Clinical Utility of Current NNRTIs and Perspectives of New Agents in This Class under Development

Highly active antiretroviral therapy (HAART) has significantly reduced the number of deaths caused by AIDS. However, the antiviral efficacy of HAART comprising protease inhibitors (PIs) and nucleoside reverse transcriptase inhibitors (NRTIs) is frequently accompanied by a decrease in patients' quality of life. PI-based therapies often fail due to poor adherence caused by heavy pill burden, complex dosing schedules and undesirable side effects. The current trend is to switch from PI-based to PI-sparing regimens consisting of non-nucleoside reverse transcriptase inhibitors (NNRTIs) and NRTIs. Despite some encouraging results from NNRTI-containing therapies, two major concerns in using the currently available NNRTIs remain: 1) low genetic barrier to the emergence of resistance and 2) cross-resistance due to single mutations that often render the whole class of NNRTIs ineffective. Clearly, new and improved NNRTIs are needed to address these concerns.

Human immunodeficiency virus type 1 resistance or cross-resistance to nonnucleoside reverse transcriptase inhibitors currently under development as microbicides

Microbicides based on nonnucleoside reverse transcriptase inhibitors (NNRTIs) are currently being developed to protect women from HIV acquisition through sexual contact. However, the large-scale introduction of these products raises two major concerns. First, when these microbicides are used by undiagnosed HIV-positive women, they could potentially select for viral resistance, which may compromise subsequent therapeutic options. Second, NNRTI-based microbicides that are inactive against NNRTI-resistant strains might promote the selective transmission of these viruses. In order to address these concerns, drug resistance was selected in vitro by the serial passage of three viral isolates from subtypes B and C and CRF02_AG (a circulating recombinant form) in activated peripheral blood mononuclear cells (PBMCs) under conditions of increasing concentrations of three NNRTIs (i.e., TMC120, UC781, and MIV-160) that are currently being developed as candidate microbicides. TMC120 and MIV-160 displayed a high genetic barrier to resistance development, whereas resistance to UC781 emerged rapidly, similarly to efavirenz and nevirapine. Phenotypically, the selected viruses appeared to be highly cross-resistant to current first-line therapeutic NNRTIs (i.e., delavirdine, nevirapine, and efavirenz), although they retained some susceptibility to the more recently developed NNRTIs lersivirine and etravirine. The ability of UC781, TMC120, and MIV-160 to inhibit the in vitro-selected NNRTI-resistant viruses was also limited, although residual activity could be observed for the candidate microbicide NNRTI MIV-170. Interestingly, only four p2/p7/p1/p6/PR/RT/INT recombinant NNRTI-resistant viruses (i.e., TMC120-resistant VI829, EFV-resistant VI829, MIV-160-resistant VI829, and EFV-resistant MP568) showed impairments in replicative fitness. Overall, these in vitro analyses demonstrate that due to potential cross-resistance, the large-scale introduction of single-NNRTI-based microbicides should be considered with caution.

[Establishment of pharmacological evaluation system for non-nucleoside reverse-transcriptase inhibitors resistant HIV-1]

Consistent non-nucleoside reverse-transcriptase inhibitors (NNRTIs) resistant HIV-1 strains occurred due to the clinical use for more than ten years of efavirenz (EFV), nevirapine (NVP), and delavirdine (DLV). In this study, we established nine cell-based pharmacological models according to most NNRTIs-resistant clinical tested strains, Resistant mutations were introduced into vector, pNL4-3.Luc.R-E-, by overlapping PCR. Then, pseudovirions were produced by co-transfection of VSV-G plasmid and pNL4-3.Luc.R-E- -mut. All nine recombinant VSVG/HIV-mut pseudovirions (VSVG/HIV-wt, VSVG/HIV(-K103N), VSVG/HIV(-Y181C), VSVG/HIV(-L100I,K103N), VSVG/HIV(-Y188L), VSVG/HIV(-K103N,Y181C), VSVG/HIV(-K103N,P225H), VSVG/HIV(-K103N,Y188L), VSVG/HIV(-K103N,G109A) and VSVG/HIV(-K103N,V108I)) had high efficient infectivity. Furthermore, they all showed resistant characteristics to EFV and NVP with IC50 changes consisting with clinical reports, not to nucleoside reverse-transcriptase inhibitors (AZT and d4T). This series safe cell-based model, which could be carried out in BSL-2 laboratory, can be used for evaluating NNRTIs candidates.

[HIV-1 genotypic resistance profiles in children failing highly active antiretroviral therapy]

OBJECTIVE

To study the genotypic resistance profiles of HIV-1 children failing highly active antiretroviral therapy (HAART) so as to provide helpful information for the treatment regime of Chinese children infected with HIV-1.

METHODS

Peripheral venous blood samples were collected from 20 HIV-1 infected children of Henan province, aged 9 (3 - 14). Nested RT-PCR was used to amplify part of the RT (40 -250 aa) gene. The PCR products of RT gene underwent nucleotide sequencing, the resulting nucleotide sequences were analyzed by the HIVdb data offered by the Stanford University web site to find the drug resistance mutations.

RESULTS

(1) Phylogenetic analysis revealed that 20 of the RT sequences were classified as subtype B. (2) According to the genotypic analysis, 20 , 15, and 13 children showed high level resistance to the nevirapine. (NVP), delavirdine (DLV), and efavirenz (EFV) respectively; 7 and 5 children showed high and intermediate level resistance to azidothymidine (AZT) respectively. Five children showed potential low-level and intermediate level resistance to lamivudine (3TC), and 11 showed high level resistance to 3TC; 11 showed intermediate and high level resistance to stavudine (d4T) and didanoside (ddI) respectively; and 19 and 12 children showed resistance to abacavir (ABC) and tenofovir (TDF) which had never been taken by these children.

CONCLUSION

The emergence of HIV resistant strains during antiretroviral therapy is one of the main reasons for treatment failure in HIV-infected children.

Emergence of NNRTI drug resistance mutations after single-dose nevirapine exposure in HIV type 1 subtype C-infected infants in India

A feasibility study for providing single-dose nevirapine (SD-NVP) prophylaxis for prevention of mother-to-child transmission (PMTCT) of HIV infection provided an opportunity to study the emergence of nonnucleoside reverse transcriptase inhibitor (NNRTI) resistance mutations as a result of single-dose administration. The study aimed at the detection of NNRTI drug resistance mutations arising as a result of SD-NVP. A total of 19 and 13 samples collected at 48 h and 2 months postpartum, respectively, from infants that were given SD-NVP were studied for the presence of NNRTI drug resistance mutations by PCR amplification and sequencing of the HIV-1 pol gene using HIV proviral DNA. The drug resistance mutational analysis of final sequences was carried out using the Stanford University HIV Drug Resistance database (http://hivdb.stanford.edu/hiv). Mutations associated with NNRTI drug resistance were observed in two (10.5%) and six (46.15%) samples at 48 h and at 2 months, respectively. K103N, one of the most common mutations, was not observed in any of the samples. The emergence of NVP resistance must be weighed against the simplicity, efficacy, and cost effectiveness of SD-NVP prophylaxis in PMTCT settings in developing countries.

