A less invasive treatment for prostate cancer is a step closer thanks to preclinical studies by researchers in the US.

Prostate cancer accounts for almost one in four of male cancers in the UK. The disease is treated mostly by surgery or radiation, however, treatment using photodynamic therapy (PDT) is currently undergoing clinical trials. The treatment uses an antitumour drug that remains inactive until it is exposed to light. Doctors shine laser light into the body through a catheter, targeting the tumour using fibre optics.

Tissues surrounding the prostate show a reduced response to photodynamic therapy

The advantages of PDT are that it can be accurately targeted, is less invasive and causes fewer side-effects than conventional treatments. But for PDT to be successful, all the glandular tissue in the prostate needs to be destroyed, said Zheng Huang from the AMC Cancer Research Center, in Denver. This means that the whole of the prostate needs to be irradiated, Huang explained, making it important to understand the treatment's effect on nearby tissues and organs.

Given this, Huang and colleagues have looked at the effect of PDT on the tissues surrounding the prostate in dogs. The researchers used a chlorophyll derivative called Tookad, which is a non-toxic, light-activated drug. It can be administered by injection for better targeting and laser activation produces a chemical that blocks blood vessels in the immediate area, cutting off the tumour's blood supply.

The team irradiated the surfaces of the bladder, colon, abdominal muscle and pelvic plexus after administrating the Tookad. They showed that these tissues were sensitive to the PDT, although not to the same extent as the prostate gland.

Huang cautioned that, despite their reduced response to PDT, tissues adjacent to the prostate should be protected during irradiation. The aim now, added Huang, is to fine tune the treatment to provide maximum protection of the adjacent tissues and make the photodynamic therapy safer.

Nicola Burton