Compounds Identified from Marine Mangrove Plant (Avicennia alba) as Potential Antiviral Drug Candidates Against WDSV, an In-Silico Approach

Walleye dermal sarcoma virus (WDSV) is a type of retrovirus, which affects most of the adult walleye fishes during the spawning time. The virus causes multiple epithelial tumors on the fish’s skin and fins that are liable for more than 50% of the mortality rate of fish around the world. Till now, no effective antiviral drug or vaccine candidates have been developed that can block the progression of the disease caused by the pathogen. It was found that the 582-amino-acid (aa) residues long internal structural gag polyprotein of the virus plays an important role in virus budding and virion maturation outside of the cell. Inhibition of the protein can block the budding and virion maturation process and can be developed as an antiviral drug candidate against the virus. Therefore, the study aimed to identify potential natural antiviral drug candidates from the tropical mangrove marine plant Avicennia alba, which will be able to block the budding and virion maturation process by inhibiting the activity of the gag protein of the virus. Initially, a homology modeling approach was applied to identify the 3D structure, followed by refinement and validation of the protein. The refined protein structures were then utilized for molecular docking simulation. Eleven phytochemical compounds have been isolated from the marine plant and docked against the virus gag polyprotein. Three compounds, namely Friedlein (CID244297), Phytosterols (CID12303662), and 1-Triacontanol (CID68972) have been selected based on their docking score −8.5 kcal/mol, −8.0 kcal/mol and −7.9 kcal/mol, respectively, and were evaluated through ADME (Absorption, Distribution, Metabolism and Excretion), and toxicity properties. Finally, molecular dynamics (MD) simulation was applied to confirm the binding stability of the protein-ligands complex structure. The ADME and toxicity analysis reveal the efficacy and non-toxic properties of the compounds, where MD simulation confirmed the binding stability of the selected three compounds with the targeted protein. This computational study revealed the virtuous value of the selected three compounds against the targeted gag polyprotein and will be effective and promising antiviral candidates against the pathogen in a significant and worthwhile manner. Although in vitro and in vivo study is required for further evaluation of the compounds against the targeted protein.

HIV-1 gag: an emerging target for antiretroviral therapy

The advances made in the treatment of HIV-1 infection represent a major success of modern biomedical research, prolonging healthy life and reducing virus transmission. There remain, however, many challenges relating primarily to side effects of long-term therapy and the ever-present danger of the emergence of drug-resistant strains. To counter these threats, there is a continuing need for new and better drugs, ideally targeting multiple independent steps in the HIV-1 replication cycle. The most successful current drugs target the viral enzymes: protease (PR), reverse transcriptase (RT), and integrase (IN). In this review, we outline the advances made in targeting the Gag protein and its mature products, particularly capsid and nucleocapsid, and highlight possible targets for future pharmacological intervention.

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.

Rhesus monkey TRIM5alpha restricts HIV-1 production through rapid degradation of viral Gag polyproteins

Mammalian cells have developed diverse strategies to restrict retroviral infection. Retroviruses have therefore evolved to counteract such restriction factors, in order to colonize their hosts. Tripartite motif-containing 5 isoform-alpha (TRIM5alpha) protein from rhesus monkey (TRIM5alpharh) restricts human immunodeficiency virus type 1 (HIV-1) infection at a postentry, preintegration stage in the viral life cycle, by recognizing the incoming capsid and promoting its premature disassembly. TRIM5alpha comprises an RBCC (RING, B-box 2 and coiled-coil motifs) domain and a B30.2(SPRY) domain. Sequences in the B30.2(SPRY) domain dictate the potency and specificity of the restriction. As TRIM5alpharh targets incoming mature HIV-1 capsid, but not precursor Gag, it was assumed that TRIM5alpharh did not affect HIV-1 production. Here we provide evidence that TRIM5alpharh, but not its human ortholog (TRIM5alphahu), blocks HIV-1 production through rapid degradation of HIV-1 Gag polyproteins. The specificity for this restriction is determined by sequences in the RBCC domain. Our observations suggest that TRIM5alpharh interacts with HIV-1 Gag during or before Gag assembly through a mechanism distinct from the well-characterized postentry restriction. This finding demonstrates a cellular factor blocking HIV-1 production by actively degrading a viral protein. Further understanding of this previously unknown restriction mechanism may reveal new targets for future anti-HIV-1 therapy.

