Antibody-free quantification of serum infliximab using LC-MS/MS

Infliximab (IFX) is the first biologic to be approved to treat inflammatory bowel disease (IBD). Serum IFX concentrations can be correlated with the clinical prognosis of IBD. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is an alternative to clinical immunoassays owing to its higher selectivity and sensitivity. An efficient antibody-free LC-MS/MS method was developed in this study to determine serum IFX levels. Methods Protein G-coated magnetic beads were used to capture IFX and the internal standard (cadonilimab [CADO]) in human serum. After enrichment, IFX and CADO were digested using trypsin, and signature peptides were selected for subsequent LC-MS/MS analysis. The results were compared with those from the corresponding immunoassay. Results The selected peptides had good specificity, and the total precision was within 10.5 %. The accuracy was between 92.8 % and 97.6 % in the linear range of 0.5-100 mg/L. The results from the sample assay were in agreement with those from the immunoassay. Conclusion Determination of IFX using LC-MS/MS is more sensitive and robust than other analytical methods. Therefore, the method reported in this study shows potential for use in therapeutical drug monitoring and developing individualized treatment modalities.