Tenofovir, adefovir, and zidovudine susceptibilities of primary human immunodeficiency virus type 1 isolates with non-B subtypes or nucleoside resistance

Tenofovir-tethered gold nanoparticles as a novel multifunctional long-acting anti-HIV therapy to overcome deficient drug delivery-: an in vivo proof of concept

BACKGROUND

The adoption of Antiretroviral Therapy (ART) substantially extends the life expectancy and quality of HIV-infected patients. Yet, eliminating the latent reservoirs of HIV to achieve a cure remains an unmet need. The advent of nanomedicine has revolutionized the treatment of HIV/AIDS. The present study explores a unique combination of Tenofovir (TNF) with gold nanoparticles (AuNPs) as a potential therapeutic approach to overcome several limitations of the current ART.

RESULTS

TNF-tethered AuNPs were successfully synthesized. Cell viability, genotoxicity, haemolysis, and histopathological studies confirmed the complete safety of the preparation. Most importantly, its anti-HIV1 reverse transcriptase activity was ~ 15 folds higher than the native TNF. In addition, it exhibited potent anti-HIV1 protease activity, a much sought-after target in anti-HIV1 therapeutics. Finally, the in vivo biodistribution studies validated that the AuNPs could reach many tissues/organs, serving as a secure nest for HIV and overcoming the problem of deficient drug delivery to HIV reservoirs.

CONCLUSIONS

We show that the combination of TNF and AuNPs exhibits multifunctional activity, viz. anti-HIV1 and anti-HIV1 protease. These findings are being reported for the first time and highlight the prospects of developing AuNP-TNF as a novel next-generation platform to treat HIV/AIDS.

Switching to Bictegravir/Emtricitabine/Tenofovir Alafenamide (B/F/TAF) From Dolutegravir (DTG)+F/TAF or DTG+F/Tenofovir Disoproxil Fumarate (TDF) in the Presence of Pre-existing NRTI Resistance

BACKGROUND

Study 4030 was a phase 3, randomized, double-blinded study of 565 HIV-1 RNA-suppressed participants switching to bictegravir/emtricitabine/tenofovir alafenamide (B/F/TAF) or dolutegravir (DTG)+F/TAF. Nucleoside reverse transcriptase inhibitor (NRTI), non-NRTI, and protease inhibitor resistance (-R) was allowed, but integrase strand transfer inhibitor-R was excluded. Here, we describe the detailed resistance analysis.

METHODS

Historical plasma HIV-1 RNA genotypes and baseline proviral DNA genotypes were analyzed. Documented or investigator-suspected NRTI-R was grouped for stratification into 3 categories of level of resistance. Viral blips were assessed through week 48. Virologic failures had genotypic and phenotypic resistance analyses at week 48, confirmed failure, or last visit, if HIV-1 RNA did not resuppress to <50 copies/mL while on study drug.

RESULTS

In total, 83% (470/565) of participants had baseline genotypic data available with NRTI-R detected in 24% (138/565), including 5% (30/565) with K65R/E/N or ≥3 thymidine analog mutations and 19% (108/565) with other NRTI-R mutations. M184V/I was present in 14% (81/565). Pre-existing integrase strand transfer inhibitor-R mutations were found in 4% (20/565) of participants. Primary non-NRTI-R and protease inhibitor-R mutations were present in 21% (118/565) and 7% (38/565) of participants. High rates of viral suppression were maintained in all groups through week 48; blips were observed in only 15 participants (2.7%). Three participants met criteria for resistance analysis (all in DTG+F/TAF arm); none developed treatment-emergent resistance to study drugs.

CONCLUSIONS

Participants with baseline NRTI resistance, much of which was previously undocumented, maintained suppression 48 weeks after switching to B/F/TAF or DTG+F/TAF triple therapy. Blips and virologic failure were uncommon using either regimen, with no treatment-emergent resistance.

