In vitro antiretroviral activity and in vitro toxicity profile of SPD754, a new deoxycytidine nucleoside reverse transcriptase inhibitor for treatment of human immunodeficiency virus infection

SPD754 (AVX754) is a deoxycytidine analogue nucleotide reverse transcriptase inhibitor (NRTI) in clinical development. These studies characterized the in vitro activity of SPD754 against NRTI-resistant human immunodeficiency virus type 1 (HIV-1) and non-clade B HIV-1 isolates, its activity in combination with other antiretrovirals, and its potential myelotoxicity and mitochondrial toxicity. SPD754 was tested against 50 clinical HIV-1 isolates (5 wild-type isolates and 45 NRTI-resistant isolates) in MT-4 cells using the Antivirogram assay. SPD754 susceptibility was reduced 1.2- to 2.2-fold against isolates resistant to zidovudine (M41L, T215Y/F, plus a median of three additional nucleoside analogue mutations [NAMs]) and/or lamivudine (M184V) and was reduced 1.3- to 2.8-fold against isolates resistant to abacavir (L74V, Y115F, and M184V plus one other NAM) or stavudine (V75T/M, M41L, T215F/Y, and four other NAMs). Insertions at amino acid position 69 and Q151M mutations (with or without M184V) reduced SPD754 susceptibility 5.2-fold and 14- to 16-fold, respectively (these changes gave values comparable to or less than the corresponding values for zidovudine, lamivudine, abacavir, and didanosine). SPD754 showed similar activity against isolates of group M HIV-1 clades, including A/G, B, C, D, A(E), D/F, F, and H. SPD754 showed additive effects in combination with other NRTIs, tenofovir, nevirapine, or saquinavir. SPD754 had no significant effects on cell viability or mitochondrial DNA in HepG2 or MT-4 cells during 28-day exposure at concentrations up to 200 microM. SPD754 showed a low potential for myelotoxicity against human bone marrow. In vitro, SPD754 retained activity against most NRTI-resistant HIV-1 clinical isolates and showed a low propensity to cause myelotoxicity and mitochondrial toxicity.

Parallel synthesis of isatin-based serine protease inhibitors

The synthesis of N-functionalised isatins using parallel, solution synthesis is described. Functionalised polymers were employed as stoichiometric and catalytic reagents as well as purification media in the exercise, and the derivatives were screened against a panel of serine proteases; high percentage inhibition was observed in several cases.

The hepatitis C virus NS5B RNA-dependent RNA polymerase activity and susceptibility to inhibitors is modulated by metal cations

OBJECTIVES

The aim of this study was to understand the effect of metal cations on the hepatitis C virus (HCV) NS5B in vitro RNA-dependent RNA polymerase (RdRp) activity and its susceptibility to various inhibitors.

METHODS

A recombinant full-length HCV NS5B protein was expressed in insect cells and purified to homogeneity. RdRp activity was assessed using standard filtration or polyacrylamide gel-based assays.

RESULTS

Efficient inhibition of the HCV NS5B RdRp activity by gliotoxin, as well as by various substrate analogs, occurs in the presence of Mn2+, but not of Mg2+. Assays performed in the presence of both cofactors suggest that, in vitro, the enzyme's affinity for Mn2+ is higher than that for Mg2+. In addition, the RdRp activity, displayed in the presence of heteropolymeric templates, is significantly increased when the metal cofactor consists of Mn2+. Finally, steady state kinetics showed that the velocity of the reaction, as well as the affinity of the enzyme for its substrate, could both be affected by the nature of the divalent metal cation used.

Drug resistance and drug combination features of the human immunodeficiency virus inhibitor, BCH-10652 [(+/-)-2'-deoxy-3'-oxa-4'-thiocytidine, dOTC]

The heterosubstituted nucleoside analogue dOTC [( )-2'-deoxy-3'-oxa-4'-thiocytidine, BCH-10652] is a racemic compound structurally related to 3TC (lamivudine), but has the oxygen and sulphur in the furanosyl ring transposed. Both the enantiomers (-)dOTC (BCH-10618) and (+)dOTC (BCH-10619) had equivalent activity against wild-type strains of HIV-1 in C8166 T-cells (EC50 1.0-10.0 microM) and in PBMCs (EC50 0.1-3.0 microM). Investigation of the activity of dOTC and its enantiomers against laboratory strains of HIV-1 with defined resistance to 3TC, AZT (zidovudine), ddl (didanosine), PMEA (adefovir), nevirapine and saquinavir indicated that sensitivity was maintained (<3-fold change in EC50) in all cases, with the exception of HIV-1RF 3TC-resistant viruses. The degree of resistance recorded for dOTC (four- to sevenfold), (-)dOTC (five- to eightfold) and (+)dOTC (five- to >18-fold) against these M1841 or M184V mutants, was significantly less than that recorded for 3TC (>100-fold). In addition, the inhibitory effect of the compounds against clinical isolates of HIV-1 recovered from patients with suspected resistance to 3TC and AZT was investigated. Clinical isolates were genotyped using the Murex Line Probe Assay (LiPA) and subgrouped into wild-type, 3TC-resistant and dual 3TC/AZT-resistant, as well as undefined or mixed genotype populations. Compared with the mean EC50 values obtained with genotypically and phenotypically wild-type clinical isolates, the mean EC50 values calculated for isolates phenotypically resistant to 3TC or 3TC and AZT were only 2.6-, 1.6- and 8.2-fold higher for dOTC, (-)dOTC and (+)dOTC, respectively. When the rate of emergence of virus resistant to dOTC and its enantiomers in vitro was investigated, virus resistant to (+)dOTC was readily selected for (<10 passages), and a methionine (ATG) to isoleucine (ATA) amino acid change at codon 184 was identified. In contrast, virus resistant to dOTC and (-)dOTC took longer to appear (15-20 passages), with a methionine (ATG) to valine (GTG) amino acid change at position 184 identified in both cases. In addition, virus passaged 20 times in the presence of dOTC also had a partial lysine (AAA) to arginine (AGA) exchange at position 65. These viruses showed only low-level resistance to dOTC and its enantiomers, but were highly resistant to 3TC. The antiviral effects of dOTC in combination with the nucleoside RT inhibitors AZT, 3TC, d4T (stavudine) and ddl, the non-nucleoside RT inhibitor nevirapine and the protease inhibitors saquinavir, ritonavir and indinavir was investigated. Two-way drug combination assays were carried out in peripheral blood mononuclear cell (PBMC) cultures by measuring the reduction in p24 viral antigen levels, and data was analysed using the MacSynergy II program. dOTC in combination with 3TC or d4T showed a moderate synergistic effect while all other combinations had an additive interaction.

A novel high throughput screening assay for HCV NS3 helicase activity

A novel assay for measurement of Hepatitis C virus (HCV) NS3 helicase activity was developed using Flashplate technology. This assay involves the use of a DNA duplex substrate and recombinant HCV NS3 produced in Escherichia coli. The DNA duplex consisted of a pair of oligonucleotides, one biotinylated, the other radiolabeled at their respective 5' termini. This DNA duplex was immobilized, via the biotin molecule, on the surface of a neutravidin-coated SMP103 Flashplate (NEN Life Science Products). Helicase activity results in the release of the radiolabeled oligonucleotide, which translates in signal reduction with respect to control wells. Biochemical characterization of the HCV NS3 helicase activity was performed using this assay. We demonstrated that the NS3-mediated unwinding is proportional to both the amount of DNA substrate in the well, and to the NS3 concentration in the reaction. Most of the NS3-mediated unwinding was achieved in the initial 60 min of incubation. As expected the reactions were ATP-dependent and found to be affected by the concentration of MgCl(2), MnCl(2), KCl, EDTA, and by pH. We found this assay to be highly reproducible since only slight variation was observed when a total of 68 helicase reactions were performed on one plate. Therefore, this Flashplate helicase assay is fast, convenient and reproducible. These criteria make it suitable for high throughput screening of potential NS3 helicase inhibitors.

Antiviral properties of a series of 1,6-naphthyridine and 7, 8-dihydroisoquinoline derivatives exhibiting potent activity against human cytomegalovirus

A series of 1,6-naphthyridine (L. Chan, H. Jin, T. Stefanac, J. F. Lavallee, G. Falardeau, W. Wang, J. Bedard, S. May, and L. Yuen, J. Med. Chem. 42:3023-3025, 1999) and isoquinoline (L. Chan, H. Jin, T. Stefanac, W. Wang, J. F. Lavallee, J. Bedard, and S. May, Bioorg. Med. Chem. Lett. 9:2583-2586, 1999) analogues exhibiting a high level of anti-human cytomegalovirus (HCMV) activity were investigated in a series of studies aimed at better understanding the mechanism of action of some representatives of this class of compounds. In vitro antiviral profiling revealed that these compounds were active against a narrow spectrum of viruses, essentially the human herpesviruses and type 2 rhinovirus. In HCMV assays, a 39- to 223-fold lower 50% inhibitory concentration was obtained for compound A1 than for ganciclovir against strains AD 169 and Towne. In addition, ganciclovir, foscarnet, cidofovir, and BDCRB (2-bromo-5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole)-resistant HCMV strains remained susceptible to 1,6-naphthyridines and 7, 8-dihydroisoquinolines tested in this study, supporting the view that a novel mechanism of action could be involved. Drug combination studies showed a small but significant synergistic antiviral effect between compound B2 and ganciclovir. Cytotoxicity profiling of representative compounds under various cell growth conditions indicated a generally similar cytotoxic effect, relative to ganciclovir, in log-phase growing cells. However, in stationary cells, a relatively higher level of toxicity was observed than that for control compound. Effect of time of drug addition showed that the anti-HCMV activity of compound A1, ganciclovir, and cidofovir was lost at approximately the same time (72 h postinfection), indicating that the compound was affecting events at the early and late stage of virus replication. This interpretation is also supported by reduction of de novo synthesis of pp65 tegument protein and lack of any effect of the compound on viral adsorption. A reduction of the HCMV enhancer-promoter-directed luciferase expression was also observed in a stably transfected cell line when compound A1 was present at relatively high concentrations.

