The Parallel Structure-Activity Relationship Screening of Three Compounds Identifies the Common Agonist Pharmacophore of Pyrrolidine Bis-Cyclic Guanidine Melanocortin-3 Receptor (MC3R) Small-Molecule Ligands.

The melanocortin receptors are involved in numerous physiological pathways, including appetite, skin and hair pigmentation, and steroidogenesis. In particular, the melanocortin-3 receptor (MC3R) is involved in fat storage, food intake, and energy homeostasis. Small-molecule ligands developed for the MC3R may serve as therapeutic lead compounds for treating disease states of energy disequilibrium. Herein, three previously reported pyrrolidine bis-cyclic guanidine compounds with five sites for molecular diversity (R1-R5) were subjected to parallel structure-activity relationship studies to identify the common pharmacophore of this scaffold series required for full agonism at the MC3R. The R2, R3, and R5 positions were required for full MC3R efficacy, while truncation of either the R1 or R4 positions in all three compounds resulted in full MC3R agonists. Two additional fragments, featuring molecular weights below 300 Da, were also identified that possessed full agonist efficacy and micromolar potencies at the mMC5R. These SAR experiments may be useful in generating new small-molecule ligands and chemical probes for the melanocortin receptors to help elucidate their roles in vivo and as therapeutic lead compounds.

Discovery of Nanomolar Melanocortin-3 Receptor (MC3R)-Selective Small Molecule Pyrrolidine Bis-Cyclic Guanidine Agonist Compounds Via a High-Throughput "Unbiased" Screening Campaign.

The central melanocortin-3 and melanocortin-4 receptors (MC3R, MC4R) are key regulators of body weight and energy homeostasis. Herein, the discovery and characterization of first-in-class small molecule melanocortin agonists with selectivity for the melanocortin-3 receptor over the melanocortin-4 receptor are reported. Identified via "unbiased" mixture-based high-throughput screening approaches, pharmacological evaluation of these pyrrolidine bis-cyclic guanidines resulted in nanomolar agonist activity at the melanocortin-3 receptor. The pharmacological profiles at the remaining melanocortin receptor subtypes tested indicated similar agonist potencies at both the melanocortin-1 and melanocortin-5 receptors and antagonist or micromolar agonist activities at the melanocortin-4 receptor. This group of small molecules represents a new area of chemical space for the melanocortin receptors with mixed receptor pharmacology profiles that may serve as novel lead compounds to modulate states of dysregulated energy balance.

Functional Mixture-Based Positional Scan Identifies a Library of Antagonist Tetrapeptide Sequences (LAtTeS) with Nanomolar Potency for the Melanocortin-4 Receptor and Equipotent with the Endogenous AGRP(86-132) Antagonist.

The melanocortin-4 receptor (MC4R) plays an important role in appetite. Agonist ligands that stimulate the MC4R decrease appetite, while antagonist compounds increase food consumption. Herein, a functional mixture-based positional scan identified novel MC4R antagonist sequences. Mixtures comprising a library of 12,960,000 tetrapeptides were screened in the presence and absence of the NDP-MSH agonist. These results led to the synthesis of 48 individual tetrapeptides, of which 40 were screened for functional activity at the melanocortin receptors. Thirteen compounds were found to possess nanomolar antagonist potency at the MC4R, with the general tetrapeptide sequence Ac-Aromatic-Basic-Aromatic-Basic-NH2. The most notable results include the identification of tetrapeptide 48 [COR1-25, Ac-DPhe(pI)-Arg-Nal(2')-Arg-NH2], an equipotent MC4R antagonist to agouti-related protein [AGRP(86-132)], more potent than miniAGRP(87-120), and possessing 15-fold selectivity for the MC4R versus the MC3R. These tetrapeptides may serve as leads for novel appetite-inducing therapies to treat states of negative energy balance, such as cachexia and anorexia.

SAR Studies of Exosite-Binding Substrate-Selective Inhibitors of A Disintegrin And Metalloprotease 17 (ADAM17) and Application as Selective in Vitro Probes.

ADAM17 is implicated in several debilitating diseases. However, drug discovery efforts targeting ADAM17 have failed due to the utilization of zinc-binding inhibitors. We previously reported discovery of highly selective nonzinc-binding exosite-targeting inhibitors of ADAM17 that exhibited not only enzyme isoform selectivity but synthetic substrate selectivity as well ( J. Biol. Chem. 2013, 288, 22871). As a result of SAR studies presented herein, we obtained several highly selective ADAM17 inhibitors, six of which were further characterized in biochemical and cell-based assays. Lead compounds exhibited low cellular toxicity and high potency and selectivity for ADAM17. In addition, several of the leads inhibited ADAM17 in a substrate-selective manner, which has not been previously documented for inhibitors of the ADAM family. These findings suggest that targeting exosites of ADAM17 can be used to obtain highly desirable substrate-selective inhibitors. Additionally, current inhibitors can be used as probes of biological activity of ADAM17 in various in vitro and, potentially, in vivo systems.

Combinatorial Libraries As a Tool for the Discovery of Novel, Broad-Spectrum Antibacterial Agents Targeting the ESKAPE Pathogens.

Mixture based synthetic combinatorial libraries offer a tremendous enhancement for the rate of drug discovery, allowing the activity of millions of compounds to be assessed through the testing of exponentially fewer samples. In this study, we used a scaffold-ranking library to screen 37 different libraries for antibacterial activity against the ESKAPE pathogens. Each library contained between 10000 and 750000 structural analogues for a total of >6 million compounds. From this, we identified a bis-cyclic guanidine library that displayed strong antibacterial activity. A positional scanning library for these compounds was developed and used to identify the most effective functional groups at each variant position. Individual compounds were synthesized that were broadly active against all ESKAPE organisms at concentrations <2 µM. In addition, these compounds were bactericidal, had antibiofilm effects, showed limited potential for the development of resistance, and displayed almost no toxicity when tested against human lung cells and erythrocytes. Using a murine model of peritonitis, we also demonstrate that these agents are highly efficacious in vivo.

Scaffold ranking and positional scanning utilized in the discovery of nAChR-selective compounds suitable for optimization studies.

Nicotine binds to nicotinic acetylcholine receptors (nAChR), which can exist as many different subtypes. The α4ß2 nAChR is the most prevalent subtype in the brain and possesses the most evidence linking it to nicotine seeking behavior. Herein we report the use of mixture based combinatorial libraries for the rapid discovery of a series of α4ß2 nAChR selective compounds. Further chemistry optimization provided compound 301, which was characterized as a selective α4ß2 nAChR antagonist. This compound displayed no agonist activity but blocked nicotine-induced depolarization of HEK cells with an IC50 of approximately 430 nM. 301 demonstrated nearly 500-fold selectivity for binding and 40-fold functional selectivity for α4ß2 over α3ß4 nAChR. In total over 5 million compounds were assessed through the use of just 170 samples in order to identify a series of structural analogues suitable for future optimization toward the goal of developing clinically relevant smoking cessation medications.