A male contraceptive that immobilises sperm for 2 hours prevented pregnancy in mice and resulted in no adverse side effects
14 February 2023
A drug that temporarily paralyses sperm could become the first on-demand male birth control pill. In mice, the contraceptive was 100 per cent effective at preventing pregnancy for about 2 hours, with full fertility returning 24 hours later.
“This is, in the male contraceptive field, totally revolutionary,” says Jochen Buck at Cornell University in New York. Most other prospective male contraceptives in clinical development are only effective after eight to 12 weeks, he says.
Previous research has shown that sperm require a protein called soluble adenylyl cyclase (sAC) to move, and that men who cannot produce sAC due to rare genetic mutations are infertile. So, Buck and his colleagues assessed whether a drug inhibiting sAC could be used as a male contraceptive. If sperm are immobile, they can’t travel up the vaginal tract to fertilise an egg.
The team assessed the movement of sperm collected from 17 male mice, eight of whom received the drug. In samples collected 2 hours after mice received the drug, only about 6 per cent of sperm were mobile on average compared with about 30 per cent in samples from control mice. The effect wore off after about 24 hours, “which means we not only have an on-demand contraceptive, but one that is also rapidly reversible”, says Melanie Balbach, also at Cornell University.
In another test, the researchers paired 52 male mice with females 30 minutes after giving the males the contraceptive drug. After 2 hours each pair had mated, but there were no resulting pregnancies, indicating the contraceptive was 100 per cent effective. The drug also didn’t cause noticeable side effects, even when mice received three times the standard dose of a comparable compound continuously for 42 days.
“What I like about the proposed contraceptive in this study is the on-demand option,” says Ulrike Schimpf at the KTH Royal Institute of Technology in Sweden. “It would act rapidly, temporarily and is efficient at the first dose.”
Buck and Balbach plan to refine the drug so that it lasts longer before testing it in humans. If all goes well, they hope to begin clinical trials by 2025.
“We need more [birth control] options, and men need an option so that the burden of contraception is not on females anymore,” says Balbach. “We’re very optimistic that once men take the inhibitor, it will have the same effect.”
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