Fluorescence Resonance Energy Transfer Visualization of Molecular Delivery from Polymeric Micelles

Polymeric micelles are important carriers for anticancer drug delivery. However, rare papers focused on the dynamic of drug in the core of micelles. In this paper, we used fluorescence resonance energy transfer (FRET) technique to investigate the dynamic diffusion of drug from polymeric micelles. mPEG-PCL diblock copolymers were used as carriers. A pair of fluorescence molecules Cy3 and Cy5 was selected to evoke the FRET phenomenon. Cy5 was immobilized on the terminal group of PCL segments, Cy3 was encapsulated in the Cy5 modified polymeric micelles as the model drug. The drug loaded polymeric micelles were incubated with 4T1 breast cancer cells. The FRET was observed to explore the dynamic of Cy3 in the micelles. The results showed that the Cy3 loaded micelles were stable in aqueous solution as the energy-transfer efficiency (ETE, I660/I565) rarely decreased even when the time was as long as 120 h. The ETE increased with the content of encapsulated Cy3. The FRET spectra showed that the ETE of the Cy3 loaded polymeric micelles lowered with the release of Cy3 in PBS. The intracellular tracking of the Cy3 loaded micelles found more than 60% loaded drug was release within 12 h with the calculation of ETE in FRET spectra and it was same to confocal laser scanning and flow cytometry results.