Asymmetric synthesis and biological evaluation of imidazole- and oxazole-containing synthetic lipoxin A4 mimetics (sLXms).

Lipoxins (LXs) are endogenously generated eicosanoids with potent bio-actions consistent with attenuation of inflammation. The costly synthesis and metabolic instability of LXs may limit their therapeutic potential. Here we report the synthesis and characterization of novel imidazole-/oxazole-containing synthetic-LX-mimetics (sLXms). The key steps of asymmetric synthesis of putative sLXms include a Suzuki reaction and an asymmetric ketone reduction. The effect of the novel compounds on inflammatory responses was assessed using a human monocyte cell line stably expressing a Nuclear Factor Kappa B (NFkB) reporter gene, by investigating downstream cytokine secretion. The potential interaction of the imidazoles/oxazoles with the molecular target of LXs, i.e. G-protein coupled receptor (GPCR) Formyl Peptide Receptor 2 (ALX/FPR2) was investigated using a cell system where ALX/FPR2 is coupled to the Gαq subunit and receptor interaction determined by mobilisation of intracellular calcium. In vivo anti-inflammatory effects were assessed using a murine zymosan-induced peritonitis model. Overall, structure-activity relationship (SAR) studies demonstrated that the (R)-epimer of 6C-dimethyl-imidazole (1R)-11 was the most potent and efficient anti-inflammatory agent, among the ten compounds tested. This molecule significantly attenuated LPS-induced NFkB activity, reduced the release of several pro-inflammatory cytokines and inhibited peritonitis-associated neutrophil infiltration in vivo. The underlying mechanism for those actions appeared to be through FPR2 activation. These data support the therapeutic potential of imidazole-containing sLXms in the context of novel inflammatory regulators.

Design and synthesis of benzo-lipoxin A4 analogs with enhanced stability and potent anti-inflammatory properties.

A new class of chemically and metabolically stable lipoxin analogs featuring a replacement of the tetraene unit of native LXA(4) with a substituted benzo-fused ring system have been designed and studied. These molecules were readily synthesized via a convergent synthetic route involving iterative palladium-mediated cross-coupling, and exhibit enhanced chemical stability, as well as resistance to metabolic inactivation via eicosanoid oxido-reductase. These new LX analogs were evaluated in a model of acute inflammation and were shown to exhibit potent anti-inflammatory properties, significantly decreasing neutrophil infiltration in vivo. The most potent among these was compound 9 (o-[9,12]-benzo-15-epi-LXA(4) methyl ester. Taken together, these findings help identify a new class of stable and easily prepared LX analogs that may serve as novel tools and as promising leads for new anti-inflammatory agents with improved therapeutic profile.

Aromatic lipoxin A4 and lipoxin B4 analogues display potent biological activities.

Lipoxins are a group of biologically active eicosanoids typically formed by transcellular lipoxygenase activity. Lipoxin A4 (LXA4) and Lipoxin B4 (LXB4) biosynthesis has been detected in a variety of inflammatory conditions. The native lipoxins LXA4 and LXB4 demonstrate potent antiinflammatory and proresolution bioactions. However, their therapeutic potential is compromised by rapid metabolic inactivation by PG dehydrogenase-mediated oxidation and reduction. Here we report on the stereoselective synthesis of aromatic LXA4 and LXB4 analogues by employing Sharpless epoxidation, Pd-mediated Heck coupling, and diastereoselective reduction as the key transformations. Subsequent biological testing has shown that these analogues display potent biological activities. Phagocytic clearance of apoptotic leukocytes plays a critical role in the resolution of inflammation. Both LXA4 analogues (1R)-3a and (1S)-3a were found to stimulate a significant increase in phagocytosis of apoptotic polymorphonuclear leukocytes (PMN) by macrophages, with comparable efficacy to the effect of native LXA4, albeit greater potency, while the LXB4 analogue also stimulated phagocytosis with a maximum effect observed at 10-11 M. LX-stimulated phagocytosis was associated with rearrangement of the actin cytoskeleton consistent with that reported for native lipoxins. Using zymosan-induced peritonitis as a murine model of acute inflammation (1R)-3a significantly reduced PMN accumulation.

Gastrointestinal safety of novel nonsteroidal antiinflammatory drugs: selective COX-2 inhibitors and beyond.

Nonsteroidal antiinflammatory drugs (NSAIDs) are frequently associated with adverse reactions, related to inhibition of cyclooxygenase (COX) in tissues where prostaglandins exert physiological effects, such as gastric mucosal defense and renal homeostasis. The discovery of two COX isoforms, namely COX-1 constitutively expressed in most tissues and COX-2 induced at sites of inflammation, led to the development of selective COX-2 inhibitors ("coxibs"), with the hope of significantly reducing the gastrointestinal toxicity associated with acute and chronic NSAID use. However, the increased knowledge of physiological roles of COX-2 enzyme in a variety of tissues, including stomach and kidney, together with the withdrawal from the market of rofecoxib and valdecoxib because of cardiovascular toxicity, have challenged the benefits of selective COX-2 inhibition. As a consequence, the interest for novel approaches has re-emerged; new therapeutic options, still under clinical evaluation, are represented by dual COX and 5-lipooxygenase (5-LOX) inhibitors, synthetic lipoxins, nitric oxide (NO)-releasing NSAIDs and, more recently, by NSAIDs releasing hydrogen sulphide (H2S). This review focuses upon the gastrointestinal (GI) safety of selective COX-2 inhibitors and of novel therapeutic strategies, in comparison with traditional NSAIDs.

