Inhibition of nucleic acid synthesis in Ehrlich tumor cells by periodate-oxidized adenosine and adenylic acid

Bioinformatics and system biology approaches to determine the connection of SARS-CoV-2 infection and intrahepatic cholangiocarcinoma

INTRODUCTION

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causal agent of coronavirus disease 2019 (COVID-19), has infected millions of individuals worldwide, which poses a severe threat to human health. COVID-19 is a systemic ailment affecting various tissues and organs, including the lungs and liver. Intrahepatic cholangiocarcinoma (ICC) is one of the most common liver cancer, and cancer patients are particularly at high risk of SARS-CoV-2 infection. Nonetheless, few studies have investigated the impact of COVID-19 on ICC patients.

METHODS

With the methods of systems biology and bioinformatics, this study explored the link between COVID-19 and ICC, and searched for potential therapeutic drugs.

RESULTS

This study identified a total of 70 common differentially expressed genes (DEGs) shared by both diseases, shedding light on their shared functionalities. Enrichment analysis pinpointed metabolism and immunity as the primary areas influenced by these common genes. Subsequently, through protein-protein interaction (PPI) network analysis, we identified SCD, ACSL5, ACAT2, HSD17B4, ALDOA, ACSS1, ACADSB, CYP51A1, PSAT1, and HKDC1 as hub genes. Additionally, 44 transcription factors (TFs) and 112 microRNAs (miRNAs) were forecasted to regulate the hub genes. Most importantly, several drug candidates (Periodate-oxidized adenosine, Desipramine, Quercetin, Perfluoroheptanoic acid, Tetrandrine, Pentadecafluorooctanoic acid, Benzo[a]pyrene, SARIN, Dorzolamide, 8-Bromo-cAMP) may prove effective in treating ICC and COVID-19.

CONCLUSION

This study is expected to provide valuable references and potential drugs for future research and treatment of COVID-19 and ICC.

The 2,2'-bipyridyl-6-carbothioamide copper (II) complex differs from the iron (II) complex in its biochemical effects in tumor cells, suggesting possible differences in the mechanism leading to cytotoxicity

2,2'-bipyridyl-6-carbothioamide (BPYTA) is an antitumor agent with chelating properties. It has previously been shown that the R2 subunit of ribonucleotide reductase (RR) is its major cellular target, but RR inhibition is observed only in the presence of ferrous iron (BPYTA-Fe, molar ratio 2:1). Because the copper (II) complex of BPYTA (BPYTA-Cu, molar ratio 1:1)) has in vitro antitumor activity comparable to that of BPYTA-Fe, we studied the mechanism of action of this new metal complex. Spectorphotometric and HPLC studies demonstrated that, at pH 7.5, BPYTA-Cu is stable at molar ratio 2:1 and copper is in its favored oxidized form [BPYTA-Cu(II)]. Electron paramagnetic resonance (EPR) studies with mouse recombinant R2 demonstrated that BPYTA-Cu destroys the R2 tyrosyl radical at the same concentration at which BPYTA-Fe does (78% vs 73% destruction at 200 microM, with 5 min of contact), but R2 inhibition is not time-dependent. Studies of the metabolism of [14C] cytidine suggest that the cytotoxic activity of BPYTA-Cu can be explained in terms of RR inhibition. However, the significant inhibition of RNA synthesis and the lack of cross-resistance to BPYTA-Cu of cell lines resistant to other RR inhibitors suggest that BPYTA-Cu may have more than one cellular target. Moreover, cell proliferation studies suggest that, unlike BPYTA-Fe, BPYTA-Cu displays its activity immediately after contact with the target cells. Our study demonstrates that significant differences in the biochemical effects of BPYTA and, perhaps, also its mechanism of action are due solely to the bonded transition metalloelement. This might also be the case with other chelators that demonstrate cytotoxic activity following metalloelement chelation.

