Development of a Novel Method for Assessing Clinical Efficacy of an On-demand Male Contraceptive

RITAGLIATI, CARLA; BALBACH, MELANIE; LEVIN, LONNY; BUCK, JOCHEN

Congreso; 47th American Society of Andrology Annual Conference; 2022

Mammalian sperm are stored in the epididymis in a dormant state; they are immotile and unable to fertilize the oocyte. After ejaculation, in the female reproductive tract, sperm begin swimming and initiate a process called capacitation, where they acquire hyperactivated motility and acrosomal responsiveness, becoming competent to fertilize.An initial event in capacitation and hyperactivation is the HCO3--induced sAC-mediated increase in cAMP level. The phenotypes of sAC KO mice and men suggest a strategy to safely and effectively deliver a sAC inhibitor to men. Two independently generated sAC KO mouse strains and humans homozygous for sAC disrupting mutations exhibit male-specific sterility. In both mice and men, sAC KO sperm are immotile, which can be rescued by cAMP analogs, and very importantly, they exhibit no other overt phenotypes. Systemic exposure of sAC inhibitors acutely inhibits male fertility. One hour after injecting male mice with one of the most potent inhibitors, their sperm are immotile, and the males have severely reduced fertility. The effect is reversible; motility returns to normal by the next day.The aim of this work was to develop methods for measuring efficacy of sAC inhibitors on human sperm functions to be used during clinical trials. The most promising sAC inhibitors in vitro dose responses were tested by measuring cAMP accumulation, PKA substrate phosphorylation, motility/hyperactivation and induced acrosome reaction in human sperm. The chosen appropriate concentrations were assayed in motility dilution experiments. Due to its tight binding kinetics, the best compounds inhibit essential functions in human sperm which withstand the dilution effects presumably encountered when ejaculated sperm enter the inhibitor-free female reproductive tract. This methodology for assessing sAC inhibitors on human sperm motility of ejaculated sperm can be leveraged as a pharmacodynamic endpoint during Phase 1/2a clinical trials. The ability to indirectly test efficacy, by visualizing the effects on sperm functions essential for fertilization during the early phases of clinical testing, defines on-demand contraceptives as relatively unique among potential therapeutics. By assessing efficacy of the compound following dilution into inhibitor-free media, analogous to the dilution that will normally occur following ejaculation into the vagina, we will be able to narrow in on a dosage range that should provide contraceptive efficacy during Phase 2b/3.