One of the potential methods for treating cancer is photodynamic therapy (PDT), which involves the targeted destruction of cancer cells through the activation of photosensitizers (PS) using light irradiation. The aim of the study was to investigate the photodynamic properties of the squaraine dyes with hydrophilic and hydrophobic substituents. Methods. Fluorescence spectroscopy, UV-VIS spectroscopy, laser scanning confocal microscopy, cytotoxicity assay. Results. It was shown that all studied dyes have maximum absorption in the far-red region, which makes them suitable for PDT. It has been investigated that the squarains can form complexes with proteins, as indicated by changes in their fluorescence. The samples demonstrated minimal dark toxicity but exhibited cytotoxicity after irradiation. The cytotoxic effect of dyes with hydrophilic groups was reduced by binding to BSA. Meanwhile, a dye with hydrophobic substituents shows a photodynamic effect in the presence of albumin. All studied dyes can penetrate through the cellular membrane, stain the cell components in the cytoplasm, and do not accumulate in nuclei. Conclusions. All dyes showed low dark toxicity. However, cytotoxicity increased after irradiation with light of a wavelength of 670 nm. The binding of the dyes with hydrophilic substitutes to albumin negatively impacted their photosensitizing properties. At the same time, the dye with the highest tendency to aggregate exhibited the most significant cytotoxic effect.
Here we synthesize a series of benzoindolium squaraine dyes with N-substituents (SQ) and examine these dyes as fluorescent probes to detect serum albumins. Methods. Organic synthesis, fluorescent spectroscopy, absorption spectroscopy, fluorescent microscopy. Results. The spectralluminescent properties of SQ dyes in the aqueous solution were investigated in the presence of bovine serum albumin (BSA), human serum albumin (HSA), equine serum albumin (ESA), ovalbumin (OVA), beta-lactoglobulin (BLG) and lysozyme (LYS), as well as in the presence of nucleic acid. The maxima of excitation spectra of the studied dyes in the buffer solution ranged within 623-673 nm, with the fluorescence emission maxima lying between 635 and 690 nm. All these dyes showed a similar increase in the fluorescence intensity with serum albumins and at the same time with the red shift up to 12 nm, which could point out the binding of the dyes to proteins. These dyes demonstrate a noticeably lower fluorescence intensity in the presence of OVA, BLG, and LYS, which structurally differ from serum albumins. The studied dyes gave no significant fluorescent response to the addition of nucleic acids. The equilibrium constants of dyes binding to BSA (K) were estimated as 3.0 ± 0.3x10 5 M -1 for SL-2411 and 2.4 ± 0.6x10 5 M -1 for SL-2412. Based on the relative values of K, we could suppose that the mechanism of dye-BSA binding is the interaction of the chromophore of the dye with the protein globule. It was shown that SL-2411 penetrates the cell membrane and distri bu tes in the cytoplasm without co-localization with MitoTracker Green. Conclusion. These dyes could apply fluorescent spectroscopy for protein detection and potentially visualize cell components with minimum to no autofluorescence.
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