title: Studies on the mechanisms of the radiosensitizing and cytotoxic properties of RSU-1069 and its analogues.
abstract: RSU 1069 is a substantially more efficient sensitizer than misonidazole when hypoxic Chinese hamster V79 cells are irradiated in vitro at room temperature; such that for 0.5 mmol dm-3 sensitizer an ER of 3.0 is obtained for RSU 1069 whereas an ER of only 1.6 is obtained for misonidazole. However, when irradiation is done at 4 degrees C, the radiosensitization caused by RSU 1069 is reduced to a level close to that obtained with misonidazole, the action remaining unaltered at the lower temperature. This temperature dependent component of sensitization for RSU 1069 suggests the involvement of a slow biochemical process that has an appreciable activation energy. The RSU 1069 analogue RB 7040 is a more efficient radiosensitizer than RSU 1069 particularly at lower concentrations. This compound has a pKa value of 8.45, in contrast to that of RSU 1069 which is 6.04. Weak bases with pKa values in excess of average intra-cellular pH can be taken up preferentially into cells from medium at pH 7.4. It is shown that RB 7040 has a 4 X higher intracellular concentration than RSU 1069 for a similar extracellular concentration. This will explain, at least in part, the greater sensitizing efficiency of this compound when compared to RSU 1069 in vitro.
mesh_terms: D000818:Animals; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D006224:Cricetinae; D066298:In Vitro Techniques; D008920:Misonidazole / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000633:toxicity; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology* / Q000633:toxicity
chemical_list: D011838:Radiation-Sensitizing Agents; C049942:RB 7040; C041712:1-(2-nitro-1-imidazolyl)-3-aziridino-2-propanol; D008920:Misonidazole