Drugs in traditional drug classes (nucleoside reverse transcriptase inhibitor/nonnucleoside reverse transcriptase inhibitor/protease inhibitors) with activity against drug-resistant virus (tipranavir, darunavir, etravirine)

Therapeutic Drug Monitoring of HIV Antiretroviral Drugs in Pregnancy: A Narrative Review

To date, therapeutic drug monitoring (TDM) has played an important role in the management of pregnant HIV patients on highly active antiretroviral therapy. Historically, in pregnant women living with HIV, the third agent in triple therapy has been either non-nucleoside reverse transcriptase inhibitors or protease inhibitors (PIs). PIs have been the preferred agents because of their robustness from the perspective of viral resistance and the dominant drug class for the management of HIV during pregnancy for the previous decade. As with many drugs used during pregnancy, pharmacokinetic changes decrease exposure to these agents as the pregnancy progresses. This can lead to viral escape at the time of pregnancy and ultimately increase the risk of mother-to-child transmission (MTCT) of HIV. TDM has been well-established for this class of highly active antiretroviral therapy, and appropriate dose adjustment studies have been performed. At present, there is a shift from the traditional treatment paradigm in pregnancy to a new drug class, integrase strand transfer inhibitors (INSTIs). Although INSTIs are affected by pharmacokinetic changes during pregnancy, they do not harbor the same issues with viral escape as seen with PIs at birth and in general eliminate the need for boosting with additional agents like ritonavir (r) and cobicistat (c) [bar elvitegravir (EVG)] that can lead to interactions with treatment of other common infections in HIV, including tuberculosis. Furthermore, INSTIs are the most successful medication for rapidly reducing the viral load (VL) in HIV patients, a useful factor where VL may be unknown, or in late presenters. These merits make INSTIs the best choice in pregnancy, although their use has been hindered in recent years by a report of neural tube defects from a large African study with dolutegravir (DTG). New data from Botswana and Brazil indicate that this risk is less significant than previously reported, necessitating further data to shed light on this critical issue. Current international guidelines including DHHS, EACS, WHO, and BHIVA (for patients with VLs >100,000 copies/mL or late presenters) now recommend INSTIs as first-line agents. The role of TDM in INSTIs shifts to cases of insufficient viral suppression with standard adherence measures, cases of drug-drug interactions, or cases where EVG/c is continued throughout pregnancy, and thus remains an important aspect of HIV care in pregnancy.

Management of Antiretroviral Therapy with Boosted Protease Inhibitors-Darunavir/Ritonavir or Darunavir/Cobicistat

A major challenge in the management of antiretroviral therapy (ART) is to improve the patient's adherence, reducing the burden caused by the high number of drugs that compose the treatment regimens for human immunodeficiency virus positive (HIV+) patients. Selection of the most appropriate treatment regimen is responsible for therapeutic success and aims to reduce viremia, increase the immune system response capacity, and reduce the incidence rate and intensity of adverse reactions. In general, protease inhibitor (PI) is one of the pillars of regimens, and darunavir (DRV), in particular, is frequently recommended, along with low doses of enzyme inhibitors as cobicistat (COBI) or ritonavir (RTV), by the international guidelines. The potential of clinically significant drug interactions in patients taking COBI or RTV is high due to the potent inhibitory effect on cytochrome CYP 450, which attracts significant changes in the pharmacokinetics of PIs. Regardless of the patient or type of virus, the combined regimens of DRV/COBI or DRV/RTV are available to clinicians, proving their effectiveness, with a major impact on HIV mortality/morbidity. This study presents current information on the pharmacokinetics, pharmacology, drug interactions, and adverse reactions of DRV; it not only compares the bioavailability, pharmacokinetic parameters, immunological and virological responses, but also the efficacy, advantages, and therapeutic disadvantages of DRV/COBI or DRV/RTV combinations.

Time to Viremia for Patients Taking their First Antiretroviral Regimen and the Subsequent Resistance Profiles

BACKGROUND

The resistance profiles for patients on first-line antiretroviral therapy (ART) regimens after viremia have not been well studied in community clinic settings in the modern treatment era.

OBJECTIVE

To determine time to viremia and the ART resistance profiles of viremic patients.

