Amyloid is associated with a diverse group of often fatal hereditary and sporadic protein misfolding disorders, characterized by the deposition of fibrils and heparan sulfate proteoglycan in vital organs and tissues. Although the most common manifestation is in patients with Alzheimer's disease, the incidence of peripheral (non-cerebral) amyloid diseases in the USA, is estimated to be ~ 5300 per yr which exceeds that for acute lymphocytic leukemia (~ 4,000 per yr). Treatment options for peripheral amyloidosis are limited and focus on reducing synthesis of the amyloidogenic protein e.g., with high dose chemotherapy and there are currently 31 new trials for treating AL, AA, and ATTR amyloidosis underway (clinicaltrials.gov). Unfortunately, there are no methods available in the USA to visualize response to these anti-amyloid therapies directly, nor to determine the extent and severity of amyloid deposits or the target organ in patients. This kind of information can be obtained by imaging, using an amyloid-specific radiotracer. There exists therefore an urgent need to identify tracers that target amyloid for whole body imaging that can be used for monitoring disease progression and response to therapy both within the clinic and as part of clinical trials.
The aim of this proposal is to target the amyloid biomarker heparan sulfate proteoglycan and test antibody-derived and peptide tracer molecules that bind specifically to this constituent of all known amyloid deposits. Our approach is based on the fact that all amyloid deposits contain heparan sulfate proteoglycan at levels as high as 250 5g per gram of diseased tissue. We have begun testing a panel of antibody-derived proteins (scFv) known to bind heparan sulfate, for their ability to bind heparan sulfate in amyloid deposits. We have shown that scFvs to hypersulfated heparin sulfate successfully imaged amyloid in vivo even though heparan sulfate was expressed in some normal tissues. Novel heparan sulfate-binding peptides will also be generated and tested. In vitro characterization of the amyloid-reactive scFv and peptides will be performed by surface plasmon resonance and ELISA to identify those scFv with equilibrium binding affinity of <1 5M - suitable for imaging in patients. Small animal SPECT, PET, and CT imaging will be used to compare the co-localization of the available and novel heparan sulfate- binding tracers and identify those with acceptable (3:1) target to background ratios. We will use an established murine model of systemic peripheral (AA) amyloidosis that recapitulates many aspects of human amyloid disease including the deposition of proteoglycans which enhances the probability that we will identify tracers for imaging amyloidosis that translate favorably into the clinic. Identifying and validating molecules that specifically bind heparan sulfate proteoglycan found in tissue amyloid will provide new reagents for the clinical evaluation of patients with this devastating disease.
Peripheral amyloidosis is a protein-misfolding condition associated with type 2 diabetes, chronic inflammatory disorders such as tuberculosis and rheumatoid arthritis, as well as certain B-cell malignancies. Currently here are no methods available in the USA that can detect the extent of amyloid deposits in patients with peripheral amyloidosis, nor to monitor their progression, or document their removal in response to therapy. This kind of information can be obtained by imaging, using an amyloid-specific radiotracer. To this end, we aim to target the amyloid biomarker heparan sulfate proteoglycan and test antibody-derived and peptide tracer molecules that bind specifically to this constituent of all known amyloid deposits for the purpose of whole body imaging that can be used to monitor disease progression and response to therapy.
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