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To: Galirayo who wrote (7703)	5/10/1998 1:08:00 AM
From: John Metcalf	Read Replies (3) \| Respond to of 9262

{PDT - photodynamic therapy} The Pharmacyclics website pharmacyclics.com has some good information on PDT. The basic technology is akin to the action of sunlight on chlorophyl in plants. Photofrin, the PDT agent of QLTIF, is a precursor of chlorophyl. Basically, the PDT agent localizes in tissue that one wants to affect. Light is applied, at a certain wavelength, perhaps through a catheter, and singlet oxygen is created (free oxygen radicals, as they say in the nutrient commercials). Free oxygen radicals destroy tissue. So that's bad, you say. No, that's good, provided that the PDT agent has localized in undesirable tissue, like cancerous tumors and atheratomous plaque in the aorta. Jonathan Sessler, at PCYC, has developed a class of PDT agents called texaphyrins ("Texas-sized porphyryns"). These have been shown to localize in tumors and plaque. They also can contain metals (gadolinium or lutetium, for example), which allow them to be imaged via MRI. You can give the texaphyrin, image the localization in tumor, and then apply light to destroy it. Lutetium texaphyrin sensitizes to radiation; viz., same sequence and then apply radiation instead of light to kill the tumor. Companies involved in PDT include: PCYC, strong last week (my choice), MRVT (nuked by a Barron's article), QLTIF (first to market with a PDT agent for cancer) and DUSA (using generic delta-aminolevulinic acid for actinic keratoses). If you find others, let me know. I'm not the expert, this is just an overview. The PCYC website should help.