mobic and sudoxicam

Meloxicam is a thiazole-containing NSAID that was approved for marketing with favorable clinical outcomes despite being structurally similar to the hepatotoxic sudoxicam. Introduction of a single methyl group on the thiazole results in an overall lower toxic risk, yet the group's impact on P450 isozyme bioactivation is unclear. Through analytical methods, we used inhibitor phenotyping and recombinant P450s to identify contributing P450s, and then measured steady-state kinetics for bioactivation of sudoxicam and meloxicam by the recombinant P450s to determine relative efficiencies. Experiments showed that CYP2C8, 2C19, and 3A4 catalyze sudoxicam bioactivation, and CYP1A2 catalyzes meloxicam bioactivation, indicating that the methyl group not only impacts enzyme affinity for the drugs, but also alters which isozymes catalyze the metabolic pathways. Scaling of relative P450 efficiencies based on average liver concentration revealed that CYP2C8 dominates the sudoxicam bioactivation pathway and CYP2C9 dominates meloxicam detoxification. Dominant P450s were applied for an informatics assessment of electronic health records to identify potential correlations between meloxicam drug-drug interactions and drug-induced liver injury. Overall, our findings provide a cautionary tale on assumed impacts of even simple structural modifications on drug bioactivation while also revealing specific targets for clinical investigations of predictive factors that determine meloxicam-induced idiosyncratic liver injury.

Topics: Activation, Metabolic; Anti-Inflammatory Agents, Non-Steroidal; Chemical and Drug Induced Liver Injury; Cytochrome P-450 CYP1A2; Cytochrome P-450 CYP2C8; Cytochrome P-450 CYP2C9; Data Mining; Deep Learning; Drug Interactions; Electronic Health Records; Female; Humans; Inactivation, Metabolic; Kinetics; Male; Meloxicam; Microsomes, Liver; Middle Aged; Substrate Specificity; Thiazines

Thiazoles are biologically active aromatic heterocyclic rings occurring frequently in natural products and drugs. These molecules undergo typically harmless elimination; however, a hepatotoxic response can occur due to multistep bioactivation of the thiazole to generate a reactive thioamide. A basis for those differences in outcomes remains unknown. A textbook example is the high hepatotoxicity observed for sudoxicam in contrast to the relative safe use and marketability of meloxicam, which differs in structure from sudoxicam by the addition of a single methyl group. Both drugs undergo bioactivation, but meloxicam exhibits an additional detoxification pathway due to hydroxylation of the methyl group. We hypothesized that thiazole bioactivation efficiency is similar between sudoxicam and meloxicam due to the methyl group being a weak electron donator, and thus, the relevance of bioactivation depends on the competing detoxification pathway. For a rapid analysis, we modeled epoxidation of sudoxicam derivatives to investigate the impact of substituents on thiazole bioactivation. As expected, electron donating groups increased the likelihood for epoxidation with a minimal effect for the methyl group, but model predictions did not extrapolate well among all types of substituents. Through analytical methods, we measured steady-state kinetics for metabolic bioactivation of sudoxicam and meloxicam by human liver microsomes. Sudoxicam bioactivation was 6-fold more efficient than that for meloxicam, yet meloxicam showed a 6-fold higher efficiency of detoxification than bioactivation. Overall, sudoxicam bioactivation was 15-fold more likely than meloxicam considering all metabolic clearance pathways. Kinetic differences likely arise from different enzymes catalyzing respective metabolic pathways based on phenotyping studies. Rather than simply providing an alternative detoxification pathway, the meloxicam methyl group suppressed the bioactivation reaction. These findings indicate the impact of thiazole substituents on bioactivation is more complex than previously thought and likely contributes to the unpredictability of their toxic potential.

Topics: Activation, Metabolic; Biotransformation; Chemical and Drug Induced Liver Injury; Electrons; Epoxy Compounds; Humans; Hydroxylation; In Vitro Techniques; Kinetics; Meloxicam; Metabolic Networks and Pathways; Microsomes, Liver; Thiazines; Thiazoles

