Breast cancer is the most frequently diagnosed cancer affecting females (but also occurs in males) and in females is the leading cause of cancer death worldwide. Tamoxifen is a SERD (selective oestrogen receptor down-regulator) that can be considered as a cytotoxic drug, designed to destroy rapidly growing cancer cells. However, hormone therapy of tamoxifen has serious side effects including increased risk of clots, stroke, cataracts, endometrial and uterine cancers, mood swings, depression and bone loss in premenopausal women. During hormone therapy changes can occur to breast cancer cells at certain times during therapy. These changes include autophagy, programmed cell death (apoptosis) or necrosis which can influence cells to perform differently. This study aims to explore the time dependent changes on the sensitivity of breast cancer cells to tamoxifen under hypoxic conditions, assessing changes in cell number and the autophagic properties of two cell lines. The assays conducted were an SRB assay, Acridine Orange assay, Immunofluorescence of LC3 Antibodies, Cell cycle assay and Annexin V/PI assay. These assays were performed on T47D cells, MCF-7 cells and MDA-MB-231 cells, human breast cancer (HBC) cell lines representing different forms of breast cancer.
From the SRB assays it was found that there is a time dependent increase in effect of Tamoxifen on cell proliferation as 5 ÂµM and 10 ÂµM from 2 hours of treatment onwards for both cell line. This decrease in cell number could be due to either necrosis of apoptosis occurring in response to Tamoxifen exposure. A critical time point of 1-2 hours after Tamoxifen treatment was found in the Acridine Orange assay. This time point indicates that at 1 hour of Tamoxifen treatment both the MCF-7 and MDA-MB-231 cells there is an increase in autophagy while at 2 hours after treatment there is a decrease in autophagy for both cells. Ongoing research is required to consider the autophagy mechanisms in both cell lines.