Reply to comments by Dr. Ali Shayanfar

Several clarifications are made pertaining to the study on the cocrystallization of 5-fluorouracil (5-FU) and gallic acid (GA). Dr. Shayanfar's perspective in the solubility and biological activity of cocrystals is recognized, and his insightful guidance on solubility determination methodologies is greatly appreciated. A misconception concerning the cytotoxicity assay methodology in the Shayanfar's comments is addressed. Furthermore, the stability of the 5-FU-GA cocrystal during solubility measurement is highlighted, as evidenced by XRD analysis of residual solids. Lastly, the independence of the elevated cytotoxicity of the cocrystal from 5-FU solubility is deliberated, aligning with preceding research outcomes.

Antibacterial and Anticancer Activity, Acute Toxicity, and Solubility of Co-crystals of 5-Fluorouracil and Trimethoprim

5-Fluorouracil is mainly used for the treatment of tumors and has relatively high toxicity. Trimethoprim is a common broad-spectrum antibiotic agent with extremely poor water solubility. We hoped to solve these problems by synthesizing co-crystals (compound 1) of 5-fluorouracil and trimethoprim. Solubility tests showed that the solubility of compound 1 was improved compared to that of trimethoprim. In vitro anticancer activity tests of compound 1 showed higher activity against human breast cancer cells than 5-fluorouracil. Acute toxicity showed that its toxicity was much lower than that of 5-fluorouracil. In the test of anti-Shigella dysenteriae activity, compound 1 showed much stronger antibacterial activity than trimethoprim.

Cocrystallization of 5-fluorouracil with gallic acid: A novel 5-fluorouracil cocrystal displaying synergistic anti-tumor activity both in oral and intraperitoneal injection administration

Gallic acid (GA) is a naturally occurring polyphenolic compound exhibiting anti-tumor activity. To clarify the capability of GA in optimizing the in vitro/in vivo properties of the first line anti-tumor drug 5-fluorouracil (5-FU) and achieve synergistically enhanced anti-tumor activity, a novel cocrystal hydrate of 5-FU-GA-H₂O was successfully screened and characterized based on various spectroscopic and experimental analysis including Fourier transform infrared spectroscopy (FT-IR), Raman spectra (Raman), powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), thermogravimetric (TG) and scanning electric microscope (SEM) techniques. The results suggested the existence of hydrogen bonding interactions between C=O group of 5-FU and O-H group of GA. Although the dissolution rate and solubility of 5-FU-GA-H₂O cocrystal were slowed and lowered compared with that of 5-FU, respectively, the membrane permeability was enhanced for cocrystal compared with that of intact 5-FU and physical mixture (PM) of 5-FU and GA. For the cocrystal, the cumulative amount per unit area of permeated 5-FU in the first 10 h was 2.56 and 9.97 times of that of pure 5-FU and PM, respectively, in the case that transmembrane behavior of 5-FU depended on the type of solution from which the powder was dissolved. Meanwhile, improvement on oral bioavailability by co-crystallization was observed; AUC_0-t of cocrystal was 2.78-fold higher than that of 5-FU. Furthermore, the cocrystal displayed a superior cytotoxic activity on 4T1 mouse breast cancer cells compared with pure 5-FU and even the PM. It was confirmed that the cocrystal solution induced higher autophagic flux than those of 5-FU and PM in 4T1 cell, suggesting that autophagy rather than apoptosis mainly mediated cell death. The obvious difference of tumor inhibition activity between PM and cocrystal in intraperitoneal injection administration indicated that some of the interactions formed in the solid cocrystal could retain in solution in some way. Benefiting from synergistic cytotoxicity, drug efficacy in vivo was enhanced through injection administration of solution from which cocrystal was dissolved.

Profoundly improved photostability of dimetronidazole by cocrystallization

Cocrystallization with saccharine (SAC) significantly improved photostability of dimetronidazole (DMZ), an veterinary antibiotic.

Energy framework and solubility: a new predictive model in the evaluation of the structure–property relationship of pharmaceutical solid forms

Crystal structures with lower interaction energy tend to present higher aqueous solubility.

Salts of rucaparib with dicarboxylic acids: synthesis, crystal structures and solubility

Three new salts of rucaparib with fumaric acid, adipic acid and pimelic acid were synthesized and characterized, and the latter two demonstrate significantly improved solubility without sacrificing hygroscopicity and physical stability.

Recent Advances in Pharmaceutical Cocrystals: From Bench to Market

The pharmacokinetics profile of active pharmaceutical ingredients (APIs) in the solid pharmaceutical dosage forms is largely dependent on the solid-state characteristics of the chemicals to understand the physicochemical properties by particle size, size distribution, surface area, solubility, stability, porosity, thermal properties, etc. The formation of salts, solvates, and polymorphs are the conventional strategies for altering the solid characteristics of pharmaceutical compounds, but they have their own limitations. Cocrystallization approach was established as an alternative method for tuning the solubility, permeability, and processability of APIs by introducing another compatible molecule/s into the crystal structure without affecting its therapeutic efficacy to successfully develop the formulation with the desired pharmacokinetic profile. In the present review, we have grossly focused on cocrystallization, particularly at different stages of development, from design to production. Furthermore, we have also discussed regulatory guidelines for pharmaceutical industries and challenges associated with the design, development and production of pharmaceutical cocrystals with commercially available cocrystal-based products.

Cocrystals of regorafenib with dicarboxylic acids: synthesis, characterization and property evaluation

Three cocrystals of regorafenib were synthesized, and two of them demonstrate significantly improved solubility and tabletability without compromising physicochemical stability.

Pharmaceutical cocrystal: a game changing approach for the administration of old drugs in new crystalline form

Pharmaceutical cocrystals are still gaining the interest of the researchers due to their potential to alter physicochemical, mechanical, and pharmacokinetic properties of active pharmaceutical ingredients without negotiating therapeutic action. The diverse new applications of cocrystals, like taste masking, reduced toxicity, patenting opportunities, commercial potential, etc. act as driving force to the rising interest of the pharmaceutical industries. Initially, cocrystals from the view of regulatory authorities, design strategies, cocrystal preparation in brief with special emphasis on scalable and solvent-free hot melt extrusion method, and practical guide to characterization have been provided. The special focus has been given to the biopharmaceutical attributes of the cocrystal. Finally, challenges before and after cocrystal preparation are presented in this review along with some commercial examples of the cocrystals.

A 5-fluorouracil–kaempferol drug–drug cocrystal: a ternary phase diagram, characterization and property evaluation

A drug–drug cocrystal of 5-fluorouracil and kaempferol was comprehensively investigated and exhibits optimized solubility behavior in comparison with individual APIs.