Development of an immune checkpoint specific protein binder for cancer therapy and diagnosis

Abstract

Strategies for cancer treatment have evolved from chemotherapy to targeted therapy. Recently, immunotherapy that activates patients’ own immune systems to fight against tumour cells is considered as the third generation of cancer therapy. One of the most promising targets for cancer immunotherapy is an immune checkpoint receptor, programmed cell death protein 1 (PD-1), and its ligand, programmed cell death 1 ligand 1 (PD-L1). Immune checkpoint inhibitors have drawn a consider attention as an effective cancer immunotherapy, and several monoclonal antibodies targeting PD-1 are clinically used for treatment of various cancers. PD-L1 is used as a biomarker to predict efficacy of immune checkpoint inhibitors. In this regard, we developed new protein binders for checkpoint blockade cancer immunotherapy and predictive biomarker detection. In chapter 1, we have focused on the development of a small-sized protein binder (MW: ~30 kDa) specific for human PD-1 which effectively inhibits the interaction between hPD-1 and its ligand, hPD-L1. The protein binder composed of leucine-rich repeat (LRR) modules was selected against hPD-1 by phage display, and its binding affinity was matured through modular evolution approach. The protein binder was shown to restore the T-cell activity and significantly suppress the tumour growth in tumour mouse model by inhibiting the interaction between PD-1 and PD-L1. In chapter 2, we developed a protein binder for detection of PD-L1 that is a predictive biomarker for checkpoint inhibitor immunotherapy. Through phage display and biopanning techniques, we selected a repebody exhibited high specificity and binding affinity for PD-L1. Through cell-based imaging assay, we confirmed that fluorescence dye-conjugated repebody could specifically detect PD-L1-expressing cells. In this study, by developing non-antibody scaffold proteins that bind to an immune checkpoint receptor and ligand, we have demonstrated the potential candidates for use in cancer immunotherapy and predictive biomarker diagnosis.