Design, synthesis and bioactions of novel stable mimetics of lipoxins and aspirin-triggered lipoxins.

The lipoxins (LX) are a class of potent endogenous oxygenated products that are enzymatically generated from arachidonic acid and have novel anti-inflammatory properties and promote resolution. Elucidation of the biochemical pathways involved in the metabolic inactivation of LX and the discovery of the aspirin-triggered lipoxins (ATL) provided the basis for the design and synthesis of stable analogs of LX and ATL. This special issue review describes the efforts that led to the design and synthesis of stable LX/ATL mimetics, which permitted the detailed elucidation of their novel biological roles, leading to the development of new anti-inflammatory agents that mimic their actions. These synthetic molecules provided the means to uncover the physiologic roles of both the LX and the ATL biosynthetic pathways which led to several unexpected discoveries. Among these findings is the involvement of polyisoprenyl phosphates (PIPP) in intracellular signaling mediated by presqualene diphosphate (PSDP), and the recognition of the novel roles of these lipid mediators in regulating cell trafficking during inflammation as well as in promoting resolution of inflammatory processes. These efforts also provided the basis for examining the potential therapeutic role of LX/ATL stable mimetics and led to the development of new analogs with improved pharmacokinetics that opened the way to potentially new approaches to treating human diseases.

A synthetic eicosanoid LX-mimetic unravels host-donor interactions in allogeneic BMT-induced GvHD to reveal an early protective role for host neutrophils.

Lipoxin A(4) (LXA(4)) and aspirin-triggered 15-epi-LXA(4) are potent endogenous lipid mediators thought to define the inflammatory set-point. We used single prophylactic administrations of a synthetic aspirin-triggered lipoxin A(4) signal mimetic, ATLa, to probe dynamics of early host-donor interactions in a mouse model for the inflammation-associated multifactorial disease of allogeneic bone marrow transplant (BMT) -induced graft-vs.-host disease (GvHD). We first demonstrated that both host and donor are responsive to the ATLa signals. The simple and restricted regimen of a single prophylactic administration of ATLa [100 ng/mL to donor cells or 1 microg (approximately 50 microg/kg) i.v. to host] was sufficient to delay death. Clinical indicators of weight, skin lesions, diarrhea and eye inflammation were monitored. Histological analyses on day 45 post-BMT showed that the degree of cellular trafficking, particularly neutrophil infiltrate, and protection of end-organ target pathology are different, depending on whether the host or donor was treated with ATLa. Taken together, these results chart some ATLa protective effects on GvHD cellular dynamics over time and identify a previously unrecognized effect of host neutrophils in the early phase post-BMT as important determinants in the dynamics of GvHD onset and progression.-Devchand, P. R., Schmidt, B. A., Primo, V. C., Zhang, Q.-y., Arnaout, M. A., Serhan, C. N., Nikolic, B. A synthetic eicosanoid LX-mimetic unravels host-donor interactions in allogeneic BMT-induced GvHD to reveal an early protective role for host neutrophils.

Novel 3-oxa lipoxin A4 analogues with enhanced chemical and metabolic stability have anti-inflammatory activity in vivo.

Lipoxin A(4) (LXA(4)) is a structurally and functionally distinct natural product called an eicosanoid, which displays immunomodulatory and anti-inflammatory activity but is rapidly metabolized to inactive catabolites in vivo. A previously described analogue of LXA(4), methyl (5R,6R,7E,9E,11Z,13E,15S)-16-(4-fluorophenoxy)-5,6,15-trihydroxy-7,9,11,13-hexadecatetraenoate (2, ATLa), was shown to have a poor pharmacokinetic profile after both oral and intravenous administration, as well as sensitivity to acid and light. The chemical stability of the corresponding E,E,E-trien-11-yne analogue, 3, was improved over 2 without loss of efficacy in the mouse air pouch model of inflammation. Careful analysis of the plasma samples from the pharmacokinetic assays for both 2 and 3 identified a previously undetected metabolite, which is consistent with metabolism by beta-oxidation. The formation of the oxidative metabolites was eliminated with the corresponding 3-oxatetraene, 4, and the 3-oxatrien-11-yne, 5, analogues of 2. Evaluation of 3-oxa analogues 4 and 5 in calcium ionophore-induced acute skin inflammation model demonstrated similar topical potency and efficacy compared to 2. The 3-oxatrien-11-yne analogue, 5, is equipotent to 2 in an animal model of inflammation but has enhanced metabolic and chemical stability and a greatly improved pharmacokinetic profile.

Synthesis of methyl (5S,6R,7E,9E,11Z,13E,15S)-16-(4-fluorophenoxy)-5,6,15-trihydroxy-7,9,11,13-hexadecatetraenoate, an analogue of 15R-lipoxin A4.

We describe a method for the synthesis of methyl (5S,6R,7E,9E,11Z,13E,15S)-16-(4-fluorophenoxy)-5,6,15-trihydroxy-7,9,11,13-hexadecatetraenoate, a compound that has been described as a metabolically stable analogue of 15R-lipoxin A(4).