Phosphorothioate 2' deoxyribose oligomers as microbicides that inhibit human immunodeficiency virus type 1 (HIV-1) infection and block Toll-like receptor 7 (TLR7) and TLR9 triggering by HIV-1

Modulation of the Innate Immune Response by Targeting Toll-like Receptors: A Perspective on Their Agonists and Antagonists

Toll-like receptors (TLRs) are a class of proteins that recognize pathogen-associated molecular patterns (PAMPs) and damaged-associated molecular patterns (DAMPs), and they are involved in the regulation of innate immune system. These transmembrane receptors, localized at the cellular or endosomal membrane, trigger inflammatory processes through either myeloid differentiation primary response 88 (MyD88) or TIR-domain-containing adapter-inducing interferon-β (TRIF) signaling pathways. In the last decades, extensive research has been performed on TLR modulators and their therapeutic implication under several pathological conditions, spanning from infections to cancer, from metabolic disorders to neurodegeneration and autoimmune diseases. This Perspective will highlight the recent discoveries in this field, emphasizing the role of TLRs in different diseases and the therapeutic effect of their natural and synthetic modulators, and it will discuss insights for the future exploitation of TLR modulators in human health.

Highly atom-economical, catalyst-free, and solvent-free phosphorylation of chalcogenides

Silica gel promoted, catalyst-free and solvent-free S-P, Se-P and Te-P bond formations are described. A variety of disulfides coupled with diarylphosphine oxides provide the corresponding phosphinothioates in excellent yields. For the first time, diselenides and ditellurides reacted with dialkyl phosphites under catalyst-free conditions to provide the corresponding phosphoroselenoates and phosphorotelluroates, respectively, in good to excellent yields.

Recent advances in photocatalytic C–S/P–S bond formation via the generation of sulfur centered radicals and functionalization

In this review, we have focused on the recent advances in photocatalytic C–S/P–S bond formation via the generation of thioyl/sulfonyl radicals and further functionalization.

Visible light photoredox catalyzed thiophosphate synthesis using methylene blue as a promoter

A novel efficient method for the synthesis of thiophosphate derivatives catalyzed by methylene blue with blue light irradiation under an air atmosphere is described.

Cs2 CO3 -Catalyzed Aerobic Oxidative Cross-Dehydrogenative Coupling of Thiols with Phosphonates and Arenes

An efficient Cs₂ CO₃ -catalyzed oxidative coupling of thiols with phosphonates and arenes that uses molecular oxygen as the oxidant is described. These reactions provide not only a novel alkali metal salt catalyzed aerobic oxidation, but also an efficient approach to thiophosphates and sulfenylarenes, which are ubiquitously found in pharmaceuticals and pesticides. The reaction proceeds under simple and mild reaction conditions, tolerates a wide range of functional groups, and is applicable to the late-stage synthesis and modification of bioactive molecules.

Azasugar-containing phosphorothioate oligonucleotide (AZPSON) DBM-2198 inhibits human immunodeficiency virus type 1 (HIV-1) replication by blocking HIV-1 gp120 without affecting the V3 region

DBM-2198, a six-membered azasugar nucleotide (6-AZN)-containing phosphorothioate (P = S) oligonucleotide (AZPSON), was described in our previous publication [Lee et al. (2005)] with regard to its antiviral activity against a broad spectrum of HIV-1 variants. This report describes the mechanisms underlying the anti-HIV-1 properties of DBM-2198. The LTR-mediated reporter assay indicated that the anti-HIV-1 activity of DBM-2198 is attributed to an extracellular mode of action rather than intracellular sequence-specific antisense activity. Nevertheless, the antiviral properties of DBM-2198 and other AZPSONs were highly restricted to HIV-1. Unlike other P = S oligonucleo-tides, DBM-2198 caused no host cell activation upon administration to cultures. HIV-1 that was pre-incubated with DBM-2198 did not show any infectivity towards host cells whereas host cells pre-incubated with DBM-2198 remained susceptible to HIV-1 infection, suggesting that DBM-2198 acts on the virus particle rather than cell surface molecules in the inhibition of HIV-1 infection. Competition assays for binding to HIV-1 envelope protein with anti-gp120 and anti-V3 antibodies revealed that DBM-2198 acts on the viral attachment site of HIV-1 gp120, but not on the V3 region. This report provides a better understanding of the antiviral mechanism of DBM-2198 and may contribute to the development of a potential therapeutic drug against a broad spectrum of HIV-1 variants.

