Designing a new generation of anti-hCG vaccines for cancer therapy

Unconventional Actions of Glycoprotein Hormone Subunits: A Comprehensive Review

The glycoprotein hormones (GPH) are heterodimers composed of a common α subunit and a specific β subunit. They act by activating specific leucine-rich repeat G protein-coupled receptors. However, individual subunits have been shown to elicit responses in cells devoid of the receptor for the dimeric hormones. The α subunit is involved in prolactin production from different tissues. The human chorionic gonadotropin β subunit (βhCG) plays determinant roles in placentation and in cancer development and metastasis. A truncated form of the thyrotropin (TSH) β subunit is also reported to have biological effects. The GPH α- and β subunits are derived from precursor genes (gpa and gpb, respectively), which are expressed in most invertebrate species and are still represented in vertebrates as GPH subunit paralogs (gpa2 and gpb5, respectively). No specific receptor has been found for the vertebrate GPA2 and GPB5 even if their heterodimeric form is able to activate the TSH receptor in mammals. Interestingly, GPA and GPB are phylogenetically and structurally related to cysteine-knot growth factors (CKGF) and particularly to a group of antagonists that act independently on any receptor. This review article summarizes the observed actions of individual GPH subunits and presents the current hypotheses of how these actions might be induced. New approaches are also proposed in light of the evolutionary relatedness with antagonists of the CKGF family of proteins.

β-hCG-induced mutant BRCA1 ignites drug resistance in susceptible breast tissue

β-hCG expression in breast cancer is highly controversial with reports supporting both protective and tumorigenic effects. It has also been reported that risk of breast cancer at an early age is increased with full-term pregnancies if a woman is a BRCA1 mutation carrier. We have already demonstrated that BRCA1-defective cells express high levels of β-hCG and that when BRCA1 is restored, β-hCG level is reduced. Also, BRCA1 can bind to the promoter and reduce the levels of β-hCG. β-hCG induces tumorigenicity in BRCA1-defective cells by directly binding to TGFBRII and induces TGFBRII-mediated cell proliferation. In this study, we analyzed the mechanism of action of β-hCG on BRCA1 expression and its influence on drug sensitivity in breast cancer cells. We demonstrate that β-hCG induces mutant BRCA1 protein expression in BRCA1 mutant cells; however, in BRCA1 wild-type cells, β-hCG reduced wild-type BRCA1 protein expression. Transcriptionally, β-hCG could induce Slug/LSD1-mediated repression of wild-type and mutant BRCA1 messenger RNA levels. However, β-hCG induces HSP90-mediated stabilization of mutant BRCA1 and hence the overexpression of mutant BRCA1 protein, resulting in partial restoration of homologous recombination repair of damaged DNA. This contributes to drug resistance to HSP90 inhibitor 17AAG in BRCA1-defective cancer cells. A combination of HSP90 inhibitor and TGFBRII inhibitor has shown to sensitize β-hCG expressing BRCA1-defective breast cancers to cell death. Targeting the β-hCG-HSP90-TGFBRII axis could prove an effective treatment strategy for BRCA1-mutated breast tumors.

The re-awakening of hCG expression. Its role in the diagnosis of cervical squamous cell carcinoma

Objectives:

To compare immunohistochemical detection of Human chorionic gonadotropin (hCG) expression in paraffin embedded tissue of squamous cell carcinomas (SCC) and high grade squamous intraepithelial lesions (HSIL).

Methods:

The samples in this retrospective study were obtained from the archives of the Pathology Department at Gaziantep University, Gaziantep, Turkey, over the period from January 2012 to September 2016. The study group consisted of 55 cases of SCC and 45 cases of HSIL. Tissue expression of hCG was detected by specific binding of anti-hCG antibody using an automated immunohistochemistry staining device. The categorical variables of intensity and coverage were analyzed statistically using Pearson Chi-Square test.

Results:

High grade squamous cell lesions cases showed weak (84.4%, n=38/45) to no (15.6%, n=7/45) staining for hCG. None of the HSIL cases showed strong positivity. Strong positivity for hCG was detected in 90.9% (n=50/55) of SCC cases.

Conclusion:

Our study supports the association of ectopic hCG expression in cancer pathogenesis by demonstrating strong hCG immunoreactivity only in SCC cases. This finding can be helpful in supporting the diagnosis of invasive carcinoma in small or fragmented biopsies, which can on their own be confusing for the pathologists.

