[Interaction of DNA Methyltransferase Dnmt3a with Phosphorus Analogs of S-Adenosylmethionine and S-Adenosylhomocysteine]

Enzymatic methyltransferase reactions are of crucial importance for cell metabolism. S-Adenosyl-L-methionine (AdoMet) is a main donor of the methyl group. DNA, RNA, proteins, and low-molecular-weight compounds are substrates of methyltransferases. In mammals, DNA methyltransferase Dnmt3a de novo methylates the C5 position of cytosine residues in CpG sequences in DNA. The methylation pattern is one of the factors that determine the epigenetic regulation of gene expression. Here, interactions with the catalytic domain of Dnmt3a was for the first time studied for phosphonous and phosphonic analogs of AdoMet and S-adenosyl-L-homocysteine (AdoHcy), in which the carboxyl group was substituted for respective phosphorus-containing group. These AdoMet analogs were shown to be substrates of Dnmt3a, and the methylation efficiency was only halved as compared with that of natural AdoMet. Both phosphorus-containing analogs of AdoHcy, which is a natural methyltransferase inhibitor, showed similar inhibitory activities toward Dnmt3a and were approximately four times less active than AdoHcy. The finding that the phosphonous and phosphonic analogs are similar in activity was quite unexpected because the geometry and charge of their phosphorus-containing groups differ substantially. The phosphorus-containing analogs of AdoMet and AdoHcy are discussed as promising tools for investigation of methyltransferases.

Identification of a Novel Substrate-Derived Spermine Oxidase Inhibitor

Homeostasis of the biogenic polyamines spermine (Spm) and spermidine (Spd), present in μM-mM concentrations in all eukaryotic cells, is precisely regulated by coordinated activities of the enzymes of polyamine synthesis, degradation, and transport, in order to sustain normal cell growth and viability. Spermine oxidase (SMOX) is the key and most recently discovered enzyme of polyamine metabolism that plays an essential role in regulating polyamine homeostasis by catalyzing the back-conversion of Spm to Spd. The development of many types of epithelial cancer is associated with inflammation, and disease-related inflammatory stimuli induce SMOX. MDL72527 is widely used in vitro and in vivo as an irreversible inhibitor of SMOX, but it is also potent towards N1-acetylpolyamine oxidase. Although SMOX has high substrate specificity, Spm analogues have not been systematically studied as enzyme inhibitors. Here we demonstrate that 1,12-diamino-2,11-bis(methylidene)-4,9-diazadodecane (2,11-Met2-Spm) has, under standard assay conditions, an IC₅₀ value of 169 μM towards SMOX and is an interesting instrument and lead compound for studying polyamine catabolism.

[Enantioselective Synthesis of (R)- and (S)-3-Methylspermidines]

Earlier unknown enantiomerically pure (R)- and (S)-1,8-diamino-3-methyl-4-azaoctane's (3-MeSpd's) were synthesized with high overall yields and optical purity starting from commercially available R- and S-isomers of N-Boc-2-aminopropanol-1. Application of R- and S-isomers of 3-MeSpd for the investigation of the stereospecificity of spermidine transporter and peculiarities of deoxyhypusine synthase reaction are discussed.

Hydroxylamine derivatives for regulation of spermine and spermidine metabolism

The biogenic polyamines spermine, spermidine, and their precursor putrescine are present in micro-to-millimolar concentrations in all cell types and are vitally important for their normal growth. High intracellular content of spermine and spermidine determines the multiplicity of the cellular functions of the polyamines. Many of these functions are not well characterized at the molecular level, ensuring the ongoing development of this field of biochemistry. Tumor cells have elevated polyamine level if compared with normal cells, and this greatly stimulates the search for new opportunities to deplete the intracellular pool of spermine and spermidine resulting in decrease in cell growth and even cell death. O-Substituted hydroxylamines occupy their own place among chemical regulators of the activity of the enzymes of polyamine metabolism. Varying the structure of the alkyl substituent made it possible to obtain within one class of chemical compounds highly effective inhibitors and regulators of the activity of all the enzymes of putrescine, spermine and spermidine metabolism (with the exception of FAD-dependent spermine oxidase and acetylpolyamine oxidase), effectors of the polyamine transport system, and even actively transported in cells "proinhibitor" of ornithine decarboxylase. Some principles for the design of specific inhibitors of these enzymes as well as the peculiarities of cellular effects of corresponding O-substituted hydroxylamines are discussed.

Biogenic polyamines spermine and spermidine activate RNA polymerase and inhibit RNA helicase of hepatitis C virus

Influence of the biogenic polyamines spermine, spermidine, and putrescine as well as their derivatives on the replication enzymes of hepatitis C virus (HCV) was investigated. It was found that spermine and spermidine activate HCV RNA-dependent RNA polymerase (NS5B protein). This effect was not caused by the stabilization of the enzyme or by competition with template-primer complex, but rather it was due to achievement of true maximum velocity V(max). Natural polyamines and their derivatives effectively inhibited the helicase reaction catalyzed by another enzyme of HCV replication - helicase/NTPase (NS3 protein). However, these compounds affected neither the NTPase reaction nor its activation by polynucleotides. Activation of the HCV RNA polymerase and inhibition of the viral helicase were shown at physiological concentrations of the polyamines. These data suggest that biogenic polyamines may cause differently directed effects on the replication of the HCV genome in an infected cell.

[Leishmania donovani: structural insignt in the recognition of C-methylated analogues of spermidine as natural polyamine]

The ability of alpha-, beta-, gamma- and omega-methylated spermidine analogues to restore the growth of L. donovani promastigotes that were depleted of putrescine and spermidine was investigated. Only beta-methylated spermidine, like natural spermidine was capable of restoring the growth of L. donovani, while the remaining three analogues turned out to be inactive. Considering that alpha-methylated spermidine is a functionally active spermidine surrogate both in vivo and in vitro, this analogue can be considered as an antidote in the host-parasite system, especially in cases where inhibitors of polyamine biosynthesis are used for the therapy of leishmaniasis.

[Methylated analogues of spermine and spermidine as tools to investigate cellular functions of polyamines and the enzymes of their metabolism]

Biogenic amines spermine and spermidine are essential factors of cellular growth. Polyamine analogues are widely used to investigate and to regulate the enzymes of polyamine metabolism and functions of spermine and spermidine in vitro and in vivo. Recently, it was demonstrated that alpha-methylated derivatives of spermine and spermidine are capable to fulfill key cellular functions of polyamines, moreover in some cases of (R)- and (S)-isomers are actually different. Using these alpha-methylated spermine and spermidine analogues it turned possible to prevent the development of acute pancreatitis of SSAT-transgenic rats and to demostrate for the first time that polyamine oxidase, spermine oxidase and deoxyhypusine synthase have dormant stereospecificity. An original approach to regulate the stereospecificity of polyamine oxidase was suggested. It was also demonstrated that the depletion of the intracellular polyamine pool has both hypusine-related consequences and also the consequences unrelated to the posttranslational modification of eukaryotic initiation translation factor eIF5A. Possible applications of a new family of C-methylated polyamine analogues for the investigation and regulation of polyamine metabolism in vitro and in vivo are discussed.