Concentrations Of Total Radioactivity Research Articles

The Metabolism and Disposition of Brepocitinib in Humans and Characterization of the Formation Mechanism of an Aminopyridine Metabolite.

Brepocitinib is an oral once-daily Janus kinase 1 and Tyrosine kinase 2 selective inhibitor currently in development for the treatment of several autoimmune disorders. Mass balance and metabolic profiles were determined using accelerator mass spectrometry in six healthy male participants following a single oral 60 mg dose of 14C-brepocitinib (∼300 nCi). The average mass balance recovery was 96.7% ± 6.3%, with the majority of dose (88.0% ± 8.0%) recovered in urine and 8.7% ± 2.1% of the dose recovered in feces. Absorption of brepocitinib was rapid, with maximal plasma concentrations of total radioactivity and brepocitinib achieved within 0.5 hours after dosing. Circulating radioactivity consisted primarily of brepocitinib (47.8%) and metabolite M1 (37.1%) derived from hydroxylation at the C5' position of the pyrazole ring. Fractional contributions to metabolism via cytochrome P450 enzymes were determined to be 0.77 for CYP3A4/5 and 0.14 for CYP1A2 based on phenotyping studies in human liver microsomes. However, additional clinical studies are required to understand the potential contribution of CYP1A1. Approximately 83% of the dose was eliminated as N-methylpyrazolyl oxidative metabolites, with 52.1% of the dose excreted as M1 alone. Notably, M1 was not observed as a circulating metabolite in earlier metabolic profiling of human plasma from a multiple ascending dose study with unlabeled brepocitinib. Mechanistic studies revealed that M1 was highly unstable in human plasma and phosphate buffer, undergoing chemical oxidation leading to loss of the 5-hydroxy-1-methylpyrazole moiety and formation of aminopyrimidine cleavage product M2. Time-dependent inhibition and trapping studies with M1 yielded insights into the mechanism of this unusual and unexpected instability. SIGNIFICANCE STATEMENT: This study provides a detailed understanding of the disposition and metabolism of brepocitinib, a JAK1/TYK2 inhibitor for atopic dermatitis, in humans as well as characterization of clearance pathways and pharmacokinetics of brepocitinib and its metabolites.

Understanding the pharmacokinetic journey of Fc-fusion protein, rhIL-7-hyFc using complementary approach of two analytical methods, accelerator mass spectrometry and ELISA.

Antibody-based therapeutics (ABTs), including monoclonal/polyclonal antibodies and fragment crystallizable region (Fc)-fusion proteins, are increasingly used in disease treatment, driving the global market growth. Understanding the pharmacokinetic (PK) properties of ABTs is crucial for their clinical effectiveness. This study investigated the PK profile and tissue distribution of efineptakin alfa, a long-acting recombinant human interleukin-7 (rhIL-7-hyFc), using enzyme-linked immunosorbent assay (ELISA) and accelerator mass spectrometry (AMS). Totally, four rats were injected intramuscularly with 1mg/kg of rhIL-7-hyFc containing 14C-rhIL-7-hyFc, which was prepared via reductive methylation. Serum total radioactivity (TRA) and serum rhIL-7-hyFc concentrations were quantified using AMS and ELISA, respectively. The TRA concentrations in organs were determined by AMS. Serum TRA peaked at 10hours with a terminal half-life of 40hours. The rhIL-7-hyFc exhibited a mean peak concentration at around 17hours and a rapid elimination with a half-life of 12.3hours. Peak concentration and area under the curve of TRA were higher than those of rhIL-7-hyFc. Tissue distribution analysis showed an elevated TRA concentrations in lymph nodes, kidneys, and spleen, indicating rhIL-7-hyFc's affinity for these organs. The study also simulated the positions of 14C labeling in rhIL-7-hyFc, identifying specific residues in the fragment of rhIL-7 portion, and provided the explanation of distinct analytes targeted by each method. Combining ELISA and AMS provided advantages by offering sensitivity and specificity for quantification as well as enabling the identification of analyte forms. The integrated use of ELISA and AMS offers valuable insights for the development and optimization of ABT.

The Disposition and Metabolism of Bempedoic Acid, A Potent Inhibitor of ATP Citrate Lyase, In Healthy Human Subjects.