Antiviral activity of 2'-deoxy-3'-oxa-4'-thiocytidine (BCH-10652) against lamivudine-resistant human immunodeficiency virus type 1 in SCID-hu Thy/Liv mice

Oral administration of 2'-deoxy-3'-oxa-4'-thiocytidine (BCH-10652), a nucleoside analog structurally similar to lamivudine (3TC), caused dose-dependent inhibition of viral replication in SCID-hu Thy/Liv mice infected with human immunodeficiency virus type 1 NL4-3 and with an NL4-3 clone containing the M184V mutation in reverse transcriptase that confers resistance to 3TC. These experiments demonstrate the utility of this mouse model for evaluating drug resistance and for performing direct comparisons between antiviral compounds in vivo.

Stability-activity relationships of a family of G-tetrad forming oligonucleotides as potent HIV inhibitors. A basis for anti-HIV drug design

Recently, we have demonstrated that T30695, a G-tetrad-forming oligonucleotide, is a potent inhibitor of human immunodeficiency virus, type I (HIV-1) integrase and the K(+)-induced loop folding of T30695 plays a key role in the inhibition of HIV-1 integrase (Jing, N., and Hogan, M. E. (1998) J. Biol. Chem. 273, 34992-34999). Here we have modified T30695 by introducing a hydrophobic bulky group, propynyl dU, or a positively charged group, 5-amino dU, into the bases of T residues of the loops, and by substitution of the T-G loops by T-T loops. Physical measurements have demonstrated that the substitution of propynyl dU or 5-amino dU for T in the T residues of the loops did not alter the structure of T30695, and these derivatives also formed an intramolecular G-quartet structure, which is an essential requirement for anti-HIV activity. Measured IC(50) and EC(50) values show that these substitutions did not induce an apparent decrease in the ability to inhibit HIV-1 integrase activity and in the inhibition of HIV-1 replication in cell culture. However, the substitution of T-T loops for T-G loops induced a substantial decrease in both thermal stability and anti-HIV activity. The data analysis of T30695 and the 21 derivatives shows a significant, functional correlation between thermal stability of the G-tetrad structure and the capacity to inhibit HIV-1 integrase activity and between thermal stability of the G-tetrad structure and the capacity to inhibit HIV-1 replication, as assessed with the virus strains HIV-1 RF, IIIB, and MN in cell culture. This relationship between thermostability and activity provides a basis for improving the efficacy of these compounds to inhibit HIV-1 integrase activity and HIV-1 replication in cell culture.

Mechanism of action and in vitro activity of 1',3'-dioxolanylpurine nucleoside analogues against sensitive and drug-resistant human immunodeficiency virus type 1 variants

(-)-Beta-D-1',3'-Dioxolane guanosine (DXG) and 2,6-diaminopurine (DAPD) dioxolanyl nucleoside analogues have been reported to be potent inhibitors of human immunodeficiency virus type 1 (HIV-1). We have recently conducted experiments to more fully characterize their in vitro anti-HIV-1 profiles. Antiviral assays performed in cell culture systems determined that DXG had 50% effective concentrations of 0.046 and 0.085 microM when evaluated against HIV-1(IIIB) in cord blood mononuclear cells and MT-2 cells, respectively. These values indicate that DXG is approximately equipotent to 2', 3'-dideoxy-3'-thiacytidine (3TC) but 5- to 10-fold less potent than 3'-azido-2',3'-dideoxythymidine (AZT) in the two cell systems tested. At the same time, DAPD was approximately 5- to 20-fold less active than DXG in the anti-HIV-1 assays. When recombinant or clinical variants of HIV-1 were used to assess the efficacy of the purine nucleoside analogues against drug-resistant HIV-1, it was observed that AZT-resistant virus remained sensitive to DXG and DAPD. Virus harboring a mutation(s) which conferred decreased sensitivity to 3TC, 2',3'-dideoxyinosine, and 2',3'-dideoxycytidine, such as a 65R, 74V, or 184V mutation in the viral reverse transcriptase (RT), exhibited a two- to fivefold-decreased susceptibility to DXG or DAPD. When nonnucleoside RT inhibitor-resistant and protease inhibitor-resistant viruses were tested, no change in virus sensitivity to DXG or DAPD was observed. In vitro drug combination assays indicated that DXG had synergistic antiviral effects when used in combination with AZT, 3TC, or nevirapine. In cellular toxicity analyses, DXG and DAPD had 50% cytotoxic concentrations of greater than 500 microM when tested in peripheral blood mononuclear cells and a variety of human tumor and normal cell lines. The triphosphate form of DXG competed with the natural nucleotide substrates and acted as a chain terminator of the nascent DNA. These data suggest that DXG triphosphate may be the active intracellular metabolite, consistent with the mechanism by which other nucleoside analogues inhibit HIV-1 replication. Our results suggest that the use of DXG and DAPD as therapeutic agents for HIV-1 infection should be explored.

Anti-human immunodeficiency virus type 1 activity, intracellular metabolism, and pharmacokinetic evaluation of 2'-deoxy-3'-oxa-4'-thiocytidine

The racemic nucleoside analogue 2'-deoxy-3'-oxa-4'-thiocytidine (dOTC) is in clinical development for the treatment of human immunodeficiency virus (HIV) type 1 (HIV-1) infection. dOTC is structurally related to lamivudine (3TC), but the oxygen and sulfur in the furanosyl ring are transposed. Intracellular metabolism studies showed that dOTC is phosphorylated within cells via the deoxycytidine kinase pathway and that approximately 2 to 5% of dOTC is converted into the racemic triphosphate derivatives, which had measurable half-lives (2 to 3 hours) within cells. Both 5'-triphosphate (TP) derivatives of dOTC were more potent than 3TC-TP at inhibiting HIV-1 reverse transcriptase (RT) in vitro. The K(i) values for dOTC-TP obtained against human DNA polymerases alpha, beta, and gamma were 5,000-, 78-, and 571-fold greater, respectively, than those for HIV RT (28 nM), indicating a good selectivity for the viral enzyme. In culture experiments, dOTC is a potent inhibitor of primary isolates of HIV-1, which were obtained from antiretroviral drug-naive patients as well as from nucleoside therapy-experienced (3TC- and/or zidovudine [AZT]-treated) patients. The mean 50% inhibitory concentration of dOTC for drug-naive isolates was 1.76 microM, rising to only 2.53 and 2.5 microM for viruses resistant to 3TC and viruses resistant to 3TC and AZT, respectively. This minimal change in activity is in contrast to the more dramatic changes observed when 3TC or AZT was evaluated against these same viral isolates. In tissue culture studies, the 50% toxicity levels for dOTC, which were determined by using [(3)H]thymidine uptake as a measure of logarithmic-phase cell proliferation, was greater than 100 microM for all cell lines tested. In addition, after 14 days of continuous culture, at concentrations up to 10 microM, no measurable toxic effect on HepG2 cells or mitochondrial DNA replication within these cells was observed. When administered orally to rats, dOTC was well absorbed, with a bioavailability of approximately 77%, with a high proportion (approximately 16.5% of the levels in serum) found in the cerebrospinal fluid.

Achieving antisense inhibition by oligodeoxynucleotides containing N(7)-modified 2'-deoxyguanosine using tumor necrosis factor receptor type 1

Antisense oligodeoxynucleotides (ODNs) are being explored as therapeutic agents for the treatment of many disorders including viral infections, cancers, and inflammatory disorders. In addition, antisense technology can be of great benefit to those attempting to assign function to the multitude of new genes being uncovered in the genomics initiative. However, the demonstration that the gene-regulating effects produced by antisense-designed ODNs are attributable to an antisense mechanism of action requires carefully designed experimentation. Critical to the assignment of an antisense mechanism of action is the availability of nuclease-stable ODNs, inside cells, that have a high binding affinity with the target mRNA and modulate gene functions in a sequence-dependent manner. To help us achieve a goal of sequence-specific antisense activity we designed antisense ODNs containing C(5)-propyne-modified 2'-deoxyuracil and N(7)-propyne-modified 7-deaza-2'-deoxyguanosine bases and partially modified (phosphorothioate) internucleoside linkages. These modified ODNs were found to have enhanced binding affinity to their target mRNA sequences as well as reduced sequence-independent side effects. We used these ODNs to specifically inhibit p55 tumor necrosis factor receptor type 1 expression and tumor necrosis factor alpha-mediated functions in culture assays.

