Effects of MAPK inhibitors on CCR4-mediated chemotaxis against thymus and activation-regulated chemokine (TARC/CCL17)

ERK/STAT3 activation through CCL17/CCR4 axis-mediated type 2 cytokine-involved signaling pathways in Th2 cells regulates cutaneous drug reactions

Cutaneous drug reactions (CDRs) are common drug-induced allergic reactions that cause severe consequences in HIV/AIDS patients. The CCL17/CCR4 axis is involved in the immune mechanism of allergic diseases, but its role in the CDRs has not been determined. Here, we aimed to determine the role of the CCL17/CCR4 axis and the underlying mechanism involved in CDRs. In this study, the serum cytokine levels in patients with CDR and healthy controls were measured. The CCL17-triggered allergic profile was screened via a PCR array. Apoptosis of keratinocytes cocultured with CCL17-stimulated Th2 cells was analyzed by flow cytometry. An NVP-induced rat CDR model was established, and dynamic inflammatory factor levels and Th2 cells in the peripheral blood of the rats were measured. Rat skin lesions and signaling pathways in Th2 cells were also analyzed. We showed that the serum CCL17 level was significantly upregulated in CDR patients (P = 0.0077), and the Th2 cell subgroup was also significantly elevated in the CDR rats. The CCL17/CCR4 axis induces Th2 cells to release IL-4 and IL-13 via the ERK/STAT3 pathway. The CCR4 antagonist compound 47 can alleviate rash symptoms resulting from NVP-induced drug eruption, Th2 cell subgroup, IL-4, and IL-13 and inhibit keratinocyte apoptosis. Taken together, these findings indicate that the CCL17/CCR4 axis mediates CDR via the ERK/STAT3 pathway in Th2 cells and type 2 cytokine-induced keratinocyte apoptosis.

Role of ERK Pathway in the Pathogenesis of Atopic Dermatitis and Its Potential as a Therapeutic Target

Atopic dermatitis (AD) is an eczematous skin disorder characterized by type 2 inflammation, barrier disruption, and intense itch. In addition to type 2 cytokines, many other cytokines, such as interferon gamma (IFN-γ), interleukin 17 (IL-17), and interleukin 22 (IL-22), play roles in the pathogenesis of AD. It has been reported that the extracellular signal-regulated kinase (ERK) is downstream of such cytokines. However, the involvement of the ERK pathway in the pathogenesis of AD has not yet been investigated. We examined the expression of p-ERK in mouse and human AD skin. We also investigated the effects of the topical application of an ERK inhibitor on the dermatitis score, transepidermal water loss (TEWL), histological change, and expression of filaggrin, using an AD-like NC/Nga murine model. The effects of an ERK inhibitor on filaggrin expression in normal human epidermal keratinocytes (NHEKs) and on chemokine production from bone marrow-derived dendritic cells (BMDCs) were also evaluated. p-ERK was highly expressed in mouse and human AD skin. Topical application of an ERK inhibitor alleviated the clinical symptoms, histological changes, TEWL, and decrease in expression of filaggrin in the AD-like NC/Nga murine model. The ERK inhibitor also restored the IL-4 induced reduction in the expression of filaggrin in NHEK, and inhibited chemokine production from BMDC induced by IL-4. These results indicate that the ERK pathway is involved in the pathogenesis of AD, and suggest that the ERK pathway has potential as a therapeutic target for AD in the future.

CCL17/TARC and CCR4 expression in Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare, highly aggressive neuroendocrine skin cancer. In more than 80% of the cases, Merkel cell polyomavirus (MCPyV) is a causal factor. The oncogenic potential of MCPyV is mediated through its viral oncoproteins, large T antigen (LT) and small t antigen (sT). To investigate the role of cytokines in MCC, a PCR array analysis for genes encoding inflammatory cytokines and receptors was performed on MCPyV-negative and MCPyV-positive MCC cell lines, respectively. We detected an increased expression of CCL17/TARC in the MCPyV-positive MKL2 cell line compared to the MCPyV-negative MCC13 cell line. Transfection studies in MCC13 cells with LT expression plasmid, and a luciferase reporter plasmid containing the CCL17/TARC promoter, exhibited stimulated promoter activity. Interestingly, the ectopic expression of CCL17/TARC upregulated MCPyV early and late promoter activities in MCC13 cells. Furthermore, recombinant CCL17/TARC activated both the mitogen-activated protein kinase and the NF-κB pathways. Finally, immunohistochemical staining on human MCC tissues showed a strong staining of CCL17/TARC and its receptor CCR4 in both LT-positive and -negative MCC. Taken together, CCL17/TARC and CCR4 may be a potential target in MCC therapy providing MCC patients with a better overall survival outcome.

