Design, Synthesis, and in Vitro and in Vivo Evaluation of Ouabain Analogues as Potent and Selective Na,K-ATPase α4 Isoform Inhibitors for Male Contraception

The uniqueness of on-demand male contraception

Because nearly half of pregnancies worldwide are unintended, available contraceptive methods are inadequate. Moreover, due to the striking imbalance between contraceptive options available for men compared to the myriad of options available to women, there is an urgent need for new methods of contraception for men. This review summarizes ongoing efforts to develop male contraceptives highlighting the unique aspects particular to on-demand male contraception, where a man takes a contraceptive only when and as often as needed.

Sperm Toolbox-A selection of small molecules to study human spermatozoa

Male contraceptive options and infertility treatments are limited, and almost all innovation has been limited to updates to medically assisted reproduction protocols and methods. To accelerate the development of drugs that can either improve or inhibit fertility, we established a small molecule library as a toolbox for assay development and screening campaigns using human spermatozoa. We have profiled all compounds in the Sperm Toolbox in several automated high-throughput assays that measure stimulation or inhibition of sperm motility or the acrosome reaction. We have assayed motility under non-capacitating and capacitating conditions to distinguish between pathways operating under these different physiological states. We also assayed cell viability to ensure any effects on sperm function are specific. A key advantage of our studies is that all compounds are assayed together in the same experimental conditions, which allows quantitative comparisons of their effects in complementary functional assays. We have combined the resulting datasets to generate fingerprints of the Sperm Toolbox compounds on sperm function. The data are included in an on-line R-based app for convenient querying.

Advances in non-hormonal male contraception targeting sperm motility

BACKGROUND

The high rates of unintended pregnancy and the ever-growing world population impose health, economic, social, and environmental threats to countries. Expanding contraceptive options, including male methods, are urgently needed to tackle these global challenges. Male contraception is limited to condoms and vasectomy, which are unsuitable for many couples. Thus, novel male contraceptive methods may reduce unintended pregnancies, meet the contraceptive needs of couples, and foster gender equality in carrying the contraceptive burden. In this regard, the spermatozoon emerges as a source of druggable targets for on-demand, non-hormonal male contraception based on disrupting sperm motility or fertilization.

OBJECTIVE AND RATIONALE

A better understanding of the molecules governing sperm motility can lead to innovative approaches toward safe and effective male contraceptives. This review discusses cutting-edge knowledge on sperm-specific targets for male contraception, focusing on those with crucial roles in sperm motility. We also highlight challenges and opportunities in male contraceptive drug development targeting spermatozoa.

SEARCH METHODS

We conducted a literature search in the PubMed database using the following keywords: 'spermatozoa', 'sperm motility', 'male contraception', and 'drug targets' in combination with other related terms to the field. Publications until January 2023 written in English were considered.

OUTCOMES

Efforts for developing non-hormonal strategies for male contraception resulted in the identification of candidates specifically expressed or enriched in spermatozoa, including enzymes (PP1γ2, GAPDHS, and sAC), ion channels (CatSper and KSper), transmembrane transporters (sNHE, SLC26A8, and ATP1A4), and surface proteins (EPPIN). These targets are usually located in the sperm flagellum. Their indispensable roles in sperm motility and male fertility were confirmed by genetic or immunological approaches using animal models and gene mutations associated with male infertility due to sperm defects in humans. Their druggability was demonstrated by the identification of drug-like small organic ligands displaying spermiostatic activity in preclinical trials.

WIDER IMPLICATIONS

A wide range of sperm-associated proteins has arisen as key regulators of sperm motility, providing compelling druggable candidates for male contraception. Nevertheless, no pharmacological agent has reached clinical developmental stages. One reason is the slow progress in translating the preclinical and drug discovery findings into a drug-like candidate adequate for clinical development. Thus, intense collaboration among academia, private sectors, governments, and regulatory agencies will be crucial to combine expertise for the development of male contraceptives targeting sperm function by (i) improving target structural characterization and the design of highly selective ligands, (ii) conducting long-term preclinical safety, efficacy, and reversibility evaluation, and (iii) establishing rigorous guidelines and endpoints for clinical trials and regulatory evaluation, thus allowing their testing in humans.