Biosensor-based kinetic characterization of the interaction between HIV-1 reverse transcriptase and non-nucleoside inhibitors

Details of the interaction between HIV-1 reverse transcriptase and non-nucleoside inhibitors (NNRTIs) have been elucidated using a biosensor-based approach. This initial study was performed with HIV-1 reverse transcriptase mutant K103N, the phenethylthioazolylthiourea compound (PETT) MIV-150, and the three NNRTIs licensed for clinical use: nevirapine, delavirdine, and efavirenz. Mathematical evaluation of the experimental data with several interaction models revealed that the four inhibitors interacted with HIV-1 RT with varying degrees of complexity. The simplest adequate model accounted for two different conformations of the free enzyme, of which only one can bind the inhibitor, consistent with a previously hypothesized population-shift model including a preformation of the NNRTI binding site. In addition, a heterogeneous binding was observed for delavirdine, efavirenz, and MIV-150, indicating that two noncompetitive and kinetically distinct enzyme-inhibitor complexes could be formed. Furthermore, for these compounds, there were indications for ligand-induced conformational changes.

Reverse transcriptase mutations 118I, 208Y, and 215Y cause HIV-1 hypersusceptibility to non-nucleoside reverse transcriptase inhibitors

BACKGROUND

HIV-1 hypersusceptibility to non-nucleoside reverse transcriptase inhibitors (NNRTI) improves the response to NNRTI-containing regimens. The genetic basis for NNRTI hypersusceptibility was partly defined in our earlier analyses of a paired genotype-phenotype dataset of viral isolates from treatment-experienced patients, in which we identified reverse transcriptase mutations V118I, H208Y, and T215Y as being strongly associated with NNRTI hypersusceptibility.

OBJECTIVES

We evaluated the role of these mutations in NNRTI hypersusceptibility by site-directed mutagenesis and phenotypic analysis of HIV-1 recombinants.

METHODS

Drug susceptibility and replication capacity were determined in single cycle assays. Hypersusceptibility was defined by a statistically significant (P < 0.01; Student's t-test) mean fold-change in 50% inhibitory concentration (IC50) of less than 0.4.

RESULTS

The single mutations V118I, H208Y, and T215Y did not show hypersusceptibility to efavirenz with mean fold-change of 0.58, 0.55, and 0.70, respectively (P < 0.01 and P = 0.12). The H208Y/T215Y and V118I/H208Y/T215Y mutants showed marked hypersusceptibility to efavirenz, having mean fold-change values of 0.27 and 0.20, respectively (P < 0.001). In addition, H208Y/T215Y, V118I/T215Y, and V118I/H208Y/T215Y were hypersusceptible to delavirdine and nevirapine. The V118I/T215Y mutant was not replication impaired; whereas H208Y/T215Y and V118I/H208Y/T215Y had significantly (P < 0.01) reduced replication capacities of 40 and 35% of wild-type, respectively.

CONCLUSION

Different combinations of V118I, H208Y, and T215Y produce NNRTI hypersusceptibility. The V118I/T215Y mutant is hypersusceptible to delavirdine and nevirapine without reduced replication capacity, whereas the H208Y/T215Y and V118I/H208Y/T215Y mutants are hypersusceptible to all NNRTI and show impaired replication. These findings suggest that more than one mechanism is involved in NNRTI hypersusceptibility.

Phenotypic drug resistance patterns in subtype A HIV-1 clones with nonnucleoside reverse transcriptase resistance mutations

We analyzed the nonnucleoside reverse transcriptase (RT) inhibitor (NNRTI) susceptibility of 29 subtype A HIV-1 clones isolated from 10 Ugandan women after single-dose nevirapine (NVP) administration. Six clones had no NNRTI resistance-associated mutations ("wild type"), eight had K103N, nine had Y181C, five had G190A, and one had Y181S. Three clones displayed unexpected phenotypic drug susceptibility/resistance based on their RT genotypes. One wild-type clone had reduced susceptibility to NVP, delavirdine (DLV), and efavirenz (EFV), one clone with K103N was susceptible to all three NNRTIs, and one clone with G190A had extreme hypersusceptibility to DLV. Three unusual HIV-1 RT amino acid substitutions may have contributed to the unexpected phenotypes of the clones: I31T, N136S, and N265D. These polymorphisms were rarely detected among 47,900 HIV-1 genotypes from clinical samples of predominantly United States origin. Further studies are needed to define the genetic correlates of antiretroviral drug resistance in nonsubtype B HIV-1.

Effects of the G190A substitution of HIV reverse transcriptase on phenotypic susceptibility of patient isolates to delavirdine

BACKGROUND

Cross resistance is common among the non-nucleoside reverse transcriptase inhibitors (NNRTIs). G190A appears in 5-15% of the patients treated with nevirapine or efavirenz who develop clinical resistance.

OBJECTIVES

In this study we investigated the effect of G190A and other NNRTI substitutions on the phenotypic susceptibility to this class of drugs.

STUDY DESIGN

We identified 15 individuals, who after treatment with NNRTIs (nevirapine or efavirenz; median exposure of 20 months), developed isolated G190A, G190A in combination with K103N, or K103N alone. Phenotypic and genotypic analyses of stored plasma specimens were performed before and after the mutations occurred to assess NNRTI susceptibility.

RESULTS

All isolates that developed only G190A substitution became less susceptible to nevirapine (median: 125-fold) and efavirenz (median: 10-fold) but were 2.5-fold more sensitive to delavirdine (Wilcoxon P = 0.06). In the group with only K103N substitution, acquisition of resistance to all NNRTIs was observed. In the group with the double substitutions, G190A and K103N, delavirdine susceptibility decreased 13-fold, while resistance to nevirapine and efavirenz decreased by 239- and 154-folds, respectively (Kruskal-Wallis H P = 0.009).

CONCLUSIONS

The data suggest that the presence of a G190A substitution attenuates the phenotypic resistance associated with a K103N substitution, although resistance is still present. The in vivo significance of the increased phenotypic susceptibility to delavirdine is not known but could be evaluated in a clinical trial.

In vivo dynamics of the 103N mutation following the withdrawal of non-nucleoside reverse transcriptase inhibitors in HIV-infected patients: preliminary results

Due to the preferential selection of the fittest HIV mutants, drug-resistant variants are often overgrown by wild-type virus after treatment interruption. Our objective was to investigate the dynamics of the 103N mutation (which usually does not reduce HIV fitness) following the withdrawal of non-nucleoside reverse transcriptase inhibitors (NNRTIs). Patients who were found to have the 103N mutation at or after failure of a NNRTI were selected from an observational database. Two groups of patients were identified: one which continued antiretroviral treatment without NNRTIs (group A) and one which discontinued all anti-retrovirals after failure of an NNRTI (group B). Genotype was obtained by direct sequencing of the replicating plasma virus. Sixty-two subjects tested between July 1998 and December 2002 were included in the analysis, 39 in group A and 23 in group B. At the time of the first resistance test, median (IQR) CD4+ T-lymphocytes and HIV-RNA were 269 (150-449) cells/microL and 25,000 (9,600-83,300) copies/mL. In 31 (50%), 30 (48%), and one case (2%), the 103N mutation was selected by nevirapine, efavirenz, and by delavirdine, respectively. A total of 149 tests were analyzed, with a median (IQR) of 2 (2-3) tests/patient. The median (IQR) interval between failure of NNRTIs and the last resistance test was 11 (5-22) months. Overall, a reversion to wild-type at position 103 was observed in 23/62 (37%) subjects, 14/39 (36%) in group A and 9/23 (39%) in group B. In group A, 14/23 (61%) patients tested within 12 months, 10/16 (63%) of those tested between 12 and 24 months, and 12/14 (86%) of those tested beyond 24 months from NNRTI discontinuation had the 103N mutation. In group B, 14/20 (70%) patients tested within 12 months, 3/4 (75%) of those tested between 12 and 24 months, and none out of two tested beyond 24 months from NNRTI discontinuation had the 103N mutation. In conclusion, following NNRTI discontinuation, in the majority of patients HIV variants carrying the 103N mutation are not overgrown for long by wild-type quasispecies at this position. This suggests that the 103N mutation per se influences minimally the viral fitness in vivo.

