Background: SmithKline Beecham synthesized camptothecin analogs and identified nogitecan hydrochloride (topotecan) with a broad spectrum of antitumor activity and less toxicity than camptothecin. Because preclinical and overseas clinical data indicated the antitumor effect of nogitecan hydrochloride with a 5-day repeat-dose schedule, we carried out phase I studies in Japan to determine the maximum tolerated dose (MTD), pharmacokinetics, and antitumor effect of nogitecan hydrochloride.
Methods: Phase I studies of nogitecan hydrochloride given by single and 5-day repeat dosing were carried out in patients with various solid tumors at 15 medical institutions in Japan. Pharmacokinetic evaluations were performed for both single and 5-day repeated dosing.
Results: The dose-limiting factor (DLF) was reversible leucopenia, and the maximum tolerated dose (MTD) was higher than 22.5 mg/m2 in the single-dose study. In the 5-day repeat-dose study, the DLF was also reversible leucopenia, and the MTD was estimated to be 1.5 mg/m2 per day. The plasma concentration of nogitecan hydrochloride increased with increasing dose, and the half-life after single dosing ranged from 3 to 5h. There was no evidence of accumulation or delayed excretion during 5-day repeat dosing.
Conclusion: Based on these results and the finding that there were responders among patients treated at 1.5 mg/m2 per day by 5-day repeat dosing in overseas studies, 5-day repeat dosing of 1.2mg/m2 per day, one dose level lower than the MTD, was selected for phase II studies in Japan.