Grand Challenges is a family of initiatives fostering innovation to solve key global health and development problems. Each initiative is an experiment in the use of challenges to focus innovation on making an impact. Individual challenges address some of the same problems, but from differing perspectives.
Eric Reiter of the Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE) in France will engineer nanobody-based biologicals to block ovulation as a practical, non-hormonal contraceptive with fewer side effects. Blocking the molecular regulators of ovulation is an attractive contraceptive mechanism. However, it can also affect steroid hormone production, which causes undesirable side-effects. Nanobodies are antigen-binding domains of antibodies that can very selectively modulate signal transduction pathways. They will identify candidate nanobodies that may selectively block ovulation using a phage display approach and functional screens. Specifically, this work will focus on identifying nanobodies that are biased ligands, triggering receptors selectively to yield only the desired downstream responses. These candidates will be engineered to produce long-lasting biologicals that will then be administered to mice and ewes to evaluate their ability to block ovulation as a proof-of-principle.
Leo Han of Oregon Health and Science University in the U.S. and colleagues at the University of North Carolina and the Marsico Lung Institute will build a hydration-based drug discovery platform for the cervix to screen drug libraries for long-lasting non-hormonal contraceptives that alter mucus hydration. Contraceptives that thicken cervical mucus to block the movement of sperm and thereby inhibit fertility would be well tolerated and may also protect against pathogens. Identifying nonhormonal drugs that work in this way, however, is difficult because of the lack of relevant cell culture systems for high-throughput testing. They have previously conditionally reprogrammed endocervical cells to grow in culture while retaining relevant physiological characteristics such as hormonal regulation and mucus production. They will adapt this method for high-throughput screens by incorporating particle-based tracking microrheology to quantify hydration of the mucus layer produced by the cells that can then be used to screen drug libraries.
Stephanie Seminara of Massachusetts General Hospital in the U.S. will perform large-scale, human genetic studies to identify gene variants that influence fertility for developing novel non-hormonal contraceptives. Globally, many women do not use contraceptives for reasons including negative side effects of hormonal methods, leading to poor method acceptability. This leads to 88 million unintended pregnancies per year globally. To identify drug targets for developing more acceptable contraceptives, they will analyze whole exome sequences and phenotypes from three existing patient populations with rare forms of infertility, such as primary ovarian insufficiency, and one new cohort with unexplained infertility. This will reveal both single nucleotide and structural variants underlying infertility, and subsequently the associated molecular pathways. They will also perform a large-scale genome-wide association study using over 1.8 million samples from multi-ethnic population biobanks to identify common variants associated with reproductive traits, which could also uncover novel genes involved in infertility.
Viviana Gradinaru of the California Institute of Technology in the U.S. will perform imaging-based, high-throughput screens using adeno-associated virus (AAV) delivery vectors to rapidly identify ovary-specific macromolecules that are essential for fertility and could be used to develop non-hormonal contraceptives. They will compile a comprehensive list of candidate ovary-specific macromolecules, including RNAs and micropeptides, by applying machine learning algorithms and structural analyses to existing datasets and also perform Riboseq on mouse and human ovarian tissues to identify all the proteins being translated. They will then test these candidates by developing an oocyte and follicle cell-based loss-of-function screening platform using AAV to safely, efficiently, and specifically deliver the macromolecule-targeting constructs to the cells. The most promising AAV-based candidates will then be tested directly in mouse follicle cultures and then in vivo to identify those that are critical for female fertility and have reversible effects.
Jeffrey Lee of the University of Toronto in Canada will engineer single-domain camelid antibodies (nanobodies) to block the interaction between two proteins exclusive to the sperm and egg that mediate their fusion and thereby fertilization, as affordable, non-hormonal contraceptives with fewer side effects. Nanobodies are exquisitely specific binding proteins that make attractive therapeutics because of their additional simplicity, stability, and smaller size compared to antibodies, also lowering the cost of their production. They hypothesize that their small size is well adapted to reach the site of sperm-egg binding and block this interaction. To generate specific nanobodies they will immunize alpacas or llamas with the purified sperm and egg proteins and use phage display and ELISA to isolate antigen-specific nanobodies. These will then be tested for their ability to block sperm-egg fusion using biophysical assays, mating, and IVF models.
