Involvement of soybean agglutinin binding cells in the lymphatic metastasis of the R3230AC rat mammary adenocarcinoma

Abstract

Many human tumors, such as those of the breast, metastasize initially via the lymphatics. The tumor cell surface is believed to play a critical role in this process. To study the cell surface properties involved in dissemination, the poorly metastasizing R3230AC rat mammary adenocarcinoma was enriched for metastasizing cells by excising rare lymph node metastases arising after the s.c. injection of 10(6) cells and reinjecting these cells into another series of rats. By repeated enrichment cycles, the frequency of lymphatic metastasis was increased from 10 to 60-100% of the animals given injections. Fluorescein-conjugated lectins were used to probe the tumor cell surface. It was found that the percentage of cells in the population able to bind high levels of the lectin, soybean agglutinin (SBA), increased from 11 to almost 80% in the highly metastatic, enriched cell populations. A linear correlation (r = 0.92; P less than 0.001) was found between the percentage of cells in the population which bound high levels of SBA and the frequency of lymphatic metastasis in a series of enriched cell lines. Clones which bound high levels of SBA metastasized to lymph nodes at a high frequency, while clones which bound only low amounts of SBA exhibited a low frequency of lymphatic metastasis regardless of the metastatic potential of the cell line from which the clones were isolated. The binding of SBA to the cell was reduced by preincubation of the lectin with galactose, completely blocked by incubation with N-acetylgalactosamine, and unaffected by incubation with glucose or mannose, demonstrating that SBA was recognizing a N-acetylgalactosamine-containing component of the cell surface. Cells enriched for lymphatic metastasis were not similarly enriched for hematogenous metastasis. While cell lines enriched for lymphatic metastasis have been previously described, this is the first report of a specific cell surface property, SBA-binding, associated with lymphatic metastasis.