Multiple-dose, safety, pharmacokinetics, and pharmacodynamics of a new selective estrogen receptor modulator, ERA-923, in healthy postmenopausal women

Estrogen receptor agonists/antagonists in breast cancer therapy: A critical review

Estrogens display intriguing tissue selective action that is of great biomedical importance in the development of optimal therapeutics for the prevention and treatment of breast cancer. There are also strong evidences to show that both endogenous and exogenous estrogens are involved in the pathogenesis of breast cancer. Tamoxifen has been the only drug of choice for more than 30years to treat patients with estrogen related (ER) positive breast tumors. There is a need therefore, for identifying newer, potential and novel candidates for breast cancer. Keeping this in view, the present review focuses on selective estrogen receptor modulators and estrogen antagonists such as sulfatase and aromatase inhibitors involved in breast cancer therapy. A succinct and critical overview of the structure of estrogen receptors, their signaling and involvement in breast carcinogenesis are herein described.

Efficacy of SERD/SERM Hybrid-CDK4/6 Inhibitor Combinations in Models of Endocrine Therapy-Resistant Breast Cancer

PURPOSE

Endocrine therapy, using tamoxifen or an aromatase inhibitor, remains first-line therapy for the management of estrogen receptor (ESR1)-positive breast cancer. However, ESR1 mutations or other ligand-independent ESR1 activation mechanisms limit the duration of response. The clinical efficacy of fulvestrant, a selective estrogen receptor downregulator (SERD) that competitively inhibits agonist binding to ESR1 and triggers receptor downregulation, has confirmed that ESR1 frequently remains engaged in endocrine therapy-resistant cancers. We evaluated the activity of a new class of selective estrogen receptor modulators (SERM)/SERD hybrids (SSH) that downregulate ESR1 in relevant models of endocrine-resistant breast cancer. Building on the observation that concurrent inhibition of ESR1 and the cyclin-dependent kinases 4 and 6 (CDK4/6) significantly increased progression-free survival in advanced patients, we explored the activity of different SERD- or SSH-CDK4/6 inhibitor combinations in models of endocrine therapy-resistant ESR1(+) breast cancer.

EXPERIMENTAL DESIGN

SERDs, SSHs, and the CDK4/6 inhibitor palbociclib were evaluated as single agents or in combination in established cellular and animal models of endocrine therapy-resistant ESR1(+) breast cancer.

RESULTS

The combination of palbociclib with a SERD or an SSH was shown to effectively inhibit the growth of MCF7 cell or ESR1-mutant patient-derived tumor xenografts. In tamoxifen-resistant MCF7 xenografts, the palbociclib/SERD or SSH combination resulted in an increased duration of response as compared with either drug alone.

CONCLUSIONS

A SERD- or SSH-palbociclib combination has therapeutic potential in breast tumors resistant to endocrine therapies or those expressing ESR1 mutations. See related commentary by DeMichele and Chodosh, p. 4999.

How First-Time-in-Human Studies Are Being Performed: A Survey of Phase I Dose-Escalation Trials in Healthy Volunteers Published Between 1995 and 2004

First-time-in-human studies are small, time-lagged dose-escalation studies including volunteer subjects evaluating safety and tolerability. There is little consensus in the design of a first-time-in-human study, and it is difficult to get an overview of studies performed. One hundred five studies comprising 3323 healthy volunteers published in the 5 major clinical pharmacology journals since 1995 were analyzed. The average trial was placebo controlled, double blind including 32 subjects at 5 dose levels but with great variation in cohort size and dose-escalation method. The parallel single-dose design was the most common design, with the crossover designs being more frequent in the early publications. Despite discussions on the optimization of phase I trials, little seems to be happening. The development of study designs and evaluation methods for cancer trials is extensive, but formal statistically based methods and more scientific study designs are unusual in phase I dose-escalation trials in healthy volunteers.

