Avaliação antitumoral da terapia fotodinâmica com azul de metileno em células neoplásicas mamárias

Abstract

Photodynamic therapy (PDT) is an alternative treatment for breast cancer, demonstrating selectivity and important cytotoxicity to malignant tissues. Such therapy involves the use of two non-toxic components: a photosensitizing substance and a light source (such as low-power lasers). In combination, they can induce cellular and tissue effects through oxygen-dependent processes, leading tumor cells to death by necrosis, apoptosis and autophagy. Thus, the objective was to evaluate the antitumor activity of photodynamic therapy using breast tumor cells in experimental models in vitro. 4T1 breast tumor cell line was cultured in RPMI medium supplemented with 10% fetal bovine serum (FBS) and 1% antibiotic at 37°C and 5% CO2. Methylene blue (MB) was dissolved in RPMI medium at concentrations 5, 10, 15, 20, 25, 50, 100 and 150 µM, filtered and the cells were incubated for 30 min at 37°C. Shortly after this incubation period, the MB solution was removed, the plates washed and a new RPMI medium added. Irradiation was performed with a low power red laser (660nm - AsGaAl), perpendicularly and punctually, in the following physical parameters: power 100mW, energy density 100 Jcm-2 , energy per spot 2.8 J, continuous light emission mode and exposure time 28s. After irradiation, cell viability was tested by MTT, cell migration was performed by wound healing method and mRNA relative levels by real time PCR. Cell viability results indicate that MB concentrations from 5 to 50 µM were not toxic to 4T1 cells, while concentrations of 100 and 150 µM showed cytotoxicity. On the other hand, 4T1 cells incubated with MB and irradiated with low power laser showed reduced viability and cell migration at 50 µM concentration. Caspase-6 mRNA relative level was not altered in the treatments tested; Bcl-2 mRNA relative level was reduced after PDT 25 µM. In conclusion, concentrations up to 100 µM and 30 min of incubation time generate cytotoxic effects on cells, reducing viability. Concentration of 50 µM demonstrated a decrease in cell viability and migration after PDT, indicating a good dose-response treatment for this cell type