Increased accumulation and retention of micellar paclitaxel in drug-sensitive and P-glycoprotein-expressing cell lines following ultrasound exposure

Ultrasound treatment has been shown to enhance the uptake of both hydrophilic and hydrophobic compounds into PC3 and Huvec cell lines using an insonation regimen of a single 10-s burst of high-frequency (4 MHz), moderate intensity (32 W/cm(2)) ultrasound. The purpose of this work was to evaluate the effect of this ultrasound regimen on the cellular accumulation of paclitaxel (PTX) loaded in copolymer micellar of methoxy poly(ethylene glycol)-block-poly(D,L-lactide) (MePEG-b-PDLLA) in both drug-sensitive (MDCKII and MCF-7) and P-glycoprotein (Pgp)-expressing (MDCKII-MDR and NCI-ADR) cell lines. There were no effects of ultrasound on hydrodynamic diameters of micelles and the release of FRET pairs, indicating the integrity of micelles was maintained. There was a two-fold increase in intracellular PTX for all ultrasound-treated drug-sensitive cell lines and their respective drug-resistant counterparts compared with no ultrasound. Significant decreases in drug efflux rates were observed at 20, 40 and 60 min for both drug-sensitive and -resistant cell lines receiving ultrasound. The enhanced accumulation and retention of PTX by ultrasound resulted in greater cytotoxicity in both MDCKII and MDCKII-MDR cell lines, as indicated by the MTS assay. These data suggest that ultrasound may facilitate the uptake of intact paclitaxel-loaded micelles into cells, allowing greater retention of drug in both Pgp and non-Pgp-expressing cells.