Heavy Atoms Can Help Destroy Tumor Cells

One of the fundamental challenges in radiation therapy is to destroy tumors with irradiation while preserving healthy tissue. With hadrontherapy, the use of fast ions as ionizing particles offers a major advantage because they deposit most of their energy in the tissue at the end of their range. This method enables tumors to be destroyed in a targeted manner by adjusting the initial energy of the particles. Also, the ions used in this technique are more effective in destroying cancerous tissue than conventional treatments (X-rays, for example).

In this work, the researchers combined, for the first time, ionic radiation with platinum-enriched cells, using agents such as cis-platinum⁽²⁾, similar to molecules used in medicine. The impact of the incident ions (protons, carbon) and the electrons ejected along the way causes the platinum atoms to become highly ionized. The process of electron capture and emission that ensues significantly increases damage to surrounding molecules and considerably enhances cell death rate. In the presence of platinum, the effectiveness of ions at their end point is increased by at least 50 percent, thus improving how well the tumor can be targeted.

These results suggest that the combination of hadrontherapy and the addition of heavy atoms like platinum can improve both tumor targeting and the effectiveness of cancer treatments while preserving healthy tissue (the onset of toxicity results from the irradiation, and the molecules used are not themselves toxic for the cell). This work paves the way for research on new, non-toxic radiosensitizing agents – molecules, nanoparticles, and lysosomes⁽³⁾ –containing large numbers of atoms⁽⁴⁾.

In practice, there are very few medical centers in the world specializing in hadrontherapy because this new technique is still very expensive. Researchers and clinicians at the Heavy Ion Medical Accelerator (HIMAC) in Chiba, Japan, were the first to demonstrate the effectiveness of carbon ions in therapeutic treatments. In France, proton therapy at the Centre de protonthérapie at the Institut Curie (Orsay) already makes it possible to treat certain cases of cancer that cannot be cured by conventional methods. Another technology is currently being developed that uses carbon ions, and although more expensive, this technique is also more effective in certain cases. In 2012, a treatment center using carbon therapy will be opened in Lyon (“Projet étoile”), which will improve cancer treatment.

Notes:

(1) Hadrontherapy uses atomic ions (such as protons or carbon ions, which are very effective in inducing therapeutic cell death) to treat cancerous tumors.

(2) Cis-platinum is a platinum-containing molecule that is frequently used in chemotherapy.

(3) Lysosomes are cellular components found in the cytoplasm. They contain proteins that break molecules and can destroy cells.

(4) In other words, high-Z atoms (atoms with a high atomic number, i.e., that have a large number of protons and electrons). (Z=78 for platinum.)

References:

N. Usami, Y. Furusawa, K. Kobayashi, S. Lacombe, A Reynaud-Angelin, E. Sage, Ting-Di Wu, A. Croisy, J-L. Guerquin-Kern and C. Le Sech. Mammalian cells loaded with Platinum-containing molecules are sensitised to fast atomic ions. International Journal of Radiation Biology, 84, July 2008.