Mini Reviews in Medicinal Chemistry - Volume 5, Issue 9, 2005

Members of the human chemokine family are considered a suitable target for therapeutic intervention, as they have a fundamental role in several important human diseases. Here we outline potential new areas of intervention based on recent findings on chemokine receptor function.

Chemokines belong to a large family of chemoattractant molecules involved in the directed migration of immune cells. They achieve their cellular effects by direct interaction with cell surface receptors. The chemokine receptor CCR1 appears to be involved in a variety of proinflammatory and autoimmune diseases and this makes it a very attractive therapeutic target. This review discusses the identification, chemistry, biology and therapeutic potential of BX 471 a potent CCR1 antagonist that is currently in the clinic for a variety of indications.

The bicyclam AMD3100 (originally called JM3100), in which the two cyclam rings are tethered by an aromatic bridge, emanated from JM2763, where the two cyclam moieties are tethered by an aliphatic linker - JM2763 in turn originated from JM1657, where the cyclam rings are directly linked to one another via a C-C bridge, and which was identified as an impurity, showing anti-HIV activity, in a commercial cyclam preparation. AMD3100 proved very effective against HIV-1 and HIV-2, inhibiting virus replication within the nM range, without toxicity for the host cells at concentrations that were > 100,000-fold higher than those required to inhibit HIV replication. The anti-HIV activity of AMD3100 appeared to be confined to the Tlymphotropic (X4) HIV strains, i.e. those strains that use the CXCR4 receptor to enter their target cells, and AMD3100 as of today still stands as one of the most potent and selective CXCR4 antagonists ever discovered. Hence, AMD3100 was found to interfere with a number of (patho)physiological processes which depend on the interaction of CXCR4 with its natural ligand, stromal derived factor (SDF-1) and which play an important role in rheumatoid, allergic and malignant diseases. AMD3100 has been shown to mobilize CD34+ stem cells from the bone marrow into the bloodstream and has also been shown to augment migration of bone marrowderived endothelial progenitor cells into sites of neovascularization after myocardial infarction. Currently, AMD3100 is actively pursued as a stem cell mobilizer for transplantation in patients with multiple myeloma and non-Hodgkin's lymphoma.

The chemokine family consists of more than 50 structurally-related small proteins which signal through type 1 G-protein coupled receptors (GPCRs) to regulate a range of immune functions, with particular focus on regulating leukocyte trafficking. They have been implicated both in normal physiological leukocyte traffic, and in recruitment of leukocytes to sites of pathological inflammation. As a result, chemokine inhibitors may have useful anti-inflammatory therapeutic properties in vivo. Compounds with chemokine-inhibitory properties that have been described to date, fall into two broad categories: receptor-specific antagonists which block the action of one or a small number of related chemokines, and broad-spectrum chemokine inhibitors (BSCIs) which block leukocyte migration in response to many, if not all, chemokines simultaneously. Since many chemokines apparently show functional redundancy in vivo, the BSCI class are attractive candidates for development as anti-inflammatory therapies. Here, we review the development of BSCIs, with particular focus on the design and characterisation of non-peptide compounds. The key structural requirements for BSCI activity are discussed, together with their implications for the mechanism of BSCI action.

Virus-encoded immune evasion mechanisms provide information on viral pathogenesis and offer a unique opportunity to identify new strategies of immune modulation. Secreted proteins that bind a broad range of chemokines have been identified in recent years in poxviruses and herpesviruses. We discuss the properties of these viral chemokine inhibitors and their potential as new therapeutics to treat human inflammatory diseases.

The dividing line between essential physiological inflammatory processes and excessive pathological inflammation is often very thin - in some circumstances, indeed, it may be non-existent. Devising anti-inflammatory medications that effectively target only the pathological component therefore remains a central challenge for the pharmaceutical industry. At present, the general rule is that the more powerful the antiinflammatory effect of a drug, the greater the side-effects that accompany it. Steroids, for example, are potent antiinflammatory medications, but they have a diverse array of side effects that substantially limit their use. Since chemokines play a central role in regulating the immune system, and in particular, the trafficking of leukocytes, inhibiting their action may represent a powerful new therapeutic strategy for treating diseases with an inflammatory component. However, this potential will only be realized if it is possible to interfere with chemokine signaling networks, without inducing unacceptable side effects. Although very little, direct human toxicology has been carried out using chemokine inhibitors, there is now a sufficient body of indirect and circumstantial evidence (for example, from genetically modified mice and from animal model studies using chemokine inhibitors) to allow a tentative assessment of the biological impact of chemokine inhibition. The purpose of this review is to outline the available data and to speculate on the likely toxicological profile resulting from chemokine inhibition. The tentative conclusion is that anti-inflammatory therapy achieved through chemokine inhibition may have fewer side effects than originally expected, even when the actions of multiple chemokines are inhibited simultaneously.

Rheumatoid arthritis and other chronic inflammatory diseases constitute a major therapeutic challenge, usually not sufficiently met by the classical antiinflammatory medications. Recent research efforts provided new insights into the molecular basis of these pathologies and disclosed new opportunities for developing improved drugs directed to the chemical mediators of the disease. The enzyme p38 MAP kinase plays a central role in the signal transduction cascade that leads to the production of both the proinflammatory cytokines, TNF-α and IL-1β, thus representing an attractive therapeutic target for novel antiinflammatory therapies. A number of p38 inhibitors belonging to different structural families have been developed as potential antiinflammatory drugs, and some of them progressed into clinical trials. The initial pyridinyl imidazole inhibitors contributed to the identification and characterization of p38 MAP kinase as the molecular target of these new drugs, and were found to act as competitive inhibitors at the ATP binding site of the enzyme. A number of variations in the pyridine and imidazole rings were subsequently introduced. Other inhibitors structurally unrelated to the pyridinylimidazoles have also been developed, such as the pyridopyridazinones, diaryl ureas, aminobenzophenones and aromatic amides. One of these structural classes, the N,N'-diarylureas, has been found to interact with a distinct allosteric site of p38 MAP kinase and requires a deep conformational change prior to binding.