Optimization of 5-aminolevulinic acid-based photodynamic therapy protocol for breast cancer cells

Photodynamic therapy (PDT) is a therapeutic strategy for the treatment of cancer. 5-aminolevulinic acid (5-ALA) as a precursor of the protoporphyrin IX (PpIX) has a great potential for PDT application. Although 5-ALA-based PDT has been studied in many pre-clinical and clinical studies for breast cancer, there are different PDT application protocols in the literature. Therefore, the aim of this study was to determine the optimal in vitro protocol for 5-ALA-based PDT in breast cancer treatment.

The therapeutic effects of 5-ALA (1 and 2.5 mM) on two different subtypes of breast cancer cell line (MCF-7 and MDA-MB-231) were evaluated by PpIX-fluorescence accumulation and WST-1 analysis. Then, the cells were irradiated with diode laser at different doses (1.5, 3, 6, 9 and 12 J/cm²). After irradiation, the anticancer effects of 5-ALA were analyzed through cell viability and cell death analysis.

Our results showed that 5-ALA exhibited a higher PpIX fluorescence in both breast cancer cells for 4 h incubation. After irradiation, 1 mM 5-ALA significantly reduced the proliferation of breast cancer cells in a laser dose-dependent manner and induced apoptotic cell death upon 24 h incubation (p < 0.05). However, MDA-MB-231 cells were more sensitive to 5-ALA-based PDT than MCF-7 cells in a dose of 9 J/cm² and 12 J/cm².

Our preliminary findings proposed an optimal in vitro protocol of 5-ALA-based PDT by using a laser diode for breast cancer. However, there is a need to investigate the underlying molecular mechanisms of 5-ALA/PDT sensitivity among the subtypes of breast cancer.