Beta-core fragment (beta-core/UGF/UGP), a tumor marker: a 7-year report

Direct analysis of hCGβcf glycosylation in normal and aberrant pregnancy by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

The analysis of human chorionic gonadotropin (hCG) in clinical chemistry laboratories by specific immunoassay is well established. However, changes in glycosylation are not as easily assayed and yet alterations in hCG glycosylation is associated with abnormal pregnancy. hCGβ-core fragment (hCGβcf) was isolated from the urine of women, pregnant with normal, molar and hyperemesis gravidarum pregnancies. Each sample was subjected to matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS) analysis following dithiothreitol (DTT) reduction and fingerprint spectra of peptide hCGβ 6–40 were analyzed. Samples were variably glycosylated, where most structures were small, core and largely mono-antennary. Larger single bi-antennary and mixtures of larger mono-antennary and bi-antennary moieties were also observed in some samples. Larger glycoforms were more abundant in the abnormal pregnancies and tri-antennary carbohydrate moieties were only observed in the samples from molar and hyperemesis gravidarum pregnancies. Given that such spectral profiling differences may be characteristic, development of small sample preparation for mass spectral analysis of hCG may lead to a simpler and faster approach to glycostructural analysis and potentially a novel clinical diagnostic test.

hCG, the wonder of today's science

BACKGROUND

hCG is a wonder. Firstly, because hCG is such an extreme molecule. hCG is the most acidic glycoprotein containing the highest proportion of sugars. Secondly, hCG exists in 5 common forms. Finally, it has so many functions ranging from control of human pregnancy to human cancer. This review examines these molecules in detail.

CONTENT

These 5 molecules, hCG, sulfated hCG, hyperglycosylated hCG, hCG free beta and hyperglycosylated free beta are produced by placental syncytiotrophoblast cells and pituitary gonadotrope cells (group 1), and by placental cytotrophoblast cells and human malignancies (group 2). Group 1 molecules are both hormones that act on the hCG/LH receptor. These molecules are central to human menstrual cycle and human pregnancy. Group 2 molecules are autocrines, that act by antagonizing a TGF beta receptor. These molecules are critical to all advanced malignancies.

CONCLUSIONS

The hCG groups are molecules critical to both the molecules of pregnancy or human life, and to the advancement of cancer, or human death.

Extragonadal actions of chorionic gonadotropin

The primary embryonic signal in primates is chorionic gonadotropin (CG, designated hCG in humans), that is classically associated with corpus luteum rescue and progesterone production. However, research over the past decade has revealed the presence of the hCG receptor in a variety of extragonadal tissues. Additionally, discoveries of the multiple variants of hCG, namely, native hCG, hyperglycosylated hCG (hyp-hCG) and the β- subunit of the hyperglycosylated hCG (hCG-free β) has established a role for extragonadal actions of hCG. For the initiation and maintenance of pregnancy, hCG mediates multiple placental, uterine and fetal functions. Some of these include development of syncytiotrophoblast cells, mitotic growth and differentiation of the endometrium, localized suppression of the maternal immune system, modulation of uterine morphology and gene expression and coordination of intricate signal transduction between the endometrium. Recurrent pregnancy loss, pre-eclampsia and endometriosis are associated with altered responses of hCG, all of which have a detrimental effect on pregnancy. A role for hyp-hCG in mediating the development of both trophoblastic and non-trophoblastic tumors has also been suggested. Other significant non-gonadal applications of hCG include predicting preeclampsia, determining the risk of Down's syndrome and gestational trophoblastic disease, along with relaxing myometrial contractility and preventing recurrent miscarriages. Presence of hCG free-β in serum of cancer patients enables its usage as a diagnostic tumor marker. Thus, the extragonadal functions of hCG encompasses a wide spectrum of applications and is an open area for continued investigation.

hCG, five independent molecules

INTRODUCTION

The hCG amino acid sequence supports 5 glycoproteins. All are called hCG forms. This review examines all 5 molecules, the hormone as produced by the placental syncytiotrophoblast cells, the sulfated hormone produced by the pituitary gonadotrope cells, the hyperglycosylated hCG autocrine made by placental cytotrophoblast cells, and the autocrine cancer promoters hyperglycosylated hCG, hCGß and hyperglycosylated hCGß as made by all malignancies. This review examines all the molecules and multiple proven functions, ranging from evolution to cancer promotion to hormone action.

