Photoinactivation of amelanotic and melanotic melanoma cells sensitized by axially substituted Si-naphthalocyanines

Abstract

The photosensitizing activity of the new far-red absorbing naphthalocyanine SiNc [OSi( n-C 10H 21) 1] [OSi(CH 3) 2(CH 2) 3N(CH 3) 2], (DAP-SiNc), and of its analogue SiNc [OSi(i-C 4H 9) 2( n-C 18H 37)] 2, (IsoBO-SiNc), was studied with two cell variants of B16 melanoma, the amelanotic clone B78H1 and the highly pigmented B16F1 cells. Upon excitation with a 776 nm diode laser, DAP-SiNc appeared to be a markedly more efficient photosensitizer than isoBO-SiNc. The higher photoefficiency of DAP-SiNc was likely to reflect its accumulation in significantly larger amounts by both cell types, as well as a much smaller tendency to undergo aggregation when bound to the cells. In any case, melanotic cells were less sensitive to the photoinactivating action of DAP-SiNc: the protective action of melanin was a consequence of an optical filtering of the 776 nm light and an appreciable shortening of the DAP-SiNc triplet lifetime (40 μs for the amelanotic vs. 17 μs for the melanotic cells). Functional and morphological studies on irradiated cells showed that cell death due to DAP-SiNc photosensitization was mainly correlated with the modification of targets located in the lysosomes and the cytoplasmic membrane.