Structure-function relationships for a new series of pyridine-2-carboxaldehyde thiosemicarbazones on ribonucleotide reductase activity and tumor cell growth in culture and in vivo

The synthesis of a new series of pyridine-2-carboxaldehyde thiosemicarbazones (HCTs) that have amino groups in the 3- and 5-positions has allowed the comparison of the structure/function relationships with regard to inhibition of ribonucleotide reductase activity, L1210 cell growth in culture and L1210 leukemia in vivo. 3-Aminopyridine-2-carboxaldehyde thiosemicarbazones are more active than the corresponding 3-hydroxy-derivatives. The 3-amino-2-pyridine carboxaldehyde thiosemicarbazones were also more active then the 5-amino-2-carboxaldehyde thiosemicarbazones in inhibiting ribonucleotide reductase activity and L1210 cell growth in culture and in vivo. N-Acetylation of the 3-amino derivative resulted in a compound that was much less active both in vitro and in vivo; N-acetylation of the 5-amino derivative did not alter the in vitro inhibitory properties, but did eliminate the antitumor properties in vivo. When the most active HCTs were studied in more detail, it was found that the incorporation of [3H]thymidine into DNA was inhibited completely without the inhibition of [3H]uridine incorporation into RNA. Further, the conversion of [14C]cytidine to deoxycytidine nucleotides and incorporation into DNA was inhibited by the HCTs without an effect on the incorporation of cytidine into RNA. These data support the conclusion that ribonucleotide reductase is the major site of action of these HCTs. The 3-aminopyridine-2-carboxaldehyde thiosemicarbazones emerge as strong candidates for development for clinical trials in cancer patients.

Inhibitors of ribonucleotide reductase. Comparative effects of amino- and hydroxy-substituted pyridine-2-carboxaldehyde thiosemicarbazones

A new series of alpha-(N)-heterocyclic carboxaldehyde thiosemicarbazones (HCTs) was studied for their effects on L1210 cell growth in culture, cell cycle transit, nucleic acid biosynthesis and ribonucleotide reductase activity. 3-Aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP) and 3-amino-4-methylpyridine-2-carboxaldehyde thiosemicarbazone (3-AMP) were the most active compounds tested with respect to inhibition of cell growth and ribonucleotide reductase activity. 5-Aminopyridine-2-carboxaldehyde thiosemicarbazone (5-AP) and 4-methyl-5-aminopyridine-2-carboxaldehyde thiosemicarbazone (5-AMP) were slightly less active. 3-AP, 3-AMP, 5-AP and 5-AMP inhibited the incorporation of [3H]thymidine into DNA without affecting the rate of incorporation of [3H]uridine into RNA. The uptake and incorporation of [14C]cytidine into cellular ribonucleotides and RNA, respectively, were not decreased by 3-AP or 3-AMP; however, the incorporation of cytidine into DNA via ribonucleotide reductase was inhibited markedly. Thus, a pronounced decrease in the formation of [14C]deoxyribonucleotides from radioactive cytidine occurred in the acid-soluble fraction of 3-AP- and 3-AMP-treated L1210 cells. Consistent with an inhibition of DNA replication that occurred at relatively low concentrations of 3-AP and 3-AMP, cells gradually accumulated in the S-phase of the cell cycle; at higher concentrations of 3-AP and 3-AMP, a more rapid accumulation of cells in the G0/G1 phase of the cell cycle occurred, with the loss of the S-phase population, implying that a second less sensitive metabolic lesion was created by the HCTs. N-Acetylation of 3-AMP resulted in a compound that was 10-fold less active as an inhibitor of ribonucleotide reductase activity and 8-fold less active as an inhibitor of L1210 cell growth. N-Acetylation of either 5-AP or 5-AMP did not alter the inhibitory properties of these compounds. The results obtained provide an experimental rationale for the further development of the HCTs, particularly 3-AP and 3-AMP, as potential drugs for clinical use in the treatment of cancer.

