Glycoprofiling of proteins as prostate cancer biomarkers: a multinational population study
The glycoprofiling of two proteins, the free form of the prostate-specific antigen (fPSA) and zinc--2-glycoprotein (ZA2G), was assessed to determine their suitability as prostate cancer (PCa) biomarkers. The glycoprofiling of proteins was performed by analysing changes in the glycan composition on fPSA and ZA2G using lectins (proteins recognising glycans, i.e. complex carbohydrates). The specific glycoprofiling of the proteins was performed using magnetic beads (MBs) modified with horseradish peroxidase (HRP) and antibodies that selectively enriched fPSA or ZA2G from human serum samples. Subsequently, the antibody-captured glycoproteins were incubated on lectin-coated ELISA plates. In addition, a novel glycoprotein standard (GPS) was used to calibrate the assay. The glycoprofiling of fPSA and ZA2G was performed in human serum samples obtained from men undergoing prostate biopsy after an elevated serum PSA, and prostate cancer patients with or without prior therapy. The results are presented in the form of a ROC (Receiver Operating Curve). A DCA (Decision Curve Analysis) to evaluate the clinical performance and net benefit of fPSA glycan-based biomarkers was also performed. While the glycoprofiling of ZA2G showed little promise as a potential PCa biomarker, the glycoprofiling of fPSA would appear to have significant clinical potential. Hence, the GIA (Glycobiopsy ImmunoAssay) test integrates the glycoprofiling of fPSA (i.e. two glycan forms of fPSA). The GIA test could be used for early diagnoses of PCa (AUC=0.84; n=501 samples) with a potential for use in therapy-monitoring (AUC=0.85; n=168 samples). Moreover, the analysis of a subset of serum samples (n=215) revealed that the GIA test (AUC=0.81) outperformed the PHI (Prostate Health Index) test (AUC=0.69) in discriminating between men with prostate cancer and those with benign serum PSA elevation.