Dienogest, a novel synthetic steroid, overcomes hormone-dependent cancer in a different manner than progestins

Antitumor progestins activity: Cytostatic effect and immune response

Progestins are used to treat some hormone-sensitive tumors. This review discusses the mechanisms of progestins' effects on tumor cells, the differences in the effects of progesterone and its analogs on different tumor types, and the influence of progestins on the antitumor immune response. Progestins cause a cytostatic effect, but at the same time they can suppress the antitumor immune response, and this can promote the proliferation and metastasis of tumor cells. Such progestins as dienogest, megestrol acetate and levonorgestrel increase the activity of NK-cells, which play a major role in the body's fight against tumor cells. The use of existing progestins and the development of new drugs with gestagenic activity may hold promise in oncotherapy.

Possible Participation of Adenine Nucleotide Translocase ANT1 in the Cytotoxic Action of Progestins, Glucocorticoids, and Diclofenac on Tumor Cells

A comparative analysis of the cytostatic effects of progestins (gestobutanoyl, megestrol acetate, amol, dienogest, and medroxyprogesterone acetate), glucocorticoids (hydrocortisone, dexamethasone), and diclofenac on tumor cells was carried out in order to confirm their in silico predicted probabilities experimentally. The results showed the different sensitivity of HeLa, MCF-7, Hep-2, K-562, and Wi-38 cell lines to progestins, glucocorticoids, and diclofenac. The minimum IC50 was found for progestin gestobutanoyl (GB) as 18 µM for HeLa cells, and varied from 31 to 38 µM for MCF-7, Hep-2, and K-562. Glucocorticoids and diclofenac were much less cytotoxic in the HeLa, MCF-7, and Hep-2 cell lines than progestins, with IC50 values in the range of 150-3000 μM. Myelogenous leukemia K-562 cells were the least sensitive to the action of progestins and glucocorticoids but the most sensitive to diclofenac, which showed a pronounced cytotoxic effect with an IC50 of 31 μM. As we have shown earlier, progestins can uniquely modulate MPTP opening via the binding of adenine nucleotide translocase. On this basis, we evaluated the expression of adenylate nucleotide translocase ANT1 (SLC25 A4) as a possible participant in cytotoxic action in these cell lines after 48 h incubation with drugs. The results showed that progestins differently regulated ANT1 expression in different cell lines. Gestobutanoyl had the opposite effect on ANT1 expression in the HeLa, K562, and Wi-38 cells compared with the other progestins. It increased the ANT1 expression more than twofold in the HeLa and K562 cells but had no influence on the Wi-38 cells. Glucocorticoids and diclofenac increased ANT1 expression in the Wi-38 cells and decreased it in the K562, MCF-7, and Hep-2 cells. The modulation of ANT1 expression discovered in our study can be a new explanation of the cytotoxic and cytoprotective effects of hormones, which can vary depending on the cell type. ANT isoforms in normal and cancerous cells could be a new target for steroid hormone and anti-inflammatory drug action.

Progestin Resistance and Corresponding Management of Abnormal Endometrial Hyperplasia and Endometrial Carcinoma

With a younger tendency in morbidity age, endometrial cancer (EC) incidence has grown year after year. Worse, even more commonly occurring is endometrial hyperplasia (EH), which is a precancerous endometrial proliferation. For young women with early EC and EH who want to preserve fertility, progestin therapy has been utilized as a routine fertility-preserving treatment approach. Nevertheless, progestin medication failure in some patients is mostly due to progestin resistance and side effects. In order to further analyze the potential mechanisms of progestin resistance in EH and EC, to provide theoretical support for effective therapeutic strategies, and to lay the groundwork for searching novel treatment approaches, this article reviews the current therapeutic effects of progestin in EH and EC, as well as the mechanisms and molecular biomarkers of progestin resistance, and systematically expounds on the potential therapeutic methods to overcome progestin resistance.

Potential alternative progestin therapy for low-grade endometrial stromal sarcoma: A case report

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LG-ESS is a rare and indolent uterine tumor which has remarkable sensitivity to hormonal agents.

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We presented the case of recurrent LG-ESS that was effectively and safely treated with Dienogest.

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Dienogest may be useful for the treatment of LG-ESS that is resistant to other progestins.

