Elucidating the Molecular Mechanism of Drug-Polymer Interplay in a Polymeric Supersaturated System of Rifaximin

Photo-induced drug release at interfaces with arylazopyrazoles

Smart responsive materials have spurred the progress in high-precision drug delivery. Enormous attention has been given to characterizing drug release in bulk aqueous solutions, however, aqueous-hydrophobic interfaces are vital components of biological systems which serve as the point of entry into cells. These interfaces are involved in many key biomolecular interactions, and while the potential for drug molecules to adsorb to these interfaces is recognized, their specific role in the context of drug release remains largely unexplored. We present a fundamental investigation on the release of encapsulated drugs at the air-water interface as a representative model to mimic the organic/aqueous interface of cells. Combining the advantages of light as an external stimulus and the superiority of arylazopyrazoles (AAP) over conventional azobenzene photoswitches, we report a micellar nanocarrier for the capture and release of the chemotherapeutic drug doxorubicin. Using a powerful combination of interface-sensitive techniques such as the Langmuir-Blodgett technique, surface tensiometry, and the interface-specific vibrational sum-frequency generation spectroscopy, we demonstrate the photoresponsive release of doxorubicin encapsulated in the micelles of AAP photosurfactants to the air-water interface. Complementary fluorescence measurements corroborate additional drug release in bulk aqueous solutions.

Targeted delivery of rifaximin using P6.2-decorated bifunctional PLGA nanoparticles for combating Staphylococcus aureus infections

The emergence of antibiotic resistance makes the treatment of bacterial infections difficult and necessitates the development of alternative strategies. Targeted drug delivery systems are attracting great interest in overcoming the limitations of traditional antibiotics. Here, we aimed for targeted delivery of rifaximin (RFX) by decorating RFX-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) with synthetic P6.2 peptide, which was used as a targeting agent for the first time. Our results showed that encapsulation of RFX into NPs increased its antibacterial activity by improving its solubility and providing controlled release, while P6.2 modification allowed targeting of NPs to S. aureus bacterial cells. A promising therapeutic approach for bacterial infections, these P6.2-conjugated RFX-loaded PLGA NPs (TR-NP) demonstrated potent antibacterial activity against both strains of S. aureus. The antibacterial activity of RFX-loaded PLGA NPs (R-NP) showed significant results with an increase of 8 and 16-fold compared to free RFX against S. aureus and MRSA, respectively. Moreover, the activity of targeted nanoparticles was found to be increased 32 or 16-fold with an MBC value of 0.0078 μg/mL. All nanoparticles were found to be biocompatible at doses where they showed antimicrobial activity. Finally, it revealed that P6.2-conjugated targeted nanoparticles extremely accumulated in S. aureus rather than E. coli.

Comparative analysis of drug-salt-polymer interactions by experiment and molecular simulation improves biopharmaceutical performance

The propensity of poorly water-soluble drugs to aggregate at supersaturation impedes their bioavailability. Supersaturated amorphous drug-salt-polymer systems provide an emergent approach to this problem. However, the effects of polymers on drug-drug interactions in aqueous phase are largely unexplored and it is unclear how to choose an optimal salt-polymer combination for a particular drug. Here, we describe a comparative experimental and computational characterization of amorphous solid dispersions containing the drug celecoxib, and a polymer, polyvinylpyrrolidone vinyl acetate (PVP-VA) or hydroxypropyl methylcellulose acetate succinate, with or without Na+/K+ salts. Classical models for drug-polymer interactions fail to identify the best drug-salt-polymer combination. In contrast, more stable drug-polymer interaction energies computed from molecular dynamics simulations correlate with prolonged stability of supersaturated amorphous drug-salt-polymer systems, along with better dissolution and pharmacokinetic profiles. The celecoxib-salt-PVP-VA formulations exhibit excellent biopharmaceutical performance, offering the prospect of a low-dosage regimen for this widely used anti-inflammatory, thereby increasing cost-effectiveness, and reducing side-effects.

Supersaturation and Precipitation Applicated in Drug Delivery Systems: Development Strategies and Evaluation Approaches

Supersaturation is a promising strategy to improve gastrointestinal absorption of poorly water-soluble drugs. Supersaturation is a metastable state and therefore dissolved drugs often quickly precipitate again. Precipitation inhibitors can prolong the metastable state. Supersaturating drug delivery systems (SDDS) are commonly formulated with precipitation inhibitors, hence the supersaturation is effectively prolonged for absorption, leading to improved bioavailability. This review summarizes the theory of and systemic insight into supersaturation, with the emphasis on biopharmaceutical aspects. Supersaturation research has developed from the generation of supersaturation (pH-shift, prodrug and SDDS) and the inhibition of precipitation (the mechanism of precipitation, the character of precipitation inhibitors and screening precipitation inhibitors). Then, the evaluation approaches to SDDS are discussed, including in vitro, in vivo and in silico studies and in vitro-in vivo correlations. In vitro aspects involve biorelevant medium, biomimetic apparatus and characterization instruments; in vivo aspects involve oral absorption, intestinal perfusion and intestinal content aspiration and in silico aspects involve molecular dynamics simulation and pharmacokinetic simulation. More physiological data of in vitro studies should be taken into account to simulate the in vivo environment. The supersaturation theory should be further completed, especially with regard to physiological conditions.

