Despite the exquisite potential of siRNA as a therapeutic, the mechanism(s) responsible for the robust indirect exposure-response relationships have not been fully elucidated. To understand the siRNA properties linked to potent activity, requires the disposition of siRNA to be characterized. A technical challenge in the characterization is the detection and quantitation of siRNA from biological samples. Described herein, a Locked Nucleic Acid (LNA) Hybridization-Ligation ECL ELISA was designed for ultra-sensitive quantification of both sense and antisense strands of siRNA independent of structural modifica-tions. This assay was applied to measure siRNA in serum and tissue homogenate in preclinical species. We observed rapid clearance of siRNA from the systemic circulation which contrasted the prolonged accumulation within the tissue. The assay was also able to distinguish and quantify free siRNA from RNA-induced silencing complex (RISC) and Argonaute 2 (Ago2) associated with therapeutic siRNA. We utilized an orthogonal method, LC-MS, to investigate 3′ exonuclease activity toward the antisense strand metabolism. Taken together, we have demonstrated that the LNA Hybridization-Ligation ECL ELISA is arobust analytical method with direct application to measuring the exposure of siRNA therapeutics seamlessly across biological matrices.

Aims AMG 181 pharmacokinetics/pharmacodynamics (PK/PD), safety, tolerability and effects after single subcutaneous (s.c.) or intravenous (i.v.) administration were evaluated in a randomized, double‐blind, placebo‐controlled study. Methods Healthy male subjects (n= 68) received a single dose of AMG 181 or placebo at 0.7, 2.1, 7, 21, 70 mg s.c. (or i.v.), 210 mg s.c. (or i.v.), 420 mg i.v. or placebo. Four ulcerative colitis (UC) subjects (n= 4, male : female 2:2) received 210 mg AMG 181 or placebo s.c. (3:1). AMG 181 concentration, anti‐AMG 181‐antibody (ADA), α4β7 receptor occupancy (RO), target cell counts, serum C‐reactive protein, fecal biomarkers and Mayo score were measured. Subjects were followed 3–9 months after dose. Results Following s.c. dosing, AMG 181 was absorbed with a median tmax ranging between 2–10 days and a bioavailability between 82% and 99%. Cmax and AUC increased dose‐proportionally and approximately dose‐proportionally, respectively, within the 70–210 mg s.c. and 70–420 mg i.v. ranges. The linear β‐phase t1/2 was 31 (range 20–48) days. Target‐mediated disposition occurred at serum AMG 181 concentrations of less than 1 μg ml−1. The PD effect on α4β7 RO showed an EC50 of 0.01 μg ml−1. Lymphocytes, eosinophils, CD4+ T cells and subset counts were unchanged. AMG 181‐treated UC subjects were in remission with mucosal healing at weeks 6, 12 and/or 28. The placebo‐treated UC subject experienced colitis flare at week 6. No ADA or AMG 181 treatment‐related serious adverse events were observed. Conclusions AMG 181 has PK/PD, safety, and effect profiles suitable for further testing in subjects with inflammatory bowel diseases.

Abstract. Biomarkers are used to study drug effects, exposure-response relationships, and facilitate early decision making during development. Denosumab, a fully human monoclonal antibody against receptor activator of nuclear factor-κB ligand, profoundly inhibits bone resorption. C-terminal telopeptides of type I collagen (CTx), a bone resorption biomarker, provides early indications of denosumab effectiveness and informs protracted clinical outcomes (e.g., bone mineral density). Because of the dynamic relationship between denosumab and CTx, a precise and robust assay was desired. Thus, we adopted a fit-for-purpose approach to modify and validate a commercial CTx diagnostic kit to meet the intended applications of a quantitative pharmacodynamic biomarker for denosumab development. Seven standards were prepared to replace five calibrators provided in the kit. Three quality controls (QC) and two sample controls were used to characterize and monitor assay performance. Robotic workstations were used for standard and QC preparation and assay execution. Method validation experiments were conducted with rigor and procedures similar to those used for drug bioanalysis. The method demonstrated a linear range of 0.0490-2.34 ng/mL with four-parameter logistic regression. Inter-assay total error of validation samples in serum was ≤26.7%. Extensive tests were conducted on selectivity in sera from target populations, specificity, stability, parallelism, and dilutional linearity. Applications to samples from numerous clinical studies confirmed that the CTx method was reliable, robust, and fit for use as an early indicator of denosumab effectiveness. Refinement supported the confidence for use in pharmacokinetic/pharmacodynamic modeling, dose selections, correlation to clinical effects, and formulation bioequivalence work.KEY WORDS: bone resorption marker; commercial immunoassay kit; method validation; pharmacodynamic (PD) biomarker; serum C-terminal telopeptides of type 1 (CTx).

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