Low-grade endometrial stromal sarcoma (LG-ESS) is a rare uterine tumor that sometimes recurs and advances. Hormonal treatment, especially high-dose progestins and aromatase inhibitors (AIs), has demonstrated efficacy against these tumors. Because the standard treatment period is uncertain and hormonal treatment is effective, hormonal agents are likely to be used long-term, especially when a residual tumor is present. However, the long-term use of high-dose progestins and AIs may cause thromboembolism, as well as musculoskeletal stiffness and pain. Dienogest, a relatively new progestin, has demonstrated safety after long-term administration; it also appears to have a more favorable long-term safety profile compared with other progestins and AIs. We encountered a young patient with recurrent LG-ESS that metastasized to the liver and exhibited resistance to high-dose medroxyprogesterone acetate (MPA). The patient was successfully treated with dienogest monotherapy. This is the first report describing the efficacy of dienogest against recurrent and metastatic LG-ESS that is resistant to MPA and other agents.

A progestin isn't a progestin: dienogest for endometriosis as a blueprint for future research - Review as a contribution for discussion

The different etiopathogenetic mechanisms and the diversity of clinical features of endometriosis has not yet allowed to identify a causal pharmacological monotherapy satisfying the unresolved medical needs in this important female disease. Therefore, despite the search for new therapeutic principles for the indication, the strategy of gradual optimization of established therapeutic principles should not be disregarded.In the case of progestins, the fact that each compound has its own, specific profile may allow to study the therapeutic relevance of the various signal cascades influenced by their receptors.Using the example of the progestin dienogest, the different genomic and non-genomic mechanisms of action are discussed. It is pharmacodynamic profile is unique compared to other progestins.In light of the emerging multitude of pathomechanisms in endometriosis, a monotherapy may not be possible, and then the search for broad spectrum compounds or combination therapies with dual or multiple mode of action in a clinically relevant dose range might be considered. The progestogenic action may greatly benefit from, by way of example, additional anti-inflammatory and/or anti-fibrotic and/or pro-apoptotic activities. Such a strategy could lead to new drug classes.

Use of dienogest in endometriosis: a narrative literature review and expert commentary

Objective: Endometriosis affects up to 10% of women of reproductive age, and the main goal of treatment is to relieve symptoms. Progestins have been the mainstay of endometriosis suppression, of which dienogest has become an important option in many parts of the world. This is an expert literature review, with recommendations on the use of dienogest in the context of various clinical considerations when treating endometriosis.Methods: A search of PubMed was conducted for papers published between 2007 and 2019 on the use of dienogest in endometriosis. Experts reviewed these and included those they considered most relevant in clinical practice, according to their own clinical experience.Results: Evidence regarding the long-term use (>15 months) of dienogest for the management of endometriosis is presented, with experts concluding that the efficacy of dienogest should be assessed primarily on its impact on pain and quality of life. Fertility preservation, the option to avoid or delay surgery, and managing bleeding irregularities that can occur with this treatment are also considered. Counseling women on potential bleeding risks before starting treatment may be helpful, and evidence suggests that few women discontinue treatment for this reason, with the benefits of treatment outweighing any impact of bleeding irregularities.Conclusions: Overall, the evidence demonstrates that dienogest offers an effective and tolerable alternative or adjunct to surgery and provides many advantages over combined hormonal contraceptives for the treatment of endometriosis. It is important that treatment guidelines are followed and care is tailored to the woman's individual needs and desires.

Development of a mouse model for testing therapeutic agents: the anticancer effect of dienogest on endometrial neoplasms

OBJECTIVE

As the number of younger women with endometrial carcinoma has increased, fertility-sparing treatments have received more attention. Although there have been several reports on conservative treatments with progestins for endometrial carcinoma, only medroxyprogesterone acetate (MPA) is available in Japan. Dienogest has been developed as a fourth-generation progestin for treating endometriosis. Because of its high progesterone activity, its antitumor activity has attracted attention. In this study, we investigated the anticancer effect of dienogest on endometrial neoplasms using mouse model of endometrial carcinoma.

METHODS/MATERIALS

Pten(loxP/loxP) mice were injected with MPA or dienogest subcutaneously to evaluate the anticancer effect against endometrial neoplasms that developed in the mice. One week after injections, histopathological analyzes were performed.

RESULTS

Endometrial neoplasms were found in one of the eight (12.5%) mice from each group treated with either dienogest or MPA. In contrast, they were found in seven of eight (87.5%) mice not treated with progestins. Each progestin treatment showed anticancer activity against endometrial neoplasms that developed in the mice compared to those without treatment.

CONCLUSIONS

Dienogest and MPA showed potent anticancer activity against endometrial neoplasms in our mouse model. The present study demonstrated that dienogest might be a useful therapeutic agent for human endometrial neoplasms.

