Protoporphyrin IX-dependent photodynamic production of endogenous ROS stimulates cell proliferation

Photodynamic therapy using methyl 5-aminolevulinate (MAL) as a precursor of the photosensitizing agent protoporphyrin IX is widely used in clinical practice for the treatment of different pathologies, including cancer. In this therapeutic modality, MAL treatment promotes the forced accumulation of the endogenous photoactive compound protoporphyrin IX in target malignant cells. Subsequent irradiation of treated tissues with an appropriate visible light source induces the production of reactive oxygen species (ROS) that, once accumulated above a critical level, promote cell death. Here we demonstrate that a photodynamic treatment with low MAL concentrations can be used to promote a moderate production of endogenous ROS, which efficiently stimulates cell growth in human immortalized keratinocytes (HaCaT). We also show that this proliferative response requires Src kinase activity and is associated to a transient induction of cyclin D1 expression. Taken together, these results demonstrate for the first time that a combination of light and a photoactive compound can be used to modulate cell cycle progression through Src kinase activation and that a moderate intracellular increase of photogenerated ROS efficiently stimulates cell proliferation. © 2011 Elsevier GmbH.
This work was supported by Grants SAF2008-00609 (Ministerio de Ciencia e Innovación, Spain) to J. Espada and FIS PS09/01099 (Ministerio de Sanidad; Spain) to A. Juarranz. A. Blázquez-Castro and E. Carrasco are recipients of FPU fellowships (Ministerio de Ciencia e Innovación, Spain). J. Espada is a hired investigator under the Programa Ramón y Cajal (Ministerio de Ciencia e Innovación, Spain).