Shell-Sheddable Poly(N-2-hydroxypropyl methacrylamide) Polymeric Micelles for Dual-Sensitive Release of Doxorubicin.

Poly(ethylene glycol) (PEG) shell-sheddable micelles are proved to be effective tools for rapid intracellular drug delivery. However, some adverse factors, such as the potential immunogenicity and the accelerated blood clearance, might be accompanied with the traditional PEG sheddable micelles. Here, a poly(N-2-hydroxypropyl methacrylamide) (PHPMA) sheddable block copolymer containing disulfide bonds on the main chain is prepared to form pH- and reduction-dual-responsive micelles. The most optimal synthetic route of the block copolymer is selected from three potential pathways. Doxorubicin is loaded via an acid-labile hydrazone bond to achieve high drug loading content and to prevent premature drug release. As expected, as-prepared shell-sheddable micelles exhibit faster intracellular drug release and more satisfactory in vitro anticancer efficacy than the nonsheddable counterpart did. This design provides a feasible guideline for the efficient synthesis of similar shell-sheddable micelles consisting of PHPMA coatings.

Well-Defined Shell-Sheddable Core-Crosslinked Micelles with pH and Oxidation Dual-Response for On-Demand Drug Delivery.

Micellar-nanocarrier-based drug delivery systems possessing characteristics such as an excellent circulation stability, inhibited premature release and on-demand site-specific release are urgently needed for enhanced therapeutic efficacy. Therefore, a novel kind of shell-sheddable core-crosslinked polymeric micelles with pH and oxidation dual-triggered on-demand drug release behavior was facilely constructed. The multifunctional micelles were self-assembled from a carefully designed amphiphilic triblock PEGylated polyurethane (PEG-acetal-PUBr-acetal-PEG) employing an acid-labile acetal linker at the hydrophilic-hydrophobic interface and pendant reactive bromo-containing polyurethane (PU) as the hydrophobic block, followed by a post-crosslinking via oxidation-cleavable diselenide linkages. These well-defined micelles exhibited an enhanced structural stability against dilution, achieved through the incorporation of diselenide crosslinkers. As expected, they were found to possess dual pH- and oxidation-responsive dissociation behaviors when exposure to acid pH (~5.0) and 50 mM H2O2 conditions, as evidenced using dynamic light-scattering (DLS) and atomic force microscopy (AFM) analyses. An in vitro drug release investigation showed that the drug indomethacin (IND) could be efficiently encapsulated in the micelles, which demonstrated an inhibited premature release compared to the non-crosslinked ones. It is noteworthy that the resulting micelles could efficiently release entrapped drugs at a fast rate in response to either pH or oxidation stimuli. Moreover, the release could be significantly accelerated in the presence of both acid pH and oxidation conditions, relative to a single stimulus, owing to the synergetic degradation of micelles through pH-induced dePEGylation and oxidation-triggered decrosslinking processes. The proposed shell-sheddable core-crosslinked micelles with a pH and oxidation dual-response could be potential candidates as drug carriers for on-demand drug delivery.

Redox Sensitive Polysaccharide Based Nanoparticles for Improved Cancer Treatment: A Comprehensive Review.

BACKGROUND: Among the numerous bio-responsive polymeric drug delivery systems developed recently, redox-triggered release of molecular payloads have gained great deal of attention, especially in the field of anticancer drug delivery. In most cases, these systems rely on disulfide bonds located either in the matrix crosslinks, or in auxiliary chains to achieve stimuli-responsive drug release. These bonds keep their stability in extracellular environments, yet, rapidly break by thiol-disulfide exchange reactions in the cytosol, due to the presence of greater levels of glutathione. Polysaccharides are macromolecules with low cost, natural abundance, biocompatibility, biodegradability, appropriate physical and chemical properties, and presence of numerous functional groups which facilitate chemical or physical cross-linking. METHODS: With regards to the remarkable advantages of polysaccharides, in the current study, various polysaccharide-based redox-responsive drug delivery systems are reviewed. In most cases the in vitro/in vivo effects of the developed system were also evaluated. RESULTS: Considering the hypoxic and reducing nature of the tumor microenvironment, with several folds higher glutathione levels than the systemic tissues, redox-sensitive polymeric systems could be implemented for tumorspecific drug delivery and the results of the previous researches in this field indicated satisfactory achievements. CONCLUSION: According to the reviewed papers, the efficiency of diverse redox-responsive polysaccharide-based nanoparticles with therapeutic payloads in cancer chemotherapy could be concluded. Nevertheless, more comprehensive studies are required to understand the exact intracellular and systemic fate of these nano-carriers, as well as their clinical efficacy for cancer treatment.

cRGD-functionalized reduction-sensitive shell-sheddable biodegradable micelles mediate enhanced doxorubicin delivery to human glioma xenografts in vivo.

Biodegradable micelles are one of the most studied systems for the delivery of hydrophobic anticancer drugs. Their therapeutic efficacy in vivo is, however, suboptimal, partly due to poor tumor cell uptake as well as slow intracellular drug release. Here, we show that cRGD-functionalized intracellularly shell-sheddable biodegradable PEG-SS-PCL micelles mediate enhanced doxorubicin (DOX) delivery to U87MG glioma xenografts in vivo, resulting in significantly improved tumor growth inhibition as compared to reduction-insensitive cRGD/PEG-PCL controls. cRGD/PEG-SS-PCL micelles revealed a small size of ca. 61nm, a decent DOX loading of 14.9wt%, and triggered drug release in a reductive environment (10mM glutathione). Flow cytometry, confocal microscopy, and MTT assays demonstrated that cRGD/PEG-SS-PCL micelles with a cRGD ligand density of 20% efficiently delivered and released DOX into αvß3 integrin overexpressing U87MG cells. The in vivo pharmacokinetics studies displayed that DOX-loaded cRGD20/PEG-SS-PCL micelles had a prolonged elimination half-life time of 3.51h, which was comparable to that of cRGD20/PEG-PCL counterparts, indicating that disulfide bonds in the PEG-SS-PCL micelles are stable in the circulation. Notably, in vivo imaging and biodistribution studies in U87MG glioma xenografts showed that cRGD20/PEG-SS-PCL micelles led to efficient accumulation as well as fast drug release in the tumor. The therapeutic outcomes demonstrated that DOX-loaded cRGD20/PEG-SS-PCL micelles exhibited little side effects and superior tumor growth inhibition as compared to non-targeting PEG-SS-PCL and reduction-insensitive cRGD20/PEG-PCL counterparts. The reduction-sensitive shell-sheddable biodegradable micelles have appeared as a fascinating platform for targeted tumor chemotherapy.