Tenofovir: a nucleotide analog for the management of human immunodeficiency virus infection

New Therapies and Strategies to Curb HIV Infections with a Focus on Macrophages and Reservoirs

More than 80 million people worldwide have been infected with the human immunodeficiency virus (HIV). There are now approximately 39 million individuals living with HIV/acquired immunodeficiency syndrome (AIDS). Although treatments against HIV infection are available, AIDS remains a serious disease. Combination antiretroviral therapy (cART), also known as highly active antiretroviral therapy (HAART), consists of treatment with a combination of several antiretroviral drugs that block multiple stages in the virus replication cycle. However, the increasing usage of cART is inevitably associated with the emergence of HIV drug resistance. In addition, the development of persistent cellular reservoirs of latent HIV is a critical obstacle to viral eradication since viral rebound takes place once anti-retroviral therapy (ART) is interrupted. Thus, several efforts are being applied to new generations of drugs, vaccines and new types of cART. In this review, we summarize the antiviral therapies used for the treatment of HIV/AIDS, both as individual agents and as combination therapies, and highlight the role of both macrophages and HIV cellular reservoirs and the most recent clinical studies related to this disease.

Determination of intracellular tenofovir-diphosphate and emtricitabine-triphosphate concentrations in dried blood spots for pre-exposure prophylaxis adherence

OBJECTIVES

We measured the intracellular concentrations of tenofovir-diphosphate (TFV-DP) and emtricitabine-triphosphate (FTC-TP) in dried blood spots (DBS) for pre-exposure prophylaxis (PrEP) adherence using sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS).

METHODS

A total of 191 DBS were obtained from 85 participants who were receiving tenofovir disoproxil fumarate (TDF; 300 mg) and emtricitabine (FTC; 200 mg) as PrEP at the Sexual Health Clinic, National Center for Global Health and Medicine, Tokyo, Japan. DBS punch (3 mm) added to 25 μL of 50% methanol and 400 μL of internal standard solution was used for solid phase extraction. Chromatographic separation was achieved on an Atlantis Premier BEH C18 AX Column (50 mm × 2.1 mm i.d.; particle size 1.7 μm) using gradient elution (flow rate: 0.6 mL/min); injection volume: 7 μL and run time: 5.5 min. Calibration curves for the two drugs were linear in the range 0.05-12.5 ng/punch.

RESULTS

We determined the intracellular TFV-DP and FTC-TP concentrations in 191 DBS obtained from 85 patients administered with TDF and FTC as PrEP. The analytical performance data (calibration curve and QC samples) for all the analytical runs met the acceptance criteria. Intracellular concentrations of TFV-DP and FTC-TP in the DBS remained stable for at least 24 h after oral administration.

CONCLUSIONS

A multiplex LC-MS/MS method was successfully developed for DBS, which can be useful for monitoring the levels of TFV-DP and FTC-TP in individuals receiving PrEP.

Integration of High-Throughput Imaging and Multiparametric Metabolic Profiling Reveals a Mitochondrial Mechanism of Tenofovir Toxicity

Nephrotoxicity is a major cause of kidney disease and failure in drug development, but understanding of cellular mechanisms is limited, highlighting the need for better experimental models and methodological approaches. Most nephrotoxins damage the proximal tubule (PT), causing functional impairment of solute reabsorption and systemic metabolic complications. The antiviral drug tenofovir disoproxil fumarate (TDF) is an archetypal nephrotoxin, inducing mitochondrial abnormalities and urinary solute wasting, for reasons that were previously unclear. Here, we developed an automated, high-throughput imaging pipeline to screen the effects of TDF on solute transport and mitochondrial morphology in human-derived RPTEC/TERT1 cells, and leveraged this to generate realistic models of functional toxicity. By applying multiparametric metabolic profiling-including oxygen consumption measurements, metabolomics, and transcriptomics-we elucidated a highly robust molecular fingerprint of TDF exposure. Crucially, we identified that the active metabolite inhibits complex V (ATP synthase), and that TDF treatment causes rapid, dose-dependent loss of complex V activity and expression. Moreover, we found evidence of complex V suppression in kidney biopsies from humans with TDF toxicity. Thus, we demonstrate an effective and convenient experimental approach to screen for disease relevant functional defects in kidney cells in vitro, and reveal a new paradigm for understanding the pathogenesis of a substantial cause of nephrotoxicity.

HIV pre-exposure prophylaxis adherence test using reverse transcription isothermal amplification inhibition assay

Current HIV antiretroviral therapy (ART) or pre-exposure prophylaxis (PrEP) therapy adherence monitoring relies on either patient self-reported adherence or monitored drug dispensing, which are not reliable. We report a proof-of-concept adherence monitoring assay which directly measures nucleotide reverse transcriptase inhibitor (NRTI) concentration using a reverse transcription isothermal amplification inhibition assay. We measure the concentration of Tenofovir diphosphate (TFV-DP) - an NRTI that functions as a deoxyadenosine triphosphate (dATP) analog and long-term adherence marker for PrEP - by measuring the inhibition of the reverse transcription of an RNA template. The completion or inhibition of reverse transcription is evaluated by recombinase polymerase amplification (RPA), an isothermal nucleic acid amplification assay commonly used for point-of-care diagnostics. We present and validate a model that predicts the amplification probability as a function of dATP and TFV-DP concentrations, nucleotide insertion sites on the RNA template, and RNA template concentration. The model can be used to rationally design and optimize the assay to operate at clinically relevant TFV-DP concentrations. We provide statistical analysis that demonstrates how the assay may be used as a qualitative or semi-quantitative tool for measuring adherence to NRTI drugs and used to support patient compliance. Due to its simple instrumentation and short runtime (<1 hour), this assay has the potential for implementation in low-complexity laboratories or point-of-care settings, which may improve access to ART and PrEP adherence monitoring.

