Nanoparticle approaches to combating drug resistance.

Multidrug resistance (MDR) among cancer cells is a serious impediment to the success of conventional chemotherapy. The emergence of nanomedicine demonstrates great promise in overcoming MDR through multiple mechanisms. Nanoparticles have been shown to overcome the MDR at the tissue level through increased intratumoral accumulation resulting from enhanced permeation and retention, neovascular cell targeting, and externally triggered local drug release. Nanoparticles have also demonstrated the ability to overcome the MDR at the cellular/subcellular level by enhancing intracellular drug accumulation, improving drug-target accessibility, or even interfering with existing MDR mechanisms.