Roundtable report: importance of antiretroviral drug concentrations in sanctuary sites and viral reservoirs

Uptake of tenofovir and emtricitabine into non-monocytic female genital tract cells with and without hormonal contraceptives

Background

Pre-exposure prophylaxis is becoming a strategic component used to control the human immunodeficiency virus (HIV-1) epidemic. The goal of this study was to characterize intracellular uptake of tenofovir and emtricitabine using five surrogate cell lines of the female genital tract and determine whether exogenous hormones influence their uptake.

Methods

Surrogate cell lines, ie, THP-1 (representing macrophages), BC-3 (CD8+), Ect1/E6E7 (squamous epithelial), HeLa (CD4+), and TF-1 (dendritic), were incubated for one hour with tenofovir and emtricitabine to assess uptake. In separate experiments, ethinyl estradiol (EE) and etonogestrel (ET) individually and together (EE/ET) were added prior to, simultaneously, and after incubation. Intracellular phosphorylated tenofovir and emtricitabine were quantified using validated tandem mass spectrometry methods.

Results

HeLa and Ect1/E6E7 cells showed significantly increased uptake relative to THP-1 controls for both antiretrovirals. Individually, ethinyl estradiol and etonogestrel significantly altered antiretroviral uptake across all cell lines, except Ect1/E6E7 for tenofovir and HeLa for emtricitabine. Cellular uptake of tenofovir and emtricitabine in BC-3 and TF-1 cells were significantly lower when dosed one hour prior to EE/ET administration compared with each antiretroviral administered in the absence of EE/ET (tenofovir, 80 versus 470 fmol/10⁶ for BC-3 and 77 versus 506 fmol/10⁶ cells for TF-1; emtricitabine, 36 versus 12 fmol/10⁶ for BC-3 and 75 versus 5 fmol/10⁶ cells for TF-1; P < 0.01 for each).

Conclusion

These data suggest that intracellular uptake of tenofovir and emtricitabine within the female genital tract varies by cell type and in the presence of hormonal contraceptives. The potential clinical implications of these findings should be further evaluated in vivo.

Low cerebrospinal fluid concentrations of the nucleotide HIV reverse transcriptase inhibitor, tenofovir

BACKGROUND

Tenofovir is a nucleotide HIV reverse transcriptase inhibitor whose chemical properties suggest that it may not penetrate into the central nervous system in therapeutic concentrations. The study's objective was to determine tenofovir's penetration into cerebrospinal fluid (CSF).

METHODS

CNS HIV Antiretroviral Therapy Effects Research is a multicenter observational study to determine the effects of antiretroviral therapy on HIV-associated neurological disease. Single random plasma and CSF samples were drawn within an hour of each other from subjects taking tenofovir between October 2003 and March 2007. All samples were assayed by mass spectrometry with a detection limit of 0.9 ng/mL.

RESULTS

One hundred eighty-three participants (age 44 ± 8 years; 83 ± 32 kg; 33 females; CSF protein 44 ± 16 mg/dL) had plasma and CSF samples drawn 12.2 ± 6.9 and 11 ± 7.8 hours post dose, respectively. Median plasma and CSF tenofovir concentrations were 96 ng/mL [interquartile range (IQR) 47-153 ng/mL] and 5.5 ng/mL (IQR 2.7-11.3 ng/mL), respectively. Thirty-four of 231 plasma (14.7%) and 9 of 77 CSF samples (11.7%) were below detection. CSF to plasma concentration ratio from paired samples was 0.057 (IQR 0.03-0.1; n = 38). Median CSF to wild-type 50% inhibitory concentration ratio was 0.48 (IQR 0.24-0.98). Seventy-seven percent of CSF concentrations were below the tenofovir wild-type 50% inhibitory concentration. More subjects had detectable CSF HIV with lower (≤ 7 ng/mL) versus higher (>7 ng/mL) CSF tenofovir concentrations (29% versus 9%; P = 0.05).

CONCLUSIONS

Tenofovir concentrations in the CSF are only 5% of plasma concentrations, suggesting limited transfer into the CSF, and possibly active transport out of the CSF. CSF tenofovir concentrations may not effectively inhibit viral replication in the CSF.

