Olaptesed pegol (NOX-A1), a pegylated Spiegelmer and chemokine CXCL12-neutralizing aptamer, inhibits CXCL12-CXCR4 axis (CXCL12, stromal cell-derived factor-1; CXCR4, C-X-C Motif Chemokine Receptor 4) responsible for tumor growth, angiogenesis, immune suppression and intercellular crosstalk within TME, in refractory GBM and recurrent GBM post-radiotherapy. Here, CXCR4 is linked to glioblastoma.