2'-Deoxy-2'-methylene derivatives of adenosine, guanosine, tubercidin, cytidine and uridine as inhibitors of L1210 cell growth in culture

The 2'-deoxy-2'-methylene derivatives of adenosine (MdAdo), guanosine (MdGuo), tubercidin (MdTu), cytidine (MdCyd) and uridine (MdUrd) were synthesized as mechanism-based inhibitors directed at ribonucleotide reductase. It was shown that MdCyd 5'-diphosphate irreversibly inactivated ribonucleotide reductase from Escherichia coli (Baker et al., J Med Chem 34: 1879-1884, 1991). In studies reported here, MdAdo/EHNA, MdGuo and MdCyd inhibited L1210 cell growth with IC50 values of 3.4, 10.6 and 1.4 microM, respectively. Since MdAdo is a substrate for adenosine deaminase, the presence of EHNA was required to give maximal growth inhibition. 8-Aminoguanosine was not required to maximize the cytotoxic effects of MdGuo. The 2'-deoxy-2'-methylene derivatives of tubercidin and uridine did not inhibit L1210 cell growth at concentrations as high as 50 microM (MdTu) or 100 microM (MdUrd). L1210 cell lines resistant to hydroxyurea (directed at the non-heme iron subunit of ribonucleotide reductase) or deoxyadenosine (directed at the effector binding subunit of ribonucleotide reductase) were not resistant to MdCyd. An L1210 cell line that was highly resistant to dGuo due to the loss of a relatively specific deoxyribonucleoside kinase (Cory et al., J Biol Chem 268: 405-409, 1993) had a 6.6-fold increase in the IC50 value toward MdCyd, but showed only a 2-fold increase in resistance to MdGuo. Another L1210 cell line that was markedly deficient in adenosine kinase activity was highly resistant to MdAdo. Analysis by flow cytometry showed that MdCyd showed the transit of the cells through the G2/M phase of the cell cycle resulting in the buildup of the G2/M population. MdAdo, MdGuo and MdCyd inhibited the incorporation of [14C]cytidine into DNA without an effect on RNA synthesis or total cellular uptake of [14C]cytidine. The conversion of [14C]cytidine to deoxycytidine nucleotides was partially inhibited by MdGuo, but not by MdAdo or MdCyd. These data show that the 2'-deoxy-2'-methylene derivatives of adenosine, guanosine and cytidine are activated via specific nucleoside kinases and that the modes of action of these compounds are not identical.

Inhibition of tumor cell ribonucleotide reductase by macrophage-derived nitric oxide

Macrophage-derived nitric oxide (NO) is cytostatic to tumor cells and microbial pathogens. We tested whether one molecular target for the cytostatic action of NO may be ribonucleotide reductase (RR), a rate-limiting enzyme in DNA synthesis. In a concentration-dependent manner, NO gas and lysates of activated macrophages that generated comparable amounts of NO led to the same degree of inhibition of partially purified RR from L1210 mouse lymphoma cells. Lysates from nonactivated macrophages, which do not produce NO, were noninhibitory. With lysates from activated macrophages, RR was protected by omitting L-arginine or by adding the NO synthase inhibitors diphenyleneiodonium, N omega-methyl-L-arginine, or N omega-amino-L-arginine. L-Arginine, but not D-arginine, abolished the protective effect of N omega-amino-L-arginine. The prototypic pharmacologic inhibitor of RR is hydroxyurea. Its structural resemblance to N omega-hydroxy-L-arginine, a reaction intermediate of NO synthase, prompted us to test if hydroxyurea can generate NO. In the presence of H2O2 and CuSO4, hydroxyurea produced NO2-/NO3-, aerobic reaction products of NO. Addition of morpholine blocked NO2-/NO3- generation from hydroxyurea and led to formation of nitrosomorpholine, as detected by gas chromatography/mass spectrometry. Thus, hydroxyurea can produce an NO-like, nitrosating rectant. L1210 cell DNA synthesis was inhibited completely by activated macrophages or by hydroxyurea, and was partially restored to the same degree in both settings by providing deoxyribonucleosides to bypass the block in RR. Thus, both NO gas and NO generated by activated macrophage lysates inhibit tumor cell RR. The RR inhibitor hydroxyurea can also generate an NO-like species. Similar, partial restoration of tumor cell DNA synthesis by deoxyribonucleosides in the presence of activated macrophages or hydroxyurea suggests that cytostasis by activated macrophages and by hydroxyurea has comparable mechanisms, including, but probably not limited to, inhibition of RR.

