Different Expression of Extracellular Signal-Regulated Kinases (ERK) 1/2 and Phospho-Erk Proteins in MBA-MB-231 and MCF-7 Cells after Chemotherapy with Doxorubicin or Docetaxel

OBJECTIVE(S): Curative treatment of breast cancer patients using chemotherapy often fails as a result of intrinsic or acquired resistance of the tumor to the drug. ERK is one of the main components of the Ras/Raf/MEK/ERK cascade, which mediates signal from cell surface receptors to transcription factors to regulate different gene expression. In this study, cytotoxicity and the expression of Erk1/2 and phospho-ERK was compared in MDA-MB-231 (ER-) and MCF-7 (ER+) cell lines after treatment with doxorubicin (DOX) or docetaxel (DOCT). MATERIALS AND METHODS: Cell cytotoxicity of DOX or DOCT was calculated using MTT assay. Immonofluorescent technique was used to show MDR-1 protein in MDA-MB-231 and MCF-7 cells after treatment with DOX or DOCT. The expression of ERK1/2 and phpspho-ERK was assayed with immunoblotting. RESULTS: Comparing IC(50) values showed that MDA-MB-231 cells are more sensitive than MCF-7 cells to DOX or DOCT. Immonofluorescent results confirmed the expression of MDR-1 in these two cell lines after DOX or DOCT treatment. In MDA-MB-231 cells the expression of ERK1/2 and phospho-ERK was decreased after DOX treatment in a dose-dependent manner. In contrast in MCF-7 cells the expression of ERK1/2 and phospho-ERK was increased after DOX treatment. DOCT treatment demonstrated the same result with less significant differences than DOX. CONCLUSION: The heterogeneity seen in cell lines actually reflects the heterogeneity of breast cancers. That is why, patients categorized in one group respond differently to a single treatment. These results emphasize the importance of a more accurate classification and a more specific treatment of breast cancer subtypes.