New and emerging treatments for estrogen receptor-positive breast cancer: focus on everolimus

Treating ER-positive breast cancer: a review of the current FDA-approved SERMs and SERDs and their mechanisms of action

Breast cancer is one of the most significant causes of mortality among women and the second most prevalent cancer worldwide. Estrogen receptor (ER)-positive breast cancers are the most common molecular subtype of breast cancer, comprising about 70% of breast carcinoma diagnoses worldwide. Endocrine therapy is the foremost strategy for the treatment of ER-positive breast cancer. In the United States, the Food and Drug Administration (FDA) has approved endocrine therapies for ER-positive breast cancers that include selective estrogen receptor modulators (SERMs), selective estrogen receptor downregulators/degraders (SERDs) and aromatase inhibitors (AIs). The approved SERMS, tamoxifen, toremifene and raloxifene, are the gold-standard treatments. The only FDA-approved SERD available for treating ER and hormone-positive breast cancers is fulvestrant, and various generations of AIs, including exemestane, letrozole, and anastrozole, have also received FDA approval. Herein, we review the major FDA-approved SERMs and SERDs for treating ER-positive breast cancer, focusing on their mechanisms of action. We also explore molecular events that contribute to the resistance of these drugs to endocrine therapies and combinational strategies with drugs such as cyclin-dependant kinases 4/6 (CDK4/6) inhibitors in clinical trials to combat endocrine drug resistance.

Integrated mutational landscape analysis of uterine leiomyosarcomas

Uterine leiomyosarcomas (uLMS) are aggressive tumors arising from the smooth muscle layer of the uterus. We analyzed 83 uLMS sample genetics, including 56 from Yale and 27 from The Cancer Genome Atlas (TCGA). Among them, a total of 55 Yale samples including two patient-derived xenografts (PDXs) and 27 TCGA samples have whole-exome sequencing (WES) data; 10 Yale and 27 TCGA samples have RNA-sequencing (RNA-Seq) data; and 11 Yale and 10 TCGA samples have whole-genome sequencing (WGS) data. We found recurrent somatic mutations in TP53, MED12, and PTEN genes. Top somatic mutated genes included TP53, ATRX, PTEN, and MEN1 genes. Somatic copy number variation (CNV) analysis identified 8 copy-number gains, including 5p15.33 (TERT), 8q24.21 (C-MYC), and 17p11.2 (MYOCD, MAP2K4) amplifications and 29 copy-number losses. Fusions involving tumor suppressors or oncogenes were deetected, with most fusions disrupting RB1, TP53, and ATRX/DAXX, and one fusion (ACTG2-ALK) being potentially targetable. WGS results demonstrated that 76% (16 of 21) of the samples harbored chromoplexy and/or chromothripsis. Clinically actionable mutational signatures of homologous-recombination DNA-repair deficiency (HRD) and microsatellite instability (MSI) were identified in 25% (12 of 48) and 2% (1 of 48) of fresh frozen uLMS, respectively. Finally, we found olaparib (PARPi; P = 0.002), GS-626510 (C-MYC/BETi; P < 0.000001 and P = 0.0005), and copanlisib (PIK3CAi; P = 0.0001) monotherapy to significantly inhibit uLMS-PDXs harboring derangements in C-MYC and PTEN/PIK3CA/AKT genes (LEY11) and/or HRD signatures (LEY16) compared to vehicle-treated mice. These findings define the genetic landscape of uLMS and suggest that a subset of uLMS may benefit from existing PARP-, PIK3CA-, and C-MYC/BET-targeted drugs.

PI3K/AKT/mTOR Signaling Pathway in Breast Cancer: From Molecular Landscape to Clinical Aspects

Breast cancer is a serious health problem worldwide, representing the second cause of death through malignancies among women in developed countries. Population, endogenous and exogenous hormones, and physiological, genetic and breast-related factors are involved in breast cancer pathogenesis. The phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) is a signaling pathway involved in cell proliferation, survival, invasion, migration, apoptosis, glucose metabolism and DNA repair. In breast tumors, PIK3CA somatic mutations have been reported, located in exon 9 and exon 20. Up to 40% of PIK3CA mutations are estrogen receptor (ER) positive and human epidermal growth factor receptor 2 (HER2) -negative in primary and metastatic breast cancer. HER2 is overexpressed in 20-30% of breast cancers. HER1, HER2, HER3 and HER4 are membrane receptor tyrosine kinases involved in HER signaling to which various ligands can be attached, leading to PI3K/AKT activation. Currently, clinical studies evaluate inhibitors of the PI3K/AKT/mTOR axis. The main purpose of this review is to present general aspects of breast cancer, the components of the AKT signaling pathway, the factors that activate this protein kinase B, PI3K/AKT-breast cancer mutations, PI3K/AKT/mTOR-inhibitors, and the relationship between everolimus, temsirolimus and endocrine therapy.

