APhase IPharmacologic and PharmacogeneticTrial of Sequential 24-Hour Infusion of Irinotecan Followedby Leucovorin and a 48-Hour Infusion of Fluorouracil in Adult Patients with SolidTumors

Purpose: In preclinical studies, sequential exposure to irinotecan (CPT-11) then fluorouracil (5-FU) is superior to concurrent exposure or the reverse sequence; a 24-hour infusion of CPT11may be better tolerated than shorter infusions. Experimental Design:CPT-11was first given at four levels (70-140mg/m/24 hours), followed by leucovorin 500 mg/m/0.5 hours and 5-FU 2,000 mg/m/48 hours on days 1and15 of a 4-week cycle. 5-FU was then increased in three cohorts up to 3,900 mg/m/48 hours. Results:Two patients had dose-limiting toxicity during cycle 1 at 140/3,900 of CPT-11/5-FU (2-week delay for neutrophil recovery; grade 3nauseadespite antiemetics); one of six patients at 140/3,120 had dose-limiting toxicity (grade 3 diarrhea, grade 4 neutropenia). Four of 22 patients with colorectal cancer had partial responses, two of which had prior bolus CPT-11/5-FU. The mean 5-FUplasma concentrationwas 5.1 Amol/L at 3,900 mg/m/48 hours.The end of infusion CPT-11plasma concentration averaged 519 nmol/L at 140 mg/m/24 hours. Patients with UDPglucuronosyltransferase (UGT1A1;TA)6/6 promoter genotype hada lower ratio of free to glucuronide form of SN-38 than in patients withz1 (TA)7 allele.Thymidylate synthase genotypes for the 28-base promoter repeat were 2/2 (13%), 2/3 (74%), 3/3 (13%); all four responders had a 2/3 genotype. Conclusions: Doses (mg/m) of CPT-11140/24 hours, leucovorin 500/0.5 hours and 5-FU 3,120/48 hours were well tolerated. The rationale for evaluating sequential i.v. infusions of irinotecan (CPT-11) over 24 hours followed by leucovorinmodulated fluorouracil (5-FU) over 48 hours is based on the following considerations. The cytotoxicity of camptothecin analogues is highly dependent on ongoing DNA replication and the fraction of cells in S phase (1, 2). Prolonged exposure to CPT-11 is active in both preclinical and clinical settings, may be better tolerated than 30to 90-minute infusions, and acute cholinergic symptoms may be diminished (3–7). From a pharmacologic perspective, a slower infusion rate may avoid saturation of glucuronidation of the active metabolite, SN-38, which in turn may be associated with less severe delayed diarrhea, and conversion of CPT-11 to SN-38 by hepatic carboxylesterase may be more efficient (8, 9). In preclinical models, CPT-11 given 6 to 24 hours prior to inhibitors of thymidylate synthase is the most effective sequence (10–17). By depleting TTP pools, thymidylate synthase inhibition in turn inhibits DNA synthesis. Because active DNA synthesis is required to convert the formation of covalent SN-38topoisomerase I–cleavable complexes to a cytotoxic lesion, inhibition of thymidylate synthase during or prior to formation of the SN-38 cleavable complex is counterproductive. An every-other-week schedule of leucovorin-modulated bolus/infusional 5-FU (LV5FU2) is superior to i.v. daily for 5 days bolus 5-FU/leucovorin every 4 weeks in terms of response rate, time to progression, and toxicity profile (18). A modified schedule using leucovorin before 5-FU on the first day only followed by a continuous infusion of 5-FU over 46 to 48 hours is more convenient than requiring the patient to return on day 2 for additional leucovorin and bolus 5-FU (19, 20). www.aacrjournals. org Clin Cancer Res 2005;11(11) June1, 2005 4144 Authors’ Affiliations: Gastrointestinal Tumor Section, Cancer Therapeutics Branch, Medical Oncology Clinical Research Unit, Center for Cancer Research, Cancer Prevention Program, National Cancer Institute, Division of Hematology andMedical Oncology, National NavalMedical Center, Bethesda,Maryland Received11/29/04; revised 2/6/05; accepted 3/10/05. The costs of publication of this article were defrayed in part by the payment of page charges.This article must therefore be hereby marked advertisement in accordance with18 U.S.C. Section1734 solely to indicate this fact. Note: This is a U.S. Government work. The views of the authors represent their personal opinions, and do not reflect the policies or positions of the National Cancer Institute, the Department of Defense, or the Department of the Navy. Requests for reprints: Jean Grem, Section of Hematology/Oncology, Nebraska Medical Center, University of Nebraska Medical Center, Omaha, NE 68198-7680. Phone: 402-559-6210; Fax: 402-559-6520; E-mail: jgrem@unmc.edu. F2005 American Association for Cancer Research. Cancer Therapy: Clinical Research. on January 8, 2018. © 2005 American Association for Cancer clincancerres.aacrjournals. org Downloaded from In addition to identifying the recommended doses of CPT-11 and 5-FU given on this sequential infusional schedule, we planned to evaluate the pharmacokinetics of 5-FU and CPT-11, and its metabolites, SN-38, in the free and glucuronide forms, and 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]carbonyloxycamptothecin (APC), and polymorphisms in the promoter region of the genes encoding for thymidylate synthase and UDP glucuronosyltransferase 1A1 (UGT1A1). The human thymidylate synthase promoter has three tandem repeats of a 28-nucleotide G/C-rich sequence in the first 100 nucleotides upstream of the AUG codon (the translation start site), as well as one inverted copy of the repeat starting at 139 (21–24). At least one tandem repeat is needed for efficient translation of thymidylate synthase mRNA; the number of repeats influences the efficiency of translation, and is polymorphic (25–27). Patients may be homozygous for a double or triple tandem repeat (2/2 or 3/3), or be heterozygous (2/3; ref. 28). Several investigators have reported an association between the genotype of the thymidylate synthase enhancer region and response to 5-FU-based therapy in patients with colorectal cancer (29–32). Glucuronidation of the SN-38 metabolite of irinotecan represents a detoxification mechanism; patients with a reduced capacity to conjugate SN-38 have a higher risk of experiencing severe or life-threatening toxicity with irinotecan therapy (8, 33–35). A polymorphism in the promoter region of the human UGT1A1 gene has been described with variation of a 2-bp doublet, TA; the (TA)6TAA element is the normal pattern (36–38). Patients with Gilbert’s syndrome, a benign form of unconjugated hyperbilirubinemia, are homozygous for the 7/7 allele (38, 39). Recent information suggests that patients who are heterozygous (6/7) or homozygous for the TA-7 repeat (7/7) have a decreased capacity to conjugate SN-38, and are more likely to have severe diarrhea and myelosuppression with irinotecan therapy (38–41).