Immunobiological activity of N-[2-(phosphonomethoxy)alkyl] derivatives of N6-substituted adenines, and 2,6-diaminopurines

Tenofovir disoproxil fumarate/emtricitabine and severity of coronavirus disease 2019 in people with HIV infection

BACKGROUND

Effective, safe, and affordable antivirals are needed for coronavirus disease 2019 (COVID-19). Several lines of research suggest that tenofovir may be effective against COVID-19, but no large-scale human studies with appropriate adjustment for comorbidities have been conducted.

METHODS

We studied HIV-positive individuals on antiretroviral therapy (ART) in 2020 at 69 HIV clinics in Spain. We collected data on sociodemographics, ART, CD4+ cell count, HIV-RNA viral-load, comorbidities and the following outcomes: laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, COVID-19 hospitalization, intensive care unit (ICU) admission and death. We compared the 48-week risks for individuals receiving tenofovir disoproxil fumarate (TDF)/emtricitabine (FTC), tenofovir alafenamide (TAF)/FTC, abacavir (ABC)/lamivudine (3TC), and other regimes. All estimates were adjusted for clinical and sociodemographic characteristics via inverse probability weighting.

RESULTS

Of 51 558 eligible individuals, 39.6% were on TAF/FTC, 11.9% on TDF/FTC, 26.6% on ABC/3TC, 21.8% on other regimes. There were 2402 documented SARS-CoV-2 infections (425 hospitalizations, 45 ICU admissions, 37 deaths). Compared with TAF/FTC, the estimated risk ratios (RR) (95% confidence interval) of hospitalization were 0.66 (0.43, 0.91) for TDF/FTC and 1.29 (1.02, 1.58) for ABC/3TC, the RRs of ICU admission were 0.28 (0.11, 0.90) for TDF/FTC and 1.39 (0.70, 2.80) for ABC/3TC, and the RRs of death were 0.37 (0.23, 1.90) for TDF/FTC and 2.02 (0.88-6.12) for ABC/3TC. The corresponding RRs of hospitalization for TDF/FTC were 0.49 (0.24, 0.81) in individuals ≥50 years and 1.15 (0.59, 1.93) in younger individuals.

DISCUSSION

Compared with other antiretrovirals, TDF/FTC lowers COVID-19 severity among HIV-positive individuals with virological control. This protective effect may be restricted to individuals aged 50 years and older.

Incidence and Severity of COVID-19 in HIV-Positive Persons Receiving Antiretroviral Therapy : A Cohort Study

BACKGROUND

The incidence and severity of coronavirus disease 2019 (COVID-19) among HIV-positive persons receiving antiretroviral therapy (ART) have not been characterized in large populations.

OBJECTIVE

To describe the incidence and severity of COVID-19 by nucleos(t)ide reverse transcriptase inhibitor (NRTI) use among HIV-positive persons receiving ART.

DESIGN

Cohort study.

SETTING

HIV clinics in 60 Spanish hospitals between 1 February and 15 April 2020.

PARTICIPANTS

77 590 HIV-positive persons receiving ART.

MEASUREMENTS

Estimated risks (cumulative incidences) per 10 000 persons and 95% CIs for polymerase chain reaction-confirmed COVID-19 diagnosis, hospitalization, intensive care unit (ICU) admission, and death. Risk and 95% CIs for COVID-19 diagnosis and hospital admission by use of the NRTIs tenofovir disoproxil fumarate (TDF)/emtricitabine (FTC), tenofovir alafenamide (TAF)/FTC, abacavir (ABC)/lamivudine (3TC), and others were estimated through Poisson regression models.

RESULTS

Of 77 590 HIV-positive persons receiving ART, 236 were diagnosed with COVID-19, 151 were hospitalized, 15 were admitted to the ICU, and 20 died. The risks for COVID-19 diagnosis and hospitalization were greater in men and persons older than 70 years. The risk for COVID-19 hospitalization was 20.3 (95% CI, 15.2 to 26.7) among patients receiving TAF/FTC, 10.5 (CI, 5.6 to 17.9) among those receiving TDF/FTC, 23.4 (CI, 17.2 to 31.1) among those receiving ABC/3TC, and 20.0 (CI, 14.2 to 27.3) for those receiving other regimens. The corresponding risks for COVID-19 diagnosis were 39.1 (CI, 31.8 to 47.6), 16.9 (CI, 10.5 to 25.9), 28.3 (CI, 21.5 to 36.7), and 29.7 (CI, 22.6 to 38.4), respectively. No patient receiving TDF/FTC was admitted to the ICU or died.