Fomes fomentarius Ethanol Extract Exerts Inhibition of Cell Growth and Motility Induction of Apoptosis via Targeting AKT in Human Breast Cancer MDA-MB-231 Cells

Fomes fomentarius, an edible mushroom, is known to have anti-cancer, anti-inflammatory, and anti-diabetes effects. However, the underlying anti-cancer mechanism of F. fomentarius is unknown. To determine the molecular mechanism of the anti-cancer effects of F. fomentarius, various methods were used including fluorescence-activated cell sorting, Western blotting, migration, and crystal violet assays. F. fomentarius ethanol extract (FFE) decreased cell viability in six cancer cell lines (MDA-MB-231, MCF-7, A549, H460, DU145, and PC-3). FFE decreased the migration of MDA-MB-231 cells without causing cell toxicity. Furthermore, FFE attenuated the expression of matrix metalloproteinase-9 and phosphorylation of Akt as well as increased E-cadherin in MDA-MB-231 cells. FFE arrested the S and G2/M populations by inhibiting the expression of cell cycle regulatory proteins such as cyclin-dependent kinase 2, cyclin A/E, and S-phase kinase-associated protein 2. FFE increased the sub-G1 population and expression of cleaved caspase-9, -3, and cleaved poly adenosine diphosphate (ADP-ribose) polymerase at 72 h and suppressed B-cell lymphoma 2. Interestingly, FFE and AKT inhibitors showed similar effects in MDA-MB-231 cells. Additionally, FFE contained betulin which inhibited p-AKT in MDA-MB-231 cells. Our findings demonstrate that FFE inhibits cell motility and growth and induces apoptosis by inhibiting the phsphoinositide 3- kinase /AKT pathway and caspase activation.

mTORC1 is a key mediator of RON-dependent breast cancer metastasis with therapeutic potential

Metastasis is the biggest challenge in treating breast cancer, and it kills >40,000 breast cancer patients annually in the US. Aberrant expression of the RON receptor tyrosine kinase in breast tumors correlates with poor prognosis and has been shown to promote metastasis. However, the molecular mechanisms that govern how RON promotes metastasis, and how to block it, are still largely unknown. We sought to determine critical effectors of RON using a combination of mutational and pharmacologic strategies. High-throughput proteomic analysis of breast cancer cells upon activation of RON showed robust phosphorylation of ribosomal protein S6. Further analysis revealed that RON strongly signals through mTORC1/p70S6K, which is mediated predominantly by the PI3K pathway. A targeted mutation approach to modulate RON signaling validated the importance of PI3K/mTORC1 pathway for spontaneous metastasis in vivo. Finally, inhibition of mTORC1 with an FDA-approved drug, everolimus, resulted in transient shrinkage of established RON-dependent metastases, and combined blockade of mTORC1 and RON delayed progression. These studies have identified a key downstream mediator of RON-dependent metastasis in breast cancer cells and revealed that inhibition of mTORC1, or combined inhibition of mTORC1 and RON, may be effective for treatment of metastatic breast cancers with elevated expression of RON.

Role for the transcriptional activator ZRF1 in early metastatic events in breast cancer progression and endocrine resistance

Breast cancer is one of the most common malignancies among women which is often treated with hormone therapy and chemotherapy. Despite the improvements in detection and treatment of breast cancer, the vast majority of breast cancer patients are diagnosed with metastatic disease either at the beginning of the disease or later during treatment. Still, the molecular mechanisms causing a therapy resistant metastatic breast cancer are still elusive. In the present study we addressed the function of the transcriptional activator ZRF1 during breast cancer progression. We provide evidence that ZRF1 plays an essential role for the early metastatic events in vitro and acts like a tumor suppressor protein during the progression of breast invasive ductal carcinoma into a more advanced stage. Hence, depletion of ZRF1 results in the acquisition of metastatic behavior by facilitating the initiation of the metastatic cascade, notably for cell adhesion, migration and invasion. Furthermore absence of ZRF1 provokes endocrine resistance via misregulation of cell death and cell survival related pathways. Taken together, we have identified ZRF1 as an important regulator of breast cancer progression that holds the potential to be explored for new treatment strategies in the future.

