (MRI). We investigated the effects of the fibroblast activation protein (FAP) inhibitor, PT100, in this model. BLM (0.5mg/kg/day) was administered on days -7, -6, -5, -2, -1, 0 in the nostrils of male mice. PT100 (40µg/mouse) or vehicle (0.9%NaCl) was dosed per os twice daily from day 1-14. MRI was performed before BLM and at days 0, 7 and 14. After the last MRI acquisition, animals were euthanised and the lungs harvested for histological and quantitative real-time polymerase chain reaction (qRT-PCR) analyses. As evidenced longitudinally by MRI, the BLM-elicited lesions in the lungs of vehicle-treated mice progressed over time. In contrast, responses elicited by BLM did not progress in animals receiving PT100. Histology demonstrated significant less fibrosis in PT100- than in vehicle-treated, BLM-challenged mice. Significant correlation (R=0.91, P<0.001, N=24) was found between the volumes of BLM-induced lesions detected in vivo by MRI and the collagen content determined histologically (picrosirius staining). FAP was overexpressed in the lungs of BLM-challenged mice. Upon PT100 treatment, FAP expression was reduced. Significant differences in the MMP-12, MIP-1α, and MCP-3 mRNA expression levels in the lungs of PT100- compared to vehicle-treated mice were also revealed by qRT-PCR. The IBA-1 level determined histologically was higher in the lungs of PT100- compared to vehicle-treated mice. Taken together, these observations suggest that treatment with PT100 in this murine model of pulmonary fibrosis had an anti-fibro-proliferative effect and increased macrophage activation.