title: Cellular uptake of misonidazole and analogues with acidic or basic functions.
abstract: Average intracellular concentrations of five radiosensitizers in hamster fibroblast-like V79-379A cells in vitro were measured by high performance liquid chromatography, varying the extracellular pH (pHe) and estimating the apparent intracellular pH from the distribution of 5,5-dimethyloxazolidine-2,4-dione. The intracellular: extracellular concentration ratio for the 2-nitroimidazole, misonidazole was constant at about 0.7 for pHe = 6.6-7.6, whereas the weak base, Ro 03-8799 (1-(2-nitro-1-imidazolyl)-3-N-piperidino-2-propanol) was concentrated intracellularly at pHe = 7.3-7.4 by a factor of 3.3, the factor increasing from about 0.8 at pHe = 6.0, to 7.5 at pHe = 7.85. The weak acid, azomycin (2-nitroimidazole) showed approximately constant uptake (factor 1.1) between pHe = 6.0-7.0, decreasing to 0.8 at pHe = 7.3 and 0.4 at pHe = 7.8. Measurements of intracellular uptake of Ro 31-0052 (the more hydrophilic and less basic 3'-hydroxypiperidino analogue of Ro 03-8799) and of Ro 31-0258 (3-(2-nitro-1-imidazolyl)propionic acid, a stronger acid than azomycin) were made for comparison. The results were compared with theoretical calculations of pH-induced concentration gradients; the time dependence of the uptake of the bases is not at present clearly understood. These measurements of uptake are broadly consistent with the distribution of misonidazole and Ro 03-8799 in human and animal tissues and provide a useful insight into the likely intracellular concentrations in the clinical use of Ro 03-8799 or other basic radiosensitizers. The measurements also resolve the apparent discrepancy in radiosensitizer efficiency for weak bases in vitro and in vivo which has been previously noted.
mesh_terms: D000818:Animals; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D006224:Cricetinae; D005110:Extracellular Space / Q000032:analysis; D005347:Fibroblasts / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008920:Misonidazole / Q000031:analogs & derivatives / Q000378:metabolism*; D009593:Nitroimidazoles / Q000378:metabolism*; D011838:Radiation-Sensitizing Agents / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013997:Time Factors
chemical_list: D009593:Nitroimidazoles; D011838:Radiation-Sensitizing Agents; C033815:pimonidazole; C045565:Ro 31-0052; D008920:Misonidazole; C045566:Ro 31-0258; C006667:azomycin