Plasma Levels Of Radioactivity Research Articles

Absorption, metabolism, and excretion of [14C]-sebetralstat (KVD900) following a single oral dose in healthy male participants

Sebetralstat is an investigational oral plasma kallikrein inhibitor for the on-demand treatment of hereditary angioedema. Six healthy male participants received one dose of 600 mg (540 µCi) [14C]-sebetralstat. Plasma concentrations of sebetralstat and levels of total radioactivity in plasma, urine, and faeces were determined. Metabolite profiles of radioactivity were generated, and major metabolites structurally characterised. Radioactivity was rapidly absorbed and was excreted with a mean of 95.8% (63.4% faeces; 32.4% urine) recovered by 216 h. Sebetralstat was the major drug-related component in urine and faeces, although metabolism predominated overall (main metabolites: M19 (des-[methoxy-fluoro-methylpyridine]-sebetralstat), M10 (N-des-pyridone-sebetralstat-carboxylic acid), M3 (pyridine O-desmethyl-sebetralstat), and M34 (pyridine dioxy-dihydro-sebetralstat)). Sebetralstat was the main radiolabelled component in plasma (mean of 64.1% of the total radioactivity AUC0–24), followed by relatively low proportions of metabolites: M19 (7.10%), M3 (4.01%), and M10 (4.00%). Although M19 was >10% of the plasma radioactivity AUC0–24, in one participant it comprised a mean of <10% of AUC0–24. Plasma levels of M19 were measured at the NOAEL dose in a rat toxicology study, where higher exposure was observed vs. that in humans. Given these findings and the lack of pharmacological activity of M19, it was concluded that there was no unique or disproportionate circulating metabolite in humans.

Revisiting the Logan plot to account for non-negligible blood volume in brain tissue

BackgroundReference tissue-based quantification of brain PET data does not typically include correction for signal originating from blood vessels, which is known to result in biased outcome measures. The bias extent depends on the amount of radioactivity in the blood vessels. In this study, we seek to revisit the well-established Logan plot and derive alternative formulations that provide estimation of distribution volume ratios (DVRs) that are corrected for the signal originating from the vasculature.ResultsNew expressions for the Logan plot based on arterial input function and reference tissue were derived, which included explicit terms for whole blood radioactivity. The new methods were evaluated using PET data acquired using [11C]raclopride and [18F]MNI-659. The two-tissue compartment model (2TCM), with which signal originating from blood can be explicitly modeled, was used as a gold standard.DVR values obtained for [11C]raclopride using the either blood-based or reference tissue-based Logan plot were systematically underestimated compared to 2TCM, and for [18F]MNI-659, a proportionality bias was observed, i.e., the bias varied across regions. The biases disappeared when optimal blood-signal correction was used for respective tracer, although for the case of [18F]MNI-659 a small but systematic overestimation of DVR was still observed.ConclusionsThe new method appears to remove the bias introduced due to absence of correction for blood volume in regular graphical analysis and can be considered in clinical studies. Further studies are however required to derive a generic mapping between plasma and whole-blood radioactivity levels.

Thomas Alfred Plumley

The aim of this study was to determine the plasma levels and the tissue distribution of otilonium bromide, measured as total radioactivity, after oral administration of 2 mg/kg of¹⁴C-labeled drug...

Disposition and Metabolism of GSK2251052 in Humans: A Novel Boron-Containing Antibiotic

(S)-3-(Aminomethyl)-7-(3-hydroxypropoxy)-1-hydroxy-1,3-dihydro-2,1-benzoxaborole (GSK2251052) is a novel boron-containing antibiotic that inhibits bacterial leucyl tRNA synthetase, and that has been in development for the treatment of serious Gram-negative infections. In this study, six healthy adult male subjects received a single i.v. dose of [¹⁴C]GSK2251052, 1500 mg infused over 1 hour. Blood, urine, and feces were collected over an extended period of 14 days, and accelerator mass spectrometry was used to quantify low levels of radioactivity in plasma at later time points to supplement the less-sensitive liquid scintillation counting technique. An excellent mass balance recovery was achieved representing a mean total of 98.2% of the dose, including 90.5% recovered in the urine. Pharmacokinetic analysis demonstrated that radioactivity was moderately associated with the blood cellular components, and together with GSK2251052, both were highly distributed into tissues. The parent compound had a much shorter half-life than total radioactivity in plasma, approximately 11.6 hours compared with 96 hours. GSK2251052 and its major metabolite M3, which resulted from oxidation of the propanol side chain to the corresponding carboxylic acid, comprised the majority of the plasma radioactivity, 37 and 53% of the area under the plasma versus time concentration curve from time zero to infinity, respectively. Additionally, M3 was eliminated renally, and was demonstrated to be responsible for the long plasma radioactivity elimination half-life. A combination of in vitro metabolism experiments and a pharmacokinetic study in monkeys with the inhibitor 4-methylpyrazole provided strong evidence that alcohol dehydrogenase, potentially in association with aldehyde dehydrogenase, is the primary enzyme involved in the formation of the M3 metabolite.