Nanoemulgel using a bicephalous heterolipid as a novel approach to enhance transdermal permeation of tenofovir

Improvements in permeation enhancement strategies, such as nanoemulsions (NEs) and nanoemulgels (NEGs), have led to a renewed interest in transdermal drug delivery (TDD). This study aimed to investigate the potential of LLA1E, a novel dendritic permeation enhancer, as an oily phase in the development of a NEG for the TDD of tenofovir (TNF). TNF loaded NEs (TNEs) were prepared and analysed for mean globule diameter (MGD), polydispersity index (PDI), zeta potential (ZP) and morphology. NEGs of the TNEs (TNEGs) were prepared and evaluated for ex vivo transdermal permeation efficacy. The skin integrity before and after the experiments was assessed using histology and transepithelial electrical resistance (TEER). TNEs had a MGD of 129.06±3.35nm, a PDI of 0.192±0.038 and a ZP of 20.9±2.02mV, with an incorporation efficiency of 91.94±0.84%. There was no significant change is these properties after incorporating the TNEs into the hydrogel, as MGD, PDI and ZP of TNEGs were found to be 136.13±5.21nm, 0.182±0.020 and -20.9±2.08mV respectively. Ex vivo permeation studies showed that the TNEG significantly enhanced the TNF permeation by 39.65-fold, with a cumulative amount of 1866.54±108.62μgcm^-2. Histological and TEER assessments showed no permanent effects on the skin by TNEG, indicating that this novel TNEG nanosystem has the potential to translate into clinical trials as treatment alternatives for HIV/AIDs patients.

Characterization of HIV-1 Resistance to Tenofovir Alafenamide In Vitro

Tenofovir alafenamide (TAF) is an investigational prodrug of the HIV-1 nucleotide reverse transcriptase (RT) inhibitor (NtRTI) tenofovir (TFV), with improved potency and drug delivery properties over the current prodrug, tenofovir disoproxil fumarate (TDF). TAF is currently in phase 3 clinical studies for the treatment of HIV-1 infection, in combination with other antiretroviral agents. Phase 1 and 2 studies have shown that TAF was associated with increased peripheral blood mononuclear cell (PBMC) drug loading and increased suppression of HIV-1 replication compared to treatment with TDF. In this study, selection of in vitro resistance to both TAF and the parent compound, TFV, led to the emergence of HIV-1 with the K65R amino acid substitution in RT with 6.5-fold-reduced susceptibility to TAF. Although TAF is more potent than TFV in vitro, the antiviral susceptibilities to TAF and TFV of a large panel of nucleoside/nucleotide RT inhibitor (NRTI)-resistant mutants were highly correlated (R(2) = 0.97), indicating that the two compounds have virtually the same resistance profile when assessed as fold change from the wild type. TAF showed full antiviral activity in PBMCs against primary HIV-1 isolates with protease inhibitor, nonnucleoside RT inhibitor (NNRTI), or integrase strand transfer inhibitor resistance but reduced activity against isolates with extensive NRTI resistance amino acid substitutions. However, the increased cell loading of TFV with TAF versus TDF observed in vivo suggests that TAF may retain activity against TDF-resistant mutant viruses.

Novel dendritic derivatives of unsaturated fatty acids as promising transdermal permeation enhancers for tenofovir

Novel dendritic ester derivatives of unsaturated fatty acids as potential transdermal permeation enhancers.

Cultivated vaginal microbiomes alter HIV-1 infection and antiretroviral efficacy in colonized epithelial multilayer cultures

There is a pressing need for modeling of the symbiotic and at times dysbiotic relationship established between bacterial microbiomes and human mucosal surfaces. In particular clinical studies have indicated that the complex vaginal microbiome (VMB) contributes to the protection against sexually-transmitted pathogens including the life-threatening human immunodeficiency virus (HIV-1). The human microbiome project has substantially increased our understanding of the complex bacterial communities in the vagina however, as is the case for most microbiomes, very few of the community member species have been successfully cultivated in the laboratory limiting the types of studies that can be completed. A genetically controlled ex vivo model system is critically needed to study the complex interactions and associated molecular dialog. We present the first vaginal mucosal culture model that supports colonization by both healthy and dysbiotic VMB from vaginal swabs collected from routine gynecological patients. The immortalized vaginal epithelial cells used in the model and VMB cryopreservation methods provide the opportunity to reproducibly create replicates for lab-based evaluations of this important mucosal/bacterial community interface. The culture system also contains HIV-1 susceptible cells allowing us to study the impact of representative microbiomes on replication. Our results show that our culture system supports stable and reproducible colonization by VMB representing distinct community state types and that the selected representatives have significantly different effects on the replication of HIV-1. Further, we show the utility of the system to predict unwanted alterations in efficacy or bacterial community profiles following topical application of a front line antiretroviral.

