PDT demonstrated without external light

Photodynamic therapy (PDT) selectively destroys cancer cells using an external light source, such as a laser. Because external light cannot penetrate internal tissue, doctors must perform invasive procedures, such as endoscopy, to deliver treatment. Luminol, however, can permeate the cell membrane and is chemiluminescent. Researchers led by Michael Firer at the College of Judea and Samaria in Ariel in collaboration with Bar-Ilan University in Ramat-Gan, both in Israel, tested a PDT technique in which luminol activates hematoporphyrin, a photoreactive drug, in Friend’s leukemia cells.

In the July 18 issue of the British Journal of Cancer, the scientists report that they exploited the ability of luminol to emit light when it reacts with hydrogen peroxide in the presence of an iron catalyst. They conjugated hematoporphyrin to the iron carrier transferrin, which not only brought more iron catalyst to the luminol, but also increased the specificity of the treatment because cancer cells tend to have more transferrin receptor. Hematoporphyrin generates reactive oxygen species, including hydrogen peroxide, which killed the cancer cells and stimulated the luminol to emit more light.

The luminol-activated PDT killed 97.5 percent of more than 10,000 Friend’s leukemia cells with a standard deviation of 12 percent across all replicates. Unlike conventional chemotherapy, the cells did not develop drug resistance after repeated treatment.

The researchers proved their concept in vitro, but Firer added that they are learning how to translate this strategy in vivo by testing it on several mouse models of cancer.