Ab locks for improving the selectivity and safety of antibody drugs

Abstract

Monoclonal antibodies (mAbs) are a major targeted therapy for malignancies, infectious diseases, autoimmune diseases, transplant rejection and chronic inflammatory diseases due to their antigen specificity and longer half-life than conventional drugs. However, long-term systemic antigen neutralization by mAbs may cause severe adverse events. Improving the selectivity of mAbs to distinguish target antigens at the disease site from normal healthy tissue and reducing severe adverse events caused by the mechanisms-of-action of mAbs is still a pressing need. Development of pro-antibodies (pro-Abs) by installing a protease-cleavable Ab lock is a novel and advanced recombinant Ab-based strategy that efficiently masks the antigen binding ability of mAbs in the normal state and selectively “turns on” the mAb activity when the pro-Ab reaches the proteolytic protease-overexpressed diseased tissue. In this review, we discuss the design and advantages/disadvantages of different Ab lock strategies, focusing particularly on spatial-hindrance-based and affinity peptide-based approaches. We expect that the development of different masking strategies for mAbs will benefit the local reactivity of mAbs at the disease site, increase the therapeutic efficacy and safety of long-term treatment with mAbs in chronic diseases and even permit scientists to develop Ab drugs for formerly undruggable targets and satisfy the unmet medical needs of mAb therapy.

Development of a structure-based computational simulation to optimize the blocking efficacy of pro-antibodies

“…Several technologies have been developed to increase the selectivity of Ab to the disease region and the safety of Ab-based therapies. 18 CytomX Therapeutics, Inc. generated an epithelial growth factor receptor (EGFR) pro-Ab by selecting a bacterial display-associated binding peptide to specifically mask the Ag-binding site of an αEGFR Ab and linking it with a substrate peptide of urokinase-type plasminogen activator (uPA). 19 The pro-αEGFR Ab exhibited 48-fold weaker Ag binding as compared to the parental Ab and the biological activity could be specifically restored in the tumor microenvironment.…”

Viro-antibody therapy: engineering oncolytic viruses for genetic delivery of diverse antibody-based biotherapeutics

“…This includes the introduction of locks into the antigen-binding site, which can be conditionally removed through proteolytic cleavage within the tumor or as a response to hypoxia or low pH. 54 Alternatively, intratumoral injections of antibody drugs are used to increase local accumulation. 55 A promising approach toward addressing some of the mentioned limitations of antibody therapy of cancer is genetic antibody delivery, especially when targeted to solid tumors.…”

“…Furthermore, strategies are available to endow bispecific T-cell engagers with mechanisms for conditional activation at the tumor site, e.g., by local liberation of the binding site through proteolytic cleavage or as a response to pH or hypoxia. 54 Finally, the exploitation of antibody fusion proteins for targeted delivery of effector moieties offers further opportunities. With a plethora of immune-regulating ligands available, new immunocytokines might be used to foster an antitumor immune response or to inhibit immuno-suppressive activities, e.g., of regulatory T-cells, in OV therapy.…”

Protease-Activation of Fc-Masked Therapeutic Antibodies to Alleviate Off-Tumor Cytotoxicity

“…Although several Fc-engineered antibodies have been approved for clinical use, all approaches result in permanently silenced and structurally altered Fc domains. In recent years, research focused on masking the paratopes of antibodies to ensure the selective activation of antibody binding properties ( 21 , 22 ). This technology requires the generation of a suitable masking unit preventing antibody-antigen binding either by a steric hindrance or due to a specific interaction with the antibody paratopes ( 23 ).…”