Conjugation of anti-My9 antibody to stealth monensin liposomes and the effect of conjugated liposomes on the cytotoxicity of immunotoxin

Abstract

The carboxylic ionophore, monensin, was successfully entrapped in stealth liposomes by employing the pH-gradient method (interior pH of liposomes 9.5; exterior pH 5.0–5.9). A maximum of 14% of monensin could be entrapped in stealth liposomes by this method. The stealth liposomes could be successfully freeze–dried having mean particle size varying between 197 and 223 nm. The stealth liposomes were conjugated to anti-My9 monoclonal antibody (targeted against CD 33 antigen) by a disulfide linkage with almost full retention of immunoreactivity. The method of conjugation of liposomes with the antibody did not alter the particle size of liposomes and resulted in only 10% leakage of monensin. In-vitro cytotoxicity studies showed that antibody-conjugated monensin liposomes (3.5×10 −8 M monensin) potentiated the cytotoxicity of anti-My9 immunotoxin by a factor of 2070, in comparison to 360-fold potentiation observed with unconjugated monensin liposomes against human HL-60 promyelocytic leukemia cells. These results indicate that it is possible to enhance the in-vitro cytotoxicity of immunotoxin by several folds using antibody-conjugated monensin liposomes.