DX-8951f: Summary of Phase I Clinical Trials

Exatecan mesylate (DX-8951f) is a new hexacyclic camptothecin analogue with favorable attributes compared to topotecan and CPT-11, including watersolubility, greater potency against topoisomerase I, lack of esterase-dependent activation, broad antitumor activity, and low cross-resistance against MDR-1 overexpressing tumors. In preclinical studies, the compound demonstrated a favorable toxicology profile with hematologic dose-limiting toxicity and moderate gastrointestinal toxicity, linear pharmacokinetics, P450 hepatic metabolism (CYP3A4 and CYP1A2), and predominately fecal excretion. The results of six U.S. and European phase I clinical trials as well as two Japanese studies are presented including total DX-8951 and lactone DX-8951 pharmacokinetics. The toxicity profile was similar for all schedules of administration. Hematologic toxicity was dose-dependent and reversible. Neutropenia was dose-limiting in minimally pretreated patients, whereas neutropenia and thrombocytopenia were dose-limiting in heavily pretreated patients. Non-hematologic toxicity included moderate gastrointestinal toxicity (nausea, vomiting > diarrhea), transient elevation of hepatic transaminases, asthenia, and alopecia. Two cases of acute pancreatitis not predicted by preclinical toxicology were also observed. Antineoplastic activity was detected in several solid tumor types: non-small cell lung cancer, extrapulmonary small cell cancer, colorectal cancer, hepatocellular cancer, and sarcoma. Antitumor activity was seen in CPT-11 and topotecan-resistant tumors. Pharmacokinetics were linear within the dose range tested. A pharmacokinetic/pharmacodynamic model predictive of DX-8951f-induced neutropenia in individual patients was developed. The daily x5, every 3-week schedule with the drug administered as a 30-minute intravenous infusion was selected for future phase II clinical trials based on its superior antitumor activity.