LIMITATION

Residual confounding by comorbid conditions cannot be completely excluded.

CONCLUSION

HIV-positive patients receiving TDF/FTC have a lower risk for COVID-19 and related hospitalization than those receiving other therapies. These findings warrant further investigation in HIV preexposure prophylaxis studies and randomized trials in persons without HIV.

PRIMARY FUNDING SOURCE

Instituto de Salud Carlos III and National Institutes of Health.

Pre-exposure prophylaxis differentially alters circulating and mucosal immune cell activation in herpes simplex virus type 2 seropositive women

OBJECTIVE

Oral tenofovir-based pre-exposure prophylaxis (PrEP) is an important tool for prevention of new HIV infections, which also reduces subclinical herpes simplex virus type 2 (HSV-2) shedding and symptomatic lesions in HIV-negative, HSV-2-seropositive individuals. However, the impact of PrEP on mucosal immunity has not been examined in detail.

DESIGN

Here we evaluate paired genital tissue and systemic immune profiles to characterize the immunological effects of PrEP in HIV-negative, HSV-2-seropositive African women sexually exposed to HIV.

METHODS

We compared local and systemic innate and T-cell characteristics in samples collected during PrEP usage and 2 months after PrEP discontinuation.

RESULTS

We found that frequencies of cervical CCR5CD4 cells, regulatory T cells, and tissue macrophages were significantly reduced during PrEP use compared with after PrEP discontinuation. In contrast, peripheral blood CD4 and CD8 T cells expressing markers of activation and trafficking were increased during PrEP usage.

CONCLUSION

Together, our data are consistent with PrEP altering immunity differentially in the female genital tract compared with circulation in HSV-2+ women. Further study including comparison with HSV-2 negative women is needed to define the overall impact and mechanisms underlying these effects. These results point to the critical need to study the human mucosal compartment to characterize immune responses to mucosal infections.

Reduced immune activation during tenofovir-emtricitabine therapy in HIV-negative individuals

BACKGROUND

Elevated immune activation is associated with an increased risk of HIV acquisition. Tenofovir (TFV) has immunomodulatory properties in vitro, but how this extends in vivo remains unknown.

METHODS

HIV-negative adults received daily coformulated TFV disoproxil fumarate 300 mg/emtricitabine (FTC) 200 mg for 30 days followed by a 30-day washout. Markers of T-cell activation, inflammation, and cytokines were measured before drug and on days 30 (on drug) and 60 (30-day washout). Data were analyzed using one-way analysis of variance/pairwise comparisons. Intracellular disposition of TFV-diphosphate and FTC-triphosphate in CD4 and CD8 T-cells and monocytes was characterized, and the relationship with immune activation was evaluated using Pearson's correlation coefficient.

RESULTS

T-cell activation was available in 19 participants. CD38/HLA-DR coexpression on CD8 T-cells decreased from baseline to day 30 (3.97% vs. 2.71%; P = 0.03) and day 60 (3.97% vs. 2.41%; P = 0.008). Soluble CD27 decreased from baseline to day 60 (184.1 vs. 168.4 pg/mL; P = 0.001). Cytokines and inflammation markers were not significantly different. TFV-diphosphate and FTC-triphosphate were approximately 4-fold higher in monocytes vs. CD4 and CD8 T-cells but neither correlated with activation markers.

CONCLUSIONS

TFV disoproxil fumarate/FTC therapy was associated with decreased T-cell activation in HIV-negative adults, which could contribute to the antiviral effect of pre-exposure prophylaxis (NCT01040091; www.clinicaltrials.gov).

Solution properties of metal ion complexes formed with the antiviral and cytostatic nucleotide analogue 9-[2-(phosphonomethoxy)ethyl]-2-amino-6-dimethylaminopurine (PME2A6DMAP)

