Phase I trial of the colloidal dispersion formulation of 9-amino-20(S)-camptothecin administered as a 72-hour continuous intravenous infusion.

The camptothecins are a class of potent cytotoxic anticancer agents that interact with the nuclear enzyme topoisomerase I to produce lethal DNA strand cleavages. 9-Amino-20(S)-camptothecin (9AC) was introduced into Phase I clinical trials in dimethylacetamide and polyethylene glycol 400 in a 10 mM phosphoric acid vehicle for i.v. solubility. A lyophilized colloidal dispersion (CD) of 9AC for reconstitution with 20% dextrose in normal saline was developed as an alternative formulation. Patients (ages 25-75 years) with normal liver and kidney function, Eastern Cooperative Oncology Group performance status < or = 2, and up to two prior chemotherapy regimens were treated. The initial infusion rate was 37.5 micrograms/m2/h as a 72-h continuous infusion (2.7 mg/m2 total dose). Patient cohorts were treated with escalating infusion rates until grade 4 hematological or other grade 3 toxicity developed. Pharmacokinetic sampling was performed on all patients, and 9AC lactone concentrations in plasma were determined by a high-performance liquid chromatographic assay. Twenty-five patients received a total of 65 courses of 9AC CD at doses from 2.70 to 4.65 mg/m2. The dose-limiting toxicity was neutropenia, with little nonhematological toxicity. Nonlinear regression analysis of pooled patient data yielded a total plasma clearance of 30.3 +/- 4.5 liters/h/m2, a half-life of 22.5 +/- 8.5 h, a mean residence time of 9.7 +/- 3.5 h, and a steady-state volume of distribution of 325 +/- 145 liters/m2. Although no objective responses were seen, 9 of 25 patients exhibited stable disease for 2-6 months. The plasma pharmacokinetics of 9AC lactone in cancer patients were comparable between the 9AC CD and soluble formulations. The dosing regimen recommended for Phase II trials of the 9AC CD formulation is 54.2 micrograms/m2/h, given as a 72-h continuous i.v. infusion every 3 weeks.