RESULTS AND DISCUSSION

hCG forms are critical super-growth factors in humans, with an exceptional wide range of functions.

New discoveries on the biology and detection of human chorionic gonadotropin

Human chorionic gonadotropin (hCG) is a glycoprotein hormone comprising 2 subunits, alpha and beta joined non covalently. While similar in structure to luteinizing hormone (LH), hCG exists in multiple hormonal and non-endocrine agents, rather than as a single molecule like LH and the other glycoprotein hormones. These are regular hCG, hyperglycosylated hCG and the free beta-subunit of hyperglycosylated hCG. For 88 years regular hCG has been known as a promoter of corpus luteal progesterone production, even though this function only explains 3 weeks of a full gestations production of regular hCG. Research in recent years has explained the full gestational production by demonstration of critical functions in trophoblast differentiation and in fetal nutrition through myometrial spiral artery angiogenesis. While regular hCG is made by fused villous syncytiotrophoblast cells, extravillous invasive cytotrophoblast cells make the variant hyperglycosylated hCG. This variant is an autocrine factor, acting on extravillous invasive cytotrophoblast cells to initiate and control invasion as occurs at implantation of pregnancy and the establishment of hemochorial placentation, and malignancy as occurs in invasive hydatidiform mole and choriocarcinoma. Hyperglycosylated hCG inhibits apoptosis in extravillous invasive cytotrophoblast cells promoting cell invasion, growth and malignancy. Other non-trophoblastic malignancies retro-differentiate and produce a hyperglycosylated free beta-subunit of hCG (hCG free beta). This has been shown to be an autocrine factor antagonizing apoptosis furthering cancer cell growth and malignancy. New applications have been demonstrated for total hCG measurements and detection of the 3 hCG variants in pregnancy detection, monitoring pregnancy outcome, determining risk for Down syndrome fetus, predicting preeclampsia, detecting pituitary hCG, detecting and managing gestational trophoblastic diseases, diagnosing quiescent gestational trophoblastic disease, diagnosing placental site trophoblastic tumor, managing testicular germ cell malignancies, and monitoring other human malignancies. There are very few molecules with such wide and varying functions as regular hCG and its variants, and very few tests with such a wide spectrum of clinical applications as total hCG.

The impact of molecular genetic diagnosis on the management of women with hCG-producing malignancies

OBJECTIVES

The diagnosis of a gestational trophoblastic tumour (GTT) should be considered in all women presenting with a malignancy and an elevated human chorionic gonadotrophin (hCG) level. Whilst some non-gestational malignancies can also produce hCG, most non-gestational tumours can be distinguished from GTT on the basis of histopathological examination. However, some non-gestational tumours can exhibit trophoblastic differentiation and so make establishing the definitive diagnosis difficult. In these cases, molecular genetic investigation can establish the differential diagnosis between gestational and non-gestational tumours and facilitate optimal management. The objective of this study is to demonstrate the clinical value of distinguishing these two diagnoses by genetic analysis in patient care at a major GTT treatment centre.

METHODS

Between 1994 and 2005, fluorescent microsatellite genotyping was used to examine the genetic origin of 35 cases of metastatic hCG-producing tumours with trophoblastic differentiation, three cases of atypical uterine tumours, three cases of uterine choriocarcinoma with a very long interval and one atypical ovarian tumour.

RESULTS

Of the 42 cases examined, 24 were proved to be of gestational origin, 14 were non-gestational and in 4 cases genetic analysis was inconclusive. We illustrate the clinical value of this diagnostic technique by presenting five individual cases in which molecular genetic results helped determine the appropriate clinical management.

CONCLUSION

Analysis of the genetic origin of atypical hCG-producing tumours in women allows the optimisation of individual patient care and should be considered in the management of these unusual cases.

Gestational trophoblastic diseases: 3. Human chorionic gonadotropin-free β-subunit, a reliable marker of placental site trophoblastic tumors

OBJECTIVES

Placental site trophoblastic tumor (PSTT) commonly presents with low and variable concentration of hCG immunoreactivity in serum which can be difficult to differentiate from early stage choriocarcinoma/gestational trophoblastic neoplasm (GTN) or quiescent gestational trophoblastic disease (quiescent GTD). Nontrophoblastic malignancies such as germ cell tumors or other tumors secreting low hCG must also be considered in the differential diagnosis. Because treatments for these conditions are different, a means of differentiating PSTT from other diagnoses is important. We investigate the usefulness of hCG-free beta-subunit to make this discrimination.

