Müllerian inhibiting substance/anti-Müllerian hormone: A novel treatment for gynecologic tumors

During early mammalian development embryos possess the capacity to produce complete female and male reproductive tracts. The Müllerian ducts will become the upper third of the vagina, the cervix, uterus, Fallopian tubes and the outer lining of the ovaries. The Wolffian ducts become the seminal vesicles, vasa deferens and epididymides. These ductal systems grow adjacent to but independent of one another. Once the genetic sex of the embryo becomes known specific changes begin to occur. For example, at about 10 weeks gestation in human the undifferentiated gonads become either testes, under the control of the SRY gene [ 1 ] or ovaries. As gonads begin to differentiate one of the reproductive tract primordia is destroyed and the other proliferates and differentiates. In females, the lack of testosterone is sufficient to allow the Wolffian ducts to atrophy while in males the ablation of the Müllerian duct is more complex. The French anatomist Dr. Alfred Jost shed some very important light on the process in males over 65 years ago [ 2 , 3 ]. At that time it was believed that the key to normal prenatal sexual development was whether testes were present. The testosterone they secrete would both stimulate the Wolffian ducts and destroy the Müllerian ducts. Professor Jost's experiments proved that testosterone alone was insufficient to the task because the gonadectomized embryos he treated with testosterone crystals had retained uteri at birth. He proposed that a "Müllerian inhibiting substance (MIS)" now also called anti-Müllerian hormone (AMH), is secreted from the newly formed testes and that it is the MIS/AMH which causes the regression of the Müllerian ducts. It was later shown that regression is due mainly to apoptosis, autophagocytosis, disruption of basement membranes, and epithelial mesenchymal transformation of cells followed by migration of some of the cells toward the mesonephros [ 4 , 5 , 6 , 7 , 8 , 9 ].

The discovery that males and females both express MIS/AMH postnatally prompted numerous studies which revealed the usefulness of measuring MIS/AMH in serum in a variety of clinical situations including ambiguous genitalia, undescended testes, delayed puberty, sex cord and granulosa cell tumors. Fortunately, three very useful human MIS/AMH-specific and highly sensitive immunoassays were developed concurrently by the Donahoe, Josso and Hutson laboratories [ 29 , 30 , 31 ] for this purpose and several are commercially available thus, impacting the practice of pediatric endocrinology, pediatric surgery and gynecologic oncology [ 29 , 30 , 31 ]. Serum MIS/AMH, is a strong predictor of the presence of testicular tissue when testes are not palpable [ 79 ]. It also is a useful indicator of testis function in these cases and in cases of sexual ambiguity. Normal MIS/AMH levels are consistent with normal testes, undetectable MIS/AMH reflects absent testes whereas, low MIS/AMH is often due to gonadal dysgenesis. Serum MIS/AMH data can be more useful than hCG stimulation tests to evaluate gonadal status. Serum MIS/AMH correlates with ovarian reserve and it is an indicator of response to in vitro fertilization protocols [ 36 , 80 , 81 , 82 , 83 , 84 , 85 ]. The vast majority of sex cord and granulosa cell tumors [ 86 , 87 ] secrete MIS/AMH in proportion to tumor burden [ 88 ] and changes in serum MIS/AMH reflect recurrences and/or response to therapy. These tumors may express the MIS/AMH receptor [ 89 ] but the tumors are not responsive to the MIS/AMH they produce. This fact implies a loss of function downstream from the receptor itself, therefore, these tumors are not considered targets for MIS/AMH therapy. Serum concentrations of MIS/AMH above the normal for age is consistent with the presence of either one of these tumors; rising serum MIS/AMH reflects tumor growth and decreases show response to therapy [ 86 ]. MIS/AMH levels can reach thousands fold the normal range without any adverse reactions that could be attributed to the MIS/AMH molecule. It is for this reason that we predict that MIS/AMH administered to cancer patients as a may have a very favorable toxicity profile (see below). Whether recombinant human MIS/AMH is toxic will be the topic of detailed toxicology studies planned for the future when clinical grade MIS/AMH is available.

Endometriosis is a common benign disease of reproductive women, especially infertile women. Ectopic endometrial cells exhibit abnormal proliferative and apoptotic regulation in endometriosis. Recent reports show that MIS induces the cell cycle arrest and apoptosis of human endometrial stromal cells and endometriosis cell line in vitro. One study shows that the celluar apoptosis was increased by causing arrest at G 1 phase and increasing cells at sub-G 0 G 1 phase in endometrial stromal cells treated with MIS for 72 hours ( Fig. 12 ) [ 118 ]. Another study shows that MIS induces autophagy through increased expression of Beclin-1 autophagy-promoting protein in endometriosis cell line [ 119 ]. These findings suggest that MIS play an important role in cellular apoptosis in endometriosis. Therefore, MIS has a potential as a therapeutic modalities in endometriosis.

The existing literature on MIS/AMH suggests that the recombinant human protein will have very little toxicity in vivo and that it should be tested against tumors expressing the MIS/AMH type II receptor, perhaps beginning with ovarian cancer as among receptor expressing tumors, since it has the most dire prognosis. The molecular tools to identify MIS/AMH receptor expressing ovarian and gynecologic tumors are already in hand, thus, it is possible to select patients for treatment. An MIS/AMH ELISA exists to follow administered doses of MIS/AMH, as well. Clinical trials await the production of sufficient supplies of recombinant human MIS/AMH for this purpose.