gms | German Medical Science

Objective: GBM adjuvant therapy using radiotherapy and/or Temozolomide (TMZ) remains inefficient due to resistance mechanisms. One possible mechanism of this observed resistance is due to proteolytic shedding of cell surface proteins. For shedding events, MMP and ADAM metalloproteases (MPs) are responsible and their expression levels are increased in GBM. Therefore they could potentially contribute to therapy resistance and recurrence of glioblastoma.

Method: MP expression levels were determined in six recurrent GBM tissues after adjuvant therapy and in six permanent and primary patient-derived GBM cell lines following TMZ treatment (100-700 microM) and/or gamma-irradiation (1-10 Gy) by qPCR. TMZ- and Radio-Sensitivity were determined in the absence or presence of hydroxamate MP inhibitors batimastat (BB-94) and marimastat (BB-2516). Downstream effects of MPs on the DNA Damage Reponse Pathway involving kinases Akt/PI3K and ERK1/2 were analysed by morphological analysis and Western blotting. TMZ and radiosensitivity were assessed in cells with high and low MP expression levels. Mechanistically, potential substrates of MPs were determined by proteomic analysis of cell supernatants and confirmed by ELISA assays.

Results: As a consequence of TMZ treatment or radiotherapy, activity levels of MMP-9 and ADAM8 are increased in recurrent GBM specimens and in primary GBM cells. Increase in ADAM8 and MMP-9 expression caused Akt and ERK1/2 phosphorylation in GBM cells. Treatment of GBM cells with BB-94, but not BB-2516 increased sensitivity to TMZ and radiotherapy-induced cell death in a cell-specific manner. Specific knockdowns and pharmacological inhibition of MMP-9 and ADAM8 sensitised GBM cells to adjuvant therapy.

Conclusions: Metalloproteases ADAM8 and MMP-9 were identified as important target molecules to improve adjuvant therapy in GBM cells. The use of selective ADAM8 and MMP-9 inhibitors appears to be a feasible treatment option to optimize TMZ chemotherapy and radiotherapy in order to prevent formation of recurrent glioblastoma in patients.