The use of ultrasound to increase the uptake and cytotoxicity of dual taxane and P-glycoprotein inhibitor loaded, solid core nanoparticles in drug resistant cells.

The objective of this study was to use ultrasound in combination with nanoparticulate formulations of taxane drugs for an additive approach to overcome multidrug resistance (MDR). Polymeric nanoparticulate formulations containing both chemotherapeutic taxane drugs and a polymeric inhibitor (MePEG17-b-PCL5) of drug resistant proteins have been previously developed in an attempt to overcome MDR in cells. High frequency (>1 MHz) ultrasound has been shown to increase the uptake of cytotoxic drugs in MDR proliferating cells and has been suggested as a different way to overcome MDR, resensitize drug resistant cancer cells and allow for chemotherapeutic efficacy. MDCK-MDR cells were incubated with docetaxel (DTX) or paclitaxel (PTX) loaded, solid core, nanoparticles made from a 50:50 ratio of two diblock copolymers, MePEG114-b-PCL200 and MePEG17-b-PCL5 (PCL200/PCL5). The accumulation of drug in MDCK-MDR cells was measured using radiolabeled drug and the viability of cells was determined using an MTS cell proliferation assay. The effect of ultrasound (4 MHz, 32 W/cm2, 10 s, 25% duty cycle) on drug uptake and cell viability was studied. Using free DTX or PTX, MDCK-MDR cells were killed at sublethal doses of drug with the P-gp inhibitor (MePEG17-b-PCL5) present at a concentration of just 0.006% (m/v) and cell death began after just 3 h of incubation. Using sublethal incubation doses of PTX or DTX in PCL200/PCL5 nanoparticles for 90 min, followed by a second exposure to blank PCL200/PCL5 nanoparticles, cell viability dropped by approximately 60% at 24 h. Drug accumulation increased by 1.43-1.9 fold following five bursts of ultrasound applied at 90 min. Both, increased ultrasound exposure and increased concentrations of blank nanoparticles during the second incubation allowed for increased levels of cell death. The combined use of ultrasound with taxane and P-gp inhibitor loaded polymeric nanoparticles may allow for increased accumulation of drug and inhibitor which may then release both agents inside cells in a controlled manner to overcome drug resistance in MDR cells.