Viral resistance to the thiazolo-iso-indolinones, a new class of nonnucleoside inhibitors of human immunodeficiency virus type 1 reverse transcriptase

Development of novel isatin thiazolyl-pyrazoline hybrids as promising antimicrobials in MDR pathogens

Microbial Multidrug Resistance (MDR) is an emerging global crisis. Derivatization of natural or synthetic scaffolds is among the most reliable strategies to search for and obtain novel antimicrobial agents for the treatment of MDR infections. Here, we successfully manipulated the synthetically flexible isatin moieties to synthesize 22 thiazolyl-pyrazolines hybrids, and assessed their potential antimicrobial activities in vitro against various MDR pathogens, using the broth microdilution calorimetric XTT reduction method. We chose 5 strains to represent the major MDR microorganisms, viz: Methicillin-resistant S. aureus (MRSA), and Vancomycin-resistant E. faecalis (VRE) as Gram-positive bacteria; Carbapenem-resistant K. pneumonia (CRKP), and Extended-spectrum beta-lactamase E. coli (ESBL-E), as Gram-negative bacteria; and Fluconazole-resistant C. albicans (FRCA), as a yeast-like unicellular fungus. The cytotoxicity of compounds 9f and 10h towards mammalian lung fibroblast (MRC-5) cells demonstrated their potential satisfactory safety margin as represented by their relatively high IC₅₀ values. The target compounds showed promising anti-MDR activities, suggesting they are potential leads for further development and in vivo studies.

As promising antimicrobials against MDR pathogens, two novel series of isatin thiazolyl-pyrazoline conjugates were developed. Compounds 9f and 10h were the most effective against the tested MDR strains.

Isolation and Characterization of HIV-1 Isolates Resistant to Oxathiin Carboxanilide Analogues: Evaluation of Variables in the Drug Resistance Selection Process

Virus isolates resistant to a variety of structural analogues of oxathiin carboxanilide (UC84) were selected in cell culture and phenotypically and mo!ecularly characterized in order to evaluate the effects of variables in the resistance selection process. The rate of appearance of the resistant viruses and the net loss of sensitivity of the virus isolates to the selecting compound were not dependent on the selective pressure employed against wild-type virus, but were associated with structural features of the compound. Although each of the compounds rapidly selected for resistant viruses, the isolates obtained varied in their overall level of resistance, in their cross-resistance to other non-nucleoside reverse transcriptase inhibitors (NNRTIs) and in the amino acid changes present in the reverse transcriptase (RT). The mutation Y181C was most commonly observed, often with a second mutation, such as K101E or V-106A. The amino acid change L100I was also observed upon selection. In order to determine the reproducibility of the in-vitro resistance selection process, 10 isolates resistant to UC84 were independently selected in parallel cultures. Mutations detected in the RT of these isolates were varied but included the commonly reported Y181C and V106A amino acid changes, as well as unique changes K101I, K101N, K103Q, G190A, T139I and A98S. These results demonstrate that from the heterogeneous wild-type population, antiviral agents, such as the UC compounds, may select a wide variety of virus isolates with resistance-engendering amino acid changes in the RT. In addition, the results also suggest that antiviral agents may select for resistant viruses at different rates and to different extents, offering the possibility that compounds might be identified which do not readily result in high level drug resistance.

A Diarylsulphone Non-Nucleoside Reverse Transcriptase Inhibitor with a Unique Sensitivity Profile to Drug-Resistant Virus Isolates

Structure-activity relationship evaluations with a series of diarylsulphone non-nucleoside reverse transcriptase (RT) inhibitors indicated that the steric properties of the molecule and compound lipophilicity primarily contributed to the overall level of activity of the compounds against human immunodeficiency virus type 1 (HIV-1). The most active compounds in the diarylsulphone series had an orthonitro group and yielded anti-HIV activity at sub-micromolar concentrations. Compounds of the diarylsulphone class exhibited antiviral properties similar to other members of the pharmacologic class of HIV-1 specific non-nucleoside reverse transcriptase inhibitors, including activity in a wide variety of established and primary human cells, activity against a wide variety of laboratory and clinical virus isolates, and activity when challenged at high multiplicity of infection. Synergistic inhibition of HIV-1 was observed when the diarylsulphone NSC 667952 was used with the nucleoside analogues AZT, ddl, 3TC and d4T, the protease inhibitor KNI 272 and the sulphonated dye resobene; additive effects were observed when NSC 667952 was used with the nucleoside analogue ddC and other non-nucleoside RT inhibitors. The diarylsulphones exhibited a unique sensitivity profile when evaluated against both virus isolates and purified reverse transcriptase containing non-nucleoside reverse transcriptase inhibitor resistance-engendering mutations. Unlike other members of the class of non-nucleoside compounds, NSC 667952 remained active against virus isolates with the L100I amino acid change in the RT. The compound was, however, highly sensitive to Y181C., K103N and K101E amino acid changes in the RT. The diarylsulphone selected for resistant virus populations which possessed the Y181C amino acid change in the reverse transcriptase and which exhibited enhanced sensitivity to the non-nucleoside inhibitors calanolide A and costatolide.

