Agostino Cilibrizzi

6-Methyl-2,4-Disubstituted Pyridazin-3(2H)-ones: A Novel Class of Small-Molecule Agonists for Formyl Peptide Receptors

Following a ligand-based drug design approach, a potent mixed formyl peptide receptor 1 (FPR1) and formyl peptide receptor-like 1 (FPRL1) agonist (14a) and a potent and specific FPRL1 agonist (14x) were identified. These compounds belong to a large series of pyridazin-3(2H)-one derivatives substituted with a methyl group at position 6 and a methoxy benzyl at position 4. At position 2, an acetamide side chain is essential for activity. Likewise, the presence of lipophilic and/or electronegative substituents in the position para to the aryl group at the end of the chain plays a critical role for activity. Affinity for FPR1 receptors was evaluated by measuring intracellular calcium flux in HL-60 cells transfected with FPR1, FPRL1, and FPRL2. Agonists were able to activate intracellular calcium mobilization and chemotaxis in human neutrophils. The most potent chemotactic agent (EC(50) = 0.6 microM) was the mixed FPR/FPRL1 agonist 14h.

Further Studies on Arylpiperazinyl Alkyl Pyridazinones: Discovery of an Exceptionally Potent, Orally Active, Antinociceptive Agent in Thermally Induced Pain†

A number of pyridazinone derivatives bearing an arylpiperazinylalkyl chain were synthesized and tested icv in a model of acute nociception induced by thermal stimuli in mice (tail flick). The most interesting and potent compound in this series was 6a, which showed an ED(50) = 3.5 microg, a value about 3-fold higher with respect to morphine by the same route of administration. When administered per os, 6a was 4-fold more potent than morphine in the same test, suggesting a significant bioavailability. The same compound also showed high potency in the hot plate test. The antinociceptive effect of 6a was completely reversed by pretreatment with yohimbine both in the hot plate test and in the tail flick test. This demonstrated the involvement of the adrenergic system, which was confirmed by in vitro radioligand binding studies.

Development of Small Molecule Non-peptide Formyl Peptide Receptor (FPR) Ligands and Molecular Modeling of Their Recognition

Formyl peptide receptors (FPRs) are G protein-coupled receptors (GPCRs) expressed on a variety of cell types. These receptors play an important role in the regulation of inflammatory reactions and sensing cellular damage. They have also been implicated in the pathogenesis of various diseases, including neurodegenerative diseases, cataract formation, and atherogenesis. Thus, FPR ligands, both agonists and antagonists, may represent novel therapeutics for modulating host defense and innate immunity. A variety of molecules have been identified as receptor subtype-selective and mixed FPR agonists with potential therapeutic value during last decade. This review describes our efforts along with recent advances in the identification, optimization, biological evaluation, and structure-activity relationship (SAR) analysis of small molecule non-peptide FPR agonists and antagonists, including chiral molecules. Questions regarding the interaction at the molecular level of benzimidazoles, pyrazolones, pyridazin-3(2H)-ones, N-phenylureas and other derivatives with FPR1 and FPR2 are discussed. Application of computational models for virtual screening and design of FPR ligands is also considered.

Optimization of N-Benzoylindazole Derivatives as Inhibitors of Human Neutrophil Elastase

Human neutrophil elastase (HNE) is an important therapeutic target for treatment of pulmonary diseases. Previously, we identified novel N-benzoylindazole derivatives as potent, competitive, and pseudoirreversible HNE inhibitors. Here, we report further development of these inhibitors with improved potency, protease selectivity, and stability compared to our previous leads. Introduction of a variety of substituents at position 5 of the indazole resulted in the potent inhibitor 20f (IC50 ∼10 nM) and modifications at position 3 resulted the most potent compound in this series, the 3-CN derivative 5b (IC50 = 7 nM); both derivatives demonstrated good stability and specificity for HNE versus other serine proteases. Molecular docking of selected N-benzoylindazoles into the HNE binding domain suggested that inhibitory activity depended on geometry of the ligand-enzyme complexes. Indeed, the ability of a ligand to form a Michaelis complex and favorable conditions for proton transfer between Hys57, Asp102, and Ser195 both affected activity.

Further studies on 2-arylacetamide pyridazin-3(2H)-ones: design, synthesis and evaluation of 4,6-disubstituted analogs as formyl peptide receptors (FPRs) agonists.

