Chemical modification potentiates the biological activities of 2-5A and its congeners

3'-Modification stabilizes mRNA and increases translation in cells

Successful implementation of mRNA gene therapy is facing many hurdles, for example poor expression levels of the exogenously delivered mRNA transcripts. Herein we describe the synthesis of various 3'-modified RNA oligonucleotides, and we show that 3'-modification drastically stabilizes these oligonucleotides in cell extracts. Modification of the 3'-terminus of gaussia luciferase mRNA results in 3-fold increased and extended (>48 h) translation of the mRNA. Our findings suggest 3'-modification of RNA-transcripts as a valid approach to increase expression levels for application in mRNA gene therapy.

Recognition of 2',5'-linked oligoadenylates by human ribonuclease L: molecular dynamics study

The capability of current MD simulations to be used as a tool in rational design of agonists of medically interesting enzyme RNase L was tested. Dimerization and enzymatic activity of RNase L is stimulated by 2',5'-linked oligoadenylates (pA₂₅A₂₅A; 2-5A). First, it was necessary to ensure that a complex of monomeric human RNase L and 25A was stable in MD simulations. It turned out that Glu131 had to be protonated. The non-protonated Glu131 caused dissociation of 2-5A from RNase L. Because of the atypical 2'-5' internucleotide linkages and a specific spatial arrangement of the 25A trimer, when a single molecule carries all possible conformers of the glycosidic torsion angle, several versions of the AMBER force field were tested. One that best maintained functionally important interactions of 25A and RNase L was selected for subsequent MD simulations. Furthermore, we wonder whether powerful GPUs are able to produce MD trajectories long enough to convincingly demonstrate effects of subtle perturbations of interactions between 25A and RNase L. Detrimental impacts of various point mutations of RNase L (R155A, F126A, W60A, K89A) on 2-5A binding were observed on a time scale of 200 ns. Finally, 2-5A analogues with a bridged 3'--O,4'--C-alkylene linkage (B) introduced into the adenosine units (A) were used to assess ability of MD simulations to distinguish on the time scale of hundreds of nanoseconds between agonists of RNase L (pA₂₅A₂₅B, pB₂₅A₂₅A, pB₂₅A₂₅B) and inactive analogs (pA₂₅B₂₅A, pA₂₅B₂₅B, pB₂₅B₂₅A, pB₂₅B₂₅B). Agonists were potently bound to RNase L during 200 ns MD runs. For inactive 2-5A analogs, by contrast, significant disruptions of their interactions with RNase L already within 100 ns MD runs were found.

Synthesis and enzymatic deprotection of fully protected 2'-5' oligoadenylates (2-5A): towards a prodrug strategy for short 2-5A

Fully protected pA2'p5'A2'p5'A trimers 1a and 1b have been prepared as prodrug candidates for a short 2'-5' oligoadenylate, 2-5A, and its 3'-O-Me analog, respectively. The kinetics of hog liver carboxyesterase (HLE)-triggered deprotection in HEPES buffer (pH 7.5) at 37° has been studied. The deprotection of 1a turned out to be very slow, and 2-5A never appeared in a fully deprotected form. By contrast, a considerable proportion of 1b was converted to the desired 2-5A trimer, although partial removal of the 3'-O-[(acetyloxy)methyl] group prior to exposure of the adjacent phosphodiester linkage resulted in 2',5'→3',5' phosphate migration and release of adenosine as side reactions.

Synthesis and enzymatic deprotection of biodegradably protected dinucleoside-2',5'-monophosphates: 3-(acetyloxy)-2,2-bis(ethoxycarbonyl)propyl phosphoesters of 3'-O-(acyloxymethyl)adenylyl-2',5'-adenosines

