Effectiveness and molecular interactions of the clinically active mTORC1 inhibitor everolimus in combination with tamoxifen or letrozole in vitro and in vivo

A systems biology approach and in vitro experiment indicated Rapamycin targets key cancer and cell cycle-related genes and miRNAs in triple-negative breast cancer cells

An anticancer drug known as Rapamycin acts by inhibiting the mammalian target of the Rapamycin pathway. This agent has recently been investigated for its potential therapeutic benefits in sensitizing drug-resistant breast cancer (BC) treatment. The molecular mechanism underlying these effects, however, is still a mystery. Using a systems biology method and in vitro experiment, this study sought to discover essential genes and microRNAs (miRNAs) targeted by Rapamycin in triple-negative BC (TNBC) cells to aid prospective new medications with less adverse effects in BC treatment. We developed the transcription factor-miRNA-gene and protein-protein interaction networks using the freely accessible microarray data sets. FANMOD and MCODE were utilized to identify critical regulatory motifs, clusters, and seeds. Then, functional enrichment analyses were conducted. Using topological analysis and motif detection, the most important genes and miRNAs were discovered. We used quantitative real-time polymerase chain reaction (qRT-PCR) to examine the effect of Rapamycin on the expression of the selected genes and miRNAs to verify our findings. We performed flow cytometry to investigate Rapamycin's impact on cell cycle and apoptosis. Furthermore, wound healing and migration assays were done. Three downregulated (PTGS2, EGFR, VEGFA) and three upregulated (c-MYC, MAPK1, PIK3R1) genes were chosen as candidates for additional experimental verification. There were also three upregulated miRNAs (miR-92a, miR-16, miR-20a) and three downregulated miRNAs (miR-146a, miR-145, miR-27a) among the six selected miRNAs. The qRT-PCR findings in MDA-MB-231 cells indicated that c-MYC, MAPK1, PIK3R1, miR-92a, miR-16, and miR-20a expression levels were considerably elevated following Rapamycin treatment, whereas PTGS2, EGFR, VEGFA, miR-146a, and miR-145 expression levels were dramatically lowered (p < 0.05). These genes are engaged in cancer pathways, transcriptional dysregulation in cancer, and cell cycle, according to the top pathway enrichment findings. Migration and wound healing abilities of the cells declined after Rapamycin treatment, and the number of apoptotic cells increased. We demonstrated that Rapamycin suppresses cell migration and metastasis in the TNBC cell line. In addition, our data indicated that Rapamycin induces apoptosis in this cell line. The discovered vital genes and miRNAs affected by Rapamycin are anticipated to have crucial roles in the pathogenesis of TNBC and its therapeutic resistance.

Chemical inhibitor anticancer drugs regulate mechanical properties and cytoskeletal structure of non-invasive and invasive breast cancer cell lines: Study of effects of Letrozole, Exemestane, and Everolimus

Regardless of their target and mechanism, anticancer drugs directly influence biological behavior of cancer cells by activating chemical signaling pathways. Due to the complex interaction between diverse signaling pathways, these drugs may profoundly impact the physical characteristics of cancer cells and regulate their mechanical properties. In this study, the effects of two Aromatase Inhibitor (Letrozole and Exemestane), and one mTOR Inhibitor (Everolimus) on cell mechanical properties, actin content/distribution, and nuclear areas of two invasive and non-invasive breast cancer cell line after 24 h treatment with concentrations previously reported were investigated. While metabolic activity of cell lines was highly affected by drug treatment, significant alterations in Young's modulus of cell bodies, nuclear areas, and actin content and distribution were reported with higher impact on invasive cells. It was concluded that regulation of mechanical behavior of cells by all three drugs emphasizes the cross talk between chemical and physical signaling cascades, and describes a correlation between biological and physical behaviors of cancer cells which might give an insight to a better understanding of mechanisms by which anti-cancer drugs function to enhance their performances.

Plasma DNA as a "liquid biopsy" incompletely complements tumor biopsy for identification of mutations in a case series of four patients with oligometastatic breast cancer

PURPOSE

Circulating tumor DNA in plasma may present a minimally invasive opportunity to identify tumor-derived mutations to inform selection of targeted therapies for individual patients, particularly in cases of oligometastatic disease where biopsy of multiple tumors is impractical. To assess the utility of plasma DNA as a "liquid biopsy" for precision oncology, we tested whether sequencing of plasma DNA is a reliable surrogate for sequencing of tumor DNA to identify targetable genetic alterations.

METHODS

Blood and biopsies of 1-3 tumors were obtained from 4 evaluable patients with advanced breast cancer. One patient provided samples from an additional 7 tumors post-mortem. DNA extracted from plasma, tumor tissues, and buffy coat of blood were used for probe-directed capture of all exons in 149 cancer-related genes and massively parallel sequencing. Somatic mutations in DNA from plasma and tumors were identified by comparison to buffy coat DNA.

RESULTS

Sequencing of plasma DNA identified 27.94 ± 11.81% (mean ± SD) of mutations detected in a tumor(s) from the same patient; such mutations tended to be present at high allelic frequency. The majority of mutations found in plasma DNA were not found in tumor samples. Mutations were also found in plasma that matched clinically undetectable tumors found post-mortem.

