Haemagglutinin mutations and glycosylation changes shaped the 2012/13 influenza A(H3N2) epidemic, Houston, Texas

While the early start and higher intensity of the 2012/13 influenza A virus (IAV) epidemic was not unprecedented, it was the first IAV epidemic season since the 2009 H1N1 influenza pandemic where the H3N2 subtype predominated. We directly sequenced the genomes of 154 H3N2 clinical specimens collected throughout the epidemic to better understand the evolution of H3N2 strains and to inform the H3N2 vaccine selection process. Phylogenetic analyses indicated that multiple co-circulating clades and continual antigenic drift in the haemagglutinin (HA) of clades 5, 3A, and 3C, with the evolution of a new 3C subgroup (3C-2012/13), were the driving causes of the epidemic. Drift variants contained HA substitutions and alterations in the potential N-linked glycosylation sites of HA. Antigenic analysis demonstrated that viruses in the emerging subclade 3C.3 and subgroup 3C-2012/13 were not well inhibited by antisera generated against the 3C.1 vaccine strains used for the 2012/13 (A/Victoria/361/2011) or 2013/14 (A/Texas/50/2012) seasons. Our data support updating the H3N2 vaccine strain to a clade 3C.2 or 3C.3-like strain or a subclade that has drifted further. They also underscore the challenges in vaccine strain selection, particularly regarding HA and neuraminidase substitutions derived during laboratory passage that may alter antigenic testing accuracy.

Mechanistic studies on the reversible metabolism of rofecoxib to 5-hydroxyrofecoxib in the rat: evidence for transient ring opening of a substituted 2-furanone derivative using stable isotope-labeling techniques

Rofecoxib is a potent and highly selective cyclooxygenase-2 inhibitor used for the treatment of osteoarthritis and pain. Following administration of [4-(14)C]rofecoxib to intact rats, the plasma C(max) (at approximately 1 h) was followed by a secondary C(max) (at approximately 10 h), which was not observed in bile duct-cannulated rats. Following administration of [4-(14)C]5-hydroxyrofecoxib to intact or bile duct-cannulated rats, radiolabeled rofecoxib was detected in plasma, and once again a secondary C(max) for rofecoxib was observed (at approximately 10 h), which occurred only in the intact animals. These results indicate that reversible metabolism of rofecoxib to 5-hydroxyrofecoxib occurs in the rat and that the process is dependent upon an uninterrupted bile flow. Studies on the contents of the gastrointestinal tract of rats showed that conversion of 5-hydroxyrofecoxib to parent compound occurs largely in the lower intestine. Treatment of rats with [5-(18)O]5-hydroxyrofecoxib, followed by liquid chromatography-tandem mass spectrometry analyses of plasma samples, confirmed that 5-hydroxyrofecoxib undergoes metabolism to the parent drug, yielding [1-(18)O]rofecoxib, [2-(18)O]rofecoxib, and unlabeled rofecoxib. Similarly, treatment with [1,2-(18)O(2)]rofecoxib afforded the same three isotopic variants of rofecoxib. These findings are consistent with a metabolic sequence involving 5-hydroxylation of rofecoxib, biliary elimination of the corresponding glucuronide, and deconjugation of the glucuronide in the lower gastrointestinal tract. Reduction of the 5-hydroxyrofecoxib thus liberated yields a hydroxyacid that cyclizes spontaneously to regenerate rofecoxib, which is reabsorbed and enters the systemic circulation. This sequence represents a novel form of enterohepatic recycling and reflects the susceptibility of 5-hydroxyrofecoxib, as well as rofecoxib itself, to reversible 2-furanone ring opening under in vivo conditions.

Role of human liver cytochrome P4503A in the metabolism of etoricoxib, a novel cyclooxygenase-2 selective inhibitor

Etoricoxib, a potent and selective cyclooxygenase-2 inhibitor, was shown to be metabolized via 6'-methylhydroxylation (M2 formation) when incubated with NADPH-fortified human liver microsomes. In agreement with in vivo data, 1'-N'-oxidation was a relatively minor pathway. Over the etoricoxib concentration range studied (1-1300 microM), the rate of hydroxylation conformed to saturable Michaelis-Menten kinetics (apparent K(m) = 186 +/- 84.3 microM; V(max) = 0.76 +/- 0.45 nmol/min/mg of protein; mean +/- S.D., n = 3 livers) and yielded a V(max)/K(m) ratio of 2.4 to 7.3 microl/min/mg. This in vitro V(max)/K(m) ratio was scaled, with respect to yield of liver microsomal protein and liver weight, to obtain estimates of M2 formation clearance (3.1-9.7 ml/min/kg of b.wt.) that agreed favorably with in vivo results (8.3 ml/min/kg of b.wt.) following i.v. administration of [(14)C]etoricoxib to healthy male subjects. Cytochrome P450 (P450) reaction phenotyping studies-using P450 form selective chemical inhibitors, immunoinhibitory antibodies, recombinant P450s, and correlation analysis with microsomes prepared from a bank of human livers-revealed that the 6'-methyl hydroxylation of etoricoxib was catalyzed largely (approximately 60%) by member(s) of the CYP3A subfamily. By comparison, CYP2C9 (approximately 10%), CYP2D6 (approximately 10%), CYP1A2 (approximately 10%), and possibly CYP2C19 played an ancillary role. Moreover, etoricoxib (0.1-100 microM) was found to be a relatively weak inhibitor (IC(50) > 100 microM) of multiple P450s (CYP1A2, CYP2D6, CYP3A, CYP2E1, CYP2C9, and CYP2C19) in human liver microsomes.

