Effects of onapristone on postmenopausal endometrium

Phase I study of onapristone, a type I antiprogestin, in female patients with previously treated recurrent or metastatic progesterone receptor-expressing cancers

INTRODUCTION

Onapristone is a type I progesterone receptor (PR) antagonist, which prevents PR- mediated DNA transcription. Onapristone is active in multiple preclinical models and two prior studies demonstrated promising activity in patients with breast cancer. We conducted a study of extended release (ER) Onapristone to determine a recommended dose and explore the role of transcriptionally-activated PR (APR), detected as an aggregated subnuclear distribution pattern, as a predictive biomarker.

METHODS

An open-label, multicenter, randomized, parallel-group, phase 1 study (target n = 60; NCT02052128) included female patients ≥18 years with PRpos tumors. APR analysis was performed on archival tumor tissue. Patients were randomized to five cohorts of extended release (ER) onapristone tablets 10, 20, 30, 40 or 50 mg BID, or immediate release 100 mg QD until progressive disease or intolerability. Primary endpoint was to identify the recommended phase 2 dose. Secondary endpoints included safety, clinical benefit and pharmacokinetics.

RESULTS

The phase 1 dose escalation component of the study is complete (n = 52). Tumor diagnosis included: endometrial carcinoma 12; breast cancer 20; ovarian cancer 13; other 7. Median age was 64 (36-84). No dose limiting toxicity was observed with reported liver function test elevation related only to liver metastases. The RP2D was 50 mg ER BID. Median therapy duration was 8 weeks (range 2-44), and 9 patients had clinical benefit ≥24 weeks, including 2 patients with APRpos endometrial carcinoma.

CONCLUSION

Clinical benefit with excellent tolerance was seen in heavily pretreated patients with endometrial, ovarian and breast cancer. The data support the development of Onapristone in endometrial endometrioid cancer. Onapristone should also be evaluated in ovarian and breast cancers along with APR immunohistochemistry validation.

Effects of antiprogestins on the uterus

Progesterone-receptor modulators (PRMs) are progesterone-receptor ligands that can exert agonistic, antagonistic or mixed agonist-antagonist effects depending on the cellular context. The mechanisms of action of these compounds are still incompletely understood. PRMs already have several applications in women's health such as emergency contraception, pregnancy termination, management of early fetal demise and cervical maturation. The main indications that will be developed in the future include dysfunctional bleeding and preoperative treatment of uterine myomas. Other future indications may include estrogen-free contraception, treatment of endometriosis and prevention and treatment of breast cancer. However, the available data from mid- to long-term continuous administration studies has raised the issue of endometrial safety. For this reason, long-term applications of PRMs are currently postponed, although windows of treatment with a short course of progestin therapy, or even by a short interruption of treatment, could improve endometrial aspects if needed.

Chronic progesterone antagonist-estradiol therapy suppresses breakthrough bleeding and endometrial proliferation in a menopausal macaque model

BACKGROUND

Clinicians routinely prescribe progestins along with estrogens during menopausal hormone therapy (HT) to block estrogen-dependent endometrial proliferation. Breakthrough bleeding (BTB) can negate the utility of this treatment. Because progestin antagonists also inhibit estrogen-dependent endometrial proliferation in women and macaques, we used a menopausal macaque model to determine whether a potent progestin antagonist (ZK 230 211, Schering AG; ZK) combined with estrogen would provide a novel mode of HT.

METHOD

Ovariectomized rhesus macaques were treated for 5 months with either estradiol (E(2)) alone, E(2) + progesterone (two doses) or E(2) + ZK (0.01, 0.05 or 0.25 mg/kg).

RESULTS

In the E(2) + progesterone groups, progesterone suppressed endometrial proliferation and induced a thick decidualized endometrium. In the E(2) + ZK 230 211 groups, all doses of ZK blocked endometrial proliferation and induced endometrial atrophy. In all ZK-treated groups, the atrophied endometrium contained some dilated glands lined by an inactive, flattened, non-mitotic epithelium. BTB was much lower in the E(2) + ZK groups (17 days of spotting, all groups) than in the E(2) and E(2) + progesterone groups (155 bleeding days, all groups). ZK suppressed E(2) effects in the cervix, but not in the vagina, oviduct or mammary glands. All serum chemistry and lipid profiles were normal.

CONCLUSION

The ability of ZK to block estrogen-dependent endometrial proliferation, induce endometrial atrophy and suppress BTB in a menopausal macaque model indicates that progestin antagonists may provide a novel mode of HT.

Molecular properties and preclinical pharmacology of JNJ-1250132, a steroidal progesterone receptor modulator that inhibits binding of the receptor to DNA in vitro

Progesterone receptor modulators have diverse potential therapeutic uses, including the treatment of endometriosis, uterine fibroids and breast cancer. Here we describe the molecular properties and preclinical pharmacology of a new steroidal progestin antagonist, JNJ-1250132. The compound is a high affinity ligand for the progesterone receptor, possessing cross-reactivity with other steroid receptors comparable to that of steroidal antagonists such as mifepristone. It inhibits progestin-inducible alkaline phosphatase gene expression in T47D human breast cancer cells, and also inhibits their in vitro proliferation. It inhibits gestation in rats and progesterone-dependent endometrial transformation in rabbits with efficacies comparable to mifepristone. Like mifepristone, it is a glucocorticoid antagonist in vivo. In cell-free DNA binding assays, the compound inhibits binding of the human progesterone receptor to a progesterone response element, and thus is similar to onapristone in this regard. In contrast, as judged by proteolytic analysis, JNJ-1250132 induces a receptor conformation more similar to that induced by mifepristone, which promotes receptor binding to DNA. Therefore, JNJ-1250132 has unique effects on the progesterone receptor that may translate into a novel clinical profile.

Selective progesterone receptor modulators and progesterone antagonists: mechanisms of action and clinical applications

Since the discovery of the antiprogestin mifepristone, hundreds of similar compounds have been synthesized, which can be grouped in a large family of progesterone receptor ligands. This family includes pure agonists such as progesterone itself or progestins and, at the other end of the biological spectrum, pure progesterone receptor antagonists (PA). Selective progesterone receptor modulators (SPRM) have mixed agonist-antagonist properties, and occupy an intermediate position of the spectrum. These compounds have numerous applications in female health care. Mifepristone is used to terminate pregnancy, and as such is commercially available in many countries. The negative abortion-related image of mifepristone has clearly limited the involvement of the major pharmaceutical companies in the development of PA and SPRM. Many PA and SPRM display direct antiproliferative effects in the endometrium, although with variable actions which seem product- and dose-dependent. This property justifies their use in the treatment of myomas and endometriosis. PA also suppress late follicular development, block the LH surge and retard endometrial maturation, which renders them potential estrogen-free contraceptive drugs. SPRM such as asoprisnil are not as effective in blocking the LH surge and appear to target the endometrium directly and produce amenorrhoea. Interestingly, clinical data show that treatment with these compounds is not associated with hypo-estrogenism and bone loss. The potential clinical applications of these compounds cover a broad field and are very promising in major public health areas. These include emergency contraception, long-term estrogen-free contraception (administered alone, or in association with a progestin-only pill to improve bleeding patterns), myomas (where they induce a marked reduction in tumour volume and produce amenorrhoea) and endometriosis. Further developments might also include hormone replacement therapy in post-menopausal women, as well as the treatment of hormone-dependent tumours.