3-O-(3',3'-dimethysuccinyl) betulinic acid inhibits maturation of the human immunodeficiency virus type 1 Gag precursor assembled in vitro

3-O-(3',3'-Dimethysuccinyl) betulinic acid (PA-457) has been shown to potently inhibit human immunodeficiency virus (HIV) replication in culture. In contrast to inhibitors that act upon the viral proteinase, PA-457 appears to block only the final maturational cleavage of p25CA-p2 to p24CA. However, attempts to replicate this effect in vitro using recombinant Gag have failed, leading to the hypothesis that activity is dependent upon the assembly state of Gag. Using a synthesis/assembly system for chimeric HIV type 1 Gag proteins, we have replicated the activity of PA-457 in vitro. The processing of assembled chimeric Gag can be inhibited by the addition of drug with only the final cleavage of p25CA-p2 to p24CA blocked. Consistent with our hypothesis and with previous findings, inhibition appears specific to Gag assembled into an immature capsid-like structure, since synthetic Gag that remains unassembled is properly processed in the presence of the compound. To further analyze the authenticity of the assay, PA-457 was tested in parallel with its inactive parental compound, betulinic acid. Betulinic acid had no effect upon p25 processing in this system. Analysis of a PA-457-resistant mutant, A1V, in this system pointed to more rapid cleavage as a possible mechanism for resistance. However, characterization of additional mutations at the cleavage site and in p2 suggests that resistance does not strictly correlate with the rate of cleavage. With the establishment of an in vitro assay for the detection of PA-457 activity, a more detailed characterization of its mechanism of action will be possible.

Drug evaluation: bevirimat--HIV Gag protein and viral maturation inhibitor

Panacos Pharmaceuticals Inc is developing the HIV Gag protein and viral maturation inhibitor bevirimat for the potential oral treatment of HIV infection. Phase II clinical trials are underway and phase III trials expected to commence in 2007.

Preclinical Evaluation of a Zinc Finger Inhibitor Targeting Lentivirus Nucleocapsid Protein in SIV-Infected Monkeys

There is a continued need to develop inexpensive and effective drugs specific for novel targets of human immunodeficiency virus type 1 (HIV-1). The HIV-1 nucleocapsid p7 (NCp7) protein plays a critical role in early and late stages of the virus life cycle and possesses two highly conserved retroviral zinc fingers that are essential for its function. We have previously shown that zinc finger inhibitors (ZFI) based on the S-acyl 2-mercaptobenzamide thioester (SAMT) chemotype specifically target HIV NCp7 and are effective at reducing levels of infectious virus in an HIV-1-transgenic mouse model. Here, we did an initial proof-of-concept study to test the potential of a lead SAMT compound to reduce virus infectivity in the simian immunodeficiency virus (SIV) nonhuman primate model. SAMT-19 had potent antiviral and virucidal effects against the primary pathogenic isolate SIV/DeltaB670 and was non-cytotoxic in vitro. Cynomolgus macaques were infected intrarectally with SIV/DeltaB670 and treated with a low dose of SAMT-19 by continuous infusion from day 8 to day 28 post infection. Monkeys in the treatment group had significantly lower levels of infectious virus in peripheral blood mononuclear cells during the course of therapy as compared to monkeys in the control group, although therapy had no demonstrable effect on virus load. SAMT-19 therapy did not alter liver, kidney or immunologic function and was well tolerated by all treated monkeys. These data demonstrate that SAMT-19 is safe and virucidal in the nonhuman primate model. Further studies directed at optimizing SAMT bioavailability and pharmacokinetics likely will result in enhanced therapeutic efficacy of this promising HIV therapeutic.