The absorption, distribution, metabolism and excretion of rofecoxib, a potent and selective cyclooxygenase-2 inhibitor, in rats and dogs

Absorption, distribution, metabolism, and excretion studies were conducted in rats and dogs with rofecoxib (VIOXX, MK-0966), a potent and highly selective inhibitor of cyclooxygenase-2 (COX-2). In rats, the nonexponential decay during the terminal phase (4- to 10-h time interval) of rofecoxib plasma concentration versus time curves after i.v. or oral administration of [(14)C]rofecoxib precluded accurate determinations of half-life, AUC(0-infinity) (area under the plasma concentration versus time curve extrapolated to infinity), and hence, bioavailability. After i.v. administration of [(14)C]rofecoxib to dogs, plasma clearance, volume of distribution at steady state, and elimination half-life values of rofecoxib were 3.6 ml/min/kg, 1.0 l/kg, and 2.6 h, respectively. Oral absorption (5 mg/kg) was rapid in both species with C(max) occurring by 0.5 h (rats) and 1.5 h (dogs). Bioavailability in dogs was 26%. Systemic exposure increased with increasing dosage in rats and dogs after i.v. (1, 2, and 4 mg/kg), or oral (2, 5, and 10 mg/kg) administration, except in rats where no additional increase was observed between the 5 and 10 mg/kg doses. Radioactivity distributed rapidly to tissues, with the highest concentrations of the i.v. dose observed in most tissues by 5 min and by 30 min in liver, skin, fat, prostate, and bladder. Excretion occurred primarily by the biliary route in rats and dogs, except after i.v. administration of [(14)C]rofecoxib to dogs, where excretion was divided between biliary and renal routes. Metabolism of rofecoxib was extensive. 5-Hydroxyrofecoxib-O-beta-D-glucuronide was the major metabolite excreted by rats in urine and bile. 5-Hydroxyrofecoxib, rofecoxib-3',4'-dihydrodiol, and 4'-hydroxyrofecoxib sulfate were less abundant, whereas cis- and trans-3,4-dihydro-rofecoxib were minor. Major metabolites in dog were 5-hydroxyrofecoxib-O-beta-D-glucuronide (urine), trans-3, 4-dihydro-rofecoxib (urine), and 5-hydroxyrofecoxib (bile).

Disposition and pharmacokinetics of the antimigraine drug, rizatriptan, in humans

The absorption and disposition of rizatriptan (MK-0462, Maxalt(TM)), a selective 5-HT(1B/1D) receptor agonist used in the treatment of migraine headaches, was investigated in humans. In a two-period, single i.v. (3 mg, 30-min infusion), and single oral (10 mg) dose study with [(14)C]rizatriptan in six healthy human males, total recovery of radioactivity was approximately 94%, with unchanged rizatriptan and its metabolites being excreted mainly in the urine (89% i.v. dose, 82% p.o. dose). Approximately 26 and 14% of i.v. and oral rizatriptan doses, respectively, were excreted in urine as intact parent drug. In a second, high-dose study (60 mg p.o.), five metabolites excreted into urine were identified using liquid chromatography-tandem mass spectrometry and NMR methods. They were triazolomethyl-indole-3-acetic acid, rizatriptan-N(10)-oxide, 6-hydroxy-rizatriptan, 6-hydroxy-rizatriptan sulfate, and N(10)-monodesmethyl-rizatriptan. Urinary excretion of triazolomethyl-indole-3-acetic acid after i.v. and oral administrations of rizatriptan accounted for 35 and 51% of the dose, respectively, whereas the corresponding values for rizatriptan-N(10)-oxide were 4 and 2% of the dose. Plasma clearance (CL) and renal clearance (CL(r)) were 1325 and 349 ml/min, respectively, after i.v. administration. A similar CL(r) value was obtained after oral administration (396 ml/min). The primary route of rizatriptan elimination occurred via nonrenal route(s) (i.e., metabolism) because the CL(r) of rizatriptan accounted for 25% of total CL. Furthermore, the CL(r) was higher than normal glomerular filtration rate ( approximately 130 ml/min), indicating that this compound was actively secreted by renal tubules. The absorption of rizatriptan was approximately 90%, but it experienced a moderate first-pass effect, resulting in a bioavailability estimate of 47%.

