IN-VITRO AND IN-VIVO GROWTH OF CLONAL SUBLINES OF HUMAN SMALL-CELL LUNG-CARCINOMA IS MODULATED BY POLYSIALIC ACID OF THE NEURAL CELL-ADHESION MOLECULE

BACKGROUND: Polysialic acid (poly Sia) of the neural cell adhesion mol ecule (N-CAM) is an oncodevelopmental antigen and is found in small ce ll lung carcinomas (SCLC) as well as cell lines derived from these tum ors. EXPERIMENTAL DESIGN: Cell heterogeneity in poly Sis expression wa s observed in primary SCLC and cell cultures of SCLC by immunostaining using a directly gold-labeled monoclonal antibody against poly Sis (M Ab 735) and antibodies against N-CAM. Clonal sublines of the N-CAM-pos itive SCLC cell line, NCI-H69 were established to study the basis of t his heterogeneity. The resulting sublines were examined for the propor tion of cells expressing poly Sis, the stability of poly Sia expressio n, and the possible involvement of DNA methylation. Two of the subline s that expressed poly Sia on 0 and 95% of the cells were used in three independent in vitro assays to investigate the importance of poly Sia in cell-cell aggregation, disaggregation and cell to substrate adhere nce. Finally, clonogenic growth of these sublines was studied in soft agar and in the nude mouse. RESULTS: The proportion of cells immunorea ctive for poly Sia was stable in serial subculture in these clones and was not affected by reducing DNA methylation. In aggregation and disa ggregation assays, poly Sia was shown to modulate both calcium-depende nt and independent cell-cell adhesion. No measurable differences in th e attachment rates to various substrates (collagen type IV, laminin, h eparan sulfate, and poly-L-Iysine) were detected between the sublines. Cells from the poly Sia-positive clonal subline formed significantly more colonies in semisolid media and more intracutaneous metastasis in the nude mouse. CONCLUSIONS: Poly Sia does not occur on all N-CAM imm unoreactive cells of SCLC. Poly Sia on SCLC cells is a clonable trait and high poly Sia expression correlates with reduced cell-cell adheren ce, a greater clonogenic ability in semisolid media, and a significant ly higher incidence of intracutaneous metastases in nude mice.