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

New insight into strategies used to develop long-acting G-CSF biologics for neutropenia therapy

Over the last 20 years, granulocyte colony-stimulating factors (G-CSFs) have become the major therapeutic option for the treatment of patients with neutropenia. Most of the current G-CSFs require daily injections, which are inconvenient and expensive for patients. Increased understanding of G-CSFs' structure, expression, and mechanism of clearance has been very instrumental in the development of new generations of long-acting G-CSFs with improved efficacy. Several approaches to reducing G-CSF clearance via conjugation techniques have been investigated. PEGylation, glycosylation, polysialylation, or conjugation with immunoglobulins or albumins have successfully increased G-CSFs' half-lives. Pegfilgrastim (Neulasta) has been successfully approved and marketed for the treatment of patients with neutropenia. The rapidly expanding market for G-CSFs has increased demand for G-CSF biosimilars. Therefore, the importance of this review is to highlight the principle, elimination's route, half-life, clearance, safety, benefits, and limitations of different strategies and techniques used to increase the half-life of biotherapeutic G-CSFs. Understanding these strategies will allow for a new treatment with more competitive manufacturing and lower unit costs compared with that of Neulasta.

C-terminal peptide (hCTP) of human chorionic gonadotropin enhances in vivo biological activity of recombinant Japanese eel follicle-stimulating hormone and luteinizing hormone produced in FreeStyle 293-F cell lines

Gonadotropins (Gths), follicle-stimulating hormone (Fsh), and luteinizing hormone (Lh) play central roles in the reproductive biology of vertebrates. In this study, recombinant single-chain Japanese eel Gths (rGth: rFsh and rLh), and recombinant chimeric Gths (rGth-hCTPs: rFsh-hCTP and rLh-hCTP; rGth-eCTPs: rFsh-eCTP and rLh-eCTP) with an extra O-glycosylation site (either a C-terminal peptide of human (hCTP) or equine (eCTP) chorionic gonadotropin), which are known to prolong the half-life of glycoprotein were produced in HEK293 cells and highly purified. Lectin blot analyses demonstrated that all these recombinant Gths contained N-glycans of the high mannose and complex types. In contrast, only rGth-hCTPs and rGth-eCTPs possessed highly sialylated O-linked oligosaccharides. Further analyses of glycans by liquid chromatography-mass spectrometry suggested that the species, amount, and degree of sialylation of N-glycans were comparable among recombinant Fshs and recombinant Lhs, while the amount of O-glycans with sialic acids in rGth-hCTPs was higher than that in the corresponding rGth-eCTPs. The serum levels of recombinant Gths in male eels significantly increased 12-24 h after a single injection of the Gths. The levels of rGth-hCTPs tended to be higher than those of the corresponding rGths and rGth-eCTPs throughout the experimental period, coinciding with the serum fluctuations of 11-ketotestosterone (11KT). The long-term treatment of male eels with these recombinant Gths also revealed the superiority of rGth-hCTPs in assisted reproduction; thus, the serum levels of 11KT and gonadosomatic indices in eels treated with rGth-hCTPs were higher than those in eels treated with the corresponding rGths and rGth-eCTPs. The induction of the entire process of spermatogenesis was only histologically observed in rGth-hCTPs-treated eels. These findings strongly suggest that hCTP enhances the in vivo biological activity of recombinant Japanese eel Gths due to the high abundance of O-linked glycans with sialylated antennae.

Pharmacokinetics Versus In Vitro Antiproliferative Potency to Design a Novel Hyperglycosylated hIFN-α2 Biobetter

PURPOSE

IFN4N is a glycoengineered version of recombinant human interferon alpha 2 (rhIFN-α2) that was modified to exhibit four N-glycosylation sites. It shows reduced in vitro specific biological activity (SBA) mainly due to R23 mutation by N23. However, it has improved pharmacokinetics and led to a high in vivo antitumor activity in mice. In order to prepare a new IFN-based biobetter, this work compares the influence of glycosylation (affecting pharmacokinetics) with the in vitro antiproliferative SBA on the in vivo efficacy.

METHODS

Based on IFN4N, three groups of muteins were designed, produced, and characterized. Group A: variants with the same glycosylation degree (4N) but higher in vitro antiproliferative SBA (R23 restored); group B: muteins with higher glycosylation degree (5N) but similar in vitro antiproliferative activity; and group C: variants with improved glycosylation (5N and 6N) and in vitro antiproliferative bioactivity.

RESULTS

Glycoengineering was successful for improving pharmacokinetics, and R23 restoration considerably increased in vitro antiproliferative activity of new muteins compared to IFN4N. Hyperglycosylation was able to improve the in vivo efficacy similarly to or even better than R23 restoration. Additionally, the highest glycosylated mutein exhibited the lowest immunogenicity.

