Inhibition of acute-, latent-, and chronic-phase human immunodeficiency virus type 1 (HIV-1) replication by a bistriazoloacridone analog that selectively inhibits HIV-1 transcription

Acridones as promising drug candidates against Oropouche virus

Oropouche virus (OROV) is an emerging vector-borne arbovirus found in South America that causes Oropouche fever, a febrile infection similar to dengue fever. It has a high epidemic potential, causing illness in over 500,000 cases diagnosed since the virus was first discovered in 1955. Currently, the prevention of human viral infection depends on vaccination, but availability for many viruses is limited, and they are classified as neglected viruses. At present, there are no vaccines or antiviral treatments available. An alternative approach to limiting the spread of the virus is to selectively disrupt viral replication mechanisms. Here, we demonstrate the inhibitory effect of acridones, which efficiently inhibited viral replication by 99.9 % in vitro. To evaluate possible mechanisms of action, we conducted tests with dsRNA, an intermediate in virus replication, as well as MD simulations, docking, and binding free energy analysis. The results showed a strong interaction between FAC21 and the OROV endonuclease, which possibly limits the interaction of viral RNA with other proteins. Therefore, our results suggest a dual mechanism of antiviral action, possibly caused by ds-RNA intercalation. In summary, our findings demonstrate that a new generation of antiviral drugs could be developed based on the selective optimization of molecules.

Cyclic peptides with a distinct arginine-fork motif recognize the HIV trans-activation response RNA in vitro and in cells

RNA represents a potential target for new antiviral therapies, which are urgently needed to address public health threats such as the human immunodeficiency virus (HIV). We showed previously that the interaction between the viral Tat protein and the HIV-1 trans-activation response (TAR) RNA was blocked by the cyclic peptide TB-CP-6.9a. This peptide was derived from a TAR-binding loop that emerged during lab-evolution of a TAR-binding protein (TBP) family. Here we synthesized and characterized a next-generation, cyclic-peptide library based on the TBP scaffold. We sought to identify conserved RNA-binding interactions, and the influence of cyclization linkers on RNA binding and antiviral activity. A diverse group of cyclization linkers, encompassing disulfide bonds to bicyclic aromatic staples, was used to restrain the cyclic peptide geometry. Thermodynamic profiling revealed specific arginine-rich sequences with low to sub-micromolar affinity driven by enthalpic and entropic contributions. The best compounds exhibited no appreciable off-target binding to related molecules, such as BIV TAR and human 7SK RNAs. A specific arginine-to-lysine change in the highest affinity cyclic peptide reduced TAR binding by 10-fold, suggesting that TBP-derived cyclic peptides use an arginine-fork motif to recognize the TAR major-groove while differentiating the mode of binding from other TAR-targeting molecules. Finally, we showed that HIV infectivity in cell culture was reduced in the presence of cyclic peptides constrained by methylene or naphthalene-based linkers. Our findings provide insight into the molecular determinants required for HIV-1 TAR recognition and antiviral activity. These findings are broadly relevant to the development of antivirals that target RNA molecules.

Advances toward Curing HIV-1 Infection in Tissue Reservoirs

A disease of more than 39.6 million people worldwide, HIV-1 infection has no curative therapy. To date, one man has achieved a sterile cure, with millions more hoping to avoid the potential pitfalls of lifelong antiretroviral therapy and other HIV-related disorders, including neurocognitive decline. Recent developments in immunotherapies and gene therapies provide renewed hope in advancing efforts toward a sterilizing or functional cure. On the horizon is research concentrated in multiple separate but potentially complementary domains: vaccine research, viral transcript editing, T-cell effector response targeting including checkpoint inhibitors, and gene editing. Here, we review the concept of targeting the HIV-1 tissue reservoirs, with an emphasis on the central nervous system, and describe relevant new work in functional cure research and strategies for HIV-1 eradication.

Current Strategies for Elimination of HIV-1 Latent Reservoirs Using Chemical Compounds Targeting Host and Viral Factors

Since the implementation of combination antiretroviral therapy (cART), rates of HIV type 1 (HIV-1) mortality, morbidity, and newly acquired infections have decreased dramatically. In fact, HIV-1-infected individuals under effective suppressive cART approach normal life span and quality of life. However, long-term therapy is required because the virus establish a reversible state of latency in memory CD4⁺ T cells. Two principle strategies, namely "shock and kill" approach and "block and lock" approach, are currently being investigated for the eradication of these HIV-1 latent reservoirs. Actually, both of these contrasting approaches are based on the use of small-molecule compounds to achieve the cure for HIV-1. In this review, we discuss the recent progress that has been made in designing and developing small-molecule compounds for both strategies.

Hepatitis C virus in vitro replication is efficiently inhibited by acridone Fac4

Hepatitis C virus (HCV) affects about 170 million people worldwide. The current treatment has a high cost and variable response rates according to the virus genotype. Acridones, a group of compounds extracted from natural sources, showed potential antiviral actions against HCV. Thus, this study aimed to evaluate the effect of a panel of 14 synthetic acridones on the HCV life cycle. The compounds were screened using an Huh7.5 cell line stably harbouring the HCV genotype 2a subgenomic replicon SGR-Feo-JFH-1. Cells were incubated in the presence or absence of compounds for 72 h and cell viability and replication levels were assessed by MTT and luciferase assays, respectively. At a concentration of 5 µM the acridone Fac4 exhibited a >90 % inhibition of HCV replication with no effect on cell viability. The effects of Fac4 on virus replication, entry and release steps were evaluated in Huh7.5 cells infected with the JFH-1 isolate of HCV (HCVcc). Fac4 inhibited JFH-1 replication to approximately 70 %, while no effect was observed on virus entry. The antiviral activity of Fac4 was also observed on viral release, with almost 80 % of inhibition. No inhibitory effect was observed against genotype 3 replication. Fac4 was able to intercalate into dsRNA, however did not inhibit NS5B polymerase activity or translation driven by the HCV IRES. Although its mode of action is partly understood, Fac4 presents significant inhibition of HCV replication and can therefore be considered as a candidate for the development of a future anti-HCV treatment.

