Assessing the Effects of Curcumin and 450 nm Photodynamic Therapy on Oxidative Metabolism and Cell Cycle in Head and Neck Squamous Cell Carcinoma: An In Vitro Study

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Simple Summary The study investigates the effects of curcumin in native conditions and after irradiation with 450 nm light on the energy metabolism, redox balance, and cellular growth of head and neck cancer cells and human primary fibroblasts. Although curcumin in native conditions already shows an anti-cancer effect, affecting energy metabolism and limiting the growth of tumor cells and cells that inhabit the surrounding microenvironment, irradiation with 450 nm light (photodynamic) enhances its effect by acting on antioxidant defenses. This study, therefore, opens up new perspectives on specific wavelengths of light that appear to be able to improve the drug's action on cancer growth and proliferation, offering hope for better patient outcomes in the future.Abstract Oral cancer is the 16th most common malignant tumor worldwide. The risk of recurrence and mortality is high, and the survival rate is low over the following five years. Recent studies have shown that curcumin causes apoptosis in tumor cells by affecting FoF1-ATP synthase (ATP synthase) activity, which, in turn, hinders cell energy production, leading to a loss of cell viability. Additionally, irradiation of curcumin within cells can intensify its detrimental effects on cancer cell viability and proliferation (photodynamic therapy). We treated the OHSU-974 cell line, a model for human head and neck squamous cell carcinoma (HNSCC), and primary human fibroblasts. The treatment involved a 1 h exposure of cells to 0.1, 1.0, and 10 mu M curcumin, followed or not by irradiation or the addition of the same concentration of pre-irradiated curcumin. Both instances involved a diode laser with a wavelength of 450 nm (0.25 W, 15 J, 60 s, 1 cm2, continuous wave mode). The treatment with non-irradiated 1 and 10 mu M curcumin caused ATP synthase inhibition and a consequent reduction in the oxygen consumption rate (OCR) and the ATP/AMP ratio, which was associated with a decrement in lipid peroxidation accumulation and a slight increase in glutathione reductase and catalase activity. By contrast, 60 s curcumin irradiation with 0.25 W-450 nm caused a further oxidative phosphorylation (OxPhos) metabolism impairment that induced an uncoupling between respiration and energy production, leading to increased oxidative damage, a cellular growth and viability reduction, and a cell cycle block in the G1 phase. These effects appeared to be more evident when the curcumin was irradiated after cell incubation. Since cells belonging to the HNSCC microenvironment support tumor development, curcumin's effects have been analyzed on primary human fibroblasts, and a decrease in cell energy status has been observed with both irradiated and non-irradiated curcumin and an increase in oxidative lipid damage and a slowing of cell growth were observed when the curcumin was irradiated before or after cellular administration. Thus, although curcumin displays an anti-cancer role on OHSU-974 in its native form, photoactivation seems to enhance its effects, making it effective even at low dosages.

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