Radiation chemical studies of sensitization by 5-bromouridine-5′-monophosphate (5-BrUMP)

Summary This study was undertaken to investigate the mechanism of chemical radiosensitization by halogenated bases incorporated into DNA. Radiation-induced base and sugar-phosphate backbone damage to 5-bromouridine-5-monophosphate (5-BrUMP) was monitored using a flow system connected in series with a recording spectrophotometer, a bromide (Br^–)-specific ion analyzer and a Technicon auto-sampler. The system was used to assay loss of UV-absorbing 5,6 double-bond, release of Br^– and inorganic phosphate (Pi) release using an automated colorimetric method, as a function of gamma-ray dose. Results obtained with radical scavengers indicate that, unlike non-halogenated nucleotides where the hydroxyl radical (· OH) is the principal damaging species, 5-BrUMP is damaged by the hydrated electron (e _aq ^– ), hydrogen atom (H·) and · OH, producing a high yield of base damage and Br^– and Pi release in anoxia. Another novel feature of 5-BrUMP radiolysis is that oxygen, by convertinge _aq ^– and H· to the unreactive superoxide radical anion (0 ₂ ^– ), has a protective effect on both base and phosphate ester damage. Under · OH-scavenging conditions, where the radiation yield of reductive debromination is 3.8, there is some Pi release, suggesting the possibility of intramolecular hydrogen atom transfer from the sugar ring to the 5-uracilyl radical and subsequent sugar-phosphate bond cleavage. This hypothesis is supported by the action of oxygen and thiols in modifying thee _aq ^– -mediated sugar-phosphate damage.     

Regulator of G-Protein Signaling – 5 (RGS5) Is a Novel Repressor of Hedgehog Signaling

Hedgehog (Hh) signaling plays fundamental roles in morphogenesis, tissue repair, and human disease. Initiation of Hh signaling is controlled by the interaction of two multipass membrane proteins, patched (Ptc) and smoothened (Smo). Recent studies identify Smo as a G-protein coupled receptor (GPCR)-like protein that signals through large G-protein complexes which contain the Gα_i subunit. We hypothesize Regulator of G-Protein Signaling (RGS) proteins, and specifically RGS5, are endogenous repressors of Hh signaling via their ability to act as GTPase activating proteins (GAPs) for GTP-bound Gα_i, downstream of Smo. In support of this hypothesis, we demonstrate that RGS5 over-expression inhibits sonic hedgehog (Shh)-mediated signaling and osteogenesis in C3H10T1/2 cells. Conversely, signaling is potentiated by siRNA-mediated knock-down of RGS5 expression, but not RGS4 expression. Furthermore, using immuohistochemical analysis and co-immunoprecipitation (Co-IP), we demonstrate that RGS5 is present with Smo in primary cilia. This organelle is required for canonical Hh signaling in mammalian cells, and RGS5 is found in a physical complex with Smo in these cells. We therefore conclude that RGS5 is an endogenous regulator of Hh-mediated signaling and that RGS proteins are potential targets for novel therapeutics in Hh-mediated diseases.     

Photobromination of 1,5-Anhydro-2,3-O-isopropylidene-β-d-ribofuranose and Synthesis of (5R) and (5S)-(5-2H1)-d-Riboses

The photobromination of 1,5-anhydro-2,3-O-isopropylidene-β-d-ribofuranose gave the corresponding (5S)-5-bromo compound. The reduction of the bromide with triphenyltindeuteride gave (5S)-(5-²H₁)-1,5-anhydro-2,3-O-isopropylidene-β-d-ribofuranose, with a chiral purity of 76% at C-5, which was converted to (5R)- and (5S)-(5-²H₁)-d-riboses and other ribofuranose derivatives.     

