title: Ugt1a is required for the protective effect of selenium against irinotecan-induced toxicity.
abstract: OBJECTIVE
  Irinotecan (CPT-11) is widely used for the treatment of patients with colorectal cancer. However, the adverse effects associated with the treatment have hindered the efficacies of irinotecan. We have shown that organic selenium compounds could significantly attenuate irinotecan-associated toxicity and enhance antitumor activity in xenograft tumor models. The objective of this study is to determine the role of a specific group of uridine diphosphate glucuronosyltransferases, which is coded by UGT1A, in detoxification process of irinotecan as well as selenium-associated protective effect against irinotecan-induced toxicity.
  
  
  METHODS
  In this study, the toxicities of irinotecan, docetaxel and cisplatin in the Ugta1 mutant rats and their wild-type controls were compared. The plasma concentrations of irinotecan and SN-38 were measured. The modulatory effect of a selenium compound on irinotecan-induced toxicity was analyzed in these rats.
  
  
  RESULTS
  We demonstrated that the maximum tolerated doses of irinotecan in the homozygous mutant rats were significantly lower than those in wild-type rats, 25 mg/kg × 1 versus 200 mg/kg × 1 and 3 mg/kg/day × 3 versus 100 mg/kg/day × 3, respectively. The enhanced sensitivity was specific to irinotecan and was not observed with other chemotherapeutic agents, such as docetaxel and cisplatin, where Ugt1a is not required for their metabolism. Our results also showed that selective protection against irinotecan-induced toxicity by 5-methylselenocysteine was achieved in the wild-type rats but not in the Ugt1a null rats.
  
  
  CONCLUSIONS
  These data support the hypothesis that expression of UGT1A is critical for 5-methylselenocysteine to exert its protective effect against irinotecan-induced toxicity.
authors.affiliation: Department of Cancer Biology, Roswell Park Cancer Institute, Elm and Carlton Streets, Buffalo, NY 14263, USA. Shousong.Cao@roswellpark.org
authors.forename: Shousong
authors.initials: S
authors.lastname: Cao
authors.forename: Farukh A
authors.initials: FA
authors.lastname: Durrani
authors.forename: Youcef M
authors.initials: YM
authors.lastname: Rustum
authors.forename: Y Eugene
authors.initials: YE
authors.lastname: Yu
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000493:pharmacokinetics / Q000633:toxicity*; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000633:toxicity; D005260:Female; D014453:Glucuronosyltransferase / Q000378:metabolism*; D008658:Inactivation, Metabolic; D000077146:Irinotecan; D020714:Maximum Tolerated Dose; D016566:Organoselenium Compounds / Q000494:pharmacology*; D051381:Rats; D011911:Rats, Gunn; D011916:Rats, Inbred F344; D000099148:UGT1A1 Enzyme
chemical_list: D000970:Antineoplastic Agents; D002166:Camptothecin; D014453:Glucuronosyltransferase; D000077146:Irinotecan; D016566:Organoselenium Compounds; C499946:Ugt1a1 protein, rat; D000099148:UGT1A1 Enzyme