New thiazole-biaryls as small molecule immunomodulators (SMIs) targeting PD-1/PD-L1 axis.

Area of Science:

• Immunology and Cancer Research
• Medicinal Chemistry
• Drug Discovery

Background:

• Immune checkpoint inhibitors (ICIs) targeting the PD-1/PD-L1 axis have transformed cancer treatment.
• Monoclonal antibody (mAb)-based ICIs face challenges including high costs, poor bioavailability, limited tumor penetration, and adverse effects.
• There is a need for alternative therapeutic strategies to overcome the limitations of current ICIs.

Purpose of the Study:

• To design, synthesize, and evaluate novel small molecules targeting the PD-1/PD-L1 interface.
• To identify potent small molecule inhibitors of PD-1/PD-L1 interaction with improved therapeutic potential.
• To assess the efficacy of these small molecules in restoring T-cell function and mediating anti-tumor activity.

Main Methods:

• Synthesis and characterization of thiazole-biphenyl-containing small molecules.
• In vitro assays including cell-based PD-1/PD-L1 blockade, isothermal titration calorimetry (ITC), and competitive ELISA to assess binding and inhibition.
• Co-culture cytokine induction assays and T-cell cytotoxicity assays to evaluate immunomodulatory effects and anti-tumor activity.
• Structure-based molecular simulations to elucidate binding interactions.

Main Results:

• Compounds 17t and 17h were identified as potent PD-1/PD-L1 inhibitors, with 17h showing stronger binding affinity (Kd = 1.43 μM) and potency (EC50 = 6.06 μM).
• These small molecules restored T-cell signaling and rescued T-cell exhaustion, demonstrated by the upregulation of pro-inflammatory cytokines (IFN-γ, IL-1α, IL-1β) and cytolytic proteins (perforin).
• 17t and 17h enhanced T-cell-mediated cancer cell lysis without intrinsic cytotoxicity, indicating selective immunomodulatory effects.
• Molecular simulations revealed key interactions, including π-π stacking with Y56 and hydrogen bonding with Y123 and I116 residues of PD-L1.

Conclusions:

• Novel thiazole-biphenyl-containing small molecules effectively inhibit the PD-1/PD-L1 interaction.
• These compounds demonstrate potential as orally bioavailable alternatives to mAb-based ICIs, with selective immunomodulatory and anti-tumor effects.
• Compounds 17t and 17h represent promising candidates for further development as cancer immunotherapies.