Studies on the mechanisms of inhibition of L1210 cell growth by 3,4-dihydroxybenzohydroxamic acid and 3,4-dihydroxybenzamidoxime

Didox and Amidox inhibit L1210 cell growth in culture. At least one of the mechanisms in the mode(s) of action of the compounds is directed at the ribonucleotide reductase site. Partially purified preparations of ribonucleotide reductase activity are inhibited by Amidox and Didox. The formation of deoxycytidine nucleotides from [14C]cytidine in intact L1210 cells is also blocked. Didox and Amidox cause the decrease in the intracellular pools of the four dNTPs. Hydroxyurea-resistant L1210 cells are not cross-resistant to either Didox or Amidox. These data suggest that Didox and Amidox are not inhibiting ribonucleotide reductase through a mechanism similar to hydroxyurea.

Inhibition of ribonucleotide reductase and growth of human colon carcinoma HT-29 cells and mouse leukemia L1210 cells by N-hydroxy-N'-aminoguanidine derivatives

A series of N-hydroxy-N'-aminoguanidine (HAG) derivatives were studied and compared for their effects on ribonucleotide reductase activity in cell-free extracts; on nucleic acid synthesis and the growth of human colon carcinoma HT-29 cells; and on mouse leukemia L1210 cells in culture. The HAG derivatives [RCH=NNHC(=NH)NHOH-tosylate] studied could be grouped as: (1) hydroxybenzylidines; (2) methoxybenzylidines; and (3) nitrobenzylidines substituted at the R position. 2'-Hydroxybenzylidine-HAG, the lead compound, was relatively active in both HT-29 cells and L1210 cells (20 +/- 5 and 13 +/- 4 microM for 50% inhibition of HT-29 and L1210 cell growth respectively). The monohydroxybenzylidene compounds were generally more active than the dihydroxy- and trihydroxybenzylidene-HAG derivatives. The methoxybenzylidene-HAGs were as active as the monohydroxybenzylidene-HAGs. 2'-Hydroxy-4'-methoxybenzylidene-HAG was much more active than 2',4'-dihydroxybenzylidene-HAG. The mononitrobenzylidene-HAGs were more active than the dinitrobenzylidene-HAG compound. In general, L1210 cells were more sensitive to the effects of the HAG compounds than were HT-29 cells. There was good agreement between the concentration of drug required to inhibit the growth of HT-29 cells and that required to inhibit the growth of L1210 cells. There was also good correlation between the ability of HAG derivatives to inhibit ribonucleotide reductase activity and to inhibit tumor cell growth. Some derivatives, such as 2',3',4'- and 3',4',5'-trihydroxybenzylidene-HAG inhibited L1210 cell growth by 50% at lower concentrations (7.8 and 11.9 microM respectively) than the concentrations needed for 50% inhibition of HT-29 cell growth (196 and 234 microM respectively) and ribonucleotide reductase activity (122 and 188 microM respectively). The studies of nucleic acid synthesis in L1210 cells using [3H]cytidine as a precursor showed that 2',3',4'-trihydroxybenzylidine-HAG inhibited DNA synthesis at a lower concentration (29 microM for 50% inhibition) than was needed for the inhibition of RNA synthesis and formation of [3H]deoxycytidine nucleotides in the acid-soluble fraction (320 and 820 microM for 50% inhibition respectively). These results indicate that 2',3',4'-trihydroxybenzylidine-HAG inhibits DNA synthesis in L1210 cells through other mechanisms rather than exclusively through the inhibition of ribonucleotide reductase activity.

