Manipulation of iron transporter genes results in the suppression of human and mouse mammary adenocarcinomas.

Since malignant cells often have a high demand for iron, we hypothesize that breast cancer cells may alter the expression of iron transporter genes including iron importers [transferrin receptor (TFRC) and solute carrier family 11 (proton-coupled divalent metal ion transporters), member 2 (SLC11A2)] and the iron exporter SLC40A1 (ferroportin), and additionally that the growth of breast cancer can be inhibited by manipulating iron transporter gene expression. To test our hypothesis, reverse transcription polymerase chain reaction (RT-PCR) was used to determine mRNA expression of iron transporter genes in normal human mammary epithelial MCF-12A cells and human breast cancer MCF-7 cells. Antisense oligonucleotides were employed to suppress the expression of TFRC gene in the 4T1 mammary adenocarcinoma in both cell culture and a mouse tumor model. We found the following: i) the MCF-7 cells have higher expression of TFRC and SLC11A2 compared with MCF-12A epithelia; ii) SLC40A1 was only expressed in MCF-12A epithelia but not in MCF-7 cells; iii) iron increased mRNA levels of the SLC11A2 gene in both MCF-12A and MCF-7 cells; iv) TFRC antisense oligonucleotides reduced TFRC mRNA levels and intracellular total iron, and inhibited the proliferation of the 4T1 cells in cell culture; v) TFRC antisense oligonucleotide inhibited tumor growth and lung metastases in the 4T1 mammary adenocarcinoma mouse model. In conclusion, breast cancer cells up-regulate the expression of iron importer genes and down-regulate the expression of iron exporter SLC40A1 to satisfy their increased demand for iron. Suppression of transferrin receptor by antisense results in inhibition of tumor growth and lung metastasis in the 4T1 mammary adenocarcinoma mouse model.