Development of analytical methods for evaluating the quality of dissociated and associated amphiphilic poly(γ-glutamic acid) nanoparticles

Formulation Stability of Amphiphilic Poly(γ-Glutamic Acid) Nanoparticle and Evaluation of Cardiotoxicity of NPs With Human iPSC-Derived 3D-Cardiomyocyte Tissues

We conducted a stability study of biodegradable and amphiphilic nanoparticles (NPs) consisting of phenylalanine-attached poly(γ-glutamic acid) for drug delivery to find the optimal formulation and define the optimal storage conditions using novel quantitative analytical methods. The stability of NP suspension and lyophilized NP powder manufactured by a dimethyl sulfoxide-based and an ethanol-based process was assessed under 5°C, 25°C/60% relative humidity and 40°C/75% relative humidity. The content of phenylalanine-attached poly(γ-glutamic acid), impurities, absolute molecular weight, appearance, clarity of solution, particle size, zeta potential, particle matter, osmolality, water content, and pH were evaluated as parameters of NP stability. Lyophilized NPs with trehalose showed better stability. The lyophilized NP formulation could therefore provide a stable and high-quality product for clinical studies and shows promise as an effective drug delivery system carrier. The cardiotoxicity of prospective impurities contained in NPs and reagents used in the manufacturing process with human-induced pluripotent stem cell-derived 3-dimensional cardiomyocyte tissues by centrifugation layer-by-layer technique was also evaluated. As a result, cardiotoxicity for NPs and reagents was not observed, and it was clarified that the potential risk to human safety from NPs is low. The applicability of the cardiotoxicity evaluation approaches with human-induced pluripotent stem cell-derived 3-dimensional cardiomyocyte tissues will be evaluated by centrifugation layer-by-layer technique.

Enhancing Membrane-Disruptive Activity via Hydrophobic Phenylalanine and Lysine Tethered to Poly(aspartic acid)

Amphiphilic polymers with pH-responsive abilities have been widely used as carriers for intracellular delivery of bioactive substances, while their membrane-disruptive activity exerted on cells is a critical characteristic that determines delivery efficiency. Herein, we present a novel method to prepare amphiphilic and pH-responsive polymers by chemically tethering l-phenylalanine methyl ester and followed by N_ε-carbobenzyloxy-l-lysine benzyl ester to the side carboxylic acid groups of poly(aspartic acid). The obtained phenylalanine- and lysine-grafted polymer (PAsp- g-Phe)- g-Lys demonstrated enhanced membrane-disruptive activity at pH 7.4 in comparison with that of PAsp- g-Phe. Moreover, the pH-responsive behavior of the grafted polymers caused by the significantly intensified hydrophobicity could be modulated by the tethered amount of hydrophobic amino acids with phenyl groups. The prepared amphiphilic (PAsp- g-Phe)- g-Lys could facilitate entry of calcein into NIH/3T3 and HeLa cells at physiological pH values, possibly due to local chemical destabilization of cell membranes by the interaction between the polymer and membrane bilayers. Therefore, we have provided a feasible approach to prepare pH-responsive polymers with enhanced membrane-disruptive activity, and the phenylalanine- and lysine-grafted polymers could be a potential candidate for intracellular delivery of bioactive molecules in biomedical applications.