Pharmacokinetics of nucleoside/nucleotide reverse transcriptase inhibitors for the treatment and prevention of HIV infection

INTRODUCTION

Despite dramatic increases in new drugs and regimens, a combination of two nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) remains the backbone of many regimens to treat HIV.

AREA COVERED

This article summarizes the pharmacokinetic characteristics of approved NRTIs that are currently in the international treatment and prevention guidelines.

EXPERT OPINION

Compared to other NRTIs, tenofovir alafenamide fumarate (TAF) is more advantageous in terms of potency and safety. It is therefore a preferred choice in combination with emtricitabine (FTC) in most HIV treatment guidelines. The efficacy of the two-drug combination of NRTI/Integrase strand-transfer inhibitor, i.e. lamivudine/dolutegravir has been approved as an option for initial therapy. This regimen however has some limitations in patients with HBV coinfection. The two NRTI combinations tenofovir disproxil fumarate (TDF)/FTC and TAF/FTC have also been approved for pre-exposure prophylaxis (PrEP). Interestingly, a promising long-acting nucleoside reverse transcriptase translocation inhibitor, islatravir, formulated for implant was well tolerated and remained effective for up to a year, suggesting its potential as a single agent for PrEP. In the next decade, it remains to be seen whether NRTI-based regimens will remain the backbone of preferred ART regimens, or if the treatment will eventually move toward NRTI-sparing regimens to avoid long-term NRTI-toxicity.

Efficacy and safety of telbivudine and tenofovir disoproxil fumarate in preventing hepatitis B vertical transmission: A real-life practice

Mother-to-child transmission (MTCT) is a major obstacle in the elimination of hepatitis B virus (HBV) infection. Telbivudine (LdT) and tenofovir disoproxil fumarate (TDF) are the two most common antiviral medicines for preventing MTCT. However, the efficacy and safety of LdT and TDF in preventing HBV vertical transmission during the second to third trimester have not been compared rigorously. Therefore, we carried out a prospective multicentre cohort study of chronic hepatitis B in mothers with HBV DNA > 10⁶  IU/mL, receiving LdT or TDF during the second to third trimester. Among the 893 mothers enrolled, 857 (LdT/TDF/untreated group (NTx) = 396/325/136) completed consecutive follow-up with 854 infants (LdT/TDF/NTx = 395/323/136). LdT and TDF treatment resulted in a similar decrease of HBV DNA in mothers at delivery. Multivariate analysis indicated that only HBsAg titre at the baseline correlated with viral DNA decrease (P = 0.015). With intention-to-treat analysis, MTCT rates in the LdT, TDF and NTx group were 4.41%, 2.42% and 22.08%, respectively. An increasing vertical transmission rate was found to be closely associated with higher HBsAg titre, 5.32% and 17.65% infection rate was estimated in infants born to mothers with HBsAg > 4 and >5 log₁₀ IU/mL, respectively. No serious side effects were reported in either mothers or infants. LdT and TDF treatments were well tolerated and showed comparable efficacy in reducing MTCT. Higher risk of MTCT was shown in pregnant women with HBsAg > 4 log₁₀ IU/mL.

Drug-Drug Interactions and HIV Therapy: What Should Pharmacists Know?

Drug-interaction issues continue to present a major dilemma for the clinician caring for complex patients such as those infected with HIV. The inherent possibility of a drug interaction is magnified by the multitude of drugs being administered in highly-active antiretroviral therapy (HAART). In addition, other classes of medications are used to alleviate side effects, reduce toxicities associated with HAART, or treat concomitant diseases. The modification of one drug by another substance or drug-drug interaction is the main focus of this article. Drug-drug interactions may result in toxicity, treatment failure, or loss of effectiveness and can significantly affect a patient’s clinical outcome. An understanding of the fundamental mechanisms of HIV drug-drug interactions may allow for the early detection or avoidance of troublesome regimens and prudent management if they develop. Although HIV drug interactions are usually thought of as detrimental, resulting in a loss of therapeutic effect or toxicity, some drug interactions such as ritonavir boosted protease inhibitor–based antiretroviral treatments are beneficial and are commonly used in clinical practice. Therefore, pharmacists need to understand drug interaction mechanisms, remember key drug interactions, and vigilantly monitor patients for potential complications.

Efficacy of telbivudine with conditional tenofovir intensification in patients with chronic hepatitis B: results from the 2-year roadmap strategy

BACKGROUND

A 2-year roadmap study was conducted to evaluate the efficacy and safety of tenofovir intensification at Week 24 in patients with chronic hepatitis B (CHB) receiving telbivudine.

SCOPE

A prospective multicenter study was conducted in treatment-naive patients with hepatitis B e antigen (HBeAg)-positive CHB. All patients received telbivudine (600 mg/day) until Week 24. Thereafter, patients with detectable hepatitis B virus (HBV) DNA (≥300 copies/mL) were administered tenofovir (300 mg/day) plus telbivudine, and patients with undetectable HBV DNA continued telbivudine monotherapy until Week 104. The primary endpoint was the proportion of patients with undetectable HBV DNA (<300 copies/mL) at Weeks 52 and 104.

