gms | German Medical Science

Objective: ADAM proteases are important mediators of tumor growth, invasion and angiogenesis. As such, ADAM8 is of clinical significance, since glioma patient survival correlates inversely with ADAM8 expression levels. In this respect we hypothesised that ADAM8 has a therapeutic window in high-grade gliomas.

Method: The mode of action of ADAM8 was explored in glioma cell lines U87 and U251 with either knockdown of endogenous ADAM8 or with glioma cells overexpressing ADAM8. These cell lines were investigated in vitro for intracellular signalling by microarray and kinase array analysis, in vitro angiogenesis assay using co-culture with HUVEC cells, and by stereotactic injection of glioma cells into striata of nude mice to assess tumors in situ.

Results: Microarray analysis of U87 vs U87-A8 knockdown (kd) cells revealed a strong positive correlation of ADAM8 expression with angiogenesis-related genes, i.e. expression of Osteopontin, CXCL-1, and IL-8, pro-angiogenic factors. Moreover, induction of anti-angiogenic genes, such as CXCL-10, CXCL-11 was detected in ADAM8 knockdown cells. Using human endothelial HUVEC cells in vitro, significant differences in the angiogenic potential of U87 vs U87-A8 kd cells were detected. Also, ADAM8 knockdown caused a reduction in Akt and ERK1/2 phosphorylation, indicating that Akt and ERK1/2 are required for the observed effects of ADAM8 expression. In situ, tumors derived from U87 with an ADAM8 knockdown show significantly reduced tumor sizes compared to U87 control cells.

Conclusions: ADAM8 mediates glioma growth in vivo by activation of intracellular kinases Akt and ERK1/2 and is important as a pro-angiogenic factor, as ADAM8 regulates several angiogenesis-relevant genes. Since angiogenesis is considered to be the "heel of Achilles" in gliomas, ADAM8 inhibition appears as an attractive route for the treatment of ADAM8-positive glioma specimen.