LNCaP prostate cancer cells contain higher esterase activity than non-tumorigenic RWPE-1 cells. A) LNCaP and RWPE-1 cell cultures were incubated with 800 μM α-naphthyl acetate, R-ANAA, or S-ANAA substrate and Fast Blue RR salt for 20 min. The dark color indicates in situ esterase activity. B) Microscopy images were analyzed with ImageJ to measure the relative staining between cell lines. Percent area threshold was defined as the percent area stained that exceeded background staining. Letters that are not the same are significantly different at P < 0.05.