Cytotoxicity of RSU 1069 in spheroids and murine tumors

Hypoxia following treatment with the alkylating nitroimidazole, RSU 1069, greatly enhanced cell killing in the Lewis lung tumor and Chinese hamster V79 spheroids. When mice were injected with RSU-1069 and tumors were excised after 3 hr to measure colony formation in soft agar, significant cell killing was observed. However, if tumors were excised 18 hr after drug injection, viability was increased, and cell killing was confined to cells distant from the blood supply. In subsequent experiments, viability observed at 3 hr could be greatly increased if the tumors were cooled to 4 degrees C immediately after excision, and were then rapidly disaggregated. This suggested that the hypoxia which occurred after animal sacrifice and during the tumor disaggregation procedure was sufficient to account for the additional cell killing at early times after drug injection. Results using V79 spheroids similarly suggest that tumor excision soon after injection of RSU 1069 can give false information on RSU 1069 toxicity if efforts are not made to prevent tumor hypoxia during processing. In spheroids, hypoxia-induced toxicity after aerobic exposure decreased as the time between RSU 1069 exposure and hypoxic incubation increased; spheroid cells exposed to RSU 1069 under air lost sensitivity to subsequent hypoxic incubation with a half-time of about 10 hr, representing the time for cell turnover and/or repair from damage produced under aerobic conditions.