A novel small-molecular CCR5 antagonist promotes neural repair after stroke.

Chemokine receptor 5 (CCR5) is one of the main co-receptors of HIV-1, and has been found to be a potential therapeutic target for stroke. Maraviroc is a classic CCR5 antagonist, which is undergoing clinical trials against stroke. As maraviroc shows poor blood-brain barrier (BBB) permeability, it is of interest to find novel CCR5 antagonists suitable for neurological medication. In this study we characterized the therapeutic potential of a novel CCR5 antagonist A14 in treating ischemic stroke mice. A14 was discovered in screening millions compounds in the Chemdiv library based on the molecular docking diagram of CCR5 and maraviroc. We found that A14 dose-dependently inhibited the CCR5 activity with an IC50 value of 4.29 µM. Pharmacodynamic studies showed that A14 treatment exerted protective effects against neuronal ischemic injury both in vitro and vivo. In a SH-SY5Y cell line overexpressing CCR5, A14 (0.1, 1 µM) significantly alleviated OGD/R-induced cell injury. We found that the expression of CCR5 and its ligand CKLF1 was significantly upregulated during both acute and recovery period in focal cortical stroke mice; oral administration of A14 (20 mg·kg-1·d-1, for 1 week) produced sustained protective effect against motor impairment. A14 treatment had earlier onset time, lower onset dosage and much better BBB permeability compared to maraviroc. MRI analysis also showed that A14 treatment significantly reduced the infarction volume after 1 week of treatment. We further revealed that A14 treatment blocked the protein-protein interaction between CCR5 and CKLF1, increasing the activity of CREB signaling pathway in neurons, thereby improving axonal sprouting and synaptic density after stroke. In addition, A14 treatment remarkably inhibited the reactive proliferation of glial cells after stroke and reduced the infiltration of peripheral immune cells. These results demonstrate that A14 is a promising novel CCR5 antagonist for promoting neuronal repair after ischemic stroke. A14 blocked the protein-protein interaction between CKLF1 and CCR5 after stroke by binding with CCR5 stably, improved the infarct area and promoted motor recovery through reversing the CREB/pCREB signaling which was inhibited by activated CCR5 Gαi pathway, and benefited to the dendritic spines and axons sprouting.

Filling the Gaps in Antagonist CCR5 Binding, a Retrospective and Perspective Analysis.

The large number of pathologies that position CCR5 as a central molecular determinant substantiates the studies aimed at understanding receptor-ligand interactions, as well as the development of compounds that efficiently block this receptor. This perspective focuses on CCR5 antagonism as the preferred landscape for therapeutic intervention, thus the receptor active site occupancy by known antagonists of different origins is overviewed. CCL5 is a natural agonist ligand for CCR5 and an extensively studied scaffold for CCR5 antagonists production through chemokine N-terminus modification. A retrospective 3D modeling analysis on recently developed CCL5 mutants and their contribution to enhanced anti-HIV-1 activity is reported here. These results allow us to prospect the development of conceptually novel amino acid substitutions outside the CCL5 N-terminus hotspot. CCR5 interaction improvement in regions distal to the chemokine N-terminus, as well as the stabilization of the chemokine hydrophobic core are strategies that influence binding affinity and stability beyond the agonist/antagonist dualism. Furthermore, the development of allosteric antagonists topologically remote from the orthosteric site (e.g., intracellular or membrane-embedded) is an intriguing new avenue in GPCR druggability and thus a conceivable novel direction for CCR5 blockade. Ultimately, the three-dimensional structure elucidation of the interaction between various ligands and CCR5 helps illuminate the active site occupancy and mechanism of action.

Structure-based identification of novel scaffolds as potential HIV-1 entry inhibitors involving CCR5.