The acidity constants of protonated 9-[2-(phosphonomethoxy)ethyl]-2-amino-6-dimethylaminopurine (H3(PME2A6DMAP)+) are considered, and the stability constants of the M(H;PME2A6DMAP)+ and M(PME2A6DMAP) complexes (M2+ = Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, or Cd2+) were measured by potentiometric pH titrations in aqueous solution (25 °C; I = 0.1 mol/L, NaNO3). In the M(H;PME2A6DMAP)+ species, H+ and M2+ (mainly outersphere) are at the phosphonate group; this is relevant for phosphoryl-diester bridges in nucleic acids because, in the present system, there is no indication for a M2+–purine binding. This contrasts, for example, with the complexes formed by 9-[2-(phosphonomethoxy)ethyl]adenine, M(H;PMEA)+, where M2+ is mainly situated at the adenine residue. Application of log [Formula: see text] vs. [Formula: see text] plots for simple phosph(on)ate ligands, R–PO32− (R being a residue that does not affect M2+ binding), proves that all M(PME2A6DMAP) complexes have larger stabilities than what would be expected for a M2+–phosphonate coordination. Comparisons with M(PME–R) complexes, where R is a noncoordinating residue of the (phosphonomethoxy)ethane chain, allow one to conclude that the increased stability is due to the formation of five-membered chelates involving the ether–oxygen of the –CH2–O–CH2–PO32− residue: the percentages of formation of these M(PME2A6DMAP)cl/O chelates, which occur in intramolecular equilibria, vary between 20% (Sr2+, Ba2+) and 50% (Zn2+, Cd2+), up to a maximum of 67% (Cu2+). Any M2+ interaction with N3 or N7 of the purine moiety, as in the parent M(PMEA) complexes, is suppressed by the (C2)NH2 and (C6)N(CH3)2 substituents. This observation, together with the previously determined stacking properties, offers an explanation why PME2A6DMAP2– has remarkable therapeutic effects.

A novel type of acyclic nucleoside phosphonates derived from 2-(phosphonomethoxy)propanoic acid

A convenient and efficient synthesis of a novel class of acyclic nucleoside phosphonates derived from 2-(phosphonomethoxy)propanoic acid has been developed. The key step of the synthesis is the optimized oxidation of the 3-hydroxy-2-(phosphonomethoxy)propyl (HPMP) analogues to the corresponding 2'-carboxy-PME (CPME) derivatives using the TEMPO/NaClO₂/NaClO oxidizing system. Although (S)-3-(adenin-9-yl)-2-(phosphonomethoxy)propanoic acid ((S)-CPMEA) has been designed as a compound with potential anti-HIV activity, none of the newly prepared CPME analogues exhibited any antiviral activity.

Differential effects of acyclic nucleoside phosphonates on nitric oxide and cytokines in rat hepatocytes and macrophages

Acyclic nucleoside phosphonates (ANP) are virostatics effective against viruses like hepatitis B virus and human immunodeficiency virus. Our previous reports indicated immunomodulatory activities of ANP in mouse and human innate immune cells. Recently, evidence has increased that hepatocytes may play an active role in immune regulation of the liver homeostasis or injury. In this study we investigated possible immunomodulatory effects of ANP on rat hepatocytes and macrophages. Nitric oxide (NO) production and secretion of cytokines (IL-1α, IL-1β, IL-2, IL-4, IL-6, IL-10, IL-13, IL-18, IFN-γ, TNF-α and GM-CSF) were analyzed under in vitro conditions. Test compounds included: 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA; adefovir); 9-[2-(phosphonomethoxy)ethyl]-2,6-diaminopurine (PMEDAP); (R)- and (S)-enantiomers of 9-[2-(phosphonomethoxy)propyl]adenine [(R)-PMPA; tenofovir] and [(S)-PMPA]; 9-[2-(phosphonomethoxy)propyl]-2,6-diaminopurine [(R)-PMPDAP] and [(S)-PMPDAP]. The group of test compounds also included their N(6)-substituted derivatives. Some of ANP which are able to induce NO production and cytokine secretion in cultured macrophages possess the same immunobiological activity in isolated hepatocytes. The extent of responses is in range of LPS/IFN-γ stimulation in both types of cells. The effects of active ANP on NO expression and cytokine secretion are dose- and time-dependent. Interestingly, the spectrum of detected cytokines induced by ANP is broader in hepatocytes. The results also confirm immunomodulatory effects of some ANP on rodent macrophages. Moreover, we demonstrate for the first time immunobiological reactivity of primary rat hepatocytes induced by exogenous ANP compounds. The potential of hepatocytes to synthesize cytokines can contribute to better understanding of liver immune function and can serve for pharmacological intervention in liver diseases.

Immunobiological properties of selected natural and chemically modified phenylpropanoids

Effects of natural and structurally transformed lignans compared with stilbenes or stilbenoids on production of nitric oxide (NO) triggered by lipopolysaccharide (LPS) and interferon-γ (IFN-γ), tested under in vitro conditions using murine resident peritoneal macrophages, are reviewed. Relation between the molecular structure and immunobiological activity was investigated, and implication of substituents, double bond stereochemistry, or cyclic attachments (double bond geometry fixation) was assessed. The focus was on lignans and stilbenoids because they were originally selected for a joint project of common interest to phytochemical and pharmacological investigation and because they represent well interesting and universally attractive groups of polyphenols with a feasible potential for therapeutic or nutraceutic utilization.