As a first step towards a viable prodrug strategy for short oligoribonucleotides, such as 2-5A and its congeners, adenylyl-2',5'-adenosines bearing a 3-(acetyloxy)-2,2-bis(ethoxycarbonyl)propyl group at the phosphate moiety, and an (acetyloxy)methyl- or a (pivaloyloxy)methyl-protected 3'-OH group of the 2'-linked nucleoside have been prepared. The enzyme-triggered removal of these protecting groups by hog liver carboxyesterase at pH 7.5 and 37° has been studied. The (acetyloxy)methyl group turned out to be too labile for the 3'-O-protection, being removed faster than the phosphate-protecting group, which results in 2',5'- to 3',5'-isomerization of the internucleosidic phosphoester linkage. In addition, the starting material was unexpectedly converted to the 5'-O-acetylated derivative. (Pivaloyloxy)methyl group appears more appropriate for the purpose. The fully deprotected 2',5'-ApA was accumulated as a main product, although, even in this case, the isomerization of the starting material takes place.

2-5A ligands--a new concept for the treatment of prostate cancer

Several potent prostate specific membrane antigen (PSMA) inhibitors have been described recently. We generated a PSMA-specific 2-5A ligand called RBI 1033 by linking 2-5A to the N-acetylaspartylglutamate (NAAG)-based inhibitor ZJ-24. We measured the inhibitory activity of RBI 1033 to the folate hydrolase activity of PSMA. Amazingly, we found that compared to ZJ-24 (IC50 = 53.9 nM), RBI 1033 was more than 10 times more potent (IC50 = 4.78 nM) as a folate hydrolase inhibitor, while SMCC 2-5A lacking the ZJ-24 part, did not show much activity (IC50 = 1974 nM). Also, RBI 1033's affinity to PSMA was found to be 10 times higher than ZJ-24 itself.

Endowing RNase H-inactive antisense with catalytic activity: 2-5A-morphants

A convergent synthetic approach was used to conjugate 2',5'-oligoadenylate (2-5A, p5'A2' [p5'A2'](n)()p5'A) to phosphorodiamidate morpholino oligomers (morphants). To provide requisite quantities of 2-5A starting material, commercially and readily available synthons for solid-phase synthesis were adapted for larger scale solution synthesis. Thus, the tetranucleotide 5'-phosphoryladenylyl(2'-->5')adenylyl(2'-->5')adenylyl(2'-->5')adenosine (p5'A2'p5'A2'](2)p5'A2', tetramer 2-5A, 9) was synthesized starting with 2',3'-O-dibenzoyl-N(6),N(6)-dibenzoyl adenosine prepared from commercially available 5'-O-(4-monomethoxytrityl) adenosine. Coupling with N(6)-benzoyl-5'-O-(4,4'-dimethoxytrityl)-3'-O-(tert-butyldimethylsilyl) adenosine-2'-(N,N-diisopropyl-2-cyanoethyl)phosphoramidite, followed by oxidization and deprotection, generated 5'-deprotected dimer 2-5A. Similar procedures lengthened the chain to form protected tetramer 2-5 A. The title product 9 p5'A(2'p5'A)(3) (tetramer 2-5A) was obtained through phosphorylation of the terminal 5'-hydroxy of the protected tetramer and removal of remaining protecting groups using concentrated ammonium hydroxide-ethanol (3:1, v/v) at 55 degrees C and tetrabutylammonium fluoride (TBAF) in THF at room temperature, respectively. The 2-5A-phosphorodiamidate morpholino antisense chimera 11 (2-5A-morphant) was synthesized by covalently linking an aminolinker-functionalized phosphorodiamidate morpholino oligomer with periodate oxidized 2-5A tetramer (p5'A2'[p5'A2'](2)p5'A). The resulting Schiff base was reduced with cyanoborohydride thereby transforming the ribose of the 2'-terminal nucleotide of 2-5A N-substituted morpholine. RNase L assays demonstrated that this novel 2-5A-antisense chimera had significant biological activity, thereby providing another potential tool for RNA ablation.

The quest for an efficacious antiviral for respiratory syncytial virus

Respiratory syncytial virus (RSV) continues as an emerging infectious disease not only among infants and children, but also for the immune-suppressed, hospitalized and the elderly. To date, ribavirin (Virazole) remains the only therapeutic agent approved for the treatment of RSV. The prophylactic administration of palivizumab is problematic and costly. The quest for an efficacious RSV antiviral has produced a greater understanding of the viral fusion process, a new hypothesis for the mechanism of action of ribavirin, and a promising antisense strategy combining the 2'-5' oligoadenylate antisense (2-5A-antisense) approach and RSV genomics.

