Nonclinical Pharmacokinetics, Disposition, and Drug-Drug Interaction Potential of a Novel d-Amino Acid Peptide Agonist of the Calcium-Sensing Receptor AMG 416 (Etelcalcetide).

AMG 416 (etelcalcetide) is a novel synthetic peptide agonist of the calcium-sensing receptor composed of a linear chain of seven d-amino acids (referred to as the d-amino acid backbone) with a d-cysteine linked to an l-cysteine via a disulfide bond. AMG 416 contains four basic d-arginine residues and is a +4 charged peptide at physiologic pH with a mol. wt. of 1048.3 Da. The pharmacokinetics (PK), disposition, and potential of AMG 416 to cause drug-drug interaction were investigated in nonclinical studies with two single (14)C-labels placed either at a potentially metabolically labile acetyl position or on the d-alanine next to d-cysteine in the interior of the d-amino acid backbone. After i.v. dosing, the PK and disposition of AMG 416 were similar in male and female rats. Radioactivity rapidly distributed to most tissues in rats with intact kidneys, and renal elimination was the predominant clearance pathway. No strain-dependent differences were observed. In bilaterally nephrectomized rats, minimal radioactivity (1.2%) was excreted via nonrenal pathways. Biotransformation occurred primarily via disulfide exchange with endogenous thiol-containing molecules in whole blood rather than metabolism by enzymes, such as proteases or cytochrome P450s; the d-amino acid backbone remained unaltered. A substantial proportion of the plasma radioactivity was covalently conjugated to albumin. AMG 416 presents a low risk for P450 or transporter-mediated drug-drug interactions because it showed no interactions in vitro. These studies demonstrated a (14)C label on either the acetyl or the d-alanine in the d-amino acid backbone would be appropriate for clinical studies.

Discovery of selective biaryl ethers as PDE10A inhibitors: improvement in potency and mitigation of Pgp-mediated efflux.

We report the discovery of a novel series of biaryl ethers as potent and selective PDE10A inhibitors. Structure-activity studies improved the potency and decreased Pgp-mediated efflux found in the initial compound 4. X-ray crystallographic studies revealed two novel binding modes to the catalytic site of the PDE10A enzyme.

Development and characterization of LLC-PK1 cells containing Sprague-Dawley rat Abcb1a (Mdr1a): comparison of rat P-glycoprotein transport to human and mouse.

INTRODUCTION: P-glycoprotein is localized in numerous tissues throughout the body and plays an important role in the disposition of many xenobiotics. The contribution of P-glycoprotein-mediated drug transport is being evaluated in early drug discovery stages, particularly for compounds targeted to the central nervous system, using in vitro tools including cell lines expressing P-glycoprotein. Previous work in our laboratory suggests there are species differences in P-glycoprotein transport activity between humans and animals. The rat Abcb1a form of P-glycoprotein (formerly known as Mdr1a), the predominate isoform in the brain, has not been described in a functional cell system. Here, we describe the development and characterization of LLC-PK1 cells expressing rat Abcb1. METHODS: We cloned rat Abcb1a and generated a stable LLC-PK1 cell line. Expression and function of the cells were evaluated by immunoblot analysis, cytotoxicity analysis, cellular accumulation assays, and transcellular transport of probe substrates. The transport ratios of structurally diverse compounds obtained from parental cells or cells stably transfected with human ABCB1, mouse Abcb1a or rat Abcb1a were compared. RESULTS: Two forms of rat Abcb1a were cloned from Sprague-Dawley cDNA that differ by six amino acids and a base pair deletion. The intact form was stably transfected in LLC-PK1 cells. Immunoblot analysis demonstrated expression of the protein. The cells demonstrated P-glycoprotein-mediated function by directional transport of dexamethasone, ritonavir, and vinblastine in a transwell assay that was inhibited in the presence of cyclosporin A, verapamil, or quinidine. Likewise, the cells showed reduced cellular accumulation of Rh123 by FACS analysis that was reversed in the presence of cyclosporin A. These cells showed >or=350-fold resistance to colchicine, doxorubicin, vinblastine, and taxol and were sensitized in the presence of verapamil or cyclosporin A. Of 179 chemically diverse compounds evaluated, approximately 20% of the compounds evaluated were predicted to be substrates in one species but not in other species. DISCUSSION: Taken together, these data suggest these cells will be useful for evaluation of rat Abcb1a-mediated transport and for evaluation of species-specific P-glycoprotein-mediated transport.

Disubstituted 1-aryl-4-aminopiperidine library synthesis using computational drug design and high-throughput batch and flow technologies.

A platform that incorporates computational library design, parallel solution-phase synthesis, continuous flow hydrogenation, and automated high throughput purification and reformatting technologies was applied to the production of a 120-member library of 1-aryl-4-aminopiperidine analogues for drug discovery screening. The application described herein demonstrates the advantages of computational library design coupled with a flexible, modular approach to library synthesis. The enabling technologies described can be readily adopted by the traditional medicinal chemist without extensive training and lengthy process development times.

From fragment screening to in vivo efficacy: optimization of a series of 2-aminoquinolines as potent inhibitors of beta-site amyloid precursor protein cleaving enzyme 1 (BACE1).

Using fragment-based screening of a focused fragment library, 2-aminoquinoline 1 was identified as an initial hit for BACE1. Further SAR development was supported by X-ray structures of BACE1 cocrystallized with various ligands and molecular modeling studies to expedite the discovery of potent compounds. These strategies enabled us to integrate the C-3 side chain on 2-aminoquinoline 1 extending deep into the P2' binding pocket of BACE1 and enhancing the ligand's potency. We were able to improve the BACE1 potency to subnanomolar range, over 10(6)-fold more potent than the initial hit (900 µM). Further elaboration of the physical properties of the lead compounds to those more consistent with good blood-brain barrier permeability led to inhibitors with greatly improved cellular activity and permeability. Compound 59 showed an IC(50) value of 11 nM on BACE1 and cellular activity of 80 nM. This compound was advanced into rat pharmacokinetic and pharmacodynamic studies and demonstrated significant reduction of Aß levels in cerebrospinal fluid (CSF).