Single-chain antibodies as new antithrombotic drugs

Antibodies are the most rapidly growing class of human therapeutics and the second largest class of drugs after vaccines. At present, several antibodies are approved for therapeutic use in diverse clinical settings, including oncology, chronic inflammatory diseases, transplantation, infectious diseases, and cardiovascular medicine. These approved antibody therapeutics include unmodified immunoglobulin G molecules, radioimmunoconjugates, antibody-drug conjugates, and fragment antigen-binding molecules. At least 150 additional antibodies are in clinical development. A major strength of therapeutic antibodies is their established properties as a drug class with high success rates from clinical trials to regulatory approvals. Much of the experience gained from the generation and optimization of one antibody is applicable to other antibodies. Antibody fragments are a subclass with growing clinical importance. This review focuses on single-chain antibodies as the smallest possible format for recombinant antibodies, and their use as antithrombotic drugs. We describe different antibody formats, the current applications of antibody fragments, and their generation by cloning from hybridoma cell lines as well as their selection from antibody libraries. We review the use of antibody fragments for thrombus targeting using fibrin and platelet-specific single-chain antibodies in combination with anticoagulants and thrombolytic agents as antithrombotic drugs.