Does dienogest influence the inflammatory response of endometriotic cells? A systematic review

OBJECTIVE AND DESIGN

A systematic review of all literature was done to assess the ability of the progestin dienogest (DNG) to influence the inflammatory response of endometriotic cells.

MAIN OUTCOME MEASURES

In vitro and in vivo studies report an influence of DNG on the inflammatory response in eutopic or ectopic endometrial tissue (animal or human).

RESULTS

After strict inclusion criteria were satisfied, 15 studies were identified that reported a DNG influence on the inflammatory response in endometrial tissue. These studies identified a modulation of prostaglandin (PG) production and metabolism (PGE2, PGE2 synthase, cyclo-oxygenase-2 and microsomal PGE synthase-1), pro-inflammatory cytokine and chemokine production [interleukin (IL)-1β, IL-6, IL-8, tumor necrosis factor-α, monocyte chemoattractant protein-1 and stromal cell-derived factor-1], growth factor biosynthesis (vascular endothelial growth factor and nerve growth factor) and signaling kinases, responsible for the control of inflammation. Evidence supports a progesterone receptor-mediated inhibition of the inflammatory response in PR-expressing epithelial cells. It also indicated that DNG inhibited the inflammatory response in stromal cells, however, whether this was via a PR-mediated mechanism is not clear.

CONCLUSIONS

DNG has a significant effect on the inflammatory microenvironment of endometriotic lesions that may contribute to its clinical efficacy. A better understanding of the specific anti-inflammatory activity of DNG and whether this contributes to its clinical efficacy can help develop treatments that focus on the inhibition of inflammation while minimizing hormonal modulation.

Recent advances in structure of progestins and their binding to progesterone receptors

The role of progesterone in women's cancers as well as the knowledge of the progesterone receptor (PR) structure has prompted the design of different therapies. The aim of this review is to describe the basic structure of PR agonists and antagonists as well as the recent treatments for illness associated with the progesterone receptor. The rational design for potent and effective drugs for the treatment of female cancer must consider the structural changes of the androgen and progestogen skeleton which are an indicator of their activity as progestins or antiprogestins. The presence of a hydroxyl group at C-17 in the progesterone skeleton brings about a loss of progestational activity whereas acetylation induces a progestational effect. The incorporation of an ethynyl functional group to the testosterone framework results in a loss of androgenic activity with a concomitant enhancement of the progestational effect. On the other hand, an ester function at C-3 of dehydroepiandrosterone skeleton induces partial antagonism to the PR.

Therapeutic effect of dienogest on adenosarcoma arising from endometriosis: a case report

Dienogest is a novel synthesized progestin used for treatment of endometriosis. This is the first case report describing a therapeutic effect of dienogest on a gynecologic malignancy. The patient was a 44-year-old woman with advanced adenosarcoma arising from the endometriosis in the rectovaginal space and infiltrating the left pelvic wall, left ureter, rectum and vagina. The residual tumor after tumor debulking surgery was resistant to both chemotherapy and radiotherapy. Dienogest was used as a substitute for medroxyprogesterone acetate because of the presence of deep vein thrombosis. Based on the RECIST criteria, partial response was obtained with oral dienogest therapy at six months and the serum CA125 level also decreased from 70 U/ml to 16 U/ml. The tumor remained stable up to 21 months. Thromboembolism or other adverse effects did not occur during the dienogest therapy. Dienogest may be useful for the treatment of adenosarcoma arising from endometriosis.

New candidate therapeutic agents for endometrial cancer: potential for clinical practice (review)

Cases of endometrial cancer have increased in recent years, but the prognosis of patients with this disease has also been improved by combined modality therapy with surgery, radiotherapy and chemotherapy. However, the development of new therapy is required from the perspectives of conservation of fertility and efficacy for recurrent and intractable cancer. New candidate therapeutic agents for endometrial cancer include fourth-generation progestins for inhibition of growth and differentiation of endometrial glands; metformin for reduction of hTERT expression in the endometrium and inhibition of the mTOR pathway by activation of AMPK, with consequent inhibition of the cell cycle; mTOR inhibitors for supressing growth of cancer cells by G1 cell cycle arrest; microRNAs involved in the molecular mechanisms of oncogenesis and progression; and HDAC inhibitors that block the growth of cancer cells by transcriptional elevation of tumor-suppressor genes, cell cycle arrest and induction of apoptosis. In this study, we review the background and early clinical evidence for these agents as new therapeutic candidates for endometrial cancer.

