gms | German Medical Science

Objective: Anti-angiogenic therapy of glioblastoma (GBM) blocking vascular endothelial growth factor-A (VEGFA) often resulted in accelerated tumor-cell invasion and upregulation of alternative angiogenic pathways. Here, we studied the role of the proangiogenic receptor APLNR and its cognate ligand apelin (APLN) on VEGF-A / VEGFR2-centered GBM therapy.

Methods: Towards this aim we investigated expression-levels and localization of APLN / APLNR in anti-VEGFA treated mouse and human GBM samples using in situ hybridization and qPCR. For functional studies of APLN-signaling we performed orthotopic implantation of human patient-derived and mouse subtype-specific GBM stem cell cultures and employed genetic and pharmacological blockade for APLN / APLNR and VEGFA / VEGFR2-signaling in our in vivo and in vitro experiments.

Results: A direct relation of APLN and VEGF-A levels was observed in a preclinical study on anti-angiogenesis in GBM. Here we found that APLN was downregulated (as compared to controls) after VEGF-A blockade. A central role for APLN / APLNR in controlling GBM-vascularization was corroborated in a serial implantation model recapitulating the angiogenic switch of human GBM. APLN / APLNR are broadly expressed in human GBM and modulating APLN-levels (by knockdown or knockout) in orthotopic implantation models massively reduced GBM vascularization, while controls maintained APLN-dependent angiogenesis. However, reducing APLN expression levels resulted in strongly accelerated GBM cell-invasion. In stereotactic biopsies of GBM patients we detected APLNR-positive cells in the tumor infiltrative zone (lacking aberrant vascularization), pointing towards an additional role for APLNR in tumor cell dissemination. Importantly, application of an APLNR antagonist was able to block both tumor angiogenesis and GBM cell invasion (by 46%). Most interestingly, combined therapeutic blockage of both VEGFR2 and APLNR in mice synergistically improved survival by 65% significantly (while single treatments prolonged survival by 28%).

Conclusion: In summary, we show that APLN-APLNR signaling controls GBM neo-vascularization as well as GSC invasion and that both pathological features are blunted by APLNR-inhibition. In combination with VEGFR2-blockade APLNR-inhibition increased survival significantly indicating that combined anti-APLNR / anti-VEGFA therapy can improve the efficiency and reduce the side effects of bevacizumab-treatment in GBM.