Improved Brain Antibody Delivery for Brain Diseases Treatment

The blood-brain barrier prevents antibodies from entering the brain. This limits the potential application of antibody therapies to brain diseases such as brain tumors.

Medical teams use more than 100 US Food and Drug Administration-approved therapeutic antibodies elsewhere in the body to treat malignancies, autoimmune, viral, and metabolic illnesses. Finding strategies to carry therapeutic antibodies across the blood-brain barrier — from the peripheral bloodstream into the central nervous system — could lead to effective treatment of brain diseases.

Researchers from the University of Alabama at Birmingham report in the journal Frontiers in Cell and Developmental Biology that the site-directed addition of an FDA-approved, biodegradable polymer at the hinge and near hinge regions of the therapeutic antibody trastuzumab effectively facilitated brain delivery of this human monoclonal IgG1 antibody. Trastuzumab is a cancer treatment that is used to treat breast cancer and other malignancies.

This innovative platform’s preliminary study comprised in vitro and mouse-model trials. The delivery mechanism needs to be improved and tested further, according to the researchers, but their straightforward technology converts antibody therapies to a brain-deliverable form while retaining the antibody’s medicinal efficacy.

“The concerns about brain-entry haunt the development of brain-disease-targeting antibody therapeutics, impeding the medical translations of laboratory-generated antibodies to clinical practices,” said Masakazu Kamata, Ph.D., study leader and associate professor in the UAB Department of Microbiology. “In this context, this simple methodology has great potential to serve as the platform to not only repurpose the current antibody therapeutics, but also encourage the design of novel antibodies, for the treatment of brain diseases.”

Poly 2-methacryloyloxyethyl phosphorylcholine, or PMPC, was employed as the biocompatible polymer, with chain lengths of 50, 100, or 200 monomers. The researchers had previously discovered that this non-immunogenic polymer, which the FDA has approved for use as a coating material for transplantable devices, could bind to two receptors on brain microvascular endothelial cells that comprise the blood-brain barrier, and that these cells could then transcytose the polymer across the blood-brain barrier. Transcytosis is a type of specialized transport in which extracellular cargo is carried into the cell, shuttled across the cytoplasm to the opposite side, and then released.

The UAB researchers were able to create thiol groups by cleaving four interchain disulfide bonds in the trastuzumab IgG1 hinge and near hinge regions. Each thiol group was subsequently conjugated to a PMPC chain, yielding trastuzumab molecules with one of three chain lengths, labeled as Tmab-PMPC50, Tmab-PMPC100, and Tmab-PMPC200.

Each of these modified antibodies retained trastuzumab-specific binding to cells expressing the HER2 antigen, trastuzumab’s target. Tmab-PMPC50 and Tmab-PMPC100 were both internalized into HER2-positive cells and triggered antibody-dependent cell death, which is how trastuzumab kills HER2+ breast cancer cells.

The researchers next demonstrated that trastuzumab PMPC conjugation increased blood-brain barrier penetration through epithelial cells on the blood-brain barrier via the transcytosis route. The translocatable Tmab-PMPC100 was the most effective in crossing the blood-brain barrier while retaining trastuzumab’s epitope recognition, or the antibody’s ability to bind to its antigen target.

Tmab-PMPC100 and Tmab-PMPC200 penetrated the brain five times better than native trastuzumab in a mouse model. In preliminary in vitro and mouse-model studies, the polymer-modified trastuzumab did not cause neurotoxicity, had no adverse effects in the liver, and did not damage the blood-brain barrier’s integrity.

“Those findings collectively indicate that PMPC conjugation achieves effective brain delivery of therapeutic antibodies, such as trastuzumab, without induction of adverse effects, at least in the liver, the blood-brain barrier or the brain,” Kamata stated in a press release.

Others have also looked into ways to transfer cargos like antibodies past the blood-brain barrier, according to the researchers.

The UAB researchers for the current study demonstrated that they could wrap various macromolecular cargos within PMPC shells, and these nanocapsules demonstrated prolonged blood circulation, reduced immunogenicity, and enhanced brain delivery in mice and non-human primates in previous work.

However, this system had flaws. The nanocapsules needed targeting ligands to bring them to their disease target and degradable crosslinkers to allow cargo release at that point. Unfortunately, disease-associated microenvironments frequently lack circumstances that can cause crosslinker breakdown.

Other researchers looking to breach the blood-brain barrier have looked into ligands derived from microorganisms and toxins, as well as endogenous proteins like lipoproteins. These have typically had unfavorable surface qualities, such as being highly immunogenic, hydrophobic, or charged. PMPC lacks these unwanted characteristics.

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