Anti-HIV-1 activities of 1,3-dioxolane guanine and 2,6-diaminopurine dioxolane

DXG and its prodrug DAPD have been demonstrated to be effective inhibitors of HIV-1 in various cells. The EC50s for DXG were 0.032 microM in CBMCs and 0.05 microM in MT-4 cells, which were generally equipotent as 3TC. 3TC-resistant, but not AZT-resistant, HIV-1 had minimum diminished sensitivity to the compounds. Both DXG and DAPD were non-toxic to cells up to 500 microM.

Pyrido [1,2a] indole derivatives identified as novel non-nucleoside reverse transcriptase inhibitors of human immunodeficiency virus type 1

Pyrido [1,2a] indole derivatives were identified as potent inhibitors of human immunodeficiency virus type 1 (HIV-1) replication during a random screening programme. The compounds showed no antiviral activity against HIV-2 or in cells chronically infected with HIV-1, but had good inhibitory effect against purified HIV-1 reverse transcriptase (RT) in an in vitro assay. They were therefore classified as non-nucleoside RT inhibitors (NNRTI). The synthesis of additional compounds of the same class revealed a structure-activity relationship. The most potent compound of the series, BCH-1, had similar antiviral activity to the licensed NNRTI nevirapine against laboratory strains of HIV-1 cultured in cell lines and primary clinical isolates of HIV-1 cultured in peripheral blood mononuclear cells. However, BCH-1 showed greater cytotoxicity, providing a narrow selectivity index in the order of 35. BCH-1 had equivalent antiviral activity against viruses resistant to the nucleoside RT inhibitors zidovudine, didanosine and lamivudine and maintained better activity (less than threefold change in IC50) than nevirapine against viruses resistant to a range of NNRTIs with the single amino acid changes L100I, K103N, E138K or Y181C in the RT. Viruses with single V106A or Y188C amino acid changes showed five- and 10-fold resistance to BCH-1, respectively, in contrast to nevirapine, which had a > 100-fold change in IC50. However, virus with both V106A and Y188C amino acid changes showed higher level resistance (> 15-fold) to BCH-1. Virus with > 10-fold resistance to BCH-1 was rapidly selected for after growth in increasing concentrations of compound and was shown to be cross-resistant to nevirapine. Sequencing of this virus revealed two amino acid changes at positions 179 (V to D) and 181 (Y to C) in the RT. BCH-1 represents a new class of NNRTI, which may act as a lead to identify more selective compounds.

A high throughput colorimetric cell proliferation assay for the identification of human cytomegalovirus inhibitors

A colorimetric assay based on the cleavage of the tetrazolium salt WST-1 has been developed for human cytomegalovirus (HCMV) antiviral susceptibility testing and adapted to a microtiter plate format. Optimal conditions were determined and the standard routine assay was calibrated with a viral input of 0.05-0.10 plaque forming unit (p.f.u.)/cell with a density of 2000 cells/well in a 96-well microtiter plate for an incubation period of 7 days. Ganciclovir (9-(2-hydroxy-1(hydroxymethyl) ethyoxymethyl) guanine; DHPG), and cidofovir ((S)-1-(3-hydroxy-2-phosphonylmethoxypropyl) cytosine; HPMPC) were used as positive control test compounds to validate the assay. The effective EC50 concentration values obtained with the two antiviral compounds in the present assay were in good agreement with plaque reduction assay results performed in parallel experiments. This method presents the advantage of being easy and rapid to perform, reliable, reproducible, and convenient for use in a high throughput screening capacity.

Human immunodeficiency virus glycoprotein gp120 as the primary target for the antiviral action of AR177 (Zintevir)

The human immunodeficiency virus (HIV) inhibitor AR177 (T30177, Zintevir) has been identified as a potent inhibitor of HIV integrase in vitro. The compound is currently the subject of clinical phase I/II trials. However, the primary target for the mechanism of action in vivo has not been identified unequivocally. We have found that AR177 inhibits syncytium formation between MOLT-4 cells and HUT-78 cells persistently infected with the HIV-1IIIB or NL4-3 strain, at a 50% effective concentration of 3 microg/ml, roughly 3-fold higher than the concentration required to inhibit HIV replication. Furthermore, flow cytometric analysis has shown that AR177 at 25 microg/ml interferes with the binding of the monoclonal antibody 9284 (directed to the V3 loop of gp120) on HIVIIIB-infected HUT-78 cells, pointing to inhibition of virus binding or virus fusion as the mechanism of action of AR177. To precisely characterize the site/target of intervention by AR177, we have selected HIV-1 (NL4-3) strains resistant to AR177. The binding of the AR177-resistant strain, unlike the parental HIV-1 NL4-3 strain, could not be inhibited by AR177. The resistant phenotype was associated with the emergence of mutations in the gp120 molecule. DNA sequence analysis revealed the presence of the K148E, Q278H, K290Q, and F391I mutations and a deletion of 5 amino acids (FNSTW) at positions 364-368 in the V4 region of the resistant strain but not of the wild-type HIV strain. Selection of resistant strains, although it takes a relatively long time to develop, may also select for strains with lower replicative capacity. No mutations were found in the integrase enzyme gene. Our data argue against HIV integrase being the primary target for the mechanism of anti-HIV action of AR177.

Convenient approaches to the synthesis of oligonucleotide macrocycles containing non-nucleotide linkers

Two convenient, practical routes to the synthesis of non-nucleotide bridged cyclic oligonucleotides have been developed. The first procedure included circularization of oligonucleotides by template-directed ligation on solid phase, while the second procedure involved preparation of a circular oligomer by non-template chemical ligation of a linear precursor in solution. Using these approaches, a series of single- and double-stranded cyclic oligonucleotides with non-nucleotide bridges has been synthesized.

Thiazolo[4,5-d]pyrimidines. Part II. Synthesis and anti-human cytomegalovirus activity in vitro of certain acyclonucleosides and acyclonucleotides derived from the guanine analogue 5-aminothiazolo[4,5-d]pyrimidine-2,7(3H,6H)-dione

The synthesis and in vitro antiviral activity of certain hydroxyalkoxymethyl, hydroxyalkyl, hydroxyalkenyl and phosphonoalkenyl derivatives of the guanine congener 5-aminothiazolo[4,5-d]pyrimidine-2,7(3H,6H)-dione are reported. The compounds of this study were selected for their structural similarity to acyclonucleosides with known anti-herpesvirus activity. 5-Amino-3-[(Z)-4-hydroxy-2-buten-1-yl]thiazolo[4,5-d]pyrimidine-2, 7(3H,6H)- dione was the only member of the series to display significant in vitro activity against human cytomegalovirus (HCMV); however, this compound did not inhibit other herpesviruses, human immunodeficiency virus type 1 or murine cytomegalovirus. It was found to have a cytotoxicity profile similar to that of ganciclovir (DHPG). The antiviral effect was found to be sensitive to the initial viral input and the time of addition during the virus replication cycle. Significantly, the compound was found to have equal anti-HCMV activity, against standard virus strains, to DHPG, but also showed potent activity against DHPG-resistant virus strains, except for a strain mutated in the UL97 (phosphotransferase) gene.

Potassium-induced loop conformational transition of a potent anti-HIV oligonucleotide

Spectroscopic, thermal denaturation and kinetic studies have revealed that DNA oligonucleotides 5'-d(GGGTGGGTGGGTGGGT) (T30695) and 5'-d(GTGGTGGGTGGGTGGGT) (T30177) from extremely stable intramolecular G-tetrads via a two-step process that involves the binding of one K+ ion to a central pair of G-quartets and two additional K+ ions, presumably, to the loops (Jing et al., (1997) Biochemistry in press). In that these oligonucleotides are potent HIV-1 inhibitors and among the most active HIV-1 integrase inhibitors yet identified, we have sought to further characterize the K(+)-induced folding process for the purpose of rational chemical modification of these anti-HIV agents. Our NMR investigation demonstrates that in the presence of Li+ ions, T30695 forms an unimolecular tetrad fold, stabilized by a pair of syn-anti-syn-anti G-quartets comprising a central core. The NMR spectrum of T30695 as a function of K+ titration reveals a well-defined transition that saturates upon addition of three K+ ions per oligomer. During this process, the initial Li(+)-dependent G-quartet structure converts into a highly symmetrical, stable form (the NMR detected melting transition temperature is increased by approximately 20 degrees C). The conformation of the G-quartet core remains unchanged, while the loosely structured loop residues become organized in a fashion which is stabilized by K+ ion binding and by interactions with the core. To explain these data, we propose a model wherein K+ binding to the loops induces structural rearrangement, to yield a planar array of loop bases in proximity to the underlying G-quartets. By reference to closely related homologues, which lack activity as an HIV-1 or integrase inhibitor, the possibility is discussed that this ion-coordinated loop structure is crucial to the biological activity of T30695.

