Contraceptive efficacy of low doses of mifepristone

OBJECTIVE

To determine whether a 5-mg dose of mifepristone is sufficient to prevent pregnancy.

DESIGN

Clinical study.

SETTING

Academic research center.

SUBJECT(S)

Healthy, fertile, sexually active female volunteers.

INTERVENTION

Volunteers received a 5-mg dose of mifepristone once weekly, starting on cycle day 2, for up to 6 months. This was their only contraceptive method.

MAIN OUTCOME MEASURE(S)

Number of pregnancies.

RESULT(S)

The treatment resulted in a significant decrease in pregnancy rate without affecting the menstrual cycle or causing disturbing side effects.

CONCLUSION(S)

A low dose of mifepristone, which does not inhibit ovulation, reduces fertility significantly by affecting the endometrium. However, the contraceptive effect needs to be improved for the drug to compete with other contraceptive methods.

Fertility impairment after mifepristone treatment to rats at proestrus. Actions on the hypothalamic-hypophyseal-ovarian axis

Accumulated evidence indicates that the antigestagen mifepristone affects the reproductive axis acting on hypothalamic, pituitary, ovarian, and uterine tissues. The purpose of this study was to further investigate which reproductive functions are impaired by the antagonist, critically compromising the reproductive process, leading to unsuccessful pregnancy. Circulating pituitary and ovarian hormones, sexual receptivity, ovulation, and implantation rates were studied in cycling rats receiving a single dose of mifepristone (1 or 10 mg/kg subcutaneously) at 12:00 proestrus, before luteinizing hormone (LH) stimulation of the ovulatory process. Mifepristone-treated rats had decreased preovulatory surges of LH and prolactin (PRL), and hypersecretion of LH, PRL, and progesterone at estrus. The sexual receptivity was dramatically affected by the antagonist as indicated by the profound decrease in the lordosis response evaluated on the night of proestrus. The number of ovulating animals and the number of oocytes recovered from the oviduct on the morning of estrus were not affected by mifepristone. The low number of rats that succeeded in mating with potent males became pregnant. However, they delivered an average of only two pups at parturition, indicating a failure in the implantation of the fertilized ova, as ovulation was not affected by the antagonist at the dose used. We conclude that a dramatic inhibition of the sexual receptivity and unsuccessful implantation, preceded by a reduction on LH and PRL secretion, are the major components leading to fertility impairment after a single dose of mifepristone administered before the preovulatory surge of LH.

Effect of follicular phase administration of mifepristone (RU486) on blastocyst implantation in the rhesus monkey

In the present study our aim was to test two hypotheses: 1) inhibition of preovulatory phase progesterone action can inhibit or delay ovulation, and 2) inhibition of preovulatory phase progesterone action can inhibit postovulatory phase endometrial receptivity for blastocyst implantation. Female rhesus monkeys showing normal cycle lengths were randomly assigned to two groups: group 1 (n = 5) and group 2 (n = 7). The pretreatment cycles were monitored for ovulatory pattern and, in treatment cycles, females were allowed to cohabit with males from cycle days 6 to 28; group 1 animals received vehicle alone, and group 2 animals received mifepristone (RU486, subcutaneously), 1 mg/animal 3 consecutive cycle days (days 7, 8, and 9 for 26-day pretreatment cycle length; and days 8, 9, and 10 for 28-day pretreatment cycle length). Follicular phase mifepristone resulted in a delay of ovulation (p < 0.01) when compared with pooled data of pretreatment and treatment cycles of group 1 and pretreatment cycles of group 2. Despite delay of ovulation, there was only a 20% decrease in the incidence of pregnancy in group 2 as compared with that in group 1. However, a delay (p < 0.05) in the appearance of CG was noted in follicular phase mifepristone-treated cycles as compared with control treatment cycles. On the other hand, ovulation could not be detected in three monkeys in group 2; and, of these, two cycles were extended, but all three cycles were negative for CG. These results support earlier reports that follicular phase mifepristone can inhibit or disrupt follicular maturation, and delay ovulation. However, follicular phase mifepristone failed to inhibit implantation, because gonadal hormones, including progesterone, resume normal functions once ovulation takes place.

Comparative effectiveness of three antiprogestins alone and in combination with anordiol in terminating pregnancy in the rat

The effectiveness of mifepristone, onapristone, and ORG 31806 alone or in combination with anordiol to terminate pregnancy in the rat was evaluated. ORG 31806 at a dose of 2 mg/kg/day, mifepristone at 4 mg/kg/day, and onapristone at 8 mg/kg/day, terminated pregnancy in all treated animals. Anordiol, an antiestrogen, at a dose of 5 mg/kg/day, terminated pregnancy in all treated animals. Anordiol acted synergistically with all three antiprogestins terminating pregnancy in the rat. The antiprogestins at doses that were either partially effective or non-effective became 100% effective when administered with a non-effective dose of anordiol. Thus, combination of ORG 31806 (1 mg/kg/day) plus anordiol (0.31 mg/kg/ day), mifepristone (1 mg/kg/day) plus anordiol (0.62 mg/ kg/day), and onapristone (2 mg/kg/day) plus anordiol (2.5 mg/kg/day) terminated pregnancy in all treated animals. These combinations of the antiprogestins and anordiol decreased significantly the serum progesterone levels but not serum 17 beta-estradiol levels. The present results indicate that the most potent combination was ORG 31806 plus anordiol.