Targeting HIV transcription: the quest for a functional cure

Antiretroviral therapy (ART) potently suppresses HIV-1 replication, but the virus persists in quiescent infected CD4(+)T cells as a latent integrated provirus, and patients must indefinitely remain on therapy. If ART is terminated, these integrated proviruses can reactivate, driving new rounds of infection. A functional cure for HIV requires eliminating low-level ongoing viral replication that persists in certain tissue sanctuaries and preventing viral reactivation. The HIV Tat protein plays an essential role in HIV transcription by recruiting the kinase activity of the P-TEFb complex to the viral mRNA's stem-bulge-loop structure, TAR, activating transcriptional elongation. Because the Tat-mediated transactivation cascade is critical for robust HIV replication, the Tat/TAR/P-TEFb complex is one of the most attractive targets for drug development. Importantly, compounds that interfere with transcription could impair viral reactivation, low-level ongoing replication, and replenishment of the latent reservoir, thereby reducing the size of the latent reservoir pool. Here, we discuss the potential importance of transcriptional inhibitors in the treatment of latent HIV-1 disease and review recent findings on targeting Tat, TAR, and P-TEFb individually or as part of a complex. Finally, we discuss the impact of extracellular Tat in HIV-associated neurocognitive disorders and cancers.

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.

The next generation of HIV/AIDS drugs: novel and developmental antiHIV drugs and targets

There are presently 42 million people worldwide living with HIV/AIDS, the majority of which have limited access to antiretrovirals. Even if worldwide penetration was possible, our current chemotherapeutic strategies still suffer from issues of cost, patient compliance, deleterious acute and chronic side effects, emerging single and multidrug resistance, and generalized treatment and economic issues. Even our best antiretroviral therapeutic strategy, highly active antiretroviral therapy (HAART), falls short of completely suppressing HIV replication. Therefore, expansion of current therapeutic options by discovering new antiretrovirals and targets will be critical in the coming years. This review addresses the current status of reverse transcriptase and protease inhibitor development, and summarizes the progress in emerging classes of HIV inhibitors, including entry (T-20, T-1249), coreceptor (SCH-C, SCH-D), integrase (beta-Diketos) and p7 nucleocapsid Zn finger inhibitors (thioesters and PATEs). In addition, the processes of virus entry, PIC transport to the nucleus, HIV interaction with nuclear pores, Tat function, Rev function and virus budding (Tsg101 and ubiquitination) are examined, and proof of concept inhibitors and potential antiviral targets discussed.

Thermodynamic Investigation and Mixed Ligand Complex Formation of 1,4-Bis-(3-aminopropyl)-piperazine and Biorelevant Ligands

Thermodynamic parameters for protonation of 1,4-bis(3-aminopropyl)-piperazine (BAPP) and its metal complexation with some divalent metal ions were determined in aqueous solution at constant ionic strength (0.1 M NaNO₃) using a potentiometric technique. The order of –ΔG⁰ and –ΔH⁰ was found to obey Co²⁺ < Ni²⁺ < Cu²⁺ > Zn²⁺, in accordance with the Irving-Williams order. The formation equilibria of zinc (II) complexes and the ternary complexes Zn(BAPP)L, where L = amino acid, amides, or DNA constituents), have been investigated. Ternary complexes are formed by a simultaneous mechanism. The concentration distribution of the complexes in solution was evaluated as a function of pH. Stoichiometry and stability constants for the complexes formed are reported and discussed. The stability of ternary complexes was quantitatively compared with their corresponding binary complexes in terms of the parameter Δlog K.

Strategies to Block HIV Transcription: Focus on Small Molecule Tat Inhibitors

After entry into the target cell, the human immunodeficiency virus type I (HIV) integrates into the host genome and becomes a proviral eukaryotic transcriptional unit. Transcriptional regulation of provirus gene expression is critical for HIV replication. Basal transcription from the integrated HIV promoter is very low in the absence of the HIV transactivator of transcription (Tat) protein and is solely dependent on cellular transcription factors. The 5' terminal region (+1 to +59) of all HIV mRNAs forms an identical stem-bulge-loop structure called the Transactivation Responsive (TAR) element. Once Tat is made, it binds to TAR and drastically activates transcription from the HIV LTR promoter. Mutations in either the Tat protein or TAR sequence usually affect HIV replication, indicating a strong requirement for their conservation. The necessity of the Tat-mediated transactivation cascade for robust HIV replication renders Tat one of the most desirable targets for transcriptional therapy against HIV replication. Screening based on inhibition of the Tat-TAR interaction has identified a number of potential compounds, but none of them are currently used as therapeutics, partly because these agents are not easily delivered for an efficient therapy, emphasizing the need for small molecule compounds. Here we will give an overview of the different strategies used to inhibit HIV transcription and review the current repertoire of small molecular weight compounds that target HIV transcription.

