Abstract B6: Cadherin switching, multicellular aggregate dynamics and metastatic success

Epithelial Ovarian Carcinoma (EOC) is the fifth leading cause of women's cancer-related death and deadliest of all gynecological cancers with 22,240 new and 14,230 fatal cases predicted in 2013 ( American Cancer Society Estimates, 2013 ), primarily due to detection at late metastatic, prognostically poor stages of the disease. As opposed to other malignancies, EOC metastasis occurs by shedding of cancer cells from the primary tumor directly into the peritoneal cavity where they form multicellular aggregates (MCAs). These metastatic units along with single cells travel with the peritoneal fluid flow, adhere to peritoneum, migrate through mesothelial cell layer into submesothelial matrix wherein they subsequently proliferate into secondary tumor masses. The contribution of MCA dynamics to metastatic success is largely unknown. A feature that distinguishes EOC from most other carcinomas is an increase of E-cadherin (Ecad) expression at early stages of metastasis, frequently together with conserved expression of N-cadherin (Ncad). Our human tumor tissue array dual label immunofluorescence microscopy data confirm simultaneous expression of both cadherins in the majority of ovarian cancer tissues. Two patterns of expression are observed: “mixed cadherin” in which distinct cells within the same tumor express E- or N-Cad and “hybrid cadherin” wherein single tumor cells simultaneously express both cadherins. The mechanisms regulating initial cell detachment, MCA generation, survival in ascitic fluid and secondary anchorage and the role of cadherin dynamics in these steps remain poorly understood. Our research has revealed striking cadherin-dependent differences in cell-cell interactions, MCA formation, aggregate surface morphology and inner ultrastructure. In particular, mesenchymal-type DOV13 and SKOV3 (Ncad+) cells formed stable, highly cohesive smooth solid spheroids, while epithelial-type OvCa433 and OvCa429 (Ecad+) cells generated less adhesive cell clusters, loosely conglomerated and covered by uniform microvilli. To recapitulate the “hybrid cadherin” phenotype observed in human tumors, OvCa433 cells (Ecad) were transfected with the CDH2 (Ncad) gene to generate hybrid cadherin cells, leading to relevant changes in MCA surface morphology with increased superficial lamellipodia and filopodia, resembling the intermediate phenotype of true hybrid OvCa432 and OVCAR3 (Ecad+/Ncad+) aggregates. Alternatively, generation of “mixed cadherin” MCAs using fluorescently tagged cell populations revealed a sorting rather than mixing phenotype, with cells sorting into individual MCAs rather than generating heterogeneous Ecad/Ncad clusters. However, cell lines with common cadherin profiles [OvCa433/OvCa429 (Ecad/Ecad); DOV13/SKOV3 (Ncad/Ncad)] readily formed homogeneous aggregates. Interestingly, hybrid OvCa433 cells (Ecad/Ncad) formed heterogeneous MCAs with DOV13 (Ncad). Our data support the hypothesis that cadherin switching may regulate MCA dynamics and thereby affect metastatic unit cohesivity, survival, and ultimate metastatic success. Citation Format: Yuliya Klymenko, M. Sharon Stack. Cadherin switching, multicellular aggregate dynamics and metastatic success. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr B6.