Marked increase in anti-HIV activity, as well as inhibitory activity against HIV entry mediated by CXCR4, linked to enhancement of the binding ability of tachyplesin analogs to CXCR4

Biological and mutational analyses of CXCR4-antagonist interactions and design of new antagonistic analogs

The chemokine receptor CXCR4 has become an attractive therapeutic target for HIV-1 infection, hematopoietic stem cell mobilization, and cancer metastasis. A wide variety of synthetic antagonists of CXCR4 have been developed and studied for a growing list of clinical applications. To compare the biological effects of different antagonists on CXCR4 functions and their common and/or distinctive molecular interactions with the receptor, we conducted head-to-head comparative cell-based biological and mutational analyses of the interactions with CXCR4 of eleven reported antagonists, including HC4319, DV3, DV1, DV1 dimer, V1, vMIP-II, CVX15, LY2510924, IT1t, AMD3100, and AMD11070 that were representative of different structural classes of D-peptides, L-peptide, natural chemokine, cyclic peptides, and small molecules. The results were rationalized by molecular modeling of CXCR4-antagonist interactions from which the common as well as different receptor binding sites of these antagonists were derived, revealing a number of important residues such as W94, D97, H113, D171, D262, and E288, mostly of negative charge. To further examine this finding, we designed and synthesized new antagonistic analogs by adding positively charged residues Arg to a D-peptide template to enhance the postulated charge-charge interactions. The newly designed analogs displayed significantly increased binding to CXCR4, which supports the notion that negatively charged residues of CXCR4 can engage in interactions with moieties of positive charge of the antagonistic ligands. The results from these mutational, modeling and new analog design studies shed new insight into the molecular mechanisms of different types of antagonists in recognizing CXCR4 and guide the development of new therapeutic agents.

Strategies and progress in CXCR4-targeted anti-HIV therapeutic development

The acquired immunodeficiency syndrome (AIDS), caused by the human immunodeficiency virus (HIV), has been a global public health challenge for several decades. The majority of HIV infection is caused by the human immunodeficiency virus type 1 (HIV-1) which enters and infects a host cell via the cell surface proteins of CD4 as the primary receptor, and chemokine receptors CXCR4 or CCR5 as the co-receptor-then undergoing replication using the cell's intracellular machinery. Whereas many drugs targeting CCR5-mediated entry or HIV-1 replication via reverse transcriptase or proteases have long been used clinically, agents targeting CXCR4 are yet to be advanced to clinical application. Here in this review we highlight some of the strategies for and progress made in the discovery of novel small molecules, peptides, and larger molecules that target CXCR4, and their future prospects for translation into the clinic as a new class of anti-HIV therapeutics.

The study of targeted blocking SDF-1/CXCR4 signaling pathway with three antagonists on MMPs, type II collagen, and aggrecan levels in articular cartilage of guinea pigs

Objective

To explore the possibility and mechanism of targeted blocking SDF-1/CXCR4 signaling pathway using three antagonists TN14003, T140, and AMD3100 in vivo, and to investigate the function of three antagonists in delay degeneration process of articular cartilage.

Methods

Ninety-six male Duncan-Hartley guinea pigs (6 months old) were divided into groups A, B, C, and D randomly. Alzet trace pump was implanted in the back subcutaneous tissue of pigs in group A, and TN14003 with concentration of 180 μg/ml was pumped every day. Alzet trace pump was implanted in the back subcutaneous tissue of pigs in group B, and T140 with concentration of 180 μg/ml was pumped every day. Alzet trace pump was implanted in the back subcutaneous tissue of pigs in group C, and AMD3100 with concentration of 180 μg/ml was pumped every day. Hartley guinea pigs in group D remained untreated as the blank control group. At 2, 4, 6, 8, 10, and 12 weeks of treatment, 5 to 8 animals in each group were randomly chosen for blood collection via cardiac puncture. SDF-1 content using enzyme-linked immunosorbent assay (ELISA). At 12 weeks, all guinea pigs were sacrificed by injecting pentobarbital sodium (30 mg/kg) into the peritoneal cavity. Cartilages from the tibial plateau in each group were harvested for PCR testing and western blot analysis. SPSS19.0 was used for data analysis.

