Compared with traditional drugs, monoclonal antibodies (MAb) are mainly targeted for the treatment of malignant tumors, infectious diseases, autoimmune diseases, transplant rejection, and chronic inflammation due to their specificity and longer half-life. However, long-term application will cause the neutralization of systemic antigens and cause serious adverse events. Improving antibody selectivity and reducing serious adverse events is still an urgent problem to be solved. The development of pro-Abs (pro-Abs) by installing a protease-cleavable Ab lock is a novel and advanced recombinant Ab-based strategy that can effectively mask the antigen binding ability of mAbs under normal conditions and selectively "turn on" mAb activity when the current antibody reaches the diseased tissue where the proteolytic protease is overexpressed.
Creative Biolabs has developed a set of integrated Ab lock design solutions, especially methods based on space constraints and affinity peptides. We expect that our development of different masking strategies for mAbs will benefit the local reactivity of mAbs at the disease site, improve the efficacy and safety of monoclonal antibodies in the long-term treatment of chronic diseases, and even allow scientists to develop Ab drugs for undruggable targets and finally meet the unmet medical needs of mAb therapy.
The systemic administration of monoclonal antibody drugs may cause serious adverse events through actions related to the mechanism of action, which means that the monoclonal antibody drugs eliminate the target antigens that maintain physiological functions in normal tissues. Since systemic depletion of antigen may cause unpredictable reactions in patients during Ab treatment, we also list several side effects of the aforementioned mAbs (Table 1). The selective improvement of mAb to distinguish target antigens or cells at disease sites from normal healthy tissues may improve the safety and therapeutic effect of mAb during treatment.
Fig.1 Side effects of monoclonal Ab drugs caused by systemic on-target toxicity. (Lin, 2020)
To improve the selectivity of monoclonal antibodies in diseased site and enable them to perform their functions locally, Ab drugs should ignore the target antigens in normal healthy tissues and give priority to their activity in the diseased site. One way to achieve this goal is to generate pro-Ab by installing a protease-cleavable Ab lock. Ab lock is defined as a molecule that can interfere with the antigen binding ability of Ab drugs. It is a novel and advanced technology. Based on the strategy of recombinant Ab, when pro Ab reaches diseased tissues overexpressing proteolytic enzymes (ie proteases), mAb activity is selectively "turned on". Pro-Ab consists of two basic parts, a "masking domain" can physically block or interfere with the antigen binding ability of mAb. A substrate peptide for disease-related proteases that connects the masking domain to the N-terminus of the mAb light chain and/or heavy chain. Adding a masking domain will greatly reduce the binding ability of mAb to its target antigen. Once exposed to the overexpressed protease at the disease site, the mAb will reactivate the original mAb binding activity, thereby increasing the selectivity of mAb (Figure 2).
Fig.2 Schematic diagram of MOA of pre-antibody in diseased area by installing protease-cleavable Ab lock. (Lin, 2020)
For a good design of Ab locks, multiple factors should be considered, including masking efficiency, immunogenicity, wide applicability, the release efficiency of Ab locks after protease cleavage, and the reduction of side effects. Creative Biolabs provides two basic Ab lock masking strategies: special hindrance-based Ab lock, and affinity-peptide based Ab lock.
Ab locks based on steric barriers, such as self-hinge domain, coiled-coil domain, LAP domain, or methods based on trivalent/tetravalent Ab, can provide high masking efficiency, high masking domain release rate, and high recovery of monoclonal antibodies After the cleavage of the antigen-binding active protease, various Ab drugs are almost universally used. Affinity-based masking strategies (ie, masking that relies on affinity peptides or mutant antigens) have demonstrated acceptable masking efficiency. In principle, two masking theories (ie methods based on space barriers or methods based on affinity peptides) can inhibit the neutralization and cleaning effects of anti-idiotypic anti-drug antibodies, which is one of the main problems caused by repetition in antibody therapy Management of monoclonal antibodies.
To sum up, the different masking strategies of Pro-Ab have different advantages. Our customized Ab lock design gives scientists more choices to develop next-generation Ab drugs corresponding to different disease types.
Fig.3 Comparison of different masking strategies of pro-Abs.
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Reference
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