AMD3465, a monomacrocyclic CXCR4 antagonist and potent HIV entry inhibitor

The chemokine receptors CCR5 and CXCR4 function as coreceptors for human immunodeficiency virus (HIV) and are attractive targets for the development of anti-HIV drugs. The most potent CXCR4 antagonists described until today are the bicyclams. The prototype compound, AMD3100, exhibits potent and selective anti-HIV activity against CXCR4-using (X4) viruses and showed antiviral efficacy in X4 HIV-1-infected persons in a phase II clinical trial. However, AMD3100 lacks oral bioavailability due to its high overall positive charge. Initial structure-activity relationship studies with bicyclam analogues suggested that the bis-macrocyclic structure was a prerequisite for anti-HIV activity. Now, we report that the N-pyridinylmethylene cyclam AMD3465, which lacks the structural constraints mentioned above, fully conserves all the biological properties of AMD3100. Like AMD3100, AMD3465 blocked the cell surface binding of both CXCL12 (the natural CXCR4 ligand), and the specific anti-CXCR4 monoclonal antibody 12G5. AMD3465 dose-dependently inhibited intracellular calcium signaling, chemotaxis, CXCR4 endocytosis and mitogen-activated protein kinase phosphorylation induced by CXCL12. Compared to the bicyclam AMD3100, AMD3465 was even 10-fold more effective as a CXCR4 antagonist, while showing no interaction whatsoever with CCR5. As expected, AMD3465 proved highly potent against X4 HIV strains (IC50: 1-10 nM), but completely failed to inhibit the replication of CCR5-using (R5) viruses. In conclusion, AMD3465 is a novel, monomacrocyclic anti-HIV agent that specifically blocks the interaction of HIV gp120 with CXCR4. Although oral bioavailability is not yet achieved, the monocyclams, with their decreased molecular charge as compared to the bicyclams, embody an important step forward in the design of oral CXCR4 antagonists that can be clinically used as anti-HIV drugs.     

Small molecule HIV entry inhibitors: Part I. Chemokine receptor antagonists: 2004 - 2010

INTRODUCTION: HIV/AIDS is one of the most devastating diseases in the world affecting > 40 million people worldwide. Morbidity and mortality from AIDS are significantly reduced due to the advent of highly active antiretroviral therapy (HAART). Long-term toxicity, emergence of drug resistant HIV strains and drug-drug interactions limit the effectiveness of HAART therapy. Chemokine receptor antagonists can provide drugs with lesser side effects and enhanced anti-HIV activity. Maraviroc, a chemokine co-receptor 5 (CCR5) antagonist from Pfizer, is already in clinical use. AREAS COVERED: This review covers patents and patent applications for small molecule CCR5 and CXC chemokine receptor 4 (CXCR4) antagonists published between 2004 and 2010 and related literature with a focus on recent developments based on lead generation and lead modification. The reader will gain information about the development of small molecule CCR5 and CXCR4 antagonists from the major pharmaceutical and biopharmaceutical companies. EXPERT OPINION: Several small lead molecules (CCR5 and CXCR4 antagonists) have been modified over this period for enhanced therapeutic activity and to obtain drug-like properties. CCR5 antagonists such as TBK-652 and TBK-220 from Tobira Therapeutics, and vicriviroc from Schering Plough showed a lot of promise in the developmental stage.     

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.     

以趋化因子受体为靶点的抗HIV药物研究进展

趋化因子受体是HIV进入宿主细胞的共受体,特别是CCR5和CXCR4在HIV进入免疫细胞过程中起着重要作用。以趋化因子受体为靶点的新型抗艾滋病药物的设计与开发已成为抗艾滋病领域研究的一个热点课题。本文对近期抗HIV-1趋化因子受体(CCR5和CXCR4)拮抗剂的研究进展进行综述。     

Development of low molecular weight CXCR4 antagonists by exploratory structural tuning of cyclic tetra- and pentapeptide-scaffolds towards the treatment of HIV infection, cancer metastasis and rheumatoid arthritis