METHODS

Data collected on cases referred to the USA hCG Reference Service for consultation served as a basis for this retrospective analysis. There were 13 cases with histology proven PSTT and 12 with nontrophoblastic malignancy. hCG-free beta-subunit was measured by immunoassay and reported as a proportion of total hCG (hCG-free beta-subunit(%)). hCG-free beta-subunit(%) results were determined for all histologically proven cases of PSTT and for the nontrophoblastic malignancies. Comparisons of hCG-free beta-subunit(%) were made and compared with those of the 82 choriocarcinoma/GTN cases and 69 quiescent GTD cases. The accuracy of hCG-free beta-subunit(%) to discriminate these malignancies was analyzed by investigating the areas under receiver-operating characteristics curve +/- standard error.

RESULTS

hCG-free beta-subunit(%) was the predominant hCG form in cases of PSTT (mean +/- standard deviation, 60 +/- 19%) and nontrophoblastic malignancies (91 +/- 11%), thus discriminating these diagnoses from choriocarcinoma/GTN (9.3 +/- 9.2%) and from quiescent GTD (5.4 +/- 7.8%). The cutoff of >35% free beta-subunit is proposed. At this cutoff, 100% detection at 0% false-positive is achieved. The accuracy of hCG-free beta-subunit(%) for this discrimination is 100 +/- 0%. At a proposed cutoff of >80%, the free beta-subunit test will also distinguish PSTT from nontrophoblastic malignancy, with 77% detection at 23% false-positive or an accuracy of 92 +/- 3.2%.

CONCLUSION

Measurement of the proportion hCG-free beta-subunit(%) was found to be useful in the diagnosis of PSTT using proposed cutoff values of >35% and >80%. While this finding needs to be confirmed by larger studies, it would be reasonable to measure hCG-free beta-subunit(%) whenever the diagnosis of PSTT is considered.

Gestation trophoblastic diseases: management of cases with persistent low human chorionic gonadotropin results

The finding of persistent low levels of human chorionic gonadotropin (hCG) raises concern, regardless of the antecedent history, and often provokes the evaluating physician to embark on further work-up. The USA hCG Reference Service was started in 1998 to aid physicians with these persistent low hCG cases. This article reviews the observations of the USA hCG Reference Service for 134 cases with persistent low hCG results. Examination of these cases provides clear insight for the appropriate management of those presenting with persistent low levels of hCG. Three distinct sources are discussed for persistent low hCG results: quiescence gestational trophoblastic disease, false-positive hCG results, and pituitary hCG.

Urine GABA levels in ovarian cancer patients: elevated GABA in malignancy

The association of malignancy with elevated diamine oxidase (DAO), an enzyme producing gamma-aminobutyric acid (GABA) is well documented. In ovarian cancer, increased DAO occurs in the malignant tissues and plasma. Since higher DAO levels cause GABA accumulation, elevated GABA may occur in ovarian cancer and be reflected in urine. We tested this hypothesis and found that half the ovarian cancer patients had a clearly elevated urine GABA, a result that is in agreement with previous reports on DAO and malignancy. The published findings on DAO, GABA and malignancy suggest that elevated GABA is associated with cancer. This proposal could lead to a GABA urine monitor or new directions in cancer treatment or research.

Preparation and analysis of the common urinary forms of human chorionic gonadotropin

Human chorionic gonadotropin (hCG) is the hormone of pregnancy and forms the basis of all pregnancy tests as well as diagnostic assays for a variety of pathological states including certain types of cancers and some diseases of pregnancy and genetic abnormalities. In recent years, the discovery of the diagnostic utility of measurement of the free subunits and fragments of the hormone, especially in urine, has proven of special use for diagnosis of very early pregnancy loss, an important phenomenon related to infertility, as well as part of screening programs for Down Syndrome and gynecological cancers. This article summarizes existing and new methods for the preparation of hCG, its subunits, and the beta core fragment from urinary sources. The methods for proper analyses of these materials are also described to enable investigators to prepare and analyze these materials in various quantities in their own laboratories.

