The Fast Track to Discovery and Engineering of Antibody Drug Candidates

15/06/2021 - 6 minutes

Antibody-based drugs hold great potential for treating cancers and inflammatory and autoimmune diseases. But clinical approvals are lagging. New technologies and workflows can deliver high-affinity, developable antibody-drug hits and a fast route to the clinic.

Antibodies are nature’s molecular recognition experts that bind foreign antigens and target them to trigger their destruction. The human body can produce over one trillion unique antibody sequences, enough to ensure that an antibody is available to bind any structure it may encounter.

When exposed to an antigen, such as proteins, peptides, or polysaccharides from bacteria or viruses, an antibody binds to it and the immune system generates more antibodies with an even higher affinity than the original.

Since the first therapeutic monoclonal antibody was approved in 1986, the interest in therapeutic antibodies has grown tremendously. Antibody-based drugs come in numerous formats: monoclonals, fragments, multi-specifics, antibody-drug conjugates, and cell-based therapies like CAR-T cell therapy. 

However, approvals of antibody therapies have lagged because their discovery and development are much more complicated than small-molecule drugs. Although technological advances make it possible to find and engineer highly specific and developable antibodies, it isn’t that simple. 

The rapid discovery of developable antibodies

antibody drug, antibody fragments, phage display, antibody engineering

Traditional methods of discovering new antibodies, including immunization followed by hybridoma generation and screening, are time-consuming and generate only a few hits. Plus, the dependence on animals adds ethical concerns.

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In vitro selection technologies, such as phage display library screening, offer an alternative. These libraries contain huge numbers of recombinant antibody fragments displayed on the surface of bacteriophage virions. An iterative selection process probes the library and generates a pool of fragment hits that bind the target with high specificity and affinity.

Not all antibody phage display libraries are created equal, however. The library size and the framework sequences that support the antigen binding site determine the quality and developability of the resulting hits.

For example, most commonly available antibody phage display libraries lack sufficient diversity to produce many good hits against more complex targets or rarer functional epitopes. Sub-optimal frameworks result in low expression or the improper folding of antibody fragments.

The solution: the SuperHuman antibody library

Charles River, Katherine Vousden, antibody drug, antibody fragments, phage display, antibody engineering
Katherine Vousden, Head of Large Molecule Research, Charles River

The US company Charles River Laboratories has developed a comprehensive antibody discovery and engineering platform that identifies antibodies with high affinity, cross-species coverage, and drug-like characteristics, allowing organizations to quickly determine their best antibody drug candidate and advance it to the clinic.

“The ability to screen computationally optimized, recombinant libraries for high-affinity antibodies and then improve their characteristics is a game-changer,” explained Katherine Vousden, Head of Large Molecule Research at Charles River. “Now, with our SuperHuman antibody library, we can fully realize the power of these exquisite molecules for clinical applications.”

The SuperHuman antibody phage display library is many orders of magnitude larger than other libraries and includes 76 billion sequence-unique, single-chain antibody fragments. 

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“The size, scope, and depth of the sequence diversity of our SuperHuman antibody library make it possible to isolate hundreds of antibody fragments for the vast majority of targets,” explained Vousden. “This just isn’t possible with other libraries.”

The in vitro-based screening process enables unique isolation approaches, such as specific steps to weed out antibodies that cannot fold properly. The SuperHuman antibody library can be screened with complex target types, such as toxins, peptides, haptens, and multi-membrane-spanning proteins.

And, because the hits are antibody fragments, it is optimal for therapeutic formats like antibody fragments or CAR-T constructs that don’t require the complete antibody.

Optimizing hits into fully developable antibody drug candidates

Lorraine Thompson, Charles River, antibody drug, antibody fragments, phage display, antibody engineering
Lorraine Thompson, Principal Scientist, Charles River

Regardless of how an antibody therapy hit is discovered, Charles River’s Tumbler antibody engineering service can optimize it into a lead drug candidate. This workflow involves creating new phage display libraries that contain a high diversity of fragments similar to the antibody hit and then screening these libraries to identify fragments with characteristics that are superior to the original. 

For example, the antibody’s affinity to the target can be increased to reduce the required dosage and potential side effects. Or, the ability of the antibody to recognize targets from other species can be altered: the use of human antibodies for studies in mice requires adding mouse cross-reactivity, while antibodies obtained via immunization of mice or rabbits must be humanized for therapeutic use in humans.

“Many antibodies fail in the clinic because they aren’t efficacious enough, but around 20% fail because they’re just not developable as therapeutics,” said Lorraine Thompson, Principal Scientist at Charles River. 

Characteristics that interfere with the antibody’s developability or manufacturability can be solved. For example, reducing the antibody’s affinity to bind immune cells can prevent immune reactions against the antibody drug. Physicochemical characteristics can be optimized to increase the antibody’s stability and prevent aggregation of the antibody therapy in the body. 

Full-service screening and engineering to find suitable antibody fragments

Charles River’s full-service antibody discovery and engineering workflow offers a fast route to the clinic. The screening of the SuperHuman antibody library identifies antibody fragments that bind the antigen of interest. 

For historically challenging drug targets, such as G-protein coupled receptors and ion channels, deep sequencing and analysis of enriched clones using the proprietary Abgenesis software can be incorporated. 

The antibody fragments can then be optimized as needed via the Tumbler antibody engineering workflow and additional studies carried out. The binding kinetics, the target binding site, the ability to bind to cells of interest, and other characteristics set apart the most promising antibody fragments. 

The top fifty antibody fragment candidates are then converted into their therapeutic modality and handed over to the client. Alternatively, they can be progressed through Charles River’s integrated drug discovery workflow, which provides additional formulation and pharmacology studies, regulatory safety support, and biologics testing. 

“Our scientists know how to tailor this iterative process to the client’s needs and make sure that the antibodies we pull out have the properties needed to bring the drug candidate of interest to fruition,” added Vousden. “This expertise is the key to our platform’s success and makes it difficult to replicate.” 

Discover Charles River’s full-service antibody discovery and engineering platform.


Images via Shutterstock.com

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