Technical considerations in the development of circulating peptides as pharmacodynamic biomarkers for angiogenesis inhibitors.

To determine the biological reproducibility and estimate relevant covariates for candidate circulating biomarkers of angiogenesis, we conducted 3 sub-studies with ≤15 subjects each. In study 1, 6 healthy subjects provided 13 blood samples across 14-24 days. In study 2, 15 advanced solid tumor patients provided single blood samples before, and approximately 8 and 40 days after sorafenib treatment. In study 3, 4 healthy subjects provided blood samples on 3 occasions over 14 days, processed simultaneously in 2 different laboratories at a single institution. Vascular endothelial growth factor (VEGFA), soluble VEGF receptor-2 (sVEGFR2), and angiopoietin-2 (Ang2) concentrations in plasma and serum were determined by standard immunoassays. Ang2 and sVEGFR2 demonstrated low variance within and high variance across individuals reflected by the high intraclass correlation coefficient (for Ang2: 0.86 for plasma, 0.89 for serum; for sVEGFR2: 0.91 for plasma, 0.87 for serum). Repeated measures linear modeling from 15 patients demonstrated increased Ang2 (P ≤ 0.05) and decreased sVEGFR2 (P ≤ 0.05) after exposure to sorafenib. VEGFA had high intraindividual variance, and study 3 demonstrated the laboratory to have significant effects on plasma measurements (P ≤ 0.05). The biological reproducibility of sVEGFR2 and Ang2 support further use of these markers in studies of vasculature-targeted therapeutics.