The synthesis of the 8-C-substituted 2,6-diamino-9-[2-(phosphonomethoxy)ethyl]purine (PMEDAP) derivatives by diverse cross-coupling reactions

Diisopropyl 8-bromo-2,6-diamino-9-[2-(phosphonomethoxy)ethyl]purine was used as a starting material for the synthesis of the 8-C-substituted 2,6-diamino-9-[2-(phosphonomethoxy)ethyl]purine (PMEDAP) analogues. A systematic screening of diverse cross-coupling reactions was carried out. Stille, Suzuki–Miyaura, Negishi, and Sonogashira cross-couplings, as well as Pd-catalysed reactions with trialkylaluminiums, were employed for the introduction of various alkyl, alkenyl, alkynyl, aryl, and hetaryl substituents to the C-8 position of the 2,6-diaminopurine moiety. In contrast to the potent parent compound PMEDAP, which exhibits potent antiretroviral and antitumor activity, none of the sixteen newly synthesized 8-C-substituted analogues of PMEDAP showed any specific antiviral activity.

Synthesis and antiviral activity of N9-[3-fluoro-2-(phosphonomethoxy)propyl] analogues derived from N6-substituted adenines and 2,6-diaminopurines

An efficient method for the synthesis of N(9)-[3-fluoro-2-(phosphonomethoxy)propyl] (FPMP) derivatives of purine bases has been developed. Both (R)- and (S)-enantiomers of the N(6)-substituted FPMP derivatives of adenine and 2,6-diaminopurine were prepared and their anti-human immunodeficiency virus (HIV) and anti-Moloney murine sarcoma virus (MSV) activity was evaluated. Whereas none of the 6-substituted FPMPA derivatives showed any antiviral activity, several FPMPDAP derivatives had a moderate antiretroviral activity. Moreover, the data obtained from the study of the substrate activity of the active derivatives towards N(6)-methyl-AMP aminohydrolase support the notion that the studied N(6)-substituted FPMPDAP derivatives act as prodrugs of the antiretroviral FPMPG analogues.

Role of tenofovir in the treatment of chronic HBV infection

Nucleoside analogues revolutionized the treatment of chronic HBV infection and have become the most important therapeutic option within the last decade. Currently, the nucleoside analogues lamivudine, telbivudine and entecavir, and the nucleotide analogue adefovir dipivoxil, are licensed. Tenofovir disoproxil fumarate (TDF) is another acyclic nucleotide analogue that has been successfully used in the treatment of HIV-infected patients, but has demonstrated significant antiviral activity in wild-type and lamivudine-resistant HBV infections. The use of TDF 300 mg/day leads to marked suppression of HBV replication below the detection limit in different patients groups with HBV mono- or HIV/HBV co-infection in most instances, and a remarkably high rate of hepatitis B e antigen loss and even hepatitis B surface antigen loss was found in small, uncontrolled studies. Belonging to the substance class of acyclic nucleotide analogues, TDF is not cross-resistant to nucleoside analogue resistance-associated mutations. In equal dosages, TDF has comparable antiviral potency as compared with its congender adefovir dipivoxil, but in clinical studies exhibits higher antiviral efficacy and generates a higher genetic barrier against the development of genotypic HBV resistance due to its approximately 24-fold higher dosage. Owing to the numerous newly developed compounds and as a consequence of the emerging problem of drug resistance, treatment concepts for chronic hepatitis B will certainly be modified in the future. Because of its quite favorable antiviral and safety properties, TDF will likely be highly regarded in the management of HBV infections in the future.

