Abstract
Background Dominant negative regulation of critical cell cycle molecules could perturb survival of cancer cells and help develop novel therapies. Methods To perturb the activity of c-Myc, which regulates G0/G1 transitions, we overexpressed Mad1 protein with an adenoviral vector, AdMad. Studies were conducted with established cell lines, including HepG2, HuH-7 and PLC/PRF/5 liver cancer cells, RAT-1A embryonic fibroblasts and U373MG astrocytoma cells. Results After AdMad-treatment, transduced cells exhibited decreased proliferation rates in culture conditions. RAT-1A embryonic fibroblasts and U373MG astrocytoma cells showed accumulations in G0/G1, whereas HepG2 and HuH-7 cells accumulated in G0/G1, and additionally in G2/M, albeit to a lesser extent. An in vitro assay using hepatocyte growth factor to stimulate proliferation in HuH-7 cells showed blunting of growth factor responsiveness, along with inhibition of cell cycle progression in AdMad-treated cells. No cytotoxicity was observed in AdMad-treated cells in culture, although cells lost clonogenic capacity in soft agar. In vivo assays using HepG2 cell tumors in immunodeficient mice showed that overexpression of AdMad prevented tumorigenesis. Conclusions These studies indicate roles of Mad in G2/M, as well as the potential of manipulating cell cycle controls for treating liver cancer. Copyright © 2000 John Wiley & Sons, Ltd.