Further report on the interceptive STS 557 in baboons

Area of Science:

• Reproductive Endocrinology
• Primate Reproductive Biology
• Pharmacology

Background:

• Hormonal contraceptives are widely used for pregnancy prevention.
• Levonorgestrel is a common progestin used in contraceptives.
• There is a need for novel contraceptive agents with different mechanisms of action.

Purpose of the Study:

• To evaluate the interceptive activity of STS 557 (17 alpha-cyanomethyl-17 beta-hydroxy-estra-4,9(10)-diene-3-one) in a nonhuman primate model.
• To compare the efficacy of STS 557 with levonorgestrel.
• To investigate the effect of STS 557 on postovulatory plasma progesterone levels.

Main Methods:

• Female nonhuman primates were treated orally with a single dose of 0.4 mg STS 557 or levonorgestrel immediately after mating.
• Pregnancy rates were assessed in treatment groups and compared to control cycles.
• Plasma progesterone levels were measured postovulation in animals treated with STS 557 and levonorgestrel.

Main Results:

• STS 557 treatment resulted in a significantly lower pregnancy rate (2.2%) compared to control cycles (30%) (P < 0.01).
• Levonorgestrel treatment also reduced pregnancy rates (11.5%) compared to controls, but less effectively than STS 557.
• STS 557 did not suppress the postovulatory rise in plasma progesterone, unlike levonorgestrel.

Conclusions:

• STS 557 exhibits high interceptive activity in this nonhuman primate model.
• STS 557 represents a potential novel contraceptive agent with a distinct mechanism of action compared to levonorgestrel.
• Further research is warranted to explore the contraceptive potential and safety of STS 557.