PROJECT SUMMARY/ABSTRACT Development of novel contraceptive strategies is central to the mission of the Contraceptive Research Branch of the NICHD. This goal is driven by a global need for effective contraceptive methods to address: 1) the glut of unintended pregnancies (~45% of US pregnancies in 2011); 2) the high rate of elective abortion (1.15M unintended pregnancies ended in abortion in 2011 in the US); and 3) the high risk of maternal mortality (~830 women/day worldwide die due to pregnancy or childbirth complications). In a search for novel male contraceptive drug targets, we identified RBM46, which is a germ cell-specific RNA binding protein expressed by germ cells on the basement membrane of seminiferous tubules (outside the blood-testis-barrier), and is essential for spermatogenesis. Indeed, Rbm46 knockout mice are sterile and have no other phenotype, raising the distinct possibility that targeting RBM46 could lead to safe and effective male contraception by blocking spermatogenesis at the differentiating spermatogonial stage. Thus, we propose to develop drugs that target degradation of RBM46 as a means of oral, non-hormonal male contraception, which will significantly advance additional safe and reversible options for male contraception towards the clinic. Specifically, we will combine: 1) exceptional expertise in drug screening and development at UTSA and UT Health San Antonio; 2) leading expertise in male reproduction, spermatogenesis, and infertility at UTSA and ECU; 3) close proximity to one of two NIH-designated Marmoset Breeding Colonies, maintained at the Southwest National Primate Research Center; 4) growing and ongoing experience collecting and assessing marmoset sperm; 5) published experience in the use of cutting- edge single-cell genomics to assess normality of spermatogenic cell types; and 6) documented expertise with spermatogonial stem cell (SSC) transplantation. In Aim 1, we will identify small molecules that bind RBM46 and could be used to develop PROTACs. In Aim 2, we will produce initial RBM46 PROTACs and validate that they degrade the protein in vitro. In Aim 3, we will use medicinal chemistry to optimize the drug-like characteristics of top validated RBM46 PROTACs. In Aims 4 and 5, we will determine whether optimized RBM46 PROTACs induce reversible contraception in vivo using mice and marmosets, respectively. Together, these Aims are designed to advance RBM46 degradation as a novel strategy to achieve reversible, non-hormonal male contraception and provide key results to justify further preclinical investigation and eventual commercialization.

PROJECT NARRATIVE A significant unmet need for worldwide population control exists due to the lack of available safe, effective, and reversible oral male contraceptives. To close this critical translational gap, we propose to target the testis-specific RNA binding protein RBM46 as a contraceptive approach. The overarching goals of this project are to screen for small molecules that bind RBM46, develop these “binders” into proteolysis targeting chimeras (PROTACs) to specifically degrade RBM46 protein in differentiating spermatogonia, and then determine whether use of these PROTACS induces reversible male sterility in both mice and marmosets, a non-human primate model with closer similarity to humans.