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Oral administration of deoxycytidine simultaneously with intraperitoneal injections of toxic doses of cytosine arabinosidetomice with advanced L1210 leukemia diminished the toxic effects preventing drug death of these mice. They developed a marked antitumor effect. The mean survival time of these mice was considerably extended as compared to that of untreated animals or those given one of these drugs alone. At the optimum schedule of treatment about 23% of the mice survived over 60 days. Deoxycytidine protection reduced the antileukemic effect of cytosine arabinoside administered in nontoxic doses. The deoxycytidine plus cytosine arabinose combination was ineffective in the treatment of transplantable myeloid leukemia in mice.

Oral administration of deoxycytidine simultaneously with intraperitoneal injections of cytosine arabinoside reduced toxicosis preventing drug death of mice with L1210 leukemia. These animals developed a marked antitumor effect having the median survival time (MST) considerably longer than that of untreated animals or of those receiving either of these drugs alone. At the optimal dose schedule 23% of mice survived 60 days. Under similar conditions mice with myeloid Graffi leukemia showed no antitumor response.