Enhanced accumulation of long-circulating liposomes modified with the nucleosome-specific monoclonal antibody 2C5 in various tumours in mice: gamma-imaging studies

Purpose: To further improve tumour targeting and delivery of imaging agents by long-circulating liposomes via the coupling of the anti-cancer monoclonal antibody 2C5 with nucleosome-restricted activity, which can recognize the surface of various tumours but not normal cells and can specifically target pharmaceutical carriers to tumour cells in vitro and in vivo. Methods: The 2C5 antibody was attached to the surface of long-circulating PEG-liposomes (LCL) by the post-insertion technique after antibody modification with a single-terminus activated PEG-lipid derivative to yield nucleosome-specific tumour-targeted liposomes. Tumour cell binding of the targeted liposomes was verified both by fluorescence microscopy and by flow cytometry in several cell lines using fluorescently labelled liposomes. In-111-radiolabelled liposomal formulations (prepared using membrane-anchored chelating groups) were used to examine in vivo biodistribution and tumour accumulation of liposomes by direct gamma scintigraphy. Results: The 2C5 antibody-modified LCL demonstrated a three- to eightfold increase in in vitro specific cell binding to various cancer cell lines of diverse origin. In-111-labelled tumour-targeted liposomes demonstrated prolonged circulation and doubled tumour accumulation compared with that of control formulations. Whole-body gamma scintigraphic imaging of mice implanted with different tumours revealed markedly faster (6 h post injection for 2C5-LCL vs 24 h for non-specific analogues) and superior in vivo tumour visualization with In-111-2C5-LCL than with the 2C5-free formulations in tested tumour models. Conclusion: The 2C5 antibody-modified LCL effectively and specifically accumulate in various tumours and can serve as delivery vehicles for imaging agents, allowing for fast and efficient tumour visualization.