Light irradiation has been used in clinical therapy for several decades. In this context, photobiomodulation (PBM) modulates signaling pathways via ROS, ATP, Ca2+, while photodynamic therapy (PDT) generates reactive oxygen species by excitation of a photosensitizer. NO generation could be an important tool when combined with both kinds of light therapy. By using a metal-based compound, we found that PBM combined with PDT could be a beneficial cancer treatment option. We used two types of ruthenium compounds, ([Ru(Pc)], Pc = phthalocyanine) and trans-[Ru(NO)(NO2)(Pc)]. The UV-vis spectra of both complexes displayed a band in the 660 nm region. In the case of 0.5 μM trans-[Ru(NO)(NO2)(Pc)], light irradiation at the Q-band reduced the percentage of viable human melanoma (A375) cells to around 50% as compared to [Ru(Pc)]. We hypothesized that these results were due to a synergistic effect between singlet oxygen and nitric oxide. Similar experiments performed with PDT (660 nm) combined with PBM (850 nm) induced more photocytotoxicity using both [Ru(Pc)] and trans-[Ru(NO)(NO2)(Pc)]. This was interpreted as PBM increasing cell metabolism (ATP production) and the consequent higher uptake of the ruthenium phthalocyanine compounds and more efficient apoptosis. The use of metal-based photosensitizers combined with light therapy may represent an advance in the field of photodynamic therapy.
Keywords: Light irradiation therapy; Metal-based drug; Nitrosyl ruthenium-phthalocyanine complex; Photobiomodulation.
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