Peptide Inhibitors Advance Cancer Immunotherapy by Bridging Antibody and Small-Molecule Gaps

Conventional cancer immunotherapy, particularly immune checkpoint blockade (ICB), has revolutionized treatment but faces significant limitations with monoclonal antibody (mAb) therapeutics. These include high molecular weight, complex synthesis, high cost, and potential immunogenicity, which restrict tissue penetration and broad applicability. A critical gap exists for agents that combine the high specificity of antibodies with the favorable pharmacokinetic properties of small molecules. Peptide inhibitors are being explored as a viable solution to overcome these therapeutic bottlenecks, offering a unique blend of attributes that could lead to more effective and accessible treatments.

This review systematically outlines recent advances in peptide-based immune checkpoint inhibitors, analyzing their potential to overcome the inherent limitations of conventional antibody therapeutics. It examines the evolution of research in this field, highlighting a significant shift from traditional empirical screening methods to more intelligent precision design strategies. The review details various approaches, including rational design based on hotspot amino acids, the integration of AI-assisted drug discovery platforms, and the development of advanced delivery systems. The primary aim is to provide a comprehensive theoretical foundation for the rational design and successful clinical translation of this emerging class of therapeutics, covering optimization of activity, stability, and targeting properties.

Peptide inhibitors demonstrate a compelling combination of attributes, bridging the gap between large monoclonal antibodies and small-molecule drugs. They possess a low molecular weight, are easy to synthesize, offer cost-effectiveness, and exhibit minimal immunogenicity, making them attractive alternatives to current immune checkpoint blockade agents. Their high specificity, akin to antibodies, is coupled with superior tissue penetration, a characteristic of small molecules, which is crucial for reaching tumor microenvironments effectively. The field is rapidly advancing, moving beyond empirical screening towards sophisticated precision design. This includes rational design focusing on key amino acid hotspots, leveraging AI-assisted drug discovery to identify novel candidates, and developing advanced delivery systems to enhance metabolic stability and oral bioavailability. These innovations are critical for optimizing the therapeutic activity, stability, and targeted delivery of peptide inhibitors. This strategic shift is positioning peptides as a key component for overcoming existing therapeutic bottlenecks. > Peptide inhibitors combine the high specificity of antibodies with the favorable tissue penetration of small molecules, representing a key direction for next-generation cancer immunotherapies.