Inhibition of multiple phases of human immunodeficiency virus type 1 replication by a dithiane compound that attacks the conserved zinc fingers of retroviral nucleocapsid proteins

Cyclic Thiosulfonates for Thiol-Mediated Uptake: Cascade Exchangers, Transporters, Inhibitors

Thiol-mediated uptake is emerging as a powerful method to penetrate cells. Cyclic oligochalcogenides (COCs) have been identified as privileged scaffolds to enable and inhibit thiol-mediated uptake because they can act as dynamic covalent cascade exchangers, i.e., every exchange produces a new, covalently tethered exchanger. In this study, our focus is on the essentially unexplored COCs of higher oxidation levels. Quantitative characterization of the underlying dynamic covalent exchange cascades reveals that the initial ring opening of cyclic thiosulfonates (CTOs) proceeds at a high speed even at a low pH. The released sulfinates exchange with disulfides in aprotic but much less in protic environments. Hydrophobic domains were thus introduced to direct CTOs into hydrophobic pockets to enhance their reactivity. Equipped with such directing groups, fluorescently labeled CTOs entered the cytosol of living cells more efficiently than the popular asparagusic acid. Added as competitive agents, CTOs inhibit the uptake of various COC transporters and SARS-CoV-2 lentivectors. Orthogonal trends found with different transporters support the existence of multiple cellular partners to account for the diverse expressions of thiol-mediated uptake. Dominant self-inhibition and high activity of dimers imply selective and synergistic exchange in hydrophobic pockets as distinguishing characteristics of thiol-mediated uptake with CTOs. The best CTO dimers with hydrophobic directing groups inhibit the cellular entry of SARS-CoV-2 lentivectors with an IC₅₀ significantly lower than the previous best CTO, below the 10 μM threshold and better than ebselen. Taken together, these results identify CTOs as an intriguing motif for use in cytosolic delivery, as inhibitors of lentivector entry, and for the evolution of dynamic covalent networks in the broadest sense, with reactivity-based selectivity of cascade exchange emerging as a distinguishing characteristic that deserves further attention.

Pan-retroviral Nucleocapsid-Mediated Phase Separation Regulates Genomic RNA Positioning and Trafficking

The duality of liquid-liquid phase separation (LLPS) of cellular components into membraneless organelles defines the nucleation of both normal and disease processes including stress granule (SG) assembly. From mounting evidence of LLPS utility by viruses, we discover that HIV-1 nucleocapsid (NC) protein condenses into zinc-finger (ZnF)-dependent LLPSs that are dynamically influenced by cytosolic factors. ZnF-dependent and Zinc (Zn2+)-chelation-sensitive NC-LLPS are formed in live cells. NC-Zn2+ ejection reverses the HIV-1 blockade on SG assembly, inhibits NC-SG assembly, disrupts NC/Gag-genomic RNA (vRNA) ribonucleoprotein complexes, and causes nuclear sequestration of NC and the vRNA, inhibiting Gag expression and virus release. NC ZnF mutagenesis eliminates the HIV-1 blockade of SG assembly and repositions vRNA to SGs. We find that NC-mediated, Zn2+-coordinated phase separation is conserved among diverse retrovirus subfamilies, illustrating that this exquisitely evolved Zn2+-dependent feature of virus replication represents a critical target for pan-antiretroviral therapies.

Thiopurine Derivative-Induced Fpg/Nei DNA Glycosylase Inhibition: Structural, Dynamic and Functional Insights

DNA glycosylases are emerging as relevant pharmacological targets in inflammation, cancer and neurodegenerative diseases. Consequently, the search for inhibitors of these enzymes has become a very active research field. As a continuation of previous work that showed that 2-thioxanthine (2TX) is an irreversible inhibitor of zinc finger (ZnF)-containing Fpg/Nei DNA glycosylases, we designed and synthesized a mini-library of 2TX-derivatives (TXn) and evaluated their ability to inhibit Fpg/Nei enzymes. Among forty compounds, four TXn were better inhibitors than 2TX for Fpg. Unexpectedly, but very interestingly, two dithiolated derivatives more selectively and efficiently inhibit the zincless finger (ZnLF)-containing enzymes (human and mimivirus Neil1 DNA glycosylases hNeil1 and MvNei1, respectively). By combining chemistry, biochemistry, mass spectrometry, blind and flexible docking and X-ray structure analysis, we localized new TXn binding sites on Fpg/Nei enzymes. This endeavor allowed us to decipher at the atomic level the mode of action for the best TXn inhibitors on the ZnF-containing enzymes. We discovered an original inhibition mechanism for the ZnLF-containing Fpg/Nei DNA glycosylases by disulfide cyclic trimeric forms of dithiopurines. This work paves the way for the design and synthesis of a new structural class of inhibitors for selective pharmacological targeting of hNeil1 in cancer and neurodegenerative diseases.

Novel epidithiodiketopiperazines as anti-viral zinc ejectors of the Feline Immunodeficiency Virus (FIV) nucleocapsid protein as a model for HIV infection

Focused libraries of multi-substituted epidithiodiketopiperazines (ETP) were prepared and evaluated for efficacy of inhibiting the nucleocapsid protein function of the Feline Immunodeficiency Virus (FIV) as a model for HIV. This activity was compared and contrasted to observed toxicity utilising an in-vitro cell culture approach. This resulted in the identification of several promising lead compounds with nanomolar potency in cells with low toxicity and a favorable therapeutic index.

Synthesis and comparison of substituted 1,2,3-dithiazole and 1,2,3-thiaselenazole as inhibitors of the feline immunodeficiency virus (FIV) nucleocapsid protein as a model for HIV infection

We report the first biological evaluation the 1,2,3-thiaselenazole class of compound and utilising a concise synthetic approach of sulfur extrusion, selenium insertion of the 1,2,3-dithiazoles. We created a small diverse library of compounds to contrast the two ring systems. This approach has highlighted new structure activity relationship insights and lead to the development of sub-micro molar anti-viral compounds with reduced toxicity. The 1,2,3-thiaselenazole represents a new class of potential compounds for the treatment of FIV and HIV.