FINDINGS

A total of 105 patients were enrolled in the trial, of which 100 were eligible for efficacy analysis. Undetectable HBV DNA levels were observed at Week 24 in 55 patients who continued on with telbivudine monotherapy. The remaining 45 patients with detectable HBV DNA received tenofovir add-on therapy. With monotherapy, 100% (55/55) and 94.5% (52/55) of patients achieved HBV DNA <300 copies/mL at Weeks 52 and 104, respectively; the corresponding values for patients with add-on therapy were 84.4% (38/45) and 93.3% (42/45). Overall, undetectable HBV DNA (<300 copies/mL) was found in 93% (93/100) and 94% (94/100) of patients at Weeks 52 and 104, respectively. HBeAg seroconversion rate was 44.4% (44/99) at Week 104 for the overall patient population. One patient in the monotherapy group and six in the intensification group demonstrated HBsAg clearance at Week 104. HBsAg seroconversion was observed in four patients at Week 104, all belonged to the tenofovir intensification group. Eight patients sustained HBsAg loss during a posttreatment follow-up period of 16 weeks. Alanine aminotransferase (ALT) normalization was constant in the telbivudine monotherapy group, whereas a progressive improvement was observed in the tenofovir intensification group. Two patients in the monotherapy and none in the intensification group experienced viral breakthrough by Week 104. There were no reports of myopathy in either group. The mean changes in estimated glomerular filtration rate (eGFR), estimated using the Modification of Diet in Renal Disease (MDRD) formula, from baseline to Week 104 were +6.145 mL/min/1.73 m(2) (p=0.0230) and +7.954 mL/min/1.73 m(2) (p=0.0154) in the telbivudine monotherapy and tenofovir intensification groups, respectively. The incidence of serious AEs was four in the telbivudine monotherapy and two in the tenofovir intensification group. The main limitation of this study was limited sample size, which made the power of the observation low, and the absence of a comparative subgroup to assess the progression of patients with detectable HBV DNA without treatment intensification.

CONCLUSIONS

Data from this 2-year roadmap study confirmed that telbivudine with add-on tenofovir was effective and well tolerated in patients with CHB. Telbivudine was associated with an improvement in eGFR from baseline in both the groups.

Hepatic and Renal Safety Profile of Tenofovir in HIV-Infected Patients with Hepatitis C, Including Patients on Interferon Plus Ribavirin

The liver safety of tenofovir (TDF) was investigated in 142 HIV+ patients exposed to the drug for longer than 12 months. No evidence of liver enzyme elevations were seen, even in 66 patients with chronic hepatitis C virus (HCV) co-infection. Given that TDF is an adenosine analogue, like didanosine, exposure to ribavirin might increase intracellular phosphorylated TDF metabolites, which could result in a higher risk of nephrotoxicity. Signs of tubular dysfunction in blood or urine were not recognized in 17 HCV-HIV co-infected patients exposed to TDF during interferon plus ribavirin therapy.

A consensus statement on the renal monitoring of Australian patients receiving tenofovir based antiviral therapy for HIV/HBV infection

A number of antiviral agents used against Human Immunodeficiency Virus (HIV) infection and hepatitis B virus (HBV) mono or co-infection have been associated with real nephrotoxicity (including tenofovir disoproxil fumarate (TDF), atazanavir, indinavir and lopinavir) or apparent changes in renal function (e.g. cobicistat, ritonavir, rilpivirine and dolutegravir). Patients with HIV are at higher risk of acute and chronic renal dysfunction, so baseline assessment and ongoing monitoring of renal function is an important part of routine management of patients with HIV.

Given the paucity of evidence in this area, we sought to establish a consensus view on how routine monitoring could be performed in Australian patients on ART regimens, especially those involving TDF. A group of nephrologists and prescribers (an HIV physician and a hepatologist) were assembled by Gilead to discuss practical and reasonable renal management strategies for patients particularly those on TDF-based combination regimens (in the case of those with HIV-infection) or on TDF-monotherapy (in the case of HBV-mono infection). The group considered which investigations should be performed as part of routine practice, their frequency, and when specialist renal referral is warranted. The algorithm presented suggests testing for serum creatinine along with plasma phosphate and an assessment of urinary protein (rather than albumin) and glucose.

Here we advocate baseline tests of renal function at initiation of therapy. If creatinine excretion inhibitors (e.g. cobicistat or rilpivirine) are used as part of the ART regimen, we suggest creatinine is rechecked at 4 weeks and this value used as the new baseline. Repeat testing is suggested at 3-monthly intervals for a year and then at least yearly thereafter if no abnormalities are detected. In patients with abnormal baseline results, renal function assessment should be performed at least 6 monthly. In HBV mono-infected patients advocate that a similar testing protocol may be logical.

Efficacy and safety of tenofovir disoproxil fumarate in pregnancy to prevent perinatal transmission of hepatitis B virus

BACKGROUND & AIMS

Perinatal transmission of hepatitis B virus still occurs despite immunoprophylaxis in approximately 9% of children from highly viraemic mothers. Antiviral therapy in this setting has been suggested, however with limited evidence to direct agent choice.

METHODS

We conducted a multi-centre, prospective, opt-in observational study of antiviral safety and efficacy in pregnant women with high viral load (>7 log IU/ml); lamivudine was used from 2007 to 2010 and tenofovir disoproxil fumarate (TDF) from late 2010. Outcomes of treated and untreated cohorts were compared.

RESULTS

120 women with 130 pregnancies used TDF (58), lamivudine (52 including four who switched due to TDF intolerance) and no therapy (20). 96% were HBeAg positive, with baseline viral load mean 7.8 log IU/ml (±0.72) and ALT median 25 U/L (18.75-33). Duration of antiviral theraphy before birth was mean 58 days (±19) TDF and 53 (±14) lamivudine. Viral load declined by 3.64 log IU/ml (±0.9) TDF and 2.81 log IU/ml (±1.33) lamivudine. Virologic failure (birth viral load >7 IU/ml) occurred in 3% and 18% respectively. Congenital abnormality rate and neonatal growth centiles were similar across cohorts. Perinatal transmission reduced significantly to 2% and 0% in TDF and lamivudine cohorts, compared with 20% in untreated.

CONCLUSIONS

TDF in this setting is safe, effective and more potent than lamivudine. Antiviral therapy did not adversely impact obstetric or infant parameters. More TDF intolerance occurred than expected. Perinatal transmission was significantly reduced in antiviral therapy cohorts.

