Evaluation of amino acid-based linkers in potent macrocyclic inhibitors of farnesyl-protein transferase

A series of amino acid-based linkers was used to investigate the effects of various substituents upon the potency, pharmacokinetic properties, and conformation of macrocyclic farnesyl-protein transferase inhibitors (FTIs). As a result of the studies described herein, highly potent FTIs with improved pharmacokinetic profiles have been identified.

Influence of beta-adrenoceptor antagonists on the pharmacokinetics of rizatriptan, a 5-HT1B/1D agonist: differential effects of propranolol, nadolol and metoprolol

AIMS

Patients with migraine may receive the 5-HT1B/1D agonist, rizatriptan (5 or 10 mg), to control acute attacks. Patients with frequent attacks may also receive propranolol or other beta-adrenoceptor antagonists for migraine prophylaxis. The present studies investigated the potential for pharmacokinetic or pharmacodynamic interaction between beta-adrenoceptor blockers and rizatriptan.

METHODS

Four double-blind, placebo-controlled, randomized crossover investigations were performed in a total of 51 healthy subjects. A single 10 mg dose of rizatriptan was administered after 7 days' administration of propranolol (60 and 120 mg twice daily), nadolol (80 mg twice daily), metoprolol (100 mg twice daily) or placebo. Rizatriptan pharmacokinetics were assessed. In vitro incubations of rizatriptan and sumatriptan with various beta-adrenoceptor blockers were performed in human S9 fraction. Production of the indole-acetic acid-MAO-A metabolite of each triptan was measured.

RESULTS

Administration of rizatriptan during propranolol treatment (120 mg twice daily for 7.5 days) increased the AUC(0, infinity) for rizatriptan by approximately 67% and the Cmax by approximately 75%. A reduction in the dose of propranolol (60 mg twice daily) and/or the incorporation of a delay (1 or 2 h) between propranolol and rizatriptan administration did not produce a statistically significant change in the effect of propranolol on rizatriptan pharmacokinetics. Administration of rizatriptan together with nadolol (80 mg twice daily) or metoprolol (100 mg twice daily) for 7 days did not significantly alter the pharmacokinetics of rizatriptan. No untoward adverse experiences attributable to the pharmacokinetic interaction between propranolol and rizatriptan were observed, and no subjects developed serious clinical, laboratory, or other significant adverse experiences during coadministration of rizatriptan with any of the beta-adrenoceptor blockers. In vitro incubations showed that propranolol, but not other beta-adrenoceptor blockers significantly inhibited the production of the indole-acetic acid metabolite of rizatriptan and sumatriptan.

CONCLUSIONS

These results suggest that propranolol increases plasma concentrations of rizatriptan by inhibiting monoamine oxidase-A. When prescribing rizatriptan to migraine patients receiving propranolol for prophylaxis, the 5 mg dose of rizatriptan is recommended. Administration with other beta-adrenoceptor blockers does not require consideration of a dose adjustment.

Plasma timolol concentrations of timolol maleate: timolol gel-forming solution (TIMOPTIC-XE) once daily versus timolol maleate ophthalmic solution twice daily

PURPOSE

The objective of this study was to compare plasma concentrations of timolol following multiple dosing of the therapeutic regimens of timolol maleate ophthalmic gel-forming solution (Timolol GS; TIMOPTIC-XE) and timolol maleate ophthalmic solution. Timolol maleate ophthalmic gel-forming solution is also referred to as Timolol GS, i.e. gel-forming solution.

METHODS

This was a masked observer, two-period crossover study in six normal male subjects randomized to receive either Timolol GS, 0.5% (TIMOPTIC-XE,) once daily (0530 hours) or timolol maleate ophthalmic solution (0.5% TIMOPTIC) twice daily (0530 and 1730 hours) for 8 days, in both eyes. On Day 8, a blood sample was obtained prior to treatment, as well as 1, 2, 4, 8, 10, 12, 13, 14, 16, and 24 hours following the morning instillation. After a 7-day inter-period washout interval, subjects received the opposite treatment.

RESULTS

Timolol GS (TIMOPTIC-XE): Plasma concentrations of timolol rarely exceeded 0.375 ng/ml (the lower limit of assay quantification). For all subjects, peak plasma concentrations of timolol averaged <0.3 ng/ml within 4 hours after the last dose. The highest single observation was 0.49 ng/ml in one subject (at hour 2). Timolol solution: For all subjects, peak plasma concentrations of timolol averaged about 0.5 ng/ml and 0.3 ng/ml within 4 hours following the first and second dose, respectively, on Day 8. The highest single observation was 0.95 ng/ml in one subject (at hour 2).

CONCLUSIONS

The data suggest that there is less systemic exposure to timolol following once-daily therapy with Timolol GS 0.5% compared with twice daily therapy with timolol maleate ophthalmic solution 0.5%.

Oxo-piperazine derivatives of N-arylpiperazinones as inhibitors of farnesyltransferase

The evaluation of SAR associated with the insertion of carbonyl groups at various positions of N-arylpiperazinone farnesyltransferase inhibitors is described herein. 1-Aryl-2,3-diketopiperazine derivatives exhibited the best balance of potency and pharmacokinetic profile relative to the parent 1-aryl-2-piperazinones.

