Delivery of PEGylated drugs from mucoadhesive formulations by pH-induced disruption of H-bonded complexes of PEG-drug with poly(acrylic acid)

Polymers and their engineered analogues for ocular drug delivery: Enhancing therapeutic precision

Ocular drug delivery is constrained by anatomical and physiological barriers, necessitating innovative solutions for effective therapy. Natural polymers like hyaluronic acid, chitosan, and gelatin, alongside synthetic counterparts such as PLGA and PEG, have gained prominence for their biocompatibility and controlled release profiles. Recent strides in polymer conjugation strategies have enabled targeted delivery through ligand integration, facilitating tissue specificity and cellular uptake. This versatility accommodates combined drug delivery, addressing diverse anterior (e.g., glaucoma, dry eye) and posterior segment (e.g., macular degeneration, diabetic retinopathy) afflictions. The review encompasses an in-depth exploration of each natural and synthetic polymer, detailing their individual advantages and disadvantages for ocular drug delivery. By transcending ocular barriers and refining therapeutic precision, these innovations promise to reshape the management of anterior and posterior segment eye diseases.

A Polymer Chemistry Point of View on Mucoadhesion and Mucopenetration

Although oral is the preferred route of administration of pharmaceutical formulations, the long-standing challenge for medically active compounds to efficiently cross the mucus layer barrier limits its wider applicability. Efforts in nanomedicine to overcome this hurdle consider mucoadhesive and mucopenetrating drug carriers by selectively designing (macromolecular) building blocks. This review highlights and critically discusses recent strategies developed in this context including poly(ethylene glycol)-based modifications, cationic and thiolated polymers, as well as particles with high charge density, zeta-potential shifting ability, or mucolytic properties. The latest advances in ex vivo test platforms are also reviewed.

Synthesis and biological assessment of folate-accepted developer (99m)Tc-DTPA-folate-polymer

A novel cancer-targetable folate-poly(2-hydroxyethyl methacrylate) (PFDH) copolymer containing DTPA segment was prepared by conventional chemical synthesis and labeled with (99m)Tc subsequently. The (99m)Tc-labled PFDH could be produced easily with high radiochemical yield of 91% and radiochemical purity of 95%. The LogP octanol-water value for the (99m)Tc-labled PFDH was -2.19 and the radiotracer was stable in phosphate-buffered saline and human serum for 2h (>95% in PBS or ∼90% in human serum). To investigate (99m)Tc-labled PFDH tumor targeting, the in vitro and in vivo stability, cell uptake, in vivo biodistribution, and SPECT imaging were evaluated, respectively. These preliminary results strongly suggest that the novel folate conjugated dendrimer maybe developed to be potential for delivery of therapeutic radionuclides.

Injectable hydrogel systems crosslinked by horseradish peroxidase

Hydrogels are widely used as reservoirs in drug delivery and scaffolds for tissue engineering. In particular, injectable hydrogel systems, which are formed by physical, chemical, or enzyme-mediated crosslinking reactions in situ, offer the advantages of minimal invasiveness, ease of application, and void-filling property. Examples of these hydrogels are provided in the first part of this paper. In the second part, hydrogels that are formed by the enzymatic activity of horseradish peroxidase (HRP) are highlighted. HRP catalyzes the crosslinking reaction of polymer-phenol conjugates in the presence of hydrogen peroxide (H2O2), resulting in hydrogels with tunable gelation rate and crosslinking density. The catalytic mechanism of the HRP-mediated crosslinking reaction is discussed in detail, and the recent biomedical applications of the HRP-crosslinked hydrogels are described. Lastly, the concerns associated with HRP-mediated crosslinking and the future outlook of HRP-crosslinked hydrogels are addressed.

Microstructured dextran hydrogels for burst-free sustained release of PEGylated protein drugs

Hydrogels have gained significant attention as ideal delivery vehicles for protein drugs. However, the use of hydrogels for protein delivery has been restricted because their porous structures inevitably cause a premature leakage of encapsulated proteins. Here, we report a simple yet effective approach to regulate the protein release kinetics of hydrogels through the creation of microstructures, which serve as a reservoir, releasing their payloads in a controlled manner. Microstructured dextran hydrogels enable burst-free sustained release of PEGylated interferon over 3 months without compromising its bioactivity. These hydrogels substantially extend the circulation half-life of PEGylated interferon, allowing for less frequent dosing in a humanized mouse model of hepatitis C. The present approach opens up possibilities for the development of sustained protein delivery systems for a broad range of pharmaceutical and biomedical applications.

Enzyme-Functionalized PLGA Nanoparticles with Enhanced Mucus Permeation Rate

The surface functionalization of poly(lactide-co-glycolide) (PLGA) nanoparticles (NPs) with various proteolytic enzymes (i.e., trypsin, papain, bromelain) via a two-step carbodiimide coupling method is presented. Depending on the initial Enzyme:NPs ratio, enzyme loadings up to 4.0 wt.%, 4.4 wt.% and 5.34 wt.% were achieved for trypsin, papain and bromelain, respectively. All three conjugated enzymes partially maintained their enzymatic activity after their coupling reaction with the NPs. NPs functionalized with papain and bromelain exhibited a three-fold higher permeability in porcine intestinal mucus compared to nonfunctionalized NPs whereas those conjugated with trypsin showed an almost two-fold higher permeability value. Measurements of the diffusion rates of intestinal mucin, using a nuclear magnetic resonance (NMR) technique, further confirmed these observations, as the enzyme-functionalized NPs were proven to be capable of disrupting the mucin gel structure. According to the reported results, the coupling of proteolytic enzymes to the PLGA NPs' surface largely increases the NPs mucus permeability, thus making it a potentially important mucus permeation strategy.

Poly(acrylic acid)-poly(ethylene glycol) nanoparticles designed for ophthalmic drug delivery

Poly(acrylic acid) (PAA) and poly(ethylene glycol) (PEG), four-arm, amine-terminated particles with nanometer size and spherical shape were obtained by the polymers cross-linking, via activation with 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide hydrochloride, in a w/o emulsion. The morphology and surface charge of the final particles are strongly dependent on the molar ratio of PAA-PEG and the PAA concentration. The physicochemical characteristics correlated with the drug-loading capacity, in vitro and ex vivo release kinetics of pilocarpine hydrochloride and biocompatibility results indicate that these nanoparticles exhibit the prerequisite behavior for use as carriers of ophthalmic drugs.