Abstract 4082: Time- and exposure-dependent pharmacodynamic changes induced by the BTK inhibitor GS-4059 in healthy subjects
Authors: Jürgensmeier Juliane M. , Truong Hoa , Zheng Lianqing , Xiao Yuanyuan , Nelson Cara , Mitra Siddhartha , Billin Andrew N. , Yu Helen 
Published: July 2017

Abstract
Bruton’s Tyrosine Kinase (BTK) plays an important role in B-cell signaling, cell proliferation and survival and is an established drug target in B-cell malignancies. GS-4059 (ONO-4059) is an irreversible, small molecule inhibitor of BTK, which is in development for hematological malignancies and rheumatoid arthritis. A Phase 1 study to evaluate the effect of organic anion transporting polypeptide (OATP) 1B1 and 1B3 inhibitors and inducers of cytochrome P450 3A (CYP3A) on GS-4059 Pharmacokinetics (PK) was performed in healthy subjects (N=15). Subjects were administered a single dose of 100 mg GS-4059 alone or in combination with a single or multiple doses of rifampin (600mg) and blood samples were collected up to 48 hours post dose to evaluate PK and Pharmacodynamic (PD) markers in peripheral blood mononuclear cells (PBMCs). PD biomarkers were exploratory endpoints and are reported here. PD was evaluated using the BTK occupancy assay and the Basophil Activation Test (BAT). A novel duplex homogeneous BTK occupancy assay was used to quantitatively measure GS-4059 binding to human BTK to assess target coverage. The assay is based on Time-Resolved Fluorescence Resonance Energy Transfer (TR-FRET) and simultaneously measures the level of free BTK as well as total BTK protein in PBMCs collected from subjects in the study. Free BTK levels in PBMCs decreased rapidly on treatment with GS-4059 with no detectable free BTK 3-24 hours post dose and no notable changes in total BTK. All subjects had free BTK levels below the limit of detection (LOD 6.8 ng/mL) 3-24 hours after dosing. Free BTK levels started to increase after 48 hours. Free BTK levels on treatment with multiple doses of rifampin plus GS-4059 followed a similar trend with no free BTK detectable 3-6 hours post dose but resulted in shorter duration of inhibition and more rapid recovery of free BTK levels. GS-4059 plasma exposure (Cmax and AUC) was ~70% lower after multiple doses of rifampin, due to a drug-drug interaction. As a second PD marker, inhibition of CD63+ basophil activation in the BAT was measured. In this functional assay the median inhibition of CD63+ basophil activation was between 90% and 100% at the time of maximum inhibition (3 hours post dose). At the peak of inhibition 13 of the 14 subjects had inhibition of basophil activation higher than 97%. In line with the BTK occupancy data, inhibition of CD63+ basophil activation was significantly lower with reduced GS-4059 plasma exposure. BTK occupancy as a direct measure of target binding and the functional assay measuring the inhibition of basophil activation showed a similar time course with maximum effect in both assays achieved at 3-6 hours post dose. These data demonstrate that a single 100 mg dose of GS-4059 results in full BTK occupancy in healthy subject PBMCs as well as functional changes measured in basophil activation as a surrogate for BTK signaling pathway inhibition.
Citation Format: Juliane M. Jürgensmeier, Hoa Truong, Lianqing Zheng, Yuanyuan Xiao, Cara Nelson, Siddhartha Mitra, Andrew N. Billin, Helen Yu. Time- and exposure-dependent pharmacodynamic changes induced by the BTK inhibitor GS-4059 in healthy subjects [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4082. doi:10.1158/1538-7445.AM2017-4082