Convergent synthesis of ribonuclease L-active 2',5'-oligoadenylate-peptide nucleic acids

2-5A was conjugated to N-(2-aminoethyl)-glycyl PNA by periodate oxidization, followed by coupling with amino-derivatized PNA and final cyanoborohydride reduction. An adduct of 2-5A pentamer with tetrameric thymine PNA activated RNase L with the same potency as earlier versions of 2-5A-PNA or 2-5A-DNA.

The 2-5A system: modulation of viral and cellular processes through acceleration of RNA degradation

The 2-5A system is an RNA degradation pathway that can be induced by the interferons (IFNs). Treatment of cells with IFN activates genes encoding several double-stranded RNA (dsRNA)-dependent synthetases. These enzymes generate 5'-triphosphorylated, 2',5'-phosphodiester-linked oligoadenylates (2-5A) from ATP. The effects of 2-5A in cells are transient since 2-5A is unstable in cells due to the activities of phosphodiesterase and phosphatase. 2-5A activates the endoribonuclease 2-5A-dependent RNase L, causing degradation of single-stranded RNA with moderate specificity. The human 2-5A-dependent RNase is an 83.5 kDa polypeptide that has little, if any, RNase activity, unless 2-5A is present. 2-5A binding to RNase L switches the enzyme from its off-state to its on-state. At least three 2',5'-linked oligoadenylates and a single 5'-phosphoryl group are required for maximal activation of the RNase. Even though the constitutive presence of 2-5A-dependent RNase is observed in nearly all mammalian cell types, cellular amounts of 2-5A-dependent mRNA and activity can increase after IFN treatment. One well-established role of the 2-5A system is as a host defense against some types of viruses. Since virus infection of cells results in the production and secretion of IFNs, and since dsRNA is both a frequent product of virus infection and an activator of 2-5A synthesis, the replication of encephalomyocarditis virus, which produces dsRNA during its life cycle, is greatly suppressed in IFN-treated cells as a direct result of RNA decay by the activated 2-5A-dependent RNase. This review covers the organic chemistry, enzymology, and molecular biology of 2-5A and its associated enzymes. Additional possible biological roles of the 2-5A system, such as in cell growth and differentiation, human immunodeficiency virus replication, heat shock, atherosclerotic plaque, pathogenesis of Type I diabetes, and apoptosis, are presented.

Efficient functionalization of 2',5'-oligoadenylates with sulfur

To derivatize the 2'-terminus of 2',5'-oligoadenylates with a thiol group, the reaction of periodate-oxidized nucleotide and 2',5'-oligonucleotide with aminothiols was explored. Two separate synthetic approaches were employed, both of which relied upon the use of S-protected thiols. In one approach, 5'AMP was oxidized with sodium periodate to dialdehyde, which was reacted with cystamine hydrochloride. Sodium cyanoborohydride reduction of the unisolated intermediate animal gave compound 4. The second approach involved reaction of S-(2-tetrahydropyranyl)cysteamine with the dialdehyde obtained by periodate oxidation of 5'AMP to yield, after reduction with Na(CN)BH3, the S-protected adduct 3. Intermediate 3 could be oxidized with aqueous iodine to give disulfide 4. Disulfide 4, obtained by either of the above routes, was reduced with dithiotreitol (DTT) to the thiol 5. This same reaction sequence was applied to 2-5A tetramer monophosphate, p5'A2'[p5'A2']2p5'A (6a), to give via 6b the 2'-terminal-modified derivative 6c. Aqueous iodine oxidation of 6c provided the disulfide 7, which reacted with DTT to give quantitative conversion to product, the free thiol 8. Both the disulfide 7 and the S-tetrahydropyranyl-protected derivative (6c) were bound effectively to the 2-5A-dependent RNase L of mouse L cells with IC50 values of 1 x 10(-9) M for 7 and 8 x 10(-10) M for 6c, not significantly different from the corresponding value for the parent unmodified 2-5A (6a) itself.

