Safety, pharmacokinetics, and activity of EZN-2208, a novel conjugate of polyethylene glycol and SN38, in patients with advanced malignancies

BACKGROUND: EZN-2208 is a water-soluble, polyethylene glycol drug conjugate of SN38, which is the active moiety of irinotecan. In this study, the authors evaluated the tolerability, pharmacokinetics (PK), and activity of EZN-2208 in adult patients with advanced solid tumors. METHODS: Patients in sequential cohorts (3 + 3 design) received intravenous EZN-2208 at doses between 1.25 mg/m² and 25 mg/m² once every 21 days. RESULTS: Thirty-nine patients received EZN-2208. The median number of prior therapies was 2 (range, 0-10 prior therapies). Seventeen patients received prior irinotecan. Two maximum tolerated doses (MTDs) were defined: EZN-2208 with (16.5 mg/m ²) and without (10 mg/m²) granulocyte-colony-stimulating factor (G-CSF). The dose-limiting toxicity (DLT) was febrile neutropenia. Two of 19 patients who were heterozygous for a polymorphism in the uridine diphosphate glucuronosyltransferase 1 family, polypeptide A1 (UGT1A1) gene (UGT1A1*28) developed DLTs (dose, 25 mg/m² with G-CSF), and 2 patients who were homozygous for UGT1A1*28 were treated without DLTs (dose, 5 mg/m²). PK analysis indicated a mean terminal half-life of 19.4 ± 3.4 hours. Sixteen patients (41%) achieved stable disease, including 6 of 39 patients (15%) who had stable disease that lasted ≥4 months. One patient with cholangiocarcinoma (no prior irinotecan) achieved a short-lived 32% tumor regression. Among 6 patients who had stable disease that lasted for ≥4 months, 3 had received prior irinotecan, and 1 had KRAS-positive colorectal cancer. CONCLUSIONS: EZN-2208 was well tolerated and produced stable disease that lasted for ≥4 months/unconfirmed partial responses in 7 of 39 heavily pretreated patients (18%) with advanced solid tumors, including those who had failed prior irinotecan therapy.