Fig. 6.

CM572-induced cytotoxicity in SK-N-SH neuroblastoma. SK-N-SH neuroblastoma cells were exposed to various doses of CM572, and cell viability was examined by MTT assay, as described in Materials and Methods. Cells were either exposed to CM572 continuously for 24 hours (heavy solid line) or exposed acutely for 30, 60, or 120 minutes, unbound compound removed, and cells allowed to incubate for 24 hours in media without CM572 (light, dashed, and dotted lines) as described in Materials and Methods. Controls were treated similarly but without ligand. During the continuous 24-hour incubation, CM572 induced cell death in a dose-dependent manner. CM572 also induced dose-dependent cell death 24 hours after acute treatments followed by washing, with no statistically significant differences from 24-hour treatment effects (P > 0.05 for all acute treatments compared with continuous 24-hour exposure at same dose, t test). With acute CM572 treatment, no cell death was observed at or below 1 µM, resulting in a trend toward a rightward shift of the dose curve with comparable maximal effect compared with the continuous condition. Data shown for 24-hour continuous and 30-minute acute exposures are the average of two experiments ± S.D. Data for 60- and 120-minute acute treatment are the average of three experiments ± S.D. Acute exposures were performed in HBSS, although similar results were observed with media. Each experiment was performed using five wells for each condition.