Fig 1. Dose-response effect of nicotine, choline, and nicotine metabolites on breast cancer cell proliferation.

Approximately 10⁴ MCF-7 cells were seeded into microwell plates and grown for 3 days in the presence of vehicle (control) or increasing concentrations of nicotine (A), choline (B), cotinine (C), and nornicotine (D). Cells were harvested and growth was determined by an MTT assay. Bars represent means ± SEM of at least 3 independent determinations. Asterisk denotes significant difference from control with p < 0.05.