mycophenolic-acid and Leukemia--Erythroblastic--Acute

The effects of three inhibitors of inosine monophosphate (IMP) dehydrogenase on a human erythroleukemic cell line, K562, were studied. Following incubation with these inhibitors, K562 cells underwent differentiation and accumulated hemoglobins. The induction of hemoglobin accumulation was dose dependent; maximum induction was observed at 100, 25, and 3 microM, respectively, for ribavirin, tiazofurin, and mycophenolic acid. The induction was associated with reduction of intracellular GTP content and was blocked by adding guanosine within 24 h after adding inducer. The effective dose for half-maximum induction by ribavirin was 3 times less than that for 50% inhibition of K562 proliferation; however, for tiazofurin and mycophenolic acid, it closely approximated the concentrations which suppressed cellular proliferation. Ribavirin was sequestered preferentially inside the K562 cells, and the induction by ribavirin had a greater than 30-fold increase in hemoglobin. Studies with isoelectric focusing, globin chain analyses, and immunochemical assays indicated that both A gamma and G gamma were detected and that the hemoglobin produced in the ribavirin-treated cells consisted of approximately 60% fetal hemoglobin and its acetylated equivalents. The adult-type alpha globin was found, while no beta globin chains were demonstrated. Thus, accumulation of fetal hemoglobin and production of alpha globin chain in ribavirin-treated cells are different from the pattern of hemoglobins induced by hemin.

Topics: Cell Compartmentation; Cell Division; Erythropoiesis; Hemoglobins; Humans; IMP Dehydrogenase; In Vitro Techniques; Ketone Oxidoreductases; Leukemia, Erythroblastic, Acute; Mycophenolic Acid; Purine Nucleotides; Ribavirin; Ribonucleosides; Tumor Cells, Cultured

Addition of certain inhibitors of RNA or protein synthesis to cells cultured in 20% serum, but not 5% serum, induces the differentiation of mouse erythroleukemia cells. Differentiation also was induced by culture at a low serum concentration (0.1%) to starve cells to quiescence, then inducing division by exposing cells to either of two high-pH regimes.

Topics: Alanine; Animals; Cell Differentiation; Cell Division; Cell Line; Cycloheximide; Friend murine leukemia virus; Hydrogen-Ion Concentration; Leukemia, Erythroblastic, Acute; Mice; Mycophenolic Acid; Protein Biosynthesis; RNA, Ribosomal

The synthetic nucleoside, ribavirin (1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide), a broad spectrum antiviral agent currently being tested in clinical studies with AIDS patients; and mycophenolic acid, a non-nucleoside inhibitor of inosinate (IMP) dehydrogenase, are effective inducers of terminal differentiation of Friend virus transformed murine erythroleukemia cells. The inhibition of cell division and the induced maturation produced by these agents appears to be a consequence of inhibition of IMP dehydrogenase, since growth inhibition is reversed and differentiation is prevented by the simultaneous exposure of cells treated with the agents to exogenous guanine or guanosine, which circumvents the effects of blockage of IMP dehydrogenase. However, while the effects mycophenolic acid, a pure IMP dehydrogenase inhibitor with no other biochemical effects, were completely reversed by guanine salvage supplies, cells exposed to ribavirin responded in a different manner. At levels of guanine salvage supplies below 50 microM, growth inhibition and cell differentiation were partially reversed. At salvage supply concentrations greater than 50 microM, while differentiation was completely blocked, the toxicity of ribavirin was increased and cell division was greatly diminished. These results indicate additional biochemical effects for ribavirin unrelated to the inhibition of IMP dehydrogenase, which may be related to its antiviral properties.

Topics: Benzidines; Cell Differentiation; Cell Line; Friend murine leukemia virus; Globins; Guanine; Guanosine; Leukemia, Erythroblastic, Acute; Mycophenolic Acid; Ribavirin; Ribonucleosides; RNA, Messenger