Preparation of cyclic 2',3'-monophosphates of oligoadenylates (A2'p)nA > p and A3'p(A2'p)n-1A > p

The action of the guanylyl-preferring RNase from Bacillus intermedius (binase) on a mixture of oligoadenylates with randomly distributed 2'-5' and 3'-5' internucleotide bonds [(A2'/3'p)n] under conditions sufficient for complete hydrolysis of poly(A) results in a mixture containing a single circular oligoadenylate and two series of linear oligoadenylates ending in cyclic 2',3'-phosphate. Individual compounds formed upon digestion of (A2'/3'p)n with binase have been isolated. Their structure was determined on the basis of their chemical and enzymatic conversions and confirmed by 1H-, 13C- and 31P-NMR spectra. According to these data, the circular triadenylate contains one 2'-5' and two 3'-5' internucleotide bonds, linear oligoadenylates of one series contain exclusively 2'-5' internucleotide bonds [(A2'p)nA > p], while each compound of the other series contains a single 3'-5' internucleotide bond connecting the 5'-ultimate nucleotide residue with the penultimate one [A3'p(A2'p)n-1A > p]. The incubation of compounds of the former series A3' p(A2'p)n > p at pH 1.0 and the subsequent action of phosphatase results in successive formation of compounds of two other new series: A3'p(A2'p)nA2'(3')p and A3'p(A2'p)nA.

Picornavirus inhibitors

Picornaviruses are among the best understood animal viruses in molecular terms. A number of important human and animal pathogens are members of the Picornaviridae family. The genome organization, the different steps of picornavirus growth and numerous compounds that have been reported as inhibitors of picornavirus functions are reviewed. The picornavirus particles and several agents that interact with them have been solved at atomic resolution, leading to computer-assisted drug design. Picornavirus inhibitors are useful in aiding a better understanding of picornavirus biology. In addition, some of them are promising therapeutic agents. Clinical efficacy of agents that bind to picornavirus particles has already been demonstrated.

A new and potent 2-5A analogue which does not require a 5'-polyphosphate to activate mouse L-cell RNase L

In order to explore the possibility of supplanting the requirement of a 5'-triphosphate moiety for the activation of the 2-5A-dependent endonuclease (RNase L) of mouse L-cells, two new tetrameric analogues of 2-5A were synthesized. The first tetramer, obtained by both a modified prebiotic synthetic approach as well as a phosphite triester solid phase oligonucleotide synthesis method, was p5'A2'p5'A2'p5'(br8A)2'p5'(br8A). The second oligonucleotide was derived from the former by a sequence involving periodate oxidation, reaction with n-hexylamine, and cyanoborohydride reduction, resulting in conversion of the 2'-terminal adenosine residue to 9-(3'-aza-4'-hexyl-1',2',3',4'-tetradeoxyhexopyranos-1(1)-yl)-8-++ +bromoadenine. Both of these oligomers, bearing only 5'-monophosphate groups, were found to be as potent as 2-5A itself as activators of the RNase L of mouse L-cells.

Purine 8-substitution modulates the ribonuclease L binding and activation abilities of 2',5'-oligoadenylates

Analogues of the 2',5'-linked adenylate trimers monophosphate (p5'A2'p5'A2'p5'A) containing 8-hydroxypropyladenosine, 8-bromoadenosine, and 8-hydroxyadenosine in the first, second, and third nucleotide positions were tested for their ability to bind to and activate RNase L of mouse L cells. p5'AHPr2'p5'AHPr2'p5'AHPr (pAHPr3) (1b) and p5'ABr2'p5'ABr2'p5'ABr (pABr3) (1d) were markedly decreased in ability to bind to the 2-5A dependent endonuclease. On the other hand, analogue of the 2',5'-linked adenylate trimer monophosphate substituted by 8-hydroxyadenosine in the first, second, and third nucleotide position was bound about as well as parent 2-5A [pppA(2'p5'A)2] (p3A3) (1e) to RNase L. Additionally, p5'AOH2'p5'AOH2'p5'AOH (pAOH3) (1c) was as active as parent 2-5A in the rRNA cleavage assay, while pAHPr3 (1b) and pABr3 (1d) were devoid of activity. The 8-substituted analogues of 2-5A were more resistant to the degradation by the (2',5') phosphodiesterase. Finally of particular interest was monophosphate, pAOH3 (1c) which possessed nearly 100% of the translation inhibitory activity of 2-5A triphosphate itself. These results suggest that changes in the base-sugar torsion angles of 2-5A may modulate both binding to and activation of mouse L cell RNase L.

