Lack of expression of a 31/33kD surface protein on human colon carcinoma cells is a marker for metastasizing potential.

Two highly metastatic human tumor cell lines, SLU-M1 SLU-M2, were established by in vivo selection in Balb/c-nu/nu mice of SLU-1 xenotransplants derived from an adenocarcinoma of the sigmoid colon. Metastatic spread was screened by transplantation of tissues from various organs of s.c.-tumor-bearing nu/nu mice. A monoclonal antibody, mab ME6H2, prepared against a membrane fraction of HT29 cells, also derived from an adenocarcinoma of the colon, showed high 125I-mab ME6H2 binding only to HT29 and SLU-1 cells, whereas hardly any binding was recorded for SLU-M1 and SLU-M2 cells. All cells of the HT29 and SLU-1 populations exhibited a positive immunofluoresence (IF) but only 1-5% of the SLU-M2 and 10-15% of the SLU-M1 subpopulation. A number of other tumor cell lines did not express the ME6H2 target antigen except for line MCF7, derived from an adenocarcinoma of the breast, which showed an IF positive reaction of 100% of the cells but only 25% of mab binding compared to HT29 and SLU-1 cells. The data indicate that expression of the ME6H2 target antigen is adenocarcinoma-specific and lack of expression is a marker for the metastatic potential of these cells. Mab ME6H2 was rapidly internalized upon binding to viable HT29 cells, resulting in an enhancement of cell growth in vitro and tumor growth in vivo. The mab ME6H2-defined target antigen was isolated from cell lysates by antibody affinity chromatography and was identified as a double band in SDS-PAGE with 31kD and 33kD molecular mass usually present in equal amounts.