conceived and designed the project

conceived and designed the project. cell-mediated cytotoxicity (ADCC). Based on immune-mediated mechanisms of action including ADCC, therapeutic IgG antibodies have revolutionized the clinical outcomes for multiple types of cancers.1 However, the potential immunogenicity of monoclonal Ufenamate antibodies (mAbs) is one of their limitations, causing side effects such as IgE-mediated anaphylaxis and the production of anti-drug antibodies in the clinic.2,3 As a potential solution to this issue, antibody-recruiting small molecules (ARMs) have been developed to induce antibody-mediated immune responses while NGF circumventing antibody administration.4 ARMs are composed of an antibody-binding terminus (ABT) and a target-binding terminus (TBT) (Fig. 1A), and redirect endogenous antibodies in the bloodstream to target cells such as tumor cells. Subsequently, recruited antibodies trigger immune responses to eliminate the target (Fig. 1B, left panel). Notably, ARMs are thought to be less immunogenic due to their small molecular size.5,6 To date, various types of TBTs have been developed.7C22 By contrast, only a few types of ABTs have shown potential power: galactose–1,3-galactose (-Gal),12,13 rhamnose,21 nitroarenes,14C16,20,22 and phosphorylcholine.23 This is because ABTs have so far been limited to antigens against endogenous antibodies present in a wide range of populace. Open in a separate windows Fig. 1 Fc-binding antibody-recruiting molecule (Fc-ARM) concept in comparison with conventional ARMs. (A) Antibody-recruiting small molecule (ARM). ABT = antibody-binding terminus; TBT = target-binding terminus. (B) Standard ARM-mediated (left) and Fc-ARM-mediated (right) induction of ADCC. (C) Molecular design of Fc-ARM1 and Fc-ARM2. However, these types of ABTs suffer from some shortcomings that limit their therapeutic application. For example, endogenous antibodies against ABTs are generally in short supply (anti–Gal accounts for 1% Ufenamate of endogenous IgG in human serum24), limiting the probability of encountering ARMs and antibodies in the human body. In addition, the efficacy of ARM-based therapy may be influenced by the polyclonal affinity of endogenous antibodies to the ABT. 4 Although immunization of patients with ABTs may help to improve the characteristics of anti-ABT endogenous antibodies,4,9,17,20,22 it increases Ufenamate the complexity of treatment procedures, and may also induce additional side effects. Thus, new methods that enable the exploitation of a larger proportion of pre-existing endogenous antibodies by constant affinity would be a breakthrough for the clinical translation of ARMs. The Fc region of an antibody is usually characterized by its conserved molecular structure, as well as a variety of biological functions. It is the Fc module that is responsible for ADCC in the development of biopharmaceuticals.25,26 A recent study revealed that this Fc region of an antibody binds to virus-infected cells and NK cells simultaneously, resulting in ADCC against the infected cells.27 This statement indicated that ADCC could be induced independently of antigenCFab interactions. Previously, we reported a new class of ARMs, namely Fc-ARMs, in which the Fc-binding cyclic peptide (Fc-III)28 is used as an ABT (Fig. 1B, right panel).29 Use of the Fc-binding peptide enables Fc-ARMs to at least access IgG1 and IgG2 with constant affinity.30 These two IgG subclasses account for more than 80% of the total IgG in humans.31,32 Thus, Fc-ARMs can theoretically exploit the majority of endogenous antibodies through their constant affinity to IgG-Fc. We previously exhibited that Fc-ARMs can recruit human IgG on the surface of malignancy cells in a selective manner.29 However, recruited antibodies did not mediate ADCC under the previous experimental conditions. Given that ADCC is usually regulated by the overall affinity of the antibody to its antigen33 and CD16a,34 we hypothesized that this alternative of the Fc-III peptide with a recently reported peptide, Fc-III4C, which has higher affinity for IgG-Fc,35 would strengthen the recruited antibody ability to activate effector cells such.