Despite being the first conjugation reaction demonstrated in humans, amino acid conjugation as a route of metabolism of xenobiotic carboxylic acids is not well characterised. This is principally due to the small number and limited structural diversity of xenobiotic substrates for amino acid conjugation. Unlike CYP and uridine 5'-diphosphate glucuronosyltransferase, which are localised in the endoplasmic reticulum, the enzymes of amino acid conjugation reside in mitochondria. Unique among drug metabolism pathways, amino acid conjugation involves initial formation of a xenobiotic acyl-CoA thioester that is then conjugated principally with glycine in humans. However, formation of the xenobiotic acyl-CoA thioester does not always infer subsequent amino acid conjugation. Evidence is presented that in the absence of glycine conjugation substrates that form acyl-CoA thioesters perturb mitochondrial function. This review discusses literature on the enzymes involved and the concept that xenobiotic substrate selectivity provides a barrier to protect the metabolic integrity of the mitochondria.

A validated database of 70 molecules known to undergo biotransformation by CYP2C9 was collated. The molecular alignment program ROCS was used with the query molecule flurbiprofen as a basis for predicting the correct active site orientation of the CYP2C9 database molecules. The quality of the results obtained was excellent, with 39 of the first 44 molecules (89%) sorted by ROCS combination score having alignments that accounted for the experimentally observed site of oxidation. Transposition of the first 39 correctly aligned molecules into the CYP2C9 active site yielded an average site of metabolism to iron heme distance of 5.21 A, in good agreement with previous experimental observations. Molecular docking studies were also undertaken, but the results were less successful than the ROCS-based alignment method, indicating that ligand-based approaches with chemical typing are important in the prediction of metabolism by CYP2C9.

Phosphorylation of eIF4E by human mitogen-activated protein kinase (MAPK)-interacting kinases (Mnks) is crucial for human tumourigenesis and development. Targeting Mnks may provide a novel anticancer therapeutic strategy. However, the lack of selective Mnk inhibitors has so far hampered pharmacological target validation and clinical drug development. Herein, we report, for the first time, the discovery of a series of 5-(2-(phenylamino)pyrimidin-4-yl)thiazole-2(3H)-one derivatives as Mnk inhibitors. Several derivatives demonstrate very potent Mnk2 inhibitory activity. The most active and selective compounds were tested against a panel of cancer cell lines, and the results confirm the cell-type-specific effect of these Mnk inhibitors. Detailed cellular mechanistic studies reveal that Mnk inhibitors are capable of reducing the expression level of anti-apoptotic protein Mcl-1, and of promoting apoptosis in MV4-11 acute myeloid leukaemia cells.