Maximizing tumour exposure to anti‐neuropilin‐1 antibody requires saturation of non‐tumour tissue antigenic sinks in mice

Neuropilin-1 (NRP1) is a VEGF receptor that is widely expressed in normal tissues and is involved in tumour angiogenesis. MNRP1685A is a rodent and primate cross-binding human monoclonal antibody against NRP1 that exhibits inhibition of tumour growth in NPR1-expressing preclinical models. However, widespread NRP1 expression in normal tissues may affect MNRP1685A tumour uptake. The objective of this study was to assess MNRP1685A biodistribution in tumour-bearing mice to understand the relationships between dose, non-tumour tissue uptake and tumour uptake. Non-tumour-bearing mice were given unlabelled MNRP1685A at 10 mg·kg(-1) . Tumour-bearing mice were given (111) In-labelled MNRP1685A along with increasing amounts of unlabelled antibody. Blood and tissues were collected from all animals to determine drug concentration (unlabelled) or radioactivity level (radiolabelled). Some animals were imaged using single photon emission computed tomography - X-ray computed tomography. MNRP1685A displayed faster serum clearance than pertuzumab, indicating that target binding affected MNRP1685A clearance. I.v. administration of (111) In-labelled MNRP1685A to tumour-bearing mice yielded minimal radioactivity in the plasma and tumour, but high levels in the lungs and liver. Co-administration of unlabelled MNRP1685A with the radiolabelled antibody was able to competitively block lungs and liver radioactivity uptake in a dose-dependent manner while augmenting plasma and tumour radioactivity levels. These results indicate that saturation of non-tumour tissue uptake is required in order to achieve tumour uptake and acceptable exposure to antibody. Utilization of a rodent and primate cross-binding antibody allows for translation of these results to clinical settings.

Afatinib pharmacokinetics and metabolism after oral administration to healthy male volunteers

To investigate the pharmacokinetics, metabolism and tolerability of afatinib (BIBW 2992), an oral irreversible ErbB family blocker, in healthy male volunteers. In this open-label, single-center study, 8 healthy male volunteers received a single oral dose of 15 mg [(14)C]-radiolabeled afatinib (equivalent to 22.2 mg of the dimaleinate salt) as a solution. Blood, urine and fecal samples were collected for at least 96 hours (h) after dosing. Plasma and urine concentrations of afatinib were analyzed using high-performance liquid chromatography-tandem mass spectrometry. [(14)C]-radioactivity levels in plasma, whole blood, urine and feces were measured by liquid scintillation counting methods. Metabolite patterns were assessed by high-performance liquid chromatography. [(14)C]-radioactivity was mainly excreted via feces (85.4%). Overall recovery of [(14)C]-radioactivity was 89.5%, indicative of a complete mass balance. Afatinib was slowly absorbed, with maximum plasma concentrations achieved at a median of 6 h after dosing, declining thereafter in a biexponential manner. The geometric mean terminal half-life of afatinib was 33.9 h in plasma and longer for [(14)C]-radioactivity in plasma and whole blood. Apparent total body clearance for afatinib was high (geometric mean 1,530 mL/min). The high volume of distribution (4,500 L) in plasma may indicate a high tissue distribution. Afatinib was metabolized to only a minor extent, with the main metabolite afatinib covalently bound to plasma proteins. Oxidative metabolism mediated via cytochrome P-450 was of negligible importance for the elimination of afatinib. Afatinib was well tolerated. Afatinib displayed a complete mass balance with the main route of excretion via feces. Afatinib undergoes minimal metabolism.

