CCR5 antagonists: host-targeted antivirals for the treatment of HIV infection

Revolutionizing Antiviral Therapeutics: Unveiling Innovative Approaches for Enhanced Drug Efficacy

Since the beginning of the coronavirus pandemic in late 2019, viral infections have become one of the top three causes of mortality worldwide. Immunization and the use of immunomodulatory drugs are effective ways to prevent and treat viral infections. However, the primary therapy for managing viral infections remains antiviral and antiretroviral medication. Unfortunately, these drugs are often limited by physicochemical constraints such as low target selectivity and poor aqueous solubility. Although several modifications have been made to enhance the physicochemical characteristics and efficacy of these drugs, there are few published studies that summarize and compare these modifications. Our review systematically synthesized and discussed antiviral drug modification reports from publications indexed in Scopus, PubMed, and Google Scholar databases. We examined various approaches that were investigated to address physicochemical issues and increase activity, including liposomes, cocrystals, solid dispersions, salt modifications, and nanoparticle drug delivery systems. We were impressed by how well each strategy addressed physicochemical issues and improved antiviral activity. In conclusion, these modifications represent a promising way to improve the physicochemical characteristics, functionality, and effectiveness of antivirals in clinical therapy.

Discovery of Novel CCR5 Ligands as Anticolorectal Cancer Agents by Sequential Virtual Screening

C-C chemokine receptor type 5 (CCR5) is a member of the G protein-coupled receptor. CCR5 and its interaction with chemokine ligands have been crucial for understanding and tackling human immunodeficiency virus (HIV)-1 entry into target cells. In recent years, the change in CCR5 expression has been related to the progression of different cancer types. Patients treated with the CCR5 ligand, maraviroc (MVC), showed a deceleration in tumor development especially for metastatic colorectal cancer. Based on the crystal structure of CCR5, we herein describe a multistage virtual screening protocol including pharmacophore screening, molecular docking, and protein-ligand interaction fingerprint (PLIF) postdocking filtration for discovery of novel CCR5 ligands. The applied virtual screening protocol led to the identification of four hits with binding modes showing access to the major and minor pockets of the MVC binding site. Compounds 2-4 showed a decrease in cellular proliferation upon testing on the metastatic colorectal cancer cell line, SW620, displaying 12, 16, and 4 times higher potency compared to MVC, respectively. Compound 3 induced apoptosis by arresting cells in the G0/G1 phase of the cell cycle similar to MVC. Further in vitro assays showed compound 3 drastically decreasing the CCR5 expression and cellular migration 48 h post treatment, indicating its ability to inhibit metastatic activity in SW620 cells. The discovered hits represent potential leads for the development of novel classes of anticolorectal cancer agents targeting CCR5.

Advances of CCR5 antagonists: From small molecules to macromolecules

C-C chemokine receptor 5(CCR5) is a cell membrane protein from G protein-coupled receptors (GPCR) family, which is an important modulator for leukocyte activation and mobilization. In the 1980s, several reports suggest that lack of the HIV-1 co-receptor, the chemokine receptor CCR5, offers protection against HIV infection. Later, it was shown that CCR5 was confirmed to be the most common co-receptor for the HIV-1 virus R5 strain. In recent years, many studies have shown that CCR5 is closely related to the development of various cancers and inflammations to facilitate the discovery of CCR5 antagonists. There are many types of CCR5 antagonists, mainly including chemokine derivatives, non-peptide small molecule compounds, monoclonal antibodies, and peptide compounds. This review focus on the recent research processes and pharmacological effects of CCR5 antagonists such as Maraviroc, TAK-779 and PRO 140. After focusing on the therapeutic effect of CCR5 antagonists on AIDS, it also discusses the therapeutic prospect of CCR5 in other diseases such as inflammation and tumor.

CCR5 Governs DNA Damage Repair and Breast Cancer Stem Cell Expansion

The functional significance of the chemokine receptor CCR5 in human breast cancer epithelial cells is poorly understood. Here, we report that CCR5 expression in human breast cancer correlates with poor outcome. CCR5+ breast cancer epithelial cells formed mammospheres and initiated tumors with >60-fold greater efficiency in mice. Reintroduction of CCR5 expression into CCR5-negative breast cancer cells promoted tumor metastases and induced DNA repair gene expression and activity. CCR5 antagonists Maraviroc and Vicriviroc dramatically enhanced cell killing mediated by DNA-damaging chemotherapeutic agents. Single-cell analysis revealed CCR5 governs PI3K/Akt, ribosomal biogenesis, and cell survival signaling. As CCR5 augments DNA repair and is reexpressed selectively on cancerous, but not normal breast epithelial cells, CCR5 inhibitors may enhance the tumor-specific activities of DNA damage response-based treatments, allowing a dose reduction of standard chemotherapy and radiation.Significance: This study offers a preclinical rationale to reposition CCR5 inhibitors to improve the treatment of breast cancer, based on their ability to enhance the tumor-specific activities of DNA-damaging chemotherapies administered in that disease. Cancer Res; 78(7); 1657-71. ©2018 AACR.

The Role of Hypoxia in Glioblastoma Invasion

Glioblastoma multiforme (GBM), a grade IV astrocytoma, is the most common and deadly type of primary malignant brain tumor, with a patient's median survival rate ranging from 15 to 17 months. The current treatment for GBM involves tumor resection surgery based on MRI image analysis, followed by radiotherapy and treatment with temozolomide. However, the gradual development of tumor resistance to temozolomide is frequent in GBM patients leading to subsequent tumor regrowth/relapse. For this reason, the development of more effective therapeutic approaches for GBM is of critical importance. Low tumor oxygenation, also known as hypoxia, constitutes a major concern for GBM patients, since it promotes cancer cell spreading (invasion) into the healthy brain tissue in order to evade this adverse microenvironment. Tumor invasion not only constitutes a major obstacle to surgery, radiotherapy, and chemotherapy, but it is also the main cause of death in GBM patients. Understanding how hypoxia triggers the GBM cells to become invasive is paramount to developing novel and more effective therapies against this devastating disease. In this review, we will present a comprehensive examination of the available literature focused on investigating how GBM hypoxia triggers an invasive cancer cell phenotype and the role of these invasive proteins in GBM progression.

CCR5-edited gene therapies for HIV cure: Closing the door to viral entry

Human immunodeficiency virus (HIV) was first reported and characterized more than three decades ago. Once thought of as a death sentence, HIV infection has become a chronically manageable disease. However, it is estimated that a staggering 0.8% of the world's population is infected with HIV, with more than 1 million deaths reported in 2015 alone. Despite the development of effective anti-retroviral drugs, a permanent cure has only been documented in one patient to date. In 2007, an HIV-positive patient received a bone marrow transplant to treat his leukemia from an individual who was homozygous for a mutation in the CCR5 gene. This mutation, known as CCR5Δ32, prevents HIV replication by inhibiting the early stage of viral entry into cells, resulting in resistance to infection from the majority of HIV isolates. More than 10 years after his last dose of anti-retroviral therapy, the transplant recipient remains free of replication-competent virus. Multiple groups are now attempting to replicate this success through the use of other CCR5-negative donor cell sources. Additionally, developments in the use of lentiviral vectors and targeted nucleases have opened the doors of precision medicine and enabled new treatment methodologies to combat HIV infection through targeted ablation or down-regulation of CCR5 expression. Here, we review historical cases of CCR5-edited cell-based therapies, current clinical trials and future benefits and challenges associated with this technology.

