Epithelial Growth Factor Receptor Expression influences 5-ALA Induced Glioblastoma Fluorescence

Background: The extent of 5-aminolevulinic acid (5-ALA) guided tumor resection has a determining impact in high-grade and glioblastoma surgery. Yet the intensity of the 5-ALA induced fluorescence may vary within the tumor. We aimed to correlate 5-ALA induced fluorescence with the expression of Epithelial Growth Factor Receptor (EGFR) in different glioblastoma (GBM) cell lines.

Methods: To elucidate the role of EGFR in the metabolism of 5-ALA in GBM cell lines (U87MG and BS153), we analyzed the activation of EGFR by its primary ligand EGF, and its downstream effect on Heme oxygenase-1 (HO-1), a key enzyme regulating the metabolism of Protoporphyrin IX (PpIX), the fluorescent metabolite of 5-ALA. Effects of direct pharmacological inhibition by Tin(IV)-Protoporphyrin (SnPP) or gene knockdown by small interfering RNA (siRNA) on HO-1 enzyme were analyzed in respect to 5-ALA induced fluorescence. Furthermore, inhibition of EGFR by Gefitinib was tested.

Results: A significant difference in 5-ALA induced fluorescence was obtained in U87MG compared with BS153 cell lines, correlating with the different quantitative and qualitative EGFR expression. Treatment of U87MG cells with EGF was able to promote HO-1 transcription and expression in a concentration-dependent manner, leading to a reduced cellular fluorescence. This effect could be reversed by EGFR-specific siRNA treatment, which reduced protein expression of ∼80%. Inhibition of HO-1 activity by SnPP or reduction of HO-1 protein levels by siRNA treatment significantly enhanced fluorescence, independently of EGFR quantitative expression. Gefitinib treatment was able to restore fluorescence after EGF stimulation in U87MG cells but not in BS153 cells, overexpressing EGFR/EGFRvIII.

Conclusion: In GBM cell lines 5-ALA induced fluorescence is variable and influenced by EGF-induced downstream activation of HO-1. HO-1 protein expression was identified as a negative regulator of 5-ALA induced fluorescence, and furthermore dependent of EGFR expression.

No conflict of interest has been declared by the author(s).