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Activated by Light

As a bio-organic chemist with an international reputation, U of A professor Bill Lown has done his share of globe-trotting, and over the past 30 years he's come back with some interesting souvenirs (including the prestigious Paul Ehrlich Prize from the French Association de recherches scientifiques Paul Neumann). But perhaps the most interesting thing ever to come back in his suitcase was some pigment from a fungus that attacks bamboo.

On a 1988 lecture trip to China, Lown kept hearing about the interesting properties of this pigment used in traditional Chinese medicine to treat skin conditions. It seemed to be energized by light, and his Chinese hosts thought it might have potential as a cancer therapy. Was Lown interested? He was, and they sent a 10 grain package of the purified pigment home with him.

That pigment, which has the name hypocrellin, is now the basis for an exciting new photodynamic cancer therapy being tested for use in treating both bladder and prostate cancer. Photodynamic therapy is a unique treatment alternative for malignancies resistant to conventional therapies. It involves the selective destruction of malignant cells with substances that become deadly to cancer cells — when they are exposed to ordinary visible red light.

Once he began studying hypocrellin, Lown became excited about its potential for photodynamic therapy and brought together a diverse group of researchers to develop an appropriate treatment method. Included were John Tulip, a laser specialist from the Department of Electrical Engineering; Jerry Miller, who undertook preclinical evaluations of the various hypocrellin derivatives which Lown was able to synthesize; and surgery professor Ron Moore.

Miller, who recently joined the Faculty of Pharmacy and Pharmaceutical Science's Noujaim Institute, explains that hypocrellin is itself nontoxic until it is excited by red light. (Fortunately, red is the color from the visible spectrum that penetrates the farthest through tissue — which is why your flesh appears red when you shine a flashlight through it).

Once the hypocrellin molecules are activated by the light they generate toxic oxygen species that are deadly to surrounding cells. Thus it is possible to administer hypocrellin to a patient and then selectively illuminate malignant tissue with a red-light laser, destroying the cancer and leaving healthy tissue untouched. Hypocrellin derivatives have now been extensively tested and they work "like a charm," says Lown."In animals we've had 100 per cent success."

Miller and Lown say that the chief advantage hypocrellin has over the product currently licensed for photodynamic therapy is that it is excreted from the body quickly - within 24 hours. Therefore the patient doesn't suffer from lingering phototoxicity and confinement to a darkened room, often for up to several weeks.

While hypocrellin is initially being tested for use with bladder cancer, Miller says that it has potential for use in fighting a   number of other cancers - including lung, esophogial and colorectal cancers — where red light, which can be delivered using an endiscope, can penetrate to a sufficient depth (about five millimetres).

"We're now very near clinical trials," says Miller, who has confidence in both hypocrellin and the future of photodynamic therapy. "The advantages," he says, "are many, including a good deal less morbidity than you see from surgery, radiation or chemotherapy."

Published Winter 1999.

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