Triaminophenaziniums as emerging theranostic agents showing light controlled imaging, cell death and siRNA delivery...

In the field of theranostics, triaminophenaziniums are promising molecules due to their intrinsic properties such as an absorbance beyond 500 nm associated with large molar extinction coefficients, high fluorescence quantum yields, as well as phototoxicity. This study explored how three triaminophenazinium salts relate in structure and activity, highlighting their potential as theranostic agents. The nature of the moiety in position 2 of the dyes was varied from H, to -CH₃ or -^tBu. All compounds exhibit suitable absorption and emission within the 550-560 nm and 610-640 nm range, respectively, that allowed their visualization within the cells (imaging) under one- or two-photon excitation. Interestingly, these dyes showed a greater toxicity in the dark toward MCF-7 cancer cells (LC₅₀ 0.7-1.5 μM) compared to healthy keratinocytes (LC₅₀ 1.5-3.5 μM). This trend was confirmed as a greater phototoxicity toward cancer cell than healthy keratinocytes at 25 nM was found for triaminophenazinium bearing the H and -CH₃ substituents. Using siRNA targeting the Inhibitor of Apoptosis Protein (IAP) at an N/P ratio of 20, the CH₃-substituted triaminophenazinium compound induced 20 % cell death in MCF-7 cells. This indicates its capacity to form complexes with siRNA and effectively photorelease it, leading to gene silencing and subsequent cell death.