S-phase modulation by irinotecan: Pilot studies in advanced solid tumors

Two studies of irinotecan (CPT-11) followed 24 h later by an antimetabolite were conducted. The objectives of the studies were: (1) to determine whether the increase in S-phase in tumor cells seen 24 h after CPT-11 administration in animal studies is seen in advanced solid tumors in patients, (2) to determine the dose of CPT-11 required to produce this effect, (3) to compare two methods (immunohistochemistry, IHC, for cyclin A, and DNA flow cytometry, FC) for evaluating S-phase in tumor biopsies from patients, and (4) to establish the maximum tolerated dose (MTD) and dose-limiting toxicity (DLT) of CPT-11, given 24 h before gemcitabine (GEM, 1000 mg/m²). In one study CPT-11 was followed 24 h later by 5-fluorouracil (5-FU), 400 mg/m² per week for 4 weeks every 6 weeks. Tumor biopsies were obtained before and 24h after CPT-11 administration before administration of 5-FU and assayed for S-phase by IHC for cyclin A and by FC. The starting dose of CPT-11 was 80 mg/m² per week with subsequent exploration of 40 and 60 mg/m² per week to establish the dose-effect relationship of the increase in tumor cells in S-phase. In the second study, CPT-11 was given 24 h before GEM 1000 mg/m² per week for 2 weeks every 3 weeks. Doses of 20-80 mg/m² were explored to establish the MTD and DLT and to study tumor cell S-phase in selected patients. CPT-11 80 mg/m² produced a mean increase in S-phase by IHC for cyclin A of 137%. Lesser increases were seen with 40 and 60 mg/m². CPT-11 followed 24 h later by 5-FU 400 mg/m² per week for 4 weeks was well tolerated. In the study of CPT-11 followed by GEM 1000 mg/m², 60 mg/m² of CPT-11 was the MTD.