Objective:To investigate the regulatory effect of cimetidine on proliferation and apoptosis of colon cancer cells LoVo in vitro.Methods:Colon cancer cell line LoVo originated from human colon carcinoma was cultured in vitro.Cell proliferation was measured by MTT colorimetric assay.Cell cycle and apoptotic percentage were detected by flow cytometry (FCM)

morphological changes of apoptotic cell were observed by light and electron microscopy

and apoptotic cells were quantitatively determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL).In addition

expression of intracellular bcl-2 protein was analysed by flow cytometric indirect immunofluorescent technique.Results:Cimetidine (1×10 -2 mol/L～3×10 -2 mol/L) inhibited LoVo cells growth significantly in a dose-dependent manner.After 48 hours of exposure to cimetidine(1×10 -2 mol/L)

the enhanced degree of apoptotic percentage was 32.7%.There were many morphologic features of apoptosis

including cell shrinkage

nuclear condensation

DNA fragmentation and formation of apoptotic bodies;apoptotic cells were also statistically significant than those of control group( P <0.05).The analysis on expression of intracellular bcl-2 protein showed cimetidine could down-regulate bcl-2 to 36.74% compared with 67.41% in the control.Conclusion:It is suggested that cimetidine can inhibit the proliferation of LoVo cell.Its anticancer effect may be related to induction of apoptosis

which appeared as a result of down-regulation of the anti-apoptotic protein bcl-2.Advanced research need to be done.