EP055

**EP055** is a small organic compound based on a 1,3,5-triazine ring structure developed as a reversible, non-hormonal male contraceptive. It binds to the C-terminal domain of **EPPIN** (epididymal protein), a sperm surface protein that interacts with semenogelin (SEMG1) and prostate-specific antigen (PSA), disrupting SEMG1 binding and causing a reversible loss of sperm progressive motility by decreasing internal sperm pH and Ca²⁺ levels. Preclinical studies in cynomolgus and rhesus macaques demonstrated rapid inhibition of sperm motility (to ~20% within 6 hours post high-dose IV infusion of 125-130 mg/kg), with EP055 detectable in semen up to 78 hours and full motility recovery by 18 days; plasma half-life is ~10-12 minutes, but tissue retention in testis/epididymis extends efficacy. Recent formulations include an in-situ forming implant (ISFI) for sustained subcutaneous release over 28 days, showing reduced sperm motility and acrosomal degradation without systemic inflammation. Developed by Eppin Pharma, it targets on-demand or long-acting contraception without hormonal disruption.