I-Labeled single-chain monoclonal antibody, NS4F5, that targets the GlcNS6S-IdoA2S motif of heparan sulfate proteoglycans for the imaging of peripheral amyloidosis

Peripheral amyloidosis is the extracellular deposition of insoluble protein fibrils in various organs of animals, including humans, and these deposits are considered to be biomarkers for diseases such as Alzheimer’s disease (AD), light chain amyloidosis (AL), etc (1). The fibrils are made up of disease-specific aggregated proteins or peptides (e.g., Aβ peptides for AD, light chains for AL or multiple myeloma, and reactive amyloidosis (AA)) that incorporate heparin sulfate proteoglycans (HSPG; heparin belongs to the heparan sulfate family of proteoglycans that contain the (GlcNS6S-IdoA2S) motif)) and the serum amyloid P component (SAP) within their structure during disease progression. A characteristic feature of the protein fibrils is that the constituent proteins form a secondary cross-β pleated sheet structure that is resistant to proteolytic digestion (for structural details, see Goldsbury et al. (2)). In addition, clinical symptoms of amyloidosis in a patient are influenced by the degree to which an organ is involved in the disease (3).The HSPG contain diverse types of oligosaccharides that are sulfated on the hydroxyl moieties to varying degrees, and these hypersulfated structures are distinct, are found specifically in the amyloid deposits, and differ from one another depending on the organ where they are located (4). In addition, the HSPG contain stretches of the disaccharide GlcNS6S-IdoA2S (HS; these motifs are abundantly found in heparin, but have limited presence in the HS of normal tissues) that inhibit cell proliferation and induce apoptosis but do not affect the attachment of cells to collagen I (5). Because the HSPG in the amyloids are hypersulfated compared to the proteoglycans in normal tissues, HSPG are considered to be suitable for the detection of amyloids with imaging techniques and to diagnose and monitor amyloidosis progression and to determine the prognosis for a patient with amyloidosis (1). Whole-body scintigraphy with radioiodinated SAP is commonly used in Europe for the detection of amyloidosis in the various parts of the body, but this technique is not approved by the United States Food and Drug Administration for clinical use in United States because the SAP used to generate the tracer is isolated from human sources (1). In an attempt to develop an amyloid imaging agent that would not require the use of human materials, Wall et al. showed that a I-labeled synthetic heparin-binding peptide, p5, could be used with single-photon emission computed tomography (SPECT) to detect amyloid deposits in H2/huIL-6 transgenic mice with severe systemic AA amyloidosis (AA mice) (1). In another study, Wall et al. evaluated the use of I-labeled single chain (scFv) antibodies (Abs) directed against HS for the detection of amyloids in AA mice that are prone to develop amyloidosis at ~4–5 months of age as described elsewhere (6). Among these radioiodinated scFv Abs, NS4F5, which binds specifically to HS (5), has been determined to be the most suitable for the noninvasive imaging of amyloids in the transgenic animals (6).