Vinblastine (VLB) is an antimitotic drug that binds to the vinca site of tubulin. The molecule possesses a high molecular weight and a complex chemical structure with many possibilities of metabolization. Despite advances in drug discovery research in reducing drug toxicity, the cause and mechanism of VLB-induced adverse drug reactions (ADRs) remains poorly understood. VLB is metabolized to at least 35 known metabolites, which have been identified and collected in this present work. This study also explores how VLB metabolites affect nausea-associated receptors such as muscarinic, dopaminergic, and histaminic. The metabolites have stronger binding interactions than acetylcholine (ACh) for muscarinic M 1 , M 4 , and M 5 receptors and demonstrate similar binding profiles to that of the natural substrate, ACh. The affinities of VLB metabolites to dopaminergic and histaminic receptors, their absorption, distribution, metabolism, excretion, toxicity properties, and the superiority of VLB to ACh for binding to M 5 R, indicate their potential to trigger activation of nausea-associated receptors during chemotherapy with VLB. It has been shown that metabolite 20-hydroxy-VLB (metabolite 10) demonstrates a stronger binding affinity to the vinca site of tubulin than VLB; however, they have similar modes of action. VLB and metabolite 10 have similar gastric solubility (FaSSGF), intestinal solubility (FeSSIF), and log P values. Metabolite 10 has a more acceptable pharmacokinetic profile than VLB, a better gastric and intestinal solubility. Furthermore, metabolite 10 was found to be less bound to plasma proteins than VLB. These are desired and essential features for effective drug bioavailability. Metabolite 10 is not a substrate of CYP2D6 and thus is less likely to cause drug–drug interactions and ADRs compared to its parent drug. The hydroxyl group added upon metabolism of VLB suggests that it can also be a reasonable starting compound for designing the next generation of antimitotic drugs to overcome P-glycoprotein-mediated multidrug resistance, which is often observed with vinca alkaloids.
5‐fluorouracil (5‐FU) is an anticancer drug, which inhibits human thymidine phosphorylase (hTP) and plays a key role in maintaining the process of DNA replication and repair. It is involved in regulating pyrimidine nucleotide production, by which it inhibits the mechanism of cell proliferation and cancerous tumor growth. However, up to 80% of the administered drug is metabolized by dihydropyrimidine dehydrogenase (DPD). This work compares binding of 5‐FU and its analogues to hTP and DPD, and suggests strategies to reduce drug binding to DPD to decrease the required dose of 5‐FU. An important feature between the proteins studied here was the difference of charge distribution in their binding sites, which can be exploited for designing drugs to selectively bind to the hTP. The 5‐FU presence was thought to be required for a closed conformation. Comparison of the calculation results pertaining to unliganded and liganded protein showed that hTP could still undergo open–closed conformations in the absence of the ligand; however, the presence of a positively charged ligand better stabilizes the closed conformation and rigidifies the core region of the protein more than unliganded or neutral liganded system. The study has also shown that one of the three hinge segments linking the two major α and α/β domains of the hTP is an important contributing factor to the enzyme's open–close conformational twist during its inactivation–activation process. In addition, the angle between the α/β‐domain and the α‐domain has shown to undergo wide rotations over the course of MD simulation in the absence of a phosphate, suggesting that it contributes to the stabilization of the closed conformation of the hTP.
The cover image is based on the Research Article Interdomain twists of human thymidine phosphorylase and its active–inactive conformations: Binding of 5‐FU and its analogues to human thymidine phosphorylase versus dihydropyrimidine dehydrogenase by Tiffany Tozer et al., DOI https://doi.org/10.1111/cbdd.13596. Cover image design © Kali. A Heale and Tiffany M Tozer
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