Evaluation of atazanavir and darunavir interactions with lipids for developing pH-responsive anti-HIV drug combination nanoparticles

We evaluated two human immunodeficiency virus (HIV) protease inhibitors, atazanavir (ATV) and darunavir (DRV), for pH-dependent solubility, lipid binding, and drug release from lipid nanoparticles (LNPs). Both ATV and DRV incorporated into LNPs composed of pegylated and non-pegylated phospholipids with nearly 100% efficiency, but only ATV-LNPs formed stable lipid-drug particles and exhibited pH-dependent drug release. DRV-LNPs were unstable and formed mixed micelles at low drug-lipid concentrations, and thus are not suitable for lipid-drug particle development. When ATV-LNPs were prepared with ritonavir (RTV), a metabolic and cellular membrane exporter inhibitor, and tenofovir (TFV), an HIV reverse-transcriptase inhibitor, stable, scalable, and reproducible anti-HIV drug combination LNPs were produced. Drug incorporation efficiencies of 85.5 ± 8.2, 85.1 ± 7.1, and 6.1 ± 0.8% for ATV, RTV, and TFV, respectively, were achieved. Preliminary primate pharmacokinetic studies with these pH-responsive anti-HIV drug combination LNPs administered subcutaneously produced detectable plasma concentrations that lasted for 7 days for all three drugs. These anti-HIV LNPs could be developed as a long-acting targeted antiretroviral therapy.

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.

Systemic and Renal Pharmacokinetics of Adefovir and Tenofovir Upon Coadministration

Adefovir and tenofovir are nucleotide analogs that undergo renal secretion by the human renal organic anion transporter. The pharmacokinetics of tenofovir and adefovir following the administration of tenofovir disoproxil fumarate and adefovir dipivoxil alone and together were determined in 24 healthy subjects in an 8-day, open-label, fixed-sequence study. Subjects received oral doses of adefovir dipivoxil on days 1 and 8 and oral doses of tenofovir disoproxil fumarate on days 2 to 8. Pharmacokinetic sampling was performed on days 1, 7, and 8. The plasma pharmacokinetics of tenofovir and adefovir were unaltered upon coadministration. Furthermore, the renal clearances (CLrenal) of tenofovir and adefovir were unaffected by their coadministration. The plasma Cmax values of tenofovir and adefovir were 33-fold and 340-fold lower than their Km values for the human renal organic anion transporter. These results demonstrate that coadministration of tenofovir disoproxil fumarate and adefovir dipivoxil does not result in substantial changes to their individual pharmacokinetic profiles.

Pharmacokinetics and topical vaginal effects of two tenofovir gels in rabbits

Tenofovir (TFV) 1% gel has proven effective in preclinical and clinical studies in preventing sexual transmission of HIV-1. The impact of changing the current gel formulation to reduce its osmolality was evaluated using pharmacokinetic assessments and local tissue effects in the rabbit. Following vaginal administration of TFV 1% gel and reduced-glycerin TFV 1% gel, TFV was measured in plasma, vaginal tissues, vaginal fluids, and iliac lymph nodes. After a single dose, plasma C(max) and AUC(0-4h) were significantly higher in the TFV 1% gel group compared with the reduced-glycerin TFV 1% gel group. After 14 days of once-daily dosing, differences in these parameters were insignificant. Vaginal fluid concentrations were ∼100 μg/ml following the first dose and up to a mean of about 500 μg/ml after 14 once-daily doses. Mean (and median) cranial TFV tissue concentrations were generally in excess of 100 μg/g following a single dose and 14 once-daily doses of both gels; concentrations in the caudal vaginal tissues were comparatively lower, although in nearly all cases mean values exceeded 10 μg/g. Treatment of tissues with phosphatase to liberate TFV from its diphosphate and monophosphate metabolites increased recovery of TFV by 60-120%. Median TFV concentrations in iliac lymph nodes ranged from 44 ng/g to 196 ng/g; differences between iliac lymph node TFV concentrations following dosing of the two gels were insignificant. There were no differences observed in histological evaluation in the cranial vagina following 14 days of once-daily dosing of either gel. There was an apparent impact of TFV on rabbit vaginal epithelium (increased secretory depletion and increased cellular vacuolization) independent of formulation. These data indicate that the reduced-glycerin TFV 1% gel may be a suitable alternative to TFV 1% gel.

Future strategies in microbicide development

The reduction in human immunodeficiency virus (HIV) infection in women demonstrated by pericoital use of tenofovir gel has encouraged the continued development of microbicides. Novel approaches include new ways to deliver tenofovir, as well as products that contain different antiretroviral drugs, either as single agents or as combinations of antiretroviral drugs. Indeed, emphasis has renewed on the development of multipurpose prevention technologies, products designed to address multiple sexually transmitted infections. Dual-purpose contraceptive antiretroviral products are also being designed to prevent HIV and pregnancy. Since consistent and correct use of these products will be critical to their effectiveness, the active pharmaceutical ingredients must be delivered in acceptable vaginal dosage forms, such as gels, films and sustained-release vaginal rings. The development of different dosage forms will help ensure that women can find a method to protect themselves from HIV, pregnancy, and potentially other sexually transmitted infections.

