Chemokine receptors in HIV-1 and SIV infection

Seven transmembrane segment (7TMS) receptors for chemokines and related molecules have been demonstrated to be essential, in addition to CD4, for HIV and SIV infection. The β-chemokine receptor CCR5 is the primary, perhaps sole, coreceptor for HIV-1 during the early and chronic phases of infection, and supports infection by most primary HIV-1 and many SIV isolates. Late-stage primary and laboratory-adapted HIV-1, HIV-2, and SIV isolates can use other 7TMS receptors. CXCR4 appears especially important in late-stage HIV infection; several related receptors can also be used. The specificity of SIV viruses is similar. Commonalities among these receptors, combined with analyses of mutated molecules, indicate that discrete, conformationally-dependent sites on the chemokine receptors determine their association with the third variable and conserved regions of viral envelope glycoproteins. These studies are useful for elucidating the mechanism and molecular determinants of HIV-1 entry, and of inhibitors to that entry.     

Immunoreactive cycloimmunogen design based on conformational epitopes derived from human immunodeficiency virus type 1 coreceptors: cyclic dodecapeptides mimic undecapeptidyl arches of extracellular loop-2 in chemokine receptor and inhibit human immunodeficiency virus type 1 infection

Human immunodeficiency virus type 1 (HIV-1) requires a chemokine receptor (CCR5 or CXCR4) as a coreceptor not only for initiate viral entry but also protecting highly conserved neutralization epitopes from the attack of neutralizing antibodies. Over the past decade, many studies have provided new insights into the HIV entry mechanism and have focused on developing an effective vaccine strategy. However, to date, no vaccine that can provide protection from HIV-1 infection has been developed. One reason for the disappointing results has been the inability of current vaccine candidates to elicit a broadly reactive immunity to viral proteins such as the envelope (env) protein. Here, we propose that chemokine receptors are attractive targets of vaccine development because their structures are highly conserved and that our synthetic cycloimmunogens can mimic conformational-specific epitopes of undecapeptidyl arches (UPAs: R(168)-C(178) in CCR5, N(176)-C(186) in CXCR4) and be useful for HIV-1 novel vaccine development.     

HIV-1 (co)receptors: implications for vaccine and therapy design

The ultimate aim of therapy or vaccine design against HIV is to eliminate ongoing virus replication or prevent HIV infection. The task at hand is daunting given the wide array of HIV variants circulating and the immense degree of variation found within the virus, especially in the envelope glycoprotein. HIV utilizes the CD4 receptor and a range of 7 transmembrane chemokine coreceptors for cell entry, specifically CCR5 and CXCR4. These receptors provide a number of targets for therapy design, however, the finding that multiple receptors allow for viral entry suggest that targeting one may cause the virus to swirch to using another receptor. The molecular interactions directing coreceptor usage are complex and can involve the same modifications associated with escape from the effect of neutralizing antibodies (NAbs), indicating that they are not unrelated and can in all liklihood impact on each other. Furthermore, a large array of other receptors, other than CD4, CCR5 and/or CXCR4 can interact with HIV with consequences for HIV tranmssion as well as disease progression.     

Rescue of HIV-1 long-time archived X4 strains to escape maraviroc

Entry of Human Immunodeficiency Virus type 1 (HIV-1) into target cells is mediated by the CD4 receptor and a coreceptor, CCR5 or CXCR4. Maraviroc interferes with HIV entry by binding the CCR5 coreceptor. Virological failure to maraviroc-containing regimens can occur through the emergence of resistance, or through tropism evolution and broadened coreceptor usage. In the latter case, the physiological relevance of minority strains is a major concern. Here we report a retrospective analysis of coreceptor-usage and evolution based on 454-ultra-deep-sequencing of plasma and Peripheral Blood Mononuclear Cell (PBMC)-derived envelope V3-loops, accounting for coreceptor usage, from a patient who failed a maraviroc-containing regimen through the emergence of X4 strains. The X4 maraviroc-escape variant resulted from recombination between a long time archived proviral sequence from 2003 (5'-portion, including the V3-loop) and the dominant R5 strains circulating in plasma at the time of maraviroc-treatment initiation (3'-portion). Phylogenetic analyses and BEAST modeling highlighted that an early diverse viral quasispecies underwent a severe bottleneck following reinitiation of HAART and repeated IL-2 cycles between 1999 and 2001, leading to the transient outgrowth and archiving of one highly homogeneous X4 population from plasma, and to the expansion in plasma of one PBMC-derived R5 strain. Under maraviroc selective pressure, the early, no longer detectable X4 strains archived in PBMC were partially rescued to provide X4-determinants to the main circulating strain.     