Metabolism and antiretroviral activity of tenofovir alafenamide in CD4+ T-cells and macrophages from demographically diverse donors

BACKGROUND

Tenofovir alafenamide (TAF) is a novel investigational prodrug of tenofovir (TFV) that permits enhanced delivery of TFV into peripheral blood mononuclear cells (PBMCs) and lymphatic tissues. A critical step in the intracellular metabolic activation of TAF is mediated by the lysosomal protease cathepsin A (CatA). Here, we investigated CatA levels together with intracellular metabolism and antiretroviral activity of TAF in primary CD4+ T-lymphocytes (CD4s) and monocyte-derived macrophages (MDMs) isolated from a demographically diverse group of blood donors.

METHODS

CD4s and MDMs were prepared from fresh PBMCs. CatA levels were quantified in cell extracts by monitoring TAF hydrolysis using HPLC. Intracellular TAF metabolites were quantified by HPLC combined with mass spectrometry. Antiviral activities in activated CD4s and MDMs were determined using HIV-1 single-cycle reporter and p24 antigen production assays, respectively.

RESULTS

The levels of CatA and intracellular TAF metabolites differed minimally in CD4s and MDMs among 13 tested donors. TAF was >600-fold and 80-fold more potent than parent TFV in CD4s and MDMs, respectively, and its relative range of antiviral activity across all tested donors was comparable to that of other HIV-1 reverse transcriptase inhibitors, with mean ±sd (range) EC50 values of 11.0 ±3.4 (6.6-19.9) nM and 9.7 ±4.6 (2.5-15.7) nM in CD4s and MDMs, respectively.

CONCLUSIONS

These results indicate consistent intracellular metabolism and antiretroviral potency of TAF in relevant target cells of HIV-1 infection across multiple donors of variable gender, age and ethnicity, supporting further clinical investigation of TAF.

Drug synergy of tenofovir and nanoparticle-based antiretrovirals for HIV prophylaxis

BACKGROUND

The use of drug combinations has revolutionized the treatment of HIV but there is no equivalent combination product that exists for prevention, particularly for topical HIV prevention. Strategies to combine chemically incompatible agents may facilitate the discovery of unique drug-drug activities, particularly unexplored combination drug synergy. We fabricated two types of nanoparticles, each loaded with a single antiretroviral (ARV) that acts on a specific step of the viral replication cycle. Here we show unique combination drug activities mediated by our polymeric delivery systems when combined with free tenofovir (TFV).

METHODOLOGY/PRINCIPAL FINDINGS

Biodegradable poly(lactide-co-glycolide) nanoparticles loaded with efavirenz (NP-EFV) or saquinavir (NP-SQV) were individually prepared by emulsion or nanoprecipitation techniques. Nanoparticles had reproducible size (d ∼200 nm) and zeta potential (-25 mV). The drug loading of the nanoparticles was approximately 7% (w/w). NP-EFV and NP-SQV were nontoxic to TZM-bl cells and ectocervical explants. Both NP-EFV and NP-SQV exhibited potent protection against HIV-1 BaL infection in vitro. The HIV inhibitory effect of nanoparticle formulated ARVs showed up to a 50-fold reduction in the 50% inhibitory concentration (IC50) compared to free drug. To quantify the activity arising from delivery of drug combinations, we calculated combination indices (CI) according to the median-effect principle. NP-EFV combined with free TFV demonstrated strong synergistic effects (CI50 = 0.07) at a 1∶50 ratio of IC50 values and additive effects (CI50 = 1.05) at a 1∶1 ratio of IC50 values. TFV combined with NP-SQV at a 1∶1 ratio of IC50 values also showed strong synergy (CI50 = 0.07).

CONCLUSIONS

ARVs with different physicochemical properties can be encapsulated individually into nanoparticles to potently inhibit HIV. Our findings demonstrate for the first time that combining TFV with either NP-EFV or NP-SQV results in pronounced combination drug effects, and emphasize the potential of nanoparticles for the realization of unique drug-drug activities.

Persistence versus reversion of 3TC resistance in HIV-1 determine the rate of emergence of NVP resistance

When HIV-1 is exposed to lamivudine (3TC) at inhibitory concentrations, resistant variants carrying the reverse transcriptase (RT) substitution M184V emerge rapidly. This substitution confers high-level 3TC resistance and increased RT fidelity. We established a novel in vitro system to study the effect of starting nevirapine (NVP) in 3TC-resistant/NNRTI-naïve clinical isolates, and the impact of maintaining versus dropping 3TC pressure in this setting. Because M184V mutant HIV-1 seems hypersusceptible to adefovir (ADV), we also tested the effect of ADV pressure on the same isolates. We draw four conclusions from our experiments simulating combination therapy in vitro. (1) The presence of low-dose (1 μM) 3TC prevented reversal to wild-type from an M184V mutant background. (2) Adding low-dose 3TC in the presence of NVP delayed the selection of NVP-associated mutations. (3) The presence of ADV, in addition to NVP, led to more rapid reversal to wild-type at position 184 than NVP alone. (4) ADV plus NVP selected for greater numbers of mutations than NVP alone. Inference about the "selection of mutation" is based on two statistical models, one at the viral level, more telling, and the other at the level of predominance of mutation within a population. Multidrug pressure experiments lend understanding to mechanisms of HIV resistance as they bear upon new treatment strategies.