Abstract 4588: Tumor distribution of anti-neuropilin-1 is affected by antibody dose level in a tumor xenograft mouse model

Abstract Neuropilin-1 (NRP1) is a VEGF165 and semaphorin receptor widely expressed by vascular endothelial cells in normal tissues and on some tumor cells. Blocking NRP1 with human IgG1 against its b domain has been shown to inhibit tumor growth in several preclinical models. The objective of this study was to assess tumor distribution of anti-NRP1 at different dose levels with the aim of supporting the clinical development of this antibody. Nude mice bearing HM7 tumors were administered [111In]-DOTA labeled anti-NRP1 in the presence of increasing amounts of unlabeled anti-NRP1 via single IV injection. Following dosing, blood and tumors were collected at pre-selected time points. Tumor distribution was evaluated by measuring the radioactivity levels in the tumor and blood samples using a gamma counter. The mice that received only the radiolabeled antibody had relatively low plasma and tumor radioactivity levels at all time points. The plasma and tumor radioactivity levels for all other dose groups were higher than those of the group that received only radiolabeled antibody due to the saturation of the normal tissue sink previously identified. Comparing the tumor to blood radioactivity ratios demonstrated that the different dose groups maintained maximum exposure in the tumor for variable lengths of time, depending on the dose level. At 24 hours post-dose, all doses greater than the radiolabeled antibody alone were able to maintain maximum exposure. Conversely, at 48 hours post-dose, doses ≥ 10 mg/kg were able to maintain that level, while at 120 hours post-dose, only doses ≥ 20 mg/kg were able to maintain maximum exposure. Taken together, this suggests that tumor distribution is both dose and time dependent. This approach has been used to aid the clinical dose selection for anti-NRP1 and may be a valuable tool for the clinical development of other targeted therapies. 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 4588. doi:10.1158/1538-7445.AM2011-4588

The bioavailability in man of ICRF-159 a new oral antineoplastic agent.

The bioavailability of the antineoplastic agent, ICRF-159, has been examined in 12 patients receiving the drug in single and subdivided dose schedules in an attempt to account for the differences in toxicity found with the different schedules clinically. Recovery of radioactivity in the urine after single large doses (13.3-19.4 g) was 8.5 +/- 3.0% of the administered dose. After doses of 3.8-5.55 g recovery was 22.7 +/- 10.5% and after the same dose subdivided into 3 equal aliquots it was 52 +/- 8.7%. Unrecovered radioactivity was largely accounted for in the faeces. Plasma radioactivity levels in 2 patients after high and low dose were equivalent. Toxicity of the drug paralleled urinary recovery of radioactivity. It is concluded that schedule dependence of toxicity of ICRF-159 is at least partly due to bioavailability factors.

The effect of digoxin dosage on the digoxin-quinidine interaction in the bile duct-cannulated rat.

Pretreating anaesthetized bile duct-cannulated rats with 9 mg kg-1 quinidine significantly decreased the cumulative biliary excretion of digoxin and its metabolites after 10 or 100 micrograms kg-1 [3H]digoxin, although the effect was more marked in animals receiving the high dose of digoxin. In contrast, however, although quinidine pretreatment raised plasma radioactivity levels by 50-80% in animals given the higher dose of digoxin, no significant effect on circulating plasma levels was observed in rats receiving 10 micrograms kg-1 digoxin. Generally, quinidine had no statistically significant effect on other aspects of digoxin disposition, although with both digoxin doses there were trends towards a reduction in the direct intestinal secretion and urinary excretion of digoxin-derived radioactivity with an increase in tissue levels of radioactivity (apart from the small intestine wall where concentrations were reduced). The radioactivity in the bile after 100 or 10 micrograms kg-1 digoxin comprised about 25 and 33% of digoxin and digoxigenin bis-digitoxoside, respectively, as well as appreciable amounts of the monodigitoxoside and a highly polar component. This metabolite profile was unaffected by quinidine. The influence of cardiac glycoside dosage shown by the present work indicates that the digoxin-quinidine interaction and possibly analogous interactions involving other cardiac glycosides, may not always be readily detectable from plasma concentration data.