CONCLUSIONS

Hyperglycosylation constitutes a successful strategy to prepare a novel IFN biobetter.

New Human Follitropin Preparations: How Glycan Structural Differences May Affect Biochemical and Biological Function and Clinical Effect

It is well accepted that pituitary follitropin is secreted into the circulation as a mixture of variants, which differ not in primary structure but rather at the level of glycosylation. These glycosidic forms vary in the number of glycosylation sites filled, complexity of glycosidic chains, and sialylation and sulfation. It is generally agreed that high sialylation, 2,3 sialic acid capping of terminal N-acetyl galactosamine or galactose leads to longer circulating half-life, by blocking binding of asialoglycoprotein receptor (ASGPR) in the liver. In contrast, 2,6 sialic acid found in humans does not prevent recognition of galactose and N-acetyl galactosamine by ASGPR. Few studies on clinical outcomes comparing differences in sialylation of follitropin found in commercially available preparations are available. Thus, there is a clear need for a consortium of open data to address this unmet need. Recently, FSH glycosylation, primarily on the β-subunit, which varies as women age, has emerged as a key modifier of follitropin action, with profound biological effects in vivo in animal models. To date, limited information of recombinant follitropin hormone preparations is available. Thus, most of the studies with FSH that is well characterized biochemically have been done in vitro, with engineered non gonadal host cells bearing recombinant receptors or in animal models. Since limited studies in human granulosa cells are available, a question is whether structural differences in glycosylation in commercially available follitropin affects biological function and clinical effect in humans. The presence of fucose, for example, has not been studied greatly even though, in the case of antibody therapy it has been shown to have a large effect on antibody targeting. This review on glycosidic variability of follitropin from the biochemical/structural point of view reflects on this question and presents an assessment in the context of available published data. If clinical differences are to be expected or not, the readers will have a better understanding of the evidence for and limitations of such expectations.

Biased Signaling and Allosteric Modulation at the FSHR

Knowledge on G protein-coupled receptor (GPCRs) structure and mechanism of activation has profoundly evolved over the past years. The way drugs targeting this family of receptors are discovered and used has also changed. Ligands appear to bind a growing number of GPCRs in a competitive or allosteric manner to elicit balanced signaling or biased signaling (i.e., differential efficacy in activating or inhibiting selective signaling pathway(s) compared to the reference ligand). These novel concepts and developments transform our understanding of the follicle-stimulating hormone (FSH) receptor (FSHR) biology and the way it could be pharmacologically modulated in the future. The FSHR is expressed in somatic cells of the gonads and plays a major role in reproduction. When compared to classical GPCRs, the FSHR exhibits intrinsic peculiarities, such as a very large NH2-terminal extracellular domain that binds a naturally heterogeneous, large heterodimeric glycoprotein, namely FSH. Once activated, the FSHR couples to Gαs and, in some instances, to other Gα subunits. G protein-coupled receptor kinases and β-arrestins are also recruited to this receptor and account for its desensitization, trafficking, and intracellular signaling. Different classes of pharmacological tools capable of biasing FSHR signaling have been reported and open promising prospects both in basic research and for therapeutic applications. Here we provide an updated review of the most salient peculiarities of FSHR signaling and its selective modulation.

Gonadotropins and Their Analogs: Current and Potential Clinical Applications

The gonadotropin receptors LH receptor and FSH receptor play a central role in governing reproductive competency/fertility. Gonadotropin hormone analogs have been used clinically for decades in assisted reproductive therapies and in the treatment of various infertility disorders. Though these treatments are effective, the clinical protocols demand multiple injections, and the hormone preparations can lack uniformity and stability. The past two decades have seen a drive to develop chimeric and modified peptide analogs with more desirable pharmacokinetic profiles, with some displaying clinical efficacy, such as corifollitropin alfa, which is now in clinical use. More recently, low-molecular-weight, orally active molecules with activity at gonadotropin receptors have been developed. Some have excellent characteristics in animals and in human studies but have not reached the market-largely as a result of acquisitions by large pharma. Nonetheless, such molecules have the potential to mitigate risks currently associated with gonadotropin-based fertility treatments, such as ovarian hyperstimulation syndrome and the demands of injection-based therapies. There is also scope for novel use beyond the current remit of gonadotropin analogs in fertility treatments, including application as novel contraceptives; in the treatment of polycystic ovary syndrome; in the restoration of function to inactivating mutations of gonadotropin receptors; in the treatment of ovarian and prostate cancers; and in the prevention of bone loss and weight gain in postmenopausal women. Here we review the properties and clinical application of current gonadotropin preparations and their analogs, as well as the development of novel orally active, small-molecule nonpeptide analogs.

