Initial treatment of head and neck squamous cell carcinoma is directed by several considerations with the single most important factor being stage of disease [1]. However, with the advent of newer chemoradiation protocols, an increase in the number of recurrent squamous cell carcinomas has been seen. These recurrent patients usually have no surgical options and need newer modalities of treatment in hopes of palliation after receiving maximum dose radiation or appearance of drug resistant tumors [1]. Tumor imaging and PDT with hypericin have been tested in vivo for therapy of pancreas and skin cancer as well as in nasopharyngeal carcinomas [5,8,11]. Experimental studies have shown that hypericin photodynamic therapy is tumoricidal for human cancer cells both in vitro and in vivo with potential application in targeting recurrent or unresectable malignancies through this minimally invasive new adjuvant procedure [2-7].
The current study supports previously reported data and provides new evidence that hypericin may prove to be clinically useful for both tumor imaging and in PDT of locally recurrent head and neck squamous cell carcinoma. As seen in Figs 5 and 6, hypericin is effective as a fluorescent tumor imaging agent when activated by a conventional operating room KTP532 surgical laser. In an earlier study, we reported that intravenous hypericin injection resulted in significant uptake by SCC tumors, but higher levels of this fluorescent dye were deposited in the lungs and other vascular organs [2]. Although 532 nm laser light was sufficient for hypericin excitation and in fluorescent tumor imaging, the in vitro SCC experiments of the current study show clearly that the higher 593 nm laser wavelength is superior in phototherapy. This conclusion also was indicated by a decreased PDT response observed for large SCC tumors after hypericin and KTP532 laser treatment even when fiberoptics were inserted directly into the tumor center to maximize the light delivery. Recent reports show hypericin phototherapy can be enhanced by multi-fraction treatment, by the addition of synthetic oxygen carriers, or by co-administration of a cyclo-oxygenase inhibitor to block prostaglandin synthesis and prevent new angiogenesis in tumor sites [9-11]. Further improvement of hypericin PDT also may be possible using 2-photon infrared pulsed laser emissions to increase tissue penetration of light during tumor imaging and treatment [7]. These advances will make hypericin and lasers a more effective cancer therapy.
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