What can be Expected from Non-nucleoside Reverse Transcriptase Inhibitors (NNRTIs) in the Treatment of Human Immunodeficiency Virus Type 1 (HIV-1) Infections?

Some Reactions of 3-Chloroisoindolium Salts with Nucleophiles: Access to Isoindole Derivatives and Ellipticine Analogues as Potential Antiviral Agents

3-Chloro-2-substituted-1-oxoisoindolium hexachloroantimonate (1) reacted with water, ethanol and dimethyl-cyanamide to give the corresponding phthalimide derivatives 2, 3 and 4 respectively. Reaction of 1a with nitriles afforded the intermediate 2-azoniaallene salts 5 which underwent cyclisation reaction upon heating to furnish the ellipticine analogues 6. The biological activities of 6a–e against HIV-1 and HBV viruses were determined.

An Approach towards the Synthesis of Potential Metal-Chelating TSAO-T Derivatives as Bidentate Inhibitors of Human Immunodeficiency virus Type 1 Reverse Transcriptase

Novel derivatives of the potent human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) inhibitor TSAO-T have been designed, synthesized and tested for their in vitro antiretro-viral activity against HIV. These TSAO-T derivatives have been designed as potential bidentate inhibitors of HIV-1 RT, which combine in their structure the functionality of a non-nucleoside RT inhibitor (TSAO-T) and a bivalent ion-chelating moiety (a β-diketone moiety) linked through an appropriate spacer to the N-3 of thymine of TSAO-T . Some of the new compounds have an anti-HIV-1 activity comparable to that of the parent compound TSAO-T, but display a markedly increased antiviral selectivity. There was a clear relationship between antiviral activity and the length of the spacer group that links the TSAO molecule with the chelating moiety. A shorter spacer invariably resulted in increased antiviral potency. None of the TSAO-T derivatives were endowed with anti-HIV-2 activity.

Synthesis and Antiviral Activity of 1,3-Disubstituted Uracils against HIV-1 and HCMV

The development of new non-nucleoside reverse transcriptase inhibitors (NNRTIs) is an efficient strategy for finding new therapeutic agents against human immunodeficiency virus (HIV). A large number of 6-substituted uracil derivatives have been prepared in order to explore new NNRTIs. However, there are few approaches to anti-HIV agents from 1,3-disubstituted uracil derivatives. Therefore, we tried to prepare several 1,3-disubstituted uracils, which were easily obtainable from uracil by preparation under alkali and Mitsunobu conditions, and examined their antiviral activity against HIV-1 and human cytomegalovirus (HCMV). We found that 1-benzyl-3-(3,5-dimethylbenzyl)uracil and 1-cyanomethyl-3-(3,5-dimethylbenzyl)-4-thiouracil showed powerful inhibition against HCMV and HIV-1, respectively.

Crystal structure of 2-(1,3,7,9-tetra-methyl-2,4,6,8-tetra-oxo-1,2,3,4,6,7,8,9-octa-hydro-pyrido[2,3-d:6,5-d']dipyrimidin-5-yl)benzamide di-methyl-formamide hemisolvate

In the crystal, the benzamide mol­ecules are linked by N—H⋯O hydrogen bonds to generate tetra­mers with an approximate square-prismatic shape, which appears to correlate with the tetra­gonal crystal symmetry.

The title compound, C₂₀H₁₈N₆O₅·0.5C₃H₇NO, crystallized as a di­methyl­formamide (DMF) solvate. In the main mol­ecule, the dihedral angle between the pyridodi­pyrimidine fused-ring system and the benzamide substituent is 82.26 (11)°. In the crystal, the benzamide mol­ecules are linked by N—H⋯O hydrogen bonds to generate tetra­mers with an approximate square-prismatic shape, which appears to correlate with the tetra­gonal crystal symmetry. The DMF mol­ecule is disordered about a crystallographic twofold axis and accepts a C—H⋯O inter­action from the benzamide mol­ecule.

Novel furocoumarins as potential HIV-1 integrase inhibitors

A series of seven novel, rationally designed N-substituted 3-{3,5-dimethylfuro[3,2-g]coumarin-6-yl}propanamides have been prepared as potential HIV-1 integrase (IN) inhibitors via a five-step pathway commencing with resorcinol and diethyl 2-acetylglutarate, and the HIV-1 IN inhibition potential of these compounds has been examined relative to raltegravir, a known HIV-1 IN inhibitor.

Evaluation of steady-state pharmacokinetic interactions between ritonavir-boosted BILR 355, a non-nucleoside reverse transcriptase inhibitor, and lamivudine/zidovudine in healthy subjects

WHAT IS KNOWN AND OBJECTIVE

BILR 355 is a second generation non-nucleoside reverse transcriptase inhibitor. It has shown promising in vitro anti-HIV-1 activities and favourable human pharmacokinetic properties after co-administration with ritonavir (RTV). Lamivudine (3TC) is a nucleoside reverse transcriptase inhibitor. It is excreted predominantly in urine by a transporter-mediated pathway. These two drugs are likely to be given together to HIV-infected patients. The objective of this study was to investigate any steady-state pharmacokinetic interactions between RTV-boosted BILR 355 and 3TC/zidovudine (ZDV).

