Design of a long-acting follitropin agonist by fusing the C-terminal sequence of the chorionic gonadotropin beta subunit to the follitropin beta subunit

Pharmacologic profiling of corifollitropin alfa, the first developed sustained follicle stimulant

Corifollitropin alfa (Elonva®, MSD, previously N.V. Organon or Schering-Plough Oss, The Netherlands) is a newly developed sustained follicle stimulant composed of the α subunit of human follicle-stimulating hormone (FSH) and a hybrid β subunit formed by fusion of the human chorionic gonadotropin β subunit carboxy terminal peptide with the β subunit of human FSH. Binding characteristics of corifollitropin alfa at the rat FSH receptor and transactivation properties at the rat FSH receptor, human luteinizing hormone (LH) receptor, and human thyroid-stimulating hormone receptor (TSH receptor) were assessed in vitro. Bioactivity of corifollitropin alfa in rats was also assessed. Serum corifollitropin alfa levels in rats and dogs were used to derive the main pharmacokinetic parameters of corifollitropin alfa. Binding and transactivation profile of corifollitropin alfa to rat FSH receptor was specific and comparable to that of recombinant human FSH, with no intrinsic TSH receptor or LH receptor activation. From pharmacokinetic studies, circulating half-life of corifollitropin alfa was calculated to be 17.3h in rats and 46.9h in dogs, 1.5- to 2-fold longer than recombinant FSH. Corifollitropin alfa demonstrated a 2- to 4-fold increase in bioactivity (ovarian weight, serum estradiol and progesterone, ovulated ova) over recombinant FSH across all in vivo parameters assessed. These data demonstrate that corifollitropin alfa is a specific ligand with high affinity for FSH receptor, lacking intrinsic activity for LH receptor and TSH receptor. By virtue of its increased in vivo half-life, corifollitropin alfa can be a valuable alternative to FSH by acting as a sustained follicle stimulant.

Corifollitropin Alfa: A Novel Long-Acting Recombinant Follicle-Stimulating Hormone Agonist for Controlled Ovarian Stimulation

The advent of recombinant technology has made the production of modified proteins with desired properties possible. Corifollitropin alfa is a successful example of the first available long-acting, follicle stimulating hormone. Corifollitropin alfa has prolonged half-life and a slower absorption rate, but has the same receptor-binding and biological activity as recombinant FSH (rFSH). Its application is associated with the arrival of a novel simplified approach for controlled ovarian stimulation in IVF patients. Different studies have proven the efficiency of a single corifollitropin alfa dose to initiate and sustain multiple follicular development in a gonadotropin-releasing hormone antagonist protocol. Finally, corifollitropin alfa is well tolerated and is not correlated with serious adverse events, except for the slightly higher incidence of ovarian hyperstimulation syndrome compared with traditional management with recombinant FSH.

Follicle stimulating hormone receptor mutations and reproductive disorders

The follicle stimulating hormone receptor (FSHR) plays a critical role in reproductive function. In the males, FSH supports spermatogenesis, whereas in females, FSH is absolutely required for ovarian follicle growth. In females, inactivating mutations in the FSHR result in ovarian dysgenesis with amenorrhea and infertility. The few males reported with severe inactivating mutations exhibited varying spermatogenic defects, but not azoospermia. While these findings may potentially suggest that FSH action is not absolutely required for spermatogenesis, it cannot be ruled out that these individuals have some residual FSHR activity. Gain-of-function mutations in the FSHR cause spontaneous ovarian hyperstimulation syndrome in females due to the inappropriate stimulation of the mutant FSHR by human choriogonadotropin.

The mammalian ovary from genesis to revelation

Two major functions of the mammalian ovary are the production of germ cells (oocytes), which allow continuation of the species, and the generation of bioactive molecules, primarily steroids (mainly estrogens and progestins) and peptide growth factors, which are critical for ovarian function, regulation of the hypothalamic-pituitary-ovarian axis, and development of secondary sex characteristics. The female germline is created during embryogenesis when the precursors of primordial germ cells differentiate from somatic lineages of the embryo and take a unique route to reach the urogenital ridge. This undifferentiated gonad will differentiate along a female pathway, and the newly formed oocytes will proliferate and subsequently enter meiosis. At this point, the oocyte has two alternative fates: die, a common destiny of millions of oocytes, or be fertilized, a fate of at most approximately 100 oocytes, depending on the species. At every step from germline development and ovary formation to oogenesis and ovarian development and differentiation, there are coordinated interactions of hundreds of proteins and small RNAs. These studies have helped reproductive biologists to understand not only the normal functioning of the ovary but also the pathophysiology and genetics of diseases such as infertility and ovarian cancer. Over the last two decades, parallel progress has been made in the assisted reproductive technology clinic including better hormonal preparations, prenatal genetic testing, and optimal oocyte and embryo analysis and cryopreservation. Clearly, we have learned much about the mammalian ovary and manipulating its most important cargo, the oocyte, since the birth of Louise Brown over 30 yr ago.

A double-blind, non-inferiority RCT comparing corifollitropin alfa and recombinant FSH during the first seven days of ovarian stimulation using a GnRH antagonist protocol

BACKGROUND

Corifollitropin alfa, a fusion protein lacking LH activity, has a longer elimination half-life and extended time to peak levels than recombinant FSH (rFSH). A single injection of corifollitropin alfa may replace seven daily gonadotrophin injections during the first week of ovarian stimulation.

METHODS

In this large, double-blind, randomized, non-inferiority trial the ongoing pregnancy rates were assessed after one injection of 150 µg corifollitropin alfa during the first week of stimulation and compared with daily injections of 200 IU rFSH using a standard GnRH antagonist protocol.

RESULTS

The study population comprised 1506 treated patients with mean age of 31.5 years and body weight of 68.6 kg. Ongoing pregnancy rates of 38.9% for the corifollitropin alfa group and 38.1% for rFSH were achieved, with an estimated non-significant difference of 0.9% [95% confidence interval (CI): −3.9; 5.7] in favor of corifollitropin alfa. Stratified analyses of pregnancy rates confirmed robustness of this primary outcome by showing similar results regardless of IVF or ICSI, or number of embryos transferred. A slightly higher follicular response with corifollitropin alfa resulted in a higher number of cumulus–oocyte-complexes compared with rFSH [estimated difference 1.2 (95% CI: 0.5; 1.9)], whereas median duration of stimulation was equal (9 days) and incidence of (moderate/severe) ovarian hyperstimulation syndrome was the same (4.1 and 2.7%, respectively P = 0.15).

CONCLUSION

Corifollitropin alfa is a novel and effective treatment option for potential normal responder patients undergoing ovarian stimulation with GnRH antagonist co-treatment for IVF resulting in a high ongoing pregnancy rate, equal to that achieved with daily rFSH. The trial was registered under ClinicalTrials.gov identifier NTC00696800.