Metabolism and Excretion of Anacetrapib, a Novel Inhibitor of the Cholesteryl Ester Transfer Protein, in Humans

Anacetrapib is a novel cholesteryl ester transfer protein inhibitor being developed for the treatment of primary hypercholesterolemia and mixed dyslipidemia. The absorption, distribution, metabolism, and excretion of anacetrapib were investigated in an open-label study in which six healthy male subjects received a single oral dose of 150 mg and 165 microCi of [(14)C]anacetrapib. Plasma, urine, and fecal samples were collected at predetermined times for up to 14 days postdose and were analyzed for total radioactivity, the parent compound, and metabolites. The majority of the administered radioactivity (87%) was eliminated by fecal excretion, with negligible amounts present in urine (0.1%). The peak level of radioactivity in plasma (approximately 2 microM equivalents of [(14)C]anacetrapib) was achieved approximately 4 h postdose. The parent compound was the major radioactive component (79-94% of total radioactivity) in both plasma and feces. Three oxidative metabolites, M1, M2, and M3, were detected in plasma and feces and were identified as the O-demethylated species (M1) and two secondary hydroxylated derivatives of M1 (M2 and M3). Each metabolite was detected at low levels, representing <or=14% of the radioactivity in plasma or fecal samples. In vitro data indicated that anacetrapib is metabolized mainly by CYP3A4 to form M1, M2, and M3. Overall, these data, along with those from other preclinical and clinical studies, indicate that anacetrapib probably exhibits a low-to-moderate degree of oral absorption in humans and the absorbed fraction of the dose is eliminated largely via CYP3A4-catalyzed oxidative metabolism, followed by excretion of metabolites by the biliary-fecal route.

Pharmacokinetics (PK) of [14C]-BIBW 2992 after administration of a single dose of 15 mg [14C]-BIBW 2992 oral solution in healthy male volunteers

14607 Background: BIBW 2992 is a novel oral, potent and irreversible inhibitor of EGFR and HER2. This study investigated the PKs and the mass balance of a single oral dose of [14C]-radiolabelled BIBW 2992 in healthy male volunteers. Safety and tolerability of BIBW 2992 were also investigated. Methods: This was a Phase I, open label, single dose study with [14C]-radiolabelled BIBW 2992 performed at one study centre in 8 healthy male subjects receiving one single dose of 15 mg of BIBW 2992 containing 2.25 MBq of [14C]-radiolabelled BIBW 2992. Observation period for the collection of samples of blood, urine and feces was at least 120 hours. Plasma and urine concentrations of BIBW 2992 were analyzed using high performance liquid chromatography coupled to tandem mass spectrometry. [14C]-radioactivity levels in plasma, whole blood, urine and feces were analyzed by Liquid Scintillation Counting methods. Results: The major route of elimination of total [14C]-radioactivity was found to be via feces (85.4%) with an overall recovery of [14C]-radioactivity of 89.5%. For BIBW 2992 as well as for [14C]-plasma and whole blood radioactivity, maximum plasma concentrations were reached around 6 hours after dosing. The gMean terminal half-life (t1/2) was 33.9 hours for BIBW 2992, 118 hours for [14C]-radioactivity in plasma and 195 hours for [14C]-radioactivity in whole blood. A relatively high apparent total body clearance (CL/F) for BIBW 2992 was determined. The gMean CL/F values for the [14C]- radioactivity in plasma and whole blood were low. BIBW 2992 as well as [14C]-radioactivity in plasma and in whole blood exhibited a high apparent volume of distribution (Vz/F) during the terminal phase. BIBW 2992 was generally tolerated with only mild adverse events of short duration (all CTCAE Grade 1) reported. Conclusions: BIBW 2992 was safe and well tolerated at a single dose of 15 mg. The major route of elimination of BIBW 2992 is via feces. The data suggest the presence of one or more metabolites of BIBW 2992 in plasma and in whole blood with a longer terminal half-life than BIBW 2992. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Expert Testimony Other Remuneration Boehringer Ingelheim Pharma GmbH & Co. KG

Application of In-Line Liquid Chromatography-Accurate Radioisotope Counting-Mass Spectrometry (LC-ARC-MS) to Evaluate Metabolic Profile of [3H]-Mefenamic Acid in Rat Plasma

Profiling of rat plasma using a highly sensitive LC-ARC-MS technique showed that [(3)H] mefenamic acid was metabolized to several products, including a sulfate conjugate and a hydroxylated analogue as major metabolites. This technique of detecting low levels of radioactivity in plasma was superior to previously used methods, such as beta-RAM detectors.