Synthesis, characterization, equilibrium study and biological activity of Cu(II), Ni(II) and Co(II) complexes of polydentate Schiff base ligand

Schiff base ligand, 1,4-bis[(2-hydroxybenzaldehyde)propyl]piperazine (BHPP), and its Cu(II), Ni(II) and Co(II) metal complexes were synthesized and characterized by elemental analysis, magnetic susceptibility, molar conductance and spectral (IR and UV-vis) studies. The ground state of BHPP ligand was investigated using the BUILDER module of MOE. Metal complexes are formed in the 1:1 (M:L) ratio as found from the elemental analysis and found to have the general formula [ML]·nH(2)O, where M=Co(II), Ni(II) and Cu(II), L=BHPP. In all the studied complexes, the (BHPP) ligand behaves as a hexadentate divalent anion with coordination involving the two azomethine nitrogen's, the two nitrogen atoms of piperazine ring and the two deprotonated phenolic OH-groups. The magnetic and spectral data indicates octahedral geometry of metal(II) complexes. The ligand and their metal chelates have been screened for their antimicrobial activities using the disc diffusion method against the selected bacteria and fungi. They were found to be more active against Gram-positive than Gram-negative bacteria. Protonation constants of (BHPP) ligand and stability constants of its Cu(2+), Co(2+) and Ni(2+) complexes were determined by potentiometric titration method in 50% DMSO-water solution at ionic strength of 0.1 M sodium nitrate. It has been observed that the protonated Schiff base ligand (BHPP) have four protonation constants. The divalent metal ions Cu(2+), Ni(2+) and Co(2+) form 1:1 complexes.

Host cell factors as antiviral targets in arenavirus infection

Among the members of the Arenaviridae family, Lassa virus and Junin virus generate periodic annual outbreaks of severe human hemorrhagic fever (HF) in endemic areas of West Africa and Argentina, respectively. Given the human health threat that arenaviruses represent and the lack of a specific and safe chemotherapy, the search for effective antiviral compounds is a continuous demanding effort. Since diverse host cell pathways and enzymes are used by RNA viruses to fulfill their replicative cycle, the targeting of a host process has turned an attractive antiviral approach in the last years for many unrelated virus types. This strategy has the additional benefit to reduce the serious challenge for therapy of RNA viruses to escape from drug effects through selection of resistant variants triggered by their high mutation rate. This article focuses on novel strategies to identify inhibitors for arenavirus therapy, analyzing the potential for antiviral developments of diverse host factors essential for virus infection.

Impact of Tat Genetic Variation on HIV-1 Disease

The human immunodeficiency virus type 1 (HIV-1) promoter or long-terminal repeat (LTR) regulates viral gene expression by interacting with multiple viral and host factors. The viral transactivator protein Tat plays an important role in transcriptional activation of HIV-1 gene expression. Functional domains of Tat and its interaction with transactivation response element RNA and cellular transcription factors have been examined. Genetic variation within tat of different HIV-1 subtypes has been shown to affect the interaction of the viral transactivator with cellular and/or viral proteins, influencing the overall level of transcriptional activation as well as its action as a neurotoxic protein. Consequently, the genetic variability within tat may impact the molecular architecture of functional domains of the Tat protein that may impact HIV pathogenesis and disease. Tat as a therapeutic target for anti-HIV drugs has also been discussed.

Synthesis and cytotoxic activity of a new potential DNA bisintercalator: 1,4-Bis{3-[N-(4-chlorobenzo[g]phthalazin-1-yl)aminopropyl]}piperazine

The synthesis of new 1,4-bisalkylamino (2-4) and 1-alkylamino-4-chloro (5-6) substituted benzo[g]phthalazines is reported. Compounds 2-4 and 6 were prepared both in the free and heteroaromatic ring protonated forms. Bifunctional 6 contains the 1,4-bisaminopropylpiperazine chain as a linker between the two heteroaromatic units, whereas 5 is its monofunctional analogue. The in vitro antitumour activity of the synthesized compounds has been tested against human colon, breast and lung carcinoma cells, and also against human glioblastoma cells. Results obtained show that all of them are active in all cases, but bifunctional 6.2HCl is remarkably effective against the four cell lines tested, exhibiting IC50 values in the range of 10(-7) M, similar to those found for doxorubicin. The bifunctional structure of 6.2HCl enhances activity with respect to the monofunctional related compounds 5 and 7, leading to the highest activity among all the compounds tested. Molecular modelling of 6 suggests that those results could be indicative of DNA bisintercalation, which should be specially favoured in the diprotonated form 6.2HCl, a compound suitable for being studied more in depth in further biological tests. Measure of the DNA thermal melting curves show that the linear rise in Tm for bifunctional 6.2HCl is nearly twice than that one obtained for monofunctional 5, and supports the DNA-binding hypothesis.

An albumin-conjugated peptide exhibits potent anti-HIV activity and long in vivo half-life

The clinical application of conventional peptide drugs often is limited by their short in vivo half-life and potential immunogenicity. Frequent injection presents challenges to the treatment of chronic diseases, such as HIV infection. We chemically modified a peptide HIV fusion inhibitor with 3-maleimidopropionic acid (MPA), which allows rapid and irreversible conjugation with serum albumin at a 1:1 molar ratio. FB006M, with an MPA modification at the 13th amino acid, rapidly formed conjugate with albumin upon intravenous injection, and it exhibited a remarkably extended in vivo half-life. The albumin conjugate of FB006M displayed potent inhibitory activity against a number of laboratory and clinical isolates of HIV-1 in vitro and in vivo. No immunogenicity or antibody formation was detected after repeated dosing. The clinical application of FB006M may decrease the cost of treatment and improve treatment compliance and patient quality of life.

