Abstract 1861: Combination of eribulin plus AKT inhibitor evokes synergistic cytotoxicity in soft tissue sarcoma cells

Abstract [Background] Prognosis of unresectable or metastatic (UM)-soft tissue sarcoma (STS) is poor, with overall survival (OS) less than 1.2 years after diagnosis. Recommended therapy for most UM-STS patients is doxorubicin (Dox) as first line palliative chemotherapy. Recently, three new drugs, pazopanib, trabectedin and eribulin, were introduced for treatment of UM-STS after Dox therapy. Only eribulin could significantly improve OS. However, outcomes with eribulin for UM-STS did not satisfy an unmet clinical need. Therefore, despite recent advances in its treatment, prognosis of UM-STS remains dismal, underscoring the need to develop novel strategies for UM-STS. Resistance to anti-cancer drugs frequently arise that would hamper results of cancer therapy. Mechanisms of eribulin resistance have been largely unknown. Overexpressed p-AKT underlies the pathogenesis of a broad range of human malignancies including STS. The high expression of p-AKT has been identified as a negative surrogate marker for survival of STS patients. Therefore, AKT is an attractive target for STS therapeutics. [Aims] Our study aimed to investigate the molecular mechanism of eribulin-resistance and to evaluate the effect of combination therapy with eribulin and AKT-inhibitor on STS cells. [Methods] Eribulin-resistant STS cell lines were established by culturing HT1080 and SK-LMS-1 cells with stepwise increases in the eribulin concentration for more than 3 months. Alterations in the phosphorylation status of kinases in eribulin-resistant cells compared to parental cells were screened using a Human Phospho-Kinase Array Kit. The effect of eribulin and AKT-inhibitor MK-2206 on STS cell lines was examined using an MTT assay. To elucidate the cytotoxic mechanism of eribulin and MK-2206, immunoblotting and flow cytometry analyses were performed. [Results] In established eribulin-resistant cell lines, those IC50s were 2.40- to 27.14-fold greater than in the parental cell lines. Phospho-Kinase Array revealed increased p-AKT (S473) levels in eribulin-resistant cells compared to the parental cells. Eribulin treatment increased p-AKT levels in STS cells in a dose-dependent fashion. Combination treatment of eribulin and AKT-inhibitor MK-2206 inhibited the proliferation of STS cells accompanied with G1 and/or G2/M arrest by down-regulating CDKs, cdc2 and cyclins. Furthermore, eribulin combined with MK-2206 synergistically induced apoptosis in STS cell lines. The apoptosis was via Caspase 8 and 9 pathways. [Conclusion] This study demonstrated that activated-AKT was associated with eribulin-resistance in STS cells and that eribulin combined with MK-2206 suppressed STS growth synergistically through G1 and G2/M arrest and caspase-dependent apoptosis. Our results uncover a potential clinical application of eribulin and MK-2206 combination therapy to improve clinical outcomes for UM-STS patients. Citation Format: Kohichi Takada, Naotaka Hayasaka, Yutaka Kawano, Hajime Nakamura, Yohei Arihara, Kazuyuki Murase, Shohei Kikuchi, Satoshi Iyama, Koji Miyanishi, Masayoshi Kobune, Junji Kato. Combination of eribulin plus AKT inhibitor evokes synergistic cytotoxicity in soft tissue sarcoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1861.