Comparison of the in vivo efficiency of Photofrin II-, mTHPC-, mTHPC-PEG- and mTHPCnPEG-mediated PDT in a human xenografted head and neck carcinoma

Background and Objective: One of the approaches to enhance the selectivity and efficiency of photodynamic therapy (PDT) was the conjugation of the pho tosensitizer meta-tetrahydroxyphenylchlorin (mTHPC) to the water-soluble po lymer polyethylene glycol (PEG). Several studies have demonstrated that mTH PC-PEG has a higher selectivity and a longer circulating half-life than fre e mTHPC, whereas no in vivo effect of this benefit could be seen. Study Design/Materials and Methods: In a model of RAG-2-mice bearing a huma n oral squamous cell carcinoma xenograft (XF 354), the in vivo efficiency a ssessed as growth retardation or remission caused by Photofrin II and free mTHPC was compared with mTHPC coupled in two different ways to polyethylene glycol (PEG). One hundred and fourty-nine female RAG-2-mice were randomise d into one control group and 13 therapy groups. Treatment parameters were a dapted from those routinely applied in animal studies. Results: Photofrin II-mediated PDT and mTHPC-mediated PDT were both in vivo highly effective, whereas mTHPC induced less scars. The in vivo results af ter mTHPC-PEG-mediated PDT were disappointing, whereas the effectiveness of mTHPCnPEG-mediated PDT, a newly coupled macromolecular photosensitizer, we re promising. Conclusions: These results demonstrated the impact of the method of linkage between the photoactive agent mTHPC and polyethylene glycol (PEG) upon the in vivo effectiveness. mTHPC and mTHPCnPEG are promising photosensitizers for the future, especially for the cosmetic treatment needs of head and nec k (C) 2001 Wiley-Liss, Inc.