The chemokine receptor, CXCR4, is a GPCR that transduces signals of its endogenous ligand, CXCL12 (stromal cell-derived factor-1, SDF-1). The CXCL12-CXCR4 system plays an important role in the migration of progenitors during embryologic development of the cardiovascular, hemopoietic, central nervous systems, etc. This system has recently been proven to be involved in several problematic diseases, including HIV infection, cancer cell metastasis, leukemia cell progression, rheumatoid arthritis (RA) and pulmonary fibrosis. Thus, CXCR4 is thought to be an important therapeutic target to overcome the above diseases. Fourteen-mer peptides, T140 and its analogs, were previously found to be specific CXCR4 antagonists that were characterized as HIV-entry inhibitors, anti-cancer-metastatic agents, anti-chronic lymphocytic/acute lymphoblastic leukemia agents and anti-RA agents. Based on our knowledge of pharmacophores of T140, CXCR4 antagonists, such as FC131, were previously found by the efficient utilization of cyclic pentapeptide libraries. This review article focuses on our recent research on the development of low molecular weight CXCR4 antagonists including FC131 analogs, in which structural tuning of the cyclic peptide ring and chemical modifications were performed for an increase in potency and a reduction of the peptide character.     

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.     

新型抗艾滋病药物——HIV进入抑制剂的研究进展

HIV与靶细胞融合的过程是药物干预的重要环节。融合过程主要由H IV包被蛋白表面亚基gp120和跨膜亚基gp41介导。H IV gp120与靶细胞上的CD4分子和辅助受体(趋化因子受体CCR5或CXCR4等)结合,导致gp41的构型发生改变,启动病毒包膜与靶细胞膜的融合。在融合过程中,病毒和靶细胞上的这些蛋白和受体均可作为药物的作用靶点,寻找抑制H IV进入靶细胞的药物用来治疗H IV感染和艾滋病。作用于gp41的肽类药物T-20已被美国FDA批准上市,表明继逆转录酶抑制剂和蛋白酶抑制剂后,H IV进入抑制剂作为第3类抗H IV药物开始在临床上应用。作为一种新机制的抗H IV药物,H IV进入抑制剂单独或与逆转录酶抑制剂和蛋白酶抑制剂联合应用,将有助于提高药物的疗效,降低毒副作用,并可望挽救对现有抗H IV药物耐药的艾滋病病人的生命。该文综述了近年来H IV进入抑制剂的研究进展。     

Small molecule CXCR4 chemokine receptor antagonists: developing drug candidates

Chemokine receptors are a target of growing interest for new therapeutic drugs, as their role in multiple disease states has been demonstrated. The CXCR4/ CXCL12 pairing has been implicated in HIV and cancer, as well as chronic inflammatory diseases, including asthma and rheumatoid arthritis. HIV uses CXCR4 or CCR5 receptors in the key binding step of the infection process, leading to the idea that drugs could be developed to block this interaction. Cancer metastasis has also been linked to cellular communication via the chemokine pathways and hence, receptor antagonists could potentially inhibit this important pathway of disease progression. A wealth of data concerning small molecule CXCR4 receptor antagonists has been generated over the last few years, as a variety of these small molecules have been tested, and the understanding of structure activity relationships has improved. Here, we review the developing area of small molecule CXCR4 antagonists and the rapidly increasing amount of data from biological studies. Both peptidic and non-peptidic compounds have been investigated. In particular, we focus on AMD3100 and bismacrocyclic analogues, the most extensively studied class of CXCR4 antagonists, and the recent developments in this area.     

HIV-1侵入抑制剂的研究进展

人类免疫缺陷病毒(HIV)-1侵入抑制剂能抑制HIV进入靶细胞,在最初环节抑制病毒的传播。具有高活性、较好药物代谢性质的肽及肽类似物不断被发现,并成为抗HIV药物研究的热点。根据HIV-1进入靶细胞的3个步骤可将侵入抑制剂分为黏附抑制剂、辅助受体结合抑制剂和融合抑制剂,并对其研发策略和研究进展进行综述。     