Results

Result of ELISA: the serum levels of SDF-1 of groups A, B, and C decreased gradually with time. Significant drop of SDF-1 level was seen in group A while increased SDF-1 was shown in group D. At the same time, the serum levels of SDF-1 of the group A were significantly lower than that of group B; those of group B were significantly lower than that of group C, which was significantly lower than that of group D, and their difference is statistically significant (P < 0.05). Real time quantitative PCR result: The mRNA levels of MMPs in group A were significantly lower than group B, and those of group B were significantly lower than group C, which was significantly lower than group D, and there was statistically significant (P < 0.05). The mRNA levels of type II collagen, aggrecan in group A were significantly more than group B; those of group B were significantly more than group C, which was significantly more than group D, and the difference was statistically significant (P < 0.05). H&E staining result: cartilage of group C was more significantly degenerative than other groups.

Conclusions

The three antagonists can target SDF-1/CXCR4 signaling pathway in vivo, reduce the expression and secretion of MMP-3, MMP-9, and MMP-13 in cartilage tissue, and reduce the degradation of collagen II and aggregating proteoglycan, thus delaying the degeneration of articular cartilage, of which TN14003 has the strongest regulatory effect. Targeted blockade of SDF-1/CXCR4 signaling pathway by TN14003 in vivo delays articular cartilage degeneration more effectively than T140 and AMD3100.

Pathogenic Viruses Commonly Present in the Oral Cavity and Relevant Antiviral Compounds Derived from Natural Products

Many viruses, such as human herpesviruses, may be present in the human oral cavity, but most are usually asymptomatic. However, if individuals become immunocompromised by age, illness, or as a side effect of therapy, these dormant viruses can be activated and produce a variety of pathological changes in the oral mucosa. Unfortunately, available treatments for viral infectious diseases are limited, because (1) there are diseases for which no treatment is available; (2) drug-resistant strains of virus may appear; (3) incomplete eradication of virus may lead to recurrence. Rational design strategies are widely used to optimize the potency and selectivity of drug candidates, but discovery of leads for new antiviral agents, especially leads with novel structures, still relies mostly on large-scale screening programs, and many hits are found among natural products, such as extracts of marine sponges, sea algae, plants, and arthropods. Here, we review representative viruses found in the human oral cavity and their effects, together with relevant antiviral compounds derived from natural products. We also highlight some recent emerging pharmaceutical technologies with potential to deliver antivirals more effectively for disease prevention and therapy.

Heparan sulfate differentially controls CXCL12α- and CXCL12γ-mediated cell migration through differential presentation to their receptor CXCR4

Chemokines stimulate signals in cells by binding to G protein (heterotrimeric guanine nucleotide-binding protein)-coupled receptors. These chemoattractant cytokines also interact with heparan sulfate (HS), which provides positional information within tissues in the form of haptotactic gradients along which cells can migrate directionally. To investigate the mechanism by which HS modulates chemokine functions, we used the CXC chemokine CXCL12, which exists in different isoforms that all signal through CXCR4 but have distinct HS-binding domains. In experiments with both cell-associated and solubilized CXCR4, we found that although CXCL12γ bound to CXCR4 with a higher affinity than did CXCL12α, CXCL12γ displayed reduced signaling and chemotactic activities. These properties were caused by the specific carboxyl-terminal region of CXCL12γ, which, by interacting with CXCR4 sulfotyrosines, mediated high-affinity, but nonproductive, binding to CXCR4. HS prevented CXCL12γ from interacting with the CXCR4 sulfotyrosines, thereby functionally presenting the chemokine to its receptor such that its activity was similar to that of CXCL12α. HS had no effects on the binding of CXCL12α to CXCR4 or its biological activity, suggesting that this polysaccharide controls CXCL12 in an isoform-specific manner. These data suggest that the HS-dependent regulation of chemokine functions extends beyond the simple process of immobilization and directly modulates receptor ligation and activation.