Properties of 5′-nucleotidase from nodules of pigeonpea (Cajanus cajan)

5′-Nucleotidase from pigeonpea nodules has been resolved into two forms, N-I and N-II, having M,s of 52 000 and 119 000, respectively. Both forms had pH optima in the acidic range (between pH 5.2 and 5.7) with either CMP, GMP, XMP, IMP or AMP as the substrate. Up to pH 6.6, both forms showed higher activity with CMP followed by GMP, XMP, IMP and AMP, respectively. However, the activity changed with pH in the alkaline range making the enzyme relatively more active with purine nucleotides. Neither of the forms had a requirement for any of the metal ions tested. Fe³⁺ inhibited the enzyme activity; the inhibition at 5, 10 and 15 mM concentrations being 11, 43 and 47%, respectively with N-I and 14,47 and 52%, respectively with N-II. K_m values for AMP, IMP, GMP, CMP and XMP were 0.10, 0.18, 0.40, 0.40 and 0.77 mM, respectively with N-I and 0.12, 0.20, 0.40, 0.40 and 0.99 mM, respectively with N-II. The enzyme was inhibited non-competitively by adenosine and inosine; K_i values being 1.78, 0.25 and 0.30; 3.50, 2.12 and 0.75 mM, respectively with AMP, IMP and XMP as the substrate.     

Synthesis and Biological Effects of 5′-Deoxy-5′-(Cyclo-Propylmethylthio)Adenosine

Abstract

A novel synthesis of the nucleoside analog, 5′-deoxy-5′-(cyclopropylmethylthio)adenosine (CPMTA, 1) has been developed. CPMTA is a closely related structural analog of 5′-deoxy-5′-(isobutylthio)-adenosine (SIBA, 2), which has been widely studied and shown to exert a multitude of biological effects. The in vitro and in vivo antitumor (L1210 leukemia) activity of CPMTA has been found to be comparable to that of SIBA, whereas its in vitro antiviral (HSV and VSV) activity is diminished. These agents are being developed as inhibitors of methylation and/or polyamine synthesis.     

Interactions of dichloro-bis(η5-cyclopentadienyl)titanium(IV) with nucleosides

The interactions of dichloro-bis(η⁵-cyclopentadienyl)titanium(IV) (titanocene dichloride, Cp₂TiCl₂) with nucleosides have been studied in methanolic solutions. Complexes of the general formula [Cp₂Ti(Nucl)MeOH]Cl₂ were isolated. The nucleoside complexes with one N(1)H ionizable imino proton (i.e. inosine and guanosine) undergo ionization in alkaline solution and complexes of the formula [Cp₂Ti(NuclH⁺)] Cl were isolated. All complexes have been characterized by elemental analyses and various spectroscopic techniques. In the first series of complexes, [Cp₂Ti(Nucl)MeOH]Cl₂, the nucleosides act as monodentate ligands with an intramolecular hydrogen bond between the coordinated methanol and the C6O group, while in the second, [Cp₂Ti(NuclH⁺)] Cl, they coordinate through both their N7 and O6 atoms.     

Synthesis of D-ring-substituted (5'R)- and (5'S)-17β-pyrazolinylandrostene epimers and comparison of their potential anticancer activities

Various steroidal benzylidenes were synthetized from pregnenolone with benzaldehyde and p-substituted benzaldehydes. The resulting 17β-chalconyl derivatives of pregnenolone were reacted with hydrazine hydrate in acetic acid solution. Regardless of the starting material, the ring-closure reaction afforded (in contrast with the literature data) a mixture of two steroidal pyrazoline epimers. The epimers were critical isomer pairs, which could be separated only in their acetylated form; their structures were investigated by NMR techniques. The in vitro inhibition of rat testicular C(17,20)-lyase activity and the antiproliferative effects on four human cancer cell lines were measured, and the results obtained from the two epimer series were compared.     

Microbiological synthesis of 5-ethyl- and (E)-5-(2-bromovinyl)-2′-deoxyuridine

Summary The title compounds were prepared by an enzymatic transdeoxyribosylation from 2 dGuo or 2 dThd to the respective heterocyclic bases, 5-ethyluracil and (E)-5-(2-bromovinyl)uracil, using the whole bacterial cells ofEscherichia coli as a biocatalyst.     

