AMG 900 inhibits p-Histone H3 in COLO 205 tumor cells using fine-needle aspirate (FNA) biopsies. (A) LSC based in vitro cell cycle assessment of COLO 205 tumor cells treated with DMSO or 100 ng/mL nocodazole. Cytospin deposited cells were immunostained with an anti-p-Histone H3 antibody and counterstained with DAPI. Plots represent the cell cycle profile indicating G2M (arrow), and p-Histone H3 (red) subpopulations. Relocation gallery of representative scanned images of p-Histone H3 positive cells in mitosis. (B and C) Mice bearing established COLO 205 tumors were orally administered a single dose of vehicle alone or AMG 900 at 15 mg/kg. Tumor FNA punch biopsies (n = 3 per tumor) were collected three hours after treatment (n = 6 per treatment group) and processed for p-Histone H3 and DNA content analysis by LSC. (B) Representative tumor FNA cell cycle profiles of vehicle (upper panel) and AMG 900 (lower panel) treatment groups. AMG 900 treatment completely abolished the p-Histone H3 positive cell population in G2M detectable in the vehicle-treated control (red). (C) Scatter plot represents the individual and mean percentage of p-Histone H3 positive G2M cells for each treatment group. Statistically significant inhibition of p-Histone H3 compared with vehicle-treated control (*P <0.0001). COLO 205 tumor cells were treated with 100 ng/mL nocodazole (Nocod +) or DMSO (Nocod -) as p-Histone H3 staining controls. (D) Column graph represents vehicle-treated control group inter-(6 tumors) and intra-tumor FNA (3 per tumor) variation in the percentage of p-Histone H3 positive G2M cells (mean + SE).