PROJECT
Probing Studies in Male Contraception

Probing studies are underway that may lead to novel contraceptive methods for men.

Adjudin
Studies have continued on a potential male contraceptive derived from the anti-cancer drug lonidamine. The compound, called Adjudin [1-(2,4-dichlorobenzyl)-1H-indazole-3-carbohydrazide, formerly known as AF-2364] has been identified as having potent antispermatogenic effects in vivo, since it was shown to induce adherens junction disruption in the testis. A recently completed subchronic toxicity study using Adjudin illustrated a narrow margin between the compound's safety and efficacy. In order to circumvent this subchronic toxicity issue, Council researchers designed a novel approach to deliver the compound specifically to the testis to induce germ cell depletion from the seminiferous epithelium. If Adjudin can bypass its unnecessary stay in other organs (e.g., the liver and kidneys), its subchronic toxicity should be greatly reduced.

In brief, the compound was chemically conjugated to a follicle-stimulating hormone (FSH) mutant produced in insect cells. Because FSH receptors are restricted to Sertoli cells in the testis in mammals (including men), the FSH mutant thus serves as a specific carrier for Adjudin. Indeed, recent studies have shown that this FSH mutant retains its ability to bind onto the FSH receptors in Sertoli cells while its intrinsic hormonal activity has been stripped owing to several mutations in the mutant protein using genetic engineering techniques. Preliminary findings have shown that this Adjudin–FSH mutant conjugate has a significant improvement in its efficacy to deplete germ cells from the testis versus the unconjugated Adjudin; the margin between safety and efficacy has been greatly widened using this approach. Work is now in progress to develop an alternative administration route and formulations for delivering this conjugate to the testis (e.g., nasal spray or skin patch) instead of the parenteral route.

Blood–testis barrier dynamics
Other ongoing studies include using different biochemical and molecular biology approaches to investigate the biology and regulation of the restructuring events that occur at the Sertoli–Sertoli and Sertoli–germ cell interface during spermatogenesis. For instance, it is known that spermatogenesis will be halted if preleptotene spermatocytes fail to traverse the blood–testis barrier during spermatogenesis. Recent studies from this laboratory have shown that the timely opening of the blood–testis barrier that facilitate preleptotene spermatocyte migration is regulated by intriguing interactions between cytokines (e.g., tumor necrosis factor-alpha and transforming growth factor-beta 3), proteases, and protease inhibitors in the testis. It is likely that cytokines produced by Sertoli and/or germ cells into the blood–testis barrier microenvironment during spermatogenesis activate a cascade of events utilizing proteases to "open" up the barrier to facilitate cell movement. These findings are exciting, as they illustrate there may be multiple targets in the testis that can be tackled to disrupt this event of cell movement, thereby disrupting spermatogenesis. Recent studies have identified several genes and their products that are crucial for regulating blood–testis barrier dynamics. Work is in progress to use these findings to manipulate blood–testis barrier function as the means to disrupt spermatogenesis.

Cadmium signaling pathways
A third ongoing project is investigating the mechanism by which environmental toxicants, such as cadmium, disrupt spermatogenesis, as it has been known for decades that environmental toxicants lower sperm count, causing male infertility. Recent research from this laboratory has identified the signaling pathways by which cadmium disrupts the blood–testis barrier via its effects on several complexes at the Sertoli–Sertoli interface. More important, Council researchers have developed means to "reverse" the cadmium-induced damage to the blood–testis barrier utilizing specific inhibitors. Work is now in progress to develop novel approaches to deliver these inhibitors to the testis specifically via systemic administration to protect the testis from environmental toxicants.

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Population Council researcher

Chuen-yan Cheng

Donors

The CONRAD Program

The Lita Annenberg Hazen Foundation

The George J. Hecht Fund

The William and Flora Hewlett Foundation

The Noopolis Foundation

US National Institutes of Health

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