Performance of a clonal-based HIV-1 tropism phenotypic assay

Adequate determination of HIV-1 tropism is important in clinical and research settings. Genotypic and phenotypic approaches to evaluate tropism have been described. Phenotypic assays are widely used to determine HIV-1 tropism because of their sensitivity to detect minor CXCR4-using variants (X4). However they cannot differentiate mixed quasi-species of R5 and X4 viruses from dual-tropic viruses. We describe here a clonal-based HIV-1 tropism phenotypic assay. Env-pseudo-typed viruses were produced by co-transfection of the env expression plasmid pcDNA3.1/V5HisTOPO and a backbone vector pNL4-3.Luc.E-R- that expresses the entire HIV-1 genome except for env and vpr in 293T cell cultures. Co-receptor use was tested by infecting U87.CD4.CCR5+ and U87.CD4.CXCR4+ cells in the presence or absence of co-receptor inhibitors, using 10 clones from each sample. The ability of the assay to detect minor variants in a viral population was assessed by mixing X4 and R5 clones using different ratios. Both R5 and X4 minority variants were detected when present at greater than 0.4% in a mixture of envelope populations. This assay can be useful in both clinical and research laboratories.

Crucial involvement of the CCL3-CCR5 axis-mediated fibroblast accumulation in colitis-associated carcinogenesis in mice

Patients with inflammatory bowel diseases often develop colon carcinoma. Combined treatment of azoxymethane (AOM) and dextran sulfate sodium (DSS) recapitulates colitis-associated cancer in mice. AOM/DSS-induced tumor formation was reduced in CCL3- or its specific receptor, CCR5-deficient mice despite the presence of a massive infiltration of inflammatory cells. However, AOM/DSS-induced type I collagen-positive fibroblast accumulation in the colon was reduced in CCL3- or CCR5-deficient mice. This was associated with depressed expression of heparin-binding epidermal growth factor-like growth factor (HB-EGF), which is expressed mainly by fibroblasts. Moreover in vitro, CCL3 induced fibroblasts to proliferate and to enhance HB-EGF expression. Furthermore, CCR5 blockade reduced tumor formation together with reduced fibroblast accumulation and HB-EGF expression, even when administered after the development of multiple colon tumors. Thus, CCL3-CCR5-mediated fibroblast accumulation may be required, in addition to leukocyte infiltration, to induce full-blown colitis-associated carcinogenesis. Our studies shed light on a therapeutic potential of CCR5 antagonist for patients with colitis-associated cancer.

Safety and immunovirologic outcomes with maraviroc combination regimens in patients with a history of past treatment failures and virologic resistance in Brazil: an open-label, multicenter phase 3b study

Maraviroc is a first-in-class chemokine coreceptor type-5 (CCR5) antagonist with demonstrated immunovirologic activity in treatment-experienced (TE) patients with CCR5 (R5)-tropic HIV-1; however, experience in regimens containing newer antiretroviral agents is limited. The primary objective of this 96-week open-label, noncomparative, multicenter Phase 3b study (NCT00478231) was to assess the safety of maraviroc in combination with optimized background therapy (OBT), which could include recently introduced agents such as darunavir and raltegravir in TE patients in Brazil with R5 HIV-1 and limited therapeutic options. Immunovirologic activity was a secondary endpoint. Of 638 patients screened, 206 were treated and 125 completed the study. Approximately 70% were male; the mean age was 43.2 years. Most patients (65.0%) received an OBT combination of protease inhibitor plus nucleoside reverse transcriptase inhibitor. Adverse event (AE) and treatment-related AE incidence was 91.3% and 36.9%, respectively. The most common AEs were diarrhea, nasopharyngitis, and headache. Serious AEs and treatment-related serious AEs occurred in 16.5% and 4.4% of patients. Only eight patients (3.9%) discontinued due to AEs. Few AIDS-defining events were observed (4.9%). The proportion of patients with viral load <400 copies/ml increased from 2.4% at baseline to 43.9% at week 8, remaining >40% until week 48. At the end of treatment, 26.7% of patients had a viral load <400 copies/ml. Median CD4(+) cell count increased throughout the study; the mean change from baseline to end of treatment was 174.1 cells/μl. In conclusion, maraviroc, combined with different agents from multiple classes, was well tolerated in highly TE patients. Maraviroc plus OBT was associated with an immunovirologic response in this population.

CCR5 inhibitors in HIV-1 therapy

BACKGROUND

The human immunodeficiency virus 1 (HIV-1) is the causative pathogen of AIDS, the world's biggest infectious disease killer. About 33 million people are infected worldwide, with 2.1 million deaths a year as a direct consequence. The devastating nature of AIDS has prompted widespread research, which has led to an extensive array of therapies to suppress viral replication and enable recovery of the immune system to prolong and improve patient life substantially. However, the genetic plasticity and replication rate of HIV-1 are considerable, which has lead to rapid drug resistance. This, together with the need for reducing drug side effects and increasing regimen compliance, has led researchers to identify antiretroviral drugs with new modes of action.

OBJECTIVE

This review describes the discovery and clinical development of CCR5 antagonists and the recent approval of maraviroc as a breakthrough in anti-HIV-1 therapy.

CONCLUSION

CCR5 inhibitors target a human cofactor to disable HIV-1 entry into the cells, and thereby provide a new hurdle for the virus to overcome. The status and expert opinion of CCR5 antagonists for the treatment of HIV-1 infection are detailed.

Trofile HIV co-receptor usage assay

BACKGROUND

The introduction of CCR5 antagonists increases the options available for constructing therapeutic drug regimens for HIV-positive patients. However, as these drugs do not inhibit HIV variants that use the CXCR4 co-receptor, a pretreatment test is required to determine accurately HIV co-receptor usage (tropism) before initiating CCR5 antagonist-based therapy.

OBJECTIVE/METHOD

To discuss the Monogram Trofile assay as a diagnostic tool for determining HIV tropism by critically reviewing reported literature and available data.

CONCLUSIONS

Monogram Trofile has become, largely by default, the de facto standard for HIV tropism assay. However, there is significant room for improvement in the speed, cost and availability of the test. Furthermore, the test is not quantitative, requires high-input HIV RNA viral loads, and produces results that are less biologically stable than expected. These technical considerations may limit the use of CCR5 antagonists in therapy. Nevertheless, this test is likely to remain the most widely used tropism diagnostic for the short term. We expect that a more practical and possibly more accurate method for measuring HIV tropism can be developed.