Darryl Russell of the University of Adelaide in Australia will use genomics approaches to identify the molecular pathways that control ovulation for developing more non-hormonal contraceptives with fewer side effects. The classical progestin-based contraceptive pill disrupts natural hormone cycles; requires long-term, regular use; and causes a range of harmful side-effects. An alternative approach is an acute treatment that directly blocks ovulation – the release of the oocyte from the ovary. This research team earlier discovered unique and specialized roles for the progesterone receptor (PGR) in regulating ovulation in a mouse model. They will further characterize these specialized molecular mechanisms upstream and downstream of PGR induction in granulosa cells, which associate with the oocyte, with a focus on chromatin and transcription factors to identify unique drug targets that could be used to develop a contraceptive with fewer side effects.
Carol Hanna of Oregon Health and Science University in the U.S. will develop an imaging platform using Positron Emission Tomography-Computed Tomography (PET-CT) to visualize the movement of sperm in the female reproductive tract to accelerate testing of non-hormonal contraceptive compounds at lower cost. Emerging research is positioned to discover non-hormonal contraceptive candidates with varying mechanisms of action. However, there is currently no simple or effective way to test them in human-relevant models, which impedes their clinical development. PET-CT is a non-invasive, highly sensitive imaging technique that uses a radioactive tracer and can penetrate deeply into tissues. They will adapt existing mitochondrial-targeted fluorescent dyes to radiolabel sperm and test the ability of PET-CT to precisely track these sperm with high resolution inside the reproductive tract of non-human primates. This technology could help advance contraceptives to clinical testing.
Francisco Diaz of Pennsylvania State University in the U.S. will develop a high-throughput screening method to identify compounds that can block two biological events essential for female fertility without affecting ovulation or hormone production in order to identify new contraceptives with fewer side effects. These two events, which occur at the same time, are cumulus expansion, whereby cumulus cells release from the oocyte to enable it to enter the oviduct, and oocyte maturation, whereby the oocyte divides to produce the egg and a smaller polar body. They will extract cumulus oocyte complexes from primed female mice and apply them to a microwell array prototype that will contain 1,024 wells coated with different test compounds and connected in groups by microfluidic channels. Oocytes in the wells will be stimulated to undergo first cumulus expansion, and, after removal of cumulus cells, oocyte maturation. The ability of each compound to inhibit each step will be assessed by automated inverted microscopy. They will first optimize their platform using known inhibitors and then test it using a library of 1,200 FDA approved molecules.
Darryl Russell of the University of Adelaide in Australia is seeking safer contraceptives that block ovulation without altering hormone levels and cause fewer side effects using an automated in-vitro screening platform that measures cell adhesion in the cumulus-oocyte complex, which is required to release the oocyte from the ovary. In Phase I, they built the screening platform by isolating cumulus-oocyte complexes from mice, culturing them in fibronectin-coated multi-well plates, and quantifying adhesion in a 96-well plate format using an automated assay. In a first run, they screened a library of 129 FDA-approved chemical compounds over four months and identified seven candidate contraceptives with known protein targets, one of which showed a strong reduction in ovulation when tested in mice. In Phase II, they will study whether one of the main target proteins identified in their first screen is a key target for blocking ovulation. They will also test whether the other candidates from their first screen can block ovulation in mice and screen larger and more diverse libraries to identify new candidate contraceptives and prioritize them for further drug development and testing.
Randall Peterson of the University of Utah in the U.S. will develop a zebrafish model for high-throughput screens to identify compounds that inhibit the formation of gametes, i.e., sperm or eggs, (gametogenesis), which could lead to male and female contraceptives that last for weeks or months after only a single dose. They will generate transgenic zebrafish lines that express a selection of four fluorescently-labeled markers for different stages of gametogenesis that can be rapidly quantified to measure the effects of candidate compounds on blocking gamete production. The suitability of these zebrafish lines for high-throughput multi-well compound screens will be tested using known inhibitors of gametogenesis.