Inhibition of CCR5-mediated infection by diverse R5 and R5X4 HIV and SIV isolates using novel small molecule inhibitors of CCR5: effects of viral diversity, target cell and receptor density

Highly active anti-retroviral therapy (HAART) has been very effective in reducing viral loads in human immunodeficiency virus (HIV)-1 patients. However, current therapies carry detrimental side effects, require complex drug regimes and are threatened by the emergence of drug-resistant variants. There is an urgent need for new anti-HIV drugs that target different stages of the replication cycle. Several synthetic small organic molecules that inhibit HIV infection by binding to the CCR5 coreceptor without causing cell activation have already been reported. Here, we have exploited a series of CCR5 antagonists to investigate their effects on diverse HIV and the simian counterpart (SIV) isolates for infection of a variety of cell types via different concentrations of cell surface CCR5. These inhibitors show no cross-reactivity against alternative HIV coreceptors including CCR3, CCR8, GPR1, APJ, CXCR4 and CXCR6. They are able to inhibit a diverse range of R5 and R5X4 HIV-1 isolates as well as HIV-2 and SIV strains. Inhibition was observed in cell lines as well as primary PBMCs and macrophages. The extent of inhibition was dependent on cell type and on cell surface CCR5 concentration. Our results underscore the potential of CCR5 inhibitors for clinical development.     

Rescue of HIV-1 long-time archived X4 strains to escape maraviroc

Entry of Human Immunodeficiency Virus type 1 (HIV-1) into target cells is mediated by the CD4 receptor and a coreceptor, CCR5 or CXCR4. Maraviroc interferes with HIV entry by binding the CCR5 coreceptor. Virological failure to maraviroc-containing regimens can occur through the emergence of resistance, or through tropism evolution and broadened coreceptor usage. In the latter case, the physiological relevance of minority strains is a major concern.Here we report a retrospective analysis of coreceptor-usage and evolution based on 454-ultra-deep-sequencing of plasma and Peripheral Blood Mononuclear Cell (PBMC)-derived envelope V3-loops, accounting for coreceptor usage, from a patient who failed a maraviroc-containing regimen through the emergence of X4 strains. The X4 maraviroc-escape variant resulted from recombination between a long time archived proviral sequence from 2003 (5′-portion, including the V3-loop) and the dominant R5 strains circulating in plasma at the time of maraviroc-treatment initiation (3′-portion). Phylogenetic analyses and BEAST modeling highlighted that an early diverse viral quasispecies underwent a severe bottleneck following reinitiation of HAART and repeated IL-2 cycles between 1999 and 2001, leading to the transient outgrowth and archiving of one highly homogeneous X4 population from plasma, and to the expansion in plasma of one PBMC-derived R5 strain. Under maraviroc selective pressure, the early, no longer detectable X4 strains archived in PBMC were partially rescued to provide X4-determinants to the main circulating strain.     

Glycoside analogs of beta-galactosylceramide, a novel class of small molecule antiviral agents that inhibit HIV-1 entry

The interaction between HIV gp120 and galactose-containing cell surface glycolipids such as GalCer or Gb(3) is known to facilitate HIV binding to both CD4(+) as well as CD4(-) cells. In an effort to develop small molecule HIV-1 entry inhibitors with improved solubility and efficacy, we have synthesized a series of C-glycoside analogs of GalCer and tested their anti HIV-1 activity. The analogs were tested for gp120 binding using a HIV-1 (IIIB) V3-loop specific peptide. Two of the six analogs that interfered with gp120 binding also inhibited HIV Env-mediated cell-to-cell fusion and viral entry in the absence of any significant cytotoxicity. Analogs with two side chains did not show inhibition of fusion and/or infection under identical conditions. The inhibition of virus infection seen by these compounds was not coreceptor dependent, as they inhibited CXCR4, CCR5 as well as dual tropic viruses. These compounds showed inhibition of HIV entry at early steps in viral infection since the compounds were inactive if added post viral entry. Temperature-arrested state experiments showed that the compounds act at the level of virus attachment to the cells likely at a pre-CD4 engagement step. These compounds also showed inhibition of VSV glycoprotein-pseudotyped virus. The results presented here show that the glycoside derivatives of GalCer with simple side chains may serve as a novel class of small molecule HIV-1 entry inhibitors that would be active against a number of HIV isolates as well as other enveloped viruses.     

