Polymeric carrier of proline analogue with antifibrotic effect in pulmonary vascular remodeling

The proline analogue cis-4-hydroxy-L-proline (cHyp) inhibits collagen accumulation but diffuses out of tissues. To prolong the antifibrotic effect, we used a copolymer of cHyp attached to a backbone of poly(ethylene glycol) (PEG) and lysine. The copolymer was encapsulated in liposomes conjugated with PEG or in liposomes coated with the polysaccharide amylopectin to improve uptake by lungs after intravenous infusion. Amylopectin-liposomes had approximately 3-fold greater uptake in cultured endothelial cells compared with PEG-liposomes and greater lung retention 1 wk after infusion (5.2 +/- 0.8% versus 2.7 +/- 0.2%, p < 0.05). Sustained antifibrotic activity, assayed by growth inhibition of smooth muscle cells and fibroblasts over 4 d, was greater for amylopectin-liposomes/copolymer than PEG-liposomes/copolymer. Inhibition of collagen accumulation in pulmonary arteries of hypoxic (10% O2) rats was used to assess antifibrotic activity. Amylopectin-liposomes/copolymer attenuated increased right ventricular pressure by approximately 50% and completely prevented excess vascular collagen 1 wk after a single intravenous injection. The copolymer in liposomes was > 1,000-fold more effective by weight than unencapsulated monomeric cHyp. Thus, the copolymer, a potent, long-acting antifibrotic agent, totally prevented collagen accumulation for 1 wk in pulmonary arteries undergoing vascular remodeling when delivered in amylopectin-liposomes.