Effect of ribonucleotide reductase inhibitors on the growth of human colon carcinoma HT-29 cells in culture

The effects of ribonucleotide reductase inhibitors on the growth of the human colon carcinoma cell line HT-29 were examined. Inhibitors were chosen for these studies that were specifically directed at each of the subunits of ribonucleotide reductase. The concentrations of drugs required to inhibit the growth of HT-29 cells by 50% (IC50) for hydroxyurea, 2,3-dihydro-lH-pyrazole-[2,3a]imidazole (IMPY), and 4-methyl-5-amino-l-formyl-isoquinoline thiosemicarbazone (MAIQ) were 206, 996, and 3.2 microM, respectively. Although the IC50 for deoxyadenosine alone was greater than 2,000 microM, in the presence of 5 microM erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA), which protects deoxyadenosine from deamination by adenosine deaminase, it was reduced to 112 microM. The IC50 for deoxyguanosine was 1,060 microM. The addition of 8-aminoguanosine to protect deoxyguanosine from phosphorolysis by purine nucleoside phosphorylase did not increase the toxicity of deoxyguanosine in HT-29 cells. The combination of MAIQ or IMPY and deoxyadenosine/EHNA gave strong synergistic inhibition of HT-29 cell growth. The results of these studies indicate that ribonucleotide reductase inhibitors effectively block the growth of human colon carcinoma HT-29 cells and that combinations of inhibitors directed at the individual subunits of reductase result in synergistic inhibition of HT-29 cell growth in culture.

Effects of cytosine arabinoside and hydroxyurea on the synthesis of deoxyribonucleotides and DNA replication in L1210 cells

Experiments were carried out in L1210 cells to examine the importance of 'substrate cycles' in regulating the intracellular levels of deoxyribonucleoside 5'-triphosphate. L1210 cells were incubated with [14C]cytidine or [14C]adenosine in the presence and absence of hydroxyurea or cytosine arabinoside (araC). These incubations were carried out for either 30 or 120 min. Inhibition of ribonucleotide reductase by hydroxyurea resulted in the blockage of the flux of ribonucleotides to deoxyribonucleotides (greater than 90%) as expected. When DNA synthesis was inhibited with araC, there was a marked decrease in the incorporation of [14C]cytidine or [14C]adenosine into DNA as deoxyribonucleotides. However, there was not a corresponding increase in the deoxyribonucleotide levels in the acid-soluble fraction or deoxyribonucleosides in the culture medium. AraC treatment decreased the total formation of deoxyribonucleotides. These data indicate that L1210 cells do not regulate the intracellular pools of dNTPs via 'substrate cycles' which involve activation of phosphatases when DNA synthesis is blocked or activation of kinases when ribonucleotide reductase is inhibited.

Metabolic activation of 2,6-diaminopurine and 2,6-diaminopurine-2'-deoxyriboside to antitumor agents

2,6-Diaminopurine (DAP) and 2,6-diaminopurine 2'-deoxyriboside (DAPdR) are analogs of adenine and deoxyadenosine, respectively. It was the purpose of this study to compare these analogs under identical conditions in order to define their inhibitory properties and the underlying mechanism in L1210 mouse leukemia cells. In a 5-day cell growth experiment, DAP exerted a significantly stronger antiproliferative effect than DAPdR. Correspondingly, colony formation of L1210 cells in soft agarose was inhibited by DAP to a greater extent than by DAPdR. A differential distribution of L1210 cells in the cell cycle resulted from an exposure to DAP and DAPdR. While DAPdR arrested cells in the G1/G0 phase of the cell cycle, DAP appeared to lead to an accumulation of G2/M cells. The diaminopurines were combined with modulatory agents to test the antiproliferative action of the combinations. Deoxycytidine partially rescued the cells from the growth inhibitory action of DAPdR without affecting the growth of DAP-treated cells. When adenine was used, the antiproliferative effect of DAPdR was slightly enhanced while the effect of DAP was completely abolished. 8-Aminoguanosine, a specific inhibitor of purine nucleoside phosphorylase, synergistically potentiated the cytostatic effect of DAPdR. However, this inhibitor did not alter DAP effects. At the biochemical level, the target of DAPdR was ribonucleotide reductase which was in line with a drastic expansion of the dGTP pool in DAPdR-treated cells. In cells exposed to DAP, high levels of DAP riboside triphosphate were measured; concomitantly, the ATP level dropped markedly. Enzymological studies revealed that DAPdR is an excellent substrate of adenosine deaminase giving rise to the formation of deoxyguanosine. DAP was found to be activated in the purine nucleoside phosphorylase reaction and in a phosphoribosyl-pyrophosphate-dependent reaction. The data from this comparative study suggest that DAPdR and DAP possess different toxicity mechanisms. DAPdR and DAP possess different toxicity mechanisms. DAPdR acts as a precursor of deoxyguanosine, and DAP is metabolically activated to DAP-containing ribonucleotide analogs. These different metabolic routes seem to account for the different effects of DAP and DAPdR at the cellular level.

