Targeting Nuclear NOTCH2 by Gliotoxin Recovers a Tumor-Suppressor NOTCH3 Activity in CLL

Area of Science:

• Oncology
• Molecular Biology
• Immunology

Background:

• NOTCH signaling is a key pathway in cancer, including chronic lymphocytic leukemia (CLL).
• Targeting NOTCH signaling offers a potential therapeutic strategy for CLL.
• Different NOTCH receptors may have distinct roles in CLL pathogenesis and treatment response.

Purpose of the Study:

• To compare the anti-neoplastic effects of a NOTCH2 inhibitor (gliotoxin) and a pan-NOTCH inhibitor (RO4929097) in primary CLL cells.
• To elucidate the individual roles of NOTCH receptors in response to these inhibitors.
• To investigate the molecular mechanisms underlying their differential effects on CLL cells.

Main Methods:

• Primary CLL cells were treated with gliotoxin and RO4929097.
• Cell viability and apoptosis were assessed.
• Expression of NOTCH receptors, CD23, and downstream targets (NR4A1, NFκB, ATF3) was analyzed.
• Chromatin accessibility was evaluated using ATAC-seq.

Main Results:

• Gliotoxin induced rapid apoptosis in all CLL cases, while RO4929097 had a variable, delayed effect.
• Gliotoxin inhibited the NOTCH2/CD23 axis and upregulated the NOTCH3/NR4A1 axis.
• RO4929097 downregulated the NOTCH3/NR4A1 axis and reduced apoptosis.
• NOTCH3 and CD23 surface expression were mutually exclusive.
• ATAC-seq showed gliotoxin targeted canonical NOTCH signaling and altered accessibility at key regulatory motifs.

Conclusions:

• Gliotoxin effectively induces apoptosis in CLL cells by modulating NOTCH signaling pathways.
• Nuclear NOTCH2 inhibition, unlike pan-NOTCH inhibition, may restore tumor-suppressing NOTCH3 activity in CLL.
• Targeting NOTCH2 specifically could be a more beneficial therapeutic approach for CLL than broad NOTCH inhibition.