Synthesis and evaluation of N-substituted acridones as antiviral agents against haemorrhagic fever viruses

BACKGROUND

In the present study, a series of N-substituted acridone derivatives was synthesized and evaluated against two haemorrhagic fever viruses (HFV).

METHODS

Compounds were tested against Junin virus (JUNV), an arenavirus agent of Argentine haemorrhagic fever, and dengue virus (DENV), a flavivirus agent of the most prevalent arthropod-borne viral disease in humans.

RESULTS

Among tested compounds, two N-allyl acridones (derivatives 3c and 3f) elicited a potent and selective antiviral activity against JUNV (strain 1V4454) and DENV-2 (strain NGC) with 50% effective concentration values between 2.5 and 5.5 microM, as determined by virus yield inhibition. No cytotoxicity was detected at concentrations up to 1,000 microM, resulting in selectivity indices >181.8-400.0. Both acridones were effective against a wide spectrum of arenaviruses and the four serotypes of DENV. Furthermore, 3c and 3f failed to inactivate virus before cell infection as well as to induce a refractory state by cell pretreatment, indicating that the inhibitory effect was exerted through a blockade in virus multiplication during the infectious process.

CONCLUSION

These data are the first demonstration that acridone derivatives have a potent antiviral activity that block in vitro multiplication of HFV belonging to Arenaviridae and Flaviviridae, such as JUNV and DENV.

Heterocyclic compounds that inhibit Rev-RRE function and human immunodeficiency virus type 1 replication

A cell-based screening assay was performed to identify compounds that inhibited the postintegration stage of the human immunodeficiency virus (HIV) life cycle. This assay utilized a cell line that contains the HIV gag and pol genes expressed in a Rev-dependent fashion. The cell line produces about 10 to 15 ng of p24 per milliliter of medium over a 24-h period in the form of viruslike particles. Any compound that inhibits a postintegration step in the HIV life cycle scores in this assay by decreasing particle production. Forty thousand compounds were screened, and 192 compounds were selected from the original screen because they showed more than 50% inhibition at a 10 muM concentration. The cumulative evidence presented in this study strongly suggests that 2 of the 192 compounds work as inhibitors of HIV Rev function. This was determined by a variety of cell-based assays, although the compounds do not interfere with Rev-RRE (Rev response element) binding in vitro. Both compounds inhibit replication of the lab isolate NL4-3 as well as an HIV primary isolate from Brazil (93BR021) and thus are promising leads as therapeutic candidates that target HIV replication through inhibition of Rev function.

A high-throughput drug screening system for HIV-1 transcription inhibitors

Identification of HIV-1 transcription inhibitors was previously performed using infectivity assays. As de novo HIV-1 infection is highly sensitive to even minor compound toxicities, these assays are plagued by extremely high levels of false-positive hits. Hit identification is further complicated because infectivity assays lack target specificity. The authors demonstrate that it is possible to overcome these limitations by establishing a stable, chronically actively HIV-1-infected reporter cell line that exclusively identifies HIV-1 transcription inhibitors. In the reporter cell line, 2 spectrally separated fluorescence proteins serve as simultaneously accessible quantitative markers of HIV-1 expression and drug toxicity. The combined analysis of these markers drastically reduces the level of false-positive hits. As determination of fluorescence intensity in a plate-based format can be performed in a noninvasive manner, repeated measurements of fluorescence levels over several days after compound addition can be used to define the kinetic and dynamic characteristics of inhibitory drug effects. In addition, because of the stable nature of the reporter cell line, the assay requires no cell manipulation during assay preparation or assay analysis, rendering the system extremely cost-effective and reliable.

Inhibition of HIV-1 virus replication using small soluble Tat peptides

Although the introduction of highly active antiretroviral therapy (HAART) has led to a significant reduction in AIDS-related morbidity and mortality, unfortunately, many patients discontinue their initial HAART regimen, resulting in development of viral resistance. During HIV infection, the viral activator Tat is needed for viral progeny formation, and the basic and core domains of Tat are the most conserved parts of the protein. Here, we show that a Tat 41/44 peptide from the core domain can inhibit HIV-1 gene expression and replication. The peptides are not toxic to cells and target the Cdk2/Cyclin E complex, inhibiting the phosphorylation of serine 5 of RNAPII. Using the Cdk2 X-ray crystallography structure, we found that the low-energy wild-type peptides could bind to the ATP binding pocket, whereas the mutant peptide bound to the Cdk2 interface. Finally, we show that these peptides do not allow loading of the catalytic domain of the cdk/cyclin complex onto the HIV-1 promoter in vivo.

A New Synthetic Agent with Potent but Selective Cytotoxic Activity against Cancer

The synthesis of novel unsymmetrical bifunctional antitumor agents was accomplished by linking an imidazoacridone moiety to another polycyclic heteroaromatic moiety via linkers of various length and rigidity. These compounds bind to cellular DNA, but it is hypothesized that biological effects become manifested when the drug-DNA complexes interact with critical DNA binding proteins that are involved in repair and transcription. The most promising compound of the series, 4ad (WMC79), consists of an imidazoacridone linked to a 3-nitronaphthalimide moiety via a 1,4-dipropanopiperazine linker. It was found to be potently, but selectively, cytotoxic against colon cancers (GI(50) = 0.5 nM, LC(50) = 32 nM) and leukemias (GI(50) = 3.5 nM, LC(50) = 33 nM). Compound 4ad, which appears to be a candidate for further development as an anticancer drug, kills sensitive cells by induction of apoptosis. It also showed significant in vivo activity against HCT-116 colon cancer xenografts in nude mice. Other compounds in the series also exhibited antitumor properties, but they were significantly lower than that of 4ad.