Synthesis of conformationally constrained 5,6,7, 8-Tetrahydroimidazo[1,5-a]pyridine inhibitors of farnesyltransferase

[reaction: see text] Synthesis of the 8-amino-5,6,7,8-tetrahydroimidazo[1,5-a]pyridine ring system was accomplished by intramolecular cyclization of an iminium ion, derived from condensation of an amine and a substituted gamma-(1-imidazolyl)butyraldehyde. The reaction was used to produce conformationally restricted farnesyltransferase inhibitor analogues which exhibit improved in vivo metabolic stability.

Combinatorial diversification of indinavir: in vivo mixture dosing of an HIV protease inhibitor library

An efficient combination solution-phase/solid-phase route enabling the diversification of the P1', P2', and P3 subsites of indinavir has been established. The synthetic sequence can facilitate the rapid generation of HIV protease inhibitors possessing more favorable pharmacokinetic properties as well as enhanced potencies. Multiple compound dosing in vivo may also accelerate the identification of potential drug candidates.

In vitro and in vivo evaluation of dihydropyrimidinone C-5 amides as potent and selective alpha(1A) receptor antagonists for the treatment of benign prostatic hyperplasia

alpha(1) Adrenergic receptors mediate both vascular and lower urinary tract tone, and alpha(1) receptor antagonists such as terazosin (1b) are used to treat both hypertension and benign prostatic hyperplasia (BPH). Recently, three different subtypes of this receptor have been identified, with the alpha(1A) receptor being most prevalent in lower urinary tract tissue. This paper explores 4-aryldihydropyrimidinones attached to an aminopropyl-4-arylpiperidine via a C-5 amide as selective alpha(1A) receptor subtype antagonists. In receptor binding assays, these types of compounds generally display K(i) values for the alpha(1a) receptor subtype <1 nM while being greater than 100-fold selective versus the alpha(1b) and alpha(1d) receptor subtypes. Many of these compounds were also evaluated in vivo and found to be more potent than terazosin in both a rat model of prostate tone and a dog model of intra-urethral pressure without significantly affecting blood pressure. While many of the compounds tested displayed poor pharmacokinetics, compound 48 was found to have adequate bioavailability (>20%) and half-life (>6 h) in both rats and dogs. Due to its selectivity for the alpha(1a) over the alpha(1b) and alpha(1d) receptors as well as its favorable pharmacokinetic profile, 48 has the potential to relieve the symptoms of BPH without eliciting effects on the cardiovascular system.

Rizatriptan, a novel 5-HT1B/1D agonist for migraine: single- and multiple-dose tolerability and pharmacokinetics in healthy subjects

Rizatriptan is a novel 5-HT1D/1B agonist for relief of migraine headache. The pharmacokinetics, metabolite profiles, and tolerability of rizatriptan were examined in a multiple-dose study in healthy subjects. Rizatriptan (N = 24) (or placebo, N = 12) was administered as a single 10 mg dose, followed 48 hours later by administration of one 10 mg dose every 2 hours for three doses on 4 consecutive days, corresponding to the maximum daily dose for a migraine attack. The AUC of rizatriptan and its active N-monodesmethyl metabolite after three 10 mg doses was approximately threefold greater than the plasma concentrations following a single 10 mg dose. Metabolite profiles were similar after single and multiple doses. Adverse events during rizatriptan were mild and transient; similar events occurred during placebo, with a somewhat reduced incidence. Diastolic blood pressure tended to increase compared with placebo (approximately 5 mmHg), particularly on the first multiple-dose day (p < .01 vs. placebo). In conclusion, rizatriptan is well tolerated by healthy subjects during multiple-dose administration, with no unexpected accumulation of drug in plasma.

The effects of sample preparation methods on the variability of the electrospray ionization response for model drug compounds

A post-column infusion system was developed in order to analyze suppression of electrospray ionization (ESI) tandem mass spectrometry response in the presence of endogenous plasma interferences. By enabling direct detection of these interfering components, this experimental system was used to analyze the ability of several common extraction procedures to remove endogenous plasma components that cause changes in the ESI response of model drug substances. Methyl-t-butyl ether (MTBE) liquid-liquid, Oasis and Empore solid-phase, and acetonitrile (ACN) protein precipitation sample preparation methods were tested using the post-column infusion system. In all cases, ACN protein precipitation samples showed the greatest amount of ESI response suppression while liquid-liquid extracts demonstrated the least. In addition, the three test compounds, phenacetin, caffeine, and a representative Merck compound, demonstrated that ESI response suppression is compound dependent. Suppression was greatest with caffeine, the most polar analyte, and the smallest for the Merck compound, the least polar analyte. Copyright 1999 John Wiley & Sons, Ltd.

The effects of sample preparation methods on the variability of the electrospray ionization response for model drug compounds

A post-column infusion system was developed in order to analyze suppression of electrospray ionization (ESI) tandem mass spectrometry response in the presence of endogenous plasma interferences. By enabling direct detection of these interfering components, this experimental system was used to analyze the ability of several common extraction procedures to remove endogenous plasma components that cause changes in the ESI response of model drug substances. Methyl-t-butyl ether (MTBE) liquid-liquid, Oasis and Empore solid-phase, and acetonitrile (ACN) protein precipitation sample preparation methods were tested using the post-column infusion system. In all cases, ACN protein precipitation samples showed the greatest amount of ESI response suppression while liquid-liquid extracts demonstrated the least. In addition, the three test compounds, phenacetin, caffeine, and a representative Merck compound, demonstrated that ESI response suppression is compound dependent. Suppression was greatest with caffeine, the most polar analyte, and the smallest for the Merck compound, the least polar analyte. Copyright 1999 John Wiley & Sons, Ltd.