RU486 (mifepristone): mechanisms of action and clinical uses

RU486 (mifepristone) has proved to be a remarkably active antiprogesterone and antiglucocorticosteroid agent in human beings. The mechanism of action involves the intracellular receptors of the antagonized hormones (progesterone and glucocorticosteroids). At the molecular level, the most important features are high binding affinity to the receptor, interaction of the phenylaminodimethyl group in the 11 beta-position with a specific region of the receptor binding pocket, and RU486-induced transconformation differences in the ligand-binding domain. These particularities have consequences at different steps of the receptor function as compared with agonists. However, the reasoning cannot be limited to the RU486-receptor interaction, and, for instance, there is the possibility of a switch from antagonistic property to agonist activity, depending on the intervention of other signaling pathways. It would be desirable to have derivatives with only one of the two antagonistic properties (antiprogestin, antiglucocorticosteroid) in spite of similarities between steroid structures, receptors involved, and responsive machineries in target cells. Clinically, the RU486-plus-prostaglandin method is ready to be used on a large scale and is close to being as convenient and safe as any medical method of abortion may be. The early use of RU486 as a contragestive as soon as a woman fears a pregnancy she does not want will help to defuse the abortion issue. Research should now be conducted to define an efficient and convenient contraceptive method with RU486 or other antiprogestins. The usefulness of RU486 for obstetric indications, including facilitation of difficult delivery, has to be assessed rapidly. Gynecologic trials, particularly in leiomyomata, should be systemically continued. The very preliminary results obtained with tumors, including breast cancers, indicate that further studies are necessary.

The possible use of antiprogestins for contraception

BACKGROUND

A number of compounds, antiprogestins, e.g. mifepristone, onapristone and lilopristone, have been developed which compete with progesterone at the receptor level. One of these, mifepristone, is in combination with a prostaglandin analogue currently in use for termination of early pregnancy. The possibility to use these compounds for contraceptive purposes is presently under evaluation.

METHODS

The possible contraceptive effect of antiprogestins has been evaluated in both clinical and experimental studies.

RESULTS

Administration of antiprogestin during the follicular phase has an inhibitory effect on follicular development and ovulation, and on endometrial development and function if administered during the secretory phase of the menstrual cycle. A high dose of mifepristone, 200 mg, administered immediately following ovulation is highly effective in preventing implantation, most likely due to an effect on endometrial receptivity. It seems that the endometrium is more sensitive to antiprogestin than is the ovulatory process. Low weekly, 2.5 mg to 5 mg, and daily doses, 0.5 mg, of mifepristone did not inhibit ovulation, but a significant effect on endometrial development and especially endometrial function judged from measurement of the expression of a number of markers for endometrial receptivity could be demonstrated.

CONCLUSION

The effect of mifepristone on the endometrium may be sufficient to prevent implantation, and if so, an oral contraceptive method could be developed which has no effect on ovarian function.

Pharmacokinetics of mifepristone after low oral doses

Relatively low doses of the antiprogestin mifepristone (RU 486) have recently proven to be efficient for a variety of possible clinical uses of the drug. However, the pharmacokinetics after low single oral doses have not been characterized. We evaluated the pharmacokinetics of mifepristone following single ingestion of 2 and 25 mg in five women as well as repeated ingestion of 8 mg in two women. Maximal serum concentrations were reached rapidly (within 0.5-2 h) with all doses used. Serum mifepristone concentrations were proportional to the oral doses taken. The mean (+/- SD) areas under the concentration curves (AUCs) (0-24 h) were 1134 (+/- 144), 4846 (+/- 64), and 17,015 (+/- 4,421) h x ng/mL following 2, 8, and 25 mg doses, respectively. No cumulative increases in serum concentrations were detected with prolonged daily administration of 8 mg of mifepristone. The study subjects appeared to vary in their ability to metabolize mifepristone, as two different half-lives (t1/2) emerged after both 2 and 25 mg single doses (24.2 +/- 0.6 [SD] h for three subjects; and 44.4 +/- 1.8 [SD] h for two subjects). We conclude that within the dose range of 2-25 mg/day, the pharmacokinetics of mifepristone are linear, unlike those seen following ingestion of higher daily doses. Keeping in mind previously published data on the biological effects of low dose mifepristone administration, these data infer that certain effects of the drug, such as inhibition of ovulation, might be achieved at serum concentrations of approximately 100 ng/mL.