Following metastatic placental site trophoblastic tumor with urine beta-core fragment

OBJECTIVE

We document a case with metastatic placental site trophoblastic tumor in a 47-year-old postmenopausal women.

METHODS

beta-core fragment was measured in urine using the Triton UGP kit. hCG was also measured using the Bayer Immuno-1hCG assay (at Memorial Sloan-Kettering Cancer Center).

RESULTS

Over 2 years the patient underwent two courses of chemotherapy and two debulking operations. During this time, hCG levels decreased from 227 to 4.1 mIU/ml. hCG levels were close to the limit of detection (<3 mIU/ml), indicating complete or near-complete regression of disease. At this point urine beta-core fragment levels were determined. High levels were detected 7.9 fmol/ml, consistent with the continued existence of tumor (>1.9 fmol/ml). High-dose chemotherapy (CEM) was started with stem cell harvesting. In the following weeks hCG levels failed to identify the tumor (4.1 to <3 mIU/ml). In the first week (during therapy) beta-core fragment levels increased (12 fmol/ml), and in the following weeks (after therapy) levels regressed to 1.2 fmol/ml.

CONCLUSION

Urine beta-core fragment may be a useful tumor maker when serum hCG levels are near to or below the limit of detection.

Cross-Reaction with Luteinizing Hormone β-Core Is Responsible for the Age-dependent Increase of Immunoreactive β-Core Fragment of Human Chorionic Gonadotropin in Women with Nonmalignant Conditions

Background: The β-core fragment of human chorionic gonadotropin (hCGβcf), also termed “β-core” and urinary gonadotropin peptide (UGP), has been reported to be present in the urine of healthy women and to increase in concentration after menopause. This could reflect cross-reaction with the equivalent metabolite of luteinizing hormone (LH), the β-LH-core.

Methods: We measured immunoreactive LH, hCG, free α-subunit, and free β-subunit hCG (hCGβ), as well as β-core, using the S504 RIA and Triton UGP enzyme immunoassay in 274 urine samples from women with nonmalignant gynecological conditions. The molar cross-reaction of each assay with purified β-LH-core was determined.

Results: Cross-reaction with β-LH-core was 100% in the LH and the S504 β-core assay, 5% in the Triton UGP assay, and &lt;0.1% in the hCG, free α-subunit, and free hCGβ assays. Median urine concentrations of all analytes showed an age-dependent increase. LH and free α-subunit concentrations were ∼103 pmol/mol creatinine; hCG and S504 β-core were ∼102 pmol/mol creatinine; free hCGβ and Triton UGP β-core were in the tens of pmol/mol creatinine. The S504 β-core concentrations were 10% of those of LH. S504 β-core was strongly correlated with LH, but not with hCG or with free hCGβ (LH, r2 = 0.45; hCG, r2 = 0.26; free hCGβ, r2 = 0.03). The concentrations of β-core detected by the Triton UGP assay, which has a 5% cross-reaction with β-LH-core, were 2% of LH and 5% of the S504 β-core concentrations. Triton UGP values correlated strongly with LH concentrations, but less well with S504 β-core, intact hCG, and free hCGβ (LH, r2 = 0.44; S504 β-core, r2 = 0.33; hCG, r2 = 0.32; free hCGβ, r2 = 0.19).

Conclusions: Immunoreactive β-core in women free of malignancies reflects cross-reaction with concentrations of the metabolite of LH, β-LH-core, within the health-related reference interval.