Pharmacokinetics and tolerability of oral rizatriptan in healthy male and female volunteers

AIMS

The pharmacokinetics and dose proportionality of rizatriptan single oral doses from 2.5 to 15 mg administered as solutions to healthy volunteers were studied.

METHODS

In a randomized, crossover study with four periods, twenty-four healthy volunteers (12 males and 12 females) took single oral doses of 2.5, 5, 10, and 15 mg rizatriptan in Periods 1-4. In a fifth period, subjects received 4 mg intravenous (i.v.) rizatriptan as a reference. Plasma and urine rizatriptan concentrations were determined at several timepoints/intervals for 12 and 24 h, respectively.

RESULTS

The arithmetic mean AUC values following single oral doses of 2.5, 5, 10, and 15-mg rizatriptan were 16, 33, 72, and 127 ng ml-1 h, respectively, in males; and 19, 42, 97, and 161 ng ml-1 h, respectively, in females. The overall bioavailability (F ) of rizatriptan was approximately 40% in males. Following the 4 mg reference i.v. dose, the apparent plasma clearance (CL) and renal clearance (CLr ) were 1042 and 225 ml min-1, respectively, in males; and 821 and 174 ml min-1, respectively, in females.

CONCLUSIONS

The disposition kinetics of oral rizatriptan were linear for doses of 2. 5-10 mg in males, and for doses of 2.5-5 mg in females. However, the degree of nonlinearity for higher doses was minor for both genders. The plasma concentrations of rizatriptan were slightly greater in women compared to men but the difference was not considered to be clinically meaningful. Also, the clearance of rizatriptan appeared to be mainly nonrenal.

Pharmacokinetics and tolerability of intravenous rizatriptan in healthy females

The pharmacokinetics and tolerability of intravenous (i.v.) rizatriptan (MK-0462), a novel 5-HT1D/1B receptor agonist for the acute oral treatment of migraine, were examined in an open, single-dose, four-period, randomized crossover study in healthy females. Results of this study indicated that i.v. rizatriptan (0.5-5 mg) was well tolerated. The disposition kinetics of rizatriptan were linear for i.v. doses up to and including 2.5 mg. Relative to the 0.5 mg dose, geometric mean dose-adjusted AUC ratios were 1.04, 1.09, and 1.18 for 1, 2.5, and 5 mg doses, respectively. Apparent plasma clearance (Cl) ranged between 859 and 941 mL min(-1) from 0.5 to 2.5 mg, but dropped to slightly below 800 mL min(-1) for the 5 mg dose. Therefore, the elimination of rizatriptan appears somewhat dose dependent at the high end of this dose range. Mean plasma half-life (t1/2) was 1.5-2.2 h across all doses while mean residence time in the body (MRT) and steady state volume of distribution (Vss) of rizatriptan remained relatively invariant across doses. Urinary excretion of rizatriptan (Ue) ranged from 14.5 to 34.6% of dose.

3-Pyridyloxypropanolamine agonists of the beta 3 adrenergic receptor with improved pharmacokinetic properties

Pyridyloxypropanolamines L-749,372 (8, beta 3 EC50 = 3.6 nM) and L-750,355 (29, beta 3 EC50 = 13 nM) are selective partial agonists of the human receptor, with 33% and 49% activation, respectively. Both stimulate lipolysis in rhesus monkeys (ED50 = 2 and 0.8 mg/kg, respectively), with minimal effects on heart rate. Oral bioavailability in dogs, 41% for L-749,372 and 47% for L-750,355, is improved relative to phenol analogs.

