Abstract 1744: ACP-196: A second generation Btk inhibitor demonstrates biologic activity in a canine model of B-cell non-Hodgkin lymphoma
Authors: Gardner* Heather L. , Harrington* Bonnie K. , Izumi Raquel , Hamdy Ahmed , Kaptein Allard , Lith Bart Van , London Cheryl A. , Byrd John C. , Johnson Amy J. , Kisseberth William C. 
Published: May 2015

Abstract
Recent recognition of B-cell receptor (BCR) signaling as a critical factor in the progression of B-cell malignancies, including non-Hodgkin lymphoma (NHL), has resulted in the development of numerous targeted therapeutics that inhibit this signaling pathway. Ibrutinib, a small molecule inhibitor of Bruton tyrosine kinase (Btk) a key signaling molecule in the BCR pathway, has demonstrated significant clinical activity in a broad range of B-cell cancers. ACP-196 is a second generation Btk inhibitor with increased target selectivity and enhanced in vivo potency compared with ibrutinib and, thus, may represent an improvement over its predecessor. With the following studies, we sought to evaluate ACP-196 in canine models of B-cell NHL with the ultimate goal of providing the preclinical data necessary to move ACP-196 into human clinical trials. Using two immunophenotypically confirmed canine B-cell lymphoma cell lines, CLBL-1 and 17-71, we demonstrate potent in vitro inhibition of activation of Btk and the downstream effectors ERK 1/2 and PLCγ2 following 1 hour of treatment with ACP-196 at concentrations as low as 10nM. In vivo studies were performed in companion dogs as part of an ongoing clinical trial. Twelve dogs with immunophenotypically confirmed, spontaneously occurring B-cell NHL were orally administered ACP-196 at dosages of 2.5mg/kg every 24 hours (6 dogs), 5mg/kg every 24 hours (5 dogs), or 10mg/kg every12 hours (1 dog). Btk occupancy in peripheral blood and lymphoma cells was assessed using a biotin-tagged probe derived from ACP-196. Using this assay we found that at 2.5mg/kg full Btk occupancy was achieved in peripheral B cells 3h after dosing for all dogs, except for a single dog with high peripheral B-cell count. At 24 hours after dosing, 83-99% Btk target occupancy was observed for all dogs. Partial response, as assessed by a modified RECIST scheme, was achieved in 2 dogs in the 2.5mg/kg group and the dog in the 10mg/kg group. Upon relapse, one of the responders in the 2.5mg/kg group was dose escalated to 10mg/kg q12 on day 42 and partial response from relapse was reestablished. Of the remaining 9 dogs, 3 achieved stable disease for &gt; 28 days and 6 discontinued the study after developing progressive disease within 28 days of starting treatment. In total, to date, 3 dogs achieved a partial response, 3 dogs stable disease, and 6 dogs progressive disease. ACP-196 was well tolerated with only mild anorexia noted in some dogs. These data demonstrate that ACP-196 has single agent biologic activity in a spontaneous large animal model of human NHL. Studies in dogs with NHL are ongoing to define regimens prior to initiation of human phase I clinical trials. Additional cohorts are planned combining ACP-196 with a phosphatidylinositide 3-kinase (PI3K) delta-specific inhibitor.
Citation Format: Heather L. Gardner*, Bonnie K. Harrington*, Raquel Izumi, Ahmed Hamdy, Allard Kaptein, Bart Van Lith, Cheryl A. London, John C. Byrd, Amy J. Johnson, William C. Kisseberth. ACP-196: A second generation Btk inhibitor demonstrates biologic activity in a canine model of B-cell non-Hodgkin lymphoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1744. doi:10.1158/1538-7445.AM2014-1744