Formulation of tenofovir-loaded functionalized solid lipid nanoparticles intended for HIV prevention

The objective of this study is to engineer polylysine-heparin functionalized solid lipid nanoparticles (fSLNs) for the use of a vaginal microbicide delivery template for HIV prevention. The fSLNs are prepared using a modified phase-inversion technique followed by a layer-by-layer deposition method. The Box-Behnken experimental design is used to analyze the influence of three factors (X(1) = bovine serum albumin concentration, X(2) = pH of the aqueous phase, and X(3) = lipid amount) on the particle mean diameter (PMD) measured by dynamic light scattering (DLS). Tenofovir is used as a model anti-HIV microbicide. The SLNs are also characterized for morphology, zeta potential (ζ ), percent drug encapsulation efficiency (EE%), and cytotoxicity on a human vaginal epithelial cell line by electron microscopy, DLS, ultraviolet, and fluorescence spectroscopy, respectively. The statistical model predicts particle size (Y) with 90% confidence and the Y values are significantly affected by X(1) and X(2) . The produced fSLNs appear noncytotoxic and exhibit a platelet-like shape with respective PMD, EE%, and ζ value of 153 nm, 8.3%, and - 51 mV. These fSLNs intended to be administered topically have the potential to enhance cellular uptake of hydrophobic microbicides and outdistance the virus during the HIV/AIDS infection process, possibly leading to more effective prevention of the disease transmission.

In vitro and ex vivo testing of tenofovir shows it is effective as an HIV-1 microbicide

BACKGROUND

Tenofovir gel has entered into clinical trials for use as a topical microbicide to prevent HIV-1 infection but has no published data regarding pre-clinical testing using in vitro and ex vivo models. To validate our findings with on-going clinical trial results, we evaluated topical tenofovir gel for safety and efficacy. We also modeled systemic application of tenofovir for efficacy.

METHODS AND FINDINGS

Formulation assessment of tenofovir gel included osmolality, viscosity, in vitro release, and permeability testing. Safety was evaluated by measuring the effect on the viability of vaginal flora, PBMCs, epithelial cells, and ectocervical and colorectal explant tissues. For efficacy testing, PBMCs were cultured with tenofovir or vehicle control gels and HIV-1 representing subtypes A, B, and C. Additionally, polarized ectocervical and colorectal explant cultures were treated apically with either gel. Tenofovir was added basolaterally to simulate systemic application. All tissues were challenged with HIV-1 applied apically. Infection was assessed by measuring p24 by ELISA on collected supernatants and immunohistochemistry for ectocervical explants. Formulation testing showed the tenofovir and vehicle control gels were >10 times isosmolar. Permeability through ectocervical tissue was variable but in all cases the receptor compartment drug concentration reached levels that inhibit HIV-1 infection in vitro. The gels were non-toxic toward vaginal flora, PBMCs, or epithelial cells. A transient reduction in epithelial monolayer integrity and epithelial fracture for ectocervical and colorectal explants was noted and likely due to the hyperosmolar nature of the formulation. Tenofovir gel prevented HIV-1 infection of PBMCs regardless of HIV-1 subtype. Topical and systemic tenofovir were effective at preventing HIV-1 infection of explant cultures.

CONCLUSIONS

These studies provide a mechanism for pre-clinical prediction of safety and efficacy of formulated microbicides. Tenofovir was effective against HIV-1 infection in our algorithm. These data support the use of tenofovir for pre-exposure prophylaxis.

HIV Genetic Diversity and Drug Resistance

Most of the current knowledge on antiretroviral (ARV) drug development and resistance is based on the study of subtype B of HIV-1, which only accounts for 10% of the worldwide HIV infections. Cumulative evidence has emerged that different HIV types, groups and subtypes harbor distinct biological properties, including the response and susceptibility to ARV. Recent laboratory and clinical data highlighting such disparities are summarized in this review. Variations in drug susceptibility, in the emergence and selection of specific drug resistance mutations, in viral replicative capacity and in the dynamics of resistance acquisition under ARV selective pressure are discussed. Clinical responses to ARV therapy and associated confounding factors are also analyzed in the context of infections by distinct HIV genetic variants.