Synthesis and in silico investigation of thiazoles bearing pyrazoles derivatives as anti-inflammatory agents

Searching novel, safe and effective anti-inflammatory agents has remained an evolving research enquiry in the mainstream of inflammatory disorders. In the present investigation series of thiazoles bearing pyrazole as a possible pharmacophore were synthesized and assessed for their anti inflammatory activity using in vitro and in vivo methods. In order to decipher the possible anti-inflammatory mechanism of action of the synthesized compounds, cyclooxygenase I and II (COX-I and COX-II) inhibition assays were also carried out. The results obtained clearly focus the significance of compounds 5d, 5h and 5i as selective COX-II inhibitors. Moreover, compound 5h was also identified as a lead molecule for inhibition of the carrageenin induced rat paw edema in animal model studies. Molecular docking results revealed significant interactions of the test compounds with the active site of COX-II, which perhaps can be explored for design and development of novel COX-II selective anti-inflammatory agents.

Natural Plant Alkaloid (Emetine) Inhibits HIV-1 Replication by Interfering with Reverse Transcriptase Activity

Ipecac alkaloids are secondary metabolites produced in the medicinal plant Psychotria ipecacuanha. Emetine is the main alkaloid of ipecac and one of the active compounds in syrup of Ipecac with emetic property. Here we evaluated emetine’s potential as an antiviral agent against Human Immunodeficiency Virus. We performed in vitro Reverse Transcriptase (RT) Assay and Natural Endogenous Reverse Transcriptase Activity Assay (NERT) to evaluate HIV RT inhibition. Emetine molecular docking on HIV-1 RT was also analyzed. Phenotypic assays were performed in non-lymphocytic and in Peripheral Blood Mononuclear Cells (PBMC) with HIV-1 wild-type and HIV-harboring RT-resistant mutation to Nucleoside Reverse Transcriptase Inhibitors (M184V). Our results showed that HIV-1 RT was blocked in the presence of emetine in both models: in vitro reactions with isolated HIV-1 RT and intravirion, measured by NERT. Emetine revealed a strong potential of inhibiting HIV-1 replication in both cellular models, reaching 80% of reduction in HIV-1 infection, with low cytotoxic effect. Emetine also blocked HIV-1 infection of RT M184V mutant. These results suggest that emetine is able to penetrate in intact HIV particles, and bind and block reverse transcription reaction, suggesting that it can be used as anti-HIV microbicide. Taken together, our findings provide additional pharmacological information on the potential therapeutic effects of emetine.

Synthesis and biological screening of 2'-aryl/benzyl-2-aryl-4-methyl-4',5-bithiazolyls as possible anti-tubercular and antimicrobial agents

A series of 2'-aryl/benzyl-2-aryl-4-methyl-4',5-bithiazolyl derivatives, 25-64 were synthesized and evaluated for inhibitory activity against Mycobacterium smegmatis MC(2) 155 strain and antimicrobial activities against four pathogenic bacteria Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Proteus vulgaris. Among them, compounds 40, 49, 50, and 54 exhibited moderate to good inhibition on the growth of the bacteria Mycobacterium smegmatis at the concentration of 30 μM. Compounds 26, 40, 44, 54 and 56 exhibited moderate to good antibacterial activity. Compound 5-(2'-(4-fluorobenzyl)thiazol-4'-yl)-2-(4-fluorophenyl)-4-methyl-thiazole (54) exhibited both antitubercular as well as antimicrobial activity against all tested strains.

HIV-1 NNRTIs: structural diversity, pharmacophore similarity, and implications for drug design

Nonnucleoside reverse transcriptase inhibitors (NNRTIs) nowadays represent very potent and most promising anti-AIDS agents that specifically target the HIV-1 reverse transcriptase (RT). However, the effectiveness of NNRTI drugs can be hampered by rapid emergence of drug-resistant viruses and severe side effects upon long-term use. Therefore, there is an urgent need to develop novel, highly potent NNRTIs with broad spectrum antiviral activity and improved pharmacokinetic properties, and more efficient strategies that facilitate and shorten the drug discovery process would be extremely beneficial. Fortunately, the structural diversity of NNRTIs provided a wide space for novel lead discovery, and the pharmacophore similarity of NNRTIs gave valuable hints for lead discovery and optimization. More importantly, with the continued efforts in the development of computational tools and increased crystallographic information on RT/NNRTI complexes, structure-based approaches using a combination of traditional medicinal chemistry, structural biology, and computational chemistry are being used increasingly in the design of NNRTIs. First, this review covers two decades of research and development for various NNRTI families based on their chemical scaffolds, and then describes the structural similarity of NNRTIs. We have attempted to assemble a comprehensive overview of the general approaches in NNRTI lead discovery and optimization reported in the literature during the last decade. The successful applications of medicinal chemistry strategies, crystallography, and computational tools for designing novel NNRTIs are highlighted. Future directions for research are also outlined.