Antiprogestins: mechanism of action and contraceptive potential

Antiprogestins are characterized by substitutions at the 11 beta and 17 alpha positions of the steroid ring system and bind strongly to both progesterone and glucocorticoid receptors. Although they function predominantly as antiprogestins and antiglucocorticoids, on occasion they display progestin agonistic and even antiestrogenic properties. The most common clinical use of the antiprogestin mifepristone is to induce a medical abortion in the early stages of pregnancy. Progesterone maintains the endometrium, transforming it from a proliferative to a secretory state. It also facilitates the luteinizing hormone surge, which initiates ovulation. As a consequence, antiprogestins may also have contraceptive potential. Although antiprogestins do delay ovulation, this effect is inconsistent unless high doses are given, and under these circumstances, the antiprogestin effect is associated with unopposed estrogen action on the endometrium. Very low doses of antiprogestins do not affect hormonal secretion or ovulation or alter bleeding patterns, but they do have contraceptive potential by inducing profound alterations in endometrial morphology. Mifepristone is also a very effective and safe postcoital agent. This new class of pharmacological agents has numerous other gynecological and obstetrical indications, such as endometriosis, uterine myoma, and expulsion of the fetus in the case of fetal death in utero. Antiprogestins may also be used in the treatment of steroid-dependent tumors. There are also therapeutic implications consequent to their antiglucocorticoid properties.

Contraception with anti-progesterone

Anti-progesterones have potential as contraceptives, acting either by the inhibition of ovulation or the inhibition of endometrial development. Clinical studies have shown that once-a-month treatment with Mifepristone in the early luteal phase is an effective contraceptive method, and that emergency post-coital contraception with Mifepristone is at least as effective as other methods currently used. Recent studies indicate that the endometrium is more susceptible to Mifepristone than are the hypothalamic and pituitary regions, and it may therefore be possible to develop a new contraceptive method based on low daily or once-weekly doses of Mifepristone that does not influence ovarian function.

The effect of antiprogestin (RU 486) and prostaglandin biosynthesis inhibitor (naproxen) on uterine fluid prostaglandin F2 alpha concentrations

In the present study the effect of the antiprogestin RU 486 and the prostaglandin biosynthesis inhibitor, naproxen, on uterine fluid concentration of prostaglandin F2 alpha (PGF2 alpha) was investigated. RU 486, 200 mg, was administered two days after the luteinizing hormone (LH) surge and naproxen, 500 mg, was given every 12th hour five times starting 4 days after the LH surge. Uterine fluid was collected in the proliferative phase at ovulation and in the mid-luteal phase in a control and treatment cycle. The amount of PGF2 alpha was measured by gas chromatography-mass spectrometry. In the control cycle, the highest concentration of PGF2 alpha was found in the mid-luteal phase, and the lowest at the time of ovulation. Both RU 486 and naproxen reduced the PGF2 alpha concentration in uterine fluid considerably, or to 22-25% of that in the control cycle at the time of implantation. PGF2 alpha produced by the endometrium is believed to be of importance for the implantation of the blastocyst. Postovulatory treatment with RU 486 effectively prevents implantation, probably mainly by inhibiting the maturation of the endometrium during the secretory phase of the cycle. It is suggested that the inhibition of PGF2 alpha release through the uterine fluid caused by RU 486 may also be of importance.

RU486: pharmacology and potential use in the treatment of endometriosis and leiomyomata uteri

More than a decade after the serendipidous discovery of RU486, numerous antiprogestins have been synthesized and studied. Interest in how antiprogestins exert their antagonist effect has led to novel information about the molecular mechanisms of progesterone action. The pivotal role that progesterone plays in reproductive biology has led to research in many areas where a potential role for these compounds may be found in health and disease. RU486 has been shown to relieve pelvic pain associated with endometriosis and to decrease American Fertility Society endometriosis scores. Uterine leiomyomata show a significant reduction in size after administration of RU486 for 3 months. Although much research remains to be carried out, RU486 appears promising as alternative therapies for these diseases.

RU486 exerts antiestrogenic activities through a novel progesterone receptor A form-mediated mechanism

The human progesterone receptor (hPR) exists in two distinct forms in most cells, hPR-A and hPR-B. Both receptor isoforms exhibit distinct biological functions and demonstrate a cell- and promoter-specific ability to regulate gene transcription. Interestingly, in cell contexts where PR-A is transcriptionally inactive, it acts as a progesterone-dependent inhibitor of estrogen receptor function. Coexpression of the human estrogen receptor with the A form (but not the B form) of the human progesterone receptor resulted in a ligand-dependent inhibition of estrogen receptor-mediated gene transcription. The antiprogestins RU486 (MIfepristone) and ZK98299 (Onapristone) and related antiprogestins were all effective "noncompetitive" inhibitors of the estrogen receptor in this assay as none of these compounds interacted directly with the estrogen receptor. This observation may explain in part the observed tissue-specific antiestrogenic effects of RU486 and further indicates that the antiestrogenic activities of antiprogestins may be intrinsic to their biological function. This important new information defines novel activities of progesterone receptor ligands and may alter the way in which we define progesterone receptor modulators for future clinical applications. In addition, these data reveal that the A form of the progesterone receptor plays a key role in modulating estrogen receptor function in cells where both receptors are expressed.