Mode of interaction of G-quartets with the integrase of human immunodeficiency virus type 1

Oligonucleotides that can form a highly stable intramolecular four-stranded DNA structure containing two stacked guanosine-quartets (G-quartets) have been reported to inhibit the replication of the human immunodeficiency virus type 1 (HIV-1) in cell culture. Two possible mechanisms for the observed antiviral activity have been proposed: interference with virus adsorption to the cell and/or inhibition of HIV-1 integrase. We investigated the molecular interaction of G-quartet-containing oligonucleotides with HIV-1 integrase in comparison with random oligonucleotides and dextran sulfate. The prototypical G-quartet-containing oligonucleotide, T30177 (Zintevir), inhibited the overall integration reaction with an IC50 value of 80 nM. A random oligonucleotide was 10-fold less potent, but dextran sulfate was more potent, with an IC50 value of 7 nM. We developed novel kinetic assays to dissect the overall integration reaction in three steps: the formation of the initial stable complex (ISC), the 3'-processing reaction, and the DNA strand-transfer step. We then analyzed the kinetics of the ISC formation and 3'-processing. The rate constant determined for the conversion of ISC into the cleaved product was 0.08 +/- 0.01 min-1. T30177 did not inhibit 3'-processing or DNA strand transfer, whereas dextran sulfate inhibited DNA strand transfer to some extent. Binding studies using surface plasmon resonance technology revealed that both T30177 and dextran sulfate were capable of preventing the binding of integrase to specific DNA. We propose a model in which the interaction of HIV-1 integrase with G-quartets results in the inhibition of the formation of the ISC between integrase and substrate DNA. Finally, we selected for an HIV-1 strain that was resistant to T30177 in cell culture. DNA sequence analysis revealed mutations in the envelope glycoprotein gp120 but not in the integrase gene. Although gp120 seems to be the main target for the antiviral activity in cell culture of G-quartets, the study of their specific inhibition of HIV-1 integrase may lead to the development of effective integrase inhibitors.

Ion selective folding of loop domains in a potent anti-HIV oligonucleotide

Previously, we have described inhibition of HIV-1 infection by T30177, 5'-(GTGGTGGGTGGGTGGGT)-3', an oligonucleotide that is a potent inhibitor of HIV-1 integrase in vitro (Mazumder et al. (1996) Biochemistry 35, 13762). Here a family of oligonucleotides, analogs of T30177, has been studied. On the basis of thermal denaturation, we show that a folded structure of T30177 is much more stable than that of the thrombin binding aptamer, which only differs with T30177 in the loop sequence. Sequence changes reveal that loop interactions are solely responsible for this observed stability difference. In the presence of K+ ion, the fold of T30695, a designed 16mer derivative, is indeed more stable than T30177. Loop folding within T30695 is very ion selective. Quantitative analysis of thermal denaturation suggests that the loops of T30695, 5'-(GGGTGGGTGGGTGGGT)-3', and T30177 confer the ability to coordinate three equivalents of K+ ion (one bound to the core octet and two bound to the loops); however, the thrombin binding aptamer is shown to bind only one K+ equivalent. Folding kinetics and CD titration demonstrate that K+-induced folding of T30695 and T30177 is a two-step process, consistent with a sequential model in which a first equivalent of K+ binds to the octet core, followed by slow K+-induced rearrangement of the loop domains. Comparing structural stability with the capacity of the folded oligomers to inhibit the HIV-1 integrase enzyme in vitro or HIV-1 infection in cell culture, we have found that the folding and activity data are highly correlated, suggesting that formation of an orderly, ion-coordinated loop structure similar to that in T30177 or T30695 may be a prerequisite for both integrase inhibition and anti-HIV-1 activity.

Sequence-specific inhibition of the tumor necrosis factor-alpha receptor I gene by oligodeoxynucleotides containing N7 modified 2'-deoxyguanosine

Tumor necrosis factor-alpha (TNF-alpha) is a highly pleiotropic cytokine produced mainly by activated macrophages. This cytokine has been found to mediate the growth of certain tumors, the replication of HIV-1, septic shock, cachexia, graft-versus-host disease, and autoimmune diseases. The binding of TNF-alpha to the p55 tumor necrosis factor receptor type I (TNFRI) is considered one of the initial steps responsible for the multiple physiologic effects mediated by TNF-alpha. The role of TNF-alpha as an inflammatory mediator through TNFRI makes both of these genes attractive targets for intervention in both acute and chronic inflammatory diseases. We have designed antisense oligodeoxynucleotides (ODNs) containing chemically modified purine and pyrimidine bases that specifically inhibit TNFRI expression and functions. These ODNs were designed to hybridize to the 3'-polyadenylation signal region of the TNFRI gene. In cell-based assays, gene-specific antisense inhibition occurred in a dose-dependent fashion at submicromolar concentrations in the presence of cellular uptake enhancing agents. Within ODN sets with a common pattern of stabilizing backbone substitution, the inhibition of the gene expression is found to be correlated with the affinity of the ODNs for their cognate mRNA target sites, providing direct evidence for an antisense mechanism of action. In addition, events triggered by the binding of TNF-alpha to TNFRI, such as the production of IL-6 and IL-8, were significantly reduced by treatment of cells with the anti-TNFRI ODN. Therefore, antisense ODNs can be used to control biologic processes mediated by TNF-alpha and may be useful as therapeutic agents to treat conditions resulting from overproduction of TNF-alpha.

Modified antisense oligonucleotides directed against tumor necrosis factor receptor type I inhibit tumor necrosis factor alpha-mediated functions

Tumor necrosis factor alpha (TNF alpha), a polypeptide produced by activated macrophages, is a highly pleiotropic cytokine which elicits inflammatory and immunological reactions. The binding of TNF alpha to tumor necrosis factor receptor type I (TNFRI) is considered the initial step responsible for some of the multiple biological functions mediated by TNF alpha. The role of TNF alpha as an inflammatory mediator through human TNFRI makes TNFRI an attractive target for intervention in both acute and chronic inflammatory diseases. In this study, we have identified partial phosphorothioate oligodeoxyribonucleotides (ODNs) containing C-5 propynyl or hexynyl derivatives of 2'-deoxyuridine which specifically inhibited TNFRI and subsequently inhibited the functions of TNF alpha mediated through TNFRI. The most active ODNs were directed against the 3'-poly adenylation signal site on the TNFRI mRNA, and in a cellular assay, gene-specific antisense inhibition occurred in a dose-dependent fashion at submicromolar concentrations, in the presence of Cellfectin. The inhibition of gene expression correlated with the binding affinity of the ODN for the target mRNA. The ODNs lowered TNFRI protein levels and TNF alpha-mediated functions by specifically reducing levels of TNFRI mRNA. These anti-TNFRI ODNs offer a novel approach for controlling biological functions of TNF alpha and may be useful as human therapeutic agents for treating diseases in which TNF alpha has been implicated.

Effect of beta-enantiomeric and racemic nucleoside analogues on mitochondrial functions in HepG2 cells. Implications for predicting drug hepatotoxicity

A group of enantiomeric nucleoside analogues with beta-D or beta-L configuration, which represent potential candidates for the treatment of hepatitis B virus (HBV) infection, were incubated in human hepatoblastoma HepG2 cells at concentrations between 0.1 and 10 microM for 4-14 days. Then the effect on mitochondrial DNA (mtDNA) content, lactic acid production, lipid droplet formation, and mitochondrial morphology were evaluated. No effect on lactic acid production was detected in cells treated with beta-L-2',3'-dideoxy-3'-thiacytidine (3TC), beta-L-2',3'-dideoxy-5-fluoro-3'-thiacytidine (beta-L-FTC), beta-D-2',3'-dideoxy-5-fluoro-3'-thiacytidine (beta-D-FTC), racemic cis 2',3'-dideoxy-5-fluoro-3'thiacytidine [(+/-)-FTC], and 2,4-diamino-7-(2,3-dideoxy-2-fluoro-beta-D-arabinofuranosyl) pyrrolo[2',3'-d]pyrimidine (T70178), whereas a slight increase was associated with beta-D-2-hydroxymethyl-5-(2,6-diaminopurin-9-yl)-1,3-dixolane++ + (beta-D-DAPD) and 4-amino-7-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)pyrrolo[2,3-d]pyrimi dine -5-thiocarboxamide (T70182) at 10 microM. A concentration-dependent increase in lactic acid production was observed in cells exposed to beta-D-2',3'-dideoxy-3'-thiacytidine [(+)-BCH-189], racemic cis 2',3'-dideoxy-3'-thiacytidine [(+/-)-BCH-189], beta-D-2',3'-dideoxy-5-fluorocytidine (beta-D-FddC), beta-L-2',3'-dideoxy-5-fluorocytidine (beta-L-FddC), beta-D-2-hydroxymethyl-5-(5-fluorocytosin-I-yl)-1,3,-dioxolane (beta-D-FDOC), 2,4-diamino-7-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl) pyrrolo[2,3-d]pyrimidine (T70080), and 4-amino-7-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)pyrrolo [2,3-d]pyrimidine (T70179). Inhibition on mtDNA content was demonstrated to be concentration-dependent with (+)-BCH-189, beta-D-FddC, and T70080, whereas 3TC, (+/-)-BCH-189, beta-L-FTC, beta-D-FTC, (+/-)-FTC, beta-L-FddC, beta-D-DAPD, T70178, T70179, and T70182 had no effect. beta-D-FDOC resulted in a marked inhibition of mtDNA synthesis at 10 microM but not at lower concentrations. Cells treated with 3TC, (+/-)-BCH-189, beta-L-FTC, beta-D-FTC, (+/-)-FTC, beta-L-FddC, beta-D-DAPD, T70178, T70179, and T70182 did not show morphological changes compared with the control. In contrast, increased cytoplasmic lipid droplets associated with a loss of cristae in mitochondria were detected in cells treated with either beta-D-FDOC, beta-D-FddC, or T70080, (+)-BCH-189 treatment resulted in loss of cristae in mitochondria. In summary, 3TC, beta-L-FTC, beta-D-FTC, (+/-)-FTC, beta-D-DAPD, T70178, and T70182 exhibited a relatively safe profile, supporting their further development.