C-C chemokine receptor 5 (CCR5), which is part of the chemokine receptor family, is a member of the G protein-coupled receptor superfamily. The interactions of CCR5 with HIV-1 during viral entry position it as an effective therapeutic target for designing potent antiviral therapies. The small-molecule Maraviroc was approved by the FDA as a CCR5 drug in 2007, while clinical trials failure has characterised many of the other CCR5 inhibitors. Thus, the continual identification of potential CCR5 inhibitors is, therefore, warranted. In this study, a structure-based discovery approach has been utilised to screen and retrieved novel potential CCR5 inhibitors from the Asinex antiviral compound (∼ 8,722) database. Explicit lipid-bilayer molecular dynamics simulation, in silico physicochemical and pharmacokinetic analyses, were further performed for the top compounds. A total of 23 structurally diverse compounds with binding scores higher than Maraviroc were selected. Subsequent molecular dynamics (MD) simulations analysis of the top four compounds LAS 51495192, BDB 26405401, BDB 26419079, and LAS 34154543, maintained stability at the CCR5 binding site. Furthermore, these compounds made pertinent interactions with CCR5 residues critical for the HIV-1 gp120-V3 loop binding such as Trp86, Tyr89, Phe109, Tyr108, Glu283 and Tyr251. Additionally, the predicted in silico physicochemical and pharmacokinetic descriptors of the selected compounds were within the acceptable range for drug-likeness. The results suggest positive indications that the identified molecules may represent promising CCR5 entry inhibitors. Further structural optimisations and biochemical testing of the proposed compounds may assist in the discovery of effective HIV-1 therapy.Communicated by Ramaswamy H. Sarma.

A "Two-Birds-One-Stone" Approach toward the Design of Bifunctional Human Immunodeficiency Virus Type 1 Entry Inhibitors Targeting the CCR5 Coreceptor and gp41 N-Terminal Heptad Repeat Region.

Previous studies have reported the stepwise nature of human immunodeficiency virus type 1 (HIV-1) entry and the pivotal role of coreceptor CCR5 and the gp41 N-terminal heptad repeat (NHR) region in this event. With this in mind, we herein report a dual-targeted drug compound featuring bifunctional entry inhibitors, consisting of a piperidine-4-carboxamide-based CCR5 antagonist, TAK-220, and a gp41 NHR-targeting fusion-inhibitory peptide, C34. The resultant chimeras were constructed by linking both pharmacophores with a polyethylene glycol spacer. One chimera, CP12TAK, exhibited exceptionally potent antiviral activity, about 40- and 306-fold over that of its parent inhibitors, C34 and TAK-220, respectively. In addition to R5-tropic viruses, CP12TAK also strongly inhibited infection of X4-tropic HIV-1 strains. These data are promising for the further development of CP12TAK as a new anti-HIV-1 drug. Results show that this strategy could be extended to the design of therapies against infection of other enveloped viruses.

Drug Re-positioning Studies for Novel HIV-1 Inhibitors Using Binary QSAR Models and Multi-target-driven In Silico Studies.

Current antiretroviral therapies against HIV involve the usage of at least two drugs that target different stages of HIV life cycle. However, potential drug interactions and side effects pose a problem. A promising concept for complex disease treatment is 'one molecule-multiple target' approach to overcome undesired effects of multiple drugs. Additionally, it is beneficial to consider drug re-purposing due to the cost of taking a drug into the market. Taking these into account, here potential anti-HIV compounds are suggested by virtually screening small approved drug molecules and clinical candidates. Initially, binary QSAR models are used to predict the therapeutic activity of around 7900 compounds against HIV and to predict the toxicity of molecules with high therapeutic activities. Selected compounds are considered for molecular docking studies against two targets, HIV-1 protease enzyme, and chemokine co-receptor CCR5. The top docking poses for all 549 molecules are then subjected to short (1 ns) individual molecular dynamics (MD) simulations and they are ranked based on their calculated relative binding free energies. Finally, 25 molecules are selected for long (200 ns) MD simulations, and 5 molecules are suggested as promising multi-target HIV agents. The results of this study may open new avenues for the designing of new dual HIV-1 inhibitor scaffolds.

Allosteric mechanism of an oximino-piperidino-piperidine antagonist for the CCR5 chemokine receptor.

The first step for the HIV-1 virus infecting host cell is bound with the CCR5 chemokine receptor. A set of allosteric inhibitors of oximino-piperidino-piperidine antagonists for CCR5 chemokine receptor was discovered. However, the allosteric mechanism of these inhibitors is still unsolved. Therefore, residue-level dynamics correlation network combining with on molecular dynamics simulation was used to investigate the allosteric mechanism. The dynamics correlation network of bound CCR5 is significantly different from that of free CCR5. The community of the most active complex suggests that the allosteric information can freely transfer from the allosteric site to the effector site of the second extracellular loop, while the information transfers bottleneck for the less active one. Here, a hypothesis was proposed that "binding-induced allosteric mechanism" was used to reveal the allosteric regulation of antagonists and the network perturbation confirmed it. Finally, the shortest path algorithm was used to identify the possible allosteric pathway with Gly173-Lys171-Thr177-Tyr89-LIG which was evaluated by the network perturbation of key residue. Furthermore, the efficiency of allostery for the most active system is the highest among these antagonist complexes. The strategy targeting the allosteric pathway can be used to design novel inhibitors of HIV-1 virus.