BRCA1 regulation on β-hCG: a mechanism for tumorigenicity in BRCA1 defective breast cancer

Human chorionic gonadotropin β (β-hCG) has been implicated in breast tumorigenesis. However, the role of this hormone is highly controversial as certain studies suggest it has anti-tumor properties while others have found it to be pro-tumorigenic. To unveil the truth, we have analyzed the expression of β-hCG in breast cancer. We identified for the first time that β-hCG expression is linked to BRCA1 status and its overexpression is seen in BRCA1 mutated breast cancer cells, BRCA1 conditional knockout mouse breast cancer tissues and BRCA1 floxed basal cell carcinoma (BCC) tissues. An analysis of three large, transcriptomic data sets from TCGA (The Cancer Genome Atlas) expression profile confirmed the inverse correlation between BRCA1 and β-hCG in human breast cancer. Using ChIP and luciferase assays, we also demonstrated that the cancer cells with wild-type but not mutant BRCA1 directly repress the expression of β-hCG by binding to its promoter. Further, β-hCG promotes migration and invasion predominantly in BRCA1 mutant breast cancer cells. Interestingly, stable overexpression of β-hCG in BRCA1 mutant but not wild-type breast cancer cells results in the formation of spheres even on monolayer cultures. The cells of these spheres show high expression of both EMT and stem cell markers. Since β-hCG belongs to a cysteine knot family of proteins like TGFβ and TGFβ signaling is deregulated in BRCA1 defective tumors, we checked whether β-hCG can mediate signaling through TGFβRII in BRCA1 mutated cells. We found for the first time that β-hCG can bind and phosphorylate TGFβRII, irrespective of LHCGR status and induce proliferation in BRCA1 defective cells. Our results confirmed that there exists a transcriptional regulation of BRCA1 on β-hCG and BRCA1 mutation promotes β-hCG mediated tumorigenesis through TGFβRII signaling. Thus inhibiting β-hCG-TGFβRII could prove an effective treatment strategy for BRCA1 mutated tumors.

The controversial role of human chorionic gonadotropin in the development of breast cancer and other types of tumors

INTRODUCTION

Breast cancer is the most often diagnosed tumor of women and one of the leading cause of cancer related death. Due to different known risk factors there are epidemiological differences. Beside genetic disorders and patient's age it is especially the age of the first full-term pregnancy and in this context the pregnancy hormone human chorionic gonadotropin that seems to play an important role.

METHODS

This review is based on a PubMed research in publications of the last 20 years. Only articles in English language were considered.

RESULTS

The effect of human chorionic gonadotropin on development of cancer is controversial. In fact, for breast cancer there is evidence that this hormone has a protective effect against tumorigenesis due the differentiation of the mammary tissue after a full term pregnancy through the downregulation of estrogen receptors.

CONCLUSION

Human chorionic gonadotropin has among promoting pregnancy important controversial functions especially in tumor development. The mechanisms that explain the pro- and anti-carcinogenic effects are not fully understood yet. It seems to have a protective effect on breast cancer through increasing differentiation and hereby decreasing susceptibility of the mammary tissue for toxicants. This knowledge might help developing a preventive agent in the next future that uses the anti-carcinogenic effect of human chorionic gonadotropin and thereby decrease the mortality out of breast cancer.

The Role of Human Chorionic Gonadotropin as Tumor Marker: Biochemical and Clinical Aspects

Tumor markers are biological substances that are produced/released mainly by malignant tumor cells, enter the circulation in detectable amounts and are potential indicators of the presence of a tumor. The most useful biochemical markers are the tumor-specific molecules, i.e., receptors, enzymes, hormones, growth factors or biological response modifiers that are specifically produced by tumor cells and not, or minimally, by the normal counterpart (Richard et al. Principles and practice of gynecologic oncology. Wolters Kluwer Health, Philadelphia, 2009). Based on their specificity and sensitivity in each malignancy, biomarkers are used for screening, diagnosis, disease monitoring and therapeutic response assessment in clinical management of cancer patients.This chapter is focused on human chorionic gonadotropin (hCG), a hormone with a variety of functions and widely used as a tumor biomarker in selected tumors. Indeed, hCG is expressed by both trophoblastic and non-trophoblastic human malignancies and plays a role in cell transformation, angiogenesis, metastatization, and immune escape, all process central to cancer progression. Of note, hCG testing is crucial for the clinical management of placental trophoblastic malignancies and germ cell tumors of the testis and the ovary. Furthermore, the production of hCG by tumor cells is accompanied by varying degrees of release of the free subunits into the circulation, and this is relevant for the management of cancer patients (Triozzi PL, Stevens VC, Oncol Rep 6(1):7-17, 1999).The name chorionic gonadotropin was conceived: chorion derives from the latin chordate meaning afterbirth, gonadotropin indicates that the hormone is a gonadotropic molecule, acting on the ovaries and promoting steroid production (Cole LA, Int J Endocrinol Metab 9(2):335-352, 2011). The function, the mechanism of action and the interaction between hCG and its receptor continue to be the subject of intensive investigation, even though many issues about hCG have been well documented (Tegoni M et al., J Mol Biol 289(5):1375-1385, 1999).

