Abstract
The pharmacokinetics, pharmacodynamics, and platelet binding of 7E3, an anti-glycoprotein IIb/IIIa (GPIIb/IIIa) monoclonal antibody, were studied in the rat in an attempt to develop a quantitative animal model of immune thrombocytopenia (ITP). 7E3, a murine IgG1 antibody developed against human GPIIb/IIIa, demonstrated cross-reactivity with rat platelets by flow cytometry and via enzyme-linked immunosorbent assay. The apparent affinity (KA) of 7E3-rat platelet binding was 1.2 ± 0.2 × 107 M−1, with 3.3 ± 0.3 × 104 binding sites per platelet. Following intravenous 7E3 administration (0.8, 4, and 8 mg/kg), plasma concentrations declined in a bi-exponential manner, with a terminal half-life of 61 ± 5 h and a steady-state volume of distribution of 62 ± 15 ml/kg. Clearance was dose-dependent, with values ranging from 0.64 ± 0.08 ml/h/kg (8 mg/kg) to 1.01 ± 0.08 ml/h/kg (0.8 mg/kg). 7E3 induced a reproducible, severe thrombocytopenia in rats and extended bleeding in a manner consistent with human ITP. Nadir platelet counts were 79 ± 33, 25 ± 6, and 17 ± 2 × 106/ml, for 7E3 doses of 0.8, 4, and 8 mg/kg, respectively. Bleeding times after a 10-mm tail incision ranged from 5 ± 3 min in control animals to 15 ± 0 min (the maximum allowed time in this study) in animals receiving 8 mg/kg. Blood volumes lost during bleeding experiments ranged from 30 ± 24 μl (control) to 349 ± 358 μl (8 mg/kg). A reproducible, quantitative rat model of ITP has been created; this model is expected to facilitate the evaluation of new treatments for this disease.
Footnotes
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This work was presented in part at the annual meeting of the American Association of Pharmaceutical Scientists, 1999 (New Orleans, LA).
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This study was supported by Grant HL 67347-01 from the National Heart, Lung and Blood Institute.
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R. J. H. is a Predoctoral Fellow of the American Foundation for Pharmaceutical Education.
- Abbreviations:
- ITP
- immune thrombocytopenic purpura
- GPIIb/IIIa
- glycoprotein IIb/IIIa
- IVIG
- intravenous immunoglobulin
- ELISA
- enzyme-linked immunosorbent assay
- PAGE
- polyacrylamide gel electrophoresis
- PBS
- phosphate-buffered saline
- Rt
- total receptor concentration
- CL
- clearance
- AUC
- area under the 7E3 plasma concentration time curve
- MRT
- mean residence time
- Vss
- volume of distribution at steady state
- Received January 31, 2001.
- Accepted March 22, 2001.
- The American Society for Pharmacology and Experimental Therapeutics
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