A Phase 1 Study to Assess Mass Balance and Absolute Bioavailability of Zimlovisertib in Healthy Male Participants Using a 14 C-Microtracer Approach

Zimlovisertib (PF‐06650833) is a selective, reversible inhibitor of interleukin‐1 receptor‐associated kinase 4 (IRAK4) with anti‐inflammatory effects. This phase 1, open‐label, fixed‐sequence, two‐period, single‐dose study aimed to evaluate the mass balance and excretion rate of zimlovisertib in healthy male participants using a ¹⁴C‐microtracer approach. All six participants received 300 mg ¹⁴C‐zimlovisertib with lower radioactivity per mass unit orally in Period A, then unlabeled zimlovisertib 300 mg orally and ¹⁴C‐zimlovisertib 135 μg intravenously (IV) in Period B. Study objectives included extent and rate of excretion of ¹⁴C‐zimlovisertib, pharmacokinetics, and safety and tolerability of oral and IV zimlovisertib. Total radioactivity recovered in urine and feces was 82.4% ± 6.8% (urine 23.1% ± 12.3%, feces 59.3% ± 9.7%) in Period A. Zimlovisertib was absorbed rapidly following oral administration, with the fraction absorbed estimated to be 44%. Absolute oral bioavailability of the 300‐mg dose was 17.4% (90% confidence interval 14.1%, 21.5%) using the dose‐normalized area under the concentration–time curve from time 0 to infinity. There were no deaths, serious adverse events (AEs), severe AEs, discontinuations or dose reductions due to AEs, and no clinically significant laboratory abnormalities. These results demonstrate that zimlovisertib had low absolute oral bioavailability and low absorption (<50%).

Discovery of Clinical Candidate 1-{[(2S,3S,4S)-3-Ethyl-4-fluoro-5-oxopyrrolidin-2-yl]methoxy}-7-methoxyisoquinoline-6-carboxamide (PF-06650833), a Potent, Selective Inhibitor of Interleukin-1 Receptor Associated Kinase 4 (IRAK4), by Fragment-Based Drug Design

Through fragment-based drug design focused on engaging the active site of IRAK4 and leveraging three-dimensional topology in a ligand-efficient manner, a micromolar hit identified from a screen of a Pfizer fragment library was optimized to afford IRAK4 inhibitors with nanomolar potency in cellular assays. The medicinal chemistry effort featured the judicious placement of lipophilicity, informed by co-crystal structures with IRAK4 and optimization of ADME properties to deliver clinical candidate PF-06650833 (compound 40). This compound displays a 5-unit increase in lipophilic efficiency from the fragment hit, excellent kinase selectivity, and pharmacokinetic properties suitable for oral administration.

Pharmacokinetics of clinafloxacin after single and multiple doses

Clinafloxacin (CI-960) is a potent broad-spectrum, fluoroquinolone antibiotic that has been studied for parenteral and oral administration in patients with serious infections. The objectives of these studies were to examine the pharmacokinetics and safety of clinafloxacin following administration of single and twice-daily intravenous (i.v.) and oral doses to volunteers. Plasma and urine samples were assayed by validated liquid chromatographic methods, and pharmacokinetic parameter values were determined by noncompartmental methods. Safety was evaluated by clinical observation and laboratory tests. Absorption was rapid after oral administration, with maximum concentrations in plasma (C(max)) generally occurring within 2 h. Concentrations in plasma declined biexponentially, with an average terminal half-life of 4 to 6 h after single doses and 5 to 7 h after multiple doses. Increases in C(max) and area under the concentration-time curves (AUC) were generally proportional to the dose. The volume of distribution was much greater than total body water. Approximately 40 to 75% of the clinafloxacin doses were excreted unchanged into urine. Absolute bioavailability of orally administered clinafloxacin was approximately 90% and did not change with increasing dose. Therefore, switching patients from i.v. to oral dosing should achieve similar concentrations in plasma. The tolerability of clinafloxacin was acceptable. No serious adverse events occurred. C(max) values and minimum plasma clinafloxacin concentrations during multiple dosing exceeded MICs for a wide range of organisms.