Metabolism of MK-499, a class III antiarrhythmic agent, in rats and dogs

MK-499 [(+)-N-[1'-(6-cyano-1, 2, 3, 4-tetrahydro-2(R)-naphthalenyl)-3, 4-dihydro-4(R)-hydroxyspiro(2H-1-benzopyran-2, 4'-piperidin)-6-yl]methanesulfonamide] monohydrochloride is an investigational class III antiarrhythmic agent for treatment of malignant ventricular tachyarrhythmias. The disposition of [3H]MK-499 and [14C]MK-499 was studied in rats and dogs after oral and iv administration. MK-499 was concentrated in organs of excretion and the heart. In the rat, urinary radioactivity elimination values after iv (0.5 mg/kg) and oral (6.25 mg/kg) doses were 21 +/- 3% and 10 +/- 2%, respectively. Corresponding fecal recoveries were 68 +/- 6% and 78 +/- 7%. Similar results were found after corresponding doses of [14C]MK-499. In dogs, urine and feces accounted for 16 +/- 3% and 75 +/- 4% of recovered radioactivity after a [3H]MK-499 iv dose (0.1 mg/kg). Corresponding recoveries after an oral dose (1 mg/kg) were 12 +/- 2% and 76 +/- 3%. Biliary (0-24 hr) excretion accounted for 39 +/- 5% and 41 +/- 18% of [3H] and [14C] oral doses in rats, respectively. Dogs excreted 34% of [3H] oral dose in (0-24 hr) bile. The data indicated that a substantial amount of MK-499 was absorbed by rats and dogs. MK-499, metabolite I (formed by loss of N-substitution), and metabolite II (an acid formed by metabolic scission across the benzopyran ring) each represented 30% of rat urinary label. Rat bile contained MK-499 (10%), II (20%), and IV (10%), which was formed by carbon-4 hydroxylation of the tetralin ring. Additionally, rat bile included glutathione (V) and N-acetyl-1-cysteine (VI) conjugates of a ring-opened metabolite. Metabolite III, a positional isomer of IV, was excreted in rat urine. The major labeled species excreted in dog bile were unchanged MK-499 and its glucuronide (VII), which, respectively, represented 50% and 30% of the biliary radioactivity. MK-499 and a small amount of I represented dog urinary radioactivity. The bioavailability of MK-499 was high in dogs (100%) but low in rats (17%). This difference was probably due to the more extensive presystemic metabolism of MK-499 in rats.

The use of stable isotope labeling and liquid chromatography-tandem mass spectrometry techniques to simultaneously determine the oral and ophthalmic bioavailability of timolol in dogs

Assays have been established for the quantitation of timolol and its 13C3- and 2H9-stable-isotope-labeled analogs in plasma and urine using liquid chromatography with atmospheric-pressure chemical-ionization tandem mass spectrometry. For the analysis of urine, underivatized timolol and its labeled analogs are monitored while timolol in plasma is assayed down to concentrations of 0.2 ng/mL after derivatization with phosgene. The great power of this technique is illustrated by simultaneously assaying three different species of timolol in plasma and urine obtained from dogs receiving simultaneous ophthalmic, oral, and intravenous doses of unlabeled and [2H9]- and [13C3]-labeled timolol. Thus, the ophthalmic and oral bioavailabilities of timolol are measured in a single experiment rather than as a three-phase crossover experiment. This approach yields accurate and precise analytical data, obviates intrasubject variability, and saves both analytical and animal resources.

A direct technique for the simultaneous determination of 10 drug candidates in plasma by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry interfaced to a Prospekt solid-phase extraction system

New drug candidates are being synthesized at an ever increasing rate and, until recently, the pharmacokinetics of only a few of these could be evaluated. Our laboratory is taking a novel approach to rapid multiple pharmacokinetic screening of potential drug candidates in which mixtures of new substances are co-administered to animals and analyzed simultaneously in plasma using liquid chromatography with tandem MS/MS detection in conjunction with a Prospekt automated on-line solid-phase extraction system. Plasma is sampled via an autosampler and extracted by the Prospekt with the eluent being introduced directly via a reverse phase HPLC column and a heated nebulizer interface to the mass spectrometer. Generic extraction and chromatographic conditions generally give good recoveries. The chromatographic run-times are less than 8 min. The accuracy and precision of these assays are carefully controlled with recoveries generally in the range 80-120% and coefficients of variation less than 20%. Lower quantifiable limits range from 2.5 to 5 ng ml-1. This approach considerably reduces the number of animals needed to screen drug candidates and its power is illustrated by determination of the pharmacokinetics of 10 substances after their simultaneous administration to dogs.

The simultaneous determination of mixtures of drug candidates by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry as an in vivo drug screening procedure

Liquid chromatography, combined with tandem mass spectrometry (LC/MS/MS) has been rapidly embraced by the pharmaceutical industry as the definitive method for the determination of drug levels in biological fluids obtained from pharmacokinetic and toxicological studies. This technique has proved to be reliable, accurate and precise for the determination of drugs and related substances (e.g. metabolites and isotope-labeled compounds) in support of preclinical and clinical studies. Our group has recently expanded the use of quantitative LC/MS/MS into the area of discovering new substances as potential drug candidates. When used as an accurate mass detector, triple quadrupole instruments have the ability to simultaneously and specifically detect minute quantities of closely-related drug substances in the extracts of biological fluids. Analytical procedures have been developed and validated that simultaneously determine plasma concentrations of up to 12 drug candidates over a concentration range of 1-1000 ng mL-1 in single analytical occasions. This approach is used to support drug discovery by rapidly providing pharmacokinetic data to a wide range of compounds following either the administration of multiple compounds to single animals, or by increasing the speed and efficiency of analyzing samples following the administration of single compounds to multiple animals. Currently, we have screened over 400 compounds in two different target classes in a period of 24 weeks. A standard operating procedure defining the acceptability of quality control data obtained during such screening experiments is described.

