Tuning Caco-2 permeability by cocrystallization: Insights from molecular dynamics simulation

Emerging evidence suggests that intestinal permeability can be potentially enhanced through cocrystallization. However, a mechanism for this effect remains to be established. In this study, we first demonstrate the enhancement in intestinal permeability, evaluated by the Caco-2 cell permeability assay, of acetazolamide (ACZ) in the presence of a conformer, p-aminobenzoic acid (PABA), delivered in the form of a 1:1 cocrystal. The binding strength of ACZ and PABA with the Pgp efflux transporter, either alone or as a mixture, was calculated using molecular dynamics simulation. Results show that PABA weakens the binding of ACZ with Pgp, which leads to a lower efflux ratio and elevated permeability of ACZ. This work provides molecular-level insights into a potentially effective strategy to improve the intestinal permeability of drugs. If the same cocrystal also exhibits higher solubility, oral bioavailability of BCS IV drugs can likely be improved by forming a cocrystal with a Pgp inhibitor.

Structural analysis of PET-degrading enzymes PETase and MHETase from Ideonella sakaiensis

The concept of biocatalytic PET degradation for industrial recycling processes had made a big step when the bacterium Ideonella sakaiensis was discovered to break PET down to its building blocks at ambient temperature. This process involves two enzymes: cleavage of ester bonds in PET by PETase and in MHET, the resulting intermediate, by MHETase. To understand and further improve this unique capability, structural analysis of the involved enzymes was aimed at from early on. We describe a repertoire of methods to this end, including protein expression and purification, crystallization of apo and substrate-bound enzymes, and modeling of PETase complexed with a ligand.

Raman and Terahertz Spectroscopic Characterization of Solid-state Cocrystal Formation within Specific Active Pharmaceutical Ingredients

Cocrystallization of specific active pharmaceutical ingredients (APIs) in the solid-state phase is becoming a feasible way to improve their corresponding physicochemical properties and ultimate bioavailability without making and breaking any covalent bonds within them. Many recent reports deal with the characterization and analysis topics of pharmaceutical APIs-based cocrystals. In this mini-review, we will focus on the recent steady-state and time-dependent spectroscopic investigation into the cocrystallization of specific APIs based on both Raman and emerging terahertz spectroscopy in pharmaceutical fields. Distinctive spectral, structural and also kinetic information of pharmaceutical APIs-based cocrystals are obtained and discussed, which would highlight the potential of vibrational spectroscopy as an attractive technique for various drug research and development during cocrystallization of specific APIs.

Dissolution Enhancement of Atorvastatin Calcium by Cocrystallization

Purpose: To enhance the dissolution rate of the poorly soluble drug atorvastatin calcium (ATC) by cocrystallization with selected coformers. Enhancement of the dissolution rate and solubility of the drug, which is classified as Class II of the Biopharmaceutical Classification System (BCS), is expected to enhance the bioavailability.

Methods: Two methods were used for preparing the cocrystals, solvent drop grinding (SDG) and solvent evaporation (SE) method using 1:1, 1:3, and 1:10 drug-coformer molar ratios. Glucosamine hydrochloride (GluN) and nicotinamide (NIC) were investigated as coformers. The cocrystals, their physical mixtures, and the raw ATC were characterized by fourier transform infrared (FTIR spectroscopy), differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), mass spectroscopy (MS), scanning electron microscopy (SEM), solubility, and dissolution rate studies.

Results: SDG and SE were effective in improving the dissolution rate of ATC with both coformers. Drug: coformer ratio 1:3 was optimum. The solubility values for ATC, GluN-, and NIC-cocrystals were 26, to 35 and 50 µg/mL, respectively. The dissolution rate of ATC from cocrystals was > 90% after 5 minutes, compared to 41% untreated ATC.

Conclusion: Cocrystallization significantly improved the solubility and dissolution, in comparison to the untreated ATC.

