Selective protection of nonmalignant cells by a novel cell surface glycopeptide

A novel glycopeptide inhibitor of cell division, isolated from bovine cerebral cortex cell surfaces, was shown to selectively protect nonmalignant cells from the cytoxic action of 5-bromo-2-deoxyuridine (5-BrdUrd). When mouse LM-22 cells (nonmalignant and devoid of gangliosides) were preincubated with GM1 ganglioside (3.0 micrograms/ml), the cell surface glycopeptide inhibitor effectively arrested cell division. In contrast to LM-22 cells, transformed mouse fibrosarcoma (No. 1316) cells were insensitive to the glycopeptide inhibitor whether or not they were preincubated with GM1 ganglioside. Mixed cultures of LM-22 cells preincubated with GM1 ganglioside and 1316 fibrosarcoma cells at an approximate ratio of 1:1 were established. Since LM-22 cells are resistant and 1316 fibrosarcoma cells are sensitive to 3.0 mM ouabain, the identity of surviving cells following BrdUrd treatment could easily be determined. Three hr after the establishment of the mixed cell population, 250 ng protein per ml of the purified bovine glycopeptide inhibitor was added to selectively arrest the mitosis of the LM-22 cells. After an additional 3 hr of incubation, 5-BrdUrd was added to a final concentration of 5.0 mM. Twelve hr later, cells were serially diluted and seeded into duplicate plates with and without 3.0 mM ouabain. LM-22 cells were effectively protected from the cytotoxic action of 5-BrdUrd (92 to 94% survival) while the majority of the 1316 fibrosarcoma cells were killed (21 to 30% survival). The selective protection of LM-22 cells was shown to be independent of differences in plating efficiency, cytotoxicity of 5-BrdUrd in the absence of the glycopeptide inhibitor, and the generation time of the two cell lines.