Binding Modes of Two Novel Non-Nucleoside Reverse Transcriptase Inhibitors, YM-215389 and YM-228855, to HIV Type-1 Reverse Transcriptase

Background:

YM-215389 and YM-228855 are thiazolidenebenzenesulfonamide (TBS) derivatives and novel non-nucleoside reverse transcriptase inhibitors (NNRTIs) that inhibit not only wild-type, but also the K103N- and Y181C-substituted reverse transcriptase (RT) of HIV type-1 (HIV-1).

Methods:

To characterize the binding modes of the TBS derivatives in detail, the anti-HIV-1 activities of YM-215389 and YM-228855 against various NNRTI-resistant clones were examined. Docking studies with HIV-1 RT were also performed.

Results:

YM-215389, which effectively inhibits various NNRTI-resistant clones, interacted with L100, K103, V106 and Y318 through the benzene ring and with E138, V179, Y181, Y188 and W229 through the thiazole ring. A single amino acid substitution confers only moderate resistance to YM-215389; indeed, four amino acid substitutions (V106L, V108I, E138K and L214F) were necessary for high- level resistance. Although the activity of YM-228855, a derivative of YM-215389 that has two bulky and rigid cyano-moieties on the benzene ring, was 10x more potent against HIV-1 than YM-215389, its anti-HIV-1 activity was readily reduced with single substitutions as with Y181I and K103N.

Conclusions:

These results provide structural information for optimizing the TBS derivatives in an attempt to construct ideal NNRTIs that maintain anti-HIV-1 activity to various HIV-1 variants.

Clinical impact of HIV-1 subtype: are there important differences?

The enormous genetic diversity of HIV-1 is a major challenge to vaccine development and may have important clinical consequences. HIV-1 group M predominates globally, with nine subtypes, several sub-subtypes and over 30 circulating recombinant forms that may exhibit differences with respect to transmissibility, pathogenicity and development of antiretroviral resistance. Subtype D appears to be more virulent than other subtypes, in particular subtype A. Subtype C may be less virulent and more transmissible, although the evidence for this is inconclusive. All group M non-B subtypes appear to be equally susceptible to combination antiretroviral therapy, but development of resistance mutations may vary significantly between subtypes. Further research into the clinical implications of HIV-1 diversity is crucial for effective HIV-1 prevention and treatment.

Impact of genetic variation of HIV-1 on drug resistance development

HIV is a particularly diverse virus and can be classified into different types, groups and subtypes. Most of the current knowledge is based on HIV-1 subtype B, which is responsible for the first recognized epidemic, mainly spreading in the developed world, while the other subtypes are responsible for the major part of the pandemic, primarily in the developing world. Interest in the so-called ‘non-B’ subtypes is increasing, with treatment programs expanding to include Africa and Asia. According to several recent studies, differences exist between subtypes regarding drug susceptibility, resistance development and therapy response. Currently, conclusions are often based on too few patients or samples, and the use of different resistance assays and analysis methods makes it difficult to compare results. A common mistake is to pool subtypes and recombinants together as ‘non-B subtypes’, although they differ among each other as much as they differ from subtype B. Europe, with large epidemics of subtype B and several non-B subtypes in similar patient populations, is well placed to take the lead in this research field.

Virologic response of zidovudine, lamivudine, and tenofovir disoproxil fumarate combination in antiretroviral-naive HIV-1-infected patients

BACKGROUND

High rates of virologic failure have been reported in antiretroviral-naive patients receiving triple-nucleoside reverse transcriptase inhibitor (NRTI) combinations containing tenofovir disoproxil fumarate (TDF) with lamivudine (3TC) and didanosine or 3TC and abacavir (ABC). A regimen of once-daily zidovudine (ZDV), 3TC, ABC, and TDF showed an acceptable virologic success rate, however.

METHODS

This was a pilot prospective cohort study. Treatment-naive subjects were offered a fixed-dose combination of ZDV/3TC (300 mg/150 mg) twice daily and 300 mg of TDF once daily.