Pilot study of MK-462 in migraine

MK-462 is a potent, selective 5HT1D receptor agonist which may be useful in treating acute migraine. We conducted a double-blind placebo-controlled inpatient study to assess the preliminary efficacy and safety of oral doses of MK-462 20 mg (n = 8) and 40 mg (n = 36) vs placebo (n = 21), administered to 65 male and post-menopausal female migraine patients aged 22-51 with moderate or severe migraine headache. Headache severity and functional disability were measured at 0.5, 1, 1.5, and 2 h post-dose. The 20 mg dose was well tolerated and 4/8 patients obtained relief in headache severity at the 2 h time point. The 40 mg dose was well tolerated and was significantly (p < 0.05) superior to placebo at the 1.5 and 2 h time points (with 27/36 or 75% obtaining relief at 2 h compared to 7/21 or 33% for placebo). Adverse events occurred in 50% of patients on 20 mg MK-462, 72% of those on 40 mg MK-462, and in 52% of placebo-treated subjects. The most common adverse events associated with MK-462 were drowsiness (20 mg 12%; 40 mg 44%; placebo 24%), dry mouth (40 mg 36%; placebo 19%), and lightheadedness/dizziness (40 mg 17%; placebo 10%). Based on these preliminary results, MK-462 appears worthy of continued study for the treatment of acute migraine.

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.

The use of stable isotope labeling and liquid chromatography/tandem mass spectrometry techniques to study the pharmacokinetics and bioavailability of the antimigraine drug, MK-0462 (rizatriptan) in dogs

MK-0462 (rizatriptan) is a 5HT1D agonist being developed for the treatment of migraine. The assay for this substance in plasma and urine is based on HPLC with tandem mass spectrometry (MS/MS) detection. The procedure has been modified to include the simultaneous determination of the [triazole-13C2, 15N3-] stable-isotope-labelled analogue for which the lower quantifiable limit was 0.1 ng mL-1. The assay has been applied to study the pharmacokinetics of MK-0462 after simultaneous oral and intravenous administration of the drug and its stable-isotope-labelled analogue to dogs. The experiment afforded an estimate of plasma clearance concomitant with a precise measurement of the drug's oral bioavailability. The increasing use of LC-MS/MS in quantitative experiments may renew interest in stable isotopes as tools for pharmaceutical research.

Pharmacokinetics and food interaction of MK-462 in healthy males

A study was conducted to assess the safety, tolerability, and pharmacokinetics of single intravenous (IV) doses of 5-90 micrograms kg-1 of MK-462, and the effect of food on the pharmacokinetics of MK-462 administered orally to healthy males. Results of this study indicate that IV doses of MK-462 from 5 to 90 micrograms kg-1 are well tolerated. The disposition kinetics of MK-462 were linear for IV doses up to and including 60 micrograms kg-1. The values of the plasma clearance (CL), steady-state volume of distribution (Vss), plasma terminal half-life (t1/2), and mean residence time in the body (MRT) of MK-462 averaged 1376 mL min-1, 140 L, 1.8 h, and 1.7 h, respectively, and remained essentially constant over the dosage range of 10-60 micrograms kg-1 of IV MK-462. However, as the dose increased from 60 to 90 micrograms kg-1, the mean value of the apparent CL decreased from 1376 to 807 mL min-1. Thus, elimination of MK-462 was dose dependent in this dosage range. Based on the disposition decomposition analysis (DDA), it was shown that the Vss value of MK-462 remained essentially constant over the dosage range of 10-90 micrograms kg-1 of IV MK-462. The following values of two dose-independent parameters were also calculated by using DDA: distribution clearance (CLd) = 2028 mL min-1, and mean transit time in the peripheral tissues (MTTT) = 0.74 h. The mean values of AUC, Cmax, tmax, and apparent t1/2 of MK-462 in 12 subjects each receiving a 40 mg tablet of MK-462 without breakfast were 330 ng.h mL-1, 77 ng mL-1, 1.6 h, and 1.8 h, respectively. Although administration of a standard breakfast prior to dosing increased the AUC value (by approximately 20%) of MK-462 and delayed its absorption, there were no significant effects of the meal on the values of Cmax and apparent t1/2 of MK-462.

The development and cross-validation of methods based on radioimmunoassay and LC/MS-MS for the quantification of the class III antiarrhythmic agent, MK-0499, in human plasma and urine

An analytical method based on radioimmunoassay (RIA) has been developed for the determination of the antiarrhythmic agent, MK-0499, in plasma and urine. Owing to the potency of the drug, the specificity of this assay in human plasma could not be adequately determined using conventional RIA procedures. A highly specific procedure, based on LC/MS-MS, was developed to cross-validate the RIA. The lower quantifiable limits of the RIA and LC/MS-MS-based methods were 0.05 and 0.013 ng ml-1, respectively. Cross-validation data, compared using paired student's t-test regression analysis, showed excellent correlation between methods. The mass spectrometric assay was also used to simultaneously measure plasma concentrations of unlabeled and 14C-labeled MK-0499 following administration of the drug at high specific activity to volunteers.

Determination of MK-383, a non-peptide fibrinogen receptor antagonist, in human plasma and urine by radioimmunoassay

MK-383 is a novel, non-peptide fibrinogen receptor antagonist. A sensitive and specific radioimmunoassay has been developed for the determination of this drug candidate in plasma and urine. The immunogen was prepared by coupling to albumin via the N-hydroxysuccinimide ester from which the radioligand was also prepared by reaction with [I125]iodotyrosine. The method was specific and no immunoreactive material other than the parent drug was detectable in plasma and urine from dosed volunteers. This direct assay, using 5 microliters of plasma or 0.5 microliter of urine, is sensitive to 1 and 10 ng ml-1, respectively, without matrix interference and has sufficient sensitivity, specificity, accuracy, and precision for the analysis of clinical samples.

