Mechanistic Insights into the Role of IGFBP-2 in Glioblastoma

Abstract

Insulin-like Growth Factor Binding Proteins (IGFBPs 1-6) regulate the half-life and bioavailability of Insulin-like Growth Factors (IGFs). They play important roles in embryonic development, postnatal growth, and disease conditions such as cancer. Beyond IGF regulation, IGFBPs exhibit diverse functions, acting as either tumor suppressors or promoters depending on the physiological context.

IGFBP-2 has been established as a tumor promoter and is upregulated in several cancers, including breast, ovarian, prostate cancer, and glioblastoma (GBM). In vitro and in vivo studies have demonstrated its role in tumor cell proliferation, migration, invasion, and chemoresistance. Elevated plasma and tissue levels of IGFBP-2 are associated with poor clinical outcomes, including therapy resistance, relapse, and reduced survival.

Objectives To study the mechanism of IGFBP-2 mediated regulation of -catenin signaling in glioma cells and its prognostic significance in GBM tissues.

To isolate and characterize a human single-chain variable fragment (scFv) against IGFBP-2 as a potential inhibitor of its pro-tumorigenic functions.

Experimental Findings Stable IGFBP-2 knockdown U251 cell line and IGFBP-2 overexpressing LN229 and U87 cell lines were established.

IGFBP-2 modulation did not alter proliferation rates but significantly affected migration and invasion.

Knockdown reduced intracellular -catenin levels, while overexpression increased -catenin, indicating IGFBP-2 regulates -catenin.

This regulation was not due to transcriptional changes or canonical Wnt ligands (Wnt1, Wnt2, Wnt3a).

GSK3 , a negative regulator of -catenin, was inactivated via phosphorylation at Ser9 in IGFBP-2 overexpressing cells. Knockdown reversed this effect.

Mechanism: IGFBP-2 binds to integrins, activating FAK, which in turn inactivates GSK3 , stabilizing -catenin.

Clinical Relevance Expression of IGFBP-2 and -catenin was analyzed in tumor tissues of 112 GBM patients.

Co-expression strongly correlated with poor prognosis, highlighting clinical relevance of IGFBP-2/ -catenin association.

The C-terminal domain of IGFBP-2 alone was sufficient to regulate -catenin and other IGFBP-2 mediated functions, underscoring its importance as a tumor-promoting region.

Development of IGFBP-2 Inhibitor A human scFv library was screened using phage display.

One scFv, B7J, bound both full-length IGFBP-2 and its C-terminal domain.

B7J inhibited IGFBP-2-cell surface interactions and downstream signaling pathways (ERK, FAK, GSK3 / -catenin).

It neutralized IGFBP-2 transcriptional targets such as MMP2 and CD24, reduced matrix metalloprotease activity, and abrogated IGFBP-2-induced migration and invasion.

Due to their small size, scFvs offer better tumor penetration and retention compared to full-length antibodies, making B7J a promising therapeutic strategy for GBM.