Inhibitor of sarco-endoplasmic reticulum Ca2+-ATPase thapsigargin stimulates production of nitric oxide and secretion of interferon-gamma

Thapsigargin is a sesquiterpene lactone of guaianolide type isolated from the Mediterranean plant Thapsia garganica L. It is widely used experimentally as a potent and selective inhibitor of sarco-endoplasmic reticulum Ca2+-ATPase (SERCA) leading to rapid elevation of intracellular calcium [Ca2+]i. Several previous reports have shown that thapsigargin interferes with production of nitric oxide (NO) by mouse peritoneal macrophages and mouse macrophage cell lines. The present data confirm that thapsigargin is a modest inducer of NO in mouse macrophages, production of NO being slightly enhanced by lipopolysaccharide. However, thapsigargin on its own very potently induces NO in macrophages of rats under conditions in vitro. The highest effect was observed after the concentration of 0.25 microM thapsigargin, producing approximately 30 microM accumulation of nitrites in supernatants of cells cultured for 24 h. The aim of our experiments was to investigate immune mechanisms implicated in activation of high-output NO biosynthesis. It has been found that thapsigargin dose-dependently induces secretion of interferon-gamma (IFN-gamma) in macrophages of both rats and mice, and also in human peripheral blood mononuclear cells. The IFN-gamma production was rather low in macrophages of mice while relatively very high levels of IFN-gamma were found in cultures of rat macrophages and human peripheral blood mononuclear cells. The concentration of IFN-gamma produced by 5 microM thapsigargin within the interval of 24 h exceeded 3 ng/ml in rat macrophages and approached 2 ng/ml in cultures of human peripheral blood mononuclear cells. The effects are mediated by mitogen-activated protein kinases (MAPKs) such as p38 mitogen-activated protein kinase (p38) and extracellular signal-regulated kinases 1/2 (ERK1/2), and by nuclear transcriptional factor NF-kappaB. In summary, the original findings demonstrate immunostimulatory potential of thapsigargin and warrant more detailed preclinical studies.

Nitric oxide production in mouse and rat macrophages: A rapid and efficient assay for screening of drugs immunostimulatory effects in human cells

Activation of inducible nitric oxide (NO) synthase (iNOS) and resulting high-output NO release is known to depend on the action of cytokines. We investigated in vitro production of NO by resident peritoneal macrophages from mice and rats, and secretion of cytokines by these cells as well as by human peripheral blood mononuclear cells (PBMC). The cells were cultured in the presence of a selected group of acyclic nucleoside phosphonates that have previously been shown to possess immunobiological potential. Several of the compounds enhanced production of NO in animal macrophages. This activity was associated with stimulatory effects on secretion of cytokines such as TNF-alpha in all mouse and rat macrophages and human PBMC, and IL-10 in mouse and human cells. Statistically highly significant correlation between the range of NO biosynthesis in rodent cells and extent of cytokine stimulation in human PBMC has been observed. It is suggested that the NO assay may be regarded as an efficient, economical and relatively reliable tool in primary screening for intrinsic immunostimulatory activity of compounds in human cell system, at least from the point of view of cytokine secretion.

Secretion of antiretroviral chemokines by human cells cultured with acyclic nucleoside phosphonates

Acyclic nucleoside phosphonates are novel class of clinically broadly used antivirotics effective against replication of both DNA viruses and retroviruses including human immunodeficiency virus (HIV). We have investigated their in vitro effects on immune defence mechanisms in human peripheral blood mononuclear cells, with the main emphasis on expression of cytokines which are able to suppress the entry of HIV in cells. Included in the study were prototype acyclic nucleoside phosphonates, i.e. 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA; adefovir), 9-[2-(phosphonomethoxy)ethyl]-2,6-diaminopurine (PMEDAP), (R)-and (S)-enantiomers of 9-[2-(phosphonomethoxy)propyl]adenine [(R)-PMPA; tenofovir] and [(S)-PMPA], and of 9-[2-(phosphonomethoxy)propyl]-2,6-diaminopurine [(R)-PMPDAP] and [(S)-PMPDAP], and their N(6)-substituted derivatives. Some of the compounds were found to substantially enhance secretion of chemokines such as macrophage inflammatory protein-1alpha (MIP-alpha/CCL3), and "regulated on activation of normal T cell expressed and secreted" (RANTES/CCL5). Secretion of MIP-1beta/CCL4 was only marginally increased, whereas production of interleukin-16 (IL-16) and interferon-gamma (IFN-gamma) remained uninfluenced. The most effective proved to be the N(6)-cyclooctyl-PMEDAP, N(6)-isobutyl-PMEDAP, N(6)-pyrrolidino-PMEDAP, N(6)-cyclopropyl-(R)-PMPDAP, and N(6)-cyclopentyl-(R)-PMPDAP derivatives. Remarkably enhanced secretion of chemokines was reached within 2-4 h of the cell culture, and was observed at concentration of 2-5 microM. It may be suggested that acyclic nucleoside phosphonates represent a new generation of antivirotics with combined antimetabolic and therapeutically prospective immunostimulatory properties.

