Abstract 3646: Synergistic activities of the histone deacetylase inhibitors with conventional cytotoxic chemotherapies in cutaneous angiosarcomas
Authors: Zhang Yingjun , Hui Connie , Wong Chi Hang , Choy Chi Tung , Tse Teresa , Tan Teresa , Kwan Sampson , Tao Qian , Loong Herbert 
Published: September 2020

Abstract
Background:
Cutaneous Angiosarcoma (CAS) is a rare aggressive malignant tumour typically arising from skin or viscera. The incidence of AS appears more common in Asia, as compared with the West. The prognosis of patients (pts) advanced/inoperable CAS remains poor. The median PFS of first line systemic treatments of 3.8 months and overall survival (OS) of &lt;12 months. Histone deacetylases inhibitors (HDACi) are epigenetic agents which have shown anti-tumour effects as single-agents. In this study, we have shown synergism of panobinostat (LBH589) and vorinostat (SAHA) when combined with doxorubicin in a CAS cell line (ISO-HAS-B). The underlying molecular mechanisms of these findings have yet been explored.
Methods:
We investigated the potential effects of LBH589 and SAHA in ISO-HAS-B. IC50 of two pan-HDACi as single agents were tested, followed by synergism studies in combination with doxorubicin. Synergy effects were calculated by synergy-finder and evaluated by synergy score as follow scale: &lt; -10 (antagonistic); -10 to 10 (additive); &gt; 10 (synergistic).The cell death or cell growth inhibition were recorded by time lapse assay under microscope at 0, 24, 48 hours after treating with SAHA, doxorubicin (DOX) alone and in combination. The inhibitory effect on apoptosis pathway were studied by treating the ISO-HAS-B with two drugs alone and in combination at their respective IC50 concentrations for 48 hours. The detection of Caspase 3 and PARP by Western blotting was used to indicate apoptotic cell death.
Results:
IC50 of two pan-HDACi were determined by Graphpad PRISM 8.0. LBH589 and SAHA were shown to have anti-tumour effects and the combination of two pan-HDACi with doxorubicin showed synergistic growth inhibition than the single agents alone. A higher level of cell death can be seen in the combination of SAHA and DOX in ISO-HAS-B in a time-dependent manner .Cell shrinkage and pyknosis were visible by light microscopy after 48-hour treatment. Apoptosis was indicated by the increase level of cleaved PARP and Cleaved Caspase3, especially in the combination group from Western blot assays.
Conclusions:
The combination of SAHA and DOX induced higher level of apoptosis at 48h incubation. It significantly activated the apoptosis pathway by increasing the expression of Cleaved PARP and Cleaved Caspase3, which suggests its effectiveness in inhibition of protein synthesis. In-vivo experiments to validate these findings are currently on-going. Combination of HDACi and doxorubicin remains a promising treatment approach for CAS.
Citation Format: Yingjun Zhang, Connie Hui, Chi Hang Wong, Chi Tung Choy, Teresa Tse, Teresa Tan, Sampson Kwan, Qian Tao, Herbert Loong. Synergistic activities of the histone deacetylase inhibitors with conventional cytotoxic chemotherapies in cutaneous angiosarcomas [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3646.