Abstract P5-03-08: Eribulin impairs the transport of TGF-β type I receptor leading to inhibition of downstream non-canonical TGF-β signaling necessary for cancer metastasis and survival
Authors: Rohena CC , Kaul R , Risinger AL , Mooberry SL 
Published: May 2016

Abstract
Microtubule targeting agents (MTAs) continue to be some of the most valuable drugs used in the treatment of breast cancers. While decades of research have shown that these drugs cause mitotic arrest in cells by suppressing the dynamic instability of microtubules, recent evidence demonstrates that the ability of MTAs to disrupt microtubule-dependent transport of key signaling components, including proteins and microRNAs, in interphase cells likely contributes to their anticancer actions. TGF-β receptors are known to undergo constant cycling from the plasma membrane to intracellular portions of the cell, a process which is microtubule dependent. This microtubule-dependent trafficking has been shown to regulate the nuclear translocation of the TGF-β type I receptor, TGFβR1. Nuclear translocation of TGFβR1 activates the expression of genes including Snail and MMP2, which facilitate the invasiveness, motility and metastasis of cancer cells. We tested the hypothesis that a 2 h treatment of breast cancer cells with eribulin or 4 other clinically relevant MTAs, would differentially disrupt interphase microtubules and alter the internalization and trafficking of TGFβR1 to the nucleus; thereby impacting downstream signaling events. Cells were serum starved for 12 hours and then treated for 2 h with concentrations of MTAs that caused comparable disruption of the interphase microtubule network; 100 nM was used for the destabilizers, eribulin and vinorelbine and 1 μM was used for the stabilizers, paclitaxel, docetaxel and ixabepilone. Following the 2 h treatment, cells were stimulated with 10 ng/mL TGF-β1 for 30 min. The results show that there are distinct differences between the effects of microtubule stabilizers and destabilizers on TGFβR1 trafficking. Eribulin and vinorelbine decreased the nuclear localization of TGFβR1 in a panel of breast cancer cell lines with initial studies suggesting that eribulin impairs this trafficking to a greater extent. In contrast, the microtubule stabilizers, particularly ixabepilone, increased TGFβR1 localization in the nucleus. Additionally, TGFβR1 was extensively localized along stabilizer-induced microtubule bundles. Overall, our work suggests that eribulin is the most effective MTA at inhibiting TGFβR1 nuclear accumulation and subsequent phosphorylation of Smads 2 and 3. The downstream signaling effects of these MTAs on TGFβR1 induced transcription of Snail and MMP2 are also being investigated. Eribulin induced inhibition of non-canonical TGF-β signaling is consistent with previous studies that show that a 7 day treatment with eribulin reversed TGF-β-mediated EMT in breast cancer cells.1,2 Our data suggest that inhibition of the nuclear transport of TGFβR1 could be a potential mechanism for the eribulin-mediated EMT reversal. These studies begin to shed light into the diverse mechanisms of MTAs and lay the groundwork to identify patient populations that might respond optimally to different MTAs.
1. Yoshida T, et al., Brit J Cancer 110(6): 1497-505, 2014.
2. Dezso Z, et al., PloS One, 9(8): e106131, 2014.
This work is funded by Eisai Inc.
Citation Format: Rohena CC, Kaul R, Risinger AL, Mooberry SL. Eribulin impairs the transport of TGF-β type I receptor leading to inhibition of downstream non-canonical TGF-β signaling necessary for cancer metastasis and survival. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P5-03-08.