Data from Quantitative <i>In Vivo</i> Immunohistochemistry of Epidermal Growth Factor Receptor Using a Receptor Concentration Imaging Approach

Abstract

<div>Abstract<p>As receptor-targeted therapeutics become increasingly used in clinical oncology, the ability to quantify protein expression and pharmacokinetics <i>in vivo</i> is imperative to ensure successful individualized treatment plans. Current standards for receptor analysis are performed on extracted tissues. These measurements are static and often physiologically irrelevant; therefore, only a partial picture of available receptors for drug targeting <i>in vivo</i> is provided. Until recently, <i>in vivo</i> measurements were limited by the inability to separate delivery, binding, and retention effects, but this can be circumvented by a dual-tracer approach for referencing the detected signal. We hypothesized that <i>in vivo</i> receptor concentration imaging (RCI) would be superior to <i>ex vivo</i> immunohistochemistry (IHC). Using multiple xenograft tumor models with varying EGFR expression, we determined the EGFR concentration in each model using a novel targeted agent (anti-EGFR affibody-IRDye800CW conjugate) along with a simultaneously delivered reference agent (control affibody-IRDye680RD conjugate). The RCI-calculated <i>in vivo</i> receptor concentration was strongly correlated with <i>ex vivo</i> pathologist-scored IHC and computer-quantified <i>ex vivo</i> immunofluorescence. In contrast, no correlation was observed with <i>ex vivo</i> Western blot analysis or <i>in vitro</i> flow-cytometry assays. Overall, our results argue that <i>in vivo</i> RCI provides a robust measure of receptor expression equivalent to <i>ex vivo</i> immunostaining, with implications for use in noninvasive monitoring of therapy or therapeutic guidance during surgery. <i>Cancer Res; 74(24); 7465–74. ©2014 AACR</i>.</p></div>