Abstract
Glioblastoma (GBM) is an aggressive and rapidly progressing brain tumor with a poor prognosis, characterized by a median survival rate of 15 months. Current treatment options remain limited, highlighting the need for novel therapeutic approaches. Improving imaging techniques to better localize and characterize GBM is one such strategy. Chlorotoxin (Ctx), a 36-amino-acid residue polypeptide derived from Leiurus quinquestriatus scorpion venom, has shown selective binding to GBM cells, making it a promising candidate for diagnostic applications and improving tumor visualization. However, the molecular targets of Ctx are unclear, with Matrix Metalloproteinase-2 (MMP-2) and Neuropilin-1 (NRP-1) being the most studied candidates. Previous studies have identified the C-terminal region of Ctx as critical for inhibiting GBM cell migration. To explore this further, we designed C-terminal peptide fragments of Ctx with various disulfide bridge modifications, hypothesizing that they could more effectively inhibit U-87 MG migration than full-length Ctx. Wound-healing assay results revealed that P78 (Ctx residues 27–34) exhibited the strongest inhibition of U-87 MG migration compared to other peptides and full-length Ctx. To investigate the molecular targets of Ctx and its fragments, biophysical techniques were utilized such as nanoDifferential Scanning Fluorimetry (nanoDSF) and Surface Plasmon Resonance (SPR). These analyses revealed that Ctx and its C-terminal fragments exhibit weak binding to NRP-1 at high micromolar affinities.Additionally, an enzymatic inhibition assay showed that Ctx and its fragments do not inhibit MMP-2 catalytic activity. Furthermore, tetrapeptides were designed to assess their binding to NRP-1. All tetrapeptides displayed submicromolar
affinities for NRP-1, suggesting that the canonical CendR motif is not essential for NRP-1 binding. Overall, these findings highlight the potential of C-terminal Ctx fragments, particularly P78, as effective inhibitors of GBM cell migration. They
also provide new insights into the interactions of peptides with NRP-1, paving the way for further exploration of their therapeutic applications.