Discovery of low-molecular weight anti-PD-L1 peptides for cancer immunotherapy

Abstract

BackgroundImmunotherapy using checkpoint inhibitors, especially PD-1/PD-L1 inhibitors, has now evolved into the most promising therapy for cancer patients. However, most of these inhibitors are monoclonal antibodies, and their large size may limit their tumor penetration, leading to suboptimal efficacy. As a result, there has been a growing interest in developing low-molecular-weight checkpoint inhibitors.MethodsWe developed a novel biopanning strategy to discover small peptide-based anti-PD-L1 inhibitors. The affinity and specificity of the peptides to PD-L1 were examined using various assays. Three-dimensional (3D) spheroid penetration study was performed to determine the tumor penetration capability of the peptides. Anti-tumor activity of the peptides was evaluated in mice bearing CT26 tumor cells.ResultsWe discover several anti-PD-L1 peptide inhibitors to block PD-1/PD-L1 interaction. The peptides exhibit high affinity and specificity to human PD-L1 protein as well as PD-L1-overexpressing human cancer cells MDA-MB-231 and DU-145. Molecular docking studies indicate that the peptide CLP002 specifically binds to PD-L1 at the residues where PD-L1 interacts with PD-1. The peptide also blocks the CD80/PD-L1 interaction, which may further enhance the immune response of tumor-infiltrating T cells. Compared to antibody, the peptide CLP002 exhibits better tumor penetration in a 3D tumor spheroid model. The peptide CLP002 restores proliferation and prevents apoptosis of T cells that are co-cultured with cancer cells. The peptide CLP002 also inhibits tumor growth and increases survival of CT26 tumor-bearing mice.ConclusionsThis study demonstrated the feasibility of using phage display to discover small peptide-based checkpoint inhibitors. Our results also suggested that the anti-PD-L1 peptide represents a promising low-molecular-weight checkpoint inhibitor for cancer immunotherapy.Electronic supplementary materialThe online version of this article (10.1186/s40425-019-0705-y) contains supplementary material, which is available to authorized users.

Human and mouse PD-L1: similar molecular structure, but different druggability profiles

“…In other studies, two peptide-based PD-1/PD-L1 inhibitors were tested in syngeneic mouse models ( Liu et al., 2019 ; Sasikumar et al., 2019 ). In these studies, however, in vivo experiments were preceded by either the in vitro examination of m PD-1/ m PD-L1 blockade ( Liu et al., 2019 ) or the proliferation rescue and IFN-γ release assay on mouse splenocytes inhibited with the m PD-L1 protein ( Sasikumar et al., 2019 ). Still, the direct binding of the tested agents to the m PD-L1 protein was not confirmed.…”

The Molecular and Functional Characteristics of HLA-G and the Interaction with Its Receptors: Where to Intervene for Cancer Immunotherapy?

“…Since this approach is ambitious, it is also essential that alternative approaches are explored to block the interaction between HLA-G and its receptors. It is important to realize that antibody-based immune checkpoint inhibitors have disadvantages, including high costs, instability, immunogenicity and poor tumor penetration [ 99 , 100 , 101 ]. Due to these disadvantages, development of immune checkpoint inhibitors has been shifted to low-molecular-weight molecules, such as small molecules and peptides.…”

“…Currently, development of small-molecule inhibitors is mainly focused on targeting PD-1 and its ligand PD-L1, where multiple compounds are in development and one small-molecule is already licensed [ 101 ]. However, designing small-molecule drugs is challenging due to the large surface area where the binding between the receptor and ligand takes place, the need for well-defined binding pockets, and the highly hydrophobic interaction between many receptors and their ligands (including between PD-1/PD-L1, and HLA-G/ILT2/4) [ 99 , 100 , 102 ]. Another approach is to target the mRNA of the HLA-G receptor with RNA interference (RNAi).…”

Progress of new strategies on screening of targeting peptides and applications in tumor immunotherapy

“…面的数量. Cheng课题组 [41] 则利用一种新的生物淘选 方法筛选出了肽CLP002, 不仅可以阻断PD-1/PD-L1通 路, 还可以阻断CD80/PD-L1的相互作用, 进一步增强 免疫反应. Liu课题组 .…”