A win-win for women's reproductive health: A nonsteroidal contraceptive and fertoprotective neoadjuvant

Overactivation or Apoptosis: Which Mechanisms Affect Chemotherapy-Induced Ovarian Reserve Depletion?

Dormant primordial follicles (PMF), which constitute the ovarian reserve, are recruited continuously into the cohort of growing follicles in the ovary throughout female reproductive life. Gonadotoxic chemotherapy was shown to diminish the ovarian reserve pool, to destroy growing follicle population, and to cause premature ovarian insufficiency (POI). Three primary mechanisms have been proposed to account for this chemotherapy-induced PMF depletion: either indirectly via over-recruitment of PMF, by stromal damage, or through direct toxicity effects on PMF. Preventative pharmacological agents intervening in these ovotoxic mechanisms may be ideal candidates for fertility preservation (FP). This manuscript reviews the mechanisms that disrupt follicle dormancy causing depletion of the ovarian reserve. It describes the most widely studied experimental inhibitors that have been deployed in attempts to counteract these affects and prevent follicle depletion.

Chemotherapy and female fertility

Chemotherapy to treat cancer is usually responsible for early ovarian follicle depletion. Ovarian damage induced by cancer treatments frequently results in infertility in surviving patients of childbearing age. Several fertility preservation techniques have been developed. Nowadays, oocyte or embryo cryopreservation with or without ovarian stimulation and cryopreservation of the ovarian cortex are the most commonly used. However, these methods may be difficult to implement in some situations, and subsequent use of the cryopreserved germ cells remains uncertain, with no guarantee of pregnancy. Improved knowledge of the molecular mechanisms and signaling pathways involved in chemotherapy-induced ovarian damage is therefore necessary, to develop new strategies for fertility preservation. The effects of various chemotherapies have been studied in animal models or in vitro on ovarian cultures, suggesting various mechanisms of gonadotoxicity. Today the challenge is to develop molecules and techniques to limit the negative impact of chemotherapy on the ovaries, using experimental models, especially in animals. In this review, the various theories concerning ovarian damage induced by chemotherapy will be reviewed and emerging approaches for ovarian protection will be explained.

The Impact of Chemotherapy on the Ovaries: Molecular Aspects and the Prevention of Ovarian Damage

Cancer treatment, such as chemotherapy, induces early ovarian follicular depletion and subsequent infertility. In order to protect gametes from the gonadotoxic effects of chemotherapy, several fertility preservation techniques—such as oocyte or embryo cryopreservation with or without ovarian stimulation, or cryopreservation of the ovarian cortex—should be considered. However, these methods may be difficult to perform, and the future use of cryopreserved germ cells remains uncertain. Therefore, improving the methods currently available and developing new strategies to preserve fertility represent major challenges in the area of oncofertility. Animal and ovarian culture models have been used to decipher the effects of different cytotoxic agents on ovarian function and several theories regarding chemotherapy gonadotoxicity have been raised. For example, cytotoxic agents might (i) have a direct detrimental effect on the DNA of primordial follicles constituting the ovarian reserve and induce apoptosis; (ii) induce a massive growth of dormant follicles, which are then destroyed; or (ii) induce vascular ovarian damage. Thanks to improvements in the understanding of the mechanisms involved, a large number of studies have been carried out to develop molecules limiting the negative impact of chemotherapy on the ovaries.

Pharmacological administration of recombinant human AMH rescues ovarian reserve and preserves fertility in a mouse model of chemotherapy, without interfering with anti-tumoural effects

PURPOSE

To determine whether pharmacological administration of recombinant human anti-Mullerian hormone (rAMH) protects the ovarian reserve and preserves fertility without interfering with anti-tumoural cytotoxic action of chemotherapy.

METHODS

Intraperitoneal delivery of rAMH and ovarian post-receptor activity were assessed with immunohistochemistry and western blot. Differential follicle counts and reproductive outcomes were assessed after cyclophosphamide (Cy) administration, with/without concurrent administration of rAMH. Interference of rAMH with Cy chemotoxicity was assessed on a human breast cancer cell line and an in vivo mouse model of human leukaemia.

RESULTS

rAMH reached the ovary after intraperitoneal injection and demonstrated post-receptor bioactivity. Cy administration in mice caused primordial follicle activation, as shown by a decrease in primordial follicle population accompanied by an increase in early growing follicles and granulosa cell proliferation. Co-administration of rAMH reduced follicle activation, thereby protecting the primordial follicle reserve, and improving long-term fertility and reproductive outcomes. rAMH co-administration did not interfere with the cytotoxic actions of Cy in vitro on breast cancer cell line or in vivo in a model of human leukaemia.

CONCLUSION

This study demonstrates that rAMH is bioactive in the ovary for a limited time, and that pharmacological administration of rAMH during chemotherapy treatment reduces follicle activation and primordial follicle loss and significantly improves reproductive outcomes in a mouse model, and does not interfere with the therapeutic actions of the treatment. Further investigation is necessary to determine whether it has similar protective effects in the human ovary.

Müllerian inhibiting substance/anti-Müllerian hormone as a fertility preservation agent

PURPOSE OF REVIEW

The nascent field of oncofertility is quickly gaining traction as novel experimental treatments are being developed, driving a renewed interest in Müllerian inhibiting substance (MIS) as an ovarian fertoprotectant.

RECENT FINDINGS

MIS is unique in its mechanisms of ovarian protection by virtue of acting directly on granulosa cells of primordial follicles and for being a benign reproductive hormone, with few side effects. We will explore in this review how it may be utilized to protect the ovary from chemotherapy, or to enhance ovarian tissue cryopreservation therapy. We will also examine potential mechanisms of action of MIS across multiple cell types, as well as current limitations in our understanding of the pharmacology of recombinant MIS.

SUMMARY

The usefulness of MIS as a fertoprotectant may be dependent on the mechanisms of gonadotoxicity of each chemotherapeutic. Further investigation is needed to determine how to best deliver and combine MIS treatment to existing fertility management strategies.