Researchers in Japan have made a breakthrough in the search for a birth control pill for men after discovering that two commonly used immunosuppressants cause reversible infertility in mice. Cyclosporin A (CsA) and Tacrolimus (FK506) are often given to organ transplant patients to prevent rejection of their new organ. Miyata et al.discovered that the target of these two drugs, an enzyme called calcineurin, is critical for sperm development and motility. They observed that continuously dosing mice with calcineurin inhibitors quickly rendered them sterile, an effect that, importantly, disappeared within a week of stopping treatment.
Mouse contraceptives are not nearly as exciting – or as profitable – as human contraceptives, so determining how these results translate to people is of great interest. Unfortunately, men show minimal (if any) loss of fertility while being treated with CsA or FK506 for immunosuppressive purposes. Furthermore, these drugs target calcineurin throughout the body and produce many harmful side effects (in addition to a systemically suppressed immune system). A drug that targets sperm-specific variants of calcineurin, however, would likely not produce these deleterious effects and could provide a promising therapeutic strategy.
The viability of this approach notwithstanding, the emergence of a male birth control pill would have profound therapeutic and social consequences. Vasalgel is a polymer-based male contraceptive that will soon enter clinical trials, but IV administration and slow reversibility (months to years) present significant inconveniences. Nevertheless, a male contraceptive drug of any kind would give men more control over their reproductive health and remove the burden from women and hormone-modulating therapies.
Acknowledgments: Many thanks to Jamie Lahvic and Olivia Weeks, graduate students in the Biological & Biomedical Sciences program at Harvard University, for providing their expertise and commentary on the topic.
Managing Correspondent: Christopher Gerry
Original Article: Sperm calcineurin inhibition prevents mouse fertility with implications for male contraceptive – Science
Media Coverage: Scientists identify potential birth control ‘pill’ for men – LA Times
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