METHODS

This was a randomized, open label, prospective study. In group A, 39 healthy subjects were given 3TC/ZDV (150 mg/300 mg) twice daily (b.i.d.) for 7 days, and then BILR 355 and RTV (BILR 355/r, 150 mg/100 mg) were co-administered with this regimen for an additional 7 days. Intensive blood samples were taken on days 7 and 14 for pharmacokinetic assessments. In group B, 12 healthy subjects were given BILR 355/r (150 mg/100 mg) b.i.d. for 7 days. The pharmacokinetic data from group B were pooled with data from group B subjects in other similar studies performed in parallel (BILR 355 alone group in BILR 355 drug-drug interaction studies with tipranavir, lopinavir/RTV, and emtricitabine/tenofovir DF; BILR 355 regimen was the same).

RESULTS AND DISCUSSION

After co-administration with BILR 355/r, the AUC(12,ss) and C(max,ss) of 3TC increased by 45% and 24%, respectively; the elimination half-life (t(1/2) ,ss) of 3TC was significantly increased. However, the pharmacokinetics of ZDV was unchanged. Co-administration with 3TC/ZDV resulted in a 22% decrease in AUC(12,ss) and a 20% decrease in C(max,ss) for BILR 355. The observed increase in exposure and prolongation of t(1/2,ss) of 3TC is potentially related to inhibition of OCT-mediated urinary excretion of 3TC.

WHAT IS NEW AND CONCLUSION

Concomitant administration of BILR 355 with 3TC/ZDV resulted in a modest decrease in exposure to BILR 355 and a 45% increase in exposure to 3TC.

Development of resistance of human immunodeficiency virus (HIV) to anti-HIV agents: how to prevent the problem?

Of the multitude of reverse transcriptase inhibitors and protease inhibitors that have been pursued for the treatment of HIV infections, nine compounds (viz. zidovudine, didanosine, zalcitabine, stavudine, lamivudine, saquinavir, ritonavir, indinavir and nevirapine) have been approved and several others (i.e. adefovir dipivoxyl [bis(POM)-PMEA], PMPA, bis(POC)-PMPA, 1592U89, delavirdine, loviride, MKC-442, nelfinavir and VX-478) are under clinical development. All these compounds can select for mutations in the reverse transcriptase or protease that confer various degrees of resistance or diminished susceptibility to the compounds. Both the reverse transcriptase and protease are able to accumulate multiple mutations in their genome, thus engendering high-level resistance. To avoid drug resistance from emerging it is recommended to use from the beginning combinations of the different drugs at sufficiently high (that is maximal tolerated) doses. If installed as soon as possible after infection, when it has become evident that the virus is replicating, these drug combinations may achieve a pronounced and sustained virus suppression. This should be reflected by a dramatic reduction of viral load in both the plasma and lymphnodes. With the most effective drug combination regimens, the viral load may even fall under the threshold of detection, and this may clinically translate into an arrest or prevention of progression to AIDS.

Quantitative structure-activity relationship studies of TIBO derivatives using support vector machines

A quantitative structure-activity relationship (QSAR) study is suggested for the prediction of anti-HIV activity of tetrahydroimidazo[4,5,1-jk][1,4]benzodiazepinone (TIBO) derivatives. The model was produced by using the support vector machine (SVM) technique to develop quantitative relationships between the anti-HIV activity and ten molecular descriptors of 89 TIBO derivatives. The performance and predictive capability of the SVM method were investigated and compared with other techniques such as artificial neural networks and multiple linear regression. The results obtained indicate that the SVM model with the kernel radial basis function can be successfully used to predict the anti-HIV activity of TIBO derivatives with only ten molecular descriptors that can be calculated directly from only molecular structure. The contribution of each descriptor to the structure-activity relationships was evaluated. Hydrophobicity of the molecule was thus found to take the most relevant part in the molecular description.

7-Chloro-11a-phenyl-2,3,5,10,11,11a-hexahydro-1H-pyrrolo[2,1-c][1,4]benzodiazepine-5,11-dione

The title compound, C₁₈H₁₅ClN₂O₂, is a potential human immunodeficiency virus type-1 (HIV-1) non-nucleoside reverse transcriptase inhibitor. The pyrrolidine ring adopts an envelope and the diazepine ring a boat conformation. In the crystal structure, two isomers (R and S) form centrosymmetric dimers via N—H⋯O hydrogen bonds.

1-Benzyl-2-(1H-indol-3-yl)-5-oxopyrrolidine-2-carbonitrile

In the title compound, C₂₀H₁₇N₃O, a potential anti-human immunodeficiency virus type 1 (HIV-1) non-nucleoside reverse-transcriptase inhibitor, the pyrrolidine ring has an envelope conformation. In the crystal structure, adjacent mol­ecules are connected into infinite chains via an N—H⋯O hydrogen bond.

1-(4-Bromo-benzo-yl)-2-phenyl-pyrrolidine-2-carboxamide

In the title compound, C(18)H(17)BrN(2)O(2), which is a potential -human immunodeficiency virus type 1 (HIV-1) non-nucleoside reverse transcriptase inhibitor, the pyrrolidine ring exhibits an envelope conformation. In the crystal structure, inter-molecular N-H⋯O hydrogen bonds [N⋯O = 2.861 (3) Å] link the mol-ecules into centrosymmetric dimers.