NCp7: targeting a multitasking protein for next-generation anti-HIV drug development part 1: covalent inhibitors

The major internal component of the HIV virion core is the nucleocapsid protein 7 (NCp7), a small, highly basic protein that is essential for multiple stages of the viral replicative cycle, and whose structure is preserved in all viral strains, including clinical isolates from therapy-experienced patients. This key protein is recognised as a potential target for an effective next-generation antiretroviral therapy, because it could offer the possibility to develop broad-spectrum agents that are less prone to select for resistant strains. Here, we provide a comprehensive overview of the covalent NCp7 inhibitors that have emerged over the past 25 years of drug discovery campaigns, emphasising, where possible, their structure-activity relationships (SARs) and pharmacophoric features.

Preclinical evaluation of a mercaptobenzamide and its prodrug for NCp7-targeted inhibition of human immunodeficiency virus

Although the effective use of highly active antiretroviral therapy results in the suppression of virus production in infected individuals, it does not eliminate the infection and low level virus production in cells harboring virus in sanctuary sites. Thus, the continued search for new antiretroviral agents with unique and different mechanisms of HIV inhibition remains critical, and compounds that can reduce the level of virus production from cells already infected with HIV, as opposed to preventing de novo infection, would be of great benefit. A mercaptobenzamide (MDH-1-38) and its prodrug (NS1040) are being developed as potential therapeutic compounds targeting the zinc finger of HIV nucleocapsid. In the presence of esterase enzymes, NS1040 is designed to be converted to MDH-1-38 which has antiviral activity. While we presume that NS1040 is rapidly converted to MDH-1-38 in all experiments, the two compounds were tested side-by-side to determine whether the presence of a prodrug affects the antiviral activity or mechanism of action. The two compounds were evaluated against a panel of HIV-1 clinical isolates in human PBMCs and monocyte-macrophages and yielded EC₅₀ values ranging from 0.7 to 13 μM with no toxicity up to 100 μM. MDH-1-38 and NS1040 remained equally active in human PBMCs in the presence of added serum proteins as well as against HIV-1 isolates resistant to reverse transcriptase, integrase or protease inhibitors. Cell-based and biochemical mechanism of antiviral action assays demonstrated MDH-1-38 and NS1040 were virucidal at concentrations of 15 and 50 μM, respectively. Cell to cell transmission of HIV in multiple passages was significantly reduced in CEM-SS and human PBMCs by reducing progeny virus infectivity at compound concentrations greater than 2 μM. The combination of either MDH-1-38 or NS1040 with other FDA-approved HIV drugs yielded additive to synergistic antiviral interactions with no evidence of antiviral antagonism or synergistic toxicity. Serial dose escalation was used in attempts to select for HIV strains resistant to MDH-1-38 and NS1040. Virus at several passages failed to replicate in cells treated at increased compound concentrations, which is consistent with the proposed mechanism of action of the virus inactivating compounds. Through 14 passages, resistance to the compounds has not been achieved. Most HIV inhibitors with mechanism of antiviral action targeting a viral protein would have selected for a drug resistant virus within 14 passages. These studies indicate that these NCp7-targeted compounds represent new potent anti-HIV drug candidates which could be effectively used in combination with all approved anti-HIV drugs.

Novel agents that downregulate EGFR, HER2, and HER3 in parallel

EGFR, HER2, and HER3 contribute to the initiation and progression of human cancers, and are therapeutic targets for monoclonal antibodies and tyrosine kinase inhibitors. An important source of resistance to these agents arises from functional redundancy among EGFR, HER2, and HER3. EGFR family members contain conserved extracellular structures that are stabilized by disulfide bonds. Compounds that disrupt extracellular disulfide bonds could inactivate EGFR, HER2, and HER3 in unison. Here we describe the identification of compounds that kill breast cancer cells that overexpress EGFR or HER2. Cell death parallels downregulation of EGFR, HER2, and HER3. These compounds disrupt disulfide bonds and are termed Disulfide Bond Disrupting Agents (DDAs). DDA RBF3 exhibits anticancer efficacy in vivo at 40 mg/kg without evidence of toxicity. DDAs may complement existing EGFR-, HER2-, and HER3-targeted agents that function through alternate mechanisms of action, and combination regimens with these existing drugs may overcome therapeutic resistance.

Identification and characterization of a new type of inhibitor against the human immunodeficiency virus type-1 nucleocapsid protein

Background

The human immunodeficiency virus type-1 (HIV-1) nucleocapsid protein (NC) is an essential and multifunctional protein involved in multiple stages of the viral life cycle such as reverse transcription, integration of proviral DNA, and especially genome RNA packaging. For this reason, it has been considered as an attractive target for the development of new anti-HIV drugs. Although a number of inhibitors of NC have been reported thus far, the search for NC-specific and functional inhibitor(s) with a good antiviral activity continues.

Results

In this study, we report the identification of A1752, a small molecule with inhibitory action against HIV-1 NC, which shows a strong antiviral efficacy and an IC₅₀ around 1 μM. A1752 binds directly to HIV-1 NC, thereby inhibiting specific chaperone functions of NC including Psi RNA dimerization and complementary trans-activation response element (cTAR) DNA destabilization, and it also disrupts the proper Gag processing. Further analysis of the mechanisms of action of A1752 also showed that it generates noninfectious viral particles with defects in uncoating and reverse transcription in the infected cells.

Conclusions

These results demonstrate that A1752 is a specific and functional inhibitor of NC with a novel mode of action and good antiviral efficacy. Thus, this agent provides a new type of anti-HIV NC inhibitor candidate for further drug development.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-015-0218-9) contains supplementary material, which is available to authorized users.