Bis-anthracycline antibiotics inhibit human immunodeficiency virus type 1 transcription

The increasing numbers of human immunodeficiency virus type 1 (HIV-1) strains that exhibit resistance to antiretroviral agents used at present require the development of new effective antiretroviral compounds. Tat transactivation was recognized early on as an attractive target for drug interference. To screen for and analyze the effects of compounds that interfere with Tat transactivation, we developed several cell-based reporter systems in which enhanced green fluorescence protein is a direct and quantitative marker of HIV-1 expression or Tat-dependent long terminal repeat activity. Using these reporter cell lines, we found that the bis-anthracycline WP631, a recently developed DNA intercalator, efficiently inhibits HIV-1 expression at subcytotoxic concentrations. WP631 also abrogated acute HIV-1 replication in peripheral blood mononuclear cells infected with various primary virus isolates. We demonstrate that WP631-mediated HIV-1 inhibition is caused by the inhibition of Tat transactivation. The data presented suggest that WP631 could serve as a lead compound for a new type of HIV-1 inhibitor.

Regulation of HIV-1 gene transcription: from lymphocytes to microglial cells

Transcription is a crucial step for human immunodeficiency virus type 1 (HIV-1) expression in all infected host cells, from T lymphocytes, thymocytes, monocytes, macrophages, and dendritic cells in the immune system up to microglial cells in the central nervous system. To maximize its replication, HIV-1 adapts transcription of its integrated proviral genome by ideally exploiting the specific cellular environment and by forcing cellular stimulatory events and impairing transcriptional inhibition. Multiple cell type-specific interplays between cellular and viral factors perform the challenge for the virus to leave latency and actively replicate in a great diversity of cells, despite the variability of its long terminal repeat region in different HIV strains. Knowledge about the molecular mechanisms underlying transcriptional regulatory events helps in the search for therapeutic agents that target the step of transcription in anti-HIV strategies.

Direct antiviral effect of cycloferon (10-carboxymethyl-9-acridanone) against adenovirus type 6 in vitro

Adenoviruses represent a broad group of human pathogens that currently have no specific and safe drugs for treatment. We demonstrated direct (non IFN-mediated) antiviral activity of cycloferon (10-carboxymethyl-9-acridanone, CMA), a potent interferon inducer, against adenovirus type 6 (Ad6) in Hep-2 cells. Virus production and details of morphogenesis were studied by ELISA with antibodies to the Ad6 hexon protein, and transmission electron microscopy, respectively. Immunoenzyme assay revealed that CMA does not inhibit viral protein synthesis but instead strongly reduces the ability of the virus to generate infectious progeny virus in a dose dependent manner. Ultrastructural study shows that CMA alters the structure of intranuclear virus-specific inclusions. We suggest that CMA suppresses the late stages of viral cycle in the infected cell.

Bisimidazoacridones: 2. Steady-state and Time-resolved Fluorescence Studies of Their Diverse Interactions with DNA¶§

Several bisimidazoacridones (BIA) are potent, selective antineoplastic agents, whereas others have potent anti-human immunodeficiency virus activity. BIA are bifunctional agents that consist of two imidazoacridone (IA) chromophores held together by various linkers. Interaction of BIA with DNA has been postulated to be required for their biological activity. Fluorescence data on free and bound BIA suggest that the binding of BIA and similar drugs to DNA is driven by a transfer of hydrophobic molecules from aqueous media to the more amphiphilic DNA environment. Binding to DNA was sensitive to sequence and depended on the length and rigidity of the linker. Time-resolved fluorescence measurements showed that BIA adopt an extended conformation upon binding and that all of the molecules are tightly associated with DNA. Gel-shift and melting assays indicated that one of the aromatic residues of BIA is intercalated, whereas the other, together with a linker, resides in a groove, probably the minor groove. A continuum of structures may be possible where intercalation and classical minor groove binding are limiting structures. In general, the hypothesis for the mechanism of action of BIA wherein the unintercalated residue, accessible for additional interactions, captures a critical protein involved in repair or transcription, is consistent with this model.

