melphalan and 1-(2-nitro-1-imidazolyl)-3-aziridino-2-propanol

A cell line, CHO-Chlr, which has elevated levels of glutathione-S-transferase (GST), is resistant to damage caused by bi-functional nitrogen mustards. This cell line has a similar radiation sensitivity to and value of oxygen enhancement ratio as the wild type cells, CHO-K1, from which the mutant line was derived. Hypoxic cell radiosensitizing efficiencies for misonidazole, etanidazole (SR2508), and pimonidazole (R0 03-8799) are similar in both cell lines with values for C1.6 of 0.5, 0.75, and 0.08 mmol dm-3 for each drug respectively. In contrast, for RSU 1069 the sensitizing efficiency is lower in the cell line showing elevated levels of GST. The hypoxic toxicity of RSU 1069 and misonidazole is similar in each cell line, whereas in air, toxicity is 2 fold less in the CHO-Chlr cells. These results suggest that reaction of the alkylating aziridine part of RSU 1069 contributes to the high sensitizing efficiency of this drug. This is likely to be a consequence of either binding of the sensitizing moiety at the target site (ie, increased local concentration or induction of sub-lethal damage that is only expressed on subsequent irradiation.

Topics: Animals; Antineoplastic Agents; Cell Line; Cell Survival; Cricetinae; Etanidazole; Glutathione Transferase; Melphalan; Misonidazole; Nitroimidazoles; Oxygen; Radiation-Sensitizing Agents

Electron affinity as measured by the one-electron reduction potential, E17, is the major factor influencing radiosensitizing efficiency in vitro. RSU 1069 has an electron affinity (E17 = -398 mV) similar to misonidazole; however, the ability of this compound to sensitize hypoxic cells is considerably greater than that of misonidazole, e.g. 0.2 mM RSU 1069 gives an enhancement ratio of 2.2 compared to 1.5 for the same concentration of misonidazole. Radiosensitization studies with the MT tumour in vivo also showed RSU 1069 to be a more efficient sensitizer than misonidazole. An administered dose of only 0.08 mg g-1 RSU 1069 yielded an enhancement of 1.8 to 1.9 using tumour cell survival and tumour cure as end-points. The ability of RSU 1069 to potentiate the cytotoxic action of melphalan towards the MT tumour was also examined. RSU 1069 (0.08 mg g-1) given to mice 1 h before melphalan resulted in an enhancement of 3.0. In contrast, previous studies had shown with a series of nitroimidazoles including misonidazole that Ro 03-8799 was the most effective potentiating agent, but this only gave an enhancement of 2.3 at a 10-fold higher dose than RSU 1069. RSU 1069 is a compound of substantial promise both as a radiosensitizer and chemopotentiating agent and warrants further investigation.

Topics: Animals; Aziridines; Azirines; Cell Survival; Cricetinae; Cricetulus; Dose-Response Relationship, Radiation; Drug Synergism; Female; Melphalan; Mice; Mice, Inbred Strains; Misonidazole; Neoplasms, Experimental; Oxygen; Radiation-Sensitizing Agents

The radiation sensitizer misonidazole (MISO) has been shown to potentiate the cytotoxic action of a variety of anti-cancer agents. Even larger enhancement ratios than those observed with MISO have been found with certain other nitroimidazoles. One agent reported to be particularly effective in combination with the chemotherapeutic agent melphalan is the sensitizer RSU 1069. The present studies therefore were designed to evaluate the effect of combining these two agents in the treatment of intramuscularly growing KHT sarcomas. Tumor response was assessed using an in vivo to in vitro clonogenic cell survival assay. When given at times ranging from 60 min before to 30 min after melphalan exposure, RSU 1069 was found to increase the tumoricidal activity of the chemotherapeutic agent. Complete dose response curves combining RSU 1069 and a range of melphalan doses then were determined. For comparison the effects of combining MISO or benznidazole (BENZO) with melphalan also were evaluated. All sensitizers were administered i.p. either 30 min before (BENZO) or simultaneously with (MISO, RSU 1069) the chemotherapeutic agent. Survival of clonogenic tumor cells assessed 22 to 24 hr after treatment was used to assay tumor response. When combined with melphalan, doses of RSU 1069 (0.38 mmol/kg), BENZO (0.3 mmol/kg) and MISO (5.0 mmol/kg) were found to yield dose modifying factors of 1.6, 1.5, and 1.4, respectively. These results indicate that potentiation of melphalan activity occurs at RSU 1069 doses which are approximately 10-fold lower than those of MISO, making this sensitizer as effective a potentiator of melphalan as so far tested in the KHT sarcoma.

Topics: Animals; Aziridines; Azirines; Cell Survival; Dose-Response Relationship, Drug; Drug Synergism; Drug Therapy, Combination; Female; Melphalan; Mice; Misonidazole; Neoplasm Transplantation; Nitroimidazoles; Radiation-Sensitizing Agents; Sarcoma, Experimental; Time Factors