Pegylated Interferon-α2b (pIFN-α) is an integral part of the drug regimen currently employed against melanoma. Interferon Regulatory Factor-1 (IRF-1) plays an important role in the transcriptional regulation of the IFN response, cell cycle and apoptosis. We have studied pIFN-α induced responses when combined with the chemotherapy agent, vinblastine in tumor and endothelial cell lines and the connection to IRF-1 signaling. Levels of IRF-1/IRF-2 protein expression were found to be decreased in tumor versus normal tissues. pIFN-α induced IRF-1 signaling in human melanoma (M14) and endothelial (EA.hy926) cells and enhanced cell death when combined with vinblastine. Upon combined IFN-α and vinblastine treatment, p21 expression, PARP cleavage and activated Bak levels were increased in M14 cells. An increase in p21 and cyclin D1 expression occurred in EA.hy926 cells after 6 h of treatment with pIFN-α which dissipated by 24 h. This biphasic response, characteristic of cellular senescence, was more pronounced upon combined treatment. Exposure of the EA.hy926 cells to pIFN-α was associated with an enlarged, multinucleated, β-galactosidase-positive senescent phenotype. The overall therapeutic mechanism of IFN-α combined with chemotherapy may be due to both direct tumor cell death via IRF-1 signaling and by premature senescence of endothelial cells and subsequent effects on angiogenesis in the tumor microenvironment.
Keywords: IFN-α2b; IRF-1; apoptosis; senescence; vinblastine.