Abasic phosphorothioate oligomers inhibit HIV-1 reverse transcription and block virus transmission across polarized ectocervical organ cultures

In the absence of universally available antiretroviral (ARV) drugs or a vaccine against HIV-1, microbicides may offer the most immediate hope for controlling the AIDS pandemic. The most advanced and clinically effective microbicides are based on ARV agents that interfere with the earliest stages of HIV-1 replication. Our objective was to identify and characterize novel ARV-like inhibitors, as well as demonstrate their efficacy at blocking HIV-1 transmission. Abasic phosphorothioate 2' deoxyribose backbone (PDB) oligomers were evaluated in a variety of mechanistic assays and for their ability to inhibit HIV-1 infection and virus transmission through primary human cervical mucosa. Cellular and biochemical assays were used to elucidate the antiviral mechanisms of action of PDB oligomers against both lab-adapted and primary CCR5- and CXCR4-utilizing HIV-1 strains, including a multidrug-resistant isolate. A polarized cervical organ culture was used to test the ability of PDB compounds to block HIV-1 transmission to primary immune cell populations across ectocervical tissue. The antiviral activity and mechanisms of action of PDB-based compounds were dependent on oligomer size, with smaller molecules preventing reverse transcription and larger oligomers blocking viral entry. Importantly, irrespective of molecular size, PDBs potently inhibited virus infection and transmission within genital tissue samples. Furthermore, the PDB inhibitors exhibited excellent toxicity and stability profiles and were found to be safe for vaginal application in vivo. These results, coupled with the previously reported intrinsic anti-inflammatory properties of PDBs, support further investigations in the development of PDB-based topical microbicides for preventing the global spread of HIV-1.

Type I interferon upregulates Bak and contributes to T cell loss during human immunodeficiency virus (HIV) infection

The role of Type I interferon (IFN) during pathogenic HIV and SIV infections remains unclear, with conflicting observations suggesting protective versus immunopathological effects. We therefore examined the effect of IFNα/β on T cell death and viremia in HIV infection. Ex vivo analysis of eight pro- and anti-apoptotic molecules in chronic HIV-1 infection revealed that pro-apoptotic Bak was increased in CD4+ T cells and correlated directly with sensitivity to CD95/Fas-mediated apoptosis and inversely with CD4+ T cell counts. Apoptosis sensitivity and Bak expression were primarily increased in effector memory T cells. Knockdown of Bak by RNA interference inhibited CD95/Fas-induced death of T cells from HIV-1-infected individuals. In HIV-1-infected patients, IFNα-stimulated gene expression correlated positively with ex vivo T cell Bak levels, CD95/Fas-mediated apoptosis and viremia and negatively with CD4+ T cell counts. In vitro IFNα/β stimulation enhanced Bak expression, CD95/Fas expression and CD95/Fas-mediated apoptosis in healthy donor T cells and induced death of HIV-specific CD8+ T cells from HIV-1-infected patients. HIV-1 in vitro sensitized T cells to CD95/Fas-induced apoptosis and this was Toll-like receptor (TLR)7/9- and Type I IFN-dependent. This sensitization by HIV-1 was due to an indirect effect on T cells, as it occurred in peripheral blood mononuclear cell cultures but not purified CD4+ T cells. Finally, peak IFNα levels and viral loads correlated negatively during acute SIV infection suggesting a potential antiviral effect, but positively during chronic SIV infection indicating that either the virus drives IFNα production or IFNα may facilitate loss of viral control. The above findings indicate stage-specific opposing effects of Type I IFNs during HIV-1 infection and suggest a novel mechanism by which these cytokines contribute to T cell depletion, dysregulation of cellular immunity and disease progression.

Gardiquimod: a Toll-like receptor-7 agonist that inhibits HIV type 1 infection of human macrophages and activated T cells

Immune response modifiers are being studied as therapeutic agents for viral infections and cancer. These molecules include agonists for the Toll-like receptors (TLR), a family of innate immune receptors. TLR7 and 8, located in cellular endosomes, bind single-stranded RNA characteristic of viral genomes, and trigger intracellular signaling pathways that induce inflammatory cytokines and antiviral innate immune factors. We studied the anti-HIV-1 effects of gardiquimod, a specific TLR7 agonist when used at concentrations below 10 μM, in macrophages and activated peripheral blood mononuclear cells (PBMCs). Gardiquimod, added prior to or within 2 days after infection with X4, R5, or dual-tropic (R5/X4) strains of HIV-1, significantly reduced infection in these cells. Cocultures of activated PBMCs added to gardiquimod-treated and HIV-1-exposed macrophages demonstrated minimal HIV-1 replication for up to 10 days, suggesting that gardiquimod inhibited activated PBMCs viral amplification from HIV-1-exposed macrophages. Gardiquimod treatment of both activated PBMCs and macrophages induced interferon-alpha (IFN-α) transcription within hours of addition, and sustained IFN-α protein secretion for several days. Treatment of cells with a peptide inhibitor to the MyD88 adaptor protein blocked the induction of IFN-α by gardiquimod, and partially reversed the anti-HIV effects in activated PBMCs. Blocking the IFN-α receptor with a neutralizing antibody also reduced the anti-HIV effect of gardiquimod. Gardiquimod inhibited HIV-1 reverse transcriptase, an early step in the life cycle of HIV-1. These findings suggest that gardiquimod, functioning as both an immune system modifier and a reverse transcriptase inhibitor, could be developed as a novel therapeutic agent to block systemic and mucosal transmission of HIV-1.