Pharmacokinetics of clinafloxacin enantiomers in humans

The pharmacokinetics of R-clinafloxacin and S-clinafloxacin enantiomers of the broad-spectrum fluoroquinolone antibiotic, clinafloxacin, were characterized in selected volunteer subjects and patients after the administration of oral and intravenous doses of racemic drug. The absorption of each enantiomer was rapid and nearly complete after a single, oral 400 mg racemic dose. The mean (+/- SD) bioavailability of R-clinafloxacin was 87.5% +/- 4.8% compared to 86.2% +/- 5.8% for S-clinafloxacin. The mean Cmax of each enantiomer was 1.19 micrograms/mL, with plasma concentrations of each enantiomer remaining above 0.1 microgram/mL for at least 12 hours. No notable differences in the disposition of R-clinafloxacin and S-clinafloxacin were observed. After a single 400 mg intravenous dose of racemic drug, mean (+/- SD) t1/2 was 5.6 +/- 0.3 hours and 5.7 +/- 0.4 hours, plasma Cl was 329 +/- 49 mL/min and 314 +/- 45 mL/min, and Vdss was 138 +/- 18 L and 134 +/- 16 L for R- and S-clinafloxacin, respectively. Two healthy volunteers each received a single 400 mg oral dose of racemic clinafloxacin (alone) and with oral administration of 1 gm probenecid separated by a 1-week washout period between treatments. With probenecid coadministration, the increase in AUC0-infinity was 75% and 83% for R-clinafloxacin and was 71% and 75% for S-clinafloxacin in each subject, respectively. Probenecid increased the total exposure (AUC) of both R-clinafloxacin and S-clinafloxacin, although it had no stereo-selective effects on the disposition of either enantiomer. The antimicrobial potency of the isomers was also evaluated. In vitro susceptibility testing showed that the two compounds were comparable in their inhibitory activities, as all MICs were within twofold for each organism tested. These results demonstrate that in addition to their similar antimicrobial potency, R- and S-clinafloxacin have nearly identical disposition characteristics and are eliminated by similar mechanisms that display no apparent enantioselectivity in man.

Achiral and chiral high-performance liquid chromatographic methods for clinafloxacin, a fluoroquinolone antibacterial, in human plasma

Achiral and chiral HPLC methods were developed for clinafloxacin, a quinolone antimicrobial agent. For achiral assay, analytes were isolated from plasma by precipitating plasma proteins. Separation was achieved on a C18 column using an isocratic eluent of ion pairing solution-acetonitrile (80:20, v/v) at 1.0 ml/min with UV detection at 340 nm. The ion pairing solution was 0.05 M citric acid, 1.15 mM tetrabutylammonium hydroxide and 0.1% ammonium perchlorate. Inter-assay accuracy was within 4.9% with an inter-assay precision of 3.7% over a quantitation range of 0.025 to 10.0 microg/ml. For chiral assay, analytes were isolated from plasma by solid-phase extraction. Separation was achieved on a Crownpak CR(+) column using an isocratic eluent of water-methanol (88:12, v/v) containing 0.1 mM decylamine at 1.0 ml/min with UV detection at 340 nm. Perchloric acid was added to adjust pH to 2. Inter-assay accuracy was within 3.5% with a inter-assay precision of 5.4% over a quantitation range of 0.040 to 2.5 microg/ml.

High-performance liquid chromatographic assay for CI-980, a novel 1-deaza-7,8-dihydropteridine anticancer agent, in human plasma and urine

