Background: Eribulin mesylate (eribulin) is a first-in-class halichondrin B-based microtubule dynamics inhibitor. To compare the anti-angiogenic activity of eribulin to that of bevacizumab, we compared tumour vessel remodelling and reoxygenation between the two agents.

Methods: Patients with advanced breast cancer with stage III/IV were eligible for the study. Patients were assigned to receive either eribulin or single-agent bevacizumab. Tissue concentrations of oxyhaemoglobin (O2Hb) and deoxyhaemoglobin (HHb), and oxygen saturation (SO2) of breast tumours before and day 7 after the first infusion were repeatedly measured using diffuse optical spectroscopic imaging (DOSI). A pair of blood samples was collected for multiplex biomarker studies.

Results: Baseline DOSI measurement of all 29 patients (eribulin, n=14 and bevacizumab, n=15) revealed significantly higher tumour concentrations of O2Hb and HHb than that in the normal breast tissue. After eribulin treatment, DOSI revealed a significant decrease in HHb concentration and increased SO2 during the observation period. This trend was not observed for bevacizumab. Instead, bevacizumab significantly decreased the concentration of O2Hb. The multiplex biomarker study revealed that both eribulin and bevacizumab decreased plasma concentrations of VEGF and bFGF, but only eribulin treatment suppressed the plasma concentration of TGF-β1.

Conclusions: Eribulin, but not bevacizumab, treatment increased tumour SO2. Suppression of TGF-β1 by eribulin could have a favourable anti-angiogenic effect. Our results suggest that differences in vascular remodelling between these two agents may account for their different effects on tumour reoxygenation.