FSH Receptor Signaling: Complexity of Interactions and Signal Diversity

FSH is synthesized in the pituitary by gonadotrope cells. By binding to and interacting with its cognate receptor [FSH receptor (FSHR)] in the gonads, this gonadotropin plays a key role in the control of gonadal function and reproduction. Upon activation, the FSHR undergoes conformational changes leading to transduction of intracellular signals, including dissociation of G protein complexes into components and activation of several associated interacting partners, which concertedly regulate downstream effectors. The canonical Gs/cAMP/protein kinase A pathway, considered for a long time as the sole effector of FSHR-mediated signaling, is now viewed as one of several mechanisms employed by this receptor to transduce intracellular signals in response to the FSH stimulus. This complex network of signaling pathways allows for a fine-tuning regulation of the gonadotropic stimulus, where activation/inhibition of its multiple components vary depending on the cell context, cell developmental stage, and concentration of associated receptors and corresponding ligands. Activation of these multiple signaling modules eventually converge to the hormone-integrated biological response, including survival, proliferation and differentiation of target cells, synthesis and secretion of paracrine/autocrine regulators, and, at the molecular level, functional selectivity and differential gene expression. In this mini-review, we discuss the complexity of FSHR-mediated intracellular signals activated in response to ligand stimulation. A better understanding of the signaling pathways involved in FSH action might potentially influence the development of new therapeutic strategies for reproductive disorders.

Influence of gonadotropins on ovarian follicle growth and developmentin vivoandin vitro

Gonadotropins are the key regulators of ovarian follicles development. They are applied in therapeutic practice in assisted reproductive technology clinics. In the present review we discuss the basic gonadotropic hormones – recombinant human follicle-stimulating hormone, its derivatives, luteinizing hormone and gonadotropin serum of pregnant mares, their origin, and application in ovarian follicle systems inin vitroculture systems.

Structure-function relationships of glycoprotein hormones and their subunits' ancestors

Glycoprotein hormones (GPHs) are the most complex molecules with hormonal activity. They exist only in vertebrates but the genes encoding their subunits' ancestors are found in most vertebrate and invertebrate species although their roles are still unknown. In the present report, we review the available structural and functional data concerning GPHs and their subunits' ancestors.

Novel pathways in gonadotropin receptor signaling and biased agonism

Gonadotropins play a central role in the control of male and female reproduction. Selective agonists and antagonists of gonadotropin receptors would be of great interest for the treatment of infertility or as non steroidal contraceptive. However, to date, only native hormones are being used in assisted reproduction technologies as there is no pharmacological agent available to manipulate gonadotropin receptors. Over the last decade, there has been a growing perception of the complexity associated with gonadotropin receptors' cellular signaling. It is now clear that the Gs/cAMP/PKA pathway is not the sole mechanism that must be taken into account in order to understand these hormones' biological actions. In parallel, consistent with the emerging paradigm of biased agonism, several examples of ligand-mediated selective signaling pathway activation by gonadotropin receptors have been reported. Small molecule ligands, modulating antibodies interacting with the hormones and glycosylation variants of the native glycoproteins have all demonstrated their potential to trigger such selective signaling. Altogether, the available data and emerging concepts give rise to intriguing opportunities towards a more efficient control of reproductive function and associated disorders.

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.

Glycosylation of therapeutic proteins: an effective strategy to optimize efficacy

During their development and administration, protein-based drugs routinely display suboptimal therapeutic efficacies due to their poor physicochemical and pharmacological properties. These innate liabilities have driven the development of molecular strategies to improve the therapeutic behavior of protein drugs. Among the currently developed approaches, glycoengineering is one of the most promising, because it has been shown to simultaneously afford improvements in most of the parameters necessary for optimization of in vivo efficacy while allowing for targeting to the desired site of action. These include increased in vitro and in vivo molecular stability (due to reduced oxidation, cross-linking, pH-, chemical-, heating-, and freezing-induced unfolding/denaturation, precipitation, kinetic inactivation, and aggregation), as well as modulated pharmacodynamic responses (due to altered potencies from diminished in vitro enzymatic activities and altered receptor binding affinities) and improved pharmacokinetic profiles (due to altered absorption and distribution behaviors, longer circulation lifetimes, and decreased clearance rates). This article provides an account of the effects that glycosylation has on the therapeutic efficacy of protein drugs and describes the current understanding of the mechanisms by which glycosylation leads to such effects.