Hunting cancer cells one by one with plasmonic resonance

Researchers at Rice University and the MD Anderson Cancer Center (Houston, Texas, USA) have presented in Nature Nanotechnology a method to detect microtumors, or even individual cancer cells, present in apparently healthy tissue. The technique can also kill cells that can not be removed surgically for any reason and, in this way, prevent the reappearance of cancer. The procedure makes use of the latest photonic technology.

The surgical techniques to remove tumors improve day by day, but before you can remove a tumor you have to find it, which is not easy. In fact, different symptoms and analytical can tell us that there is a tumor in some general area but detecting where exactly is an important problem in the case of many aggressive tumors that appear in the head, neck, brain, lungs or chest. In these cases, in addition, complete excision of the tumor visible to the surgeon can leave behind separate nodules in healthy tissue, which is known as microscopic residual disease (MRE).

The ERM can sometimes consist of only a few tens of cells in total and, therefore, be invisible to the naked eye, which does not prevent them from being enough for the cancer to reappear and kill. The only technique currently in clinical use to detect MRE is the analysis of tissue samples, but this takes time and has a very limited sensitivity. Therefore, surgeons have to take preventive measures by eye while they are performing the removal of the tumor and clean up millimeters or even centimeters of seemingly healthy tissue around the tumor (which is popularly known as cutting for good), trying to find a balance between the health effects of removing healthy tissue against the risk of the cancer reappearing or spreading. Radiation therapy and chemotherapy may be useful to neutralize MRE, but they are not always effective and may have important side effects. The worst situation is when the ERM can be located but it can not be surgically attacked.

Researchers have now taken another step in a technique that they have been developing for six years. They have used gold nanoparticles coupled to antibodies that only bind to receptors that are present exclusively in cancer cells. These nanoparticles are injected into the bloodstream and end up accumulating in the cells of the ERM. If the area is now irradiated with brief pulses of infrared laser, the nanoparticles transform this radiation into heat through a process called plasmonic resonance. This produces locally the equivalent of inflating a balloon until it explodes; The plasmonic resonance converts the liquid inside the cancer cells into vapor, causing them to explode without damaging healthy surrounding cells. These small explosions produce a shock wave that can be detected using an ultrasound probe, with which the researchers could locate tumors of 50 microns in size or, what is the same, of only 30 cells. The current level of clinical detection is 1 millimeter or 1 million cells.

In experimental tests conducted with mice, the researchers found that the mice in which the technique had been applied lived significantly more than those receiving a standard treatment, even if the ERM had not been surgically removed. This would prove that the procedure kills many of the cells. Many, not all. There is nothing effective one hundred percent.

The next step is to transfer the technique to the operating rooms. Gold nanoparticles are already clinically approved for use in humans, so researchers are already preparing trials with upper aerodigestive tract (head and neck) tumor surgery in Belarus.