A rapid and specific assay, based on liquid chromatography-atmospheric pressure chemical ionization mass spectrometry, for the determination of MK-434 (a 5 alpha-reductase inhibitor) and its metabolites in plasma

MK-434 is a new 5 alpha-reductase inhibitor. A sensitive and specific assay based on combined liquid chromatography-mass spectrometry (LC-MS) has been developed for the determination of this compound in plasma. The analyte was isolated from plasma by solid-phase extraction on a C18 cartridge. A related substance, L-654,066, was used as the internal standard. Extracts were separated on a 5-cm C18-reversed-phase high performance liquid chromatography column interfaced via the heated nebulizer probe to a corona discharge chemical ionization source. The mass spectrometer was operated in the positive ion MS-MS mode. The method had sufficient sensitivity, precision, accuracy, and selectivity for the analysis of clinical samples containing MK-434 and its two principal metabolites at concentrations in the range 0.5-50 ng ml-1. The chromatographic run time was < 5 min.

Determination of L-691,121, a new class III antiarrhythmic, and its principal metabolite in plasma by differential radioimmunoassay

A sensitive and specific method based on radioimmunoassay (RIA) has been developed for the analysis of L-691,121, a new antiarrhythmic agent, and its major metabolite, L-692,199, in plasma. Two RIAs using immunogens and radioligands prepared from different derivatives of L-691,121 were used in conjunction to determine both parent compound and metabolite concentrations by solving simultaneous equations, since neither assay alone was adequately specific. Variable cross-reactivity factors were incorporated into the calculations to correct for non-parallel drug and metabolite displacement curves. The direct assay using 30 microliters of plasma is sensitive to 0.1 ng ml-1 and has sufficient precision, accuracy and specificity for the analysis of clinical samples.

Metabolism of 3-[2-(benzoxazol-2-yl)ethyl]-5-ethyl-6-methylpyridin-2 (1H)-one (L-696,229), an HIV-1 reverse transcriptase inhibitor, by rat liver slices and in humans

Healthy subjects were administered single oral doses of 800 mg or 400 mg 3-[2-(benzoxazol-2-yl)ethyl]-5-ethyl-6-methylpyridin-2(1H)-o ne (L-696,229), a nonnucleoside inhibitor of the human immunodeficiency virus-type 1 (HIV-1) reverse transcriptase (RT). Plasma or urine samples were collected over a period of 48 hr. Pooled plasma (0.5-6 hr) and urine (0-24 hr) samples were analyzed by HPLC-UV and HIV-1 RT inhibition assay using poly rC.dG as a template primer. The parent compound and several common metabolites were detected in both samples. The metabolic profiles were also similar to those obtained from a rat liver slice incubation with [3H]L-696,229. The in vitro metabolites were identified by NMR and MS as 5 alpha-hydroxyethyl- (major), 5,6-dihydrodiol-, 6'-hydroxy-, 6-hydroxymethyl-, and 5-vinyl analogs, and a benzoxazole ring hydrolysis product. Most of the significant metabolites in human plasma and urine were found to be identical to the in vitro metabolites, as established by HPLC-UV and MS. Hydrolysis of the plasma and urine with beta-glucuronidase/sulfatase indicated the presence of significant amounts of conjugates of the parent compound and 5 alpha-hydroxyethyl metabolite. Most of the other primary metabolites were also present in conjugated forms, albeit in small quantities. In addition, two secondary metabolites were isolated and identified from the hydrolyzed urine as 5-acetyl-6'-hydroxy- and 5 alpha-hydroxyethyl-6-hydroxymethyl- analogs.(ABSTRACT TRUNCATED AT 250 WORDS)

Incorporation of dinitrophenyl derivatives of proteins S6, S13, S16, and S18 into the 30 S subunit of Escherichia coli ribosomes by total reconstitution

This is the third paper in a series (Olah, T. V., Olson, H. M., Glitz, D. G., and Cooperman, B. S. (1988) J. Biol. Chem. 263, 4795-4800; Olson, H. M., Olah, T., Cooperman, B. S., and Glitz, D. G. (1988) J. Biol. Chem. 263, 4801-4806) describing the use of 2,4-dinitrophenyl (DNP) derivatives of Escherichia coli 30 S ribosomal proteins to locate the positions of these proteins within the 30 S subunit by immune electron microscopy. In it we describe the derivatization of proteins S6, S13, S16, and S18 with [3H]2,4-dinitrofluorobenzene, identify the nature of the derivatized amino acids within each protein, and demonstrate that each DNP protein, denoted DNP-Sx, can be taken up into a reconstituted 30 S subunit when added to a reconstitution mixture containing 16 S rRNA and total 30 S protein depleted in Sx. We further demonstrate that each DNP-Sx binds within the 30 S subunit in a position identical or similar to that of the unmodified Sx protein, as judged by its meeting one or more of the following three criteria: (i) unmodified Sx competes with the uptake of DNP-Sx into 30 S subunits; (ii) DNP-Sx restores functional activity to those single protein omission reconstitution particles lacking full activity; (iii) DNP-Sx induces the uptake of proteins into 30 S subunits that depend on the presence of Sx. The fourth paper in this series (Montesano-Roditis, L., McWilliams, R., Glitz, D. G., Olah, T. V., Perrault, A. R., and Cooperman, B. S. (1993) J. Biol. Chem. 268, 18701-18709), which follows this one, describes the localization of the DNP-Sx proteins within the 30 S subunit by immune electron microscopy.

