State of the Art in HIV Drug Resistance: Surveillance and Regional Gaps.

This article is the second of a two-part review aiming to identify gaps in the knowledge and management of human immunodeficiency virus type 1 drug resistance (HIVDR) from global and regional perspectives. Here, we examine the policy and programmatic gaps in HIVDR surveillance, the affected populations and settings, and implications for clinical practice. The expert authorship of this review convened to identify gaps in HIVDR surveillance, with a particular focus on specific regional variations within and between Europe and Asia, to highlight directions for research and implementation. Further, evidence was gathered from a review of published studies, guidelines, and current practices. This review found that despite recent progress in the development, harmonization, and implementation of guidelines on HIVDR reporting and surveillance, programmatic, and policy gaps reflect the regional variability in HIV epidemics, clinical practice, and resources. The need for representative surveillance was identified as a key gap that has the potential to inform management policies. Monitoring must keep up with the evolution of transmission routes to adapt appropriately, and this will be further impacted by migration from areas with increasing levels of resistance. Analysis of the latest clinical data, regional practice, policy, and guidelines has identified a number of gaps in HIVDR population monitoring and surveillance. More efforts are needed to align surveillance platforms with harm reduction and patient education, particularly in vulnerable subgroups. Addressing these gaps will facilitate research into and progress in the management of HIV across a wide range of health-care settings.

State of the Art in HIV Drug Resistance: Science and Technology Knowledge Gap.

Resistance to antiretroviral therapy (ART) threatens the efficacy of human immunodeficiency virus type 1 (HIV-1) treatment. We present a review of knowledge gaps in the science and technologies of acquired HIV-1 drug resistance (HIVDR) in an effort to facilitate research, scientific exchange, and progress in clinical management. The expert authorship of this review convened to identify data gaps that exist in the field of HIVDR and discuss their clinical implications. A subsequent literature review of trials and current practices was carried out to provide supporting evidence. Several gaps were identified across HIVDR science and technology. A summary of the major gaps is presented, with an expert discussion of their implications within the context of the wider field. Crucial to optimizing the use of ART will be improved understanding of protease inhibitors and, in particular, integrase strand transfer inhibitors (INSTI) in the context of HIVDR. Limited experience with INSTI represents an important knowledge gap in HIV resistance science. Utilizing such knowledge in a clinical setting relies on accurate testing and analysis of resistance-associated mutations. As next-generation sequencing becomes more widely available, a gap in the interpretation of data is the lack of a defined, clinically relevant threshold of minority variants. Further research will provide evidence on where such thresholds lie and how they can be most effectively applied. Expert discussion identified a series of gaps in our knowledge of HIVDR. Addressing prefsuch gaps through further research and characterization will facilitate the optimal use of ART therapies and technologies.

Population pharmacokinetic/pharmacodynamic analysis of CCR5 receptor occupancy by maraviroc in healthy subjects and HIV-positive patients.

BACKGROUND: Maraviroc, a noncompetitive antagonist of the CCR5 coreceptor, was recently approved in the USA as a treatment of HIV infection. For antiretroviral agents that target the virus, antiviral effect can be related to some extent to plasma drug concentrations. For CCR5 antagonists that target the host cells, receptor occupancy in vivo might be a better predictor of efficacy. AIMS To develop a population pharmacokinetic (PK)-pharmacodynamic (PD) model that describes CCR5 receptor occupancy by maraviroc after oral administration at different doses in healthy volunteers and HIV-positive patients and to assess the relevance of receptor occupancy in predicting the decrease in viral load (HIV-1 RNA copies ml(-1)) in HIV-positive patients. METHODS: Receptor occupancy data from 88 individuals enrolled in two multiple dose trials were included in the population PK-receptor binding model. Out of the 88 individuals, 25 were HIV-1-infected patients and had viral load measurements, whereas the remaining 63 were healthy volunteers. Doses ranged from 3 mg b.i.d. to 600 mg q.d. A previously published PK-PD disease model describing the effect of maraviroc on the viral load was updated by replacing its PD module by the receptor occupancy model. Simulated viral load-time profiles with the updated model were compared with the profiles observed in patients. RESULTS: The majority of measured plasma concentrations were associated with receptor occupancy > or = 50% even at the lowest dose of 3 mg b.i.d. A simple direct E(max) model appeared to describe satisfactorily the PK-receptor occupancy relationship. The estimated K(D) was around 0.0894 ng ml(-1), far below the operational in vivo antiviral IC(50) of 8 ng ml(-1). Accordingly, simulations led to marked overprediction of the decrease in viral load-time profiles. CONCLUSIONS: Maraviroc receptor occupancy close to the maximum is required to induce a significant decrease in viral load, indicating that in vivo CCR5 receptor occupancy by maraviroc is not a direct measure of drug inhibitory activity. Considering the imprecision of the measurement in the upper flat part of the maraviroc concentration vs. percent CCR5 occupancy curve, it can reasonably be concluded that routine monitoring of receptor occupancy as a biomarker for maraviroc efficacy will not be helpful. Based on this analysis, it was decided not to use receptor occupancy as a biomarker of viral load inhibition during the development of CCR5 antagonist compounds.