Toll-like receptor (TLR)-7 and -8 modulatory activities of dimeric imidazoquinolines

Toll-like receptors (TLRs) are pattern recognition receptors that recognize specific molecular patterns present in molecules that are broadly shared by pathogens but are structurally distinct from host molecules. The TLR7-agonistic imidazoquinolines are of interest as vaccine adjuvants given their ability to induce pronounced Th1-skewed humoral responses. Minor modifications on the imidazoquinoline scaffold result in TLR7-antagonistic compounds which may be of value in addressing innate immune activation-driven immune exhaustion observed in HIV. We describe the syntheses and evaluation of TLR7 and TLR8 modulatory activities of dimeric constructs of imidazoquinoline linked at the C2, C4, C8, and N(1)-aryl positions. Dimers linked at the C4, C8, and N(1)-aryl positions were agonistic at TLR7; only the N(1)-aryl dimer with a 12-carbon linker was dual TLR7/8 agonistic. Dimers linked at C2 position showed antagonistic activities at TLR7 and TLR8; the C2 dimer with a propylene spacer was maximally antagonistic at both TLR7 and TLR8.

Potent adjuvantic activity of a CCR1-agonistic bis-quinoline

A bis-quinoline compound, (7-chloro-N-(4-(7-chloroquinolin-4-ylamino)butyl)quinolin-4-amine; RE-660) was found to have C-C chemokine receptor type 1 (CCR1)-agonistic properties. RE-660 displayed strong adjuvantic activity in mice when co-administered with bovine α-lactalbumin used as a model subunit protein antigen. RE-660 evoked a balanced Th1 (IgG2)/Th2 (IgG1) antibody profile, and the quality of antibodies elicited by the bis-quinoline was found to be superior to that evoked by glucopyranosyl lipid A by surface plasmon resonance experiments. No evidence of proinflammatory activity was observed in human blood ex vivo models. In preliminary acute toxicity studies, the compound was found to be of lower toxicity than chloroquine in mice, and was non-mutagenic in an Ames screen.

Plasmacytoid dendritic cells in HIV infection

Plasmacytoid dendritic cells (pDCs) are innate immune cells that are specialized to produce interferon-alpha (IFNα) and participate in activating adaptive immune responses. Although IFNα inhibits HIV-1 (HIV) replication in vitro, pDCs may act as inflammatory and immunosuppressive dendritic cells (DCs) rather than classical antigen-presenting cells during chronic HIV infection in vivo, contributing more to HIV pathogenesis than to protection. Improved understanding of HIV-pDC interactions may yield potential new avenues of discovery to prevent HIV transmission, to blunt chronic immune activation and exhaustion, and to enhance beneficial adaptive immune responses. In this chapter we discuss pDC biology, including pDC development from progenitors, trafficking and localization of pDCs in the body, and signaling pathways involved in pDC activation. We focus on the role of pDCs in HIV transmission, chronic disease progression and immune activation, and immunosuppression through regulatory T cell development. Lastly, we discuss potential future directions for the field which are needed to strengthen our current understanding of the role of pDCs in HIV transmission and pathogenesis.

Targeting HIV-1 innate immune responses therapeutically

PURPOSE OF REVIEW

The early stage of HIV-1 infection is when the virus is most vulnerable, and should therefore offer the best opportunity for therapeutic interventions. This review addresses the recent progress in the understanding of innate immune responses against HIV-1 with focus on the potential targets for prevention of viral acquisition, replication and dissemination.

RECENT FINDINGS

Research indicates that the host-derived factor trappin-2/elafin is protective against HIV, whereas semen-derived enhancer of viral infection and defensins 5 and 6 enhance viral transmission. Further, studies suggest that stimulation of TLR4 and inhibition of TLR7-9 pathways may be HIV suppressive. The regulation and function of viral restriction factors tetherin and APOBEC3G have been investigated and a molecule mimicking the premature uncoating achieved by TRIM5α, PF74, has been identified. Chloroquine has been shown to inhibit plasmacytoid dendritic cell activation and suppress negative modulators of T-cell responses. Blockade of HMBG1 has been found to restore natural-killer-cell-mediated killing of infected dendritic cells, normally suppressed by HIV-1. Interestingly, when used as adjuvants, EAT-2 and heat shock protein gp96 reportedly enhance innate immune responses.

SUMMARY

Several targets for innate immunity-mediated therapeutics have been identified. Nonetheless, more research is required to unveil their underlying mechanisms and interactions before testing these molecules in clinical trials.