Development of orally active oxytocin antagonists: studies on 1-(1-[4-[1-(2-methyl-1-oxidopyridin-3-ylmethyl)piperidin-4-yloxy]-2- methoxybenzoyl]piperidin-4-yl)-1,4-dihydrobenz[d][1,3]oxazin-2-one (L-372,662) and related pyridines

The previously reported oxytocin antagonist L-371,257 (2) has been modified at its acetylpiperidine terminus to incorporate various pyridine N-oxide groups. This modification has led to the identification of compounds with improved pharmacokinetics and excellent oral bioavailability. The pyridine N-oxide series is exemplified by L-372,662 (30), which possessed good potency in vitro (Ki = 4.1 nM, cloned human oxytocin receptor) and in vivo (intravenous AD50 = 0.71 mg/kg in the rat), excellent oral bioavailability (90% in the rat, 96% in the dog), good aqueous solubility (>8.5 mg/mL at pH 5.2) which should facilitate formulation for iv administration, and excellent selectivity against the human arginine vasopressin receptors. Incorporation of a 5-fluoro substituent on the central benzoyl ring of this class of oxytocin antagonists enhanced in vitro and in vivo potency but was detrimental to the pharmacokinetic profiles of these compounds. Although lipophilic substitution around the pyridine ring of compound 30 gave higher affinity in vitro, such substituents were a metabolic liability and caused shortfalls in vivo. Two approaches to prevent this metabolism, addition of a cyclic constraint and incorporation of trifluoromethyl groups, were examined. The former approach was ineffective because of metabolic hydroxylation on the constrained ring system, whereas the latter showed improvement in plasma pharmacokinetics in some cases.

Quantitation of the 5HT1D agonists MK-462 and sumatriptan in plasma by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry

The 5HT1D agonist sumatriptan is efficacious in the treatment of migraines. MK-462 is a drug of the same class which is under development in our laboratories. Bioanalytical methods of high efficiency, specificity and sensitivity were required to support the preclinical and clinical programs. These assays were based on HPLC with tandem MS-MS detection. MK-462 and sumatriptan were extracted using an automated solid-phase extraction technique on a C2 Varian Bond-Elut cartridge. The n-diethyl analogues of MK-462 and sumatriptan were used as internal standards. The analytes were chromatographed using reversed-phase (nitrile) columns coupled via a heated nebulizer interface to an atmospheric pressure chemical ionization source. The chromatographic run times were less than 7 min. Both methods were precise, accurate and selective down to plasma concentrations of 0.5 ng/ml. The assay for MK-462 was adapted to separately monitor the unlabeled and 14C-labeled species of the drug following intravenous administration of radiolabeled material to man.

Biotransformation of lovastatin. V. Species differences in in vivo metabolite profiles of mouse, rat, dog, and human

Lovastatin is a prodrug lactone whose open-chain 3,5-dihydroxy acid is a potent, competitive inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, the rate-limiting enzyme in cholesterol biosynthesis. The compound undergoes extensive and complex metabolism in animals and humans, with the metabolites excreted predominantly in bile. Radiochromatograms of bile from three human subjects and of bile and liver homogenates from mouse, rat, and dog displayed obvious species differences. Biotransformation of lovastatin occurred by three distinct routes, namely hydrolysis of the lactone ring to yield the pharmacologically active dihydroxy acid, cytochrome P-450-mediated oxidation of the fused-ring system, and beta-oxidation of the dihydroxy acid side chain. The first two reactions occurred in all four species, but the last was observed in mouse and rat only. The P-450 reactions, hydroxylation and a novel dehydrogenation reaction, yielded a 6'-hydroxylated metabolite of the dihydroxy acid and a 6'-exomethylene derivative as major and minor metabolites, respectively, in the bile of rat and dog. Human bile, which contained predominantly polar metabolites, yielded these metabolites in similar proportions only after mild hydrolysis at pH 5.0. In mouse and rat an atypical beta-oxidation of the dihydroxy acid side chain occurred to give a pentanoic acid derivative that was observed in liver homogenates. This metabolite was subsequently conjugated with taurine and excreted in the bile. From these studies, cytochrome P-450 oxidation is the primary route of phase I metabolism for lovastatin in human and dog, but beta-oxidation plays a major metabolic role in rodents.