Pharmacokinetics and bioavailability of diisopropanolamine (DIPA) in rats following intravenous or dermal application

This study was conducted to determine the relative dermal bioavailability (absorption), distribution, metabolism, and excretion (ADME) of diisopropanolamine (DIPA), an alcohol amine used in a number of industrial and personal care products. Groups of 4 female Fischer 344 rats received either a single bolus i.v. dose of 19.0 mg/kg 14C-DIPA in water or a dermal application of 19.5 mg/kg 14C-DIPA in acetone to an area of 1 cm 2 on the back and covered with a bandage. Time-course blood and excreta were collected and radioactivity determined. Urine was analyzed for DIPA and monoisopropanolamine (MIPA). Following i.v. administration, DIPA was rapidly cleared from the plasma and excreted into urine in a biexponential manner ( t 1/2 α , 0.4 h; t 1/2 β , 2.9 h). The levels of radioactivity in plasma dropped below the limit of detection 12 h post-dosing. A total of 97 ± 4% of the dose was actively excreted in urine by kidney, most (∼71%) within 6 h of dosing, virtually all as parent compound; renal clearance exceeded the glomerular filtration rate. Following dermal application, ∼20% of the dose was absorbed in 48 h with the steady-state penetration rate of ∼0.2%/h. Most (14.4%) of the applied radioactivity was excreted in urine at a relatively constant rate due to the presence of large amount of the 14C-DIPA at the application site. Fecal elimination was <0.2% of the dose. The absorbed DIPA did not accumulate in tissues; only ∼0.1% of the administered dose was found in liver and kidney. The absolute systemic dermal bioavailability (dose corrected AUC dermal/AUC i.v.) of 14C-DIPA was 12%. The ADME of DIPA contrasts that of its diethanol analogue, diethanolamine, which displays a broad spectrum of toxicity in rats and mice. Toxicologically significant concentrations of DIPA are unlikely to be achieved in the systemic circulation and/or tissues as a result of repeated dermal application of products containing DIPA due to slow absorption from the skin, rapid unchanged elimination in urine, and majority of the products contain ⩽1% DIPA.

THE EVALUATION OF RADIOLABELED ARTESUNATE ON TISSUE DISTRIBUTION IN RATS AND PROTEIN BINDING IN HUMANS

The present study reports the tissue distribution, pharmacokinetics, mass balance, and elimination of [(14)C] artesunate (AS) following single intravenous administration in rats. Protein binding was performed with rat and human plasma. Radioactivity and drug levels in blood, plasma, tissues, urine, and feces up to 192 hours were collected and measured. The mean terminal half-life of plasma (76 h) and blood (105 h) radioactivity was prolonged compared with that of unchanged AS (0.43 h) and dihydroartemisinin (0.75 h), an active metabolite of AS. Drug was widely distributed after 1 hour in select tissues. After 24 hours, the radioactivity rapidly declined in all tissues except spleen until 96 hours. Only 1% of total radioactivity was detected in brain tissue. AS revealed a higher binding capacity with human and rat plasma proteins (73-81%). The radioactivity in whole blood was higher (two to fourfold) than that in plasma throughout the period of the treatment, suggesting that AS binding to RBCs may relate to its powerful antimalarial activity.

Synthesis of radiolabelled 1-trichloromethyl-1,2,3,4-tetrahydro-β-carboline (TaClo), a neurotoxic chloral-derived mammalian alkaloid, and its biodistribution in rats

Chloral hydrate, the oldest synthetic hypnotic, is still among the most common agents used for conscious sedation of infants and children. Chloral (Clo) spontaneously condenses with the biogenic amine tryptamine (Ta) giving rise to the endogenous formation of 1-trichloromethyl-1,2,3,4-tetrahydro-β-carboline (TaClo). TaClo constitutes a mammalian alkaloid and a potent neurotoxin, which is capable of inducing a slowly developing degeneration of the dopaminergic system in rats. Due to the late onset of parkinsonian-type symptoms after TaClo administration, this agent has been postulated to be a potential natural inducer of Parkinson's disease. In order to elucidate its pharmacokinetics, its tissue distribution and excretion profile, radiolabelled [3- 14C]-TaClo was prepared in a convenient four-step synthetic pathway. Studies on rats intraperitoneally treated with a single dose of 2.1 mg/kg (0.6 μCi/kg) of [3- 14C]-TaClo·HCl (specific activity: 0.28 μCi/mg) revealed the radioactivity to be rapidly incorporated with the highest concentrations of 14C found in the excretory organs. [3- 14C]-TaClo was poorly absorbed systemically, as indicated by the very low plasma radioactivity levels. Maximum levels of 14C were reached between 2 and 6 h postdose, with the exception of large intestine peaking at 12 h after dosing. Total mean percent recovery of the radioactive dose was about 96% within the 48-h period examined. Urinary excretion accounted for ca. 34.5%, with the majority of the applied dose being eliminated by the hepatobiliary pathway.

