Photocleavage Technology for Blood-based Multi-Biomarker Alzheimer's Disease Assay

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Summary/Abstract Alzheimer's Disease (AD) is a chronic neurodegenerative disease characterized by progressively worsening dementia, a syndrome associated with deterioration in cognitive function, behavior and ability to perform everyday activities. AD currently affects over 5.7 million persons in the U.S. with over 70% over the age of 65 and approximately 30 million world-wide. The public health costs due to AD is expected to grow exponentially due to the large expansion of the population over 65 which is estimated to reach over 100 million by 2060. Importantly, early diagnosis of AD is critical for application of therapeutics early in the disease progression, offering the promise of reducing debilitating effects and extending life span. Although the major clinical methods of diagnosing AD rely either on detection of biomarkers such as β-amyloid and tau proteins from cerebrospinal fluid (CSF) or PET imaging, these assays are limited by their invasiveness (e.g. lumbar puncture) or high costs, respectively, and not suitable as a front-line AD diagnostic. In contrast, a blood-based assay would be highly suitable for screening large population groups (e.g. persons over 60) for early AD. While blood-based assays of single biomarkers show significant promise for early detection of AD (e.g. for β-amyloid), it is likely that a panel of several biomarkers measured using a multiplex assay will ultimately emerge as necessary to achieve sufficient specificity to have clinical utility, especially in distinguishing different neurodegenerative diseases that have similar phenotypes. An additional major problem in the development of sensitive and accurate blood-based AD assays is the matrix effect. This effect is caused by the presence of the much more abundant molecules in blood which interfere with detection of the low-abundance biomarkers. We evaluated and successfully demonstrated during Phase I a new approach to multiplex serological AD assays termed PC-PURE™ which is designed to both enrich low-abundance biomarkers and eliminate the matrix effect. This technology is based on the use of novel photocleavable (PC) linkers developed by AmberGen which are incorporated into affinity capture agents such as aptamers or antibodies. We successfully demonstrated the feasibility of PC-PURE™ AD immunoassays by enrichment and multiplex detection of 3 model AD biomarkers (Aβ40, Aβ42 and tau). Our results show that PC-PURE™ when applied as a “front-end” to a commercially available multiplexed Luminex® xMAP® assay improves sensitivity by 30 to 667-fold compared to the same assay without PC-PURE™. Furthermore, PC-PURE™ provides a much more accurate estimate of absolute biomarker concentration since both the calibration curves and biomarkers extracted from the biospecimen are measured in a similar medium. During Phase II, PC-PURE™ will be further optimized for measurement of a model panel of 16 AD biomarkers using 300 AD confirmed and control serum samples and compared to results obtained using a bead- based immuno-MALDI-MS method that is currently one of the most accurate means of measuring AD biomarkers in serum. Commercial products will include PC-PURE™ multiplex immunoassay kits targeting AD biomarkers.