Transcriptional repressor ZEB2 promotes terminal differentiation of CD8+ effector and memory T cell populations during infection

ZEB2 is a multi-zinc-finger transcription factor known to play a significant role in early neurogenesis and in epithelial-mesenchymal transition-dependent tumor metastasis. Although the function of ZEB2 in T lymphocytes is unknown, activity of the closely related family member ZEB1 has been implicated in lymphocyte development. Here, we find that ZEB2 expression is up-regulated by activated T cells, specifically in the KLRG1(hi) effector CD8(+) T cell subset. Loss of ZEB2 expression results in a significant loss of antigen-specific CD8(+) T cells after primary and secondary infection with a severe impairment in the generation of the KLRG1(hi) effector memory cell population. We show that ZEB2, which can bind DNA at tandem, consensus E-box sites, regulates gene expression of several E-protein targets and may directly repress Il7r and Il2 in CD8(+) T cells responding to infection. Furthermore, we find that T-bet binds to highly conserved T-box sites in the Zeb2 gene and that T-bet and ZEB2 regulate similar gene expression programs in effector T cells, suggesting that T-bet acts upstream and through regulation of ZEB2. Collectively, we place ZEB2 in a larger transcriptional network that is responsible for the balance between terminal differentiation and formation of memory CD8(+) T cells.

Nucleocapsid Protein: A Desirable Target for Future Therapies Against HIV-1

The currently available anti-HIV-1 therapeutics is highly beneficial to infected patients. However, clinical failures occur as a result of the ability of HIV-1 to rapidly mutate. One approach to overcome drug resistance is to target HIV-1 proteins that are highly conserved among phylogenetically distant viral strains and currently not targeted by available therapies. In this respect, the nucleocapsid (NC) protein, a zinc finger protein, is particularly attractive, as it is highly conserved and plays a central role in virus replication, mainly by interacting with nucleic acids. The compelling rationale for considering NC as a viable drug target is illustrated by the fact that point mutants of this protein lead to noninfectious viruses and by the inability to select viruses resistant to a first generation of anti-NC drugs. In our review, we discuss the most relevant properties and functions of NC, as well as recent developments of small molecules targeting NC. Zinc ejectors show strong antiviral activity, but are endowed with a low therapeutic index due to their lack of specificity, which has resulted in toxicity. Currently, they are mainly being investigated for use as topical microbicides. Greater specificity may be achieved by using non-covalent NC inhibitors (NCIs) targeting the hydrophobic platform at the top of the zinc fingers or key nucleic acid partners of NC. Within the last few years, innovative methodologies have been developed to identify NCIs. Though the antiviral activity of the identified NCIs needs still to be improved, these compounds strongly support the druggability of NC and pave the way for future structure-based design and optimization of efficient NCIs.

Advances in targeting nucleocapsid-nucleic acid interactions in HIV-1 therapy

The continuing challenge of HIV-1 treatment resistance in patients creates a need for the development of new antiretroviral inhibitors. The HIV nucleocapsid (NC) protein is a potential therapeutic target. NC is necessary for viral RNA packaging and in the early stages of viral infection. The high level of NC amino acid conservation among all HIV-1 clades suggests a low tolerance for mutations. Thus, NC mutations that could arise during inhibitor treatment to provide resistance may render the virus less fit. Disruption of NC function provides a unique opportunity to strongly dampen replication at multiple points during the viral life cycle with a single inhibitor. Although NC exhibits desirable features for a potential antiviral target, the structural flexibility, size, and the presence of two zinc fingers makes small molecule targeting of NC a challenging task. In this review, we discuss the recent advances in strategies to develop inhibitors of NC function and present a perspective on potential novel approaches that may help to overcome some of the current challenges in the field.

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.

A phenyl-thiadiazolylidene-amine derivative ejects zinc from retroviral nucleocapsid zinc fingers and inactivates HIV virions

Background

Sexual acquisition of the human immunodeficiency virus (HIV) through mucosal transmission may be prevented by using topically applied agents that block HIV transmission from one individual to another. Therefore, virucidal agents that inactivate HIV virions may be used as a component in topical microbicides.

Results

Here, we have identified 2-methyl-3-phenyl-2H-[1,2,4]thiadiazol-5-ylideneamine (WDO-217) as a low-molecular-weight molecule that inactivates HIV particles. Both HIV-1 and HIV-2 virions pretreated with this compound were unable to infect permissive cells. Moreover, WDO-217 was able to inhibit infections of a wide spectrum of wild-type and drug-resistant HIV-1, including clinical isolates, HIV-2 and SIV strains. Whereas the capture of virus by DC-SIGN was unaffected by the compound, it efficiently prevented the transmission of DC-SIGN-captured virus to CD4⁺ T-lymphocytes. Interestingly, exposure of virions to WDO-217 reduced the amount of virion-associated genomic RNA as measured by real-time RT-qPCR. Further mechanism-of-action studies demonstrated that WDO-217 efficiently ejects zinc from the zinc fingers of the retroviral nucleocapsid protein NCp7 and inhibits the cTAR destabilization properties of this protein. Importantly, WDO-217 was able to eject zinc from both zinc fingers, even when NCp7 was bound to oligonucleotides, while no covalent interaction between NCp7 and WDO-217 could be observed.

Conclusion

This compound is a new lead structure that can be used for the development of a new series of NCp7 zinc ejectors as candidate topical microbicide agents.