C-Nucleosides via Glycosyl Alkynyl Ketones. Synthesis of 5(3)-Phenyl-3(5)-(β-D-ribofuranosyl) Pyrazole

Abstract

A β-D-ribofuranosyl phenylethynyl ketone (3) has been synthesized and shown to be a suitable intermediate for heterocyclic elaboration to C-nucleosides. Cyclization of 3 with hydrazine hydrate produces the title C-nucleoside.     

A Solid-Phase Synthesis of 2′,5′-Linked Oligoadenylates (2-5A)

Abstract

2′,5′-Oligoadenylate 5′-triphosphates (2-5A) as products of 2-5A synthetase and activators of ribonuclease L (RNase L), are mediators in one of the mechanisms of interferon′s antiviral action. Upon activation, RNase L inhibits protein synthesis due to the degradation of RNAs. This activity of 2-5A could possibly find an application in virus or cancer chemotherapy, but two major barriers prevent the use of 2′,5′-linked oligoadenylates as therapeutic agents. The 2-5A is readily degraded by a 2′,5′ phosphodiesterase and as a highly negatively charged molecule, is not readily taken up by cells. One possible solution to this latter limitation might be found in chemical modifications of the 2-5A structure. Many analogues of 2-5A have been already obtained with modified base, ribose or phosphate moieties. While these have provided some important information about the enzyme- activator interactions, the cell permeability problem still remains unsolved. One of the major obstacles in this study is lack of a convenient method of synthesis of 2′,5′ ribonucleotides of widely varying structure.     

Acycloadenosine Derivatives as Inhibitors of 5′-Deoxy-5′-Methylthioadenosine Phosphorylase (MesADo PASE)

Abstract

Four classes of acyclo amlogs of 5′-methylthioadenosine were synthesized and tested as inhibitors of mammalian methylthicadenosine phosphorylase. Halogenated dihydroxypropyl acycloadenosires were most potent, i.e. K_i = 0.2 - 0.7 uM.     

Effect of hypoxia (6,060 m) and cold (−5°C) on sexual organs of male rabbits

Studies have been carried out on 18 adult male rabbits divided into three groups. One group (hypoxic) was exposed to a simulated altitude (6,060 m for 6 h daily for 21 days), the second group was exposed to the same altitude plus cold (–5°C) for the same duration, and the third acted as control. The results showed no difference in the body weight of the three groups, but the weights of the sex organs in the exposed groups were significantly reduced. In both these groups the number, motility and survival time of spermatozoa decreased significantly; the sex organs showed atrophy on histological examination; and there was an increase in the alkaline and acid phosphatase activity and cholesterol concentration, and a fall in GPC level. These changes were more marked in the cold plus altitude group than in the group exposed to altitude alone. It has been concluded that hypoxia affects not only the testis but also the epididymis and the vas deferens. The spermatozoal quality of rabbits deteriorates. When cold and hypoxia are combined, their effects are additive.     

Structural and thermodynamic analysis of the conformational states of self-complementary hexanucleotides 5′-d(GCATGC) and 5′-d(GCTAGC) in Aqueous Solution

The conformational states of hexanucleotides 5′-d(GCATGC) and 5′-d(GCTAGC) capable of forming hairpins in aqueous solution were studied by 1D and 2D ¹H NMR and molecular dynamics. The equilibrium thermodynamic parameters were determined for the formation of duplexes and hairpins, and the spatial structures were computed for the GCATGC and GCTAGC conformers. The mobility of the hexamer constituents was evaluated by nanosecond molecular dynamics simulation. The possible causes of the observed difference in the thermodynamic stability of the duplex and the hairpin are discussed.     

Synthesis of the inosine 5′-monophosphate dehydrogenase (IMPDH) inhibitors

Abstract

Inosine 5′-monophosphate dehydrogenase (IMPDH) is important molecular target for potential anticancer, antiviral, antibacterial and immunosuppressive agents. A lot of compounds were obtained to establish their activity toward this enzyme, and to improve therapeutic properties of IMPDH inhibitors used as the drugs. Some of the recently reported analogs exhibited promising results during in vitro and in vivo examinations in comparison to substances applied in clinic. In this review, we describe synthesis and biological activity evaluations of the newly designed IMPDH inhibitors.