Abstract B44: Development of a serum test for the detection of lung cancer based on oncogenic BARD1 isoform expression

Abstract

Abstract The BARD1 protein was originally identified as binding partner of the breast cancer gene product, BRCA1. Highly upregulated expression of aberrant isoforms of BARD1, derived from differential splicing, was correlated with poor prognostic factors in breast and ovarian cancer (Wu et al. Int J Can, 2006; Li et al. Can Res, 2007) and decreased patient survival in lung cancer (Zhang et al. Int J Can, 2011). Previous and ongoing studies have shown that BARD1 isoforms act antagonistically to the functions of BARD1 and BRCA1 as ubiquitin ligase. In particular, BARD1beta is promoting cell proliferation by stabilizing the Aurora kinases (Ryser et al. Can Res 2009; Bosse et al. submitted). Isoforms BARD1-beta and BARD1-pi are specifically upregulated in lung cancer and correlated with poor prognosis (Zhang et al., Int J Can, 2011). Thus, BARD1 isoforms might be drivers of tumorigenesis and potential markers of lung cancer progression, if detectable in the patients' sera. To this goal, we performed ELISA tests with antibodies against different regions of BARD1 for the detection of BARD1 isoforms in the blood of lung cancer patients. We also generated a peptide library representing 40 epitopes mimicking BARD1 isoforms, for the detection of autoimmune antibodies recognizing epitopes expressed by BARD1 isoforms. BARD1 protein isoforms could be detected by ELISA in various serum samples, however this detection was always reproducible due to the BARD1 protein instability. We then performed inverse ELISA assays, using peptides for capturing autoimmune antibodies directed against BARD1 isoforms. Using serum samples from 60 non-small cell lung cancer (NSCLC) from time of diagnosis, and 40 control sera from phenotypically healthy volunteers, we could distinguish NSCLC cancer patients and controls. When applying a combination of seven peptides lung cancer was detected with 87 percent sensitivity and 68 percent specificity. Thus, our data show convincingly that antibodies against BARD1 isoforms are telltales of lung cancer and their detection can be further developed towards a blood test for the early detection of lung cancer. Experiments including larger patients and control group numbers, sera from patients with different types of lung cancer, as well as the comparison of this BARD1 isoform test with the standard test for lung cancer detection (CT scan), are currently ongoing, and should lead to optimized test conditions and a definition of the target patient set.