CONCLUSIONS

The incomplete overlap of genetic alteration profiles of plasma and tumors warrants caution in the sole reliance of plasma DNA to identify therapeutically targetable alterations in patients and indicates that analysis of plasma DNA complements, but does not replace, tumor DNA profiling.

TRIAL REGISTRATION

Subjects were prospectively enrolled in trial NCT01836640 (registered April 22, 2013).

Anti-cell growth and anti-cancer stem cell activity of the CDK4/6 inhibitor palbociclib in breast cancer cells

BACKGROUND

A cyclin-dependent kinase (CDK) 4/6 inhibitor, palbociclib, has been used to treat patients with estrogen receptor (ER)-positive (+) and human epidermal growth factor receptor (HER) 2-negative (-) advanced breast cancer. To investigate the mechanisms underlying the antitumor activity of palbociclib, we conducted a preclinical study on the anti-cell growth and anti-cancer stem cell (CSC) activity of palbociclib in breast cancer cells.

METHODS

The effects of palbociclib on Rb phosphorylation, cell growth, cell cycle progression, apoptosis, cell senescence and the proportion of CSCs were investigated in five human breast cancer cell lines of different subtypes. To investigate the mechanisms of the anti-CSC activity of palbociclib, small-interfering RNAs for CDK4 and/or CDK6 were used. Palbociclib dose-dependently reduced Rb phosphorylation and cell growth in association with G1-S cell cycle blockade and the induction of cell senescence, but without increased apoptosis, in all breast cancer cell lines.

RESULTS

The anti-cell growth activity of palbociclib widely differed among the cell lines. Palbociclib also dose-dependently reduced the CSC proportion measured by three different assays in four of five cell lines. The inhibition of CDK4 expression, but not CDK6 expression, reduced the increased proportion of putative CSCs induced by estradiol in ER (+)/HER2 (-) cell lines.

CONCLUSIONS

These results suggest that palbociclib exhibits significant anti-cell growth and anti-CSC activity in not only ER (+) breast cancer cell lines but also ER (-) cell lines. CDK4 inhibition induced by palbociclib may be responsible for its anti-CSC activity.

Combination of mTORC1/2 inhibitor vistusertib plus fulvestrant in vitro and in vivo targets oestrogen receptor-positive endocrine-resistant breast cancer

Background

Endocrine therapies are still the main strategy for the treatment of oestrogen receptor-positive (ER+) breast cancers (BC), but resistance remains problematic. Cross-talk between ER and PI3K/AKT/mTORC has been associated with ligand-independent transcription of ER. We have previously reported the anti-proliferative effects of the combination of everolimus (an mTORC1 inhibitor) with endocrine therapy in resistance models, but potential routes of escape via AKT signalling can lead to resistance; therefore, the use of dual mTORC1/2 inhibitors has met with significant interest.

Methods

To address this, we tested the effect of vistusertib, a dual mTORC1 and mTORC2 inhibitor, in a panel of endocrine-resistant and endocrine-sensitive ER+ BC cell lines, with varying PTEN, PIK3CA and ESR1 mutation status. End-points included proliferation, cell signalling, cell cycle and effect on ER-mediated transcription. Two patient-derived xenografts (PDX) modelling endocrine resistance were used to assess the efficacy of vistusertib, fulvestrant or the combination on tumour progression, and biomarker studies were conducted using immunohistochemistry and RNA-seq technologies.

Results

Vistusertib caused a dose-dependent decrease in proliferation of all the cell lines tested and reduced abundance of mTORC1, mTORC2 and cell cycle markers, but caused an increase in abundance of EGFR, IGF1R and ERBB3 in a context-dependent manner. ER-mediated transcription showed minimal effect of vistusertib. Combined therapy of vistusertib with fulvestrant showed synergy in two ER+ PDX models of resistance to endocrine therapy and delayed tumour progression after cessation of therapy.

Conclusions

These data support the notion that models of acquired endocrine resistance may have a different sensitivity to mTOR inhibitor/endocrine therapy combinations.

Reprogramming of Amino Acid Transporters to Support Aspartate and Glutamate Dependency Sustains Endocrine Resistance in Breast Cancer

Endocrine therapy (ET) is the standard of care for estrogen receptor-positive (ER+) breast cancers. Despite its efficacy, ∼40% of women relapse with ET-resistant (ETR) disease. A global transcription analysis in ETR cells reveals a downregulation of the neutral and basic amino acid transporter SLC6A14 governed by enhanced miR-23b-3p expression, resulting in impaired amino acid metabolism. This altered amino acid metabolism in ETR cells is supported by the activation of autophagy and the enhanced import of acidic amino acids (aspartate and glutamate) mediated by the SLC1A2 transporter. The clinical significance of these findings is validated by multiple orthogonal approaches in a large cohort of ET-treated patients, in patient-derived xenografts, and in in vivo experiments. Targeting these amino acid metabolic dependencies resensitizes ETR cells to therapy and impairs the aggressive features of ETR cells, offering predictive biomarkers and potential targetable pathways to be exploited to combat or delay ETR in ER+ breast cancers.

