Abstract 5452: Whole transcriptome analysis of ovarian cancer cells reveals the mechanism of action for a potent organometallic anticancer agent
Authors: Hearn Jessica M. , Romero-Canelón Isolda , Ying Fu , Wild David L. , Sadler Peter J. 
Published: May 2015

Introduction. Ovarian cancer is a diverse disease and remains one of the most difficult-to-treat cancers, with over 70% of epithelial ovarian cancers (EOC) not diagnosed until late stage. Platinum anticancer agents are often used as first-line treatments for EOC, however, patient relapse and subsequent platinum resistance present clinical problems.

New metal-based chemotherapeutics, which are equally, or more potent in EOC and platinum resistant EOC show promise as effective second-line treatments. Complex 1 ([Os(η6-p-cym)(NMe2-azpy)I]+) is an osmium-based organometallic agent, with equipotent activity in A2780 human EOC cells and their cisplatin-resistant counterpart, A2780cis [1]. Although highly active in vitro and in vivo, the mechanism of action (MOA) of complex 1 is unknown [2].

Results & Discussion. We perform whole transcriptome analysis for A2780 cells exposed to 1 over a 48 h time course, using RNAseq. The estimated chromosome-wide expression across the time series reveals a majority number of mapped reads to the mitochondrial chromosome, with differential mapping between control and treated cells. Assessing the number of differentially expressed genes (DEGs) between control and treated cells, shows a rapid cellular response after 4 h and the highest number of DEGs at 48 h.

Analysis of all DEGs using pathway analysis provides insights into cellular response across the time series. After 24 h, the NRF2 oxidative stress response pathway is most significantly involved in cellular response, although key components in this pathway are active after just 4 h. This pathway is linked to the production of reactive oxygen species (ROS) by the mitochondria, activating downstream antioxidant proteins and increasing cellular levels of GSH. High levels of ROS were detected by flow cytometry, and interestingly when cells are co-incubated with a GSH inhibitor, there is a dramatic decrease in IC50 and increase in ROS [3].

Cell viability assays suggest that cell death is activated between 24 and 72 h exposure, down-regulation of apoptotic caspases suggests cell death does not proceed through a normal apoptotic process. Caspase-1, which activates pro-interleukins to elicit an immune response, is differentially up-regulated throughout the time series. This caspase is closely linked to cellular ROS and can activate an alternative mode of cell death, pyroptosis.

Conclusions. We have elucidated the MOA of complex 1 through whole transcriptome analysis: cancer cell death through mitochondrial effects and production of ROS. Activation of non-apoptotic cell death can be beneficial as cancer cells often develop resistance mechanisms to evade apoptosis.

[1] Fu, Y. et al. (2010) J. Med. Chem. 53: 8192-8196

[2] Shnyder, S. et al. (2011) Med. Chem. Comm. 2: 666-668

[3] Romero-Canelón, I. et al. (2013) Inorg. Chem. 52: 12276-12291

Citation Format: Jessica M. Hearn, Isolda Romero-Canelón, Fu Ying, David L. Wild, Peter J. Sadler. Whole transcriptome analysis of ovarian cancer cells reveals the mechanism of action for a potent organometallic anticancer agent. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5452. doi:10.1158/1538-7445.AM2014-5452