Effect of Excipients on Salt Disproportionation during Dissolution: A Novel Application of In Situ Raman Imaging

We have employed a bespoke setup combining confocal Raman microscopy and an ultraviolet-visible (UV-Vis) spectroscopy flow cell to investigate the effect of excipients on the disproportionation kinetics of Pioglitazone HCl (PioHCl) in tablets during dissolution. Three binary formulations of PioHCl, containing citric acid monohydrate (CA), lactose monohydrate (LM), or magnesium stearate (MgSt), respectively, were used as models to study the influence of excipients' physicochemical properties on the rate of salt disproportionation kinetics and dissolution performance in different aqueous pH environments. It was found that formulation excipients can induce or prevent salt disproportionation by modulating the microenvironmental pH regardless of the pH of the dissolution media. Incorporating CA in PioHCl tablets preserves the salt form and enhances the dissolution performance of the salt in the acidic medium (pH = 1.2). In contrast, LM and MgSt had a detrimental effect on in vitro drug performance by inducing salt disproportionation in the tablet during dissolution in the same acidic medium. Dissolution in the neutral medium (pH = 6.8) showed rapid formation of the free base upon contact with the dissolution medium. The Raman maps of the cross-sectioned tablets revealed the formation of a shell consisting of the free base around the edge of the tablet. This shell decreased the rate of penetration of the dissolution medium into the tablet, which had significant implications on the release of the API into the surrounding solution, as shown by the UV-vis absorption spectroscopy drug release data. Our findings highlight the utility of the Raman/UV-vis flow cell analytical platform as an advanced analytical technique to investigate the effect of excipients and dissolution media on salt disproportionation in real time. This methodology will be used to enhance our understanding of salt stability studies that may pave the way for more stable multicomponent formulations.

Advanced polymeric nanotechnology to augment therapeutic delivery and disease diagnosis

Therapeutic and diagnostic payloads are usually associated with properties that compromise their efficacy, such as poor aqueous solubility, short half-life, low bioavailability, nonspecific accumulation and diverse side effects. Nanotechnological solutions have emerged to circumvent some of these drawbacks, augmenting therapeutic and/or diagnostic outcomes. Nanotechnology has benefited from the rise in polymer science research for the development of novel nanosystems for therapeutic and diagnostic purposes. Polymers are a widely used class of biomaterials, with a considerable number of regulatory approvals for application in clinics. In addition to their versatility in production and functionalization, several synthetic and natural polymers demonstrate biocompatible properties that dictate their successful biological performance. This article highlights the physicochemical characteristics of a variety of natural and synthetic biocompatible polymers, as well as their role in the manufacture of nanotechnology-based systems, state-of-art applications in disease treatment and diagnosis, and current challenges in finding a way to clinics.

Facile Dye-Initiated Polymerization of Lactide-Glycolide Generates Highly Fluorescent Poly(lactic-co-glycolic Acid) for Enhanced Characterization of Cellular Delivery

Poly(lactic-co-glycolic acid) (PLGA) is a versatile synthetic copolymer that is widely used in pharmaceutical applications. This is because it is well-tolerated in the body, and copolymers of varying physicochemical properties are readily available via ring-opening polymerization. However, native PLGA polymers are hard to track as drug delivery carriers when delivered to subcellular spaces, due to the absence of an easily accessible "handle" for fluorescent labeling. Here we show a one-step, scalable, solvent-free, synthetic route to fluorescent blue (2-aminoanthracene), green (5-aminofluorescein), and red (rhodamine-6G) PLGA, in which every polymer chain in the sample is fluorescently labeled. The utility of initiator-labeled PLGA was demonstrated through the preparation of nanoparticles, capable of therapeutic subcellular delivery to T-helper-precursor-1 (THP-1) macrophages, a model cell line for determining in vitro biocompatibility and particle uptake. Super resolution confocal fluorescence microscopy imaging showed that dye-initiated PLGA nanoparticles were internalized to punctate regions and retained bright fluorescence over at least 24 h. In comparison, PLGA nanoparticles with 5-aminofluorescein introduced by conventional nanoprecipitation/encapsulation showed diffuse and much lower fluorescence intensity in the same cells and over the same time periods. The utility of this approach for in vitro drug delivery experiments was demonstrated through the concurrent imaging of the fluorescent drug doxorubicin (λ_ex = 480 nm, λ_em = 590 nm) with carrier 5-aminofluorescein PLGA, also in THP-1 cells, in which the intracellular locations of the drug and the polymer could be clearly visualized. Finally, the dye-labeled particles were evaluated in an in vivo model, via delivery to the nematode Caenorhabditis elegans, with bright fluorescence again apparent in the internal tract after 3 h. The results presented in this manuscript highlight the ease of synthesis of highly fluorescent PLGA, which could be used to augment tracking of future therapeutics and accelerate in vitro and in vivo characterization of delivery systems prior to clinical translation.