Sex‐Based Differences in Saquinavir Pharmacology and Virologic Response in AIDS Clinical Trials Group Study 359

AIDS Clinical Trials Group study 359 was a controlled study of saquinavir with either ritonavir or nelfinavir, together with delavirdine, adefovir, or both, in indinavir-experienced persons. Saquinavir was common in all study arms, and the study investigated relationships among characteristics of patients, saquinavir area under the curve (AUC) and trough concentrations (C(min)), and virologic response. Concentrations of saquinavir were higher when it was combined with ritonavir than when it was combined with nelfinavir and were lower with adefovir-containing regimens. Females had higher AUC and C(min) values than did males. Higher saquinavir AUC and C(min) values were associated with a greater likelihood of human immunodeficiency virus (HIV) RNA levels </=500 copies/mL (P=.008) and were better predictors of response than was the saquinavir inhibitory quotient. Males had a lower probability of having HIV RNA levels </=500 copies/mL at week 16 than did females (28% vs. 42%; adjusted odds ratio, 0.43). In this study, a greater proportion of females had HIV RNA levels </=500 copies/mL than did males, which can be attributed to higher concentrations of saquinavir in females than in males.

Amino acid substitutions at position 190 of human immunodeficiency virus type 1 reverse transcriptase increase susceptibility to delavirdine and impair virus replication

Suboptimal treatment of human immunodeficiency virus type 1 (HIV-1) infection with nonnucleoside reverse transcriptase inhibitors (NNRTI) often results in the rapid selection of drug-resistant virus. Several amino acid substitutions at position 190 of reverse transcriptase (RT) have been associated with reduced susceptibility to the NNRTI, especially nevirapine (NVP) and efavirenz (EFV). In the present study, the effects of various 190 substitutions observed in viruses obtained from NNRTI-experienced patients were characterized with patient-derived HIV isolates and confirmed with a panel of isogenic viruses. Compared to wild-type HIV, which has a glycine at position 190 (G190), viruses with 190 substitutions (A, C, Q, S, V, E, or T, collectively referred to as G190X substitutions) were markedly less susceptible to NVP and EFV. In contrast, delavirdine (DLV) susceptibility of these G190X viruses increased from 3 to 300-fold (hypersusceptible) or was only slightly decreased. The replication capacity of viruses with certain 190 substitutions (C, Q, V, T, and E) was severely impaired and was correlated with reduced virion-associated RT activity and incomplete protease (PR) processing of the viral p55(gag) polyprotein. These defects were the result of inadequate p160(gagpol) incorporation into virions. Compensatory mutations within RT and PR improved replication capacity, p55(gag) processing, and RT activity, presumably through increased incorporation of p160(gagpol) into virions. We observe an inverse relationship between the degree of NVP and EFV resistance and the impairment of viral replication in viruses with substitutions at 190 in RT. These observations may have important implications for the future design and development of antiretroviral drugs that restrict the outgrowth of resistant variants with high replication capacity.

Differential modulation of P-glycoprotein expression and activity by non-nucleoside HIV-1 reverse transcriptase inhibitors in cell culture

PURPOSE

This study investigated the effects of the non-nucleoside HIV-1 reverse transcriptase inhibitors (NNRTI) nevirapine (NVR), efavirenz (EFV), and delavirdine (DLV) on P-glycoprotein (P-gp) activity and expression to anticipate P-gp related drug-drug interactions associated with combination therapy.

METHODS

NNRTIs were evaluated as P-gp substrates by measuring differential transport across Caco-2 cell monolayers. Inhibition of P-gp mediated rhodaminel23 (Rh123) transport in Caco-2 cells was used to assess P-gp inhibition by NNRTIs. Induction of P-gp expression and activity in LS180V cells following 3-day exposure to NNRTIs was measured by western blot analysis and cellular Rh123 uptake, respectively.

RESULTS

The NNRTIs showed no differential transport between the basolateral to apical and apical to basolateral direction. NNRTI transport in either direction was not affected by the P-gp inhibitor verapamil. DLV inhibited Rh123 transport, causing a reduction to 15% of control at 100 microM (IC50 = 30 microM). NVR caused a concentration-dependent induction of P-gp expression in LS180V cells resulting in a 3.5-fold increase in immunoreactive P-gp at 100 microM NVR. Induction attributable to EFV and DLV was quantitatively smaller. NVR significantly reduced cellular uptake of Rh123 into LS180V cells, indicating increased drug efflux due to induced P-gp activity; effects of EFV and DLV were smaller. Acute DLV treatment of LS180V cells previously induced with NVR or ritonavir did not reverse the decreased Rh123 cell accumulation.

CONCLUSIONS

NNRTIs show differential effects on P-gp activity and expression in vitro. Clinical studies are required to elucidate the clinical importance of potential drug interactions.

Synthesis and anti-HIV-1 activity of new delavirdine analogues carrying arylpyrrole moieties

In our search for novel anti-human immunodeficiency virus (HIV)-1 agents, 14 delavirdine analogues were synthesized and evaluated as potential anti-HIV-1 agents in cell-based assays. Compound 1Aa exhibited potent and selective anti-HIV-1 activity in acutely infected MT4 cells, with effective concentration (EC50) values in the submicromolar range.

Delavirdine: clinical pharmacokinetics and drug interactions

Delavirdine, a non-nucleoside reverse transcriptase inhibitor (NNRTI), is a potent and specific inhibitor of HIV-1 reverse transcriptase. The approved therapeutic regimen for delavirdine is 400mg 3 times daily in combination with appropriate antiretroviral agents; however, a dose of 600mg twice daily appears to provide similar systemic exposure. The steady-state pharmacokinetics of delavirdine are not appreciably affected by food. Delavirdine undergoes extensive metabolism by cytochrome P450 (CYP) with little urinary excretion of unchanged drug. Metabolic drug interactions between delavirdine and nucleoside reverse transcriptase inhibitors are unlikely as their metabolic pathways differ; delavirdine has no effect on the pharmacokinetics of zidovudine. Concomitant use of CYP inducers, such as rifampicin (rifampin), rifabutin, phenytoin, phenobarbital or carbamazepine, should be avoided since delavirdine plasma concentrations are significantly lowered. Reduction in gastric acidity (pH > 3) decreases the extent of delavirdine absorption, so administration of antacids and the buffered formulations of didanosine should be separated from that of delavirdine by at least 1 hour. Delavirdine, unlike other currently available NNRTI agents, is an inhibitor rather than an inducer of CYP isozymes. Consequently, the drug interaction profile and rationale for combining delavirdine with other antiretroviral agents is unique among the current NNRTI agents. Delavirdine inhibits the CYP3A4-mediated metabolism of HIV protease inhibitors and thereby increases systemic exposure to protease inhibitors. The ability of delavirdine to enhance the pharmacokinetic profiles of protease inhibitors may permit the use of simplified administration regimens. Combining delavirdine and indinavir removes the food restrictions during indinavir administration. Furthermore, the superior virological response observed in antiretroviral regimens containing delavirdine and protease inhibitors has been attributed to the favourable pharmacokinetic interactions and the introduction of a new drug class in NNRTI-naïve therapy-experienced patients. Pharmacokinetic drug interactions are an important consideration in selecting an HIV treatment regimen, due to the multiplicity of drugs that are coadministered and the varying direction and magnitude of interaction that can occur. Considerations for utilising delavirdine in a treatment regimen are different than for other NNRTI agents due to the unique drug interaction profile of delavirdine.