Non-Hormonal Contraception

While hormonal contraceptives are efficacious and available in several forms for women, perception of safety and concern over side effects are a deterrent for many. Existing non-hormonal contraceptives include permanent sterilization, copper intrauterine devices (IUDs), chemical/physical barriers such as spermicides and condoms, as well as traditional family planning methods including withdrawal and the rhythm method. Individuals who wish to retain their fertility in the future can achieve highest adherence and efficacy with long-acting, reversible contraceptives (LARCs), though there is only one, the copper IUD, that is non-hormonal. As rates of unintended pregnancies remain high with existing contraceptive options, it is becoming increasingly attractive to develop novel pregnancy prevention methods for both women and men. Non-hormonal contraceptives can target a variety of critical reproductive processes discussed here. This review focuses on identified non-hormonal contraceptive targets and subsequent drug candidates in development.

A minireview of 1,2,3-triazole hybrids with O-heterocycles as leads in medicinal chemistry

Over the past few decades, the dynamic progress in the synthesis and screening of heterocyclic compounds against various targets has made a significant contribution in the field of medicinal chemistry. Among the wide array of heterocyclic compounds, triazole moiety has attracted the attention of researchers owing to its vast therapeutic potential and easy preparation via copper and ruthenium-catalyzed azide-alkyne cycloaddition reactions. Triazole skeletons are found as major structural components in a different class of drugs possessing diverse pharmacological profiles including anti-cancer, anti-bacterial, anti-fungal, anti-viral, anti-oxidant, anti-inflammatory, anti-diabetic, anti-tubercular, and anti-depressant among various others. Furthermore, in the past few years, a significantly large number of triazole hybrids were synthesized with various heterocyclic moieties in order to gain the added advantage of the improved pharmacological profile, overcoming the multiple drug resistance and reduced toxicity from molecular hybridization. Among these synthesized triazole hybrids, many compounds are available commercially and used for treating different infections/disorders like tazobactam and cefatrizine as potent anti-bacterial agents while isavuconazole and ravuconazole as anti-fungal activities to name a few. In this review, we will summarize the biological activities of various 1,2,3-triazole hybrids with copious oxygen-containing heterocycles as lead compounds in medicinal chemistry. This review will be very helpful for researchers working in the field of molecular modeling, drug design and development, and medicinal chemistry.

Semisynthesis of (-)-Bufospirostenin A Enabled by Photosantonin Rearrangement Reaction

An enantioselective semisynthesis of (-)-bufospirostenin A is described. The key steps in the synthesis involve use of our proposed biomimetic and diastereoselective photosantonin rearrangement reaction for construction of the 5/7 bicyclic motif, and a Co-catalyzed reversible double-bond isomerization reaction for installing the double bond in the seven-membered ring.

Structure and Function of Na,K-ATPase-The Sodium-Potassium Pump

Na,K-ATPase is an ubiquitous enzyme actively transporting Na-ions out of the cell in exchange for K-ions, thereby maintaining their concentration gradients across the cell membrane. Since its discovery more than six decades ago the Na-pump has been studied extensively and its vital physiological role in essentially every cell has been established. This article aims at providing an overview of well-established biochemical properties with a focus on Na,K-ATPase isoforms, its transport mechanism and principle conformations, inhibitors, and insights gained from crystal structures. © 2021 American Physiological Society. Compr Physiol 11:1-21, 2021.

Natural Products with Potential for Nonhormonal Male Contraception

Despite increased access to contraception over the last 60 years, unplanned pregnancies continue to contribute to economic disparities and overpopulation. Additionally, the burden of family planning falls primarily on women, as a reliable pharmaceutical male contraceptive has yet to be developed. The objective of this literature-based systematic review was to identify compounds for future study from natural sources with potential nonhormonal male contraceptive activity. After the exclusion of extracts and compounds with known hormonal mechanisms, 26 unique compounds were identified from natural species. The plant source, compound class, structure, target, mechanism of action, safety/toxicity profile, and in vitro, in vivo, and human studies for each compound were evaluated and discussed. β-Caryophyllene, embelin, oleanolic acid, triptonide, and N-butyldeoxynojirimycin (NB-DNJ) were selected as the five most promising compounds for future study using prespecified criteria such as number of studies, efficacy and safety profile, reversibility, and previous use in humans for any indication. In order to move forward with development of a male contraceptive from a natural source, additional studies are needed to determine the predicted safety and efficacy for in vivo and human clinical trials.

