Brain pharmacokinetics of anti-transferrin receptor antibody affinity variants in rats determined using microdialysis

Abstract

Receptor-mediated transcytosis (RMT) is used to enhance the delivery of monoclonal antibodies (mAb) into the central nervous system (CNS). While the binding to endogenous receptors on the brain capillary endothelial cells (BCECs) may facilitate the uptake of mAbs in the brain, a strong affinity for the receptor may hinder the efficiency of transcytosis. To quantitatively investigate the effect of binding affinity on the pharmacokinetics (PK) of anti-transferrin receptor (TfR) mAbs in different regions of the rat brain, we conducted a microdialysis study to directly measure the concentration of free mAbs at different sites of interest. Our results confirmed that bivalent anti-TfR mAb with an optimal dissociation constant (K D) value (76 nM) among four affinity variants can have up to 10-fold higher transcytosed free mAb exposure in the brain interstitial fluid (bISF) compared to lower and higher affinity mAbs (5 and 174 nM). This bell-shaped relationship between K D values and the increased brain exposure of mAbs was also visible when using whole-brain PK data. However, we found that mAb concentrations in postvascular brain supernatant (obtained after capillary depletion) were almost always higher than the concentrations measured in bISF using microdialysis. We also observed that the increase in mAb area under the concentration curve in CSF compartments was less significant, which highlights the challenge in using CSF measurement as a surrogate for estimating the efficiency of RMT delivery. Our results also suggest that the determination of mAb concentrations in the brain using microdialysis may be necessary to accurately measure the PK of CNS-targeted antibodies at the site-of-actions in the brain.

Brain Disposition of Antibody-Based Therapeutics: Dogma, Approaches and Perspectives

“…In addition to classical ADME studies, generation of in silico physiologically based pharmacokinetic (PBPK) models by incorporating PKPD data and safety profiles as a tool for the treatment of CNS diseases has attracted great interest from pharmaceutical scientists and are likely to be crucial to the development of novel antibody-based therapeutics [ 28 , 29 , 108 , 109 , 110 , 111 ]. Further, the high-throughput and low-cost nature of these models permit a more streamlined drug development process in which the identification of antibody structural optimization can be guided based on a parallel investigation of CNS uptake and safety, along with activity [ 112 ].…”

“…This is mainly due to the lack of availability until recently of large molecular weight cutoff (MWCO) probes and the need for a complicated push–pull system to perform microdialysis with large pore probes [ 27 ]. Although the push–pull microdialysis procedure for antibodies is challenging and requires extensive training, recent studies have shown that it can provide direct in vivo measurement of free antibody concentration in selected regions of the brain in freely moving animals [ 28 , 29 ]. This technique can avoid the detection of bound antibodies to the brain capillary endothelial cells and the neurons, and readouts of free antibody concentration in the brain interstitial ISF tend to better represent the required therapeutic concentration at the site-of-action in the brain.…”

Modeling Pharmacokinetics and Pharmacodynamics of Therapeutic Antibodies: Progress, Challenges, and Future Directions

“…RMT-based antibody delivery has gained momentum as a viable method to treat central nervous system (CNS) disorders [78,[165][166][167][168]. Most of our RMT-based antibody delivery experience was gained from anti-TfR antibodies, which significantly increased antibody brain uptakes compared to the conventional antibodies [78,169]. There is a tradeoff between antibody affinity to TfR and RMT efficiency.…”

“…A very-high anti-TfR1 affinity would alter the TfR trafficking and make antibodies trapped in endosomes, reducing RMT efficiency. A bell-shaped relationship between TfR affinity and antibody brain exposure has been well documented [78,169]. Yu et al developed a series of bsAbs to target TfR and beta-secretase 1 (BACE1) with different affinities to TfR [78].…”

Kinetics of Blood–Brain Barrier Transport of Monoclonal Antibodies Targeting the Insulin Receptor and the Transferrin Receptor

“…High affinity TfRMAbs have a dissociation constant (K D ) of binding to the TfR ranging from 0.1 to 3 nM [21][22][23][24][25][26][27][28]. Moderate-affinity TfRMAbs have a KD of binding to the TfR ranging from 14 to 76 nM [26,27,[29][30][31][32]. Low-affinity TfRMAbs have a KD of binding to the TfR ranging from 111 to 300 nM [6,20,33,34].…”