The disposition and metabolism of bempedoic acid, a selective inhibitor of ATP citrate lyase, were examined in healthy male subjects. After a single administration of [14C] bempedoic acid (240 mg, 113 μCi) oral solution, mean concentrations of total radioactivity in plasma as a function of time indicated absorption was rapid with peak concentrations achieved at 1 hour after dose administration. Radioactivity was decreased in a multiexponential fashion with an estimated elimination half-life of 26.0 hours. Radiolabeled dose was predominantly recovered in urine (62.1% of dose) and a smaller amount in feces (25.4% of dose). Bempedoic acid was extensively metabolized with 1.6% to 3.7% of dose excreted unchanged in urine and feces combined. Overall, the major clearance route of bempedoic acid is metabolism by uridine 5'‑diphosphate glucuronosyltransferases. Metabolism in hepatocyte cultures of human and nonclinical species were generally in agreement with clinical metabolite profiles. Pooled plasma samples were characterized by the presence of bempedoic acid, which accounted for 59.3% of total plasma radioactivity, ESP15228 (a reversible keto metabolite of bempedoic acid), and their respective glucuronide conjugates. The acyl glucuronide of bempedoic acid represented 23% to 36% of radioactivity in plasma and accounted for approximately 37% of dose excreted in urine. In feces, the majority of radioactivity was associated with a co-eluting mixture of a carboxylic acid metabolite of bempedoic acid, a taurine conjugate of bempedoic acid and hydroxymethyl-ESP15228, which collectively accounted for 3.1% to 22.9% of bempedoic acid dose across subjects. Significance Statement This study characterizes the disposition and metabolism of bempedoic acid, an inhibitor of ATP citrate lyase for hypercholesterolemia. This work provides further understanding of bempedoic acid clinical pharmacokinetics and clearance pathways in adult subjects.

Metabolic disposition of the EGFR covalent inhibitor furmonertinib in humans.

Furmonertinib was designed for the treatment of non-small cell lung cancer (NSCLC) patients with EGFR T790M mutation. In this study, we investigated the metabolic disposition and mass balance in humans and tissue distribution in rats. After a single oral administration of 97.9 μCi/81.5 mg [14C]-furmonertinib mesylate to six healthy male volunteers, the absorption process of furmonertinib was fast with a tmax of total plasma radioactivity at 0.75 h. Afterward, furmonertinib was extensively metabolized, with the parent drug and active metabolite AST5902 accounting for 1.68% and 0.97% of total radioactivity in plasma. The terminal t1/2 of total radioactivity in plasma was as long as 333 h, suggesting that the covalent binding of drug-related substances to plasma proteins was irreversible to a great extent. The most abundant metabolites identified in feces were desmethyl metabolite (AST5902), cysteine conjugate (M19), and parent drug (M0), which accounted for 6.28%, 5.52%, and 1.38% of the dose, respectively. After intragastric administration of 124 μCi/9.93 mg/kg [14C]-furmonertinib to rats, drug-related substances were widely and rapidly distributed in tissues within 4 h. The concentration of total radioactivity in the lung was 100-fold higher than that in rat plasma, which could be beneficial to the treatment of lung cancer. Mass balance in humans was achieved with 77.8% of the administered dose recovered in excretions within 35 days after administration, including 6.63% and 71.2% in urine and feces, respectively. In conclusion, [14C]-furmonertinib is completely absorbed and rapidly distributed into lung tissue, extensively metabolized in humans, presented mostly as covalent conjugates in plasma, and slowly eliminated mostly via fecal route.

Efficacy of systemic administration of riboflavin on a rabbit model of corneal alkali burn

Changes in the barrier mechanisms in the eye should determine the rational route for the administration and dosage of each drug in the treatment of traumatic injuries and other pathologies. The aim of this study was to examine the efficacy of intra-arterial delivery of 14C-riboflavin (as an “indicator”) and compare it with intravenous and intramuscular administration in an animal model of chemical eye burn. 14C-riboflavin (14C-I) was administered by intra-arterial (carotid artery), intravenous (femoral vein) and intramuscular (femoral muscle) routes. The total radioactivity was determined over 2 h in the plasma and structures of the rabbit’s eyes using a scintillation counter. The results of the study show that intravascular administration of 14C-I gives significantly higher concentrations of total radioactivity in the blood and is accompanied by a significant increase in the permeability of the blood-barrier and barrier in eyes suffering from burns. The highest concentration in the plasma and aqueous humour of the anterior chamber of the eye was observed during the first hour with the intra-arterial route of administration of 14C-I in either burnt and unburnt eyes. The distribution of total radioactivity in the structures of the eye over the 2 h of the experiment showed a higher level of the drug under intra-arterial administered in the uveal regions, namely: the iris, ciliary body, choroid, retina and also the sclera and cornea. This experimental model shows that intra-arterial administration can increase the bioavailability of a drug to the structures of the eye within a short period of time.

Metabolism and disposition in rats, dogs, and humans of erdafitinib, an orally administered potent pan-fibroblast growth factor receptor (FGFR) tyrosine kinase inhibitor

This article describes in vivo biotransformation and disposition of erdafitinib following single oral dose of 3H-erdafitinib and 14C-erdafitinib to intact and bile duct-cannulated (BC) rats (4 mg/kg), 3H-erdafitinib to intact dogs (0.25 mg/kg), and 14C-erdafitinib to humans (12 mg; NCT02692677). Peak plasma concentrations of total radioactivity were achieved rapidly (T max: animals, 1 h; humans, 2–3 h). Recovery of drug-derived radioactivity was significantly slower in humans (87%, 384 h) versus animals (rats: 91–98%, 48 h; dogs: 81%, 72 h). Faeces was the primary route of elimination in intact rats (95%), dogs (76%), and humans (69%); and bile in BC rats (48%). Renal elimination of radioactivity was relatively low in animals (2–12%) versus humans (19%). Unchanged erdafitinib was major component in human excreta (faeces, 17%; urine, 11%) relative to animals. M6 (O-desmethyl) was the major faecal metabolite in humans (24%) and rats (intact, 46%; BC, 11%), and M2 (O-glucuronide of M6) was the prevalent biliary metabolite in rats (14%). In dogs, besides M6, majority of radioactive dose in faeces was composed of multiple minor metabolites. In humans, unchanged erdafitinib was the major circulating entity. O-demethylation of erdafitinib was the major metabolic pathway in humans and animals.

