Abstract 1045: Combined targeting of actin/tropomyosin and microtubules underlies a potential treatment strategy of epithelial ovarian cancer with cell-cycle dependent synergy
Authors: Xu Xing , Wang Yao , Bryce Nicole , Tang Katrina , Meagher Nicola S. , Kang Eun Young , Kelemen Linda E. , Köbel Martin , Ramus Susan J. , Friedlander Michael , Ford Caroline E. , Hardeman Edna C. , Gunning Peter W. 
Published: July 2021

Abstract
Anti-microtubule agents are widely used to treat ovarian cancers in the first line and recurrent setting either in combination with platinum or as single agents. However, the majority of patients will experience a recurrence, and most will die with drug resistant disease. We investigated co-targeting the actin cytoskeleton in combination with anti-microtubule agents to increase efficacy of treatment in epithelial ovarian cancers and potentially overcome resistance mechanisms. We examined the presence of actin/tropomyosin 3.1 (Tpm3.1) filaments in a large cohort of clinical specimens from patients with epithelial ovarian cancer of all histotypes using immunohistochemistry. Combinatorial effects of an anti-Tpm3.1 compound (ATM) with both vinorelbine and paclitaxel were evaluated in three ovarian cancer cell lines using cell viability and apoptosis assays. The mechanisms of synergy of both combinations were established using live-cell imaging, fluorescent microscopy, and pathway analysis. We found that Tpm3.1 is abundant and overexpressed in 97% of ovarian cancers examined (558 of 577) representing all histotypes of epithelial ovarian cancer. High levels of Tpm3.1 were also present in all sites sampled and similar at primary diagnosis and at recurrence. ATM displayed both single agent activity as well as synergy with both anti-microtubule drugs to reduce cell viability in all ovarian cancer cell lines tested, including one with platinum resistance. Only vinorelbine, however, synergised with ATM in the induction of apoptosis. Vinorelbine-induced mitotic arrest was significantly prolonged by ATM with elevated activity of the spindle assembly checkpoint, leading to almost one third of total cells dying in mitosis. In contrast, ATM showed minor impact on paclitaxel-induced mitotic defects. Both combinations resulted in a substantial increase in cells arrested in the subsequent G1 phase with a large decrease of both cyclin D1 and E1 as compared to single agents. Upregulation of p21Cip and p27Kip were associated with both combinations. In summary, targeting Tpm3.1-associated actin filaments in combination with anti-microtubule drugs is a promising treatment strategy that should be tested in clinical trials and is potentially applicable to all histotypes of ovarian cancer.
Citation Format: Xing Xu, Yao Wang, Nicole Bryce, Katrina Tang, Nicola S. Meagher, Eun Young Kang, Linda E. Kelemen, Martin Köbel, Susan J. Ramus, Michael Friedlander, Caroline E. Ford, Edna C. Hardeman, Peter W. Gunning. Combined targeting of actin/tropomyosin and microtubules underlies a potential treatment strategy of epithelial ovarian cancer with cell-cycle dependent synergy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1045.