Abstract B83: The histone deacetylase inhibitor, panobinostat (LBH589) exerts antiproliferative effect as single agent and synergizes with topotecan or etoposide in cervical cancer cells
Authors: Wasim Lubna , Chopra Madhu 
Published: May 2016

Abstract
Cervical carcinoma is one of the most common malignancies of women worldwide. Genetic alterations together with epigenetic changes have been identified both in the genome of host cell and human papillomavirus (HPV) during cervical cancer progression. Studies showing the aberrant recruitment and /or overexpression of histone deacetylases (HDACs) in many human cancers, and promising anticancer results through induction of cell cycle arrest, apoptosis and autophagy with HDAC inhibitors (HDACi) have been reported. Combination of HDACi with other anticancer drugs that target genomic DNA have shown synergistic effects and enhanced apoptosis because of the increased accessibility of these agents to the chromatin. Panobinosat (LBH589), is a nonselective HDACi, showing anticancer activity against both hematological and solid malignancies. However, the anticancer effect of panobinostat in cervical cancer cells has not been tested. Therefore, in the present study, we investigated the effects of panobinostat on cell growth and death in human cervical cells alone and in combination with topoisomerase inhibitors. MTT assay was used to evaluate the antiproliferative effect of panobinostat on HeLa and SiHa cell lines. Flow cytometry was used for analyzing cell cycle kinetics using PI staining and apoptosis using annexin V-FITC. Agarose gel electrophoresis was done for DNA fragmentation. DCF-DA assay was used to measure ROS levels. Combination index (CI) of panobinostat with topoisomerase inhibitors was calculated at fixed ratio following three different treatment schedules, either simultaneous or sequential (with 24 h delay between the two agents) according to Chou and Talalay using CompuSyn software. The results showed that panobinostat is more potent in SiHa than in HeLa cells for inhibiting cell proliferation. Cell cycle analysis, revealed G1 arrest in HeLa cells but G2-M arrest in SiHa cells after 24 h of treatment. These results demonstrate that panobinostat exerts antiproliferative effects on cervical cancer cells. In combination it was found that simultaneous treatment was synergistic for panobinostat and topotecan/etoposide combination in both cell lines having CI&lt;1. Topoisomerase inhibitors induced G2+M and late S phase arrest, in Hela and Siha cell lines, respectively. The hypodiploid sub-G1 population and annexin V-FITC and PI positive cells were markedly increased in combination in comparison to single agents. Clear ladder pattern was seen in combination treatment and demonstrated that apoptosis was the main mechanism for the observed synergistic interaction. Induction of apoptosis was found to be correlated to enhanced ROS levels in combination treatment. Furthermore, coadministration of antioxidant L-NAC substantially blocked the panobinostat and topotecan/etoposide mediated ROS levels. In conclusion, to our knowledge, this study is the first to show, the antiproliferative effect of panobinostat, and a synergistic cytotoxicity effect between panobinostat and topoisomerase inhibitors in a cervical cancer cell model.
Citation Format: Lubna Wasim, Madhu Chopra. The histone deacetylase inhibitor, panobinostat (LBH589) exerts antiproliferative effect as single agent and synergizes with topotecan or etoposide in cervical cancer cells. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B83.