The phosphodiesterase 3 inhibitor ORG 9935 inhibits oocyte maturation during gonadotropin-stimulated ovarian cycles in rhesus macaques

Cyclic nucleotide phosphodiesterase inhibitors: possible therapeutic drugs for female fertility regulation

Cyclic nucleotide phosphodiesterases (PDEs) are group of enzymes responsible for the hydrolysis of cyclic adenosine 3', 5' monophosphate (cAMP) and cyclic guanosine 3', 5' monophosphate (cGMP) levels in wide variety of cell types. These PDEs are detected in encircling granulosa cells or in oocyte with in follicular microenvironment and responsible for the decrease of cAMP and cGMP levels in mammalian oocytes. A transient decrease of cAMP level initiates downstream pathways to cause spontaneous meiotic resumption from diplotene arrest and induces oocyte maturation. The nonspecific PDE inhibitors (caffeine, pentoxifylline, theophylline, IBMX etc.) as well as specific PDE inhibitors (cilostamide, milrinone, org 9935, cilostazol etc.) have been used to elevate cAMP level and inhibit meiotic resumption from diplotene arrest and oocyte maturation, ovulation, fertilization and pregnancy rates both in vivo as well as under in vitro culture conditions. The PDEs inhibitors are used as powerful experimental tools to demonstrate cyclic nucleotide mediated changes in ovarian functions and thereby fertility. Indeed, non-hormonal nature and reversible effects of nonspecific as well as specific PDE inhibitors hold promise for the development of novel therapeutic drugs for female fertility regulation.

Development of WEE2 kinase inhibitors as novel non-hormonal female contraceptives that target meiosis†

WEE2 oocyte meiosis inhibiting kinase is a well-conserved oocyte specific kinase with a dual regulatory role during meiosis. Active WEE2 maintains immature, germinal vesicle stage oocytes in prophase I arrest prior to the luteinizing hormone surge and facilitates exit from metaphase II arrest at fertilization. Spontaneous mutations at the WEE2 gene locus in women have been linked to total fertilization failure indicating that selective inhibitors to this kinase could function as non-hormonal contraceptives. Employing co-crystallization with WEE1 G2 checkpoint kinase inhibitors, we revealed the structural basis of action across WEE kinases and determined type I inhibitors were not selective to WEE2 over WEE1. In response, we performed in silico screening by FTMap/FTSite and Schrodinger SiteMap analysis to identify potential allosteric sites, then used an allosterically biased activity assay to conduct high-throughput screening of a 26 000 compound library containing scaffolds of known allosteric inhibitors. Resulting hits were validated and a selective inhibitor that binds full-length WEE2 was identified, designated GPHR-00336382, along with a fragment-like inhibitor that binds the kinase domain, GPHR-00355672. Additionally, we present an in vitro testing workflow to evaluate biological activity of candidate WEE2 inhibitors including; (1) enzyme-linked immunosorbent assays measuring WEE2 phosphorylation activity of cyclin dependent kinase 1 (CDK1; also known as cell division cycle 2 kinase, CDC2), (2) in vitro fertilization of bovine ova to determine inhibition of metaphase II exit, and (3) cell-proliferation assays to look for off-target effects against WEE1 in somatic (mitotic) cells.

Proteomic analysis of germinal vesicles in the domestic cat model reveals candidate nuclear proteins involved in oocyte competence acquisition

STUDY QUESTION

Do nuclear proteins in the germinal vesicle (GV) contribute to oocyte competence acquisition during folliculogenesis?

SUMMARY ANSWER

Proteomic analysis of GVs identified candidate proteins for oocyte competence acquisition, including a key RNA processing protein-heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNPA2B1).

WHAT IS KNOWN ALREADY

The domestic cat GV, which is physiologically similar to the human GV, gains the intrinsic ability to resume meiosis and support early embryo development during the pre-antral-to-antral follicle transition. However, little is known about nuclear proteins that contribute to this developmental process.

