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McKibbin T, Panetta JC, Fouladi M, Gajjar A, Bai F, Okcu MF, Stewart CF. Clinical pharmacokinetics of amifostine and WR1065 in pediatric patients with medulloblastoma. Clin Cancer Res 2010; 16:1049-57. [PMID: 20103669 PMCID: PMC2818675 DOI: 10.1158/1078-0432.ccr-09-1997] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
PURPOSE We evaluated the pharmacokinetics of amifostine and WR1065 in pediatric patients with newly diagnosed medulloblastoma to assess the influence of patient covariates, including demographics, clinical characteristics, and genetic polymorphisms, on amifostine and WR1065 pharmacokinetic parameters. EXPERIMENTAL DESIGN We assessed the pharmacokinetics of amifostine and WR1065 in 33 children who received amifostine (1-minute infusion, 600 mg/m(2)) just before the start of and 3 hours into a 6-hour cisplatin infusion. Serial blood samples were collected after doses 1 (0 hour) and 2 (3 hours) of course 1. Amifostine and WR1065 were quantitated by high performance liquid chromatography with electrochemical detection. A pharmacokinetic model was simultaneously fit to amifostine and WR1065 plasma or whole blood concentration-versus-time data. The influence of demographic, biochemical, and pharmacogenetic covariates on amifostine and WR1065 disposition was evaluated. RESULTS Body surface area was the primary size-based covariate for amifostine pharmacokinetics explaining 53% and 56% of interindividual variability in plasma and whole-blood amifostine clearance, respectively. The population-predicted values for amifostine clearance, volume, and apparent WR1065 clearance from the plasma data were 107 L/h/m(2), 5.53 L/m(2), and 30.6 L/h/m(2). The population-predicted values for amifostine clearance, volume, and apparent WR1065 clearance from whole blood data were 136 L/h/m(2), 7.23 L/m(2), and 12.5 L/h/m(2). CONCLUSIONS These results support using body surface area for calculating doses of amifostine in children. Similar to data in adults, amifostine and WR1065 are rapidly cleared from plasma and whole blood in children.
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Affiliation(s)
- Trevor McKibbin
- Department of Clinical Pharmacy, University of Tennessee, Memphis, TN
| | - John C. Panetta
- Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital (SJCRH), Memphis, TN
- Department of Pharmaceutical Sciences, University of Tennessee, Memphis, TN
| | - Maryam Fouladi
- Department of Oncology, St. Jude Children's Research Hospital, Memphis, TN
| | - Amar Gajjar
- Department of Oncology, St. Jude Children's Research Hospital, Memphis, TN
| | - Feng Bai
- Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital (SJCRH), Memphis, TN
| | - M. Fatih Okcu
- Texas Children's Cancer Center; Department of Pediatrics, Hematology-Oncology, Baylor College of Medicine, Houston, TX
| | - Clinton F. Stewart
- Department of Clinical Pharmacy, University of Tennessee, Memphis, TN
- Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital (SJCRH), Memphis, TN
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Cassatt DR, Fazenbaker CA, Bachy CM, Kifle G, McCarthy MP. Amifostine (ETHYOL) protects rats from mucositis resulting from fractionated or hyperfractionated radiation exposure. Int J Radiat Oncol Biol Phys 2005; 61:901-7. [PMID: 15708273 DOI: 10.1016/j.ijrobp.2004.10.032] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2004] [Revised: 09/30/2004] [Accepted: 10/10/2004] [Indexed: 11/21/2022]
Abstract
PURPOSE The cytoprotective drug amifostine (Ethyol) protects rats from oral mucositis resulting from a single dose of gamma-irradiation. We expanded earlier studies to determine whether multiple doses of amifostine protect against fractionated or hyperfractionated radiation and whether the active metabolite of amifostine (WR-1065) accumulates in tissues upon repeated administration. METHODS AND MATERIALS Rats received amifostine daily for 5 days in conjunction with a 1-week fractionated radiation schedule and were evaluated for oral mucositis. Rats also received amifostine before the am or pm exposure or b.i.d. in conjunction with hyperfractionated radiation. To determine the pharmacokinetics of WR-1065 after repeated dosing, amifostine was given 5 days a week for 1 or 3 weeks, and rat tissue and plasma were collected at intervals during and after treatment and analyzed for WR-1065. RESULTS Amifostine protected rats from mucositis resulting from fractionated or hyperfractionated radiation. When the number of days of amifostine administration was reduced, protection was diminished. A dose of 100 mg/kg given in the morning or 2 doses at 50 mg/kg provided the best protection against hyperfractionated radiation. WR-1065 did not accumulate in tissues or tumor upon repeated administration. CONCLUSIONS Amifostine prevented radiation-induced mucositis in a rat model; protection was dose and schedule dependent.