An expanded model of HIV cell entry phenotype based on multi-parameter single-cell data

Background

Entry of human immunodeficiency virus type 1 (HIV-1) into the host cell involves interactions between the viral envelope glycoproteins (Env) and the cellular receptor CD4 as well as a coreceptor molecule (most importantly CCR5 or CXCR4). Viral preference for a specific coreceptor (tropism) is in particular determined by the third variable loop (V3) of the Env glycoprotein gp120. The approval and use of a coreceptor antagonist for antiretroviral therapy make detailed understanding of tropism and its accurate prediction from patient derived virus isolates essential. The aim of the present study is the development of an extended description of the HIV entry phenotype reflecting its co-dependence on several key determinants as the basis for a more accurate prediction of HIV-1 entry phenotype from genotypic data.

Results

Here, we established a new protocol of quantitation and computational analysis of the dependence of HIV entry efficiency on receptor and coreceptor cell surface levels as well as viral V3 loop sequence and the presence of two prototypic coreceptor antagonists in varying concentrations. Based on data collected at the single-cell level, we constructed regression models of the HIV-1 entry phenotype integrating the measured determinants. We developed a multivariate phenotype descriptor, termed phenotype vector, which facilitates a more detailed characterization of HIV entry phenotypes than currently used binary tropism classifications. For some of the tested virus variants, the multivariant phenotype vector revealed substantial divergences from existing tropism predictions. We also developed methods for computational prediction of the entry phenotypes based on the V3 sequence and performed an extrapolating calculation of the effectiveness of this computational procedure.

Conclusions

Our study of the HIV cell entry phenotype and the novel multivariate representation developed here contributes to a more detailed understanding of this phenotype and offers potential for future application in the effective administration of entry inhibitors in antiretroviral therapies.

Mutations in gp41 are correlated with coreceptor tropism but do not improve prediction methods substantially

BACKGROUND

The main determinants of HIV-1 coreceptor usage are located in the V3-loop of gp120, although mutations in V2 and gp41 are also known. Incorporation of V2 is known to improve prediction algorithms; however, this has not been confirmed for gp41 mutations.

METHODS

Samples with V3 and gp41 genotypes and Trofile assay (Monogram Biosciences, South San Francisco, CA, USA) results were taken from the HOMER cohort (n=444) and from patients screened for the MOTIVATE studies (n=1,916; 859 with maraviroc outcome data). Correlations of mutations with tropism were assessed using Fisher's exact test and prediction models trained using support vector machines. Models were validated by cross-validation, by testing models from one dataset on the other, and by analysing virological outcome.

RESULTS

Several mutations within gp41 were highly significant for CXCR4 usage; most strikingly an insertion occurring in 7.7% of HOMER-R5 and 46.3% of HOMER-X4 samples (MOTIVATE 5.7% and 25.2%, respectively). Models trained on gp41 sequence alone achieved relatively high areas under the receiver-operating characteristic curve (AUCs; HOMER 0.713 and MOTIVATE 0.736) that were almost as good as V3 models (0.773 and 0.884, respectively). However, combining the two regions improved predictions only marginally (0.813 and 0.902, respectively). Similar results were found when models were trained on HOMER and validated on MOTIVATE or vice versa. The difference in median log viral load decrease at week 24 between patients with R5 and X4 virus was 1.65 (HOMER 2.45 and MOTIVATE 0.79) for V3 models, 1.59 for gp41-models (2.42 and 0.83, respectively) and 1.58 for the combined predictor (2.44 and 0.86, respectively).

CONCLUSIONS

Several mutations within gp41 showed strong correlation with tropism in two independent datasets. However, incorporating gp41 mutations into prediction models is not mandatory because they do not improve substantially on models trained on V3 sequences alone.

Resistance to the CCR5 inhibitor 5P12-RANTES requires a difficult evolution from CCR5 to CXCR4 coreceptor use

Viral resistance to small molecule allosteric inhibitors of CCR5 is well documented, and involves either selection of preexisting CXCR4-using HIV-1 variants or envelope sequence evolution to use inhibitor-bound CCR5 for entry. Resistance to macromolecular CCR5 inhibitors has been more difficult to demonstrate, although selection of CXCR4-using variants might be expected. We have compared the in vitro selection of HIV-1 CC1/85 variants resistant to either the small molecule inhibitor maraviroc (MVC) or the macromolecular inhibitor 5P12-RANTES. High level resistance to MVC was conferred by the same envelope mutations as previously reported after 16–18 weeks of selection by increasing levels of MVC. The MVC-resistant mutants were fully sensitive to inhibition by 5P12-RANTES. By contrast, only transient and low level resistance to 5P12-RANTES was achieved in three sequential selection experiments, and each resulted in a subsequent collapse of virus replication. A fourth round of selection by 5P12-RANTES led, after 36 weeks, to a “resistant” variant that had switched from CCR5 to CXCR4 as a coreceptor. Envelope sequences diverged by 3.8% during selection of the 5P12-RANTES resistant, CXCR4-using variants, with unique and critical substitutions in the V3 region. A subset of viruses recovered from control cultures after 44 weeks of passage in the absence of inhibitors also evolved to use CXCR4, although with fewer and different envelope mutations. Control cultures contained both viruses that evolved to use CXCR4 by deleting four amino acids in V3, and others that maintained entry via CCR5. These results suggest that coreceptor switching may be the only route to resistance for compounds like 5P12-RANTES. This pathway requires more mutations and encounters more fitness obstacles than development of resistance to MVC, confirming the clinical observations that resistance to small molecule CCR5 inhibitors very rarely involves coreceptor switching.

Twenty-six years of HIV science: an overview of anti-HIV drugs metabolism

From the identification of HIV as the agent causing AIDS, to the development of effective antiretroviral drugs, the scientific achievements in HIV research over the past twenty-six years have been formidable. Currently, there are twenty-five anti-HIV compounds which have been formally approved for clinical use in the treatment of AIDS. These compounds fall into six categories: nucleoside reverse transcriptase inhibitors (NRTIs), nucleotide reverse transcriptase inhibitors (NtRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs), protease inhibitors (PIs), cell entry inhibitors or fusion inhibitors (FIs), co-receptor inhibitors (CRIs), and integrase inhibitors (INIs). Metabolism by the host organism is one of the most important determinants of the pharmacokinetic profile of a drug. Formation of active or toxic metabolites will also have an impact on the pharmacological and toxicological outcomes. Therefore, it is widely recognized that metabolism studies of a new chemical entity need to be addressed early in the drug discovery process. This paper describes an overview of the metabolism of currently available anti-HIV drugs.

Novel 4,4-disubstituted piperidine-based C-C chemokine receptor-5 inhibitors with high potency against human immunodeficiency virus-1 and an improved human ether-a-go-go related gene (hERG) profile

We recently described ( J. Med. Chem. 2008 , 51 , 6538 - 6546 ) a novel class of CCR5 antagonists with strong anti-HIV potency. Herein, we detail SAR converting leads 1 and 2 to druglike molecules. The pivotal structural motif enabling this transition was the secondary sulfonamide substituent. Further fine-tuning of the substituent pattern in the sulfonamide paved the way to enhancing potency and bioavailability and minimizing hERG inhibition, resulting in discovery of clinical compound 122 (GSK163929).

Genome-wide association study implicates PARD3B-based AIDS restriction

BACKGROUND

Host genetic variation influences human immunodeficiency virus (HIV) infection and progression to AIDS. Here we used clinically well-characterized subjects from 5 pretreatment HIV/AIDS cohorts for a genome-wide association study to identify gene associations with rate of AIDS progression.