LDH hybrid thermosensitive hydrogel for intravaginal delivery of anti-HIV drugs.

Microbicides based on hydrogel have become an effective way to prevent the HIV replication and transmission because of their convenience and prolonging drug release. In this study, a hybrid thermo-sensitive hydrogel constituted by nanosized layered double hydroxides and poloxamer 407 (P407) was constructed and co-loaded with both hydrophobic and hydrophilic drug. The LDH-P407 hydrogel could achieve sol-gel transition at body temperature. The in vivo experiment showed that LDH-P407 hydrogel can achieve controlled release of theaflavin and Nile red (hydrophobic drug model) into blood by vaginal drug delivery, meanwhile the hydrogel showed barely mucosal irritation. In addition, ex vivo experiment showed that the nifeviroc-loaded LDH-P407 hydrogel was able to specifically bind co-receptor CCR5 of DCs cells. Therefore, the LDH-P407 hydrogel would be a promising carrier for intravaginal delivery of anti-HIV drugs.

Activity and structural analysis of GRL-117C: a novel small molecule CCR5 inhibitor active against R5-tropic HIV-1s.

CCR5 is a member of the G-protein coupled receptor family that serves as an essential co-receptor for cellular entry of R5-tropic HIV-1, and is a validated target for therapeutics against HIV-1 infections. In the present study, we designed and synthesized a series of novel small CCR5 inhibitors and evaluated their antiviral activity. GRL-117C inhibited the replication of wild-type R5-HIV-1 with a sub-nanomolar IC50 value. These derivatives retained activity against vicriviroc-resistant HIV-1s, but did not show activity against maraviroc (MVC)-resistant HIV-1. Structural modeling indicated that the binding of compounds to CCR5 occurs in the hydrophobic cavity of CCR5 under the second extracellular loop, and amino acids critical for their binding were almost similar with those of MVC, which explains viral cross-resistance with MVC. On the other hand, one derivative, GRL-10018C, less potent against HIV-1, but more potent in inhibiting CC-chemokine binding, occupied the upper region of the binding cavity with its bis-THF moiety, presumably causing greater steric hindrance with CC-chemokines. Recent studies have shown additional unique features of certain CCR5 inhibitors such as immunomodulating properties and HIV-1 latency reversal properties, and thus, continuous efforts in developing new CCR5 inhibitors with unique binding profiles is necessary.

CCR5/CXCR4 Dual Antagonism for the Improvement of HIV Infection Therapy.

HIV entry in the host cell requires the interaction with the CD4 membrane receptor, and depends on the activation of one or both co-receptors CCR5 and CXCR4. Former selective co-receptor antagonists, acting at early stages of infection, are able to impair the receptor functions, preventing the viral spread toward AIDS. Due to the capability of HIV to develop resistance by switching from CCR5 to CXCR4, dual co-receptor antagonists could represent the next generation of AIDS prophylaxis drugs. We herein present a survey on relevant results published in the last few years on compounds acting simultaneously on both co-receptors, potentially useful as preventing agents or in combination with classical anti-retroviral drugs based therapy.

Penicillixanthone A, a marine-derived dual-coreceptor antagonist as anti-HIV-1 agent.

Marine micro-organisms have been proven to be excellent sources of bioactive compounds against HIV-1. Several natural products obtained from marine-derived Aspergillus fungi were screened for their activities to inhibit HIV-1 infection. Penicillixanthone A (PXA), a natural xanthone dimer from jellyfish-derived fungus Aspergillus fumigates, displayed potent anti-HIV-1 activity by inhibiting infection against CCR5-tropic HIV-1 SF162 and CXCR4-tropic HIV-1 NL4-3, with IC50 of 0.36 and 0.26 µM, respectively. Molecular docking study was conducted to understand the possible binding mode of PXA with the CCR5/CXCR4. The results revealed that, the marine-derived PXA, as a CCR5/CXCR4 dual-coreceptor antagonist, presents a new type of potential lead product for the development of anti-HIV therapeutics.

