Abstract B54: Single and collective cell dissemination modes in ovarian cancer.
Authors: Al-Habyan Sara , Szymborski Joseph , Tonin Patricia , McCaffrey Luke 
Published: May 2016

Background: Ovarian cancer (OvCa) results in over 114,000 worldwide deaths annually, and is the most lethal malignancy of the female reproductive system. During its progression, OvCa can shed cells into the peritoneal cavity, which can later metastasize to distant pelvic, abdominal, or extra-peritoneal organs. Disordered tumor blood vessels often allow for lymphatic leakage into the abdomen, causing an accumulation of excess ascites fluid that is abundant in growth factors supporting the survival and growth of disseminated tumour cells (DTCs). DTCs were found to exist in ascites both as single cells and as multicellular spheroids, however it is unknown whether cells disseminate in a single or collective manner. Biological and clinical characteristics of DTC spheroids have been under investigation in a number of cancer subtypes, as cells within spheroids exhibit enhanced resistance to multiple chemotherapeutics, increased invasive properties, and faster tumorigenic potential. Therefore, understanding and targeting cancer spheroids can help improve patient prognosis and limit disease progression.

Methods: In this study, we examine the modes of dissemination of ovarian cancer cells as single or multi-cellular units using Ov-90 chemo naïve cells and OVCAR-3 cells, which were each derived from human ascites. We utilize in-vitro 2D monolayer cultures and 3D ‘organoids' to characterize the dissemination of cells in suspension for cellular viability, and protein expression and localization. Live imaging is conducted on free-floating, hanging drop generated clusters to visualize dissemination. To confirm in-vitro experiments, ovarian orthotopic transplants in mice are used as an in-vivo system by injecting fluorescently labelled cells.

Results: Our novel live imaging models showed that cells disseminate as both single cells and groups of cells. Disseminated cells in culture are frequently observed as cell clusters with a higher live/dead ratio than cells seeded at single cells in suspension, indicating that clusters may have a survival advantage. In addition, immunofluorescence staining of disseminated cells suggests that the transcription factor Zeb1 may be involved in driving cell dissemination by regulating mosaic E-cadherin expression in the absence of complete EMT.

Conclusion: Ovarian cancer cells can disseminate as either single cells or clusters. Many gaps in our understanding exist in the early stages of dissemination of ovarian cancer despite intensive research throughout the later time points in metastasis. We predict that a deeper understanding of the mechanisms of dissemination will provide insights to greatly improve patient prognosis and response to chemotherapeutics.

Citation Format: Sara Al-Habyan, Joseph Szymborski, Patricia Tonin, Luke McCaffrey. Single and collective cell dissemination modes in ovarian cancer. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: Exploiting Vulnerabilities; Oct 17-20, 2015; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(2 Suppl):Abstract nr B54.