Secretory trafficking signal encoded in the carboxyl-terminal region of the CGbeta-subunit

Although the LHbeta- and chorionic gonadotropin-beta- (CGbeta) subunits share a high degree of sequence identity (>85%) in the first 114 amino acids, there is considerable sequence divergence at their carboxy ends. The CGbeta-subunit terminates with a unique carboxyl-terminal extension (115-145; carboxyl-terminal peptide), which contains four O-linked oligosaccharides, whereas the LHbeta-subunit bears a hydrophobic heptapeptide (115-121) at its carboxy terminus. LH is released through the regulated pathway in the pituitary, whereas CG is secreted constitutively from the placenta. We previously demonstrated in rat somatotroph-derived GH(3) cells that the LH is associated primarily with a regulated routing, and although the majority of CG was released constitutively from the cells, there was a fraction that was segregated through the regulated pathway. Moreover, we showed that the LHbeta heptapeptide is a determinant for the regulated secretion of LH. Given that the primary evolutionary change between LHbeta and CGbeta occurred at the carboxy terminus, these data suggested that the presence of the CGbeta carboxyl-terminal peptide region is responsible for the constitutive secretion of CG. A CG114 mutant (CGDeltaT) was constructed and expressed in GH(3) cells. Steady-state labeling and pulse-chase experiments demonstrated that the CGDeltaT entered the regulated pathway resulting in over 4-fold increase in the intracellular pool. The secretagogue, forskolin, stimulated CGDeltaT release over 3-fold, which was accompanied by a parallel intracellular decrease, and only marginal stimulation of CG was seen. Immunofluorescence demonstrated a unique membrane pattern of staining for CGDeltaT compared with dispersed cytoplasmic puncta for CG. Stimulation with forskolin caused a significant reduction in the relative fluorescence of CGDeltaT cells compared with a minor reduction for CG. These data show that the CGDeltaT analog resembles LH in its intracellular trafficking, further supporting the hypothesis that determinants at the carboxyl-terminal end of the CGbeta-subunit evolved from the LHbeta-subunit primarily to overcome the slow release and intracellular storage of LH resulting in rapid secretion of CG from the placenta.

Efficacy of native and hyperglycosylated follicle-stimulating hormone analogs for promoting fertility in female mice

OBJECTIVE

To compare the efficacy of recombinant human FSH (rhFSH) with rhFSH with four additional O-linked carbohydrates (rhFSH-CTP), rhFSH with four additional N-linked carbohydrates (rhFSH-N4), and the current gold standard for rodent ovarian stimulation, pregnant mare serum gonadotropin (PMSG), on fertility parameters in mice.

DESIGN

Animal study.

SETTING

Academic research center.

ANIMAL(S)

Adult C57Bl/6J female mice.

INTERVENTION(S)

Ovarian stimulation with 5 IU of rhFSH, rhFSH-CTP, rhFSH-N4, or PMSG. Forty-six hours later, 5 IU of hCG was injected to promote ovulation and females were mated overnight.

MAIN OUTCOME MEASURE(S)

Eggs retrieved after ovulation, in vitro embryo development, delivery rate, and litter size.

RESULT(S)

The hyperglycosylated FSH analogs, rhFSH-CTP and rhFSH-N4, enhanced ovulation and embryo maturation significantly better than rhFSH. RhFSH-N4 produced more eggs (28.5 +/- 1.9 per mouse) and embryos (17.8 +/- 1.6) compared with rhFSH-CTP (18.3 +/- 1.2 and 9.0 +/- 1.0, respectively). Treatment with rhFSH, rhFSH-N4, and PMSG produced statistically equivalent delivery rates and litter sizes. The delivery rate was surprisingly lower with rhFSH-CTP (14%) compared with PMSG (33%).

CONCLUSION(S)

Compared with rhFSH, treatment with hyperglycosylated rhFSH-CTP and rhFSH-N4 led to superior rates of ovulated eggs and subsequent in vitro embryo development. RhFSH-N4 was equivalent to PMSG, while all of the fertility parameters studied were lower with rhFSH-CTP than with PMSG therapy.

Development of a long-acting erythropoietin by fusing the carboxyl-terminal peptide of human chorionic gonadotropin beta-subunit to the coding sequence of human erythropoietin

Human erythropoietin (EPO) is a glycoprotein hormone secreted from the kidney and controls red blood cell production. EPO has a wide clinical use in the treatment of anemia associated with renal disease, certain chronic diseases, and anemia related to chemotherapy and radiotherapy. One major issue regarding the clinical use of EPO is its relatively short half-life due to its clearance by glomerular filtration. Thus, the therapeutic protocol used in the treatment of patient-required frequent injections of EPO. To address this issue, we constructed a chimeric gene that contains the sequence of the carboxyl-terminal peptide (CTP) of human chorionic gonadotropin-beta subunit bearing four O-linked oligosaccharide recognition sites and the coding sequence of human EPO cDNA. Fusing the CTP to the carboxyl-terminal of EPO did not affect secretion, receptor binding affinity, or in vitro bioactivity. However, both in vivo potency and half-life of EPO-CTP were significantly enhanced. A single injection dose (660 IU/kg) of EPO wild-type administered once a week had no significant effect on haematocrit levels. However, EPO-CTP administered as 660 IU/kg once a week was effective as well as the same total dose of EPO wild-type administered as 220 IU/kg three times a week. This may emphasize the importance of sustained blood levels rather than total dose of administration for in vivo bioactivity. These data established the rationale for using this chimera as a long-acting EPO analog. The therapeutic efficacy of EPO-CTP analog needs to be established in higher animals and human clinical trials.

Strategies for construction of luteinizing hormone beta subunit analogs with carboxyl terminal extensions in non-primate, non-equid mammalian species

Chorionic gonadotropins (CG) are unique because they have a carboxyl terminal peptide (CTP) extension on their beta subunits that prolongs circulatory survival. CGbeta genes from the human being and horse have evolved from ancestral luteinizing hormone (LH) beta genes by different pathways that involve deletions that change the reading frames and yield a CTP. Here we further review our previous analysis, aimed at determining whether LHbeta genes in non-primate, non-equid species inherently possess DNA sequences that encode CTP-like domains. In multiple mammalian species, simple frame-shift mutations using either the human or equine CGbeta gene as a model can be used to construct LHbeta analogs with putative CTP domains. Furthermore, DNA sequences from mammalian LHbeta genes can be aligned to maximize similarity with CGbeta genes in order to devise more refined strategies for construction of CTP-bearing LHbeta analogs as exemplified in the bovine case. Thus, mammalian LHbeta genes have DNA sequences that can be potentially expressed in order to construct CTP-bearing glycoprotein hormone analogs.

