Offsetting Low-Affinity Carbohydrate Binding with Covalency to Engage Sugar-Specific Proteins for Tumor-Immune...

Area of Science:

• Immunology
• Chemical Biology
• Cancer Therapeutics

Background:

• Carbohydrate-binding receptors are crucial for innate immunity, inflammation, and adaptive immune responses.
• Existing cancer immunotherapies utilize multivalent scaffolds to engage these receptors, but face challenges like complexity and off-target effects.
• Low-affinity carbohydrate-protein interactions (K_d ≈ 10^-3-10^-6 M) limit therapeutic applications.

Purpose of the Study:

• To develop small bifunctional molecules for cancer immunotherapy that engage low-affinity carbohydrate-binding receptors.
• To investigate if covalent engagement can overcome the limitations of weak binding in carbohydrate-protein interactions.
• To test the hypothesis that a large inactivation rate (k_inact) can compensate for a less favorable binding affinity (K_I).

Main Methods:

• Designed and synthesized small bifunctional chimeric molecules with a monovalent antibody-binding domain (ABD) and a tumor-binding domain (TBD).
• Incorporated optimized electrophiles (SuFEx or activated ester) for covalent protein engagement.
• Utilized a model system with rhamnose-specific antibodies to induce tumor-immune proximity and assess tumoricidal function.

Main Results:

• Synthetic chimeric molecules rapidly covalently engaged natural antirhamnose antibodies via a single low-affinity rhamnose monosaccharide ABD.
• Molecules with covalent engagement demonstrated significant tumoricidal function.
• Chimeric molecules lacking an electrophile, relying solely on noncovalent binding, completely lacked tumoricidal activity.

Conclusions:

• Covalency is a critical strategy for engaging low-affinity carbohydrate-specific proteins in cancer immunotherapy.
• Small bifunctional molecules can effectively induce tumor-immune proximity and tumoricidal function by coupling weak binding with covalent engagement.
• This approach overcomes limitations associated with larger, multivalent scaffolds and offers a promising avenue for novel cancer therapeutics.