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Affiliation(s)
- David R Cassatt
- Department of Molecular Biology/Biochemistry, MedImmune Inc. One MedImmune Way, Gaithersburg, MD 20878, USA
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Cassatt DR, Fazenbaker CA, Kifle G, Bachy CM. Effects of dose and schedule on the efficacy of Ethyol: preclinical studies1 1The authors are employees and shareholders of MedImmune Inc. Semin Oncol 2003; 30:31-9. [PMID: 14727238 DOI: 10.1053/j.seminoncol.2003.11.039] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The chemo- and radioprotectant drug amifostine (Ethyol; MedImmune, Inc, Gaithersburg, MD) is approved for intravenous (IV) administration; however, the subcutaneous (SC) route is being explored as a practical alternative. We have previously reported equivalence between IV and SC administration using a rat model of radioprotection and active metabolite (WR-1065) tissue pharmacokinetics. To examine the more clinically relevant fractionated and hyperfractionated radiation schedules and the effects of variations in the time of amifostine administration, we expanded these studies to include radioprotection and pharmacokinetic studies of WR-1065 using multiple dosing. To measure radioprotection using a fractionated radioprotection model, rats were given amifostine over a 1-week period at various doses (25 mg/kg, 50 mg/kg, 100 mg/kg; or 162.5 mg/m(2), 325 mg/m(2), 650 mg/m(2), respectively) IV or SC daily 30 minutes before exposure to 7.5 Gy/dose. Rats were fully protected from mucositis at the highest amifostine dose, with protection diminishing as the amifostine was decreased. Equivalent protection was observed whether the drug was given IV or SC. When the number of days of amifostine administration was reduced, protection was diminished. Amifostine also protected against radiation delivered using a 1-week hyperfractionated schedule (4.5 Gy/exposure twice daily), with optimal protection occurring when the drug was administered bid 30 minutes before each exposure (50 mg/kg) or every day before the morning exposure (100 mg/kg). The need for daily dosing to achieve optimal radioprotection was consistent with the tissue pharmacokinetics of the active metabolite. We found that WR-1065 did not accumulate in tissues or in SC-implanted tumors when amifostine was administered daily for 3 weeks. In addition, tissue and tumor levels of WR-1065 declined to baseline 24 hours after each amifostine dose. In a monkey pharmacokinetic model, plasma levels of WR-1065 (characterized by a pronounced spike of WR-1065 immediately after IV administration that was absent when the drug was given SC) were similar to those of humans; however, levels of WR-1065 in the tissues were higher 30 minutes following SC administration and were equivalent 60 minutes following IV or SC administration. These results suggest that maximum tissue levels and protection occur when amifostine is given 30 to 60 minutes before radiation exposure, that treatment breaks reduce the radioprotection by amifostine, and that protection from hyperfractionated radiation is dependent on amifostine dose and schedule.
