Targeting malignant B cells with an immunotoxin against ROR1

Area of Science:

• Oncology
• Immunology
• Molecular Biology

Background:

• Receptor tyrosine kinase-like orphan receptor 1 (ROR1) is selectively expressed on the surface of chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL) cells.
• This selective expression makes ROR1 a promising therapeutic target for monoclonal antibody (mAb)-based treatments.

Purpose of the Study:

• To develop and characterize novel ROR1-targeting agents, including monoclonal antibodies and immunotoxins, for potential therapeutic applications in B cell malignancies.

Main Methods:

• Generation of four mouse monoclonal antibodies (mAbs) against human ROR1 using hybridoma technology.
• Epitope mapping to identify N-terminal and C-terminal binding sites.
• Construction of a ROR1-targeting immunotoxin (BT-1) using recombinant DNA technology.
• Assessment of binding affinity, internalization, and in vitro cytotoxicity against ROR1-expressing and ROR1-negative cell lines.

Main Results:

• Four mAbs demonstrated specific binding to human ROR1, with distinct epitope specificities (N-terminal and C-terminal).
• The ROR1-immunotoxin BT-1 and the mAb 2A2-IgG selectively bound to primary CLL and MCL cells and cell lines.
• BT-1 exhibited potent, dose-dependent apoptosis induction in ROR1-expressing MCL cell lines (EC50 = 16 pM–16 nM) without affecting ROR1-negative cells.

Conclusions:

• ROR1-targeting agents, particularly immunotoxins like BT-1, show significant therapeutic potential.
• BT-1 demonstrates selective cytotoxicity against ROR1-expressing B cell malignancies, suggesting its utility as a targeted therapy for CLL, MCL, and potentially other cancers.