METHODS

European American HIV seroconverters (n = 755) were interrogated for single-nucleotide polymorphisms (SNPs) (n = 700,022) associated with progression to AIDS 1987 (Cox proportional hazards regression analysis, co-dominant model).

RESULTS

Association with slower progression was observed for SNPs in the gene PARD3B. One of these, rs11884476, reached genome-wide significance (relative hazard = 0.3; P =3. 370 × 10(-9)) after statistical correction for 700,022 SNPs and contributes 4.52% of the overall variance in AIDS progression in this study. Nine of the top-ranked SNPs define a PARD3B haplotype that also displays significant association with progression to AIDS (hazard ratio, 0.3; P = 3.220 × 10(-8)). One of these SNPs, rs10185378, is a predicted exonic splicing enhancer; significant alteration in the expression profile of PARD3B splicing transcripts was observed in B cell lines with alternate rs10185378 genotypes. This SNP was typed in European cohorts of rapid progressors and was found to be protective for AIDS 1993 definition (odds ratio, 0.43, P = .025).

CONCLUSIONS

These observations suggest a potential unsuspected pathway of host genetic influence on the dynamics of AIDS progression.

Genotypic tropism testing by massively parallel sequencing: qualitative and quantitative analysis

BACKGROUND

Inferring viral tropism from genotype is a fast and inexpensive alternative to phenotypic testing. While being highly predictive when performed on clonal samples, sensitivity of predicting CXCR4-using (X4) variants drops substantially in clinical isolates. This is mainly attributed to minor variants not detected by standard bulk-sequencing. Massively parallel sequencing (MPS) detects single clones thereby being much more sensitive. Using this technology we wanted to improve genotypic prediction of coreceptor usage.

METHODS

Plasma samples from 55 antiretroviral-treated patients tested for coreceptor usage with the Monogram Trofile Assay were sequenced with standard population-based approaches. Fourteen of these samples were selected for further analysis with MPS. Tropism was predicted from each sequence with geno2pheno[coreceptor].

RESULTS

Prediction based on bulk-sequencing yielded 59.1% sensitivity and 90.9% specificity compared to the trofile assay. With MPS, 7600 reads were generated on average per isolate. Minorities of sequences with high confidence in CXCR4-usage were found in all samples, irrespective of phenotype. When using the default false-positive-rate of geno2pheno[coreceptor] (10%), and defining a minority cutoff of 5%, the results were concordant in all but one isolate.

CONCLUSIONS

The combination of MPS and coreceptor usage prediction results in a fast and accurate alternative to phenotypic assays. The detection of X4-viruses in all isolates suggests that coreceptor usage as well as fitness of minorities is important for therapy outcome. The high sensitivity of this technology in combination with a quantitative description of the viral population may allow implementing meaningful cutoffs for predicting response to CCR5-antagonists in the presence of X4-minorities.

Synthesis of benzocycloheptanones through coupling of δ,ε-unsaturated chromium carbene complexes and 2-alkynylbenzoyl derivatives

The coupling of pentenylcarbene complexes and 2-alkynylbenzoyl derivatives affords naphthocycloheptanones in a single step involving simultaneous construction of both the seven-membered ring and one of the aromatic rings. Aryl tethered systems undergo intramolecular cyclopropanation.

Pharmacokinetics and pharmacodynamics of TBR-652, a novel CCR5 antagonist, in HIV-1-infected, antiretroviral treatment-experienced, CCR5 antagonist-naïve patients

TBR-652 is a novel CCR5 antagonist with potent in vitro anti-HIV activity. The objective of this study was to determine the pharmacokinetics (PK) and pharmacodynamics (PD) of TBR-652 in HIV-1-infected, antiretroviral treatment-experienced, CCR5 antagonist-naïve patients. A double-blind, placebo-controlled, randomized, dose-escalating study of TBR-652 monotherapy given once daily orally for 10 days was performed, followed by a 40-day follow-up period. Approximately 10 patients/dose level received 25, 50, 75, 100, and 150 mg TBR-652 or placebo (4:1). Blood was collected at different intervals for PK and HIV-1 RNA assessments. PK analysis of TBR-652 was performed using noncompartmental methods. PK/PD was modeled using a maximum inhibitory effect model (E(max)) and 50% inhibitory concentrations (IC₅₀). TBR-652 was well absorbed in the systemic circulation. TBR-652 concentration levels declined slowly, with mean elimination half-lives ranging from 22.5 to 47.62 h across dose levels. TBR-652 treatment resulted in potent, dose-dependent decreases in viral load, with statistically significant decreases in nadir HIV-1 RNA compared to baseline for all dose levels. Suppression of HIV-1 RNA persisted over the 40-day follow-up period. A steep exposure-effect relationship was observed, with an E(max) of -1.43 log₁₀ copies/ml and IC₅₀ of 13.1 ng/ml. TBR-652 was generally safe and well tolerated at all dose levels studied. Short-term monotherapy treatments of TBR-652 in HIV-1-infected patients resulted in promising PK and PD results, with a clear exposure-response relationship at the current dose levels studied. Data from this study support further development of TBR-652 in HIV-infected patients.

Persistence and emergence of X4 virus in HIV infection

Approximately 50% of late-stage HIV patients develop CXCR4-tropic (X4) virus in addition to CCR5-tropic (R5) virus. X4 emergence occurs with a sharp decline in CD4+ T cell counts and accelerated time to AIDS. Why this phenotypic switch to X4 occurs is not well understood. Previously, we used numerical simulations of a mathematical model to show that across much of parameter space a promising new class of antiretroviral treatments, CCR5 inhibitors, can accelerate X4 emergence and immunodeficiency. Here, we show that mathematical model to be a minimal activation-based HIV model that produces a spontaneous switch to X4 virus at a clinically-representative time point, while also matching in vivo data showing X4 and R5 coexisting and competing to infect memory CD4+ T cells. Our analysis shows that X4 avoids competitive exclusion from an initially fitter R5 virus due to X4v unique ability to productively infect nave CD4+ T cells. We further justify the generalized conditions under which this minimal model holds, implying that a phenotypic switch can even occur when the fraction of activated nave CD4+ T cells increases at a slower rate than the fraction of activated memory CD4+ T cells. We find that it is the ratio of the fractions of activated nave and memory CD4+ T cells that must increase above a threshold to produce a switch. This occurs as the concentration of CD4+ T cells drops beneath a threshold. Thus, highly active antiretroviral therapy (HAART), which increases CD4+ T cell counts and decreases cellular activation levels, inhibits X4 viral growth. However, we show here that even in the simplest dual-strain framework, competition between R5 and X4 viruses often results in accelerated X4 emergence in response to CCR5 inhibition, further highlighting the potential danger of anti-CCR5 monotherapy in multi-strain HIV infection.