A single amino acid change at Leu-188 in the reverse transcriptase of HIV-2 and SIV renders them sensitive to non-nucleoside reverse transcriptase inhibitors

Non-nucleoside reverse transcriptase inhibitors (NNRTIs) are selective for human immunodeficiency virus type 1 (HIV-1) and generally not effective on HIV-2 or simian immunodeficiency virus (SIV). Only SIVagm was found to be sensitive to NNRTIs. When the amino acid differences in RT between SIVmac and SIVagm were compared with the known amino acid substitutions of NNRTI-resistance variants of HIV-1, we came to consider that the amino acid residue Leu-188 of HIV-2 and SIVmac might be related to their resistance to NNRTIs. To test this hypothesis, we substituted Leu-188 to Cys or Tyr in HIV-2 and SIVmac, and examined sensitivity of the mutant molecular clones to NNRTIs. The L188Y mutant of HIV-2 became completely sensitive to delavirdine and efavirenz, while that of SIVmac was also significantly sensitive to these NNRTIs. We further isolated NNRTI-resistant variants from these mutant viruses and determined amino acid substitutions in RT. The roles of the observed substitutions in NNRTI-resistance were further confirmed by site-directed mutagenesis. Our study reveals the crucial role of L188 in the natural resistance of HIV-2 and SIVmac to NNRTIs. Furthermore, the observed substitutions in RT of HIV-2 and SIVmac support the common mechanism of action of NNRTIs against HIV-1, HIV-2 and SIV.

Impact of clinical reverse transcriptase sequences on the replication capacity of HIV-1 drug-resistant mutants

We have shown that the HIV-1 laboratory strain NL4-3 that contains P236L [a reverse transcriptase mutation conferring resistance to the nonnucleoside reverse transcriptase inhibitor (NRTI) delavirdine] replicates more slowly than wild-type NL4-3. Other NNRTI-resistance mutations, such as K103N and Y181C, do not reduce the replication capacity of NL4-3 as much as P236L and develop more frequently in HIV-1 isolates from patients failing delavirdine. However, a minority of patients on delavirdine therapy still have isolates with P236L. We postulated that reverse transcriptase (RT) sequences from these patient isolates contain other mutations that compensate for the adverse effect of P236L. To test this hypothesis, we created 15 chimeric NL4-3 isolates that contained delavirdine-resistant RT sequences derived from eight patient isolates and characterized their replication kinetics. Nine of 10 patient-derived clones containing P236L replicated as slowly as NL4-3 with P236L. In contrast, three of five clones that did not have P236L (but had either K103N or Y181C) replicated significantly better than NL4-3 with P236L. Thus, the majority of patients who acquire P236L during delavirdine therapy do not have RT mutations that compensate for the replication defect conferred by P236L. We hypothesize that HIV-1 isolates with P236L may have a compensatory mutation outside RT. Alternatively, variants of HIV-1 with reduced replication fitness may be selected during antiretroviral therapy, suggesting that stochastic events rather than viral replication fitness may determine which drug-resistant mutants emerge early during antiretroviral failure. In some isolates, it appears that the background RT sequence can contribute significantly to the replication fitness of drug-resistant HIV-1 variants.

Genotypic correlates of phenotypic resistance to efavirenz in virus isolates from patients failing nonnucleoside reverse transcriptase inhibitor therapy

Efavirenz (also known as DMP 266 or SUSTIVA) is a potent nonnucleoside inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) activity and of HIV-1 replication in vitro and in vivo. Most patients on efavirenz-containing regimens have sustained antiviral responses; however, rebounds in plasma viral load have been observed in some patients in association with the emergence of mutant strains of HIV-1. Virus isolates from the peripheral blood mononuclear cells (PBMCs) of patients with such treatment failures, as well as recombinant viruses incorporating viral sequences derived from patient plasma, show reduced in vitro susceptibility to efavirenz in association with mutations in the RT gene encoding K103N, Y188L, or G190S/E substitutions. Patterns of RT gene mutations and in vitro susceptibility were similar in plasma virus and in viruses isolated from PBMCs. Variant strains of HIV-1 constructed by site-directed mutagenesis confirmed the role of K103N, G190S, and Y188L substitutions in reduced susceptibility to efavirenz. Further, certain secondary mutations (V106I, V108I, Y181C, Y188H, P225H, and F227L) conferred little resistance to efavirenz as single mutations but enhanced the level of resistance of viruses carrying these mutations in combination with K103N or Y188L. Viruses with K103N or Y188L mutations, regardless of the initial selecting nonnucleoside RT inhibitor (NNRTI), exhibited cross-resistance to all of the presently available NNRTIs (efavirenz, nevirapine, and delavirdine). Some virus isolates from nevirapine or delavirdine treatment failures that lacked K103N or Y188L mutations remained susceptible to efavirenz in vitro, although the clinical significance of this finding is presently unclear.

Isolation and characterization of simian immunodeficiency virus variants that are resistant to nonnucleoside reverse transcriptase inhibitors

Non-nucleoside reverse transcriptase inhibitors (NNRTIs) act quite specifically on human immunodeficiency virus type 1 (HIV-1). In general, they are not effective on human immunodeficiency virus type 2 (HIV-2) or simian immunodeficiency virus (SIV). Only SIV strains from African green monkeys are sensitive to several NNRTIs. Here we isolated NNRTI- and 3TC-resistant SIVagm variants. Viruses resistant to delavirdine contained V112I and M231I substitutions, while those resistant to 3TC contained a M 185I substitution. These amino acids are highly conserved in HIV-1, HIV-2, SIVmac and SIVagm, and the M184I (M185I in SIVagm) substitution was observed in 3TC-resistant HIV-1 and SIVmac. The roles of the observed mutations in NNRTI-resistance of SIVagm and HIV-1 were further confirmed by site-directed mutagenesis. The present results have provided a new insight into the common mechanism of sensitivity of HIV- 1 and SIVagm to NNRTIs.

