Background Tocilizumab(TCZ) is a humanized anti-human interleukin-6(IL-6) receptor monoclonal antibody. To establish the optimal dosage strategy prediction based on the PK/Biomarker relationship is one of the important tool during the drug development. The optimal dosage of tocilizumab (8mg/kg/4wk) was originally simulated using serum trough TCZ concentration and CRP relationship. Most of the monoclonal antibody drug development, serum concentration levels were determined conventional enzyme-linked immunosolvent assay (ELISA). Although ELISA were time consuming and labour intensive, we have evaluated the alternative technologies using quartz-crystal microbalance (QCM) biosensor system which is the novel and rapid quantitative method to monitor the serum TCZ concentration.
Methods For rapid and direct quantification of Tocilizumab in human plasma, we used QCM biosensor system that can be monitored a real-time binding amount of analyte without any troublesome steps such as enzyme amplification and washing plates. Concentrations of Tocilizumab were directly determined by analyzing binding kinetics of Tocilizumab to IL-6R-precoated sensor chip. In the validation step of QCM, reproducibility, repeatability and calibration range was demonstrated. Finally the serum tocilizumab concentration in patients with active rheumatoid arthritis under TCZ therapy, was compared between QCM and ELISA.
Results The lower quantification limit with the quantification range is between 3.25 to 100 ug/mL, and an intra-day standard deviation (SD) of 5.26-12.5% and an inter-day SD of 8.38% at 10 ug/mL in serum. The lower quantification level is 3 ug/mL which is three times lower sensitivity than conventional ELISA (LLOQ=1ug/mL).
Correlation between ELISA and QCM was demonstrated that the correlation coefficient showed r2=0.98 (n=15), and the deviation between two methods were within ±2 μg/mL within quantification range of this QCM.
Conclusions When the requirements of cost and running time are beyond the scope of conventional ELISA, this QCM is one of the solution to save these two points and is able to keep the equivalent accuracy and repeatability. From this study, we need to try to find the well-optimaized condition which focused on the equivalent level of lower quantification level.
Disclosure of Interest S. Ota: None Declared, T. Ozeki Employee of: ULVAC Inc, H. Hoshino Employee of: ULVAC Inc, K. Terao Employee of: Chugai Pharmaceutical Co.,Ltd
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