Research has uncovered the way a compound in green tea kills cancer cells while leaving healthy cells untouched.

The findings could lead to treatments for oral cancer as well as other types of cancer.

Penn State food scientists show that epigallocatechin-3-gallate -- EGCG -- the compound triggers a process in the mitochondria that leads to oral cancer cell death.

"EGCG is doing something to damage the mitochondria and that mitochondrial damage sets up a cycle causing more damage and it spirals out, until the cell undergoes programmed cell death," said Joshua Lambert, associate professor of food science and co-director of Penn State's Center for Plant and Mushroom Foods for Health.

With continuing mitochondrial damage, the cancer cell also reduces the expression of anti-oxidant genes, further lowering its defences.

Earlier studies had shown this action by EGCG on oral cancer cells but researchers did not understand the reasons for its ability to target the cancer cells.

The present study suggests EGCG causes the formation of reactive oxygen species in cancer cells, which damages the mitochondria, and the mitochondria responds by making more reactive oxygen species.

It was seen that a protein called sirtuin 3 -- SIRT3 -- is critical to the process.

"It plays an important role in mitochondrial function and in anti-oxidant response in lots of tissues in the body, so the idea that EGCG might selectively affect the activity of sirtuin 3 in cancer cells -- to turn it off -- and in normal cells -- to turn it on -- is probably applicable in multiple kinds of cancers," Lambert said.

Fortunately, the EGCG did not cause this reaction in normal cells but on the contrary increases protective capabilities of the cell.

The findings are published in Molecular Nutrition and Food Research.

The researchers studied normal human oral cells side-by-side with human oral cancer cells to determine how EGCG was affecting cancer cells differently than normal cells.

Both the normal and oral cancer human cells were grown on petri dishes and then exposed them to EGCG, the major polyphenol found in green tea, at concentrations typically found in the saliva after chewing green-tea chewing gum.

Tests on animals and humans

The next step would be to study the mechanism in animals. If those tests and human trials are successful, the researchers then hope to create anti-cancer treatments that are as effective without the harmful side effects as seen with chemotherapy.

Early chemotherapy drugs just target rapidly dividing cancer cells, but in the process also harm normally dividing cells.

Green tea is made from unfermented leaves and believed to contain the highest concentration of powerful antioxidants called polyphenols. Antioxidants fight free radicals -- damaging compounds in the body that change cells, damage DNA, and cause cell death.

Polyphenols contained in teas are classified as catechins. Green tea contains six primary catechin compounds: catechin, gallaogatechin, epicatechin, epigallocatechin, epicatechin gallate, and apigallocatechin gallate (also known as EGCG).

EGCG is the most studied polyphenol component in green tea and the most active.

Clinical studies indicate that the antioxidant properties of green tea may help prevent atherosclerosis, lower total cholesterol and raise HDL, protect against cancer
and kill cancerous cells and stop them from growing.