Chemotherapy Modulates Endocrine Therapy-Related Resistance Mutations in Metastatic Breast Cancer

PURPOSE: Accumulation of PIK3CA, ESR1, and GATA3 mutations results in resistance to endocrine therapy in breast cancer patients; however, the response of these genes to chemotherapy is unclear. Therefore, we sought to evaluate the genetic response of circulating tumor DNA (ctDNA) to chemotherapy in metastatic breast cancer patients. METHODS: The mutation frequency of 1021 genes was examined prior to chemotherapy in ctDNA of 44 estrogen receptor–positive metastatic breast cancer patients. These genes were evaluated again in a subset of patients (n=24) following chemotherapy. Mutation frequency was defined as the percentage of mutations found in ctDNA compared to total cell-free DNA. RESULTS: Prior to chemotherapy, PIK3CA was the most commonly mutated gene, with mutation found in 22 of the metastatic breast cancer patients. Following chemotherapy, 16 patients exhibited progressive disease (PD), and 8 patients experienced no progression (non-PD). PIK3CA mutation frequency increased in 56.25% (9/16) of the PD patients but decreased in 62.5% (5/8) of the non-PD patients. As a result, more PD patients exhibited increased PIK3CA mutation frequency than non-PD patients (56.25% vs 0%, P=.002). Further, ESR1 and GATA3 mutations correlated with PIK3CA mutation. Interestingly, patients receiving the mTOR inhibitor everolimus exhibited a lower progression rate (0% vs 62.5%, P=.001), and the combination of everolimus and chemotherapy effectively suppressed PIK3CA, ESR1, and GATA3 gene mutations. CONCLUSION: Together, these results suggest that mTOR inhibition may be a useful chemotherapy adjuvant to suppress chemotherapy-induced gene mutations that render tumors resistant to endocrine therapy in metastatic breast cancer patients with PD.

Targeting tumour re-wiring by triple blockade of mTORC1, epidermal growth factor, and oestrogen receptor signalling pathways in endocrine-resistant breast cancer

Background

Endocrine therapies are the mainstay of treatment for oestrogen receptor (ER)-positive (ER⁺) breast cancer (BC). However, resistance remains problematic largely due to enhanced cross-talk between ER and growth factor pathways, circumventing the need for steroid hormones. Previously, we reported the anti-proliferative effect of everolimus (RAD001-mTORC1 inhibitor) with endocrine therapy in resistance models; however, potential routes of escape from treatment via ERBB2/3 signalling were observed. We hypothesised that combined targeting of three cellular nodes (ER, ERBB, and mTORC1) may provide enhanced long-term clinical utility.

Methods

A panel of ER⁺ BC cell lines adapted to long-term oestrogen deprivation (LTED) and expressing ESR1^wt or ESR1^Y537S, modelling acquired resistance to an aromatase-inhibitor (AI), were treated in vitro with a combination of RAD001 and neratinib (pan-ERBB inhibitor) in the presence or absence of oestradiol (E2), tamoxifen (4-OHT), or fulvestrant (ICI182780). End points included proliferation, cell signalling, cell cycle, and effect on ER-mediated transactivation. An in-vivo model of AI resistance was treated with monotherapies and combinations to assess the efficacy in delaying tumour progression. RNA-seq analysis was performed to identify changes in global gene expression as a result of the indicated therapies.

Results

Here, we show RAD001 and neratinib (pan-ERBB inhibitor) caused a concentration-dependent decrease in proliferation, irrespective of the ESR1 mutation status. The combination of either agent with endocrine therapy further reduced proliferation but the maximum effect was observed with a triple combination of RAD001, neratinib, and endocrine therapy. In the absence of oestrogen, RAD001 caused a reduction in ER-mediated transcription in the majority of the cell lines, which associated with a decrease in recruitment of ER to an oestrogen-response element on the TFF1 promoter. Contrastingly, neratinib increased both ER-mediated transactivation and ER recruitment, an effect reduced by the addition of RAD001. In-vivo analysis of an LTED model showed the triple combination of RAD001, neratinib, and fulvestrant was most effective at reducing tumour volume. Gene set enrichment analysis revealed that the addition of neratinib negated the epidermal growth factor (EGF)/EGF receptor feedback loops associated with RAD001.

Conclusions

Our data support the combination of therapies targeting ERBB2/3 and mTORC1 signalling, together with fulvestrant, in patients who relapse on endocrine therapy and retain a functional ER.

Electronic supplementary material

The online version of this article (10.1186/s13058-018-0983-1) contains supplementary material, which is available to authorized users.

mTOR signalling: jack-of-all-trades 1

The mechanistic target of rapamycin (mTOR) is an evolutionarily conserved serine/threonine kinase that senses and integrates environmental information into cellular regulation and homeostasis. Accumulating evidence has suggested a master role of mTOR signalling in many fundamental aspects of cell biology and organismal development. mTOR deregulation is implicated in a broad range of pathological conditions, including diabetes, cancer, neurodegenerative diseases, myopathies, inflammatory, infectious, and autoimmune conditions. Here, we review recent advances in our knowledge of mTOR signalling in mammalian physiology. We also discuss the impact of mTOR alteration in human diseases and how targeting mTOR function can treat human diseases.

