Growth-inhibitory and differentiation-inducing activity of dimethylformamide in cultured human malignant glioma cells

OBJECTIVE: To determine the growth-inhibitory and differentiation- inducing activity of dimethylformamide (DMF) on a human glioma cell line (SHG-44). DMF is a type of polar solvent and a potent differentiation- inducing agent in many kinds of human solid tumors, yet its effect on human glioma remains unclear. METHODS: The effects of DMF on cell proliferation using 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay, cell cycle distribution (with flow cytometry), colony-forming efficiency in double-layer soft agar, tumorigenicity in athymic nude mice, morphological changes, and glial fibrillary acidic protein expression were studied. RESULTS: At dose ranges of 0.25, 0.5, 0.75, and 1.0%, DMF caused a dose- dependent proliferation inhibitory effect in monolayers and a marked dose- dependent suppression of colony-forming efficiency in double-layer soft agar with a complete loss of colony-forming ability in cells exposed to 0.75 and 1.0% DMF. Accumulation of cells in G₀/G₁ phases was observed in DMF- treated (0.5 and 1.0%) cells, also in a dose-dependent manner. SHG-44 cells exposed to DMF (0.5 and 1.0%) for 15 days changed morphologically from small spindle-shaped to large polygonal and flattened stellate cells with multiple slender processes. These cells were still tumorigenic in athymic nude mice, but the growth of xenografts was remarkably reduced, especially in the 1.0% DMF-treated group. The expression of glial fibrillary acidic protein was notably increased by DMF (0.5 and 1.0%). Washout experiments revealed that the effects of DMF on cell proliferation and cell cycle distribution were reversible. CONCLUSION: Our results suggest that DMF drove the SHG-44 cells to a more mature phenotype with inhibited growth.