METHODS

HIV-positive patients aged ≥16 years initiating a three-drug regimen were retrospectively identified from 01/01/06 to 12/31/12. The regimens were a backbone of two nucleoside reverse transcriptase inhibitors (NRTIs) and a third agent: a protease inhibitor (PI), non-nucleoside reverse transcriptase inhibitor (NNRTI), or an integrase inhibitor (II). Time to viremia was compared using a proportional hazards model, adjusting for demographic and clinical factors. Resistance profiles were described in those with baseline and follow-up genotypes.

RESULTS

For 653 patients, distribution of third-agent use and viremia was: 244 (37%) on PIs with 80 viremia, 364 (56%) on NNRTIs with 84 viremia, and 45 (7%) on II with 11 viremia. Only for NNRTIs, time to viremia was longer than PIs (p = 0.04) for patients with a CD4 count ≥200 cells/mm(3). Of the 175 with viremia, 143 (82%) had baseline and 37 (21%) had follow-up genotype. Upon viremia, emerging ART resistance was rare. One new NNRTI (Y181C) mutation was identified and three patients taking PI-based regimens developed NRTI mutations (M184 V, M184I, and T215Y).

CONCLUSIONS

Time to viremia for NNRTIs was longer than PIs. With viremia, ART resistance rarely developed without PI or II mutations, but with a few NRTI mutations in those taking PI-based regimens, and NNRTI mutations in those taking NNRTI-based regimens.

Evaluation of cystatin C activities against HIV

BACKGROUND & OBJECTIVES

Several host defense proteins known to possess antimicrobial activities are present on mucosal surfaces and are consequently found in body fluids of vertebrates. Naturally occurring protease inhibitors like cystatins, especially cystatin C (cys C), are abundantly present in human seminal plasma. Although its antiviral activity against herpes simplex virus (HSV) has been demonstrated, the role of this protein against HIV is not well studied. Therefore, the aim of the present study was to evaluate the anti-HIV activities of cys C, which is present innately in the male reproductive tract.

METHODS

Protein-protein interaction of cys C with various HIV proteins was studied using a commercially available HIV blot and specific interaction with HIV protease was studied by dot-blot technique using commercially available cys C. To purify biologically active cys C from human seminal plasma to be used for subsequent experiments, gel-permeation chromatography followed by affinity chromatography was used. The HIV infectivity inhibition activity of the purified cystatin C was tested in TZM-bl cells. To study its activity on HIV protease, time-course enzyme kinetics studies were performed using spectrometric assay.

RESULTS

Cystatin C reacted with some HIV proteins including HIV protease. Biologically active cys C was purified using gel permeation chromatography followed by affinity chromatography. When tested in TZM-bl cells, purified cystatin C demonstrated HIV-infectivity inhibitory activity (IC 50: 0.28 μM). Enzyme kinetic studies demonstrated that it abrogated the action of HIV protease on its substrate.

INTERPRETATION & CONCLUSIONS

The present data demonstrate that cystatin C possesses anti-HIV activities. Molecular models need to be designed with this protein which would assist towards prevention/ therapeutics against HIV.

Therapeutic drug monitoring in HIV-infected pregnant women with a focus on protease inhibitors

The goals of HIV therapy in pregnant patients are to ensure health of mother and to prevent mother to child transmission of HIV to the unborn child. Pregnancy is a time of significant physiological alterations that affect all pharmacological aspects of the antiretroviral (ARV) drugs. Studies point toward lower levels of ARVs in maternal blood especially during late stages of pregnancy. Therapeutic drug monitoring is a strategy to ensure that maternal blood contains adequate level of ARVs to achieve these targets. Pharmacokinetics and therapeutic drug monitoring studies of protease inhibitors are reviewed in this article with emphasis on darunavir which is a newer protease inhibitor gaining popularity as a therapeutic choice in pregnant patients.