Studies on the Mechanism of Inactivation of the HIV-1 Nucleocapsid Protein NCp7 with 2-Mercaptobenzamide Thioesters

The HIV-1 nucleocapsid protein (NCp7) is a small basic protein with two CysCysHisCys zinc-binding domains that specifically recognizes the Psi-site of the viral RNA. NCp7 plays a number of crucial roles in the viral lifecycle, including reverse transcription and RNA encapsidation. Several classes of potential anti-HIV compounds have been designed to inactivate NCp7 through zinc ejection, including a special class of thioester compounds. We have investigated the mechanism of action of two N-substituted-S-acyl-2-mercaptobenzamide compounds (compounds 1 and 2) that target NCp7. UV/Visible spectroscopy studies demonstrated that both thioesters were able to eject metal from NCp7. NMR and mass spectroscopy studies showed that the thioester compounds specifically ejected zinc from the carboxyl-terminal zinc-binding domain of NCp7 by covalent modification of Cys(39). Exposure of NCp7 to compounds 1 and 2 destroyed its ability to specifically bind RNA, whereas NCp7 already bound to RNA was protected from zinc ejection by the thioesters. The thiol component of the thioesters (compound 3, 2-mercaptobenzoyl-beta-alaninamide) did not eject zinc from NCp7, but when compound 3 was incubated with acetyl CoA prior to incubation with NCp7, we observed extensive metal ejection. Thus, the thiol released by the reaction of compounds 1 and 2 could be re-acylated in vivo by acyl CoA to form a new thioester compound that is able to react with NCp7. These studies provide a better understanding of the mechanism of action of thioester compounds, which is important for future design of anti-HIV-1 compounds that target NCp7.

Involvement of p38 MAPK signaling pathway in IFN-γ and HTLV-I expression in patients with HTLV-I-associated myelopathy/tropical spastic paraparesis

We analyzed the relationship between the expression of interferon (IFN)-gamma and HTLV-I p19 antigen and activation of p38 mitogen-activated protein kinase (p38 MAPK) in two HTLV-I-infected T cell lines derived from two patients (HCT-1 and HCT-4) with HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP), and three HTLV-I-infected T cell lines derived from three patients with adult T cell leukemia (ATL). Expression of phosphorylated (activated)-p38 MAPK was markedly increased concomitant with high levels of both IFN-gamma and HTLV-I p19 antigen expression in both HCT-1 and HCT-4 compared with cell lines derived from ATL patients. Treatment with SB203580, a specific inhibitor of p38 MAPK, suppressed IFN-gamma and HTLV-I p19 antigen expression levels in HCT-1, HCT-4 and peripheral blood CD4(+) T cells of HAM/TSP patients. These findings strongly suggest that activation of p38 MAPK signaling pathway is involved in the up-regulation of IFN-gamma expression with high HTLV-I proviral load in HAM/TSP patients.

Intracellularly expressed single-domain antibody against p15 matrix protein prevents the production of porcine retroviruses

The presence of porcine endogenous retroviruses presents a potential risk of transmission of infectious diseases (xenozoonosis) if tissues and organs from genetically modified pigs are to be used in xenotransplantation. Here, we report that intracellular expression of a llama single-domain antibody against p15, the matrix domain protein of the porcine endogenous retrovirus Gag polyprotein, blocks retrovirus production, providing the possibility of eliminating the risk of infection in xenotransplantation.

