Radiolabeling, pharmacoscintigraphic evaluation and antiretroviral efficacy of stavudine loaded 99mTc labeled galactosylated liposomes

The study was aimed to optimize radiolabeling with Tc-99m, to determine the antiretroviral activity and to study the biodistribution of Tc-99m labeled galactosylated liposomes loaded with stavudine. Liposomes were prepared using reverse-phase evaporation method followed by extrusion through 200 nm polycarbonate membranes. The galactosylated liposomes were assessed for in vitro ligand-specific activity and the aggregation of galactosylated liposomes was found to increase as lectin concentration was increased from 5 mu g/ml to 30 mu g/ml. Free stavudine and stavudine loaded plain and galactosylated liposomes were radiolabeled with Tc-99m by direct labeling method using stannous chloride as a reducing agent. Labeling method was optimized for stannous chloride quantity to achieve maximum labeling efficiency >95%. Antiretroviral activity was determined using human immunodeficiency virus-1 (HIV) infected MT2 cell line. A dose-dependent inhibition of p24 production was observed upon treatment of HIV-1 infected MT2 cells with stavudine loaded liposomes and galactosylated liposomes. Scintigraphic imaging and quantitative biodistribution of Tc-99m labeled drug and liposomes showed that liposomal formulations were better taken up by the liver and spleen. Free drug solution was cleared from the blood. Further, a significantly higher (P<0.05) liver and spleen retention was observed over a period of 24h in case of galactosylated liposomes as compared to free drug and plain liposomes. Reduced uptake of the galactosylated liposomes in bone and higher and prolonged accumulation in mononuclear phagocyte system (MPS)-rich organs indicates the excellent potential of this formulation in the treatment of HIV infection. (C) 2007 Elsevier B.V. All rights reserved.