Acquired resistance to everolimus in aromatase inhibitor-resistant breast cancer

We previously reported the establishment of several types of long-term estrogen-depleted-resistant (EDR) cell lines from MCF-7 breast cancer cells. Type 1 EDR cells exhibited the best-studied mechanism of aromatase inhibitor (AI) resistance, in which estrogen receptor (ER) expression remained positive and PI3K signaling was upregulated. Type 2 EDR cells showed reduced ER activity and upregulated JNK-related signaling. The mTOR inhibitor everolimus reduced growth in cells similar to Type 1 EDR cells. The present study generated everolimus-resistant (EvR) cells from Types 1 and 2 EDR cells following long-term exposure to everolimus in vitro. These EvR cells modeled resistance to AI and everolimus combination therapies following first-line AI treatment failure. In Type 1 EvR cells, everolimus resistance was dependent on MAPK signaling; single agents were not effective, but hormonal therapy combined with a kinase inhibitor effectively reduced cell growth. In Type 2 EvR cells, ER expression remained negative and a JNK inhibitor was ineffective, but a Src inhibitor reduced cell growth. The mechanism of acquired everolimus resistance appears to vary depending on the mechanism of AI resistance. Strategies targeting resistant tumors should be tailored based on the resistance mechanisms, as these mechanisms impact therapeutic efficacy.

Targeting the receptor tyrosine kinase RET in combination with aromatase inhibitors in ER positive breast cancer xenografts

The majority of breast cancers are estrogen receptor positive (ER+). Blockade of estrogen biosynthesis by aromatase inhibitors (AIs) is the first-line endocrine therapy for post-menopausal women with ER+ breast cancers. However, AI resistance remains a major challenge. We have demonstrated previously that increased GDNF/RET signaling in ER+ breast cancers promotes AI resistance. Here we investigated the efficacy of different small molecule RET kinase inhibitors, sunitinib, cabozantinib, NVP-BBT594 and NVP-AST487, and the potential of combining a RET inhibitor with the AI letrozole in ER+ breast cancers. The most effective inhibitor identified, NVP-AST487, suppressed GDNF-stimulated RET downstream signaling and 3D tumor spheroid growth. Ovariectomized mice were inoculated with ER+ aromatase-overexpressing MCF7-AROM1 cells and treated with letrozole, NVP-AST487 or the two drugs in combination. Surprisingly, the three treatment regimens showed similar efficacy in impairing MCF7-AROM1 tumor growth in vivo. However in vitro, NVP-AST487 was superior to letrozole in inhibiting the GDNF-induced motility and tumor spheroid growth of MCF7-AROM1 cells and required in combination with letrozole to inhibit GDNF-induced motility in BT474-AROM3 aromatase expressing cells. These data indicate that inhibiting RET is as effective as the current therapeutic regimen of AI therapy but that a combination treatment may delay cancer cell dissemination and metastasis.

Estrogen receptor alpha drives mTORC1 inhibitor-induced feedback activation of PI3K/AKT in ER+ breast cancer

The mTORC1 inhibitor RAD001 (everolimus) is approved for treatment of recurrent/metastatic estrogen receptor (ER)-positive breast cancer in combination with the aromatase inhibitor (AI) exemestane. The benefits of A) continued anti-estrogen therapy for anti-estrogen-resistant disease in the context of mTORC1 inhibition, and B) adjuvant everolimus in combination with anti-estrogen therapy for early-stage disease are being tested clinically, but molecular rationale remains unclear. We hypothesized that mTORC1 inhibition activates the IGF-1R/InsR/IRS-1/2 axis in an ER-dependent manner to drive PI3K/AKT and promote cancer cell survival, implicating ER in survival signaling induced by mTORC1 inhibition. Anti-estrogen treatment synergized with RAD001 to inhibit ER+ breast cancer cell growth. Inhibition of ER, IGF-1R/InsR, or IRS-1/2 suppressed AKT activation induced by mTORC1 inhibition. RAD001 primed IGF-1R/InsR for activation, which was enhanced by ER signaling. Post-menopausal patients with early-stage ER+ breast cancer were treated presurgically +/- the AI letrozole. Viable tumor fragments from surgical specimens were treated with RAD001 and/or OSI-906 ex vivo; RAD001 increased AKT activation, which was abrogated by presurgical letrozole. Letrozole decreased IGF-1R and IRS-1/2 tumor levels. These data suggest that ER drives PI3K/AKT activation in response to mTORC1 inhibition, providing molecular rationale for therapeutic combinations of anti-estrogens and mTORC1 inhibitors in endocrine-sensitive disease.

