u-18666a and Glioma

The hypocholesterolemic agent 3 beta-(2-diethylaminoethoxy)androst-5-en-17-one . HCl (U18666A) is known to induce experimental epilepsy. The possibility that this drug interferes with cholesteryl ester formation in glioblastoma cells was examined. The incorporation of radioactive oleic acid into cellular cholesteryl ester was drastically and specifically inhibited by U18666A. The inhibitory effect of U18666A persisted in different oleic acid concentrations. Kinetic studies revealed the rapidity of U18666A action. U18666A was found to be ineffective in inhibiting acyl-CoA:cholesterol acyltransferase activity when it was added directly to the cell homogenates. In contrast, the acyltransferase activity was greatly diminished in homogenates derived from U18666A-treated cells. Thus, U18666A appeared to block cellular cholesteryl ester biosynthesis by indirectly inactivating acyl-CoA:cholesterol acyltransferase activity in a cell-dependent manner. The potent inhibition of cholesteryl ester formation by U18666A represents one unique aspect of the drug which might contribute to its ability to induce chronic epileptiform activity.

Topics: Androstenes; Animals; Anticholesteremic Agents; Cell Line; Cholesterol Esters; Desmosterol; Glioma; Ketocholesterols; Neuroglia; Oleic Acid; Oleic Acids; Rats; Squalene; Sterol O-Acyltransferase; Time Factors

To investigate the perturbation of ubiquinone biosynthesis by a hypocholesterolemic drug, 3 beta-(2-diethylaminoethoxy)androst-5-en-17-one hydrochloride (U18666A), we measured the incorporation of radioactive mevalonate, methionine, tyrosine, and 4-hydroxybenzoic acid into ubiquinone in glioblastoma cells. These four precursors unanimously showed that ubiquinone biosynthesis was not significantly altered by U18666A, which blocked cholesterol biosynthesis at steps beyond mevalonate formation. The fluctuation of the endogenous mevalonate level had little effect on ubiquinone biosynthesis, implying the relative stability of cellular ubiquinone biosynthesis. Furthermore, exogenously added mevalonate did not have an appreciable effect on ubiquinone biosynthesis. The major ubiquinone produced in rat glioblastoma cells was identified as ubiquinone-9. The mevalonate-derived products accumulated in the U18666A-treated cells differed significantly from those reported in a broken cell study, suggesting the existence of delicate mechanisms regulating the formation of cholesterol intermediates.

Topics: Androstenes; Animals; Anticholesteremic Agents; Cell Line; Glioma; Hydroxybenzoates; Hydroxymethylglutaryl-CoA Reductase Inhibitors; Lovastatin; Methionine; Mevalonic Acid; Naphthalenes; Parabens; Rats; Tyrosine; Ubiquinone

Ubiquinone synthesis has been studied in cultured C-6 glial and neuroblastoma cells by utilizing an inhibitor, 3-beta-(2-diethylaminoethoxy) androst-5-en-17-one hydrochloride (U18666A), of cholesterol biosynthesis. Exposure of C-6 glial cells to nanomolar quantities of U18666A caused a marked inhibition of total sterol synthesis from [14C]acetate or [3H]mevalonate within minutes. A 95% inhibition was apparent after a 3-h exposure to 200 ng/ml of U18666A. These observations, together with studies of the incorporation of radioactivity from the two precursors into cholesterol, desmosterol, lanosterol, and squalene, indicated that although the most sensitive site to inhibition by U18666A is desmosterol reduction to cholesterol, a major site of inhibition is demonstrable at a more proximal site, perhaps squalene synthetase. As a consequence of the latter inhibition, exposure of C-6 glial cells to U18666A caused a marked stimulation of incorporation of [14C]acetate or [3H]mevalonate into ubiquinone. Over a wide range of U18666A concentrations, the increase in ubiquinone synthesis was accompanied by an approximately similar decrease in total sterol synthesis. Whereas in the absence of U18666A only approximately 7% of the radioactivity incorporated from [3H]mevalonate into isoprenoid compounds was found in ubiquinone, in the presence of the drug approximately 90% of incorporated radioactivity was found in ubiquinone. The reciprocal effects of U18666A on ubiquinone and sterol syntheses were apparent also in the neuronal cells. THe data thus demonstrate a tight relationship between ubiquinone and sterol biosyntheses in cultured cells of neural origin. In such cells ubiquinone synthesis is exquisitely sensitive to the availability of isoprenoid precursors derived from the cholesterol biosynthetic pathway.

Topics: Acetates; Androstenes; Animals; Anticholesteremic Agents; Carbon Radioisotopes; Cell Line; Glioma; Kinetics; Mevalonic Acid; Neuroblastoma; Rats; Sterols; Ubiquinone