CR UK, AZ researchers pioneer new antibody maturation technique

Researchers at the Cancer Research UK-AstraZeneca Antibody Alliance Laboratory in Cambridge, UK, have developed a new technique able to generate an inhibitory, high-affinity antibody against Arginase 2 (ARG2), an enzyme implicated in major human diseases.

ARG2 targets and destroys L-arginine, an amino acid critical for immune cells to fight diseases such as cancer as well as infections.

The enzyme is over-expressed in various types of cancer, including pancreatic ductal adenocarcinoma, bowel cancer and acute myeloid leukaemia.

Excess ARG2 decimates the levels of L-arginine around tumours and so prevents immune cells from functioning properly, which creates an immunosuppressive local environment that allows tumours to grow.

Therefore, the enzyme is a target for inhibitory therapeutic antibodies that could help restore immune function against cancer cells, the researchers note.

Dr Maria Groves and her team at the Cancer Research UK-AstraZeneca Antibody Alliance Laboratory in Cambridge, in collaboration with the late Professor Cerundolo and his team at Oxford University, and Professor Mark Carr’s structural biology group at the University of Leicester, have generated a highly promising potential therapeutic antibody against ARG2.

The lead antibody, called C0021158, is the first product of the researchers’ innovative antibody affinity maturation approach and, according to the researchers, offers a full complement of desirable properties, such as high affinity binding and complete inhibition of ARG2 activity.

The innovative affinity maturation technique developed by the team differs from standard approaches, which have focused on exploring sequence diversity in only a few specific regions of antibodies, limiting the improvements that could be obtained in candidate therapeutics.

The new approach used to develop C0021158 allowed the researchers to identify antibodies with non-predictable combinations of amino acid sequence changes that generated a significantly-improved affinity and potency of inhibition against ARG2.

“Characterisation of C0021158 highlighted the resounding success of the researchers in generating a therapeutic candidate, which demonstrates complete and highly potent inhibition of ARG2 activity; in laboratory assays, the antibody restored the proliferation of immune cells that were suppressed by ARG2-driven arginine deficiency,” said CR UK.

“Protein crystallography performed at the University of Leicester provided key structural and molecular insights into the mechanism of antibody-mediated inhibition, revealing dramatic changes in antibody interaction with ARG2 resulting from affinity maturation. The inhibitory antibody binding induced dramatic changes in the structure of ARG2, resulting in conformation changes at the active site of the enzyme that prevent both ARG2 activity and productive binding of its arginine target.”

The researchers expect that the techniques described will launch the discovery of a new generation of high-affinity and high-potency therapeutics made possible by unbiased affinity maturation.

Study author Dr Maria Groves, from the Cancer Research UK-AstraZeneca Antibody Alliance Laboratory, said: “It takes a tremendous amount of time and resources to bring a new therapeutic antibody to the clinic, so we need them to be the best they can be. This first success gives me confidence that our unbiased libraries will produce stronger, more efficient antibodies, and support the delivery of novel oncology therapeutics in the future.”

“The outstanding success of the ARG2 therapeutic antibody project is an exemplar of the substantial benefits to be gained in drug discovery from harnessing the complementary scientific expertise and knowledge available in the pharmaceutical industry, biomedical charity and university sectors of the UK life sciences community,” noted structural biology lead for the project, Professor Mark Carr, from the Institute of Structural and Chemical Biology at the University of Leicester.

“The outcomes from this project point to a successful future for the joint CRUK-AstraZeneca Antibody Alliance Laboratory and my structural biology group look forward to further successful collaborations.”