Maraviroc: the first chemokine coreceptor 5 inhibitor

HIV viral entry occurs via viral interaction with host cell CD4 receptors and a second coreceptor, most commonly chemokine coreceptor (CCR)5. As a result, CCR5 antagonists have been developed to block HIV entry into CD4+ cells, thereby inhibiting viral replication. The first CCR5 inhibitor approved for use in the treatment of HIV was maraviroc. Maraviroc has been shown to be successful in reducing HIV replication in both antiretroviral treatment-experienced and treatment-naive populations. Since maraviroc is only efficacious against CCR5-tropic HIV virus, it is imperative to perform viral tropism testing prior to initiation of maraviroc. The currently available enhanced sensitivity Trofile™ assay (Monogram Biosciences, CA, USA) is the reference standard of tropism tests. Although it is highly sensitive, it remains a barrier to maraviroc use because it is expensive and has a long turnaround time. The development of simpler tropism assays may allow for more widespread use of maraviroc in the future. At present, maraviroc remains a highly useful drug in the management of HIV-infected persons infected with CCR5-tropic viruses.

Maternal-fetal pharmacokinetics and dynamics of a single intrapartum dose of maraviroc in rhesus macaques

Single-dose nevirapine (NVP) is effective in reducing mother-to-child transmission (MTCT) of HIV; however, the subsequent development of drug resistance is problematic. The pharmacokinetic profile of the HIV entry inhibitor maraviroc after a single intrapartum dose in rhesus macaques was studied to determine whether maraviroc could serve as an alternative to NVP in a single-dose strategy. Four pregnant macaques received an oral dose of maraviroc 2 h before delivery, and both infant and maternal plasma maraviroc concentrations and CCR5 receptor occupancy on CD4(+) lymphocytes were measured over time. Maximum plasma maraviroc concentrations were found at delivery (2-h-postintrapartum dose) in both the mothers and infants, with median concentrations of 974 ng/ml (range, 86 to 2,830 ng/ml) and 22 ng/ml (range, 4 to 99 ng/ml), respectively. Maraviroc was detected in the plasma of mothers up to 48 h after dosing but only as long as 3.5 h in the infants. The median fetal-maternal area under the concentration-time curve (AUC) ratio was 0.009 (range, 0.000 to 0.015). Maraviroc receptor occupancy data showed evidence of unprotected CCR5 receptors on CD4(+) cells in the mothers 24 to 48 h after dosing. Extremely low CCR5 expression on CD4(+) cells of newborn macaques prevented determination of receptor occupancy in the infants. In rhesus macaques, maraviroc was poorly transferred across the placenta and was quickly cleared from the infants' blood. The low concentrations of fetal maraviroc and short pharmacokinetic profile in infants suggest that a single maternal intrapartum dose of maraviroc would not be effective in reducing the risk of MTCT of HIV.

Platelet-derived chemokines: pathophysiology and therapeutic aspects

The identification of chemokines in blood platelets has strengthened our view of these cells as participants in immune host defense. Platelet chemokines representing prestored and rapidly releasable proteins may play a major role as first-line inflammatory mediators. This is evident from their capability to recruit early inflammatory cells such as neutrophil granulocytes and monocytes and even to exhibit direct antimicrobial activity. However, insight is growing that platelet chemokines may be also long-term regulators, e.g., by activating T lymphocytes, by modulating the formation of endothelium and even thrombocytopoiesis itself. This review deals with the individual and cooperative functionality of platelet chemokines, as well as their potential as a basis for therapeutic intervention in the pathology of inflammation, infection, allergy and tumors. Within this context, therapeutic strategies based on the use of antibodies, modified chemokines, chemokine-binding proteins and chemokine receptor antagonists as well as first clinical studies will be addressed.

Positive selection of HIV host factors and the evolution of lentivirus genes

BACKGROUND

Positive selection of host proteins that interact with pathogens can indicate factors relevant for infection and potentially be a measure of pathogen driven evolution.

RESULTS

Our analysis of 1439 primate genes and 175 lentivirus genomes points to specific host factors of high genetic variability that could account for differences in susceptibility to disease and indicate specific mechanisms of host defense and pathogen adaptation. We find that the largest amount of genetic change occurs in genes coding for cellular membrane proteins of the host as well as in the viral envelope genes suggesting cell entry and immune evasion as the primary evolutionary interface between host and pathogen. We additionally detect the innate immune response as a gene functional group harboring large differences among primates that could potentially account for the different levels of immune activation in the HIV/SIV primate infection. We find a significant correlation between the evolutionary rates of interacting host and viral proteins pointing to processes of the host-pathogen biology that are relatively conserved among species and to those undergoing accelerated genetic evolution.

CONCLUSIONS

These results indicate specific host factors and their functional groups experiencing pathogen driven evolutionary selection pressures. Individual host factors pointed to by our analysis might merit further study as potential targets of antiretroviral therapies.

Personalized healthcare: how to improve outcomes by increasing benefit and decreasing risk through the use of biomarkers

The use of personalized healthcare is beginning to show promise as a means of increasing benefit and decreasing risk for patients, but much work needs to be done in order to fully exploit the advances in medical science that have occurred over the last 30 years. In particular, molecular approaches that aim to characterize patient individuality must be combined with genetic approaches to capture the promise of this potential revolution in the practice of medicine.

[CCR5-antagonists: contribution of a new antiretroviral class to the management of HIV infection]

Maraviroc, the first approved CCR5-antagonist, is indicated for treatment-experienced adult patients infected with mainly detectable CCR5-tropic HIV-1, which predominates throughout infection. The antiretroviral effectiveness of maraviroc in combination with an optimized ARV therapy has been reported in clinical trials including previously treated patients. The significantly greater increase in CD4 cell counts in patients treated with maraviroc could result from a specific action as well as a better capacity to diffuse in deep compartments. According to available reports, a tropic switch from R5 to X4 induced by maraviroc treatment is not expected. These observations, combined with the predominance of R5-virus throughout the disease, support the early use of maraviroc as soon as patients fail their therapy. Provided genotypic tests assessing R5 tropism are available when the plasma viral load is not detectable, the good safety profile of maraviroc, which includes lipid parameters, could justify its use in patients with successful regimen in order to reduce the subsequent risk of major adverse events.

Pharmacokinetic/pharmacodynamic modeling of the antiretroviral activity of the CCR5 antagonist Vicriviroc in treatment experienced HIV-infected subjects (ACTG protocol 5211)

OBJECTIVE

This substudy of AIDS Clinical Trials Group (ACTG) Protocol 5211 explored the relationship between antiretroviral effect and plasma concentrations of vicriviroc, an investigational CCR5 antagonist for HIV infection.

METHODS

Eighty-six treatment-experienced subjects failing their current antiretroviral regimens were randomized to add vicriviroc 5, 10, or 15 mg once daily or placebo for 2 weeks. Beyond week 2, subjects were changed to optimized background antiretroviral treatment while continuing vicriviroc or placebo. Plasma samples collected at weeks 2 and 8 were assayed for vicriviroc concentrations and combined with vicriviroc concentration data from 110 seronegatives enrolled in 5 phase 1 studies. An inhibitory Emax model was used to assess pharmacokinetic (PK)/pharmacodynamic relationships and recursive partitioning was applied to determine the breakpoint in vicriviroc PK parameters associated with virologic suppression.

