Artemisinin Cocrystals for Bioavailability Enhancement: In vitro Formulation Design, In vivo and Physiologically Based Pharmacokinetic models

Artemisinin (ART) is the most promising antimalarial agent, which is both effective and well tolerated in patients, however, has therapeutic limitations due to its low solubility, bioavailability, short half-life and neurotoxicity. The objective of this work was to explore the possibility of formulating ART cocrystals, i.e., Artemisinin-Orcinol (ART-ORC) and Artemisinin-Resorcinol (ART2-RES) as oral dosage forms to deliver ART molecules for bioavailability enhancement. The aim of this research was to develop a simple and effective ART cocrystal formulation which can be used on an appropriate animal model to evaluate their preclinical pharmacokinetics for further development. The research reports the evaluation and prediction of pharmacokinetics (PK) performance of ART cocrystal formulations using in vivo murine animal and Physiologically Based Pharmacokinetic (PBPK) models. The study was divided into five tasks: (1) Formation and characterisation of Artemisinin cocrystals: Two pharmaceutical cocrystals of poorly water soluble active pharmaceutical ingredient (API) ART were synthesised, including 1:1 Artemisinin-Orcinol (ART-ORC) and 2:1 Artemisinin-Resorcinol (ART2-RES). The formation of pure cocrystals was confirmed by the characterisation techniques such as Infrared Spectroscopy (IR), Differential Scanning Calorimetry (DSC) and Powder X-Ray Diffraction (PXRD). (2) Formulation design of Artemisinin cocrystals The physiochemical properties of ART cocrystals were measured to provide valuable information for the strategy of formulation development. It was found that the ART solubility can be increased significantly by its cocrystals, i.e., 26-fold by ART-ORC and 21-fold by ART2-RES respectively. Copolymer Polyvinylpyrrolidone/vinyl Acetate (PVP-VA) was found to be the most effective crystallisation inhibitor through screening a set of polymers widely used in pharmaceutical products, including Polyvinylpyrrolidone (PVP), Hydroxypropyl Methylcellulose (HPMC) and Hydroxypropyl Methylcellulose Acetate Succinate (HPMC-AS) based on the powder dissolution performance parameter (DPP) analysis. The optimal concentration of PVP-VA at 0.05mg/mL within a formulation was then determined by a dissolution/permeability (D/P) method which represented a simplified permeation model to simultaneously evaluate the effects of a crystallization inhibitor on the dissolution and permeation performance of ART cocrystals. VII (3) Mechanistic understandings of effect of the polymeric excipient on Artemisinin cocrystal dissolution and permeation properties The surface dissolution of single ART cocrystals was monitored by Raman spectroscopy and Scanning Electron Microscope (SEM) and the diffusion properties of ART in solution were measured by 1H and diffusion-ordered spectroscopy (DOSY) nuclear magnetic resonance (NMR) spectroscopy. These experiments were conducted to gain an insight into how the excipient affects the ART cocrystal dissolution performance and bioavailability. (4) In vivo bioavailability of Artemisinin Cocrystals The efficacy of the ART cocrystal formulations along with the parent drug ART were tested in mice infected with Plasmodium berghei. Cocrystal formulations resulted in a five-fold reduction in parasitaemia in mice compared to ART alone at the same dose. The PK parameters including Cmax, Tmax, AUC were obtained by determining drug concentrations in the plasma using Liquid Chromatography-High Resolution Mass Spectrometry (LC-HRMS), showing enhanced ART levels after dosage with the cocrystal formulations. The dose-response tests revealed that a significantly lower dose of the ART cocrystals in the formulation was required to achieve a similar therapeutic effect as ART alone formulation. (5) Physiologically based pharmacokinetic (PBPK) modelling of Artemisinin Cocrystals A PBPK model was developed using a PBPK mouse simulator to accurately predict the in vivo behaviour of the cocrystal formulations by combining in vitro dissolution profiles with the properties of the parent drug ART. The study illustrated that information from classical in vitro and in vivo experimental investigations of the parent drug of ART formulation can be coupled with PBPK modelling to predict the PK parameters of an ART cocrystal formulation in an efficient manner. Therefore, the proposed modelling strategy could be used to establish structure−activity relationships for different cocrystals intended to improve dissolution properties and to support clinical candidate selection, contributing to assessment of cocrystal developability and formulation development.