Lack of inhibition by oxipurinol of 5-FU toxicity against human tumor cell lines

Allopurinol has been reported to decrease the gastrointestinal and bone marrow toxicity of 5-FU when administered in a high dose by continuous infusion. The effect of oxipurinol, the major metabolite of allopurinol, on 5-FU cytotoxicity against three human tumor cell lines was studied using a soft agar clonogenic assay. For both WiDR (colon) and T-47 (breast), 5-FU cytotoxicity was greater in the presence of oxipurinol than in its absence. Oxipurinol did not significantly affect 5-FU cytotoxicity against Hec-1A (endometrial). In none of the three lines was a protective effect of oxipurinol noted.