Revealing the roles of polymers in supersaturation stabilization from the perspective of crystallization behaviors: A case of nimodipine

Formulating drugs into amorphous solid dispersions (ASDs) represents an attractive means to enhance the aqueous solubility of drugs. Furthermore, water-soluble polymers have proven highly advantageous for stabilizing supersaturated solutions of ASDs. However, the performance and mechanism of various polymers in stabilizing supersaturated drug solutions have not been well-studied. The aim of this study was to investigate the effects of different commercial polymers on the dissolution behaviors and supersaturation stabilization of the ASDs and to further explore the mechanism of polymer mediated supersaturation maintenance by studying the crystallization behaviors of the ASDs. In this study, nimodipine (NMD) was used as a model drug because of its poor water-solubility and fast crystallization rate in aqueous solution, and three polymers polyvinylpyrrolidone (PVP), vinylpyrrolidone-vinyl acetate copolymer (PVP VA), and polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft co-polymer (Soluplus) was selected as the drug carriers to form the ASDs with NMD. Solid-state characterizations of the ASDs confirmed the amorphous state of the ASD systems. ASD_{PVP VA} demonstrated superior supersaturation maintenance in dissolution experiments compared to the other two ASD systems. Among the polymers tested, PVP VA most efficiently maintained dissolution of NMD and prevented its crystallization from the supersaturated solution. The ability of PVP VA to most-effectively maintain supersaturation of the drug was manifested by inhibition of crystal nucleation rather than inhibition of crystal growth following nucleation. These results suggest that nucleation inhibition was instrumental in enabling the polymer-mediated supersaturation maintenance, at least with NMD.

Explicating the molecular level drug-polymer interactions at the interface of supersaturated solution of the model drug: Albendazole

Supersaturation as a formulation principle relates to the aqueous solubility of poorly soluble drugs in solution . However, supersaturation state of drugs tends to crystallize because of its thermodynamic instability thereby compromising the solubility and biopharmaceutical performance of drugs. The present study aims to investigate the supersaturation potential of albendazole (ABZ) and its precipitation via nucleation and crystal growth. We hypothesized the use of polymers will avoid ABZ precipitation by interacting with drug molecules. The drug polymer interactions are characterized using conventional methods of Fourier transform infrared (FTIR), Nuclear magnetic resonance (NMR) and Polarized light microscopy (PLM). We have used a novel approach of sum frequency generation (SFG) vibrational spectroscopic in exploring the drug polymer interactions at air-water interface. Recently we have reported the SFG for e rifaximin-polymer interactions (Singh et al., 2021). The supersaturation assay, saturation solubility studies and nucleation induction time analysis revealed polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP K30) as effective precipitation inhibitors thereby enhancing the ABZ equilibrium solubility and in vitro supersaturation maintenance of ABZ. Further, modification in the solid state of ABZ has confirmed the influence of polymers on its precipitation behaviour. We conclude that PVA and PVP K30 act as nucleation and crystal growth inhibitor, respectively for the precipitation inhibition of ABZ.

Amorphous Salts Solid Dispersions of Celecoxib: Enhanced Biopharmaceutical Performance and Physical Stability

Numerous amorphous solid dispersion (ASD) formulations of celecoxib (CEL) have been attempted for enhancing the solubility, dissolution rate, and in vivo pharmacokinetics via high drug loading, polymer combination, or by surfactant addition. However, physical stability for long-term shelf life and desired in vivo pharmacokinetics remains elusive. Therefore, newer formulation strategies are always warranted to address poor aqueous solubility and oral bioavailability with extended shelf life. The present investigation elaborates a combined strategy of amorphization and salt formation for CEL, providing the benefits of enhanced solubility, dissolution rate, in vivo pharmacokinetics, and physical stability. We generated amorphous salts solid dispersion (ASSD) formulations of CEL via an in situ acid-base reaction involving counterions (Na⁺ and K⁺) and a polymer (Soluplus) using the spray-drying technique. The generated CEL-Na and CEL-K salts were homogeneously and molecularly dispersed in the matrix of Soluplus polymer. The characterization of generated ASSDs by differential scanning calorimetry revealed a much higher glass-transition temperature (T_g) than the pure amorphous CEL, confirming the salt formation of CEL in solid dispersions. The micro-Raman and proton nuclear magnetic resonance spectroscopy further confirmed the formation of salt at the -S═O position in the CEL molecules. CEL-Na-Soluplus ASSD exhibited a synergistic enhancement in the aqueous solubility (332.82-fold) and in vivo pharmacokinetics (9.83-fold enhancement in the blood plasma concentration) than the crystalline CEL. Furthermore, ASSD formulations were physically stable for nearly 1 year (352 days) in long-term stability studies at ambient conditions. Hence, we concluded that the ASSD is a promising strategy for CEL in improving the physicochemical properties and biopharmaceutical performance.