MT1-MMP Expression Levels and Catalytic Functions Dictate LDL Receptor-Related Protein-1 Ligand Internalization Capacity in U87 Glioblastoma Cells

Modulations in cell surface receptor ectodomain proteolytic shedding significantly impact receptor function and the expression of cancer biomarkers. Therapeutic strategies have focused on exploiting the LDL receptor-related protein-1 (LRP-1)-mediated internalization of Angiopep-2 (An2), a brain-penetrating peptide that enables An2-drug conjugates to cross the blood-brain tumor barrier (BBTB).

Because LRP-1 is proteolytically shed from the cell surface through matrix metalloproteinase (MMP) activity, the balance between MMP expression and LRP-1-mediated An2 internalization remains unclear.

In this study, we observed that the expression of membrane type-1 (MT1)-MMP increased from grade 1 to grade 4 brain tumors, while LRP-1 expression decreased in an inverse manner. Pharmacological inhibition of MMPs using agents such as Ilomastat, Doxycycline, and Actinonin enhanced An2 internalization by up to 2.5-fold in a human grade IV-derived U87 glioblastoma cell model.

Transient siRNA-mediated silencing of MT1-MMP resulted in increased basal An2 cell surface binding and intracellular uptake, whereas overexpression of recombinant MT1-MMP reduced both cell surface LRP-1 expression and An2 internalization. Notably, adding Ilomastat to cells overexpressing recombinant MT1-MMP restored LRP-1 expression at the cell surface and An2 uptake to levels comparable to control cells.

Collectively, these findings suggest that MT1-MMP expression governs An2-mediated internalization by regulating cell surface LRP-1 functions. This evidence supports the preclinical evaluation of combined MMP inhibitor and An2-drug conjugate therapies to potentially enhance treatment outcomes for brain tumors exhibiting high MT1-MMP expression.