This first-in-human, phase I clinical trial was designed to determine the dose-limiting toxicities (DLTs) and the dose for phase II trials (P2D) of elisidepsin (PM02734) administered as a 30-min or as a 3-h intravenous infusion every 3 weeks (q3wk). Between March 2006 and April 2011, 53 patients with advanced malignant solid tumors were enrolled and treated with elisidepsin on the two different q3wk infusion schedules: 22 (30-min) and 31 (3-h), respectively. Doses evaluated ranged from 0.1 to 1.6 mg/m(2) (30-min q3wk) and from 2.0 to 11.0 mg flat dose (FD) (3-h q3wk). In the 30-min q3wk schedule, transient grade 3/4 increases in hepatic transaminases were the DLT, which appeared at the highest doses tested (from 1.1 to 1.6 mg/m(2)). No DLTs were observed on the 3-h schedule at doses up to 11.0 mg q3wk. Common adverse events were grade 1/2 pruritus, nausea, fatigue and hypersensitivity. Of note, myelotoxicity was not observed. Plasma maximum concentration and total drug exposure increased linearly with dose. Prolonged (a parts per thousand yen3 months) disease stabilization was observed in pretreated patients with pleural mesothelioma (n = 1) in the 30-min q3wk arm, and with colorectal adenocarcinoma (n = 3), esophagus adenocarcinoma, endometrium adenocarcinoma, pleural mesothelioma, and head and neck carcinoma (n = 1 each) in the 3-h q3wk arm. In conclusion, elisidepsin doses of 1.1 mg/m(2) (equivalent to a FD of 2.0 mg) and 11.0 mg FD are the dose levels achieved for further phase II trials testing the 30-min q3wk and 3-h q3wk schedules, respectively.