Chemokines coordinate many aspects of leukocyte migration. As chemoattractants they play an important role in the innate and acquired immune response. There is good experimental evidence that N-terminal truncation by secreted or cell surface proteases is a way of modulating chemokine action. The localization of CD26/ dipeptidyl peptidase IV on cell surfaces and in biological fluids, its primary specificity, and the type of naturally occurring truncated chemokines are consistent with such a function.We determined the steady-state catalytic parameters for a relevant selection of chemokines (CCL3b, CCL5, CCL11, CCL22, CXCL9, CXCL10, CXCL11, and CXCL12) previously reported to alter their chemotactic behavior due to CD26/dipeptidyl peptidase IV-catalyzed truncation. The results reveal a striking selectivity for stromal cell-derived factor-1␣ (CXCL12) and macrophage-derived chemokine (CCL22). The kinetic parameters support the hypothesis that CD26/dipeptidyl peptidase IV contributes to the degradation of certain chemokines in vivo. The data not only provide insight into the selectivity of the enzyme for specific chemokines, but they also contribute to the general understanding of CD26/dipeptidyl peptidase IV secondary substrate specificity.
Fibroblast activation protein (FAP) is a serine protease related to dipeptidyl peptidase IV (DPPIV). It has been convincingly linked to multiple disease states involving remodeling of the extracellular matrix. FAP inhibition is investigated as a therapeutic option for several of these diseases, with most attention so far devoted to oncology applications. We previously discovered the N-4-quinolinoyl-Gly-(2S)-cyanoPro scaffold as a possible entry to highly potent and selective FAP inhibitors. In the present study, we explore in detail the structure-activity relationship around this core scaffold. We report extensively optimized compounds that display low nanomolar inhibitory potency and high selectivity against the related dipeptidyl peptidases (DPPs) DPPIV, DPP9, DPPII, and prolyl oligopeptidase (PREP). The log D values, plasma stabilities, and microsomal stabilities of selected compounds were found to be highly satisfactory. Pharmacokinetic evaluation in mice of selected inhibitors demonstrated high oral bioavailability, plasma half-life, and the potential to selectively and completely inhibit FAP in vivo.
Fibroblast activation protein (FAP) is a serine protease that is generally accepted to play an important role in tumor growth and other diseases involving tissue remodeling. Currently there are no FAP inhibitors with reported selectivity toward both the closely related dipeptidyl peptidases (DPPs) and prolyl oligopeptidase (PREP). We present the discovery of a new class of FAP inhibitors with a N-(4-quinolinoyl)-Gly-(2-cyanopyrrolidine) scaffold. We have explored the effects of substituting the quinoline ring and varying the position of its sp 2 hybridized nitrogen atom. The most promising inhibitors combined low nanomolar FAP inhibition and high selectivity indices (>10 3 ) with respect to both the DPPs and PREP. Preliminary experiments on a representative inhibitor demonstrate that plasma stability, kinetic solubility, and log D of this class of compounds can be expected to be satisfactory.
Accumulation of unfolded proteins in the endoplasmic reticulum (ER) causes a state of cellular stress known as ER stress. The cells respond to ER stress by activating the unfolded protein response (UPR), a signaling network emerging from the ER-anchored receptors IRE1α, PERK and ATF6. The UPR aims at restoring ER protein-folding homeostasis, but turns into a toxic signal when the stress is too severe or prolonged. Recent studies have demonstrated links between the UPR and inflammation. Consequently, small molecule inhibitors of IRE1α and PERK have become attractive tools for the potential therapeutic manipulation of the UPR in inflammatory conditions. TNF is a master pro-inflammatory cytokine that drives inflammation either directly by promoting gene activation, or indirectly by inducing RIPK1 kinase-dependent cell death, in the form of apoptosis or necroptosis. To evaluate the potential contribution of the UPR to TNF-induced cell death, we tested the effects of two commonly used PERK inhibitors, GSK2606414 and GSK2656157. Surprisingly, we observed that both compounds completely repressed TNF-mediated RIPK1 kinase-dependent death, but found that this effect was independent of PERK inactivation. Indeed, these two compounds turned out to be direct RIPK1 inhibitors, with comparable potency to the recently developed RIPK1 inhibitor GSK'963 (about 100 times more potent than NEC-1s). Importantly, these compounds completely inhibited TNF-mediated RIPK1-dependent cell death at a concentration that did not affect PERK activity in cells. In vivo, GSK2656157 administration protected mice from lethal doses of TNF independently of PERK inhibition and as efficiently as GSK'963. Together, our results not only report on new and very potent RIPK1 inhibitors but also highlight the risk of misinterpretation when using these two PERK inhibitors in the context of ER stress, cell death and inflammation.
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