Cyclin D1 Antisense Oligonucleotide Inhibits Cell Growth Stimulated by Epidermal Growth Factor and Induces Apoptosis of Gastric Cancer Cells

The cyclin Dl protein is one of the cell cycle regulators required for cell cycle progression through Gl phase to S phase. The cyclin Dl‐cyclin‐dependent kinase (CDK) system is thought to control the cell cycle through mediating extracellular signals from mitogens, such as epidermal growth factor (EGF). In this study, we attempted to examine the therapeutic effect of cyclin Dl antisense oligonucleotides (AS/D1) on cell proliferation and apoptosis of the gastric cancer cell line MKN‐74, in the presence and absence of EGF‐stimulation. Evaluation of cell survival and DNA synthesis revealed that enhanced cell growth following EGF‐stimulation was completely inhibited by a 24 h pre‐incubation with 100 nM AS/D1. This inhibition was down to 19.3% compared with maximal DNA synthesis after stimulation with 3 nM EGF alone. Western blotting demonstrated that while EGF‐stimulation led to cyclin Dl over‐expression, AS/D1 inhibited cyclin Dl protein expression. We also demonstrated the induction of apoptosis in MKN‐74 cells by AS/D1. In conclusion, EGF‐stimulated MKN‐74 cell proliferation was inhibited by AS/D1, which could overcome EGF‐induced cyclin Dl over‐expression. AS/D1 also affected cell survival by inducing apoptosis through cell cycle arrest following cyclin Dl depletion. Thus, AS/D1 may be a candidate for use as a novel cancer therapy specifically targeted against the over‐expression of cyclin Dl enhanced by EGF in malignant cells