Therapeutic Ligands Antagonize Estrogen Receptor Function by Impairing Its Mobility

Efficacy of a novel orally active SERD AZD9496 against hormone dependent post-menopausal breast cancer depends on inhibition of cellular aromatase activity

Treatment of hormone sensitive breast cancer tumors with endocrine therapy such as antiestrogens or aromatase inhibitors has improved the outcome significantly. Studies including our own have shown that downregulation of ERα with pure antiestrogen fulvestrant in combination with aromatase inhibitors may prolong responsiveness of the tumors to endocrine therapy. Fulvestrant has been studied as second line or first line treatment for post-menopausal hormone receptor positive breast cancers as a single agent or in combination with AIs. Studies have also suggested that further escalation of dose may improve benefit. However, dose escalation of fulvestrant, which is administered via intramuscular injection, is difficult due to its poor solubility. To overcome this shortcoming of an injectable drug, a novel orally active antiestrogen, AZD9496 was developed. In addition to being orally active, AZD9496 is designed as a selective ERα downregulator (SERD). In the current study, we compared the effect of AZD9496 and fulvestrant on the growth of MCF-7Ca (human estrogen receptor positive MCF-7 cells stably transfected with human placental aromatase gene) xenografts grown in ovariectomized athymic nude mice. AZD9496 was also compared to fulvestrant in vitro as a single agent or in combination with anastrozole. Our current study shows that AZD9496 is equally effective as fulvestrant at controlling the growth of hormone sensitive human breast cancer tumors. Similar to fulvestrant, AZD9496 inhibits cellular aromatase activity through ERα mediated signaling. However, unlike fulvestrant, combination of AZD9496 with anastrozole did not produce increased tumor inhibition. Our results show that AZD9496 was significantly better at inhibiting cellular aromatase which contributed to its anticancer activity. Next, we measured the effect of AZD9496 on the mouse uterus. Uterine weight of mice treated with AZD9496 was significantly lower than that for mice treated with androstenedione. This reduction in uterine weight was due to AZD9496 mediated inhibition of aromatase activity and not a direct effect on uterine ERα expression. We also observed that anti-cancer efficacy of AZD9496 depended on its ability to inhibit cellular aromatase. These results suggest that AZD9496 may be a better alternative to fulvestrant due to its selectivity for mammary ER and ability to inhibit aromatase in addition of downregulating ERα that can be obtained upon oral administration. As such, AZD9496 may prove to be a better option than fulvestrant for the treatment of hormone sensitive human breast cancer.

Managing therapeutic resistance in breast cancer: from the lncRNAs perspective

Breast cancer (BC) is the most common female malignancy and the second leading cause of cancer-related death worldwide. In spite of significant advances in clinical management, the mortality of BC continues to increase due to the frequent occurrence of treatment resistance. Intensive studies have been conducted to elucidate the molecular mechanisms underlying BC therapeutic resistance, including increased drug efflux, altered drug targets, activated bypass signaling pathways, maintenance of cancer stemness, and deregulated immune response. Emerging evidence suggests that long noncoding RNAs (lncRNAs) are intimately involved in BC therapy resistance through multiple modes of action. Therefore, an in-depth understanding of the implication of lncRNAs in resistance to clinical therapies may improve the clinical outcome of BC patients. Here, we highlight the role and underlying mechanisms of lncRNAs in regulating BC treatment resistance with an emphasis on lncRNAs-mediated resistance in different clinical scenarios, and discuss the potential of lncRNAs as novel biomarkers or therapeutic targets to improve BC therapy response.

Big data-driven precision medicine: Starting the custom-made era of iatrology

Precision medicine is a new therapeutic concept and method emerging in recent years. The rapid development of precision medicine is driven by the development of omics related technology, biological information and big data science. Precision medicine is provided to implement precise and personalized treatment for diseases and specific patients. Precision medicine is commonly used in the diagnosis, treatment and prevention of various diseases. This review introduces the application of precision medicine in eight systematic diseases of the human body, and systematically presenting the current situation of precision medicine. At the same time, the shortcomings and limitations of precision medicine are pointed out. Finally, we prospect the development of precision medicine.

