A research collaboration between the Medical College of Wisconsin (MCW) and the Children’s Research Institute in Milwaukee has found that extremely small particles of elemental selenium are highly toxic to leukemia and certain solid tumor cells but well tolerated by normal cells. The small particles are generated when certain selenium-containing dyes are exposed to light, and this small size appears to be essential for the anti-cancer effect.
The findings are published in Photochemistry and Photobiology as Photochemically Generated Elemental Selenium Forms Conjugates with Serum Proteins That Are Preferentially Cytotoxic to Leukemia and Selected Solid Tumor Cells
When selenium is split-off from the dye molecules, it binds to proteins such as albumin, which is a primary source of amino acids and energy for tumors. This allows albumin to act as a “Trojan horse” and deliver the toxic selenium particles preferentially to tumor cells as part of a physiological process. In a typical experiment, a one-hour exposure to albumin-bound selenium is sufficient to kill 99.999% of leukemia cells, while virtually all normal cells survive
“Selenium has had a long and colorful history in cancer therapy,” said Fritz Sieber, PhD, Professor of Pediatricsand Medicine at MCW with joint appointments in the Department of Cell Biology, Neurobiology & Anatomyand the Department of Microbiology and Molecular Genetics, and a researcher with Children’s Research Institute. ”Some 100 years ago, selenium was the first agent to be used for the systemic chemotherapy of cancer. Right now, selenium is attracting renewed interest as an agent to protect patients from the toxic side effects of radiation and chemotherapy, as an agent to sensitize tumors to radiation and chemotherapy, and as an anti-cancer agent in its own right.”
Dr. Sieber said a particularly attractive aspect of the novel selenium-based anti-cancer agent is that it is also effective against cancer cells that have become resistant to conventional chemotherapy.
However, the dyes used in these experiments are expensive, and developing a more cost-effective alternative will be necessary to develop this technology into an anti-cancer drug suitable for clinical use.