RESEARCHERS ARE hoping that the triple threat of light, oxygen, and light-sensitive drugs will usher in a new age in cancer treatment. The new weapon, called photodynamic therapy, uses laser light to activate a cytotoxic drug selectively in tumor cells.
The drugs involved, hematoporphyrin and its more potent derivative, dihematoporphyrin ether (DHE, Photofrin) (Quadra Logic Technologies, Vancouver, Canada), have been known to be light activated since early in this century. But it was not until the 1970s that the first systemic use of photodynamic therapy was pioneered by Thomas Dougherty, PhD, and his group at Roswell Park Memorial Institute, the New York State facility in Buffalo.
The drug enters both normal and malignant cells. However, it is retained to a greater degree by neoplastic cells.
Thus, 48 to 72 hours after administration, there is a gradient between the normal cells and the tumor. Photodynamic therapy seeks to exploit this.