Synergy between Androgen Receptor Antagonism and Inhibition of mTOR and HER2 in Breast Cancer

The androgen receptor (AR) is widely expressed in breast cancer, and evidence suggests dependence on AR signaling for growth and survival. AR antagonists such as enzalutamide and seviteronel have shown success in preclinical models and clinical trials of prostate cancer and are currently being evaluated in breast cancer. Reciprocal regulation between AR and the HER2/PI3K/mTOR pathway may contribute to resistance to HER2- and mTOR-targeted therapies; thus, dual inhibition of these pathways may synergistically inhibit breast cancer growth. HER2+ and triple-negative breast cancer cell lines were treated with AR antagonist plus anti-HER2 mAb trastuzumab or mTOR inhibitor everolimus. Apoptosis, cell proliferation, and drug synergy were measured in vitro Pathway component genes and proteins were measured by qRT-PCR, Western blot, and reverse phase protein array. In vivo, HER2+ breast cancer xenografts were treated with enzalutamide, everolimus, trastuzumab, and combinations of these drugs. AR antagonists inhibited proliferation of both HER2+ and TNBC cell lines. Combining AR antagonist and either everolimus or trastuzumab resulted in synergistic inhibition of proliferation. Dihydrotestosterone caused increased phosphorylation of HER2 and/or HER3 that was attenuated by AR inhibition. Everolimus caused an increase in total AR, phosphorylation of HER2 and/or HER3, and these effects were abrogated by enzalutamide. Growth of trastuzumab-resistant HER2+ xenograft tumors was inhibited by enzalutamide, and combining enzalutamide with everolimus decreased tumor viability more than either single agent. AR antagonists synergize with FDA-approved breast cancer therapies such as everolimus and trastuzumab through distinct mechanisms. Treatment combinations are effective in trastuzumab-resistant HER2+ breast cancer cells in vivoMol Cancer Ther; 16(7); 1389-400. ©2017 AACR.

mTOR function and therapeutic targeting in breast cancer

The mTOR pathway was discovered in the late 1970s after the compound and natural inhibitor of mTOR, rapamycin was isolated from the bacterium Streptomyces hygroscopicus. mTOR is serine/threonine kinase belonging to the phosphoinositide 3-kinase related kinase (PIKK) family. It forms two distinct complexes; mTORC1 and mTORC2. mTORC1 has a key role in regulating protein synthesis and autophagy whilst mTORC2 is involved in regulating kinases of the AGC family. mTOR signaling is often over active in multiple cancer types including breast cancer. This can involve mutations in mTOR itself but more commonly, in breast cancer, this is related to an increase in activity of ErbB family receptors or alterations and mutations of PI3K signaling. Rapamycin and its analogues (rapalogues) bind to the intercellular receptor FKBP12, and then predominantly inhibit mTORC1 signaling via an allosteric mechanism. Research has shown that inhibition of mTOR is a useful strategy in tackling cancers, with it acting to slow tumor growth and limit the spread of a cancer. Rapalogues have now made their way into the clinic with the rapalogue everolimus (RAD-001/Afinitor) approved for use in conjunction with exemestane, in post-menopausal breast cancer patients with advanced disease who are HER-2 negative (normal expression), hormone receptor positive and whose prior treatment with non-steroidal aromatase inhibitors has failed. Testing across multiple trials has proven that everolimus and other rapalogues are a viable way of treating certain types of cancer. However, rapalogues have shown some drawbacks both in research and clinically, with their use often activating feedback pathways that counter their usefulness. As such, new types of inhibitors are being explored that work via different mechanisms, including inhibitors that are ATP competitive with mTOR and which act to perturb signaling from both mTOR complexes.

Diminished DYRK2 sensitizes hormone receptor-positive breast cancer to everolimus by the escape from degrading mTOR

Mammalian target of rapamycin (mTOR) inhibitor, everolimus, provides benefit for metastatic hormone receptor positive breast cancer after failure of the endocrine therapy. The present report highlights Dual Specificity Tyrosine Phosphorylation Regulated Kinase 2 (DYRK2) as a predictive marker for everolimus sensitivity. The key node and KEGG pathway analyses revealed that mTORC1 pathway is activated in DYRK2-depleted cells. Everolimus was more effective in DYRK2-depleted cells compared with control cells. In xenograft model, everolimus treatment significantly inhibited tumor growth compared with vehicle or eribulin treatment. In clinical analysis, patients with low DYRK2 expression acquired longer treatment period and had higher clinical benefit rate than those with high DYRK2 expression (171 vs 82 days; P < 0.05 and 50% vs 12.5%, respectively). We further investigated the underlying mechanism by which DYRK2 regulates mTORC1 pathway. The ectopic expression of DYRK2 promoted phosphorylation of Thr631 for the ubiquitination and degradation of mTOR. DYRK2 expression levels may thus predict clinical responses to everolimus.