Placement of dinitrophenyl-modified ribosomal proteins in totally reconstituted Escherichia coli 30 S subunits. Localization of proteins S6, S13, S16, and S18 by immune electron microscopy

Purified Escherichia coli ribosomal proteins S6, S13, S16, and S18 were dinitrophenylated at their amino termini and/or at one or more internal lysine residues. Each dinitrophenyl protein was then separately incorporated into reconstituted small ribosomal subunits. Modified proteins were localized on the 30 S subunit surface by electron microscopy of reconstituted subunits complexed with antibodies to dinitrophenol (DNP). DNP protein S13 was placed on the subunit head above the platform and on the surface that faces the large subunit. DNP-S18 was localized to the subunit platform below the tip and in a region associated with binding to 50 S subunits. DNP proteins S6 and S16 were both localized near the junction of the subunit body and platform; DNP-S6 was available to antibody in 70 S ribosomes and was placed on the cytoplasm-facing side of the subunit in an area that overlaps the platform and body of the particle. DNP-S16 in 70 S ribosomes was not bound by antibody. It was localized to the 30 S body near its junction with the platform and on the surface facing the 50 S particle. The results complement and clarify data obtained using other approaches.

Biotransformation of 5-chloro-3-phenylthioindole-2-carboxamide (L-734,005) in rhesus monkeys and rat liver microsomes to a potent HIV-1 reverse transcriptase inhibitor

Rhesus monkeys were dosed orally with 10 mg/kg 5-chloro-3-phenylthioindole-2-carboxamide (L-734,005), a nonnucleoside human immunodeficiency virus type 1 (HIV-1) reverse transcriptase inhibitor, in polyethylene glycol 300. Plasma samples from these monkeys demonstrated greater bioactivity in an HIV-1 reverse transcriptase inhibition assay than anticipated from the parent compound concentrations as determined by an HPLC-UV assay. One major and three minor metabolites, as well as the parent compound, were detected in the plasma. One of the minor metabolites was determined to be several-fold more active, and the major metabolite one-half as active as the parent compound in the inhibition assay. Identical metabolites were formed during an incubation of L-734,005 with rat liver microsomes. The most active minor metabolite was identified as a sulfone analog (L-737,126) of the parent compound by NMR and MS analyses. The less active major metabolite and two relatively inactive minor metabolites were similarly identified as the sulfoxide, 4-hydroxythiophenyl and 6-hydroxyindole analogs of L-734,005. The synthetic sulfone analog was highly potent against HIV-1, with a 95% inhibitory concentration of 3.0 nM for the spread of virus infection in a cell culture.

Determination of MK-852, a new fibrinogen receptor antagonist, in plasma and urine by radioimmunoassay

MK-852 is a novel fibrinogen receptor antagonist. A sensitive and specific radioimmunoassay has been developed for the determination of this drug candidate in plasma and urine. The immunogen was prepared by coupling to albumin via a dinitrophenylene bridge and the radioligand by reaction of the drug with the 125I-labelled Bolton-Hunter reagent. The method was specific and no immunoreactive material other than parent drug was detectable in plasma from dosed volunteers. The direct assay using 0.05 ml of plasma is sensitive to 0.2 ng ml-1 without matrix interference and has sufficient sensitivity, precision, accuracy, and selectivity for the analysis of clinical samples. The lower quantifiable limit in (diluted) urine is 50 ng ml-1.

Determination of the beta-adrenergic blocker timolol in plasma by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry

A method based on LC-MS-MS has been developed for the determination of timolol in plasma using the (CD3)3-labelled species as the internal standard. Timolol is isolated from plasma by a simple solid-phase extraction and converted to its oxazolidin-2-one prior to analysis on a 50 x 4.6 mm reversed-phase high-performance liquid chromatography column packed with SynChropak, C18, 5 microns. The column eluate is passed by means of a heated nebulizer interface into a corona discharge atmospheric pressure chemical ionization source where the analyte and its internal standard are detected using multiple reaction monitoring (MRM). The very high specificity of this technique permits chromatographic run times of less than 2 min. The method has a lower quantifiable limit of 0.5 ng ml-1, with intra- and inter-day relative standard deviations less than 10%, and enables the determination of timolol in plasma after ocular administration to volunteers.

Determination of L-654,066, a new 5 alpha-reductase inhibitor in plasma by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry

L-654,066 is a new 5 alpha-reductase inhibitor. A sensitive and specific assay based on combined liquid chromatography/mass spectrometry has been developed for the determination of this drug candidate in plasma. The analyte was isolated from plasma by solid-phase extraction on a C-18 cartridge. A related substance, L-683,838, was used as the internal standard. Extracts were chromatographed on a 5 cm C18 reverse-phase high-performance liquid chromatography column interfaced via the heated nebulizer probe to a corona discharge chemical ionization source. The mass spectrometer was operated in the positive ion tandem mode. The method has sufficient sensitivity, precision, accuracy and selectivity for the analysis of clinical samples containing L-654,066 at concentrations in the range 0.5-20 ng ml-1. The chromatographic run time is less than 2 min.

