Biodistribution and photodynamic therapy with hypericin in a human NPC murine tumor model

The use of photodynamic therapy (PDT) for the treatment of recurrent and residual nasopharyngeal carcinoma (NPC) has been encouraging. To determine the potential of hypericin as a PDT tool in the treatment of NPC, we investigated the effect of hypericin-mediated PDT on subcutaneously implanted NPC/HK1 tumor cells and the relationship between the biodistribution of hypercin and photodynamic effects. The plasma hypericin level increased rapidly and reached its peak concentration at 1 h after injection. The uptake of hypercin in tumor tissue was maximal 6 h after hypericin administration, at which time the drug concentration in the circulation was low. The efficacy of hypericin-mediated PDT was maximal when light irradiation was performed at 6 h after hypericin administration. Tumor relative regression percentage (RRP) induced by PDT at 1-h interval was comparable to that at 6-h interval, whereas light treatment performed at other time intervals induced less tumor RRP, albeit significant when compared to the control group. Hypericin appears to be an effective photosensitizer for the treatment of NPC. It is likely that hypericin-mediated PDT induces both vascular damage and direct tumor cell killing, thereby bringing about tumor necrosis and shrinkage.