Acyclic nucleoside phosphonate antivirals activate gene expression of monocyte chemotactic protein 1 and 3

Acyclic nucleoside phosphonates are potent antiviral agents effective against replication of DNA viruses and retroviruses including human immunodeficiency virus (HIV). In addition to their antimetabolic mode of antiviral action, acyclic nucleoside phosphonates also possess immunomodulatory properties. We have shown recently that a number of them stimulate secretion of cytokines including chemokines RANTES/CCL5 ("regulated upon activation, normal T cell expressed and secreted") and MIP-1 alpha/CCL3 (macrophage inflammatory protein-1 alpha) that may inhibit entry of HIV in cells. In present experiments we analyzed effects of acyclic nucleoside phosphonates on gene expression of other members of the beta family of chemokines, monocyte chemotactic proteins (MCPs), which have also been implicated in the control of HIV infection. The following compounds differing at the type of heterocyclic base, i.e. adenine (A), or 2,6-diaminopurine (DAP), at the 6-amino group of the base, and at the N ( 9 )-side chain represented by 9-[2-(phosphonomethoxy)ethyl] (PME) and 9-[2-(phosphonomethoxy)propyl] (PMP) moieties were included in the study: (1) (R)-PMPA, ie. tenofovir, (2) N ( 6 )-cyclopropyl-(R)-PMPDAP, (3) N ( 6 )-cyclopentyl-(R)-PMPDAP, (4) N ( 6 )-dimethylaminoethyl-(R)-PMPDAP, (5) N ( 6 )-cyclopentyl-PMEDAP, (6) N ( 6 )-isobutyl-PMEDAP, (7) N ( 6 ) -cyclohexylmetyl-PMEDAP, and (8) N ( 6 ) -cyclooctyl-PMEDAP. These compounds are able to activate production of MCP-1 and MCP-3, and none of them influences gene expression of MCP-2, and MCP-5. Enhancement of monocyte chemotactic protein expression was found to be mediated by transcriptional factor nuclear factor-kappaB (NF-kappaB).

Antiviral acyclic nucleoside phosphonates structure activity studies

This review concerns acyclic nucleoside phosphonates (ANP) and describes the concept of the design of isopolar and isosteric nucleotide analogues resistant towards degradation by enzymes in vivo. It describes the development of research which led to the discovery of several structurally related potent antivirals and ultimately resulted in the development of drugs directed against HIV, HBV and DNA-virus infections in general, namely adefovir, cidofovir and tenofovir. In addition to these "classical compounds" the review describes the present development in the field of ANP, the "open-ring ANP" and discusses the present achievements, concept of prodrug design and application.

Nucleotide analogues with immunobiological properties: 9-[2-Hydroxy-3-(phosphonomethoxy)propyl]-adenine (HPMPA), -2,6-diaminopurine (HPMPDAP), and their N6-substituted derivatives

Newly developed acyclic nucleoside phosphonates, derivatives of adenine and 2,6-diaminopurine bearing the 2-hydroxy-3-(phosphonomethoxy)propyl (HPMP) moiety at the N9-side chain (i.e., HPMPA and HPMPDAP, respectively) were screened for in vitro immunobiological activity, using mouse resident peritoneal macrophages and splenocytes. Both HPMPA and HPMPDAP augmented the interferon-gamma-triggered production of NO as well as expression of inducible nitric oxide synthase (iNOS) mRNA in macrophages. HPMPDAP activated secretion of tumor necrosis factor-alpha (TNF-alpha), chemokines "regulated-upon-activation, normal T cell expressed and secreted" (RANTES) and macrophage inflammatory protein-1alpha (MIP-1alpha), and marginally also secretion of interleukin-10 (IL-10) in both macrophages and splenocytes. The HPMPA, less prominently than HPMPDAP, elevated only secretion of RANTES and TNF-alpha. The compounds also activated secretion of TNF-alpha (HPMPDAP > HPMPA) in human peripheral blood mononuclear cells (PBMC). Distinct N6-substituted derivatives, i.e., N6-dimethyl-, N6-cyclopropyl-, N6-piperidin-1-yl-, N6-(2-methoxyethyl)-, N6-(2-hydroxyethyl)-, N6-allyl- and N6-2-(dimethylamino)ethyl-HPMPA/HPMPDAP as well as 6-thio and 6-hydroxy derivatives usually showed loss of the activity compared to the parent compounds. The immunomodulatory effects were found to be at least in part dependent on P1 purinoreceptors, and mediated by transcriptional factor nuclear factor-kappaB.

