Purpose: This is a first-in-human, phase I, dose-escalation study to determine the maximum tolerated dose (MTD) of intravenous, flat-dosed ST-1968 (namitecan), a new hydrophilic camptothecan derivative.
Methods: Namitecan was administered intravenously over 2 h on day 1 and day 8 every 21 days (D1-D8-Q21D), starting at a flat dose of 2.5 mg, and increased according to a 3 + 3 cohort design. Due to frequent skipping of day 8 dosing for cytopenias, the study was expanded to test namitecan dosing on day 1 every 21 days (D1-Q21) at a starting dose of 17.5 mg. Major dose-limiting toxicity (DLT) was defined as grade (G) 4 neutropenia persisting >5 days, febrile neutropenia, G3 thrombocytopenia or G2 non-hematological toxicity.
Results: Thirty-four patients were included into the D1-D8-Q21D group (2.5, 5, 10, 15, 17.5, 20 mg dosing cohorts), 29 patients into the D1-21D group (17.5, 20, 23, 27, 30 mg dosing cohorts). Neutropenia was the DLT in both groups, with 15 mg being defined as the recommended dose (RD) for the D1-D8-Q21D group, and 23 mg for the D1-Q21D group. Non-hematological toxicity was negligible. One patient with endometrial cancer in the D1-D8-Q21D group and one patient with cholangiocellular carcinoma in the D1-Q21D group experienced a partial remission. Namitecan exhibited fully dose-proportional pharmacokinetics.
Conclusions: This study demonstrates clinical safety, favourable pharmacokinetics and preliminary antitumor activity of the novel hydrophilic camptothecin analogue namitecan in patients with heavily pretreated solid malignancies, when given either on a 2 out of 3 weeks or 3-weekly regimen.