Overcoming endosomal barrier by amphotericin B-loaded dual pH-responsive PDMA-b-PDPA micelleplexes for siRNA delivery. ACS Nano 5:9246-9255

Department of Pharmacology, Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, USA.
ACS Nano (Impact Factor: 12.88). 11/2011; 5(11):9246-55. DOI: 10.1021/nn203503h
Source: PubMed


The endosomal barrier is a major bottleneck for the effective intracellular delivery of siRNA by nonviral nanocarriers. Here, we report a novel amphotericin B (AmB)-loaded, dual pH-responsive micelleplex platform for siRNA delivery. Micelles were self-assembled from poly(2-(dimethylamino)ethyl methacrylate)-block-poly(2-(diisopropylamino)ethyl methacrylate) (PDMA-b-PDPA) diblock copolymers. At pH 7.4, AmB was loaded into the hydrophobic PDPA core, and siRNA was complexed with a positively charged PDMA shell to form the micelleplexes. After cellular uptake, the PDMA-b-PDPA/siRNA micelleplexes dissociated in early endosomes to release AmB. Live cell imaging studies demonstrated that released AmB significantly increased the ability of siRNA to overcome the endosomal barrier. Transfection studies showed that AmB-loaded micelleplexes resulted in significant increase in luciferase (Luc) knockdown efficiency over the AmB-free control. The enhanced Luc knockdown efficiency was abolished by bafilomycin A1, a vacuolar ATPase inhibitor that inhibits the acidification of the endocytic organelles. These data support the central hypothesis that membrane poration by AmB and increased endosomal swelling and membrane tension by a "proton sponge" polymer provided a synergistic strategy to disrupt endosomes for improved intracellular delivery of siRNA.

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    • "It was envisioned that retaining the PEG component of these polymers would be important not only for micelle assembly but also to retard internalization of the NPs following surface conjugation and to minimize the perturbation of the surface properties of the cells – as coupling just PDPAEMA NPs to the surface would introduce islands of cationic density. While PDPAEMA has been used as a component of pH-responsive NPs for delivering siRNA [41], it was unknown if the biotinylated PEG- PDPAEMA would be effective in releasing a small molecule in a pHdependent fashion. To assess this, biotinylated NPs were loaded with nile red, a fluorescently active model small (340 Da), hydrophobic drug (Fig. 2a). "
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    • "There are examples of agents that have been demonstrated specifically to enhance endosomal release of co-delivery micelleplexes. Yu and colleagues created poly(2-(dimethylamino)ethyl methacrylate)-block- poly(2-(diisopropylamino)ethyl methacrylate) (PDMA-b-PDPA) copolymer micelles complexed with siRNA and loaded with amphotericin B (Yu et al., 2011). Amphotericin B is an antifungal drug which creates pores in cell membranes, and its release was shown to increase the delivery of siRNA by overcoming the endosomal barrier. "
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    • "Importantly, the net cationic charge displayed by the PNP can be modulated simply by changing the molar ratios of P1:P2. This mixed micelle approach negates the need for extensive and time-consuming resynthesis of PNPs as, unlike triblock copolymers (ABC or ABA) [23] [24] [25], and single diblock copolymers (AB) [26] [27], the two independent amphiphilic diblock copolymers (AB and CB) open the possibility of constructing rapidly numerous mixed micelle compositions. Eleven PNPs were prepared (Table 1), in which the molar ratio of P1: P2 was changed from 100:0 to 0:100 in 10% intervals to afford PNP0– PNP100, where the number indicates the percentage of cationic polymer P1 chain within the mixed micelle. "
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