Dysregulation of Aromatase in Breast, Endometrial, and Ovarian Cancers: An Overview of Therapeutic Strategies

Aromatase is the rate-limiting enzyme in the biosynthesis of estrogens, which play crucial roles on a spectrum of developmental and physiological processes. The biological actions of estrogens are classically mediated by binding to two estrogen receptors (ERs), ERα and ERβ. Encoded by the cytochrome P450, family 19, subfamily A, polypeptide 1 (CYP19A1) gene, aromatase is expressed in a wide variety of tissues, as well as benign and malignant tumors, and is regulated in a pathway- and tissue-specific manner. Overexpression of aromatase, leading to elevated systemic levels of estrogen, is unequivocally linked to the pathogenesis and growth of a number malignancies, including breast, endometrium, and ovarian cancers. Aromatase inhibitors (AIs) are routinely used to treat estrogen-dependent breast cancers in postmenopausal women; however, their roles in endometrial and ovarian cancers remain obscure. While AI therapy is effective in hormone sensitive cancers, they diminish estrogen production throughout the body and, thus, generate undesirable side effects. Despite the effectiveness of AI therapy, resistance to endocrine therapy remains a major concern and is the leading cause of cancer death. Considerable advances, toward mitigating these issues, have evolved in conjunction with a number of histone deacetylase (HDAC) inhibitors for countering an assortment of diseases and cancers, including the aforesaid malignancies. HDACs are a family of enzymes that are frequently dysregulated in human tumors. This chapter will discuss the current understanding of aberrant regulation and expression of aromatase in breast, endometrial, and ovarian cancers, and potential therapeutic strategies for prevention and treatment of these life-threatening diseases.

Everolimus downregulates estrogen receptor and induces autophagy in aromatase inhibitor-resistant breast cancer cells

Background

mTOR inhibition of aromatase inhibitor (AI)-resistant breast cancer is currently under evaluation in the clinic. Everolimus/RAD001 (Afinitor®) has had limited efficacy as a solo agent but is projected to become part of combination therapy for AI-resistant breast cancer. This study was conducted to investigate the anti-proliferative and resistance mechanisms of everolimus in AI-resistant breast cancer cells.

Methods

In this study we utilized two AI-resistant breast cancer cell lines, MCF-7:5C and MCF-7:2A, which were clonally derived from estrogen receptor positive (ER+) MCF-7 breast cancer cells following long-term estrogen deprivation. Cell viability assay, colony formation assay, cell cycle analysis and soft agar anchorage-independent growth assay were used to determine the efficacy of everolimus in inhibiting the proliferation and tumor forming potential of MCF-7, MCF-7:5C, MCF-7:2A and MCF10A cells. Confocal microscopy and transmission electron microscopy were used to evaluate LC3-II production and autophagosome formation, while ERE-luciferase reporter, Western blot, and RT-PCR analyses were used to assess ER expression and transcriptional activity.

Results

Everolimus inhibited the proliferation of MCF-7:5C and MCF-7:2A cells with relatively equal efficiency to parental MCF-7 breast cancer cells. The inhibitory effect of everolimus was due to G1 arrest as a result of downregulation of cyclin D1 and p21. Everolimus also dramatically reduced estrogen receptor (ER) expression (mRNA and protein) and transcriptional activity in addition to the ER chaperone, heat shock protein 90 protein (HSP90). Everolimus restored 4-hydroxy-tamoxifen (4OHT) sensitivity in MCF-7:5C cells and enhanced 4OHT sensitivity in MCF-7 and MCF-7:2A cells. Notably, we found that autophagy is one method of everolimus insensitivity in MCF-7 breast cancer cell lines.

Conclusion

This study provides additional insight into the mechanism(s) of action of everolimus that can be used to enhance the utility of mTOR inhibitors as part of combination therapy for AI-resistant breast cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2490-z) contains supplementary material, which is available to authorized users.

Effects of letrozole on breast cancer micro-metastatic tumor growth in bone and lung in mice inoculated with murine 4T1 cells

Breast cancer (BC) is the leading cancer in women worldwide. Metastasis occurs in stage IV BC with bone and lung being common metastatic sites. Here we evaluate the effects of the aromatase inhibitor letrozole on BC micro-metastatic tumor growth in bone and lung metastasis in intact and ovariectomized (OVX) mice with murine estrogen receptor negative (ER-) BC cells inoculated in tibia. Forty-eight BALB/c mice were randomly assigned to one of four groups: OVX, OVX + Letrozole, Intact, and Intact + Letrozole, and injected with 4T1 cells intra-tibially. Letrozole was subcutaneously injected daily for 23 days at a dose of 1.75 µg/g body weight. Tumor progression was monitored by bioluminescence imaging (BLI). Following necropsy, inoculated tibiae were scanned via µCT and bone response to tumor was scored from 0 (no ectopic mineralization/osteolysis) to 5 (extensive ectopic mineralization/osteolysis). OVX mice had higher tibial pathology scores indicative of more extensive bone destruction than intact mice, irrespective of letrozole treatment. Letrozole decreased serum estradiol levels and reduced lung surface tumor numbers in intact animals. Furthermore, mice receiving letrozole had significantly fewer tumor colonies and fewer proliferative cells in the lung than OVX and intact controls based on H&E and Ki-67 staining, respectively. In conclusion, BC-inoculated OVX animals had higher tibia pathology scores than BC-inoculated intact animals and letrozole reduced BC metastases to lungs. These findings suggest that, by lowering systemic estrogen level and/or by interacting with the host organ, the aromatase inhibitor letrozole has the potential to reduce ER- BC metastasis to lung.

