Abstract 2336: E-cadherin re-expression affects the growth and survival of breast cancer cells in metastatic colonization of the liver

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Numerous studies have shown that loss of E-cadherin through an epithelial to mesenchymal transition (EMT) contributes to tumor invasiveness. However, these studies focus only on the role of E-cadherin in initial dissemination. Interestingly, histopathology of metastases often appear more differentiated than the primary tumor, and several studies have shown that metastases often express E-cadherin despite loss from the primary tumor. We hypothesize that breast cancer cells re-express E-cadherin through a mesenchymal to epithelial transition (MET) to enable colonization within the liver, a common site of breast cancer metastases. We have previously shown that coculture of E-cadherin-negative MDA-MB-231 breast cancer cells with hepatocytes results in re-expression of E-cadherin, which leads to both ligation between cancer cells and hepatocytes as well as activation of the Erk and Akt signaling pathways. To explore the role of E-cadherin in hepatic colonization, we stably transfected full-length E-cadherin and E-cadherin shRNA constructs into MDA-MB-231 (231) cells. Wild-type 231 and single cell clones of 231-Ecad and 231-shEcad cells were seeded onto a hepatocyte monolayer and cultured for 5 days. Cancer cells were RFP-labeled and the number of cancer cells in each coculture was counted daily. Expression of E-cadherin affected the initial attachment of cancer cells to the hepatocyte monolayer, as twice as many 231-Ecad cells were counted 1 day after seeding compared to their E-cadherin-negative counterparts. In addition, wild-type 231 and 231-shEcad cells initially exhibited similar growth curves but began to diverge after 3 days of coculture, with 231 cells expanding twice as fast as 231-shEcad cells. The divergence coincides with a time course of E-cadherin re-expression. After 5 days of coculture, E-cadherin expression was observed by immunofluoresence in 231 and 231-Ecad cells but not in 231-shEcad cells as expected. Immunostaining also revealed that despite E-cadherin re-expression, vimentin expression persisted in 231 cells, suggesting that E-cadherin re-expression may not result in a full MET. Because E-cadherin-based adhesions have been shown to protect against cell death, all three cell lines were treated with staurosporine in the absence of hepatocytes and assayed for cell survival with calcein AM staining. 231-Ecad cells were more chemoresistant compared to 231 cells, and addition of an E-cadherin antibody abrogated this protection. Future studies will evaluate whether E-cadherin re-expression has a chemoprotective role in hepatocyte coculture and in vivo animal models. The role of E-cadherin down-regulation as a key initiator of metastasis has been clearly established. However, our work suggests that phenotypic plasticity of the metastatic cancer cell through E-cadherin re-expression may also be important for colonization and survival at distant sites. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2336.