Preclinical contraceptive development for men and women

This manuscript endeavors to present research considerations for the preclinical development of non-hormonal contraceptives. Topics include (1) how advances in genomics and bioinformatics impact the identification of novel targets for non-hormonal contraception, (2) the importance of target validation prior to investment in a contraceptive development campaign, (3) considerations on targeting gametogenesis vs gamete maturation/function, (4) how targets from the male reproductive system are expanding women's options for 'on demand' contraception, and (5) some emerging non-hormonal methods that are not based on a specific molecular target. Also presented are ideas for developing a pipeline of non-hypothalamic-pituitary-gonadal-acting contraceptives for men and women while balancing risk and innovation, and our perspective on the pros and cons of industry and academic environments on contraceptive development. Three product development programs are highlighted that are biologically interesting, innovative, and likely to influence the field of contraceptive development in years to come.

Update on Novel Hormonal and Nonhormonal Male Contraceptive Development

BACKGROUND

The advent of new methods of male contraception would increase contraceptive options for men and women and advance male contraceptive agency. Pharmaceutical R&D for male contraception has been dormant since the 1990s. The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) has supported a contraceptive development program since 1969 and supports most ongoing hormonal male contraceptive development. Nonhormonal methods are in earlier stages of development.

CONTENT

Several hormonal male contraceptive agents have entered clinical trials. Novel single agent products being evaluated include dimethandrolone undecanoate, 11β-methyl-nortestosterone dodecylcarbonate, and 7α-methyl-19-nortestosterone. A contraceptive efficacy trial of Nestorone®/testosterone gel is underway. Potential nonhormonal methods are at preclinical stages of development. Many nonhormonal male contraceptive targets that affect sperm production, sperm function, or sperm transport have been identified.

SUMMARY

NICHD supports development of reversible male contraceptive agents. Other organizations such as the World Health Organization, the Population Council, and the Male Contraception Initiative are pursuing male contraceptive development, but industry involvement remains limited.

Quo vadis Cardiac Glycoside Research?

Cardiac glycosides (CGs), toxins well-known for numerous human and cattle poisoning, are natural compounds, the biosynthesis of which occurs in various plants and animals as a self-protective mechanism to prevent grazing and predation. Interestingly, some insect species can take advantage of the CG’s toxicity and by absorbing them, they are also protected from predation. The mechanism of action of CG’s toxicity is inhibition of Na⁺/K⁺-ATPase (the sodium-potassium pump, NKA), which disrupts the ionic homeostasis leading to elevated Ca²⁺ concentration resulting in cell death. Thus, NKA serves as a molecular target for CGs (although it is not the only one) and even though CGs are toxic for humans and some animals, they can also be used as remedies for various diseases, such as cardiovascular ones, and possibly cancer. Although the anticancer mechanism of CGs has not been fully elucidated, yet, it is thought to be connected with the second role of NKA being a receptor that can induce several cell signaling cascades and even serve as a growth factor and, thus, inhibit cancer cell proliferation at low nontoxic concentrations. These growth inhibitory effects are often observed only in cancer cells, thereby, offering a possibility for CGs to be repositioned for cancer treatment serving not only as chemotherapeutic agents but also as immunogenic cell death triggers. Therefore, here, we report on CG’s chemical structures, production optimization, and biological activity with possible use in cancer therapy, as well as, discuss their antiviral potential which was discovered quite recently. Special attention has been devoted to digitoxin, digoxin, and ouabain.

Promising results in development of male contraception

Nowadays, conscious planning of the family is very important for many people. The possibility of using protective measures against unplanned pregnancy is a great comfort. Most forms of contraceptives are intended for women, although their use can be ruled out in various health conditions. Scientists have been trying to develop a different type of method for men for many years. More and more research is being done and there have been promising results. It is hoped that soon both genders will have a similar range of contraceptive options to enable responsible family planning.

