Phototoxicity Mechanism of a Kryptocyanine Dye in Human Red Cell Membranes and Isolated Murine Mitochondria

Abstract

The phototoxicity mechanism of a kryptocyanine dye, N,N′-bis(2-ethyl-1,3-dioxolane)kryptocyanine (EDKC⁺), has been studied in RBC membranes and isolated mitochondria. Lipophilic, positively charged dyes, such as EDKC⁺, may be useful as tumor-cell-selective, light-activated cytotoxic agents. Exposure of the RBC membranes to 700-nm light and EDKC⁺ inhibited membrane acetylcholinesterase and photo-decomposed EDKC⁺ in air-purged but not argon-purged samples. Photoinactivation of acetylcholinesterase was the same in D₂O as in H₂O and was not quenched by superoxide dismutase. Ascorbate and azide (10 mm) quenched or slightly enhanced, respectively, the inactivation. In argon-purged samples containing methyl viologen, EDKC⁺ photodecomposed, but acetylcholinesterase activity was unaffected. The mechanism may involve electron transfer to oxygen and subsequent formation of toxic photoproducts from EDKC⁺.

In contrast, exposure of murine mitochondria to EDKC⁺ and 700-nm light caused inhibition of mitochondrial respiration in both the presence and absence of oxygen. The photodecomposition of EDKC⁺ correlated with inhibition of respiration. Thus, the phototoxicity of EDKC⁺ in mitochondria may be due to electron transfer from photoexcited EDKC⁺ to oxygen and electron acceptors in the membrane. These studies indicate that dyes such as EDKC⁺ may be useful for photochemotherapy of hypoxic regions in tumors.