Hydrolysis of ibuprofenoyl-CoA and other 2-APA-CoA esters by human acyl-CoA thioesterases-1 and -2 and their possible role in the chiral inversion of profens

The synergistic effect of typical chiral organic acids and solution chemistry conditions on the transport of 2-arylpropionic acid chiral derivatives in porous media

The hazards of man-made chiral compounds are of great public concern, with reports of worrying stereoselective compounds and an urgent need to assess their transport. This study evaluated the transport of 2-arylpropionic acid derivatives enantiomers (2-APA) in porous media under a variety of solution chemistry conditions via column packing assays. The results revealed the introduction of Malic acid (MA) enantiomers enhanced the mobility of 2-APA enantiomers, but the enhancement effect was different for different 2-APA enantiomers. Batch sorption experiments confirmed that the MA enantiomers occupied the sorption site of the quartz sand, thus reducing the deposition of the 2-APA enantiomer. Homo- or heterochirality between 2-APA and MA dominates the transport of 2-APA enantiomers, with homochirality between them triggering stronger retention and vice versa. Further evaluating the effect of solution chemistry conditions on the transport of 2-APA enantiomers, increased ionic strength attenuated the mobility of 2-APA enantiomers, whereas introduced coexisting cations enhanced the retention of 2-APA enantiomers in the column. The redundancy analyses corroborated these solution chemistry conditions were negatively correlated with the transport of 2-APA enantiomers. The coupling of pH and these conditions reveals electrostatic forces dominate the transport behavior and stereoselective interactions of 2-APA enantiomers. Distinguishing the transport of enantiomeric pair helps to understand the difference in stereoselectivity of enantiomers and promises to remove the more hazardous one.

Analysis of enzyme reactions using NMR techniques: A case study with α-methylacyl-CoA racemase (AMACR)

α-Methylacyl-CoA racemase (AMACR; P504S) catalyzes the conversion of R-2-methylacyl-CoA esters into their corresponding S-2-methylacyl-CoA epimers enabling their degradation by β-oxidation. The enzyme also catalyzes the key epimerization reaction in the pharmacological activation pathway of ibuprofen and related drugs. AMACR protein levels and enzymatic activity are increased in prostate cancer, and the enzyme is a recognized drug target. Key to the development of novel treatments based on AMACR inhibition is the development of functional assays. Synthesis of substrates and purification of recombinant human AMACR are described. Incubation of R- or S-2-methylacyl-CoA esters with AMACR in vitro resulted in formation of epimers (at a near 1-1 ratio at equilibrium) via removal of their α-protons to form an enolate intermediate followed by reprotonation. Conversion can be conveniently followed by incubation in buffer containing 2H2O followed by 1H NMR analysis to monitor conversion of the α-methyl doublet to a single peak upon deuterium incorporation. Incubation of 2-methylacyl-CoA esters containing leaving groups results in an elimination reaction, which was also characterized by 1H NMR. The synthesis of substrates, including a double labeled substrate for mechanistic studies, and subsequent analysis is also described.

Recombinant protein production for structural and kinetic studies: A case study using M. tuberculosis α-methylacyl-CoA racemase (MCR)

Modern drug discovery is a target-driven approach in which a particular protein such as an enzyme is implicated in the disease process. Commonly, small-molecule drugs are identified using screening, rational design, and structural biology approaches. Drug screening, testing and optimization is typically conducted in vitro, and copious amounts of protein are required. The advent of recombinant DNA technologies has resulted in a rise in proteins purified by affinity techniques, typically by incorporating an "affinity tag" at the N- or C-terminus. Use of these tagged proteins and affinity techniques comes with a host of issues. This chapter describes the production of an untagged enzyme, α-methylacyl-CoA racemase (MCR) from Mycobacterium tuberculosis, using a recombinant E. coli system. Purification of the enzyme on a 100 mg scale using tandem anion-exchange chromatographies (DEAE-sepharose and RESOURCE-Q columns), and size-exclusion chromatographies is described. A modified protocol allowing the purification of cationic proteins is also described, based on tandem cation-exchange chromatographies (using CM-sepharose and RESOURCE-S columns) and size-exclusion chromatographies. The resulting MCR protein is suitable for biochemical and structural biology applications. The described protocols have wide applicability to the purification of other recombinant proteins and enzymes without using affinity chromatography.

