title: Role of uridine phosphorylase for antitumor activity of 5'-deoxy-5-fluorouridine.
abstract: 5'-Deoxy-5-fluorouridine (5'-DFUR) was parenterally and orally effective on various transplantable tumors and its activity was better than that of other fluorinated pyrimidines. However, like 5-fluorouracil and 2'-deoxy-5-fluorouridine (FUdR), 5'-DFUR was ineffective on L1210 leukemia resistant to 5-fluorouracil, suggesting that it would exert its antitumor activity through converted 5-fluorouracil. In tissue culture, 5'-DFUR inhibited the growth of various tumor cells similarly to ther fluorinated pyrimidines. However, 5'-DFUR was unique in that uridine completely reversed its inhibitory effect. Enzymological study clarified that uridine inhibited the conversion of 5'-DFUR to 5-fluorouracil by a uridine phosphorylase, in parallel to its reverse effect on cell growth inhibition by 5'-DFUR. Furthermore, a subline of L1210 leukemia resistant to 5'-DFUR but not to 5-fluorouracil was found to lack the uridine phosphorylase. These results indicate that 5'-DFUR is a depot form of 5-fluorouracil which can be promptly activated by uridine phosphorylase. In addition, the uridine phosphorylase was found to be abundant in sarcoma-180 solid tumor, leading to a significantly higher concentration of converted 5-fluorouracil in this tumor than in other normal tissues. This provides a good explanation for the high chemotherapeutic index of 5'-DFUR against this tumor, which may be applicable also for other tumors.
mesh_terms: D000818:Animals; D001711:Biotransformation; D005467:Floxuridine / Q000378:metabolism / Q000627:therapeutic use*; D005472:Fluorouracil / Q000627:therapeutic use; D007939:Leukemia L1210 / Q000188:drug therapy* / Q000201:enzymology; D008297:Male; D051379:Mice; D010430:Pentosyltransferases / Q000378:metabolism*; D012510:Sarcoma 180 / Q000188:drug therapy* / Q000201:enzymology; D005641:Tegafur / Q000378:metabolism / Q000627:therapeutic use; D013936:Thymidine / Q000494:pharmacology; D014529:Uridine / Q000494:pharmacology; D014543:Uridine Phosphorylase / Q000378:metabolism*
chemical_list: D005467:Floxuridine; D005641:Tegafur; D010430:Pentosyltransferases; D014543:Uridine Phosphorylase; D005472:Fluorouracil; C025034:doxifluridine; D013936:Thymidine; D014529:Uridine