HYPERICIN UPTAKE IN RABBITS AND NUDE-MICE TRANSPLANTED WITH HUMAN SQUAMOUS-CELL CARCINOMAS - STUDY OF A NEW SENSITIZER FOR LASER PHOTOTHERAPY

Tissue uptake and biodistribution of hypericin was measured in rabbits and in nu/nu mice xenografted with P3 human squamous cell carcinoma t o assess the value of this dye as an in vivo sensitizer for laser phot oinactivation of solid tumors. Hypericin has absorption maxima at 545 and 590 nm with a fluorescence emission peak at 640 nm in ethanol. Dye uptake after intravenous injection was tested at 4 and 24 hours in ra bbit tissues by ethanol extraction and quantitative fluorescence spect rophotometry. Maximum dye levels were seen at 4 hours in most vascular organs with lung having fivefold higher uptake than spleen followed b y liver, blood, and kidney. Mice were examined after 2, 4, 6, 8, and 2 4 hours and after 3 and 7 days for dye uptake. The peak concentration of hypericin in murine organs was reached at 4 hours with uptake per g ram of tissue as follows: n>liver>blood>kidney>heart>gut>tumor>stomach >skin> muscle>brain. Elimination of hypericin was rapid in most murine organs with residual dye under 10% of maximum by 7 days compared to 2 5% to 30% retention for the squamous cell tumors and several normal ti ssues. These results suggest that hypericin may be a useful photosensi tizer for KTP/532 laser interstitial therapy of human cancer.