Ribonucleotide reductase activity and growth of glutathione-depleted mouse leukemia L1210 cells in vitro

L1210 cells treated with L-buthionine-(S/R)-sulfoximine (BSO) had glutathione (GSH) and non-protein thiol levels only 15% that of control. These GSH-depleted cells grew as well as the control L1210 cells and there was no decrease in ribonucleotide reductase activity in situ as measured by the conversion of [14C]cytidine to deoxytidine nucleotides and incorporation into DNA. Further, when these BSO-stressed cells were treated with hydroxyurea or IMPY, there was no potentiation of the inhibition caused by hydroxyurea or IMPY alone. These data indicate that the glutathione/glutaredoxin system of ribonucleotide reductase is not the sole carrier of reducing equivalents from NADPH for the reduction of the 2'-position of the corresponding ribonucleoside 5'-diphosphate; and that glutathione is not critical in regenerating the tyrosyl free-radical on the M2 subunit which is destroyed by the hydroxyurea or 2,3-dihydro-1H-pyrazolo-[2,3-alpha]imidazole (IMPY) treatment.

Inhibition of ribonucleotide reductase and L1210 cell growth by N-hydroxy-N'-aminoguanidine derivatives

A series of N-hydroxy-N'-aminoguanidine derivatives was studied for their effects on L1210 cell growth and ribonucleotide reductase activity. With the twelve compounds studied, there was a good correlation between the inhibition of L1210 cell growth and the inhibition of ribonucleotide reductase activity. The most potent compound required concentrations of only 1.4 and 2 microM for 50% inhibition of L1210 cell growth and ribonucleotide reductase activity respectively. These guanidine analogs specifically inhibited the conversion of [14C]cytidine and deoxycytidine nucleotides in the nucleotide pool and the incorporation of [14C]cytidine into DNA without altering the incorporation of [14C]cytidine into RNA. Ribonucleotide reductase activity in drug-treated cells was reduced markedly. Iron-chelating agents did not either increase or decrease the inhibition caused by the N-hydroxy-N'-aminoguanidine derivatives. No evidence was obtained that these derivatives selectively inactivated one of the subunits of ribonucleotide reductase. These compounds appear to inhibit ribonucleotide reductase by a mechanism different from hydroxyurea or the thiosemicarbazone derivatives.

Effect of the dialdehyde derivative of 5'-deoxyinosine on pyrimidine deoxyribonucleoside metabolism in L1210 cells

The effects of the dialdehyde derivatives of inosine (Inox) and 5'-deoxyinosine (5'-dInox) on L1210 cells were compared. The growth of L1210 cells was inhibited to a greater extent by 5'-dInox than by Inox. The increased inhibition of L1210 cell growth by 5'-dInox was also reflected by the increased inhibition of the incorporation of precursors into RNA, DNA and proteins. Even though 5'-dInox was a more potent inhibitor, Inox accumulated in the L1210 cells to levels 4- to 5-fold greater than 5'-dInox. The metabolism of [5-3H]deoxycytidine and [5-3H]deoxyuridine by L1210 cells in culture, in the presence of Inox or 5'-dInox, indicated that dCMP deaminase was an intracellular site of action for 5'-dInox. The dCMP deaminase activity in cell-free extracts prepared from 5'-dInox-treated cells was reduced markedly. This decrease in activity was not reversed by increased substrate concentrations nor was the activity subject to allosteric activation by dCTP. Deoxyuridine and deoxycytidine were able to reverse the effects of 5'-dInox on the inhibition of L1210 cell growth.