RESULTS

A 2-compartment model was fitted to the drug concentration data. At week 2, a higher vicriviroc Cmin was associated with a greater mean drop in HIV RNA (viral load) and a higher percentage of subjects experiencing a >1 log10 copies/mL drop in viral load. In subjects with Cmin > 54 ng/mL, the mean viral load decrease was 1.35 log10 copies/mL vs. 0.76 log10 with Cmin < 54 ng/mL (P = 0.003, Student t test). At this Cmin breakpoint, 70% of subjects with the higher Cmin had a >1 log drop in HIV RNA, compared with 44% with a lower Cmin (P = 0.048, Fisher exact test). Similar results were seen with an area under the curve breakpoint of 1460 ng h/mL. At weeks 16 and 24, all vicriviroc-treated subjects experienced better viral load responses than placebo recipients, but there was no apparent relationship between PK and change in viral load among these vicriviroc-treated subjects.

CONCLUSIONS

There was a positive correlation between vicriviroc Cmin, area under the curve, and viral load changes at week 2 in treatment-experienced HIV-infected subjects receiving no other new active antiretroviral drugs. This correlation did not persist beyond week 16, probably because treatment response at that point also depended on having other active drugs in the regimen.

CCR5 antagonists: host-targeted antiviral agents for the treatment of HIV infection, 4 years on

The chemokine coreceptor 5 (CCR5) antagonists are antiretroviral agents with an extracellular, host-targeted mechanism of action against HIV. Maraviroc, the first-in-class CCR5 antagonist, received regulatory approval in 2007, becoming the first oral antiretroviral from a new class in more than 10 years. Other compounds in this class are in various stages of clinical development. In 2005, we reviewed the limited clinical data then available on CCR5 antagonists. In this follow-up review, we revisit the field and assess the clinical and virological data that have emerged in the 4 years since, with particular reference to maraviroc for which the most comprehensive data currently exist.

Canadian consensus guidelines for the optimal use of maraviroc in the treatment of HIV-infected adults

BACKGROUND AND OBJECTIVES

A Canadian group, consisting of six physicians and an HIV researcher with significant experience and knowledge in HIV management, reviewed the available data and developed guidelines for Canadian health care providers (who treat HIV infection) on the appropriate use of maraviroc (UK-427,857) in HIV-infected adults.

METHODS

Evidence from the published literature and conference presentations, as well as the expert opinions of the group members were considered and evaluated to develop the recommendations. Feedback on the draft recommendations was obtained from this core group, as well as from four other physicians across Canada with expertise in HIV treatment and experience with the use of maraviroc. The final recommendations represent the core group's consensus agreement once all feedback was considered.

RESULTS/CONCLUSIONS

Recommendations were developed to guide physicians and other health care providers in the optimal use of maraviroc. The recommendations were considered in light of the fact that the decision to include maraviroc in an antiretroviral regimen depends not only on issues that concern all antiretroviral agents, such as efficacy, safety, resistance and drug interactions, but also on the issue of viral tropism, which is unique to maraviroc and other CCR5 inhibitors.

Increasing selectivity of CC chemokine receptor 8 antagonists by engineering nondesolvation related interactions with the intended and off-target binding sites

The metabolic stability and selectivity of a series of CCR8 antagonists against binding to the hERG ion channel and cytochrome Cyp2D6 are studied by principal component analysis. It is demonstrated that an efficient way of increasing metabolic stability and selectivity of this series is to decrease compound lipophilicity by engineering nondesolvation related attractive interactions with CCR8, as rationalized by three-dimensional receptor models. Although such polar interactions led to increased compound selectivity, such a strategy could also jeopardize the DMPK profile of compounds. However, once increased potency is found, the lipophilicity can be readjusted by engineering hydrophobic substituents that fit to CCR8 but do not fit to hERG. Several such lipophilic fragments are identified by two-dimensional fragment-based QSAR analysis. Electrophysiological measurements and site-directed mutagenesis studies indicated that the repulsive interactions of these fragments with hERG are caused by steric hindrances with residue F656.

Pharmacogenetics of antiretrovirals

The introduction of highly active antiretroviral therapy (HAART) as standard of care has changed the natural history of HIV infection into a manageable chronic disease requiring long-term antiretroviral (ARV) treatment. However, response to HAART is often limited by the occurrence of toxicity or by the emergence of drug resistance. Antiretroviral treatment is characterized by differing rates of adverse events and responses. Genetic variations between human beings account for a relevant proportion of this variability. A relevant number of associations between human genetic variants and predisposition to adverse events have been described and for some antiretroviral drugs a clear and casual genotype-phenotype correlation has already been established. The strong association between abacavir hypersensitivity reaction and HLA-B*5701 has been demonstrated in both observational and blinded randomized clinical trials in racially diverse populations and represents the best example of the clinical utility of pharmacogenetic screening in HIV medicine. Genotyping for HLA-B*5701 before prescribing an abacavir containing regimen has been introduced into routine clinical practice as the standard of care for all patients. Other well-established associations include CYP2B6 alleles and efavirenz central nervous system side effects, UGT1A1 alleles and atazanavir-associated hyperbilirubinemia and HLA class II allele HLA-DRB*0101 and nevirapine-associated hypersensitivity. Despite genetic associations having been described for peripheral neuropathy, lipodystrophy, hyperlipidaemia, pancreatitis and renal proximal tubulopathy, numerous barriers exist to the successful introduction of widespread genetic testing to the clinic. Future prospects point in the direction of individualization of antiretroviral therapy through insights from host genetics. The present paper is aimed to provide a comprehensive review of the published literature and to summarize the state of research in this area. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of antiretroviral drug discovery and development, Vol 85, issue 1, 2010.

A quantitative affinity-profiling system that reveals distinct CD4/CCR5 usage patterns among human immunodeficiency virus type 1 and simian immunodeficiency virus strains

The affinity of human immunodeficiency virus (HIV) envelope for CD4 and CCR5 appears to be associated with aspects of R5 virus (virus using the CCR5 coreceptor) pathogenicity. However, entry efficiency results from complex interactions between the viral envelope glycoprotein and both CD4 and CCR5, which limits attempts to correlate viral pathogenicity with surrogate measures of envelope CD4 and CCR5 affinities. Here, we present a system that provides a quantitative and comprehensive characterization of viral entry efficiency as a direct interdependent function of both CD4 and CCR5 levels. This receptor affinity profiling system also revealed heretofore unappreciated complexities underlying CD4/CCR5 usage. We first developed a dually inducible cell line in which CD4 and CCR5 could be simultaneously and independently regulated within a physiologic range of surface expression. Infection by multiple HIV type 1 (HIV-1) and simian immunodeficiency virus isolates could be examined simultaneously for up to 48 different combinations of CD4/CCR5 expression levels, resulting in a distinct usage pattern for each virus. Thus, each virus generated a unique three-dimensional surface plot in which viral infectivity varied as a function of both CD4 and CCR5 expression. From this functional form, we obtained a sensitivity vector along with corresponding metrics that quantified an isolate's overall efficiency of CD4/CCR5 usage. When applied to viral isolates with well-characterized sensitivities to entry/fusion inhibitors, the vector metrics were able to encapsulate their known biological phenotypes. The application of the vector metrics also indicated that envelopes derived from elite suppressors had overall-reduced entry efficiencies compared to those of envelopes derived from chronically infected viremic progressors. Our affinity-profiling system may help to refine studies of R5 virus tropism and pathogenesis.

