Quantitation of regional distribution of antibodies in rat brain following systemic and intra-CNS administration

Antibody therapy has demonstrated great potential for treating central nervous system (CNS) disorders. Since therapeutic efficacy relies on sufficient exposure in specific brain regions, quantitative understanding of antibody distribution within the brain is crucial. Additionally, insights into antibody brain distribution help elucidate how pathological antibodies accumulate during encephalitis. Accordingly, this study investigated the regional distribution of a non-target-binding antibody (trastuzumab) and a brain-target-binding antibody (anti-NMDAR1) following systemic and intra-CNS administration in rats. After systemic administration, both antibodies showed similar distribution across brain regions, with the olfactory bulb exhibiting significantly higher concentrations. Other regions had comparable exposure, with the striatum or hippocampus showing the lowest exposure. Intra-CSF administration resulted in similar distribution patterns but achieved significantly higher concentrations than systemic administration. In contrast, intra-striatal administration led to diverse distribution, with the highest concentrations near the injection site. Calculations based on striatum and interstitial fluid (ISF) concentrations indicated antibody accumulation in the perivascular space after intra-CNS administration. Target binding influenced distribution primarily after intra-CSF administration, where anti-NMDAR1 showed lower ISF concentrations early and reduced CSF concentrations later. These findings provide valuable quantitative insights for optimizing brain-targeted antibody therapies and understanding pathological antibody distribution in CNS disorders.