Spectroscopic analysis of the influence of various external factors on ethenzamide-glutaric acid (1:1) cocrystal formation

Cocrystal formation may affect manufacturability (flow, compaction and processability) as well as solubility/dissolution, hygroscopicity and stability properties of drugs. Therefore, cocrystallization could be used to improve the pharmaceutical properties of low-soluble drugs such as ethenzamide. In this project, solid-state nuclear magnetic resonance and Fourier transform infrared spectroscopy studies were performed for ethenzamide-glutaric acid to obtain more information about the ethenzamide cocrystallization process. The impact of the grinding time of the physical mixture (ethenzamide-glutaric acid) on cocrystal formation and the further spontaneous cocrystallization was evaluated using spectroscopic methods and curve-fitting analysis of the spectra. The influence of pressure on the yield of cocrystal formation was also described. Additionally, studies on the effect of magic-angle spinning during solid-state nuclear magnetic resonance spectra collection on the initiation of cocrystal formation, have been performed. Based on this research, conclusions regarding the influence of the different external factors, such as pressure during the tableting process and grinding time, on the cocrystal formation have been drawn for ethenzamide cocrystals.

Discovery, cocrystallization and biological evaluation of novel piperidine derivatives as high affinity Ls-AChBP ligands possessing α7 nAChR activities

A series of novel pyridine-substituted piperidine derivatives were discovered as low nanomolar Ls-AChBP ligands with α7 nAChR partial agonism or antagonism activities. A high-resolution antagonist-bound Ls-AChBP complex was successfully resolved with a classic Loop C opening phenomenon and unique sulfur-π interactions which deviated from our previous docking mode to a large extent. With the knowledge of the co-complex, 27 novel piperidine derivatives were designed and synthesized. The structure-activity relationships (SARs) of the aromatic and pyridine regions were well established and binding modes were illustrated with the help of molecular docking which indicated that interactions with Trp 143 and the "water bridge" are essential for the high binding affinities. Halogen bonding as well as the space around 5'- or 6'- position of the pyridine ring was also proposed to influence the binding conformation of the compounds. Notably, two enantiomers of compound 2 showed opposite functions toward α7 nAChR and compound (S)-2 showed sub-nanomolar affinity (K_i = 0.86 nM) on Ls-AChBP and partial agonism (pEC₅₀ = 4.69 ± 0.11,Emax = 36.1%) on α7 nAChR with reasonable pharmacokinetics (PK) properties and fine ability of blood-brain-barrier (BBB) penetration. This study provided promising hits to develop candidates targeting nAChR-related CNS diseases.

Improving solid-state properties of berberine chloride through forming a salt cocrystal with citric acid

Berberine chloride (BCl) can exist as an anhydrate, monohydrate, dihydrate, and tetrahydrate. Therefore, it faces the problem of humidity dependent solid phase change when environmental humidity varies during manufacturing and storage of berberine tablets. We have discovered a new 1:1 cocrystal formed between berberine chloride and citric acid (BCl-CA) that exhibits better stability against variations in humidity while maintaining similar thermal stability, solubility, dissolution rate, and tabletability. Thus, BCl-CA is a good alternative crystal form for use in formulation to manufacture berberine tablets.

Crystallization of Liganded Phosphatases in the HAD Superfamily

Phosphotransferases catalyze reactions on chemically diverse molecules in organisms from all domains of life. The haloalkanoate dehalogenase superfamily (HADSF) is a model system for phosphoryl transfer enzymes as members catalyze phosphoester hydrolase, phosphonate hydrolase, and phosphomutase reactions on sugars, lipids, nucleotides, and peptides. Because these reactions are fundamental to essential metabolic transformations, understanding the mechanism and determinants of substrate specificity in the HADSF is critical. Structure/function relationships in the superfamily have also been leveraged in the development of methodologies for the assignment of enzyme function. Enzyme complexes with substrate, product, and analogs of the ground state or intermediate/transition state can be studied via high-resolution macromolecular crystallography to provide insight to the relative location of residues and ligands, as well as associated enzyme conformational states. This knowledge can aid in inhibitor design for phosphohydrolase reactions and target-specific therapeutics. Here we describe experimental approaches to capture liganded X-ray crystallographic structures of HADSF members. A number of these methods can be employed generally, including other families of phosphohydrolases and enzymes catalyzing phosphoryl transfer.

