Balancing brain exposure, pharmacokinetics and safety of transferrin receptor antibodies for delivery of neuro-therapeutics.

Progress in developing effective large-molecule therapies for neurological diseases is limited by exposure at the sites of action, beyond the blood-brain barrier (BBB). While transferrin receptor (TfR1)-mediated transport is gaining validation as a mechanism to deliver medicines of multiple modalities to the brain, there is much still to be learned about maximizing the potential of TfR1 targeting. We systematically vary for the first time affinity and valency of two anti‑TfR1 antibodies, which have distinct epitopes and pH sensitivities, to investigate their effects on cellular trafficking, biodistribution, safety, and pharmacokinetics. We establish how transcytosis and receptor degradation trend with affinity and connect these in-vitro functions to in-vivo behaviors in brain uptake and reticulocyte depletion. We identify unique anti-TfR1 antibody profiles for either short-term maximal or long-term sustained brain delivery and demonstrate the utility of these shuttles for different pharmacological applications. Our results show that bivalent anti-TfR1 antibodies can be equally effective in brain uptake as monovalent antibodies if engineered to have similar cell-surface TfR1 binding strength, with prolonged brain exposure and less severe adverse effects, but epitope, as well as affinity and valency, factors into selecting a shuttle with maximal performance. These results challenge the view that monovalent formats are inherently superior and instead establish that affinity, valency, and epitope can be tuned to select TfR1 shuttles optimized for different therapeutic needs.