Discovery of GNE-149 as a Full Antagonist and Efficient Degrader of Estrogen Receptor alpha for ER+ Breast Cancer

Estrogen receptor alpha (ERα) is a well-validated drug target for ER-positive (ER+) breast cancer. Fulvestrant is FDA-approved to treat ER+ breast cancer and works through two mechanisms-as a full antagonist and selective estrogen receptor degrader (SERD)-but lacks oral bioavailability. Thus, we envisioned a "best-in-class" molecule with the same dual mechanisms as fulvestrant, but with significant oral exposure. Through lead optimization, we discovered a tool molecule 12 (GNE-149) with improved degradation and antiproliferative activity in both MCF7 and T47D cells. To illustrate the binding mode and key interactions of this scaffold with ERα, we obtained a cocrystal structure of 6 that showed ionic interaction of azetidine with Asp351 residue. Importantly, 12 showed favorable metabolic stability and good oral exposure. 12 exhibited antagonist effect in the uterus and demonstrated robust dose-dependent efficacy in xenograft models.

Monovalent protein-degraders - Insights and future perspectives

The therapeutic potential of interfering with dysregulated proteins by inducing its selective degradation has been pursued using different mechanisms. In the present article, we review representative examples of monovalent protein-degraders that, contrary to the proteolysis targeting chimeras, achieve target degradation without displaying recognition motifs for the recruitment of E3 ubiquitin ligases. We also highlight new technologies and assays that may brought to bear on the discovery of common elements that could predict and enable the selective degradation of pathogenic targets by monovalent protein-degraders. The successful application of these methods would pave the way to the advancement of new drugs with unique efficacy and tolerability properties.

Overcoming Endocrine Resistance in Breast Cancer

Estrogen receptor-positive (ER+) breast cancer is the most common breast cancer subtype. Treatment of ER+ breast cancer comprises interventions that suppress estrogen production and/or target the ER directly (overall labeled as endocrine therapy). While endocrine therapy has considerably reduced recurrence and mortality from breast cancer, de novo and acquired resistance to this treatment remains a major challenge. An increasing number of mechanisms of endocrine resistance have been reported, including somatic alterations, epigenetic changes, and changes in the tumor microenvironment. Here, we review recent advances in delineating mechanisms of resistance to endocrine therapies and potential strategies to overcome such resistance.

G1T48, an oral selective estrogen receptor degrader, and the CDK4/6 inhibitor lerociclib inhibit tumor growth in animal models of endocrine-resistant breast cancer

Purpose

The combination of targeting the CDK4/6 and estrogen receptor (ER) signaling pathways with palbociclib and fulvestrant is a proven therapeutic strategy for the treatment of ER-positive breast cancer. However, the poor physicochemical properties of fulvestrant require monthly intramuscular injections to patients, which limit the pharmacokinetic and pharmacodynamic activity of the compound. Therefore, an orally available compound that more rapidly reaches steady state may lead to a better clinical response in patients. Here, we report the identification of G1T48, a novel orally bioavailable, non-steroidal small molecule antagonist of ER.

Methods

The pharmacological effects and the antineoplastic mechanism of action of G1T48 on tumors was evaluated using human breast cancer cells (in vitro) and xenograft efficacy models (in vivo).

Results

G1T48 is a potent and efficacious inhibitor of estrogen-mediated transcription and proliferation in ER-positive breast cancer cells, similar to the pure antiestrogen fulvestrant. In addition, G1T48 can effectively suppress ER activity in multiple models of endocrine therapy resistance including those harboring ER mutations and growth factor activation. In vivo, G1T48 has robust antitumor activity in a model of estrogen-dependent breast cancer (MCF7) and significantly inhibited the growth of tamoxifen-resistant (TamR), long-term estrogen-deprived (LTED) and patient-derived xenograft tumors with an increased response being observed with the combination of G1T48 and the CDK4/6 inhibitor lerociclib.