The male genital tract is not a pharmacological sanctuary from efavirenz

Many antiretroviral (ARV) drugs have large blood plasma-to-seminal plasma (BP/SP) concentration ratios. Concern exists that these drugs do not adequately penetrate the male genital tract (MGT), resulting in the MGT becoming a "pharmacological sanctuary" from these agents, with ineffective MGT concentrations despite effective blood concentrations. Efavirenz (EFV) is the most highly protein-bound ARV drug, with >99% binding in blood plasma and the largest BP/SP total EFV concentration ratio, reportedly ranging from 11 to 33. To evaluate protein binding as an explanation for the differences between the drug concentrations in blood and semen, we developed a novel ultrafiltration method, corrected for the duration of centrifugation, to measure protein binding in the two matrices. In six subjects, protein-free EFV concentrations were the same in blood and semen; the median (interquartile range (IQR)) protein-free EFV SP/BP ratio was 1.21 (0.99-1.35); EFV protein binding was 99.82% (99.79-99.86) in BP and 95.26% (93.24-96.67) in SP. This shows that the MGT is not a sanctuary from EFV.

Darunavir, ritonavir, and etravirine pharmacokinetics in the cervicovaginal fluid and blood plasma of HIV-infected women

We report darunavir, ritonavir, and etravirine pharmacokinetics in cervicovaginal fluid and blood plasma for women from the Gender, Race and Clinical Experience (GRACE) study. Eight women received darunavir-ritonavir (600/100 mg) twice daily (b.i.d.); two also received etravirine (200 mg) b.i.d. Week 4 paired blood plasma and cervicovaginal fluid samples were collected over 12 h. Darunavir and etravirine cervicovaginal fluid exposures were higher than blood plasma exposures; ritonavir cervicovaginal fluid exposure was lower than blood plasma exposure. The high exposures of darunavir and etravirine in cervicovaginal fluid warrant further evaluation of these drugs for use in HIV-1 prevention.

Efavirenz concentrations in CSF exceed IC50 for wild-type HIV

OBJECTIVES

HIV-associated neurocognitive disorders remain common despite use of potent antiretroviral therapy (ART). Ongoing viral replication due to poor distribution of antivirals into the CNS may increase risk for HIV-associated neurocognitive disorders. This study's objective was to determine penetration of a commonly prescribed antiretroviral drug, efavirenz, into CSF.

METHODS

CHARTER is an ongoing, North American, multicentre, observational study to determine the effects of ART on HIV-associated neurological disease. Single random plasma and CSF samples were drawn within 1 h of each other from subjects taking efavirenz between September 2003 and July 2007. Samples were assayed by HPLC or HPLC/mass spectrometry with detection limits of 39 ng/mL (plasma) and <0.1 ng/mL (CSF).

RESULTS

Eighty participants (age 44 ± 8 years; 79 ± 15 kg; 20 females) had samples drawn 12.5 ± 5.4 h post-dose. The median efavirenz concentrations after a median of 7 months [interquartile range (IQR) 2-17] of therapy were 2145 ng/mL in plasma (IQR 1384-4423) and 13.9 ng/mL in CSF (IQR 4.1-21.2). The CSF/plasma concentration ratio from paired samples drawn within 1 h of each other was 0.005 (IQR 0.0026-0.0076; n = 69). The CSF/IC(50) ratio was 26 (IQR 8-41) using the published IC(50) for wild-type HIV (0.51 ng/mL). Two CSF samples had concentrations below the efavirenz IC(50) for wild-type HIV.

CONCLUSIONS

Efavirenz concentrations in the CSF are only 0.5% of plasma concentrations but exceed the wild-type IC(50) in nearly all individuals. Since CSF drug concentrations reflect those in brain interstitial fluids, efavirenz reaches therapeutic concentrations in brain tissue.

High concentration of raltegravir in semen of HIV-infected men: results from a substudy of the EASIER-ANRS 138 trial

Raltegravir concentrations and human immunodeficiency virus type 1 (HIV-1) RNA levels in semen samples from 10 treatment-experienced HIV-1-infected patients were measured after 24 weeks of raltegravir-based highly active antiretroviral therapy (HAART). Semen and plasma HIV-1 RNA levels were below 100 copies/ml and 50 copies/ml, respectively, in all samples. The median raltegravir concentrations in semen samples (n=10) and in plasma samples (n=9) drawn simultaneously were 345 (range, 83 to 707) ng/ml and 206 (range, 106 to 986) ng/ml, respectively. The median semen-to-plasma ratio of raltegravir concentration was 1.42 (range, 0.52 to 6.66), indicating good although variable levels of drug penetration of raltegravir in the seminal compartment.