PA-457: a potent HIV inhibitor that disrupts core condensation by targeting a late step in Gag processing

New HIV therapies are urgently needed to address the growing problem of drug resistance. In this article, we characterize the anti-HIV drug candidate 3-O-(3',3'-dimethylsuccinyl) betulinic acid (PA-457). We show that PA-457 potently inhibits replication of both WT and drug-resistant HIV-1 isolates and demonstrate that the compound acts by disrupting a late step in Gag processing involving conversion of the capsid precursor (p25) to mature capsid protein (p24). We find that virions from PA-457-treated cultures are noninfectious and exhibit an aberrant particle morphology characterized by a spherical, acentric core and a crescent-shaped, electron-dense shell lying just inside the viral membrane. To identify the determinants of compound activity we selected for PA-457-resistant virus in vitro. Consistent with the effect on Gag processing, we found that mutations conferring resistance to PA-457 map to the p25 to p24 cleavage site. PA-457 represents a unique class of anti-HIV compounds termed maturation inhibitors that exploit a previously unidentified viral target, providing additional opportunities for HIV drug discovery.

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.

In vivo antiviral activity of novel human immunodeficiency virus type 1 nucleocapsid p7 zinc finger inhibitors in a transgenic murine model

Control of human immunodeficiency virus through the use of inexpensive chemotherapeutics, with minimal side effects and decreased potential for engendering resistant virus, is a long-term therapeutic goal. In principle, this goal can be accomplished if viral replication in reservoirs of chronically and latently infected cells is addressed. As a first step, we have developed novel antiviral compounds based on a 2-mercaptobenzamide thioester chemotype, including the pyridinioalkanoyl thioesters, which specifically target the zinc fingers of the human immunodeficiency virus nucleocapsid protein (NCp7). Using these compounds in a murine transgenic model, in which infectious human immunodeficiency virus is induced from an integrated provirus, we show inhibition of transgenic spleen cell p24 expression with potencies comparable to acute infection assays using human peripheral blood lymphocytes. More importantly, transgenic mice treated in vivo with two 2-mercaptobenzamide thioesters expressed significantly lower plasma p24, and splenocytes from these animals produced fewer infectious virions. Thus, these thioesters may provide an effective means for inhibiting the expression of human immunodeficiency virus from integrated viral reservoirs.

Molecular docking and 3D-QSAR studies on gag peptide analogue inhibitors interacting with human cyclophilin A

The interaction of a series gag peptide analogues with human cyclophilin A (hCypA) have been studied employing molecular docking and 3D-QSAR approaches. The Lamarckian Genetic Algorithm (LGA) and divide-and-conquer methods were applied to locate the binding orientations and conformations of the inhibitors interacting with hCypA. Good correlations between the calculated interaction free energies and experimental inhibitory activities suggest that the binding conformations of these inhibitors are reasonable. A novel interaction model was identified for inhibitors 11, 15, and 17 whose N-termini were modified by addition of the deaminovaline (Dav) group and the C-termini of 15 and 17 were modified by addition of a benzyl group. Accordingly, two new binding sites (sites A and D in Figure 1) were revealed, which show a strong correlation with inhibitor potency and thus can be used as a starting point for new inhibitor design. In addition, two predictive 3D-QSAR models were obtained by CoMFA and CoMSIA analyses based on the binding conformations derived from the molecular docking calculations. The reasonable r(cross)(2) (cross-validated) values 0.738 and 0.762 were obtained for CoMFA and CoMSIA models, respectively. The predictive ability of these models was validated by four peptide analogues test set. The CoMFA and CoMSIA field distributions are in general agreement with the structural characteristics of the binding groove of hCypA. This indicates the reasonableness of the binding model of the inhibitors with hCypA. Considering all these results together with the valuable clues of binding from references published recently, reasonable pharmacophore elements have been suggested, demonstrating that the 3D-QSAR models about peptide analogue inhibitors are expected to be further employed in predicting activities of the novel compounds for inhibiting hCypA.

