Abstract C4: Targeting ROR1 inhibits epithelial-mesenchymal transition and metastasis

The receptor tyrosine kinase-like orphan receptor 1 (ROR1) is an evolutionarily-conserved, type-I membrane glycoprotein that is expressed in embryonic development, but not by virtually all normal post-partum tissues. Recent studies have found the ROR1 protein expressed by a variety of different cancers, particularly those that appear less differentiated and/or have high-grade histology ( Am J Pathol . 2012, PMID 23041612). Because there appeared to be a tight association between gene and protein expression, we interrogated the gene-expression data on breast adenocarcinomas from each of 582 patients (pt) for ROR1. Because of our earlier observation that approximately a third of breast cancer pt in a different cohort had tumors' with high-level expression of ROR1 protein ( PLoS One , 2012, PMID 22403610), we divided the cohort of 582 pt into tertiles based upon their tumors' relative expression of ROR1. Pt in the tertile with cancers having the highest expression of ROR1 (ROR1H) had a significantly higher rate of metastases than did pt with tumors having the mid (ROR1M) or lowest (ROR1L) expression of ROR1 (e.g. 61% vs. 35% or 41%, respectively, p< 0.0001). Moreover, pt with ROR1H tumors had a higher rate of early relapse and poorer survival than did pt with ROR1L/M tumors, irrespective of ER or HER2 status (HR=2.3, p<0.0001). We also examined for ROR1 expression in 14 distinct breast-cancer epithelial cell-lines, including 6 basal-type breast cancer cell-lines and 8 luminal-type breast cancer cell-lines. All 6 basal-type, metastases-prone, cell-lines expressed ROR1, which was not the case for low-invasive, luminal-type cell-lines. Silencing ROR1 in the basal cell-lines attenuated expression of proteins associated with epithelial-mesenchymal transition (EMT) (e.g. vimentin, SNAIL-1/2, and ZEB1), enhanced expression of epithelial cytokeratins and tight-junction proteins (e.g. CK-19 and ZO-1), and impaired each cell-line's migration/invasion capacity in vitro and metastatic potential in immune-deficient mice. Moreover, silencing ROR1 in parental MDA-MB-231 cells (or its derivatives LM2-4175 and BoM-1833, which preferentially metastasize to the lung or bone, respectively) inhibited each cell-line's capacity to generate orthotopic lung metastases or experimental lung and bone metastases in vivo. Treatment of MDA-MB-231 or other basal-type cell-lines with a monoclonal antibody (mAb) specific for ROR1 down-modulated vimentin and inhibited each cancer-cell-line's migration/invasion capacity in vitro. This mAb also significantly inhibited tumor metastasis when given to immune-deficient mice engrafted with MDA-MB-231 cells. Collectively, this study indicates that ROR1 may regulate EMT and metastasis, and that antibodies targeting ROR1 can inhibit cancer progression and metastasis. Citation Format: Bing Cui, Suping Zhang, Liguang Chen, Jianqiang Yu, George F. Widhopf, II, Jessie-F Fecteau, Laura Z. Rassenti, Thomas J. Kipps. Targeting ROR1 inhibits epithelial-mesenchymal transition and metastasis. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr C4.