Antiretroviral activity of mechanism-based irreversible inhibitors of S-adenosylhomocysteine hydrolase

Anionic cascade reactions. One-pot assembly of (Z)-chloro-exo-methylenetetrahydrofurans from β-hydroxyketones

The assembly of (Z)-chloro-exo-methylenetetrahydrofurans by an original and connective anionic cascade sequence is reported. Base-catalysed condensation of β-hydroxyketones with 1,1-dichloroethylene generates, in moderate to good yields, the corresponding (Z)-chloro-exo-methylenetetrahydrofurans. Acidic treatment of this motif leads to several unexpected dimers, possessing unique structural features.

Inhibition of transmethylation down-regulates CD4 T cell activation and curtails development of autoimmunity in a model system

Transmethylation affects several cellular events, including T cell activation, and blockade of this pathway may curtail inflammatory/autoimmune responses. Here, we demonstrate that transmethylation inhibition by a novel reversible S-adenosyl-l-homocysteine hydrolase inhibitor leads to immunosuppression by reducing phosphorylation of several key proteins involved in TCR signaling, including Akt, Erk1/2, and NF-kappaB. Remarkably, this effect was largely restricted to CD4 T cells and correlated with reduced arginine methylation of Vav1, an essential guanine nucleotide exchange factor in T cell stimulation. Treatment with the transmethylation inhibitor averted, and even ameliorated, the CD4-mediated autoimmune disease, experimental autoimmune encephalomyelitis. The data suggest that transmethylation is required for CD4 T cell activation, and its inhibition may be a novel approach in the treatment of multiple sclerosis, and other CD4-mediated autoimmune diseases.

Broad resistance to plant viruses in transgenic plants conferred by antisense inhibition of a host gene essential in S-adenosylmethionine-dependent transmethylation reactions

S-Adenosylhomocysteine hydrolase (SAHH) is a key enzyme in transmethylation reactions that use S-adenosylmethionine as the methyl donor. Because of the importance of SAHH in a number of S-adenosylmethionine-dependent transmethylation reactions, particularly the 5' capping of mRNA during viral replication, SAHH has been considered as a target of potential antiviral agents against animal viruses. To test the possibility of engineering a broad type of resistance to plant viruses, we expressed the antisense RNA for tobacco SAHH in transgenic tobacco plants. As expected, transgenic plants constitutively expressing an anti-sense SAHH gene showed resistance to infection by various plant viruses. Among those plants, about half exhibited some level of morphological change (typically stunting). Analysis of the physiological change in those plants showed that they contained excess levels of cytokinin. Because cytokinin has been found to induce acquired resistance, there is also a strong possibility that the observed resistance was induced by cytokinin.

Comparison of the inhibition of type A and type B S-adenosylhomocysteine hydrolase: effects of cofactor content on inhibition behavior and nucleoside binding

The enzyme S-adenosylhomocysteine hydrolase (E.C.3.3.1.1) occurs in two forms in bovine liver: Type A, which carries four moles of NAD+ per mole of enzyme tetramer, and Type B, which carries two moles of NAD+ per mole of tetramer. The inhibition of these two forms of the enzyme with 2',2'-difluoro-2'-deoxyadenosine has been investigated. The studies examined the binding stoichiometry and stability of the enzyme-inhibitor complexes formed from each type of the enzyme, the degree of NAD+ reduction and NAD+ release, and the possibility of covalent bond formation between the enzyme and the inhibitor. Significant differences in the behavior of the two forms of the enzyme were encountered which may have important implications for the design of S-adenosylhomocysteine hydrolase inhibitors as therapeutic agents.

Effects of novel anti-viral adenosine analogues on the activity of S-adenosylhomocysteine hydrolase from human liver

Some adenosine analogues have been found previously to inhibit S-adenosylhomocysteine (SAH)-hydrolase activity in erythrocyte lysates. In this study, the enzyme was purified 500-fold from human liver and its M(r) found to be 190,000. Its kinetics in the synthase direction were studied, the Km for adenosine being determined as 32 microM. Several purine nucleoside analogues currently used in antitumour and antiviral therapy were tested for their influence on SAH-hydrolase activity. The results confirmed our previous findings for the unpurified human erythrocyte enzyme, and demonstrated that the most potent inhibitors of human liver SAH-hydrolase were neplanocin A, 7-deaza-adenosine (tubercidin), 2'-deoxyadenosine, and 9-beta-D-arabino-furanosyladenine. Analogues showing intermediate inhibition were 2'3'-dideoxyadenosine (2'3'-ddAdo), 5'-deoxy-5'-methyl-thioadenosine, 3'-deoxy-adenosine, 2-chloroadenosine, 1,2,4-triazole-3-carboxamide riboside (ribavirin), delta-adenosylornithine (sinefungin), S-adenosylmethionine, 5-amino-4-imidazole carboxamide riboside (AICAR), and 5'-iodo-5'-deoxyadenosine (5'I,5'-dAdo). Weak or no inhibition was noted with 5'-deoxyadenosine, 5-hydroxyimidazole-4-carboxamideriboside (bredinin), inosine and its deoxy analogues, and acyclovir. Our results show that drugs such as 2'3'-dideoxyadenosine (used in HIV therapy) and ribavirin (an inhibitor of inosinate dehydrogenase), in addition to their other known mechanisms of action, have an inhibitory effect on SAH-hydrolase activity, which may be of significance in their antiviral action.