Accelerated discovery of biomarkers by protein chips: Autoantibodies to KDR and PIM-1 differentiate prostate cancer from benign prostatic hyperplasia

A26 Autoantibody profiling using custom, disease-focused protein-arrays provides an accelerated approach to identify diagnostic-quality biomarkers for cancer. A custom prostate-cancer-targeted protein microarray (96 proteins) was screened for the presence of autoantibodies using sera from prostate cancer (PCa) patients and benign prostatic hyperplasia (BPH) patients. The goal of the study was to discover prostate-cancer tumor-associated antigens (biomarkers) that could clearly discriminate PCa from BPH. Biomarkers found in this manner, would be stable in blood, easily measured using ~ 1 uL of serum (or plasma) and could differentiate true prostate cancer from the closely-related benign prostatic hyperplasia, the major weakness in the current, clinically used, PSA-based prostate cancer diagnostic test. Autoantibody profiling on two pooled samples from thirty-two prostate cancer patients and thirty-two benign prostatic hyperplasia patients revealed twenty tumor associated antigens, including KDR and PIM-1, that induced significant humoral autoantibody response. Additional experiments using all 64 non-pooled serum samples applied to a low content protein chip showed that autoantibodies against KDR and PIM-1 differentiated prostate cancer from benign prostatic hyperplasia with 90.6% sensitivity and 84.4% specificity. Protein array signals were specific, and could be competed away by spiking pure antigen into the sera in a dose dependent manner. Additionally, fluorescence immunohistochemistry of prostate cancer tissue arrays showed that KDR and PIM-1 were differentially expressed in prostate cancer tissues with reduced expression in benign prostatic hyperplasia tissues, suggesting over expression of KDR and PIM-1 tumor antigens lead to the aberrant humoral response.