Metabolic activation of irinotecan during intra-arterial chemotherapy of metastatic colorectal cancer.

Biotransformation of irinotecan (CPT-11) into its pharmacologic active metabolite SN-38 was investigated in patients treated for advanced colorectal cancer. A dose of 180 mg/m(2) CPT-11 was administered to 6 patients by 60 min hepatic intra-arterial infusion (HAI) via a surgically implanted Port-a-Cath® system. Blood samples were collected from 0 to 360 min after start of HAI, and CPT-11 plus metabolites were analysed by a selective reversed phase HPLC method. The objective of this study was to evaluate the extent to which SN-38 is generated after HAI of irinotecan given at a low dose of 180 mg/m(2). In a second investigation, CPT-11 was administered via conventional intravenous infusion (dose 180 mg/m(2), 60 min infusion time, 11 patients) and CPT-11 plus metabolites were quantified using identical analytical procedure. Compared to i.v. infusion, the pharmacokinetics of CPT-11 and SN-38 were altered by HAI. The mean c(max) of CPT-11 after HAI was reduced by 37%, whereas the mean c(max) of SN-38 increased by 60%. HAI resulted in a desired, increased metabolic conversion of CPT-11 into SN-38 and might improve the regional availability of the pharmacologic active metabolite SN-38 at the site of tumor. Plasma concentrations of the metabolites SN-38 glucuronide and APC remained unaffected by the route of administration.