Inhibition of Junin virus RNA synthesis by an antiviral acridone derivative

There are no specific approved drugs for the treatment of agents of viral hemorrhagic fevers (HF) and antiviral therapies against these viruses are urgently needed. The present study characterizes the potent and selective antiviral activity against the HF causing arenavirus Junin virus (JUNV) of the compound 10-allyl-6-chloro-4-methoxy-9(10H)-acridone, designated 3f. The effectiveness of 3f to inhibit JUNV multiplication was not importantly affected by the initial multiplicity of infection, with similar effective concentration 50% (EC(50)) values in virus yield inhibition assays performed in Vero cells in the range of 0.2-40 plaque forming units (PFU)/cell. Mechanistic studies demonstrated that 3f did not affect the initial steps of adsorption and internalization. The subsequent process of viral RNA synthesis was strongly inhibited, as quantified by real time RT-PCR in compound-treated cells relative to non-treated cells. The addition of exogenous guanosine rescued the infectivity and RNA synthesis of JUNV in 3f-treated cells in a dose-dependent manner, but the reversal was partial, suggesting that the reduction of the GTP pool contributed to the antiviral activity of 3f, but it was not the main operative mechanism. The comparison of 3f with two other viral RNA inhibitors, ribavirin and mycophenolic acid, showed that ribavirin did not act against JUNV through the cellular enzyme inosine monophosphate dehydrogenase (IMPDH) inhibition whereas the anti-JUNV activity of mycophenolic acid was mainly targeted at this enzyme.

Beyond plasma membrane targeting: role of the MA domain of Gag in retroviral genome encapsidation

The MA (matrix) domain of the retroviral Gag polyprotein plays several critical roles during virus assembly. Although best known for targeting the Gag polyprotein to the inner leaflet of the plasma membrane for virus budding, recent studies have revealed that MA also contributes to selective packaging of the genomic RNA (gRNA) into virions. In this Review, we summarize recent progress in understanding how MA participates in genome incorporation. We compare the mechanisms by which the MA domains of different retroviral Gag proteins influence gRNA packaging, highlighting variations and similarities in how MA directs the subcellular trafficking of Gag, interacts with host factors and binds to nucleic acids. A deeper understanding of how MA participates in these diverse functions at different stages in the virus assembly pathway will require more detailed information about the structure of the MA domain within the full-length Gag polyprotein. In particular, it will be necessary to understand the structural basis of the interaction of MA with gRNA, host transport factors and membrane phospholipids. A better appreciation of the multiple roles MA plays in genome packaging and Gag localization might guide the development of novel antiviral strategies in the future.

Inhibition of HIV-1 replication by a bis-thiadiazolbenzene-1,2-diamine that chelates zinc ions from retroviral nucleocapsid zinc fingers

The human immunodeficiency virus type 1 (HIV-1) nucleocapsid p7 (NCp7) protein holds two highly conserved "CCHC" zinc finger domains that are required for several phases of viral replication. Basic residues flank the zinc fingers, and both determinants are required for high-affinity binding to RNA. Several compounds were previously found to target NCp7 by reacting with the sulfhydryl group of cysteine residues from the zinc fingers. Here, we have identified an N,N'-bis(1,2,3-thiadiazol-5-yl)benzene-1,2-diamine (NV038) that efficiently blocks the replication of a wide spectrum of HIV-1, HIV-2, and simian immunodeficiency virus (SIV) strains. Time-of-addition experiments indicate that NV038 interferes with a step of the viral replication cycle following the viral entry but preceding or coinciding with the early reverse transcription reaction, pointing toward an interaction with the nucleocapsid protein p7. In fact, in vitro, NV038 efficiently depletes zinc from NCp7, which is paralleled by the inhibition of the NCp7-induced destabilization of cTAR (complementary DNA sequence of TAR). A chemical model suggests that the two carbonyl oxygens of the esters in this compound are involved in the chelation of the Zn(2+) ion. This compound thus acts via a different mechanism than the previously reported zinc ejectors, as its structural features do not allow an acyl transfer to Cys or a thiol-disulfide interchange. This new lead and the mechanistic study presented provide insight into the design of a future generation of anti-NCp7 compounds.

Real time PCR for rapid determination of susceptibility of adenovirus to antiviral drugs

Human adenoviruses (HAdV) are associated with respiratory, ocular and gastrointestinal infections as well as potentially fatal disseminated disease in highly immunocompromised patients. Although there is no specific FDA approved treatment for HAdV infections, some antivirals are used in certain patients. The in vitro antiviral assays for HAdV are not standardized and are usually time consuming. The objective of this study was to evaluate a real time PCR assay for rapid determination of susceptibility of HAdV to antiviral drugs. The nucleoside analogue stavudine (d4T) was used as test drug in A549 cells infected with HAdV5. The antiviral assay measured the reduction of the HAdV DNA levels in culture supernatants by real time PCR using specific primers that amplify a conserved region of the hexon gene. This real time PCR assay demonstrated that stavudine was a selective inhibitor for HAdV5, since the effective concentration 50% (EC(50)) ranged from 0.08 to 0.12 mM at multiplicity of infection between 0.001 and 1. Furthermore, EC(50) showed a high correlation with plaque reduction and virus yield inhibition assays (r(2)=0.9938 and r(2)=0.9468, respectively). In conclusion, the real time PCR-based antiviral assay is rapid, reproducible and could replace classical and more labor-intensive infectivity assays.

Effect of Cysteine vs. Histidine on the Electronic Structure of Zn2+Upon Complex Formation

The local electronic structure at Zn2+ions during complex formation with histidine and cysteine has been studied by near edge x-ray absorption fine structure spectroscopy at the Zn L-edge. At pH ≅ 5 both histidine and cysteine have carboxylate and amino groups able to form complexes with cations in solution such as Zn2+. Compared to histidine, cysteine has an extra thiolate group which can chelate Zn2+. This investigation shows that histidine is chelating the Zn2+ion mainly via the amino group, while cysteine chelates primarily via the thiolate group. The nature of the empty molecular orbitals involved in the transitions has been analyzed using density functional theory including the solvent effects. By comparing the calculated results with the experimental observations, we conclude that histidine affects primarily the Zn2+electronic states of d-symmetry, while cysteine affects both s- and d-states. This mechanism is important for understanding the zinc sulfhydryl bond in zinc finger proteins, where cysteine and histidine in the protein are chelating Zn2+.