RESULTS

Fifty-one patients were enrolled between April 2002 and March 2005. At baseline, the median CD4 count was 230 cells/microL (range: 23-425 cells/microL), 20 (39%) of 51 subjects had CD4 counts of < 200 cells/microL, the median HIV-1 viral load was 4.89 log (3.14 to >5.87 log), and 24 (47%) of 51 subjects had a viral load >5 log. The median follow-up was 12 months (range: 1 week to 38 months). On-treatment analysis showed a median HIV RNA load decrease of -1.7 log after 1 to 2 weeks of treatment and -2.41 log after 1 month, and 34 (89%) of 38 subjects had a viral load < 50 copies/mL at month 6, 21 (78%) of 27 at month 12, and 13 (81%) of 16 after 18 months (intent-to-treat results were 34 [72%] of 47 subjects, 21 [56%] of 36 subjects, and 13 [50%] of 25 subjects at months 6, 12, and 18, respectively). The median CD4 count increase at month 18 was 142 cells/microL. Nine (17.6%) of 51 treatment interruptions for adverse effects were seen. Six viral failures occurred, including 2 with K65R mutations (alone or associated with Y115F and M184V).

CONCLUSION

The combination of ZDV/3TC + TDF in treatment-naive HIV-infected subjects induces a rapid and sustained HIV-1 RNA decrease and is associated with a good immunologic response. No severe adverse events occurred. This triple-NRTI combination needs to be evaluated further.

In vitro human immunodeficiency virus type 1 resistance selections with combinations of tenofovir and emtricitabine or abacavir and lamivudine

Human immunodeficiency virus type 1 (HIV-1) resistance development was evaluated in vitro by using combinations of the drugs tenofovir and emtricitabine or abacavir and lamivudine, as well as by using the compounds individually. Emtricitabine- and lamivudine-resistant HIV-1 isolates with the M184I or M184V mutation in reverse transcriptase were readily selected in the cultures with emtricitabine alone, lamivudine alone, and the two drug combinations and conferred high-level resistance to emtricitabine and lamivudine. Tenofovir-resistant HIV-1 isolates with the K65R mutation occurred in both the culture with tenofovir alone and the culture with the combination of emtricitabine and tenofovir. The S68N and S68K mutations were also observed in the tenofovir cultures, with no detectable impact on resistance, suggesting a possible compensatory role in viral fitness. At low concentrations of emtricitabine and tenofovir, the M184I mutation appeared first, followed by the K65R mutation, in a subset of viruses. At intermediate concentrations of emtricitabine and tenofovir, viruses harboring the K65R mutation or a novel K65N and K70R double mutation grew before they gave rise to mutants with K65R and M184V/I double mutations at higher emtricitabine concentrations. Abacavir resistance was characterized by the accumulation of the M184V, Y115F, and K65R mutations in the abacavir culture, while the M184V and L74V mutations were selected in combination with lamivudine. In the presence of the abacavir resistance mutations, viral growth was strong even in the presence of high concentrations of abacavir. In contrast, viral growth was markedly impaired in the cultures with high tenofovir concentrations, even in the presence of K65R. In conclusion, these studies show that HIV-1 mutants with a K65R and M184V genotype are generated under maximum selection pressure from the combination of tenofovir and emtricitabine.

Resistance to New Anti-HIV Agents: Problems in the Pathway of Drug Registration

Resistance data are now requested by the regulatory agencies as an integral part of the approval process of new antiretroviral drugs. We examined the means by which resistance data was gathered during pre-clinical and clinical Phases I, II and III of drug development, and how the public and academic experts access these proprietary data. The analysis identified various opportunities for improvement of the current process, in particular the need for standards in generating and reporting resistance data on new antiretroviral drugs, and the need to enforce warnings in the product labelling on the drug combinations that can potentially lead to resistance and treatment failure.

Diminished replicative fitness of primary human immunodeficiency virus type 1 isolates harboring the K65R mutation

The human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) resistance mutation K65R confers intermediate levels of resistance to several RT inhibitors, including a three- to fourfold reduction of tenofovir susceptibility. Here, we have used for the first time primary HIV-1 isolates from individuals who developed the K65R mutation while enrolled in a clinical trial of tenofovir to analyze the impact of this mutation on HIV-1 replicative fitness. A marked impairment in replicative fitness was observed in association with the selection of viruses carrying the K65R mutation in all patients. The mean replicative fitness among these viruses was 20% relative to the corresponding baseline wild-type virus, ranging from 10 to 32% depending on the accompanying RT mutations. These results support a reduction in in vivo replication for K65R mutant viruses.

Impact of HIV-1 subtype and antiretroviral therapy on protease and reverse transcriptase genotype: results of a global collaboration

BACKGROUND

The genetic differences among HIV-1 subtypes may be critical to clinical management and drug resistance surveillance as antiretroviral treatment is expanded to regions of the world where diverse non-subtype-B viruses predominate.