CI-980, a 1-deaza-7,8-dihydropteridine, is a novel anticancer agent that is a potent mitotic inhibitor acting as a tubulin binder similar to the vinca alkaloids. CI-980 has shown equivalent or superior anticancer activity in vitro compared to vincristine and retains full activity against vincristine resistant tumors in vitro. A high-performance liquid chromatographic (HPLC) assay was developed and validated for human plasma and urine to support Phase 1 clinical trials. CI-980 and PD 080658, internal standard, were isolated from 2-ml samples of human plasma and urine by solid-phase extraction with Bond-Elut C18 cartridges. Urine samples must be pretreated with bovine serum albumin (BSA) to minimize the binding of CI-980 to glass and some plastics. The eluate from the cartridges for both matrices was evaporated to dryness and taken up in mobile phase. Zorbax RX C18 columns, mobile phase buffer of 10 mM ammonium dihydrogen phosphate at pH 7.5 and a flow-rate of 0.75 ml/min were used for both matrices. Column dimensions, column temperature and mobile phase acetonitrile-buffer ratio were 300 mm x 4.6 mm I.D., 30 degrees C and 38:62 (v/v), respectively, for the plasma assay and 250 mm x 4.6 mm I.D., 35 degrees C and 40:60 (v/v), respectively, for the urine assay. Column effluent was monitored fluorometrically for the plasma method using excitation and emission wavelengths of 388 nm and 473 nm, respectively. Ultraviolet detection at 380 nm was used for the urine method. Peak-area ratios were proportional to CI-980 concentrations from 0.2 to 25 ng/ml and 1 to 100 ng/ml for plasma and urine, respectively. CI-980 in water will bind to glass and plastics but not PTFE or stainless steel. Urine calibration standards were frozen prior to use in order to compensate for loss of CI-980 due to freezing in this matrix. The accuracy of the assay was within 4.7%, with a precision of 5.6% for both matrices. Recoveries ranged from 93.8 to 102% and 90.7 to 92.3% for plasma and urine, respectively. CI-980 was stable in plasma and urine for at least 275 and 217 days, respectively, when stored at -70 degrees C. The assay is suitable for studying the clinical pharmacokinetics of CI-980.

Comparative studies of the in vitro metabolism and covalent binding of 14C-benzene by liver slices and microsomal fraction of mouse, rat, and human

Metabolism of benzene by the liver has been suggested to play an important role in the hepatotoxicity of benzene. The role of the different benzene metabolites and the causes of species differences in benzene hepatotoxicity are, however, not known. The metabolism and covalent binding of 14C-benzene by liver microsomal fractions and liver slices from rat, mouse, and human subjects have been studied. Rat microsomal fraction formed phenol at a rate of 0.32 nmol/min/mg of protein; mouse microsomal fraction formed phenol at 0.64 nmol/min/mg and hydroquinone at 0.03 nmol/min/mg; and human microsomal fraction formed phenol at 0.46 nmol/min/mg and hydroquinone at 0.07 nmol/min/mg. Covalent binding of 14C-benzene metabolites to rat, mouse, and human liver microsomal protein was 29, 113, and 169 pmol/min/mg of protein, respectively. The rates of metabolite formation from benzene by liver slices in nmol/min/g of tissue were: rat, phenol 0.15, hydroquinone 0.26, and phenylsulfate 1.22; mouse: phenol 0.13, hydroquinone 0.29, phenylsulfate 1.37, and phenylglucuronide 1.34; and human: phenol 0.16, hydroquinone 0.27, phenylsulfate 0.83, and phenylglucuronide 0.52. trans,trans-Muconic acid formation was not detected with liver slices of any species. Covalent binding of 14C-benzene metabolites to rat, mouse, and human liver slices was 8.2, 79.7, and 27.3 pmol/min/g liver, respectively. There was no correlation between ascorbic acid levels in the human liver slices and covalent binding of 14C-benzene metabolites. The results show that phenol and hydroquinone found in extrahepatic tissues, including bone marrow, of animals exposed to benzene could originate from the liver. There was no evidence for the release of highly reactive benzene metabolites such as trans,trans-muconaldehyde or p-benzoquinone from liver cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Preclinical pharmacologic studies of the new antitumor agent carmethizole (NSC-602668) in the mouse and beagle dog