Na+/K+-ATPase Revisited: On Its Mechanism of Action, Role in Cancer, and Activity Modulation

Maintenance of Na⁺ and K⁺ gradients across the cell plasma membrane is an essential process for mammalian cell survival. An enzyme responsible for this process, sodium-potassium ATPase (NKA), has been currently extensively studied as a potential anticancer target, especially in lung cancer and glioblastoma. To date, many NKA inhibitors, mainly of natural origin from the family of cardiac steroids (CSs), have been reported and extensively studied. Interestingly, upon CS binding to NKA at nontoxic doses, the role of NKA as a receptor is activated and intracellular signaling is triggered, upon which cancer cell death occurs, which lies in the expression of different NKA isoforms than in healthy cells. Two major CSs, digoxin and digitoxin, originally used for the treatment of cardiac arrhythmias, are also being tested for another indication—cancer. Such drug repositioning has a big advantage in smoother approval processes. Besides this, novel CS derivatives with improved performance are being developed and evaluated in combination therapy. This article deals with the NKA structure, mechanism of action, activity modulation, and its most important inhibitors, some of which could serve not only as a powerful tool to combat cancer, but also help to decipher the so-far poorly understood NKA regulation.

Total Synthesis of the Cardiotonic Steroid (+)-Cannogenol

The total synthesis of (+)-cannogenol, an aglycon common to various biologically important cardiotonic glycosides, has been achieved. Synthesis of the versatile intermediate involves Mizoroki-Heck and intramolecular Diels-Alder reactions from the enantiomerically pure CD-ring segment, newly prepared in a multidecagram scale this time. Total synthesis by the site-selective transformations of the versatile intermediate demonstrated the applicability of our synthetic approach.

The Na+ and K+ transport system of sperm (ATP1A4) is essential for male fertility and an attractive target for male contraception†

One of the mechanisms that cells have developed to fulfil their specialized tasks is to express different molecular variants of a particular protein that has unique functional properties. Na,K-ATPase (NKA), the ion transport mechanism that maintains the transmembrane Na+ and K+ concentrations across the plasma membrane of cells, is one of such protein systems that shows high molecular and functional heterogeneity. Four different isoforms of the NKA catalytic subunit are expressed in mammalian cells (NKAα1, NKAα2, NKAα3, and NKAα4). NKAα4 (ATP1A4) is the isoform with the most restricted pattern of expression, being solely produced in male germ cells of the testis. NKAα4 is abundant in spermatozoa, where it is required for sperm motility and hyperactivation. This review discusses the expression, functional properties, mechanism of action of NKAα4 in sperm physiology, and its role in male fertility. In addition, we describe the use of NKAα4 as a target for male contraception and a potential approach to pharmacologically block its ion transport function to interfere with male fertility.

Cyclometalated Ir(III)-8-oxychinolin complexes acting as red-colored probes for specific mitochondrial imaging and anticancer drugs

A new class of luminescent Ir^III antitumor agents, namely, [Ir(CP1)(PY1)₂] (Ir-1), [Ir(CP1)(PY2)₂] (Ir-2), [Ir(CP1)(PY4)₂] (Ir-3), [Ir(CP2)(PY1)₂] (Ir-4), [Ir(CP2)(PY4)₂] (Ir-5), [Ir(CP3)(PY1)₂]⋅CH₃OH (Ir-6), [Ir(CP4)(PY4)₂]⋅CH₃OH (Ir-7), [Ir(CP5)(PY2)₂] (Ir-8), [Ir(CP5)(PY4)₂]⋅CH₃OH (Ir-9), [Ir(CP6)(PY1)₂] (Ir-10), [Ir(CP6)(PY2)₂]⋅CH₃OH (Ir-11), [Ir(CP6)(PY3)₂] (Ir-12), [Ir(CP6)(PY41)₂] (Ir-13), and [Ir(CP7)(PY1)₂] (Ir-14), supported by 8-oxychinolin derivatives and 1-phenylpyrazole ligands was prepared. Compared with SK-OV-3/DDP and HL-7702 cells, the Ir-1-Ir-14 compounds exhibited half maximal inhibitory concentration (IC₅₀) values within the high nanomolar range (50 nM-10.99 μM) in HeLa cells. In addition, Ir-1 and Ir-3 accumulated and stained the mitochondrial inner membrane of HeLa cells with high selectivity and exhibited a high antineoplastic activity in the entire cervical HeLa cells, with IC₅₀ values of 1.22 ± 0.36 μM and 0.05 ± 0.04 μM, respectively. This phenomenon induced mitochondrial dysfunction, suggesting that these cyclometalated Ir^III complexes can be potentially used in biomedical imaging and Ir(III)-based anticancer drugs. Furthermore, the high cytotoxicity activity of Ir-3 is correlated with the 1-phenylpyrazole (H-PY4) secondary ligands in the luminescent Ir^III antitumor complex.

