Poly(lactide)-containing Multifunctional Nanoparticles: Synthesis, Domain-selective Degradation and Therapeutic Applicability

Construction of nanoassemblies from degradable components is desired for packaging and controlled release of active therapeutics, and eventual biodegradability in vivo. In this study, shell crosslinked micelles composed of biodegradable poly(lactide) (PLA) core were prepared by the self-assembly of an amphiphilic diblock copolymer synthesized by a combination of ring opening polymerization (ROP) and reversible addition-fragmentation chain transfer (RAFT) polymerization. Enzymatic degradation of the PLA cores of the nanoparticles was achieved upon the addition of proteinase K (PK). Kinetic analyses and comparison of the properties of the nanomaterials as a function of degradation extent will be discussed. Building upon our findings from selective-excavation of the PLA core, enzyme- and redox-responsive nanoparticles were constructed for the encapsulation and stimuli-responsive release of an antitumor drug. This potent chemotherapeutic, otherwise poorly soluble in water was dispersed into aqueous solution by the supramolecular co-assembly with an amphiphilic block copolymer, and the release from within the core of these nanoparticles were gated by crosslinking the hydrophilic shell region with a reduction-responsive crosslinker. Enzyme- and reduction-triggered release behavior of the antitumor drug was demonstrated along with their remarkably high in vitro efficacy. As cationic nanoparticles are a promising class of transfection agents for nucleic acid delivery, in the next part of the study, synthetic methodologies were developed for the conversion of the negatively-charged shell of the enzymatically-degradable shell crosslinked micelles to positively-charged cationic nanoparticles for the complexation of nucleic acids. These degradable cationic nanoparticles were found to efficiently deliver and transfect plasmid DNA in vitro. The hydrolysis of the PLA core and crosslinkers of the nanocarriers may provide a mechanism for their programmed disassembly within endosomes, which would in-turn promote endosomal disruption by osmotic swelling, and release of active therapeutics from the polymeric assemblies. In the last part, a comparative degradation study was performed between the anionic and cationic micellar assemblies in the presence of two model enzymes, and electrostatic interaction-mediated preferential hydrolysis was demonstrated between the oppositely-charged enzyme-micelle pairs. These findings may be of potential significance toward the design of charge-mediated enzyme-responsive nanomaterials that are capable of undergoing environmentally-triggered therapeutic release, disassembly or morphological alterations under selective enzyme conditions

Degradability of Poly(Lactic Acid)-Containing Nanoparticles: Enzymatic Access through a Cross-Linked Shell Barrier

Comparative studies of bulk samples of hydrolytically degradable poly­(lactic acid) (PLA) vs core–shell block copolymer micelles having PLA cores revealed remarkable acceleration in the proteinase K enzymatic hydrolysis of the nanoparticulate forms and demonstrated that even with amidation-based shell cross-linking the core domain remained accessible. Kinetic analyses by ¹H NMR spectroscopy showed less than 20% lactic acid released from enzymatically catalyzed hydrolysis of poly­(l-lactic acid) in bulk, whereas ca. 70% of the core degraded within 48 h for block copolymer micelles of poly­(<i>N</i>-(acryloyloxy)­succinimide-<i>copolymer</i>-<i>N</i>-acryloylmorpholine)-<i>block</i>-poly­(L-lactic acid) (P­(NAS-<i>co</i>-NAM)-<i>b</i>-PLLA), with only a slight reduction to ca. 50% for the shell cross-linked derivatives. Rigorous characterization measurements by NMR spectroscopy, fluorescence spectroscopy, dynamic light scattering, atomic force microscopy, and transmission electron microscopy were employed to confirm core excavation. These studies provide important fundamental understanding of the effects of nanoscopic dimensions on protein–polymer interactions and polymer degradability, which will guide the development of these degradable nanoconstructs to reach their potential for controlled release of therapeutics and biological clearance

<i>In Vitro</i> Efficacy of Paclitaxel-Loaded Dual-Responsive Shell Cross-Linked Polymer Nanoparticles Having Orthogonally Degradable Disulfide Cross-Linked Corona and Polyester Core Domains

Paclitaxel-loaded shell cross-linked polymeric nanoparticles having an enzymatically and hydrolytically degradable poly­(lactic acid) core and a glutathione-responsive disulfide cross-linked poly­(oligoethylene glycol)-containing corona were constructed in aqueous solution and investigated for their stimuli-responsive release of the embedded therapeutics and <i>in vitro</i> cytotoxicity. Paclitaxel release from the nanoparticles in PBS buffer was accelerated in the presence of glutathione at both pH 5.5 and pH 7.4, reaching <i>ca</i>. 65% cumulative drug release after 8 d, whereas only <i>ca</i>. 50% and 35% extents of release were observed in the absence of glutathione at pH 5.5 and pH 7.4, respectively. Enzyme-catalyzed hydrolysis of the nanoparticle core resulted in the degradation of <i>ca</i>. 30% of the poly­(lactic acid) core to lactic acid within 12 h, with coincidently triggered paclitaxel release of <i>ca</i>. 37%, as opposed to only <i>ca</i>. 17% release from the uncatalyzed nanoparticles at pH 7.4. While empty nanoparticles did not show any inherent cytotoxicity at the highest tested concentrations, paclitaxel-loaded nanoparticles showed IC₅₀ values that were similar to those of free paclitaxel at 72 h incubation with KB cells and were more efficacious at <i>ca</i>. 3-fold lower IC₅₀ value (0.031 μM vs 0.085 μM) at 2 h of incubation. Against human ovarian adenocarcinoma cells, the paclitaxel-loaded nanoparticles exhibited a remarkable <i>ca</i>. 11-fold lower IC₅₀ than a Taxol-mimicking formulation (0.0007 μM vs 0.008 μM) at 72 h of incubation. These tunable dual-responsive degradable nanoparticles show great promise for delivery of paclitaxel to tumor tissues, given their superior <i>in vitro</i> efficacies compared to that of free paclitaxel and Taxol-mimicking formulations