STUDY DESIGN SIZE, DURATION

GVs were enriched from pre-antral (incompetent) and antral (competent) follicles from 802 cat ovaries. Protein lysates were subjected to quantitative proteomic analysis to identify differentially expressed proteins in GVs from the two follicular categories.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Two biological replicates (from independent pools of ovaries) of pre-antral versus antral samples were labeled by tandem mass tags and then assessed by liquid chromatography-tandem mass spectrometry. Proteomic data were analyzed according to gene ontology and a protein-protein interaction network. Immunofluorescent staining and protein inhibition assays were used for validation.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 174 nuclear proteins was identified, with 54 being up-regulated and 22 down-regulated (≥1.5-fold) after antrum formation. Functional protein analysis through gene ontology over-representation tests revealed that changes in molecular network within the GVs during this transitional phase were related to chromatin reorganization, gene transcription, and maternal RNA processing and storage. Protein inhibition assays verified that hnRNPA2B1, a key nuclear protein identified, was required for oocyte meiotic maturation and subsequent blastocyst formation.

LARGE SCALE DATA

Data are available via ProteomeXchange with identifier PXD007211.

LIMITATIONS REASONS FOR CAUTION

Proteins identified by proteomic comparison may (i) be involved in processes other than competence acquisition during the pre-antral-to-antral transition or (ii) be co-expressed in other macrostructures besides the GV. Expressional and functional validations should be performed for candidate proteins before downstream application.

WIDER IMPLICATIONS OF THE FINDINGS

Collective results generated a blueprint to better understand the molecular mechanisms involved in GV competence acquisition and identified potential nuclear competence markers for human fertility preservation.

STUDY FUNDING AND COMPETING INTEREST(S)

Funded by the National Center for Research Resources (R01 RR026064), a component of the National Institutes of Health (NIH) and currently by the Office of Research Infrastructure Programs/Office of the Director (R01 OD010948). The authors declare that there is no conflict of interest.

Syntheses of PDE3A inhibitor ORG9935 and determination of the absolute stereochemistries of its enantiomers by X-ray crystallography

Two synthetic methods were developed for the synthesis of PDE3A inhibitor ORG9935. The first one proceeds in six steps and 34% overall yield and the second one in five steps and an overall yield of 69% starting from commercially available starting material 5,6-dimethoxybenzo[b]thiophene-2-carboxylic acid (6). The enantiomers of ORG9935 were separated by chiral column chromatography and the absolute stereochemistry of the (+)-enantiomer, ORG20865 was determined by X-ray crystallography to possess the (S)-configuration. The (-)-enantiomer, ORG20864, was therefore assigned the (R)-stereochemistry. The biologically less active (+)-isomer ORG20865 was converted to racemic ORG9935 under basic conditions, which then can be separated again into the enantiomers. The crystal structure of ORG20865 is notable for having the highest Z' for any known pharmaceutical substance.

Phosphodiesterase 3 (PDE3) inhibition with cilostazol does not block in vivo oocyte maturation in rhesus macaques (Macaca mulatta)

OBJECTIVE

Studies in mice suggest that cilostazol, an FDA-approved phosphodiesterase 3 (PDE3) inhibitor, might have a contraceptive effect within the approved dose range. We sought to evaluate the potential contraceptive effects of cilostazol in a nonhuman primate model.

STUDY DESIGN

Adult female rhesus macaques were stimulated to develop multiple preovulatory follicles by administering human recombinant gonadotropins, and oocytes were collected by follicle aspiration 36 h after an ovulatory stimulus (human chorionic gonadotropin). Monkeys received no further treatment (controls) or the PDE3 inhibitor cilostazol at the maximum approved human dose of 100mg twice daily starting 6 days prior to follicle aspiration. Recovered oocytes were scored for meiotic stage [germinal vesicle (GV) intact, GV breakdown], and metaphase II stage oocytes were fertilized in vitro and observed for normal embryo development.

RESULTS

Similar proportions of GV stage oocytes were recovered from control (27%±4%) and cilostazol (27%±9%)-treated females, and the proportion of embryos that developed into blastocysts was also similar for both groups (7%±5% control vs. 15%±8% cilostazol).

CONCLUSION

Oral dosing of cilostazol tablets during controlled ovarian stimulation protocols did not prevent oocyte maturation or embryo development in macaques.

