Cause of Pain in the Treatment

Photo: Experiment with red light

Forty per cent of those treated
experience pain during the light
irradiation; © RUB

Researchers of the Ruhr-Universität Bochum (RUB) identified the ion channels involved and signalling molecules secreted by the cancer cells. “The results may provide a starting point for suppressing the pain”, says Doctor Ben Novak.

In contrast to normal cells, cancer cells are equipped with different enzymes and have a much higher metabolism. If you apply a molecule called aminolevulinic acid to the skin in the form of a gel, cancer cells take up considerably more of this substance than healthy cells. If aminolevulinic acid accumulates in the cells, the mitochondria – the power plants of the cells – form the molecule protoporphyrin IX. When irradiated with red light, protoporphyrin IX reacts with oxygen. This produces highly reactive oxygen species, free radicals, which destroy the cancer cells. Approximately ten minutes of red light irradiation is sufficient to successfully treat superficial forms of non-melanoma skin cancers such as actinic keratosis. Doctors also remove warts in this way.

“The catch is: it is terribly painful”, says Novak. Forty per cent of those treated experience pain during the light irradiation, which they assess on a scale of 0 to 10 (whereby 10 corresponds to an excruciating pain like a heart attack) as 7 to 8. Using injections, like at the dentist, it is possible to numb the nerves involved. “But that also always involves a risk”, he says.

The pain is generated by two mechanisms. In a cell culture experiment, the team showed that not only cancer cells but also pain-sensitive nerve cells in the skin take up aminolevulinic acid – and its derivative methyl aminolevulinic acid – from the ointment. Using calcium imaging, the animal physiologists followed the activity of nerve cells which they had treated with aminolevulinic acid and cells that were not exposed to the substance. Treated nerve cells fired when the researchers exposed them to light. In a living organism, this would mean that the cells would send a pain stimulus to the brain. Without the aminolevulinic acid, the pain-sensitive cells remained inactive under red light. In further experiments, the scientists showed that the activity of the nerve cells is caused by sodium channels and voltage-gated calcium channels in the cell membrane. “A drug that targets these channels would, conceivably, be able to suppress the pain – but that’s still in the future”, says Novak.; Source: Ruhr-Universität Bochum