A multi-institutional team of Boston-area researchers has discovered a chemical that works in mice to kill the rare but aggressive cells within breast cancers that have the ability to seed new tumors.

These cells, known as cancer stem cells, are thought to enable cancers to spread - and to reemerge after seemingly successful treatment.

"Evidence is accumulating rapidly that cancer stem cells are responsible for the aggressive powers of many tumors," says Robert Weinberg, a Member of Whitehead Institute for Biomedical Research and one of the authors of the study.

"The ability to generate such cells in the laboratory, together with the powerful techniques available at the Broad Institute, made it possible to identify this chemical. There surely will be dozens of others with similar properties found over the next several years."

"Many therapies kill the bulk of a tumor only to see it regrow," says Eric Lander, Director of the Broad Institute of MIT and Harvard, and an author of the Cell paper. "This raises the prospect of new kinds of anti-cancer therapies."

An emerging idea in cancer biology is that tumors (breast, prostate, colon, lung, etc.) harbor a group of cells with the unique ability to regenerate cancers. In addition to promoting tumor growth, these so-called cancer stem cells are largely resistant to current cancer therapies. If it were possible to identify chemicals that selectively kill cancer stem cells, such chemicals might become critical candidates for future drug development.

However, researchers have struggled to study cancer stem cells directly in the laboratory. The cells' relative scarcity compared to other tumor cells, combined with a tendency to lose their stem cell-like properties when grown outside of the body, have severely limited the amount of material available for analysis.

To overcome these hurdles, Broad and Whitehead Institute researchers drew upon recent findings from Weinberg and his colleagues that suggested a way to generate in the laboratory large numbers of cancer cells with stem cell-like qualities. The technique works by coaxing adult cells to undergo a critical change (known as an "epithelial-to-mesenchymal transition") that alters their shape and motility. At the same time, the cells also adopt similar properties as stem cells.

"In a comparison of a control to the chemical identified by the Weinberg/Lander team, called salinomycin, the tumor cells (stained dark purple in the slide above) were unaffected by the control, but salinomycin killed many tumor cells (stained pink). (Credit: Piyush Gupta, Kai Tao, Charlotte Kuperwasser, Cell, August 21, 2009.)"

Source: Whitehead Institute for Biomedical Research