The chemical breakdown of carmethizole [1-methyl-2-methylthio-4,5-bis-(hydroxymethyl)imidazole-4',5'- bis(N-methylcarbamate)hydrochloride] and its pharmacokinetics in the mouse and beagle dog were studied. Carmethizole was relatively unstable in aqueous media, having a half-life of less than or equal to 1 h in 0.9% sodium chloride, human whole blood, human plasma, and dog urine at 37 degrees C. Its major breakdown product in 0.9% sodium chloride and pH 5.0 sodium phosphate buffer was carmethizole diol. When carmethizole was added to pH 7.0 or pH 9.0 sodium phosphate buffer, the major breakdown product was carmethizole diol-4'-monophosphate. Carmethizole reacted directly with glutathione at pH 8.0, forming a glutathione adduct of carmethizole monocarbamate. Elimination of the drug from the plasma of the beagle dog following i.v. bolus doses of 22.4 and 4.3 mg/kg was biphasic. At these doses the terminal half-life was 39 and 46 min, respectively, and the respective total body clearance was 4.6 and 7.7 ml/min per kg. The 22.4 mg/kg dose was lethal to the beagle dog by day 4. Elimination of carmethizole from the plasma of mice following an i.v. bolus dose of 115 mg/kg was monoexponential, with a half-life of 11.6 min and a total body plasma clearance of 43.6 ml/min per kg. When the drug was infused at 230 mg/kg over 8 h into mice, the total body clearance was 40.8 ml/min per kg. Following the i.v. bolus administration of carmethizole to mice, 30% of the total dose was excreted in urine over 3 h as carmethizole diol, 10%, as carmethizole diol-sulfate, 3.4%, as carmethizole 4'-monocarbamate, and 2.4%, as unchanged drug.

Gas chromatographic assay for the new antitumor agent sulfamic acid diester (NSC 329680) and its stability in buffer, blood and plasma

A sensitive gas chromatographic assay with electron-capture detection has been developed for sulfamic acid diester (sulfamic acid 1,7-heptanediyl ester, NSC 329680) based on its conversion to 1,7-diiodoheptane in the presence of excess sodium iodide. The assay is linear up to 1 microgram/ml sulfamic acid diester and has a lower limit of detection of 25 ng/ml from 0.5 ml plasma. The coefficient of variation of the assay is 6.4% at 1 microgram/ml and 8.0% at 100 ng/ml. Sulfamic acid diester is relatively stable in 0.9% sodium chloride and 0.1 M sodium phosphate buffers, pH 7.0-9.0, with half-lives greater than 38 h. The major breakdown product of sulfamic acid diester is sulfamic acid 1,7-heptane-monoyl ester. When added to whole blood sulfamic acid diester shows concentration-dependent breakdown. At 50 and 100 micrograms/ml sulfamic acid diester, the half-time in whole blood is 6.9 h and 65% of the drug is sequestered by the blood cells. At 10 micrograms/ml sulfamic acid diester in blood, there is no detectable breakdown of the drug over 24 h and all of the drug is sequestered by the blood cells. Protein binding of sulfamic acid diester in human plasma is 82% at 10 micrograms/ml and 68% at 100 micrograms/ml.

Disposition and metabolism of the antitumor agent pyrazine-2-diazohydroxide in mouse and beagle dog

The pharmacokinetics and metabolism of pyrazine-2-diazohydroxide have been studied in the beagle dog and mouse. When pyrazine-2-diazohydroxide was administered to beagle dogs at a dose of 18.6 mg/kg (428 mg/m2) by i.v. bolus, the plasma half-life (t1/2) was 7.3 min, the apparent volume of distribution (Vd) 577 ml/kg, and the total body clearance (Cl) 55 ml/min per kg. In mice given pyrazine-2-diazohydroxide by i.v. bolus at 100 mg/kg (428 mg/m2), the t1/2 was 5.8 min, the Vd 250 ml/kg, and the Cl 30 ml/min per kg. When [2-14C]pyrazine-2-diazohydroxide was infused i.v. to mice at 100 mg/kg over 8 h, the Cl for parent drug was 122 ml/min per kg. The major product formed from pyrazine-2-diazohydroxide was 2-hydroxypyrazine, which accounted for 80% of the total radioactivity in the plasma after a 6-h drug infusion. There were three other metabolites in plasma, two more polar than pyrazine-2-diazohydroxide, which accounted for 7% of the radioactivity, and one less polar, which accounted for 5% of the radioactivity. Following an i.v. bolus dose of [2-14C]pyrazine-2-diazohydroxide, 79% of the radioactivity was excreted in the urine in 24 h, 3% in the feces, and 0.4% in the expired air; 18% remained in the carcass. The liver and kidney showed the highest tissue levels of radioactivity. 2-Hydroxypyrazine accounted for 45% of the urinary radioactivity, pyrazine-2-diazohydroxide for 14%, and a glucuronide or sulfate conjugate of 2-hydroxypyrazine for 17%. Twenty-four percent of the radioactivity eluted near the void volume on high-performance liquid chromatography and was not identified.

