Liposome transduction into cells enhanced by haptotactic peptides (Haptides) homologous to fibrinogen C-termini

Haptides are 19-21mer cell-binding peptides equivalent to sequences on the C-termini of fibrinogen β chain (Cβ), γ chain (preCγ) and the extended αE chain of fibrinogen (CαE). In solution, Haptides accumulated in cells by non-saturable kinetics [Exp. Cell Res. 287 (2003) 116]. This study describes Haptide interactions with liposomes and Haptide-mediated liposome uptake by cells. Haptides became incorporated into negatively charged liposomes, changing their zeta potential. Atomic force microscopy and particle sizing by light scattering showed that the liposomes dissolved Haptide nanoparticles and absorbed them from solution. Pre-mixing fluorescent rhodamine-containing liposomes or "stealth" doxorubicin (DOX)-containing liposomes (Doxil) with Cβ, preCγ or to a lesser degree CαE, significantly enhanced their uptake by fibroblasts and endothelial cells. Confocal microscopy showed Haptide-induced liposome uptake saturated above ∼40 μM Haptide. Cytotoxicity tests with lower concentrations of Doxil liposomes indicated that premixing with ∼40 μM Cβ or preCγ increased their toxicity by one order of magnitude. It was evident that the liposomes complexed with an amphiphilic Haptide are transduced through cell membranes, probably by a non-receptor-mediated process. These results suggest that Cβ or pre-Cγ could be employed to augment the cellular uptake of drugs in liposomal formulations.