A Phase I Study of Eribulin Mesylate (E7389), a Mechanistically Novel Inhibitor of Microtubule Dynamics, in Patients with Advanced Solid Malignancies

Abstract Purpose: Eribulin mesylate (E7389), a non-taxane microtubule dynamics inhibitor, is a structurally simplified, synthetic analogue of halichondrin B that acts via a mechanism distinct from conventional tubulin-targeted agents. This phase I study determined the maximum tolerated dose (MTD) and pharmacokinetics of eribulin administered on a 3 of 4 week schedule in patients with advanced solid malignancies. Experimental Design: Patients received eribulin mesylate (1-hour i.v. infusion) on days 1, 8, and 15 of a 28-day cycle. Dosing began at 0.25 mg/m2 with escalation guided by dose-limiting toxicities (DLT). MTD, DLTs, safety, pharmacokinetics, and antitumor activity were characterized. Results: Thirty-two patients received eribulin mesylate (0.25, 0.5, 0.7, 1.0, or 1.4 mg/m2). Neutropenia was the principal DLT: At 1.4 mg/m2, two patients experienced grade 4 neutropenia, one of whom also developed grade 3 fatigue; three additional patients experienced grade 3 neutropenia and were not treated during cycle 1 on day 15. Therefore, the MTD was 1.0 mg/m2. Fatigue (53% overall, 13% grade 3, no grade 4), nausea (41%, all grade 1/2), and anorexia (38% overall, 3% grade 3, no grade 4) were the most common eribulin-related adverse events. Eight patients reported grade 1/2 neuropathy (no grade 3/4). Eribulin pharmacokinetics were dose-proportional over the dose range studied. One patient (cervical cancer) achieved an unconfirmed partial response lasting 79 days. Ten patients reported stable disease. Conclusions: Eribulin mesylate, given on days 1, 8, and 15 of a 28-day cycle, exhibits manageable tolerability at 1.0 mg/m2 with further dose escalation limited by neutropenia and fatigue.