A new weapon that strengthens drug delivery to the brain

Cell growth and repair are stimulated
by biomolecules such as cytokines and growth factors.
Unfortunately, delivering enough concentrations of these molecules to the brain to treat neurological disorders such as Alzheimer's disease is a challenge, as they either clear from the blood quickly or do not penetrate nerve tissue
efficiently 。 The research team, led by Kunio Matsumoto and Katsuya Sakai of Kanazawa University, in collaboration with Junichi Takagi, Osaka University and Hiroaki Suga of the University of Tokyo, has now used a technique called "socketing" to design molecules that replicate growth factors so that they remain in the body longer and penetrate the brain
.

The team synthesized a molecular entity containing two components: a macrocyclic peptide (called Fc) in which the antibody fragment is inserted (Figure 1a).

Macrocyclic peptides are truncated proteins that can be engineered to resemble growth factors
.
Using lasso grafting, a method previously developed by the researchers, selected peptides are inserted into
the loop found on Fc.
Lasso grafting now ensures that macrocyclic peptides are easily exposed while maintaining the structural integrity and functional integrity
of the peptide and Fc.
FC is used for this purpose because it stays in the body long enough to easily add the functionality
of the chosen Fab.

Using this process, design molecules that replicate hepatocyte growth factor (HGF) were created for the first time
.
HGF binds to a docking protein on the cell surface called Met, which initiates signals for cell growth and survival
.
Therefore, aMD4 and aMD5, two macrocyclic peptides, which can also bind to Met, were discovered
for the first time.
They are then grafted to different positions on Fc until the optimal insertion position
is found.
When in contact with cells, Fc (aMD4) and Fc (aMD5) do lock onto Met receptors and initiate cell signaling similar to HGF (Figure 1b).

Next, the lifespan
of Fc (aMD4) was studied compared to Fc and HGF alone.
When mice were injected, the concentration of HGF dropped significantly after one hour, while Fc(aMD4) persisted at a level sufficient to activate Met for up to 200 h
.
Markers of cell replication were also active
in these mice.
Therefore, Fc (aMD4) has longevity and biological activity
.
The final step is to determine the penetration
of these design molecules into the brain.
To do this, aMD4 is inserted into the Fc of an antitransferrin receptor (TfR) antibody that accumulates in the mouse brain after peripheral administration (Figure 1c).

In fact, TfR (aMD4) exhibits higher accumulation and retention
in mouse brain tissue compared to Fc (aMD4) alone.

This study describes a novel strategy to induce the effects of growth factors and cytokines that enhance retention
in brain tissue.
In addition, depending on the macrocyclic peptide and antibody selected, this technique can be used to mimic multiple growth factors
.
"As a result, lasso transplantation enables the design of protein therapies with ideal physicochemical stability and controllable pharmacokinetics, as well as rapid engineering
of antibodies with multiple functions," the researchers said.

Macrocyclic peptides are short fragments
of proteins.
Their cyclic structure facilitates strong binding
to proteins of interest.
Macrocyclic peptides are being studied in drug development because advanced techniques, such as in vitro displays, can now easily discover that peptides can bind to desired targets
.
The lasso grafting method developed by the researchers also conveniently binds macrocyclic peptides into protein scaffolds to generate multifunctional proteins
.