Synthesis and redox-enzyme modulation by amino-1,4-dihydro-benzo[d][1,2]dithiine derivatives

A convenient method to prepare a series of benzodithiine derivatives was developed, via the synthesis of cyclic disulfide building blocks containing an amino-group linker. Some of the novel cyclic disulfide compounds are shown to modulate the activity of the redox-enzyme glutathione reductase.

Identification by high throughput screening of small compounds inhibiting the nucleic acid destabilization activity of the HIV-1 nucleocapsid protein

Due to its highly conserved zinc fingers and its nucleic acid chaperone properties which are critical for HIV-1 replication, the nucleocapsid protein (NC) constitutes a major target in AIDS therapy. Different families of molecules targeting NC zinc fingers and/or inhibiting the binding of NC with its target nucleic acids have been developed. However, their limited specificity and their cellular toxicity prompted us to develop a screening assay to target molecules able to inhibit NC chaperone properties, and more specifically the initial NC-promoted destabilization of the nucleic acid secondary structure. Since this destabilization is critically dependent on the properly folded fingers, the developed assay is thought to be highly specific. The assay was based on the use of cTAR DNA, a stem-loop sequence complementary to the transactivation response element, doubly labelled at its 5' and 3' ends by a rhodamine 6G fluorophore and a fluorescence quencher, respectively. Addition of NC(12-55), a peptide corresponding to the zinc finger domain of NC, to this doubly-labelled cTAR, led to a partial melting of the cTAR stem, which increases the distance between the two labels and thus, restores the rhodamine 6G fluorescence. Thus, positive hits were detected through the decrease of rhodamine 6G fluorescence. An "in-house" chemical library of 4800 molecules was screened and five compounds with IC(50) values in the micromolar range have been selected. The hits were shown by mass spectrometry and fluorescence anisotropy titration to prevent binding of NC(12-55) to cTAR through direct interaction with the NC folded fingers, but without promoting zinc ejection. These non-zinc ejecting NC binders are a new series of anti-NC molecules that could be used to rationally design molecules with potential anti-viral activities.

Targeting human immunodeficiency virus type 1 assembly, maturation and budding

The targets for licensed drugs used for the treatment of human immunodeficiency virus type 1 (HIV-1) are confined to the viral reverse transcriptase (RT), protease (PR), and the gp41 transmembrane protein (TM). While currently approved drugs are effective in controlling HIV-1 infections, new drug targets and agents are needed due to the eventual emergence of drug resistant strains and drug toxicity. Our increased understanding of the virus life-cycle and how the virus interacts with the host cell has unveiled novel mechanisms for blocking HIV-1 replication. This review focuses on inhibitors that target the late stages of virus replication including the synthesis and trafficking of the viral polyproteins, viral assembly, maturation and budding. Novel approaches to blocking the oligomerization of viral enzymes and the interactions between viral proteins and host cell factors, including their feasibility as drug targets, are discussed.

Characterization of human immunodeficiency virus type 1 (HIV-1) containing mutations in the nucleocapsid protein at a putative HIV-1 protease cleavage site

The HIV-1 nucleocapsid protein (NC) has been hypothesized to be cleaved by the viral protease (PR) during early infection. Characterization of viruses, with amino-acid substitutions that modulate PR cleavage of NC in vitro, was performed in cell culture. Two of the NC mutants, NCN17F and NCN17G, had decreased infectivity and exhibited severe H9 replication defects. Examination of viral DNA after infections revealed defects in reverse transcription and integration, although integration defects were cell-type dependent. However, while the defects in reverse transcription and integration correlate with lowered infectivity in a single-round of infection, they did not approach the magnitude of the replication defect measured in H9 cells over multiple rounds. Importantly, we fail to see evidence that H9 cells are re-infected with the NCN17G and NCN17F viruses 24 h after the initial infection, which suggests that the principal defect caused by these NC mutations occurs during late events of viral replication.

Molecular characterization of the HIV-1 gag nucleocapsid gene associated with vertical transmission

BACKGROUND

The human immunodeficiency virus type 1 (HIV-1) nucleocapsid (NC) plays a pivotal role in the viral lifecycle: including encapsulating the viral genome, aiding in strand transfer during reverse transcription, and packaging two copies of the viral genome into progeny virions. Another gag gene product, p6, plays an integral role in successful viral budding from the plasma membrane and inclusion of the accessory protein Vpr within newly budding virions. In this study, we have characterized the gag NC and p6 genes from six mother-infant pairs following vertical transmission by performing phylogenetic analysis and by analyzing the degree of genetic diversity, evolutionary dynamics, and conservation of functional domains.

RESULTS

Phylogenetic analysis of 168 gag NC and p6 genes sequences revealed six separate subtrees that corresponded to each mother-infant pair, suggesting that epidemiologically linked individuals were closer to each other than epidemiologically unlinked individuals. A high frequency (92.8%) of intact open reading frames of NC and p6 with patient and pair specific sequence motifs were conserved in mother-infant pairs' sequences. Nucleotide and amino acid distances showed a lower degree of viral heterogeneity, and a low degree of estimates of genetic diversity was also found in NC and p6 sequences. The NC and p6 sequences from both mothers and infants were found to be under positive selection pressure. The two important functional motifs within NC, the zinc-finger motifs, were highly conserved in most of the sequences, as were the gag p6 Vpr binding, AIP1 and late binding domains. Several CTL recognition epitopes identified within the NC and p6 genes were found to be mostly conserved in 6 mother-infant pairs' sequences.

CONCLUSION

These data suggest that the gag NC and p6 open reading frames and functional domains were conserved in mother-infant pairs' sequences following vertical transmission, which confirms the critical role of these gene products in the viral lifecycle.

