Abstract B205: Evaluation of circulating CD34+ cells following treatment with anti-EGFL7 in preclinical models of efficacy

Abstract

Abstract A significant existing challenge for anti-angiogenic therapy is that there are no validated biomarkers to either monitor dosing, response to therapy or escape from therapy. This limitation is a more significant challenge when the therapy in question targets a novel pathway with a unique MOA. Some generalized biomarkers have been identified to follow administration of anti-angiogenic therapy, and included in this class are circulating endothelial cells or CECs. CECs are a well-established marker of on-going and active angiogenesis1. In this report we describe the utility of measuring CECs in response to targeting a novel angiogenic protein, EGFL7. EGFL7 is an extracellular matrix protein that is highly expressed in endothelial cells of angiogenic vessels, including embryonic, tumor and injured vasculature. Inhibition of EGFL7 activity by anti-EGFL7 results in a reduction of tumor microvascular density and tumor growth in genetically engineered models of cancer such as RIP-T Ags. In order to identify a circulating biomarker for this response, we first explored the effect of anti-EGFL7 treatment on circulating CD34+ cells in preclinical tumor models, particularly in RIP-T Ag and MDA - MB-231. Analysis of circulating CD34+ cells showed a statistically significant decrease in circulating CD31−/CD34+/CD45dim cells in the blood of tumorbearing mice treated with anti-EGFL7. In order to characterize their molecular profiles, we isolated the two subpopulations of CD34+ cells - CD31−/CD34+/CD45dim and CD31+/CD34dim/CD45dim cells - from healthy adult human peripheral blood by flow cytometry. Subsequent microarray analysis of the two populations indicated that the gene expression profile of CD31+/CD34dim/CD45dim was indicative of terminally differentiated circulating endothelial cells (CEC), whereas the profile of CD31−/CD34+/CD45dim was suggestive of circulating progenitor cells (CPC.) Further evaluation by RT-PCR confirmed expression of EGFL7 in both CECs and CPCs. Additionally, we compared the prevalence of CD31+/CD34dim/CD45dim cells in whole blood from healthy adult and treatment naive NSCLC whole blood and confirmed that CD34+ cells could be used to follow administration of anti-EGFL7 in humans. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B205.