Synthesis, physico-chemical investigations of Co(II), Ni(II) and Cu(II) complexes and their in vitro microbial, cytotoxic, DNA cleavage studies

A series of metal complexes of cobalt(II), nickel(II), and copper(II) have been synthesized with newly derived biologically active ligands. These ligands were synthesized by the condensation of 2-amino-4-phenyl-1,3-thiazole with 8-formyl-7-hydroxy- 4-methylcoumarin. The probable structure of the complexes has been proposed on the basis of analytical and spectroscopic data (IR, UV-Vis, ESR, FAB-mass, and thermoanalytical). Electrochemical study of the complexes is also reported. Elemental analysis of the complexes confined them to stoichiometry of the type ML(2).2H(2)O [M = Co(II), Ni(II), and Cu(II)]. The Schiff base and its metal(II) complexes have been screened for their antibacterial (Escherichia coli, Staphylococcus aureus, Staphylococcus pyogenes, and Pseudomonas aeruginosa) and antifungal activities (Aspergillus niger, Aspergillus flavus, and Cladosporium) by the MIC method. The brine shrimp bioassay was carried out to study their in vitro cytotoxic properties, and also the Schiff base and its metal(II) complexes have been studied for DNA cleavage.

The search for potent, small molecule NNRTIs: A review

AIDS has become the leading pandemic disease, and is the cause of death worldwide. Presently, HAART treatment, a combination of reverse transcriptase (RT) and protease inhibitors is also unsuccessful due to the virus getting resistant to the drugs because of mutational changes. Two types of RT inhibitors exist namely nucleoside reverse transcriptase inhibitors (NRTIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs). The NNRTIs which bind to an allosteric site on RT are an important arsenal of drugs against HIV-1. The specificity of NNRTIs towards HIV-1 has led to extensive structural and molecular modelling studies of enzyme complexes and chemical synthesis of second and third-generation NNRTIs. The major drawbacks of NNRTIs are generation of resistance and pharmacokinetic problems. By mutational studies of non-nucleoside inhibitor binding pocket (NNIBP) some amino acids which were found to play an important role in proper binding resulted less prone to mutation. In this review we present a chronological history of NNRTI development, also highlighting the need for small molecules belonging to the NNRTI class for the management of AIDS.

Studies on hydrazone derivatives as antifungal agents

The increasing clinical importance of drug-resistant fungal pathogens has urged additional need to fungal research and new antifungal compound development. For this purpose, some N-(1-benzyl-2-phenylethylidene)-N'-[4-(aryl)thiazol-2-yl]hydrazone (1a-e) and N-(1-phenylbutylidene)-N'-[4-(aryl)thiazol-2-yl]hydrazone (2a-e) derivatives were synthesised and evaluated for antifungal activity. Their antifungal activities against standard and clinical strands of Candida albicans, Candida glabrata, Candida utilis, Candida tropicalis, Candida krusei, Candida zeylanoides, and Candida parapsilosis were investigated. A significant level of activity was observed.

Synthesis of Schiff bases of naphtha[1,2-d]thiazol-2-amine and metal complexes of 2-(2'-hydroxy)benzylideneaminonaphthothiazole as potential antimicrobial agents

OBJECTIVE

A series of 2-benzylideneaminonaphthothiazoles were designed and synthesized incorporating the lipophilic naphthalene ring to render them more capable of penetrating various biomembranes.

METHODS

Schiff bases were synthesized by the reaction of naphtha[1,2-d]thiazol-2-amine with various substituted aromatic aldehydes. 2-(2'-Hydroxy)benzylideneaminonaphthothiazole was converted to its Co(II), Ni(II) and Cu(II) metal complexes upon treatment with metal salts in ethanol. All the compounds were evaluated for their antibacterial activities by paper disc diffusion method with Gram positive Staphylococcus aureus and Staphylococcus epidermidis and Gram negative Escherichia coli and Pseudomonas aeruginosa bacteria. The minimum inhibitory concentrations of all the Schiff bases and metal complexes were determined by agar streak dilution method.

RESULTS

All the compounds moderately inhibited the growth of Gram positive and Gram negative bacteria. In the present study among all Schiff bases 2-(2'-hydroxy)benzylideneaminonaphthothiazole showed maximum inhibitory activity and among metal complexes Cu(II) metal complex was found to be most potent.

CONCLUSION

The results obtained validate the hypothesis that Schiff bases having substitution with halogens, hydroxyl group and nitro group at phenyl ring are required for the antibacterial activity while methoxy group at different positions in the aromatic ring has minimal role in the inhibitory activity. The results also indicated that the metal complexes are better antibacterial agents as compared to the Schiff bases.

Synthesis and antimicrobial activity of 1-(4-aryl-2-thiazolyl)-3-(2-thienyl)-5-aryl-2-pyrazoline derivatives

Several 1-(4-aryl-2-thiazolyl)-3-(2-thienyl)-5-aryl-2-pyrazoline derivatives were synthesized by reacting substituted 3-(2-thienyl)-5-aryl-1-thiocarbamoyl-2-pyrazolines with phenacyl bromides in ethanol. The structures of the synthesized compounds were confirmed by (1)H NMR, (13)C NMR, and EIMS spectral data. Their antimicrobial activities against Escherichia coli (NRRL B-3704), Staphylococcus aureus (NRLL B-767), Salmonella typhimurium (NRRL B-4420), Bacillus cereus (NRRL B-3711), Streptococcus faecalis (NRRL B-14617), Aeromonas hydrophila (Ankara Uni. Fac. of Veterinary), Candida albicans and Candida glabrata (isolates obtained from Osmangazi Uni. Fac. of Medicine) were investigated. A significant level of activity was observed.