METHODS AND FINDINGS

To assess the impact of HIV-1 subtype and antiretroviral treatment on the distribution of mutations in protease and reverse transcriptase, a binomial response model using subtype and treatment as explanatory variables was used to analyze a large compiled dataset of non-subtype-B HIV-1 sequences. Non-subtype-B sequences from 3,686 persons with well characterized antiretroviral treatment histories were analyzed in comparison to subtype B sequences from 4,769 persons. The non-subtype-B sequences included 461 with subtype A, 1,185 with C, 331 with D, 245 with F, 293 with G, 513 with CRF01_AE, and 618 with CRF02_AG. Each of the 55 known subtype B drug-resistance mutations occurred in at least one non-B isolate, and 44 (80%) of these mutations were significantly associated with antiretroviral treatment in at least one non-B subtype. Conversely, of 67 mutations found to be associated with antiretroviral therapy in at least one non-B subtype, 61 were also associated with antiretroviral therapy in subtype B isolates.

CONCLUSION

Global surveillance and genotypic assessment of drug resistance should focus primarily on the known subtype B drug-resistance mutations.

Tenofovir resistance and resensitization

Human immunodeficiency viruses in 321 samples from tenofovir-naïve patients were retrospectively evaluated for resistance to this nucleotide analogue. All virus strains with insertions between amino acids 67 and 70 of the reverse transcriptase (n = 6) were highly resistant. Virus strains with the Q151M mutation were divided into susceptible (n = 12) and highly resistant (n = 8) viruses. This difference was due to the absence or presence of the K65R mutation, which was confirmed by site-directed mutagenesis. Viral clones with various combinations of the mutations M41L, K70R, L210W, and T215F or T215Y were analyzed for cross-resistance induced by thymidine analogue mutations (TAMs). The levels of increased resistance induced by single, double, and triple mutations at the indicated positions could be ranked as follows: for mutants with single mutations, mutations at positions 41 > 215 > 70; for mutants with double mutations, mutations at positions 41 and 215 > 70 and 215 = 210 and 215 > 41 and 70; for mutants with triple mutations, mutations at positions 41, 210, and 215 > 41, 70, and 215. Viral clones with M184V or M184I exhibited slightly increased susceptibilities to tenofovir (0.7-fold). Almost all clones with TAM-induced resistance were resensitized when M184V was present (P < 0.001). Among the viruses in the clinical samples, the rate of tenofovir resistance significantly increased with the number of TAMs both in the samples with 184M and in those with 184V (P = 0.005 and P = 0.003, respectively). A resensitizing effect of M184V was confirmed for all samples exhibiting at least one TAM (P = 0.03). However, accumulation of at least two TAMs resulted in more than 2.0-fold reduced susceptibility to tenofovir, irrespective of the presence of M184V. Decision tree building, a classical machine learning technique, was used to generate models for the interpretation of mutations with respect to tenofovir resistance. The application of previously proposed cutoffs for a reduced response to therapy and treatment failure demonstrated the central roles of positions 215 and 65 for 1.5- and 4.0-fold reduced susceptibilities, respectively. Thus, clinically relevant resistance may be conferred by the accumulation of TAMs, and the resensitizing effect of M184V should be considered only minor.

Clinical potential of the acyclic nucleoside phosphonates cidofovir, adefovir, and tenofovir in treatment of DNA virus and retrovirus infections

The acyclic nucleoside phosphonates HPMPC (cidofovir), PMEA (adefovir), and PMPA (tenofovir) have proved to be effective in vitro (cell culture systems) and in vivo (animal models and clinical studies) against a wide variety of DNA virus and retrovirus infections: cidofovir against herpesvirus (herpes simplex virus types 1 and 2 varicella-zoster virus, cytomegalovirus [CMV], Epstein-Barr virus, and human herpesviruses 6, 7, and 8), polyomavirus, papillomavirus, adenovirus, and poxvirus (variola virus, cowpox virus, vaccinia virus, molluscum contagiosum virus, and orf virus) infections; adefovir against herpesvirus, hepadnavirus (human hepatitis B virus), and retrovirus (human immunodeficiency virus types 1 [HIV-1] and 2 [HIV-2], simian immunodeficiency virus, and feline immunodeficiency virus) infections; and tenofovir against both hepadnavirus and retrovirus infections. Cidofovir (Vistide) has been officially approved for the treatment of CMV retinitis in AIDS patients, tenofovir disoproxil fumarate (Viread) has been approved for the treatment of HIV infections (i.e., AIDS), and adefovir dipivoxil (Hepsera) has been approved for the treatment of chronic hepatitis B. Nephrotoxicity is the dose-limiting side effect for cidofovir (Vistide) when used intravenously (5 mg/kg); no toxic side effects have been described for adefovir dipivoxil and tenofovir disoproxil fumarate, at the approved doses (Hepsera at 10 mg orally daily and Viread at 300 mg orally daily).