A novel RING-type ubiquitin ligase breast cancer-associated gene 2 correlates with outcome in invasive breast cancer

The RING finger family of proteins possess ubiquitin ligase activity and play pivotal roles in protein degradation and receptor-mediated endocytosis. In this study, we examined whether the breast cancer-associated gene 2 (BCA2), a novel RING domain protein, has E3 ubiquitin ligase activity and investigated its expression status in breast tumors. The full-length BCA2 gene was cloned from the human breast cancer cell line MDA-MB-468. It encodes an open reading frame of 304 amino acids and contains a RING-H2 domain. BCA2 maps to chromosome 1q21.1, a region known to harbor cytogenetic aberrations in breast cancers. We found that the BCA2 protein has an intrinsic autoubiquitination activity, the hallmark of E3 ligases, whereas mutant RING protein is not autoubiquitinated. This indicates that the BCA2 ubiquitin ligase activity is dependent on the RING-H2 domain. Using tissue microarrays and immunohistochemistry, we found strong to intermediate BCA2 staining in 56% of 945 invasive breast cancers cases, which was significantly correlated with positive estrogen receptor status [odds ratio (OR), 1.51; P = 0.004], negative lymph node status (OR, 0.73; P = 0.02), and an increase in disease-free survival for regional recurrence (OR, 0.45; P = 0.03). Overexpression of BCA2 increased proliferation and small interfering RNA inhibited growth of T47D human breast cancer cells and NIH3T3 mouse cells. The autoubiquitination activity of BCA2 indicates that it is a novel RING-type E3 ligase. Its association with clinical measures and its effects on cell growth indicate that BCA2 may be important for the ubiquitin modification of proteins crucial to breast carcinogenesis and growth.

Optimization of unique, uncharged thioesters as inhibitors of HIV replication

A combinatorial chemistry approach was employed to prepare a restricted library of N-substituted S-acyl-2-mercaptobenzamide thioesters. It was shown that many members of this chemotype display anti-HIV activity via their ability to interact with HIV-1, HIV-2, SIV-infected cells, cell-free virus, and chronically and latently infected cells in a manner consistent with targeting of the highly conserved HIV-1 NCp7 zinc fingers. Compounds were initially screened using two different in vitro antiviral assays and evaluated for stability in neutral buffer containing 10% pooled human serum using a spectrophotometric assay. These data revealed that there was no significant correlation between thioester stability and antiviral activity, however, a slight inverse correlation between serum stability and virucidal activity was noted. Based on the virucidal capability and the ability to select lead compounds to inhibit virus expression from latently infected TNFalpha-induced U1 cells, we next determined if these compounds could prevent HIV cell-to-cell transmission. Several thioesters demonstrated potent inhibition of HIV cell-to-cell transmission with EC50 values in the 80-100 nM range. Thus, we have optimized a series of restricted thioesters and provided evidence that serum stability is not required for antiviral activity. Moreover, selected compounds show potential for development as topical microbicides.

A general carbometalation, three component coupling strategy for the synthesis of α,β-unsaturated γ-sultines including thio-rofecoxib, a selective COX-2 inhibitor

Magnesium mediated carbometalation (Grignard addition) to appropriate propargyl alcohols to synthesize a cross-section of variably substituted alpha,beta-unsaturated gamma-sultines is described. Thio-rofecoxib, a selective COX-2 inhibitor (12), is synthesized by this method and its IC(50), microM COX-1 and COX-2 inhibition, and whole blood stability values reported.

Understanding HIV resistance, fitness, replication capacity and compensation: targeting viral fitness as a therapeutic strategy

The increasingly prevalent emergence of drug-resistant virus strains in patients being treated with highly active antiretroviral regimens and the increasing rates of transmission of drug-resistant virus strains have focused attention on the critical need for additional antiretroviral agents with novel mechanisms of action and enhanced potency. Furthermore, novel means of employing highly active antiretroviral therapy are needed to reduce or eliminate the virological treatment failures that currently occur. Over the past several years, evidence has mounted supporting the fact that the emergence of resistant strains is associated with reductions in viral fitness, yielding decreases in plasma virus load in treated patients harbouring resistant populations of the virus. Additional mutations that serve to modify fitness (compensatory mutations) and mutations that impact the viral replication capacity also emerge under the selective pressure of drug treatment, and have both negative and positive effects on virus growth. Fitness is generally accepted to refer to the ability of HIV to replicate in a defined environment and thus is used to describe the viral replication potential in the absence of the drug. Although viral fitness and replication capacity are related in some ways, it is important to recognise that viral fitness is not the same as viral replication capacity. This review will assess the recent literature on antiviral drug resistance, viral fitness and viral replication capacity, and discuss means by which the adaptability of HIV to respond rapidly to antiviral treatment through mutation may be used against it. This would be done by treating patients with an aim to lock the deleterious mutations into the resistant virus genome, resulting in a positive therapeutic outcome despite the presence of resistance to the selecting agents. The review will specifically discuss the literature on nucleoside and non-nucleoside reverse transcriptase inhibitors, protease inhibitors, integrase inhibitors, fusion inhibitors, as well as other biological factors involved in viral fitness.

A system of protein target sequences for anti-RNA-viral chemotherapy by a vitamin B6-derived zinc-chelating trioxa-adamantane-triol

