The Interaction among Protein C Inhibitor, Prostate-Specific Antigen, and the Semenogelin System

BACKGROUND Biomarker validation remains one of the most challenging constraints to the development of new diagnostic assays. To facilitate biomarker validation, we previously developed a chromatography-free stable isotope standards and capture by antipeptide antibodies (SISCAPA)-MALDI assay allowing rapid, high-throughput quantification of protein analytes in large sample sets. Here we applied this assay to the measurement of a surrogate proteotypic peptide from protein C inhibitor (PCI) in sera from patients with prostate cancer. METHODS A 2-plex SISCAPA-MALDI assay for quantification of proteotypic peptides from PCI and soluble transferrin receptor (sTfR) was used to measure these peptides in 159 trypsin-digested sera collected from 51 patients with prostate cancer. These patients had been treated with radiation with or without neoadjuvant androgen deprivation. RESULTS Patients who experienced biochemical recurrence of prostate cancer showed decreased serum concentrations of the PCI peptide analyte within 18 months of treatment. The PCI peptide concentrations remained increased in the sera of patients who did not experience cancer recurrence. Prostate-specific antigen concentrations had no predictive value during the same time period. CONCLUSIONS The high-throughput, liquid chromatography–free SISCAPA-MALDI assay is capable of rapid quantification of proteotypic PCI and sTfR peptide analytes in complex serum samples. Decreased serum concentrations of the PCI peptide were found to be related to recurrence of prostate cancer in patients treated with radiation with or without hormone therapy. However, a larger cohort of patients will be required for unequivocal validation of the PCI peptide as a biomarker for clinical use.

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Quantitative immunoassay for complexes of prostate-specific antigen with alpha2-macroglobulin

Clinical Chemistry ◽

10.1093/clinchem/42.4.545 ◽

1996 ◽

Vol 42 (4) ◽

pp. 545-550 ◽

Cited By ~ 24

Author(s):

F España ◽

J Sánchez-Cuenca ◽

A Estellés ◽

J Gilabert ◽

J H Griffin ◽

...

Keyword(s):

Detection Limit ◽

Prostate Specific Antigen ◽

Protein C ◽

Seminal Fluid ◽

Specific Antigen ◽

The Other ◽

Diagnostic Significance ◽

Healthy Men ◽

Free Psa ◽

Quantitative Immunoassay

Abstract We have developed two ELISAs for quantifying complexes of prostate-specific antigen (PSA) with alpha2-macroglobulin (alpha2M), using partially purified PSA:alpha2M complex as the calibrator. One ELISA was designed to evaluate )SA:alpha2M complex in fluids containing a huge excess of PSA over the amount of complex (semen-derived fluids), the other for use in fluids containing an excess of alpha2M over PSA (blood plasma). The range of the assays was 2-1000 micrograms/L for PSA complexed to alpha2M; the detection limit was 3 micrograms/: Intra- and interassay CVs were 7-13% and 11-17%, respectively, at complexed PSA concentrations of 6-500 micrograms/L. Seminal fluid from healthy men (n = 60) contained 5.2 +/- 2.6 micrograms/L PSA complexed with alpha2M. Prostatic and seminal vesicle fluids contained 6.5 +/- 2.9 ad 0.3 +/- 0.2 mg/L PSA complexed to alpha2M, respectively. When purified PSA was incubated with citrated plasma, between 45% and 65% of the added PSA was recovered as free PSA, whereas approximately 25% formed complexes with alpha2M, 10% complexed with alpha1-antichymotrypsin, and only 0.1-6% was complexed with protein C inhibitor. Of 30 patients with prostate disease, 20 showed detectable plasma PSA:alpha2M complexes; however, the potential diagnostic significance of this complex requires further investigation.

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