Simultaneous delivery of tenofovir and acyclovir via an intravaginal ring

Vaginal microbicides may play an important role in protecting women from HIV infection. A strong synergy between HSV and HIV has been observed, and epidemiological studies demonstrate that HSV infection increases the risk of HIV acquisition. Incorporation of the antiretroviral tenofovir (TFV) along with the antiherpetic acyclovir (ACV) into combination intravaginal rings (IVRs) for sustained mucosal delivery of both compounds could lead to increased microbicide product adherence and efficacy compared with conventional vaginal formulations. A novel, dual-protection "pod IVR" platform developed in-house and delivering ACV and TFV was evaluated in rabbit and sheep models. The devices were safe and exhibited sustained release of both drugs independently and at controlled rates over the 28-day studies. Daily release rates were estimated based on residual drug content of the used devices: rabbits, 343 ± 335 μg day(-1) (ACV) and 321 ± 207 μg day(-1) (TFV); sheep, 174 ± 14 μg day(-1) (ACV) and 185 ± 34 μg day(-1) (TFV). Mean drug levels in sheep vaginal samples were as follows: secretions, 5.25 ± 7.31 μg ml(-1) (ACV) and 20.6 ± 16.2 μg ml(-1) (TFV); cervicovaginal lavage fluid, 118 ± 113 ng ml(-1) (ACV) and 191 ± 125 ng ml(-1) (TFV); tissue, 173 ng g(-1) (ACV) and 93 ng g(-1) (TFV). An in vitro-in vivo correlation was established for both drugs and will allow the development of future formulations delivering target levels for prophylaxis and therapy. These data suggest that the IVR based on the pod design has potential in the prevention of transmission of HIV-1 and other sexually transmitted pathogens.

Antiretroviral pharmacology: special issues regarding pregnant women and neonates

Antiretrovirals may be used in pregnant women infected with the HIV and their newborns both for treatment of maternal HIV disease and for prevention of mother-to-child transmission of HIV. More than 25 antiretroviral agents in 5 classes have been approved, with new drugs and classes in development. This article reviews current knowledge of the pharmacology of these drugs during pregnancy and in the newborn period, highlighting those pharmacologic issues critical to the safe and effective use of antiretrovirals in these populations.

Renal impairment after switching from stavudine/lamivudine to tenofovir/lamivudine in NNRTI-based antiretroviral regimens

BACKGROUND

During stavudine phase-out plan in developing countries, tenofovir is used to substitute stavudine. However, knowledge regarding whether there is any difference of the frequency of renal injury between tenofovir/lamivudine/efavirenz and tenofovir/lamivudine/nevirapine is lacking.

METHODS

This prospective study was conducted among HIV-infected patients who were switched NRTI from stavudine/lamivudine to tenofovir/lamivudine in efavirenz-based (EFV group) and nevirapine-based regimen (NVP group) after two years of an ongoing randomized trial. All patients were assessed for serum phosphorus, uric acid, creatinine, estimated glomerular filtration rate (eGFR), and urinalysis at time of switching, 12 and 24 weeks.

RESULTS

Of 62 patients, 28 were in EFV group and 34 were in NVP group. Baseline characteristics and eGFR were not different between two groups. At 12 weeks, comparing mean ± SD measures between EFV group and NVP group were: phosphorus of 3.16 ± 0.53 vs. 2.81 ± 0.42 mg/dL (P = 0.005), %patients with proteinuria were 15% vs. 38% (P = 0.050). At 24 weeks, mean ± SD phosphorus and median (IQR) eGFR between the corresponding groups were 3.26 ± 0.78 vs. 2.84 ± 0.47 mg/dL (P = 0.011) and 110 (99-121) vs. 98 (83-112) mL/min (P = 0.008). In NVP group, comparing week 12 to time of switching, there was a decrement of phosphorus (P = 0.007) and eGFR (P = 0.034). By multivariate analysis, 'receiving nevirapine', 'old age' and 'low baseline serum phosphorus' were associated with hypophosphatemia at 24 weeks (P < 0.05). Receiving nevirapine and low baseline eGFR were associated with lower eGFR at 24 weeks (P < 0.05).

CONCLUSION

The frequency of tenofovir-associated renal impairment was higher in patients receiving tenofovir/lamivudine/nevirapine compared to tenofovir/lamivudine/efavirenz. Further studies regarding patho-physiology are warranted.

Aryloxy phosphoramidate triesters: a technology for delivering monophosphorylated nucleosides and sugars into cells

Prodrug technologies aimed at delivering nucleoside monophosphates into cells (protides) have proved to be effective in improving the therapeutic potential of antiviral and anticancer nucleosides. In these cases, the nucleoside monophosphates are delivered into the cell, where they may then be further converted (phosphorylated) to their active species. Herein, we describe one of these technologies developed in our laboratories, known as the phosphoramidate protide method. In this approach, the charges of the phosphate group are fully masked to provide efficient passive cell-membrane penetration. Upon entering the cell, the masking groups are enzymatically cleaved to release the phosphorylated biomolecule. The application of this technology to various therapeutic nucleosides has resulted in improved antiviral and anticancer activities, and in some cases it has transformed inactive nucleosides to active ones. Additionally, the phosphoramidate technology has also been applied to numerous antiviral nucleoside phosphonates, and has resulted in at least three phosphoramidate-based nucleotides progressing to clinical investigations. Furthermore, the phosphoramidate technology has been recently applied to sugars (mainly glucosamine) in order to improve their therapeutic potential. The development of the phosphoramidate technology, mechanism of action and the application of the technology to various monophosphorylated nucleosides and sugars will be reviewed.

The effects of cotrimoxazole or tenofovir co-administration on the pharmacokinetics of maraviroc in healthy volunteers

AIMS

To assess the potential of cotrimoxazole and tenofovir, drugs which are inhibitors and/or substrates of renal transporters, to alter the pharmacokinetic profile of maraviroc.