Identification of HIV-1 nucleocapsid protein: nucleic acid antagonists with cellular anti-HIV activity

The crucial functions of HIV-1 nucleocapsid-p7 protein (NC-p7) at different stages of HIV replication are dependent on its nucleic acid binding properties. In this study, a search has been made to identify antagonists of the interaction between NC-p7 and d(TG)(4). A chemical library of approximately 2000 small molecules (the NCI Diversity Set) was screened, of the 26 active inhibitors that were identified, five contained a xanthenyl ring structure. Further analysis of 63 structurally related compounds led to the identification of 2,3,4,5-tetrachloro-6-(4('),5('),6(')-trihydroxy-3(')-oxo-3H-xanthen-9(')-yl)benzoic acid, which binds to NC-p7 stoichiometrically. This compound exerted a significant anti-HIV activity in vitro with an IC(50) of 16.6+/-4.3 microM (means+/-SD). Synthetic variants lacking the two hydroxyls at positions 4(') and 5(') in the xanthenyl ring system failed to bind NC-p7 and showed significantly less protection against HIV infection. Molecular modeling predicts that these hydroxyl groups would bind to the amide nitrogen of Gly(35) with other contacts at the carbonyl oxygens of Gly(40) and Lys(33).

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.

Experimental determination and calculations of redox potential descriptors of compounds directed against retroviral zinc fingers: Implications for rational drug design

A diverse set of electrophilic compounds that react with cysteine thiolates in retroviral nucleocapsid (NC) proteins and abolish virus infectivity has been identified. Although different in chemical composition, these compounds are all oxidizing agents that lead to the ejection of Zn(II) ions bound to conserved structural motifs (zinc fingers) present in retroviral NC proteins. The reactivity of a congeneric series of aromatic disulfides toward the NC protein of the human immunodeficiency virus type 1 (HIV-1), NCp7, has been characterized by HPLC separation of starting reagents from reaction products. We calculated the absolute redox potentials of these compounds in the gas phase and in aqueous solvent, using a density functional theory method and a continuum solvation model. Pulsed polarography experiments were performed and showed a direct correlation between calculated and experimentally determined redox propensities. A dependence between protein reactivity and redox potential for a specific compound was shown: Reaction with NCp7 did not take place below a threshold value of redox potential. This relationship permits the distinction between active and nonactive compounds targeted against NCp7, and provides a theoretical basis for a scale of reactivity with retroviral zinc fingers. Our results indicate that electrophilic agents with adequate thiophilicity to react with retroviral NC fingers can now be designed using known or calculated electrochemical properties. This may assist in the design of antiretroviral compounds with greater specificity for NC protein. Such electrophilic agents can be used in retrovirus inactivation with the intent of preparing a whole-killed virus vaccine formulation that exhibits unaffected surface antigenic properties.

Inactivation of HIV-1 nucleocapsid protein P7 by pyridinioalkanoyl thioesters. Characterization of reaction products and proposed mechanism of action

The synthesis and antiviral properties of pyridinioalkanoyl thioester (PATE) compounds that target nucleocapsid p7 protein (NCp7) of the human immunodeficiency virus type 1 (HIV-1) have been described previously (Turpin, J. A., Song, Y., Inman, J. K., Huang, M., Wallqvist, A., Maynard, A., Covell, D. G., Rice, W. G., and Appella, E. (1999) J. Med. Chem. 42, 67-86). In the present study, fluorescence and electrospray ionization-mass spectrometry were employed to determine the mechanism of modification of NCp7 by two lead compounds, N-[2-(5-pyridiniovaleroylthio)benzoyl]sulfacetamide bromide and N-[2-(5-pyridiniovaleroylthio)benzoyl]-4-(4-nitrophenylsulfonyl )anili ne bromide (compounds 45 and 47, respectively). Although both compounds exhibit antiviral activity in cell-based assays, we failed to detect appreciable ejection of zinc from NCp7 under conditions in which previously described NCp7-active disulfides readily eject zinc. However, upon "activation" by Ag(+), compound 45 reacted with NCp7 resulting in the zinc ejection from both zinc fingers. The reaction followed a two-step mechanism in which zinc was ejected from the carboxyl-terminal zinc finger faster than from the amino-terminal zinc finger. Both compounds covalently modified the protein with pyridinioalkanoyl groups. Compound 45 modified cysteines 36 and 49 of the carboxyl-terminal zinc finger. The results obtained herein demonstrate that PATE compounds can be constructed that selectively target only one of the two zinc fingers of NCp7, thus providing an impetus to pursue development of highly selective zinc finger inhibitors.

