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 molecule (N-CAM) is an oncodevelopmental antigen and is found in small cell lung carcinomas (SCLC) as well as cell lines derived from these tumors.

EXPERIMENTAL DESIGN

Cell heterogeneity in poly Sia expression was observed in primary SCLC and cell cultures of SCLC by immunostaining using a directly gold-labeled monoclonal antibody against poly Sia (MAb 735) and antibodies against N-CAM. Clonal sublines of the N-CAM-positive SCLC cell line, NCI-H69 were established to study the basis of this heterogeneity. The resulting sublines were examined for the proportion of cells expressing poly Sia, the stability of poly Sia expression, and the possible involvement of DNA methylation. Two of the sublines 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 adherence. Finally, clonogenic growth of these sublines was studied in soft agar and in the nude mouse.

RESULTS

The proportion of cells immunoreactive for poly Sia was stable in serial subculture in these clones and was not affected by reducing DNA methylation. In aggregation and disaggregation assays, poly Sia was shown to modulate both calcium-dependent and independent cell-cell adhesion. No measurable differences in the attachment rates to various substrates (collagen type IV, laminin, heparan sulfate, and poly-L-lysine) 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 immunoreactive cells of SCLC. Poly Sia on SCLC cells is a clonable trait and high poly Sia expression correlates with reduced cell-cell adherence, a greater clonogenic ability in semisolid media, and a significantly higher incidence of intracutaneous metastases in nude mice.