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Affiliation(s)
- David R Cassatt
- Department of Molecular Biology/Biochemistry, MedImmune, Inc, Gaithersburg, MD 20878, USA
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Fouladi M, Stempak D, Gammon J, Klein J, Grant R, Greenberg ML, Koren G, Baruchel S. Phase I trial of a twice-daily regimen of amifostine with ifosfamide, carboplatin, and etoposide chemotherapy in children with refractory carcinoma. Cancer 2001; 92:914-23. [PMID: 11550166 DOI: 10.1002/1097-0142(20010815)92:4<914::aid-cncr1401>3.0.co;2-s] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
BACKGROUND Amifostine protects normal tissues against chemotherapy and radiation-induced toxicity without loss of antitumor effects. Evidence suggests that multiple daily doses of amifostine may improve its cytoprotective effects. The purpose of this study was to assess the dose-limiting toxicities (DLTs) and maximum tolerated dose (MTD) of twice-daily doses of amifostine with ifosfamide, carboplatin, and etoposide (ICE) chemotherapy for children with refractory malignancies and to determine the pharmacokinetic properties of amifostine, WR-1065, and the disulfide metabolites of amifostine. METHODS Patients with refractory malignancies were treated with amifostine 15 minutes before and 2 hours after chemotherapy with ifosfamide (3 g/m(2) per dose on Days 1 and 2) and carboplatin (635 mg/m(2) on Day 3). Etoposide was administered on Days 1 and 2 (150 mg/m(2)). The starting dose of amifostine was 740 mg/m(2). Pharmacokinetic studies were performed after the first dose of amifostine. RESULTS Twelve patients received 23 courses of ICE and amifostine. Dose-limiting toxicities for amifostine at 740 mg/m(2) were somnolence and anxiety. The other Grade 3 and 4 toxicities included asymptomatic, reversible hypocalcemia, vomiting, and reversible hypotension. At a dose of 600 mg/m(2), amifostine was well tolerated. Hypocalcemia, due to rapid, transient suppression of parathyroid hormone production, required close monitoring and aggressive intravenous calcium supplementation. Pharmacokinetic studies revealed high interpatient variability with rapid plasma clearance of amifostine and WR-1065. The median elimination half-life of amifostine (9.3 minutes) and WR-1065 (15 minutes) was much shorter than the disulfide metabolites (74.4 minutes). CONCLUSIONS The recommended pediatric dose of amifostine for a twice-daily regimen is 600 mg/m(2) per dose (1200 mg/m(2)/day) with DLTs of anxiety and somnolence, lower than the previously recommended single dose of 1650 mg/m(2).
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Affiliation(s)
- M Fouladi
- New Agents and Innovative Therapy Program, The Hospital for Sick Children, University of Toronto, 555 University Avenue, Toronto, Ontario, M5G 1X8, Canada
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Abstract
Mammalian cells become more susceptible to radiation-induced death and mutagenesis when restricted in their production of the natural polyamines putrescine, spermidine and spermine. The effects of polyamine deprivation are reversed by N-(2-mercaptoethyl)-1, 3-diaminopropane (WR1065), a simple aminothiol that has been extensively studied for its radioprotectant properties. Because this compound and its oxidized derivative WR33278 bear some resemblance to the polyamines, it was hypothesized that radioprotection by WR1065 or its metabolites is derived, at least in part, from their ability to supplement the natural polyamines. To evaluate the ability of these aminothiol compounds to emulate polyamine function in intact cells, rat liver hepatoma (HTC) cells were treated with radioprotective doses of WR1065; the ability of this compound to affect various aspects of normal polyamine metabolism was monitored. Although cellular WR1065 was maintained at levels exceeding those of the polyamines, this aminothiol did not have any polyamine-like effect on the initial polyamine biosynthetic enzyme, ornithine decarboxylase, or on polyamine degradative reactions. On the contrary, treatment with relatively low levels of WR1065 resulted in an unexpected increase in putrescine and spermidine synthesis. WR1065 treatment enhanced the stability, and consequently the activity, of ornithine decarboxylase. This stabilization seems to result from a WR1065-induced delay in the synthesis of antizyme, a critical regulatory protein required in the feedback modulation of polyamine synthesis and transport. The increase in cellular spermidine induced by WR1065 might explain its antimutagenic properties, but is probably not a factor in protection against cell killing by radiation. This is the first evidence that compounds can be designed to control polyamine levels by targeting the activity of the regulatory protein antizyme.
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Affiliation(s)
- J L Mitchell
- Department of Biological Sciences, Northern Illinois University, DeKalb, IL 60115, USA.
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Calabro-Jones PM, Aguilera JA, Ward JF, Fahey RC. The limits to radioprotection of Chinese hamster V79 cells by WR-1065 under aerobic conditions. Radiat Res 1998; 149:550-9. [PMID: 9611093] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Clonogenic survival and drug content for Chinese hamster V79-171 cells incubated in suspension with WR-1065 prior to gamma irradiation have been determined. Factors that might influence the radioprotection by WR-1065 were investigated in control studies. Intracellular drug levels studied ranged between 0-36 nmol per 10(6) cells. In control studies, it was established that extracellular drug toxicity was not significant for cells in suspension at 10(6) per milliliter over short periods but was important when residual drug was present above 2 microM in the final plating of cells. Accumulation of intracellular drug above 30 nmol per 10(6) cells produced significant cytotoxicity in unirradiated cells. Irradiation with doses as high as 150 Gy produced no significant change in the total drug level or the thiol/disulfide ratio, either for the drug in the cells or for the drug in the medium. Preirradiation with 8 Gy did not change the ability of cells to import the drug but did appear to increase the cytotoxicity of the intracellular drug at levels above 25 nmol per 10(6) cells. There was no qualitative difference in the ability of WR-1065 to protect viable cells preirradiated with 8 Gy compared with protection of unirradiated cells. For a given gamma-ray dose from 2 to 40 Gy, there is a limiting value for surviving fraction which cannot be increased by further elevation of the intracellular drug level in V79-171 cells. Such limiting radioprotection was demonstrated for HT-29/SP-ld, HeLa, Me-180-VCII and OV-2008-VI human tumor cells.
