Immunoproteasome β5i-Selective Dipeptidomimetic Inhibitors

Area of Science:

• Biochemistry
• Medicinal Chemistry
• Pharmacology

Background:

• N,C-capped dipeptides are known noncovalent proteasome inhibitors.
• Proteasomes, particularly the constitutive proteasome (β5c) and immunoproteasome (β5i), are critical cellular machinery.
• Targeting specific proteasome subtypes is a strategy for therapeutic intervention.

Purpose of the Study:

• To investigate the impact of incorporating a β-amino acid into N,C-capped dipeptides.
• To determine the selectivity of these modified dipeptides for human constitutive proteasome (β5c) versus human immunoproteasome (β5i).
• To explore the therapeutic potential of β5i-selective inhibitors for autoimmune and inflammatory diseases.

Main Methods:

• Synthesis of N,C-capped dipeptides containing a β-amino acid.
• In vitro assays to measure inhibitory potency against purified human β5c and β5i proteasome subunits.
• Structure-activity relationship (SAR) studies to understand molecular interactions.
• Assessment of T cell proliferation inhibition.

Main Results:

• Insertion of a β-amino acid significantly reduced inhibitory potency against β5c.
• Potent inhibitory activity against β5i was maintained, resulting in thousands-fold selectivity for β5i over β5c.
• Structure-activity relationship studies indicated differential tolerance of β5c and β5i to the β-amino acid modification.
• One compound demonstrated inhibition of human T cell proliferation in vitro.

Conclusions:

• Modified N,C-capped dipeptides with β-amino acids exhibit high selectivity for the immunoproteasome (β5i).
• These compounds may offer a therapeutic window for autoimmune and inflammatory diseases by sparing the constitutive proteasome (β5c).
• Reduced mechanism-based cytotoxicity compared to non-selective proteasome inhibitors is a potential advantage.