Health Scan: Can cancer be turned against itself?

The human immune system can use proteins from melanoma, the most serious type of skin cancer, to kill off cancer cells, according to researchers at Tel Aviv University.

A small group of proteins of the Ras “family” controls a large number of cellular functions, including cell growth, differentiation and survival; because the protein has a hand in cellular division, mutated Ras – which can be detected in one-third of all tumors – contributes to many human cancers by allowing for the rapid growth of diseased cells.

Prof. Yoel Kloog of Tel Aviv University’s neurobiology department, Dr. Itamar Goldstein of TAU’s Sackler Faculty of Medicine and the Sheba Medical Center and colleagues have found cancer-promoting oncogenic Ras can also alert the immune system to the presence of cancer cells. The team published their findings in the Journal of Immunology.

For the first time, the researchers have shown the transfer of oncogenic Ras in human cells from melanoma cells to T cells, which are white blood cells in the immune system.

This transfer allows the immune cells to gather crucial intelligence on what they are fighting and develop the necessary cytokines, or signalling molecules, to kill the melanoma cells.

Kloog suggests that a drug that enhances the transfer of the oncogene from the tumor to the immune cells is a potential therapy to augment the anti-cancer immune response.

Although they found that immune cells often exchange proteins among themselves, the discovery that melanoma cells transfer mutated Ras is an intriguing first. And it’s this initial transfer that begins a “positive feedback loop” – the scientists incubated T-cells from patients with human melanoma cells that had originated from tumors. They uncovered a circuit that runs between the cancer and immune cells. Once the melanoma cells pass oncogenic Ras to the T-cells, the T-cells are activated and begin to produce cytokines, which enhances their capacity to kill cancer cells.

As these melanoma cells pass along the mutated Ras, the immune cells become increasingly active.

Eventually, enough oncogenic material is transferred across the immune cells’ threshold, causing the T-cells to act on the melanoma cells from which the oncogenic Ras was derived. Ultimately, this transfer tips the scales in favor of the immune cells, the researchers say.

The next step is to develop a therapy to enhance the transfer in patients with cancers linked to oncogenic Ras.

Although their research has so far focused on melanoma, which is known to elicit the response of the immune system, he believes that this finding could be applicable to other types of cancers. The researchers believe their research will lead to a better understanding of how the immune system fights tumors.

“It’s a part of the interaction between cancer and the immune system that is not well known,” they said.

“We are trying to gather more comprehensive data on all the proteins that are being passed around and how this information impacts the immune system’s response to cancer.”

GREEN IS BEAUTIFUL Women who drink green tea may lower their risk of developing some digestive system cancers, especially cancers of the stomach, esophagus and colon/rectum, according to a study led by researchers from Vanderbilt- Ingram Cancer Center in Tennessee.

The study was headed by Prof. Sarah Nechuta and published in the American Journal of Clinical Nutrition.

To determine green tea’s impact on cancer risk, the investigators surveyed women enrolled in the Shanghai Women’s Health Study, a populationbased study of approximately 75,000 middle-aged and older Chinese women. During the initial interview participants were asked if they drank tea, the type of tea consumed and how much they consumed. Most of the Chinese women reported drinking primarily green tea.

The researchers found that regular tea consumption, defined as tea consumption at least three times a week for more than six months, was associated with a 17 percent reduced risk of all digestive cancers combined. A further reduction in risk was found to be associated with an increased level of tea drinking. Specifically, those who consumed about two to three cups per day (at least 150 grams of tea monthly) had a 21% reduced risk of digestive system cancers, especially stomach/esophageal and colorectal cancers.

“For all digestive system cancers combined, the risk was reduced by 27% among women who had been drinking tea regularly for at least 20 years,” said Nechuta. “For colorectal cancer, risk was reduced by 29% among the long-term tea drinkers.

These results suggest long-term cumulative exposure may be particularly important.”

Tea contains polyphenols or natural chemicals that include catechins like EGCG and ECG. Catechins have antioxidant properties and may inhibit cancer by reducing DNA damage and blocking tumor cell growth and invasion.