GROWTH INHIBITORY EFFECTS OF HYDROCORTISONE ON MOUSE LYMPHOMA ML-388 IN VITRO

¹ Department of Pharmacology, Stanford University School of Medicine, Palo Alto, California

A new bioassay for steroids is described, involving the growth inhibition of a mouse lymphoma cell line cultured in vitro. Structure-activity relationships reveal the response in general parallels the anti-inflammatory activity of corticoids. Under the conditions of our assay, hydrocortisone can inhibit growth of these cells by 50% at a concentration of less than 10-⁷ M. Several synthetic compounds are many times as active as hydrocortisone, while other steroids (estrogens, androgens, cholesterol and others) are devoid of activity.

The mechanism of this effect of hydrocortisone was studied by attempting to reverse the growth inhibition by a great variety of alterations and additions to the culture medium, all of which were uniformly ineffective. Studies on the accumulation of cellular constituents revealed a diminution of the cellular protein, deoxynucleic acid, and amino acid pool size as early as 12 hours after steroid addition. Experiments with radioactive leucine conclusively demonstrated an inhibition of protein synthesis as early as 12 hours, with no effect on protein catabolism. Examination of the amino acid pattern in the cold acid-soluble, intracellular pool revealed that at 12 hours, the intracellular pools of aspartate and glutamate were depressed, while alanine was occasionally increased in the steroid-treated cell as compared to controls.