A water-soluble dye has all of the properties needed for use in a non-invasive form of cancer treatment, say scientists in Turkey.

Engin Akkaya, at the Middle East Technical University, Ankara, and colleagues have made water-soluble dyes that they say are highly promising reagents for use in photodynamic therapy (PDT).  PDT, still a relatively young technique, uses a light-sensitive drug (or photosensitiser) and visible light energy to produce reactive oxygen species that attack any surrounding cancer cells.

PDT uses a red laser or light-emitting diode as a light source, because red light penetrates tissue more deeply.  The photosensitising dye is introduced into the cells before light is shone on to the tumour. To produce reactive oxygen species, the dye must strongly absorb red light in the wavelength range 650 to 800 nanometers, which is known as the therapeutic window. For use in cells, the dye must also be water soluble.  The most commonly used porphyrin-based PDT reagents are not very efficient at absorbing light within the therapeutic window.

Akkaya's team took some well-known fluorescent dyes called boradiazaindacenes, or BODIPY dyes, and modified them in two ways to satisfy the sensitiser requirements.  The researchers improved the red light absorption of the dyes by incorporating bromine groups, and increased the dyes' solubility in water by adding water soluble triethyleneglycol groups. When tested on human cancer cells, the dyes showed what the researchers described as 'spectacular' photoinduced cytotoxicity, at very low concentrations.

 'With these superior properties, this novel class of dyes could be a very valuable addition to the current and limited arsenal of PDT reagents,' said Akkaya.

Sue Askey