Eribulin alone or in combination with the PLK1 inhibitor BI 6727 triggers intrinsic apoptosis in Ewing sarcoma cell lines.

Lilly Magdalena Weiß,Manuela Hugle,Simone Fulda

doi:10.18632/oncotarget.17190

Lilly Magdalena Weiß, Manuela Hugle + Show 1 more

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https://doi.org/10.18632/oncotarget.17190

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Abstract

In this study, we investigated the molecular mechanisms of eribulin-induced cell death and its therapeutic potential in combination with the PLK1 inhibitor BI 6727 in Ewing sarcoma (ES). Here, we show that eribulin triggers cell death in a dose-dependent manner in a panel of ES cell lines. In addition, eribulin at subtoxic, low nanomolar concentrations acts in concert with BI 6727 to induce cell death and to suppress long-term clonogenic survival. Mechanistic studies reveal that eribulin monotherapy at cytotoxic concentrations and co-treatment with eribulin at subtoxic concentrations together with BI 6727 arrest cells in the M phase of the cell cycle prior to the onset of cell death. This mitotic arrest is followed by increased phosphorylation of BCL-2 and BCL-xL as well as downregulation of MCL-1, suggesting inactivation of these antiapoptotic BCL-2 family proteins. Consistently, eribulin monotherapy and eribulin/BI 6727 co-treatment trigger activation of BAX, a key proapoptotic BCL-2 family protein, and increase proteolytic activation of caspase-9 and -3. Importantly, overexpression of BCL-2 or addition of the broad-range caspase inhibitor zVAD.fmk significantly rescue eribulin- as well as eribulin/BI 6727-induced cell death. Together, these findings demonstrate that eribulin induces cell death via the intrinsic pathway of apoptosis in ES cells, both alone at cytotoxic concentrations and in combination with BI 6727 at subtoxic concentrations. Thus, our study highlights the therapeutic potential of eribulin for the treatment of ES alone or in rational combination therapies.

Highlights

Ewing sarcoma (ES) is the second most common primary pediatric bone tumor predominantly affecting adolescents and young adults that tends to metastasize at an early stage making a cure quite challenging [1,2,3,4]
To address the question as to how cell death induced by eribulin alone at cytotoxic doses and by eribulin at subtoxic concentrations together with the polo-like kinase 1 (PLK1) inhibitor BI 6727 is mediated on a molecular level we focused our subsequent studies on two ES cell lines, i.e. A4573 and SK-ES-1
These results show that eribulin as single agent triggers cell death in a dose-dependent manner and reduces long-term survival of ES cells

Summary

Introduction

Ewing sarcoma (ES) is the second most common primary pediatric bone tumor predominantly affecting adolescents and young adults that tends to metastasize at an early stage making a cure quite challenging [1,2,3,4]. Despite a combination of surgery, irradiation and aggressive chemotherapy, the overall survival of patients with metastasis or relapse is still poor [3, 4]. Apoptosis represents one of the best characterized forms of programmed cell death and is mediated via two major signaling pathways, i.e. the extrinsic and the intrinsic pathway [6]. This eventually results in the activation of caspases, known as key effector molecules [6, 7]. The interaction and the ratio of pro- (i.e. BAX) and antiapoptotic (i.e. BCL-2, BCL-xL and MCL-1) proteins of the BCL-2 family are involved in the control of mitochondrial outer membrane permeabilization, a process that promotes caspase activation, e.g. by the release of mitochondrial intermembrane space proteins [8, 9]

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