The science behind 25 years of ovarian stimulation for in vitro fertilization

To allow selection of embryos for transfer after in vitro fertilization, ovarian stimulation is usually carried out with exogenous gonadotropins. To compensate for changes induced by stimulation, GnRH analog cotreatment, oral contraceptive pretreatment, late follicular phase human chorionic gonadotropin, and luteal phase progesterone supplementation are usually added. These approaches render ovarian stimulation complex and costly. The stimulation of multiple follicular development disrupts the physiology of follicular development, with consequences for the oocyte, embryo, and endometrium. In recent years, recombinant gonadotropin preparations have become available, and novel stimulation protocols with less detrimental effects have been developed. In this article, the scientific background to current approaches to ovarian stimulation for in vitro fertilization is reviewed. After a brief discussion of the relevant aspect of ovarian physiology, the development, application, and consequences of ovarian stimulation strategies are reviewed in detail.

The role of O-linked and N-linked oligosaccharides on the structure-function of glycoprotein hormones: development of agonists and antagonists

Thyrotropin (TSH) and the gonadotropins; follitropin (FSH), lutropin (LH) and human chorionic gonadotropin (hCG) are a family of heterodimeric glycoprotein hormones. These hormones composed of two noncovalently linked subunits; a common alpha and a hormone specific beta subunits. Assembly of the subunits is vital to the function of these hormones. However, genetic fusion of the alpha and beta subunits of hFSH, hCG and hTSH resulted in active polypeptides. The glycoprotein hormone subunits contain one (TSH and LH) or two (alpha, FSHbeta and hCGbeta) asparagine-linked (N-linked) oligosaccharides. CGbeta subunit is distinguished among the beta subunits because of the presence of a carboxyl-terminal peptide (CTP) bearing four O-linked oligosaccharide chains. To examine the role of the oligosaccharide chains on the structure-function of glycoprotein hormones, chemical, enzymatic and site-directed mutagenesis were used. The results indicated that O-linked oligosaccharides play a minor role in receptor binding and signal transduction of the glycoprotein hormones. In contrast, the O-linked oligosaccharides are critical for in vivo half-life and bioactivity. Ligation of the CTP bearing four O-linked oligosaccharide sites to different proteins, resulted in enhancing the in vivo bioactivity and half-life of the proteins. The N-linked oligosaccharide chains have a minor role in receptor binding of glycoprotein hormones, but they are critical for bioactivity. Moreover, glycoprotein hormones lacking N-linked oligosaccharides behave as antagonists. In conclusion, the O-linked oligosaccharides are not important for in vitro bioactivity or receptor binding, but they play an important role in the in vivo bioactivity and half-life of the glycoprotein hormones. Addition of the O-linked oligosaccharide chains to the backbone of glycoprotein hormones could be an interesting strategy for designing long acting agonists of glycoprotein hormones. On the other hand, the N-linked oligosaccharides are not important for receptor binding, but they are critical for bioactivity of glycoprotein hormones. Deletion of the N-linked oligosaccharides resulted in the development of glycoprotein hormone antagonists. In the case of hTSH, development of an antagonist may offer a novel therapeutic strategy in the treatment of thyrotoxicosis caused by Graves' disease and TSH secreting pituitary adenoma.

FSH and folliculogenesis: from physiology to ovarian stimulation

FSH is a glycoprotein hormone consisting of two peptide subunits. The role of FSH in folliculogenesis is well known: to stimulate the formation of a large pre-ovulatory follicle that, because of its FSH-dependent maturation, is capable of ovulation and forming a corpus luteum in response to the mid-cycle surge of LH. FSH is widely used in ovarian stimulation for assisted reproduction techniques. Ovarian stimulation protocols combine the use of human menopausal gonadotrophin, urinary FSH or recombinant FSH with gonadotrophin-releasing hormone (GnRH) agonists or antagonists in order to increase oocyte number and to avoid premature LH surge. Recently, the availability of recombinant LH has permitted new stimulation protocols, combining recombinant FSH, recombinant LH and GnRH antagonists. Due to the limitations of the new Italian law in terms of the number of oocytes that can be fertilized, protocols with a softer ovarian stimulation are now considered, reducing risk of ovarian hyperstimulation syndrome, multiple pregnancies and emotional and physical burdens on the patients. Long-acting FSH preparations are also under clinical study. Knowledge of the stereochemical three-dimensional structure of FSH and its receptor will allow the study of new non-peptide orally administered molecules that fit the FSH receptors.

Effects of long-acting recombinant human follicle-stimulating hormone analogs containing N-linked glycosylation on murine folliculogenesis

OBJECTIVE

To evaluate the efficacy of two novel long-acting rhFSH analogs, rhFSH-N2 and rhFSH-N4, in stimulating murine folliculogenesis.

DESIGN

Experimental study.

SETTING

Academic research environment.

ANIMAL(S)

Immature female mice.

INTERVENTION(S)

Recombinant hFSH-N2 and -N4 were administered via single IP injection to 3-week-old female mice (n = 10) who were killed 48 hours later for dissection and histologic examination of reproductive organs and serum inhibin A. Results were compared with other groups of mice who received either single or q 12 hour injections for 48 hours of commercial rhFSH, or a single injection of pregnant mare serum gonadotropin (PMSG). A subgroup of the mice receiving rhFSH-N4 was supplemented with daily injections of small doses of hCG to simulate LH add-back.

MAIN OUTCOME MEASURE(S)

Serum inhibin A levels, ovarian and uterine weights, and ovarian antral follicle counts.

RESULTS(S)

Recombinant human FSH-N2 and -N4 administration induced a statistically significant increase in ovarian weights, uterine weights, and inhibin A levels compared with single and twice-daily injection of rhFSH. PMSG induced the greatest increases in all three measured parameters. There was no statistical difference between rhFSH-N2 and rhFSH-N4 for any parameter analyzed. A single injection of rhFSH-N2 or -N4 induced a greater number of antral follicles than did either single or q 12 hour injections of rhFSH. The addition of small doses of hCG to rhFSH-N4 increased inhibin A levels and antral follicle number to reach statistical equivalence to PMSG treatment.

CONCLUSION(S)

Addition of a synthetic polypeptide containing two or four N-linked glycosylation sites to rhFSH increases in vivo bioactivity of the hormone compared to commercial rhFSH. After a single injection, both rhFSH-N2 and rhFSH-N4 effectively induced a greater follicular response in the mouse than did rhFSH.