A computational approach to finding novel targets for existing drugs

Repositioning existing drugs for new therapeutic uses is an efficient approach to drug discovery. We have developed a computational drug repositioning pipeline to perform large-scale molecular docking of small molecule drugs against protein drug targets, in order to map the drug-target interaction space and find novel interactions. Our method emphasizes removing false positive interaction predictions using criteria from known interaction docking, consensus scoring, and specificity. In all, our database contains 252 human protein drug targets that we classify as reliable-for-docking as well as 4621 approved and experimental small molecule drugs from DrugBank. These were cross-docked, then filtered through stringent scoring criteria to select top drug-target interactions. In particular, we used MAPK14 and the kinase inhibitor BIM-8 as examples where our stringent thresholds enriched the predicted drug-target interactions with known interactions up to 20 times compared to standard score thresholds. We validated nilotinib as a potent MAPK14 inhibitor in vitro (IC50 40 nM), suggesting a potential use for this drug in treating inflammatory diseases. The published literature indicated experimental evidence for 31 of the top predicted interactions, highlighting the promising nature of our approach. Novel interactions discovered may lead to the drug being repositioned as a therapeutic treatment for its off-target's associated disease, added insight into the drug's mechanism of action, and added insight into the drug's side effects.

Identification and structure-activity relationships of chromene-derived selective estrogen receptor modulators for treatment of postmenopausal symptoms

As part of a program aimed at the development of selective estrogen receptor modulators (SERMs), novel chromene scaffolds, benzopyranobenzoxapanes, were discovered. Many compounds showed binding affinity as low as 1.6-200 nM, displayed antagonist behaviors in the MCF-7 human breast adenocarcinoma cell line as well in Ishikawa cell line with IC(50) values in the range 0.2-360 nM. On the basis of the side chain substitution, various compounds demonstrated strong inhibitory activity in anti-uterotropic assay. Compound 7-(R) and its major metabolites 5-(R) and 6-(R) were evaluated in several in vivo models of estrogen action. Relative to a full estrogen agonist (ethynyl estradiol) and the SERM raloxifene, 7-(R) was found to be a potent SERM that behaved as antagonist in the uterus and exhibited estrogen agonistic activity on bone, plasma lipids, hot flush, and vagina. The overall pharmacokinetic profile and stability were significantly improved compared to those of the phase 2 development compound 9-(R).

Selective estrogen receptor modulators: an update on recent clinical findings

Recent clinical data on selective estrogen receptor modulators (SERMs) have provided the basis for reassessment of the SERM concept. The molecular basis of SERM activity involves binding of the ligand SERM to the estrogen receptor (ER), causing conformational changes which facilitate interactions with coactivator or corepressor proteins, and subsequently initiate or suppress transcription of target genes. SERM activity is intrinsic to each ER ligand, which accomplishes its unique profile by specific interactions in the target cell, leading to tissue selective actions. We discuss the estrogenic and anti-estrogenic effects of early SERMs, such as clomiphene citrate, used for treatment of ovulation induction, and the triphenylethylene, tamoxifen, which has ER antagonist activity in the breast, and is used for prevention and treatment of ER-positive breast cancer. Since the development of tamoxifen, other triphenylethylene SERMs have been studied for breast cancer prevention, including droloxifene, idoxifene, toremifene, and ospemifene. Other SERMs have entered clinical development more recently, including benzothiophenes (raloxifene and arzoxifene), benzopyrans (ormeloxifene, levormeloxifene, and EM-800), lasofoxifene, pipendoxifene, bazedoxifene, HMR-3339, and fulvestrant, an anti-estrogen which is approved for breast cancer treatment. SERMs have effects on tissues containing ER, such as the breast, bone, uterine and genitourinary tissues, and brain, and on markers of cardiovascular risk. Current evidence indicates that each SERM has a unique array of clinical activities. Differences in the patterns of action of SERMs suggest that each clinical end point must be evaluated individually, and conclusions about any particular SERM can only be established through appropriate clinical trials.

Single and multiple ascending dose studies of a novel tissue-selective oestrogen receptor modulator, CHF 4227, in healthy postmenopausal women

AIMS

We evaluated the tolerability, adverse events profile, pharmacokinetics, and pharmacodynamics of CHF 4227, a new selective oestrogen receptor modulator (SERM), in healthy postmenopausal women.