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Affiliation(s)
- P M Calabro-Jones
- Department of Radiology, University of California, San Diego, La Jolla 92093, USA
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Abstract
The pharmacokinetics of the cytoprotective agent amifostine (EthyolR; WR 2721) and its main metabolites (WR 1065 and the disulphides) were studied in patients participating in two phase I trials concerning carboplatin or cisplatin in combination with amifostine. Patients were treated with a single dose or three doses of amifostine (740 or 910 mg/m2). The single or first dose was given as a 15 min i.v. infusion just before administration of the chemotherapeutic agent. The additional two infusions were administered 2 and 4 h thereafter. Amifostine was rapidly cleared from the plasma, due to, at least in part, the fast conversion into WR 1065. A biphasic decrease with a final half-life of 0.8 h was observed. The active metabolite WR 1065 was cleared from the plasma with a final half-life of 7.3 +/- 3.6 h. The short initial half-life of WR 1065 can be explained by its fast uptake in tissues and the formation of disulphides. The disulphides were cleared with a final half-life of 8.4-13.4 h and were detectable for at least 24 h after treatment. They may serve as an exchangeable pool of WR 1065. The amifostine peak values at the end of each 15 min infusion did not accumulate in the multiple dosing schedule. For WR 1065 a trend towards an increase in the peak levels was observed [C1,max: 47.5 +/- 11.9 microM, C2,max: 79.0 +/- 13.2 microM, C3,max: 84.8 +/- 15.1 microM, (n = 6)], whereas a trend towards a small decrease was observed for the peak levels of the disulphides [C1,max: 184.2 +/- 12.6 microM, C2,max: 175.0 +/- 23.7 microM, C3,max: 166.0 +/- 17.2 microM, (n = 6)]. This latter finding might suggest a saturation of the disulphide formation or a change in the uptake or elimination of WR 1065, which would result in higher WR 1065 levels in plasma and tissues, after multiple doses of amifostine.
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Affiliation(s)
- A E Korst
- Department of Medical Oncology, University Hospital of Vrije Universiteit, Amsterdam, The Netherlands
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Korst AE, Gall HE, Vermorken JB, van der Vijgh WJ. Pharmacokinetics of amifostine and its metabolites in the plasma and ascites of a cancer patient. Cancer Chemother Pharmacol 1996; 39:162-6. [PMID: 8995515 DOI: 10.1007/s002800050553] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The pharmacokinetics of amifostine, a protector against chemotherapy and radiation-induced toxicities, was investigated in the plasma and ascites of a cancer patient. A high-performance liquid chromatography (HPLC) procedure with electrochemical detection was used to measure amifostine, its active metabolite, WR 1065, and the disulfides (symmetrical plus mixed disulfides). Both amifostine and WR 1065 were rapidly cleared from the plasma (95% and 50% of the peak concentration within 1 h, respectively). The disulfides, which were rapidly formed from WR 1065, were cleared much more slowly (final half-life 13.6 h). Multiple dosing resulted in a tendency toward increasing peak levels of WR 1065 and decreasing peak levels of the disulfides. Only 1% of the delivered dose appeared in the ascites. Therefore, it is not plausible that the presence of ascites or other third spaces would have an impact on the pharmacokinetics of amifostine.
