Advanced methylene blue — nanoemulsions for in vitro photodynamic therapy on oral and cervical human carcinoma

Photodynamic therapy (PDT) is a therapeutic modality with high contributions in the treatment of cancer. This approach is based on photophysical principles, which presents as a less invasive strategy than conventional therapies. Combined with nanotechnology, the therapy becomes more efficient because nanoparticles (NPs) have advantageous characteristics such as biocompatibility, controlled, and targeted release, promoting solubility and decreasing the toxicity and side effects involved. In this work were developed nanoemulsions containing the methylene blue photosensitizer (MB) (MB/NE) and in the empty form (unloaded/NE). Subsequently, the mentioned nanomaterials were characterized by the measurement of dynamic light scattering (DLS). The MB/NE and unloaded/NE showed appropriate physical and chemical characteristics, with particle size ≤ 200 nm, polydispersity index close to 0.3, and zeta potential exhibiting negative charge, showing stable values during the analysis. The incorporation of the MB did not cause changes in the photophysical profile of the photosensitizer. The quantification performed showed an incorporation rate of 81.9%. Viability studies showed an absence of cytotoxicity for MB/NE in the concentrations of 10–75 µmol·L⁻¹, free MB at the concentration of 75 µmol·L⁻¹, and unloaded NE 47.5% (v/v), presenting viability close to 90%, respectively. PDT in vitro protocols applied to OSCC and HeLa cells showed a decrease in cell viability through only one irradiation, evidencing the photodynamic activity of the formulation when applied to cancer cells. The results obtained were superior to those found in the literature where they use free MB, showing that the association between nanotechnology and PDT optimizes the proposed protocol. From the results obtained, it is possible to indicate that the NE have high stability, with satisfactory physical–chemical parameters, in addition to not presenting cytotoxicity in the tested concentrations, showing their in vitro biocompatibility, in addition to presenting satisfactory effects when combined MB/NE with PDT, showing the potential of MB/NE as a very promising nanostructured photosensitizer for the treatment of some types of cancer.