Triple helix-forming oligodeoxyribonucleotides targeted to the human tumor necrosis factor (TNF) gene inhibit TNF production and block the TNF-dependent growth of human glioblastoma tumor cells

Synthetic oligodeoxyribonucleotides (ODNs) designed to selectively inhibit the transcription or translation of specific genes are being used to modulate the activity of the targeted gene. Because multiple copies of mRNA can be transcribed from one actively expressed gene, ODNs that target double-stranded DNA and form triple helices upon binding with the gene itself have an advantage over ODNs that target the gene product (mRNA) in an antisense fashion. For the present studies, we designed four different triple helix-forming phosphodiester ODNs (TFOs) targeted to the tumor necrosis factor (TNF) gene and examined their effect on production of TNF and on cellular growth of tumors in which TNF acts as an autocrine growth factor. The ODNs J-109-50 and J-108-57 were designed to interact with polypurine oligonucleotides corresponding to the binding sites for nuclear factors kB (-237 to -208) and Sp1 (-58 to -33), respectively; J111-51 was designed to interact with a polypurine oligonucleotide in the third intron (+1429 to +1456) of the TNF gene. To enhance the cellular penetration and prevent degradation by cellular nucleases, the TFOs were modified at their 3' ends by either a cholesterol side chain or a propanolamine blocking group. Treatment of the human promonocytic cell line THP-1 with TNF-TFOs at a nontoxic concentration (2 microM) reduced the production of TNF. All of the TNF-TFOs tested were effective, and control-irrelevant TFOs were ineffective in inhibiting TNF production. The activity of the most efficacious TNF-TFOs also correlated with a decrease in TNF mRNA as observed by using reverse transcriptase PCR assays. In several tumors in which TNF acts as an autocrine growth factor, we examined the antiproliferative activity of J111-51. We found that in the human glioblastoma tumor cell line U-251, TNF-induced growth was blocked by J111-51 in a dose-dependent manner. Thus, overall results demonstrate that oligonucleotides directed to the specific regions of TNF can be designed, which may have a potential in cancer therapy.

Inhibition of the human immunodeficiency virus type 1 integrase by guanosine quartet structures

An oligonucleotide (T30177) composed entirely of deoxyguanosine and thymidine has previously been shown to fold upon itself in the presence of potassium into a highly stable four-stranded DNA structure containing two stacked deoxyguanosine quartets (G4s). T30177 also protects host cells from the cytopathic effects of human immunodeficiency virus type 1 (HIV-1). We report that this G4 oligonucleotide is the most potent inhibitor of HIV-1 integrase identified to date, with IC50 values in the nanomolar range. Both the number of quartets formed and the sequence of the loops between the quartets are important for optimal activity. T30177 binds to HIV-1 integrase without being processed and blocks the binding of the normal viral DNA substrate to the enzyme. The normal DNA substrate was not able to compete off T30177 binding to HIV-1 integrase, indicating a tight binding of G4s to the enzyme. Experiments with truncated HIV-1 integrases indicate that the N-terminal region containing a putative zinc finger is required for inhibition by T30177 and that T30177 binds better to full-length or deletion mutant integrases containing the zinc finger region than to a deletion mutant consisting of only the central catalytic domain. The N-terminal region of integrase alone is able to bind efficiently to T30177, but not the linear viral DNA substrate, in the presence of zinc. Hence, G4s represent the first class of compounds that inhibit HIV-1 integrase by interacting with the enzyme N-terminal domain. The greater inhibitory potency of T30177 in buffer containing magnesium versus manganese suggests that divalent metal ion coordination along the phosphodiester backbone may play a role in the inhibitory activity. T30177 inhibited HIV-2 integrase with similar potency as HIV-1 but inhibited feline and simian immunodeficiency virus integrases at higher concentrations, suggesting selectivity can be achieved. We propose that novel AIDS therapies could be based upon guanosine quarters as inhibitors of HIV-1 integrase.

The N-terminal 303 amino acids of the human cytomegalovirus envelope glycoprotein B (UL55) and the exon 4 region of the major immediate early protein 1 (UL123) induce a cytotoxic T-cell response

We reported earlier that an adenovirus (Ad) recombinant expressing the full-length human cytomegalovirus (HCMV) glycoprotein B (gB) gene induces gB-specific cytotoxic T lymphocyte (CTL) responses in CBA (H-2k) mice (Berencsi et al., J. Gen. Virol. 74, 257-2512, 1993). Here we show that mice immunized with Ad recombinant viruses expressing truncated forms of the gB gene containing the first 700 (Ad-700), 465 (Ad-465) or 303 (Ad-303) amino acids of gB or an Ad construct containing exon 4 (E4) of the HCMV immediate early 1 (IEI) gene (Ad-IEI (E4)) demonstrate HCMV-specific CTL responses. These data suggest the importance of the first 303 amino acids of the gB polypeptide and the IEI E4 product in designing a vaccine to induce anti-HCMV CTL responses.

The performance of e23(Fv)PEs, recombinant toxins targeting the erbB-2 protein

The overexpression of the erbB-2 (HER-2, neu) gene has attracted significant interest as a molecular target for the rational design of cancer therapies. This review examines the design and preclinical testing phase for one such experimental therapy, recombinant toxins targeted to the erbB-2 protein, termed e23(Fv)PEs.

Intramolecular G-quartet motifs confer nuclease resistance to a potent anti-HIV oligonucleotide

We have identified a potentially therapeutic anti-human immunodeficiency virus (HIV)-1 oligonucleotide composed entirely of deoxyguanosines and thymidines (T30177, also known as AR177: 5'-g.tggtgggtgggtggg.t-3', where asterisk indicates phosphorothioate linkage). In acute assay systems using human T-cells, T30177 and its total phosphodiester homologue T30175 inhibited HIV-1-induced syncytium production by 50% at 0.15 and 0.3 microM, respectively. Under physiological conditions, the sequence and composition of the 17-mer favors the formation of a compact, intramolecularly folded structure dominated by two stacked guanine quartet motifs that are connected by three loops of TGs. The molecule is stabilized by the coordination of a potassium ion between the two stacked quartets. We now show that these guanine quartet-containing oligonucleotides are highly resistant to serum nucleases, with t1/2 of 5 h and >4 days for T30175 and T30177, respectively. Both oligonucleotides were internalized efficiently by cells, with intracellular concentrations reaching 5-10-fold above the extracellular levels after 24 h of incubation. In contrast, single-base mutated variants or random sequence control oligonucleotides that could not form the compactly folded structure had markedly reduced half-lives (t1/2 from approximately 3 to 7 min), low cellular uptake, and no sequence-specific anti-HIV-1 activity. These data suggest that the tertiary structure of an oligonucleotide is a key determinant of its nuclease resistance, cellular uptake kinetics, and biological efficacy.

Inhibition of episomal hepatitis B virus DNA in vitro by 2,4-diamino-7- (2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-pyrrolo[2,3-d]pyrimidine

The nucleoside analog 2,4-diamino-7-(2-deoxy-2-fluoro-beta-D- arabinofuranosyl)pyrrolo[2,3-d]pyrimidine (T70080) and several related compounds were evaluated for anti-hepatitis B virus (HBV) activity by using cultured 2.2.15 cells. T70080 reduced episomal viral replication in these cells by 50% at a concentration of 0.7 microgram/ml. At the same time, T70080 reduced cellular proliferation by 50% at a concentration in excess of 100 micrograms/ml, yielding a therapeutic index of > 143. In cells cultured for 12 days in the presence of 10 or 50 micrograms of T70080 per ml and then with drug-free medium, for an additional 12 days, viral DNA replication was completely inhibited initially but resumed between 6 and 12 days post-drug removal. In view of the potent anti-HBV activity shown, T70080 is a good candidate for further evaluation as a treatment of human HBV infection.