New anti-HIV agents and targets

Virtually all the compounds that are currently used or are subject of advanced clinical trials for the treatment of HIV infections, belong to one of the following classes: (i) nucleoside reverse transcriptase inhibitors (NRTIs): i.e., zidovudine, didanosine, zalcitabine, stavudine, lamivudine, abacavir, emtricitabine and nucleotide reverse transcriptase inhibitors (NtRTIs) (i.e., tenofovir disoproxil fumarate); (ii) non-nucleoside reverse transcriptase inhibitors (NNRTIs): i.e., nevirapine, delavirdine, efavirenz, emivirine; and (iii) protease inhibitors (PIs): i.e., saquinavir, ritonavir, indinavir, nelfinavir, amprenavir, and lopinavir. In addition to the reverse transcriptase and protease reaction, various other events in the HIV replicative cycle can be considered as potential targets for chemotherapeutic intervention: (i) viral adsorption, through binding to the viral envelope glycoprotein gp120 (polysulfates, polysulfonates, polycarboxylates, polyoxometalates, polynucleotides, and negatively charged albumins); (ii) viral entry, through blockade of the viral coreceptors CXCR4 (i.e., bicyclam (AMD3100) derivatives) and CCR5 (i.e., TAK-779 derivatives); (iii) virus-cell fusion, through binding to the viral envelope glycoprotein gp41 (T-20, T-1249); (iv) viral assembly and disassembly, through NCp7 zinc finger-targeted agents [2,2'-dithiobisbenzamides (DIBAs), azadicarbonamide (ADA)]; (v) proviral DNA integration, through integrase inhibitors such as 4-aryl-2,4-dioxobutanoic acid derivatives; (vi) viral mRNA transcription, through inhibitors of the transcription (transactivation) process (flavopiridol, fluoroquinolones). Also, various new NRTIs, NNRTIs, and PIs have been developed that possess, respectively: (i) improved metabolic characteristics (i.e., phosphoramidate and cyclosaligenyl pronucleotides by-passing the first phosphorylation step of the NRTIs), (ii) increased activity ["second" or "third" generation NNRTIs ( i.e., TMC-125, DPC-083)] against those HIV strains that are resistant to the "first" generation NNRTIs, or (iii), as in the case of PIs, a different, modified peptidic (i.e., azapeptidic (atazanavir)) or non-peptidic scaffold (i.e., cyclic urea (mozenavir), 4-hydroxy-2-pyrone (tipranavir)). Non-peptidic PIs may be expected to inhibit HIV mutant strains that have become resistant to peptidomimetic PIs.

Synthesis of substituted diarylmethylenepiperidines (DAMPs), a novel class of anti-HIV agents

Substituted diarylmethylenepiperidines (DAMPs) were synthesized as conformationally restricted analogues of the alkenyldiarylmethane (ADAM) class of non-nucleoside reverse transcriptase inhibitors (NNRTIs). Although, like the ADAMs, the DAMPs were found to inhibit the cytopathic effect of HIV-1(RF) in CEM-SS cells, they were completely inactive as inhibitors of HIV-1 reverse transcriptase. The DAMPs were assessed for inhibition of HIV attachment and fusion. DAMP was active in both assays with IC(50) values of 26.5 microM (TI 3.8) and 12.1 microM (TI: >8), respectively. DAMP also inhibited HIV fusion with an IC(50 )12.8 microM (TI: >6), but not virus attachment. However, attempts to verify inhibition of virus attachment and fusion as antiviral targets using time-of-addition experiments failed to confirm these observations, and instead identified an antiviral target occurring after completion of reverse transcription. DAMPs, and were found to inhibit virus replication if added 8 h post virus exposure, and DAMP was equipotent at inhibition of virus replication if added 24 h after virus addition. DAMPs, and did not inhibit virus replication in TNF-alpha induced latently infected U1 cells, a model for post-integrative antiviral targets. When tested in both 3' end-processing and strand-transfer assays in the presence of HIV-1 integrase, none of the DAMPs showed any inhibitory activity, indicating that HIV-1 integrase is not involved in the mechanism of the antiviral action. Thus, the DAMPs are novel conformationally restricted analogues of the previously published ADAM series with an unidentified antiviral target bounded by the completion of reverse transcription and virus integration.

New developments in anti-HIV chemotherapy

Virtually all the compounds that are currently used, or are subject of advanced clinical trials, for the treatment of human immunodeficiency virus (HIV) infections, belong to one of the following classes: (i) nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs): i.e. zidovudine (AZT), didanosine (ddI), zalcitabine (ddC), stavudine (d4T), lamivudine (3TC), abacavir (ABC), emtricitabine [(-)FTC], tenofovir disoproxil fumarate; (ii) non-nucleoside reverse transcriptase inhibitors (NNRTIs): i.e. nevirapine, delavirdine, efavirenz, emivirine; and (iii) protease inhibitors (PIs): i.e. saquinavir, ritonavir, indinavir, nelfinavir, amprenavir and lopinavir. In addition to the reverse transcriptase (RT) and protease reaction, various other events in the HIV replicative cycle can be considered as potential targets for chemotherapeutic intervention: (i) viral adsorption, through binding to the viral envelope glycoprotein gp120 (polysulfates, polysulfonates, polycarboxylates, polyoxometalates, polynucleotides, and negatively charged albumins); (ii) viral entry, through blockade of the viral coreceptors CXCR4 [bicyclam (AMD3100) derivatives] and CCR5 (TAK-779 derivatives); (iii) virus-cell fusion, through binding to the viral envelope glycoprotein gp41 (T-20, T-1249); (iv) viral assembly and disassembly, through NCp7 zinc finger-targeted agents [2,2'-dithiobisbenzamides (DIBAs), azadicarbonamide (ADA)]; (v) proviral DNA integration, through integrase inhibitors such as 4-aryl-2,4-dioxobutanoic acid derivatives; (vi) viral mRNA transcription, through inhibitors of the transcription (transactivation) process (flavopiridol, fluoroquinolones). Also, various new NRTIs, NNRTIs and PIs have been developed that possess, respectively: (i) improved metabolic characteristics (i.e. phosphoramidate and cyclosaligenyl pronucleotides by-passing the first phosphorylation step of the NRTIs), (ii) increased activity ["second" or "third" generation NNRTIs (i.e. TMC-125, DPC-083)] against those HIV strains that are resistant to the "first" generation NNRTIs, or (iii) as in the case of PIs, a different, nonpeptidic scaffold [i.e. cyclic urea (mozenavir), 4-hydroxy-2-pyrone (tipranavir)]. Nonpeptidic PIs may be expected to inhibit HIV mutant strains that have become resistant to peptidomimetic PIs. Given the multitude of molecular targets with which anti-HIV agents can interact, one should be cautious in extrapolating the mode of action of these agents from cell-free enzymatic assays to intact cells. Two examples in point are L-chicoric acid and the nonapeptoid CGP64222, which were initially described as an integrase inhibitor or Tat antagonist, respectively, but later shown to primarily act as virus adsorption/entry inhibitors, the latter through blockade of CXCR4.

