PHOTODYNAMIC THERAPY OF B16 PIGMENTED MELANOMA WITH LIPOSOME-DELIVERED SI(IV)-NAPHTHALOCYANINE

The possibility of extending photodynamic therapy to the treatment of highly pigmented neoplastic lesions was tested by using Si(IV)-naphtha locyanine (SiNc) as a tumor-localizing agent. Si(IV)-naphthalocyanine displays intense absorbance at 776 nm (epsilon = 5 x 10(5) M(-1) cm(-1 )), where melanin absorption becomes weaker. As an experimental model we selected B16 pigmented melanoma subcutaneously transplanted to C57B L mice. Upon injection of 0.5 or 1 mg kg(-1) of liposome-incorporated SiNc, maximal accumulation of the photosensitizer in the tumor was obs erved at 24 h with recoveries of 0.35 and 0.57 mu g g(-1), respectivel y. However, the tumor targeting by SiNc shows essentially no selectivi ty, since the photosensitizer concentrations in the skin (peritumoral tissue) were very similar to those found in the tumor at all postinjec tion times examined by us. Irradiation of SiNc-loaded melanoma with 77 6 nm light from a diode laser at 24 h postinjection induces tumor necr osis and delay of tumor growth. The effect appears to be of purely pho tochemical nature at dose rates up to 260 mW cm(-2); at higher dose ra tes, thermal effects are likely to become important.