Recognition and photo-induced cleavage and cross-linking of nucleic acids by oligonucleotides covalently linked to ellipticine

Oligopyrimidines covalently linked to ellipticine derivatives form duplex and triplex structures with target single-stranded oligopurine sequences. They also bind to duplex DNA at homopurine-homopyrimidine sequences where they form local triple helices. Irradiation at wavelengths longer than 300 nm of the complex formed by an oligonucleotide-ellipticine conjugate with its target sequence induced (i) cleavage of the target at bases located in close proximity to the dye and (ii) cross-linking of the target sequence to the derivatized oligonucleotide. Both cross-linking and cleavage reactions decreased when temperature increased with a half-transition corresponding to the dissociation of the oligonucleotide-ellipticine conjugate from its target nucleic acid, demonstrating that the observed photochemical effects are dependent on hybrid formation. When the target was a double-stranded DNA, photochemical reactions were observed on both strands of the duplex. Photo-induced cross-linking was more efficient than cleavage when the target was single-stranded; the reverse was observed when the target was duplex DNA.

Characterization of two murine (2'-5')(A)n-dependent endonucleases of different molecular mass

RNase L is considered as the major if not unique target of (2'-5')(A)n and therefore as an important intracellular mediator of interferon action. It behaves as an 185-kDa species in various cell extracts when analyzed by gel filtration. SDS/PAGE analysis of the polypeptides covalently labelled with a (2'-5')(A)4-3'-[32P]pCp probe reveals a single 80-kDa species, thus attesting a multimeric form of the 185-kDa protein. At variance with such data, mouse spleen extracts reveal an additional 40-kDa polypeptide with (2'-5')(A)n-dependent ribonucleolytic activity. This seemingly new form of RNase L migrates as a 40-kDa polypeptide when analyzed under native or denaturing conditions. It bears some structural similarity with the larger-molecular-mass RNase L as revealed by partial proteolysis. It is probably not generated through proteolytic degradation of the 185-kDa RNase L during extract preparation, although its physiological significance is unknown. Indeed various protease inhibitors do not significantly alter the ratio of 40-kDa and 185-kDa (2'-5')(A)n-dependent ribonucleases; moreover, the (2'-5')(A)n-binding capacity of the 40-kDa polypeptide is more stable than that of the 185-kDa one.

Mechanisms of degradation of 2'-5' oligoadenylates

We have studied the mechanisms of breakdown of 2'-5' oligoadenylates. We monitored the time-courses of degradation of ppp(A2'p5')nA (dimer to tetramer) and of 5'OH-(A2'p5')nA (dimer to pentamer) in unfractionated L1210 cell extract. The 5' triphosphorylated 2'-5' oligoadenylates are converted by a phosphatase activity. However, 2'-5' oligoadenylates are degraded mainly by phosphodiesterase activity which splits the 2'-5' phosphodiester bond sequentially at the 2' end to yield 5' AMP and one-unit-shorter oligomers. The nonlinear least-squares curve-fitting program CONSAM was used to fit these kinetics and to determine the degradation rate constant of each oligomer. Trimers and tetramers, whether 5' triphosphorylated or not, are degraded at the same rate, whereas 5' triphosphorylated dimer is rapidly hydrolyzed and 5'-OH dimer is the most stable oligomer. The interaction between degradation enzymes and the substrate strongly depends on the presence of a 5' phosphate group in the vicinity of the phosphodiester bond to be hydrolyzed; indeed, when this 5' phosphate group is present, as in pp/pA2'p5'A/or A2'/p5'A2'p5'A/, affinity is high and maximal velocity is low. Such a degradation pattern can control the concentration of 2'-5' oligoadenylates active on RNAse L either by limiting their synthesis (5' triphosphorylated dimer is the primer necessary for the formation of longer oligomers) and/or by converting them into inhibitory (e.g., monophosphorylated trimer) or inactive (e.g., nonphosphorylated oligomers) molecules.