Synthesis, characterization and thermal behavior of 4-chloromethyl-2-(2-hydroxybenzilidenehydrazino) thiazole and its complexes with Cr(III), Co(II), Ni(II) and Cu(II)

A new ligand, 4-chloromethyl-2-(2-hydroxybenzilidenehydrazino) thiazole, has been synthesized from dicholoroacetone and 2-hydroxybenzylidenethiosemicarbazon. Metal complexes of the ligand were prepared from acetate salts of Co(II), Cu(II), Ni(II) and chloride of Cr(III) in dry acetone. Characterization of the ligand and its complexes was made by microanalyses, FT-IR, 13C, 1H NMR and UV-vis spectroscopy, magnetic susceptibility and thermogravimetric analysis. In the light of these results, it was suggested that two ligands coordinate to each metal atom by hydroxyl oxygen, imino nitrogen and thiazole ring nitrogen to form high spin octahedral complexes with Cr(III), Co(II), Ni(II) and Cu(II).

Structure-Based Design, Parallel Synthesis, Structure−Activity Relationship, and Molecular Modeling Studies of Thiocarbamates, New Potent Non-Nucleoside HIV-1 Reverse Transcriptase Inhibitor Isosteres of Phenethylthiazolylthiourea Derivatives

In this paper we describe our structure-based ligand design, synthetic strategy, and structure-activity relationship (SAR) studies that led to the identification of thiocarbamates (TCs), a novel class of non-nucleoside reverse transcriptase inhibitors (NNRTIs), isosteres of phenethylthiazolylthiourea (PETT) derivatives. Assuming as a lead compound O-[2-(phthalimido)ethyl]phenylthiocarbamate 12, one of the precursors of the previously described acylthiocarbamates (Ranise, A.; et al. J. Med. Chem. 2003, 46, 768-781), two targeted solution-phase TC libraries were prepared by parallel synthesis. The lead optimization strategy led to para-substituted TCs 31, 33, 34, 39, 40, 41, 44, 45, and 50, which were active against wild-type HIV-1 in MT-4-based assays at nanomolar concentrations (EC50 range: 0.04-0.01 microM). The most potent congener 50 (EC50 = 0.01 microM) bears a methyl group at position 4 of the phthalimide moiety and a nitro group at the para position of the N-phenyl ring. Most of the TCs showed good selectivity indices, since no cytotoxic effect was detected at concentrations as high as 100 microM. TCs 31, 37, 39, 40, and 44 significantly reduced the multiplication of the Y181C mutant, but they were inactive against K103R and K103N + Y181C mutants. Nevertheless, the fold increase in resistance of 41 was not greater than that of efavirenz against the K103R mutant in enzyme assays. The docking model predictions were consistent with in vitro biological assays of the anti-HIV-1 activity of the TCs and related compounds synthesized.

Design, synthesis, SAR, and molecular modeling studies of acylthiocarbamates: a novel series of potent non-nucleoside HIV-1 reverse transcriptase inhibitors structurally related to phenethylthiazolylthiourea derivatives

A novel series of potent, selective HIV-1 N-acylthiocarbamate (ATC) nonnucleoside reverse transcriptase inhibitors (NNRTIs) is described. The title compounds were synthesized through a highly convergent, one-pot procedure. In cell-based assays, the lead compound (17c) prevented the HIV-1 multiplication with an EC(50) of 8 microM. The lead optimization strategy was developed by single or multiple modifications of the three molecular portions, in which 17c was notionally divided. Molecular modeling studies led to the synthesis of O-(2-phthalimidoethyl)-N-(p-substituted phenyl)-N-acylthiocarbamates, which showed in vitro activities against HIV-1 in the low nanomolar range. Nevertheless, the title compounds retained low potency against HIV-1 strains carrying mutations (K103R, Y181C, and K103N/Y181C) responsible for NNRTI resistance. The hypothetical docking model of RT/17c and RT/25c, derived from X-ray crystallographic structure of a PETT derivative in complex with HIV-1 RT, revealed that the model structures of ATCs do not approximate the NNRTI butterfly-like conformation. Analysis of these hypotetical complexes helps to rationalize some SARs and resistance data.

