Cell survival recovery kinetics in the KHT sarcoma following treatment with five alkylating agents and misonidazole

Abstract

In order to determine the role of recovery of tumor cell survival in the enhanced tumor responses resulting from chemotherapeutic agent-sensitizer combinations, cell survival in KHT sarcomas as a function of time after treatment with the alkylating agents 1-(2-chloroethyl)-3-cyclohexyl-l-nitrosourea (CCNU), 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), cyclophosphamide (CYC), phenylalanine mustard (L-PAM) and 2-[3-(2-chloroethyl)-3-nitrosoureidol-D-glucopyranose (chlorozotozin; CLZ) either alone or in combination with the radiosensitizer misonidazole (MISO) was evaluated. Tumor-bearing mice were treated with single doses of CCNU, BCNU, CYC, L-PAM and CLZ, respectively. The doses, chosen to obtain approximately the same level of cell kill with each treatment, were administered either alone or in simultaneous combination with a 1.0 mg/g dose of MISO. Tumors were excised at 1, 2, 4, 8, 16 and 24 hr after drug injection. Clonogenic cell survival was assessed at these times using an in vivo to in vitro excision assay. The results showed that following treatment with each of the chemotherapeutic agents, tumor cell survival reached a minimum at ∼2–8 hr. Subsequently cell survival remained relatively constant for CYC, but increased with time by a factor of ∼10–100 for L-PAM, CCNU, BCNU and CLZ. The addition of MISO potentiated the cell killing effects of CYC, L-PAM, CCNU and BCNU, but not of CLZ. Also, in animals treated with certain of these chemotherapeutic agents plus the sensitizer, cell survival recovery was impaired. This effect was particularly marked when the nitrosourea CCNU was used in combination with MISO (i.e. 24 hr after treatment with CCNU plus MISO, tumor cell survival was a factor of ∼50 lower than observed in tumors of mice given only CCNU). These findings indicate that the enhancement of cell killing in the KHT sarcoma observed 24 hr after treatment with chemotherapeutic agent-MISO combinations may be at least in part the result of altered recovery in tumor cell survival.