Sequential regimen of the antiprogesterone RU486 and synthetic progestin for contraception

OBJECTIVE

To examine the effect of sequential use of the antiprogesterone RU486 and synthetic progestin on ovarian function of healthy women.

DESIGN

Healthy women were given a sequential antiprogesterone-progestin treatment. Blood samples were taken twice a week during one control cycle and one to three treatment cycles; prospective analysis.

SETTING

The outpatient clinic of the Helsinki City Maternity Hospital, Helsinki, Finland, and Steroid Research Laboratory, Department of Medical Chemistry, University of Helsinki, Helsinki, Finland.

PATIENTS

Eleven healthy women, volunteers, 20 to 34 years of age.

INTERVENTIONS

A dose of 25 mg/d of RU486 was given during cycle days 1 to 21, and synthetic progestin (5 mg of norethisterone to six and 5 mg of medroxyprogesterone acetate to five women) during cycle days 22 to 31.

MAIN OUTCOME MEASURES

Serum P, E2, FSH, and LH were measured from serum samples.

RESULTS

In 20 of the 24 treatment cycles analyzed the serum concentrations of P were anovulatory. In the remaining 4 cycles, P levels rose above 3 ng/mL, suggestive of ovulation. Folliculogenesis was not completely inhibited, but serum E2 profiles were subnormal and delayed. Bleeding control was satisfactory.

CONCLUSIONS

Antiprogesterone RU486 hampers or delays follicular development, suggesting a possible use as an estrogen-free oral contraceptive. However, the synthetic progestins used in this regimen induced serum P rises in some cycles. The synthetic progestin provides the cycle control, but its possible effect on the reliability of the method remains to be evaluated.

Pharmacokinetic study of RU 486 and its metabolites after oral administration of single doses to pregnant and non-pregnant women

RU 486 and three of its metabolites (RU 42633-monodemethyl, RU 42848-didemethyl, and RU 42698-hydroxymetabolite) were determined by HPLC in plasma from nine non-pregnant and 36 pregnant women. Each non-pregnant subject took an oral dose of RU 486 (25, 100, 400 and 600 mg consecutively) once per menstrual cycle. Six of the nine women also received a dose of 200 mg. The 36 pregnant women were randomized into four groups which were given a single dose of 25, 100, 400 or 600 mg RU 486. Blood samples were taken up to 120 h after dosing. Peak concentrations of RU 486 occurred on most occasions within 2 h. Plasma concentrations at 1 h and at 24 h increased in proportion to log dose. There was a wide variability (up to ten-fold) in the pharmacokinetic parameters within each dose group. Plasma concentrations of RU 42633 were similar to those of RU 486 but concentrations of RU 42848 and RU 42698 were much lower. As with RU 486, the plasma concentrations of the metabolites were maintained at high levels for up to 48-72 h after dosing. The findings were consistent with a rapid metabolism of RU 486 to RU 42633; removal of the second methyl group leading to RU 42698 occurred much more slowly and to a much less extent than removal of the first. There appeared to be no significant differences between the non-pregnant and pregnant women in either the plasma concentrations or pharmacokinetic parameters of RU 486 and its metabolites.

Dose-response relationships of RU 486

Clinical experience has indicated that the effects of RU 486 can be divided into dose-dependent and dose-independent effects. Examples of the dose-dependent effects include the antiglucocorticoid effects of RU 486, whereas pregnancy termination or dilatation of the cervix can be considered dose-independent with the various regimens tested so far. Following oral intake in man, the serum levels of RU 486 are in the micromolar range, and the half-life is approximately 30 hours. The concentrations of RU 486 in myometrial tissue are approximately one-third of those measured in serum. However, due to saturation of alpha 1-acid glycoprotein (AAG), the serum binding protein for RU 486, the serum levels remain similar within the dose range of 100-800 mg of RU 486. The unbound RU 486 is metabolized by two-step demethylation or by hydroxylation. The demethylated and hydroxylated metabolites of RU 486 retain considerable affinities of 9-21% towards the human progesterone receptor, and 45-61% towards the human glucocorticoid receptor (RU 486 = 100%), suggesting a biological role for the metabolites. Rat serum lacks a specific binding protein for RU 486. Even though the levels of RU 486 in rat adipose tissue are 40 times as high as those seen in serum, the concentrations of RU 486 in rat brain are only 28% of the serum levels. This indicates that diffusion of RU 486 into the central nervous system is restricted by the blood-brain barrier. Hence, the dose-dependency of certain centrally mediated effects of RU 486 might be explained by the limited diffusion of RU 486 into hypothalamic/hypophyseal sites, which seem to be reached only after ingestion of high doses of RU 486. However, the peripheral effects of RU 486, such as termination of pregnancy, are mediated via steroid receptors in target tissues. This suggests that similar biological effects can be attained at considerably lower doses than the ones currently in use.

