Molecular aspects of photodynamic therapy: low energy pre-sensitization of hypericin-loaded human endometrial carcinoma cells enhances photo-tolerance, alters gene expression and affects the cell cycle

Photosensitization of HEC1-B cells with a low concentration of hypericin and doses of light below 10 J/cm2 caused cell death (apoptosis occurred mainly at doses between 2 and 5 J/cm2, whereas necrosis prevailed above 6 J/cm2). However, pre-exposure of cells to innocuous irradiation (2 J/cm2) and successive challenge with a light dose that normally induced apoptosis (5 J/cm2) altered the expression of the proteins involved in the regulation of apoptosis, stress response and cell cycle. This change resulted in a significant increase in cell phototolerance.