IMPLICATIONS

Since administration of the maximum approved human dose of cilostazol (an FDA-approved PDE3 inhibitor) to macaques did not prevent oocyte maturation or fertilization, it is not likely that this dose would be contraceptive in women.

Identification of phosphodiesterase 9A as a cyclic guanosine monophosphate-specific phosphodiesterase in germinal vesicle oocytes: a proposed role in the resumption of meiosis

OBJECTIVE

To identify a cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase (PDE) in nonhuman primate germinal vesicle (GV) oocytes and establish a proposed effect on oocyte maturation through preliminary experiments in mouse GV oocytes.

DESIGN

Controlled nonhuman primate and rodent experiments.

SETTING

Academic research institution.

ANIMAL(S)

Rhesus macaques and B6/129F1 mice.

INTERVENTION(S)

Stimulation of Rhesus macaques with follicle-stimulating hormone (FSH) to collect GV oocytes and cumulus for gene expression analysis, and stimulation of female mice with pregnant mare serum gonadotropin to collect GV oocytes.

MAIN OUTCOME MEASURE(S)

Expression of PDE transcript in primate GV oocytes and cumulus cells, measurement of fluorescence polarization of phosphodiesterase 3A (PDE3A) activity, and analysis of spontaneous resumption of meiosis in mouse GV oocytes.

RESULT(S)

Of five PDE transcripts detected in Rhesus GV oocytes, only PDE9A was cGMP-specific. The fluorescence polarization assays indicated cGMP has an inhibitory effect on PDE3A while the phosphodiesterase 9A (PDE9) inhibitor, BAY73-6691, does not. Similarly, BAY73-6691 had little effect on preventing spontaneous maturation in oocytes, but did augment the inhibitory effects of cGMP. Inclusion of 0 μM (control), 10 μM, 100 μM, and 1 mM BAY73-6691 statistically significantly increased the proportion of mouse oocytes maintaining GV arrest in the presence of the cGMP analog 8-Br-cGMP at 100 μM (8.8%, 11.4%, 18.8%, and 28%), 500 μM (21.1%, 38.1%, 74.5%, and 66.5%), and 1 mM (57.8%, 74.5%, 93.9%, and 94.0%), respectively.

CONCLUSION(S)

Phosphodiesterase 9A (PDE9A) is a cGMP-specific hydrolyzing enzyme present in primate oocytes, and PDE9 antagonists augment the inhibitory effect of cGMP during spontaneous in vitro maturation of GV mouse oocytes.

The role of cilostazol, a phosphodiesterase 3 inhibitor, on oocyte maturation and subsequent pregnancy in mice

It is important to identify effective contraceptive drugs that cause minimal disruption to physiological processes. Phosphodiesterase 3 (PDE3) inhibitors suppress meiosis in oocytes by decreasing the level of cAMP and blocking the extrusion of the first polar body. In this study, we tested the PDE3 inhibitor, cilostazol, as a potential contraceptive agent. The effects of cilostazol treatment in vitro and in vivo on the suppression of oocyte maturation in a mouse model were investigated. The results indicated that treatment with increasing concentrations of cilostazol led to a dose-dependent arrest in meiosis progression. The effective in vitro concentration was 1 µM and was 300 mg/kg in vivo. The effect of cilostazol was reversible. After removal of the drug, meiosis resumed and mouse oocytes matured in vitro, and showed normal chromosome alignment and spindle organization. After fertilization using an ICSI method, the oocytes showed normal morphology, fertilization rate, embryo cleavage, blastocyst formation, and number of viable pups when compared with controls. The offspring showed similar body weight and fertility. In vivo, the mice became infertile if the drug was injected sequentially, and became pregnant following discontinuation of cilostazol. More importantly, no side effects of cilostazol were observed in treated female mice as demonstrated by blood pressure and heart rate monitoring. It is concluded that cilostazol, a drug routinely used for intermittent claudication, can effectively inhibit oocyte maturation in vitro and in vivo, does not affect the developmental potential of oocytes following drug removal and has few side effects in female mice treated with this drug. These findings suggest that cilostazol may be a potential new contraceptive agent that may facilitate an efficacy and safety study of this drug.

