Synthetic Immune Recruitment – A New Way To Fight Tumors
As the subject of the 2018 Nobel Prize in Medicine, tumor immunotherapy has proven to be an exciting cancer treatment strategy. Most immunotherapies to date have focused on T cell function; however, more natural killer (NK) cell-based therapies that involve monoclonal antibodies (mAbs) that target tumor antigens are emerging. mAbs have shown clinical success for the treatment of both hematological cancers and previously difficult to treat solid tumors. One fundamental mechanism through which mAbs can kill tumor cells is antibody-dependent cellular cytotoxicity (ADCC). ADCC refers to when mAbs elicit an immune response through the activation of NK cells and is triggered by the bi-specific binding of an antibody to both a NK cell activation receptor (CD16α) and a target cancer cell protein antigen. This binding results in the release of cyto-toxic molecules that lead to targeted cancer cell death. While promising, mAbs are potentially immunogenic, can degrade in vivo and experience difficulties trafficking to the site of solid tumors. Furthermore, large doses of the mAb need to be administered intravenously. This increases manufacturing costs, resulting in higher drug prices and limiting general patient accessibility. An approach to utilize tumor immunotherapeutic antibodies directly in vivo using small immune recruiting molecules coined as “covalent immune recruiters” (CIRs) was developed. CIRs selectively link to naturally abundant serum antibodies and redirect them to the sur-face of tumor cells. The resultant display of tumor coated antibodies activates stimulatory receptors on innate immune cells, such as CD16α on NK cells, and triggers an antitumor immune response. The efficacy of these CIRs as modulators of protein proximity can be characterized by the Octet® Bio-Layer Interferometry (BLI) platform. Octet® systems are capable of real-time, high-throughput analysis of small molecule and biomolecule binding kinetics under equilibrium conditions. Due to its flexibility and compatibility for alternative assay format arrangements, it is a powerful tool for characterizing the CIR dependent binding equilibrium (e.g., tumor antigen:CIR:Ab) in addition to its use in determining CIR-antibody covalent recruitment kinetics. The label-free and highly sensitive nature of the Octet® BLI technology also enables analysis under dilute conditions, conserving expensive biologic reagents and attenuating aggregation phenomena intrinsic to isothermal titration calorimetry (ITC) and fluorescence polarization (FP) assays. Octet® systems also present a unique method to simultaneously characterize multiple protein binding and covalent labeling processes and discern reversible binding from a covalent reaction. Octet® system can be employed to efficiently characterize CIR binding affinities against both a prostate tumor antigen and human serum antibodies, as well as measure the selective covalent recruitment of these antibodies to the tumor antigen. These assays can accelerate the advancement of lead compounds to in vivo validation studies, and have additional utility in characterizing emerging classes of covalent inhibitor drugs.