Vertical inhibition of the PI3K/Akt/mTOR pathway is synergistic in breast cancer

Deregulation and activation of the phosphoinositide 3-kinase (PI3K)/Akt/mammalian (or mechanistic) target of rapamycin (mTOR) pathway have a major role in proliferation and cell survival in breast cancer. However, as single agents, mTOR inhibitors have had modest antitumor efficacy. In this study, we evaluated the effects of vertical inhibition of mTOR and Akt in breast cancer cell lines and xenografts. We assessed the effects of mTOR inhibitor rapamycin and Akt inhibitor MK-2206, given as single drugs or in combination, on cell signaling, cell proliferation and apoptosis in a panel of cancer cell lines in vitro. The antitumor efficacy was tested in vivo. We demonstrated that MK-2206 inhibited Akt phosphorylation, cell proliferation and apoptosis in a dose-dependent manner in breast cancer cell lines. Rapamycin inhibited S6 phosphorylation and cell proliferation, and resulted in lower levels of apoptosis induction. Furthermore, the combination treatment inhibited phosphorylation of Akt and S6, synergistically inhibited proliferation and induced apoptosis with a higher efficacy. In vivo combination inhibited tumor growth more than either agent alone. Our data suggest that a combination of Akt and mTOR inhibitors have greater antitumor activity in breast cancer cells, which may be a viable approach to treat patients.

Activation of phosphoinositide 3-kinase/Akt/mechanistic target of rapamycin pathway and response to everolimus in endocrine receptor-positive metastatic breast cancer - A retrospective pilot analysis and viewpoint

Introduction:

Biomarkers predictive of response to mechanistic target of rapamycin (mTOR) inhibitor, everolimus, in endocrine receptor (ER)-positive metastatic breast cancer (MBC) are a work in progress. We evaluated the feasibility of directly measuring mTOR activity and phosphatase and tensin homolog (PTEN) expression and correlating their expression with response and survival.

Materials and Methods:

MBC patients who received everolimus with endocrine therapy (ET) after progression on an aromatase inhibitor and had adequate tissue preservation for estimation of mTOR activity and PTEN expression were selected for analysis from a prospectively maintained database. Progression-free survival (PFS) and overall survival (OS) were estimated by Kaplan–Meier method, and correlation between mTOR activity and PTEN expression with survival was done by log-rank test.

Results:

Thirteen ER-positive MBC patients were available for analysis. PTEN expression was lost in 11/13 (84.6%) patients and retained in 2/13 patients (15.4%). mTOR activity was absent in four patients (30.7%), weak in six patients (46.1%), and moderate in 3 patients (23.2%). Median PFS for the entire population was 2.5 months while median OS was not reached. Patients with an absent mTOR activity showed a longer PFS (5 vs. 1.5 vs. 2 months) than those with weak and moderate activity, respectively (P = 0.043). There was no correlation between loss of PTEN expression and PFS.

Conclusions:

Measurement of direct mTOR activity in patients with MBC receiving everolimus/ET combination appears feasible. Absent mTOR activity may predict for longer PFS with everolimus-ET combination and requires further study.

Potential role for mammalian target of rapamycin inhibitors as first-line therapy in hormone receptor-positive advanced breast cancer

Despite advances in cytotoxic chemotherapy and targeted therapies, 5-year survival rates remain low for patients with advanced breast cancer at diagnosis. This highlights the limited effectiveness of current treatment options. An improved understanding of cellular functions associated with the development and progression of breast cancer has resulted in the creation of a number of novel targeted molecular therapies. However, more work is needed to improve outcomes, particularly in the first-line recurrent or metastatic hormone receptor-positive breast cancer setting. The phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (mTOR) pathway is a major intracellular signaling pathway that is often upregulated in breast cancer, and overactivation of this pathway has been associated with primary or developed resistance to endocrine treatment. Clinical data from the Phase III Breast Cancer Trials of Oral Everolimus-2 (BOLERO-2) study of the mTOR inhibitor everolimus combined with exemestane in hormone receptor-positive advanced breast cancer were very promising, highlighting the potential role of mTOR inhibitors in combination with endocrine therapies as a first-line treatment option for these patients. It is hoped that the use of mTOR inhibitors combined with current standard-of-care endocrine therapies, such as aromatase inhibitors, in the first-line advanced breast cancer setting may result in greater antitumor effects and also delay or reverse treatment resistance.

mTORC1 directly phosphorylates and activates ERα upon estrogen stimulation

Breast cancer is the leading cause of cancer-related deaths among women. Approximately 75% of breast cancers are estrogen receptor α (ERα) positive, underscoring the dependence of cancer cells on estrogen for growth and survival. Patients treated with endocrine therapy often develop resistance, either de novo or acquired, which in some cases is caused by aberrations within the growth factor signaling pathways. The mechanistic target of rapamycin complex 1 (mTORC1) has emerged as a critical node in estrogenic signaling. We have previously shown that mTORC1 can phosphorylate and activate ERα on S167 via its effector the 40S ribosomal S6 kinase 1 (S6K1). Presently, we have uncovered a direct link between mTORC1 and ERα. We found that ERα binds to regulatory-associated protein of mTOR (Raptor) and causes it to translocate to the nucleus upon estrogen stimulation. Additionally, we identified mTOR as the kinase that phosphorylates ERα on S104/106 and activates transcription of ER target genes. Our findings show a direct link between mTORC1 and ERα, which further implicates mTORC1 signaling in the pathogenesis of ER-positive breast cancer and provides rationale for FDA-approved use of mTORC1 inhibitors in combination with endocrine agents for treatment of this disease.