471 Investigating the Tissue Distribution of [14C]-Prucalopride Following a Single Oral Dose in Rats

INTRODUCTION: Prucalopride is a selective, high-affinity agonist of the 5-hydroxytryptamine-4 (5-HT4) receptor and is indicated for the treatment of adult patients with chronic constipation. In humans, prucalopride is rapidly absorbed and extensively distributed, reaching maximum plasma concentration 2–3 h after a 2 mg oral dose. We report three studies investigating tissue distribution of prucalopride in rats. METHODS: A single oral dose of 14C-labelled prucalopride at 5mg base-equivalent(eq)/kg was administered to 30 SPF Wistar rats (5 males, seven groups of 3 non-pregnant females and 4 pregnant females [dose administered on day 18 of gestation]). Total radioactivity (TR) in various tissues was measured up to 96h. In females, the area under the TR concentration curve for up to 8h (AUC0–8h) and the AUC0–8h tissue:plasma ratio was calculated. The tissue concentration of unchanged drug (UD) was measured up to 48 h. RESULTS: The highest mean TR for all rats was detected in the pancreas (8.9µg-eq/g within 30 min of dosing; below the limit of detection [LOD] after 24 h), the liver (12.5 µg-eq/g within 20 min; 0.3 µg-eq/g after 96 h) and the small intestine (15.6µg-eq/g within 30 min; below the LOD after 24 h). The highest mean concentration of UD in non-pregnant females was detected in the small intestine (10.1 µg-eq/g within 20 min; below the LOD after 24 h). The lowest mean TR was detected in the brain, in males (0.12 µg-eq/g within 30 min), non-pregnant females (0.21 µg-eq/g within 1 h) and pregnant females (0.21 µg-eq/g within 30 min). TR in the brain was below the LOD within 2, 24 and 8 h of dosing, respectively. In non-pregnant females, the highest AUC0–8h and AUC0–8h tissue:plasma ratios of TR were observed in the small intestine (75.3 and 31.3, respectively); the lowest values were observed in the brain (0.85 and 0.35, respectively). Findings were similar for UD. In pregnant females the highest AUC0–8h and AUC0–8h tissue:plasma ratios of TR were observed in rectal (mucosa) and salivary gland tissue (122 and 20.5, respectively, for both); the lowest values were observed in the brain (0.33 and 0.17 [AUC0–2h], respectively). CONCLUSION: After a single oral dose of prucalopride, high concentrations were detected in the pancreas, liver and small intestine, and very low concentrations in the brain (∼0.05% of the dose in non-pregnant female rats). Mean concentrations of TR and UD in the brain were below the LOD within 24h of dosing, suggesting prucalopride is not unduly retained in the brain.

Evaluation of absorption, distribution, metabolism, and excretion of [14C]-rucaparib, a poly(ADP-ribose) polymerase inhibitor, in patients with advanced solid tumors

SummaryRucaparib, a poly(ADP-ribose) polymerase inhibitor, is licensed for use in recurrent ovarian, fallopian tube, or primary peritoneal cancer. We characterized the absorption, distribution, metabolism, and elimination of rucaparib in 6 patients with advanced solid tumors following a single oral dose of [14C]-rucaparib 600 mg (≈140 μCi). Total radioactivity (TRA) in blood, plasma, urine, and feces was measured using liquid scintillation counting. Unchanged rucaparib concentrations in plasma were determined using validated liquid chromatography with tandem mass spectrometry. Maximum concentration (Cmax) of TRA and unchanged rucaparib in plasma was 880 ng Eq/mL and 428 ng/mL, respectively, at approximately 4 h post dose; terminal half-life was >25 h for both TRA and rucaparib. The plasma TRA-time profile was parallel to yet higher than that of rucaparib, suggesting the presence of metabolites in plasma. Mean blood:plasma ratio of radioactivity was 1.0 for Cmax and 0.8 for area under the concentration-time curve from time zero to infinity. Mean postdose recovery of TRA was 89.3% over 12 days (71.9% in feces; 17.4% in urine). Unchanged rucaparib and M324 (oxidative metabolite) were the major components in plasma, contributing to 64.0% and 18.6% of plasma radioactivity, respectively. Rucaparib and M324 were the major rucaparib-related components (each ≈7.6% of dose) in urine, whereas rucaparib was the predominant component (63.9% of dose) in feces. The high fecal recovery of unchanged rucaparib could be attributed to hepatic excretion and/or incomplete oral absorption. Overall, these data suggest that rucaparib is eliminated through multiple pathways, including metabolism and renal and biliary excretion.

