Targeted degradation of HIPK4 for non-hormonal male contraception - Safe, effective, and reversible methods for contraception are necessary to address the 85 million unplanned pregnancies that occur worldwide each year. These unintended pregnancies pose significant risks to women’s health and threaten our efforts to achieve global sustainability. Since the invention of “the Pill” in the 1950s, most birth control options have been female-directed, including estrogen or progestin treatments, barrier methods, intrauterine devices, and tubal ligation. In contrast, men remain limited to condoms and vasectomy, which have high failure rates and incomplete reversibility, respectively. Pharmacological strategies for male contraception would help overcome these disparities in reproductive health. Due to the undesirable side effects associated with hormone-based therapies, ongoing efforts to develop male contraceptives have focused on non-hormonal agents. Current drug candidates include those that inhibit retinoic acid receptors, bromodomain testis-specific protein, soluble adenylate cyclase, or serine/threonine kinase 33. However, these signaling proteins or their paralogs have somatic functions that will likely limit their potential as contraceptive targets. Small molecules that disrupt the functions of testis-specific proteins would bridge this gap, and our project focuses on dual-specificity kinase that is selectively expressed in developing sperm: homeodomain-interacting protein kinase 4 (HIPK4). Our research team has found that male mice lacking HIPK4 function are infertile but otherwise appear to have normal development, physiology, and behavior. Sperm produced by HIPK4-deficient mice misshapen and incompetent for in vitro fertilization, and these defects stem from a critical role for HIPK4 in spermatid maturation. Consistent with the Hipk4 knockout phenotypes, HIPK4 mutations have been discovered in infertile men. These findings establish HIPK4 as a promising target for non-hormonal male contraception, and we recently identified a quinoline-based HIPK4 inhibitor in a high-throughput chemical screen. This ATP-competitive compound exhibits nanomolar potency in vitro and selectively targets HIPK4 over structurally related paralogs (HIPK1, HIPK2, and HIPK3) and is highly specific in a cell-based kinome-profiling platform. We are now developing HIPK4 degraders based on this scaffold, as this catalytic mode of drug action can achieve enhanced target specificity and greater efficacy than traditional inhibitors. During our initial exploration of candidate proteolysis targeting chimeras (PROTACs), we made the unexpected discovery that certain quinoline derivatives are intrinsically able promote HIPK4 degradation. Our preliminary structure-activity-relationship analyses have identified structural features that correlate with degrader activity, and our mechanistic studies support a model in which these quinolines induce HIPK4 degradation in spermatids through autophagy. Our project goals are to develop HIPK4 degraders with optimized potency and selectivity in spermatids (Aim 1), to further elucidate their mechanism of action (Aim 2), and to evaluate their efficacy in animal models (Aim 3).