Direct Cyclopropanation of 1-Alkynylphosphonates by Cp2ZrCl2/2EtMgBr/2AlCl3 To Afford Cyclopropylmethylphosphonates

[reaction: see text] The reagent system Cp2ZrCl2/2EtMgBr/2AlCl3 converts 1-alkynylphosphonates into cyclopropylmethylphosphonates 3 in good isolated yields. Ethers, chlorides, and other cyclopropyl groups are compatible with the reaction conditions. Deuterium labeling is consistent with the formation of stable cyclopropylmethylbimetallic phosphonates by ring contraction of the corresponding aluminacyclopentenylphosphonate. Temperature is crucial; apparently, the cyclopropylmethylbimetallic phosphonates are in equilibrium with the aluminacyclopentenylphosphonates. Low temperature favors the former. We surmise that the negative charges of the intermediate are stabilized by the phosphonate group. Thus, diphenylacetylene and 3-hexyne failed to give cyclopropyl products under the same reaction conditions.

Purine P1 receptor-dependent immunostimulatory effects of antiviral acyclic analogues of adenine and 2,6-diaminopurine

Acyclic nucleoside phosphonates are widely recognised antivirals. The oral prodrugs of prototype compounds, e.g., 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA; adefovir), and 9-(R)-[2-(phosphonomethoxy)propyl]adenine [(R)-PMPA; tenofovir] were approved by FDA for treatment of hepatitis B (Hepsera), and acquired immunodeficiency syndrome (AIDS) (Viread), respectively. A number of acyclic nucleoside phosphonates possess immunostimulatory activity. The present experiments demonstrate that activation of cytokine and chemokine secretion is mediated by adenosine receptors. Included in the study were 9-(R)-[2-(phosphonomethoxy)propyl]adenine [tenofovir], N(6)-cyclopentyl-(R)-9-[2-(phosphonomethoxy)propyl]-2,6-diaminopurine, N(6)-cyclopropyl-(R)-9-[2-(phosphonomethoxy)propyl]-2,6-diaminopurine, and N(6)-isobutyl-9-[2-(phosphonomethoxy)ethyl]-2,6-diaminopurine. All of them activate secretion of tumor necrosis factor-alpha (TNF-alpha), interleukin-10 (IL-10), "regulated on activation of normal T cell expressed and secreted" (RANTES/CCL5), and macrophage inflammatory protein-1alpha (MIP-1alpha/CCL3) in murine macrophages. With exception of MIP-1alpha, the effects were inhibited by antagonists of adenosine A(1), A(2B), and A(3) receptors (not by adenosine A(2A) receptor antagonist). The adenosine A(1) receptor antagonist inhibited TNF-alpha, IL-10, and RANTES, adenosine A(2B) receptor antagonist inhibited TNF-alpha and RANTES, and adenosine A(3) receptor antagonist inhibited IL-10 and RANTES. The suppression is due to decreased transcription of cytokine mRNA. It may be suggested that acyclic nucleoside phosphonates are nonspecific ligands for purine P(1) receptors.

Cytotoxicity of pivoxil esters of antiviral acyclic nucleoside phosphonates: adefovir dipivoxil versus adefovir

Biological effectiveness of antiviral acyclic nucleoside phosphonate adefo vir, 9-[2-(phosphonomethoxy)ethy]ade nine (PMEA) and its more lipophilic (bis)pivaloyloxymethyl ester prodrug adefovir dipivoxil (bis-POM-PMEA) were compared under in vitro conditions in mammalian cell systems. Proliferation of murine splenocytes was inhibited in a concentration-dependent manner, the bis-POM-PMEA being more effective than PMEA. In contrast to PMEA, bis-POM-PMEA inhibited production of nitric oxide (NO) in macrophages activated with interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS). Viability of both splenocytes and macrophages remained uninfluenced by PMEA, whereas pronounced cytocidal effects were exhibited by bis-POM-PMEA. The IC(50)s reached the values of 15 microM and 30 microM in cultures of macrophages and splenocytes, respectively (assayed at the interval of 24 hrs). The effects could partly be mimicked by formaldehyde, a decomposition product of the pivoxil moiety of bis-POM-PMEA. The other possible product, pivalic acid, was ineffective in this respect. The present data are consistent with the view that pivoxil prodrug of PMEA, bis-POM-PMEA possesses enhanced but also broader spectrum of biological effects than the parent compound.

