Photodynamic therapy: a new modality for the treatment of cancer.

Photodynamic therapy is a promising new modality for the treatment of neoplastic disease. Currently, Photofrin is the only photosensitizer approved for the treatment of human cancers. In the search for new, chemically pure second generation photosensitizing agents which absorb in the deep red region of the visible spectrum, a novel and unique photosensitizer, CDS1, an iminium salt of copper octaethylbenzochlorin, was developed. This new photosensitizer is chemically pure, cationic, and possesses a strong (epsilon = 35000 M-1.cm-1) absorption peak at 750 nm (in dichloromethane). With copper in the aromatic cavity and a triplet lifetime which is not measurable (< 20 nsec), the photodynamic activity of CDS1 was unexpected. Preliminary in vitro and in vivo animal studies with a transplantable urothelial tumor indicate that CDS1 is an effective photosensitizing agent when used in conjunction with a broad band xenon arc light source or a low frequency, high peak power pulsed alexandrite laser.