Liposomes targeted via two different antibodies: assay, B-cell binding and cytotoxicity

The selective toxicity of anticancer drugs can be improved with the use of antibody-targeted liposomes. We hypothesize that liposomes targeted via antibodies against two or more receptor populations will increase the apparent receptor density on the target cells, resulting in improved therapeutic affects. A fluorescent assay was developed, using the fluorophores Alexa Fluor 350 and 532 to label monoclonal antibodies (mAb), and used to quantitate two different mAb populations coupled to the same liposome surface to within +/-10% of the values obtained with radiolabeled antibody (125I) tracers. The binding and uptake of targeted liposomes by B lymphoma (Namalwa) cells were examined for either individual populations of alphaCD19-targeted or alphaCD20-targeted liposomes, mixed populations (1:1) of alphaCD19-targeted liposomes plus alphaCD20-targeted liposomes, and dual-targeted liposomes, i.e., equal amount of both alphaCD19 and alphaCD20 on the same liposomes. At similar antibody densities, the binding and uptake of the dual-targeted liposomes were greater than that of either individually targeted liposomes alone, and showed additivity. At the same total lipid and antibody densities, 1:1 mixtures of individually targeted liposomes gave similar results to dual-targeted liposomes. Cytotoxicity was also improved, with DXR-loaded dual-targeted liposomes appearing to have higher cytotoxicity than 1:1 mixtures of individually targeted liposomes.