Human thyrotropin (TSH) variants designed by site-directed mutagenesis block TSH activity in vitro and in vivo

TSH is a heterodimeric glycoprotein hormone synthesized in the pituitary and composed of a specific beta-subunit and a common alpha-subunit shared with FSH, LH, and human chorionic gonadotropin. The heterodimer was previously converted into a biologically active single chain protein by genetic fusion of the genes coding to both subunits in the presence of the carboxy-terminal sequence of human (h) chorionic gonadotropin-beta subunit as a linker [hTSHbeta-carboxyl-terminal peptide (CTP)-alpha]. N-linked carbohydrate-free single-chain TSH variants were constructed by site-directed mutagenesis and overlapping PCR: one devoid of both N-linked oligosaccharide chains on the alpha-subunit (hTSHbeta-CTP-alpha(deg)) and the other lacking also the oligosaccharides on the beta-subunit (hTSHbeta(deg)-CTP-alpha(deg)). These variants were expressed in Chinese hamster ovary cells and secreted into the culture media. We have previously reported that the variants block the activities of hTSH and thyroid-stimulating immunoglobulins in cultured human thyroid follicles. In the present study, binding affinity of hTSH variants to hTSH receptor and the localization of the antagonistic effect were examined. Moreover, the effect of these variants on TSH activity was tested in vivo. The results of the present study indicate that the hTSH variants bind to the hTSH receptor with high affinity. Experiments using forskolin also indicated that the N-linked carbohydrate-free TSH single-chain variants inhibit TSH activity at the receptor-binding site and not at a postreceptor level. Moreover, the variants significantly inhibited (about 50%) TSH activity with respect to thyroid hormone secretion in vivo in mice. These variants may offer a novel therapeutic strategy in treating hyperthyroidism.

Molecular pharmacology of gonadotropins

Gonadotropins have been studied in biological systems for decades and many of their properties are well defined. These include pharmacological properties such as affinity, stability, and pharmacokinetics also used to characterize drugs. Technologies applied to research on gonadotropins have led to the creation of hormone analogs with alterations to one or more of these proper-ties. Some of these analogs have potential therapeutic applications. A challenge to realizing this potential is the accurate prediction of how these compounds will perform in humans. This could be facilitated by advances in biological models and the understanding of specific effects of the hormones on their receptors.

The LHbeta gene of several mammals embeds a carboxyl-terminal peptide-like sequence revealing a critical role for mucin oligosaccharides in the evolution of lutropin to chorionic gonadotropin in the animal phyla

The expression of a previously untranslated carboxylterminal sequence is associated with the ancestral lutropin (LH) beta to the beta-subunit gene evolution of choriogonadotropins (CG). The peptide extension (denoted as CTP) is rich in mucin-type O-glycans and confers new hormonal properties on CG relative to the LH. Although the LHbeta gene is conserved among mammals and only a few frameshift mutations account for the extension, it is merely seen in primates and equids. Bioinformatics identified a CTP-like sequence that is encrypted in the LHbeta gene of several mammalian species but not in birds, amphibians, or fish. We then examined whether or not decoding of the cryptic CTP in the bovine LHbeta gene (boCTP) would be sufficient to generate the LHbeta species of a ruminant with properties typical to the CGbeta subunit. The mutated bovine LHbeta-boCTP subunit was expressed and N-glycosylated in transfected Chinese hamster ovary cells. However, unlike human (h) CGbeta CTP, the cryptic boCTP was devoid of mucin O-glycans. This deficiency was further confirmed when the boCTP domain was substituted for the natural CTP in the human CGbeta subunit. Moreover, when expressed in polarized Madin-Darby canine kidney cells, this hCGbeta-boCTP chimera was secreted basolaterally rather than from the apical compartment, which is the route of the wild type hCGbeta subunit, a sorting function attributed to the O-glycans attached to the CTP. This result shows that the cryptic peptide does not orientate CG to the apical face of the placenta, to the maternal circulation as seen in primates. The absence of this function, which distinguishes CG from LH, provides an explanation as to why the LHbeta to CGbeta evolution did not occur in ruminants. We propose that in primates and equids, further natural mutations in the progenitor LHbeta gene resulted in the efficient O-glycosylation of the CTP, thus favoring the retention of an elongated reading frame.

Production of biologically active tethered tilapia LHbetaalpha by the methylotrophic yeast Pichia pastoris

In fish, luteinizing hormone (LH) stimulates processes leading to final oocyte maturation and ovulation in females, and spermiation in males. The hormone is a heterodimeric glycoprotein composed of two non-covalently associated subunits. In this study, we describe the expression of tilapia LH (tLH) as a biologically active, single-chain polypeptide using the methylotrophic yeast Pichia pastoris. The tLHbeta and alpha mature protein-coding sequences were joined to form a fusion gene that encodes a "tethered" polypeptide in which the tLHbeta-chain forms the N-terminal part and the alpha-chain forms the C-terminal part. A "linker" sequence of six amino acids (three Gly-Ser pairs) was placed between the beta- and alpha-chains to assist in the chimerization of the subunits, and a six-His tail was placed at the end of the beta-subunit, to enable purification of the recombinant protein. Western blot analysis of the pituitary LH resolved by SDS-PAGE yielded a band of 35 kDa, while the recombinant tLHbetaalpha had a molecular mass of 45 kDa, and was found to possess only N-linked carbohydrates. Recombinant tLHbetaalpha stimulated the release of 11-ketotestosterone from mature testes, whereas its release from immature testes was less pronounced.

Recombinant follicle-stimulating hormone: gold standard or not?

Recombinant follicle stimulating hormone has been available now for almost 10 years and many couples have benefited from its use. Its clinical efficacy, purity and safety profile have been extensively documented in numerous publications. Because of growing public concerns on the safety of gonadotrophins extracted from human urine, the future will lie in the recombinant technology, which will also enable the design of more convenient tailor-made gonadotrophins.

Historical perspectives in gonadotrophin therapy

The 20th century witnessed the steady development of knowledge about the reproductive process in animals and humans. These advances led to the identification of higher centres governing the dynamics of ovarian function and to the discovery of gonadotrophic hormones. As the mechanisms of action of these hormones became increasingly understood, they began to be used in the management of infertility during the early 1930s. Hormone extracts were originally prepared from animal pituitaries and pregnant mare serum, as well as from human pituitaries, placenta and urine, with pregnancies reported following their use in the late 1930s. This review traces the constant quest to reduce risks and improve safety and efficacy of hormone preparations for patients. It describes the complex path and perils leading to the pure hormone preparations that are available today, concluding with an optimistic glimpse towards the future. Small molecules that are orally active and specific are currently being investigated, some with the capacity to bypass many parts of the receptor conformation. Here lies the immediate future of this field, utilizing low-cost, small, defined molecules to stimulate follicle growth, ovulation and corpus luteum formation. Perhaps one day the classical gonadotrophins will no longer be required in clinical treatment.

