Blood-Brain Barrier (BBB)-Targeted Drug Delivery Key Targets & Research Tools

Schematic diagram of BBB structure

Schematic diagram of BBB structure

The blood–brain barrier (BBB), composed of tightly connected brain microvascular endothelial cells, the basement membrane, pericytes, and astrocytic end-feet, is an essential physiological structure sustaining central nervous system (CNS) homeostasis. Unlike the leaky capillaries in peripheral tissues, brain microvascular endothelial cells assemble dense tight junctions to build this selectively permeable barrier.
This specialized architecture effectively blocks most exogenous molecules from penetrating the brain parenchyma. In particular, it hinders the translocation of antibodies, enzymes, and other macromolecular biologics, only allowing a limited subset of small molecules, lipophilic compounds, and vital brain nutrients to traverse the barrier. As a result, many promising drug candidates that show efficacy in vitro or in peripheral tissues often exhibit markedly attenuated therapeutic potency within the CNS.
Therefore, leveraging endogenous BBB transport systems to safely and efficiently deliver therapeutics to intracerebral targets has become a major focus in CNS drug development.
The BBB: Not Simply a Barrier, but a Gateway for Drug Delivery
Rather than serving solely as a physical barrier, the BBB functions as a tightly regulated transport system. The brain relies on multiple receptor- and transporter-mediated pathways to import vital nutrients, providing natural routes that can be exploited for therapeutic delivery. Current BBB delivery strategies are primarily based on receptor-mediated transcytosis (RMT), carrier-mediated transport (CMT), and other auxiliary mechanisms.
RMT is the most established and widely adopted strategy for delivering large biologics across the BBB. Therapeutic molecules bind to receptors highly expressed on brain endothelial cells, followed by receptor-dependent internalization and transcytosis into brain parenchyma. This approach forms the basis of many CNS delivery platforms for antibodies and fusion proteins. Key RMT targets include the Transferrin receptor (TfR), CD98, Insulin receptor (INSR), and LRP1.
CMT mediates the trans-BBB permeation of nutrients such as glucose, amino acids, and certain ions. While inherently limited in accommodating large biomolecules, CMT can still be harnessed through structural mimicry or conjugation strategies. Among these, SLC2A1 (GLUT1) stands out as a prominent target for developing brain delivery approaches based on CMT.
Beyond RMT and CMT, some targets do not directly mediate BBB translocation; instead, they boost CNS drug exposure by modulating BBB integrity, the local pathological microenvironment, or drug clearance—CD147 serves as a representative example of this category.
Biological transport mechanisms for crossing the BBB

Biological transport mechanisms for crossing the BBB

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RMT-Related Targets & Research Tools
CMT- and Other-Mechanism-Related Targets & Research Tools

Transferrin R (TfR1/CD71) is highly expressed on brain capillary endothelial cells, specifically binding diferric transferrin to form complexes that enter cells through clathrin-mediated endocytosis. Endosomal acidification liberates iron, and empty TfR1 recycles back to the cell membrane for continuous transport. This natural recycling pathway enables efficient BBB transcytosis of therapeutics modified with TfR1 antibodies or ligands. Since TfR1 is far more abundant in brain endothelium than in peripheral tissues, it serves as a “natural gateway” for CNS drug delivery, combining strong selectivity with efficient trans-barrier translocation. As such, TfR1 has emerged as one of the most mature BBB-penetrating targets, with multiple anti-TfR antibody–based brain-targeted formulations now advancing through clinical trials.

Validation Data of TfR1 Proteins

Protein Validation Data 1

The purity of Human Transferrin R, His Tag (Cat. No. CD1-H5243)is more than 95% and the molecular weight of this protein is around 145-180 kDa verified by SEC-MALS.

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Protein Validation Data 2

Immobilized Human Transferrin R, His Tag (Cat. No. CD1-H5243) at 2 μg/mL (100 μL/well) can bind Biotinylated Human Transferrin Protein, His,Avitag (Cat. No. TRN-H82E3) with a linear range of 0.04-2 ng/mL (QC tested).

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Protein Validation Data 3

Captured Monoclonal Anti-CD71 Antibody, Mouse IgG1 (5B5) (Cat. No. CD1-MY2101) on CM5 chip via anti-mouse antibodies surface can bind Human Transferrin R, His Tag (Cat. No. CD1-H5243) with an affinity constant of 0.821 nM as determined in a SPR assay (Biacore 8K) (Routinely tested).

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Protein Validation Data 4

Trontinemab captured on Protein A Chip can bind Human Transferrin R, His Tag (Cat. No. CD1-H5243) with an affinity constant of 33.6 nM as determined in a SPR assay (Biacore 8K) (Routinely tested).

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Validation Data of TfR1 Functional Cell Lines

Functional Cell Lines Validation Data

Expression analysis of human Transferrin R on HEK293/Human Transferrin R Stable Cell Line by FACS. Cell surface staining was performed on HEK293/Human Transferrin R Stable Cell Line (Cat. No. CHEK-ATP089) or negative control cell using FITC-Labeled anti-Transferrin Receptor Antibody.

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Validation Data of TfR1 TR-FRET Kit

TR-FRET Kit Validation Data

In this TR-FRET assay, Human Transferrin Protein Europium-chelate is used as the Donor and FA Labeled Human Transferrin R is used as the Acceptor. An inhibition Assay was performed to evaluate the interaction between human transferrin and human transferrin R using Human Transferrin Protein resulting in a typical IC50 of 1.466 nM (QC tested).

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Resources

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References

1. Gong Z, Zhou D, Wu D, et al. Challenges and material innovations in drug delivery to central nervous system tumors[J]. Biomaterials, 2025, 319: 123180. https://doi.org/10.1016/j.biomaterials.2025.123180

2. Terstappen G C, Meyer A H, Bell R D, et al. Strategies for delivering therapeutics across the blood–brain barrier[J]. Nature Reviews Drug Discovery, 2021, 20(5): 362-383. https://doi.org/10.1038/s41573-021-00139-y

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