International perspectives on antiretroviral resistance. Nonnucleoside reverse transcriptase inhibitor resistance

Although understanding of nonnucleoside reverse transcriptase inhibitor (NNRTI) resistance is less clearly established than that of other classes of antiretroviral drugs, certain facts have been established. The treatment-associated genetic mutation profiles of the available NNRTIs have been mapped, and resistance has been found to develop rapidly after initiation of NNRTI therapy. Despite the chemical diversity of the NNRTIs, cross-resistance among agents of this class is nearly universal. Although the viral replicative capacity ("fitness") of NNRTI-induced viral variants has not been extensively studied, available data suggest that NNRTI-selected mutations confer little damage to viral fitness, and thus a single point mutation produces a strain that is both resistant and fit. Furthermore, with continued therapy, viral evolution persists, creating species with greater numbers of mutations and higher level phenotypic resistance. Taken together, these facts suggest that continued use of NNRTIs after emergence of resistance will produce variants of complex mutational patterns that limit future treatment options, and, therefore, strong consideration should be given to discontinuing NNRTIs after virologic failure is confirmed. This article describes the scientific literature establishing the efficacy and limitations of NNRTI therapy and attempts to define a role for this class of drug in the long-term treatment of HIV-1 disease.

Inhibition of human cytochrome P450 isoforms by nonnucleoside reverse transcriptase inhibitors

The capacity of three clinically available nonnucleoside reverse transcriptase inhibitors (NNRTIs) to inhibit the activity of human cytochromes P450 (CYPs) was studied in vitro using human liver microsomes. Delavirdine, nevirapine, and efavirenz produced negligible inhibition of phenacetin O-deethylation (CYP1A2) or dextromethorphan O-demethylation (CYP2D6). Nevirapine did not inhibit hydroxylation of tolbutamide (CYP2C9) or S-mephenytoin (CYP2C19), but these CYP isoforms were importantly inhibited by delavirdine and efavirenz. This indicates the likelihood of significantly impaired clearance of CYP2C substrate drugs (such as phenytoin, tolbutamide, and warfarin) upon initial exposure to these two NNRTIs. Delavirdine and efavirenz (but not nevirapine) also were strong inhibitors of CYP3A, consistent with clinical hazards of initial cotreatment with either of these drugs and substrates of CYP3A. The in vitro microsomal model provides relevant predictive data on probable drug interactions with NNRTIs when the mechanism is inhibition of CYP-mediated drug biotransformation. However, the model does not incorporate interactions attributable to enzyme induction.

Interaction of delavirdine with human liver microsomal cytochrome P450: inhibition of CYP2C9, CYP2C19, and CYP2D6

Delavirdine, a non-nucleoside inhibitor of HIV-1 reverse transcriptase, is metabolized primarily through desalkylation catalyzed by CYP3A4 and CYP2D6 and by pyridine hydroxylation catalyzed by CYP3A4. It is also an irreversible inhibitor of CYP3A4. The interaction of delavirdine with CYP2C9 was examined with pooled human liver microsomes using diclofenac 4'-hydroxylation as a reporter of CYP2C9 catalytic activity. As delavirdine concentration was increased from 0 to 100 microM, the K(M) for diclofenac metabolism rose from 4.5+/-0.5 to 21+/-6 microM, and V(max) declined from 4.2+/-0.1 to 0.54+/-0.08 nmol/min/mg of protein, characteristic of mixed-type inhibition. Nonlinear regression analysis revealed an apparent K(i) of 2.6+/-0.4 microM. There was no evidence for bioactivation as prerequisite to inhibition of CYP2C9. Desalkyl delavirdine, the major circulating metabolite of delavirdine, had no apparent effect on microsomal CYP2C9 activity at concentrations up to 20 microM. Several analogs of delavirdine showed similar inhibition of CYP2C9. Delavirdine significantly inhibited cDNA-expressed CYP2C19-catalyzed (S)-mephenytoin 4'-hydroxylation in a noncompetitive manner, with an apparent K(i) of 24+/-3 microM. Delavirdine at concentrations up to 100 microM did not inhibit the activity of CYP1A2 or -2E1. Delavirdine competitively inhibited recombinant CYP2D6 activity with a K(i) of 12.8+/-1.8 microM, similar to the observed K(M) for delavirdine desalkylation. These results, along with previously reported experiments, indicate that delavirdine can partially inhibit CYP2C9, -2C19, -2D6, and -3A4, although the degree of inhibition in vivo would be subject to a variety of additional factors.

Delavirdine: a review of its use in HIV infection

Delavirdine, a bisheteroarylpiperazine derivative, is a non-nucleoside reverse transcriptase inhibitor (NNRTI) that allosterically binds to HIV-1 reverse transcriptase, inhibiting both the RNA- and DNA-directed DNA polymerase functions of the enzyme. Delavirdine in combination with nucleoside reverse transcriptase inhibitors (NRTIs) produced sustained reductions in plasma viral loads and improvements in immunological responses in large randomised, double-blind, placebo-controlled studies of 48 to 54 weeks' duration. In patients with advanced HIV infection, triple therapy with delavirdine, zidovudine and lamivudine, didanosine or zalcitabine for 1 year significantly prolonged the time to virological failure compared with dual therapy (delavirdine plus zidovudine or 2 NRTIs; p < 0.0001). After 50 weeks' treatment, plasma HIV RNA levels were below the limit of detection (LOD; <50 copies/ml) for 40% of patients receiving triple therapy but for only 6% of those receiving dual NRTI therapy. Preliminary results suggest that delavirdine also has beneficial effects on surrogate markers as a component of protease inhibitor-containing triple or quadruple regimens. At 16 to 48 weeks, the minimum mean reduction in plasma viral load from baseline was 2.5 log10 copies/ml and mean CD4+ counts increased by 100 to 313 cells/microl. The proportion of patients with plasma HIV RNAlevels below the LOD (usually 200 to 500 copies/ml) ranged from 48 to 100% after > or = 16 weeks. Delavirdine was also effective as a component of saquinavir soft gel capsule-containing salvage regimens. Since delavirdine shares a common metabolic pathway (cytochrome P450 3A pathway) with other NNRTIs, HIV protease inhibitors and several drugs used to treat opportunistic infections in patients infected with HIV, the drug is associated with a number of pharmacokinetic interactions. Some of these drug interactions are clinically significant, necessitating dosage adjustments or avoidance of co-administration. Delavirdine is not recommended for use with lovastatin, simvastatin, rifabutin, rifampicin, sildenafil, ergot derivatives, quinidine, midazolam, carbamazepine, phenobarbital or phenytoin. Importantly, the drug favourably increases the plasma concentration of several protease inhibitors. Delavirdine is generally well tolerated. Skin rash is the most frequently reported adverse effect, occurring in 18 to 50% of patients receiving delavirdine-containing combination therapy in clinical trials. Although a high proportion of patients developed a rash, it was typically mild to moderate in intensity, did not result in discontinuation or adjustment of treatment in most patients and resolved quickly. The occurrence of Stevens-Johnson syndrome was rare (1 case in 1,000 patients). A retrospective analysis of pooled clinical trial data indicated that there was no significant difference in the incidence of liver toxicity, liver failure or noninfectious hepatitis between delavirdine-containing and non-delavirdine-containing antiretroviral treatment groups. In addition, the incidence of lipodystrophy, metabolic lipid disorders, hyperglycaemia and hypertriglyceridaemia was not significantly different between these 2 treatment groups.