Use of protein knobs to characterize the position of conserved alpha-subunit regions in lutropin receptor complexes

Efforts to identify the manner in which human choriogonadotropin (hCG) contacts lutropin receptors (LHR) have been stymied by the complex structure of the hormone and the likelihood that it contacts the receptor at multiple sites. During studies of hCG assembly in mammalian cells, we found that addition of a cysteine to the long disordered beta-subunit COOH terminus (betaCT) enabled it to become cross-linked by a disulfide to cysteines that are substituted for residues in loop alpha2 or in the alpha-subunit COOH terminus (alphaCT). This created a "knob" on the alpha-subunit at the location of the cysteine. Knobs of various sizes and charges were useful for probing surfaces of the alpha-subunit thought previously to contact the LHR. Attachment of the betaCT to residues in loop alpha2 facing loops beta1 and beta3 reduced hormone activity only a few fold revealing that this surface does not participate in essential high affinity receptor contacts, a finding inconsistent with our earlier view of the hCG-LHR complex. In contrast, this approach showed that the opposite surface of loop alpha2 appeared to be nearer the receptor interface. Although attachment of knobs to portions of the alphaCT reduced hormone activity substantially, this finding was difficult to interpret. As discussed, this procedure should be adapted readily to other proteins and may facilitate the introduction of fluorophores, enzymes, or other reagents at specific sites on protein surfaces. It may also permit one to cross-link proteins or to obscure specific protein surfaces during the development of "Trojan Horse" therapeutics.

Luteinizing Hormone and Follicle-Stimulating Hormone Exhibit Different Secretion Patterns from Cultured Madin-Darby Canine Kidney Cells

LH, FSH, and chorionic gonadotropin (CG) are comprised of a common alpha subunit and a hormone-specific beta subunit. Using Madin-Darby canine kidney (MDCK) epithelial cells to examine the polarized secretion of human CG/LH, we previously reported that CG and LH were detected in the apical and basolateral compartments, respectively, and the carboxyl terminal end of the CGbeta subunit contains a strong apical signal. Here we show that the carboxyl seven amino acids in the LHbeta subunit contribute to the basolateral secretion of LH, and an LH chimera bearing the CGbeta apical signal is redirected from the basolateral to the apical compartments. Because LH and FSH are synthesized in the same cell, we also compared the secretion polarity of LH with FSH. MDCK cells expressing the FSH dimer displayed an almost equal distribution of protein into the apical and basolateral compartments. Given that the LHbeta and CGbeta carboxy terminal sequences, which differ from that in the FSHbeta subunit, occupy a pivotal role in their polarized behavior, the results support the hypothesis that pituitary exit of LH and FSH occur via different secretion pathways, and are released spatially from the pituitary via different circulatory routes.

Processing of O-linked glycosylation in the chimera consisting of alpha-subunit and carboxyl-terminal peptide of the human chorionic gonadotropin beta-subunit is affected by dimer formation with follicle-stimulating hormone beta-subunit

hCG, LH, FSH, and TSH are a family of heterodimeric glycoprotein hormones that contain a common alpha-subunit, but differ in their hormone-specific beta-subunits. hCGbeta is unique among beta-subunits due to a carboxyl-terminal peptide (CTP) bearing four O-linked oligosaccharides. We previously reported that there were differences in O-glycosylation between two chimeras consisting of alpha-subunit and CTP, i.e. a variant with CTP at the N-terminal region (Calpha) and another analog with CTP at the C-terminus (alphaC) of the alpha-subunit. To address whether O-glycosylation is influenced by the heterodimer formation, Calpha and alphaC were expressed alone or with FSHbeta-subunit in Chinese hamster ovary cells. The O-linked glycosylation was assessed by continuous labeling with [(35)S]methionine/cysteine, immunoprecipitation with anti-alpha or anti-FSH serum, serial digestion with endoglycosidase-F and neuraminidase, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The decrease in molecular weight of dimeric chimeras digested with endoglycosidase-F was greater in Calpha than that in alphaC after treatment with neuraminidase, revealing that both chimeras have different numbers of sialic acids on O-linked carbohydrates. By treating with endoglycosidase-F, the dimeric alphaC migrated faster than its free form, whereas the mobility difference between assembled and unassembled forms of Calpha was very little. These data indicate that processing of O-glycosylation is affected by the backbone polypeptide chain(s).

Glycosylation of an N-terminal extension prolongs the half-life and increases the in vivo activity of follicle stimulating hormone

FSH is a key component in assisted reproductive technologies. Because of rapid clearance of the hormone, patients have to be treated with daily injections. To address this problem, a long-acting FSH mutein was created by introduction of additional N-linked glycosylation into the molecule. New glycosylation sites were introduced by two different approaches: structure-aided, site-directed introduction of sites within the FSH molecule and addition of N-terminal extensions. A mutein with the extension sequence ANITVNITV at the N terminus of the alpha-chain (FSH1208) was efficiently glycosylated at both new sites. This resulted in a molecule with increased size and charge, factors known to reduce renal clearance of proteins. FSH1208 was found to have a 3- to 4-fold increased serum half-life, compared with wild-type recombinant FSH. Furthermore, in spite of a lower in vitro activity, FSH1208 had a markedly increased in vivo potency, as shown by increased ability to augment the ovarian weight and stimulate the serum estradiol levels in rats. These characteristics make FSH1208 a possible candidate for improved infertility treatment.

First live birth after ovarian stimulation using a chimeric long-acting human recombinant follicle-stimulating hormone (FSH) agonist (recFSH-CTP) for in vitro fertilization

OBJECTIVE

To report the first pregnancy and live birth after ovarian stimulation using a chimeric long-acting human recombinant FSH agonist (recFSH-CTP) for IVF.

DESIGN

Case report.

SETTING

Tertiary fertility center.

PATIENT(S)

A 32-year-old woman with a 7-year history of primary infertility.

INTERVENTION(S)

Ovarian stimulation with a single SC injection of 180 microg recFSH-CTP on cycle day 3, followed by daily injections of 150 IU recFSH from cycle day 10 onward, combined with daily GnRH antagonist 0.25 mg SC to prevent a premature LH rise. Final oocyte maturation was induced by 10,000 IU hCG.

MAIN OUTCOME MEASURE(S)

First ongoing pregnancy obtained with recFSH-CTP.

RESULT(S)

Twelve oocytes were retrieved. Ten oocytes were fertilized in vitro by intracytoplasmic sperm injection, and from these 10 oocytes, two embryos were subsequently transferred after 3 days of culture. A pregnancy test 2 weeks after ET was positive, and ultrasound investigation revealed an intact, intrauterine, singleton pregnancy after 12 weeks.

CONCLUSION(S)

The first pregnancy and live birth was achieved after ovarian stimulation using recFSH-CTP for IVF.

