Monoclonal antibodies to the exon 18 encoded moiety of NCAM

Abstract

Aim: Exon 18 expression of NCAM has been recognized as a biomarker for small cell lung cancer (SCLC). To use this finding for an improved diagnosis of SCLC and personalized treatment of patients, techniques to identify and quantitate E18, the exon 18 encoded protein moiety of NCAM, are needed. We developed three monoclonal antibodies for this purpose. Methods: The his-tagged E18 antigen was expressed in E. coli and, after purification, used to immunize mice. Hybridoma's were isolated by standard procedures and tested for their reaction with E18. Results: Three monoclonal antibodies, MUM-1, MUM-4 and MUM-6 were obtained. They reacted with E18 in western blots, with SCLC cell line NCI-H82, but not with unrelated his-tagged proteins. Only permeabilized NCI-H82 cells stained with the antibodies, confirming the intracellular position of E18. Next an enzyme-linked immunosorbent assay was developed using the earlier isolated monoclonal antibody MUMi-21B2, coated on the surface of microtiter wells as capture antibody and biotinylated MUM-6 as second antibody. Using streptavidin conjugated to horse radish peroxidase a linear dose response curve to his-tagged E18 antigen was obtained between 0 and 5 µg/mL with a sensitivity of at least 0.5 µg/mL or 50 ng/well. Conclusion: Four monoclonal antibodies are available to be used in assays for the identification and quantification of SCLC biomarker E18. This will enable the development of liquid biopsies to follow the tumor load in patients.

Molecular profiling of pulmonary carcinoids : insight into tumor biology and identification of prognostic markers

“…Human tumor cell lines, as well as 31 primary SCLCs have been reported to express exclusively the NCAM 140 variant. However, other studies have also demonstrated the presence of the NCAM 180 variant in SCLC and/or SCLC cell lines and even shown its specificity for these tumors [19,[129][130][131]. An additional NCAM 95 variant is also present in SCLC tumors and cell lines [129].…”

“…By definition, a tumorlet > 5 mm in diameter is termed carcinoid [128]. Although they were originally described as being of benign nature, tumorlets behave like carcinoids, are reported to cause Cushing's syndrome [22,130,131], and may metastasize to lymph nodes [20,130] or even distantly [22]. Reactive PNEC hyperplasias resulting from chronic pulmonary disease can also progress to a tumorlet phase.…”