Mode of action of RU 486

RU 486 is a 19-norsteroid which has a specific high affinity binding to the progesterone and glucocorticoid receptor. It is generally accepted that RU 486 acts as a pure progesterone antagonist almost without agonistic activity. RU 486 acts mainly directly on the target organ, such as the endometrium, but also to some extent indirectly through an effect on the pituitary gonadotrophin secretion. The effect of RU 486 during the menstrual cycle is dependent on time of treatment. Treatment before ovulation will result in a prolongation of the proliferative phase of the menstrual cycle, while treatment during the mid- and late luteal phase will invariably induce bleeding, often followed by a second bleeding episode at the expected time of menstruation. The only treatment period which does not influence the menstrual cycle is treatment immediately following ovulation. Treatment during the proliferative phase has no effect on endometrial morphology but inhibits follicular development and delays oestrogen and LH surge. Treatment on the first days following ovulation has no effect on ovarian steroid concentration, but will significantly delay endometrial development, cause a change in the concentration of oestrogen and progesterone receptor concentration enzyme activity and production of substances thought to be progesterone dependent. The change in endometrial development is sufficient to prevent implantation. In mid- and late luteal phase, treatment with RU 486 will result in endometrial shedding in spite of normal progesterone levels. Post-ovulatory treatment with RU 486 will also significantly change uterine contractility. In early pregnancy, withdrawal of progesterone inhibition will result in uterine contractility and a significant increase in the sensitivity of the myometrium to prostaglandin.(ABSTRACT TRUNCATED AT 250 WORDS)

Delayed endometrial maturation induced by daily administration of the antiprogestin RU 486: a potential new contraceptive strategy

OBJECTIVE

Our objective was to determine if a progesterone antagonist might interdict the development of a secretory endometrium.

STUDY DESIGN

Eleven normally cycling women not at risk for pregnancy received RU 486 (1 mg/day orally) or placebo throughout one menstrual cycle in a randomized, double-blind, crossover fashion. Estradiol, progesterone, and placental protein 14 were measured every 3 days; luteinizing hormone was measured until the midcycle surge was detected. An endometrial biopsy was performed on luteal phase day 7 to 9 and interpreted with Noyes' criteria. Differences between treatment groups were analyzed by the Student t test.

RESULTS

RU 486 delayed ovulation, retarded endometrial maturation, and reduced peak levels of placental protein 14 without affecting gonadal steroid production. The abnormalities in endometrial morphology and function are similar to those seen in infertile women with luteal phase defects.

CONCLUSION

We hypothesize that this regimen of antiprogestin administration may prevent implantation and offer a novel strategy for fertility control.

The mechanism of RU486 antagonism is dependent on the conformation of the carboxy-terminal tail of the human progesterone receptor

The human progesterone receptor form B (hPR-B) was expressed in Saccharomyces cerevisiae together with a specific reporter plasmid. To understand the mechanism underlying antagonist ligand activity, libraries of hormone binding domain (HBD)-mutated hPR-B molecules were prepared. A mutant receptor was identified that had lost the ability to bind either progesterone or R5020; it could still bind RU486 and, surprisingly, fully activated transcription in the presence of this "antagonist" and other antiprogestins. When this receptor mutant was assayed in mammalian cells, RU486 again demonstrated agonistic activity. Sequence analysis indicated that the mutant phenotype was due to truncation of the carboxy (C)-terminal 42 aa. We conclude that amino acids in the extreme C-terminal region are required for the receptor to bind progesterone, while antagonists bind to a site located more N-terminal of the HBD. Our results suggest that the extreme C-terminal region of the receptor contains an inhibitory function that silences receptor transactivation in the absence of agonist and in the presence of antagonist.

The steroid hormone antagonist RU486. Mechanism at the cellular level and clinical applications

The cellular and molecular mechanism of RU486, a steroid hormone antagonist, is discussed in detail. Principally, RU486 opposes the action of two types of hormones: progesterone and glucocorticosteroids. The clinical applications are also described, as well as the future outlook.

Transplacental passage of mifepristone and its influence on maternal and fetal steroid concentrations in the second trimester of pregnancy

The maternal and fetal endocrine effects of the maternal administration of the anti-progestin mifepristone in mid-pregnancy have been investigated. Mifepristone and the metabolite RU 42,633 were detected in the fetal circulation and in the amniotic fluid 4, 24 and 48 h after oral ingestion. Maximum fetal plasma concentrations of mifepristone occurred 4 h after treatment indicating rapid placental transfer of the drug. No significant changes in progesterone, cortisol, oestradiol or aldosterone concentrations were detected in the maternal circulation after mifepristone treatment. No significant changes occurred in the fetal progesterone, oestradiol or cortisol concentrations, but a significant increase in fetal aldosterone occurred 4 and 24 h after treatment. The significance of these results is discussed in relation to the possible therapeutic uses of mifepristone for inducing labour.

Changes in circulating alphafetoprotein following administration of mifepristone in first trimester pregnancy

The occurrence of fetomaternal haemorrhage was investigated in 30 women by measuring maternal serum alphafetoprotein (AFP) levels before and after the administration of mifepristone (RU 486) for termination of first trimester pregnancy. A significant rise in AFP levels was seen in 21 women (70%), the increase ranging from 6 to 660% of baseline levels. The apparent frequency of fetomaternal haemorrhage was similar to that reported previously for surgical termination of first trimester pregnancies.