Reliability of one-point blood sampling method for calculating input function in Na18F PET

Conventional methods of quantitative Na18F positron emission tomography require multiple arterial blood sampling in order to obtain the input function, and the procedures are invasive and complicated. This study aims to establish a simplified and reliable technique for obtaining the input function. Multiple arterial blood sampling was performed on 12 persons. The time point for one-point sampling was determined as the time when (1) the plasma radioactivity obtained showed the highest correlation to the real integrated value, which was calculated from the input function, and (2) the coefficient of variation of the real integrated value divided by plasma radioactivity obtained at each time point became the minimum. Scaling factors were obtained in order to estimate the plasma radioactivity at each time point, and a reference table was produced in order to estimate the input function. The optimal timing for one-point sampling was 12 min after intravenous injection of Na18F. The estimated integrated value obtained from arterial blood sampling at 12 min and the reference table was highly correlated with the real integrated value (P<0.001). Levels of plasma radioactivity of arterial blood and venous blood were almost the same at 12 and 40 min after Na18F injection. Percentage errors in the estimation of the integrated value were 2.63% (n=12) for the arterial blood collected at 12 min and 4.14% (n=12) for the venous blood collected at 30 min. This simplified method is clinically applicable and would replace traditional methods that require multiple blood sampling.

Pharmacokinetics, metabolism and excretion of an inhibitor of inducible nitric oxide synthase, L-NIL-TA, in dog

1. The pharmacokinetics, metabolism and excretion of L-NIL-TA, an inducible nitric oxide synthase inhibitor, were investigated in dog.2. The dose of [14C]L-NIL-TA was rapidly absorbed and distributed after oral and intravenous administration (5 mg kg−1), with Cmax of radioactivity of 6.45–7.07 μg equivalents g−1 occurring at 0.33–0.39-h after dosing. After oral and intravenous administration, radioactivity levels in plasma then declined with a half-life of 63.1 and 80.6-h, respectively.3. Seven days after oral and intravenous administrations, 46.4 and 51.5% of the radioactive dose were recovered in urine, 4.59 and 2.75% were recovered in faeces, and 22.4 and 22.4% were recovered in expired air, respectively. The large percentages of radioactive dose recovered in urine and expired air indicate that [14C]L-NIL-TA was well absorbed in dogs and the radioactive dose was cleared mainly through renal elimination. The mean total recovery of radioactivity over 7 days was approximately 80%.4. Biotransformation of L-NIL-TA occurred primarily by hydrolysis of the 5-aminotetrazole group to form the active drug L-N6-(1-iminoethyl)lysine (NIL or M3), which was further oxidized to the 2-keto acid (M5), the 2-hydroxyl acid (M1), an unidentified metabolite (M2) and carbon dioxide. The major excreted products in urine were M1 and M2, representing 22.2 and 21.2% of the dose, respectively.

An excretion balance and pharmacokinetic study of the novel anticancer agent E7070 in cancer patients.

E7070 is a novel sulfonamide anticancer agent that arrests the G /S phase of the cell cycle. Preclinical and phase I studies have demonstrated non-linear pharmacokinetics of the drug. The objective of this study was to quantify the excretion of E7070 and the metabolite 1,4-benzene-sulfonamide (M1) in cancer patients. E7070 (1,000 mg) radiolabeled by (14)C in the benzene disulfonamide moiety (cohort 1, n = 6) or in the indole moiety (cohort 2, n = 7) was i.v. infused over 1 h. The levels of radioactivity in plasma, red blood cells, urine and feces were determined by liquid scintillation counting, and the E7070 and M1 concentrations in plasma, urine and feces were determined by coupled liquid chromatography-tandem mass spectrometry (LC/ESI-MS/MS). In plasma, the mean area under the concentration-time curve (AUC) based on radio-activity measurements (32.5 and 28.9 h. mM in cohorts 1 and 2, respectively) was substantially higher than the mean AUC of E7070 (3.8 h x mmol/l) and M1 (0.1 h x mmol/l) in all patients. The excretion of radioactivity (mean +/- SD) as a percentage of administered radioactivity was higher in urine [63.7 +/- 9.8% (cohort 1) and 61.5 +/- 5.5% (cohort 2)] than in feces [22.7 +/- 2.6% (1) and 21.1 +/- 3.1% (2)] during a mean collection period of 11 days. In both cohorts, the contribution of urinary and fecal recovery of E7070 (2.3 and 2.7%, respectively) and M1 (5.3 and 5.1%, respectively) was low. Subsequent HPLC analysis with online radioisotope detection of urine showed that the high radioactivity levels are caused by compounds other than E7070 and M1. The major metabolite is formed by glucuronidation of a hydroxylated metabolite of E7070. In conclusion, the excretion of the benzene sulfonamide and the indole moieties of E7070 was the same with a higher renal than gastrointestinal excretion. E7070 is extensively converted into currently unidentified metabolites. Glucuronidation is a major metabolic pathway.

