Researchers have discovered a method to kill cancer cells by targeting their biological clock.

The study, conducted at the University of Texas Southwestern Medical Center in Dallas, focused on using a small molecule to stop the growth of cancer cells in culture and shrink tumors in mice.

The molecule, 6-thiodG, interferes with the cell's mechanism for maintaining the length telomeres, which cap the ends of cell's chromosomes to protect them from damage. The telomeres shorten every time the cell divides. When they shrink to a critical length, the cell can no longer divide and dies.

"We observed broad efficacy against a range of cancer cell lines with very low concentrations of 6-thiodG, as well as tumor burden shrinkage in mice," said Dr. Jerry Shay, one of the lead researchers.

Cancer cells are protected by an enzyme called telomerase, which keeps telomeres from shrinking when cells divide. Other research has focused on drugs to block telomerase, but the problem with them has been that they have to be used over a long period, becoming toxic to the body.

Because 6-thiodG is not normally used in telomeres, the compound acts as an 'alarm' signal instead that is recognized by the cell as damage. As a result, the cell stops dividing and dies.

The researchers said using telomerase to kill cells represents a potentially promising therapy against cancer.

"Using telomerase to incorporate toxic products into telomeres is remarkably encouraging at this point," said Dr. Woodring Wright, a lead researcher.

The mice did not suffer any serious side effects in the blood, liver and kidneys, the researchers said.

"Since telomerase is expressed in almost all human cancers, this work represents a potentially innovative approach to targeting telomerase-expressing cancer cells with minimal side effects on normal cells," said Dr. Jerry Shay, another lead researcher. "We believe this small molecule will address an unmet cancer need in an underexplored area that will be rapidly applicable to the clinic."

-- Lynne Terry