How HIV changes its tropism: evolution and adaptation?

PURPOSE OF REVIEW

To present recent information on the evolution of coreceptor use from CCR5 alone to CCR5 and CXCR4, the impact CCR5 inhibitors have on this process, and new insights into HIV-1 binding to CD4 and CCR5.

RECENT FINDINGS

The findings that are summarized include resistance to CCR5 inhibitors, genotypic predictors of coreceptor use, the link between coreceptor use and cell tropism, and new data on CCR5 structure and function.

SUMMARY

Resistance to CCR5 inhibitors is uncommon, and frequently involves selection of minor populations of R5X4 virus. Genotypic predictors of coreceptor use need to take into account the entire envelope sequence, not just V3. Genetic polymorphisms in humans that affect CCR5 or chemokines that bind CCR5 affect not only virus entry but also immune reconstitution.

Characterization of a human immunodeficiency virus type 1 V3 deletion mutation that confers resistance to CCR5 inhibitors and the ability to use aplaviroc-bound receptor

The human immunodeficiency virus type 1 (HIV-1) V3 loop is essential for coreceptor binding and principally determines tropism for the CCR5 and CXCR4 coreceptors. Using the dual-tropic virus HIV-1(R3A), we previously made an extensive panel of V3 deletions and identified subdomains within V3 that could differentially mediate R5 and X4 tropism. A deletion of residues 9 to 12 on the N-terminal side of the V3 stem ablated X4 tropism while leaving R5 tropism intact. This mutation also resulted in complete resistance to several small-molecule CCR5 inhibitors. Here, we extend these studies to further characterize a variant of this mutant, Delta9-12a, adapted for growth in CCR5(+) SupT1 cells. Studies using coreceptor chimeras, monoclonal antibodies directed against the CCR5 amino terminus (NT) and extracellular loops, and CCR5 point mutants revealed that, relative to parental R3A, R5-tropic Delta9-12a was more dependent on the CCR5 NT, a region that contacts the gp120 bridging sheet and V3 base. Neutralization sensitivity assays showed that, compared to parental R3A, Delta9-12a was more sensitive to monoclonal antibodies b12, 4E10, and 2G12. Finally, cross-antagonism assays showed that Delta9-12a could use aplaviroc-bound CCR5 for entry. These studies indicate that increased dependence on the CCR5 NT represents a mechanism by which HIV envelopes acquire resistance to CCR5 antagonists and may have more general implications for mechanisms of drug resistance that arise in vivo. In addition, envelopes such as Delta9-12a may be useful for developing new entry inhibitors that target the interaction of gp120 and the CCR5 NT.

Anti-HIV drugs: 25 compounds approved within 25 years after the discovery of HIV

In 2008, 25 years after the human immunodeficiency virus (HIV) was discovered as the then tentative aetiological agent of acquired immune deficiency syndrome (AIDS), exactly 25 anti-HIV compounds have been formally approved for clinical use in the treatment of AIDS. These compounds fall into six categories: nucleoside reverse transcriptase inhibitors (NRTIs: zidovudine, didanosine, zalcitabine, stavudine, lamivudine, abacavir and emtricitabine); nucleotide reverse transcriptase inhibitors (NtRTIs: tenofovir); non-nucleoside reverse transcriptase inhibitors (NNRTIs: nevirapine, delavirdine, efavirenz and etravirine); protease inhibitors (PIs: saquinavir, ritonavir, indinavir, nelfinavir, amprenavir, lopinavir, atazanavir, fosamprenavir, tipranavir and darunavir); cell entry inhibitors [fusion inhibitors (FIs: enfuvirtide) and co-receptor inhibitors (CRIs: maraviroc)]; and integrase inhibitors (INIs: raltegravir). These compounds should be used in drug combination regimens to achieve the highest possible benefit, tolerability and compliance and to diminish the risk of resistance development.

Cataloguing the HIV type 1 human protein interaction network

Although many interactions between HIV-1 and human proteins have been reported in the scientific literature, no publicly accessible source for efficiently reviewing this information was available. Therefore, a project was initiated in an attempt to catalogue all published interactions between HIV-1 and human proteins. HIV-related articles in PubMed were used to develop a database containing names, Entrez GeneIDs, and RefSeq protein accession numbers of interacting proteins. Furthermore, brief descriptions of the interactions, PubMed identification numbers of articles describing the interactions, and keywords for searching the interactions were incorporated. Over 100,000 articles were reviewed, resulting in the identification of 1448 human proteins that interact with HIV-1 comprising 2589 unique HIV-1-to-human protein interactions. Preliminary analysis of the extracted data indicates 32% were direct physical interactions (e.g., binding) and 68% were indirect interactions (e.g., upregulation through activation of signaling pathways). Interestingly, 37% of human proteins in the database were found to interact with more than one HIV-1 protein. For example, the signaling protein mitogen-activated protein kinase 1 has a surprising range of interactions with 10 different HIV-1 proteins. Moreover, large numbers of interactions were published for the HIV-1 regulatory protein Tat and envelope proteins: 30% and 33% of total interactions identified, respectively. The database is accessible at http://www.ncbi.nlm.nih.gov/RefSeq/HIVInteractions/ and is cross-linked to other National Center for Biotechnology Information databases and programs via Entrez Gene. This database represents a unique and continuously updated scientific resource for understanding HIV-1 replication and pathogenesis to assist in accelerating the development of effective therapeutic and vaccine interventions.

Maraviroc: a CCR5-receptor antagonist for the treatment of HIV-1 infection

BACKGROUND

The emergence of viral resistance is one of the greatest challenges in the treatment of HIV infection. Maraviroc is the first member of a new class of antiretroviral medications, the CCR5-receptor antagonists. It is approved by the US Food and Drug Administration (FDA) for use in combination with other antiretroviral agents in treatment-experienced patients infected with multidrug-resistant, CCR5-tropic HIV-1.

OBJECTIVE

This article provides an overview of the pharmacology, efficacy, and tolerability of maraviroc in the treatment of HIV-1 infection.

METHODS

Relevant information was identified through a search of MEDLINE (January 2000-May 2008) using the terms maraviroc, UK-427,857, and CCR5-receptor antagonist. Also consulted were abstracts from the International AIDS Society Conference, the Conference on Retroviruses and Opportunistic Infections, and other relevant scientific meetings. Additional publications were found by searching the reference lists of the identified articles and the FDA Web site.