Development of gonadotrophins for clinical use

The 20th century witnessed the steady development of knowledge about reproductive physiology and endocrinology in animals and humans. These advances led to the identification of higher centres governing the ovary and its follicles. Effects of X-rays on the head and other agents, or excision of the pituitary gland, led to anomalies in oestrous and menstrual cycles in animals and women, respectively. Studies on pituitary and placental extracts revealed the presence of hormones regulating the ovarian follicles and the corpus luteum for the implanting embryo. These were identified as follicle stimulating hormone (FSH), luteinizing hormone (LH) and human chorionic gonadotrophin (HCG). Increasing understanding of the mechanisms of action of these hormones led to treatments of animals and amenorrhoeic women with FSH- and LH-containing preparations in order to induce the growth of follicles and ovulation. Human FSH-rich preparations were obtained by extracting urinary gonadotrophins from the urine of post-menopausal women, and thousands of amenorrhoeic and/or anovulatory patients were treated with human menopausal gonadotrophin (HMG) and HCG to induce multifolliculation and ovulation. The introduction of IVF greatly increased the numbers of women treated in this fashion, now including cyclic women. By the mid-1980s, following the appearance of Creutzfeld-Jakob disease in women treated with gonadotrophins extracted from human pituitaries, and other safety considerations, attempts were being made to purify urinary gonadotrophin preparations, using antibodies. Increasing interest in recombinant preparations, which were pure, highly specific and highly active preparations, characterized the last years of the 20th century and the new millennium. These preparations included recombinant FSH (rFSH), recombinant LH (rLH) and recombinant HCG (rHCG). Yet, in one sense, the recombinant preparations could change the procedures of ovarian stimulation, because they focused attention on the membranal receptor in the follicle, and how best to stimulate it. Small molecules are currently being investigated, with some proving to be very active and specific, and even capable of bypassing many parts of the receptor conformation. Here lies the immediate future of this field, utilizing small, defined molecules at low cost to stimulate follicle growth, ovulation and luteinization, and perhaps one day to remove the need for gonadotrophins in clinical work.

Development and characterization of a long-acting recombinant hFSH agonist

BACKGROUND

Fusion of the carboxyterminal peptide (CTP) of hCG to FSH results in a follitropin agonist with an extended half-life, presumably due to the four O-oligosaccharides on the CTP. Alternatively, an rhFSH analogue containing additional N-linked carbohydrate is described in this report.

METHODS

A DNA sequence containing two N-oligosaccharide signal sequences was ligated into a vector containing hFSHbeta- and alpha-subunit encoding cDNA, and expressed in CHO-K1 cells. In-vitro bioactivity of the single-chain hormone was assessed in CHO cells expressing the hFSH receptor. Pharmacokinetic values were derived from serial serum assays of the analogue in immature female rats following a single i.v. injection. In-vivo bioactivity was assessed by measuring ovarian weight gain 3 days post-injection.

RESULTS

rhFSH-N2 and native rhFSH induced comparable levels of cAMP in vitro. t(1/2) for native rhFSH, rhFSH-CTP and rhFSH-N2 were 3.7, 7.1 and 7.3 h respectively. Rats receiving rhFSH-N2 had a mean +/- SD ovarian weight 3 days post-i.v. injection (22 +/- 3.6 mg) significantly greater than rats receiving rhFSH and saline (16.7 +/- 1.5 and 15.3 +/- 0.47 mg respectively, P < 0.05).

CONCLUSIONS

rhFSH-N2 has prolonged half-life and increased bioactivity compared with native rhFSH. This rhFSH agonist, and other analogues containing additional N-oligosaccharides may have important clinical applications.

New developments in gonadotrophin pharmacology

This article reviews the past, present, and future of gonadotrophin therapy, including purification of gonadotrophins from animal or human urine sources and production of gonadotrophins through recombinant technology. With the advent of recombinant DNA methodologies combined with site-directed mutagenesis, a variety of structural modifications becomes possible.

Unmasking a new recognition signal for O-linked glycosylation in the chorionic gonadotropin beta subunit

hCGbeta subunit is distinguished among the other members of the family of the glycoprotein hormones by the presence of four serine O-linked oligosaccharide units in the last 25 amino acids. This carboxy terminal peptide (CTP) influences the intracellular behavior of the subunit and is important for maintaining the biological half-life of hCG. To examine how the O-linked oligosaccharides affect the metabolic behavior of hCG, we generated a CGbeta mutant devoid of the native O-linked acceptor sites. An alternative site not used in the native subunit was glycosylated and the structure of this oligosaccharide differed from the wild-type O-linked carbohydrates. This glycosylation occurred at serine 130 in the CTP and in contrast to the wild type O-linked oligosaccharides, sialic acid is a major component of the alternatively linked carbohydrate. The data show that deleting the native acceptor sites exposes a new site for O-glycosylation and promotes a differential intracellular processing of the beta subunit. These results support the hypothesis that the CTP participates in the folding of the newly synthesized subunit, which is manifested by the post-translational changes reported here.

Pharmacokinetics and pharmacodynamics of single-chain recombinant human follicle-stimulating hormone containing the human chorionic gonadotropin carboxyterminal peptide in the rhesus monkey

OBJECTIVE

To compare the pharmacokinetics of a long-acting FSH analog containing the hCG-beta carboxyterminal peptide (recombinant hFSH-CTP) with native recombinant hFSH and describe the pharmacodynamics of recombinant hFSH-CTP after SC injection in female rhesus monkeys.

DESIGN

Rhesus monkey study.

SETTING

Academic research environment.

ANIMAL(S)

Ten female rhesus monkeys.

INTERVENTION(S)

Recombinant hFSH and recombinant hFSH-CTP were administered via a single SC or IV dose to rhesus monkeys, and serial phlebotomy was performed (n = 2 and n = 4 for SC recombinant hFSH and recombinant hFSH-CTP, respectively; for IV dosing, n = 1 in each group). An additional two monkeys were pretreated with SC ganirelix and received SC recombinant hFSH-CTP after confirmation of pituitary suppression.

MAIN OUTCOME MEASURE(S)

Plasma disappearance rate of recombinant hFSH and recombinant hFSH-CTP and serum estradiol levels.

RESULT(S)

The elimination half-life of recombinant hFSH-CTP was twofold and fourfold longer than that for recombinant hFSH after SC and IV dosing, respectively. The absorption half-life was approximately threefold longer for recombinant hFSH-CTP than for recombinant hFSH after SC administration. Recombinant hFSH-CTP stimulates estradiol secretion for 5-7 days after an isolated SC dose.

CONCLUSION(S)

Addition of the hCG-beta carboxyterminal peptide to hFSH-beta results in an FSH analog with longer absorption and elimination half-lives compared with native hormone. This analog is capable of prolonged ovarian stimulation in rhesus monkeys after an isolated SC injection.

