The antibody-based cancer immunotherapies targeting the Programmed cell Death1-Programmed Cell Death Ligand 1 (PD1-PDL1) interaction have shown unprecedented clinical success again several types of cancer. Our present study aims to discover small molecule PD1-PDL1 inhibitors that may offer several advantages as compared to antibodies, such as higher oral bioavailability, lower cost, better tumor infiltration, and relatively shorter half-life that is especially helpful in controlling any potential adverse immune reactions.
We identified several small molecule inhibitors based on the available crystal structures of human PD1-PDL1 complex as well as apo forms of PD1 and PDL1. Specifically, we first carried out long molecular dynamics simulations to identify “druggable” binding pockets on the binding interfaces of PD1 and PDL1 proteins, followed by molecular docking and consensus-scoring of approved and experimental drugs into those pockets. The top virtually selected compounds were then tested in AlphaLISA and ELISA assays measuring inhibition of the PD1-PDL1 interaction, followed by functional cell-based assays.
Through integrated virtual and experimental screening protocols, we have identified several potent PD1-PDL1 inhibitors with remarkable activities in both the cell-free and cell-based assays. Notably, one of our top active molecules showed activity as comparable to that of the anti-PD1 antibody used as the positive control in these studies. This is remarkable considering the newly-discovered molecules have relatively low molecular weight and still are capable of inhibiting PD1-PDL1 protein-protein interaction with large binding interface of ∼1,970 Å2. Our results provide support for future investigation of these molecules in vivo.
In summary, we have been successful in identifying novel, non-peptide small molecule inhibitors of PD1-PDL1 interaction through rational design. Considering their remarkable activity and clinical status, they may present immediate clinical potential against cancers expressing PDL1. They may also prove to be ideal starting points for the design of more potent, selective drug-like inhibitors of PD1-PDL1 interaction.
Widener University, Chester, PA, USA.
W. W. Smith Charitable Trust.
All authors have declared no conflicts of interest.