Development of an in vitro model for the evaluation of phototoxicity of drugs with different affinity to melanin using a solar simulator – the study of cellular, molecular and biochemical mechanisms of the phototoxic reaction

<p><strong>Objective:</strong> The aim of the study was to evaluate the phototoxic potential of selected drugs that form complexes with melanin, using normal human skin cells.</p><p><br /></p><p><strong>Methods:</strong> The study was conducted on normal human cells: melanocytes and fibroblasts, which were exposed to sunlight simulator irradiation. After irradiation, cell viability was assessed using NRU and WST-1 tests, and cell cycle and reduced glutathione levels were analysed. In addition, cell subpopulations in the sub-G1 phase were analysed to assess the degree of apoptosis and DNA damage. Two different experimental models took into account different incubation times of cells with drugs prior to irradiation, which allowed for the assessment of the effect of drug accumulation on phototoxicity.</p><p><br /></p><p><strong>Results:</strong> The drugs showed different levels of cytotoxicity and phototoxicity in melanocyte and fibroblast cells, which affected the PIF values and the interpretation of the results. Additional analyses, such as the assessment of the sub-G1 cell subpopulation and reduced glutathione levels, provided a better understanding of the mechanisms of phototoxicity and the differences in the response of pigmented and non-pigmented cells. </p><p><br /></p><p><strong>Conclusions:</strong> An in vitro model that takes into account pigmentation and response to solar radiation allows for a more precise assessment of the phototoxicity risk of drugs, which is important for the safety of therapy and the development of new drugs.</p>