1-Benzyl-6-phenyl-imino-5-(pyrrol-2-yl-idene)hexa-hydro-pyrimidine-2,4-dione

In the title compound, C₂₁H₂₀N₄O₂, a potential anti-human immunodeficiency virus type 1 (HIV-1) non-nucleoside reverse transcriptase inhibitor, the pyrrolidine ring adopts an envelope conformation, while the hydrogenated pyrimidine ring adopts a weakly expressed twist conformation. The mol­ecules are connected into infinite chains via N—H⋯O hydrogen bonds.

Newer aminopyrimidinimino isatin analogues as non-nucleoside HIV-1 reverse transcriptase inhibitors for HIV and other opportunistic infections of AIDS: design, synthesis and biological evaluation

Human immuno deficiency virus (HIV) weakens the immune system so that many opportunistic infections (OIs) like tuberculosis, hepatitis, bacterial infections etc can develop. In this paper, we designed aminopyrimidinimino isatin lead compound as a novel non-nucleoside reverse transcriptase inhibitor (NNRTI) with broad-spectrum chemotherapeutic properties for the effective treatment of AIDS and AIDS-related OIs. Compound 1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-[[N4-[3'-(4'-amino-5'-trimethoxybenzyl pyrimidin-2'-yl)imino-1'-(5-methylisatinyl)]methyl]-N1-piperazinyl]-3-quinoline carboxylic acid (10) emerged as the most potent broad-spectrum chemotherapeutic agent active against HIV, HCV, Mycobacterium tuberculosis and various pathogenic bacteria.

Anti-HIV-1 activities in extracts from some medicinal plants as assessed in anin vitro biochemical HIV-1 reverse transcriptase assay

An in vitro HIV-1 reverse transcriptase (RT) assay was used for screening of anti-HIV activity of extracts obtained from some Kenyan medicinal plants. The assay utilises [3H]-methyl thymidine triphosphate (dTTP) as the enzyme substrate and polyadenylic acid.oligodeoxythymidylic acid [poly(rA).p(dT)(12-18)] as the template-primer dimmer. This assay was optimised and standardised with respect to the various experimental parameters in a microtiter plate methodology. The assay was then applied to test for potential antiviral activities of several Kenyan medicinal plant extracts and the concentrations producing 50% inhibition (IC50) of the HIV-1 RT were determined. This assay is described in this report and results obtained with some of the extracts are presented.

Design, synthesis and biological evaluation of novel non-nucleoside HIV-1 reverse transcriptase inhibitors with broad-spectrum chemotherapeutic properties

Acquired immunodeficiency syndrome (AIDS) results from infection by the retrovirus, human immunodeficiency virus (HIV). HIV is the most significant risk factor for many opportunistic infections like tuberculosis, hepatitis, bacterial infections, etc. In this paper, we designed aminopyrimidinimino isatin lead compound as a novel non-nucleoside reverse transcriptase inhibitor with broad-spectrum chemotherapeutic properties for the effective treatment of AIDS and AIDS-related opportunistic infections. Compound 1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7[[N(4)-[3'-(4'-amino-5'-trimethoxybenzylpyrimidin-2'-yl)imino-1'-(5-fluoroisatinyl)]methyl]-N(1)-piperazinyl]-3-quinoline carboxylic acid (12) emerged as the most potent broad-spectrum chemotherapeutic agent active against HIV, HCV, Mycobacterium tuberculosis and various pathogenic bacteria.

Synthesis of alkenyldiarylmethane (ADAM) non-nucleoside HIV-1 reverse transcriptase inhibitors with non-identical aromatic rings

The existing methods for the synthesis of alkenyldiarylmethane (ADAM) non-nucleoside reverse transcriptase inhibitors proceed from symmetrical benzophenones and therefore result in products with identical aromatic rings. New methods have therefore been devised for the preparation of stereochemically defined ADAMs with non-identical aromatic rings. The new routes rely on palladium-catalyzed reactions, including Sonogashira, Suzuki, Stille, and hydroarylation methodology. Several of the new ADAMs inhibited the cytopathic effect of HIV-1 in cell culture and HIV-1 reverse transcriptase at submicromolar concentrations.

3-Benzamido, ureido and thioureidoimidazo[1,2-a]pyridine derivatives as potential antiviral agents

This work reports the synthesis and the antiviral activities of 3-benzamido, 3-phenylureido and 3-phenylthioureido derivatives in the imidazo[1,2-a]pyridine series. The structure was proven by NMR spectroscopy. The synthesized compounds were evaluated against a large number of viruses. The 3-phenylthioureido derivative 7 showed moderate activity against human cytomegalovirus (HCMV) in vitro. The crystallographic data for 8 are also reported and explain the absence of activity against human immunodeficiency virus (HIV).

Ellipticine analogues and related compounds as inhibitors of reverse transcriptase and as inhibitors of the efflux pump

Ten polycyclic derivatives related to ellipticine have been synthesised and tested for their intercalating, reverse transcriptase (RT) inhibitory and multidrug resistance efflux pump inhibitory properties. The intercalating activity and the RT inhibitory activity of the derivatives suggest that ellipticine analogues bind at an allosteric binding site on RT or that this inhibition could be controlled at the DNA level. The MDR efflux pump inhibitory activities of these derivatives, however, appears to be unrelated to the DNA binding ability.

Novel inhibitors of HIV-reverse transcriptase catalyzed DNA strand transfer: can we alter the infidelity of the enzyme?