Prevention of perinatal HIV transmission: a review of novel strategies

Significant progress has been made in preventing transmission of HIV-1 from mother to infant. With combination antiretroviral therapies, transmission rates lower than 2% have been achieved in clinical studies. Abbreviated regimens covering labour and the first few days of neonatal life have shown considerable promise in the developing world. Several questions and challenges remain, however. These include choice of the optimal antiretroviral agent(s) and duration of the regimens, availability of antiretroviral agents in developing countries, long-term safety of antiretrovirals during pregnancy and early neonatal life and the problem of breastfeeding transmission in countries where alternatives to breastfeeding are not available. A wider array of strategies for prevention of mother-to-child transmission of HIV-1 during breastfeeding, including passive and active immunisation, may offer much needed answers to the problem of continued HIV transmission from mother to infant.

Tenofovir disoproxil fumarate

OBJECTIVE

To review the pharmacology, virology, pharmacokinetics, efficacy, safety, resistance profile, and clinical use of tenofovir disoproxil fumarate.

DATA SOURCES

A MEDLINE search was performed (1966-August 2002) using the following terms: tenofovir, tenofovir disoproxil fumarate, PMPA (9-(R)-[2-(phosphonomethoxy)propyl]adenine), and Viread. Abstracts from HIV-related meetings were reviewed. DATA EXTRACTION AND STUDY SELECTION: Publications and meeting abstracts regarding tenofovir were reviewed. The most recent and pertinent items were included.

DATA SYNTHESIS

Tenofovir disoproxil fumarate is a nucleotide prodrug that is diphosphorylated to its active moiety, tenofovir diphosphate. In this form, tenofovir acts as a reverse transcriptase inhibitor to inhibit HIV-1 replication. In clinical trials, tenofovir was effective at suppressing HIV-1 RNA and boosting CD4+ cell counts. Tenofovir has a long intracellular half-life, which permits once-daily dosing. Since tenofovir does not interact with the cytochrome P450 pathway, it exhibits minimal drug interactions, with the exception of didanosine. Compared with other reverse transcriptase inhibitors, tenofovir may have advantages in terms of toxicity and medication adherence profiles. Ongoing studies are also analyzing tenofovir's activity against hepatitis B virus.

CONCLUSIONS

Tenofovir has been shown to be active against HIV-1 in combination with other antiretrovirals. The drug's benefit as a single-agent intensifier of highly active antiretroviral therapy in treatment-experienced patients has been established, and preliminary data for treatment-naïve patients are encouraging.

Comparative response of African HIV-1-infected individuals to highly active antiretroviral therapy

OBJECTIVE

Few data exist on the virological response to antiretroviral therapy of individuals infected with African HIV-1 subtypes. Our objective was to compare the response, in our clinic, of African HIV-1-infected patients with their British and European contemporaries treated with the same regimes.

DESIGN

The St Mary's Hospital HIV database was used to identify drug-naive African and European patients starting a highly active antiretroviral therapy (HAART) regimen.

METHODS

HIV-1 subtype was determined by phylogenetic analysis of pol sequences. Kaplan-Meier survival analysis was used to estimate the proportion of patients achieving undetectable viral loads (< 500 copies/ml). The longer-term response to therapy was assessed by changes in CD4 cell counts and viral loads from baseline.

RESULTS

A total of 265 patients were classified as 'European' and 97 as 'African', confirmed by sequence. The time to first undetectable viral load was similar for the two groups (P = 0.9). Although there were no statistically significant differences in the CD4 cell count responses (P = 0.11), there was evidence of an increase in viral load after 9 months for the African group, resulting in a widening viral load gap between the two cohorts; the effect of ethnic group was statistically significant (P < 0.001).

CONCLUSION

The initial virological and immunological responses of the African and European cohorts to HAART were similar; although the longer-term virological response was poorer in the African cohort, which may be related to adherence. On the basis of these findings, there is no justification for withholding HAART from Africa on virological grounds.