The synthesis of the structurally unusual heterotricyclic compound 1-[3-hydroxy-5-(hydroxymethyl)-2-methyl-4-pyridinyl]-2,8,9-trioxaadamantane-3,5,7-triol (trivially named bananin, BN) from pyridoxylidenephloroglucinol and a theoretical prospect on possible biological activities of BN are presented in this report. Pyridoxylidenephloroglucinol is synthesized by Knoevenagel condensation of the vitamin B6 aldehyde pyridoxal with phloroglucinol. Pyridoxylidenephloroglucinol rearranges to light-yellow (4'RS)-1',4'-dihydrobananin by refluxing in 5M hydrochloric acid. Air oxidation subsequently forms BN in the heat which immediately yields orange-yellow (4'RS)-4'-chloro-1',4'-dihydrobananin by 1,4-addition of hydrogen chloride. This intermediate could be isolated but, interestingly, not a BN hydrochloride. Brown BN is finally achieved by base-catalyzed elimination of hydrogen chloride from (4'RS)-4'-chloro-1',4'-dihydrobananin. Regarding possible biological activities, it was demonstrated that BN acts as zinc (Zn2+) chelator. Therefore, a target of interest could be the human immunodeficiency virus type 1 (HIV-1) zinc finger HIV-1 RNA-binding nucleocapsid protein p7 (NCp7). Through suggested zinc ejection from HIV-1 genomic RNA psi-element-binding and HIV-1-RNA-duplex packaging NCp7 by BN, thus rendering NCp7 functionally obsolete, it is deduced that HIV-1 replication and effective infectious virion encapsidation could be inhibited by BN. Furthermore, theoretical and structural considerations propose that BN is converted into bananin 5'-monophosphate (BNP) by the cell type-ubiquitous human enzyme pyridoxal kinase (EC 2.7.1.35). Together with the putative antilentiviral retinoid vitamin A-vitamin B6 conjugate analogue B6RA (Kesel, A. J. Biochem. Biophys. Res. Comm. 2003, 300, 793), BNP is postulated to serve as effector in a system of protein target sequences RX(D/E) of RNA virus components. Human immunodeficiency Retroviridae (HIVs) could possibly be influenced by B6RA and BNP. In addition, candidate targets of B6RA and BNP could be adsorption, transcription and/or viral RNA replication of an interestingly wide RNA virus selection including Picornaviridae (poliovirus, human coxsackievirus, hepatitis A virus), Flaviviridae (yellow fever virus, Dengue virus, West Nile virus, Kunjin virus, St. Louis encephalitis virus, hepatitis C virus), Togaviridae (rubella virus), Coronaviridae (human coronavirus, human SARS-associated coronavirus), Rhabdoviridae (rabies virus), Paramyxoviridae (human parainfluenza virus, measles virus, human respiratory syncytial virus), Filoviridae (Marburg virus, Ebola virus), Bornaviridae (Borna disease virus), Bunyaviridae (Hantaan virus), Arenaviridae (Lassa virus), and Reoviridae (human rotavirus). The postulated scope of 'metabolically trapped' BNP might resemble the antiviral spectrum of the RNA-viral virustatic ribavirin.

Synthesis, resolution, and determination of the absolute configuration of the enantiomers of cis-4,5-dihydroxy-1,2-dithiane 1,1-dioxide, an HIV-1NCp7 inhibitor

The anti-HIV activity of (+/-)-cis-4,5-dihydroxy-1,2-dithiane 1,1-dioxide [(+/-)-cis-1,1-dioxo-[1,2]-dithiane-4,5-diol, NSC-624151] and its attack on the zinc finger domain of the HIV-1 nucleocapsid p7 (NCp7) protein has been established [Rice, W. G.; Baker, D. C.; Schaeffer, C. A.; Graham, L.; Bu, M.; Terpening, S.; Clanton, D.; Schultz, R.; Bader, J. P.; Buckheit, R. W.; Field, L.; Singh, P. K. Turpin, J. A. Antimicrob. Agents Chemother. 1997, 41, 419]. In order to determine which enantiomer of NSC-624151 is the more active component, the compound was resolved via its bis-'Mosher ester', which was prepared via its reaction with two equiv of (-)-(R)-alpha-methoxy-alpha-(trifluoromethyl)phenylacetyl chloride. The diastereoisomeric esters were separated, and each ester was hydrolyzed to yield enantiomers with (D)(21) +151 degrees (c 0.5, MeOH) and (D)(21) -146 degrees (c 0.5, MeOH). Single-crystal X-ray analysis of the (-)-bis-'Mosher ester' showed that the (-)-enantiomer is the (4S, 5R)-compound. The (-)-enantiomer (NSC 693195) was ca. twice as active (EC(50) 8.8+/-0.2 microM) as its (+)-counterpart (NSC 693194) (EC(50) 16.2+/-2.4 microM) in the XTT assay against HIV-1. All three compounds were found to be approximately equally effective in promoting Zn ejection from the NCp7 zinc finger. As the more anti-HIV active enantiomer is only slightly more active than the racemic form, it appears to offer no advantages over the racemic form.

Differential inhibitory action of two azoic compounds against arenaviruses

The action of five azo-based compounds against the arenaviruses Junin (JUNV) and Tacaribe (TCRV) was evaluated in vitro by a virus yield inhibition assay in Vero cells and a cell-free virion inactivation assay. The compound 2-azo-(1'-(2'-nitroso)naphthyl)-benzoate (ANNB) was the most effective inhibitor of arenavirus production in Vero cells with EC(50) (effective concentration 50%) values in the range 6.5-26.2 microM and without inactivating properties. By contrast, the azodicarbonamide (ADA) was very effective in inactivating both arenaviruses with IC(50) (inactivating concentration 50%) values of 7.6 and 5.3 microM against JUNV and TCRV, respectively. The virucidal activity of ADA was time- and temperature-dependent. ANNB had no inhibitory action on virus binding or penetration of target cells and did not affect the synthesis of viral proteins. The most likely event susceptible to ANNB would be the process of intracellular virion assembly.

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.