Dissecting the signaling pathways involved in the function of sperm flagellum

The mammalian flagellum is a specific type of motile cilium required for sperm motility and male fertility. Effective flagellar movement is dependent on axonemal function, which in turn relies on proper ion homeostasis within the flagellar compartment. This ion homeostasis is maintained by the concerted function of ion channels and transporters that initiate signal transduction pathways resulting in motility changes. Advances in electrophysiology and super-resolution microscopy have helped to identify and characterize new regulatory modalities of the mammalian flagellum. Here, we discuss what is currently known about the regulation of flagellar ion channels and transporters that maintain sodium, potassium, calcium, and proton homeostasis. Identification of new regulatory elements and their specific roles in sperm motility is imperative for improving diagnostics of male infertility.

Complexes of oxoplatin with rhein and ferulic acid ligands as platinum(iv) prodrugs with high anti-tumor activity

We herein designed two new Pt^IV prodrugs of oxoplatin (cis,cis,cis-[PtCl₂(NH₃)₂(OH)₂]), [Pt^IVCl₂(NH₃)₂(O₂C-FA)₂] (Pt-2) and [Pt^IVCl₂(NH₃)₂(O₂C-RH)₂] (Pt-3), by conjugating with ferulic acid (FA-COOH) and rhein (RH-COOH) which have well-known biological activities. Three other Pt(iv) complexes of [Pt^IVCl₂(NH₃)₂(O₂C-BA)₂] (Pt-1), [Pt^IVCl₂(NH₃)₂(O₂C-CA)₂] (Pt-4) and [Pt^IVCl₂(NH₃)₂(O₂C-TCA)₂] (Pt-5) (where BA-COOH = benzoic acid, CA-COOH = crotonic acid and TCA-COOH = trans-cinnamic acid) were also prepared for the comparative study. Like most Pt^IV prodrug complexes, the cytotoxicity of Pt-3 containing the biologically active rhein (RH-COOH) ligand against lung carcinoma (A549 and A549/DDP) cells was higher than those of Pt-1, Pt-2, Pt-4, cisplatin and Pt-5. Moreover, the cytotoxicity of Pt-3 in HL-7702 normal cells was lower than those of Pt^IV derivatives bearing BA-COOH, FA-COOH, TCA-COOH and CA-COOH ligands. The highly efficacious Pt-2 and Pt-3 were found to accumulate strongly in the A549/DDP cells, with the prodrug Pt-3 showing highest levels of penetration into the mitochondria. The prodrug Pt-3 effectively entered the A549/DDP cells and caused mitochondrial damage, significantly greater than Pt-2. In addition, the prodrug Pt-3 exhibited higher antitumor efficacy (inhibition rates (IR) = 67.45%) than Pt-2 (28.12%) and cisplatin (33.05%) in the A549/DDP xenograft mouse model. Thus, the prodrug Pt-3 containing the rhein (RH-COOH) ligand is a promising candidate drug targeting the mitochondria.

Mitochondria-localizing dicarbohydrazide Ln complexes and their mechanism of in vitro anticancer activity

Dicarbohydrazide Ln complexes trigger SK-OV-3/DDP cell apoptosis via a mitochondrial dysfunction pathway.