Hierarchically Assembled Theranostic Nanostructures for siRNA Delivery and Imaging Applications

Dual functional hierarchically assembled nanostructures, with two unique functions of carrying therapeutic cargo electrostatically and maintaining radiolabeled imaging agents covalently within separate component building blocks, have been developed via the supramolecular assembly of several spherical cationic shell cross-linked nanoparticles clustered around a central anionic shell cross-linked cylinder. The shells of the cationic nanoparticles and the hydrophobic core domain of the anionic central cylindrical nanostructure of the assemblies were utilized to complex negatively charged nucleic acids (siRNA) and to undergo radiolabeling, respectively, for potential theranostic applications. The assemblies exhibited exceptional cell transfection and radiolabeling efficiencies, providing an overall advantage over the individual components, which could each facilitate only one or the other of the functions

<i>In Vitro</i> Efficacy of Paclitaxel-Loaded Dual-Responsive Shell Cross-Linked Polymer Nanoparticles Having Orthogonally Degradable Disulfide Cross-Linked Corona and Polyester Core Domains

Paclitaxel-loaded shell cross-linked polymeric nanoparticles having an enzymatically and hydrolytically degradable poly­(lactic acid) core and a glutathione-responsive disulfide cross-linked poly­(oligoethylene glycol)-containing corona were constructed in aqueous solution and investigated for their stimuli-responsive release of the embedded therapeutics and <i>in vitro</i> cytotoxicity. Paclitaxel release from the nanoparticles in PBS buffer was accelerated in the presence of glutathione at both pH 5.5 and pH 7.4, reaching <i>ca</i>. 65% cumulative drug release after 8 d, whereas only <i>ca</i>. 50% and 35% extents of release were observed in the absence of glutathione at pH 5.5 and pH 7.4, respectively. Enzyme-catalyzed hydrolysis of the nanoparticle core resulted in the degradation of <i>ca</i>. 30% of the poly­(lactic acid) core to lactic acid within 12 h, with coincidently triggered paclitaxel release of <i>ca</i>. 37%, as opposed to only <i>ca</i>. 17% release from the uncatalyzed nanoparticles at pH 7.4. While empty nanoparticles did not show any inherent cytotoxicity at the highest tested concentrations, paclitaxel-loaded nanoparticles showed IC₅₀ values that were similar to those of free paclitaxel at 72 h incubation with KB cells and were more efficacious at <i>ca</i>. 3-fold lower IC₅₀ value (0.031 μM vs 0.085 μM) at 2 h of incubation. Against human ovarian adenocarcinoma cells, the paclitaxel-loaded nanoparticles exhibited a remarkable <i>ca</i>. 11-fold lower IC₅₀ than a Taxol-mimicking formulation (0.0007 μM vs 0.008 μM) at 72 h of incubation. These tunable dual-responsive degradable nanoparticles show great promise for delivery of paclitaxel to tumor tissues, given their superior <i>in vitro</i> efficacies compared to that of free paclitaxel and Taxol-mimicking formulations

Holistic Assessment of Covalently Labeled Core–Shell Polymeric Nanoparticles with Fluorescent Contrast Agents for Theranostic Applications

The successful development of degradable polymeric nanostructures as optical probes for use in nanotheranostic applications requires the intelligent design of materials such that their surface response, degradation, drug delivery, and imaging properties are all optimized. In the case of imaging, optimization must result in materials that allow differentiation between unbound optical contrast agents and labeled polymeric materials as they undergo degradation. In this study, we have shown that use of traditional electrophoretic gel-plate assays for the determination of the purity of dye-conjugated degradable nanoparticles is limited by polymer degradation characteristics. To overcome these limitations, we have outlined a holistic approach to evaluating dye and peptide–polymer nanoparticle conjugation by utilizing steady-state fluorescence, anisotropy, and emission and anisotropy lifetime decay profiles, through which nanoparticle–dye binding can be assessed independently of perturbations, such as those presented during the execution of electrolyte gel-based assays. This approach has been demonstrated to provide an overall understanding of the spectral signature–structure–function relationship, ascertaining key information on interactions between the fluorophore, polymer, and solvent components that have a direct and measurable impact on the emissive properties of the optical probe. The use of these powerful techniques provides feedback that can be utilized to improve nanotheranostics by evaluating dye emissivity in degradable nanotheranostic systems, which has become increasingly important as modern platforms transition to architectures intentionally reliant on degradation and built-in environmental responses