Silencing ROR1 Slows Breast Cancer Growth

A protein active in developing embryos but silenced in normal adult cells was found to be highly expressed in certain types of human breast cancer and may be a potential target for breast cancer therapy.

Tumor cells of patients with breast cancer frequently express a protein called the receptor-tyrosine-kinase-like orphan receptor 1, or ROR1. This protein is expressed at high levels during embryogenesis, during which time it plays an important role in regulating embryonic muscle and skeletal development. At some stage during fetal development, the expression of this protein is turned off, and normal cells and tissues in adults do not typically express ROR1.

Investigators at the University of California, San Diego (USA) examined the effect of blocking ROR1 expression in breast tumor cells. They reported in the March 5, 2012, online edition of the journal PLoS One that if the protein was silenced in human breast tumor cells, the cancer cells had slower rates of growth in both culture and a mouse xenograft model.

“There was a qualitative difference,” said senior author Dr. Thomas J. Kipps, professor of medicine at the University of California, San Diego. “When ROR1 was knocked down, it took away some of the growth advantage enjoyed by cancer cells. Their capacity to survive also was impaired. This could affect the capacity of the cancer cells to survive treatment with other anticancer agents or generate tumors altogether. That suggests ROR1 could be a good target for treating the most aggressive kinds of breast cancer, particularly the ones that lack expression of hormone receptors or the marker HER2/neu, which already can be targeted by monoclonal antibodies.”

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