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 days1, 8, and 15 of a 28-day cycle. Dosing began at 0.25 mg/m 2 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/m 2 ). Neutropenia was the principal DLT: At 1.4 mg/m 2 , 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 1on day 15. Therefore, the MTD was 1.0 mg/m 2 . 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/m 2 with further dose escalation limited by neutropenia and fatigue.

Background Antimitotic agents are essential components for curative therapy of pediatric acute leukemias and many solid tumors. Eribulin is a novel agent that differs from both Vinca alkaloids and taxanes in its mode of binding to tubulin polymers. Procedures Eribulin was tested against the PPTP in vitro cell line panel at concentrations from 0.1 nM to 1.0 μM and against the PPTP in vivo xenograft panels at a dose of 1 mg/kg (solid tumors) or 1.5 mg/kg (ALL models) using a q4dx3 schedule repeated at Day 21. Results In vitro eribulin demonstrated cytotoxic activity, with a median relative IC50 value of 0.27 nM, (range <0.1–14.8 nM). Eribulin was well tolerated in vivo, and all 43 xenograft models were considered evaluable for efficacy. Eribulin induced significant differences in event-free survival (EFS) distribution compared to control in 29 of 35 (83%) of the solid tumors and in 8 of 8 (100%) of the ALL xenografts. Objective responses were observed in 18 of 35 (51%) solid tumor xenografts. Complete responses (CR) or maintained CR were observed in panels of Wilms tumor, Ewing sarcoma, rhabdomyosarcoma, glioblastoma, and osteosarcoma xenografts. All eight ALL xenografts achieved CR or MCR. Conclusions The high level of activity observed for eribulin against the PPTP preclinical models makes this an interesting agent to consider for pediatric evaluation. The activity pattern observed for eribulin in the solid tumor panels is equal or superior to that observed previously for vincristine.

Chemotherapy-induced peripheral neuropathy (CIPN) is a major cause of disability in cancer survivors. CIPN investigations in preclinical model systems have focused on either behaviors or acute changes in nerve conduction velocity (NCV) and amplitude, but greater understanding of the underlying nature of axonal injury and its long-term processes is needed as cancer patients live longer. In this study, we used multiple independent endpoints to systematically characterize CIPN recovery in mice exposed to the antitubulin cancer drugs eribulin, ixabepilone, paclitaxel, or vinorelbine at MTDs. All of the drugs ablated intraepidermal nerve fibers and produced axonopathy, with a secondary disruption in myelin structure within 2 weeks of drug administration. In addition, all of the drugs reduced sensory NCV and amplitude, with greater deficits after paclitaxel and lesser deficits after ixabepilone. These effects correlated with degeneration in dorsal root ganglia (DRG) and sciatic nerve and abundance of Schwann cells. Although most injuries were fully reversible after 3-6 months after administration of eribulin, vinorelbine, and ixabepilone, we observed delayed recovery after paclitaxel that produced a more severe, pervasive, and prolonged neurotoxicity. Compared with other agents, paclitaxel also displayed a unique prolonged exposure in sciatic nerve and DRG. The most sensitive indicator of toxicity was axonopathy and secondary myelin changes accompanied by a reduction in intraepidermal nerve fiber density. Taken together, our findings suggest that intraepidermal nerve fiber density and changes in NCV and amplitude might provide measures of axonal injury to guide clinical practice. This detailed preclinical study of the long-term effects of widely used antitubulin cancer drugs on the peripheral nervous system may help guide clinical evaluations to improve personalized care in limiting neurotoxicity in cancer survivors. .

Chemotherapy-induced peripheral neuropathy (CIPN) is a dose-limiting side effect of many antineoplastic agents, but the mechanisms underlying the toxicities of certain drugs are unclear. At their maximal tolerated doses (MTD), the microtubule-binding drugs paclitaxel and ixabepilone induce more severe neuropathy in mice relative to eribulin mesylate, paralleling their toxicity profiles in clinic. We hypothesized that the severity of their neurotoxic effects might be explained by the levels at which they accumulate in the peripheral nervous system. To test this hypothesis, we compared their pharmacokinetics and distribution in peripheral nerve tissue. After administration of a single intravenous dose, each drug was rapidly cleared from plasma but all persisted in the dorsal root ganglia (DRG) and sciatic nerve (SN) for up to 72 hours. Focusing on paclitaxel and eribulin, we performed a two week MTD-dosing regimen followed by a determination of drug pharmacokinetics, tissue distribution and multiple functional measures of peripheral nerve toxicity for four weeks. Consistent with the acute dosing study, both drugs persisted in peripheral nervous tissues for weeks, in contrast to their rapid clearance from plasma. Notably, although eribulin exhibited greater DRG and SN penetration than paclitaxel, the neurotoxicity produced biologically was consistently more severe with paclitaxel. Overall, our results argued that sustained exposure of microtubule-binding chemotherapeutic agents in peripheral nerve tissues cannot by itself account for their associated neurotoxicity.

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