Strategies in the design of antiviral drugs

A decade ago, just five drugs were licensed for the treatment of viral infections. Since then, greater understanding of viral life cycles, prompted in particular by the need to combat human immunodeficiency virus, has resulted in the discovery and validation of several targets for therapeutic intervention. Consequently, the current antiviral repertoire now includes more than 30 drugs. But we still lack effective therapies for several viral infections, and established treatments are not always effective or well tolerated, highlighting the need for further refinement of antiviral drug design and development. Here, I describe the rationale behind current and future drug-based strategies for combating viral infections.

Therapeutic targeting of human immunodeficiency virus type-1 latency: current clinical realities and future scientific possibilities

Factors affecting HIV-1 latency present formidable obstacles for therapeutic intervention. As these obstacles have become a clinical reality, even with the use of potent anti-retroviral regimens, the need for novel therapeutic strategies specifically targeting HIV-1 latency is evident. However, therapeutic targeting of HIV-1 latency requires an understanding of the mechanisms regulating viral quiescence and activation. These mechanisms have been partially delineated using chronically infected cell models and, clearly, HIV-1 activation from latency involves several key viral and cellular components. Among these distinctive therapeutic targets, cellular factors involved in HIV-1 transcription especially warrant further consideration for rational drug design. Exploring the scientific possibilities of new therapies targeting HIV-1 latency may hold new promise of eventual HIV-1 eradication.

Retroviral integrase inhibitors year 2000: update and perspectives

HIV-1 integrase is an essential enzyme for retroviral replication and a rational target for the design of anti-AIDS drugs. A number of inhibitors have been reported in the past 8 years. This review focuses on the recent developments in the past 2 years. There are now several inhibitors with known sites of actions and antiviral activity. The challenge is to convert these leads into drugs that will selectively target integrase in vivo, and can be added to our antiviral armamentarium.

Novel compounds in preclinical/early clinical development for the treatment of HIV infections

Virtually all the compounds that are currently used, or under advanced clinical trial, for the treatment of HIV infections, belong to one of the following classes: (i) nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs), (ii) non-nucleoside reverse transcriptase inhibitors (NNRTIs) and (iii) protease inhibitors (PIs). In addition to the reverse transcriptase and protease step, various other events in the HIV replicative cycle are potential targets for chemotherapeutic intervention: (i) viral adsorption, through binding to the viral envelope glycoprotein gp120 (polysulphates, polysulphonates, polyoxometalates, zintevir, negatively charged albumins); (ii) viral entry, through blockade of the viral coreceptors CXCR4 and CCR5 [bicyclams (AMD3100), polyphemusins (T22), TAK-779]; (iii) virus-cell fusion, through binding to the viral glycoprotein gp41 [T-20 (DP-178), siamycins, betulinic acid derivatives]; (iv) viral assembly and disassembly, through NCp7 zinc finger-targeted agents [2,2'-dithiobisbenzamides (DIBAs), azadicarbonamide (ADA)]; (v) proviral DNA integration, through integrase inhibitors such as L-chicoric acid; (vi) viral mRNA transcription, through inhibitors of the transcription (transactivation) process (peptoid CGP64222, fluoroquinolone K-12, Streptomyces product EM2487). Also, in recent years new NRTIs, NNRTIs and PIs have been developed that possess, respectively, improved metabolic characteristics (i.e. phosphoramidate and cyclosaligenyl pronucleotides of d4T), or increased activity against NNRTI-resistant HIV strains, or, in the case of PIs, a different, non-peptidic scaffold. Given the multitude of molecular targets with which anti-HIV agents can interact, one should be cautious in extrapolating from cell-free enzymatic assays to the mode of action of these agents in intact cells. A number of compounds (i.e. zintevir and L-chicoric acid, on the one hand; and CGP64222 on the other hand) have recently been found to interact with virus-cell binding and viral entry in contrast to their proposed modes of action targeted at the integrase and transactivation process, respectively.

Acridone derivatives are selective inhibitors of HIV-1 replication in chronically infected cells

In our extensive screening of anti-HIV-1 agents in chronically infected cell lines, we have found acridone derivatives to be selective inhibitors of HIV-1 replication. Among the acridone derivatives, 1-hydroxy-10-methyl-9,10-dihydroacrid-9-one (RD6-5071) suppressed tumor necrosis factor (TNF)-alpha-induced HIV-1 expression in the latently infected cell line OM-10.1, U1, and ACH-2. Its 50% effective concentration for HIV-1 p24 antigen production was 2.0 microg/ml in OM-10.1 cells, while its 50% cytotoxic concentration was 18 microg/ml. The compound also inhibited phorbol 12-myristate 13-acetate (PMA)-induced HIV-1 expression in these cell lines. Furthermore, RD6-5071 was inhibitory to HIV-1 replication in acutely infected U937 and peripheral blood mononuclear cells. The compound was found to suppress TNF-alpha-induced HIV-1 long terminal repeat-driven gene expression. An inhibition assay for protein kinase C (PKC) revealed that RD6-5071 could reduce the enzyme activity. Furthermore, the compound was a moderate inhibitor of PMA-induced nuclear factor kappaB (NF-kappaB) activation, as determined by a gel mobility shift analysis. These results suggest that the acridone derivatives suppress HIV-1 replication at the transcriptional level primarily through a mechanism of PKC inhibition.

