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In this article we report on the development of polymeric micelles that can integrate multiple functions in one system, including the capability to accommodate a combination of therapeutic entities with different physicochemical properties (i.e., siRNA and doxorubicin; DOX), passive and active cancer targeting, cell membrane translocation, and pH-triggered drug release. A micellar system was constructed from degradable poly(ethylene oxide)-block-poly(ε-caprolactone) (PEO-b-PCL) block copolymers with functional groups on both blocks. The functional group on the PCL block was used to incorporate short polyamines for complexation with siRNA or to chemically conjugate DOX via a pH-sensitive hydrazone linkage. A virus mimetic shell was conferred by attaching two ligands, i.e., the integrin αvβ3-specific ligand (RGD4C) for active cancer targeting and the cell-penetrating peptide TAT for membrane activity. This system was used to improve the efficacy of DOX in multidrug-resistant MDA-MB-435 human tumor models that overexpress P-glycoprotein (P-gp), by simultaneous intracellular delivery of DOX and siRNA against P-gp expression. The carrier was tagged with near-infrared fluorescent imaging probes to provide a means to follow the fate of the system in vivo upon intravenous administration. Dy677-labeled siRNA was also used to assess the in vivo stability of the siRNA carrier. This multifunctional polymeric micellar system was shown to be capable of DOX and siRNA delivery to their intracellular targets, leading to the inhibition of P-gp-mediated DOX resistance in vitro and targeting of αvβ3-positive tumors in vivo.
Xiong et al. (Tue,) studied this question.