CONCLUSIONS

In combination with NRTIs. delavirdine produces sustained improvements in surrogate markers of HIV disease and prolongs the time to virological failure in adult patients with HIV infection. Preliminary data of delavirdine as a component of protease inhibitor-containing triple or quadruple highly active antiretroviral therapy regimens indicate that patients achieve marked improvements in virological and immunological markers. The drug is generally well tolerated, with a transient skin rash, typically of mild to moderate intensity, being the most common adverse effect. Delavirdine is an effective component of recommended antiretroviral treatment strategies for adult patients with HIV infection and, in combination with 2 NRTIs as a first-line therapy, the drug has the advantage of sparing protease inhibitors for subsequent use. Since delavirdine favourably increases plasma concentrations of several protease inhibitors, the drug may also be beneficial as a component of salvage therapy in combination with protease inhibitors.

Long-term exposure of HIV type 1-infected cell cultures to combinations of the novel quinoxaline GW420867X with lamivudine, abacavir, and a variety of nonnucleoside reverse transcriptase inhibitors

The novel quinoxaline GW420867X has been combined with a variety of nucleoside reverse transcriptase inhibitors (NRTIs) and nonnucleoside reverse transcriptase inhibitors (NNRTIs) in HIV-1(IIIB)-infected CEM cell cultures. Whereas the antiviral efficacy of combinations of GW420867X with the NRTIs lamivudine (3TC) and abacavir (ABC) proved additive when administered to HIV-1-infected cells in a short-term (4-day) infection experiment, combination of GW420867X with the NRTIs 3TC and ABC resulted in a marked delay of virus breakthrough compared with the single drugs alone in a long-term (2-month) infection experiment. Delay of virus breakthrough was less pronounced for combinations of GW420867X with the NNRTIs. Combination of GW420867X with the NRTIs and NNRTIs resulted in additive inhibitory effects on recombinant HIV-1 reverse transcriptase as evident from isobolograms. Lamivudine plus GW420867X selected for the 3TC-specific M184I mutation and a number of NNRTI-characteristic mutations (i.e., V106A, V108I, and Y188H). Abacavir plus GW420867X selected only for NNRTI-specific mutations (i.e., K101E, K103R, V106A, and Y181C), including the novel L100V mutation. Combination of GW420867X with five different NNRTIs selected solely for NNRTI-specific mutations, and also for the L100V mutation in the combined presence of efavirenz, nevirapine, or emivirine, respectively. Five single-, two double-, and two triple-mutated HIV-1 strains that emerged from this study were evaluated for their sensitivity/resistance to AZT, lamivudine, and seven different NNRTIs. In all cases, efavirenz, GW420867X, and UC-781 retained pronounced antiviral potency. Our data suggest that combinations of GW420867X with 3TC, ABC, and NNRTIs (e.g., efavirenz) would be worth pursuing as therapeutic modalities against HIV-1 infections.

Novel 1,5-diphenylpyrazole nonnucleoside HIV-1 reverse transcriptase inhibitors with enhanced activity versus the delavirdine-resistant P236L mutant: lead identification and SAR of 3- and 4-substituted derivatives

Through computationally directed broad screening, a novel 1, 5-diphenylpyrazole (DPP) class of HIV-1 nonnucleoside reverse transcriptase inhibitors (NNRTIs) has been discovered. Compound 2 (PNU-32945) was found to have good activity versus wild-type (IC(50) = 2.3 microM) and delavirdine-resistant P236L (IC(50) = 1.1 microM) reverse transcriptase (RT). Also, PNU-32945 has an ED(50) for inhibition of viral replication in cell cultures of 0.1 microM and was shown to be noncytotoxic with a CC(50) > 10 microM. Structure-activity relationship studies on the 3- and 4-positions of PNU-32945 led to interesting selectivity and activity within the class. In particular, the 3-hydroxyethyl-4-ethyl congener 29 is a potent inhibitor of the P236L mutant (IC(50) = 0.65 microM), whereas it is essentially inactive versus the wild-type enzyme (IC(50) > 50 microM). Furthermore, this compound was significantly more active versus the P236L mutant than delavirdine. The synthesis and RT inhibitory activity of various 3- and 4-substituted analogues are discussed.

Delavirdine susceptibilities and associated reverse transcriptase mutations in human immunodeficiency virus type 1 isolates from patients in a phase I/II trial of delavirdine monotherapy (ACTG 260)

The development of human immunodeficiency virus type 1 resistance to delavirdine (DLV) was studied in subjects receiving DLV monotherapy. Phenotypic resistance developed in 28 of 30 subjects within 8 weeks. K103N and Y181C, which confer nonnucleoside reverse transcriptase inhibitor (NNRTI) cross-resistance, were the predominant reverse transcriptase mutations. P236L, which confers DLV resistance but hypersensitivity to other NNRTIs, developed in <10% of isolates.

Non-nucleoside reverse transcriptase inhibitor resistance among patients failing a nevirapine plus protease inhibitor-containing regimen

OBJECTIVE

To determine the rate of nevirapine resistance in patients failing a nevirapine plus protease inhibitor (PI)-based regimen, and whether these isolates remain susceptible to other non-nucleoside reverse transcriptase inhibitors (NNRTI).

DESIGN AND SETTING

A retrospective cohort study in two tertiary university hospitals.

PATIENTS

Eighty-eight HIV-infected, NNRTI-naive patients receiving nevirapine plus PI as a rescue regimen after PI treatment failure.

MAIN OUTCOME MEASURES

Genotypic and phenotypic resistance data at inclusion (73 and 60 plasma samples, respectively) and after 24 weeks (53 and 42 samples).

RESULTS

Baseline phenotypic susceptibility to nevirapine was found in 70% of patients, and similar data were observed for efavirenz (91%) and delavirdine (71%). NNRTI resistance-associated mutations were found in 11 patients (12.5%). At 24 weeks, resistant isolates to nevirapine were found in 92% of patients, and correlated with similar resistance to efavirenz (68%) and delavirdine (73%). In the genotypic analysis, the Y181 C mutation was observed in 76% of mutants, and the most common changes were a combination of mutations at positions Y181C/K103N (23%) and the single mutation Y181C (15%). The development of nevirapine resistance was associated with baseline resistance to PI included in the regimen (P= 0.01). For isolates containing the single amino acid substitution Y181C, 29% remained fully susceptible to efavirenz, whereas 14% showed intermediate resistance to efavirenz and delavirdine.

CONCLUSION

The failure of a nevirapine plus PI-containing regimen is associated with nevirapine resistance in most patients, with the most common mutation occurring at amino acid residue 181. Although there is a high degree of cross-resistance among NNRTI, nearly one third of resistant isolates carrying the single Y181C mutation remain susceptible to efavirenz.

Activity of non-nucleoside reverse transcriptase inhibitors against HIV-2 and SIV

BACKGROUND

After the initial discovery of 1-(2-hydroxyethoxymethyl)-6-(phenylthio)thymine (HEPT) and tetrahydroimidazo[4,5,1-jk][1,4]benzodiazepin-2(1H)-one and thione (TIBO) derivatives, several other non-nucleoside reverse transcriptase (RT) inhibitors (NNRTI), including nevirapine (BI-RG-587), pyridinone derivatives (L-696,229 and L-697,661), delavirdine (U-90152), alpha-anilinophenylacetamides (alpha-APA) and various other classes of NNRTI have been described. The hallmark of NNRTI has been based on their ability to interact with a specific site ('pocket') of HIV-1 RT.