Isoquinolinesulphonamide derivatives inhibit transcriptional elongation of human immunodeficiency virus type 1 RNA in a promyelocytic model of latency

Using the OM-10.1 promyelocytic model of inducible human immunodeficiency virus type 1 (HIV-1) infection, we tested a panel of known protein kinase inhibitors for an ability to block tumour necrosis factor-alpha-induced HIV-1 expression. Among the compounds tested, the broad-spectrum protein kinase inhibitor H-7 uniquely blocked HIV-1 expression at the level of viral transcription, but did not inhibit nuclear factor kappaB activation or function. In structure-activity analysis this inhibitory activity of H-7 on HIV-1 expression corresponded with the known structural requirements for the interaction of H-7 with the ATP-binding region of protein kinase C, suggesting that it was indeed related to the kinase inhibitory properties of H-7. The mechanism of H-7 transcriptional inhibition did not involve chromatin remodelling at the HIV-1 long terminal repeat promoter, as shown by nuc-1 disruption, and appeared to involve HIV-1 RNA elongation but not initiation. Therefore, H-7 and related isoquinolinesulphonamide analogues are most likely inhibiting a kinase target essential for HIV-1 transcriptional elongation whose identity may provide new therapeutic targets for intervention.

Extension of the polyanionic cosalane pharmacophore as a strategy for increasing anti-HIV potency

The anti-HIV agent cosalane inhibits both the binding of gp120 to CD4 as well as an undefined postattachment event prior to reverse transcription. Several cosalane analogues having an extended polyanionic "pharmacophore" were designed based on a hypothetical model of the binding of cosalane to CD4. The analogues were synthesized, and a number of them displayed anti-HIV activity. One of the new analogues was found to possess enhanced potency as an anti-HIV agent relative to cosalane itself. Although the new analogues inhibited both HIV-1 and HIV-2, they were more potent as inhibitors of HIV-1 than HIV-2. Mechanism of action studies indicated that the most potent of the new analogues inhibited fusion of the viral envelope with the cell membrane at lower concentrations than it inhibited attachment, suggesting inhibition of fusion as the primary mechanism of action.

Synthesis and biological properties of novel pyridinioalkanoyl thiolesters (PATE) as anti-HIV-1 agents that target the viral nucleocapsid protein zinc fingers

Nucleocapsid p7 protein (NCp7) zinc finger domains of the human immunodeficiency virus type 1 (HIV-1) are being developed as antiviral targets due to their key roles in viral replication and their mutationally nonpermissive nature. On the basis of our experience with symmetrical disulfide benzamides (DIBAs; Rice et al. Science 1995, 270, 1194-1197), we synthesized and evaluated variants of these dimers, including sets of 4,4'- and 3,3'-disubstituted diphenyl sulfones and their monomeric benzisothiazolone derivatives (BITA). BITAs generally exhibited diminished antiviral potency when compared to their disulfide precursors. Novel, monomeric structures were created by linking haloalkanoyl groups to the benzamide ring through -NH-C(=O)- (amide) or -S-C(=O)- (thiolester) bridges. Amide-linked compounds generally lacked antiviral activity, while haloalkanoyl thiolesters and non-halogen-bearing analogues frequently exhibited acceptable antiviral potency, thus establishing thiolester benzamides per se as a new anti-HIV chemotype. Pyridinioalkanoyl thiolesters (PATEs) exhibited superior anti-HIV-1 activity with minimal cellular toxicity and appreciable water solubility. PATEs were shown to preferentially target the NCp7 Zn finger when tested against other molecular targets, thus identifying thiolester benzamides, and PATEs in particular, as novel NCp7 Zn finger inhibitors for in vivo studies.

Human immunodeficiency virus gene regulation as a target for antiviral chemotherapy

Inhibitors interfering with human immunodeficiency virus (HIV) gene regulation may have great potential in anti-HIV drug (combination) therapy. They act against different targets to currently used anti-HIV drugs, reduce virus production from acute and chronically infected cells and are anticipated to elicit less virus drug resistance. Several agents have already proven to inhibit HIV gene regulation in vitro. A first class of compounds interacts with cellular factors that bind to the long terminal repeat (LTR) promoter and that are needed for basal level transcription, such as NF-kappa B and Sp1 inhibitors. A second class of compounds specifically inhibits the transactivation of the HIV LTR promoter by the viral Tat protein, such as the peptoid CGP64222. A third class of compounds prevents the accumulation of single and unspliced mRNAs through inhibition of the viral regulator protein Rev, such as the aminoglycosidic antibiotics. Most of these compounds have been tested in specific transactivation assays. Whether they are active at the postulated target in virus replication assays has, for many of them, not been ascertained. Toxicity data are often lacking or insufficient. Yet these data are crucial in view of the toxicity that may be expected for compounds that primarily interact with cellular factors. Although a promising lead, considerable research is still required before gene regulation inhibitors may come of age as clinically useful agents.