Variation of Macrophage Tropism among HIV-1 R5 Envelopes in Brain and Other Tissues

Human immunodeficiency virus (HIV)-positive individuals frequently suffer from progressive encephelopathy, which is characterized by sensory neuropathy, sensory myelopathy, and dementia. Our group and others have reported the presence of highly macrophage-tropic R5 variants of HIV-1 in brain tissue of patients with neurological complications. These variants are able to exploit low amounts of CD4 and/or CCR5 for infection and potentially confer an expanded tropism for any cell types that express low CD4 and/or CCR5. In contrast to the brain-derived envelopes, we found that envelopes from lymph node tissue, blood, or semen were predominantly non-macrophage-tropic and required high amounts of CD4 for infection. Nevertheless, where tested, the non-macrophage-tropic envelopes conferred efficient replication in primary CD4⁺ T-cell cultures. Determinants of R5 macrophage tropism appear to involve changes in the CD4 binding site, although further unknown determinants are also involved. The variation of R5 envelopes also affects their sensitivity to inhibition by ligands and entry inhibitors that target CD4 and CCR5. In summary, HIV-1 R5 viruses vary extensively in macrophage tropism. In the brain, highly macrophage-tropic variants may represent neurotropic or neurovirulent viruses. In addition, variation in R5 macrophage tropism may also have implications (1) for transmission, depending on what role macrophages or cells that express low CD4 and/or CCR5 play in the establishment of infection in a new host, and (2) for pathogenesis and depletion of CD4⁺ T cells (i.e., do highly macrophage-tropic variants confer a broader tropism among CD4⁺ T-cell populations late in disease and contribute to their depletion?).     

Maraviroc: the evidence for its potential in the management of HIV

Introduction:

New antiretroviral agents that are more convenient, better tolerated with fewer short- and long-term side effects, and that have novel resistance patterns are needed at all lines of therapy in patients infected with human immunodeficiency virus (HIV). Therefore, next generation products of current classes and alternative classes of antiretroviral agents are needed. The CC-chemokine receptor 5 (CCR5) antagonists are a novel class of antiretroviral agents that prevent the entry of HIV into host cells by blocking the CCR5 coreceptor. Within this class, maraviroc is the agent furthest along in development.

Aims:

The aim of this review is to evaluate the emerging evidence for the use of the CCR5 antagonist maraviroc in antiretroviral treatment-naïve and treatment-experienced patients with HIV-1 infection.

Evidence review:

Preliminary evidence from phase I/IIa short-term studies suggest that maraviroc monotherapy is effective at reducing HIV viral load, and is generally well tolerated. In-vitro evidence suggests that maraviroc will be effective in drug-naïve patients with CCR5-tropic virus, as well as in those with CCR5-tropic virus who have developed HIV resistance to existing antiretroviral regimens. However, it is not known how quickly resistance may develop to maraviroc in clinical practice.

Clinical potential:

Current evidence supports the continued development of maraviroc as a potentially useful, alternative treatment for the management of HIV infection. Maraviroc monotherapy has a high potency and long half-life, allowing single-pill dosing. Therefore, it is expected that maraviroc will have a beneficial effect on patient adherence and viral load in combination with other antiretroviral agents. Maraviroc is only effective against CCR5-tropic virus, which predominates throughout infection but is more common in patients at the early asymptomatic stage of infection.     

Oral CCR5 inhibitors: will they make it through?

The therapeutic armamentarium against HIV has recently gained a drug belonging to a novel class of antiretrovirals, the entry inhibitors. The last decade has driven an in-depth knowledge of the HIV entry process, unravelling the multiple engagements of the HIV envelope proteins with the cellular receptorial complex that is composed of a primary receptor (CD4) and a co-receptor (CCR5 or CXCR4). The vast majority of HIV-infected subjects exhibit biological viral variants that use CCR5 as a co-receptor. Individuals with a mutated CCR5 gene, both homo- and heterozygotes, appear to be healthy. For these and other reasons, CCR5 represents an appealing target for treatment intervention, although certain challenges can not be ignored. Promising small-molecule, orally bioavailable CCR5 antagonists are under development for the treatment of HIV-1 infection.     

Oral CCR5 inhibitors: will they make it through?

