Although 5-fluorouracil (Fura) is the drug of choice for the treat ment of patients with advanced colorectal cancer, this agent has limited effectiveness with a reported response rate of 10-20% and a duration of response of only 6-9 months. The large percentage of treatment failures with this agent has spurred a continuing effort to delineate the mechanism(s) of resistance to Fura and to evaluate approaches that would selectively modulate the therapeutic efficacy of this agent. The therapeutic efficacy of FUra has been attributed to its selec tive incorporation into RNA and to its inhibition...