Screening Methods for Antifertility Agents

Screening Methods for Antifertility Agents

1. Definition, scope & rationale

• Antifertility agents are compounds that prevent fertility by interfering with one or more steps of the normal reproductive cycle, in either sex; screening methods are the validated bench-to-animal assays used to detect and quantify that interference before clinical contraceptive development (SK Gupta, Drug Screening Methods, Ch.8, p.132).
• This topic is a drug-screening / experimental-pharmacology subject (G&G virtual ch.79) — the unit of study is the validated model + endpoint + reference (standard) drug, NOT clinical contraceptive pharmacotherapy (SK Gupta Ch.8, p.132).
• Driver for the field: an ideal contraceptive would be 100% effective, safe, reversible, aesthetically/culturally acceptable, affordable, legal, and applicable at all reproductive stages; no single existing method meets all criteria, so newer-agent screening — especially for developing nations — remains imperative (SK Gupta Ch.8, p.132).
• Two screening axes organise the whole field: (a) target sex — female methods vs male methods; (b) hormonal mechanism class screened — estrogenic / anti-estrogenic, progestational / anti-progestational, androgenic / anti-androgenic, plus the integrated fertility endpoints (anti-ovulatory, anti-implantation, abortifacient, anti-spermatogenic/spermicidal) (SK Gupta Ch.8, pp.132–151).
• Each assay is reported against a standard (reference) drug so that test-compound potency is expressed as an ED₅₀ ratio or % response relative to the standard — e.g. estradiol-17β for estrogenic assays, progesterone / medroxyprogesterone acetate for progestational assays, testosterone / methyltestosterone / testosterone propionate for androgenic assays, cyproterone (acetate) for anti-androgenic assays (Vogel 4e V4 Part XIV — Ovarian Hormones, pp.3448–3467; Testicular Steroid Hormones, pp.3483–3489).

Mechanistic targets screened (female) — five interception points (SK Gupta Ch.8, p.132):

• Inhibition of ovulation.
• Prevention of fertilization.
• Interference with transport of the ovum (oviduct → endometrium).
• Interference with implantation of the fertilized ovum.
• Destruction of the early implanted embryo (abortifacient / contragestational).

Mechanistic target screened (male) (SK Gupta Ch.8, p.144):

• Interference with spermatogenesis (oligospermia / aspermia) or with sperm function, without loss of libido or secondary sexual characteristics — the central design constraint of male antifertility screening.