N,N-Dimethylformamide treatment of cell cultures established from a transplantable murine rhabdomyosarcoma-induced morphological differentiation and a marked reduction in the tumorigenicity of the sarcoma cells. Fourteen of 17 CE/J mice receiving injections of inducer-treated cells did not develop tumors after 6 months, whereas all 21 mice receiving inocula of untreated sarcoma cells died of disease between 11 and 31 days. The drug-treated cells did not grow in soft agar; untreated tumor cells grew in the semisolid medium. The untreated tumor cells showed a reduced serum requirement and had a higher saturation density compared to drug-treated cells. Thus the reduction in tumorigenicity of N,N-dimethylformamide-treated cells correlates with certain in vitro growth properties that are more characteristic of normal, mesenchymally derived cells than of sarcoma cells.

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This work was supported by USPHS NIH Grants CA14520, CA13548, and CA13943. Part of this study was completed at the Wisconsin Clinical Cancer Center, University of Wisconsin, Madison, Wis. 53706.

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