Structure-Based Design of 1-Heteroaryl-1,3-propanediamine Derivatives as a Novel Series of CC-Chemokine Receptor 5 Antagonists.

CC-chemokine receptor 5 (CCR5) is an attractive target for preventing the entry of human immunodeficiency virus 1 (HIV-1) into human host cells. Maraviroc is the only CCR5 antagonist, and it was marketed in 2007. To overcome the shortcomings of maraviroc, structure-based drug design was performed to minimize CYP450 inhibition and to enhance anti-HIV potency and bioavailability. Thirty-four novel 1-heteroaryl-1,3-propanediamine derivatives (1-34) were synthesized, displaying CCR5-antagonist activities in the 2.3-296.4 nM range. Among these, compounds 21 and 34 were the most potent CCR5 antagonists, with excellent in vitro anti-HIV-1 activity, low cytotoxicity, and an acceptable pharmacokinetic profile. Furthermore, the X-ray crystal structures of compounds 21 and 34 bound to CCR5 were determined at 2.8 Å resolution. Compound 34 exhibited no CYP450-inhibition activity at 25 µM, which overcomes the potential drug-drug interaction of maraviroc. Compound 34 represents a promising drug candidate for HIV-infection treatment.

Recent updates for designing CCR5 antagonists as anti-retroviral agents.

The healthcare system faces various challenges in human immunodeficiency virus (HIV) therapy due to resistance to Anti-Retroviral Therapy (ART) as a consequence of the evolutionary process. Despite the success of antiretroviral drugs like Zidovudine, Zalcitabine, Raltegravir WHO ranks HIV as one of the deadliest diseases with a mortality of one million lives in 2016. Thus, there emerges an urgency of developing a novel anti-retroviral agent that combat resistant HIV strains. The clinical development of ART from a single drug regimen to current triple drug combination is very slow. The progression in the structural biology of the viral envelope prompted the discovery of novel targets, which can be demonstrated a proficient approach for drug design of anti-retroviral agents. The current review enlightens the recent updates in the structural biology of the viral envelope and focuses on CCR5 as a validated target as well as ways to overcome CCR5 resistance. The article also throws light on the SAR studies and most prevalent mutations in the receptor for designing CCR5 antagonists that can combat HIV-1 infection. To conclude, the paper lists diversified scaffolds that are in pipeline by various pharmaceutical companies that could provide an aid for developing novel CCR5 antagonists.

The applications of PCA in QSAR studies: A case study on CCR5 antagonists.

Principal component analysis (PCA), as a well-known multivariate data analysis and data reduction technique, is an important and useful algebraic tool in drug design and discovery. PCA, in a typical quantitative structure-activity relationship (QSAR) study, analyzes an original data matrix in which molecules are described by several intercorrelated quantitative dependent variables (molecular descriptors). Although extensively applied, there is disparity in the literature with respect to the applications of PCA in the QSAR studies. This study investigates the different applications of PCA in QSAR studies using a dataset including CCR5 inhibitors. The different types of preprocessing are used to compare the PCA performances. The use of PC plots in the exploratory investigation of matrix of descriptors is described. This work is also proved PCA analysis to be a powerful technique for exploring complex datasets in QSAR studies for identification of outliers. This study shows that PCA is able to easily apply to the pool of calculated structural descriptors and also the extracted information can be used to help decide upon an appropriate harder model for further analysis.

Structure of CC Chemokine Receptor 5 with a Potent Chemokine Antagonist Reveals Mechanisms of Chemokine Recognition and Molecular Mimicry by HIV.

CCR5 is the primary chemokine receptor utilized by HIV to infect leukocytes, whereas CCR5 ligands inhibit infection by blocking CCR5 engagement with HIV gp120. To guide the design of improved therapeutics, we solved the structure of CCR5 in complex with chemokine antagonist [5P7]CCL5. Several structural features appeared to contribute to the anti-HIV potency of [5P7]CCL5, including the distinct chemokine orientation relative to the receptor, the near-complete occupancy of the receptor binding pocket, the dense network of intermolecular hydrogen bonds, and the similarity of binding determinants with the FDA-approved HIV inhibitor Maraviroc. Molecular modeling indicated that HIV gp120 mimicked the chemokine interaction with CCR5, providing an explanation for the ability of CCR5 to recognize diverse ligands and gp120 variants. Our findings reveal that structural plasticity facilitates receptor-chemokine specificity and enables exploitation by HIV, and provide insight into the design of small molecule and protein inhibitors for HIV and other CCR5-mediated diseases.

