| Abstract | The blood-brain barrier (BBB) is a formidable obstacle for brain delivery of therapeutic antibodies. However, antibodies against the transferrin receptor (TfR), enriched in brain endothelial cells, have been developed as delivery carriers of therapeutic cargos into the brain via a receptor-mediated transcytosis pathway. In vitro and in vivo studies demonstrated that either a low-affinity or mono-valent binding of these antibodies to the TfR improves their release on the abluminal side of the BBB and target engagement in brain parenchyma. However, these studies have been performed with mouse-selective TfR antibodies that recognize different TfR epitopes and have varied binding characteristics. In this study, we evaluated serum pharmacokinetics, brain and CSF exposure of the rat TfR-binding antibody OX26 affinity variants, having Kds of 5 nM, 76 nM, 108 nM and 174 nM; all binding the same epitope in bi-valent format. Pharmacodynamic responses were tested in Hargreaves chronic pain model after conjugation of OX26 affinity variants with the analgesic and anti-epileptic peptide, galanin. OX26 variants with affinities of 76 nM and 108 nM showed enhanced brain and CSF exposure and higher potency in Hargreaves model, compared to a 5 nM affinity variant; lowering affinity to 174 nM resulted in prolonged serum pharmacokinetics, but reduced brain and CSF exposure. The study demonstrates that binding affinity optimization of TfR-binding antibodies could improve their brain and CSF exposure even in the absence of mono-valent TfR engagement. |
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