Antiviral Host Defence Peptides

The ongoing global mortality and morbidity associated with viral pathogens highlights the need for the continued development of effective, novel antiviral molecules. The antiviral activity of cationic host defence peptides is of significant interest as novel therapeutics for treating viral infection and predominantly due to their broad spectrum antiviral activity. These peptides also display powerful immunomodulatory activity and are key mediators of inflammation. Therefore, they offer a significant opportunity to inform the development of novel therapeutics for treating viral infections by either directly targeting the pathogen or by enhancing the innate immune response. In this chapter, we review the antiviral activity of cathelicidins and defensins, and examine the potential for these peptides to be used as novel antiviral agents.

Mechanisms and modifications of naturally occurring host defense peptides for anti-HIV microbicide development

Despite advances in the treatment of HIV infection, heterosexual transmission of HIV remains high, and vaccines to prevent HIV acquisition have been unfruitful. Vaginal microbicides, on the other hand, have demonstrated considerable potential for HIV prevention, and a variety of compounds have been screened for their activity and safety as anti-HIV microbicides. Among these are the naturally occurring host defense peptides, small peptides from diverse lineages with intrinsic antiviral activity. Naturally occurring host defense peptides with anti-HIV activity are promising candidates for vaginal microbicide development. Their structural variance and accompanying mechanistic diversity provide a wide range of inhibitors whose antiviral activity can be exerted at nearly every stage of the HIV lifecycle. Additionally, peptide modification has been explored as a method for improving the anti-HIV activity of host defense peptides. Structure- and sequence-based alterations have achieved varying success in improving the potency and specificity of anti-HIV peptides. Overall, peptides have been discovered or engineered to inhibit HIV with therapeutic indices of > 1000, encouraging their advancement toward clinical trials. Here we review the naturally occurring anti-HIV host defense peptides, demonstrating their breadth of mechanistic diversity, and exploring approaches to enhance and optimize their activity in order to expedite their development as safe and effective anti-HIV vaginal microbicides.

Retrocyclins and their activity against HIV-1

Primate theta-defensins are physically distinguished as the only known fully-cyclic peptides of animal origin. Humans do not produce theta-defensin peptides due to a premature stop codon present in the signal sequence of all six theta-defensin pseudogenes. Instead, since the putative coding regions of human theta-defensin pseudogenes have remained remarkably intact, their corresponding peptides, called “retrocyclins”, have been recreated using solid-phase synthetic approaches. Retrocyclins exhibit an exceptional therapeutic index both as inhibitors of HIV-1 entry and as bactericidal agents, which makes retrocyclins promising candidates for further development as topical microbicides to prevent sexually transmitted diseases. This review presents the evolution, antiretroviral mechanism of action, and potential clinical applications of retrocyclins to prevent sexual transmission of HIV-1.

CXCR4, inhibitors and mechanisms of action

In this review, the author discusses recent advances in anti-HIV inhibitors, targeting CXCR4, including natural and modified chemokines, peptides and organic compounds, their mechanisms of action, and the molecular process of virus invasion of immune cells. Peptides with strong anti-HIV activity exhibit several common features, such as electrostatic charges, cyclization, beta-turns and dimerization induced by a sulphide bond. Organic compounds, such as cyclams, display a unique metal-mediated mechanism in the binding process to its target CXCR4. Understanding of their mechanisms of action may be useful for the design of more effective drugs. Consecutive interactions of viral glycoprotein gp120 with CD4 and the co-receptor, CXCR4 or another co-receptor CCR5 on the cell surface leads to virus invasion into host cells. The molecular details of the binding between HIV glycoproteins and the co-receptors also provide a basis for anti-HIV therapy.

Exploratory studies on development of the chemokine receptor CXCR4 antagonists toward downsizing

Seven transmembrane (7TM) G-protein-coupled receptor (GPCR) families are important targets for drug discovery, and specific antagonists for GPCR can accelerate research in the field of medicinal chemistry. The chemokine receptor CXCR4 is a GPCR that possesses a unique ligand CXCL12/stromal cell-derived factor-1 (SDF-1). The interaction between CXCL12 and CXCR4 is essential for the migration of progenitor cells during embryonic development of the cardiovascular, hemopoietic and central nervous systems, and also involved in several intractable disease processes, including HIV infection, cancer cell metastasis, progression of acute and chronic leukemias, rheumatoid arthritis and pulmonary fibrosis. Thus, CXCR4 may be an important therapeutic target in all of these diseases, and various CXCR4 antagonists have been proposed as potential drugs. Fourteen-mer peptides, T140 and its analogs, and downsized cyclic pentapeptides have been developed by us as potent CXCR4 antagonists. This article describes the development of a number of specific CXCR4 antagonists in our laboratory, including downsizing.