Reverse transcription of viral RNA by the enzyme HIV1-reverse transcriptase (HIV1-RT) involves two DNA-strand transfers (DNA-ST). We report here a time-dependent inactivation of DNA-strand transfer by specific DNA-strand transfer inhibitors that do not affect the polymerase activity of the enzyme. Irreversible inhibitors of this type may be useful in characterizing the sites on the enzyme responsible for DNA-strand transfer.

Site-directed mutagenesis of human immunodeficiency virus type 1 reverse transcriptase at amino acid position 138

TSAO derivatives represent a class of nonnucleoside reverse transcriptase inhibitors (NNRTIs) that consistently select for the Glu138Lys resistance mutation in HIV-1 reverse transcriptase (RT). Seven RT mutants (i.e., Ala, Asp, Gln, Gly, Lys, Phe, and Tyr) were constructed by site-directed mutagenesis. The mutant Glu138Asp, Glu138Lys, Glu138Gln, Glu138Ala, and Glu138Gly RTs retained marked catalytic activity. In contrast, the Glu138Phe and Glu138Tyr RT mutants showed poor RNA-dependent DNA polymerase activity (30 and 4% of wild-type, respectively). TSAO derivatives lost their inhibitory activity against all mutant enzymes, except against the closely related Glu138Asp RT mutant that remained as sensitive to TSAOs as did wild-type RT. Other NNRTIs, including delavirdine, emivirine, and UC-781, and the NRTI ddGTP retained pronounced inhibitory activity against all mutant enzymes. When the amino acid mutations at position 138 of RT were introduced in recombinant virus clones, the sensitivity/resistance spectrum obtained toward the TSAOs and other NNRTIs was similar to those observed for the isolated recombinant mutant enzymes. The Glu138Lys RT mutant virus had the most marked resistance to TSAOs, followed by the Glu138Gln, Glu138Phe, Glu138Gly, Glu138Tyr, and Glu138Ala virus mutants. The Glu138Asp RT mutant virus kept full sensitivity to the TSAO derivatives. Mixtures of Glu138Lys RT mutant virus with the other virus clones mutated at the 138 position resulted in all cases, except for the Glu138Asp and Glu138Gly RT mutant viruses, in an outgrowth of the Glu138Lys RT mutant virus. Since the Glu138Lys RT proved most resistant to TSAO derivatives, was among the most catalytically efficient enzymes, and resulted in highly replication-competent virus, our data explain why the Glu138Lys RT mutant virus strains but not virus strains containing other amino acids at position 138 invariably emerge in cell cultures under TSAO drug pressure.

SJ-3366, a unique and highly potent nonnucleoside reverse transcriptase inhibitor of human immunodeficiency virus type 1 (HIV-1) that also inhibits HIV-2

We have identified and characterized a potent new nonnucleoside reverse transcriptase (RT) inhibitor (NNRTI) of human immunodeficiency virus type 1 (HIV-1) that also is active against HIV-2 and which interferes with virus replication by two distinct mechanisms. 1-(3-Cyclopenten-1-yl)methyl-6-(3,5-dimethylbenzoyl)-5-ethyl-2,4-pyrimidinedione (SJ-3366) inhibits HIV-1 replication at concentrations of approximately 1 nM, with a therapeutic index of greater than 4 x 10(6). The efficacy and toxicity of SJ-3366 are consistent when evaluated with established or fresh human cells, and the compound is equipotent against all strains of HIV-1 evaluated, including syncytium-inducing, non-syncytium-inducing, monocyte/macrophage-tropic, and subtype virus strains. Distinct from other members of the pharmacologic class of NNRTIs, SJ-3366 inhibited laboratory and clinical strains of HIV-2 at a concentration of approximately 150 nM, yielding a therapeutic index of approximately 20,000. Like most NNRTIs, the compound was less active when challenged with HIV-1 strains possessing the Y181C, K103N, and Y188C amino acid changes in the RT and selected for a virus with a Y181C amino acid change in the RT after five tissue culture passages in the presence of the compound. In combination anti-HIV assays with nucleoside and nonnucleoside RT and protease inhibitors, additive interactions occurred with all compounds tested with the exception of dideoxyinosine, with which a synergistic interaction was found. Biochemically, SJ-3366 exhibited a K(i) value of 3.2 nM, with a mixed mechanism of inhibition against HIV-1 RT, but it did not inhibit HIV-2 RT. SJ-3366 also inhibited the entry of both HIV-1 and HIV-2 into target cells. On the basis of its therapeutic index and multiple mechanisms of anti-HIV action, SJ-3366 represents an exciting new compound for use in HIV-infected individuals.