Steady-state kinetic analysis of reversible enzyme inhibitors: A case study on calf intestine alkaline phosphatase

Enzymes are important drug targets and inhibition of enzymatic activity is an important therapeutic strategy. Enzyme assays measuring catalytic activity are utilized in both the discovery and development of new drugs. Colorimetric assays based on the release of 4-nitrophenol from substrates are commonly used. 4-Nitrophenol is only partly ionized to 4-nitrophenolate under typical assay conditions (pH 7-9) leading to under-estimation of product formation rates due to the much lower extinction coefficient of 4-nitrophenol compared to 4-nitrophenolate. Determination of 4-nitrophenol pKa values based on absorbance at 405 nm as a function of experimental pH values is reported, allowing for calculation of a corrected extinction coefficient at the assay pH. Characterization of inhibitor properties using steady-state enzyme kinetics is demonstrated using calf intestine alkaline phosphatase and 4-nitrophenyl phosphate as substrate at pH ∼8.2. The following kinetic parameters were determined: Km= 40±3 µM; Vmax= 72.8±1.2 µmolmin-1mg protein-1; kcat= 9.70±0.16 s-1; kcat/Km= 2.44±0.16 × 105 M-1s-1 (mean± SEM, N = 4). Sodium orthovanadate and EDTA were used as model inhibitors and the following pIC50 values were measured using dose-response curves: 6.61±0.08 and 3.07±0.03 (mean±SEM, N = 4). Rapid dilution experiments determined that inhibition was reversible for sodium orthovanadate and irreversible for EDTA. A Ki value for orthovanadate of 51±8 nM (mean±SEM, N = 3) was determined. Finally, data analysis and statistical design of experiments are discussed.

High Expression of ACOT2 Predicts Worse Overall Survival and Abnormal Lipid Metabolism: A Potential Target for Acute Myeloid Leukemia

Acyl-CoA thioesterase (ACOT) plays a considerable role in lipid metabolism, which is closely related to the occurrence and development of cancer, nevertheless, its role has not been fully elucidated in acute myeloid leukemia (AML). To explore the role of ACOT2 in AML and to provide a potential therapeutic target for AML, the expression pattern of ACOT was investigated based on the TNMplot, Gene Expression Profiling Interactive Analysis (GEPIA), and Cancer Cell Line Encyclopedia (CCLE) database, and diagnostic value, prognostic value, and clinical phenotype of ACOT were explored based on data from The Cancer Genome Atlas (TCGA). Functional annotation and enrichment analysis of the common targets between ACOT2 coexpressed and AML-related genes were further performed by Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Gene Set Enrichment Analysis (GSEA) analyses. The protein-protein interaction (PPI) network of ACOT2 coexpressed genes and functional ACOT2-related metabolites association network were constructed based on GeneMANIA and Human Metabolome Database. Among ACOTs, ACOT2 was highly expressed in AML compared to normal control subjects according to TNMplot, GEPIA, and CCLE database, which was significantly associated with poor overall survival (OS) in AML ( $P=0.003$ ). Moreover, ACOT2 exhibited excellent diagnostic efficiency for AML (AUC: 1.000) and related to French-American-British (FAB) classification and cytogenetics. GO, KEGG, and GSEA analyses of 71 common targets between ACOT2 coexpressed and AML-related genes revealed that ACOT2 is closely related to ACOT1, ACOT4, enoyl-acyl carrier protein reductase, mitochondrial (MECR), puromycin-sensitive aminopeptidase (NPEPPS), SWI/SNF-related matrix-associated actin-dependent regulator of chromatin subfamily B member 1 (SMARCB1), and long-chain fatty acid-CoA ligase 1 (ACSL1) in PPI network, and plays a significant role in lipid metabolism, that is, involved in fatty acid elongation and biosynthesis of unsaturated fatty acids. Collectively, the increase of ACOT2 may be an important characteristic of worse OS and abnormal lipid metabolism, suggesting that ACOT2 may become a potential therapeutic target for AML.