Therapeutic potential of the chemokine receptor CXCR4 antagonists as multifunctional agents

The chemokine receptor CXCR4 possesses multiple critical functions in normal and pathologic physiology. CXCR4 is a G-protein-coupled receptor that transduces signals of its endogenous ligand, the chemokine CXCL12 (stromal cell-derived factor-1, SDF-1). The interaction between CXCL12 and CXCR4 plays an important role in the migration of progenitors during embryologic development of the cardiovascular, hemopoietic, central nervous systems, and so on. This interaction is also known to be involved in several intractable disease processes, including HIV infection, cancer cell metastasis, leukemia cell progression, rheumatoid arthritis (RA), and pulmonary fibrosis. It is conjectured that this interaction may be a critical therapeutic target in all of these diseases, and several CXCR4 antagonists have been proposed as potential drugs. Fourteen-mer peptides, T140 and its analogues, were previously developed in our laboratory as specific CXCR4 antagonists that were identified as HIV-entry inhibitors, anti-cancer-metastatic agents, anti-chronic lymphocytic/acute lymphoblastic leukemia agents, and anti-RA agents. Cyclic pentapeptides, such as FC131 [cyclo(D-Tyr-Arg-Arg-L-3-(2-naphthyl)alanine-Gly)], were also previously found as CXCR4 antagonist leads based on pharmacophores of T140. This review article describes the elucidation of multiple functions of CXCR4 antagonists and the development of a number of low-molecular weight CXCR4 antagonists involving FC131 analogues and other compounds with different scaffolds including linear-type structures.

Peptide antimicrobial agents

Antimicrobial host defense peptides are produced by all complex organisms as well as some microbes and have diverse and complex antimicrobial activities. Collectively these peptides demonstrate a broad range of antiviral and antibacterial activities and modes of action, and it is important to distinguish between direct microbicidal and indirect activities against such pathogens. The structural requirements of peptides for antiviral and antibacterial activities are evaluated in light of the diverse set of primary and secondary structures described for host defense peptides. Peptides with antifungal and antiparasitic activities are discussed in less detail, although the broad-spectrum activities of such peptides indicate that they are important host defense molecules. Knowledge regarding the relationship between peptide structure and function as well as their mechanism of action is being applied in the design of antimicrobial peptide variants as potential novel therapeutic agents.

Development of a Moloney murine leukemia virus-based pseudotype anti-HIV assay suitable for accurate and rapid evaluation of HIV entry inhibitors

There has been increasing interest in the identification of novel HIV entry inhibitors. For the discovery of these entry inhibitors, robust surrogate anti-HIV assays are highly desired. The authors report a novel anti-HIV assay system using Moloney murine leukemia viruses (MMLVs) pseudotyped with cytoplasmic tail-truncated HIV envelope protein gp140. These pseudotyped MMLV-HIVgp140 viral particles carry luciferase transcripts; therefore, robust luciferase signal can be detected in cells infected by these pseudotypes. Polycationic agent polybrene and spinoculation markedly enhanced the infection efficiency of these pseudotypes. It was demonstrated that the tropism of these pseudotypes is dependent on the pseudotyped HIV envelope proteins. MMLV viruses pseudotyped with gp140 from an R5 HIV virus specifically infect CCR5-expressing cells, and viruses pseudotyped with gp140 from an X4 HIV virus specifically infect CXCR4-expressing cells. Furthermore, CCR5 antagonists inhibited only MMLV-gp140(R5) infections, and CXCR4 antagonists inhibited only MMLV-gp140(X4) infections. A variety of known HIV entry inhibitors were tested in both R5- and X4-dependent pseudotype antiviral assays, and the IC50 values generated were consistent with published results. The pseudotype antiviral assay was also used in the characterization of hundreds of novel CCR5 antagonists. The IC50 values determined in this assay were compared with those determined in HIV antiviral and cell-cell fusion (CCF) assays, and good correlation was found between pseudotype antiviral assay and HIV antiviral assay (R2 = 0.9) or CCF assay (R2 = 0.8).