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Affiliation(s)
- A E Korst
- University Hospital Vrije Universiteit, Clinical Research Laboratory of Oncology, Amsterdam, The Netherlands
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Newton GL, Aguilera JA, Kim T, Ward JF, Fahey RC. Transport of aminothiol radioprotectors into mammalian cells: passive diffusion versus mediated uptake. Radiat Res 1996; 146:206-15. [PMID: 8693070] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Water:n-octanol partition coefficients (KD) were determined for a series of radioprotective thiols to ascertain whether these could be used to estimate reliably their rates of uptake into mammalian cells by passive diffusion. Values of KD determined for thiols in 0.1 M potassium phosphate, pH 7.4, at 22 degrees C were: N-(2-mercaptoethyl)-1,3-diaminopropane (WR-1065, WRSH), 2.0 x 10(3); dithiothreitol, 1.4; 2-mercaptoethanol, 1.7; cysteamine, 180; 3-mercaptopropanoic acid, 450; mercaptosuccinic acid, 5 x 10(6) (extrapolated value). Predictions of uptake rates by passive diffusion into mammalian cells using these values and values for the membrane diffusion rate derived from empirical evaluation of appropriate values from the literature for erythrocyte permeability paralleled the experimental rates for WR-1065 and dithiothreitol but were about threefold lower. Although the utility of KD values for quantitative prediction of uptake rates is limited, the analysis clearly indicated that uptake of aminothiols having three or more ionized amino groups will not occur at useful rates by passive diffusion. Studies of WR-1065 import by Chinese hamster V79-171 cells at micromolar levels of WR-1065 revealed an uptake that could not be explained by passive diffusion. This uptake was not inhibited by substrates for common amino acid transport systems but was inhibited by polyamines and by 1 mM DTT, which suggested that WR-33278 (WRSSWR) formed by oxidation of WRSH was being transported by a polyamine transport system. This was confirmed by showing that WRSSWR is imported efficiently by V79-171 cells treated with D,L-2-difluoromethylornithine to deplete intracellular polyamines and hence enhance their transport. Spermine inhibited uptake of WRSSWR and WRSSWR inhibited uptake of [14C]spermine, confirming that a common system is involved in the uptake of these similar molecules, both having +4 charge. It was shown that after import WRSSWR is reduced to WRSH and that uptake at low micro-molar concentrations of WRSSWR results in marked cellular concentration of the drug. These results indicate that the spermidine/spermine transport system may also provide a feasible route for import of radioprotective aminothiols bearing net charges of +3 or +4 into mammalian cells.
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Affiliation(s)
- G L Newton
- Department of Chemistry, University of California, San Diego, La Jolla 92093, USA
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Eisenhut M, Lehmann WD, Becker W, Behr T, Elser H, Strittmatter W, Steinsträsser A, Baum RP, Valerius T, Repp R, Deo Y. Bifunctional NHS-BAT ester for antibody conjugation and stable technetium-99m labeling: conjugation chemistry, immunoreactivity and kit formulation. J Nucl Med 1996; 37:362-70. [PMID: 8667077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
UNLABELLED Conjugation chemistry and kit formulated binding of the NHS ester of 6-(4'-(4"-carboxyphenoxy)butyl)-2, 10-dimercapto-2,10-dimethyl-4,8-diazaundecane (NHS-BAT ester) to monoclonal antibodies (MAbs) was investigated. The functionalities of the resulting BAT conjugated and 99mTc-labeled MAbs BW 431/26, MAb 425 and bispecific MDX210 (fragment construct) were tested by immunoreactivity and immunoscintigraphy. METHODS The kinetics and chemistry of the conjugation reaction were monitored by high-performance liquid chromatography, size-exclusion chromatography and positive fast-atom-bombardment mass spectra (FAB-MS). The 99mTc BAT-MAbs were tested with various immunoreactivity assays. The biodistribution of 99mTc-BAT-BW 431/26 in rats was compared with directly labeled BW 431/26. RESULTS At pH 8.5 and 25 degrees C, the reactivity of the NHS-BAT ester was high with 90% completion after 30 min. The conjugation yield of 19 microM MAb and 228 microM NHS-BAT ester amounted to 30%. Higher NHS-BAT ester concentrations afforded higher BAT-to-MAb ratios. According to FAB-MS, the conjugation competing hydrolysis surprisingly occurred at the NHS ring. Almost quantitative 99mTc labeling was achieved after 5 min at 25 degrees C. Immunoreactivity of the 99mTc-BAT antibodies showed > 90% recovery and proved to be insensitive to BAT-to-MAb ratios of up to 10. The 99mTc-BAT-BW 431/26 showed similar organ distribution but revealed less urinary excretion compared with the directly labeled BW 431/26. Immunoscintigraphy with 99mTc-labeled and BAT-BW 431/26 and BAT-MAb 425 showed the respective biological function in vivo. CONCLUSION According to straightforward conjugation chemistry, the ease of 99mTc labeling and the application of a simple ultrafiltration technique, the NHS-BAT ester represents a nondestructive, universally applicable biofunctional ligand to introduce stable 99mTc protein binding sites. Kit formulated conjugation/labeling can be performed with little time requirements and laboratory experience.
