A new treatment target for deadly brain tumors

2nd August 2012

A study by UT Southwestern Medical Center published online yesterday in Nature reveals new insight into why the most common, deadly kind of brain tumor in adults recurs and identifies a potential target for future therapies.

Glioblastoma multiforme (GBM), seen on the right of the image below, is currently considered incurable. Despite responding to initial therapy, the cancer almost always returns. GBM is a fast-growing, malignant brain tumor that occurred in 15 percent of the estimated 22,000 Americans diagnosed with brain and nervous system tumors in 2010. The median survival rate is about 15 months, according to the National Cancer Institute.

"We identified a subset of brain tumor cells that are slower growing, or remain at rest, and appear to be the source of cancer recurrence after standard therapy in which the drug temozolomide is given to stop the tumor's growth," said Dr. Luis Parada, chairman of developmental biology and director of the Kent Waldrep Center for Basic Research on Nerve Growth and Regeneration. "Current therapy targets fast-growing tumor cells, but not those responsible for new tumors. To the best of our knowledge, this is the first identification of a cancer stem-like cell in a spontaneously forming tumor inside a mammal."

Using a genetically engineered mouse model of GBM, the researchers found that the resting tumor cells behave more like stem cells – the non-cancerous cells the body uses to repair and replenish itself – which exist in a resting state until needed, he explained.

The existence of cancer stem cells in solid tumors remains controversial, Dr. Parada said, with some scientists in the field taking the concept for granted and others rejecting it outright. In addition, the definition of a cancer stem cell is a moving target, hence the use of the term "stem-like cell" in this study, he said.

“We are trying to better understand these cells. The important point is that we now are faced with technical obstacles, not conceptual ones,” said Dr. Parada.

White arrows point to a subset of tumor cells that express green fluorescent protein (GFP) but rarely stain for Ki67, a marker of proliferation. This indicates that the tumor cells that appear green are in a resting state. (Image courtesy of Nature)

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