Induction of apoptosis and inhibition of c-erbB-2 in breast cancer cells by flavopiridol

Flavopiridol is a flavone that inhibits several cyclin-dependent kinases an d exhibits potent growth-inhibitory activity against a number of human tumo r cell lines, both in vitro and when grown as xenografts in mice. It is pre sently being investigated as a novel antineoplastic agent in the primary sc reen conducted by the Developmental Therapeutics Program, National Cancer I nstitute. Because breast cancer is the most common cancer and second leadin g cause of cancer-related deaths in women in the United States, we investig ated whether flavopiridol could be an effective agent against a series of i sogenic breast cancer cell lines having different levels of erbB-2 expressi on and differential invasion and metastatic characteristics. Flavopiridol w as found to inhibit the growth of MDA-MB-435 (parental) and 435.eB (stable transfectants) cells that were established by transfecting c-erbB-2 cDNA in to, MDA-MB-435. Induction of apoptosis was also observed in these cell line s when treated with flavopiridol, as measured by DNA laddering, PARP, and C PP32 cleavages. We also found modest up-regulation of fax and down-regulati on of Bcl-2, but there was a significant down-regulation of c-erbB-2 in fla vopiridol-treated cells. Gelatin zymography showed that flavopiridol inhibi ts the secretion of matrix metalloproteinase (MMP; MMPs 2 and 9) in the bre ast cancer cells and that the inhibition of c-erbB-2 and MMPs may be respon sible for the inhibition of cell invasion observed in flavopiridol-treated cells. Collectively, these molecular effects of flavopiridol, however, were found to be independent of c-erbB-2 overexpression, suggesting that flavop iridol may be effective in all breast cancer, From these results, we conclu de that flavopiridol inhibits the growth of MDA-MB-435 breast cancer cells, induces apoptosis, regulates the expression of genes, and inhibits invasio n and, thus, may inhibit metastasis of breast cancer cells. These findings suggest that flavopiridol may be an effective chemotherapeutic or preventiv e agent against breast cancer.