PHOTODYNAMIC THERAPY FOR DEEP TUMOURS

FOR THE TREATMENT OF DEEP TUMOURS, RESEARCHERS HAVE DEVELOPED A NEW PHOTODYNAMIC THERAPY

Edited by, SNEHA MAVIS

A Chinese research team has recently created a novel form of photodynamic tumour therapy that does not require external irradiation for the treatment of deep tumors. According to the findings published in the journal Angewandte Chemie, the light source is incorporated into the drug and is selectively activated in tumor microenvironments. 

This "intelligent" drug is made up of four parts that are bonded together to form a single molecule: a photosensitizer (pyropheophorbide-a), pH sensor (disopropylamino group), a polymer (polyethylene glycol), and the "lamp" (the amino acid tyrosine carrying a radioactive iodine-131 isotope). 

The molecules are tightly aggregated into nanoparticles at pH values found in healthy tissues. The "irradiation" is turned off (quenched) in this compact form and the drug has no effect. Tumorous tissue, on the other hand has a somewhat acidic pH value. The pH sensor changes structure in this environment, and the nanoparticles fall apart-the irradiation is activated and reactive oxygen species are generated, which destroy the tumor cells.

How does the "built-in light" function?

The radioactive iodine isotope I-131 emits ß-radiation and 𝛄-radiation as it decays. When electrons move, their charges polarise atoms, resulting in dipole oscillations that emit electromagnetic waves or light. Usually, these waves cancel each other immediately. Yet, the electrons sent out by I-131 travel faster then light in the dense aqueous environment of the cells. The quenching of the waves is incomplete in this situation, resulting in Cherenkov radiation, a bluish light. This activates the photosensitizers, causing tumor cells to die.  

The novel drug showed potent tumor suppression in cell cultures and animal models, with low toxicity and few side effects on healthy tissue.