"Dual-Key-and-Lock" dual drug carrier for dual mode imaging guided chemo-photothermal therapy

Drug resistance and side effects are the two main problems of chemotherapy. In order to address these big challenges, p-PB@d-SiO₂, which has the ability to co-deliver both the hydrophobic drug doxorubicin hydrochloride (DOX) and the hydrophilic drug ibuprofen (IBU), is constructed to achieve synergistic treatment. The drug-loaded nanoparticle consists of porous Prussian blue (p-PB) as the core and dendrimer-like SiO₂ (d-SiO₂) as the shell, which is further thiolated and coated with polyethylene glycol thiol (HS-PEG) to form the "Dual-Key-and-Lock" drug carrier p-PB@d-SiO₂-SS-PEG. The locked drugs can only be released in the presence of cooperative triggers, i.e., a high glutathione concentration (the first key) and an acidic environment (the second key). The "dual key"-triggered release is much more significant in cancer lesions than in normal tissues, reducing side effects. Furthermore, cell viability experiments highlight the superior therapeutic efficacy of the dual-drug-loaded nanoparticles compared with the single-drug systems (60%, 73% and 86% vs. 56%, 68%, and 76% at 100, 200 and 500 μg mL^-1, respectively). In vitro and in vivo experiments demonstrate the potential application of p-PB@d-SiO₂-SS-PEG for dual-mode fluorescence and magnetic-resonance-imaging-guided chemo-photothermal therapy. The "Dual-Key-and-Lock" drug carrier system exhibits the "1 + 1 > 2" effect, demonstrating its excellent performance in synergy therapy for improved therapeutic efficiency and thereby reducing conventional drug resistance and side effects.

Study on the determination and chiral inversion of R-salbutamol in human plasma and urine by liquid chromatography-tandem mass spectrometry

The chiral inversion has been a concerned issue during the research and development of a chiral drug. In this study, a sensitive chiral liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for determination of salbutamol enantiomers in human plasma and urine. The chiral inversion mechanism of R-salbutamol was fully investigated for the first time by studying the effects of physicochemical factors, including pH, temperature and time. A fitted model to predict the chiral inversion ratio of R-salbutamol was proposed using a Box-Behnken design. All the samples were separated on an Astec Chirobiotic T column and detected by a tandem mass spectrometer in multiple reaction monitoring mode. Lower limit of quantification of 0.100ng/mL was achieved under the optimized conditions. The method was fully validated and successfully applied to the clinical pharmacokinetic study of R-salbutamol in healthy volunteers. Chiral inversion of R-salbutamol to S-salbutamol has been detected in urine samples. The results indicated that pH and temperature were two dominant factors that caused the chiral inversion of R-salbutamol, which should be taken into consideration during the analysis of chiral drugs. The chiral inversion of R-salbutamol determined in this study was confirmed resulted from the gastric acid in stomach rather than caused by the analysis conditions. Moreover, the calculated results of the fitted model matched very well with the enantioselective pharmacokinetic study of R-salbutamol, and the individual difference of the chiral inversion ratio of R-salbutamol was related to the individual gastric environment. On the basis of the results, this study provides important and concrete information not only for the chiral analysis but also for the metabolism research of chiral drugs.

A study on the chiral inversion of mandelic acid in humans

Mandelic acid is a chiral metabolite of the industrial pollutant styrene and is used in chemical skin peels, as a urinary antiseptic and as a component of other medicines. In humans, S-mandelic acid undergoes rapid chiral inversion to R-mandelic acid by an undefined pathway but it has been proposed to proceed via the acyl-CoA esters, S- and R-2-hydroxy-2-phenylacetyl-CoA, in an analogous pathway to that for Ibuprofen. This study investigates chiral inversion of mandelic acid using purified human recombinant enzymes known to be involved in the Ibuprofen chiral inversion pathway. Both S- and R-2-hydroxy-2-phenylacetyl-CoA were hydrolysed to mandelic acid by human acyl-CoA thioesterase-1 and -2 (ACOT1 and ACOT2), consistent with a possible role in the chiral inversion pathway. However, human α-methylacyl-CoA racemase (AMACR; P504S) was not able to catalyse exchange of the α-proton of S- and R-2-hydroxy-2-phenylacetyl-CoA, a requirement for chiral inversion. Both S- and R-2-phenylpropanoyl-CoA were epimerised by AMACR, showing that it is the presence of the hydroxy group that prevents epimerisation of R- and S-2-hydroxy-2-phenylacetyl-CoAs. The results show that it is unlikely that 2-hydroxy-2-phenylacetyl-CoA is an intermediate in the chiral inversion of mandelic acid, and that the chiral inversion of mandelic acid is via a different pathway to that of Ibuprofen and related drugs.