The therapeutic potential of CXCR4 antagonists in the treatment of HIV infection, cancer metastasis and rheumatoid arthritis

CXCR4 is the receptor of the chemokine CXCL12, which is involved in progression and metastasis of several types of cancer cells, HIV infection and rheumatoid arthritis. The authors developed selective CXCR4 antagonists, T22 and T140, initially as anti-HIV agents, which inhibit T cell line-tropic (X4-) HIV-1 infection through their specific binding to CXCR4. Recently, T140 analogues have also been shown to inhibit CXCL12-induced migration of breast cancer cells, leukaemia T cells, pancreatic cancer cells, small cell lung cancer cells, chronic lymphocytic leukaemia B cells, pre-B acute lymphoblastic leukaemia cells and so on in vitro. Biostable T140 analogues significantly suppressed pulmonary metastasis of breast cancer cells and melanoma cells in mice. Furthermore, these compounds significantly suppressed the delayed-type hypersensitivity response induced by sheep red blood cells and collagen-induced arthritis, which represent in vivo mouse models of arthritis. Thus, T140 analogues proved to be attractive lead compounds for chemotherapy of these problematic diseases. This article reviews recent research on T140 analogues, referring to several other CXCR4 antagonists.

Identification of a CXCR4 antagonist, a T140 analog, as an anti-rheumatoid arthritis agent

Several recent papers support the involvement of an interaction between stromal cell-derived factor-1 (SDF-1/CXCL12) and its receptor, chemokine receptor CXCR4, in memory T cell migration in the inflamed rheumatoid arthritis (RA) synovium. Analogs of the 14-mer peptide T140 were previously found to be specific CXCR4 antagonists that were characterized as not only HIV-entry inhibitors but also anti-cancer-metastatic agents. In this study, a T140 analog, 4F-benzoyl-TN14003, was proven to inhibit CXCL12-mediated migration of human Jurkat cells and mouse splenocyte in a dose-dependent manner in vitro (IC(50)=0.65 and 0.54 nM, respectively). Furthermore, slow release administration by subcutaneous injection (s.c.) of 4F-benzoyl-TN14003 using an Alzet osmotic pump significantly suppressed the delayed-type hypersensitivity response induced by sheep red blood cells in mice, and significantly ameliorated clinical severity in collagen-induced arthritis in mice. As such, T140 analogs might be attractive lead compounds for chemotherapy of RA.

The therapeutic potential of CXCR4 antagonists in the treatment of HIV

Since the identification of the chemokine receptors CXCR4 and CCR5 as co-receptors for HIV-1 entry, several antagonists against these receptors have been synthesised. A highly selective CXCR4 antagonist, T22, and its downsized analogues T140 and TC14012, which inhibit X4-HIV-1 infection through their specific binding to CXCR4, have been identified. Besides T22 analogues, several other CXCR4 antagonists have been reported, such as AMD3100, ALX40-4C, KRH-1120 and AMD8664. Discovery of entry inhibitors, such as chemokine antagonists, may lead to the development of a new generation of antiHIV agents, since these inhibitors are thought to be useful for the clinical treatment of HIV-1-infected patients, especially at the late stage of treatment for AIDS patients developing multi-drug-resistant strains. In this review, recent research into CXCR4 antagonists in comparison with development of other antagonists is summarised.

