Ptx and 17-AAG present similar loading efficiencies in double loaded micelles probably due to interactions of drugs with each other and also with the copolymer. In contrast, unequal drug loading properties are observed for triple loaded micelles. Rapamycin shows very weak interactions with the copolymer, and displays the lowest loading efficiency.
In vitro release of drugs from micelles was realized in pH 7.4 phosphate buffered saline at 37 °C, and monitored by HPLC. Similar release profiles are observed for the three drugs: a strong burst followed by slower release. Nevertheless, Ptx release from micelles is significantly slower as compared to 17-AAG and Rap, probably due to interactions of NH and OH groups of Ptx with the carbonyl group of PLA.
In vitro cytotoxicity of Ptx/17-AAG/Rap loaded micelles and a mixture of free drugs was determined. Drug loaded micelles exhibit advantageous effect of prolonged drug release and cytotoxic activity against Caco-2 cells, which makes them a promising solution for simultaneous drug delivery to solid tumors. Therefore, understanding of interactions within multidrug micelles should be a valuable approach for the development of concurrent delivery systems of anticancer drugs with tailored properties.