A non-hormonal reversible contraceptive targeting GSK3α, a protein kinase, essential for epididymal sperm maturation.

Background and objectives: Epididymal transit renders key competence to mammalian spermatozoa for fertilizing eggs. Generally, the two paralogs of glycogen synthase kinase 3, GSK3α and GSK3β, functionally overlap except in testis and sperm. We showed that GSK3α is essential for epididymal sperm maturation and fertilization. Male infertility is the only phenotype of mice with a global or testis-specific knockout (KO) of Gsk3α. Their sperm maturation is impaired, and sperm cannot fertilize eggs in vitro and in vivo. This suggests that GSK3α is a "male fertility kinase" in mammals and that GSK3α-selective inhibitor is a potential male contraceptive.

Materials and methods: A set of eight heterozygous Gsk3α(±) male mice received daily intraperitoneal injections of BRD0705, an isoform-selective GSK3α inhibitor, at 20 mg/kg body weight for 1 week. Five vehicle-treated and BRD0705-treated mice were tested for in vivo fertility and the remaining mice were sacrificed; their caudal spermatozoa were examined for motility and biochemical properties.

Results: The treated mice did not sire any pups while the control group sired 46 pups with a normal gestation period of 19-23 days. Continued fertility testing up to 6 weeks post-treatment, showed that the treated mice regained fertility siring 56 pups, with 76 in the control group. Sperm motility was impaired, its abnormal morphology increased during epididymal transit, Adenosine triphosphate (ATP) levels were low, and tyrosine-phosphorylation of hexokinase was absent: these phenotypes imitated those observed in Gsk3α KO mice. Tyrosine²⁷⁹-phosphorylation of GSK3α was reduced in sperm from the treated mice showing that the GSK3α activity was inhibited. The altered sperm phenotypes returned to normal following recovery of fertility.

Conclusions: Complete infertility resulted after 1 week of BRD0705-treatment and fertility recovered after cessation of the treatment. Work is ongoing to determine the minimum dose and treatment time and the testing of new compounds with increased selectivity and inhibitory activity against GSK3α.