Inhibition by Ketoconazole of Mitogen-induced DNA Synthesis and Cholesterol Biosynthesis in Lymphocytes

The effects of ketoconazole on mitogen-induced DNA synthesis and cholesterol biosynthesis in human and murine lymphocytes have been examined. Ketoconazole concentrations which do not affect cell viability (0.1 to 10 micrograms/ml) in culture led to a dose-dependent inhibition of DNA synthesis, as measured by [3H]thymidine incorporation, induced by either T-cell or B-cell mitogens. At drug concentrations 5- to 10-fold lower, ketoconazole inhibited the incorporation of [14C]acetate into cholesterol, with a resultant accumulation of [14C]lanosterol. The suppressive effects of ketoconazole on DNA synthesis were reversed by increasing the concentration of human serum in the culture medium from 5 to 20%. The depletion of lipoproteins in human serum by density centrifugation reduced the cholesterol content by 90% but did not affect the ability of the serum to overcome the inhibition by ketoconazole of DNA synthesis. Unlike DNA synthesis, cholesterol biosynthesis was not restored by 20% fresh human serum or lipoprotein-depleted human serum. These results demonstrate that ketoconazole potently inhibits DNA synthesis and cholesterol synthesis in mitogen-stimulated lymphocytes at drug concentrations obtained therapeutically. Further, the uncoupling of endogenous cholesterol synthesis and DNA synthesis indicates at least two levels of action of ketoconazole in mammalian lymphocytes.