"That observation was reminiscent of a normal stem cell environment," Parada said. "If we go back to adult stem cells, the stem cells are mostly quiescent. That means they rarely divide."
In healthy brain tissue, he said, a few stem cells eventually enter the cell cycle, and give rise to progenitor cells that divide frequently before becoming neurons in the brain. The researchers wanted to show that cancer cells had a similar cycle.
Their next experiment was to apply the chemotherapy drug temozolomide to the tumor-ridden mice, which got rid of all the currently dividing tumor cells. But when the chemotherapy stopped, the tumors resumed cell division.
The cells not eradicated -- that were still giving rise to new cancer cells -- were the specially marked green cells that behave similarly to stem cells in healthy tissues.
In a final experiment, "we were able to give the mice temozolomide to get rid of the highly dividing cells, plus ganciclovir to get rid of the stem cells. And when we did that, the tumors were unable to form," Parada said.
Just what are the implications for human cancer?
"With a solid tumor that's formed by cancer stem cells in a hierarchical fashion, the critical cells to identify, understand and target with chemotherapy are the cancer stem cells," he said.
The research is still in early stages, Parada noted. "Now, knowing that these cells exist and being able to identify them inside of the tumors, we're trying to isolate them, purify them and study them in great detail," he added.
His caveat: Their work with glioblastoma may not apply to different kinds of cancers. "Each cancer has to be studied in this same way to determine if the cancers grow in this fashion or not," Parada said.
A second study in the same Nature issue investigated the growth of squamous skin canc
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