Colours combine to curb cancer

A colourful combination of red light, blue dye and a plant hormone can be used to kill cancer cells with a lethal flurry of chemicals, according to a study by Cancer Research UK scientists.

The researchers believe that they have discovered a way of overcoming problems with normal forms of photodynamic therapy (PDT), which involves destroying tumours with beams of light.

PDT is a developing technique which can potentially destroy unwanted tissue while sparing normal tissue. First, a drug called a photosensitiser is administered to the patient, usually by injection. By itself the photosensitiser is harmless and has no effect on healthy or abnormal tissue. However, when light (often from a laser) is directed on to tissue containing the drug, the drug becomes activated and the tissue is rapidly destroyed but only precisely where the light has been directed.

Thus, by careful application of the light beam, the technique can be targeted selectively to the abnormal tissue. Some of the drugs being developed for use in PDT also have the desirable property of concentrating in tumours (and certain other kinds of proliferating tissue) relative to the surrounding healthy tissue and which also helps in targeting.

The new study shows that this type of treatment could be much more effective when combined with a plant hormone that in nature helps plants grow towards the sun.

The scientists treated cancer cells with a special blue dye that becomes chemically energised in response to light. When they shone red light on the cells and dye with the plant hormone, the hormone shattered to produce toxic chemicals called free radicals. These form poisonous by-products with the potential to kill cancer cells.

The problem with conventional photodynamic therapy is that the dye relies on activating molecules of oxygen to kill tumour cells and therefore does not work in the low oxygen conditions that exist in many tumours. But the new method uses molecules of plant hormone to attack cancer cells instead and so could work right in the core of many tumours, where oxygen levels are often very low.