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

Abstract

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 straindependent 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 transportermediated 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.

Pharmacokinetics, Biotransformation, and Excretion of [14C]Etelcalcetide (AMG 416) Following a Single Microtracer Intravenous Dose in Patients with Chronic Kidney Disease on Hemodialysis

“…These findings were consistent with the role of renal clearance determined in rats [5]. Based on the nonclinical findings that biotransformation of etelcalcetide only occurs by reversible disulfide exchange [9], and because renal clearance is the primary mechanism of elimination in animals and humans with intact renal function [5, 7], dialytic clearance was expected to be the main elimination pathway in patients with limited or no kidney function undergoing hemodialysis. In previous clinical studies [8, 10, 11], the duration of pharmacokinetic data collections was limited and the effect of hemodialysis on the pharmacokinetics of etelcalcetide was unknown.…”

“…1; hydrochloride salt; specific activity 70.9 nCi/mg of etelcalcetide freebase; high-performance liquid chromatography [LC] purity 99.5 %) was synthesized at Amgen Inc. (Thousand Oaks, CA, USA). The C-14 label was placed on the carbonyl carbon of the N -acetyl moiety in the d -amino acid backbone and the stability of the radiolabel at this position was demonstrated in nonclinical studies [5]. The drug substance was formulated as a single 10 mg dose of etelcalcetide with 26.3 kBq (710 nCi; approximately 10 µg) of [ 14 C]etelcalcetide in 2 mL liquid solution for bolus intravenous administration at the end of hemodialysis.…”

“…Structure assignments of etelcalcetide and its biotransformation products were based on comparisons to known structures from nonclinical studies [5], authentic standards, calculations, and interpretations from high-resolution MS and LC–MS/MS data.…”

“…Pharmacokinetic profiles of etelcalcetide and [ 14 C]etelcalcetide-derived radioactivity (referred to as ‘total C-14’) in rat plasma showed a multiphase decline with a long terminal half-life ( t ½ ) [5]. In rats with intact kidneys, total C-14 following a single intravenous dose was predominantly excreted in urine (77–84 % of administered dose; approximately 90 % of recovered dose).…”

“…Etelcalcetide biotransformation occurred in whole blood primarily by disulfide exchange with endogenous thiol-containing molecules; the d -amino acid backbone was unaltered. The predominant biotransformation product present in plasma was a covalently bound serum albumin peptide conjugate (SAPC) [5]. …”