Structure-activity relationships for inhibition of inosine monophosphate dehydrogenase by nuclear variants of mycophenolic acid.

Structure-activity relationships in the region of the phthalide ring of the inosine monophosphate dehydrogenase inhibitor mycophenolic acid have been explored. Replacement of the lactone ring with other cyclic moieties resulted in loss of potency, especially for larger groups. Replacement of the ring by acyclic substituents also indicated a strong sensitivity to steric bulk. A phenolic hydroxyl group, with an adjacent hydrogen bond acceptor, was found to be essential for high potency. The aromatic methyl group was essential for activity; the methoxyl group could be replaced by ethyl to give a compound with 2-4 times the potency of mycophenolic acid in vitro and in vivo.

Some antioxidants inhibit, in a co-ordinate fashion, the production of tumor necrosis factor-alpha, IL-beta, and IL-6 by human peripheral blood mononuclear cells.

Some antioxidants, including butylated hydroxyanisole (BHA), tetrahydropapaveroline (THP), nordihydroguiauretic acid, and 10,11-dihydroxyaporphine (DHA), were found to be potent inhibitors of the production of tumor necrosis factor (TNF)-alpha, IL-1 beta, and IL-6 by human peripheral blood mononuclear cells (PBMC) stimulated by lipopolysaccharide (LPS) (IC50s in the low micromolar range). Inhibition of cytokine production was gene selective and not due to general effects on protein synthesis. Inhibition of cytokine production by PBMC was observed also when other inducers were used (staphylococci, silica, zymosan). Much higher concentrations of other antioxidants--including ascorbic acid, trolox, alpha-tocopherol, butylated hydroxytoluene, and the 5-lipoxygenase inhibitor zileuton--did not affect the production of these cytokines. The active compounds did not inhibit IL-1-induced production of IL-6 in fibroblasts, showing the cell selectivity of the effect. Antioxidant-mediated inhibition of cytokine production was correlated with low levels of the corresponding messenger RNAs. Nuclear run-on experiments showed that THP inhibited transcription of the IL-1 beta gene. THP decreased the concentration of the transcription factors NF-kappa B and AP-1 detected in nuclear extracts of PBMC cultured in the presence or absence of LPS. THP and DHA markedly decreased the levels of TNF-alpha and IL-1 beta in the circulation of mice following LPS injection. Thus antioxidants vary widely in potency as inhibitors of the activation of transcription factors and of the transcription of genes for pro-inflammatory cytokines. Coordinate inhibition of the transcription of genes for inflammatory cytokines could provide a strategy for therapy of diseases with inflammatory pathogenesis and for septic shock.