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Restoration of Growth Control in Malignantly Transformed Mouse Fibroblasts Grown in a Chemically Defined Medium¹

Department of Experimental Therapeutics, Grace Cancer Drug Center, Roswell Park Memorial Institute, Buffalo, New York 14263

The expression of growth control and morphological transformation was studied in methylcholanthrene-transformed C3H/10T CL8 cells serially propagated in CDM by first exposing cells to albumin (0.1%) before dispersing them with trypsin (50 µg/ml). In serum-supplemented media, methylcholanthrene-transformed C3H/10T CL8 cells exhibit various aspects of the transformed phenotype such as irregular morphology, extensive cell overlap, lack of density-dependent inhibition of division, a saturation density of 1.1 x 10⁵ cells/sq cm and tumorigenicity in vivo. Cell phenotype in CDM was dramatically altered. Methylcholanthrene-transformed C3H/10T CL8 cells adapted to CDM exhibited a regular epithelioid morphology with no cell overlap and formed confluent monolayers of nonproliferating cells at a saturation density of 5 x 10⁴ cells/sq cm. The mean generation time of logarithmic-phase cells was 25 to 27 hr. Reversion to the transformed phenotype followed addition of albumin (0.1%) or serum (2%) to logarithmic-phase cultures or exposure (30 to 60 sec) to trypsin (10 µg/ml). Cultures in CDM reexposed to serum remained highly tumorigenic in vivo. The data suggest that absorbed proteins may block transformation-sensitive cell surface sites responsible for growth control and that these sites are inactivated by trypsin.

¹ Supported in part by Grants CA-13038 and CA-21359 from the National Cancer Institute, USPHS.

² Recipient of Institutional Training Grant CA-09072 from the National Cancer Institute, USPHS.

³ To whom requests for reprints should be addressed.

Received 5/31/77. Accepted 11/11/77.