WEE2 is an oocyte-specific meiosis inhibitor in rhesus macaque monkeys

WEE1 homolog 2 (WEE2, also known as WEE1B) is a newly identified member of the WEE kinase family that is conserved from yeast to humans. The aim of the present study was to determine the spatiotemporal expression pattern and the function of WEE2 during oocyte maturation in a nonhuman primate species, the rhesus macaque. Among 11 macaque tissues examined, WEE2 transcript is predominantly expressed in the ovary and only weakly detectable in the testis. Within the ovary, WEE2 mRNA is exclusively localized in the oocyte and appears to accumulate during folliculogenesis, reaching the highest level in preovulatory follicles. Microinjection of a full-length WEE2-GFP (green fluorescent protein) fusion mRNA indicates a specific nuclear localization of WEE2 protein in both growing and fully grown germinal vesicle (GV)-intact oocytes. Taking the long double-stranded RNA-mediated RNA interference approach, we found that down-regulation of WEE2 led to meiotic resumption in a subset of GV oocytes even in the presence of a phosphodiesterase 3 inhibitor. On the other hand, overexpression of WEE2 delays the reentry of oocytes into meiosis in both mice and monkeys. These findings suggest that WEE2 is a conserved oocyte-specific meiosis inhibitor that functions downstream of cAMP in nonhuman primates.

Evaluation of the phosphodiesterase 3 inhibitor ORG 9935 as a contraceptive in female macaques: initial trials

BACKGROUND

The study was conducted to determine whether a phosphodiesterase (PDE) 3 inhibitor has potential as a novel contraceptive in primates.

METHODS

Regularly cycling adult female cynomolgus macaques of proven fertility (n=16) were treated for 7 months with placebo (controls) or the PDE3 inhibitor ORG 9935 as a daily food treat (150 mg/kg) or as a weekly depot injection (150 mg/kg, sc). After 1 month, a male of proven fertility was introduced into each group. Females underwent weekly monitoring of progesterone (P) and ultrasound evaluation for pregnancy if P remained elevated (1.0 ng/mL) >3 weeks. ORG 9935 values were evaluated using high-performance liquid chromatography.

RESULTS

Overall, the pregnancy rate in ORG 9935-treated monkeys (4/8, 50%) did not differ from controls (7/8, 88%; p=.5). However, no animal became pregnant in a cycle when the serum level of ORG 9935 exceeded 300 nmol/L. Moreover, two treated monkeys who mated throughout the treatment phase and did not conceive became pregnant within four cycles after stopping ORG 9935. The other two animals were discontinued prematurely from the protocol.

CONCLUSIONS

These results demonstrate that ORG 9935 may prevent pregnancy in primates at serum concentrations above 300 nmol/L and that the effect is reversible.

Encapsulated three-dimensional culture supports development of nonhuman primate secondary follicles

In vitro ovarian follicle cultures may provide fertility-preserving options to women facing premature infertility due to cancer therapies. An encapsulated three-dimensional (3-D) culture system utilizing biomaterials to maintain cell-cell communication and support follicle development to produce a mature oocyte has been developed for the mouse. We tested whether this encapsulated 3-D system would also support development of nonhuman primate preantral follicles, for which in vitro growth has not been reported. Three questions were investigated: Does the cycle stage at which the follicles are isolated affect follicle development? Does the rigidity of the hydrogel influence follicle survival and growth? Do follicles require luteinizing hormone (LH), in addition to follicle-stimulating hormone (FSH), for steroidogenesis? Secondary follicles were isolated from adult rhesus monkeys, encapsulated within alginate hydrogels, and cultured individually for </=30 days. Follicles isolated from the follicular phase of the menstrual cycle had a higher survival rate (P < 0.05) than those isolated from the luteal phase; however, this difference may also be attributed to differing sizes of follicles isolated during the different stages. Follicles survived and grew in two hydrogel conditions (0.5% and 0.25% alginate). Follicle diameters increased to a greater extent (P < 0.05) in the presence of FSH alone than in FSH plus LH. Regardless of gonadotropin treatment, follicles produced estradiol, androstenedione, and progesterone by 14-30 days in vitro. Thus, an alginate hydrogel maintains the 3-D structure of individual secondary macaque follicles, permits follicle growth, and supports steroidogenesis for </=30 days in vitro. This study documents the first use of the alginate system to maintain primate tissue architecture, and findings suggest that encapsulated 3-D culture will be successful in supporting the in vitro development of human follicles.