Allosteric effects of antagonists on signalling by the chemokine receptor CCR5.

Antagonists of the chemokine receptor, CCR5, may provide important new drugs for the treatment of HIV-1. In this study we have examined the mechanism of action of two functional antagonists of the chemokine receptor CCR5 (UK-396,794, UK-438,235) in signalling and internalisation assays using CHO cells expressing CCR5. Both compounds were potent inverse agonists versus agonist-independent [(35)S]GTPgammaS binding to membranes of CHO cells expressing CCR5. Both compounds also acted as allosteric inhibitors of CCL5 (RANTES) and CCL8 (MCP-2)-stimulated [(35)S]GTPgammaS binding to CHO-CCR5 membranes, reducing the potency and maximal effects of the two chemokines. The data are consistent with effects of the allosteric inhibitors on both the binding and signalling of the chemokines. Both compounds inhibited CCR5 internalisation triggered by chemokines. When CHO-CCR5 cells were treated with either of the two compounds for prolonged periods of time (24 h) an increase (approximately 15%) in cell surface CCR5 was detected.

A pharmacokinetic-pharmacodynamic disease model to predict in vivo antiviral activity of maraviroc.

BACKGROUND: The viral dynamics of human immunodeficiency virus (HIV) infection has been widely studied and expressed as mathematic equations. For most of the current registered antiretroviral drugs, the pharmacokinetics is well characterized and some relationships with the viral load-time profiles in plasma from HIV patients have been established. The integration of these models in a pharmacokinetic (PK)-pharmacodynamic (PD)-disease model can help toward a better understanding of the complexity of the interactions, as well as in the identification and clarification of the current model assumptions. METHODS: This work describes the development of a generic PK-PD disease model for a short-term (10 days) monotherapy phase IIa study with a novel anti-HIV drug, maraviroc (UK-427,857). The disease component of the model was based on the model published by Bonhoeffer et al, which was adapted for short-term treatment and for the new mechanism of action, CCR5-receptor antagonism. The model parameters were derived from the literature, as well as from a model-based analysis of available phase IIa clinical data from another investigational antiretroviral drug. The PD component that links the plasma concentrations of maraviroc to the inhibition of virus replication was based on in vitro measurements of drug potency and took into account the difference in the in vitro and in vivo protein binding and the uncertainties regarding the interpretation of the in vitro to in vivo extrapolation of the 50% inhibitory concentration. Finally, the PK component was based on information obtained from a single-dose study in healthy volunteers. RESULTS: The integrated PK-PD disease modeling allowed prediction of the effect on viral load of different maraviroc doses given as monotherapy to drug-naive patients. CONCLUSIONS: By making use of the available PK-PD disease model, the possible range of active oral doses for maraviroc in HIV-positive patients was estimated by simulation before any clinical trials were taking place. The use of a model-based approach for selecting doses for clinical phase IIa has improved and accelerated the drug's development. This model was a powerful tool for assisting in the design of clinical studies on new agents for treating HIV/acquired immunodeficiency syndrome.

Molecular cloning and radioligand binding characterization of the chemokine receptor CCR5 from rhesus macaque and human.

The aim of this study was to determine if macaque represents a suitable species for the pre-clinical evaluation of novel CCR5 antagonists, such as maraviroc (UK-427,857). To do this we cloned and expressed CCR5 from rhesus macaque and compared the binding properties of [125I]-MIP-1beta and [3H]-maraviroc with human recombinant CCR5. [125I]-MIP-1beta bound with similar high affinity to CCR5 from macaque (K(d) = 0.24 +/- 0.05 nM) and human (K(d) = 0.23 +/- 0.05 nM) and with similar kinetic properties. In competition binding studies the affinity of a range of human chemokines for macaque CCR5 was also similar to human CCR5. Maraviroc inhibited binding of [125I]-MIP-1beta to CCR5 from macaque and human with similar potency (IC50 = 17.50 +/- 1.24 nM and 7.18 +/- 0.93 nM, respectively) and antagonised MIP-1beta induced intracellular calcium release mediated through CCR5 from macaque and human with similar potency (IC50 = 17.50 +/- 3.30 nM and 12.07 +/- 1.89, respectively). [3H]-maraviroc bound with high affinity to CCR5 from macaque (K(d) = 1.36+/-0.07 nM) and human (K(d) = 0.86 +/- 0.08 nM), but was found to dissociate approximately 10-fold more quickly from macaque CCR5. However, as with the human receptor, maraviroc was shown to be a high affinity, potent functional antagonist of macaque CCR5 thereby indicating that the macaque should be a suitable species in which to evaluate the pharmacology, safety and potential mechanism-related toxicology of novel CCR5 antagonists.