Maraviroc concentrates in the cervicovaginal fluid and vaginal tissue of HIV-negative women

OBJECTIVE

To compare single- and multiple-dose maraviroc exposures in cervicovaginal fluid (CVF) and vaginal tissue (VT) with blood plasma (BP) and quantify maraviroc protein binding in CVF.

DESIGN

Open-label pharmacokinetic study.

METHODS

In 12 HIV-negative women, 7 paired CVF and BP samples were collected over 12 hours after 1 maraviroc dose. Subjects then received maraviroc twice daily for 7 days. After the last dose, subjects underwent CVF and BP sampling as on day 1, with additional sampling during terminal elimination. VT biopsies were obtained at steady state.

RESULTS

Day 1 and day 7 median maraviroc CVF AUCtau were 1.9- and 2.7-fold higher, respectively, than BP. On day 1, 6 of 12 subjects had detectable maraviroc CVF concentrations within 1 hour; 12 of 12 were detectable within 2 hours, and all exceeded the protein-free IC90. On day 7, maraviroc CVF protein binding was 7.6% and the VT AUCtau was 1.9-fold higher than BP. Maraviroc CVF concentrations 72 hours after dose and BP concentrations 12 hours after dose were similar.

CONCLUSIONS

Higher maraviroc exposure in the female genital tract provides a pharmacologic basis for further evaluation of chemokine receptor 5 antagonists in HIV infection prophylaxis. This is the first study to report antiretroviral VT concentrations, CVF protein binding, and CVF terminal elimination.

HIV infection and the central nervous system: a primer

The purpose of this brief review is to prepare readers who may be unfamiliar with Human Immunodeficiency Virus/Acquired Immune Deficiency Syndrome (HIV/AIDS) and the rapidly accumulating changes in the epidemic by providing an introduction to HIV disease and its treatment. The general concepts presented here will facilitate understanding of the papers in this issue on HIV-associated neurocognitive disorders (HAND). Toward that end, we briefly review the biology of HIV and how it causes disease in its human host, its epidemiology, and how antiretroviral treatments are targeted to interfere with the molecular biology that allows the virus to reproduce. Finally, we describe what is known about how HIV injures the nervous system, leading to HAND, and discuss potential strategies for preventing or treating the effects of HIV on the nervous system.

Low atazanavir concentrations in cerebrospinal fluid

OBJECTIVE

Protease inhibitors may not penetrate into the central nervous system in therapeutic concentrations, which may allow ongoing HIV replication and injury. The objective of this study was to determine atazanavir penetration into cerebrospinal fluid (CSF).

DESIGN

Single random plasma or paired plasma and CSF samples were drawn from participants enrolled in a multicenter, observational cohort study and taking atazanavir with or without ritonavir between October 2003 and October 2005.

METHODS

Plasma samples were assayed by high performance liquid chromatography and immunoassay; lower limit of detection was 45 ng/ml. CSF samples were assayed by immunoassay (ARK ATV-test); lower limit of detection was 5 ng/ml.

RESULTS

One hundred and seventeen participants (43 +/- 7.7 years, 79% men, 81 +/- 15 kg) had plasma or plasma and CSF paired samples drawn a median (interquartile range) of 10 (5-17) h postdose. Median (interquartile range) plasma atazanavir concentrations with or without ritonavir were 1278 (525-2265) and 523 (283-1344) ng/ml. The median (interquartile range) CSF concentrations with or without ritonavir were 10.3 (<5-21.1) and 7.9 (6.6-22) ng/ml. Nineteen of 79 (24%) CSF samples were less than 5 ng/ml. CSF concentrations were less than 1% of plasma concentrations and near the atazanavir wild-type IC50 of 1-11 ng/ml.

CONCLUSION

Atazanavir CSF concentrations are highly variable and 100-fold lower than plasma concentrations, even with ritonavir boosting. CSF concentrations of atazanavir do not consistently exceed the wild-type IC50 of atazanavir and may not protect against HIV replication in the CSF.

