Enzyme Immunoassay of Urinary -Core Fragment of Human Chorionic Gonadotropin as a Tumor Marker for Ovarian Cancer
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2072
Human chorionic gonadotropin (hCG), a glycoprotein hormone composed of two nonidentical α- and β-subunits, is normally produced by trophoblasts. Serum and urine from some patients with nontrophoblastic tumors are found to contain similar immunoactivity to the β-subunit of hCG and this phenomenon has been recognized as an ectopic hCGβ production ( 1 ). Elevated levels of ectopic hCGβ are detected more frequently in urine than in serum. Recent studies have shown that urinary ectopic hCGβ mainly represents hCGβ-core fragment (β-CF) ( 2 ). Urinary β-CF consists of residues 6-40 disulfide bridged to residues 55-92 of the β-subunit of hCG ( 3 , 4 ), suggesting that it may be a degradative product of hCGβ. Such partial identity of the amino acid sequence between intact hCG, free hCGβ, and β-CF makes their specific measurements difficult. The existence of two more antigenic sites unique to hCGβ has been demonstrated. The one domain locates in the β-core portion and the other in COOH- terminal region of the β-subunit of hCG Fig. 1 ). By selecting appropriate pairs of antibodies to construct sandwich enzyme immunoassays (EIAs), it is possible to design methods that measure either intact hCG, free hCGβ, or β-CF Table 1 ). By using this EIA, the authors assessed the clinical usefulness of urinary β-CF as a tumor marker for nontrophoblastic tumors ( 5 , 6 ). Here, the authors describe the methods to measure urinary β-CF in patients with ovarian cancer.
Fig. 1. Two antigenic sites: the first domain is located in the β-core portion and the second domain is located in the COOH-terminal region of the β-subunit of hCG.
Table 1 Specificities and Sensitivities of Enzyme-Immunoassays Specific for Intact hCG(EIA-1), Free hCGβ(EIA-2), and β-CF(EIA-3)
|
First antibody |
Second antibody |
Cross-reactivity (%) |
|||||||
|---|---|---|---|---|---|---|---|---|---|
|
Sensitivity |
Intact |
Free |
|||||||
|
Assay |
Code |
Epitope |
Code |
Epitope |
Specificity |
(ng/ml) |
hCG |
hCGβ |
β-CF |
|
EIA-1 |
No.277(MoAb) |
β-CTP |
No.224(MoAb) |
hcGa |
Intact hCG |
0.01 |
100 |
15 |
1.0 |
|
EIA-2 |
No.209(MoAb) |
hCGβ |
No.115(PoAb) |
β-core |
Free hCGβ |
0.01 |
1.9 |
100 |
1.9 |
|
EIA-3 |
No.229(MoAb) |
β-core |
No.105(PoAb) |
β-core |
β-CF |
0.01 |
3.3 |
100 |
100 |
MoAb: monoclonal antibody.
PoAb: polyclonal antibody.
