Arsenic turns stem cells into cancer-causing cells

National Institutes of Health (NIH) scientists have made an interesting discovery with regard to arsenic and its effects on stem cells. Arsenic can turn normal stem cells into cancerous cells that grow uncontrollably and cause tumors. Arsenic is a common pollutant of drinking water in some parts of the world, and has previously been shown to be a cancer-causing chemical (carcinogen). Interestingly, cancer is probably a stem cell-based disease. Therefore, arsenic seems to convert the healers of our bodies from profitable entities to the makers of tumors.

Michael Waalkes, who heads a research team at the National Toxicology Program Laboratory, National Institute of Environmental Health Sciences (which is part of the NIH), has shown previously that treatment of normal cells with arsenic causes them to become cancerous. However, the present study shows that when these converted cancer cells are placed in proximity to normal stem cells, but not in contact with them, the normal stem cells quickly acquire the characteristics of cancer stem cells. Thus malignant cells can send molecular signals that transfer the message to grow uncontrollably to other cells. In fact, the placement of a semi-permeable membrane, between the cancer cells and the normal stem cells does not prevent the transformation from occurring. This demonstrates that small molecules that are made by the arsenic-transformed cell can are small enough to pass through the membrane and signal to the normal stem cells to turn them into cancer stem cells.

“This paper shows a different and unique way that cancers can expand by recruiting nearby normal stem cells and creating an overabundance of cancer stem cells,” said Waalkes. “The recruitment of normal stem cells into cancer stem cells could have broad implications for the carcinogenic process in general, including tumor growth and metastases.”

Waalkes’ lab started working with stem cells about five years ago. The researchers used a prostate stem cell line, not embryonic stem cells. “Using stem cells to answer questions about disease is an important new growing area of research. Stem cells help to explain a lot about carcinogenesis, and it is highly likely that stem cells are contributing factors to other chronic diseases,” Waalkes said.

Stem cells are unique in the body. They stay around for a long time and are capable of dividing and renewing themselves. “Most cancers take 30 or 40 years to develop,” said Linda Birnbaum, Ph.D., director of NIEHS and NTP. “It makes sense that stem cells may play a role in the developmental basis of adult disease. We know that exposures to toxicants during development and growth can lead to diseases later in life.”

Next, Waalkes’ group will look to see if this finding is unique to arsenic or if other organic and inorganic carcinogens also show these effects on normal stem cells.

This paper reveals an extremely important aspect of arsenic carcinogenesis. Additionally it may explain why arsenic often causes multiple tumors of many types that form on the skin or inside the body. The paper is online in Environmental Health Perspectives.