Adenovirus expressing mutant p27^kip1 enhanced apoptosis and inhibited the growth of xenografted human breast cancer

Purpose. To evaluate the anti-tumor effects of a novel adenovirus expressing mutant p27^kip1 (Adp27-mt), which consists of a mutation of Thr-187/Pro-188 to Met-187/Ile-188. Methods. Using the human breast cancer cell lines, MDA-MB-231, ZR-75-1, and MCF-7, we tested Adp27-mt for cell cycle assay, growth inhibition assay, and TdT-mediated dUTP-biotin nick end labeling in a human breast cancer-grafted severe combined immunodeficiency (SCID) mouse model. Results. The mutant p27^kip1 induced stronger apoptosis in the breast cancer cell lines than adenovirus expressing wild-type p27^kip1 (Adp27-wt). Adp27-mt inhibits cell growth significantly; being about 5- and 3.5-fold stronger for IC50 than Adp27-wt in the breast cancer cell lines, MDA-MD-231 and ZR-75-1, respectively. In the human breast cancer-grafted SCID mouse model, Adp27-mt induced tumor regression and antitumor effects significantly better than Adp27-wt. Furthermore, Adp27-mt mainly caused G2/M arrest in the cell cycle progression, whereas Adp27-wt mediated a G1/S arrest 48 h after infection. Conclusion. The mutant p27^kip1 protein induced apoptosis, and inhibited cell growth more efficiently with stronger anti-tumor effects than wild-type p27^kip1. Thus, the recombinant adenovirus expressing mutant p27^kip1 could be useful in gene therapy against breast cancer.