Tumor-Associated Microglia/Macrophages as a Predictor for Survival in Glioblastoma and Temozolomide-Induced Changes in CXCR2 Signaling with New Resistance Overcoming Strategy by Combination Therapy.

Tumor recurrence is the main challenge in glioblastoma (GBM) treatment. Gold standard therapy temozolomide (TMZ) is known to induce upregulation of IL8/CXCL2/CXCR2 signaling that promotes tumor progression and angiogenesis. Our aim was to verify the alterations on this signaling pathway in human GBM recurrence and to investigate the impact of TMZ in particular. Furthermore, a combi-therapy of TMZ and CXCR2 antagonization was established to assess the efficacy and tolerability. First, we analyzed 76 matched primary and recurrent GBM samples with regard to various histological aspects with a focus on the role of TMZ treatment and the assessment of predictors of overall survival (OS). Second, the combi-therapy with TMZ and CXCR2-antagonization was evaluated in a syngeneic mouse tumor model with in-depth immunohistological investigations and subsequent gene expression analyses. We observed a significantly decreased infiltration of tumor-associated microglia/macrophages (TAM) in recurrent tumors, while a high TAM infiltration in primary tumors was associated with a reduced OS. Additionally, more patients expressed IL8 in recurrent tumors and TMZ therapy maintained CXCL2 expression. In mice, enhanced anti-tumoral effects were observed after combi-therapy. In conclusion, high TAM infiltration predicts a survival disadvantage, supporting findings of the tumor-promoting phenotype of TAMs. Furthermore, the combination therapy seemed to be promising to overcome CXCR2-mediated resistance.

The CXCR2/CXCL2 signalling pathway - An alternative therapeutic approach in high-grade glioma.

OBJECTIVE: Besides VEGF, alternative signalling via CXCR2 and its ligands CXCL2/CXCL8 is a crucial part of angiogenesis in glioblastoma. Our aim was to understand the role of CXCR2 for glioma biology and elucidate the therapeutic potential of its specific inhibition. METHODS: GL261 glioma cells were implanted intracranially in syngeneic mice. The 14 or 7 days of local or systemic treatment with CXCR2-antagonist (SB225002) was initiated early on the day of tumour cell implantation or delayed after 14 days of tumour growth. Glioma volume was verified using MRI before and after treatment. Immunofluorescence staining was used to investigate tumour progression, angiogenesis and microglial behaviour. Furthermore, in vitro assays and gene expression analyses of glioma and endothelial cells were performed to validate inhibitor activity. RESULTS: CXCR2-blocking led to significantly reduced glioma volumes of around 50% after early and delayed local treatments. The treated tumours were comparable with controls regarding invasiveness, proliferation and apoptotic cell activity. Furthermore, no differences in CXCR2/CXCL2 expression were observed. However, immunostaining revealed reduction in vessel density and accumulation of microglia/macrophages, whereas interaction of these myeloid cells with tumour vessels was enhanced. In vitro analyses of the CXCR2-antagonist showed its direct impact on proliferation of glioma and endothelial cells if used at higher concentrations. In addition, expression of CXCR2/CXCL2 signalling genes was increased in both cell types by SB225002, but VEGF-relevant genes were unaffected. CONCLUSION: The CXCR2-antagonist inhibited glioma growth during tumour initiation and progression, whereas treatment was well-tolerated by the recipients. Thus, the CXCR2/CXCL2 signalling represents a promising therapeutic target in glioma.