We recently have demonstrated that a C-terminal deletion mutant of the human progesterone receptor (hPRB891) fails to bind to progesterone but can bind RU 486 (Mifepristone) and other progesterone antagonists. Most significantly, this mutant receptor activates transcription of a reporter gene containing the progesterone response element in the presence of these antagonists. Taking advantage of this finding and the modular nature of functional domains of steroid receptors, we constructed a chimeric regulator (pGL-VP) by fusing the ligand-binding domain of human progesterone receptor hPRB891 to the yeast transcriptional activator GAL4 DNA-binding domain and the herpes simplex virus protein VP16 activation domain. We demonstrated that this chimeric regulator activates target genes containing the GAL4-binding sites in transient transfection assays in response to RU 486. In addition, this regulatory system has been validated by ex vivo transplantation of a stable cell line containing both the regulator and a reporter gene into rats. The dosage of RU 486 used is significantly lower than that required for antagonizing progesterone action. The gene-switch system reported here represents a regulatory system, which could be applicable for gene-transfer studies involving animals, as well as humans, in which the delivered gene(s) can be specifically turned on/off in response to an exogenous compound.

A regulatory system for use in gene transfer

Emergency postcoital contraception may be defined as the use of a drug or device to prevent pregnancy after intercourse. Unwanted pregnancy is common; worldwide, about 50 million pregnancies are terminated each year.1 It has been calculated that each year the widespread use of emergency contraception in the United States could prevent over 1 million abortions and 2 million unintended pregnancies that end in childbirth.2 A variety of different methods of emergency contraception are available (Table 1). The first to be described was high-dose estrogen, although currently the most widely used is a combination of estrogen and progestin. Recent interest in . . .

https://www.nejm.org/doi/pdf/10.1056/NEJM199710093371507?listPDF=true

Emergency Postcoital Contraception

Background. Mifepristone (RU 486) is a synthetic steroid with potent antiprogestational and antiglucocorticoid properties that provides an effective medical method of inducing abortion in early pregnancy. Since progesterone is essential for implantation, we tested the use of mifepristone for emergency postcoital contraception. Methods. We studied 800 women and adolescents requesting emergency postcoital contraception who had had unprotected intercourse within the preceding 72 hours. A total of 398 women and adolescents were randomly assigned to treatment with 100 μg of ethinyl estradiol and 1 mg of norgestrel, each given twice 12 hours apart (standard therapy), and 402 women and adolescents were randomly assigned to receive 600 mg of mifepristone. Results. None of the women and adolescents who received mifepristone became pregnant, as compared with four of those who received standard therapy; the difference in failure rates between the two regimens was not statistically significant. The number of...

https://www.nejm.org/doi/pdf/10.1056/NEJM199210083271501

Mifepristone (RU 486) Compared with High-Dose Estrogen and Progestogen for Emergency Postcoital Contraception

Antiprogestins, agents that inhibit the action of progesterone, are among the most controversial and yet the more interesting therapeutic compounds developed in the past 20 years. These agents provide the most effective and safest means of medical abortion, and in addition they may be used for the treatment of patients with cancer, Cushing's syndrome, and gynecologic disorders and for contraception. The first effective antiprogestin was mifepristone (also known as RU 486),1 a derivative of the progestin norethindrone (Figure 1). By analogy with the antiestrogens, it is likely that the substitution at the 11 beta position is responsible for the antiprogestin . . .

Mifepristone (RU 486) -- A Modulator of Progestin and Glucocorticoid Action

The human endometrium displays characteristic features, both structural and functional, across the menstrual cycle. It is the sex steroid hormones, oestrogen and progesterone, that drive the endometrium through the different phases of the cycle. Oestrogen and progesterone act sequentially to regulate cellular concentrations of their respective receptors, this interaction initiates gene transcription. Thereafter a cascade of local events prepares the endometrium for implantation, but in the absence of pregnancy, progesterone withdrawal leads to menstruation and cyclic repair. Withdrawal of progesterone from an oestrogen-progesterone primed endometrium is the initiating event for the cascade of molecular and cellular interactions that result in menstruation. Progesterone withdrawal first affects cells with progesterone receptors. Early events in the menstrual process are vasoconstriction and cytokine up-regulation. The activation of lytic mechanisms is a later event and involves cells that may lack progesterone receptors, for example, uterine leucocytes and epithelial cells. Hence progesterone withdrawal results in a local increase of inflammatory mediators and the enzymes responsible for tissue breakdown. The total complex of local factors implicated in normal menstrual and aberrant menstrual bleeding are yet to be fully defined.

The endocrinology of menstruation--a role for the immune system.

This study investigated the effect of a single dose of RU 486 administered very early in the secretory phase on endometrial development and levels of progesterone receptors on plasma levels of gonadotropins and ovarian hormones and on the pattern of menstrual bleeding. 24 regularly menstruating subjects participated and were studied during a control a treatment and a follow-up cycle. In the treatment cycle a single dose of 200 mg of RU 486 was given in the evening of the 2nd day after urinary LH peak. Plasma was collected from cycle day 10 until menstruation in both control and treatment cycles. The lengths of the control treatment and follow-up cycles were equal. 3 of the subjects had slight vaginal bleeding in association with RU 486 intake which however did not disturb their normal menstrual rhythm. Plasma levels of estradiol progesterone and FSH were not affected in the treatment cycle whereas LH levels increased slightly. The elimination 1/2-life of RU 486 was 28.6 hours. An endometrial biopsy was taken 12 36 or 84 hours (LH + 3 LH + 4 and LH + 6) after drug intake (8 subjects in each group) and another biopsy was taken on the corresponding day in the control cycle. The specimens were assessed by morphometric analysis and for cytosolic progesterone receptor concentrations. Endometrial biopsies taken 12 hours (on LH + 3) after RU 486 intake contained significantly (p<0.001) lower levels of cytosolic progesterone receptors than in the control cycle but levels at 36 and 84 hours were similar. Morphometric analysis revealed a retardation of endometrial development as early as 12 hours after RU 486 intake. The degree of retardation was more marked after 36 and 84 hours. These results suggest that the effect on the endometrium of a single dose of RU 486 immediately after the LH peak may be sufficient to prevent implantation. Thus treatment with RU 486 in the early secretory phase of the menstrual cycle might be considered for use as a once-a-month pill for fertility control. (authors)

B. Masironi

Papers

The effect of RU 486 administered during the early luteal phase on bleeding pattern, hormonal parameters and endometrium