Stable C-N axial chirality in 1-aryluracil scaffold and differences in in vitro metabolic clearance between atropisomers of PDE4 inhibitor

We report herein the stable C-N axial chirality in a 1-phenyl-6-aminouracil scaffold owing to the presence of various functional groups at the ortho-position of the N(1)-phenyl group. Racemic 1-phenyl-6-aminouracils were first separated by chiral HPLC or converting them to the corresponding diastereomers using a chiral resolving agent. We then determined the rotational barrier of each atropisomer by a thermal racemization method and found that these compounds have rotational barriers similar to other C-N axially chiral biaryls. In addition, there was a good correlation between the rotational barriers and van der Waals radii of an ortho-substituent of the N(1)-phenyl group. To explore the possibility of the chiral 1-phenyl-6-aminouracil scaffold as a drug lead, we synthesized both atropisomers as phosphodiesterase-4 inhibitors 10. The atropisomers showed significantly different metabolic stabilities while their PDE4 inhibitory activities were somewhat similar. This finding demonstrates the potential utility of stable C-N bond atropisomers in the development of chiral drugs.

Surrogate antibodies that specifically bind and neutralize CCL17 but not CCL22

The chemokines CCL17 (TARC) and CCL22 (MDC) function through the same receptor, CCR4, but have been proposed to differentially affect the immune response. To better understand the role of the individual ligands, a panel of rat anti-mouse CCL17 surrogate antibodies was generated that can be used to differentiate CCL17 and CCL22 function in vitro and in vivo. We have successfully identified a panel of neutralizing antibodies by screening hybridomas for the ability to inhibit CCL17-mediated calcium mobilization. Chemotaxis in response to CCL17 is also inhibited, providing further evidence that the antibodies in this panel are antagonistic. Using a recombinant cell line expressing human CCR4, we show that the antibodies block β-arrestin recruitment as evidence that the antibodies are specifically blocking CCL17 signaling through CCR4. The antibodies within this panel inhibit calcium mobilization with varying potency in the calcium flux assay, having apparent IC50 ranging from approximately 1 to >400 ng/mL. Although both CCL17 and CCL22 function through CCR4, only a single antibody was identified as having detectable binding to CCL22. This panel of CCL17-specific antibodies provides tools that can be used to differentiate CCL17 and CCL22 function through CCR4 interaction in vitro and in vivo.

Engagement of two distinct binding domains on CCL17 is required for signaling through CCR4 and establishment of localized inflammatory conditions in the lung

CCL17 (TARC) function can be completely abolished by mAbs that block either one of two distinct sites required for CCR4 signaling. This chemokine is elevated in sera of asthma patients and is responsible for establishing inflammatory sites through CCR4-mediated recruitment of immune cells. CCL17 shares the GPCR CCR4, with CCL22 (MDC) but these two chemokines differentially affect the immune response. To better understand chemokine mediated effects through CCR4, we have generated chimeric anti-mouse CCL17 surrogate antibodies that inhibit function of this ligand in vitro and in vivo. The affinities of the surrogate antibodies for CCL17 range from 685 pM for B225 to 4.9 nM for B202. One antibody, B202, also exhibits weak binding to CCL22 (KD∼2 µM) and no binding to CCL22 is detectable with the second antibody, B225. In vitro, both antibodies inhibit CCL17-mediated calcium mobilization, β-arrestin recruitment and chemotaxis; B202 can also partially inhibit CCL22-mediated β-arrestin recruitment. Both B202 and B225 antibodies neutralize CCL17 in vivo as demonstrated by reduction of methacholine-induced airway hyperreactivity in the A. fumigatus model of asthma. That both antibodies block CCL17 function but only B202 shows any inhibition of CCL22 function suggests that they bind CCL17 at different sites. Competition binding studies confirm that these two antibodies recognize unique epitopes that are non-overlapping despite the small size of CCL17. Taking into consideration the data from both the functional and binding studies, we propose that effective engagement of CCR4 by CCL17 involves two distinct binding domains and interaction with both is required for signaling.

Leukocyte navigation mechanisms as targets in airway diseases

Respiratory diseases, including asthma and chronic obstructive pulmonary disease, are among the most significant diseases in terms of their disabling effects and healthcare burden. A characteristic feature of almost all respiratory diseases is the accumulation and activation of inflammatory leukocytes in the lung or airway. Recent advances in the understanding of the molecules and intracellular signalling events controlling these processes are now translating to new therapeutic entities. In this article, the process of leukocyte accumulation is summarized, together with the preclinical and clinical evidence supporting the utility of the individual components of this process as targets for disease therapy.