CCR2-Mediated Uptake of Constitutively Produced CCL2: A Mechanism for Regulating Chemokine Levels in the Blood.

C-C chemokine receptor 2 (CCR2) is a key driver of monocyte/macrophage trafficking to sites of inflammation and has long been considered a target for intervention in autoimmune disease. However, systemic administration of CCR2 antagonists is associated with marked increases in CCL2, a CCR2 ligand, in the blood. This heretofore unexplained phenomenon complicates interpretation of in vivo responses to CCR2 antagonism. We report that CCL2 elevation after pharmacological CCR2 blockade is due to interruption in a balance between CCL2 secretion by a variety of cells and its uptake by constitutive internalization and recycling of CCR2. We observed this phenomenon in response to structurally diverse CCR2 antagonists in wild-type mice, and also found substantially higher CCL2 plasma levels in mice lacking the CCR2 gene. Our findings suggest that CCL2 is cleared from blood in a CCR2-dependent but G protein (Gαi, Gαs or Gαq/11)-independent manner. This constitutive internalization is rapid: on a given monocyte, the entire cell surface CCR2 population is turned over in <30 minutes. We also found that constitutive receptor internalization/recycling and ligand uptake are not universal across monocyte-expressed chemokine receptors. For example, CXCR4 does not internalize constitutively. In summary, we describe a mechanism that explains the numerous preclinical and clinical reports of increased CCL2 plasma levels following in vivo administration of CCR2 antagonists. These findings suggest that constitutive CCL2 secretion by monocytes and other cell types is counteracted by constant uptake and internalization by CCR2-expressing cells. The effectiveness of CCR2 antagonists in disease settings may be dependent upon this critical equilibrium.

Efficacy of Chemokine Receptor Inhibition in Treating IL-36α-Induced Psoriasiform Inflammation.

Several types of psoriasiform dermatitis are associated with increased IL-36 cytokine activity in the skin. A rare, but severe, psoriasis-like disorder, generalized pustular psoriasis (GPP), is linked to loss-of-function mutations in the gene encoding IL-36RA, an important negative regulator of IL-36 signaling. To understand the effects of IL-36 dysregulation in a mouse model, we studied skin inflammation induced by intradermal injections of preactivated IL-36α. We found the immune cells infiltrating IL-36α-injected mouse skin to be of dramatically different composition than those infiltrating imiquimod-treated skin. The IL-36α-induced leukocyte population comprised nearly equal numbers of CD4+ αß T cells, neutrophils, and inflammatory dendritic cells, whereas the imiquimod-induced population comprised γδ T cells and neutrophils. Ligands for chemokine receptors CCR6 and CXCR2 are increased in both GPP and IL-36α-treated skin, which led us to test an optimized small-molecule antagonist (CCX624) targeting CCR6 and CXCR2 in the IL-36α model. CCX624 significantly reduced the T cell, neutrophil, and inflammatory dendritic cell infiltrates and was more effective than saturating levels of an anti-IL-17RA mAb at reducing inflammatory symptoms. These findings put CCR6 and CXCR2 forward as novel targets for a mechanistically distinct therapeutic approach for inflammatory skin diseases involving dysregulated IL-36 signaling, such as GPP.

IL-17-Secreting γδ T Cells Are Completely Dependent upon CCR6 for Homing to Inflamed Skin.

mAbs that neutralize IL-17 or its receptor have proven efficacious in treating moderate-to-severe psoriasis, confirming IL-17 as an important driver of this disease. In mice, a rare population of T cells, γδT17 cells, appears to be a dominant source of IL-17 in experimental psoriasis. These cells traffic between lymph nodes and the skin, and are identified by their coexpression of the TCR variable regions γ4 and δ4. These cells are homologous to the Vγ9Vδ2 T cell population identified in human psoriatic plaques. In this study we report that a potent and specific small molecule antagonist of the CCR6 chemokine receptor, CCX2553, was efficacious in reducing multiple aspects of psoriasis in two different murine models of the disease. Administration of CCX2553 ameliorated skin inflammation in both the IL-23-induced ear swelling model and the topical imiquimod model, and significantly reduced the number of γδT17 cells in inflamed skin. γδT17 cells were greatly reduced in imiquimod-treated skin of CCR6-/- mice, but adoptively transferred wild-type (CCR6+/+) γδT17 cells homed normally to the skin of imiquimod-treated CCR6-/- mice. Our data suggest that γδT17 cells are completely dependent on CCR6 for homing to psoriasiform skin. Thus, CCR6 may constitute a novel target for a mechanistically distinct therapeutic approach to treating psoriasis.

The total synthesis of tubulysin D.

The first total synthesis of tubulysin D is reported. The development and application of new tert-butanesulfinamide methods allowed for rapid syntheses of the tubuvaline and tubuphenylalanine fragments. Most significantly, a route was devised and implemented to introduce and carry forward the highly labile N,O-acetal functionality. Tubulysin D is the most active member of the tubulysin family, and the efficient synthetic route described herein will allow for the rapid syntheses of analogues to probe the biological activity of this important class of natural products.

Asymmetric conjugate addition of copper reagents to alpha,beta-unsaturated tert-butanesulfinyl imines.

[reaction: see text] Addition of organocuprates to N-sulfinyl alpha,beta-unsaturated imines proceeds in good yields and with good diastereoselectivities. alpha,beta-Unsaturated sulfinyl ketimines and aldimines have both been shown to be suitable substrates for this reaction.

Highly stereoselective addition of organometallic reagents to N-tert-butanesulfinyl imines derived from 3- and 4-substituted cyclohexanones.

Addition of alkyl or aryl Grignard reagents to N-sulfinyl imines derived from 3- and 4-substituted cyclohexanones proceeds with good yields and with excellent diasteroselectivity. The selectivity of the reaction is controlled by the ring substituent rather than the sulfinyl group stereochemistry, and therefore racemic tert-butanesulfinamide can be employed.