Multiple effects of an anti-human immunodeficiency virus nucleocapsid inhibitor on virus morphology and replication

Human immunodeficiency virus type 1 nucleocapsid protein is a major structural component of the virion core and a key factor involved in proviral DNA synthesis and virus formation. 2,2'-Dithiobenzamides (DIBA-1) and related compounds that are inhibitors of NCp7 are thought to eject zinc ions from NCp7 zinc fingers, inhibiting the maturation of virion proteins. Here, we show that the presence of DIBA-1 at the time of virus formation causes morphological malformations of the virus and reduces proviral DNA synthesis. Thus, it seems that DIBA-1 is responsible for a "core-freezing effect," as shown by electron microscopy analyses. DIBA-1 can also directly interfere with the fate of the newly made proviral DNA in a manner independent of its effects on virion core formation. These data strongly suggest that nucleocapsid protein is a prime target for new compounds aimed at inhibiting human immunodeficiency virus and other retroviruses.

Nucleomimetic strategy for the inhibition of HIV-1 nucleocapsid protein NCp7 activities

We report the synthesis and biological properties of three modified dinucleotides T*G, G*T and T*T in which the natural phosphodiester linkage has been replaced by a methylene carboxamide unit. They have been designed to act as nucleomimetics of a sequence recognized by the HIV-1 nucleocapsid protein NCp7 and to inhibit this interaction.

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.

Anti-HIV agents that selectively target retroviral nucleocapsid protein zinc fingers without affecting cellular zinc finger proteins

Agents that target the two highly conserved Zn fingers of the human immunodeficiency virus (HIV) nucleocapsid p7 (NCp7) protein are under development as antivirals. These agents covalently modify Zn-coordinating cysteine thiolates of the fingers, causing Zn ejection, loss of native protein structure and nucleic acid binding capacity, and disruption of virus replication. Concentrations of three antiviral agents that promoted in vitro Zn ejection from NCp7 and inhibited HIV replication did not impact the functions of cellular Zn finger proteins, including poly(ADP-ribose) polymerase and the Sp1 and GATA-1 transcription factors, nor did the compounds inhibit HeLa nuclear extract mediated transcription. Selectivity of interactions of these agents with NCp7 was supported by molecular modeling analysis which (1) identified a common saddle-shaped nucleophilic region on the surfaces of both NCp7 Zn fingers, (2) indicated a strong correspondence between computationally docked positions for the agents tested and overlap of frontier orbitals within the nucleophilic loci of the NCp7 Zn fingers, and (3) revealed selective steric exclusion of the agents from the core of the GATA-1 Zn finger. Further modeling analysis suggests that the thiolate of Cys49 in the carboxy-terminal finger is the site most susceptible to electrophilic attack. These data provide the first experimental evidence and rationale for antiviral agents that selectively target retroviral nucleocapsid protein Zn fingers.

Structure, biological functions and inhibition of the HIV-1 proteins Vpr and NCp7

The Gag-encoded nucleocapsid protein NCp7 (72 amino acids) from HIV-1, the regulatory protein, Vpr (96 amino acids) and numerous derivatives have been synthesized by solid phase method and their structures determined by 2D NMR. In NCp7, the two highly folded zinc fingers of the Cx2Cx4Hx4C type are in close spacial proximity and the replacement of H by C in the first zinc finger or P by L in the short interdigital domain led to structural modifications evidenced by NMR. In vivo, these point mutations induced a complete loss of viral infectivity by interrupting critical step(s) of the retroviral life cycle. To account for these findings, a model of the complex between NCp7 and d (ACGCC) has been proposed from NMR data, showing the intercalation of Trp37 in the oligonucleotide. This model could also explain the role of NCp7 in the formation of viral particles and agrees with the modifications in morphology of the virions containing mutations in the NCp7 zinc fingers. Vpr is essentially constituted by two long helical domains at its N- and C-terminals and the side chains of Leu60 and Leu67 participate in a leucine-zipper mode of intramolecular interaction. The results obtained have been used to try to develop new antiviral agents inhibiting NCp7 functions and thus possibly devoid of the resistance effects found with inhibitors of HIV enzymes (reverse transcriptase and protease).