Anti-HIV activity of extracts and compounds from algae and cyanobacteria

The human immunodeficiency virus (HIV) is the retrovirus that causes the acquired immune deficiency disease syndrome (AIDS). This review discusses the anti-HIV activity of extracts and compounds isolated from freshwater and marine algae, and cyanobacteria (formerly called "blue-green algae"). Compounds and extracts with anti-HIV activity are also active against other retroviruses such as herpes simplex virus (HSV), but the amount of antiviral activity varies with the compound and the virus. Most of the research has focused on sulfated homopolysaccharides and heteropolysaccharides. Sulfoglycolipids, carrageenans, fucoidan, sesquiterpene hydroquinones, and other classes of compounds with anti-HIV activity that have been isolated from algae have received less attention. Most studies have used in vitro test systems, but a few in vivo studies have been carried out using compounds isolated from algae or analogs produced synthetically or isolated from other natural sources. Sulfated homopolysaccharides are more potent than sulfated heteropolysaccharides. The presence of the sulfate group is necessary for anti-HIV activity, and potency increases with the degree of sulfation. Studies using nonsulfated and sulfated homo- and heteropolysaccharides isolated from algae or other natural sources, or synthesized, have revealed the mechanisms of binding of drugs to the virion, and the mechanisms of viral binding to host cells. However, given the few classes of compounds investigated, most of the pharmacopeia of compounds in algae and cyanobacteria with antiretroviral activity is probably not known.

Synthesis, antibacterial, antifungal and anti-HIV activities of Schiff and Mannich bases derived from isatin derivatives and N-[4-(4'-chlorophenyl)thiazol-2-yl] thiosemicarbazide

Isatin, its 5-chloro and 5-bromo derivatives have been reacted with N-[4-(4'-chlorophenyl)thiazol-2-yl] thiosemicarbazide to form Schiff bases and the N-Mannich bases of these compounds were synthesized by reacting them with formaldehyde and three secondary amines. Their chemical structures have been confirmed by means of IR, 1H-NMR data and by elemental analysis. Investigation of antimicrobial activity of compounds was done by agar dilution method against 28 pathogenic bacteria, 8 pathogenic fungi and anti-HIV activity against replication of HIV-1 (IIIB) in MT-4 cells. Among the compounds tested 1-[N,N-dimethylaminomethyl]-5-bromo isatin-3-{1'-[4"-(p-chlorophenyl) thiazol-2"-yl] thio semicarbazone} 10 showed the most favourable antimicrobial activity.

Crystallographic analysis of the binding modes of thiazoloisoindolinone non-nucleoside inhibitors to HIV-1 reverse transcriptase and comparison with modeling studies

We have determined the crystal structures of thiazoloisoindolinone non-nucleoside inhibitors in complex with HIV-1 reverse transcriptase to high-resolution limits of 2.7 A (BM +21.1326) and 2. 52 A (BM +50.0934). We find that the binding modes of this series of inhibitors closely resemble that of "two-ring" non-nucleoside reverse transcriptase inhibitors. The structures allow rationalization of stereochemical requirements, structure-activity data, and drug resistance data. Comparisons with our previous structures suggest modifications to the inhibitors that might improve resilience to drug-resistant mutant forms of reverse transcriptase. Comparison with earlier modeling studies reveals that the predicted overlap of thiazoloisoindolinones with TIBO was largely correct, while that with nevirapine was significantly different.

Perspectives of non-nucleoside reverse transcriptase inhibitors (NNRTIs) in the therapy of HIV-1 infection

Non-nucleoside reverse transcriptase inhibitors (NNRTIs) have, in addition to the nucleoside reverse transcriptase inhibitors (NRTIs) and protease inhibitors (PIs), gained a definitive place in the treatment of HIV-1 infections. Starting from the HEPT and TIBO derivatives, more than thirty structurally different classes of compounds have been identified as NNRTIs, that is compounds that are specifically inhibitory to HIV-1 replication and targeted at the HIV-1 reverse transcriptase (RT). Two NNRTIs (nevirapine and delavirdine) have been formally licensed for clinical use and several others are (or have been) in preclinical and/or clinical development [tivirapine (TIBO R-86183), loviride (alpha-APA R89439), thiocarboxanilide UC-781, HEPT derivative MKC-442, quinoxaline HBY 097, DMP 266 (efavirenz), PETT derivatives (trovirdine, PETT-4, PETT-5) and the dichlorophenylthio(pyridyl)imidazole derivative S-1153]. The NNRTIs interact with a specific 'pocket' site of HIV-1 RT that is closely associated with, but distinct from, the NRTI binding site. NNRTIs are notorious for rapidly eliciting resistance due to mutations of the amino acids surrounding the NNRTI-binding site. However, the emergence of resistant HIV strains can be circumvented if the NNRTIs, preferably in combination with other anti-HIV agents, are used from the start at sufficiently high concentrations. In vitro, this procedure has been shown to 'knock-out' virus replication and to prevent resistance from arising. In vivo, various triple-drug combinations containing NNRTIs, NRTIs and/or PIs may result in an effective viral suppression and ensuing immune recovery. However, this so-called HAART (highly active antiretroviral therapy) may also fail, and this necessitates the design of new and more effective drugs and drug cocktails.

