Abstract 2059: In situ imaging of antibody drug conjugate (ADC) binding and pharmacodynamic biomarkers of response in models of human cancer
Authors: Golas Jonathon , Hooper Andrea T. , Lucas Justin , Jones Heather , Nichols Timothy , Khandke Kiran , Charati Manoj , Conant Roger , Cinque Michael , Lucas Judy , Damelin Marc , Geles Ken , Teresa Caiazzo , Loganzo Frank , Sapra Puja , Gerber Hans-Peter , May Chad 
Published: May 2015

Abstract
Antibody drug conjugates (ADCs) are clinically validated as a modality for targeted therapy of solid and hematological cancer due to advancements in target selection, conjugation chemistry and linker technology. However, much about mechanism of action (MoA) is yet to be fully understood. Our goal was to interrogate ADC pharmacokinetics and pharmacodynamics establishing proof of mechanism (PoM) of drug action with a diverse panel of ADCs. Herein, we describe the development of novel immunohistochemical (IHC) methods for in situ visualization of ADCs binding to target expressing cells and their cognate downstream biomarkers of response in formalin fixed paraffin embedded cells/tissues. We demonstrate specific binding of 4 different ADCs spanning 2 solid tumor targets and an endothelial cell target using IHC with anti-human IgG in human tumor xenograft models expressing the respective targets. ADC binding to target is observed as early as 20 minutes after a single dose of ADC at 3 mg/kg. Utilizing an anti-microtubule inhibitor (MTI) payload-specific antibody we additionally detect ADC binding to tumor cells by monitoring the cytotoxic payload. The cell type where the antibodies and payload localized was identified by double and triple IHC. Pharmacodynamic biomarkers of response for two payload classes (DNA damaging agents and MTIs) were detected with antibodies against phospho-Histone H2AX and phospho-Histone H3, respectively - confirming the expected ADC MoAs. Downstream apoptosis of target cells was detected with cleaved caspase 3 IHC. The kinetics of biomarker response and downstream cellular impact was quantified via image analysis with biomarkers evident as early as 24 hours after a single dose for both tumor cell and vascular targets. Furthermore, we observed a correlation between biomarkers of response and efficacy of the ADCs as measured by statistically significant tumor growth inhibition for the 4 ADCs we studied. These data suggest that IHC interrogations of drug action should be used to further the clinical development of ADCs via demonstration of pharmacodynamic activities at the cellular level, establishing PoM data, and enabling predictive preclinical oncology models in order to reduce clinical attrition of ADCs.
Citation Format: Jonathon Golas, Andrea T. Hooper, Justin Lucas, Heather Jones, Timothy Nichols, Kiran Khandke, Manoj Charati, Roger Conant, Michael Cinque, Judy Lucas, Marc Damelin, Ken Geles, Caiazzo Teresa, Frank Loganzo, Puja Sapra, Hans-Peter Gerber, Chad May. In situ imaging of antibody drug conjugate (ADC) binding and pharmacodynamic biomarkers of response in models of human cancer. [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 2059. doi:10.1158/1538-7445.AM2014-2059