How to win the HIV-1 drug resistance hurdle race: running faster or jumping higher?

Infections by the human immunodeficiency virus type 1 (HIV-1), the causative agent of the acquired immunodeficiency syndrome (AIDS), are still totaling an appalling 36.7 millions worldwide, with 1.1 million AIDS deaths/year and a similar number of yearly new infections. All this, in spite of the discovery of HIV-1 as the AIDS etiological agent more than 30 years ago and the introduction of an effective combinatorial antiretroviral therapy (cART), able to control disease progression, more than 20 years ago. Although very effective, current cART is plagued by the emergence of drug-resistant viral variants and most of the efforts in the development of novel direct-acting antiviral agents (DAAs) against HIV-1 have been devoted toward the fighting of resistance. In this review, rather than providing a detailed listing of all the drugs and the corresponding resistance mutations, we aim, through relevant examples, at presenting to the general reader the conceptual shift in the approaches that are being taken to overcome the viral resistance hurdle. From the classic 'running faster' strategy, based on the development of novel DAAs active against the mutant viruses selected by the previous drugs and/or presenting to the virus a high genetic barrier toward the development of resilience, to a 'jumping higher' approach, which looks at the cell, rather than the virus, as a source of valuable drug targets, in order to make the cellular environment non-permissive toward the replication of both wild-type and mutated viruses.

Design and Elaboration of a Tractable Tricyclic Scaffold To Synthesize Druglike Inhibitors of Dipeptidyl Peptidase-4 (DPP-4), Antagonists of the C-C Chemokine Receptor Type 5 (CCR5), and Highly Potent and Selective Phosphoinositol-3 Kinase δ (PI3Kδ) Inhibitors.

A novel molecular scaffold has been synthesized, and its incorporation into new analogues of biologically active molecules across multiple target classes will be discussed. In these studies, we have shown use of the tricyclic scaffold to synthesize potent inhibitors of the serine peptidase DPP-4, antagonists of the CCR5 receptor, and highly potent and selective PI3K δ isoform inhibitors. We also describe the predicted physicochemical properties of the resulting inhibitors and conclude that the tractable molecular scaffold could have potential application in future drug discovery programs.

Identification of potential CCR5 inhibitors through pharmacophore-based virtual screening, molecular dynamics simulation and binding free energy analysis.

CC chemokine receptor 5 (CCR5), a member of G protein-coupled receptors (GPCRs), plays a vital role in inflammatory responses to infection. Alterations in the expression of CCR5 have been correlated with disease progression in many types of cancers. The idea of using CCR5 as a target for therapeutic intervention has been demonstrated to prevent disease progression. To date, only a few compounds have been reported as CCR5 inhibitors. In this study, a series of CCR5 antagonists were used to construct pharmacophore models. Then the optimal model was utilized as a 3D query to identify novel chemical entities from structural databases. After refinement by molecular docking, drug-likeness analysis, molecular dynamics simulations (MDS) and binding free energy analysis, three potential inhibitors (25, 29 and 45) were identified. MD simulations suggested that the screened compounds retained the important common binding mode known for CCR5 inhibitors (maraviroc and nifeviroc), which occupied the bottom of a pocket and stabilized the conformation of CCR5. During the binding process, van der Waals interactions provided the substantial driving force. The most favorable contributions were from Tyr37, Trp86, Tyr89, Tyr108, Phe109, Phe112, Gln194, Thr195, Ile198, Trp248, Tyr251, Leu255, Thr259, Met279, Glu283 and Met287. The above results suggest that the hybrid strategy would provide a basis for rational drug design.

3D-QSAR Studies on the Biological Activity of Imidazolidinylpiperidinylbenzoic Acids as Chemokine Receptor Antagonists.

