a) Human cancer cells were plated at 1 104 cells/well in 96-well plates,
incubated overnight and treated with compounds for 48 h. Cytotoxic assays
were performed using a XTT kit (Roche Applied Science Mannheim, Penzberg,
Upper Bavaria, Germany) in accordance with the manufacturer’s instructions.
The XTT labeling mixture was prepared by mixing 50 volumes of 1 mg/mL
sodium 30-[1-(phenylaminocarbonyl)-3,4-tetrazolium]-bis(4-methoxy-6-
nitro) benzenesulfonic acid hydrate with 1 volume of 0.383 mg/ml of Nmethyldibenzopyrazine
methyl sulfate. This XTT labeling mixture was
subsequently added to the cultures and incubated for 2 h at 37 C.
Absorbance was measured at 490 nm, with 650 nm as a reference
wavelength.