Integrative analyses identify modulators of response to neoadjuvant aromatase inhibitors in patients with early breast cancer

INTRODUCTION

Aromatase inhibitors (AIs) are a vital component of estrogen receptor positive (ER+) breast cancer treatment. De novo and acquired resistance, however, is common. The aims of this study were to relate patterns of copy number aberrations to molecular and proliferative response to AIs, to study differences in the patterns of copy number aberrations between breast cancer samples pre- and post-AI neoadjuvant therapy, and to identify putative biomarkers for resistance to neoadjuvant AI therapy using an integrative analysis approach.

METHODS

Samples from 84 patients derived from two neoadjuvant AI therapy trials were subjected to copy number profiling by microarray-based comparative genomic hybridisation (aCGH, n=84), gene expression profiling (n=47), matched pre- and post-AI aCGH (n=19 pairs) and Ki67-based AI-response analysis (n=39).

RESULTS

Integrative analysis of these datasets identified a set of nine genes that, when amplified, were associated with a poor response to AIs, and were significantly overexpressed when amplified, including CHKA, LRP5 and SAPS3. Functional validation in vitro, using cell lines with and without amplification of these genes (SUM44, MDA-MB134-VI, T47D and MCF7) and a model of acquired AI-resistance (MCF7-LTED) identified CHKA as a gene that when amplified modulates estrogen receptor (ER)-driven proliferation, ER/estrogen response element (ERE) transactivation, expression of ER-regulated genes and phosphorylation of V-AKT murine thymoma viral oncogene homolog 1 (AKT1).

CONCLUSIONS

These data provide a rationale for investigation of the role of CHKA in further models of de novo and acquired resistance to AIs, and provide proof of concept that integrative genomic analyses can identify biologically relevant modulators of AI response.

Use of rodents as models of human diseases

Advances in molecular biology have significantly increased the understanding of the biology of different diseases. However, these discoveries have not yet been fully translated into improved treatments for patients with diseases such as cancers. One of the factors limiting the translation of knowledge from preclinical studies to the clinic has been the limitations of in vivo diseases models. In this brief review, we will discuss the advantages and disadvantages of rodent models that have been developed to simulate human pathologies, focusing in models that employ xenografts and genetic modification. Within the framework of genetically engineered mouse (GEM) models, we will review some of the current genetic strategies for modeling diseases in the mouse and the preclinical studies that have already been undertaken. We will also discuss how recent improvements in imaging technologies may increase the information derived from using these GEMs during early assessments of potential therapeutic pathways. Furthermore, it is interesting to note that one of the values of using a mouse model is the very rapid turnover rate of the animal, going through the process of birth to death in a very short timeframe relative to that of larger mammalian species.

Acquired resistance to endocrine treatments is associated with tumor-specific molecular changes in patient-derived luminal breast cancer xenografts

PURPOSE

Patients with luminal breast cancer (LBC) often become endocrine resistant over time. We investigated the molecular changes associated with acquired hormonoresistances in patient-derived xenografts of LBC.

EXPERIMENTAL DESIGN

Two LBC xenografts (HBCx22 and HBCx34) were treated with different endocrine treatments (ET) to obtain xenografts with acquired resistances to tamoxifen (TamR) and ovariectomy (OvaR). PI3K pathway activation was analyzed by Western blot analysis and IHC and responses to ET combined to everolimus were investigated in vivo. Gene expression analyses were performed by RT-PCR and Affymetrix arrays.

RESULTS

HBCx22 TamR xenograft was cross-resistant to several hormonotherapies, whereas HBCx22 OvaR and HBCx34 TamR exhibited a treatment-specific resistance profile. PI3K pathway was similarly activated in parental and resistant xenografts but the addition of everolimus did not restore the response to tamoxifen in TamR xenografts. In contrast, the combination of fulvestrant and everolimus induced tumor regression in vivo in HBCx34 TamR, where we found a cross-talk between the estrogen receptor (ER) and PI3K pathways. Expression of several ER-controlled genes and ER coregulators was significantly changed in both TamR and OvaR tumors, indicating impaired ER transcriptional activity. Expression changes associated with hormonoresistance were both tumor and treatment specific and were enriched for genes involved in cell growth, cell death, and cell survival.

CONCLUSIONS

PDX models of LBC with acquired resistance to endocrine therapies show a great diversity of resistance phenotype, associated with specific deregulations of ER-mediated gene transcription. These models offer a tool for developing anticancer therapies and to investigate the dynamics of resistance emerging during pharmacologic interventions. Clin Cancer Res; 20(16); 4314-25. ©2014 AACR.

