Disabling of the erbB Pathway Followed by IFN-γ Modifies Phenotype and Enhances Genotoxic Eradication of Breast Tumors

Reversion of the malignant phenotype of erbB2-transformed cells can be driven by anti-erbB2/neu monoclonal antibodies (mAbs), which disrupt the receptor’s kinase activity. We examined the biologic effects of IFN-γ alone or after anti-erbB2/neu mAb treatment of erbB2-positive cells. IFN-γ had no effect on its own. Treatment of the tumors with anti-erbB2/neu mAbs followed by IFN-γ led to dramatic inhibition of tumor growth in vitro and in vivo with minimal mAb dosing. Sequential therapy enhanced the effects of chemotherapy. Moreover, IFN-γ with mAb treatment of mice with IFNγR knockdown tumors did not demonstrate marked synergistic eradication effects, indicating an unexpected role of IFN-γ on the tumor itself. Additionally, mAb and IFN-γ treatment also induced immune host responses that enhanced tumor eradication. Biochemical analyses identified loss of Snail expression in tumor cells, reflecting diminution of tumor-stem-cell-like properties as a consequence of altered activity of GSK3-β and KLF molecules.