Male Contraceptive Development: Update on Novel Hormonal and Nonhormonal Methods

BACKGROUND

Development of new methods of male contraception would address an unmet need for men to control their fertility and could increase contraceptive options for women. Pharmaceutical research and development for male contraception was active in the 1990s but has been virtually abandoned. The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) has supported a contraceptive development program since 1969 and supports the majority of hormonal male contraceptive development. Nonhormonal methods are also in development but are at earlier stages.

CONTENT

Several hormonal male contraceptive agents have entered clinical trials. Single-agent products being evaluated include dimethandrolone undecanoate, 11β-methyl-nortestosterone dodecyl carbonate, and 7α-methyl-19-nortestosterone. A contraceptive efficacy trial of Nestorone^® gel and testosterone gel in a single application will begin in 2018. Potential nonhormonal methods are at preclinical stages of development. Many nonhormonal male contraceptive targets that affect either sperm production or sperm function have been identified. Targeted pathways include the retinoic acid pathway, bromodomain and extraterminal proteins, and pathways for Sertoli cell-germ cell adhesion or sperm motility. Druggable targets include CatSper, the sperm Na+/K+-exchanger, TSSK, HIPK4, EPPIN, and ADAMs family proteins. Development of a procedure to reversibly block the vas deferens (initially developed in India in the 1980s) is undergoing early stage research in the US under the trade name Vasalgel™.

SUMMARY

NICHD has supported the development of reversible male contraceptive agents. Other organizations such as the World Health Organization and the Population Council are pursuing male contraceptive development, but industry involvement remains dormant.

Synthesis of Oxy-Functionalized Steroidal Skeletons via Mizoroki-Heck and Intramolecular Diels-Alder Reactions

Estrogenic and cardiotonic steroidal skeletons were concisely constructed via Mizoroki-Heck and intramolecular Diels-Alder (IMDA) reactions. Simple modification of the dienophile unsaturation of the IMDA precursor enabled representative AB-ring systems of both steroid classes to be accessed from the same intermediate. The diastereoselectivity of the IMDA reaction used to access the cardiotonic steroidal skeleton was found to be significantly enhanced by performing the reaction in water.

1,2,3-Triazole-containing hybrids as leads in medicinal chemistry: A recent overview

The 1,2,3-triazole ring is a major pharmacophore system among nitrogen-containing heterocycles. These five-membered heterocyclic motifs with three nitrogen heteroatoms can be prepared easily using 'click' chemistry with copper- or ruthenium-catalysed azide-alkyne cycloaddition reactions. Recently, the 'linker' property of 1,2,3-triazoles was demonstrated, and a novel class of 1,2,3-triazole-containing hybrids and conjugates was synthesised and evaluated as lead compounds for diverse biological targets. These lead compounds have been demonstrated as anticancer, antimicrobial, anti-tubercular, antiviral, antidiabetic, antimalarial, anti-leishmanial, and neuroprotective agents. The present review summarises advances in lead compounds of 1,2,3-triazole-containing hybrids, conjugates, and their related heterocycles in medicinal chemistry published in 2018. This review will be useful to scientists in research fields of organic synthesis, medicinal chemistry, phytochemistry, and pharmacology.

A new anti-inflammatory flavonoid glycoside from tetraena aegyptia

The chromatographic reinvestigation the methanol extract of Tetraena aegyptia led to the separation of a new flavonoid glycoside, isorhamnetin-3-O-[2```,3```-O-isopropylidene-α-L-rhamnopyranosyl]-(1```→6``)-O-β-D-glucopyranoside (1), together with two known flavonoids, isorhamnetin (2) and isorhamnetin-3-O-glucoside (3), isolated for the first time from the plant. The new compound was evaluated for the anti-inflammatory activity by using LPS-induce RAW 264.7 cells model. Compound 1 showed significant inhibitory effect on NO release. ELISA assay showed a pronounced effect of 1 on the secretion of cytokines IL-6 and TNF-α, in a dose-dependent manner. Consistent results were obtained by qRT-PCR which revealed that compound 1 markedly reduced the mRNA expression of IL-6 and TNF-α. Together these data, we demonstrated the anti-inflammatory activity of compound 1.