In a recent study published in the American Journal of Obstetrics and Gynecology, researchers developed a novel contraceptive ‘ZB-06’ a vaginal film containing a human contraceptive antibody (HCA) called HC4-N that agglutinates sperm.
In addition, they tested its safety, efficacy, and mucosal and systemic pharmacokinetics (PK) using a postcoital test (PCT). Furthermore, they modeled the pharmacodynamics (PD) of a single dose of the ZB-06 film in vitro.
Hormones-based contraceptives are safe and highly effective. However, some women might have medical contraindications or side effects due to them. Likewise, non-hormonal methods, e.g., copper intrauterine devices, cause heavy menstrual bleeding and dysmenorrhea.
Likewise, nonoxynol-9 (N9)-based spermicides, female condoms, and diaphragms have many potential drawbacks; as such, their uptake is low worldwide. Consequently, there is an urgent need for safer and more acceptable contraceptives to meet their growing demand as the unplanned pregnancy rate exceeds 50% across several countries.
About the study
The researchers performed a phase I, open-label, proof-of-concept study among 20 healthy women in Norfolk, Virginia, United States of America (USA). They also assessed the clinical safety of this film among eight heterosexual couples who met the study inclusion criteria. The researchers checked all potential volunteers’ metabolic panels and complete blood count (CBC). Additionally, they tested whether or not they were free from pathogenic microbial infections from herpes simplex virus type 2 (HSV-2), human immunodeficiency virus (HIV-1), etc.
Post-screening, the researchers demonstrated how to insert the vaginal film using an instructional video. They performed a speculum exam to ensure proper insertion of the vaginal contraceptive film (VCF), which they later removed with ring forceps.
The team arranged three visits for all study enrollees across three cycles, baseline, i.e., no product use, ZB-06 use PCT, and safe recovery cycles. They assessed the concentration of HC4-N antibody in vaginal fluid and cervical mucus (CM) at visits four, seven, and 10 (V4, V7, V10) by anti-idiotype enzyme-linked immunosorbent assay (ELISA) that confirmed the recovery of normal ovulatory CM interactions one month after ZB-06 use.
The team also assessed vaginal fluid, CM, and serum samples for sperm agglutinating antibodies in vitro, a surrogate PD marker using a sperm agglutination kinetic assay. They measured treatment-emergent adverse events (TEAEs) in female participants and respective male partners and colposcopy between V3 and V8. Moreover, they performed a Nugent score before and after product use, i.e., at V6 and V8.
This study’s sub-clinical safety endpoints were the changes in the concentration of soluble pro-inflammatory cytokines and vaginal Nugent score after single film use. The researchers structured sample size consistent with recent phase I PCT trials typically performed first-in-woman. They statistically analyzed continuous variables with more than two conditions using analysis of variance (ANOVA) and used Wilcoxon matched-pairs signed rank tests for comparisons.
All women participants were 18 to 50 years old, did not use hormone-based contraceptives, and had regular menstrual cycles with timely ovulation. More importantly, they were sexually active with a male partner with no history of male sterility. After using an HC4-N-containing ZB-06 vaginal film once 30 minutes before unprotected penile intercourse with intravaginal ejaculation, all eight female participants had markedly less sperm motility in their ovulatory cervical mucus. Its use was safe and passed the current surrogate contraceptive efficacy benchmark for the PCT test of less than five PMS/hpf, averaging over nine hpfs at 400X magnification.
The mean progressively motile sperm (PMS) per high power field (hpf) in a PCT performed on ovulatory CM at baseline was 25.9 (± 30.6). After single product use, this number dropped to 0.04 (± 0.06) PMS/hpf. One month after ZB-06 use, the mean PMS/hpf was 47.4 (± 37.4), indicating contraceptive reversibility. The PK and surrogate PD data favored that this film provided enough mucosal anti-sperm antibodies for three hours post-use. Furthermore, there were no overt changes in the Nugent score before and after its use.
Reassuringly, several cytokines and chemokines following vaginal application of ZB-06 film remained the same, and except in one, anti-sperm antibodies were undetectable in the serum of all eight male partners.
To conclude, the study demonstrated that ZB-06, a novel, non-hormonal, topically-applied vaginal film is safe for use. Since it might meet unmet women’s contraceptive needs in the future, it should be further developed and tested. However, the researchers plan to evaluate the vaginal microbiome and the sub-clinical inflammatory state of the CV mucosa in future extended-use safety studies of ZB-06.