Pre-discard estimation of radioactivated materials in positron emission tomography cyclotron systems and concrete walls of a cyclotron vault.

The concrete vault, cyclotron body, and peripheral equipment in a cyclotron room become radioactivated by neutrons generated by operating an unshielded cyclotron. Radionuclides and the amounts of radioactivated materials must be identified before discarding a cyclotron system. The present study aimed to reduce the amounts of concrete from cyclotron vaults, as well as cyclotron components and peripheral equipment, that will be disposed of as radioactivated waste by clarifying the nature and quantity of radioactivated materials remaining in facilities after cyclotron operations have ceased. Cylindrical concrete cores were bored into all four walls, ceiling, and floor of a room where a Cypris 370 cyclotron had been operated for 22.8yr and then cooled for 40months. The accelerated particles comprised protons and deuterons with constant energy of 18 and 10MeV, respectively. The types and amounts of radionuclides in these cores, in 38 components of the cyclotron including the yoke, and in 13 pieces of equipment in the room, were determined by γ-ray spectrometry. Concentrations of radioactivity were also calculated using an updated version of Particle and Heavy Ion Transport System and DCHAIN-SP. Amounts of materials with both measured and calculated total radioactivity concentration (ΣD) of <0.1Bq/g were identified as being nonradioactivated. The major radionuclides in the concrete were 60 Co and 152 Eu. The radioactivated concrete was distributed to a depth of <38cm. Most cyclotron components and equipment were radioactivated by neutrons. The major radionuclides in cyclotron components and equipment were 54 Mn, 60 Co, and 65 Zn. A 33% volume of the yoke was regarded as nonradioactivated. The estimated amount of radioactivated waste in the concrete was about 70,000kg (12.5% of the total concrete). Most components of the cyclotron except for the 33% volume of the yoke (20% of the cyclotron body), as well as most peripheral equipment in the room, were radioactivated. Part-by-part assessments of radioactive materials using measurements and calculations could distinguish nonradioactive from radioactive materials before they are discarded.

Mass balance, metabolic disposition, and pharmacokinetics of a single oral dose of regorafenib in healthy human subjects

PurposeTo evaluate the mass balance, metabolic disposition, and pharmacokinetics of a single dose of regorafenib in healthy volunteers. In addition, in vitro metabolism of regorafenib in human hepatocytes was investigated.MethodsFour healthy male subjects received one 120 mg oral dose of regorafenib containing approximately 100 µCi (3.7 MBq) [14C]regorafenib. Plasma concentrations of parent drug were derived from HPLC–MS/MS analysis and total radioactivity from liquid scintillation counting (LSC). Radiocarbon analyses used HPLC with fraction collection followed by LSC for all urine samples, plasma, and fecal homogenate extracts. For the in vitro study, [14C]regorafenib was incubated with human hepatocytes and analyzed using HPLC–LSC and HPLC–HRMS/MS.ResultsRegorafenib was the major component in plasma, while metabolite M-2 (pyridine N-oxide) was the most prominent metabolite. Metabolites M-5 (demethylated pyridine N-oxide) and M-7 (N-glucuronide) were identified as minor plasma components. The mean concentration of total radioactivity in plasma/whole blood appeared to plateau at 1–4 h and again at 6–24 h post-dose. In total, 90.5% of administered radioactivity was recovered in the excreta within a collection interval of 12 days, most of which (71.2%) was eliminated in feces, while excretion via urine accounted for 19.3%. Regorafenib (47.2%) was the most prominent component in feces and was not excreted into urine. Excreted metabolites resulted from oxidative metabolism and glucuronidation.ConclusionsRegorafenib was eliminated predominantly in feces as well as by hepatic biotransformation. The multiple biotransformation pathways of regorafenib decrease the risk of pharmacokinetic drug–drug interactions.

What's NORMal for Fracking? Estimating Total Radioactivity of Produced Fluids.

