Development of a highly sensitive chemiluminescence immunoassay using a novel signal-enhanced detection system for quantitation of durvalumab, an immune-checkpoint inhibitor monoclonal antibody used for immunotherapy of lung cancer

Durvalumab (DUR) is a human monoclonal antibody used for the immunotherapy of lung cancer. It is a novel immune-checkpoint inhibitor, which blocks the programmed death 1 (PD-1) and programmed death-ligand 1 (PD-L1) proteins and works to promote the normal immune responses that attack the tumour cells. To support the pharmacokinetic (PK) studies, therapeutic drug monitoring (TDM) and refining the safety profile of DUR, an efficient assay is required, preferably immunoassay. This study describes, for the first time, the development of a highly sensitive chemiluminescence immunoassay (CLIA) for the quantitation of DUR in plasma samples with enhanced chemiluminescence detection system. The CLIA protocol was conducted in 96-microwell plates and involved the non-competitive binding reaction of DUR to its specific antigen (PD-L1 protein). The immune complex of DUR with PD-L1 formed onto the inner surface of the assay plate wells was quantified by a chemiluminescence (CL)-producing horseradish peroxidase (HRP) reaction. The reaction employed 4-(1,2,4-triazol-1-yl)phenol (TRP) as an efficient enhancer of the HRP-luminol-hydrogen peroxide (H2O2) CL reaction. The optimum protocol of the proposed CLIA was established, and its validation parameters were assessed as per the guidelines for the validation of immunoassays for bioanalysis. The working dynamic range of the assay was 10-800 pg mL-1 with a limit of detection (LOD) of 10.3 pg mL-1. The assay enables the accurate and precise quantitation of DUR in human plasma at a concentration as low as 30.8 pg mL-1. The CLIA protocol is simple and convenient; an analyst can analyse several hundreds of samples per working day. This high throughput property enables the processing of many samples in clinical settings. The proposed CLIA has a significant benefit in the quantitation of DUR in clinical settings for assessment of its PK, TDM and refining the safety profile.