Cell-surface-expressed HIV-1 envelope induces the death of CD4 T cells during GP41-mediated hemifusion-like events

Cells expressing the HIV-1 envelope glycoprotein complex (gp120/gp41, Env) induce the death of target cells either after cell-to-cell fusion or after cell-to-cell contact in a fusion-independent fashion. Here, we demonstrate that Env-induced death of single cells (including primary CD4 T cells) required gp120 and gp41 function. The gp41 peptide C34, which blocked syncytium formation, completely inhibited the death of single target cells by specifically acting on gp41 function. Moreover, Env-induced single cell death was exclusively observed in CD4 cells and was associated with specific gp41-mediated transfer of lipids from the membrane of Env-expressing cells to the target cell but not with detectable cytoplasm mixing (complete fusion). We conclude that after gp120 function, gp41 mediates close cell-to-cell contacts, thereby triggering cell death in single uninfected cells in the absence of detectable cell-to-cell fusion.

Synthesis and evaluation of pseudopeptide analogues of a specific CXCR4 inhibitor, T140: the insertion of an (E)-alkene dipeptide isostere into the betaII'-turn moiety

A 14-residue peptide, T140, strongly inhibits the T-cell line-tropic HIV-1 (X4-HIV-1) infection, since this peptide functions as a specific antagonist against a chemokine receptor, CXCR4. T140 takes an antiparallel beta-sheet structure with a type II' beta-turn. In the present paper, we have designed and synthesized several T140 analogues, in which an (E)-alkene dipeptide isostere was inserted into the type II' beta-turn moiety, as a bridging study to develop nonpeptidic CXCR4 inhibitors. It has been proven that the turn region of T140 can be replaced by the above surrogate with the maintenance of strong anti-HIV activity.

Antimicrobial dendrimeric peptides

Dendrimeric peptides selective for microbial surfaces have been developed to achieve broad antimicrobial activity and low hemolytic activity to human erythrocytes. The dendrimeric core is an asymmetric lysine branching tethered with two to eight copies of a tetrapeptide (R4) or an octapeptide (R8). The R4 tetrapeptide (RLYR) contains a putative microbial surface recognition BHHB motif (B = basic, H = hydrophobic amino acid) found in protegrins and tachyplesins whereas the octapeptide R8 (RLYRKVYG) consists of an R4 and a degenerated R4 repeat. Antimicrobial assays against 10 organisms in high- and low-salt conditions showed that the R4 and R8 monomers as well as their divalent dendrimers contain no to low activity. In contrast, the tetra- and octavalent R4 and R8 dendrimers are broadly active under either conditions, exhibiting relatively similar potency with minimal inhibition concentrations < 1 microm against both bacteria and fungi. Based on their size and charge similarities, the potency and activity spectrum of the tetravalent R4 dendrimer are comparable to protegrins and tachyplesins, a family of potent antimicrobials containing 17-19 residues. Compared with a series of linearly repeating R4 peptides, the R4 dendrimers show comparable antimicrobial potency, but are more aqueous soluble, more stable to proteolysis, less toxic to human cells and more easily synthesized chemically. These results suggest repeating peptides that cluster the charge and hydrophobic residues may represent a primitive form of microbial pattern-recognition. Incorporating such knowledge in a dendrimeric design therefore presents an attractive approach for developing novel peptide antibiotics.

[Development of selective antagonists against an HIV second receptor]

The authors have discovered a highly selective CXCR4 antagonist, T22 ([Tyr5,12, Lys7]-polyphemusin II), and its shortened potent analogs, T140 and TC14012, which strongly inhibit the T-cell line-tropic HIV-1 (X4-HIV-1) infection through their specific binding to a chemokine receptor, CXCR4. CXCR4 is a major coreceptor (second receptor) for the entry of X4-HIV-1 into T-cells. These peptides have been found through the structure-activity relationship (SAR) study on tachyplesins and polyphemusins, which function as self-defense peptides of horseshoe crabs with immature immune systems. T140 and TC14012 showed the highest level of anti-HIV activity and antagonism of target cell entry by X4-HIV-1 among all the CXCR4 antagonists that have been reported to date. Additionally, bifunctional anti-HIV agents based on the specific CXCR4 antagonists (T140 analogs)-3'-azido-3'-deoxythymidine (AZT) conjugation have been synthesized and evaluated, since T140 analogs can possibly work as a carrier of AZT targeting T-cells due to their specific affinity for CXCR4 on T-cells. T22 have two disulfide bonds and a Trp residue in the molecule. In connection with this study, novel facile and side-reaction-free methodologies for disulfide bond formation have been established for the increase of the efficiency of SAR studies. Furthermore, the completely stereocontrolled synthetic process for a couple of (E)-alkene dipeptide isosteres starting from L-amino acid has been established in order to facilitate nonpeptidylation studies on peptide-lead candidates. In this review, the authors wish to summarize our recent research on the development of specific antagonists against the HIV second receptor CXCR4, involving studies on the establishment of efficient methodologies for the facile synthesis of peptides and peptide mimetics.

