d-HMVEC and HBMEC were plated under proliferative conditions or non-proliferative conditions. a) Representative composite color images of d-HMVEC cells are shown; Draq (blue; nuclei), and Ki67 (green). Under proliferative conditions, the number of nuclei and Ki67 positive staining are similar; whereas under non-proliferative conditions, the number of nuclei with positive Ki67 staining is much lower. b) Total nuclei count and Ki67 expressing nuclei fraction of untreated cells for both cell lines under proliferative and non-proliferative conditions on day 1 and day 7 after plating (3 independent experiments; 3-21 replicates per experiment). Cells were exposed for 144hrs to increasing drug concentrations (1-100,000 picoM). Total nuclei count as well as nuclei expressing Ki67 expressing counts were normalized to counts obtained from control untreated cells. Representative data for d-HMVEC and HBMEC exposed to SN-38 is shown (3 independent experiments; 3 replicates per experiment +/- SEM). Statistical significance is indicated (*p-value < 0.0001) between total nuclei count of proliferative and non-proliferative cells.