Peptide-containing nerves in the human pregnant uterine cervix: an immunohistochemical study exploring the effect of RU 486 (mifepristone)

The presence of several neuropeptides (neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP), substance P (SP), galanin (GAL), enkephalin (ENK), somatostatin (SOM) was established in the early pregnant human cervix using indirect immunofluorescence immunohistochemistry. Several peptides (VIP, NPY, CGRP, GAL) were present both in free nerves among smooth muscle cells and around blood vessels. Others (SP, SOM) were only seen as single varicosities among smooth muscle cells. Randomized treatment of patients with RU 486 (mifepristone) prior to surgical sampling revealed no clearcut differences in peptide immunoreactivities. After RU 486 treatment, however, there was a tendency towards a decrease of NPY- and VIP-immunoreactivity, and an increase of CGRP-immunoreactivity.

Pharmacokinetics of the antiprogesterone RU 486: no correlation to clinical performance of RU 486

The pharmacokinetics and metabolism of RU 486 were characterized in 17 women who received a single dose of 600 mg of RU 486 for termination of an early unwanted pregnancy. Based on the clinical outcome and serum chorionic gonadotropin values, the subjects were divided into two groups: those who aborted completely (i.e. responders: N = 13) and those who did not respond to RU 486 treatment (i.e. non-responders: N = 4). The serum levels of RU 486, the monodemethylated, didemethylated and hydroxylated metabolites of RU 486 were measured by HPLC preceded by column chromatography. There were no significant differences in the serum levels of RU 486 or its metabolites between the two groups. The serum concentrations of alpha 1-acid glycoprotein, the binding protein for RU 486, were quantitated by immunoturbidimetry. The alpha 1-acid glycoprotein concentrations were similar in responders and non-responders. The metabolism of RU 486 was also studied by fractionating extracts of serum pools of responders and non-responders on thin-layer chromatography, and subsequent RIA analysis of the eluates of the sliced thin-layer chromatography. Spots with similar distribution and percentages of cross-reactivity were found in both groups on the chromatography; the results were also similar to those from a serum pool to which synthetic RU 486 and its three metabolites had been added. Hence it is concluded that failure to abort in response to RU 486 therapy is not associated with altered pharmacokinetics or metabolism of RU 486.

Effects of RU486 on progesterone secretion by human preovulatory granulosa cells in culture

The effects of RU486 on progesterone synthesis were studied in human preovulatory granulosa cells in culture. No effect was observed at 1 and 10 micrograms/mL, but at 100 micrograms/mL, RU486 inhibited the simulation of progesterone secretion induced by LH and cAMP. It is suggested that the main target of RU486 is the cytochrome P450scc function [catalyzing the formation of pregnenolone (D5P) from cholesterol], since no accumulation of D5P or hydroxy derivatives of progesterone was observed. As RU486 is an antiglucocorticosteroid and antiprogesterone agent, the effects of dexamethasone and progesterone were also investigated. Dexamethasone did not modify progesterone secretion, but progesterone inhibited its own synthesis in both the presence and absence of LH. Thus, under these experimental conditions RU486 displayed a progesterone-like effect. However, since the effect of RU486 was observed only at a concentration around 10(-4) M, the mechanism of action may not involve a receptor pathway and may not apply to most clinical circumstances.

Effect of mifepristone on dilatation of the pregnant and non-pregnant cervix

The effect of the progesterone antagonist mifepristone on the cervix was investigated in two randomised double-blind placebo-controlled trials, the first in 30 women undergoing first trimester surgical termination of pregnancy and the second in 30 non-pregnant premenopausal women. 600 mg mifepristone, given orally 48 h before surgery, increased the mean preoperative cervical dilatation in both pregnant and non-pregnant treatment groups and also reduced the force required to dilate the pregnant and non-pregnant cervix.

The placental transfer of mifepristone (RU 486) during the second trimester and its influence upon maternal and fetal steroid concentrations

A double-blind, placebo-controlled study has assessed the maternal and fetal endocrine effects of the maternal administration of the anti-progestin mifepristone in mid-pregnancy. There were six women in each group. Four hours after oral administration of 600 mg mifepristone, the drug was detected in both maternal and fetal circulations and in the amniotic fluid. No significant changes in progesterone, cortisol, oestradiol, or aldosterone concentrations were detected in the maternal circulation after treatment with mifepristone or placebo. In women treated with mifepristone, the mean fetal aldosterone level was 1699 (SD 217) pmol/l which was significantly higher than the mean level of 999 (SD 84) pmol/l in the control group but no significant changes occurred in the fetal progesterone, oestradiol or cortisol concentrations. The significance of these results is discussed in relation to the possible therapeutic uses of mifepristone for inducing labour.