Spectroscopic investigation on structure and pH dependent Cocrystal formation between gamma-aminobutyric acid and benzoic acid

Vibrational spectroscopic methods, including terahertz absorption and Raman scattering spectroscopy, were utilized for the characterization and analysis of gamma-aminobutyric acid (GABA), benzoic acid (BA), and the corresponding GABA-BA cocrystal formation under various pH values of aqueous solution. Vibrational spectroscopic results demonstrated that the solvent GABA-BA cocrystal, similar as grinding counterpart, possessed unique characteristic features compared with that of starting parent compounds. The change of vibrational modes for GABA-BA cocrystal comparing with starting components indicates there is strong inter-molecular interaction between GABA and BA molecules during its cocrystallization process. Formation of GABA-BA cocrystal under slow solvent evaporation is impacted by the pH value of aqueous solution. Vibrational spectra indicate that the GABA-BA cocrystal could be stably formed with the solvent condition of 2.00≤pH≤7.00. In contrast, such cocrystallization did not occur and the cocrystal would dissociate into its parent components when the pH value of solvent is lower than 2.00. This study provides experimental benchmark to discriminate and identify the structure of cocrystal and also pH-dependent cocrystallization effect with vibrational spectroscopic techniques in solid-state pharmaceutical fields.

In-line monitoring of cocrystallization process and quantification of carbamazepine-nicotinamide cocrystal using Raman spectroscopy and chemometric tools

A cocrystallization process may involve several molecular species, which are generally solid under ambient conditions. Thus, accurate monitoring of different components that might appear during the reaction is necessary, as well as quantification of the final product. This work reports for the first time the synthesis of carbamazepine-nicotinamide cocrystal in aqueous media with a full conversion. The reactions were monitored by Raman spectroscopy coupled with Multivariate Curve Resolution - Alternating Least Squares, and the quantification of the final product among its coformers was performed using Raman spectroscopy and Partial Least Squares regression. The slurry reaction was made in four different conditions: room temperature, 40°C, 60°C and 80°C. The slurry reaction at 80°C enabled a full conversion of initial substrates into the cocrystal form, using water as solvent for a greener method. The employment of MCR-ALS coupled with Raman spectroscopy enabled to observe the main steps of the reactions, such as drug dissolution, nucleation and crystallization of the cocrystal. The PLS models gave mean errors of cross validation around 2.0 (% wt/wt), and errors of validation between 2.5 and 8.2 (% wt/wt) for all components. These were good results since the spectra of cocrystals and the physical mixture of the coformers present some similar peaks.

A review of pharmaceutical extrusion: critical process parameters and scaling-up

Hot melt extrusion has been a widely used process in the pharmaceutical area for three decades. In this field, it is important to optimize the formulation in order to meet specific requirements. However, the process parameters of the extruder should be as much investigated as the formulation since they have a major impact on the final product characteristics. Moreover, a design space should be defined in order to obtain the expected product within the defined limits. This gives some freedom to operate as long as the processing parameters stay within the limits of the design space. Those limits can be investigated by varying randomly the process parameters but it is recommended to use design of experiments. An examination of the literature is reported in this review to summarize the impact of the variation of the process parameters on the final product properties. Indeed, the homogeneity of the mixing, the state of the drug (crystalline or amorphous), the dissolution rate, the residence time, can be influenced by variations in the process parameters. In particular, the impact of the following process parameters: temperature, screw design, screw speed and feeding, on the final product, has been reviewed.