Differential gene expression studies of apoptosis related genes in ZR-75-1 cells in response to doxorubicin using oligonucleotide microarrays

Breast cancer is the most common type of cancer among women in the USA and it is the second leading cause of cancer death in women, after lung cancer. In this study, the cytotoxicity of varying concentrations of DOX on ZR-75-1 cells was studied at different time points using the MTT assay. An EC50 range, was determined for the 72 hr time point, to be 0.3--2.1 microM. The Caspase-3/7 assay was performed in a dose and time dependent manner. The best dose and time point at which optimal levels of caspase-3/7 activity were observed in DOX treated ZR-75-1 cells was 1.5 microM and 48 hr respectively. Total RNA isolated from untreated and DOX treated ZR-75-1 cells was quantified and used for synthesis of aminoallyl labeled cDNA. Aminoallyl labeled cDNA from each sample was labeled with either Cy3 or Cy5 dye for dye swap experiments using Human Discover ChipsRTM to analyze 71 apoptosis related genes; gene expression of 28 of these genes were also analyzed by qRT-PCR with the intent of validation. The death mechanism induced by DOX in ZR-75-1 cells is not by caspase cascade. The possible death mechanism in ZR-75-1 cells in response to DOX could be stress induced cell cycle arrest or apoptosis mediated by p53 or TNF alpha or by necrosis. A mixed type of cell death was observed in ZR-75-1 cells in response to DOX.