Chemokine receptors in airway disease: which receptors to target?

Many disease states within the airway result in the co-ordinated infiltration of key inflammatory cells. The cellular influx is choreographed through the temporal and spatially-regulated expression of chemokines, which potentiate the migration of cells along gradients of chemotactic ligands. Chemokines act as ligands for the chemokine receptors; a distinct class of G-protein-coupled receptor. Over 40 chemokine ligands and 18 chemokine receptors have been identified on human cells. Chemokine receptors are divided into several classes; the two most prominent of which are the CC- and CXC-chemokine receptors, classified through the spatial arrangement of two conserved cysteine residues. The role of chemokine receptors such as CCR2, CCR3, CCR4, CCR8 and the CXC chemokine receptors; CXCR1 and CXCR2 on cell types of relevance to respiratory diseases such as asthma, chronic obstructive pulmonary disease (COPD) and chronic bronchitis will be explored in this review. Chemokines have proven to be amenable drug targets for the development of low molecular weight antagonists by the pharmaceutical industry. So far, no chemokine receptor antagonist has entered the clinic in trials for respiratory disease, but over the next few years it is expected that many will do so, at which time the potential of these exciting new targets will be fully realised.

Development of specific CXCR4 inhibitors possessing high selectivity indexes as well as complete stability in serum based on an anti-HIV peptide T140

We previously reported a truncated polyphemusin peptide analogue, T140, which efficiently inhibits infection of target cells by T-cell line-tropic strains of HIV-1 (X4-HIV-1) through its specific binding to a chemokine receptor, CXCR4. We have found that T140 is not stable in feline serum due to the cleavage of the C-terminal Arg,(14) indispensable for anti-HIV activity. On the other hand, a C-terminally amidated analogue of T140, TZ14004, has been found to be completely stable in incubation in the serum for 2 days. The C-terminal amide is thought to be needed for stability in serum. However, TZ14004 does not have fairly strong anti-HIV activity, but has relatively strong cytotoxicity, probably due to an increase by +1 charge from total +7 charges of T140. In our previous study, the number of total +6 charges seemed to be a suitable balance between activity and cytotoxicity. In this study, we have conducted a double-L-citrulline (Cit)-scanning study on TZ14004 based on the C-terminally amidated form in due consideration of the total net charges in the whole molecule to find novel effective CXCR4 inhibitors, TN14003 ([Cit(6)]-T140 with the C-terminal amide) and TC14012 ([Cit(6), D-Cit(8)]-T140 with the C-terminal amide), which possess high selectivity indexes (SIs) and complete stability in feline serum.

Biological and genetic characterization of a human immunodeficiency virus strain resistant to CXCR4 antagonist T134