Synthesis and anti-DNA viral activities in vitro of certain 2,4-disubstituted-7-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)pyrrolo[2,3-d d pyrimidine nucleosides

Several novel 2,4-disubstituted-7-(2-deoxy-2-fluoro-beta-D- arabinofuranosyl)pyrrolo[2,3-d]pyrimidines have been synthesized and evaluated for their anti-human cytomegalovirus (HCMV), anti-hepatitis B virus (HBV), and anti-herpes simplex virus (HSV) activities in vitro. These nucleosides were prepared starting from 2-amino-4-chloro-7-(2-deoxy-2-fluoro- 3,5-di-O-benzoyl-beta-D-arabinofuranosyl)pyrrolo[2,3-d]pyrimidine (3), which in turn was synthesized by direct glycosylation of the sodium salt of 2-amino-4-chloropyrrolo[2,3-d]pyrimidine (1) with 2-deoxy-2-fluoro-3,5-di-O-benzoyl-alpha-D-arabinofuranosyl bromide (2). Displacement of the 4-chloro group of 3 with OH, NH2, NHOH, SH, and SeH nucleophiles furnished the corresponding nucleosides 6-8, 12, and 14, respectively. The 3'-deoxygenation of 2-amino-4-chloro-7- (2-deoxy-2-fluoro-beta-D-arabinofuranosyl)pyrrolo[2,3-d]pyrimidine (4) and subsequent amination gave 2,4-diamino-2',3'-dideoxy derivative 19. Catalytic hydrogenation of 3 followed by debenzoylation afforded 2-aminopyrrolo[2,3-d]pyrimidine nucleoside 23. Among the compounds evaluated for their ability to inhibit the growth of HCMV (strain AD169) in MRC-5 cells using a plaque reduction assay, only 7 was significantly active in vitro with a 50% inhibitory concentration (IC50) of 3.7 micrograms/mL (TI > 125), whereas the IC50 value of ganciclovir (DHPG) was 3.2 micrograms/mL. Strain D16 of HCMV was more resistant to 7 (IC50 11 micrograms/mL) than the AD169 strain. When 7 was tested in combination with DHPG, the resultant anti-HCMV activity was found to be moderately synergistic with no evidence of antagonism. Nucleoside 7 also reduced episomal HBV replication in human hepatoblastoma 2.2.15 cells with an IC50 of 0.7 micrograms/mL (TI > 143). Development of cells harboring HBV which had become resistant to the drug was not observed with 7. Compound 7 also exhibited significant activity against herpes simplex virus types 1 and 2 (IC50 of 4.1 and 6.3 micrograms/mL, respectively) in Vero cells.

Inhibition of high affinity basic fibroblast growth factor binding by oligonucleotides

Oligonucleotides can be used to inhibit the binding of basic fibroblast growth factor to cells. Though standard phosphodiester oligonucleotides show a slight inhibition of binding, the oligonucleotides with phosphorothioate internucleoside linkages have inhibition levels equivalent to that of the polyanion heparin. Variations in sequence of the oligonucleotides does lead to differences in the inhibitory action of the oligonucleotides. This inhibition of basic fibroblast growth factor by phosphorothioate oligonucleotides may account for much of the published data on inhibition of various genes by proposed antisense oligonucleotides and needs to be taken into account when considering the mechanism of action of oligonucleotides in biological systems.

Two-phase approach for the expression of high-affinity human anti-human immunodeficiency virus immunoglobulin Fab domains in Escherichia coli

We describe here a two-phase approach for the development of high-affinity human anti-HIV immunoglobulin Fab domains in a bacterial expression system. The first phase of this technique involves the generation of human hybridoma cell lines producing high-affinity antibodies (MAbs). Anti-HIV-1 human MAbs from peripheral blood lymphocytes (PBLs) were prepared from an HIV-1-seropositive patient and from an HIV-1-seronegative volunteer immunized with HIV-1 rgp160. One MAb (T15G1), derived from the blood of the seropositive donor, was specific for HIV-1 gp41, recognized gp41 on the surface of HIV-1-infected cells and bound this antigen with an apparent dissociation constant of 4 x 10(-10) M. A second MAb (M7B5), developed from the immunized volunteer, was specific for HIV-1 gp120 with a dissociation constant on the order of 8 x 10(-10) M, but was unable to recognize cell surface antigen. In the second phase of this technique the Fab domains of these two MAbs were molecularly cloned into a bacterial expression vector. mRNA was isolated from the M7B5 and T15G1 hybridoma cell lines and used as a template for the production of cDNA. The cDNA was amplified using the polymerase chain reaction (PCR) technique, and then fused, in frame, into a bacterial expression vector. The recombinant Fabs (rFabM7B5 and rFabT15G1) were expressed as dicistronic messages in bacteria using the IPTG-inducible lactose promoter (LacZ). DNA sequencing was used to define the gamma chain isotypes and the VH and VL chain gene usage. The binding specificities of rFabM7B5 and rFabT15G1 were indistinguishable from their respective intact MAbs.(ABSTRACT TRUNCATED AT 250 WORDS)

Suppression of human immunodeficiency virus type 1 activity in vitro by oligonucleotides which form intramolecular tetrads

An oligonucleotide (I100-15) composed of only deoxyguanosine and thymidine was able to inhibit human immunodeficiency virus type-1 (HIV-1) in culture assay systems. I100-15 did not block virus entry into cells but did reduce viral-specific transcripts. As assessed by NMR and polyacrylamide gel methods, I100-15 appears to form a structure in which two stacked guanosine tetrads are connected by three two-base long loops. Structure/activity experiments indicated that formation of intramolecular guanosine tetrads was necessary to achieve maximum antiviral activity. The single deoxyguanosine nucleotide present in each loop was found to be extremely important for the overall antiviral activity. The toxicity of I100-15 was determined to be well above the 50% effective dose (ED50) in culture which yielded a high therapeutic index (> 100). The addition of a cholesterol moiety to the 3' terminus of I100-15 (I100-23) reduced the ED50 value to less than 50 nM (from 0.12 microM for I100-15) and increased the duration of viral suppression to greater than 21 days (versus 7-10 days for I100-15) after removal of the drug from infected cell cultures. The favorable therapeutic index of such molecules coupled with the prolonged suppression of HIV-1, suggest that such compounds further warrant investigation as potential therapeutic agents.

Inhibition of herpes simplex virus in culture by oligonucleotides composed entirely of deoxyguanosine and thymidine

Oligodeoxynucleotides (ODNs) composed entirely of deoxyguanosine and thymidine, but not specifically designed to act as antisense agents, were able to significantly inhibit herpes simplex virus growth in acute infection assay systems. The guanosine/thymidine (GT) ODNs which demonstrated this antiviral activity contained either natural phosphodiester (PO) or phosphorothioate (PS) modified internucleoside linkages. In all experiments, the antiviral activity of the ODNs was enhanced when the backbone was modified to contain the PS linkages. When present during the time of virus addition, the ODNs were able to block the adsorption of virus to Vero cells. In this assay the PS-containing ODNs had ID50 values of approximately 0.020 microM for HSV-2 and of 0.3 microM for HSV-1. When these same PS-containing ODNs were used against HSV-2 in single-cycle viral yield assays, designed to minimize the effects due to external blockage of virus, the ID50 values rose to 0.2 microM. Analysis of viral DNA obtained 14 h post-HSV-2 infections in the single-cycle assay, revealed a decrease in replicated viral DNA in cells treated with PS-ODNs. Analysis of viral mRNA obtained 4 h post-HSV-2 infection revealed, in cells treated with the PS-ODNs, a decrease in measurable HSV-2 alpha- and beta-mRNAs. Although the mechanism of action of the antiviral activity (beyond adsorption blocking) is not fully understood, the toxicity of these compounds was low, giving high therapeutic indices for the GT-rich PS-ODNs. The good therapeutic index of GT-ODNs make this a class of compounds which warrant investigation as therapeutic agents to be used against herpes viruses.

Inhibition of human cytomegalovirus in culture by alkenyl guanine analogs of the thiazolo[4,5-d]pyrimidine ring system

A series of alkyl and alkenyl guanine analogs containing a thiazolo[4,5-d]pyrimidine ring system were prepared by reaction of the appropriate alkyl halide with the sodium salt of the heterocycle. In preliminary antiviral efficacy evaluations against laboratory strains of both human cytomegalovirus (HCMV) and herpes simplex virus types 1 and 2, it was determined that two of the compounds (T70072 and T01132) were more active and less toxic in stationary-phase cell monolayers than were the other derivatives tested. T01132 and T70072, which have 2-pentenyl and 3-methyl-2-butenyl moieties attached to position 3 of the 5-aminothiazolo[4,5-d]pyrimidine-2,7-dione, respectively, were then more extensively evaluated for anti-HCMV activity. The concentrations of T01132 and T70072 required to inhibit HCMV by 50% in plaque reduction assays were approximately 0.5 and 6.8 microM, respectively. These two compounds inhibited the growth of KB, MRC-5, or Vero cells at concentrations of 75 to 150 microM, depending upon the cell line. In bone marrow progenitor cells T01132 was slightly less toxic than ganciclovir (DHPG). The 50% inhibitory concentrations of T01132 against clinical isolates and DHPG-resistant strains of HCMV were approximately the same as those obtained for laboratory strains of HCMV (approximately 0.5 microM). When tested in combination with DHPG, the resultant antiviral activity was determined to be additive but not synergistic. Experiments performed using variations of the viral multiplicity of infection (MOI) demonstrated that T01132 was more active than DHPG at a low MOI (0.002 or 0.02). However, when a higher MOI (0.2 or 2.0) was used, DHPG was more efficacious than T01132. In experiments in which drug was added at various times post-viral infection, T01132 was most effective when added within the first 24 h post-HCMV infection while DHPG was able to protect cells in this assay system when added up to 48 h postinfection, indicating that T01132 is exerting its antiviral effect on events leading up to and possibly including viral DNA synthesis. The data presented in this report suggest that the antiviral activity of alkenyl-substituted thiazolopyrimidine derivatives may represent a mechanism of action against herpesviruses alternative to that of classical nucleoside analogs such as acyclovir or DHPG.