Chemical synthesis of the β-subunit of human luteinizing (hLH) and chorionic gonadotropin (hCG) glycoprotein hormones

Human luteinizing hormone (hLH) and human chorionic gonadotropin (hCG) are human glycoprotein hormones each consisting of two subunits, an identical α-subunit and a unique β-subunit, that form noncovalent heterodimers. Structurally, β-hCG shares a high degree of sequence similarity with β-hLH, including a common N-glycosylation site at the N-terminus but differs mainly in the presence of an extended C-terminal portion incorporating four closely spaced O-linked glycans. These glycoproteins play important roles in reproduction and are used clinically in the treatment of infertility. In addition, the role of hCG as a tumor marker in a variety of cancers has also attracted significant interest for the development of cancer vaccines. In clinical applications, these hormones are administered as mixtures of glycoforms due to limitations of biological methods in producing homogeneous samples of these glycoproteins. Using the powerful tools of chemical synthesis, the work presented herein focuses on the highly convergent syntheses of homogeneous β-hLH and β-hCG bearing model glycans at all native glycosylation sites. Key steps in these syntheses include a successful double Lansbury glycosylation en route to the N-terminal fragment of β-hCG and the sequential installation of four O-linked glycosyl-amino acid cassettes into closely spaced O-glycosylation sites in a single, high-yielding solid-supported synthesis to access the C-terminal portion of the molecule. The final assembly of the individual glycopeptide fragments involved a stepwise native chemical ligation strategy to provide the longest and most complex human glycoprotein hormone (β-hCG) as well as its closely related homologue (β-hLH) as discrete glycoforms.

Serum total hCGβ level is an independent prognostic factor in transitional cell carcinoma of the urothelial tract

Background:

Serum total human chorionic gonadotrophin β subunit (hCGβ) level might have prognostic value in urothelial transitional cell carcinoma (TCC) but has not been investigated for independence from other prognostic variables.

Methods:

We utilised a clinical database of patients receiving chemotherapy between 2005 and 2011 for urothelial TCC and an independent cohort of radical cystectomy patients for validation purposes. Prognostic variables were tested by univariate Kaplan–Meier analyses and log-rank tests. Statistically significant variables were then assessed by multivariate Cox regression. Total hCGβ level was dichotomised at < vs ⩾2 IU l⁻¹.

Results:

A total of 235 chemotherapy patients were eligible. For neoadjuvant chemotherapy, established prognostic factors including low ECOG performance status, normal haemoglobin, lower T stage and suitability for cisplatin-based chemotherapy were associated with favourable survival in univariate analyses. In addition, low hCGβ level was favourable when assessed either before (median survival not reached vs 1.86 years, P=0.001) or on completion of chemotherapy (4.27 vs 0.42 years, P=0.000002). This was confirmed in multivariate analyses and in patients receiving first- and second-line palliative chemotherapy, and in a radical cystectomy validation set.

Conclusions:

Serum total hCGβ level is an independent prognostic factor in patients receiving chemotherapy for urothelial TCC in both curative and palliative settings.

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.

Minimally-aggressive gestational trophoblastic neoplasms

INTRODUCTION

We have previously defined a new syndrome "Minimally-aggressive gestational trophoblastic neoplasms" in which choriocarcinoma or persistent hydatidiform mole has a minimal growth rate and becomes chemorefractory. Previously we described a new treatment protocol, waiting for hCG rise to >3000 mIU/ml and disease becomes more advanced, then using combination chemotherapy. Initially we found this treatment successful in 8 of 8 cases, here we find this protocol appropriate in a further 16 cases. Initially we used hyperglycosylated hCG, a limited availability test, to identify this syndrome. Here we propose also using hCG doubling rate to detect this syndrome.

METHODS

Minimally aggressive gestational trophoblastic disease can be detected by chemotherapy resistance or low hyperglycosylated hCG, <40% of total hCG. It can also be identified by hCG doubling rate, with doubling time greater than 2 weeks.

RESULTS

Nineteen new cases were identified as having minimally aggressive gestational trophoblastic disease by hyperglycosylated hCG and by hCG doubling test. All were recommended to hold off further chemotherapy until hCG >3000mIU/ml. One case died prior to the start of the study, one case withdrew because of a lung nodule and one withdrew refusing the suggested combination chemotherapy. The remaining 16 women were all successfully treated.

