Quantification of the Therapeutic Antibody Ocrelizumab in Mouse Brain Interstitial Fluid by Cerebral Open Flow Microperfusion and Simultaneous Monitoring of the Blood Brain Barrier Integrity

Abstract

Abstract Background: Pharmacokinetic (PK) assessment of drugs in brain is especially challenging, as the blood-brain-barrier (BBB) impedes the access of substances to the brain. However, rising incidence of monoclonal antibodies as treatment option for diseases of the central nervous system makes continuous measurement of their brain PK profile with verifiably intact BBB increasingly relevant. Such measurements can be performed with continuous brain interstitial fluid (ISF) sampling techniques like e.g., cerebral open flow microperfusion (cOFM). Although cOFM has already provided antibody concentrations in brain ISF in a time-resolved manner, accurate time-resolved quantification of antibody in brain to record the PK profile requires continuous sampling over an extended period of time and knowledge on the BBB integrity for the respective study drug during the entire sampling period. We thus aimed to absolutely quantify the therapeutic antibody ocrelizumab (OCR) in mouse brain ISF over 96 hours, and to record its PK profile. OCR, with a target on human CD20+ B-cells, was selected as study drug. We also aimed to monitor the BBB integrity during the entire study duration using an endogenous antibody as tracer with similar molecular size as OCR. Methods: Direct and absolute OCR quantification was performed using cOFM combined with the quantification protocol Zero Flow Rate, and data were corrected with the cOFM probe´s in vivo relative recovery. For PK profile recording the cOFM samples were collected bi-hourly, and brain tissue and plasma at the end of the sampling period. BBB monitoring was performed simultaneously during the entire PK profile recording using the endogenous mIgG1. This study was performed in male C57Bl/6 mice. Results: We directly, absolutely quantified OCR, and reliably recorded its brain PK profile over 96 hours. BBB integrity was sustained during the entire study. Conclusions: Results demonstrated that cOFM is able to accurately, absolutely quantify OCR in brain ISF and to record its brain PK profile over a prolonged duration with verifiably intact BBB. Our data provide the basis for reliable PK assessment of therapeutic antibodies in brain, which is likely to promote the development of therapeutic monoclonal antibodies to treat neurological diseases.