Mammalian target of rapamycin (mTOR) inhibitors and combined chemotherapy in breast cancer: a meta-analysis of randomized controlled trials

The mammalian target of rapamycin (mTOR) inhibitor, in combination with other chemotherapeutic drugs, has been used for treatment of breast cancer that develops resistance to endocrine therapy. However, the efficacy and safety need further evaluation. Here, we report a meta-analysis of randomized controlled trials (RCT) in breast cancer patients undergoing chemotherapy using steroid (exemestane) or nonsteroid (letrozole) aromatase inhibitors with or without mTOR inhibitors (everolimus). The overall response rate (ORR), progression-free survival (PFS), clinical benefi;t rate with 95% confidence interval (CI), and the major toxicities/adverse effects were analyzed. Data were extracted from twelve studies that meet the selection criteria. Among these, six studies that enrolled 3693 women received treatment of everolimus plus exemestane, or placebo with exemestane. The results showed that everolimus plus exemestane significantly increased the ORR relative risk (relative risk = 9.18, 95% CI = 5.21-16.15), PFS hazard ratio (hazard ratio = 0.44, 95% CI = 0.41-0.48), and clinical benefi;t rate (relative risk = 1.92, 95% CI 1.69-2.17) compared to placebo control, while the risks of stomatitis, rash, hyperglycemia, diarrhea, fatigue, anorexia and pneumonitis also increased. Three studies that enrolled 715 women who received everolimus as neoadjuvant therapy were analyzed. Compared to chemotherapy with placebo, chemotherapy plus everolimus did not increase the ORR relative risk (relative risk = 0.90, 95% CI = 0.77-1.05). Meanwhile, two other studies that enrolled 2104 women examined the efficacy of temsirolimus (or placebo control) plus letrozole. The results indicated that emsirolimus plus letrozole did not increase the ORR relative risk and clinical benefi;t rate (p > 0.05). Together, these data suggest that the combined mTOR inhibitor (everolimus) plus endocrine therapy (exemestane) is superior to endocrine therapy alone. As a neoadjuvant, everolimus did not increase the ORR, while temsirolimus plus letrozole treatment has limited effect on the ORR and the CBR of breast cancer patients.

Metabolic control of tumour progression and antitumour immunity

PURPOSE OF REVIEW

Loss of cell growth control is not sufficient to explain why tumours form as the immune system recognizes many malignant cells and keeps them in check. The local inflammatory microenvironment is a pivotal factor in tumour formation, as tumour-associated inflammation actively suppresses antitumour immunity. The purpose of this review is to evaluate emerging evidence that amino acid catabolism is a key feature of tumour-associated inflammation that supports tumour progression and immune resistance to therapy.

RECENT FINDINGS

Enhanced amino acid catabolism in inflammatory tumour microenvironments correlates with carcinogen resistance and immune regulation mediated by tumour-associated immune cells that protect tumours from natural and vaccine-induced immunity. Interfering with metabolic pathways exploited by tumours is a promising antitumour strategy, especially when combined with other therapies. Moreover, molecular sensors that evolved to detect pathogens may enhance evasion of immune surveillance to permit tumour progression.

SUMMARY

Innate immune sensing that induces amino acid catabolism in tumour microenvironments may be pivotal in initiating and sustaining local inflammation that promotes immune resistance and attenuates antitumour immunity. Targeting molecular sensors that mediate these metabolic changes may be an effective strategy to enhance antitumour immunity that prevents tumour progression, as well as improving the efficacy of cancer therapy.

The PI3K/AKT/mTOR pathway in breast cancer: targets, trials and biomarkers

The phosphoinositide 3 kinase (PI3K)/Akt/mammalian (or mechanistic) target of rapamycin (mTOR) pathway is a complicated intracellular pathway, which leads to cell growth and tumor proliferation and plays a significant role in endocrine resistance in breast cancer. Multiple compounds targeting this pathway are being evaluated in clinical trials. These agents are generally well tolerated and can be used in combination with targeted therapies, endocrine therapy or cytotoxic agents. The identification of subtypes of tumors more likely to respond to these therapeutics cannot be overemphasized, since breast cancer is a very heterogeneous malignancy. Activation of pathways such as KRAS and MEK can act as escape mechanisms that lead to resistance, thus a combination of agents targeting multiple steps of the intracellular machinery is promising. There is evidence that tumors with PIK3CA mutations are more sensitive to inhibitors of the PI3K pathway but this has yet to be validated. Large clinical trials with correlative studies are necessary to identify reliable biomarkers of efficacy.