Nanoparticle-directed sub-cellular localization of doxorubicin and the sensitization breast cancer cells by circumventing GST-mediated drug resistance.

Resistance to single or multiple chemotherapeutic drugs is a major complication in clinical oncology and is one of the most common treatment limitations in patients with reoccurring cancers. Nanoparticle (NP)-based drug delivery systems (DDS's) have been shown to overcome drug resistance in cancer cells mainly by avoiding the activation of efflux pumps in these cells. We demonstrate in this work that polyester-based hyperbranched dendritic-linear (HBDL)-based NPs carrying doxorubicin (Dox) can effectively overcome microsomal glutathione transferase 1 (MGST1)-mediated drug resistance in breast cancer cells. Our DDS was much more effective at considerably lower intracellular Dox concentrations (IC50 6.3 μm vs. 36.3 μm) and achieved significantly greater reductions in viability and induced higher degrees of apoptosis (31% vs. 14%) compared to the free drug in the resistant cells. Dox-loaded HBDL NPs were found to translocate across the membranes of resistant cells via active endocytic pathways and to be transported to lysosomes, mitochondria, and the endoplasmic reticulum. A significantly lower amount of Dox accumulated in these cytoplasmic compartments in resistant cells treated with free Dox. Moreover, we found that Dox-HBDL significantly decreased the expression of MGST1 and enhanced mitochondria-mediated apoptotic cell death compared to free Dox. Dox-HBDL also markedly activated the JNK pathway that contributes to the apoptosis of drug-resistant cells. These results suggest that HBDL NPs can modulate subcellular drug distribution by specific endocytic and trafficking pathways and that this results in drug delivery that alters enzyme levels and cellular signaling pathways and, most importantly, increases the induction of apoptosis. Our findings suggest that by exploiting the cell transport machinery we can optimize the polymeric vehicles for controlled drug release to overcome drug resistance combat drug resistance with much higher efficacy.