Gene sets with 2 fold or more Veliparib FDA difference in mRNA level and p value cut off are presented in Table 1. Statistical analysis The effect of doxorubicin or NS398 on breast cancer cell proliferation was analyzed using one way ANOVA followed by Turkeys multiple test. The data of in vitro cancer cell invasion and tumor incidence in the mice were analyzed using Students t test. Results Resistance of MCF 7 DOX cells to doxorubicin Doxorubicin is one of the most commonly used drugs in the treatment of cancer, but its inhibitory effect on cell proliferation varies in several cancer cell lines. Therefore, we investigated whether doxorubicin has the same anti proliferative effect in MDA MB 231, MCF 7, MCF 7 DOX, and T 47D cell lines. The cells were treated with the indicated concentrations of doxorubicin for 72 h and cell proliferation was measured using the MTT assay.

Doxorubicin inhibited cell proliferation in a concentra tion dependent manner in MCF 7 and T47D cells, and to a lesser extent in MDA MB 231 cells. By contrast, doxorubicin mediated inhibition was significantly reduced in MCF 7 DOX cells. We next mea sured the growth of MCF 7 and MCF 7 DOX cells at lower doxorubicin concentrations and MCF 7 DOX cells were consistently resistant to doxorubicin. We then tested whether the doxorubicin mediated growth inhibition was mediated by apoptosis. After MCF 7 and MCF 7 DOX cells were treated with 1 uM doxorubicin for 48 h, terminal deoxynucleotidyl trans ferase mediated dUTP nick end labeling based fluores cence activated cell sorting analysis showed that doxorubicin did not induce apoptosis in MCF 7 DOX cells.

however, doxorubicin did induce apoptosis in MCF 7 cells. We further confirmed the resistance of MCF 7 DOX cells to doxorubicin by Wes tern blot analysis. Induction of PARP cleavage in MCF 7 cells confirmed that doxorubicin induced apoptosis in these cells. However, PARP was not cleaved in MCF 7 DOX cells treated with doxorubi cin. Acquisition of invasive and metastatic properties in MCF 7 DOX cells Intrinsic or acquired drug resistance results in disease recurrence and metastasis. We analyzed changes in gene expression in doxorubicin resistant MCF 7 DOX cells using DNA array analysis. Differentially expressed genes related with invasion are listed in Table 1. We next examined whether MCF 7 DOX cells acquired metastatic properties.

First, we measured the enzymatic activities of MMP 9, MMP 2, and uPA in MCF 7 and MCF 7 DOX cells by gelatin and fibrino gen plasminogen zymography. The enzymatic activities of MMP 2, MMP 9, and uPA were markedly higher in MCF 7 DOX cells than in non invasive MCF 7 cells. Increased levels of MMP 9 and MMP 2 expression have been correlated with an invasive pheno type of cancer Batimastat cells. Thus, we assessed the invasive ness of MCF 7 and MCF 7 DOX cells using in vitro invasion assays. As expected, the MCF 7 DOX cells were significantly more invasive than MCF 7 cells.