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Affiliation(s)
- M Eisenhut
- Department of Nuclear Medicine, University of Heidelberg, Germany
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Abstract
Chinese hamster V79 cells in Eagle's minimum essential medium in vitro at room temperature were incubated with the aminothiol, WR-1065, or glutathione (GSH) at extracellular concentrations of approximately 1 mmol dm-3. Average intracellular concentrations of GSH, cysteine, and WR-1065 were measured by high performance liquid chromatography, and the effective reducing environment near DNA probed by staining the cells with acridine orange (AO) and measuring the delayed fluorescence. Exposure to either thiol resulted in a rapid, 10-fold increase in average intracellular cysteine concentrations (to about 1 mmol dm-3). Adding extracellular GSH after prior depletion of GSH by treatment with L-buthionine sulfoximine (BSO) did not restore intracellular GSH, but intracellular cysteine was elevated 10-fold. These results are ascribed to thiol/disulfide exchange with cystine in the medium. WR-1065 slowly concentrated intracellularly to approximately 160% of the extracellular concentration. Chemical conjugation of GSH in cells decreased the reducing environment near DNA, but BSO treatment altered the uptake of AO. The electrostatic attraction of WR-1065 toward isolated DNA was markedly affected by ionic strength.
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Affiliation(s)
- P Wardman
- Gray Laboratory, Cancer Research Campaign, Mount Vernon Hospital, Northwood, Middlesex, U.K
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12
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Abstract
A circulating in situ rat small intestine absorption model was used to study the lumenal metabolism and absorption of [14C]WR-1065. WR-1065 was found to be more tissue reactive and toxic than its phosphorylated form, ethiofos, at equimolar perfusate concentrations. The disappearance profiles of the radiolabeled drug and free WR-1065 indicate that WR-1065 is extensively metabolized in the intestinal lumen prior to absorption. Coadministration of disodium ethylenediaminetetraacetic acid enhances the absorption of the free thiol although not to the same extent as seen with ethiofos. Perfusion of WR-1065 in citrate buffer decreased lumenal degradation of the drug but resulted in decreased absorption. The total material converted to WR-1065 portal blood profiles following ethiofos and WR-1065 perfusion were altered possibly due to distribution and metabolism differences. This study coupled with earlier work completed on ethiofos have increased our understanding of the significant barriers to absorption observed following oral administration of these compounds.
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Affiliation(s)
- R S Geary
- Southwest Research Institute, San Antonio, Texas 78228-0510
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Geary RS, Swynnerton NF, Miller MA, Mangold DJ, Ludden T. Intraduodenal administration of ethiofos (WR-2721): dose proportionality study in the rhesus monkey. Res Commun Chem Pathol Pharmacol 1989; 65:147-59. [PMID: 2555852] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
A dose progression crossover study of ethiofos (WR-2721) was conducted in three healthy male rhesus monkeys. Each subject was tested with three single intraduodenal doses containing 150, 300, and 600 mg/kg. Blood samples were drawn as a function of time and the concentrations of ethiofos, WR-1065 (free thiol metabolite), and total drug convertible to the free thiol (total WR-1065) were determined by HPLC using electrochemical detection. Ethiofos levels in plasma were usually below quantifiable limits of detection (0.23 mumol/L) at all three dose levels, but free WR-1065 plasma levels increased with increasing dose. Analysis of the free WR-1065 bioavailability values indicated large variability and an unpredictable dose response among subjects. Bound WR-1065 appears to reach saturable levels over the dose range, suggesting a saturable pool of binding sites in plasma. The time-to-peak plasma levels for WR-1065 were variable regardless of the administered dose and ranged from 1.0-2.5 hours. The high variability in the data may be a result of poor permeability or absorption of the parent compound (ethiofos), saturable binding to a variable pool of binding sites in plasma and/or high first-pass metabolism of ethiofos involving the gut lumen, gut wall (epithelium), and liver.
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Affiliation(s)
- R S Geary
- Southwest Research Institute, San Antonio, Texas 78284
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