Determination of L-365,260, a new cholecystokinin receptor (CCK-B) antagonist, in plasma by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry

L-365,260 is a novel cholecystokinin receptor antagonist. A sensitive and specific liquid chromatographic/mass spectrometric assay has been developed for the determination of the drug in plasma using the CD3-labeled species as the internal standard. Plasma extracts were separated on a 3 cm C18 reverse-phase high-performance liquid chromatography column. The column eluate passed, by means of a heated nebulizer interface, into a corona discharge atmospheric chemical ionization source. The mass spectrometer was operated in the positive ion tandem mass spectrometric mode. The method has sufficient sensitivity, specificity, precision, accuracy and selectivity for the determination of drug concentrations in clinical samples. The chromatographic run time is less than 2 min.

The protein composition of reconstituted 30S ribosomal subunits: the effects of single protein omission

Using reverse phase HPLC, we have been able to quantify the protein compositions of reconstituted 30S ribosomal subunits, formed either with the full complement of 30S proteins in the reconstitution mix or with a single protein omitted. We denote particles formed in the latter case as SPORE (single protein omission reconstitution) particles. An important goal in 30S reconstitution studies is the formation of reconstituted subunits having uniform protein composition, preferably corresponding to one copy of each protein per reconstituted particle. Here we describe procedures involving variation of the protein:rRNA ratio that approach this goal. In SPORE particles the omission of one protein often results in the partial loss in uptake of other proteins. We also describe procedures to increase the uptake of such proteins into SPORE particles, thus enhancing the utility of the SPORE approach in defining the role of specific proteins in 30S structure and function. The losses of proteins other than the omitted protein provide a measure of protein:protein interaction within the 30S subunit. Most of these losses are predictable on the basis of other such measures. However, we do find evidence for several long-range protein:protein interactions (S6:S3, S6:S12, S10:S16, and S6:S4) that have not been described previously.

Incorporation of single dinitrophenyl-modified proteins into the 30 S subunit of Escherichia coli ribosomes by total reconstitution

In this first of two consecutive papers, the main objective of which is to present a new approach to the systematic localization of individual proteins located in the Escherichia coli ribosome by immunoelectron microscopy, we describe the derivatization of several purified 30 S proteins (S12, S21, S14, S19, S18, S17) with 2,4-[3,5-3H]dinitrofluorobenzene at pH 7.4 and 8.4 and the uptake of each dinitrophenylated protein in place of the corresponding unmodified protein into totally reconstituted 30 S subunits. Reverse-phase high performance liquid chromatography is used to purify the proteins, to separate and characterize the products of 2,4-[3,5-3H]dinitrofluorobenzene modification, and to analyze the protein composition of the reconstituted subunits. The extent of dinitrophenyl (DNP) modification is estimated by both radioactivity and integrated peak areas, using dual wavelength monitoring at 214 and 360 nm. DNP derivatives of each of the six proteins are efficiently incorporated into reconstituting 30 S subunits. Incorporation of any of the six DNP-modified proteins does not interfere with binding of Phe-tRNA(Phe) in a poly(U)-dependent manner. This result, as well as data showing that unmodified protein competes with DNP-protein for uptake during reconstitution, provide evidence that each DNP-protein occupies the same position in 30 S subunit as does unmodified protein. In general, for a given protein, unmodified and/or less modified forms are incorporated in preference to more modified forms. Modification of protein S19 at pH 7.4 proceeds with selective formation of one derivative in high yield. Reverse-phase high performance liquid chromatography analysis of acid hydrolysates of a purified sample of this derivative, as well as of peptides derived from it by digestion with Staphylococcus aureus protease, show the N-terminal proline to be the predominant site of DNP-derivatization.

Immune electron microscopic localization of dinitrophenyl-modified ribosomal protein S19 in reconstituted Escherichia coli 30 S subunits using antibodies to dinitrophenol

Escherichia coli small ribosomal subunits have been reconstituted from RNA and high performance liquid chromatography-purified proteins including protein S19 that had been modified at its amino-terminal proline residue with 1-fluoro-2,4-dinitrobenzene. As detailed in the accompanying paper (Olah, T. V., Olson, H. M., Glitz, D. G., and Cooperman, B. S. (1988) J. Biol. Chem. 263, 4795-4800), dinitrophenyl (DNP)-S19 was efficiently incorporated into the site ordinarily occupied by S19. Antibodies to DNP bound effectively to the reconstituted subunits and did not cause dissociation of the modified protein from the subunit. Electron microscopy of the immune complexes was used to localize the modified protein on the subunit surface. More than 95% of the antibody binding sites seen were consistent with a single location of protein S19 on the upper portion or head of the subunit, on the surface that faces the 50 S particle in a 70 S ribosome, and in an area relatively distant from the subunit platform. The S19 site is close to the region in which 30 S subunits are photoaffinity labeled with puromycin. Protein S19 is thus near protein S14 in the small subunit and in proximity to the peptidyl transferase center of the 70 S ribosome.