Predictors of failed attempted abortion with the antiprogestin mifepristone (RU 486)

The experience of 271 patients who received mifepristone (RU 486) in experimental protocols from July 1984 to January 1989 was analyzed by logistic regression methods. The regimen used was the strongest predictor of failure, followed by Quetelet's index and initial beta-human chorionic gonadotropin level. The relative risk of failure was 2.3 times with 7-day regimens and 6.3 times with the other regimens that obtained with regimens of 600 mg given once or twice. The relative risk of failure increased with increasing Quetelet's index; women in the top quartile were 2.9 times more likely to fail to abort than were women in the bottom quartile. The risk of failure increased with increasing initial beta-human chorionic gonadotropin level; those with an initial level greater than 19,800 mIU/ml were 2.8 times more likely to fail to abort than were women with an initial value less than or equal to 6350 mIU/ml. Body mass appears to influence the likelihood of abortion with mifepristone.

The antiprogesterone steroid, RU 486 (mifepristone)

RU 486 (Mifepristone) represents a major development in the field of hormone antagonists as the first effective antiprogestogen. A number of therapeutic roles for the drug are envisaged. It is already being used extensively around the world for the procurement of first trimester abortion--particularly in combination with prostaglandins. It also has been shown to be effective as a cervical ripening agent and for the induction of labour. Initial human studies have involved nonviable pregnancies and more work is needed in animal models before the drug can be deemed safe for use in viable human pregnancies in the third trimester.

Pharmacokinetic study of orally administered RU 486 in non-pregnant women

A method based on HPLC was devised for the estimation of RU 486 in blood and utilised to study the pharmacokinetics of a single dose of 50 mg RU 486 administered orally to 12 women on day 7 of the cycle. The dose was rapidly absorbed with peak plasma concentration between 1 and 2 hours. Distribution was also rapid (mean t1/2 alpha: 1.4h), whereas elimination was slow (mean t1/2 beta: 28.3 h). RU 486 was still detectable in some women at 72 h after administration. The plasma concentrations fitted the equation for a two-compartment open model from which the pharmacokinetic parameters were calculated. The mean total plasma clearance was 3.0 l/h, and the comparison of our data with those published studies suggests that the pharmacokinetics of RU 486 in Chinese women are similar to those of other populations.

Interaction of RU 486, a glucocorticoid and progestin antagonist with human circulating mononuclear leukocytes

The glucocorticoid and progestin antagonist, RU 486 (17 beta-hydroxy-11 beta-[4-dimethylaminophenyl]-17 alpha-[1-propynyl]-estra-4, 9-dien-3-one), antagonizes the suppressive effect of dexamethasone on [14C]2-deoxyglucose uptake by intact human mononuclear leukocytes in a concentration-dependent fashion. The authors found at least two types of specific-binding sites for this compound in the mononuclear leukocytes. The first type of sites (receptor content [Ro], 10.8 +/- 1.6 fmoles/10(6) cells [mean +/- SD of 4 experiments]; equilibrium dissociation constant (Kd), 0.3 +/- 0.1 nM) have a capacity similar to that of the dexamethasone binding site (Ro, 11.2 fmoles/10(6) cells; Kd, 1.2 nM). The second type of sites (Ro, 56 +/- 27 fmoles/10(6) cells: Kd, 19 +/- 5 nM) have a higher capacity and lower affinity for RU 486 than the first type of sites and do not interact with dexamethasone. The authors were unable to demonstrate the presence of the second type of binding sites in subcellular fractions. This finding suggests that this site is unstable and lost in the fractionation process. The role of the second type of low-affinity, high-capacity RU 486 specific-binding site in intact human mononuclear leukocytes, as well as its possible occurrence in other tissue, requires further investigation.

Variable effects of RU 486 on endometrial maintenance in the luteal phase extended by exogenous hCG

This study was designed to assess the features and conditions for endometrial bleeding induction with the synthetic antiprogestin and antiglucocorticoid RU 486 during hCG-induced prolongation of the luteal phase. Eighteen healthy, surgically sterilized women and another five women with an intrauterine contraceptive device (IUD) participated. All subjects received hCG which was injected daily in increasing doses (500 to 15,000 IU) from day 9 to day 15 of the luteal phase. Ten subjects received hCG alone, and groups of three to 16 subjects received hCG combined with RU 486 (25, 50, 100, 200 or 400 mg/day). RU 486 administration was commenced on day 12 following the LH surge and given either for 1, 4 or 7 consecutive days. In certain cycles, tamoxifen (20 mg/day) was given for 4 consecutive days with hCG, or with hCG and RU 486. All treatment cycles were separated by one or two resting cycles. Frequent blood samples were taken to monitor the endocrine response. Treatment with hCG alone or with the various combinations of RU 486 produced similar serum levels of oestradiol and progesterone which were equivalent to those observed during early pregnancy. With hCG alone, the onset of bleeding was on day 21-24 after the LH surge, coinciding with the drop in oestradiol and progesterone. With RU 486 doses of 50 mg/day or more, an early bleeding episode almost invariably occurred on day 14-17 after the LH surge in the presence of high circulating steroid levels. In contrast, 25 mg/day RU 486 for 4 days failed to induce this early onset of bleeding in three out of six cases.(ABSTRACT TRUNCATED AT 250 WORDS)

Disruption of follicular maturation and delay of ovulation after administration of the antiprogesterone RU486

