Irinotecan, sold under the brand name Camptosar among others, is a medication used to treat colon cancer, and small cell lung cancer. For colon cancer it is used either alone or with fluorouracil. For small cell lung cancer it is used with cisplatin. It is given intravenously.Common side effects include diarrhea, vomiting, bone marrow suppression, hair loss, shortness of breath, and fever. Other severe side effects include blood clots, colon inflammation, and allergic reactions. Those with two copies of the UGT1A1*28 gene variant are at higher risk for side effects. Use during pregnancy can result in harm to the baby. Irinotecan is a topoisomerase inhibitor—it blocks the topoisomerase I enzyme, resulting in DNA damage and cell death.Irinotecan was approved for medical use in the United States in 1996. It is on the World Health Organizations List of Essential Medicines. It is made from the natural compound camptothecin which is found in the Chinese ornamental tree Camptotheca acuminata. Medical uses
Its main use is in colon cancer, in particular, in combination with other chemotherapy agents. This includes the regimen FOLFIRI, which consists of infusional 5-fluorouracil, leucovorin, and irinotecan. The regimen XELIRI consists of capecitabine and irinotecan.It may also be used together with fluorouracil and folinic acid for pancreatic cancer following failure of initial treatment. Side effects
The most significant adverse effects of irinotecan include diarrhea, nausea and vomiting, neutropenia and fever, infections of blood or lungs (sepsis, pneumonia), shock, dehydration, kidney failure and thrombocytopenia (low levels of blood platelets).
Diarrhea
Irinotecan-associated diarrhea is severe and clinically significant, sometimes leading to severe dehydration requiring hospitalization or intensive care unit admission. This side-effect is managed with the aggressive use of antidiarrheals such as loperamide or atropine with the first loose bowel movement. Immunosuppression
The immune system is adversely impacted by irinotecan. This is reflected in – sometimes dramatically – lowered white blood cell counts in the blood, in particular the neutrophils. The patient may experience neutropenia (a clinically significant decrease of neutrophils in the blood). Mechanism of action
Camptothecin, one of the four major structural classifications of plant-derived anti-cancerous compounds, is a cytotoxic alkaloid which consists of a pentacyclic ring structure containing a pyrrole (3, 4 β) quinoline moiety, an S-configured lactone form, and a carboxylate form. Camptothecin is an inhibitor of topoisomerase I. Its analogue, irinotecan, is activated by hydrolysis to SN-38, and is then inactivated by glucuronidation by uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1). The inhibition of topoisomerase I by the active metabolite SN-38 eventually leads to inhibition of both DNA replication and transcription.The molecular action of irinotecan occurs by trapping a subset of topoisomerase-1-DNA cleavage complexes, those with a guanine +1 in the DNA sequence. One irinotecan molecule stacks against the base pairs flanking the topoisomerase-induced cleavage site and poisons (inactivates) the topoisomerase 1 enzyme. Interactive pathway
Click on genes, proteins and metabolites below to link to respective articles. Pharmacokinetics
Administration
Irinotecan can be administrated by 30- or 90-minute intravenous infusions of either 125 mg/m2 weekly for four of every six weeks or 350 mg/m2 every three weeks.