Cognitive functioning during highly active antiretroviral therapy interruption in human immunodeficiency virus type 1 infection

Although no longer considered therapeutically beneficial, antiretroviral treatment interruptions (TIs) still occur frequently among patients with human immunodeficiency virus (HIV) infection for a variety of reasons. TIs typically result in viral rebound and worsening immunosuppression, which in turn are risk factors for neurocognitive decline and dementia. We sought to determine the extent of neurocognitive risk with TIs and subsequent reintroduction of highly active antiretroviral therapy (HAART) by using a comprehensive, sensitive neuropsychological assessment and by concurrently determining changes in plasma and cerebrospinal fluid (CSF) viral load and CD4 counts. Prospective, serial, clinical evaluations including neuropsychological (NP) testing and measurement of plasma HIV RNA and CD4 count and mood state were performed on HIV-1-infected individuals (N=11) at three time points: (1) prior to a TI, while on HAART; (2) after TIs averaging 6 months; and (3) after reinitiating HAART therapy. During TI, plasma HIV RNA increased and CD4 counts declined significantly, but NP performance did not change. Following reinitiation of HAART, viral loads fell below pre-TI levels, and CD4 counts rose. Improved viral suppression and immune restoration with reinitiation of HAART resulted in significant improvement in neurocognitive performance. No changes on comprehensive questionnaires of mood state were observed in relation to TI.NP performance and mood state remained stable during TIs despite worsened viral loads and CD4 counts. Because "practice effects" are generally greatest between the first and second NP testing sessions, improvement at the third, post-TI time point was unlikely to be accounted for by practice. TIs of up to 6 months appear to be neurocognitively and psychiatrically safe for most patients.

Quantification of antiretroviral drugs for HIV-1 in the male genital tract: current data, limitations and implications for laboratory analysis

Antiretroviral therapy has reduced the morbidity and mortality associated with HIV-1/AIDS in developed countries. Viral replication in blood plasma is suppressed by antiretroviral drugs, whereas virus in the male genital tract is genetically and phenotypically unique and may not be suppressed. This viral compartmentalization affects antiretroviral drug penetration of the male genital tract and capacity for antiretroviral therapy to reduce sexual transmission. The problem of having two distinct viral populations within any given individual is compounded by the fact that antiretroviral drugs penetrate semen to varying degrees. Incomplete suppression of genital tract virus may yield drug-resistant virus and increase the risk of sexual transmission. This review critically appraises current studies of antiretroviral drug quantification in semen and suggests recommendations to address observed limitations.

Intracellular and plasma pharmacokinetics of efavirenz in HIV-infected individuals

OBJECTIVES

The site of action of efavirenz is inside HIV-infected cells. Measurement of intracellular (IC) concentrations of efavirenz may therefore provide further understanding of therapeutic failure, especially where virological rebound occurs despite adequate plasma levels, and a lack of detectable viral resistance. Here, we determined IC and plasma pharmacokinetics of efavirenz and their relationship with plasma protein binding and P-glycoprotein (P-gp, an active drug efflux transporter) expression.

PATIENTS AND METHODS

Venous blood samples from 10 HIV-infected patients receiving efavirenz (600 mg once a day plus two nucleoside reverse transcriptase inhibitors) were collected over the 24 h dosing interval. Plasma and peripheral blood mononuclear cells (PBMCs) were isolated. Plasma protein bound and unbound efavirenz were separated using ultrafiltration. IC (or cell-associated), total plasma and unbound plasma efavirenz levels were quantified using HPLC-UV. P-gp expression was measured by flow cytometry. Area under the concentration-time curves (AUC0-24) were then calculated using non-compartmental analyses and the IC accumulation expressed as a ratio of IC to plasma AUC0-24.

RESULTS

The median (range) % unbound and IC accumulation ratio was 0.6% (0.4-1.5%) and 1.3 (0.7-3.3), respectively. There was a linear relationship between IC and total AUC0-24 (r2= 0.59, P = 0.01) but not unbound AUC0-24 (r2= 0.13, P = 0.75). An inverse correlation between IC AUC0-24 and % unbound was observed (r2= 41, P = 0.05). There was no relationship between IC AUC0-24 and P-gp expression on the cell surface (r2< 0.01, P = 0.98).

CONCLUSIONS

There was a direct relationship between % bound efavirenz in plasma and IC accumulation implying that the IC accumulation of efavirenz is related to binding to IC proteins or other cellular constituents. Studies investigating the unbound concentration of antiretrovirals inside the cell are now required.

Population pharmacokinetics of abacavir in plasma and cerebrospinal fluid

The distribution of abacavir into the cerebrospinal fluid (CSF) was assessed by use of a population pharmacokinetic analysis. Plasma and CSF abacavir concentrations in 54 subjects were determined. The abacavir CSF/plasma ratio averaged 36% and increased throughout the dose interval. Abacavir penetrates into the CSF in adequate concentrations to inhibit local human immunodeficiency virus replication.