With half of all pregnancies in US and globally being unplanned, it is evident that existing contraceptives fail to meet many women's needs. Beyond a desire for user-controlled, non-hormonal options, there is critical lack of multi-purpose prevention technologies (MPTs), which protect against sexually transmitted infections (STIs) and bacterial vaginosis. Currently, condoms are the only devices that even partially meet these criteria, yet they remain outside a woman's control, exhibit relatively high failure rates, and do not promote a healthy vaginal microbiome. The Population Council is currently developing an innovative non-hormonal intravaginal ring (IVR) MPT, designed to fill this gap in the contraceptive market. The active pharmaceutical ingredients released from this ring include Cu2+ from copper salts and lactic acid from lactide. Initial studies of the anti-sperm activity of these APIs focused on inhibition of sperm motility. However, concentrating solely on motility has drawbacks. Some sperm are propelled quickly through the cervix; brief exposure windows may require high concentrations of APIs to completely inhibit motility, increasing risk of unwanted toxic effects. Contraception might alternatively be achieved by targeting sperm organelles or essential pathways that can be disrupted at lower concentrations and shorter exposure times than needed for motility inhibition.

One attractive target is the plasma membrane (PM). Sperm have very high surface area: volume ratios and exposure to APIs is immediate, not requiring internalization or intracellular metabolism. Detergents such as nonoxynol-9 take advantage of these properties, but injure vaginal epithelial cells. APIs targeting the PM need to attack attributes unique to sperm. One set of targets have been sperm-specific ion channels and transporters essential for various functions. An understudied set of targets, which are the focus of this proposal, are the PM's lipid composition and biophysical fluidity. Far more than somatic cells, sperm carefully modulate their PM sterol content to control membrane fluidity and fusogenicity. This occurs during "capacitation," a process required for acrosome exocytosis (AE), hyperactivated motility, and fertilization. APIs targeting the PM can have contraceptive efficacy by impacting diverse sperm functions beyond motility.

In this regard, we investigated how short-term (5-minute) exposure to MPT-APIs impacted PM fluidity, spontaneous AE, and viability. This brief exposure to varying concentrations of Cu2+ not only reduced long-term progressive motility, but also led to pathological dysregulation of membrane fluidity, resulting in premature AE and cell death 3 hours after the Cu2+ had been washed away. Our preliminary data indicate that even short-term exposure to Cu2+ (such as experienced by "vanguard sperm" that enter the cervix quickly), will lead to long-term generation of reactive oxygen species that result in fatal lipid peroxidation. These compelling data demonstrate that Cu2+ can achieve contraception by interfering with multiple essential sperm functions. However, to advance Cu2+ as a key component of an MPT, we must determine the minimal effective concentrations and exposure times. This information will be essential for future regulatory approval.