Safety assessment, in vitro and in vivo, and pharmacokinetics of emivirine, a potent and selective nonnucleoside reverse transcriptase inhibitor of human immunodeficiency virus type 1

Emivirine (EMV), formerly known as MKC-442, is 6-benzyl-1-(ethoxymethyl)-5-isopropyl-uracil, a novel nonnucleoside reverse transcriptase inhibitor that displays potent and selective anti-human immunodeficiency virus type 1 (HIV-1) activity in vivo. EMV showed little or no toxicity towards human mitochondria or human bone marrow progenitor cells. Pharmacokinetics were linear for both rats and monkeys, and oral absorption was 68% in rats. Whole-body autoradiography showed widespread distribution in tissue 30 min after rats were given an oral dose of [(14)C]EMV at 10 mg/kg of body weight. In rats given an oral dose of 250 mg/kg, there were equal levels of EMV in the plasma and the brain. In vitro experiments using liver microsomes demonstrated that the metabolism of EMV by human microsomes is approximately a third of that encountered with rat and monkey microsomes. In 1-month, 3-month, and chronic toxicology experiments (6 months with rats and 1 year with cynomolgus monkeys), toxicity was limited to readily reversible effects on the kidney consisting of vacuolation of kidney tubular epithelial cells and mild increases in blood urea nitrogen. Liver weights increased at the higher doses in rats and monkeys and were attributed to the induction of drug-metabolizing enzymes. EMV tested negative for genotoxic activity, and except for decreased feed consumption at the high dose (160 mg/kg/day), with resultant decreases in maternal and fetal body weights, EMV produced no adverse effects in a complete range of reproductive toxicology experiments performed on rats and rabbits. These results support the clinical development of EMV as a treatment for HIV-1 infection in adult and pediatric patient populations.

Synthesis and anti-HIV activity of 1,1,3-trioxo-2H,4H-thieno[3,4-e][1,2,4]thiadiazines (TTDs): a new family of HIV-1 specific non-nucleoside reverse transcriptase inhibitors

The anti-HIV activity of a novel series of 1,1,3-trioxo-2H,4H-thieno[3,4-e][1,2,4]thiadiazines (TTDs) has been described. The compounds were synthesized via Curtius rearrangement of appropriate sulfamoylcarboxy azides which, in turn, were prepared from known starting materials. Several 4-substituted-2-benzyl-derivatives were found to selectively inhibit human immunodeficiency virus type 1 [HIV-1 (IIIB)] replication in MT-4 and CEM cells. These TTDs were also effective against other strains of HIV-1 (RF, HE, MN, NDK), including those that are resistant to AZT, but not against HIV-2 (ROD) or simian immunodeficiency virus [SIV(MAC251)] at subtoxic concentrations. Some of the test compounds exhibited antiviral activity against L100I RT mutant virus, but significantly lost antiviral activity against K103N, V106A, E138K, Y181C and Y188H RT mutant viruses. Compounds 6d, 6f and 6g were inhibitory to HIV-1 RT at concentrations that rank between 16.4 and 59.8 microM (nevirapine: IC50 = 4.5 microM against HIV-1 RT). Inhibition of HIV-1 RT by compound 6g was purely non-competitive with respect to the natural substrate (dGTP), which is in agreement with the nature of inhibition shown by other NNRTIs such as nevirapine and delarvidine. A structure-activity relationship was established for the anti-HIV activity of these heterocyclic compounds. TTDs represent a new chemical class of non-nucleoside HIV-1 reverse transcriptase inhibitors (NNRTIs).

Unique anti-human immunodeficiency virus activities of the nonnucleoside reverse transcriptase inhibitors calanolide A, costatolide, and dihydrocostatolide

(+)-Calanolide A (NSC 650886) has previously been reported to be a unique and specific nonnucleoside inhibitor of the reverse transcriptase (RT) of human immunodeficiency virus (HIV) type 1 (HIV-1) (M. J. Currens et al., J. Pharmacol. Exp. Ther., 279:645-651, 1996). Two isomers of calanolide A, (-)-calanolide B (NSC 661122; costatolide) and (-)-dihydrocalanolide B (NSC 661123; dihydrocostatolide), possess antiviral properties similar to those of calanolide A. Each of these three compounds possesses the phenotypic properties ascribed to the pharmacologic class of nonnucleoside RT inhibitors (NNRTIs). The calanolide analogs, however, exhibit 10-fold enhanced antiviral activity against drug-resistant viruses that bear the most prevalent NNRTI resistance that is engendered by amino acid change Y181C in the RT. Further enhancement of activity is observed with RTs that possess the Y181C change together with mutations that yield resistance to AZT. In addition, enzymatic inhibition assays have demonstrated that the compounds inhibit RT through a mechanism that affects both the K(m) for dTTP and the V(max), i.e., mixed-type inhibition. In fresh human cells, costatolide and dihydrocostatolide are highly effective inhibitors of low-passage clinical virus strains, including those representative of the various HIV-1 clade strains, syncytium-inducing and non-syncytium-inducing isolates, and T-tropic and monocyte-tropic isolates. Similar to calanolide A, decreased activities of the two isomers were observed against viruses and RTs with amino acid changes at residues L100, K103, T139, and Y188 in the RT, although costatolide exhibited a smaller loss of activity against many of these NNRTI-resistant isolates. Comparison of cross-resistance data obtained with a panel of NNRTI-resistant virus strains suggests that each of the three stereoisomers may interact differently with the RT, despite their high degree of structural similarity. Selection of viruses resistant to each of the three compounds in a variety of cell lines yielded viruses with T139I, L100I, Y188H, or L187F amino acid changes in the RT. Similarly, a variety of resistant virus strains with different amino acid changes were selected in cell culture when the calanolide analogs were used in combination with other active anti-HIV agents, including nucleoside and nonnucleoside RT and protease inhibitors. In assays with combinations of anti-HIV agents, costatolide exhibited synergy with these anti-HIV agents. The calanolide isomers represent a novel and distinct subgroup of the NNRTI family, and these data suggest that a compound of the calanolide A series, such as costatolide, should be evaluated further for therapeutic use in combination with other anti-HIV agents.