Naturally occurring radioactive materials (NORM) found in liquid wastes from hydraulic fracturing are an emerging environmental health concern.1 The heavily drilled Marcellus Shale, for example, contains isotopes of radium, polonium, and lead.2,3 However, the few studies that have focused on NORM in fracking wastewater (produced fluids) have reported on a single element—radium.4,5 In this issue of EHP, researchers estimate total reactivity for a mixture of isotopes present in liquid fracking waste from the Marcellus Shale.3 Decay chains—the series of transformations that radionuclides undergo until a stable isotope is produced—are important in planning for the treatment, management, and disposal of radioactive waste.6 Long-lived radioactive elements (such as 226radium) transform into shorter-lived decay products (such as 210lead and 210polonium). Some decay products approach the same radioactivity concentration as the parent radionuclide in a matter of days, while others do so over many decades. In heavily drilled areas like the Marcellus Shale region, fracking activities often take place near homes and workplaces. For the study, researchers at the University of Iowa modeled how concentrations of radionuclides in fracking waste, and thus levels of radioactivity, would change over time. The researchers obtained a sample of fracking wastewater collected from the Marcellus Shale region in 2012 and sealed in a 200-liter drum. They used gamma and alpha spectrometry to measure existing levels of radionuclides in the sealed sample. Using models to account for radioactive decay and ingrowth (increasing concentrations of decay products), the researchers estimated how the total radioactivity concentration of the produced fluids would change in the foreseeable future. “Much of the work we present here was used to develop and validate a rapid radioactivity measurement method for a federal agency,” says lead author Andrew Nelson, a Presidential Graduate Research Fellow and PhD candidate in human toxicology. “We had to have a controlled environment so we could be sure what we were measuring and confident in our analyses. If we left the cap open always, the values would be changing unpredictably.” Under the closed-system conditions, the researchers estimated that the radioactivity concentration would increase by a factor of more than five within 15 days as a result of radioactive ingrowth. They measured an increase in the decay products 210lead and 228thorium in the closed system, and they predicted that radioactivity would continue to increase for more than 100 years with the formation of the decay products 210lead and 210polonium. “We know so little about the extent to which these contaminants represent major health concerns,” says James Burch, an associate professor in the University of South Carolina Department of Epidemiology and Biostatistics. “This study lays the foundation for a more detailed investigation of the health impacts of radioactive waste that may be generated from fracking.” Burch was not involved in the current study. Because fracking activities and wastewater disposal often take place in close proximity to where people live and work, there’s a potential for human exposure, according to Burch. “The technology is vastly outpacing what we know about the health effects,” he says. A few cases of radioactive contamination outside of wastewater treatment facilities have been documented. In one notable example, researchers studied wastewater effluent discharged by the Josephine Brine Treatment Facility in Pennsylvania. In stream sediments near the facility, the researchers measured concentrations of 226radium that were approximately 200 times higher than would normally be expected.7 The authors of the current study conclude that future studies and risk assessments should include radium decay products in assessing the potential for environmental contamination from fracking”5 Nelson calls the current research a “conversation starter” that aims to inform risk assessment and waste handling. “If you don’t have an accurate measurement of the radiochemical parameters, you can’t have an accurate dose assessment,” he says. While the experimental design represents a starting point, it’s unclear how applicable the projections would be under real-world conditions where fluids are being moved around, handled, and exposed to the air, says Arthur Rose, an environmental geochemist and professor emeritus at Pennsylvania State University, who was not involved in the research. “In this study you have a worst-case scenario in which all the decay products remain in the water,” Rose says. “A more likely scenario would be that some of the radon would escape into the air. Future studies need to look at radon release.” In ongoing field studies, Nelson and colleagues are applying new methods they developed to real-world scenarios. One study is looking at how radioactivity concentrations of naturally occurring radionuclides and their decay products change over time at a wastewater treatment facility that handles unconventional drilling waste.

Biodistribution and Metabolism Studies of Lipid Nanoparticle–Formulated Internally [3H]-Labeled siRNA in Mice

Absorption, distribution, metabolism, and excretion properties of a small interfering RNA (siRNA) formulated in a lipid nanoparticle (LNP) vehicle were determined in male CD-1 mice following a single intravenous administration of LNP-formulated [(3)H]-SSB siRNA, at a target dose of 2.5 mg/kg. Tissue distribution of the [(3)H]-SSB siRNA was determined using quantitative whole-body autoradiography, and the biostability was determined by both liquid chromatography mass spectrometry (LC-MS) with radiodetection and reverse-transcriptase polymerase chain reaction techniques. Furthermore, the pharmacokinetics and distribution of the cationic lipid (one of the main excipients of the LNP vehicle) were investigated by LC-MS and matrix-assisted laser desorption ionization mass spectrometry imaging techniques, respectively. Following i.v. administration of [(3)H]-SSB siRNA in the LNP vehicle, the concentration of parent guide strand could be determined up to 168 hours p.d. (post dose), which was ascribed to the use of the vehicle. This was significantly longer than what was observed after i.v. administration of the unformulated [(3)H]-SSB siRNA, where no intact parent guide strand could be observed 5 minutes post dosing. The disposition of the siRNA was determined by the pharmacokinetics of the formulated LNP vehicle itself. In this study, the radioactivity was widely distributed throughout the body, and the total radioactivity concentration was determined in selected tissues. The highest concentrations of radioactivity were found in the spleen, liver, esophagus, stomach, adrenal, and seminal vesicle wall. In conclusion, the LNP vehicle was found to drive the kinetics and biodistribution of the SSB siRNA. The renal clearance was significantly reduced and its exposure in plasma significantly increased compared with the unformulated [(3)H]-SSB siRNA.

