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Autoantibodies as Diagnostic Biomarkers

Readily Detectable Agents Are Suitable for Presymptomatic and Early Diagnosis of Disease

• Michael McAndrew, Ph.D.
• ,
• Colin Wheeler, Ph.D.
• ,
• Rachel Fallon
• ,
• John Anson, Ph.D.

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Platform

Figure 1. BCCP fusion tags ensure that only correctly folded proteins are immobilized. Click Image To Enlarge +

Figure 1. BCCP fusion tags ensure that only correctly folded proteins are immobilized.

OGT’s protein biomarker platform, developed through its Sense Proteomic subsidiary, enables detection of circulating serum autoantibodies using a functional protein microarray technology. Binding of autoantibodies in patient serum to proteins on the arrays is used to identify a subset of protein antigens that provides a characteristic fingerprint for a given disease.

In our discovery studies, clinically relevant autoantibodies and their cognate antigens were identified and characterized to formulate a panel of antigens, which provided specific diagnostic information for the particular disease. This is then followed by validation of the panel using additional patient samples and development of a diagnostic test with clinical utility.

Sense Proteomic has developed an array with ~1,300, folded, functional human proteins. The proteins were selected on the basis of important cellular processes or disease association and have clinical relevance to cancer and autoimmune disease. The proteins are individually expressed as recombinant fusion proteins with a biotin-carboxyl carrier protein (BCCP) tag that is biotinylated in the host cell only when the target protein and tag are correctly folded (Figure 1). This enables specific, on-array affinity purification of folded proteins using streptavidin-coated slide chemistry.

Many autoantibody reactive epitopes are conformation-dependent structures (i.e., discontinuous epitopes) that may not be detectable using peptides or proteins that are not in the correct conformation. Sense’s technology ensures that only fully folded proteins with native epitopes presented are immobilized on the array surface, thereby offering maximum likelihood of discovering multiple clinically relevant autoantibodies in a single assay (Figure 2).

Development

Figure 2. Sense Proteomic’s functional protein technology ensures maximum specificity and sensitivity of biomarker detection. (A) In vivo, autoantibodies bind to complex 3-D epitopes on auto-antigens. (B) On the Sense discovery array, the BCCP tag ensures that only correctly folded, functional recombinant proteins are biotinylated and present. This is vital for correct presentation of complex native epitopes. Correctly folded, functional proteins ensure maximum sensitivity and specificity of autoantibody biomarker detection. Click Image To Enlarge +

Figure 2. Sense Proteomic’s functional protein technology ensures maximum specificity and sensitivity of biomarker detection. (A) In vivo, autoantibodies bind to complex 3-D epitopes on auto-antigens. (B) On the Sense discovery array, the BCCP tag ensures that only correctly folded, functional recombinant proteins are biotinylated and present. This is vital for correct presentation of complex native epitopes. Correctly folded, functional proteins ensure maximum sensitivity and specificity of autoantibody biomarker detection.

Sense Proteomic has developed diagnostic biomarker panels for prostate cancer  and systemic lupus erythematosus using its functional protein array technology.

Screening for prostate cancer is generally performed by digital rectal examination and measurement of blood prostate specific antigen (PSA) titers. Men with elevated levels of PSA are usually referred for a prostate biopsy, but the majority of the biopsies prove to be negative. In practice, the PSA cut-off point of 4 ng/mL is considered sensitive but relatively nonspecific (86% sensitivity and 33% specificity), and there is a need for a diagnostic test with greater discriminatory power to assist in the early diagnosis of prostate cancer and reduce unnecessary treatments. 

Using Sense Proteomic’s functional protein array technology, serum samples were assayed against more than 900 selected recombinant proteins. Advanced data analysis methods identified biomarkers that successfully distinguished prostate cancer from control samples. These were validated by two independent permutation assays that confirmed that the chosen biomarkers were related to the disease status of the sera.

The set of biomarkers identified were able to distinguish prostate cancer from control samples with both sensitivity and specificity above 90%. Further development and validation of this panel is continuing using a larger cohort of patient samples.