Resistance mutations selected in vivo under therapy with anti-HIV drug HBY 097 differ from resistance pattern selected in vitro

The quinoxaline derivative HBY 097, an orally active nonnucleoside inhibitor of HIV-1 reverse transcriptase (NNRTI), showed an efficient suppression of viral load in a dose-escalating phase I study with mean trough concentrations increasing from 137-1299 ug/l [Rübsamen-Waigmann et al., Lancet 349:1517]. Half-maximal inhibitory concentrations (IC50) for viruses grown from the patients at entry of the study were 0.1-3 nM, except for one patient who had a virus with reduced susceptibility to HBY 097 at entry (IC50: 160 nM). During therapy, only two patients developed a virus with a moderately increased IC50 (2.2 and 15 nM). This reduced susceptibility was associated with the known NNRTI-resistance mutation K ==> N at position 103, in contrast to resistance selection in vitro, which had yielded predominant mutations at positions 179 and 190. The Tyr mutation at position 181, inducing high resistance for other NNRTIs, was never observed. The resistant virus at study entry (IC50 = 160 nM) had a mutation at position 103 as well, combined with an AZT resistance mutation (K ==> R) at position 70, suggesting that nucleoside-resistance mutations may help increasing resistance to HBY 097. This is in line with our in vitro selection studies, where resistance mutations at the 'nucleoside sites' 74 and 75 increased the resistance phenotype of NNRTI mutations. Our findings highlight the crucial importance of IC50 determinations from cultured virus for determination of phenotypic resistance development during therapy and demonstrate that in vivo resistance development cannot be predicted from in vitro selection.

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.

Mutational analysis of Tyr-318 within the non-nucleoside reverse transcriptase inhibitor binding pocket of human immunodeficiency virus type I reverse transcriptase

The highly conserved Tyr-318 is part of the non-nucleoside reverse transcriptase inhibitor (NNRTI)-specific lipophilic pocket of human immunodeficiency virus type I reverse transcriptase (RT) and makes contact within 4 A with the NNRTIs in all reported RT/NNRTI complexes. Using site-directed mutagenesis, six mutant RTs were constructed bearing the mutations Y318H, Y318K, Y318L, Y318C, Y318W, and Y318F. We found that only the Y318W and Y318F mutant RTs retained substantial RT activity, whereas the catalytic activities of the Y318K, Y318C, Y318H, and Y318L RT mutants were less than 5% of the wild-type activity. The Y318F mutant RT retained substantial sensitivity to the majority of NNRTIs tested, whereas the Y318W mutant RT showed varying degrees of resistance to NNRTIs. Subunit-specific site-directed mutagenesis revealed that there was no difference in the catalytic activity or resistance/sensitivity spectrum toward NNRTIs regardless of whether the Tyr-318 mutation was introduced in both subunits or only in the p66 subunit of RT. Recombinant viruses harboring the Y318F or Y318W mutation in the RT showed a similar resistance/sensitivity pattern to NNRTIs as their corresponding 318 mutant recombinant RTs. Our findings stress a functional or structural role for Tyr-318 in wild-type RT and argue for the design of novel NNRTIs that interact more closely with this amino acid in the NNRTI-specific pocket of human immunodeficiency virus type I RT.

Crystal structures of HIV-1 reverse transcriptase in complex with carboxanilide derivatives

The carboxanilides are nonnucleoside inhibitors (NNIs) of HIV-1 reverse transcriptase (RT), of potential clinical importance. The compounds differ in potency and in their retention of potency in the face of drug resistance mutations. Whereas UC-84, the prototype compound, only weakly inhibits many RTs bearing single point resistance mutations, inhibition by UC-781 is little affected. It has been proposed that UC-38 and UC-781 may form quaternary complexes with RT at a site other than the known binding pocket of other NNIs. X-ray crystal structures of four HIV-1 RT-carboxanilide complexes (UC-10, UC-38, UC-84, and UC-781) reported here reveal that all four inhibitors bind in the usual NNI site, forming binary 1:1 complexes with RT in the absence of substrates with the amide/thioamide bond in cis conformations. For all four complexes the anilide rings of the inhibitors overlap aromatic rings of many other NNIs bound to RT. In contrast, the second rings of UC-10, UC-84, and UC-781 do not bind in equivalent positions to those of other "two-ring" NNIs such as alpha-APA or HEPT derivatives. The binding modes most closely resemble that of the structurally dissimilar NNI, Cl-TIBO, with a common hydrogen bond between each carboxanilide NH- group and the main-chain carbonyl oxygen of Lys101. The binding modes differ slightly between the UC-10/UC-781 and UC-38/UC-84 pairs of compounds, apparently related to the shorter isopropylmethanoyl substituents of the anilide rings of UC-38/UC-84, which draws these rings closer to residues Tyr181 and Tyr188. This in turn explains the differences in the effect of mutated residues on the binding of these compounds.

