Functional Importance Of Epcam For The Activity Of Tumor-Initiating Cancer Cells And Their Eradication By Epcam/Cd3-Bispecific Antibody Mt110

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL We have recently shown that tumor-initiating cells (TICs) derived from colorectal cancer tissue express EpCAM and can be eradicated in cell culture experiments as well as established xenograft mouse models by EpCAM/CD3-bispecific BiTE antibody MT110 (Hermann et al., 2010; PLoS ONE, 5: [e13474][1]). Here we show that TICs derived from liver and breast cancer tissue grow tumors in SCID mice at cell doses as low as 100 after a latency period of 37-58 days. Like colorectal cancer tissue-derived TICs, they expressed EpCAM and grew colonies in soft agar. In the presence of human T cells, breast and liver cancer-derived TICs could be eradicated by BiTE antibody MT110 as tested in a sensitive soft agar assay. In order to assess the role of EpCAM expression in colorectal TICs, we used short hairpin RNA molecules for specifically knocking down EpCAM expression. A shRNA molecule binding to the coding, non-translated 3’-UTR of the EpCAM mRNA showed the highest efficacy (ca 10-fold) in suppressing EpCAM expression, as shown at the mRNA level by RT-PCR and at the surface expression level by FACS analysis. Although the EpCAM knockdown was not complete and left ca 10% of the normal EpCAM expression, a strong impact on the phenotype of colorectal TICs was observed. Morphologically, TICs with reduced EpCAM expression adopted in cell culture an epithelial-like phenotype, could no longer efficiently close a scratch in a cell culture experiment, and reduced the expression of epithelial-mesenchymal transition (EMT)-associated proteins such as fibronectin, vimentin and slug. Compared to non-sense control shRNA, colony formation of TICs in soft agar was reduced by >60%. Most importantly, the tumor-initiating potential of TICs appeared to depend on a high level of EpCAM expression. TICs expressing the EpCAM-specific shRNA could no longer form a tumor at a dose of 500 cells after 116 days, whereas the non-sense shRNA-expressing TICs formed during this period a tumor of 0.5 cm3. Our data suggest that a certain EpCAM expression level is required for maintenance of a stem cell-like phenotype of colorectal TICs. This is consistent with a signal transducing role of EpCAM within a non-canonical wnt pathway (Maetzel et al. 2009; Nature Cell Biol. 11: 162-171), and in the process of EMT of colorectal cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1790. doi:10.1158/1538-7445.AM2011-1790 [1]: /lookup/external-ref?link_type=GEN&access_num=e13474&atom=%2Fcanres%2F71%2F8_Supplement%2F1790.atom