Phantom hCG and phantom choriocarcinoma

Phantom hCG and phantom choriocarcinoma syndrome (pseudohypergonadotropinemia) refers to persistent mild elevations of hCG, leading physicians to treat patients with cytotoxic chemotherapy for choriocarcinoma when in reality no true hCG or trophoblast disease is present. We report here three cases of the phantom hCG and phantom choriocarcinoma syndrome referred to the hCG Reference Service. In the first case, low levels of hCG were detected in serum (49 to 89 IU/liter) 11 months after the patient had a miscarriage. The presumptive diagnosis of choriocarcinoma was made. After two courses of chemotherapy and a hysterectomy low levels of hCG were still detected. Samples were sent to the hCG Reference Service. While low levels of hCG were detected in serum by three different assays (17, 22, and 9.2 IU/ml), no hCG was detected in the urine. When serum was diluted, levels did not decrease parallel to the dilution. The lack of dilutional parallelism and absence of urine reactivity indicated that the molecule measured was a pseudogonadotropin or phantom hCG, an interfering substance in hCG tests. Therapy was halted. In the second case, a positive serum pregnancy test was recorded 7 years after a normal pregnancy. A pelvic ultrasound and a laparoscopy revealed no pregnancy. Blood hCG levels stayed between 48 and 74 IU/liter over a 3-month period. Samples were sent to the hCG Reference Service. Low levels of hCG, free beta-subunit, and beta-core fragment were detected in serum using four specific assays. No hCG immunoreactivity was found in the urine sample. None of the four assay results declined parallel to dilution. Again, phantom hCG was diagnosed. In the third case, a positive serum pregnancy test was recorded 1 year after the patient had a normal pregnancy. A pelvic ultrasound revealed no fetal sac. Low levels of hCG (51-135 IU/liter) persisted for 3 months. A preumptive diagnosis of choriocarcinoma was again made. After three cycles of chemotherapy, low levels of hCG were still detected. Samples were sent to the hCG Reference Service. Low levels of hCG immunoreactivity were detected in serum in just one of three hCG assays (13 IU/liter). No immunoreactivity was detected in the urine sample. Again, phantom hCG was diagnosed, and all therapy was halted. Care is needed in interpreting persistent low levels of hCG in patients with no history of trophoblast disease. It is important for the laboratory to show dilutional parallelism in the hCG results and presence of hCG in serum and urine samples in order to exclude phantom hCG before diagnosing choriocarcinoma.

The prognostic significance of beta human chorionic gonadotrophin and its metabolites in women with cervical carcinoma

AIMS

To examine long term survival of women with primary and recurrent cervical carcinoma in relation to (1) excretion of beta-core (a urinary metabolite of beta human chorionic gonadotrophin (beta hCG)) and (2) beta hCG immunostaining of the tumours, to determine the suitability of these markers for assessing prognosis.

METHODS

This was a prospective observational study undertaken in a gynaecological oncology centre: 57 women with primary cervical cancer and 42 with recurrent disease were recruited between January 1990 and September 1992. Kaplan-Meier survival analysis with the log rank test was used to assess survival differences with survival rate given per year of follow up.

RESULTS

In primary disease, the four year survival for the beta-core negative group was 79%, compared with 14% for the beta-core positive group (p = 0.001). This was still significant for early stage disease or squamous lesions alone. In recurrent disease, beta-core positivity was not prognostically significant. Immunohistochemistry was of no prognostic significance in either group.

CONCLUSIONS

beta-core excretion appears to be useful in assessing prognosis of primary cervical cancer but not of recurrent disease. A large prospective study of urinary beta-core in early stage cervical cancer is needed to determine whether it can be used as an index for modifying treatment.

Analysis of hCG: clinical applications and assay requirements

Study of the glycoprotein hormones, including hCG, is complex and evolving, and has benefited from recent major advances in analytical technology and molecular biology. It is important to be aware of the effect that these technological advances have, both on the analytical and the clinical requirements for provision of a diagnostic service for hCG. Some aspects of particular relevance are summarized in Table 10.

Immunoassay of human chorionic gonadotropin, its free subunits, and metabolites

Multiple hCG-related molecules are present in pregnancy serum and urine samples. These include nonnicked hCG (the hormone), nicked hCG, hyper- and hypoglycosylated hCG, hCG missing the C-terminal extension, free α-subunit, large free α-subunit, free β-subunit, nicked free β-subunit, and β-core fragment. Over 100 immunoassays are sold for quantifying hCG-related molecules in serum or urine. Each measures nonnicked hCG and one of seven combinations of the other hCG-related molecules. This is the source of interassay discordance in hCG determinations. Whereas minor variations are noted in different kit results in normal pregnancy samples (more than twofold variation), much larger variations may be found in two immunoassay results in irregular gestations (spontaneous abortion, aneuploidy, preeclampsia, cancers, and trophoblast disease). Care is needed in choosing an immunoassay. What the assay measures may be more important than its cost or speed. This article reviews the structure of hCG and related molecules. It examines the stability and degradation of hCG, and recognition of hCG-related molecules by different types of immunoassay. Also reviewed are new assays for specifically detecting these other hCG-related molecules.