pH-sensitive micelles for the intracellular co-delivery of curcumin and Pluronic L61 unimers for synergistic reversal effect of multidrug resistance.

Pluronic L61 unimers, which are biomacromolecular modulators, and curcumin, a small-molecule modulator, were co-formulated into pH-sensitive micelles to reveal the full synergistic potential of combination drug treatments to reverse multidrug resistance (MDR). Compared to monotherapy, combined therapy significantly improved the cytotoxicity, cellular uptake and apoptotic effects of doxorubicin (DOX) against MCF-7/ADR cells. In mechanistic studies, both L61 and curcumin enhanced the cytotoxic effect by acting on mitochondrial signalling pathways. The compounds selectively accumulated in the mitochondria and disabled the mitochondria by dissipating the mitochondrial membrane potential, decreasing the ATP levels, and releasing cytochrome c, which initiated a cascade of caspase-9 and caspase-3 reactions. Furthermore, both curcumin and L61 down-regulated the expression and function of P-gp in response to drug efflux from the MCF-7/ADR cells. In the MCF-7/ADR tumour-bearing mouse model, intravenous administration of the combined therapy directly targeted the tumour, as revealed by the accumulation of DiR in the tumour site, which led to a significant inhibition of tumour growth without measurable side effects. In conclusion, co-formulation consisting of L61 and curcumin in pH-sensitive micelles induced significant synergistic effects on the reversal of MDR. Therefore, the intracellular co-delivery of various MDR modulators has great potential to reverse MDR in tumours.