BACKGROUND: Human immunodeficiency virus type 1 (HIV-1) infection ultimately leading to acquired immunodeficiency syndrome (AIDS), remains a significant problem. CCR5 is a member of the chemokine receptor family that is utilized in the early stage of the replication cycle by the most commonly transmitted M-tropic strains of HIV-1. In this study, we developed 3D-QSAR models using CoMFA and CoMSIA methods on a series of 71 imidazolidinylpiperidinylbenzoic acid CCR5 antagonists, in order to better understand the substituent requirements and get more potent antagonists of CCR5. METHODS: The research of 3D-QSAR modeling of imidazolidinylpiperidinylbenzoic acids as chemokine receptor 5 (CCR5) antagonists was conducted using comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA). RESULTS: For this study, a dataset containing 71 imidazolidinyl-piperidinyl-benzoic acids was divided into a training set of 22 compounds and a test set of 49 compounds. The results obtained from the CoMFA/CoMSIA model exhibited a statistical significance r(2) of 0.996 (0.984) with an estimated standard error of 0.109 (0.209). CONCLUSION: Both CoMFA and CoMSIA models provided valuable insight into the structural requirements for improving the activity of then CCR5 antagonists.

Incompatible Natures of the HIV-1 Envelope in Resistance to the CCR5 Antagonist Cenicriviroc and to Neutralizing Antibodies.

Cenicriviroc is a CCR5 antagonist which prevents human immunodeficiency virus type 1 (HIV-1) from cellular entry. The CCR5-binding regions of the HIV-1 envelope glycoprotein are important targets for neutralizing antibodies (NAbs), and mutations conferring cenicriviroc resistance may therefore affect sensitivity to NAbs. Here, we used the in vitro induction of HIV-1 variants resistant to cenicriviroc or NAbs to examine the relationship between resistance to cenicriviroc and resistance to NAbs. The cenicriviroc-resistant variant KK652-67 (strain KK passaged 67 times in the presence of increasing concentrations of cenicriviroc) was sensitive to neutralization by NAbs against the V3 loop, the CD4-induced (CD4i) region, and the CD4-binding site (CD4bs), whereas the wild-type (WT) parental HIV-1 strain KKWT from which cenicriviroc-resistant strain KK652-67 was obtained was resistant to these NAbs. The V3 region of KK652-67 was important for cenicriviroc resistance and critical to the high sensitivity of the V3, CD4i, and CD4bs epitopes to NAbs. Moreover, induction of variants resistant to anti-V3 NAb 0.5γ and anti-CD4i NAb 4E9C from cenicriviroc-resistant strain KK652-67 resulted in reversion to the cenicriviroc-sensitive phenotype comparable to that of the parental strain, KKWT. Resistance to 0.5γ and 4E9C was caused by the novel substitutions R315K, G324R, and E381K in the V3 and C3 regions near the substitutions conferring cenicriviroc resistance. Importantly, these amino acid changes in the CCR5-binding region were also responsible for reversion to the cenicriviroc-sensitive phenotype. These results suggest the presence of key amino acid residues where resistance to cenicriviroc is incompatible with resistance to NAbs. This implies that cenicriviroc and neutralizing antibodies may restrict the emergence of variants resistant to each other.

Molecular Gymnastics: Mechanisms of HIV-1 Resistance to CCR5 Antagonists and Impact on Virus Phenotypes.

Human immunodeficiency virus type 1 (HIV-1) enters host cells through the binding of its envelope glycoproteins (Env) to the host cell receptor CD4 and then subsequent binding to a chemokine coreceptor, either CCR5 or CXCR4. CCR5 antagonists are a relatively recent class addition to the armamentarium of anti-HIV-1 drugs. These compounds act by binding to a hydrophobic pocket formed by the transmembrane helices of CCR5 and altering the conformation of the extracellular domains, such that they are no longer recognized by Env. Maraviroc is the first drug within this class to be licenced for use in HIV-1 therapy regimens. HIV resistance to CCR5 antagonists occurs either through outgrowth of pre-existing CXCR4-using viruses, or through acquisition of the ability of CCR5-using HIV-1 to use the antagonist bound form of CCR5. In the latter scenario, the mechanism underlying resistance is through complex alterations in the way that resistant Envs engage CCR5. These significant changes are unlikely to occur without consequence to the viral entry phenotype and may also open up new avenues to target CCR5 antagonist resistant viruses. This review discusses the mechanism of action of CCR5 antagonists, how HIV resistance to CCR5 antagonists occurs, and the subsequent effects on Env function.