The effect of misonidazole on the cytotoxicity and repair of potentially lethal damage from alkylating agents in vitro

Abstract

Chinese hamster HA-1 cells in the stationary phase of growth were used to study the chemosensitizing effect of misonidazole (MISO) on alkylating agents. Experiments were carried out in monolayer, at 37°C, under aerobic conditions. Results were analyzed using a survival assay and by measurement of the interactions with DNA as determined by the alkaline elution technique. Post-incubation of HA-1 cells in nutritionally-“spent” media for 24 hours following a 1 hour exposure to the alkylating agents melphalan (L-PAM), cyclophosphamide (CYC) and methyl methanesulfonate (MMS) showed that these cells are capable of repairing potentially lethal damage (PLD). If MISO (5 mM) was present during the exposure to these drugs, it enhanced the toxicity seen at both 0 and 24 hours after treatment with L-PAM and CYC, but did not inhibit the repair occurring during the 24 hour drug-free (and MISO free) post-treatment interval. On the other hand, MISO had no effect on the toxicity from MMS. If MISO was present during the post-incubation period it had very little additional effect on the toxicity due to L-PAM, but significantly enhanced the cell killing by MMS. Preliminary data from alkaline elution studies showed that L-PAM caused DNA-crosslinks while MMS gave rise to single strand breaks. No repair of L-PAM induced DNA damage was observed, while virtually all DNA damage produced by MMS was repaired within 24 hours. The presence of MISO during the 1 hour exposure to either alkylating agent did not change the elution profiles.