Inhibition of HIV-1 replication by cyclosporine A or related compounds correlates with the ability to disrupt the Gag-cyclophilin A interaction

The HIV-1 Gag polyprotein specifically incorporates the cellular peptidylprolyl isomerase cyclophilin A into virions. HIV-1 replication is inhibited by cyclosporine A, an immunosuppressive drug which binds with high affinity to cyclophilin A and precludes interaction with the Gag polyprotein. Using a panel of four drugs, including cyclosporine A, two nonimmunosuppressive analogues of cyclosporine A which bind to cyclophilin A but which cannot form a tertiary complex with the calcium-dependent phosphatase calcineurin, and the structurally unrelated immunosuppressant FK506, we demonstrated that the antiviral effect of cyclosporine A is not due to blockade of calcineurin-mediated signal transduction pathways. Rather, the effectiveness of cyclosporine A and related compounds at inhibiting HIV-1 replication correlates with cyclophilin A-binding affinity and with the ability to disrupt the interaction between cyclophilin A and the HIV-1 Gag polyprotein. These results support the contention that the Gag-cyclophilin A interaction is required for HIV-1 replication.

Inhibition of HTLV-I induction and virus-induced syncytia formation by oligodeoxynucleotides

HTLV-I is an exogenous human retrovirus that is a causative agent of adult T cell leukemia (ATL). In addition to the structural genes (gag, pol and env), a gene termed pX is postulated to be associated with leukemogenesis in ATL. Since no effective chemotherapy is currently available, it is important to find suitable therapeutic means against ATL. Here, we tested the inhibitory effect of antisense oligodeoxynucleotides (ODNs) on HTLV-I infection in different systems. ODNs were synthesized with the phosphorothioate backbone targeted to either structural genes or transactivator genes. The phosphorothioate ODNs were found to have two distinct target sites to exert their effect on HTLV-I infection: 1) Several ODNs, including sense ODNs and random oligomers, blocked syncytium formation induced by HTLV-I at a concentration of 0.1 microM. Their inhibitory effect on syncytium formation seemed to be exerted in a nonantisense manner, most probably due to their interaction with the cell membrane. 2) Efficient suppression by ODNs of gag gene expression after chemical induction was observed in HTLV-I-transformed T cells in an antisense manner. In this suppression, tax-antisense ODN showed virtually complete inhibition of gag protein expression, but not RNA expression, at the concentration of 0.1 microM, whereas tax-sense ODN displayed a weak inhibitory effect. Our results suggest that the influence of the phosphorothioate compound should be considered from the aspect of two separated mechanisms of antiviral activity, the effects on early (viral adsorption) and late (translation) phase infection.

Inhibitors of HIV nucleocapsid protein zinc fingers as candidates for the treatment of AIDS

Strategies for the treatment of human immunodeficiency virus-type 1 (HIV-1) infection must contend with the obstacle of drug resistance. HIV-1 nucleocapsid protein zinc fingers are prime antiviral targets because they are mutationally intolerant and are required both for acute infection and virion assembly. Nontoxic disulfide-substituted benzamides were identified that attack the zinc fingers, inactivate cell-free virions, inhibit acute and chronic infections, and exhibit broad antiretroviral activity. The compounds were highly synergistic with other antiviral agents, and resistant mutants have not been detected. Zinc finger-reactive compounds may offer an anti-HIV strategy that restricts drug-resistance development.