In vitro covalent binding assessments of drugs have been useful in providing retrospective insights into the association between drug metabolism and a resulting toxicological response. On the basis of these studies, it has been advocated that in vitro covalent binding to liver microsomal proteins in the presence and the absence of NADPH be used routinely to screen drug candidates. However, the utility of this approach in predicting toxicities of drug candidates accurately remains an unanswered question. Importantly, the years of research that have been invested in understanding metabolic bioactivation and covalent binding and its potential role in toxicity have focused only on those compounds that demonstrate toxicity. Investigations have not frequently queried whether in vitro covalent binding could be observed with drugs with good safety records. Eighteen drugs (nine hepatotoxins and nine nonhepatotoxins in humans) were assessed for in vitro covalent binding in NADPH-supplemented human liver microsomes. Of the two sets of nine drugs, seven in each set were shown to undergo some degree of covalent binding. Among hepatotoxic drugs, acetaminophen, carbamazepine, diclofenac, indomethacin, nefazodone, sudoxicam, and tienilic acid demonstrated covalent binding, while benoxaprofen and felbamate did not. Of the nonhepatotoxic drugs evaluated, buspirone, diphenhydramine, meloxicam, paroxetine, propranolol, raloxifene, and simvastatin demonstrated covalent binding, while ibuprofen and theophylline did not. A quantitative comparison of covalent binding in vitro intrinsic clearance did not separate the two groups of compounds, and in fact, paroxetine, a nonhepatotoxin, showed the greatest amount of covalent binding in microsomes. Including factors such as the fraction of total metabolism comprised by covalent binding and the total daily dose of each drug improved the discrimination between hepatotoxic and nontoxic drugs based on in vitro covalent binding data; however, the approach still would falsely identify some agents as potentially hepatotoxic.

Topics: Acetaminophen; Binding Sites; Buspirone; Carbamazepine; Diclofenac; Diphenhydramine; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Hepatocytes; Humans; Indomethacin; Meloxicam; Microsomes, Liver; Molecular Structure; Paroxetine; Piperazines; Propranolol; Raloxifene Hydrochloride; Simvastatin; Structure-Activity Relationship; Thiazines; Thiazoles; Ticrynafen; Toxicity Tests; Triazoles

Sudoxicam and meloxicam are nonsteroidal anti-inflammatory drugs (NSAIDs) from the enol-carboxamide class. While the only structural difference between the two NSAIDs is the presence of a methyl group on the C5-position of the 2-carboxamidothiazole motif in meloxicam, a marked difference in their toxicological profile in humans has been discerned. In clinical trials, sudoxicam was associated with several cases of severe hepatotoxicity that led to its discontinuation, while meloxicam has been in the market for over a decade and is devoid of hepatotoxicity. In an attempt to understand the biochemical basis for the differences in safety profile, an in vitro investigation of the metabolic pathways and covalent binding of the two NSAIDs was conducted in NADPH-supplemented human liver microsomes. Both compounds demonstrated NADPH-dependent covalent binding to human liver microsomes; however, the extent of binding of [(14)C]-meloxicam was approximately 2-fold greater than that of [(14)C]-sudoxicam. While inclusion of glutathione (GSH) in microsomal incubations resulted in a decrease in covalent binding for both NSAIDs, the reduction in binding was more pronounced for meloxicam. Metabolite identification studies on [(14)C]-sudoxicam in NADPH-supplemented human liver microsomes indicated that the primary route of metabolism involved a P450-mediated thiazole ring scission to the corresponding acylthiourea metabolite (S3), a well-established pro-toxin. The mechanism of formation of S3 presumably proceeds via (a) epoxidation of the C4-C5-thiazole ring double bond, (b) epoxide hydrolysis to the corresponding thiazole-4,5-dihydrodiol derivative, which was observed as a stable metabolite (S2), (c) ring opening of the thiazole-4,5-dihydrodiol to an 2-oxoethylidene thiourea intermediate, and (d) hydrolysis of the imine bond within this intermediate to yield S3. In the case of meloxicam, the corresponding acylthiourea metabolite M3 was also observed, but to a lesser extent; the main route of meloxicam metabolism involved hydroxylation of the 5'-methyl group, a finding that is consistent with the known metabolic fate of this NSAID. Inclusion of GSH led to a decrease in the formation of M3 with the concomitant formation of an unusual two-electron reduction product (metabolite M7). The formation of M7 is proposed to arise via reduction of the imine bond in 2-oxopropylidene thiourea, an intermediate in the thiazole ring scission pathway in meloxicam. In conclusion, the results

Topics: Amides; Anti-Inflammatory Agents, Non-Steroidal; Binding Sites; Hepatocytes; Humans; Ketones; Meloxicam; Microsomes, Liver; Molecular Structure; Stereoisomerism; Structure-Activity Relationship; Thiazines; Thiazoles