PREPARATION AND CHARACTERIZATION OF DOXORUBICIN-LOADED STERICALLY STABILIZED IMMUNOLIPOSOMES

Purpose. To compare the performance of sterically stabilized, doxorubi cin-looded liposomes with and without surface attached specific antibo dies (D-SSIL and D-SSL. respectively). Methods. Small (less than or eq ual to 120 nm) unilamellar liposomes were prepared composed of hydroge nated soy phosphatidylcholine, hydrogenated phosphatidylethanolamine ( HPE), cholesterol, and (2000)Da polyethylene glycol ((2000)PEG) attach ed to the primary amino group of distearoyl phosphatidylethanolamine. Doxorubicin was remote-loaded into these liposomes by an ammonium sulf ate gradient to form the D-SSL. Monoclonal IgG(3) NI32/2 antibodies di rected against a polyoma virus tumor-associated antigen expressed on A 9 etc 102 murine fibrosarcoma cells were attached to the D-SSL HPE via a thioether bond to form the D-SSIL-32/2. A control of nonspecific D- SSIL was prepared by attaching nonspecific IgG(3)-enriched immunoglobu lins to D-SSL. All liposomes were physically and chemically characteri zed and then tested in vitro for tumor cell binding, specificity, and uptake by macrophages; and in vivo for the drug plasma pharmacokinetic s after intravenous administration in mice. Results. (i) The attachmen t of antibodies to D-SSL did not impair their chemical or physical sta bility and had a minimal effect on their size and level of loaded drug . (ii) The combination of specific antibodies and (2000)PEG grafted in the liposomes improved the specific binding to relevant target cells by reducing the level of unspecific binding to nonrelevant cells, (iii ) D-SSIL retained the prolonged circulation and slow clearance typical of SSL lacking the antibodies. Conclusions. Sterically stabilized imm unoliposomes exhibited stability, ability to recognize target cells, a nd prolonged circulation time. This study also shows that it is feasib le to prepare them in pharmaceutically acceptable dosage form. Thus, f urther investigation for tumor targeting and efficacy is warranted.