新霉素A、B及其衍生物抗HIV作用的研究

人类免疫缺陷病毒(human immunodeficieney virus,HIV)自20世纪80年代被发现以来在全世界范围内迅速蔓延,严重地威胁到人类的健康,故研制高效、低毒的抗HIV药物迫在眉睫.本文综述了新霉素A、B及其衍生物作用于HIV的3个不同途径,包括:(1)与HIV RNA上的TAR和RRE结合;(2)与gp120-gp41竞争性地和CD4,CXCR4\CCR5结合;(3)作用于HIV的171-met ψ-RNA.此外,还针对这3个不同途径分别阐述了其相应的作用机制.新霉素及其衍生物抗HIV作用的研究结果为抗HIV药物的研究提供了更多的研究方向及可借鉴的研究方法.     

Design and cellular kinetics of dansyl-labeled CADA derivatives with anti-HIV and CD4 receptor down-modulating activity

A new class of anti-retrovirals, cyclotriazadisulfonamide (CADA) and its derivatives, specifically down-regulate CD4, the main receptor of HIV, and prevent HIV infection in vitro. In this work, several CADA derivatives, chemically labeled with a fluorescent dansyl group, were evaluated for their biological features and cellular uptake kinetics. We identified a derivative KKD-016 with antiviral and CD4 down-modulating capabilities similar to those of the parental compound CADA. By using flow cytometry, we demonstrated that the dose-dependent cellular uptake of this derivative correlated with CD4 down-modulation. The uptake and activity of the dansyl-labeled compounds were not dependent on the level of expression of CD4 at the cell surface. Removal of the CADA compounds from the cell culture medium resulted in their release from the cells followed by a complete restoration of CD4 expression. The inability of several fluorescent CADA derivatives to down-modulate CD4 was not associated with their lower cellular uptake and was not reversed by facilitating their cell penetration by a surfactant. These results prove the successful integration of the dansyl fluorophore into the chemical structure of a CD4 down-modulating anti-HIV compound, and show the feasibility of tracking a receptor and its down-modulator simultaneously. These fluorescent CADA analogs with reversible CD4 down-regulating potency can now be applied in further studies on receptor modulation, and in the exploration of their potentials as preventive and therapeutic anti-HIV drugs.     

Identification of a new class of low molecular weight antagonists against the chemokine receptor CXCR4 having the dipicolylamine-zinc(II) complex structure

Several low molecular weight nonpeptide compounds having the dipicolylamine-zinc(II) complex structure were identified as potent and selective antagonists of the chemokine receptor CXCR4. These compounds showed strong inhibitory activity against CXCL12 binding to CXCR4, and the top compound exhibited significant anti-HIV activity. Zinc(II)-dipicolylamine unit-containing compounds proved to be useful and attractive lead compounds for chemotherapy of these diseases as nonpeptide CXCR4 antagonists possessing the novel scaffold structure.     

Insight into the binding mode for cyclopentapeptide antagonists of the CXCR4 receptor

The finding that the chemokine receptor CXCR4 is involved in T‐cell HIV entry has encouraged the development of antiretroviral drugs targeting this receptor. Additional evidence that CXCR4 plays a crucial role in both angiogenesis and metastasis provides further motivation for the development of a CXCR4 inhibitor for therapeutic applications in oncology. To facilitate the design of such ligands, we have investigated the possible binding modes for cyclopentapeptide CXCR4 antagonists by docking 11 high/medium affinity cyclopentapeptides to a developed three‐dimensional model of the CXCR4 G‐protein‐coupled receptor's transmembrane region. These ligands, expected to bind in the same mode to the receptor, were docked in the previously deduced receptor‐bound conformation [Våbenøet al., in press; doi 10.1002/bip.20508]. Ligand–receptor complexes were generated using an automated docking procedure that allowed ligand flexibility. By comparing the resulting ligand poses, only two binding modes common for all 11 compounds were identified. Inspection of these two ligand–receptor complexes identified several CXCR4 contact residues shown by mutation to be interaction sites for ligands and important for HIV gp120 binding. Thus, the results provide further insight into the mechanism by which these cyclopentapeptides block HIV entry as well as a basis for rational design of CXCR4 mutants to map potential contacts with small peptide ligands.