Dienogest: a new therapeutic agent for the treatment of endometriosis

Dienogest (DNG), a progestin of 19-nortestosterone derivative, has good oral bioavailability and is highly selective for progesterone receptors. Owing to its antiovulatory, antiproliferative activities in endometrial cells, and its inhibitory effects on the secretion of cytokines, DNG is expected to be an effective treatment for endometriosis. Progesterone receptor-binding affinity is higher for DNG than for progesterone. Several pilot studies demonstrated that after 24 weeks of DNG treatment, there was a significant decrease in terms of dysmenorrhea, premenstrual pain, dyspareunia and diffuse pelvic pain. Most of the cases of genital bleeding occurring in the DNG treatment were spotting or breakthrough bleeding, which decreased with continued treatment and resolved either during treatment or after the end of treatment. The therapeutic effects of DNG 2 mg/day and norethisterone acetate 10 mg/day for endometriotic symptoms during a period of 24 weeks were almost similar. The only disadvantage of DNG seems to be the irregular bleeding. Good efficacy and tolerability of DNG in patients with endometriosis have been demonstrated in an open, randomized European clinical trial as compared with norethisterone acetate. In Japan, a Phase III, randomized, double-blind, multicenter, controlled trial was conducted to compare the efficacy and safety of DNG with intranasal buserelin acetate in patients with endometriosis. The study demonstrated that DNG is as effective as intranasal buserelin acetate in alleviating endometriosis symptoms, and causes less bone mineral density loss, resulting in the use on a commercial basis for endometriosis patients in Japan from 2008. This paper provides summarized data on this new promising drug for endometriosis.

Dienogest and the breast

In a clinical pilot study, 21 women with endometriosis have been primarely treated with dienogest 2 x 10 mg daily p.o. for 24 weeks. Besides the effect on endometriosis the action of such high-dose progestogen treatment on the breast was evaluated by breast ultrasound prior to medication and at 24 weeks of medical treatment. In all women, a significant size reduction of the mammary gland (p < 0.023) and regression of mastopathic changes were observed. There was a non-significant reduction (p = 0.089) of the maximum diameter of the ducts. The portion of the fatty tissue increased slightly, but not significantly (p = 0.348).

The effect of progesterone, testosterone and synthetic progestogens on growth factor- and estradiol-treated human cancerous and benign breast cells

OBJECTIVE

The effects of progesterone (P), testosterone (T), chlormadinone acetate (CMA), medroxyprogesterone acetate (MPA), norethisterone (NET), levonorgestrel (LNG), dienogest (DNG), gestodene (GSD) and 3-ketodesogestrel (KDG) were investigated in normal human breast epithelial MCF10A cells. In addition, the effects of these steroids were tested in estrogen and progesterone receptor positive HCC1500 human primary breast cancer cells.

STUDY DESIGN

MCF10A cells were incubated with each progestogen at 1 microM and 100 nM for 7 days with growth factors epidermal growth factor (EGF), fibroblast growth factor (FGF) and insulin-like growth factor (IGF-I) (GFs, each 1 pM), and HCC1500 cells with GFs and/or estradiol (E2) 100 pM. Cell proliferation rate was measured by ATP-assay and cell death by photometric enzyme immunoassay. Ratios of cell death:proliferation were calculated.

RESULTS

MPA and CMA with GFs induced proliferation of MCF10A cells. P, T, NET, LNG, DNG, GSD and KDG had no significant effect. In HCC1500 cells, MPA and CMA with GFs had an inhibitory effect compared to GFs alone. NET, LNG, DNG, GSD, KDG and T enhanced the proliferative effect of GFs. P had no significant effect. No progestogen could further enhance the stimulatory effect of E2 on HCC1500 cells; all but KDG inhibited it. MPA, GSD, T, CMA and NET had an anti-proliferative effect on the mitotic GF and E2 combination. P, LNG, DNG and KDG had no significant effect.

CONCLUSIONS

Estrogens and mitogenic growth factors from stromal breast tissue are significant in growth-regulation of breast cells and may alter responses to progestogens. Certain progestogens are able to induce proliferation of or inhibit growth of benign or malignant human breast epithelial cells independently of the effects of growth factors and E2; therefore, choice of progestogen for hormone therapy may be important in terms of influencing possible breast cancer risk.