DISCUSSION

A total of 8 plus 16 or 24 of 24 women were successfully treated using the proposed protocol, holding back on chemotherapy until hCG >3000mIU/ml.

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.

Is there a role for immunocontraception?

The world's population is continuing to grow at an alarming rate and yet no novel methods of contraception have been introduced since 1960s. The paucity of our current contraceptive armoury is indicated by the 46 million abortions that are performed each year, largely in developing countries where population growth is greatest. Thus, whatever new forms of fertility control we develop for the next millennium, the particular needs of developing countries should be borne in mind. Contraceptive vaccines have the potential to provide safe, effective, prolonged, reversible protection against pregnancy in a form that can be easily administered in the Third World. In this review we consider the contraceptive targets that might be pursued, how vaccines might be engineered and the problems generated by inter-individual variations in antibody titre. We conclude that the specifications for a safe, effective, reversible vaccine are more likely to be met in animals than man.

Evaluation of the immunogenicity of a single chain chimeric peptide composed of hCGβ and oLHα for inhibition of the growth of hCGβ-expressing cancer cells

Human chorionic gonadotropin (hCG) is a membrane-associated protein highly expressed in several types of human cancer cells. The expression in the cancer cells indicates that hCG may be a potential target molecule for cancer immunotherapy. The objective of this study was to develop a novel immunogenic molecule, which can efficiently induce the neutralizing antibody against hCG and which is also suitable for mass production. The immunogenicity of the recombinant single chain chimeric protein of hCGβ-oLHα expressed by yeast was examined. Additionally, the inhibitory effects of the anti-hCGβ-oLHα antibody on the growth of hCG-positive cancer cells were determined. It was found that hCGβ-oLHα yielded high titers of anti-hCG rabbit antibody that could effectively neutralize the bioactivity of hCG. The rabbit anti-hCGβ-oLHα IgG inhibited the proliferation of hCG-expressing human colorectal cancer cells (LS-174, HCT-116, HCT-15 and KM-12) in a dose-dependent manner. Furthermore, an intact anti-tumor vaccine was prepared by conjugating hCGβ-oLHα with tetanus toxoid (TT) and this was used to immunize Balb/c mice bearing hCG-expressing SP2/0 tumor cells. The progression of tumors in these immunized mice was remarkably inhibited. These results suggest that hCGβ-oLHα is a new promising immunogenic molecule for the development of an anti-hCG-based cancer vaccine.

Does hCG or hCGβ play a role in cancer cell biology?

The role that hCG might play in the oncogenic process in cancer is certainly complex. We know that the expression of hCG and its beta subunit is a widespread phenomenon which has been described in many cancer subtypes. However, hCG's involvement in breast cancer has been antithetical: the detection of ectopically expressed hCG(β) by breast tumors has been employed as a biomarker of malignancy, and hCG has been proposed as a ligand vehicle for toxic drugs, with the aim of targeting the LH/hCG receptor which is reported to be expressed by malignant breast tissue. However, it has also been proposed that hCG is a protective agent against the development of breast cancer, leading some to advocate hCG administration to non-pregnant women as a prophylactic measure against cancer. Nevertheless, suggestions that hCG is involved in the angiogenesis, metastasis and immune escape that are central to cancer progression - are phenomena which clearly apply to breast cancer. Indeed, a tumor vaccine based upon hCG has very recently been shown to protect against mammary tumors in mice. We propose that this apparent paradox is resolved if the free beta subunit of hCG produced by tumors acts as an autocrine anti-apoptotic and angiogenic growth factor, whilst intact heterodimeric hCG, as in pregnancy, is part of developmental signaling that initiates tissue differentiation (including breast ductal tissue development), and hence reduces the population of stem-like cells which are susceptible to oncogenic factors.

Biological functions of hCG and hCG-related molecules

BACKGROUND

hCG is a term referring to 4 independent molecules, each produced by separate cells and each having completely separate functions. These are hCG produced by villous syncytiotrophoblast cells, hyperglycosylated hCG produced by cytotrophoblast cells, free beta-subunit made by multiple primary non-trophoblastic malignancies, and pituitary hCG made by the gonadotrope cells of the anterior pituitary.