METHODS

Two randomized, placebo-controlled, two-way crossover studies were conducted in healthy male and female subjects. In study 1, 16 subjects, aged 18-45 years, received maraviroc (300 mg b.i.d.) with and without cotrimoxazole (960 mg b.i.d.; 160 mg trimethoprim and 800 mg sulfamethoxazole). In study 2, 12 subjects, aged 21-45 years, received maraviroc (300 mg b.i.d.) with and without tenofovir (300 mg q.d.). For study 1, blood was collected predose and on days 1-7. In study 2, blood was collected predose, on day 1 and days 3-7. In both studies, blood was collected at intervals up to 12 h postdose on day 7. Urine was collected on day 7, 0-12 h post morning dose. Blood and urine were analysed for maraviroc using liquid chromatography/tandem mass spectrometry.

RESULTS

The geometric mean ratios for C(max) and AUC(12) were 119% and 111%, respectively, for maraviroc plus cotrimoxazole and 104% and 103%, respectively, for maraviroc plus tenofovir, compared with maraviroc plus placebo. Renal clearance of maraviroc plus placebo was 8.3 l h(-1) and 8.5 l h(-1) and was 7.8 l h(-1) for maraviroc plus cotrimoxazole and maraviroc plus tenofovir. There were no serious or severe adverse events or any clinically significant changes in laboratory tests, blood pressure, or electrocardiograms.

CONCLUSIONS

Neither cotrimoxazole nor tenofovir caused a clinically significant effect on the pharmacokinetics of maraviroc. Maraviroc 300 mg b.i.d. was well tolerated when co-administered with either cotrimoxazole or tenofovir.

Activation of 9-[(R)-2-[[(S)-[[(S)-1-(Isopropoxycarbonyl)ethyl]amino] phenoxyphosphinyl]-methoxy]propyl]adenine (GS-7340) and other tenofovir phosphonoamidate prodrugs by human proteases

9-[(R)-2-[[(S)-[[(S)-1-(Isopropoxycarbonyl)ethyl]amino] phenoxyphosphinyl]-methoxy]propyl]adenine (GS-7340) is an isopropylalaninyl phenyl ester prodrug of the nucleotide HIV reverse transcriptase inhibitor tenofovir (TFV; 9-[(2-phosphonomethoxy)propyl]adenine) exhibiting potent anti-HIV activity and enhanced ability to deliver parent TFV into peripheral blood mononuclear cells (PBMCs) and other lymphatic tissues in vivo. The present study focuses on the intracellular metabolism of GS-7340 and its activation by a variety of cellular hydrolytic enzymes. Incubation of human PBMCs in the presence of GS-7340 indicates that the prodrug is hydrolyzed slightly faster to an intermediate TFV-alanine conjugate (TFV-Ala) in quiescent PBMCs compared with activated cells (0.21 versus 0.16 pmol/min/10(6) cells). In contrast, the conversion of TFV-Ala to TFV and subsequent phosphorylation to TFV-diphosphate occur more rapidly in activated PBMCs. The activity of GS-7340 hydrolase producing TFV-Ala in PBMCs is primarily localized in lysosomes and is sensitive to inhibitors of serine hydrolases. Cathepsin A, a lysosomal serine protease has recently been identified as the primary enzyme activating GS-7340 in human PBMCs. Results from the present study indicate that in addition to cathepsin A, a variety of serine and cysteine proteases cleave GS-7340 and other phosphonoamidate prodrugs of TFV. The substrate preferences displayed by these enzymes toward TFV amidate prodrugs are nearly identical to their preferences displayed against oligopeptide substrates, indicating that GS-7340 and other phosphonoamidate derivatives of TFV should be considered peptidomimetic prodrugs of TFV.

Steady-state pharmacokinetics of emtricitabine and tenofovir disoproxil fumarate administered alone and in combination in healthy volunteers

The approved antiretroviral drugs, emtricitabine and tenofovir disoproxil fumarate, were considered good candidates for a fixed-dose combination product that could be administered as a single pill once daily (qd), thereby simplifying existing treatment regimens and promoting patient adherence. As both drugs are extensively renally eliminated, a randomized, 3-way crossover study was conducted in 19 healthy volunteers to formally evaluate the potential pharmacokinetic interaction when the drugs are administered alone and together (ie, 200 mg emtricitabine qd for 7 days, 300 mg tenofovir disoproxil fumarate qd for 7 days, and 200 mg emtricitabine plus 300 mg tenofovir disoproxil fumarate qd for 7 days) with no washout between treatments. Steady-state pharmacokinetic parameters (AUC(tau), C(max), and C(min)) of emtricitabine and tenofovir (as tenofovir disoproxil fumarate) in combination were essentially equivalent versus each drug alone, providing a pharmacokinetic rationale for combining these products in emtricitabine/tenofovir disoproxil fumarate fixed-dose tablets.

Evaluation of hypophosphataemia in tenofovir disoproxil fumarate (TDF)-exposed and TDF-unexposed HIV-infected out-patients receiving highly active antiretroviral therapy

OBJECTIVES

Cases of hypophosphataemia (often coincident with renal dysfunction) have been reported in HIV-infected patients taking tenofovir disoproxil fumarate (TDF), but randomized placebo-controlled trials of HIV-infected persons with normal baseline renal function have found a comparable incidence of hypophosphataemia in the TDF and placebo groups. We assessed the incidence of grade 2 and higher hypophosphataemia in the HIV Outpatient Study (HOPS).

METHODS

We analysed a prospective cohort of patients who initiated either a TDF-containing highly active antiretroviral therapy (HAART) regimen [TDF-exposed (TDF+) group; n = 165] or a TDF-sparing HAART regimen [TDF-unexposed (TDF-) group; n = 90], and who had normal baseline phosphate and creatinine values.

