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

A quantitative method of analyzing nanoparticles (NPs) for drug delivery is urgently required by researchers and industry. Therefore, we developed new quantitative analytical methods for biodegradable and amphiphilic NPs consisting of polymeric γ-PGA-Phe [phenylalanine attached to poly(γ-glutamic acid)] molecules. These γ-PGA-Phe NPs were completely dissociated into separate γ-PGA-Phe molecules by adding sodium dodecyl sulfate (SDS). The dissociated NPs were chromatographically separated to analyze parameters such as the γ-PGA-Phe content in the NPs, the impurities present [using reverse-phase (RP) HPLC with an ultraviolet (UV) detector], and the absolute MW [using size-exclusion chromatography (SEC) with refractive index detection (RI) and multiangle light scattering (MALS) detection, i.e., SEC-RI/MALS]. The chromatographic patterns of the NPs were equivalent to those of the component polymer (γ-PGA-Phe), and excellent chromatographic separation for the quantitative evaluation of NPs was achieved. To the best of our knowledge, this is the first report of the quantitative evaluation of NPs in the field of NP-based delivery systems. Furthermore, these methods were applied to optimize and evaluate the NP manufacturing process. The results showed that impurities were effectively removed from the γ-PGA-Phe during the manufacturing process, so the purity of the final γ-PGA-Phe NPs was enhanced. In addition, the appearance, clarity of solution, particle size, zeta potential, particle matter, osmolarity, and pH of the product were evaluated to ensure that the NPs were of the required quality. Our approach should prove useful for product and process characterization and quality control in the manufacture of NPs. γ-PGA-Phe NPs are known to be a powerful vaccine adjuvant, so they are expected to undergo clinical development into a practical drug-delivery system. The analytical methods established in this paper should facilitate the reliable and practical quality testing of NP products, thus aiding the clinical development of γ-PGA-Phe-based drug-delivery systems. Moreover, since these analytical methods employ commonly used reagents and chromatographic systems, the methods are expected to be applicable to other NP-based drug-delivery products too. Graphical abstract NPs were completely dissociated into separate γ-PGA-Phe polymeric molecules, which yielded a similar chromatogram to that seen for the NPs.