Inhibition of Friend murine leukemia virus activity by guanosine/thymidine oligonucleotides

Oligonucleotides consisting of only deoxyguanosine and deoxythymidine were stable in culture and were able to significantly inhibit Friend Murine Leukemia Virus (FMLV) production in acute cell culture assay systems. The oligonucleotides did not share homology with, or possess any complementary (antisense) sequence motifs to the FMLV genome. The guanosine/thymidine-containing oligonucleotides (GTOs) which demonstrated anti-FMLV activity in acute infection assays were synthesized with natural phosphodiester (PD) linkages (backbones). The observed antiviral activities of these oligonucleotides increased significantly when the PD backbone was replaced with a phosphorothioate (PT) backbone. Experiments designed to investigate a potential antiviral mechanism of action demonstrated that oligonucleotides tested were capable of blocking virus adsorption. In addition, GTOs with PD backbones were competitive inhibitors of FMLV reverse transcriptase (RT). When the same experiments were performed using oligonucleotides with PT backbones, all compounds tested demonstrated significant competitive inhibition of FMLV RT. The measured inhibitory activity of all compounds tested in culture assays was enhanced by at least a factor of 10 when the PD linkages were replaced with PT. The enhanced antiviral activity exhibited by the sulfur group on the oligonucleotide backbone, and the lack of any designed, sequence-specific interactions, suggest that a large percentage of the reported antiviral activity of oligonucleotides containing a phosphorothioate backbone is due to factors other than rationally designed, sequence-specific interactions. The ability of GTOs to inhibit FMLV in culture, potentially via a number of different mechanisms, makes this a class of compounds which warrants investigation as therapeutic agents to be used against retroviral infections.

Early region 3-replacement adenovirus recombinants are less pathogenic in cotton rats and mice than early region 3-deleted viruses

BACKGROUND

Adenovirus type-5 (Ad5) recombinant viruses with replacement of the 1.9 kb XbaI fragment in the early region 3 (E3) by foreign genes have been constructed with the ultimate goal of inducing immune responses to the product of the inserted gene against a variety of virus infections. The pathogenicity of these recombinants, however, has not been studied.

EXPERIMENTAL DESIGN

Histopathologic changes induced in cotton rat and mouse lung by E3-replacement-Ad5 recombinant or wild-type Ad (Wt-Ad) or E3-deleted mutant (Ad5-delta E3) viruses were compared. Expression of viral mRNA and replication of these viruses in cotton rat and mouse lungs, as well as in human tissue culture cells, were assayed. Expression of class I major histocompatibility complex antigens and the E3-14.7 kilodalton protein in virus-infected cells were also analyzed.

RESULTS

An Ad5 recombinant, Ad-human cytomegalovirus glycoprotein B (Ad-HCMV.gB), in which the E3 region is replaced by the full-length gB gene of HCMV and with a genome size exceeding that of Wt-Ad, induced mild histopathologic responses in cotton rat and mouse lungs, comparable with those of Wt-Ad, but less severe than those of Ad5-delta E3. Analysis indicated that neither class I major histocompatibility complex expression on the cell surface nor differential expression of the protective E3-14.7 kilodalton protein underlies the pathologic differences observed in cells infected with Ad5-delta E3 or the Ad-HCMV.gB recombinant. In the mouse lung, another Ad-E3 replacement recombinant, Ad-herpes simplex glycoprotein B (HSV.gB), containing the complete HSV.gB gene and with a genome size larger than that of Wt-Ad, also induced a very mild inflammatory response. However, two recombinants with truncated forms of the HCMV.gB (Ad-HCMV.gB.155) or HSV.gB genes (Ad-HSV.gB.147) produced more severe histopathologic changes than the Wt-Ad or the recombinants with the full complement of HCMV.gB or HSV.gB genes. Ad5 and some of the recombinants replicated in mouse and cotton rat lung, and the extent of replication was inversely proportional to genome size, both in the lung and in human tissue culture cells. Infectious virus titers were, however, higher in cotton rat than in mouse lung. In situ hybridization analysis of cotton rat and mouse lung infected with Wt-Ad, Ad5-delta E3, or Ad-HCMV.gB virus revealed expression of Ad early/late mRNA predominantly in bronchial epithelial cells.

CONCLUSIONS

These data not only confirm that E3-deleted viruses induce more severe pathologic changes in cotton rat lungs than Wt-Ad viruses (Ginsberg et al., Proc Natl Acad Sci USA 1989;86:3823-7) but led to the observation that some E3 replacement recombinants also lacking the expression of the 19 and 14.7 kilodalton proteins are significantly less pathogenic in cotton rats and mice than an E3-deleted virus. Pathogenicity and replication of the recombinant viruses inversely correlate with the genomic size.

Inhibition of human immunodeficiency virus type 1 activity in vitro by oligonucleotides composed entirely of guanosine and thymidine

Oligonucleotide compounds composed of only deoxyguanosine and deoxythymidine were able to significantly inhibit human immunodeficiency virus type -1 (HIV-1)-induced syncytium formation and virus production (as measured by p24 core antigen expression) in an acute infection assay system. The oligonucleotides did not share any homology with or possess any complementary (antisense) sequence motifs to the HIV-1 genome. The guanosine/thymidine-containing oligonucleotides (GTOs) that showed this anti-HIV activity contained natural phosphodiester (PD) linkages (backbones) between the nucleosides. One of the PD oligonucleotide sequence motifs tested was capable of inhibiting HIV-1-induced syncytium formation and p24 production with a median effective dose in culture (ED50) in the submicromolar range. In addition, oligonucleotides tested were able to significantly suppress HIV-1 p24 levels > or = 7 days after removal of the drug from the infected cell culture medium. The growth inhibition properties (toxicity) of this genre of oligonucleotides was determined to be well above the ED50 values yielding high selective indexes. In vitro results showed that GTOs with PD backbones were potent competitive inhibitors of HIV-1 reverse transcriptase. These same molecules were capable of blocking the interaction between gp120 and CD4. All measured activities of these molecules were increased by factors of 10-500 when the PD backbone was replaced with a PT backbone in a sequence-dependent manner. The enhanced antiviral activity displayed by the sulfur group on the oligonucleotide backbone and the lack of any sequence-specific interactions suggest that a percentage of antiviral activity of oligonucleotide-based therapeutics is due to mechanisms other than those originally postulated for oligonucleotides. The good selective index of GTOs coupled with the prolonged suppression of HIV-1 in culture after removal of oligonucleotides from the infected cell culture make this a class of compounds that warrant investigation as therapeutic agents to be used against HIV-1.

Inhibition of T7 and T3 RNA polymerase directed transcription elongation in vitro

A class of oligonucleotides which binds to naturally-occurring duplex DNA sites at physiologic pH to form triple helical structures was used as transcription attenuators in an in vitro transcription assay. Oligonucleotides were designed to form triple helices with a purine-rich, double-stranded target by binding in the major groove in an orientation anti-parallel to the most purine-rich strand of the target. A 45 base-pair purine-rich region located within the gag gene of Friend Murine Leukemia Virus (FMLV) was used as the duplex target. The target DNA was inserted by molecular cloning downstream of either the bacterial T7- or T3 promoter. The sequence-specific interaction of the triple helix-forming oligonucleotide (TFO) with the FMLV target was confirmed by DNAse I footprint analysis. The affinity of the TFO, as measured by the equilibrium dissociation constant of the TFO for the duplex, was determined by band shift analysis. When a TFO was allowed to form a triple helix with the target duplex in well-defined buffer conditions before the transcription reaction, truncated transcripts of a predicted size were observed. Attenuation of transcription was observed only when buffer conditions favorable to triple helix formation were used. In addition, oligonucleotides containing a high percentage of guanosine residues were able to inhibit mRNA production of the bacterial T7 polymerase by a mechanism independent of transcription attenuation. The ability of an oligonucleotide-directed triple helical structure to slow down, or even completely stop, RNA chain elongation may expand the utility of triple helix technology in the area of gene regulation.

Murine cytotoxic T cell response specific for human cytomegalovirus glycoprotein B (gB) induced by adenovirus and vaccinia virus recombinants expressing gB

A murine model of the cytotoxic T lymphocyte (CTL) response to glycoprotein B (gB) of human cytomegalovirus (HCMV) was developed based on the use of adenovirus (Ad) and vaccinia virus (Vac) recombinants expressing gB. Mice of different major histocompatibility haplotypes [CBA (H-2k), BALB/k (H-2k) and BALB/c (H-2d)] infected with the Ad-gB recombinant developed an Ad-specific CTL response. However, only the H-2k mice developed a significant HCMV gB-specific CTL response, as indicated by the major histocompatibility complex class I-restricted lysis of Vac strain Copenhagen (VacC)-gB recombinant-infected target cells by H-2k mouse immune spleen cells. The VacC-gB recombinant elicited only a weak gB-specific CTL response in these mice, indicating that the observed gB-specific CTL response in mice is dependent on the expression vector used for immunization. The gB-specific cytotoxicity observed in H-2k mice was mediated by the CD8 lymphocyte subset.

