gms | German Medical Science

Objective: Intercellular communication, driven by tumor-associated microglia/macrophages and metalloproteases engaged in limited proteolysis are important factors contributing to the grim prognosis of GBM patients. We investigated the occurrence of anti-tumorigenic M1 or pro-tumorigenic M2 macrophages in GBM, their association with particular metalloproteases and the impact on patient outcome.

Methods: Expression levels of mRNAs associated with M1 (CXCL9, CXCL10) and M2 macrophages (CCL13, CD206), as well as metalloproteases (ADAM8, ADAM10, ADAM17, MMMP9, MMP14) were quantified by qPCR in GBM tissue. All patients (n=20, median age=61.5 years, female/male=3/17) received a therapy consisting of GTR, radiation and chemotherapy, and died of tumor progress. To assess heterogeneity within one tumor sample, 15 specimens from different areas were analyzed. The macrophage marker expression was correlated with extent of necrosis, determined by MRI.

Results: Both M1- and M2-markers showed a correlation in their respective expression (CXCL9/CXCL10:R=0.25, p=0.29; CCL13/CD206:R=0.71, p<0.001). However, intra-patient samples showed a high level of heterogeneity for all markers except CCL13, with constant expression levels in all samples, qualifying it as the most reliable marker. Higher expression levels of M2-markers were found, especially in tumors with high extent of necrosis.

MMP9 and MMP14 show a correlation with each other (R=0.812, p<0.001) and with occurrence of M2 macrophages (MMP9/CCL13:R=0.54, p=0.01; MMP9/CD206:R=0.16, p=0.49; MMP14/CCL13:R=0.79, p<0.001; MMP14/CD206:R=0.49, p=0.03). Likewise ADAM10 and 17 showed a correlation (R=0.87, p<0.001) with linkage to M1 macrophage marker CXCL10 (A10/CXCL10:R=0.65, p<0.01; A17/CXCL10:R=0.53, p=0.02). In contrast, ADAM8 showed no clear association with one macrophage subtype and no effect on survival. Although not statistically significant, pearson correlation revealed trends, that ADAM10 and 17 have a positive effect on survival (A10:R=0.26, p=0.26; A17:R=0.16, p=0.51), whereas MMP9 and 14 were linked to a worse patient outcome (MMP9:R=-0.11, p=0.64; MMP14:R=-0.11, p=0.63).

Conclusion: The grim prognosis for GBM patients can be attributed to the occurrence of tumor-associated macrophages in the microenvironment. We showed that macrophages, depending on their polarization, secrete distinct metalloproteases, which might have direct roles for the invasive phenotype of GBM, making them therapeutically exploitable.