The role of non-nucleoside reverse transcriptase inhibitors (NNRTIs) in the therapy of HIV-1 infection

Non-nucleoside reverse transcriptase inhibitors (NNRTIs) have, in addition to the nucleoside reverse transcriptase inhibitors (NRTIs) and protease inhibitors (PIs), gained a definitive place in the treatment of HIV-1 infections. Starting from the HEPT and TIBO derivatives, more than 30 structurally different classes of compounds have been identified as NNRTIs, that is compounds that are specifically inhibitory to HIV-1 replication and targeted at the HIV-1 reverse transcriptase (RT). Two NNRTIs (nevirapine and delavirdine) have been formally licensed for clinical use and several others are in preclinical or clinical development [thiocarboxanilide UC-781, HEPT derivative MKC-442, quinoxaline HBY 097 and DMP 266 (efavirenz)]. The NNRTIs interact with a specific 'pocket' site of HIV-1 RT that is closely associated with, but distinct from, the NRTI binding site. NNRTIs are notorious for rapidly eliciting resistance due to mutations of the amino acids surrounding the NNRTI-binding site. However, the emergence of resistant HIV strains can be circumvented if the NNRTIs, alone or in combination, are used from the start at sufficiently high concentrations. In vitro, this procedure has proved to 'knock-out' virus replication and to prevent resistance from arising. In vivo, various triple-drug combinations of NNRTIs (nevirapine, delavirdine or efavirenz) with NRTIs (AZT, 3TC, ddI or d4T) and/or PIs (indinavir or nelfinavir) have been shown to afford a durable anti-HIV activity, as reflected by both a decrease in plasma HIV-1 RNA levels and increased CD4 T-lymphocyte counts.

Efficacy, pharmacokinetics, and in vivo antiviral activity of UC781, a highly potent, orally bioavailable nonnucleoside reverse transcriptase inhibitor of HIV type 1

A series of compounds related to oxathiin carboxanilide has been identified as nonnucleoside reverse transcriptase inhibitors (NNRTIs) of HIV-1, and structure-activity relationships have been described (Buckheit RW, et al.: Antimicrob Agents Chemother 1995;39:2718-2727). Three new analogs (UC040, UC82, and UC781) inhibited laboratory and clinical isolates of HIV-1, including isolates representative of the various clades of HIV-1 found worldwide, in both established and fresh human cells. Virus isolates with the amino acid changes L100I, K103N, V106I, and Y181C in the reverse transcriptase were partially resistant to these compounds. However, UC781 inhibited these virus isolates at low nontoxic concentrations, presenting a broad in vitro therapeutic index. As with other NNRTIs, each of the compounds synergistically interacted with AZT to inhibit HIV-1 replication. UC781 possesses a favorable pharmacokinetic profile in mice with a high level of oral bioavailability. Plasma concentrations reached maximum levels within 2 to 4 hr of oral administration and remained in excess of those required for in vitro anti-HIV activity for at least 24 hr after a single oral dose. When evaluated in a murine hollow fiber implant model of HIV infection, UC781 dosed orally or parenterally was able to suppress HIV replication completely in this model system, providing evidence of the in vivo efficacy of the compound.

Highly potent oxathiin carboxanilide derivatives with efficacy against nonnucleoside reverse transcriptase inhibitor-resistant human immunodeficiency virus isolates

The structure-activity relationships of a series of compounds related to the nonnucleoside reverse transcriptase (RT) inhibitor (NNRTI) oxathiin carboxanilide have been described (R. W. Buckheit, Jr., T. L. Kinjerski, V. Fliakas-Boltz, J. D. Russell, T. L. Stup, L. A. Pallansch, W. G. Brouwer, D. C. Dao, W. A. Harrison, R. J. Schultz, J. P. Bader, and S. S. Yang, Antimicrob. Agents Chemother. 39:2718-2727, 1996). From these studies, the furanyl-containing analog UC10 was identified as the most potent inhibitor of human immunodeficiency virus type 1 (HIV-1) replication and a promising candidate for further development. Three new UC analogs (UC040, UC82, and UC781) have been determined to inhibit laboratory-derived and low-passage-number, primary virus isolates at low nanomolar concentrations in both established and fresh human cells. Each of the compounds synergistically interacted with the nucleoside analogs zidovudine, dideoxyinosine, dideoxycytosine, and lamivudine to inhibit HIV-1 replication. As a group, the UC compounds were found to be less active against viruses with the L100I, K103N, and Y181C amino acid changes in the RT and, upon in vitro selection, yielded resistant virus with the Y181C mutation in the RT. The most potent of the three new compounds, UC781, contains a furanyl side chain, similar to UC10, but differs in having an extended ether side chain instead of an oxime chain. The broad therapeutic index of UC781 (>62,000) resulted in effective inhibition of NNRTI-resistant virus isolates at high nanomolar concentrations. Furthermore, UC781 and the NNRTI costatolide were able to synergistically inhibit HIV-1 replication when used in combination, suggesting that UC781 may interact with the RT differently than the other UC analogs. The favorable anti-HIV properties of the UC compounds suggest they should be considered for further clinical development.

All-atom models for the non-nucleoside binding site of HIV-1 reverse transcriptase complexed with inhibitors: a 3D QSAR approach

Several molecular modeling techniques were used to generate an all-atom molecular model of a receptor binding site starting only from Ca atom coordinates. The model consists of 48 noncontiguous residues of the non-nucleoside binding site of HIV-1 reverse transcriptase and was generated using a congeneric series of nevirapine analogs as structural probes. On the basis of the receptor-ligand atom contacts, the program HINT was used to develop a 3D quantitative structure activity relationship that predicted the rank order of binding affinities for the series of inhibitors. Electronic profiles of the ligands in their docked conformations were characterized using electrostatic potential maps and frontier orbital calculations. These results led to the development of a 3D stereoelectronic pharmacophore which was used to construct 3D queries for database searches. A search of the National Cancer Institute's open database identified a lead compound that exhibited moderate antiviral activity.