RESULTS AND DISCUSSION

hCG has numerous functions. hCG promotes progesterone production by corpus luteal cells; promotes angiogenesis in uterine vasculature; promoted the fusion of cytotrophoblast cell and differentiation to make syncytiotrophoblast cells; causes the blockage of any immune or macrophage action by mother on foreign invading placental cells; causes uterine growth parallel to fetal growth; suppresses any myometrial contractions during the course of pregnancy; causes growth and differentiation of the umbilical cord; signals the endometrium about forthcoming implantation; acts on receptor in mother's brain causing hyperemesis gravidarum, and seemingly promotes growth of fetal organs during pregnancy. Hyperglycosylated hCG functions to promote growth of cytotrophoblast cells and invasion by these cells, as occurs in implantation of pregnancy, and growth and invasion by choriocarcinoma cells. hCG free beta-subunit is produced by numerous non-trophoblastic malignancies of different primaries. The detection of free beta-subunit in these malignancies is generally considered a sign of poor prognosis. The free beta-subunit blocks apoptosis in cancer cells and promotes the growth and malignancy of the cancer. Pituitary hCG is a sulfated variant of hCG produced at low levels during the menstrual cycle. Pituitary hCG seems to mimic luteinizing hormone actions during the menstrual cycle.

Human chorionic gonadotropin and associated molecules

When considering human chorionic gonadotropin (hCG) and hCG tests, it is important to realize that it is not a single biological molecule. The regular form of hCG produced by differentiated syncytotrophoblast cells (regular hCG) is a hormone made with the primary function of maintaining the myometrial and decidual spiral arteries and the vascular supply of the placenta during the full course of pregnancy. Hyperglycosylated hCG (hCG with double-size O-linked oligosaccharides) is made by undifferentiated cytotrophoblast cells. This is an autocrine hormone with separate functions, it maintains invasion as in implantation of pregnancy and malignancy in gestational trophoblastic diseases. A hyperglycosylated free beta-subunit is produced by a high proportion of all malignancies. This functions as an autocrine hormone to promote the growth and invasion of the malignancy. It is important to realize when ordering an hCG test what you are measuring and whether the test ordered will detect appropriately these three variant of hCG as well as their degradation products. Most automated commercial laboratory tests, point-of-care test and over-the-counter tests are limited in what is detected, focusing only on regular hCG. This is in part due to the US FDA, who only consider hCG as a pregnancy test, and to whom only detection of regular hCG is critical. This may be a cause of test errors since primarily hyperglycosylated hCG is produced in early pregnancy, choriocarcinoma and germ cell testicular malignancies, and only free beta-subunit may be produced in other germ cell malignancies (all applications for hCG test). The exceptions are the older style hCGbeta radioimmunoassay and the Siemen's Immulite platform hCG test which detect all variant and their degradation product appropriately. Regardless of test specificity limitations, assays for hCG variants are widely used clinically in pregnancy detection, early pregnancy detection, prediction of spontaneously aborting and ectopic pregnancies and prediction of trisomy pregnancies. hCG tests are essential in managing gestational trophoblastic diseases, whether hydatidiform mole, invasive mole or choriocarcinoma, and are very useful in management of testicular malignancies and other germ cell malignancies.

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.

Kinetic analysis of a human chorionic gonadotropin-beta epitope-paratope interaction

Kinetics of protein-protein or ligand-ligate interaction has predominantly been studied by optical spectroscopy (particularly fluorescence) and surface plasmon resonance biosensors. Almost all such studies are based on association kinetics between ligand-ligate and suffer from certain methodological and interpretational limitations. Therefore, kinetic analyses of dissociation data of such interactions become indispensable. In the present investigation, the radiolabeled human chorionic gonadotropin-beta ((125)IhCGbeta) was employed as a probe and nitrocellulose (NC) as a solid support to immobilize monoclonal antibody (MAb) G(1)G(10).1. The NC-G(1)G(10).1-(125)IhCGbeta complex (NC(com)) was prepared and the dissociation of radiolabeled hCGbeta was carried out in the presence of excess unlabeled ligate. From the experimental dissociation data under varying ionic strength, dissociation constants (k(- 1)), association constants (k(+1)) and affinity constants (k(a)) were calculated. The values obtained were utilized in exploring the amino acid residues constituting an epitopic region of hCGbeta involved in interaction with the complementary paratope on MAb G(1)G(10).1. Kinetic data of the present study supported our recently published findings [using single step-solid phase radioimmunoassay (SS-SPRIA)] that the core region of hCGbeta epitope consists of Arg (94,95) and Asp (99) while a Lys (104) and a His (106) are in proximity to the core epitopic region. Based on the results of present investigation, we conclude that dissociation kinetics coupled with SS-SPRIA unequivocally provides considerable insight into the study of ligand-ligate interactions and epitope analysis.