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    Pathway Description
      Irinotecan Topoisomerase Inhibitor Action Pathway
Homo sapiens
            Category:
                Metabolite Pathway
                Sub-Category:
                Drug Action
            Created: 2021-05-07
          Last Updated: 2023-10-25
        
          Irinotecan is a semi-synthetic analogue of camptothecin which is a topoisomerase IB inhibitor. It is used to treat colorectal cancer. It's mechanism of action against topoisomerase I is that it forms a tertiary complex between the DNA and the topoisomerase I enzyme causing double strand breaks. It first has to be metabolized by liver carboxylesterase 1 into SN-38, which is the active metabolite that inhibits topoisomerase. SN-38 can be inactivated by UGT1A1 into SN-38 glucuronide which upregulated in some individuals leading to irinotecan resistance. Individuals might also have a reduced function variant of UGT1A1 which can lead to increased metabolism of irinotecan and leads to irinotecan toxicity. Toxicity of irinotecan leads to gastrointestinal complications as well as nausea, vomiting and headaches. Irinotecan is administered usually intravenously as a solution. 
        
      References
      
      Irinotecan Topoisomerase Inhibitor Pathway References
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              Kuhn JG: Pharmacology of irinotecan. Oncology (Williston Park). 1998 Aug;12(8 Suppl 6):39-42.
                  Pubmed: 9726089
              Munger JS, Shi GP, Mark EA, Chin DT, Gerard C, Chapman HA: A serine esterase released by human alveolar macrophages is closely related to liver microsomal carboxylesterases. J Biol Chem. 1991 Oct 5;266(28):18832-8.
                  Pubmed: 1918003
              Kroetz DL, McBride OW, Gonzalez FJ: Glycosylation-dependent activity of baculovirus-expressed human liver carboxylesterases: cDNA cloning and characterization of two highly similar enzyme forms. Biochemistry. 1993 Nov 2;32(43):11606-17. doi: 10.1021/bi00094a018.
                  Pubmed: 8218228
              Shibata F, Takagi Y, Kitajima M, Kuroda T, Omura T: Molecular cloning and characterization of a human carboxylesterase gene. Genomics. 1993 Jul;17(1):76-82. doi: 10.1006/geno.1993.1285.
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              Levesque E, Girard H, Journault K, Lepine J, Guillemette C: Regulation of the UGT1A1 bilirubin-conjugating pathway: role of a new splicing event at the UGT1A locus. Hepatology. 2007 Jan;45(1):128-38. doi: 10.1002/hep.21464.
                  Pubmed: 17187418
              Ritter JK, Crawford JM, Owens IS: Cloning of two human liver bilirubin UDP-glucuronosyltransferase cDNAs with expression in COS-1 cells. J Biol Chem. 1991 Jan 15;266(2):1043-7.
                  Pubmed: 1898728
              Ritter JK, Chen F, Sheen YY, Tran HM, Kimura S, Yeatman MT, Owens IS: A novel complex locus UGT1 encodes human bilirubin, phenol, and other UDP-glucuronosyltransferase isozymes with identical carboxyl termini. J Biol Chem. 1992 Feb 15;267(5):3257-61.
                  Pubmed: 1339448
              Nagase T, Ishikawa K, Nakajima D, Ohira M, Seki N, Miyajima N, Tanaka A, Kotani H, Nomura N, Ohara O: Prediction of the coding sequences of unidentified human genes. VII. The complete sequences of 100 new cDNA clones from brain which can code for large proteins in vitro. DNA Res. 1997 Apr 28;4(2):141-50. doi: 10.1093/dnares/4.2.141.
                  Pubmed: 9205841
              Nakajima D, Okazaki N, Yamakawa H, Kikuno R, Ohara O, Nagase T: Construction of expression-ready cDNA clones for KIAA genes: manual curation of 330 KIAA cDNA clones. DNA Res. 2002 Jun 30;9(3):99-106. doi: 10.1093/dnares/9.3.99.
                  Pubmed: 12168954
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                  Pubmed: 15164053
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