OBJECTIVE

To investigate whether, in addition to HIV-1, different strains of HIV-2 (ROD and EHO) and SIV (mac251, agm3 and mndGB1) are sensitive to a selection of NNRTI i.e. delavirdine, the HEPT derivative I-EBU (MKC-442), 8-chloro-TIBO (tivirapine), alpha-APA (loviride), nevirapine and the pyridinone derivative L-697,661.

METHODS AND RESULTS

The NNRTI tested inhibited the replication of the different strains of HIV-2 and SIV at micromolar concentrations. The inhibitory effects of the NNRTI on HIV-2-induced cytopathicity correlated well with their inhibitory effects on HIV-2 RT activity. Drug-resistant HIV-2 (EHO) variants containing the Ser102Leu and/or Glu219Asp mutations in their RT were selected after passaging the virus in MT-4 cells in the presence of increasing concentrations of delavirdine. The EHO virus mutants were at least 20-fold less susceptible to the antiviral effects of delavirdine. Some cross-resistance, depending on the mutant strain, was observed with the other NNRTI tested (i.e. MKC-442, tivirapine, loviride and pyridinone L-697,661).

CONCLUSIONS

Our data demonstrate that NNRTI are not exclusively specific for HIV-1 but are also inhibitory to different HIV-2 and SIV strains. These observations will have important implications for the development of new NNRTI with higher activity against both HIV-1 and HIV-2. Furthermore, in view of their anti-SIV activity, NNRTI could be evaluated further for their in vivo anti-retrovirus efficacy in non-human primate models.

The P236L delavirdine-resistant human immunodeficiency virus type 1 mutant is replication defective and demonstrates alterations in both RNA 5'-end- and DNA 3'-end-directed RNase H activities

The nonnucleoside reverse transcriptase (RT) inhibitor (NNRTI) delavirdine (DLV) selects in vitro for the human immunodeficiency virus type 1 (HIV-1) RT mutation P236L, which confers high-level resistance to DLV but not other NNRTIs. Unexpectedly, P236L has developed infrequently in HIV-1 isolates obtained from patients receiving DLV; K103N is the predominant resistance mutation observed in that setting. We characterized the replication fitness of viruses derived from pNL4-3 containing P236L or K103N in both H9 and primary human peripheral blood mononuclear cell cultures infected in parallel with the two mutants. In the absence of DLV, p24 production by wild-type virus occurred more rapidly and to higher levels than with either mutant; P236L consistently demonstrated a two- to threefold decrease in p24 relative to K103N. At low levels of DLV, growth of wild-type virus was severely inhibited, and K103N replicated two- to threefold more efficiently than P236L. At high concentrations of DLV, P236L replication and K103N replication were both inhibited. Recombinant RTs containing K103N or P236L were analyzed for DNA polymerization on heteropolymeric RNA templates and RNase H degradation of RNA-DNA hybrids. Neither mutant demonstrated defects in polymerization. K103N demonstrated normal RNA 5'-end-directed RNase H cleavage and slowed DNA 3'-end-directed RNase H cleavage compared to wild-type RT. P236L demonstrated slowing of both DNA 3'-end- and RNA 5'-end-directed RNase H cleavage, consistent with its reduced replication efficiency relative to K103N. These data suggest that NNRTI resistance mutations can lead to reductions in the efficiency of RNase H cleavage, which may contribute to a reduction in the replication fitness of HIV-1.

Microsomal metabolism of delavirdine: evidence for mechanism-based inactivation of human cytochrome P450 3A

Administration of delavirdine, an HIV-1 reverse transcriptase inhibitor, to rats or monkeys resulted in apparent loss of hepatic microsomal CYP3A and delavirdine desalkylation activity. Human CYP3A catalyzes the formation of desalkyl delavirdine and 6'-hydroxy delavirdine, an unstable metabolite, while CYP2D6 catalyzes only desalkyl delavirdine. CYP2D6 catalyzed desalkyl delavirdine formation was linear with time (up to 30 min) but when catalyzed by cDNA expressed CYP3A4 or human liver microsomes the reaction rate declined progressively with time. Coincubation with triazolam showed that delavirdine caused a time- and NADPH-dependent loss of CYP3A4 activity in human liver microsomes as measured by triazolam 1'-hydroxylation. The catalytic activity loss was saturable and was characterized by a Ki of 21.6 +/- 8.9 microM and a kinact of 0.59 +/- 0.08 min-1. An apparent partition ratio of 41 was determined with cDNA expressed CYP3A4, based on the substrate depletion method. Incubation of [14C]delavirdine with microsomes from several species resulted in irreversible association with an approximately 50 kDa protein, as demonstrated by SDS-PAGE/autoradiography. Binding to the protein was NADPH dependent, glutathione insensitive, proportional to the level of CYP3A expression and was inhibited by ketoconazole, a specific CYP3A inhibitor. NADPH-dependent irreversible binding to human and rat total microsomal protein was demonstrated following exhaustive extraction of microsomal protein. Binding was decreased in the presence of glutathione and appeared to be related to expression level of CYP3A. These results suggest that delavirdine can inactivate CYP3A and has the potential to slow the metabolism of coadministered CYP3A substrates.

Pyrimidine thioethers: a novel class of HIV-1 reverse transcriptase inhibitors with activity against BHAP-resistant HIV

A series of pyrimidine thioethers was synthesized and evaluated for inhibitory properties against wild-type HIV-1 reverse transcriptase (RT) and an RT carrying the resistance-conferring mutation P236L. Modifications of both the pyrimidine and the functionality attached through the thioether yielded several analogues, which demonstrated activity against both enzyme types, with IC50 values as low as 190 nM against wild-type and 66 nM against P236L RT. Evaluation of a select number of pyrimidine thioethers in cell culture showed that these compounds have excellent activity against HIV-1IIIB-WT and retain good activity against a laboratory-derived HIV-1MF delavirdine-resistant variant.

Pharmacokinetic drug-drug interaction study of delavirdine and indinavir in healthy volunteers

The potential pharmacokinetic drug-drug interaction between delavirdine, a nonnucleoside analogue reverse transcriptase inhibitor, and indinavir, an inhibitor of HIV protease, was evaluated in healthy volunteers. Subjects received a single 800-mg dose of indinavir sulfate on day 1 (baseline). Delavirdine mesylate 400 mg was administered three times daily on days 2 through 10. On day 9, a single 400-mg dose and on day 10 a single 600-mg dose of indinavir were given along with morning doses of delavirdine. Pharmacokinetic evaluations of indinavir were made on days 1, 9, and 10, and of delavirdine on days 8, 9, and 10. Fourteen healthy male volunteers completed the study. Single doses of indinavir had no clinically important effects on the pharmacokinetics of delavirdine. Mean indinavir Cmax values for the 400-mg and 600-mg doses administered concomitantly with delavirdine were dose proportionally lower than that observed following the 800-mg dose administered alone. Mean Tmax values were similar and ranged from 1.0 +/- 0.3/hour for indinavir 800 mg administered alone to 1.3 +/- 0.4/hour for indinavir 600 mg administered with delavirdine. These results indicate that delavirdine had no clinically important effect on the rate of indinavir absorption. In contrast, the mean indinavir AUC0-infinity, value following the 400-mg dose administered with delavirdine was only 14% lower than the baseline value determined for the 800-mg indinavir dose (25,400 +/- 6960 nM hour versus 29,600 +/- 7920 nM hour), and the mean indinavir AUC0-infinity value for the 600-mg indinavir dose administered with delavirdine (42,700 +/- 9800 nM hour) was 44% greater than the baseline value. All differences among mean AUC0-infinity values were statistically significant. Mean indinavir half-life values were slightly longer when indinavir was given in a dose with delavirdine than when indinavir was administered alone. These results suggest that delavirdine inhibits metabolism of indinavir and support the possibility of a reduction in the magnitude or frequency of indinavir dosage when given in combination with delavirdine.

