ABSTRACT
A liquid flow rapid-mixing apparatus has been used to study the role of lipophilicity (octanol: water partition coefficient, P) in the sensitization of hypoxic V79 cells by nitroimidazoles. Sensitization by seven neutral 2-nitroimidazoles of similar reduction potential but widely differing partition (0.11-77) and one basic 2-nitroimidazole (pKa=8.9; p=8.5 (of free base)) was studied as a function of pre-irradiation contact time ca. 3-40 ms. With increasing P, sensitization occurs at increasingly shorter pre-irradiation contact times. The results suggest that even though factors other than passive diffusion control the sensitization observed with the base Ro 03-8799 it is able to diffuse to the target site faster than midonidazole.
Subject(s)
Cell Survival/radiation effects , Nitroimidazoles/pharmacology , Radiation-Sensitizing Agents/pharmacology , Animals , Cell Line , Cell Survival/drug effects , Cricetinae , Dose-Response Relationship, Radiation , Misonidazole/analogs & derivatives , Misonidazole/pharmacologySubject(s)
Escherichia coli/drug effects , Lactococcus lactis/drug effects , Nitroimidazoles/pharmacology , Radiation-Sensitizing Agents , Cell Membrane/drug effects , Dose-Response Relationship, Drug , Escherichia coli/radiation effects , Gamma Rays , Lactococcus lactis/radiation effects , Oxygen , SolubilityABSTRACT
The efficiency of 35 nitroaromatic and nitroheterocyclic compounds in radiosensitizing hypoxic Chinese Hamster cells in vitro was determined. The concentration C of the compound required to achieve an enhancement ratio of 1.6 was measured, and the redox and partition properties were quantified as the one-electron reduction potential at pH 7, E, and the octanol: water partition coefficient, P, respectively. Most of the compounds studied were 2-nitroimidazoles, but some 4- and 5-nitromidazoles, 5-nitrofurans and nitrobenzenes were investigated for comparison. Together with data for nine nitroimidazoles previously reported, the results were fitted to a structure-activity relationship of the form -log C = b0 + b1E + b2 log P + b3 (log P)2 using multiple linear regression analysis. Statistical tests showed that the coefficients b2 and b3 were not significantly different from zero and the simpler equation, obtained by omitting the terms in log P, explained 85 per cent of the variance in log C. Earlier reports that the radiosensitization efficiency of nitro compounds in vitro largely depends on the reduction potential were confirmed. The conclusive demonstration that P is unimportant in vitro is valuable in interpreting the results of experiments in vivo, where P is expected to have a much greater influence on biological response.
