A buildup of chemical bonds on certain cancer-promoting genes, a process known as hypermethylation, is widely known to render cells cancerous by disrupting biological brakes on runaway growth. Now, Johns Hopkins scientists say the reverse process demethylation which wipes off those chemical bonds may also trigger more than half of all cancers.
One potential consequence of the new research is that demethylating drugs now used to treat some cancers may actually cause new cancers as a side effect.
"It's much too early to say for certain, but some patients could be at risk for additional primary tumors, and we may find that they need a molecular profile of their cancer before starting demethylating therapy," says Joseph Califano, M.D., professor of otolaryngologyhead and neck surgery and oncology at Johns Hopkins.
The findings, based on studies of normal and cancer cells from human mouth, nose and throat tissue, provide more evidence that important regulators of gene activity occur outside as well as inside DNA in a cell's nucleus.
"While cancer-causing and other mutations alter vital protein-making pathways by rewriting the gene's DNA code, epigenetic changes affect genes without changing the code itself. The new studies tell us that such changes occur not only when methyl groups bond to a gene's on-off switch, but also when they come unglued," says Califano.
Califano says sporadic reports of demethylation as a tool in activating cancer-promoting genes led his team to develop a systematic way to discover these epigenetic changes and show how the process is linked to cancer.
To gather their evidence, Califano and his group treated two cell lines from normal oral tissue with the demethylating drug 5-azacytidine and collected a list of genes that were activated as a result. They used special silicon chips carrying pieces of genetic material that allow thousands of genes to be analyzed at one time to locat
|Contact: Vanessa Wasta|
Johns Hopkins Medical Institutions