Drug action on ribonucleotide reductase

Ribonucleotide reductase catalyzes the rate-limiting step in DNA synthesis. It represents a key metabolic site at which specific inhibitors have been directed as potential antitumor agents. Several different classes of ribonucleotide reductase inhibitors have been generated and studied. Because of the nature of the DNA polymerase reaction in which all four dNTPs are required, the initial velocity vs dNTP concentration curve gives sigmoidal rather than hyperbolic kinetics. As a result, a 50 per cent decrease in ribonucleotide reductase activity causes a decrease in DNA polymerase activity of 75 per cent or greater depending on the ratio of [dNTP] to its Km. This has been demonstrated with theoretical calculations, actual DNA polymerase determinations and precursor studies in intact tumor cells. The structural requirements for a compound to serve as a specific inhibitor of ribonucleotide reductase, either as the non-heme iron or effector-binding subunit, are stringent. Each protein subunit comprising the active enzyme can be specifically and independently inhibited. When combinations of agents, each directed at one of the subunits of ribonucleotide reductase, are used, strong synergistic inhibition of L1210 cell growth and synergistic cytotoxicity result.

Affinity labeling of ribonucleotide reductase by the 2',3'-dialdehyde derivatives of ribonucleotides

Ribonucleotide reductase from Corynebacterium nephridii is rapidly inactivated by the 2',3'-dialdehyde derivatives of CDP (dial-CDP) and ADP (dial-ADP). The analog of CDP causes the progressive inactivation of ribonucleotide reductase activity with Ki of 0.26 mM and a maximum inactivation rate of 0.092 min-1 at saturating concentrations of dial-CDP. The modified enzyme remains inactive even after extensive dialysis. The four common nucleoside diphosphates (ADP, GDP, CDP, and UDP) protect the enzyme against inactivation by dial-CDP. Experiments with [3H]dial-CDP, [14C]dial-ADP, and [32P]dial-ADP demonstrate that the nucleoside moieties of these nucleotide analogs become covalently attached to the enzyme and that inorganic pyrophosphate is eliminated. The stoichiometry of this inactivation, determined with [3H]dial-CDP and [14C]dial-ADP, is 0.6-0.8 site modified per subunit of enzyme. The results suggest that the enzyme catalyzes the elimination of pyrophosphate and that the resulting alpha, beta-unsaturated nucleoside dialdehyde or its corresponding alpha, beta-unsaturated dihydroxymorpholino derivative is attacked by a nucleophilic residue in the active site.

Dialdehydes derived from adenine nucleosides as substrates and inhibitors of adenosine aminohydrolase

A series of nucleoside dialdehydes have been obtained as powders after treatment of various adenine nucleosides with paraperiodic acid. Thus, oxidation gave dialdehydes derived from adenosine (1), 9-alpha-D-mannopyranosyladenine (2), 9-(5-deoxy-alpha-D-arabinofuranosyl)adenine (3), 9-alpha-L-rhamnopyranosyladenine (4), 9-beta-L-fucopyranosyladenine (5), 9-beta-D-fucopyranosyladenine (6), 9-alpha-D-arabinopyranosyladenine (7), 9-beta-D-ribopyranosyladenine (8), and 9-(5-deoxy-beta-D-erythro-pent-4-enofuranosyl)adenine (9). Nucleoside dialdehydes 1-3 and 6-8 were weak substrates for adenosine aminohydrolase from calf intestinal mucosa. Dialdehyde 8 had the strongest affinity, but 1 had the highest Vmax. All of the dialdehydes except 5 were inhibitors of the enzyme. The best inhibitors were 9 (Ki = 4 microM) and 4 (ki = 28 microM), and neither were substrates. The inhibitors did not exhibit time-dependent inhibition and did not appear to form covalent bonds with the protein. The data strongly suggest that the active form of the dialdehydes is as the open-chain dihydrates. The alcohol obtained by reduction of 9 (compound 10) was the strongest inhibitor (Ki = 0.9 microM among the related alcohols and the nucleoside dialdehydes.