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  2. Eribulin induces irreversible mitotic blockade: implications of cell-based pharmacodynamics for in vivo efficacy under intermittent dosing conditions

Eribulin induces irreversible mitotic blockade: implications of cell-based pharmacodynamics for in vivo efficacy under intermittent dosing conditions

  • Cancer Res. 2011 Jan 15;71(2):496-505. doi: 10.1158/0008-5472.CAN-10-1874.
Murray J Towle 1 Kathleen A Salvato Bruce F Wels Kimberley K Aalfs Wanjun Zheng Boris M Seletsky Xiaojie Zhu Bryan M Lewis Yoshito Kishi Melvin J Yu Bruce A Littlefield
Affiliations

Affiliation

  • 1 Division of Biology, Eisai Inc., Andover, Massachusetts, USA.
Abstract

Eribulin (E7389), a mechanistically unique microtubule inhibitor in phase III clinical trials for Cancer, exhibits superior efficacy in vivo relative to the more potent compound ER-076349, a fact not explained by different pharmacokinetic properties. A cell-based pharmacodynamic explanation was suggested by observations that mitotic blockade induced by eribulin, but not ER-076349, is irreversible as measured by a flow cytometric mitotic block reversibility assay employing full dose/response treatment. Cell viability 5 days after drug washout established relationships between mitotic block reversibility and long-term cell survival. Similar results occurred in U937, Jurkat, HL-60, and HeLa cells, ruling out cell type-specific effects. Studies with other tubulin agents suggest that mitotic block reversibility is a quantifiable, compound-specific characteristic of antimitotic agents in general. Bcl-2 phosphorylation patterns parallel eribulin and ER-076349 mitotic block reversibility patterns, suggesting persistent Bcl-2 phosphorylation contributes to long-term cell-viability loss after eribulin's irreversible blockade. Drug uptake and washout/retention studies show that [3H]eribulin accumulates to lower intracellular levels than [3H]ER-076349, yet is retained longer and at higher levels. Similar findings occurred with irreversible vincristine and reversible vinblastine, pointing to persistent cellular retention as a component of irreversibility. Our results suggest that eribulin's in vivo superiority derives from its ability to induce irreversible mitotic blockade, which appears related to persistent drug retention and sustained Bcl-2 phosphorylation. More broadly, our results suggest that compound-specific reversibility characteristics of antimitotic agents contribute to interactions between cell-based pharmacodynamics and in vivo pharmacokinetics that define antitumor efficacy under intermittent dosing conditions.

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