Matrix metalloproteinase 2 and tissue inhibitor of metalloproteinase 2 expression is not regulated by norgestimate or norelgestromin

Steroid hormones regulate endometrial expression of matrix metalloproteinases (MMPs) and their inhibitors. Synthetic progestins are widely used in oral contraceptives and for hormone replacement therapy. To assess whether the synthetic progestins norgestimate and its derivative norelgestromin (17-deacetylnorgestimate) modulate the expression of MMPs, Ishikawa endometrial cancer cells were separately treated with 17 beta-estradiol, 17 alpha-hydroxyprogesterone, norgestimate and norelgestromin. Culture supernatants were assayed for MMPs 2, 3 and 9, and for tissue inhibitors of MMPs (TIMP-1 and TIMP-2) by enzyme-linked immunosorbent assays (ELISAs). No marked modulation of MMP-2 and TIMP-2 expression was observed upon incubation of the cells with the synthetic progestins. By ELISA, neither MMP-3 or MMP-9 nor TIMP-1 immunoreactivity was detected. Interestingly, TIMP-2 expression was down-regulated by 17 beta-estradiol and 17 alpha-hydroxyprogesterone.

HEC-1 cells

HEC-1 cell line was the first in vitro cell line of a human endometrial adenocarcinoma which enabled us to perform research work on the endometrium and endometrial carcinoma at a simplified cellular system, contributing cell and molecular biological studies on endometrial carcinoma. Once a cell line is established, it provides a stable experimental system that facilitates and progresses in the study of the tissues and/or neoplasias from which they are derived. In this article we report how HEC-1 cells have been established and cleared the proposed requirements to characterize the established cell line. Also to show the usefulness of the cell line for research work, once it was established, we illustrate these concepts by recalling results obtained with HEC-1 cells and reviewing the literature on what has been achieved by using these cells.

Estradiol valerate/dienogest

Estradiol valerate 2mg/dienogest 2mg is an oral estrogen/ progestogen formulation that has been approved throughout the European Union for the treatment of climacteric symptoms in postmenopausal women. Dienogest is a progestogen that combines the properties of both progesterone and 19-nortestosterone derivatives. It has moderate affinity for the progesterone receptor, significant antiproliferative and antiandrogenic activity, and produces secretory transformation of the endometrium. Estradiol valerate is an esterified form of natural 17beta-estradiol, the most potent endogenous human ovarian estrogen, and is hydrolysed to estradiol soon after oral administration. Results from a randomised, double-blind, multicentre trial showed that oral estradiol valerate 2mg/dienogest 2mg and estradiol valerate 2mg/dienogest 3mg once daily for 1 year were each as effective as estradiol 2mg/estriol 1mg/norethisterone acetate 1mg in the treatment of climacteric symptoms in 581 postmenopausal women; reductions from baseline in Kupperman Index scores were 78.5, 74.5 and 75.0%, respectively. The number of days without any type of bleeding was lowest in patients treated with estradiol valerate 2mg/dienogest 2mg (8.7 days), and highest in the estradiol valerate 2mg/ dienogest 3mg group (12.1 days). During the twelfth month of treatment with estradiol valerate 2mg/dienogest 2mg, the percentage of patients who reported bleeding was 14.5%. Endometrial biopsy results were similar in patients treated with estradiol valerate 2mg/dienogest 2mg, estradiol valerate 2mg/dienogest 3mg or estradiol 2mg/estriol 1mg/norethisterone acetate 1mg once daily for 1 year; 90.8, 87.4 and 87.5% of samples, respectively, contained atrophic material. Proliferative material was found in 4.2, 2.5 and 4.4% of the biopsies, respectively; there was no incidence of hyperplasia in any of the treatment groups. A noncomparative multicentre study in 1501 postmenopausal women demonstrated that adverse events associated with estradiol valerate 2mg/dienogest 2mg once daily for 48 weeks included breakthrough bleeding, mastalgia, headache, abdominal pain, hypertension, thrush, migraine, weight gain, increase in endometrial thickness and metrorrhagia.

Hormonal treatment of endometrial carcinoma

Endometrial cancer has typically been regarded as a relatively benign disease. However, survival rates for patients with advanced-stage or recurrent disease are very poor and more adequate systemic treatment is certainly needed. Being a tumor that arises from a hormone responsive tissue, endometrial cancer is a logical target for endocrine manipulation. This article gives an overview of our current knowledge on hormonal therapy and highlights the large potential for improvement in results of such therapy. Target areas for future research are described.