SDZ PRI 053, an orally bioavailable human immunodeficiency virus type 1 proteinase inhibitor containing the 2-aminobenzylstatine moiety

A series of inhibitors of human immunodeficiency virus type 1 (HIV-1) proteinase containing the 2-aralkyl-amino-substituted statine moiety as a novel transition-state analog was synthesized, with the aim to obtain compounds which combine anti-HIV potency with oral bioavailability. The reduced-size 2-aminobenzylstatine derivative SDZ PRI 053, which contains 2-(S)-amino-3-(R)-hydroxyindane in place of an amino acid amide, is a potent and orally bioavailable inhibitor of HIV-1 replication. The antiviral activity of SDZ PRI 053 was demonstrated in various cell lines, in primary lymphocytes, and in primary monocytes, against laboratory strains as well as clinical HIV-1 isolates (50% effective dose = 0.028 to 0.15 microM). Cell proliferation was impaired only at 100- to 300-fold-higher concentrations. The mechanism of antiviral action of the proteinase inhibitor SDZ PRI 0.53 was demonstrated to be inhibition of gag precursor protein processing. The finding that the inhibitory potency of SDZ PRI 053 in chronic virus infection, determined by p24 release, was considerably lower than that in de novo infection may be explained by the fact that the virus particles produced in the presence of SDZ PRI 053 are about 50-fold less infectious than those from untreated cultures. Upon intravenous administration, half-lives in blood of 100 and 32 min in mice and rats, respectively, were measured. Oral bioavailability of SDZ PRI 053 in rodents was 20 to 60%, depending on the dose. In mice, rats, and dogs, the inhibitor levels after oral administration remained far above the concentrations needed to efficiently block HIV replication in vitro for a prolonged period. This compound is thus a promising candidate for clinical use in HIV disease.

The molecular biology of HIV. Insights into pathogenesis and targets for therapy

In the past 10 years, a large number of investigators have produced an enormous amount of information concerning the molecular biology of HIV. These studies at the most basic biological level have provided essential insights into the pathogenesis of the disease. They have supplied the information necessary for the creation of the antiviral therapies now available and have indicated the direction for the development of new therapies now in clinical trials and under investigation. Although the relatively ineffective therapies currently available serve as a constant source of disappointment for those practitioners who care for HIV-infected patients, there is some comfort to be gained from the rapid pace of investigation into the basic biology of the virus and the certainty that any more effective therapy must build upon the basic biological knowledge already obtained. A detailed study of some of the unique features observed during pediatric and perinatal HIV infection, particularly the relatively shortened time from infection to symptoms and the relative importance of CNS disease, may suggest new therapeutic approaches that will benefit both adult and pediatric patients. Finally, a comprehensive knowledge of HIV biology is an essential requirement for therapeutic maneuvers designed to interrupt the transmission of HIV from mother to child.

Inhibition of Human T Cell Leukemia Virus by the Plant Flavonoid Baicalin (7-Glucuronic Acid, 5,6-Dihydroxyflavone)

The ability of baicalin (7-glucuronic acid, 5,6-dihydroxyflavone), a flavonoid compound purified from the Chinese medicinal herb, Scutellaria baicalensis georgi, to inhibit human T cell leukemia virus type I (HTLV-I) was examined. Baicalin produced concentration-dependent inhibition of HTLV-I replication in productively infected T and B cells. Moreover, baicalin treatment selectively reduced the detectable levels of HTLV-I p19 gag protein in infected cells by greater than 70% at concentrations that produced insignificant effects on total cellular protein and DNA synthesis with no loss in cell viability. Resistance to HTLV-I infection and virus-mediated transformation was noted in uninfected peripheral blood lymphocytes pretreated with baicalin before cocultivation with lethally irradiated chronically infected cells. Baicalin inhibited reverse transcriptase activity in HTLV-I-infected cells as well as the activity of purified reverse transcriptase from Moloney murine leukemia virus and Rous-associated virus type 2. These results suggest that baicalin may be a potential therapeutic agent against HTLV-I-associated T cell diseases.