2',5'-Phosphodiesterase activity depends upon the presence of a 3'-hydroxyl moiety in the penultimate position of the oligonucleotide substrate

3'-Deoxyadenosine (3'dA, cordycepin)-substituted analogs of 2-5A core 5'-monophosphate (p5'A2'p5'A2'p5'A) were examined for their sensitivity toward degradation by the 2'-phosphodiesterase activity in cytoplasmic extracts of mouse L cells. The analogs, p5'(3'dA)-2'p5'A2'p5'A, p5'(3'dA)2'p5'A2'p5'(3'dA) and p5'A2'p5'A2'p5'(3'dA) were degraded at a rate comparable to p5'A2'p5'A2'p5'A itself. On the other hand, under the assay conditions examined p5'A2'p5'(3'dA)2'p5'A, like p5'(3'dA)2'p5'(3'dA)2'p5'(3'dA), was completely resistant to degradation. The data imply that sensitivity to the 2',5'-phosphodiesterase activity of mouse L cells requires the presence of 3'-hydroxyl moiety in the penultimate nucleotide.

Antiviral activity of a chemically stabilized 2-5A analog upon microinjection into HeLa cells

2-5A[ppp(A2'p)n5'A] has been implicated as a mediator in the antiviral action of interferon. Its direct evaluation as an indicator of virus replication is hampered by two limitations: its inability to penetrate intact cells, and its rapid intracellular degradation by (2'-5')phosphodiesterase. These problems could be overcome by using a microinjection technique whereby a phosphodiesterase-resistant analog of 2-A, in which the 2'-terminals adenosine residue is replaced by 2-(9-adenyl)-6-hydroxy-methyl-4-hexylmorpholine, was injected into individual HeLa cells before infection with mengovirus or vesicular stomatitis virus (VSV). This comparative assay with two representatives of different virus classes in a single experimental system pointed to the high sensitivity of VSV to inhibition by 2-5A oligonucleotides, in contrast with the low sensitivity of mengovirus. Microinjection of the hexylmorpholine 2-5A analog led to a much greater reduction in mengovirus yield than did microinjection of 2-5A itself.

Antiviral activity in L1210 cells of liposome-encapsulated (2'-5')oligo(adenylate) analogues

Evidence is available for a role of a (2'-5')(A)n-activated endoribonuclease (RNase L) in the antiviral activity of interferon for several RNA viruses. (2'-5')(A)n and their analogues might thus provide an interesting alternative to exogenous interferons or their inducers in antiviral chemotherapy. In addition, the evaluation of the activity of (2'-5)(A)n as mediators of interferon's biological activities or as cell growth regulators requires biochemical studies using agonists or antagonists of the system. Non-disruptive techniques for the introduction of (2'-5')(A)n and their analogues into cell lines or tissues are required for these studies since these highly charged compounds are cell impermeable. (2'-5')(A)n oligomers and analogues of increased stability towards phosphodiesterases were derived by chemical modification of their 2' end and encapsulated in protein-A-bearing liposomes. The specific delivery of liposome contents into L1210 mouse leukemic cells was achieved with the help of monoclonal antibodies directed against the appropriate class I major histocompatibility complex-encoded proteins expressed by these cells. This intracellular delivery led to transient inhibition of protein synthesis and an antiviral activity, both compatible with activation of RNase L. This activity was enhanced for the analogues designed to resist degradation, with respect to the natural product.

n-Decyl-NHpppA2'p5'A2'p5'A A phosphatase-resistant, active pppA2'p5'A2'p5'A analog

n-Decyl-NHpppA2'p5'A2'p5'A, a gamma-substituted, phosphatase-resistant pppA2'p5'A2'p5'A analog, gives similar rRNA degradation pattern in interferon-treated HeLa cell extracts--even at a concentration of 10(-9)M--as the natural compound does.

