Despite decades of research into the pathogenesis of amyloid disease, and improvements in patient survival, most of these disorders remain invariably fatal due to significant cardiac and renal loads of organ- compromising amyloid present at the time of diagnosis. Consequently, there is an urgent need for agents that remove patient tissue amyloid, to complement current therapies designed to reduce the production of amyloid- forming protein. Immunotherapy, using amyloid-binding antibodies or antibody fragments such as peptibodies (peptide-fused antibody fragments), to recruit cells capable of clearing amyloid, is still the principle method of choice for achieving amyloid clearance. However, translation of these reagents requires demonstration of amyloid-binding in patients. This can be achieved by molecular imaging, thereby enhancing clinical trial design and patient selection in the clinic. Our goal is to develop and characterize a novel pan-amyloid-binding human peptibody that is readily la- beled of imaging and capable of clearing tissue amyloid. The agents we propose incorporate our amyloid-reac- tive synthetic peptides, which we have already shown bind amyloid in patients in a Phase 1 imaging trial. These will be fused to a human immunoglobulin Fc domain to generate a functional peptibodies, which can engage macrophages through Fc-receptors and facilitate clearance of tissue amyloid. We have already devel- oped and characterized a murine peptibody that exhibits excellent amyloid binding and stimulates macro- phages in vitro. This proposal will assess the efficacy of various peptides in the context of humanized peptibod- ies with the goal of identifying a lead candidate for clinical translation. The smaller size of peptibodies, relative to antibodies may allow more efficient accumulation in tissue amyloid, notably in the heart and kidney, and the choice of peptide will influence many biological factors that impact therapeutic efficacy. We have developed several quantitative assays to assess peptibody function using both synthetic amyloid- like fibrils and patient-derived human amyloid extracts. A well-characterized murine model of systemic amyloidosis will be used to evaluate the specific binding of radiolabeled peptibody with amyloid in vivo by SPECT imaging, tissue biodistribution measurements, and microautoradiography. Optical imaging of dual fluorophore-labeled human amyloid implanted in mice will be used to assess macrophage-mediated phagocytosis and dissolution of amyloid in real time. Other assays including stability, structural characterization, developability, and induction of phagocytosis are planned. Our long term goal is to generate an immunotherapeutic peptibody that can also serve as a companion imaging agent to enhance the development program and serve as a patient-selection tool in the clinic. The combination of identifying patients that would benefit from peptibody therapy, and an efficacious pan-amyloid reactive reagent could result in significant clinical benefit for patients with these diseases.
Systemic amyloidosis is a rare but devastating pathology characterized by the extracellular deposition of protein fibrils in major organs and tissues, notably the heart and kidneys. Despite decades of research into the pathogenesis of these disorders and improvements in patient survival rates, they remain invariably fatal due to the inability to effectively remove tissue amyloid. The goal of this proposal is to develop an amyloid-binding reagent capable of harnessing the cells of the immune system to effect amyloid clearance, and that can also be used to image amyloid deposits, yielding new options for clinical trial design, patient stratification, and improved patient outcomes.