Immunochemical measurement of early pregnancy isoforms of HCG: potential applications to fertility research, prenatal diagnosis, and cancer

Human chorionic gonadotropin, the glycoprotein hormone of pregnancy, is found naturally in blood and urine in a variety of isoforms. These variants are related to both peptide bond cleavages (such as the nicked forms of hCG) and the beta core fragment urinary metabolite, as well as the larger variety of species resulting from carbohydrate heterogeneity. We have recently developed immunoassay systems that can measure nicked forms of hCG (antibody B151) as well as particular high carbohydrate variants (hyperglycosylated forms) of hCG (B152), which are associated with cancers producing hCG. Using the assay system for nicked hCG, we found that nicked hCG does not appear to be present as a significant hCG isoform during normal pregnancies if the urine specimens are well preserved. Applying the assay for hyperglycosylated hCG isoforms, we discovered that these forms are prevalent during very early pregnancy and decline rapidly to low concentration after the first 6 weeks of pregnancy. Persistence of these early pregnancy forms does not bode well for the pregnancy. Other investigators report that measurement of such hCG isoforms may aid in diagnosis of Down syndrome pregnancies. In summary, measurement of the hyperglycosylated hCG isoforms are useful for evaluation of healthy progress of normal pregnancy, as an additional detection marker for Down syndrome pregnancies, and as a potential new marker of trophoblastic malignancy. New reference preparations will soon be available for the calibration of assay systems for measurement of many of these hCG variants and metabolites.

The position of the alpha and beta subunits in a single chain variant of human chorionic gonadotropin affects the heterodimeric interaction of the subunits and receptor-binding epitopes

The glycoprotein hormone family represents a class of heterodimers, which include the placental hormone human chorionic gonadotropin (CG) and the anterior pituitary hormones follitropin, lutropin, and thyrotropin. They are composed of common alpha subunit and a hormone-specific beta subunit. Based on the CG crystal structure, it was suggested that the quaternary subunit interactions are crucial for biological activity. However, recent observations using single chain glycoprotein hormone analogs, where the beta and alpha subunits are linked (NH(2)-CGbeta-alpha; CGbetaalpha orientation), implied that the heterodimeric-like quaternary configuration is not a prerequisite for receptor binding/signal transduction. To study the heterodimeric alignment of the two subunit domains in a single chain and its role in the intracellular behavior and biological action of the hormone, a single chain CG variant was constructed in which the carboxyl terminus of alpha was fused to the CGbeta amino terminus (NH(2)-alpha-CGbeta; alphaCGbeta orientation). The secretion rate of alphaCGbeta from transfected Chinese hamster ovary cells was less than that seen for CGbetaalpha. The alphaCGbeta tether was not recognized by dimer-specific monoclonal antibodies and did not bind to lutropin/CG receptor. To define if one or both subunit domains were modified in alphaCGbeta, it was co-transfected with a monomeric alpha or CGbeta gene. In each case, alphaCGbeta/alpha and alphaCGbeta/CGbeta complexes were formed indicating that CG dimer-specific epitopes were established. The alphaCGbeta/alpha complex bound to receptor indicating that the beta domain in the alphaCGbeta tether was still functional. In contrast, no significant receptor binding of alphaCGbeta/CGbeta was observed indicating a major perturbation in the alpha domain. These results suggest that although dimeric-like determinants are present in both alphaCGbeta/alpha and alphaCGbeta/CGbeta complexes, the receptor binding determinants in the alpha domain of the tether are absent. These results show that generating heterodimeric determinants do not necessarily result in a bioactive molecule. Our data also indicate that the determinants for biological activity are distinct from those associated with intracellular behavior.

Novel recombinant gonadotropins

The gonadotropin hormones chorionic gonadotropin, luteinizing hormone and follicle-stimulating hormone are heterodimers that consist of a common alpha subunit noncovalently associated with a hormone-specific beta subunit. Site-directed mutagenesis and gene transfer techniques have been invaluable tools for elucidating structure-function determinants of these hormones. Here, we review how questions about the structural biology of these glycoprotein hormones have provided crucial information for creating analogs (agonists and antagonists) that can be used to treat infertility in the clinic. The ability to manipulate the protein structure of these hormones will enable the engineering of both long- and short-acting therapeutic agents.

Engineering a potential antagonist of human thyrotropin and thyroid-stimulating antibody

Thyrotropin (TSH) and the gonadotropins (FSH, LH, hCG) are a family of heterodimeric glycoprotein hormones composed of two noncovalently linked subunits, alpha and beta. We have recently converted the hTSH heterodimer to a biologically active single chain (hTSHbeta.CTPalpha) by fusing the common alpha-subunit to the C-terminal end of the hTSH beta-subunit in the presence of a approximately 30-amino acid peptide from hCGbeta (CTP) as a linker. The hTSHbeta.CTPalpha single chain was used to investigate the role of the N-linked oligosaccharides of alpha- and beta-subunits in the secretion and function of hTSH. Using overlapping PCR mutagenesis, two deglycosylated variants were prepared: one lacking both oligosaccharide chains on the alpha-subunit (hTSHbeta.CTPalpha(1+2)) and the other lacking the oligosaccharide chain on the beta-subunit (hTSHbeta.CTPalpha(deg)). The single chain variants were expressed in CHO cells and were secreted into the medium. hTSH variants lacking the oligosaccharide chains were less potent than hTSHbeta.CTPalpha wild-type with respect to cAMP formation and thyroid hormone secretion in cultured human thyroid follicles. Both deglycosylated variants competed with hTSH in a dose-dependent manner. The hTSHbeta.CTPalpha(1+2) variant blocked cAMP formation and thyroid hormone secretion stimulated by hTSH as well as by the antibody, thyroid-stimulating immunoglobulins, responsible for the most common cause of hyperthyroidism, Graves disease. Thus, this variant behaves as a potential antagonist, offering a novel therapeutic strategy in the treatment of thyrotoxicosis caused by Graves' disease and TSH-secreting pituitary adenoma.

Identification of twelve O-glycosylation sites in equine chorionic gonadotropin beta and equine luteinizing hormone ss by solid-phase Edman degradation

The O-glycosylation sites for equine LHss (eLHss) and eCGss were identified by solid-phase Edman degradation of four glycopeptides derived from the C-terminal region. Both subunits were O-glycosylated at the same 12 positions, rather than the 4-6 sites anticipated. These sites were partially glycosylated, with carbohydrate attachment ranging from 20% to 100% for eCGss and from 10% to 100% for eLHss. When the C-terminal peptide containing all but one of the O-linked oligosaccharides was removed by mild acid hydrolysis of either eLHss or eCGss, hybrid hormones could be obtained by reassociating eLHalpha,eFSHalpha, or eCGalpha with the truncated ss subunit derivatives. These hybrid hormones were identical in LH receptor-binding activity when des(121-149)eLHss or des(121-149)eCGss were combined with the same alpha subunit preparation. Thus, O-glycosylation appears to be responsible for the ss subunit contribution to the substantial difference in LH receptor-binding activity between eLH and eCG. Comparison of the equid LH/CGss sequences with those available for the primate CGss subunits indicated a greater conservation of glycosylation patterns in the former.