Novel 1,1,3-trioxo-2H,4H-thieno[3,4-e][1,2,4]thiadiazine derivatives as non-nucleoside reverse transcriptase inhibitors that inhibit human immunodeficiency virus type 1 replication

The 1,1,3-trioxo-2H,4H-thieno[3,4-e][1,2,4]thiadiazines (TTDs) represent a recently discovered chemical class of non-nucleoside reverse transcriptase inhibitors that selectively block human immunodeficiency virus type 1 replication. In a search for a better understanding of their mode of binding and with the aim of obtaining novel lead compounds, a second series of TTD derivatives was synthesized and evaluated for antiviral activity. The design of the new compounds was based on a variety of chemical modifications which were carried out in the original prototype 20a (QM 96521). Substitution of a halogen at the meta position of the N-2 benzyl group resulted in an improvement of the antiviral activity by 1 order of magnitude. Compounds bearing at the N-4 position a cyanomethyl, propargyl, or benzyl substituent were found to be the most potent of the series. Modifying the thieno[3,4-e] ring fused to the 1,2,4-thiadiazine moiety to other heterocyclic ring systems decreased the potency. The results obtained in this investigation have provided new indications for the design of even more effective TTDs.

Biaryl acids: novel non-nucleoside inhibitors of HIV reverse transcriptase types 1 and 2

A series of biaryl acids has been found to show micromolar inhibition of the HIV reverse transcriptase (RT) from types 1 and 2 with IC50S in the micromolar range. The series was discovered by consideration of the polymerase active site and sub-structure searching of the company compound collection. Synthesis of analogues to investigate the SAR is described. Two of these compounds have shown inhibition of HIV-2 RT only.

New alkenyldiarylmethanes with enhanced potencies as anti-HIV agents which act as non-nucleoside reverse transcriptase inhibitors

Twenty-two new alkenyldiarylmethanes (ADAMs) were synthesized and evaluated for inhibition of HIV-1 replication. The most potent compound proved to be methyl 3',3"-dichloro-4',4"-dimethoxy-5', 5"-bis(methoxycarbonyl)-6,6-diphenyl-5-hexenoate (ADAM II), which displayed an EC50 of 13 nM for inhibition of the cytopathic effect of HIV-1RF in CEM-SS cells. ADAM II inhibited HIV-1 reverse transcriptase with an IC50 of 0.3 microM but was inactive as an inhibitor of HIV-1 attachment/fusion to cells, protease, integrase, and the nucleocapsid protein. Molecular target-based and cell-based assays revealed that ADAM II acted biologically as a nonnucleoside reverse transcriptase inhibitor (NNRTI). ADAM II inhibited replication of a wide variety of laboratory, clinical, and clade-representative isolates of HIV-1 in T cell lines and cultures of peripheral blood mononuclear cells or monocyte/macrophages. Mutations that conferred resistance to ADAM II clustered at residues 101, 103, 108, 139, 179, 181, and 188, which line the nonnucleoside binding pocket of HIV-1 reverse transcriptase. However, HIV-1 NL4-3 strain expressing a mutation at residue 100 of reverse transcriptase, and an AZT-resistant virus, displayed increased sensitivity to ADAM II. Thus, ADAM II could serve as an adjunct therapy to AZT and NNRTIs that select for L100I resistance mutations.

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.

1,1,3-Trioxo-2H,4H-thieno[3,4-e][1,2,4]thiadiazine (TTD) derivatives: a new class of nonnucleoside human immunodeficiency virus type 1 (HIV-1) reverse transcriptase inhibitors with anti-HIV-1 activity

We report the development of a new group of nonnucleoside reverse transcriptase inhibitors (NNRTIs). One of the most active congeners of this series of 1,1,3-trioxo-2H,4H-thieno[3,4-e] [1,2,4]thiadiazine (TTD) derivatives, i.e., 2-(3-fluorobenzyl)-4-cyanomethylen-l,1,3-trioxo-2H,4H- thieno [3,4-e] [1,2,4] thiadiazine) (QM96639) was found to inhibit human immunodeficiency virus (HIV) type 1 [HIV-1 (IIIB)] replication in MT-4 cells at a concentration of 0.09 microM. This compound was toxic for the host cells only at a 1,400-fold higher concentration. The TTD derivatives proved effective against a variety of HIV-1 strains, including those that are resistant to 3'-azido-3'-deoxythymidine (AZT), but not against HIV-2 (ROD) or simian immunodeficiency virus (SIV/ MAC251). HIV-1 strains containing the L100I, K103N, V106A, E138K, Y181C, or Y188H mutations in their reverse transcriptase (RT) displayed reduced sensitivity to the compounds. Their cross-resistance patterns correlated with that of nevirapine. 2-Benzyl-4-cyanomethylen-1,1,3-trioxo-2H,4H-thieno[3,4-e] [1,2,4]thiadiazine (QM96521) enhanced the anti-HIV-1 activity of AZT and didanosine in a subsynergistic manner. HIV-1-resistant virus containing the V179D mutation in the RT was selected after approximately six passages of HIV-1 (IIIB) in CEM cells in the presence of different concentrations of QM96521. From structure-activity relationship analysis of a wide variety of TTD derivatives, a number of restrictions appeared as to the chemical modifications that were compatible with anti-HIV activity. Modelling studies suggest that in contrast to most other NNRTIs, but akin to nevirapine, QM96521 does not act as a hydrogen bond donor in the RT-drug complex.