RESULTS

The TDF+ and TDF- groups had comparable median follow-up times (10.9 vs 8.8 months, respectively; P = 0.18) and number of phosphate measurements (median = 3 for both) and were similar on most clinical and demographic factors. During follow up, 12.7% of TDF+vs 6.7% of TDF-patients developed grade 2 hypophosphataemia (2.0-2.4 mg/dL), and 2.4% of TDF+ patients vs 0% of TDF-patients developed grade 3 hypophosphataemia (1.0-1.9 mg/dL); none developed grade 4 hypophosphataemia (<1.0 mg/dL). The incidence of grade 2 or higher hypophosphataemia was 16.7 per 100 person-years among TDF+ patients vs 8.0 per 100 person-years among TDF-patients (P = 0.11).

CONCLUSIONS

The incidence of hypophosphataemia was somewhat elevated in HOPS patients who took TDF-containing HAART compared with those who took TDF-sparing HAART during the first 1 to 2 years of observation, but the difference was not statistically significant. Longer follow-up of a larger population is needed to determine if this trend towards an association achieves statistical significance and to evaluate the clinical consequences of hypophosphataemia.

Cathepsin A is the major hydrolase catalyzing the intracellular hydrolysis of the antiretroviral nucleotide phosphonoamidate prodrugs GS-7340 and GS-9131

GS-7340 and GS-9131 {9-[(R)-2-[[(S)-[[(S)-1-(isopropoxycarbonyl)ethyl]amino]phenoxyphosphinyl]methoxy]-propyl]adenine and 9-(R)-4'-(R)-[[[(S)-1-[(ethoxycarbonyl)ethyl]amino]phenoxyphosphinyl]methoxy]-2'-fluoro-1'-furanyladenine, respectively} are novel alkylalaninyl phenyl ester prodrugs of tenofovir {9-R-[(2-phosphonomethoxy)propyl]adenine} (TFV) and a cyclic nucleotide analog, GS-9148 (phosphonomethoxy-2'-fluoro-2', 3'-dideoxydidehydroadenosine), respectively. Both prodrugs exhibit potent antiretroviral activity against both wild-type and drug-resistant human immunodeficiency virus type 1 strains and excellent in vivo pharmacokinetic properties. In this study, the main enzymatic activity responsible for the initial step in the intracellular activation of GS-7340 and GS-9131 was isolated from human peripheral blood mononuclear cells and identified as lysosomal carboxypeptidase A (cathepsin A [CatA]; EC 3.4.16.5). Biochemical properties of the purified hydrolase (native complex and catalytic subunit molecular masses of 100 and 29 kDa, respectively; isoelectric point [pI] of 5.5) matched those of CatA. Recombinant CatA and the isolated prodrug hydrolase displayed identical susceptibilities to inhibitors and identical substrate preferences towards a panel of tenofovir phosphonoamidate prodrugs. Incubation of both enzymes with 14C-labeled GS-7340 or [3H]difluorophosphonate resulted in the covalent labeling of identical 29-kDa catalytic subunits. Finally, following a 4-h incubation with GS-7340 and GS-9131, the intracellular concentrations of prodrug metabolites detected in CatA-negative fibroblasts were approximately 7.5- and 3-fold lower, respectively, than those detected in normal control fibroblasts. Collectively, these data demonstrate the key role of CatA in the intracellular activation of nucleotide phosphonoamidate prodrugs and open new possibilities for further improvement of this important class of antiviral prodrugs.

HIV pharmacology: barriers to the eradication of HIV from the CNS

Total eradication of HIV-1 is not yet achievable, in part because reservoirs of latent HIV-1 can develop within lymphoid tissue, the testes, and the central nervous system (CNS). The presence of HIV-1 in the CNS is clinically significant because of its association with the development of HIV dementia, which occurs in up to one fifth of untreated patients. This review summarizes current theory regarding HIV-1 infection within the CNS, describes physiologic and pharmacologic factors limiting CNS penetration of antiretroviral drugs used to treat HIV-1 infection, and reviews current treatment of CNS HIV-1 infection and HIV encephalopathy.

The development of hypophosphataemic osteomalacia with myopathy in two patients with HIV infection receiving tenofovir therapy

We report two cases in which osteomalacia developed in patients on tenofovir-containing highly active antiretroviral therapy (HAART) in the context of Fanconi syndrome with hypophosphataemia. Bone pain was the presenting feature and myopathy followed in one case. Disability was reversed with withdrawal of the drug and with mineral supplementation. The cases highlight the importance of considering the diagnosis of osteomalacia in patients treated with tenofovir. A possible association with incipient acute renal failure, particularly during nonsteroidal anti-inflammatory drug (NSAID) use, needs further investigation.

[Assessment of renal abnormalities in 107 HIV patients treated with tenofovir]

OBJECTIVES

The objectives of our study were to assess frequency, severity and outcome of renal abnormalities, as well as to determine the risk of developing hypophosphataemia in HIV-infected patients receiving tenofovir.

METHODS

An observational study was conducted in real-life conditions, during a 6-month period, in 107 HIV patients receiving tenofovir.

RESULTS

Mild-to-moderate hypophosphataemia (<0.77 mmol/L) occurred during follow-up, at least once in 43% of patients and at least twice in 27%. Antiretroviral therapy including ritonavir + lopinavir was significantly associated with the occurrence of hypophosphataemia (relative risk = 2.6; p = 0.03). Frequency of abnormal proteinuria was 22%.

CONCLUSION

Creatinine clearance, phosphataemia, proteinuria and glycosuria should be closely monitored in patients receiving tenofovir therapy.

Pharmacokinetics of saquinavir hard gel/ritonavir (1000/100 mg twice daily) when administered with tenofovir diproxil fumarate in HIV-1-infected subjects

AIMS

To investigate whether the administration of tenofovir diproxil fumarate 300 mg once daily alters the plasma pharmacokinetics of the saquinavir hard gel/ritonavir combination in HIV-1 infected individuals.

