Abstract 901: Specificities of CYFRA monoclonal antibodies KS 19.1 and BM 19.21 to cytokeratin 19

CYFRA 21-1 measures cytokeratin fragments of cytokeratin 19 with the aid of two specific monoclonal antibodies (mAb), BM 19.21 and KS 19.1. CYFRA 21-1 has been adopted in several immunoassays as a tumor marker for non-small-cell lung cancer (Sanchez-Carbayo et al. Clin Chem 1999; 45: 1944-1953). We evaluated the binding of these antibodies to cytokeratin 19 and three other types of cytokeratin. Potential cross-reactivity of these antibodies with six cancer biomarker antigens was also evaluated. METHODS: SDS-PAGE and Western blotting were used to observe the binding of KS 19.1 and BM 19.21 with recombinant cytokeratin 8, 14, 18 and 19. An ARCHITECT CYFRA 21-1 assay was used to investigate whether cancer biomarker antigens AFP, beta-HCG, CA 125, CA 15-3, CA 19-9 and CEA interfere with the binding of these two antibodies to cytokeratin 19. 10 – 100 fold of the normal reference levels (8 ng/mL AFP, 5 mIU/mL beta-HCG, 35 U/mL CA 125, 37 U/mL CA 19-9 and 5 ng/mL CEA) of these biomarker antigens were spiked into five (5) serum samples. The concentration of the biomarker antigen CA 15-3 used for this study was 10 and 17 fold of its normal reference levels (31.3 U/mL). RESULTS: SDS-PAGE and Western blotting showed that KS 19.1 and BM 19.21 antibodies bind specifically to cytokeratin 19. KS 19.1 and BM 19.21 antibodies exhibited no binding to cytokeratin 8, 14 and 18 even though the total amount of cytokeratin 19 loaded was less than that of the other three cytokeratin9s. Cancer biomarker antigens AFP, beta-HCG, CA 125, CA 15-3, CA 19-9 and CEA did not interfere with the binding of these two antibodies to cytokeratin 19 significantly. Mean cross reactivity of each biomarker was 5% (1% – 11%) for AFP, 4% (0% – 7%) for beta-HCG, 4% (0% – 15%) for CA 125, 6% (0% – 15%) for CA 15-3, 3% (0% – 6%) for CA 19-9 and 2% (0% – 4%) for CEA. CONCLUSIONS: Monoclonal antibodies KS 19.1 and BM 19.21 bound to cytokeratin 19 specifically and showed no cross reactivity with cytokeratin 8, 14 and 18 in Western blotting. Also cytokeratin 19-binding specificity was not significantly interfered significantly by cancer biomarker antigens AFP, beta-HCG, CA 125, CA 15-3, CA 19-9 and CEA in an ARCHITECT CYFRA 21-1 assay. 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 901. doi:10.1158/1538-7445.AM2011-901