Intratumoral Hypericin and KTP Laser Therapy for Transplanted Squamous Cell Carcinoma

Objectives/Hypothesis To test intratumoral photodynamic therapy (IPDT) as a new treatment for squamous cell carcinoma in a preclinical tumor model. Study Design and Methods Human P3 squamous carcinoma cells were transplanted subcutaneously in athymic nude mice and allowed to grow into 300‐ to 500‐mm3 tumors. Hypericin dye at 1 μg/gm of body weight was injected intratumorally (IT) or intravenously (IV). After 4 hours hypericin biodistribution was assessed in ethanol extracts from tissues by fluorescence spectroscopy. IPDT also was tested by KTP laser fiberoptic insertion in tumors 4 hours after IT dye injection compared to KTP532 laser therapy alone (532 nm, 1W, 40–60 J, 0.6‐mm fiber). Results Hypericin concentration in tissues was as follows: (IT vs. IV) for tumors (3660 vs. 135 ng dye/gm tissue), lung (760 vs. 6345), liver (75 vs. 935), blood (65 vs. 480) compared to skin (465 vs. 110) or muscle (335 vs. 80) adjacent to the squamous cell tumors. Four hours after dye injection, the tumor e‐hibited bright orange fluorescence when e‐cited by KTP 532‐nm green laser light. The IPDT‐treated tumors had a 3.32 ± 0.32‐mm radius of cell destruction when H&E‐stained sections were e‐amined compared with 2.5 ± 0.38 mm for the laser only control group (n = 10, P = .003). Conclusions This pilot study indicates laser IPDT with hypericin induces a significant increase in tumor necrosis compared with laser alone and may be useful as a less invasive adjuvant treatment for recurrent or inoperable human squamous cell cancers of the head and neck.