Targeted polymeric micelle system for delivery of combretastatin A4 to tumor vasculature in vitro.

To develop an efficient tumor vasculature-targeted polymeric micelle delivery system for combretastatin A4 (CA4), a novel antivascular agent. CA4-loaded micelles were prepared from poly (ethylene glycol)-b-poly (d, l-lactide) copolymers. RGD peptides that target integrins alphavbeta3 and alphavbeta5, markers of angiogenic endothelial cells, were coupled to the surface of micelles. The micelles were characterized in terms of particle size, morphology, drug loading, and drug release. Cellular uptake of micelles was evaluated by fluorometric determination and confocal microscopy. Anti-proliferation of targeted micelles was also evaluated by SRB method. The mean diameters of CA4-loaded targeted micelles were 25.9 +/- 1.3 nm and spherical in shape. Approximately 4 mg/mL of micellar CA4 loading was obtained with an entrapment efficiency of 97.2 +/- 1.4%. In vitro release studies revealed that targeted micelles release CA4 in a sustained-release manner within 48 h. In vitro cellular uptake studies demonstrated that targeted micelles significantly facilitated the intracellular delivery of the encapsulated agents via integrin-mediated endocytosis. Anti-proliferation studies showed that targeted micelles containing CA4 present superior efficacy over nontargeted micelles. These results suggested that RGD conjugated PEG-PLA micelles loading CA4 have potential as a new formulation for targeting angiogenic tumor vasculature.