Electrical charge on protein regulates its absorption from the rat small intestine.

The effect of the electrical charge on the intestinal absorption of a protein was studied in normal adult rats. Chicken egg lysozyme (Lyz), a basic protein with a molecular weight of 14,300, was selected and several techniques for chemical modification were applied. Then the intestinal absorption of Lyz derivatives was evaluated by measuring the radioactivity in plasma and tissues, after the administration of an (111)In-labeled derivative to an in situ closed loop of the jejunum. After the administration of (111)In-Lyz, the level of radioactivity in plasma was comparable with the lytic activity of Lyz, supporting the fact that the radioactivity represents intact Lyz. (111)In-cationized Lyz showed a 2-3 times higher level of radioactivity in plasma, whereas the radioactivity of (111)In-anionized Lyz was much lower. The absorption rate of (111)In-Lyz derivatives calculated by a deconvolution method was correlated for the strength of their positive net charge. A similar relationship was observed using superoxide dismutase. These findings indicate that the intestinal absorption of a protein is, at least partially, determined by its electrical charge.

Absorption, distribution and excretion of 3H-labeled cephaeline- and emetine-spiked ipecac syrup in rats.

The maximum plasma radioactivity levels of tritium (3H)-labeled cephaeline, (24.3, 28.7 and 40.6 ng eq./mL) were reached at 2.00-3.33 hours following oral dosing of ipecac syrup. The maximum plasma radioactivity levels of 3H-emetine (2.71, 6.47 and 9.62 ng eq./mL) were reached at 1.08-2.33 hours following ipecac syrup administration. The Cmax values of 3H-cephaeline were followed by a biexponential decrease with half-lives t 1/2(lambda z) of 3.45-9.40 hours. On the other hand, the t 1/2 (lambda z)of 3H-emetine were 65.4-163 hours, which revealed a biexponential decrease. The radioactivity of both tritium-labeled compounds was distrbuted maximally in most tissues at 24 hours. For 3H-cephaeline, the maximum radioactivity levels in tissues were approximately 100-150 times greater than in plasma. For 3H-emetine, the radioactivity levels in tissues were approximately 1000-3000 times greater than in plasma. Tissue radioactivity levels decreased at a substantially slower rate than that observed in plasma. Tissue radioactivity of 3H-emetine decreased more slowly than that of 3H-cephaeline. For 3H-cephaeline, the cumulative biliary excretion of radioactivity was 57.5% at 48 hours. The cumulative urinary and fecal excretion of radioactivity in these rats was 16.5% and 29.1%, respectively, of the dose at 48 hours following dosing. For 3H-emetine, the cumulative biliary excretion of radioactivity was 12.5% at 48 hours. The cumulative urinary and fecal excretion of radioactivity was 9.4% and 34.1%, respectively, of the administered dose at 48 hours. The radioactivity level of 3H-emetine remaining in the carcasses at 48 hours was equivalent to approximately 50% of the dose. A portion of each tritium-labeled compound was subjected to entero-hepatic circulation. Thus, the absorption rate of 3H-cephaeline and 3H-emetine was estimated to be approximately 70% on the basis of the data obtained from excretion studies. There was no difference in the absorption process between these two compounds. However, the difference was admitted in the biliary clearance, which is the main excretion route of both compounds. Delayed excretion of 3H-emetine may be primarily due to its resorption as related to entero-hepatic circulation and tissue retention. This study has determined the absorption, distribution and excretion of 3H-cephaeline and 3H-emetine in rats.