The phosphodiesterase 3 inhibitor ORG 9935 inhibits oocyte maturation in the naturally selected dominant follicle in rhesus macaques

BACKGROUND

The study was conducted to determine whether the phosphodiesterase (PDE) 3 inhibitor ORG 9935 prevents the resumption of meiosis in primate oocytes during natural menstrual cycles.

STUDY DESIGN

Regularly cycling adult female macaques (n=8) were followed during the follicular phase and then started on a 2-day treatment regimen of human recombinant gonadotropins to control the timing of ovulation. Monkeys received no further treatment (controls) or ORG 9935. Oocytes were recovered by laparoscopic follicle aspiration 27 h after an ovulatory stimulus, cultured in vitro in the absence of inhibitor and inseminated. The primary outcome was the meiotic stage of the oocyte.

RESULTS

In six ORG 9935 cycles, five of the recovered oocytes were germinal vesicle (GV)-intact, and one exhibited GV breakdown (GVBD). In contrast, all three oocytes that recovered during control cycles were GVBD (p<.05). None of the ORG 9935-treated oocytes underwent fertilization compared with 2/3 (67%) from controls.

CONCLUSIONS

These results demonstrate that ORG 9935 blocks resumption of meiosis in the naturally selected dominant follicle in primates and suggest that PDE3 inhibitors have potential clinical use as contraceptives in women.

The non-human primate oocyte and embryo as a model for women, or is it vice versa?

The role of the non-human primate (NHP) oocyte and embryo in translational research is considered here including both in vitro activities directly involving oocytes or embryos as well as animal studies that impact reproductive function. Reasons to consider NHPs as animal research models along with their limitations are summarized. A case is made that in limited instances, such as in the development and application of the assisted reproductive technologies or in the study of embryonic stem cells, the human oocyte and embryo have acted as models for the monkey. The development of strategies for the preservation of fertility is used as an example of ongoing research in the non-human primate that cannot be conducted in women for ethical reasons. In animal studies, monitoring reproductive potential, responses to embryonic stem cell transplantation, along with translational research in the field of contraceptive development for women are considered as subjects that benefit from the availability of a NHP model.

Use of controlled ovulation of the dominant follicle to assess oocyte maturation during natural menstrual cycles in rhesus macaques

To determine the practicality of controlled ovulation of the dominant follicle as a technique to study meiotic maturation of oocytes during contraceptive research, we developed a technique for aspiration of the single dominant follicle using a dual-needle continuous irrigation technique 27 hours after an ovulatory stimulus. All of the oocytes (3/3) recovered from control animals, but only 1/6 (17%) of oocytes from animals treated with the meiotic inhibitor ORG 9935 exhibited germinal vesicle breakdown, indicating resumption of meiosis.

Molecular mechanisms of ovulation: co-ordination through the cumulus complex

Successful ovulation requires that developmentally competent oocytes are released with appropriate timing from the ovarian follicle. Somatic cells of the follicle sense the ovulatory stimulus and guide resumption of meiosis and release of the oocyte, as well as structural remodelling and luteinization of the follicle. Complex intercellular communication co-ordinates critical stages of oocyte maturation and links this process with release from the follicle. To achieve these outcomes, ovulation is controlled through multiple inputs, including endocrine hormones, immune and metabolic signals, as well as intrafollicular paracrine factors from the theca, mural and cumulus granulosa cells and the oocyte itself. This review focuses on the recent advances in understanding of molecular mechanisms that commence after the gonadotrophin surge and culminate with release of the oocyte. These mechanisms include intracellular signalling, gene regulation and remodelling of tissue structure in each of the distinct ovarian compartments. Most critical ovulatory mediators exert effects through the cumulus cell complex that surrounds and connects with the oocyte. The convergence of ovulatory signals through the cumulus complex co-ordinates the key mechanistic processes that mediate and control oocyte maturation and ovulation.