To investigate the role of progesterone in the follicular phase, we examined the effects of RU486 in eight normal cycling women studied with daily and frequent blood sampling (every 10 min for 10 h) during three menstrual cycles (control-treatment-recovery). RU486 (3 mg/kg, orally) was administered for 3 consecutive days after ultrasound documentation of a dominant follicle. In six of the eight women, RU486 was given after emergence of the dominant follicle, while in two women, RU486 was initiated during the preovulatory period when estradiol levels had exceeded 917 pmol/L. In the six women given RU486 after emergence of the dominant follicle, RU486 significantly prolonged the follicular phase duration from 15.6 +/- 1.9 (+/- SD) to 28.6 +/- 9.3 days (P less than 0.01) and extended the treatment cycle length to 42.3 +/- 9.1 (+/- SD) days (P less than 0.01). During RU486 treatment, mean serum estradiol levels decreased from 385 +/- 43 to 228 +/- 28 pmol/L (P less than 0.01), while LH, FSH, ACTH, cortisol, and progesterone levels changed little. LH pulse frequency and amplitude on the last day of RU486 administration did not differ from control values. Collapse of the dominant follicle was evident on ultrasound after RU486 administration and was not accompanied by uterine bleeding. In the two women treated during the preovulatory period, the follicular phase was not prolonged, and RU486 failed to delay the onset of the LH surge. Our findings indicate that RU486 treatment during the follicular phase interrupts normal follicular development, resulting in a delay of ovulation and a reinitiation of follicular recruitment.

Intravaginal administration of RU 486 in humans and rats: inadequate absorption in humans

Vaginal absorption of the antiprogesterone steroid RU 486 was studied in humans and rats. In rats, RU 486 was sufficiently absorbed to terminate early pregnancy following vaginal, oral or intramuscular administration. The quantitation of RU 486 in serum showed that the ratios of the areas under the concentration curves per mg administered were 1:2.8:3.4 for the vaginal, intramuscular and oral routes, respectively. Female volunteers received RU 486 vaginally in polyethylene glycol (PEG) suppositories, in tampons and in oil solution. Following vaginal (PEG-suppository) and oral administration of 100 mg of RU 486, the ratio of the areas under the serum concentration curves was 1:56, respectively. From tampons and oil, RU 486 was absorbed in a similar manner to that of the PEG-suppositories, resulting in nanomolar serum concentrations. In humans no biological effects were noted following vaginal administration of RU 486. These data suggest that vaginal release of RU 486 is not a successful route of administration in humans.

Differences in the association of the progesterone receptor ligated by antiprogestin RU38486 or progestin ORG 2058 to chromatin components

We assessed the hypothesis that due to variations in the conformation of the progesterone receptor induced by the antiprogestin RU38486 compared to the progestin ORG 2058, differences may result in the association of the receptor with some of the chromatin components. The physical properties of the receptor-bound chromatin fragments released by micrococcal nuclease digestion were characterized by sucrose gradient sedimentation and by gel filtration on Agarose A-1.5m or Agarose A-5m columns. The nuclear fraction was isolated from T47D cells previously exposed to 0.1 microM [3H]RU38486 or 0.1 microM [3H]ORG 2058. Micrococcal nuclease digestion solubilized two receptor forms sedimenting at 4.4 S and 6.3 S for the antiprogestin bound receptor and only one receptor at 4.4 S for the progestin ligated receptor. High-salt buffer dissociated either the antiprogestin or the progestin-bound receptor to smaller receptor forms sedimenting at 3.5 S. Chemical cross-linking with the cross-linker 2-iminothiolane of the micrococcal nuclease solubilized receptor forms resulted in 6.7-S and 4.4-S forms sedimenting on 0.4 M KCl gradients for the antiprogestin and progestin ligated receptors, respectively. Stokes radii of 7.3 nm and 6.4 nm were determined by gel filtration in 0.4 M KCl for the 6.7-S and the 4.4-S receptor forms, respectively. Using the sedimentation coefficient and the Stokes radius, molecular weights of 202,000 and 116,000 were calculated for the antiprogestin and progestin ligated receptors. We conclude that the micrococcal nuclease solubilized antiprogestin ligated receptor is associated with additional or different chromatin components compared to the progestin bound receptor.

Fertility control with RU 486

RU 486 is a synthetic steroid possessing antiprogestin and antiglucocorticoid activities. This paper summarizes the main pharmacological properties of this molecule. It is now under the phase II-III clinical studies in the world for early pregnancy interruption. By itself, the drug shows a 85% complete efficacy provided it is given at the dose of 600 mg (3 X 200 mg) once in pregnancies below or equal to 41 days of amenorrhea. The clinical tolerance of the drug is extremely satisfactory, but metrorrhagia can in some instances be heavy, thus necessitating an adequate medical monitoring. The antiglucogenic activity of the molecule has no clinical relevance. In the future, soma data suggest that adjunction of a synthetic prostaglandin analog could somehow increase the success rate, but further studies are necessary to evaluate the effectiveness of such a combination.