Abstract
This work presents a new procedure to synthesize ruthenium–phthalocyanine complexes and uses diverse spectroscopic techniques to characterize trans-[RuCl(Pc)DMSO] (I) (Pc = phthalocyanine) and trans-[Ru(Pc)(4-ampy)2] (II) (4-ampy = 4-aminopyridine). The triplet excited-state lifetimes of (I) measured by nanosecond transient absorption showed that two processes occurred, one around 15 ns and the other around 3.8 μs. Axial ligands seemed to affect the singlet oxygen quantum yield. Yields of 0.62 and 0.14 were achieved for (I) and (II), respectively. The lower value obtained for (II) probably resulted from secondary reactions of singlet oxygen in the presence of the ruthenium complex. We also investigate how axial ligands in the ruthenium–phthalocyanine complexes affect their photo-bioactivity in B16F10 murine melanoma cells. In the case of (I) at 1 μmol/L, photosensitization with 5.95 J/cm2 provided B16F10 cell viability of 6%, showing that (I) was more active than (II) at the same concentration. Furthermore, (II) was detected intracellularly in B16F10 cell extracts. The behavior of the evaluated ruthenium–phthalocyanine complexes point to the potential use of (I) as a metal-based drug in clinical therapy. Changes in axial ligands can modulate the photosensitizer activity of the ruthenium phthalocyanine complexes.
Highlights
In recent years, the use of metal–photosensitizer compounds in photodynamic therapy (PDT) has been proposed: such compounds allow a combinatory approach involving chemo and light irradiation therapy to be applied against cancer (Zhang et al, 2018)
Metal–phthalocyanine synthesis is key to improving the use of these complexes in PDT (Allison et al, 2004; Boyar and Çamur, 2019; Fujishiro et al, 2019)
Ruthenium– phthalocyanine has emerged as a promising molecule because ruthenium complexes generally have octahedral geometry, and ruthenium–phthalocyanine is a hexacoordinated species that can still bind two new axial ligands (Heinrich et al, 2014; Teles Ferreira et al, 2017)
Summary
The use of metal–photosensitizer compounds in photodynamic therapy (PDT) has been proposed: such compounds allow a combinatory approach involving chemo and light irradiation therapy to be applied against cancer (Zhang et al, 2018). Where std is the singlet oxygen quantum yield for the standard ZnPc ( std = 0.67 in DMSO); R and Rstd are the photobleaching rates after irradiation of (I) or (II) and the standard, respectively; and Iabs and Iastbds are the rates of light absorption by (I) or (II) and the standard, respectively. The cells were incubated at room temperature for 15 min, 400 μl of 1× annexin-binding buffer was added, the mixture was mixed gently, and the samples were kept on ice. For flow cytometry analysis, the cells were exposed to 2% propidium iodide solution. Results with P < 0.05 were considered statistically significant
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