N,N-dimethylformamide-induced alteration of cell culture characteristics and loss of tumorigenicity in cultured human colon carcinoma cells.

Human colon carcinoma cell lines established in this laboratory were treated in vitro with N,N-dimethylformamide. This polar solvent caused morphological changes in the cells as well as alterations in their growth properties. Untreated cells had cloning efficiencies of up to 77% in soft agar; treatment with N,N-dimethylformamide resulted in a complete loss of clonogenicity in semisolid medium. Growth in the presence of the polar solvent also effected a marked reduction in the tumorigenicity of the cells. Ten of ten nude mice that received a s.c. inoculum of 1 X 10(6) untreated cells developed tumors histologically similar to colonic adenocarcinomas in 10 to 14 days, whereas nine of ten nude mice inoculated with 1 X 10(6) treated cells have shown no sign of tumor 3 to 6 months postinjection. Removal of the polar solvent from the culture medium was accompanied by the reappearance of tumorigenicity and the original cell culture characteristics. Therefore, it appears that N,N-dimethylformamide can reversibly effect the reversion of cultured human colon carcinoma cells to less malignant cell types.