RESULTS

Maraviroc is a selective, reversible, small-molecule CCR5-receptor antagonist. In vitro, it has potent anti-HIV-1 activity, with a mean 90% inhibitory concentration of 2.0 nmol/L. It is widely distributed, with a V(d) of approximately 194 L. Maraviroc is moderately metabolized in the liver (65.3%), primarily via the cytochrome P450 3A4 isozyme. It has an elimination t(1/2) of 15.9 to 22.9 hours. Until more data are available, maraviroc should be avoided in patients with severe hepatic insufficiency; dose adjustment does not appear to be necessary on the basis of age, sex, or renal function. In 2 Phase IIb/III studies, maraviroc 300 mg PO QD or BID was found to be more efficacious than placebo in reducing the viral load at 48 weeks in treatment-experienced, CCR5-tropic HIV-1-infected patients receiving an optimized background regimen (difference vs placebo-QD arm: -0.89 log(10) copies/mL [97.5% CI, -1.17 to -0.62]; BID arm: -1.05 log(10) copies/mL [97.5% CI, -1.33 to -0.78]). The proportion of patients with a viral load < 50 copies/mL was 43.2% in the QD arm and 45.5% in the BID arm, compared with 16.7% in the placebo arm (P < 0.001, both treatment arms vs placebo). In treatment-naive patients infected with CCR5-tropic virus only, maraviroc 300 mg PO BID was not noninferior to oral efavirenz 600 mg QD (difference = -4.2%; lower bound of the 1-sided 97.5% CI, -10.9 [predefined statistical cutoff for noninferiority, -10]). Maraviroc was generally well tolerated in clinical trials. The most frequently reported (> or = 5%) adverse events were upper respiratory tract infection (20.0%), cough (12.7%), pyrexia (12.0%), rash (9.6%), musculoskeletal complaints (8.7%), gastrointestinal and abdominal pain (8.2%), dizziness (8.2%), appetite disorders (7.3%), insomnia (7.0%), herpes infection (6.8%), sinusitis (6.3%), joint complaints (6.1%), bronchitis (5.9%), and constipation (5.4%). The recommended dose of maraviroc differs based on concomitant medications, ranging from 150 to 600 mg BID.

CONCLUSION

When used in combination with other antiretroviral agents, maraviroc appears to be a promising agent for treatment-experienced patients infected with multidrug-resistant, CCR5-tropic HIV-1.

Emergence and persistence of CXCR4-tropic HIV-1 in a population of men from the multicenter AIDS cohort study

We examined the emergence of CXCR4 (i.e., X4) tropism in 67 male human immunodeficiency virus type 1 (HIV-1) seroconverters from the Multicenter AIDS Cohort Study (MACS) who were selected to reflect the full spectrum of rates of HIV-1 disease progression. A mean of 10 serial samples per donor were evaluated by a laboratory-validated, commercially available assay to determine phenotypic coreceptor use. A total of 52% of men had dual- or mixed-tropic HIV-1 detected at 1 or more of the time points tested. Use of X4 by HIV-1 was detected more frequently among men who developed AIDS (defined as a CD4(+) T cell count of <200 cells/muL and/or an AIDS-defining illness) < or =11 years after seroconversion than among those who did not (P = .005), as well as among men who exhibited a total T cell count decline (i.e., a CD3(+) inflection point), compared with those who did not (P = .03). For men in whom both X4 virus and an inflection point were detected, emergence of X4 virus preceded the inflection point by a median of 0.83 years. The median CD4(+) T cell count at first detection of X4 viruses before the onset of AIDS was 475 cells/microL. We conclude that HIV-1 variants that used X4 frequently emerged at high CD4(+) T cell counts and may contribute to the decrease in T cell numbers during late HIV-1 infection.

Maraviroc, risks and benefits: a review of the clinical literature

BACKGROUND

Maraviroc represents the first licensed CCR5 co-receptor antagonist from the new antiretroviral (ARV) drug-class of entry inhibitors.

RESULTS

Results of Phase III clinical trials in three-drug-class experienced patients have presented maraviroc as a promising new agent for treatment of HIV-1-infection. Maraviroc (b.i.d./q.d.) + optimised background therapy (OBT) provided significantly superior virological control and CD4+ increases compared with placebo + OBT at 48 weeks, with no clinically relevant differences in the safety profile between the maraviroc and the placebo groups.

CONCLUSION

Its proven efficacy in cases of virological failure and three-class ARV-drug resistance is a major benefit of maraviroc compared to the so far commercially available drugs from existing (non-) nucleoside reverse transcriptase inhibitors ([N]NRTI) and protease inhibitors drug-classes, particularly in times of increasing ARV drug resistance. Moreover, the tolerability profile of the drug makes maraviroc particularly appealing as a combination partner in ARV therapy. As maraviroc however is only effective against CCR5-tropic HIV-1, tropism testing is required before initiation of treatment. Tropism-testing possibilities are still limited, and presently only possible at high costs. The main constraints to be considered in the clinical use of maraviroc are the declining number of CCR5-tropic patients with advanced HIV-1 disease owing to tropism-shifting and the occurrence of drug-drug interactions, requiring regular dose adaptations. The true clinical value of this new substance and its future role in the treatment of HIV-1-infection remains to be defined by further data from clinical studies and by future experiences of practitioners.

Maraviroc for previously treated patients with R5 HIV-1 infection

BACKGROUND

CC chemokine receptor 5 antagonists are a new class of antiretroviral agents.

METHODS

We conducted two double-blind, placebo-controlled, phase 3 studies--Maraviroc versus Optimized Therapy in Viremic Antiretroviral Treatment-Experienced Patients (MOTIVATE) 1 and MOTIVATE 2--with patients who had R5 human immunodeficiency virus type 1 (HIV-1) only. They had been treated with or had resistance to three antiretroviral-drug classes and had HIV-1 RNA levels of more than 5000 copies per milliliter. The patients were randomly assigned to one of three antiretroviral regimens consisting of maraviroc once daily, maraviroc twice daily, or placebo, each of which included optimized background therapy (OBT) based on treatment history and drug-resistance testing. Safety and efficacy were assessed after 48 weeks.

RESULTS

A total of 1049 patients received the randomly assigned study drug; the mean baseline HIV-1 RNA level was 72,400 copies per milliliter, and the median CD4 cell count was 169 per cubic millimeter. At 48 weeks, in both studies, the mean change in HIV-1 RNA from baseline was greater with maraviroc than with placebo: -1.66 and -1.82 log(10) copies per milliliter with the once-daily and twice-daily regimens, respectively, versus -0.80 with placebo in MOTIVATE 1, and -1.72 and -1.87 log(10) copies per milliliter, respectively, versus -0.76 with placebo in MOTIVATE 2. More patients receiving maraviroc once or twice daily had HIV-1 RNA levels of less than 50 copies per milliliter (42% and 47%, respectively, vs. 16% in the placebo group in MOTIVATE 1; 45% in both maraviroc groups vs. 18% in MOTIVATE 2; P<0.001 for both comparisons in each study). The change from baseline in CD4 counts was also greater with maraviroc once or twice daily than with placebo (increases of 113 and 122 per cubic millimeter, respectively, vs. 54 in MOTIVATE 1; increases of 122 and 128 per cubic millimeter, respectively, vs. 69 in MOTIVATE 2; P<0.001 for both comparisons in each study). Frequencies of adverse events were similar among the groups.

CONCLUSIONS

Maraviroc, as compared with placebo, resulted in significantly greater suppression of HIV-1 and greater increases in CD4 cell counts at 48 weeks in previously treated patients with R5 HIV-1 who were receiving OBT. (ClinicalTrials.gov numbers, NCT00098306 and NCT00098722.)