EFFECT OF METHOTREXATE ON CYCLIC-AMP LEVELS IN CULTURED L5178Y CELLS

L5178Y murine lymphoma cells were cultured for 48 hr in Fischer's medium containing 10% horse serum. The cells were then treated with 10-6 m methotrexate (MTX) for additional periods of time. Cyclic AMP concentrations increased 1.65-fold compared to untreated controls (P < 0.01) after 1 hr of MTX treatment. Cyclic AMP levels were increased further after 3 hr of MTX treatment (P < 0.05), fell by 6 hr (P < 0.05), and remained depressed after 16 hr (P < 0.05). Cell numbers did not increase during MTX treatment. Inhibition by MTX of cyclic AMP phosphodiesterase activity of homogenates prepared from L5178Y cells was not observed. The data are discussed in relation to a possible block in the G1 to S transition of the cell cycle as an early consequence of MTX treatment. Basal cyclic AMP levels of L5178Y cells grown in medium containing 3.3 × 10-5 m hypoxanthine for 1 hr were increased significantly over those of control cultures. Thus, variations in basal cyclic AMP levels of cells could be attributed, at least in part, to the purine content of the cells and/or the horse serum of the culture medium. However, the increases in cyclic AMP caused by hypoxanthine and MTX were additive. © 1979.