Stem cell arsenic exposure raises cancer risk

A study published online in Environmental Health Perspectives reports that researchers from the National Institutes of Health have discovered how normal stem cells can turn into cancer stem cells and spur tumor growth through exposure to arsenic. Evidence of earlier studies shows that the drinking water of millions of people worldwide is affected by inorganic arsenic, which is a human carcinogen. Progressively mounting evidence indicates that cancer is a stem-cell based disease; whilst normal stem cells are vital for normal tissue regeneration and to stabilize organisms and processes, cancer stem cells are considered to be the driving force in terms of formation, growth, and spread of tumors. In an earlier study, Michael Waalkes, Ph.D., and his colleagues from the National Toxicology Program Laboratory and the National Institute of Environmental Health Sciences, which is part of NIH, demonstrated that normal cells become cancerous when treated with inorganic arsenic. The team's new study demonstrates that normal stem cells very quickly acquire the characteristics of cancer stem cells, when these cancer cells are placed near, but not in contact with the normal stem cells. This proves that malignant cells have the ability to transmit molecular signals through a semi-permeable membrane that is generally impassable for cells, which turn normal stem cells into cancer stem cells. Waalkes remarks: "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. 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." The findings represent a potentially significant factor of arsenic carcinogenesis. This may also prove beneficial for researchers who work with arsenic in explaining why arsenic often causes various types of multiple tumors on the skin or inside the body. Waalkes' lab started working with prostate stem cells, not embryonic stem cells, about five years ago. Waalkes declared: "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." The body's stem cells are unique; they exist for a long time and can divide and renew themselves. Linda Birnbaum, Ph.D., director of NIEHS and NTP concludes: "Most cancers take 30 or 40 years to develop. 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." The team will be investigating whether this finding is unique to arsenic or whether it also applies to organic and inorganic carcinogens.