Abstract 353: Dickkopf-1 as a biomarker and a molecular target for antibody-based cancer immunotherapy (2011)

Abstract In order to identify molecules which could be useful as diagnostic biomarkers as well as for the development of novel drugs, we have established an effective screening strategy as follows; i) To identify up-regulated genes in lung cancers by genome-wide screening using the cDNA microarray representing 27,648 genes and pure populations of tumor cells taken from 120 lung cancer tissues by laser microdissection, ii) To verify the candidate genes for their no or very low level of expression in normal tissues by northern-blot analysis, iii) To validate the clinicopathological significance of its over-expression by means of tissue microarray containing hundreds of archived lung-cancer samples, iv) To verify whether the target gene is essential for the cell growth, survival, or motility of cancer cells by RNA interference (RNAi) and cell growth/invasion assays, and v) To evaluate it for usefulness as a serum diagnostic/prognostic biomarker for lung cancer by ELISA, if they are tumor-specific transmembrane or secretory proteins. As a result of this process, we identified 30 druggable oncoproteins, some of which are being applied as serum biomarkers and therapeutic targets. We further identified a secreted protein, Dickkopf-1 (DKK1) as a candidate. Immunohistochemical staining using tumor tissue microarrays consisting of 279 archived non-small cell lung cancers (NSCLCs) demonstrated that a high level of DKK1 expression was associated with poor prognosis for patients with NSCLC (P=0.0039), and multivariate analysis confirmed its independent prognostic value. In addition, exogenous expression of DKK1 increased the invasive activity of mammalian cells. We established an ELISA system to measure serum levels of DKK1 and found that serum DKK1 levels were significantly higher in serologic samples from 1252 patients with various cancers than in 207 healthy controls. The proportions of the serum DKK1-positive cases was 70.0% for NSCLC (126 of 180), 69.4% for SCLC (59 of 85), 63.0% for esophageal cancer (51 of 81), 50.8% for pancreatic cancer (91 of 179), 38.6% for gastric cancer (39 of 101), 53.0% for hepatocellular carcinoma (89 of 168), 29.9% for bile duct cancer (32 of 107), 65.1% for breast cancer (110 of 169), and 59.3% for cervical cancer (108 of 182), while only 10 (4.8%) of 207 healthy volunteers were falsely diagnosed as positive. Anti-DKK1 antibody inhibited the invasive activity and the growth of lung cancer cells in vitro, and also suppressed the in vivo growth of the tumors inoculated into BALB/c mice. When tumor tissues were treated with anti-DKK1 antibody, the significant fibromatic changes and apoptosis of cancer cells were observed without any obvious toxicity in mice. Here we provide evidence to indicate that the molecules identified can be regarded as potential targets for the development of highly sensitive and specific biomarkers as well as being useful in the development of small-molecular compounds and antibodies. 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 353. doi:10.1158/1538-7445.AM2011-353