Formyl peptide receptors (FPRs) play an essential role in the regulation of endogenous inflammation and immunity. In the present studies, a large series of pyridazin-3(2H)-one derivatives bearing an arylacetamide chain at position 2 was synthesized and tested for FPR agonist activity. The pyridazin-3(2H)-one ring was confirmed to be an appropriate scaffold to support FPR agonist activity, and its modification at the 4 and 6 positions led to the identification of additional active agonists, which induced intracellular Ca(2+) flux in HL-60 cells transfected with either FPR1, FPR2, or FPR3. Seven formyl peptide receptor 1 (FPR1)-specific and several mixed FPR1/FPR2 dual agonists were identified with low micromolar EC50 values. Furthermore, these agonists also activated human neutrophils, inducing intracellular Ca(2+) flux and chemotaxis. Finally, molecular docking studies indicated that the most potent pyridazin-3(2H)-ones overlapped in their best docking poses with fMLF and WKYMVM peptides in the FPR1 and FPR2 ligand binding sites, respectively. Thus, pyridazinone-based compounds represent potential lead compounds for further development of selective and/or potent FPR agonists.

Synthesis, enantioresolution, and activity profile of chiral 6-methyl-2,4-disubstituted pyridazin-3(2H)-ones as potent N-formyl peptide receptor agonists.

A series of chiral pyridazin-3(2H)-ones was synthesized, separated as pure enantiomers, and evaluated for N-formyl peptide receptor (FPR) agonist activity. Characterization of the purified enantiomers using combined chiral HPLC and chiroptical studies (circular dichroism, allowed unambiguous assignment of the absolute configuration for each pair of enantiomers). Evaluation of the ability of racemic mixtures and purified enantiomers to stimulate intracellular Ca(2+) flux in FPR-transfected HL-60 cells and human neutrophils and to induce β-arrestin recruitment in FPR-transfected CHO-K1 cells showed that many enantiomers were potent agonists, inducing responses in the sub-micromolar to nanomolar range. Furthermore, FPRs exhibited enantiomer selectivity, generally preferring the R-(-)-forms over the S-(+)-enantiomers. Finally, we found that elongation of the carbon chain in the chiral center of the active compounds generally increased biological activity. Thus, these studies provide important new information regarding molecular features involved in FPR ligand preference and report the identification of a novel series of FPR agonists.

Cinnoline derivatives as human neutrophil elastase inhibitors

Abstract Compounds that can effectively inhibit the proteolytic activity of human neutrophil elastase (HNE) represent promising therapeutics for treatment of inflammatory diseases. We present here the synthesis, structure–activity relationship analysis, and biological evaluation of a new series of HNE inhibitors with a cinnoline scaffold. These compounds exhibited HNE inhibitory activity but had lower potency compared to N-benzoylindazoles previously reported by us. On the other hand, they exhibited increased stability in aqueous solution. The most potent compound, 18a, had a good balance between HNE inhibitory activity (IC50 value = 56 nM) and chemical stability (t1/2 = 114 min). Analysis of reaction kinetics revealed that these cinnoline derivatives were reversible competitive inhibitors of HNE. Furthermore, molecular docking studies of the active products into the HNE binding site revealed two types of HNE inhibitors: molecules with cinnolin-4(1H)-one scaffold, which were attacked by the HNE Ser195 hydroxyl group at the amido moiety, and cinnoline derivatives containing an ester function at C-4, which is the point of attack of Ser195.

Design, synthesis and evaluation of N-benzoylindazole derivatives and analogues as inhibitors of human neutrophil elastase

Human neutrophil elastase (HNE) plays an important role in tumour invasion and inflammation. A series of N-benzoylindazoles was synthesized and evaluated for their ability to inhibit HNE. We found that this scaffold is appropriate for HNE inhibitors and that the benzoyl fragment at position 1 is essential for activity. The most active compounds inhibited HNE activity with IC₅₀ values in the submicromolar range. Furthermore, docking studies indicated that the geometry of an inhibitor within the binding site and energetics of Michaelis complex formation were key factors influencing the inhibitors biological activity. Thus, N-benzoylindazole derivatives and their analogs represent novel structural templates that can be utilized for further development of efficacious HNE inhibitors.

Functionalized pyrazoles and pyrazolo[3,4-d]pyridazinones: Synthesis and evaluation of their phosphodiesterase 4 inhibitory activity

A series of pyrazoles and pyrazolo[3,4-d]pyridazinones were synthesized and evaluated for their PDE4 inhibitory activity. All the pyrazoles were found devoid of activity, whereas some of the novel pyrazolo[3,4-d]pyridazinones showed good activity as PDE4 inhibitors. The most potent compounds in this series showed an IC(50) in the nanomolar range. The ability to inhibit TNF-alpha release in human PBMCs was determined for two representative compounds, finding values in the sub-micromolar range. SARs studies demonstrated that the best arranged groups around the heterocyclic core are 2-chloro-, 2-methyl- and 3-nitrophenyl at position 2, an ethyl ester at position 4 and a small alkyl group at position 6. Molecular modeling studies performed on a representative compound allowed to define its binding mode to the PDE4B isoform.

Synthesis and Pharmacological Evaluation of New Pyridazin‐Based Thioderivatives as Formyl Peptide Receptor (FPR) Agonists

Preclinical Research