Comparison of the dark and light-induced toxicity of thio and seleno analogues of the thiopyrylium dye AA1 Original Research Article

2,6-Bis(4-anilino)-4-(4-N,N-dimethylanilino)thiopyrylium chloride (AA1) and -selenopyrylium chloride (AA1-Se) and 2,6-bis(4-anilino)-4-(4-N-morpholinophenyl)thiopyrylium chloride (1) and -selenopyrylium chloride (2) were prepared via the addition of 4-N,N-dimethylanilino magnesium bromide and 4-N-morpholinophenyl magnesium bromide to chalcogenopyranones 3 followed by treatment with HCl gas then water. Cellular uptake of these dyes varied from 12 ± 3 fmol/cell for AA1 to 150 ± 40 fmol/cell for AA1-Se. upon exposure to 5 × 10−5 M solutions of the dyes for 3 h. Exposure of cell cultures to 1.8 J/cm2 of 360–750-nm light following incubation with 1 × 10−6 M of either AA1, 1, or 2 for 24 h resulted in no significant additional phototoxicity while AA1-Se showed a significant (P<0.05) reduction in cell viability from 81% to 46%. Thiopyrylium dyes AA1 and 1 showed significant dark toxicity relative to selenopyrylium dyes AA1-Se and 2, respectively. AA1 was the only one of the four dyes to show inhibition of whole-cell mitochondrial cytochrome c oxidase activity in the dark. Irradiation of whole cells or mitochondrial suspensions treated with AA1, AA1-Se, or 2 gave inhibition of mitochondrial cytochrome c oxidase activity. Studies of JC-1-efflux indicated that all four cationic dyes accelerated the loss of JC-1 from the mitochondria, which suggests that all four dyes target the mitochondria.