β-D-glucan inhibits endocrine-resistant breast cancer cell proliferation and alters gene expression

Endocrine therapies have been successfully used for breast cancer patients with estrogen receptor α (ERα) positive tumors, but ∼40% of patients relapse due to endocrine resistance. β-glucans are components of plant cell walls that have immunomodulatory and anticancer activity. The objective of this study was to examine the activity of β-D-glucan, purified from barley, in endocrine-sensitive MCF-7 versus endocrine-resistant LCC9 and LY2 breast cancer cells. β-D-glucan dissolved in DMSO but not water inhibited MCF-7 cell proliferation in a concentration-dependent manner as measured by BrdU incorporation with an IC₅₀ of ∼164±12 μg/ml. β-D-glucan dissolved in DMSO inhibited tamoxifen/endocrine-resistant LCC9 and LY2 cell proliferation with IC₅₀ values of 4.6±0.3 and 24.2±1.4 μg/ml, respectively. MCF-10A normal breast epithelial cells showed a higher IC₅₀ ∼464 μg/ml and the proliferation of MDA-MB-231 triple negative breast cancer cells was not inhibited by β-D-glucan. Concentration-dependent increases in the BAX/BCL2 ratio and cell death with β-D-glucan were observed in MCF-7 and LCC9 cells. PCR array analysis revealed changes in gene expression in response to 24-h treatment with 10 or 50 μg/ml β-D-glucan that were different between MCF-7 and LCC9 cells as well as differences in basal gene expression between the two cell lines. Select results were confirmed by quantitative real-time PCR demonstrating that β-D-glucan increased RASSF1 expression in MCF-7 cells and IGFBP3, CTNNB1 and ERβ transcript expression in LCC9 cells. Our data indicate that β-D-glucan regulates breast cancer-relevant gene expression and may be useful for inhibiting endocrine-resistant breast cancer cell proliferation.

Impact of dual mTORC1/2 mTOR kinase inhibitor AZD8055 on acquired endocrine resistance in breast cancer in vitro

Introduction

Upregulation of PI3K/Akt/mTOR signalling in endocrine-resistant breast cancer (BC) has identified mTOR as an attractive target alongside anti-hormones to control resistance. RAD001 (everolimus/Afinitor®), an allosteric mTOR inhibitor, is proving valuable in this setting; however, some patients are inherently refractory or relapse during treatment requiring alternative strategies. Here we evaluate the potential for novel dual mTORC1/2 mTOR kinase inhibitors, exemplified by AZD8055, by comparison with RAD001 in ER + endocrine resistant BC cells.

Methods

In vitro models of tamoxifen (TamR) or oestrogen deprivation resistance (MCF7-X) were treated with RAD001 or AZD8055 alone or combined with anti-hormone fulvestrant. Endpoints included growth, cell proliferation (Ki67), viability and migration, with PI3K/AKT/mTOR signalling impact monitored by Western blotting. Potential ER cross-talk was investigated by immunocytochemistry and RT-PCR.

Results

RAD001 was a poor growth inhibitor of MCF7-derived TamR and MCF7-X cells (IC₅₀ ≥1 μM), rapidly inhibiting mTORC1 but not mTORC2/AKT signalling. In contrast AZD8055, which rapidly inhibited both mTORC1 and mTORC2/AKT activity, was a highly effective (P <0.001) growth inhibitor of TamR (IC₅₀ 18 nM) and MCF7-X (IC₅₀ 24 nM), and of a further T47D-derived tamoxifen resistant model T47D-tamR (IC₅₀ 19 nM). AZD8055 significantly (P <0.05) inhibited resistant cell proliferation, increased cell death and reduced migration. Furthermore, dual treatment of TamR or MCF7-X cells with AZD8055 plus fulvestrant provided superior control of resistant growth versus either agent alone (P <0.05). Co-treating with AZD8055 alongside tamoxifen (P <0.01) or oestrogen deprivation (P <0.05) also effectively inhibited endocrine responsive MCF-7 cells. Although AZD8055 inhibited oestrogen receptor (ER) ser167 phosphorylation in TamR and MCF7-X, it had no effect on ER ser118 activity or expression of several ER-regulated genes, suggesting the mTOR kinase inhibitor impact was largely ER-independent. The capacity of AZD8055 for ER-independent activity was further evidenced by growth inhibition (IC₅₀18 and 20 nM) of two acquired fulvestrant resistant models lacking ER.

Conclusions

This is the first report demonstrating dual mTORC1/2 mTOR kinase inhibitors have potential to control acquired endocrine resistant BC, even under conditions where everolimus fails. Such inhibitors may prove of particular benefit when used alongside anti-hormonal treatment as second-line therapy in endocrine resistant disease, and also potentially alongside anti-hormones during the earlier endocrine responsive phase to hinder development of resistance.

Targeting receptor tyrosine kinases in HER2-negative breast cancer

PURPOSE OF REVIEW

The targeting of receptor tyrosine kinases (RTKs) has been a major area for breast cancer therapy, exemplified by the targeting of HER2-amplified breast cancer.

RECENT FINDINGS

We review the data on the activation of RTKs in HER2-negative breast cancer, and discuss the clinical translational challenge of identifying cancers that are reliant on a specific kinase for growth and survival. Substantial evidence suggests that subsets of breast cancer may be reliant on specific kinases, and that this could be exploited therapeutically. The heterogeneity of breast cancer, however, and the potential for adaptive switching between RTKs after inhibition of a single RTK, present challenges to targeting individual RTKs in the clinic

SUMMARY

Targeting of RTKs in HER2-negative breast cancer presents a major therapeutic opportunity in breast cancer, although robust selection strategies will be required to identify cancers with activation of specific RTKs if this potential is to be realized.