HIV-1 reverse transcriptase resistance to nonnucleoside inhibitors

The parameters governing the polymerization mechanism of reverse transcriptase containing the tyrosine to cysteine mutation at position 181 (Y181C) were determined using pre-steady-state techniques. The pathway for single nucleotide incorporation catalyzed by Y181C is similar to that determined for wild-type RT where a rate-limiting conformational change precedes fast chemistry and is followed by slow steady-state release of the primer/template. The Y181C mutant enzyme binds a 25/45-mer duplex DNA tightly with a Kd of 11 nM. However, the Y181C mutation weakens the nucleotide affinity 2-3-fold relative to the wild-type complex. We also determined the parameters governing the mechanism of nonnucleoside inhibitor resistance with Y181C. The Kd value of Nevirapine with the mutant E.DNA complex increased approximately 500-fold. The decreased affinity of Nevirapine for the mutant enzyme is a consequence of a faster inhibitor dissociation rate from the enzyme complex of Y181C relative to that of the wild-type. The E.DNA complex of Y181C may be saturated with Nevirapine, and the I.E.DNA complex is capable of a maximum incorporation rate of 0.1 s-1 (a 10-fold faster rate than that of the wild-type I.E.DNA complex). The overall two-step binding of nucleotide to Y181C in the presence of Nevirapine remains unaffected.

Structure-activity and cross-resistance evaluations of a series of human immunodeficiency virus type-1-specific compounds related to oxathiin carboxanilide

A series of compounds related to the nonnucleoside reverse transcriptase (RT) inhibitor (NNRTI) oxathiin carboxanilide (UC84) were evaluated for activity against the human immunodeficiency virus (HIV) to determine structural requirements for anti-HIV activity. Twenty-seven compounds representative of the more than 400 Uniroyal Chemical Company (UC) compounds were evaluated for structure-activity relationships. Several of the compounds evaluated were highly active, with 50% effective concentrations in the nanomolar range and therapeutic indices of > 1,000. Highly synergistic anti-HIV activity was observed for each compound when used in combination with 3'-azido-3'-deoxythymidine; additive to slightly synergistic interactions were observed with the compounds used in combination with dideoxycytidine. In combination with the NNRTI costatolide, only UC38 synergistically inhibited HIV type 1. Residues in the RT which, when mutated, impart resistance to the virus isolates selected in cell culture, against virus variants with site-directed mutations, and against RTs containing defined single amino acid changes. The mutations included changes in RT amino acids 100, 101, 103, 106, 108, and 181. The results with isolates selected in cell culture indicate that the carboxanilide compounds interact with the RT at two vulnerable sites, selecting UC-resistant virus isolates with the Y-to-C mutation at position 181 (Y181C) or the L100I substitution. A resistant virus isolate containing both Y181C combination with calanolide A, an NNRTI which retains activity against virus with the single Y181C mutation, UC10 rapidly selected a virus isolate with the K103N mutation. The merits of selecting potential candidate anti-HIV agents to be used in rational combination drugs design as part of an armamentarium of highly active anti-HIV compounds are discussed.

Anti-human immunodeficiency virus (HIV) activities of halogenated gomisin J derivatives, new nonnucleoside inhibitors of HIV type 1 reverse transcriptase

Halogenated gomisin J (a derivative of lignan compound), represented by the bromine derivative 1506 [(6R, 7S, S-biar)-4,9-dibromo-3,10-dihydroxy-1,2,11,12-tetramethoxy-6, 7-dimethyl-5,6,7,8- tetrahydrodibenzo[a,c]cyclo-octene], was found to be a potent inhibitor of the cytopathic effects of human immunodeficiency virus type 1 (HIV-1) on MT-4 human T cells (50% effective dose, 0.1 to 0.5 microM). Gomisin J derivatives were active in preventing p24 production from acutely HIV-1-infected H9 cells. The selective indices (toxic dose/effective dose) of these compounds were as high as > 300 in some systems. 1506 was active against 3'-azido-3'-deoxythymidine-resistant HIV-1 and acted synergistically with AZT and 2',3'-ddC. 1506 inhibited HIV-1 reverse transcriptase (RT) in vitro but not HIV-1 protease. From the time-of-addition experiment, 1506 was found to inhibit the early phase of the HIV life cycle. A 1506-resistant HIV mutant was selected and shown to possess a mutation within the RT-coding region (at position 188 [Tyr to Leu]). The mutant RT expressed in Escherichia coli was resistant to 1506 in the in vitro RT assay. Some of the HIV strains resistant to other nonnucleoside HIV-1 RT inhibitors were also resistant to 1506. Comparison of various gomisin J derivatives with gomisin J showed that iodine, bromine, and chlorine in the fourth and ninth positions increased RT inhibitory activity as well as cytoprotective activity.

