Cell viability assay. The status of cancer cell line viability was determined by of MTT (3-[4,5-dimethylthiazol-2-yl]-2,5diphenyltetrazolium bromide; thiazolyl blue) assay (Sigma, New York, USA). Exponentially growing cell lines were adjusted to 1.0×104 cells/cm2 with DMEM, plated in 96-well plates at 200 μl/well and then incubated for 24 h according to routine procedure. After treatment with lycopene and beta-carotene (0.5-10 μM) and incubation for 48 h and 96 h (six wells for each sample), 20 μl of MTT (5 g/l) were added to each well. After 4 h of incubation, the medium was then removed and 100 μl/well sodium dodecyl sulfate (SDS) was added to dissolve the reduced formazan product. Finally, the plate was read in an enzyme-linked immunosorbent microplate reader (Bio-Rad 2550 at 490 nm. The cellular proliferation inhibition rate (CPIR) was calculated using the following formula: CPIR=(1–average absorbance value of experimental group/average absorbance value of control group)×100%.