A-E Microvascular leak and tumor cell extravasation were modeled in vitro using modified Boyden chamber experiments where lung HMVECs (A-C) and dermal HMVECs (D-E) were grown to 100% confluence over 8-μm-pore insert membranes. ECs were first treated with Vasculotide (VT), PBS (vehicle/negative control), Ang1 (positive control), PEG-Cys (polyethylene glycol backbone), T7c (non-PEGylated CHHHRHSF peptides), or VT in the presence of 100-fold molar excess of T7c. The concentrations used, 10-20 ng/mL VT and 200-400 ng/mL Ang1, are estimated molar equivalents (0.71-1.43 nM). Thirty minutes later, ECs were stimulated with thrombin, 0.1% BSA (vehicle/negative control), or EDTA (positive control). Another 30mins later, the amount of FITC-dextran diffusion into the lower chambers (A, D) provides a measure of endothelial permeability. CMTPX-labeled tumor cells (TCs) were then dispensed into inserts, and the amount of TC fluorescence emitting from the underside of insert membranes after 20 h (B-C) or 28 h (E) reflects the efficiency of trans-endothelial TC migration. Representative fluorescent images (10×) of membrane undersides are shown in (C), where DAPI-stained nuclei of ECs/TCs are shown in blue, 'extravasated' CMTPX-labeled TCs are shown in red, and the # of CMTPX+ pixels are shown numerically in red. Means ± SEM are shown (A,B,D,E). Three experiments (twice with HMVEC-LBl and once with HMVEC-DBl) were run with n = 3-5 inserts (independent biological replicates) per group and analyzed by two-sampled unpaired t-tests. 