Effect of GFP expression on the sensitivity of glioma cell lines to photodynamic therapy

Enhanced green fluorescent protein (EGFP)-expressing cells are customarily used in a variety of in vitro and in vivo studies and assays to ease visualization and localization. Nonetheless, the effects of EGFP expression on cellular responsivity to Photodynamic therapy (PDT), a combination therapy combining a photoactive drug and light, have yet to be characterized. To address this effect, rat astrocytoma cells (CNS-1), a lentivirus-transduced EGFP variant (CNS-1 GFP), human glioblastoma (U-87), and the transfected EGFP variant (U-87 GFP) are analyzed in terms of cell survival following PDT mediated by two different photoactive drugs. Cell survival is quantified via colony forming assays and Alamar blue assays, as a function of light dose, using the photosensitizers Photofrin (1ug ml -1 for 24h) and ALA (200ug ml -1 for 5h). Furthermore, effect of GFP expression on the responsivity to Cisplatin, a DNA-binding chemotherapeutic agent is determined for these cell lines. Our results show that EGFP expression does not affect the responsivity of Photofrin-PDT in comparison to parental cell lines (non GFP expressing cells), but does alter that of ALA-PDT. No change in responsivity is observed for Cisplatin treatment for either cell line. These results can be explained by oxidative stress induced by EGFP expression. This work will establish under which circumstances it is appropriate to use EGFP-expressing cell lines in the context of PDT preclinical research in vivo and in vitro .