Biodistribution of single-walled carbon nanotubes in rats

Background: Carbon nanotube (CNT) mediated drug delivery systems have recently aroused a great deal of interest. Such delivery systems for drugs, proteins and genes have been preliminarily studied using cellular and animal models. For further study of the related biological behaviours of CNTs in vivo, a fast and convenient tracing method is particularly necessary. Methods: We adopted concentrated nitric acid/concentrated sulfuric acid oxidation combined with ultrasonication to treat SWCNTs, then detected and analyzed the samples before and after treatment by transmission electron microscopy (TEM), Fourier transform infrared spectrometry (FT-IR), energy dispersive X-ray spectrometry (EDX) and X-ray photoelectron spectroscopy (XPS). The iodogen oxidative method was used to synthesize iodinated single-walled carbon nanotubes, followed by intratracheal instillation of 125I-labelled SWCNTs to determine their distribution in rats. Results: SWCNTs form more hydroxyl and carboxyl functional groups with no change in their essential characteristics after treatment by violet acid oxidation combined with ultrasonication. 125I can easily form C–I covalent bonds to SWCNTs. The proportion of iodine-125 labelled SWCNTs is 46.14%, the radiochemical purity is 98.95%. In order of total radioactivity concentration in the main organs/tissues and body fluids for 125I-SWCNTs, it was shown that trachea > urine > stomach > small intestine > serum > bladder > blood vessel > kidney > liver > lung > adrenal > femoral head > spleen > testis > thymus > thyroid > heart > fat > muscle > brain. Conclusions: In this paper, we developed a generally adoptable tracing method for studying the biodistribution of SWCNTs (single walled carbon nanotubes) in vivo. SWCNTs could be labelled with radioactive 125I atoms. The 125I labelling method is reliable and effective and affords a quantitative analysis of CNTs accumulated in animal tissues. This result will provide an important reference for future research into the biomedical and pharmacological applications of SWCNTs.

Metabolism and Disposition of the Metabotropic Glutamate Receptor 5 Antagonist (mGluR5) Mavoglurant (AFQ056) in Healthy Subjects

The disposition and biotransformation of (14)C-radiolabeled mavoglurant were investigated in four healthy male subjects after a single oral dose of 200 mg. Blood, plasma, urine, and feces collected over 7 days were analyzed for total radioactivity, mavoglurant was quantified in plasma by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS), and metabolite profiles were generated in plasma and excreta by high-performance liquid chromatography (HPLC) and radioactivity detection. The chemical structures of mavoglurant metabolites were characterized by LC-MS/MS, wet-chemical and enzymatic methods, NMR spectroscopy, and comparison with reference compounds. Mavoglurant was safe and well tolerated in this study population. Mavoglurant absorption was ≥50% of dose reaching mean plasma Cmax values of 140 ng/ml (mavoglurant) and 855 ng-eq/ml (total radioactivity) at 2.5 and 3.6 hours, respectively. Thereafter, mavoglurant and total radioactivity concentrations declined with mean apparent half-lives of 12 and 18 hours, respectively. The elimination of mavoglurant occurred predominantly by oxidative metabolism involving primarily 1) oxidation of the tolyl-methyl group to a benzyl-alcohol metabolite (M7) and subsequently to a benzoic acid metabolite (M6), and 2) oxidation of the phenyl-ring leading to a hydroxylated metabolite (M3). The subjects were mainly exposed to mavoglurant and seven main metabolites, which combined accounted for 60% of (14)C-AUC0-72 h (area under the concentration-time curve from time 0 to infinity). The primary steps of mavoglurant metabolism observed in vivo could partially be reproduced in vitro in incubations with human liver microsomes and recombinant cytochrome P450 enzymes. After 7 days, the mean balance of total radioactivity excretion was almost complete (95.3% of dose) with 36.7% recovered in urine and 58.6% in feces.

Absorption, disposition, metabolic fate and elimination of the anti-epileptic drug lacosamide in humans: mass balance following intravenous and oral administration

The absorption, distribution, metabolism and elimination of the anti-epileptic drug lacosamide were determined in 10 healthy male volunteers following intravenous or oral administration in a single-center, open-label, single-dose trial. Volunteers were randomized to receive either a continuous intravenous infusion of 100 mg (40 μCi) [¹⁴C]-lacosamide administered over 60 min, or a 100 mg (40 μCi) [¹⁴C]-lacosamide dose given as an oral solution. During the infusion, total radioactivity concentrations reached peak levels at 1 h post dose followed by a decline of 71 % within 24 h. More than 97 % of radioactivity was excreted within 168 h; 96.8 % in urine and 0.3 % in feces. Following oral administration, total radioactivity concentrations increased to peak levels within 0.5 h followed by a decline of 65 % within 24 h. Approximately 94.6 % of radioactivity was excreted within 168 h after oral administration, 94.2 % by the kidneys and 0.4% in feces. A comparison of AUC values (po/iv) of unchanged lacosamide indicates a high absolute bioavailability. The metabolic profile was analyzed using pooled urine samples, and following intravenous and oral administration, respectively, a total of 38 and 34 % unchanged lacosamide, 28 and 28 % of the desmethyl metabolite and 19 and 17 % of a polar fraction were measured. Additional metabolites were identified only in small amounts (<3 %). In plasma at maximum concentration, most of the total radioactivity was found as unchanged drug after intravenous and oral dose. The plasma concentration curves of total radioactivity following intravenous and oral administration were similar.

