Carboplatin, a member of the platinum family of alkylating agents, is often used in combination with radiotherapy. Some studies, including a recent publication from our laboratory, have suggested that the cytotoxic effects of platinum compounds may be altered by changes in the post-treatment oxygenation. The study reported here assessed whether post-treatment changes in tumor oxygenation caused by oxygen breathing alone or in combination with efaproxiral (RSR13) altered the effects of carboplatin. Efaproxiral, which allosterically modifies hemoglobin-oxygen binding to increase tumor pO2, has been shown to increase the effects of radiation in animal tumor models and is in a second, confirmatory phase III clinical trial as an adjuvant to radiotherapy. These studies with EMT6 tumors in BALB/c Rw mice used clonogenic assays to assess tumor cell survival and tumor growth studies to assess antineoplastic activity and treatment-related toxicity. Efaproxiral plus oxygen breathing for 5 hrs after carboplatin treatment significantly increased the antineoplastic effects of carboplatin. The increased antineoplastic effects of carboplatin produced by efaproxiral plus oxygen breathing occurred without a concomitant increase in host toxicity. These findings suggest that the increases in tumor oxygenation produced by Efaproxiral plus oxygen breathing increased the therapeutic ratio of carboplatin.
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