Mode of inactivation of arenaviruses by disulfide-based compounds

Several disulfide-based compounds, including intermolecular aromatic disulfides of the type Ph-S-S-Ph and dithianes with the sulfur atoms tethered in a ring structure, have shown effective inhibitory activity against the arenaviruses Junin (JUNV), agent of Argentine hemorrhagic fever, and Tacaribe (TCRV). These compounds showed a strong virucidal effect with inactivating concentration 50% (IC(50)) values in the range 0.6-5.0 microM, and also were effective to reduce virus yields from infected cells. The mode of inactivating action of two active compounds, the aromatic bis disulfide NSC20625 and the dithiane NSC624152, was further studied. Both compounds were able to inactivate arenaviruses after a few minutes of direct contact with virions, in a concentration- and time-dependent manner. The ability of drug-treated virus to perform several steps of the replication cycle was analyzed. The killed virus particles were found to bind and enter to Vero cells with the same efficacy as infectious native virions, but the ability of inactivated virions to synthesize viral proteins in Vero cells was abolished. Thus, treatment of JUNV and TCRV with these compounds destroyed virion infectivity, generating particles which entered the host cell but were unable to complete the viral biosynthetic processes.

Considerations and development of topical microbicides to inhibit the sexual transmission of HIV

The increased incidence of HIV/AIDS disease in women aged 15 - 49 years has identified the urgent need for a female-controlled, efficacious and safe vaginal topical microbicide. To meet this challenge, new topical microbicide candidates consisting of molecules or formulations that modify the genital environment (BufferGel, engineered Lactobacillus, over-the-counter lubricants), surfactants (C31D/Savvy, sodium dodecyl sulfate, sodium lauryl sulfate), polyanionic polymers (PRO 2000, beta-cyclodextrin, Carraguard, CAP, D2S, SPL-7013), proteins (cyanovirin-N, monoclonal antibodies, thromspondin-1 peptides, Pokeweed antiviral protein and others), reverse transcription inhibitors (PMPA [Tenofovir ]), UC-781, SJ-3366, DABO and thiourea) and other molecules (NCp7-specific virucides, chemokine receptor agonists/antagonists, WHI-05 and WHI-07) are currently being investigated for activity, safety and efficacy. This review will assess the development of these molecules in the context of cervicovaginal defences and the clinical failure of nonoxynol-9.

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.

Synthesis and biological properties of amino acid amide ligand-based pyridinioalkanoyl thioesters as anti-HIV agents

Hyper-mutable retroviruses such as HIV can become rapidly resistant to drugs used to treat infection. Strategies for coping with drug-resistant strains of virus include combination therapies, using viral protease and reverse transcriptase inhibitors. Another approach is the development of antiviral agents that attack mutationally nonpermissive targets that have functions essential for viral replication. Thus, the highly conserved nucleocapsid protein, NCp7, was chosen as a prime target in our search for novel anti-HIV agents that can overcome the problem of viral drug resistance. Recently, we reported (J. Med. Chem. 1999, 42, 67) a novel chemotype, the pyridinioalkanoyl thioesters (PATEs), based on 2-mercaptobenzamides as the thiol component and having its amide nitrogen substituted with various phenylsulfonyl moieties. These compounds were identified as relatively nontoxic anti-HIV agents in the XTT cytoprotection assay. In this study, we wish to report a separate genre of active PATEs wherein the thiol component consists of an N-2-mercaptobenzoyl-amino acid derivative. Active derivatives (EC(50) < 10 microM) reported herein were confined to amino acid primary amides or methyl amides having side chains no larger than isobutyl. Amino acids terminating in free carboxyl or carboxylic acid ester groups were mostly inactive. Selected compounds were shown to be active on chronically infected CEM/SK-1, TNFalpha-induced U1, ACH-2 cells and virucidal on cell-free virus, latently infected U1 cells and acutely infected primary peripheral blood mononuclear cells (PBMCs).

Benzamide-based thiolcarbamates: a new class of HIV-1 NCp7 inhibitors

The HIV-1 nucleocapsid protein NCp7, which contains two highly conserved zinc fingers, is being used as a novel target for AIDS therapy due to its pivotal role in viral replication and its mutationally intolerant nature. Herein we report a new class of NCp7 inhibitors that possess good antiviral activity with low cellular toxicity.

Reactive sulfur species: an emerging concept in oxidative stress

The ingredients of oxidative stress include a variety of reactive species such as reactive oxygen and reactive nitrogen species (ROS, RNS). While sulfur is usually considered as part of cellular antioxidant systems there is mounting evidence that reactive sulfur species (RSS) with stressor properties similar to the ones found in ROS are formed under conditions of oxidative stress. Thiols as well as disulfides are easily oxidised to sulfur species with sulfur in higher oxidation states. Such agents include thiyl radicals, disulfides, sulfenic acids and disulfide-S-oxides. They rapidly oxidise and subsequently inhibit thiol-proteins and enzymes and can be considered as a separate class of oxidative stressors providing new antioxidant drug targets.

Hypothesis: the role of reactive sulfur species in oxidative stress

Oxidative stress arises from an imbalance in the metabolism of redox-active species promoting the formation of oxidizing agents. At present, these species are thought to include reactive oxygen, reactive nitrogen, and reactive nitrogen oxygen species (ROS, RNS, and RNOS, respectively). Reactive species have their origin in enzymatic synthesis, environmental induction, or by the further chemical reaction of an active species with other endogenous molecules to generate a second-generation reactive species. These second-generation species possess a different spectrum of activity to the parent species, with different redox reactions and biological targets. We now propose that an additional group of redox active molecules termed "reactive sulfur species" (RSS) are formed in vivo under conditions of oxidative stress. RSS are likely to include disulfide-S-oxides, sulfenic acids, and thiyl radicals, and are predicted to modulate the redox status of biological thiols and disulfides.

New developments in anti-HIV chemotherapy

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): i.e. zidovudine, didanosine, zalcitabine, stavudine, lamivudine, abacavir, emtricitabine, tenofovir (PMPA) 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 and amprenavir. In addition, 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; (ii) viral entry, through blockade of the viral coreceptors CXCR4 and CCR5; (iii) virus-cell fusion; (iv) viral assembly and disassembly; (v) proviral DNA integration; (vi) viral mRNA transcription. Also, new NRTIs, NNRTIs and PIs have been developed that possess respectively improved metabolic characteristics, or increased activity against NNRTI-resistant HIV strains or, as 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.