The therapeutic armamentarium against HIV has recently gained a drug belonging to a novel class of antiretrovirals, the entry inhibitors. The last decade has driven an in-depth knowledge of the HIV entry process, unravelling the multiple engagements of the HIV envelope proteins with the cellular receptorial complex that is composed of a primary receptor (CD4) and a co-receptor (CCR5 or CXCR4). The vast majority of HIV-infected subjects exhibit biological viral variants that use CCR5 as a co-receptor. Individuals with a mutated CCR5 gene, both homo- and heterozygotes, appear to be healthy. For these and other reasons, CCR5 represents an appealing target for treatment intervention, although certain challenges can not be ignored. Promising small-molecule, orally bioavailable CCR5 antagonists are under development for the treatment of HIV-1 infection.     

Δ9-Tetrahydrocannabinol Treatment During Human Monocyte Differentiation Reduces Macrophage Susceptibility to HIV-1 Infection

The major psychoactive component of marijuana, Δ⁹-tetrahydrocannabinol (THC), also acts to suppress inflammatory responses. Receptors for THC, CB₁, CB₂, and GPR55, are differentially expressed on multiple cell types including monocytes and macrophages, which are important modulators of inflammation in vivo and target cells for HIV-1 infection. Use of recreational and medicinal marijuana is increasing, but the consequences of marijuana exposure on HIV-1 infection are unclear. Ex vivo studies were designed to investigate effects on HIV-1 infection in macrophages exposed to THC during or following differentiation. THC treatment of primary human monocytes during differentiation reduced HIV-1 infection of subsequent macrophages by replication competent or single cycle CCR5 using viruses. In contrast, treatment of macrophages with THC immediately prior to or continuously following HIV-1 exposure failed to alter infection. Specific receptor agonists indicated that the THC effect during monocyte differentiation was mediated primarily through CB₂. THC reduced the number of p24 positive cells with little to no effect on virus production per infected cell, while quantitation of intracellular viral gag pinpointed the THC effect to an early event in the viral life cycle. Cells treated during differentiation with THC displayed reduced expression of CD14, CD16, and CD163 and donor dependent increases in mRNA expression of selected viral restriction factors, suggesting a fundamental alteration in phenotype. Ultimately, the mechanism of THC suppression of HIV-1 infection was traced to a reduction in cell surface HIV receptor (CD4, CCR5 and CXCR4) expression that diminished entry efficiency.     

HIV-1协同受体及其抑制剂研究进展

协同受体CCR5和CXCR4分别是嗜巨噬细胞性HIV-1和嗜T细胞性TIV-1侵入靶细胞的主要受体。CCR5抑制剂如TAK-779、SCH—C等，和CXCR4抑制剂如AMD3100、T22等，能分别与CCR5和CXCR4结合，从而阻断HIV-1侵入靶细胞。本文综述了HIV-1与CCR5和CXCR4的结合机制及其抑制剂的研究进展。     

Maraviroc

Maraviroc is a specific, slowly reversible, noncompetitive, small-molecule antagonist of the CCR5 chemokine receptor, which also serves as an HIV-1 coreceptor. By acting as an antagonist at the CCR5 coreceptor, maraviroc inhibits HIV-1 from entering host cells. Clinical data for maraviroc are available from two large, well designed, ongoing phase IIb/III trials (MOTIVATE-1 and MOTIVATE-2) conducted in patients infected with R5-tropic HIV-1 who had previously received at least one agent from three of the four classes of antiretroviral drugs and/or were triple-class resistant. According to 24-week interim results of the MOTIVATE-1 and -2 trials, a significantly greater reduction in viral load occurred in patients receiving maraviroc 150 or 300mg (depending on optimised background therapy [OBT]) twice daily plus OBT compared with placebo plus OBT. This significant difference was maintained at 48 weeks in MOTIVATE-1. In the MOTIVATE-1 and -2 trials, a significantly greater proportion of patients receiving maraviroc plus OBT achieved an HIV-1 RNA level <400 and <50 copies/mL compared with those receiving placebo plus OBT. In addition, the CD4+ cell count was increased to a significantly greater extent with maraviroc plus OBT compared with placebo plus OBT. The 48-week results of MOTIVATE-1 also report a significant difference in favour of maraviroc for all these endpoints. In general, maraviroc at dosages of up to 300mg twice daily was well tolerated in treatment-experienced patients infected with R5-tropic HIV-1.