Darunavir: a review of its use in the management of HIV-1 infection

The latest HIV-1 protease inhibitor (PI) darunavir (Prezista™) has a high genetic barrier to resistance development and is active against wild-type HIV and HIV strains no longer susceptible to some older PIs. Ritonavir-boosted darunavir, as a component of antiretroviral therapy (ART), is indicated for the treatment of HIV-1 infection in adult and paediatric patients (aged ≥3 years), with or without treatment experience (details vary depending on region of approval). Several open-label or partially-blinded trials have evaluated the efficacy of ritonavir-boosted darunavir ART regimens for up to 192 weeks in these settings. In treatment-naïve adults, once-daily boosted darunavir was no less effective in establishing virological suppression than once- or twice-daily boosted lopinavir, yet was more effective at maintaining suppression long term. Moreover, treatment-experienced adults with no darunavir resistance-associated mutations (RAMs) had no less effective viral load suppression with once-daily than with twice-daily boosted darunavir. In treatment-experienced adults, including some with multiple major PI RAMs, twice-daily boosted darunavir was more effective than twice-daily boosted lopinavir or boosted control PIs in reducing viral load, and provided virological benefit as part of a salvage regimen in those with few remaining treatment options. Boosted darunavir also reduced viral load when administered once-daily in treatment-naïve adolescents or twice-daily in treatment-experienced children and adolescents. Boosted darunavir is generally well tolerated, with gastrointestinal disturbances and lipid abnormalities among the most common tolerability issues. It has a lipid profile more favourable than that of boosted lopinavir in terms of total cholesterol and triglyceride changes and, when administered once daily, its lipid effects are generally similar to those of boosted atazanavir. Thus, boosted darunavir is a useful option for the ART regimens of adult and paediatric patients with HIV-1 infection.

Winning the arms race by improving drug discovery against mutating targets

Enzymes are often excellent drug targets. Yet drug pressure on an enzyme target often fosters the rise of cells with resistance-conferring mutations, some of which may compromise fitness and others that compensate to restore fitness. This review presents, first, a structural analysis of a diverse group of wild-type and mutant enzyme targets and, second, an in-depth analysis of five diverse targets to elucidate a broader perspective of the effects of resistance-conferring mutations on protein or organismal fitness. The structural analysis reveals that resistance-conferring mutations may introduce steric hindrance or eliminate critical interactions, as expected, but that they may also have indirect effects such as altering protein dynamics and enzyme kinetics. The structure-based development of the latest generation of inhibitors targeting HIV reverse transcriptase, P. falciparum and S. aureus dihydrofolate reductase, neuraminidase, and epithelial growth factor receptor (EGFR) tyrosine kinase, is highlighted to emphasize lessons that may be applied to future drug discovery to overcome mutation-induced resistance. Successful next-generation drugs tend to be more flexible and exploit a greater number of interactions mimicking those of the substrate with conserved residues.

TMC310911, a novel human immunodeficiency virus type 1 protease inhibitor, shows in vitro an improved resistance profile and higher genetic barrier to resistance compared with current protease inhibitors

TMC310911 is a novel human immunodeficiency virus type 1 (HIV-1) protease inhibitor (PI) structurally closely related to darunavir (DRV) but with improved virological characteristics. TMC310911 has potent activity against wild-type (WT) HIV-1 (median 50% effective concentration [EC(50)], 14 nM) and a wide spectrum of recombinant HIV-1 clinical isolates, including multiple-PI-resistant strains with decreased susceptibility to currently approved PIs (fold change [FC] in EC(50), >10). For a panel of 2,011 recombinant clinical isolates with decreased susceptibility to at least one of the currently approved PIs, the FC in TMC310911 EC(50) was ≤ 4 for 82% of isolates and ≤ 10 for 96% of isolates. The FC in TMC310911 EC(50) was ≤ 4 and ≤ 10 for 72% and 94% of isolates with decreased susceptibility to DRV, respectively. In vitro resistance selection (IVRS) experiments with WT virus and TMC310911 selected for mutations R41G or R41E, but selection of resistant virus required a longer time than IVRS performed with WT virus and DRV. IVRS performed with r13025, a multiple-PI-resistant recombinant clinical isolate, and TMC310911 selected for mutations L10F, I47V, and L90M (FC in TMC310911 EC(50) = 16). IVRS performed with r13025 in the presence of DRV required less time and resulted in more PI resistance-associated mutations (V32I, I50V, G73S, L76V, and V82I; FC in DRV EC(50) = 258). The activity against a comprehensive panel of PI-resistant mutants and the limited in vitro selection of resistant viruses under drug pressure suggest that TMC310911 represents a potential drug candidate for the management of HIV-1 infection for a broad range of patients, including those with multiple PI resistance.