Biotransformation of lovastatin. I. Structure elucidation of in vitro and in vivo metabolites in the rat and mouse

Structures of in vitro microsomal and in vivo metabolites of lovastatin, a new cholesterol-lowering drug, were elucidated with the combined application of HPLC, UV, fast atom bombardment-MS, and NMR spectroscopy. Liver microsomes from rats and mice catalyzed the biotransformation of lovastatin, primarily at the 6'-position of the molecule, to form 6'-hydroxy-lovastatin and a novel 6'-exomethylene derivative. Hydroxylation at the 6'-position occurred stereoselectively, giving 6'-beta-hydroxy-lovastatin. Stereoselective hydroxylation at the 3"-position of the methylbutyryl side chain and hydrolysis of the lactone group to the corresponding hydroxy acid were the other two pathways of microsomal metabolism. 3'-Hydroxy-iso-delta 4',5'-lovastatin was isolated, but is not believed to be a direct metabolite since 6'-beta-hydroxy-lovastatin rearranges to this compound under mildly acidic conditions. The major metabolites excreted in bile of rats treated with the hydroxy acid form of the drug were identified as the 3'-hydroxy analog and a taurine conjugate of a beta-oxidation product of lovastatin. The pentanoic acid derivative of lovastatin, formed by beta-oxidation of the heptanoic acid moiety, was a major metabolite in livers of mice dosed with the hydroxy acid form of lovastatin. The microsomal metabolites, in their hydroxy acid forms, were active inhibitors of HMG-CoA reductase. The relative enzyme inhibitory activities of hydroxy acid forms of lovastatin, 6'-beta-hydroxy-, 6'-exomethylene-, and 3"-hydroxy-lovastatin were 1, 0.6, 0.5, and 0.15, respectively.

The physiological disposition of lovastatin

Lovastatin is a pro-drug lactone whose open chain beta-hydroxy-acid (HA) is a potent inhibitor of hydroxymethylglutaryl-CoA-reductase and thus of cholesterol synthesis. Because the liver is the major site of cholesterolgenesis, it is the principal target organ for agents of this class. In animals, lovastatin is not as well absorbed as HA given per se, but that fraction that is absorbed reaches the portal circulation largely unchanged and is more efficiently extracted by the liver, after which it is reversibly biotransformed to HA and irreversibly to other enzymatically active products. These, like HA, maintain high hepatic gradients relative to all tissues examined. The minimal systemic burden for HA is attributable in part to the metabolic equilibrium, lovastatin in equilibrium HA, the opposing reactions for which appear to be present in most tissues. Excretion is very largely biliary in all species. Detailed comparisons of absorption, distribution, metabolism, and excretion profiles presented here and elsewhere indicate dogs to be the most appropriate paradigm for humans for study of lovastatin disposition.

Metabolism and hepatotoxicity of the naturally occurring benzo[b]pyran precocene I

The in vitro metabolism of precocene I by liver microsomes from control and treated rats and the effects of precocene I on the function and histology of the rat liver were examined. The major metabolites (80-90% of total metabolites) from all microsomal preparations were the cis and trans 3,4-diols of precocene I produced with a cis/trans isomer ratio of 1:2. These diols appear to arise mainly by spontaneous hydrolysis of precocene I 3,4-oxide. (+)-(3R,4R)-cis- and (-)-(3R,4S)-trans-precocene I 3,4-diols were the predominant enantiomers of the 3,4-diol formed. The enantiomeric excess of these diols (2-50%) is dependent on the microsomal preparation, with microsomes from control rats exhibiting the highest stereoselectivity and microsomes from phenobarbital-treated rats the least. 6-Hydroxyprecocene I was the next major metabolite and was formed to the extent of 5% (control), 10% and 17% (phenobarbital and 3-methylcholanthrene treatment, respectively) of total metabolites. Treatment of rats with a single i.p. dose of precocene I (300 mg/kg) resulted in extensive hepatic damage as evidenced by a marked increase of plasma glutamic pyruvic transaminase levels and histologic observation in liver sections of severe centrolobular necrosis. Although phenobarbital treatment of rats increased the rate of liver microsomal metabolism of precocene I by approximately 50% (nmol products/nmol cytochrome P-450/min) compared to liver microsomes from control rats, hepatic damage caused by precocene I was not significantly affected. Depletion of glutathione levels in the rats with diethyl maleate prior to precocene I treatment dramatically increased the severity of hepatic insult, whereas treatment of the rats with the mixed function oxidase inhibitor piperonyl butoxide prior to treatment with precocene I blocked hepatic damage. Treatment of rats with cysteamine prior to treatment with precocene I protected the animals against the toxic effects. Neither cis nor trans precocene I 3,4-diol nor 3,4-dihydroprecocene I elicited impaired liver function or cellular damage. The above results are consistent with the view that precocene I 3,4-oxide is the metabolite responsible for the hepatotoxic effects observed when precocene I is injected into rats.