Flavin-containing monooxygenase and ascorbic acid deficiency. Qualitative and quantitative differences

Ascorbic acid deficiency causes qualitative and quantitative differences in the guinea pig hepatic flavin-containing monooxygenase (FMO). Kinetic studies with purified FMO indicated no significant change in the apparent Km of dimethylaniline or NADPH in ascorbate-supplemented or -deficient animals. Following purification of ascorbate-deficient guinea pig FMO by DEAE-cellulose and blue agarose chromatography, exogenous FAD was required for 15% of the FMO microsomal activity recovered. In contrast, only 5% of the total microsomal enzyme recovered from ascorbate-supplemented animals required exogenous FAD. Furthermore, there was an enhanced sensitivity to time-dependent nonlinearity with the purified ascorbate-deficient guinea pig FMO. The degree of time-dependent nonlinearity was related to the concentration of substrate. Also, purified ascorbate-supplemented guinea pig FMO was stable for 4 weeks at -20 degrees, whereas the ascorbate-deficient enzyme was inactivated. A decrease in the quantity of ascorbate-deficient guinea pig FMO compared to ascorbate-supplemented was indicated by a marked reduction in total FMO activity recovered from blue agarose chromatography and reduced protein staining intensity with SDS-PAGE at 56,000 daltons.

Modulation of the flavin-containing monooxygenase in guinea pigs by ascorbic acid and food restriction

Modulation of the flavin-containing monooxygenase (FMO) by varying the ascorbic acid and food intake was investigated. Hepatic activity of the FMO in ascorbic acid-deficient guinea pigs fed a restricted amount of diet which resulted in a 10-15% body weight loss, was 17% of that in animals fed restricted amounts of the adequate diet. FMO hepatic activity in ascorbic acid-supplemented guinea pigs on a food-restricted regimen was 176% of that found in animals fed the adequate diet ad libitum. This increase in activity was not related to stress. Alteration in the activity of this important drug-metabolizing enzyme system by a combination of ascorbic acid deficiency and reduced food intake could potentially alter the rate of metabolism of a great variety of pharmaceutical drugs and environmental chemicals.

Ascorbic acid deficiency and the flavin-containing monooxygenase

Activity of the flavin-containing monooxygenase (FMO) was reduced significantly in ascorbic acid deficient guinea pigs. Reduction in oxidation of dimethylaniline (DMA) and of thiobenzamide was associated with a decrease in the activity of the FMO. In both ascorbate supplemented and deficient guinea pig hepatic 12,000 g supernatant fractions, SKF-525A and n-octylamine did not inhibit DMA N-oxidation. Phenobarbital pretreatment did not increase the rate of N-oxidation of DMA. In addition, hepatic supernatant fractions thermally treated at 50 degree were unable to N-oxidize DMA, but 80% of the cytochrome P-450 activity was retained. Also, N-oxidation of DMA was reduced by 53% at pH 7.0, while oxidation of cytochrome P-450 specific substrates was inhibited by only 19%. Kinetic studies of DMA N-oxidation indicate no significant change in the apparent Km in ascorbate supplemented or deficient animals. The in vitro addition of ascorbic acid had no effect on the activity of the FMO. The toxicological implications of the reduction in FMO activity in ascorbic acid deficiency are discussed.