Because an enhanced therapeutic gain might be expected with co-administration of a hypoxic cell selective cytotoxin and a compound that induces hemorrhagic necrosis in tumors, the combination of CI-1010 (a potent bioreductive hypoxia selective cyto toxin) and 5,6-dimethylxanthenone-4-acetic acid (DMXAA) has been evaluated against advanced stage (>150 mg) murine colon carcinoma 26 (C26). CI-1010 and DMXAA were administered intraperitoneally over a range of toxic to ineffective doses as single agents and in combination to adult BALB/c x DBA/2 F1 hybrid mice bearing s.c. implants of C26. Both CI-1010 and DMXAA were ineffective as single agents, but regimens combining these two agents were highly active. The administration of DMXAA at 20 mg/kg/inj on days 9, 13, and 17 and CI-1010 at 65 mg/kg/inj on days 9-17 resulted in 60% of the animals tumor free on day 92 of the study. The remaining animals that were not tumor free survivors achieved a delay in tumor growth of 22.4 days. However, this treatment regimen was also considered toxic resulting in 2/10 treatment related deaths. Modification of the CI-1010 treatment schedule to intermittent delivery 24 h after each scheduled dose of DMXAA reduced treatment related toxicity while retaining efficacy. On this schedule the combination of CI-1010 (95 mg/kg/inj) given 24 h after DMXAA (20 mg/kg/inj) on days 9, 13, and 17 resulted in 60% of the treated animals tumor free on day 98 of the study. Treatment failures experienced a tumor growth delay of 11.6 days. Combination chemotherapy with CI-1010 and DMXAA was ineffective when DMXAA was administered 1 h prior to CI-1010, simultaneously with CI-1010, or 1 h after the administration of CI-1010. These results suggest that an enhanced therapeutic interaction between CI-1010 and DMXAA is achievable in vivo and that this interaction requires the development of substantial DMXAA induced tumor hypoxia prior to administration of CI-1010.

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