Molecular architecture and biorecognition processes of the cystine knot protein superfamily: part I. The glycoprotein hormones

In this review article, the reader is introduced to recent advances in our knowledge on a subset of the cystine knot superfamily of homo- and hetero-dimeric proteins, from the perspective of the endocrine glycoprotein hormone family of proteins: follitropin (FSH), Iutropin (LH), thyrotropin. (TSH) and chorionic gonadotropin (CG). Subsequent papers will address the structure-function behaviour of other members of this increasingly significant family of proteins, including various members of the transforming growth factor-beta (TGF-beta) family of proteins, the activins, inhibins, bone morphogenic growth factor, platelet derived growth factor-beta, nerve growth factor and more than 35 other proteins with similar topological features. In the present review article, specific emphasis has been placed on advances with the glycoprotein hormones (GPHs) that have facilitated greater insight into their physiological functions, molecular structures and most importantly the basis of the molecular recognition events that lead to the formation of hetero-dimeric structures as well as their specific and selective recognition by their corresponding receptors and antibodies. Thus, this review article focuses on the structural motifs involved in receptor recognition and the current techniques available to identify these regions, including the role of immunological methodology, peptide fragment design and synthesis and mutagenesis to delineate their structure-function relationships and molecular recognition behaviour.

Additional N-glycosylation at Asn(13) rescues the human LHbeta-subunit from disulfide-linked aggregation

CG, LH, FSH, and TSH are a family of heterodimeric glycoprotein hormones that contain a common alpha-subunit, but differ in their hormone-specific beta-subunits. Despite the considerable homology between LHbeta and CGbeta, we previously demonstrated that, when expressed in GH(3) cells, the secreted form of LHbeta showed mispaired disulfide-linked aggregation in addition to monomer, whereas no aggregation was observed in CGbeta. To determine the domains which are associated with the LHbeta-aggregation and which prevent CGbeta-aggregation, mutant beta-subunits in glycosylation and carboxy-terminus were expressed in GH(3) cells, and the occurrence of aggregation was assessed by continuous labeling with [35S]methionine/cysteine, immunoprecipitation with anti-hCGbeta serum, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis in a non-reducing condition. No aggregation was seen when N-linked oligosaccharides were attached to the Asn(13) of LHbeta. Removal of the carbohydrate unit at the Asn(13) of CGbeta caused aggregation, although the amount was less than 10% of monomer. The carboxy-terminal regions of neither LHbeta nor CGbeta were associated with their aggregation. Both CGbeta wild-type (WT) and CGbeta lacking N-glycosylation at Asn(13) (CGbeta-N13) showed aggregates in lysate. However, in contrast to CGbeta-N13, CGbetaWT revealed no aggregation in medium. These results indicate that the backbone structure consisting of 114 amino acids and N-linked glycosylation at Asn(30) is involved in the aggregation of LHbeta. Moreover, N-glycosylation at Asn(13) does not prevent such aggregation, but instead plays an important role in correct folding for both LHbeta- and CGbeta-subunits to be secreted as monomer.

Role of glycosylation in function of follicle-stimulating hormone

The oligosaccharide structures of heterodimeric glycoprotein hormones, such as follicle-stimulating hormone (FSH), have been shown to play an important role in the biosynthesis, secretion, metabolic fate, and regulation of potency of the hormone. The oligosaccharide structures attached to each subunit of the protein seem to exhibit distinct roles in some of these functions. Glycans attached to the alpha-subunit are critical for dimer assembly, integrity, and secretion, as well as for signal transduction; although beta-subunit glycans are also important for dimer assembly and secretion, they play a crucial role in clearance of the dimer from the circulation. Alternative glycosylation on FSH and other glycoprotein hormones not only may affect the metabolic clearance and net in vivo biopotency of the hormone, but also offers the interesting possibility that some glycosylation variants of the hormone may provoke differential or even unique effects at the target cell level. Glycosylation of FSH is regulated by hypothalamic and/or end products from the glands under the control of this hormone. In particular, estrogens regulate terminal sialylation and thus some functional properties of the gonadotropin influenced by sialic acid. Through these extrapituitary inputs, the gonadotroph may regulate not only the amount but also the intensity of the gonadotropin signal to be secreted by the pituitary in a given physiological condition.

A large non-immunized human Fab fragment phage library that permits rapid isolation and kinetic analysis of high affinity antibodies

We report the design, construction, and use of the first very large non-immunized phage antibody library in Fab format, which allows the rapid isolation and affinity analysis of antigen-specific human antibody fragments. Individually cloned heavy and light chain variable region libraries were combined in an efficient two-step cloning procedure, permitting the cloning of a total of 3.7 x 10(10) independent Fab clones. The performance of the library was determined by the successful selection of on average 14 different Fabs against 6 antigens tested. These include tetanus toxoid, the hapten phenyl-oxazolone, the breast cancer-associated MUC1 antigen, and three highly related glycoprotein hormones: human chorionic gonadotropin, human luteinizing hormone, and human follicle-stimulating hormone. In the latter category, a panel of either homone-specific or cross-reactive antibodies were identified. The design of the library permits the monitoring of selections with polyclonal phage preparations and to carry out large scale screening of antibody off-rates with unpurified Fab fragments on BIAcore. Antibodies with off-rates in the order of 10(-2) to 10(-4) s-1 and affinities up to 2.7 nM were recovered. The kinetics of these phage antibodies are of the same order of magnitude as antibodies associated with a secondary immune response. This new phage antibody library is set to become a valuable source of antibodies to many different targets, and to play a vital role in target discovery and validation in the area of functional genomics.

Protein glycosylation: implications for in vivo functions and therapeutic applications

The glycosylation machinery in eukaryotic cells is available to all proteins that enter the secretory pathway. There is a growing interest in diseases caused by defective glycosylation, and in therapeutic glycoproteins produced through recombinant DNA technology route. The choice of a bioprocess for commercial production of recombinant glycoprotein is determined by a variety of factors, such as intrinsic biological properties of the protein being expressed and the purpose for which it is intended, and also the economic target. This review summarizes recent development and understanding related to synthesis of glycans, their functions, diseases, and various expression systems and characterization of glycans. The second section covers processing of N- and O-glycans and the factors that regulate protein glycosylation. The third section deals with in vivo functions of protein glycosylation, which includes protein folding and stability, receptor functioning, cell adhesion and signal transduction. Malfunctioning of glycosylation machinery and the resultant diseases are the subject of the fourth section. The next section covers the various expression systems exploited for the glycoproteins: it includes yeasts, mammalian cells, insect cells, plants and an amoeboid organism. Biopharmaceutical properties of therapeutic proteins are discussed in the sixth section. In vitro protein glycosylation and the characterization of glycan structures are the subject matters for the last two sections, respectively.