Sub-additive effects of photodynamic therapy combined with erlotinib for the treatment of epidermoid carcinoma: An in vitro study

Background: Photodynamic therapy (PDT) is an antitumour treatment that employs the combination of a photosensitive compound, oxygen and visible light. To improve the antitumour activity of PDT, the present study used the strategy of combining PDT with erlotinib (ERL), a drug frequently used in the treatment of epidermoid carcinoma. Methods: An MTT cell viability assay was used to evaluate the cytotoxicity of PDT combined with ERL on A431 epidermoid carcinoma cells in vitro. This study evaluated the cytotoxicity of the following treatments: red laser irradiation (660 nm) at different power densities (1.25-180 J/cm(2)), the photosensitizer methylene blue (MB) at concentrations of 0.39-100 mu M, PDT (12.5 mu M MB and laser power densities from 1.25 to 180 J/cm(2)), and PDT (12.5 mu M MB and a laser density of 120 J/cm(2)) plus ERL (1 mu M). Results: The laser power densities that were tested showed no cytotoxicity in A431 cells. MB showed a dose-dependent cytotoxicity. In PDT, an increase in the dose of light resulted in an increase in the cytotoxicity of MB. In addition, there was a sub-additive effect between PDT and ERL compared to the effect of each therapy alone. Conclusions: The sub-additive effect between PDT and ERL suggests that their combination may be an important strategy in the treatment of epidermoid carcinoma. (C) 2017 Elsevier B.V. All rights reserved.