Comparison of the efficacy and endometrial safety of two estradiol valerate/dienogest combinations and Kliogest for continuous combined hormone replacement therapy in postmenopausal women

OBJECTIVE

To compare the efficacy and endometrial safety of two estradiol valerate/dienogest combinations with Kliogest in the treatment of postmenopausal symptoms.

DESIGN

This was a double-blind, randomized, multicenter study.

METHODS

Patients were randomized to estradiol valerate 2.0 mg/dienogest 2.0 mg (Climodien), estradiol valerate 2.0 mg/dienogest 3.0 mg (E2Val 2/DNG 3); or estradiol 2.0 mg/estriol 1.0 mg/norethisterone acetate 1.0 mg (Kliogest) once daily for 1 year. The primary efficacy variable was the Kupperman index. Endometrial safety was determined primarily by biopsy.

RESULTS AND CONCLUSIONS

Climodien and E2Val 2/DNG 3 were therapeutically equivalent to Kliogest (mean changes in Kupperman index -20.1, -19.0 and -18.3, respectively). No statistically significant differences existed between treatment groups in the severity of postmenopausal symptoms. The incidences of endometrial atrophy were similar in all groups. Climodien appeared to be superior to Kliogest in terms of vaginal bleeding pattern, whereas E2Val 2/DNG 3 was associated with a slightly higher incidence and greater intensity of vaginal bleeding. The incidences of adverse events were similar in all groups. A greater proportion of women in the Kliogest and E2Val 2/DNG 3 groups experienced vaginal bleeding, whereas breast problems were more common with Climodien. Climodien and E2Val 2/DNG 3 induced desirable changes in insulin-like growth factor I (decrease) and sex hormone binding globulin (increase) that were not seen with Kliogest.

Dienogest, a synthetic steroid, suppresses both embryonic and tumor-cell-induced angiogenesis

Orally administered dienogest (17alpha-cyanomethyl-17beta-hydroxy-estra-4,9-diene-3-one) is efficacious against human hormone-dependent cancer xenografts in severely immunodeficient mice and in rats with experimental endometriosis, but its mechanisms of action remain unclear. We assessed the effect of dienogest on angiogenesis, because these two diseases that are sensitive to dienogest are known to be angiogenesis-dependent. Topical dienogest treatment dose-dependently inhibited embryonic angiogenesis, the ID(50) value being 6.4 nmol/egg. Oral administration of dienogest (1 mg kg(-1) day(-1)) for 5 consecutive days significantly suppressed angiogenesis induced by S-180 mouse tumor cells in the mouse dorsal air sac assay. In vitro experiments showed that dienogest at concentrations up to 10 microM had little or no effect on the proliferation of plasminogen activator activity or formation of tube-like structures by microvascular endothelial cells. These results suggest that dienogest is a new, orally active antagonist of angiogenesis, and that its anti-angiogenic action may be involved in its therapeutic effects on cancer xenografts and endometriosis that we observed previously.

Hormonal treatment of endometrial cancer

This article summarizes the endocrine background of women with endometrial cancer at both peripheral and tissue levels, and the current status of clinical trials of hormonal, cytotoxic, and combination regimens. Because significant advances in systemic therapy are required to improve the prognosis of endometrial cancer, recommendations for future clinical investigations will be based on these recent biologic observations.

Effects of dienogest (a synthetic steroid) on coagulation, fibrinolysis, and platelet aggregation in female monkeys

We investigated the effects of dienogest (0.1-10 mg/kg per day, p.o.) on coagulation, fibrinolysis and platelet aggregation in female rhesus monkeys. Then, we also examined those of medroxyprogesterone acetate (MPA, 10 mg/kg per day, p.o.) or danazol (10-1000 mg/kg per day, p.o.) on these parameters in the same species. In addition, we assessed the effects of dienogest (1 and 3 mg/kg per day, p.o.) or MPA (10 mg/kg per day, p.o.) on platelet aggregation and platelet lipids in female cynomolgus monkeys. At doses of 0.3 mg/kg or greater, dienogest increased the levels of several coagulation and anticoagulation factors, but had no effect on the prothrombin time, activated partial thromboplastin time, fibrinolysis, or platelet aggregation. MPA (10 mg/kg) had no effect on coagulation or fibrinolysis, but significantly potentiated platelet aggregation in response to ADP and collagen and also increased the platelet cholesterol-to-phospholipid ratio. Danazol (10 mg/kg or more) increased the activities of coagulation factors V, VII, VIII, X, XI, and XII in comparison to dienogest and MPA. Consequently, dienogest caused less potentiation of platelet aggregation than MPA and less potentiation of coagulation than danazol.