Endocrine Abstracts

Expression of the Sodium Iodide symporter (NIS) in the breast was thought to be restricted to lactation but recently have been shown in breast cancer and benign breast disease. CpG island methylation of the promoter region of NIS is known to decrease iodide uptake in the thyroid. No such information has been documented in the breast. The aim of this study was to investigate the effect of demethylating agents on iodide uptake in breast cancer cell lines MCF-7 (oestrogen (E) and progesterone (P) receptor positive) and MDA-MB-231 (E and P receptor negative). Cells were incubated in the presence of 125I and the level of uptake measured. The effect of demethylating agents phenyl acetate (5mM & 10mM), 5 azacytidine (0.5 & 1 mmol) and DMSO (25mmol) on iodide uptake was determined. Methylation specific PCR was also used to identify the methylation status of the NIS gene in the breast cancer cell lines. Extracted DNA was subjected to a bisulphite modification step where cytosines are converted to uracil but those that are methylated are resistant to the change. The modified DNA was then amplified using RT-PCR with both methylated and unmethylated primer pairs. Treatment with demethylating agents caused a significant increase in iodide uptake in the oestrogen and progesterone receptor positive MCF-7 cells : 5mmol PhAc (+) 66%, 5 azacytidine ; 0.5mmol (+) 91%, 1mmol (+) 105% and 25mmol DMSO (+) 152%. The E and P receptor negative MDA-MB-231 cells on the other hand did not show an increase in iodide uptake in the presence of demethylating agents. Increased 125 I uptake concurred with decreased expression of methylated NIS product. The demonstration that breast cancer cells can be manipulated chemically to increase iodide uptake increases the potential for the use of radioactive iodide as a systemic adjuvant therapy.