New dual monoclonal ELISA for measuring plasma osteopontin as a biomarker associated with survival in prostate cancer: clinical validation and comparison of multiple ELISAs.
BACKGROUND
A previously developed monoclonal/polyclonal ELISA (Mono/Poly) to detect plasma concentrations of osteopontin (OPN) was shown to provide prognostic information in breast, prostate, and other cancers. Here we describe the clinical validation of a new dual monoclonal (Dual Mono) assay. We compared both assays with 4 assays that recognize defined regions of OPN protein (dual polyclonal systems 5-1, 4-1, 4-3 and polyclonal-monoclonal system 1-3).


METHODS
OPN sequences recognized by the monoclonal antibodies that make up the Dual Mono ELISA were identified by Pepscan CLIPS analysis. Using the 6 ELISAs, we measured OPN in plasma from 66 patients with castration-resistant prostate cancer, and we assessed the ability of each assay to predict patient survival.


RESULTS
The assays varied in measured plasma OPN concentrations, with median values ranging from 112 to 1740 mug/L, and ability to predict patient survival. By Cox univariable regression of survival by tertiles of OPN, the Mono/Poly and Dual Mono ELISAs had the highest log-rank chi(2) values. After adjustment for risk factors independently associated with survival in our samples, OPN remained associated with survival only for the Mono/Poly and Dual Mono systems.


CONCLUSIONS
OPN plasma values varied significantly depending on the assay used. Only the Mono/Poly and Dual Mono systems were independently associated with survival in a population of men with castration-resistant prostate cancer. The availability of a clinically validated, dual monoclonal-based ELISA will provide consistent reagents for studies of OPN plasma concentrations in cancer and other pathologies.
Anborgh
Pieter H
PH
London Regional Cancer Program, London, Ontario, Canada.
Wilson
Sylvia M
SM
Tuck
Alan B
AB
Winquist
Eric
E
Schmidt
Nancy
N
Hart
Russell
R
Kon
Shigeyuki
S
Maeda
Masahiro
M
Uede
Toshimitsu
T
Stitt
Larry W
LW
Chambers
Ann F
AF