Photodynamic Therapy Offers New Medical Treatments

For years now, doctors have used ultraviolet lamps to treat psoriasis and to kill airborne tuberculosis bacteria, and lasers have made deep inroads as "bloodless scalpels." Recently, the US Food and Drug Administration (FDA) approved a treatment that takes advantage of the specificity of certain photosensitive chemicals to treat a variety of maladies.

Shown to be effective at treating early-stage cancers, photodynamic therapy uses a photosensitive drug that creates a toxic form of oxygen, called singlet oxygen, when exposed to light. Because the drug remains in cancerous tissue longer than in healthy tissue, the treatment can destroy tissue selectively.

. . . To complement these new drugs, however, all of the drug companies are aggressively examining cost-effective, user-friendly ways to activate them. Since most of the cost of photodynamic therapy is tied up in expensive laser systems, companies are exploring alternatives to minimize this cost. As a result, researchers are looking at two sources: diode lasers and lamps.

. . . . Other companies, too, are developing their own light sources in hopes of caturing what many think will be a lucrative market. The American Cancer Society estimates the direct medical costs of treating breast, lung and prostate cancers amount to more than $18 billion annually. Mark Gart, the managing director of the Ci-tec UK Ltd.'s LumaCare project in Newport Beach, Calif., said his company, whose products have yet to receive the FDA's nod, hopes to offer alternative light sources for many photodynamic therapy applications. "We want to be there when the market ripens," Gart said. The company is developing a line of fiber optic-coupled lamps based on a halogen source tunable in the 600-nm range.

The future of photodynamic therapy looks bright. Michael Berns, director of the Beckman Laser Institute in Irvine, Calif., said many compounds are in some stage of testing. Researchers are flocking to try the technique on diseases as varied as heart disease, breast cancer, bladder cancer, psoriasis, macular degeneration and a host of others.

But which compound works best? The jury is still out, Berns said. He explained that, in general, the treatment is effective, but which drug works best may depend on the individual and the type of cancer. "I think that it will take another five or 10 years before we have a large enough database to see how effective PDT is at curing cancer," he said.

Excerpted from Photonics Spectra, May 1998
Kevin Robinson, "Technology Close-Up: Photodynamic Therapy Offers New Medical Treatments," 219-224.