Pharmacokinetics and toxicity of the human immunodeficiency virus inhibitor 1-ethoxymethyl-6-phenylselenenyl-5-ethyluracil in rodents

1-(Ethoxymethyl)-6-(phenylselenenyl)-5-ethyluracil (E-EPSeU) has been shown to exhibit potent and selective activity against human immunodeficiency virus type 1 in vitro. The pharmacokinetics of E-EPSeU were characterized after intravenous administration of 5, 10 and 15 mg/kg to rats. Plasma and urine concentrations of E-EPSeU were determined by HPLC. The plasma protein binding of E-EPSeU averaged 86 +/- 4% and the blood: plasma concentration ratio was unity. E-EPSeU concentrations after the 5 mg/kg dose were too low to reliably characterize the pharmacokinetics. The pharmacokinetics of E-EPSeU were independent of dose over the range of 10-15 mg/kg. Plasma concentrations of E-EPSeU declined in a bi-exponential manner with terminal half-life of 0.45 +/- 0.12 h (mean +/- S.D.). The steady-state volume of distribution was 0.091 +/- 0.031 1/kg, suggesting the compound distributed primarily into blood. The systemic clearance (0.63 +/- 0.13 1/h/kg) was moderate and limited, in part, by protein binding. No parent compound was detected in urine. E-EPSeU-related toxicities were observed at high doses. One rat, out of 5, died 4 h after 15 mg/kg of E-EPSeU was administered and two rats administered 20 and 25 mg/kg died within 1 h. Two mice, out of 5, administered 30 mg/kg/day of E-EPSeU intraperitoneally for 6 days died during the experiment, while significant loss of body weight was observed in the surviving mice. However, body weight of the surviving mice returned to control values within 2 weeks after E-EPSeU treatment was stopped.(ABSTRACT TRUNCATED AT 250 WORDS)

Antiviral therapy for human immunodeficiency virus infections

Depending on the stage of their intervention with the viral replicative cycle, human immunodeficiency virus inhibitors could be divided into the following groups: (i) adsorption inhibitors (i.e., CD4 constructs, polysulfates, polysulfonates, polycarboxylates, and polyoxometalates), (ii) fusion inhibitors (i.e., plant lectins, succinylated or aconitylated albumins, and betulinic acid derivatives), (iii) uncoating inhibitors (i.e., bicyclams), (iv) reverse transcription inhibitors acting either competitively with the substrate binding site (i.e., dideoxynucleoside analogs and acyclic nucleoside phosphonates) or allosterically with a nonsubstrate binding site (i.e., non-nucleoside reverse transcriptase inhibitors), (v) integration inhibitors, (vi) DNA replication inhibitors, (vii) transcription inhibitors (i.e., antisense oligodeoxynucleotides and Tat antagonists), (viii) translation inhibitors (i.e., antisense oligodeoxynucleotides and ribozymes), (ix) maturation inhibitors (i.e., protease inhibitors, myristoylation inhibitors, and glycosylation inhibitors), and finally, (x) budding (assembly/release) inhibitors. Current knowledge, including the therapeutic potential, of these various inhibitors is discussed. In view of their potential clinical the utility, the problem of virus-drug resistance and possible strategies to circumvent this problem are also addressed.

High resolution structures of HIV-1 RT from four RT-inhibitor complexes

We have determined the structures of four complexes of HIV-1 reverse transcriptase with non-nucleoside inhibitors, three fully refined at high resolution. The highest resolution structure is of the RT-nevirapine complex which has an R-factor of 0.186 and a root-mean-square bond length deviation of 0.015 A for all data to 2.2 A. The structures reveal a common mode of binding for these chemically diverse compounds. The common features of binding are largely hydrophobic interactions and arise from induced shape complementarity achieved by conformational rearrangement of the enzyme and conformational/configurational rearrangement of the compounds.

Biological and biochemical anti-HIV activity of the benzothiadiazine class of nonnucleoside reverse transcriptase inhibitors

A series of benzothiadiazine derivatives were screened against the human immunodeficiency virus (HIV) and certain structure-activity relationships were defined for anti-HIV activity in this chemical class. The selected representative NSC 287474 was a highly potent inhibitor of HIV-induced cell killing and HIV replication in a variety of human cell lines, as well as in fresh human peripheral blood lymphocytes and macrophages. The compound was active against a panel of biologically diverse laboratory and clinical strains of HIV-1, including the AZT-resistant strain G910-6. However, the agent was inactive against HIV-2, and also against both nevirapine- and pyridinone-resistant strains (N119 and A17) of HIV-1, which are cross-resistant to several structurally diverse nonnucleoside reverse transcriptase inhibitors. The compound selectively inhibited HIV-1 reverse transcriptase, but not HIV-2 reverse transcriptase. Combination of NSC 287474 with AZT synergistically inhibited HIV-1-induced cell killing in vitro. The compound did not inhibit the replication of the Rauscher murine leukemia retrovirus or the simian immunodeficiency virus. The benzothiadiazine class of compounds represents a new active anti-HIV-1 chemotype within the diverse group of nonnucleoside reverse transcriptase inhibitors.