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.

A proline-to-histidine substitution at position 225 of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) sensitizes HIV-1 RT to BHAP U-90152

Two mutant virus strains in which the novel P225H mutation appeared in a V106A reverse transcriptase (RT)-mutated genetic background upon treatment of human immunodeficiency virus type 1 (HIV-1) with quinoxaline S-2720 were isolated. Surprisingly, the addition of the P225H mutation to the V106A RT mutant genetic background resensitized the V106A RT mutant virus to the non-nucleoside RT inhibitor (NNRTI) BHAP U-90152, but not to other NNRTIs. Construction of both recombinant viruses and recombinant RTs containing the V106A, P225H and V106A+P225H mutations revealed that P225H was indeed responsible for the marked potentiation of the antiviral activity of BHAP against the P225H single-mutant virus and the V106A+P225H double-mutant virus when compared to wild-type and V106A single-mutant viruses, respectively. An explanation for the markedly increased sensitivity of the P225H mutant HIV-1 RT to BHAP and not to the other NNRTIs was provided by the unique features of the X-ray structure of the RT-BHAP complex.

Retention of marked sensitivity to (S)-4-isopropoxycarbonyl-6-methoxy-3-(methylthiomethyl)-3,4-di hydroquin oxaline-2(1H)-thione (HBY 097) by an azidothymidine (AZT)-resistant human immunodeficiency virus type 1 (HIV-1) strain subcultured in the combined presence of quinoxaline HBY 097 and 2',3'-dideoxy-3'-thiacytidine (lamivudine)

An azidothymidine (AZT)-resistant virus strain (HIV-1/AZT) (containing the 67 Asp --> Asn, 70 Lys --> Arg, 215 Thr --> Phe and 219 Lys --> Gln mutations into its reverse transcriptase) was grown in the combined presence of 2',3'-dideoxy-3'-thiacytidine (3TC, lamivudine) and the nonnucleoside reverse transcriptase inhibitor (S)-4-isopropoxycarbonyl-6-methoxy-3-(methylthiomethyl)-3,4-dih ydroquinoxaine-2(1H)-thione (quinoxaline HBY 097). Replication of HIV-1/AZT was inhibited to a significantly greater extent by the combination of 3TC and quinoxaline HBY 097 than by either drug alone. Virus breakthrough was markedly delayed in the combined presence of 3TC and HBY 097 at drug concentrations as low as 0.05 microg/mL and 0.0025 microg/mL, respectively. The virus that was recovered after exposure to the compounds (3TC and HBY 097) individually had acquired, in the genetic AZT-resistance background of HIV-1/AZT, 103 Lys --> Glu and 106 Val --> Ala mutations. The 103 Lys --> Glu mutation had not been observed before. However, both virus mutants retained marked sensitivity to HBY 097. In all cases, the genotypic AZT-resistance mutations were maintained in the mutant virus RT genomes, and the viruses also remained phenotypically resistant to AZT. Given the exquisite potency of a concomitant combination of 3TC and HBY 097 in suppressing virus replication, this drug combination should be further pursued in clinical trials in HIV-1-infected individuals.

Colorimetric assays for evaluation of the mode of action of human immunodeficiency virus type 1 non-nucleoside reverse transcriptase inhibitors

Four non-nucleoside reverse transcriptase (RT) inhibitors, 9-CI-TIBO [(+)-S-4,5,6,7-tetrahydro-9- chloro-5-methyl-6-(3-methyl-2-butenyl)imidazo(4,5,1-jk)(1,4)- benzodiazepin-2(1H)-thione)], nevirapine (6,11-dihydro-11-cyclopropyl-4-methyl-dipyrido[2,3-b:2',3'-e]-[1,4]di azepin- 6-one), MSA-300 (N-[cis-2-(2-hydroxy-3-acetyl-6-methoxy-phenyl)-cyclopropyl]-N'- (5-chloropyrid-2-yl)-thiourea) and delavirdine ¿1-(5-methanesulphonamido-1H-indol-2-yl-carbonyl)-4-[3- (1-methylethylamino)pyridinyl]piperazine¿ were analysed for the mode of action of their inhibition of human immunodeficiency virus type 1 (HIV-1) RT in three different assays utilizing a 96-well microtitre plate format, with solid-phase conjugated poly(rA) as template. These were: (i) direct RT assay, for determination of IC50 values of RT inhibitors; (ii) RT template/primer binding inhibition (BIC) assay, for measuring the effect of various substances on the RT activity binding to template/primer; (iii) RT protein ELISA, for measuring RT protein binding to template/primer with a monoclonal antibody reactive against a peptide in the RNase H region. MSA-300 and delavirdine gave the lowest IC50 values, ranging from 0.17 microM to 0.24 microM for MSA-300 and from 0.12 microM to 0.38 microM for delavirdine, whereas higher IC50 values of approximately 20 microM were obtained for 9-CI-TIBO at all primer concentrations. None of the non-nucleoside substances had inhibiting effects on the binding of template, primer, or template/primer to RT protein. Their inhibition of RT activity was not due to prevention of RT binding to template/primer. TIBO, nevirapine and delavirdine bound to RT reversibly, and they bound more tightly to RT template/primer ternary than to RT template binary complex. MSA-300 showed a comparatively high affinity for the enzyme. The utility of the three assays in relation to screening and analysis of RT inhibitory substances is discussed.

In-vitro selection of HIV-1 variants resistant to non-nucleoside reverse transcriptase inhibitors in monocyte-derived macrophages

Unlike the selection of HIV-1 variants resistant to anti-retroviral drugs in human peripheral blood mononuclear cells and T cell lines, induction of resistance in monocyte-derived macrophages has not been widely studied. Since macrophages serve as a potential HIV-1 reservoir in humans, knowledge of the effect of anti-retroviral drugs on macrophage-tropic HIV-1 isolates may help in the design of a strategy for prolonged suppression of viral replication. In-vitro selection and drug susceptibility testing of macrophage-tropic HIV-1 variants with reduced sensitivity to two non-nucleoside reverse transcriptase inhibitors, atevirdine and delavirdine (both bis-heteroarylpiperazines), is described here. The atevirdine-resistant isolate was cross-resistant to delavirdine, and the delavirdine-resistant isolate was cross-resistant to atevirdine. Interestingly, the atevirdine-resistant isolate, but not the delavirdine-resistant isolate, was also cross-resistant to nevirapin while the inhibition of viral replication of both isolates in macrophages by zidovudine was the same as that in the parental HIV-1 strain. Nucleotide sequence analysis of the resistant macrophage-tropic HIV-1 isolates showed that the atevirdine-induced resistance was due to a single amino acid change at codon 106 and that the delavirdine-induced resistance could be attributed to an amino acid change at codon 236. This study demonstrates that monocyte-derived macrophages can be used to investigate the phenotypic and genotypic acquisition of anti-retroviral drug resistance of macrophage-tropic HIV-1.