ET-09 ACQUIRED MALIGNANT BEHAVIORS OF NPE6-PDT-SURVIVED GLIOBLASTOMA CELLS ARE SUPPRESSED BY USING MEK1/2 INHIBITOR TRAMETINIB

INTRODUCTION: In this study, we tried to investigate alteration of oncogenic properties and their molecular regulatory mechanism of talaporfin sodium (NPe6)-mediated photodynamic therapy (NPe6-PDT)-survived glioblastoma (GBM) cells. METHODS: As the in-vitro NPe6-PDT model, human GBM cell lines (T98G, U87MG, U343), and patient derived GBM stem cells (GSY03, GSC23, MGG152) were pretreated with 0-30ug/ml NPe6 for 4 hours followed by laser irradiation (wave length 664 nm, laser-power 33 mW/cm2, total amount of irradiation 10 J/cm2) using a semiconductor laser irradiator (Panasonic Healthcare Co., Ltd., Tokyo, Japan). Cell death after PDT was evaluated by vital dye exclusion assay using Hoechst3342 and propidium iodide or CellTiter-Glo. Survived cells after NPe6-PDT (PDT-R cells) were repropagated, and alteration of intracellular molecular signaling or migration/invasion capability were analyzed by immunoblotting or Boyden chamber assay. RESULTS: In both human GBM cell lines and patient derived GBM cells, cellular viability after NPe6-PDT was decreased with dose-dependent manner of pretreated NPe6. PDT-R cells showed not only resistance against NPe6-PDT-induced cell death but also higher invasiveness and migration capability compared with pre-PDT treated cells (PDT-Con cells), and immunoblot analysis demonstrated upregulation of ERK1/2 phosphorylation in PDT-R cells in comparison with PDT-Con cells. Furthermore, these acquired malignant behavior of PDT-R cells were repressed by concomitant use of MEK1/2 inhibitor Trametinib with NPe6-PDT. CONCLUSION: We discovered PDT-R cells demonstrated higher malignant phenotypes via ERK1/2-dependent machinery compared with parent pre-PDT-treated cells. It was also suggested concomitant treatment with MEK1/2 inhibitor during PDT therapy in GBM cases would contribute to better outcome.