Absorption, distribution, metabolism, and excretion of macitentan, a dual endothelin receptor antagonist, in humans

Macitentan is a tissue-targeting, dual endothelin receptor antagonist, currently under phase 3 investigation in pulmonary arterial hypertension.In this study the disposition and metabolism of macitentan were investigated following administration of a single oral 10 mg dose of 14C-macitentan to six healthy male subjects.The total radioactivity in matrices was determined using liquid scintillation counting. The proposed structure of metabolites was based on mass spectrometry characteristics and, when available, confirmed by comparison with reference compounds.Mean (± SD) cumulative recovery of radioactivity from faeces and urine was 73.6% (±6.2%) of the administered radioactive dose, with 49.7% (±3.9%) cumulative recovery from urine, and 23.9% (±4.8%) from faeces. In plasma, in addition to parent macitentan, ACT-132577, a pharmacologically active metabolite elicited by oxidative depropylation and the carboxylic acid metabolite ACT-373898 were identified. In urine, four entities were identified, with the hydrolysis product of ACT-373898 as the most abundant one. In faeces, five entities were identified, with the hydrolysis product of macitentan and ACT-132577 as the most abundant one. Concentrations of total radioactivity in whole blood were lower compared to plasma, which indicates that macitentan and its metabolites poorly bind to or penetrate into erythrocytes.

Abstract 1291: A phase 1 open-label single-radiolabeled dose study of PF299804 in healthy male volunteers

Abstract Objectives: To characterize the primary routes of elimination of the second-generation, oral, irreversible, pan-HER tyrosine kinase inhibitor, PF299804; to evaluate the pharmacokinetics (PK) of total radioactivity and of PF299804; and to identify the metabolites of PF299804 in plasma, urine, and feces in healthy volunteers (HVs). Methods: This Phase 1 study evaluated the mass balance and PK of PF299804 in HVs (18-55 yrs), following a single 45-mg oral dose containing ∼100 µCi [14C] PF299804. Serial samples were collected over an 18-day period. Radioactivity measurements of blood, plasma, urine, and feces were conducted by liquid scintillation spectroscopy. Plasma samples were analyzed for PF299804 and the metabolite PF5199265 using high-performance liquid chromatography with atmospheric pressure ionization tandem mass spectrometry. Plasma, urine, and fecal samples were analyzed for metabolic profiling of PF299804; major metabolites of PF299804 were identified where possible. Results: 6 HVs (male; median age 31.5 yrs) received treatment and were evaluated for PK and safety. 78.8% of the radiolabeled material was excreted in feces, and a further 3.2% was recovered in urine. Peak concentrations of PF299804 in plasma generally occurred 12 hrs after oral dosing, and 6 hrs post-dose for PF5199265. Plasma exposure for the metabolite was approximately one-third of that for the parent compound. Terminal plasma half-life (t1/2) averaged about 55 hrs for PF299804 and 73 hrs for PF5199265. Peak concentrations of total radioactivity in plasma occurred at 12 hrs. Geometric mean Cmax was approximately 2-fold higher and total exposure (AUCinf) was almost 6-fold higher for total radioactivity than for PF299804 in plasma. t1/2 for plasma radioactivity was 182 hrs. PF299804 and its O-desmethyl metabolite, PF5199265, were the major drug-related components in plasma. Other trace components were observed in the profile. The most abundant drug-related components identified in excreta were proposed to be PF299804, PF5199265, a cysteine conjugate (M2), and a mono-oxygenated metabolite (M7). There were no serious adverse events (AEs), severe AEs, or deaths during the study. Mild AEs were reported in 2 HVs: dermatitis acneiform, dizziness, insomnia, and photophobia (all considered related to study drug). Conclusions: Following single-dose administration of [14C] PF299804 the radiolabeled material was primarily eliminated in feces (78.8%) and, to a lesser degree, in urine (3.2%). Estimates of exposure for total radioactivity in plasma (Cmax and AUCinf) were 2- and 6-fold higher, respectively, than exposure for plasma PF299804, indicating the presence of circulating metabolic product(s). The metabolic profiles indicated that [14C] PF299804 underwent oxidative and conjugative metabolism in HVs. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1291. doi:10.1158/1538-7445.AM2011-1291

Mass Balance and Pharmacokinetics of [ 14 C]Telavancin following Intravenous Administration to Healthy Male Volunteers

