A Single Domain Shark Antibody Targeting the Transferrin Receptor 1 Delivers a TrkB Agonist Antibody to the Brain and Provides Full Neuroprotection in a Mouse Model of Parkinson’s Disease

Abstract

Single domain shark antibodies that bind to the transferrin receptor 1 (TfR1) on brain endothelial cells have been used to shuttle antibodies and other cargos across the blood brain barrier (BBB) to the brain. For these studies the TXB4 brain shuttle was fused to a TrkB neurotrophin receptor agonist antibody. The TXB4-TrkB fusion retained potent agonist activity at its cognate receptor and after systemic administration showed a 12-fold increase in brain levels over the unmodified antibody. Only the TXB4-TrkB antibody fusion was detected within the brain and localized to TrkB positive cells in the cortex and tyrosine hydroxylase (TH) positive dopaminergic neurons in the substantia nigra pars compacta (SNc), where it was associated with activated ERK1/2 signaling. When tested in the 6-hydroxydopamine (6-OHDA) mouse model of Parkinson’s disease (PD), TXB4-TrkB, but not the unmodified antibody, completely prevented the 6-OHDA induced death of TH positive neurons in the SNc. In conclusion, the fusion of the TXB4 brain shuttle allows a TrkB agonist antibody to reach neuroprotective concentrations in the brain parenchyma following systemic administration.

Designing receptor agonists with enhanced pharmacokinetics by grafting macrocyclic peptides into fragment crystallizable regions

“…As a demonstration of this, we generated BBB-permeable agonists by lasso grafting an anti-TfR antibody, thereby leveraging an established BBB-permeation technique [8][9][10] . At present, there are several efforts in developing anti-TfR Fab fusion antibodies with blocking properties, but only few that attempt to develop agonist antibodies 51 . Lasso-grafting could be used to design agonist BBB-permeating antibodies, in addition to antagonistic ones.…”

Advanced Blood–Brain Barrier Drug Delivery

“…The peptide or MAb acts as a molecular Trojan horse to ferry the biologic agent across the BBB via RMT on the endogenous peptide receptor at the brain endothelium. This Special Issue includes seven articles that describe the use of MAb-based Trojan horses targeting the IR, TfR1, IGF1R, or an orphan receptor [ 2 , 3 , 4 , 5 , 6 , 7 , 8 ], and one article on the use of peptides as a BBB Trojan horse [ 9 ].…”

“…The two sources of sdAbs are sharks, where the shark VH is designated as a variable new antigen receptor (VNAR) antibody, and camelids (e.g., llama), where the camelid VH is designated a VHH. In this Special Issue, the study of Clarke et al [ 6 ] describe the genetic engineering of a BSA comprising a therapeutic antibody and a shark VNAR. Yogi et al [ 7 ] describe the genetic engineering of a fusion protein derived from a camelid VHH and the neuroactive peptide, neurotensin.…”

“…Clarke et al [ 6 ] describe the genetic fusion of the 29D7 TrkB agonist antibody and a single-domain shark VNAR antibody against the TfR1, and designated TXB4. The TXB4-TrkB BSA retained high-affinity binding (low nM KD) to both the transporter target, the TfR1, and to the therapeutic target, TrkB [ 6 ]. The therapeutic efficacy of the TXB4-TrkB BSA was assessed in a murine 6-hydroxydopamine model of PD.…”

“…This dose of toxin in the mouse produces a partial lesion, and the number of cells in the substantia nigra immunoreactive with an antibody against tyrosine hydroxylase (TH) was reduced by 27% on the lesioned side compared to the non-lesioned side in the PBS treated mice. However, there was only a 3% reduction in striatal TH on the lesioned side, relative to the contralateral or non-lesioned side, in the PD mice treated with the TXB4-TrkB BSA [ 6 ]. Since the BSA was administered 24 h before neurotoxin injection, future work can examine the neuroprotective effects of delayed treatment with the TxB4-TrkB fusion protein following toxin administration.…”