Conclusions

These data show that G1T48 has the potential to be an efficacious oral antineoplastic agent in ER-positive breast cancer.

Electronic supplementary material

The online version of this article (10.1007/s10549-020-05575-9) contains supplementary material, which is available to authorized users.

Design and Synthesis of Basic Selective Estrogen Receptor Degraders for Endocrine Therapy Resistant Breast Cancer

The clinical steroidal selective estrogen receptor (ER) degrader (SERD), fulvestrant, is effective in metastatic breast cancer, but limited by poor pharmacokinetics, prompting the development of orally bioavailable, nonsteroidal SERDs, currently in clinical trials. These trials address local breast cancer as well as peripheral metastases, but patients with brain metastases are generally excluded because of the lack of blood-brain barrier penetration. A novel family of benzothiophene SERDs with a basic amino side arm (B-SERDs) was synthesized. Proteasomal degradation of ERα was induced by B-SERDs that achieved the objectives of oral and brain bioavailability, while maintaining high affinity binding to ERα and both potency and efficacy comparable to fulvestrant in cell lines resistant to endocrine therapy or bearing ESR1 mutations. A novel 3-oxyazetidine side chain was designed, leading to 37d, a B-SERD that caused endocrine-resistant ER+ tumors to regress in a mouse orthotopic xenograft model.

Building Bridges in a Series of Estrogen Receptor Degraders: An Application of Metathesis in Medicinal Chemistry

Herein we report the use of metathesis to construct a novel tetracyclic core in a series of estrogen receptor degraders. This improved the chemical stability, as assessed using an NMR-MS based assay, and gave a molecule with excellent physicochemical properties and pharmacokinetics in rat. X-ray crystallography established minimal perturbation of the bridged compounds relative to the unbridged analogues in the receptor binding pocket. Unfortunately, despite retaining excellent binding to ERα, this adversely affected the ability of the compounds to degrade the receptor.

Pharmacokinetic and pharmacodynamic analysis of fulvestrant in preclinical models of breast cancer to assess the importance of its estrogen receptor-α degrader activity in antitumor efficacy

Purpose

Fulvestrant is a selective estrogen receptor downregulator (SERD) that is approved for first- or second-line use as a single agent or in combination with cyclin dependent kinase or phosphatidylinositol 3-kinase inhibitors for the treatment of metastatic breast cancer. Fulvestrant exhibits exceptionally effective antitumor activity in preclinical models of breast cancer, a success that has been attributed to its robust SERD activity despite modest receptor downregulation in patient tumors. By modeling human exposures in animal models we probe the absolute need for SERD activity.

Methods

Three xenograft models of endocrine therapy-resistant breast cancer were used to evaluate the efficacy of fulvestrant administered in doses historically used in preclinical studies in the field or by using a dose regimen intended to model clinical exposure levels. Pharmacokinetic and pharmacodynamic analyses were conducted to evaluate plasma exposure and intratumoral ER downregulation.

Results

A clinically relevant 25 mg/kg dose of fulvestrant exhibited antitumor efficacy comparable to the historically used 200 mg/kg dose, but at this lower dose it did not result in robust ER downregulation. Further, the antitumor efficacy of the lower dose of fulvestrant was comparable to that observed for other oral SERDs currently in development.

Conclusion

The use of clinically unachievable exposure levels of fulvestrant as a benchmark in preclinical development of SERDs may negatively impact the selection of those molecules that are advanced for clinical development. Further, these studies suggest that antagonist efficacy, as opposed to SERD activity, is likely to be the primary driver of clinical response.

Electronic supplementary material

The online version of this article (10.1007/s10549-019-05454-y) contains supplementary material, which is available to authorized users.