The chemokine receptors CXCR4 and CCR5 are considered to be potential targets for the inhibition of HIV-1 replication. We have reported that T134 and T140 inhibited X4 HIV-1 infection specifically because they acted as CXCR4 antagonists. In the present study, we have generated a T134-resistant virus (trHIV-1(NL4-3)) in a cell culture with gradually increasing concentrations of the compound. The EC(50) of T134 against trHIV-1(NL4-3) recovered after 145 passages was 15 times greater than that against wild-type HIV-1(NL4-3). This adapted virus was resistant to other CXCR4 antagonists, T140, AMD3100, and ALX40-4C, and SDF-1; from 10 to 145 times greater than that against wild-type HIV-1(NL4-3). On the other hand, T134, T140, and ALX40-4C were still active against AMD3100-resistant viruses (arHIV-1(018A)). The trHIV-1(NL4-3) contained the following mutations in the V3 loop of gp120: N269K, Q278T, R279K, A284V, F285L, V286Y, I288T, K290E, N293D, M294I, and Q296K; an insertion of T at 290; and Delta274-275 (SI). In addition, many other mutations were recognized in the V1, V2, and V4 domains. Thus, resistance to T134 may be the consequence of amino acid substitutions in the envelope glycoprotein of X4 HIV-1. The trHIV-1(NL4-3) could not utilize CCR5 as an HIV infection coreceptor, although many amino acid substitutions were recognized. The trHIV-1(NL4-3) acquired resistance to vMIP II, which could inhibit both X4 and R5 HIV-1 infection. However, neither the ligands of CCR5, RANTES, and MIP-1alpha, nor a CCR5 low molecular antagonist, TAK-779, were able to influence the infection of trHIV-1(NL4-3). Those results indicated that alternation of coreceptor usage of trHIV-1(NL4-3) was not induced.

Increase of R5 HIV-1 infection and CCR5 expression in T cells treated with high concentrations of CXCR4 antagonists and SDF-1

The chemokine receptors CXCR4 and CCR5 are considered to be potential targets for the inhibition of HIV-1 replication. We found that the synthetic peptides T134 and T140 (see text for full names) inhibited X4 HIV-1 infection with selectivity and low toxicity because they acted as CXCR4 antagonists. However, high concentrations of T134, T140, and ALX40-4C (see text for full name) increased the expression of CCR5 and R5 HIV-1 infection, as did stromal cell-derived factor 1 (SDF-1). In contrast to CXCR4 antagonists and SDF-1, viral monocyte inflammatory protein (vMIP) II inhibited not only anti-CXCR4 monoclonal antibody (MAb) but also inhibited anti-CCR5 MAb binding to human peripheral blood mononuclear cells, and inhibited both X4 and R5 HIV-1 strains. T134, T140, ALX40-4C, and SDF-1 increased viral transcription in the treated cells. In addition, ALX40-4C and SDF-1 also increased nuclear transcription factor (NF)-kappaB. However, the mechanisms of action of T134 and T140 are different from those of clinically used anti-HIV drugs. Thus, synergistic activities were observed in the concomitant treatment with T134 and reverse transcriptase inhibitors or protease inhibitors. Our findings, presented here, are noteworthy in regard to the potential clinical use of these agents as drugs for the treatment of AIDS.

The possible involvement of CXCR4 in the inhibition of HIV-1 infection mediated by DP178/gp41

The N- (N36/DP107) and C-terminal peptides (C34/DP178) from two alpha-helical domains of human immunodeficiency virus type 1 (HIV-1) gp41 inhibited HIV infection. A single-round infection using pseudotyped virus clarified that a greater amount of gp41-derived peptides was necessary for the inhibition of R5 virus (ADA) infection than for that of X4 virus (LAI) infection. Furthermore, R5X4 virus (89.6) infection via CCR5 needs more peptides for inhibition than its infection via CXCR4 does. A high sensitivity of X4 virus was partially ascribed to the inhibition of the 12G5 binding to CXCR4 by DP178LAI.

The chemokine/chemokine-receptor family: potential and progress for therapeutic intervention

The chemokines are a large superfamily of chemotactic cytokines that are utilized to direct the trafficking and migration of leukocytes within the immune system. The chemokines mediate their activity through a large family of G-protein-coupled receptors, and thus are highly tractable as therapeutic targets. Exciting advances have been made in the field within the past year, not the least of which is the disclosure of potent antagonists of several chemokine receptors. Several CCR5 antagonists have demonstrated potent antiviral activity and may represent novel therapeutic agents for the treatment of AIDS. In addition, new biological insights have been gained from the demonstration that the targeting of cells to inflammatory sites is tissue specific, such that different chemokine/chemokine-receptor pairs are utilized in recruitment of T-lymphocytes to the skin and to the intestine. Also, utilization of neutralizing antibodies to the CXCR3 ligand Mig in murine allograft transplantation models has demonstrated the importance of CXCR3 in orchestrating T-cell-mediated tissue rejection.