Tamoxifen resistance in breast cancer elucidating mechanisms

Introduction: Estrogen receptor positive breast tumors frequently become resistant to Tamoxifen therapy.

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Currently, we are exploring whether FOXO1 may play a similar role in resistance to Tamoxifen in ER positive breast cancer cells.

We hypothesize that loss of function of FOXO1 may contribute to Tamoxifen resistance and reactivation may restore sensitivity to tamoxifen.

Methods: We have generated two tamoxifen resistant clones and in addition have studied a Tamoxifen resistant clone called MCF-7 TAMR/HER2 (HER2-transfected).

tamoxifen resistant clones were generated by passaging wildtype MCF-7 (WT) cells through sphere cultures in the presence of tamoxifen.

These clones are termed MCF-7 TAMR7 and MCF-7 TAMR26, representing 7 and 26 passages in sphere culture respectively.

Cell line characteristics were assayed by immunohistochemistry (IHC) and RT-Q-PCR.

Furthermore, MTT assays were used to test for E2 response in WT and TAMR cells.

Results: Tamoxifen resistance was acquired by utilizing the sphere assay in the presence of Tamoxifen.

IHC results revealed a significant loss of ER receptor in TAMR7 and TAMR26 clones.

RT-Q-PCR demonstrated 85% loss of ER receptor m RNA in the TAMR7 and TAMR26 compared to WT cells.

There was no difference in ER expression in WT and TAMR/HER2 cells.