Comparative cytotoxicity and anti-proliferative effects of doxycycline. 2 × 104 HT 29 cells/ml were treated with doxycycline for 24 hours and 3 days in the wells of 6 well plates. The cytotoxicity and cell proliferation studies were performed with Alamar blue assay and Picogreen assay according to the manufacturer's instructions respectively. Data are depicted as means of six experiments ± standard deviation. (* - Denotes statistically significant difference in the activity).