Post-translational modifications (PTMs), particularly glycosylation, affect a protein drug’s activity, effectiveness, and safety, but not always in predictable ways. Some glycans are known to be immunogenic, while the presence or absence of others influences the mode of action of a given drug.
For example, the absence of fucose on antibodies enhances antibody-dependent cellular cytotoxicity (ADCC), a desired property of cancer treatment. Eliminating fucose could therefore improve prospects for development-stage drugs through some combination of reducing toxicity while increasing activity.
That was PerkinElmer’s strategy for expanding its Horizon Discovery CHOSOURCE™ platform to include a new expression cell line, CHO-K1 ADCC+, which was created by knocking out a gene involved in the fucosylation pathway in Horizon’s established CHO-K1 GS line. Interest in afucosylated antibodies and fusion proteins is expanding for applications in oncology, but also for infectious diseases, and more recently, autoimmune conditions.
“The composition of antibody glycoforms modulates their biological activity, from regulating half-life to controlling ADCC or complement-dependent cytotoxicity among others,” says Jesús Zurdo, PhD, global head for cell, gene therapy, and bioproduction at Horizon.
“Antibodies lacking fucose in their Fc glycoform show up to 50-fold increased binding to FcγIIIa receptors in natural killer (NK) cells that mediate ADCC responses. Afucosylated antibodies improve responses and outcomes irrespective of the amino acid present at position 158 of the NK’s FcγIIIa receptor, which reduces cross-population differences in responses to a given treatment.
“The presence or absence of fucose in an antibody has no effect on target recognition, so it does not directly affect off-target activity. However, the increased activity observed in afucosylated antibodies can affect the doses required to achieve a given therapeutic outcome, thus reducing the amount of monoclonal antibody administered to the patient, thereby potentially reducing the incidence of events in off-target tissues that present lower expression of a target antigen.”
The new cell line complements, rather than replaces, Horizon’s original and well-characterized CHO-K1 GS KO cell line, which remains the company’s main protein expression platform. CHO-K1 ADCC+ is targeted primarily to drug developers with programs in oncology, infectious diseases (including viruses), and autoimmune indications, where better control over ADCC effector function activity is desirable.
Modulating or eliminating fucosylation is not a novel idea. It is possible to modify cell lines already used in production (or development), to reduce or eliminate the presence of this sugar from protein candidates. Many third-party research service organizations will do this for cells you are already familiar with (Google “fucose knockout antibody”).
However, new expression lines require extensive validation and documented traceability, (including all raw materials used), which is complex to implement and consumes substantial amount of time and effort. Development-stage companies, in particular, often do not have such capabilities, and can benefit from an established cell line with a complete regulatory package.