Efficacy of the acyclic nucleoside phosphonates (S)-9-(3-fluoro-2-phosphonylmethoxypropyl)adenine (FPMPA) and 9-(2-phosphonylmethoxyethyl)adenine (PMEA) against feline immunodeficiency virus

The acyclic nucleoside phosphonates (S)-9-(3-fluoro-2-phosphonylmethoxypropyl)adenine (FPMPA) and 9-(2-phosphonylmethoxyethyl)adenine (PMEA) were evaluated for their efficacy and side effects in a double-blind placebo-controlled trial using naturally occurring feline immunodeficiency virus (FIV)-infected cats. This natural retrovirus animal model is considered highly relevant for the pathogenesis and chemotherapy of HIV in humans. Both PMEA and FPMPA proved effective in ameliorating the clinical symptoms of FIV-infected cats, as measured by several clinical parameters including the incidence and severity of stomatitis, Karnofsky's score, immunologic parameters such as relative and absolute CD4+ lymphocyte counts, and virologic parameters including proviral DNA levels in peripheral blood mononuclear cells (PBMC) of drug-treated animals. In contrast with PMEA, FPMPA showed no hematologic side effects at a dose that was 2.5-fold higher than PMEA.

Synthesis of a non-nucleoside reverse transcriptase inhibitor in the alkenyldiarylmethane (ADAM) series with optimized potency and therapeutic index

A novel alkenyldiarylmethane (ADAM) analog has been synthesized with enhanced potency as an anti-HIV agent. The new compound (ADAM II) inhibits the cytopathic effect of HIV-1RF in CEM-SS cells with an EC50 of 13 nM, while it shows cytotoxicity with a CC50 of 31.6 microM, providing a therapeutic index of 2430. ADAM II is a non-nucleoside reverse transcriptase inhibitor, displaying an IC50 of 0.3 microM with poly(rC) oligo(dG) as the template/primer.

Characteristics of the Pro225His mutation in human immunodeficiency virus type 1 (HIV-1) reverse transcriptase that appears under selective pressure of dose-escalating quinoxaline treatment of HIV-1

Treatment of human immunodeficiency virus type 1 (HIV-1)-infected CEM cell cultures with escalating concentrations of the quinoxaline S-2720 resulted in an ordered appearance of single and multiple mutant virus strains that gradually became resistant to the quinoxaline and other nonnucleoside reverse transcriptase (RT) inhibitors (NNRTIs). A novel mutation, Pro225His, consistently appeared in a Val106Ala RT-mutated genetic background. The contribution of this mutation to the resistance of the mutant HIV-1 RT to NNRTIs was additive to the resistance caused by the Val106Ala mutation. Interestingly, site-directed mutagenesis studies revealed that the Pro225His-mutated RT had acquired markedly greater sensitivity to bis(heteroaryl)piperazine (BHAP U-90152) (delavirdine) but not to any of the other NNRTIs. The kinetics of inhibition of the Pro225His mutant RT by the NNRTIs (including BHAP U-90152) was not substantially different from that observed for the wild-type RT. The hypersensitivity of the mutant enzyme and virus to BHAP U-90152 could be rationally explained by the molecular-structural determinants of the RT-BHAP complex, which has recently been resolved by X-ray crystallography.

In search of a selective antiviral chemotherapy

This article describes several approaches to a selective therapy of virus infections: (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU [brivudin]) for the therapy of herpes simplex virus type 1 and varicella-zoster virus infections: (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (HPMPC [cidofovir]) for the therapy of various DNA virus (i.e., herpesvirus, adenovirus, papillomavirus, polyomavirus, and poxvirus) infections; 9-(2-phosphonylmethoxyethyl)adenine (PMEA [adefovir]) for the therapy of retrovirus, hepadnavirus, and herpesvirus infections; (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA) for the therapy and prophylaxis of retrovirus and hepadnavirus infections; and nonnucleoside reverse transcriptase inhibitors (NNRTIs), such as tetrahydroimidazo[4,5,1-jk][1,4]-benzodiazepin-2(IH)-one and -thione (TIBO), 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymine (HEPT), alpha-anilinophenylacetamide (alpha-APA), and 2',5'bis-O-(tert-butyldimethylsilyl)-3'-spiro-5"-(4"-amino-1",2"-oxat hiole- 2",2"-dioxide)pyrimidine (TSAO) derivatives, and thiocarboxanilides for the treatment of human immunodeficiency virus type 1 (HIV-1) infections. For the clinical use of NNRTIs, some guidelines have been elaborated, such as starting treatment with combinations of different compounds at sufficiently high concentrations to effect a pronounced and sustained suppression of the virus. Despite the diversity of the compounds described here and the different viruses at which they are targeted, they have a number of characteristics in common. As they interact with specific viral proteins, the compounds achieve a selective inhibition of the replication of the virus, which, in turn, should be able to develop resistance to the compounds. However, as has been established for the NNRTIs, the problem of viral resistance may be overcome if the compounds are used from the start at sufficiently high doses, which could be reduced if different compounds are combined. For HIV infections, drug treatment regimens should be aimed at reducing the viral load to such an extent that the risk for progression to AIDS will be minimized, if not avoided entirely. This may result in a real "cure" of the disease but not necessarily of the virus infection, and in this sense, HIV disease may be reduced to a dormant infection, reminiscent of the latent herpesvirus infections. Should virus replication resume after a certain time, the armamentarium of effective anti-HIV and anti-herpesvirus compounds now available, if applied at the appropriate dosage regimens, should make the virus return to its dormant state before it has any chance to damage the host. It is unlikely that this strategy would eradicate the virus and thus "cure" the viral infection, but it definitely qualifies as a cure of the disease.