METHODS

On day 1, 12 h pharmacokinetic profiles for saquinavir/ritonavir (1000/100 mg given twice daily) were obtained for 18 subjects. All subjects were receiving ongoing treatment with a saquinavir/ritonavir-containing regimen. Tenofovir diproxil fumarate 300 mg given once daily was then added to the regimen and blood sampling was repeated at days 3 and 14. Saquinavir and ritonavir concentrations were measured by HPLC-MS/MS, and tenofovir concentrations by HPLC with UV detection.

RESULTS

Following the addition of tenofovir diproxil fumarate to the regimen, saquinavir and ritonavir plasma concentrations were not significantly different compared with day 1. Thus the geometric mean ratios (95% confidence intervals) for the area under the concentration-time curve were 1.16 (0.97, 1.59) and 0.99 (0.87, 1.30) for saquinavir and 1.05 (0.92, 1.28) and 1.08 (0.97, 1.30) for ritonavir, on days 3 and 14, respectively.

CONCLUSIONS

Tenofovir diproxil fumarate did not alter the pharmacokinetics of saquinavir hard gel/ritonavir.

[Recent progress in anti-HIM-1 research]

Establishment of highly active antiretroviral therapy (HAART) has brought about dramatic improvement of the prognosis of HIV-1 infection. On the other hand, several drawbacks associated with long-term HARRT have been demonstrated. Among them, emergence of drug-resistant viruses is a serious problem; therefore compounds with novel mechanisms of action have been investigated to overcome the problem. Novel reverse transcriptase inhibitors (RTIs) and protease inhibitors (PIs) recently approved for clinical use are effective against existing resistant strains by once daily administration. In addition, the virus entry (fusion) inhibitor has also been licensed. Since this compound targets a molecule other than reverse transcriptase and protease for inhibition of HIV-1 replication, it is active against HIV-1 highly resistant to RTIs and PIs. Furthermore, clinical trials with CCR 5 (coreceptor of HIV-1) antagonists are in progress, and inhibitors of integrase, HIV-1 gene expression, and virion assembly have been identified.

Effect of Tenofovir Disoproxil Fumarate on the Pharmacokinetics and Pharmacodynamics of Total, R-, and S-Methadone

STUDY OBJECTIVE

To evaluate the potential effect of tenofovir disoproxil fumarate (DF) on the pharmacokinetics of methadone.

DESIGN

Phase I, open-label, fixed-sequence, pharmacokinetic drug-drug interaction study.

SETTING

Clinical research center.

SUBJECTS

Fourteen volunteers receiving stable methadone maintenance therapy who were not infected with the human immunodeficiency virus.

INTERVENTION

Tenofovir DF was added to the subjects' methadone regimens.

MEASUREMENTS AND MAIN RESULTS

The pharmacokinetics of total, R-, and S-methadone were evaluated at baseline and after 2 weeks of daily tenofovir DF coadministration with a light meal. Steady-state tenofovir DF pharmacokinetics were evaluated at day 15. Bioequivalence testing was conducted of total, R-, and S-methadone area under the serum or plasma concentration-time curve during the 24-hour dosing interval at steady state (AUCss) and maximum concentration in serum or plasma (Cmax). Subjects were evaluated for changes in methadone pharmacodynamics by the Short Opiate Withdrawal Scale (SOWS) and pupillary diameter measurements at frequent intervals. Coadministration with tenofovir DF did not affect the pharmacokinetics of methadone. Geometric mean R-methadone systemic exposures, AUCss and Cmax, differed by 5% or less when methadone was dosed with tenofovir DF. Similar results were observed for S-methadone and for total methadone. Both AUCss and Cmax met the strict criteria for bioequivalence between the two study periods for total, R-, and S-methadone, indicating a lack of drug interaction when tenofovir DF was coadministered with methadone. No significant changes in SOWS scores or pupillary diameter measurements occurred, and no notable clinical adverse events were reported.

CONCLUSION

Tenofovir DF pharmacokinetics were comparable to previously reported values of tenofovir DF in HIV-infected patients. Coadministration of methadone with tenofovir DF did not alter the pharmacokinetics or pharmacodynamics of total, R-, or S-methadone. Tenofovir DF may be given as part of a once-daily antiretroviral regimen in patients receiving methadone maintenance therapy.

Improvement of dyslipidemia in patients switching from stavudine to tenofovir: preliminary results

In a prospective, multicentre, switch study to identify the most frequently occurring nucleoside reverse transcriptase inhibitor (NRTI)-associated toxicities that cause NRTI withdrawal in virologically suppressed HIV-infected patients, among those who underwent stavudine substitution by tenofovir, 271 had hypertriglyceridemia and 193 had hypercholesterolemia. After 12 weeks of switching from stavudine to tenofovir, triglyceride and cholesterol levels showed significant de-creases, which suggests that such a switch may reverse, at least partly, stavudine-associated dyslipidaemia.

Renal Tubular Dysfunction Associated With Tenofovir Therapy

We describe 7 cases of renal tubular injury in HIV-infected patients receiving an antiretroviral regimen containing tenofovir. Our patients (5 women and 2 men) developed renal tubular dysfunction, with hypophosphatemia, normoglycemic glycosuria, proteinuria, and decrease of creatinine clearance. The first biologic signs of renal toxicity were observed after duration of tenofovir treatment from 5 weeks to 16 months, and they resolved less than 4 months after discontinuation of tenofovir. Six patients had a low body weight (<60 kg). Five patients received low doses of ritonavir, and 1 received didanosine. In 5 patients, the signs resolved with the discontinuation of only the tenofovir. A renal biopsy performed in 1 patient was consistent with tubulointerstitial injury. Proximal tubulopathy appears to be a rare adverse effect of long-term tenofovir therapy. In patients with low weight or mild preexisting renal impairment, regular monitoring of tubulopathy markers could lead to early detection of this dysfunction.