The mass balance and pharmacokinetics of telavancin, a semisynthetic lipoglycopeptide antimicrobial agent, were characterized in an open-label, phase 1 study of six healthy male subjects. After a single 1-h intravenous infusion of 10 mg/kg [14C]telavancin (0.68 microCi/kg), blood, urine, and feces were collected at regular intervals up to 216 h postdose. Whole blood, plasma, urine, and fecal samples were assayed for total radioactivity using scintillation counting; plasma and urine were also assayed for parent drug and metabolites using liquid chromatography with tandem mass spectrometry. The concentration-time profiles for telavancin and total radioactivity in plasma were comparable from 0 to 24 h after the study drug administration. Telavancin accounted for >95% and 83% of total radioactivity in plasma at 12 h and 24 h, respectively. By 216 h, approximately 76% of the total administered dose was recovered in urine while only 1% was collected in feces. Unchanged telavancin accounted for most (83%) of the eliminated dose. Telavancin metabolite THRX-651540 along with two other hydroxylated metabolites (designated M1 and M2) accounted for the remaining radioactivity recovered from urine. The mean concentrations of total radioactivity in whole blood were lower than the concentration observed in plasma, and mean concentrations of THRX-651540 in plasma were minimal relative to mean plasma telavancin concentrations. These observations demonstrate that most of an administered telavancin dose is eliminated unchanged via the kidneys. Intravenous telavancin at 10 mg/kg was well tolerated by all subjects.

Absorption, Disposition, Metabolic Fate, and Elimination of the Dopamine Agonist Rotigotine in Man: Administration by Intravenous Infusion or Transdermal Delivery

The dopamine agonist rotigotine was developed for the treatment of Parkinson's disease and restless legs syndrome. Disposition, metabolism, elimination, and absolute bioavailability of rotigotine were determined in six healthy male subjects by using two different forms of administration in a randomized sequence with a crossover design. Treatment A (continuous infusion) consisted of a single radiolabeled 12-h intravenous infusion of 1.2 mg of rotigotine (0.6 mg of [(14)C] and 0.6 mg of unlabeled rotigotine, 3.7 MBq) solution. Treatment B (transdermal application) consisted of a single 10-cm(2) patch containing 4.5 mg of unlabeled rotigotine with a patch-on period of 24 h. During the 12 h-infusion, total radioactivity concentration rapidly increased within 2 h; there was a slight additional increase toward the end of infusion. Plasma concentrations of total radioactivity declined by 75% within 12 h after completion of infusion. More than 94% of the radioactivity was excreted 216 h after the start of infusion, 71% by the kidneys and 23% by feces. Renal elimination of the parent compound was <1%. Systemically absorbed rotigotine was rapidly metabolized. The major rotigotine biotransformation pathway was conjugation of the parent compound, mainly by sulfation; a second pathway was the formation of phase 1 metabolites (N-desalkylation) with subsequent conjugation. Plasma concentration-time profiles of unchanged rotigotine during and after infusion and during and after patch administration were comparable. Absolute bioavailability of transdermally applied rotigotine was 37%.

Pharmacokinetics, tissue distribution and mass balance of radiolabeled dihydroartemisinin in male rats

BackgroundDihydroartemisinin (DHA), a powerful anti-malarial drug, has been used as monotherapy and artemisinin-based combination therapy (ACT) for more than decades. So far, however, the tissue distribution and metabolic profile of DHA data are not available from animal and humans.MethodsPharmacokinetics, tissue distribution, mass balance, and elimination of [14C] DHA have been studieded in rats following a single intravenous administration. Protein binding was performed with rat and human plasma. Drug concentrations were obtained up to 192 hr from measurements of total radioactivity and drug concentration to determine the contribution by the parent and metabolites to the total dose of drug injected from whole blood, plasma, urine and faecal samples.ResultsDrug was widely distributed after 1 hr and rapidly declined at 24 hr in all tissues except spleen until 96 hrs. Only 0.81% of the total radioactivity was detected in rat brain tissue. DHA revealed a high binding capacity with both rat and human plasma proteins (76–82%). The concentration of total radioactivity in the plasma fraction was less than 25% of that in blood total. Metabolism of DHA was observed with high excretion via bile into intestines and approximately 89–95% dose of all conjugations were accounted for in blood, urine and faeces. However, the majority of elimination of [14C] DHA was through urinary excretion (52% dose). The mean terminal half-lives of plasma and blood radioactivity (75.57–122.13 h) were significantly prolonged compared with that of unchanged DHA (1.03 h).ConclusionIn rat brain, the total concentration of [14C] was 2-fold higher than that in plasma, indicating the radioactivity could easily penetrate the brain-blood barrier. Total radioactivity distributed in RBC was about three- to four-fold higher than that in plasma, suggesting that the powerful anti-malarial potency of DHA in the treatment of blood stage malaria may relate to the high RBC binding. Biliary excretion and multiple concentration peaks of DHA have been demonstrated with high urinary excretion due to a most likely drug re-absorption in the intestines (enterohepatic circulation). The long lasting metabolites of DHA (> 192 hr) in the rats may be also related to the enterohepatic circulation.