METHODS

Two phase I studies were conducted according to a double-bind, placebo-controlled design. Subjects were randomized to receive six single (5-400 mg) or five multiple oral doses of CHF 4227 for 28 days (5-100 mg).

RESULTS

No vaginal bleeding and no changes in either endometrial thickness or the placenta protein 14 marker were found after 4 weeks of treatment. The compound did not induce negative effects on the fibrinolytic system. After 28 days of treatment, CHF 4227 decreased both total and LDL cholesterol concentrations (maximum decreases from baseline of 17.4% (95% CI 7.0, 27.7) and 27.6% (95% CI 9.0, 46.3), respectively). Decreases in both serum and urinary type-I C-terminal collagen telopeptide were also observed producing maximum changes of 40.6% (95% CI 29.5, 51.7), and 41.7% (95% CI 20.3, 56.8), respectively. CHF4227 (5 and 10 mg) induced near maximal oestrogen-like effects on bone markers and serum lipids without causing hot flushes. The pharmacokinetics of CHF 4227 were characterized by a slow absorption, a long elimination half-life (31-42 h after single administration) and dose linearity with respect to C(max) and AUC up to 100 mg.

CONCLUSIONS

CHF 4227 is a well-tolerated SERM when administered once daily for 28 days. It is potentially active on bone resorption and serum lipids, without affecting the endometrium and without worsening hot flushes. CHF 4227 is a promising agent for the treatment of several conditions in postmenopausal women.

Clinical development of fulvestrant ("Faslodex")

This paper outlines the development of fulvestrant, the first in a new class of antioestrogen agents with no agonist effects, to be used for the treatment of hormone receptor-positive advanced breast cancer in postmenopausal women. The role of the oestrogen receptor in breast cancer growth and development and the evolution of pharmacological strategies to manipulate it are also discussed. Preclinical and clinical evidence for the efficacy of fulvestrant are also reviewed, along with the tolerability profile of this agent in relation to other endocrine therapies. Further research will define the role of this exciting new agent in the endocrine treatment of breast cancer.

Endocrinology and hormone therapy in breast cancer: selective oestrogen receptor modulators and downregulators for breast cancer - have they lost their way?

Although tamoxifen has been an effective treatment for breast cancer, several novel anti-oestrogen compounds have been developed with a reduced agonist profile on breast and gynaecological tissues. These include selective oestrogen receptor modulators (SERMs; both 'tamoxifen-like' and 'fixed-ring' SERMs) and selective oestrogen receptor downregulators (SERDs), although none has been proved superior in efficacy to tamoxifen in various advanced breast cancer trials. Thus, many have questioned whether a need for SERMs in breast cancer still exists, although chemoprevention remains a possible niche setting. In contrast, SERDs may have useful efficacy following aromatase inhibitors because of their unique mechanism of action, and clinical trials to determine their optimal use or sequence are ongoing.

Selective oestrogen receptor modulators/new antioestrogens: a clinical perspective

Following tamoxifen, the first selective oestrogen receptor modulator (SERM), a number of other antioestrogens have been developed. The first-generation SERMs exhibit cross-resistance with tamoxifen and have agonist effects on the uterus. Toremifene has equal efficacy to tamoxifen and may be useful as a tamoxifen alternative. Efficacy results for droloxifene and idoxifene were disappointing and their clinical development ceased. Response rates for second-generation SERMs such as raloxifene and arzoxifene are also not high, although raloxifene shows promise in the chemoprevention of breast cancer. Paradoxically, high-dose oestrogens are proving to be effective breast cancer treatment with similar responses to tamoxifen in postmenopausal women with advanced disease, although these drugs are not well tolerated. Fulvestrant is a new type of oestrogen receptor (ER) antagonist with no agonist effects, which binds, blocks and degrades the ER. Fulvestrant produces high response rates compared with the SERMs, is not cross-resistant with SERMs or aromatase inhibitors (AIs) and is equally as effective as the AI anastrozole in the treatment of postmenopausal women with advanced breast cancer who have progressed after prior antioestrogen therapy. Pure antioestrogens such as the ER antagonist fulvestrant provide opportunities for therapeutic sequencing with tamoxifen and AIs and offer exciting possibilities for the future treatment of breast cancer.