Mechanism of inhibition of herpesvirus growth by 2'-5'-linked trimer of 9-beta-D-xylofuranosyladenine

The 2'-5'-linked trimer of 9-beta-D-xylofuranosyladenine (XyloA)3 is an extremely potent inhibitor of growth of herpes simplex viruses 1 and 2. Evidence is presented that in spite of its increased stability in cell-free extracts (D.A. Eppstein, Y.V. Marsh, B.B. Schryver, M.A. Larsen, J.W. Barnett, J.P.H. Verheyden, and E.J. Prisbe, J. Biol. Chem. 257, 13390-13397, 1982), intact (XyloA)3 was not detected in Vero cells, but instead was rapidly degraded in the medium to monomeric 9-beta-D-xylofuranosyladenine (XyloA). The XyloA thus formed was rapidly taken up by cells, phosphorylated to its triphosphate, and produced inhibition of RNA synthesis. The observed inhibition of DNA synthesis (D.A. Eppstein, Y.V. Marsh, B.B. Schryver, M.A. Larsen, J.W. Barnett, J.P.H. Verheyden, and E.J. Prisbe, J. Biol. Chem. 257, 13390-13397, 1982) and herpesvirus growth by (XyloA)3 (D.A. Eppstein, J.W. Barnett, Y.V. Marsh, G. Gosselin, and J.L. Imbach, Nature (London) 302, 723, 724, 1983) is most likely the result of inhibition of RNA synthesis by its degradation product XyloA.

Increased stability and antiviral activity of 2'-O-phosphoglyceryl derivatives of (2'-5')oligo(adenylate)

Metabolically stable analogues of (2'-5')oligo(adenylate), (2'-5')(A)n, might constitute a new class of antiviral agents as they mimic some of the effects of interferons. 2'-O-phosphoglyceryl derivatives of (2'-5')(A)n oligomers, (2'-5')(A)n-PGro have been synthesized by chemical modification of their terminal ribose residue. Such analogues are resistant to degradation by phosphodiesterases but remain sensitive to phosphatase activity, at least in cell-free extracts. In line with its increased stability, (2'-5')(A)n-PGro has a powerful antiviral activity against an RNA virus when microinjected with micropipettes into the cytoplasm of intact cells. This antiviral activity remains transient however, possibly as a consequence of degradation in intact cells. Since (2'-5')(A)n and its derivatives do not easily cross cell membranes, their possible use in antiviral chemotherapy is tightly linked with the development of vectors suitable for their administration in vivo.

A sensitive immunoenzymometric assay for 2',5'-oligoadenylate. Detection of elevated 2',5'-oligoadenylate synthetase in human peripheral mononuclear cells

A competition immunoenzymometric assay for 2',5'-oligoadenylate was developed and employed to measure the interferon-inducible enzyme 2',5'-oligoadenylate synthetase in cell extracts. Microtiter plates coated with a novel conjugate of p5'A2'p5'A2'p5'A and N-(2-aminoethyl)-carbamylmethylated-Ficoll (AECM-Ficoll) bound rabbit polyclonal or mouse monoclonal antibody directed against 2',5'-oligoadenylate. Binding was inhibited by soluble 2',5'-oligoadenylate. Estimates of 2',5'-oligoadenylate concentrations based on inhibition of antibody binding compared favorably with those obtained using a protein synthesis inhibition assay. Low concentrations of 2',5'-oligoadenylate synthesized in vitro by extracts of human peripheral mononuclear cells were conveniently estimated using less than or equal to 10(6) cells. Virtually identical results were obtained when either total extract or synthetase bound to poly(I) . poly(C)-agarose was used for the in vitro incubation. When peripheral mononuclear cells were incubated in vitro with interferon, the normally low levels of 2',5'-oligo(A) synthetase rose dramatically. The assay was employed to measure synthetase levels in peripheral mononuclear cells isolated from patients with systemic lupus erythematosus. Some of these patients were found to have elevated levels of 2',5'-oligoadenylate synthetase.