A recombinant human Fab expressed in Escherichia coli neutralizes rabies virus

A recombinant human anti-rabies monoclonal antibody (MAb-57) Fab was prepared by cloning the heavy (Fd)- and light-chain domains into the same bacterial expression vector. To construct the recombinant Fab, mRNA was extracted from MAb-57-producing hybridoma cells, reverse transcribed, and then amplified by polymerase chain reaction (PCR) by using oligonucleotides specific for immunoglobulin heavy- and light-chain DNA sequences. PCR-amplified Fd-chain cDNA was fused, in frame, between a bacterial leader peptide (PelB) at the amino terminus and a 10-amino-acid peptide tag at the carboxy terminus. The PCR-amplified lambda-chain cDNA was also fused to the PelB leader peptide. The immunoglobulin Fab was then expressed as a dicistronic message in bacteria by using the isopropyl-beta-D-thiogalactopyranoside-inducible lactose promotor (lacZ). DNA sequencing was used to define the gamma-chain isotype (immunoglobulin G1) and VH (VHI) chain and VL (V lambda II) chain gene usage. The recombinant Fab (rFab57) specifically bound the rabies virus coat glycoprotein, while the Fd and lambda chains, when expressed individually, did not. The binding specificity of rFab57 was indistinguishable from that of the intact MAb in direct enzyme-linked immunosorbent assays; however, the dissociation constant of rFab57 for rabies virus protein G was approximately 1 log10 U lower than that of complete MAb-57 in competition enzyme-linked immunosorbent assays. A fluorescent-focus inhibition assay showed that bacterially expressed rFab was capable of neutralizing rabies virus strain CVS-11. We conclude that a human Fab expressed in bacteria maintains its specificity and biologic activity.

Detection of human serum antibodies that neutralize infectious human papillomavirus type 11 virions

A selection of human sera were tested for the presence of antibodies that neutralized infectious human papillomavirus (HPV) type 11. Neutralizing antibodies were detected by prevention of HPV-11-induced condylomatous transformation of human foreskin chips transplanted subrenally into athymic mice. Test sera were obtained from 21 female patients with genital condylomas and eight patients with laryngeal papillomas. Control patients consisted of 57 adult random blood donors and five asymptomatic children. ELISAs demonstrated that all sera from patients with genital papillomas were strongly reactive to disrupted papillomavirus (PV) antigens of HPV-11, bovine PV type 1 and cottontail rabbit PV, but only two were weakly reactive to intact HPV-11. None of the eight sera from the laryngeal papilloma bearers reacted significantly to disrupted PV antigens, but four of the eight showed strong specific responses to intact HPV-11 only. The majority of the sera that were reactive to intact HPV-11 by ELISA neutralized HPV-11 infectivity in the athymic mouse xenograft system. The data indicated that ELISA reactivity to intact HPV-11 virions was a good predictor for the presence of HPV-11 neutralizing antibodies.

The clinical role of human papilloma virus typing

Patients with abnormal Pap smears underwent repeat Pap smear, colposcopy, biopsy, and human papilloma virus (HPV) typing to identify the presence of CIN and to assess the correlation of HPV type to grade of CIN and behavior of CIN. A total of 334 patients underwent evaluation and typing with Southern blot methodology. Fifty-five percent (185) of the patients demonstrated HPV viral sequences; 98 of the 185 positive patients demonstrated HPV types 16, 18. The presence of HPV sequences was not associated with a higher frequency of positive cytology of CIN II or III. High-grade CIN (II or III) was seen in 17.3, 13.5, 13.8, and 10.7% of patients with HPV 16, 18; 6, 11; 31, 33, 35; or no HPV sequences. Of 52 patients with normal cytology and biopsy revealing less than or equal to CIN I, no patients with types 6, 11, 3/5 patients with 31, 33, 35, 3/15 patients with 16, 18, and 2/23 patients with no HPV sequences progressed to greater than or equal to CIN II. These data do not support a role for HPV typing in predicting the initial histology. Typing may be of some value in monitoring patients with low-grade lesions.

Studies on the transmission of viral disease via the CO2 laser plume and ejecta

While recent reports have noted the presence of viral DNA sequences in the laser plume, no significant effort has been made to study transmission of the virus in vivo via airborne laser debris. Studies were undertaken to identify potential hazards to operating room occupants in gynecologic laser surgery. ACO2 laser in the continuous wave mode using a power density of 666 W/cm2 was fired through a 5-cm metal cylinder at virus-infected tissues. Airborne particulate debris, 100-200 microns, was removed from the cylinder's inner surfaces. In one instance, deposition of the debris was found on the surgeon's eyeglasses 1 m from the site of impact despite the use of a smoke evacuator. The first set of studies involved confirmed human papillomavirus (HPV) lesions of the human female lower genital tract. Specimens were collected for electron microscopy and Southern Blot viral hybridization. Additional cervical electron microscopy specimens were recovered from the speculum during pulsed CO2 laser treatment at 13 W average power during conization. Electron microscopy of the vulvar debris revealed only anucleate keratinized squamous epithelial cells. Cervical specimens demonstrated similar cells with nearly instantaneous vaporization of intracellular water and apparent condensation of cellular carbon. HPV Southern Blot testing revealed insufficient quantities of DNA for that technique. The second set of studies involved bovine papillomavirus lesions from dairy cattle. The debris was transmitted to susceptible animals. The bovine studies failed to demonstrate the transmission of disease in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

An adenovirus recombinant that expresses the human cytomegalovirus major envelope glycoprotein and induces neutralizing antibodies

The gene of the human cytomegalovirus (HCMV) major envelope glycoprotein, gB, was cloned from the Towne strain and inserted into adenovirus type 5 downstream of the E3 promoter. The recombinant virus, Ad-gB, expressed antigenically related proteins of 58, 30, 25, and 23 kDa in A549 and MRC-5 cells; the 58-kDa protein had the same mobility as the native gB from HCMV-infected MRC-5 cells and virions. All four proteins were detected by a monospecific polyclonal antiserum and by a monoclonal antibody in immunoblot and immunofluorescence assays. Hamsters infected intranasally with live Ad-gB developed protein-specific and HCMV-neutralizing antibody. This study confirms the importance of gB in the generation of the neutralizing immune response to HCMV and demonstrates the potential of live adenoviruses as vaccine vectors.

Characterization of multiple molecular interactions between human cytomegalovirus (HCMV) and human immunodeficiency virus type 1 (HIV-1)

In transient gene expression assays we observed an increase in expression of the bacterial chloramphenicol acetyl-transferase (CAT) gene, under the transcriptional control of the HIV-1 LTR (pLTR-CAT), when this plasmid was cotransfected into Vero or MRC-5 cells with a plasmid containing either the HCMV immediate early 1 and 2 (E1, IE2) genes (pRL43a) or just the IE2 gene (pMP18). When the HCMV IE1 gene (pMP12) was cotransfected with pLTR-CAT into Vero cells the level of measurable CAT gene activity was below the level observed when pLTR-CAT was cotransfected with a nonspecific carrier plasmid (pGEM3). The negative influence of the HCMV IE1 gene product on the HIV-1 LTR in Vero cells was also observed when the HIV-1 tat gene (pLTR-TAT) was contransfected into Vero cells with pLTR-CAT and pMP12. However, when the HCMV IE1 gene was cotransfected into rhabdomyosarcoma (RD) cells with proviral HIV-1 DNA, an increase in viral production, as monitored by measurement of HIV-1 reverse transcriptase activity, was observed. In electrophoretic mobility shift assays, nuclear extracts obtained 15 hr post-HCMV infection (hpi) were found to contain a lower level of interaction with an oligonucleotide which corresponded to the HIV-1 LTR Sp-1 binding motif. Nuclear extracts obtained 40 hpi of MRC-5 cells had a greater level of interaction with, and changed the mobility of, the Sp-1 oligonucleotide relative to the uninfected nuclear extracts. HCMV-infected MRC-5 cell nuclear extracts also contain a factor(s) which interacted with the HIV-1 LTR between nucleotide positions -15 to -2 relative to the HIV-1 mRNA start site.

Reciprocal enhancement of gene expression and viral replication between human cytomegalovirus and human immunodeficiency virus type 1

Biological interactions between human cytomegalovirus (HCMV) and the human immunodeficiency virus type 1 (HIV-1) were analysed in transfection and infection experiments, carried out in a human osteogenic sarcoma cell line (HOS) and in the same cell line chronically infected with HCMV (E155). When HOS and E155 cells were transfected with recombinant plasmids containing the HIV long terminal repeat (LTR) linked to the bacterial chloramphenicol acetyltransferase (CAT) gene, LTR-directed CAT expression was 20 times higher in E155 cells than in HOS cells. HOS cells co-infected with HCMV and HIV-1 showed enhanced production of the HIV-1 p24 antigen. In reciprocal experiments, an increase in HCMV immediate early gene expression was observed when HCMV-infected HOS cells and E155 cells were either transfected with a recombinant plasmid containing the HIV transactivator gene (pTAT), or when infected with HIV-1. DNA hybridization analysis of E155 and HCMV-infected HOS cells revealed higher levels of HCMV DNA in cells transfected with pTAT than in cells transfected with other non-specific recombinant plasmids. E155 cells transfected with pTAT also produced higher titres of infectious HCMV than control cultures of E155 cells transfected with other recombinant plasmids, including pMTAT carrying a mutant tat gene. The functional reciprocity in vitro between HCMV and HIV is discussed with respect to its possible implications for the clinical development of AIDS.