Synthesis of 9-alkyl and 9-heteroalkyl substituted 2-amino-6-guanidinopurines and their influence on the NO-production in macrophages

9-Alkyl and 9-heteroalkyl substituted derivatives of the 2-amino-6-guanidinopurine were synthesized by alkylation of 2-amino-6-chloropurine and subsequent guanidinolysis. The activity of the thus prepared compounds on murine macrophages was examined. Compounds 4a, 4b, and 4d inhibit the LPS+IFN-gamma-induced NO production in murine macrophages while compound 4h stimulates this production.

Involvement of adenosine A1 receptors in upregulation of nitric oxide by acyclic nucleotide analogues

Acyclic nucleoside phosphonates are a novel class of virostatics effective against replication of both DNA-viruses and retroviruses. They are synthetic analogues of natural nucleotide monophosphates, and purine derivatives thus represent counterparts of AMP. Mono- and di-phosphorylated species are analogues of natural ADP and ATP, respectively. A number of these compounds are endowed with immunostimulatory and immunomodulatory potential. We investigated whether their augmenting effect on the interferon-gamma-primed production of nitric oxide (NO) by murine macrophages is mediated by purinoceptors. The test compounds comprise alterations at the N(6)-group of the heterocyclic base, i.e., adenine or 2,6-diaminopurine, and at the N(9)-side chain, represented by 9-[2-(phosphonomethoxy)ethyl] and 9-[2-(phosphonomethoxy)propyl] moieties: 9-[2-(phosphonomethoxy)propyl]adenine [(R)-PMPA; tenofovir], N(6)-cyclopropyl-(R)-9-[2-(phosphonomethoxy)propyl]2,6-diaminopurine [N(6)-cyclopropyl-(R)-PMPDAP], N(6)-cyclopentyl-(R)-9-[2-(phosphonomethoxy)propyl]2,6-diaminopurine [N(6)-cyclopentyl-(R)-PMPDAP], N(6)-dimethylaminoethyl-(R)-9-[2-(phosphonomethoxy)propyl]2,6-diaminopurine [N(6)-dimethylaminoethyl-(R)-PMPDAP], N(6)-isobutyl-9-[2-(phosphonomethoxy)ethyl]2,6-diaminopurine (N(6)-isobutyl-PMEDAP), N(6)-cyclopentyl-9-[2-(phosphonomethoxy)ethyl]2,6-diaminopurine (N(6)-cyclopentyl-PMEDAP), N(6)-cyclooctyl-9-[2-(phosphonomethoxy)ethyl]2,6-diaminopurine (N(6)-cyclooctyl-PMEDAP), and N(6)-cyclohexylmethyl-9-[2-(phosphonomethoxy)ethyl]2,6-diaminopurine (N(6)-cyclohexylmethyl-PMEDAP). The cells were cultured in the presence of interferon-gamma (5000 pg/ml) and test compounds (2-50 microM). Formation of nitrites was determined after 24 h using Griess reagent. It was inhibited by specific and nonspecific antagonists of adenosine A(1) receptors (IC(50) for 8-cyclopentyl-1,3-dipropylxanthine [CPX] was approximately 10 microM), while all other purine P(1) and purine P(2) receptor antagonists remained ineffective to suppress the NO-synergistic effect of acyclic nucleoside phosphonates.

Tenofovir primes rhesus macaque cells in vitro for enhanced interleukin-12 secretion

We investigated if the antiviral drug tenofovir has immunomodulatory effects in macaques, similar to those described in murine models. While in vivo experiments were complicated by high individual and temporal variability of immune parameters, tenofovir primed macaque peripheral blood mononuclear cells in vitro for enhanced IL-12 secretion following exposure to bacterial antigens.

CD8+-cell-mediated suppression of virulent simian immunodeficiency virus during tenofovir treatment

The ability of tenofovir to suppress viremia in simian immunodeficiency virus (SIV)-infected macaques for years despite the presence of virulent viral mutants with reduced in vitro susceptibility is unprecedented in this animal model. In vivo cell depletion experiments demonstrate that tenofovir's ability to suppress viremia during acute and chronic infection is significantly dependent on the presence of CD8+ lymphocytes. Continuous tenofovir treatment was required to maintain low viremia. Although it is unclear whether this immune-mediated suppression of viremia is linked to tenofovir's direct antiviral efficacy or is due to independent immunomodulatory effects, these studies prove the concept that antiviral immune responses can play a crucial role in suppressing viremia during anti-human immunodeficiency virus drug therapy.