Met induces diverse mammary carcinomas in mice and is associated with human basal breast cancer

Suppression of TNBC metastasis by doxazosin, a novel dual inhibitor of c-MET/EGFR

BACKGROUND

Triple-negative breast cancer (TNBC) is characterized by aggressive growth and a high propensity for recurrence and metastasis. Simultaneous overexpression of c-MET and EGFR in TNBC is associated with worse clinicopathological features and unfavorable outcomes. Although the development of new c-MET inhibitors and the emergence of 3rd-generation EGFR inhibitors represent promising treatment options, the high costs involved limit the accessibility of these drugs. In the present study, we sought to investigate the therapeutic potential of doxazosin (DOXA), a generic drug for benign prostate hyperplasia, in targeting TNBC.

METHODS

The effect of DOXA on TNBC cell lines in vitro was evaluated in terms of cell viability, apoptosis, c-MET/EGFR signaling pathway, molecular docking studies and impact on cancer stem cell (CSC)-like properties. An in vivo metastatic model with CSCs was used to evaluate the efficacy of DOXA.

RESULTS

DOXA exhibits notable anti-proliferative effects on TNBC cells by inducing apoptosis via caspase activation. Molecular docking studies revealed the direct interaction of DOXA with the tyrosine kinase domains of c-MET and EGFR. Consequently, DOXA disrupts important survival pathways including AKT, MEK/ERK, and JAK/STAT3, while suppressing CSC-like characteristics including CD44high/CD24low subpopulations, aldehyde dehydrogenase 1 (ALDH1) activity and formation of mammospheres. DOXA administration was found to suppress tumor growth, intra- and peri-tumoral angiogenesis and distant metastasis in an orthotopic allograft model with CSC-enriched populations. Furthermore, no toxic effects of DOXA were observed in hepatic or renal function.

CONCLUSIONS

Our findings highlight the potential of DOXA as a therapeutic option for metastatic TNBC, warranting further investigation.

Ecdysoneless Overexpression Drives Mammary Tumorigenesis through Upregulation of C-MYC and Glucose Metabolism

Ecdysoneless (ECD) protein is essential for embryogenesis, cell-cycle progression, and cellular stress mitigation with an emerging role in mRNA biogenesis. We have previously shown that ECD protein as well as its mRNA are overexpressed in breast cancer and ECD overexpression predicts shorter survival in patients with breast cancer. However, the genetic evidence for an oncogenic role of ECD has not been established. Here, we generated transgenic mice with mammary epithelium-targeted overexpression of an inducible human ECD transgene (ECDTg). Significantly, ECDTg mice develop mammary hyperplasia, preneoplastic lesions, and heterogeneous tumors with occasional lung metastasis. ECDTg tumors exhibit epithelial to mesenchymal transition and cancer stem cell characteristics. Organoid cultures of ECDTg tumors showed ECD dependency for in vitro oncogenic phenotype and in vivo growth when implanted in mice. RNA sequencing (RNA-seq) analysis of ECDTg tumors showed a c-MYC signature, and alterations in ECD levels regulated c-MYC mRNA and protein levels as well as glucose metabolism. ECD knockdown-induced decrease in glucose uptake was rescued by overexpression of mouse ECD as well as c-MYC. Publicly available expression data analyses showed a significant correlation of ECD and c-MYC overexpression in breast cancer, and ECD and c-MYC coexpression exhibits worse survival in patients with breast cancer. Taken together, we establish a novel role of overexpressed ECD as an oncogenesis driver in the mouse mammary gland through upregulation of c-MYC-mediated glucose metabolism.

IMPLICATIONS

We demonstrate ECD overexpression in the mammary gland of mice led to the development of a tumor progression model through upregulation of c-MYC signaling and glucose metabolism.

Racial differences in breast cancer outcomes by hepatocyte growth factor pathway expression

PURPOSE

Black women have a 40% increased risk of breast cancer-related mortality. These outcome disparities may reflect differences in tumor pathways and a lack of targetable therapies for specific subtypes that are more common in Black women. Hepatocyte growth factor (HGF) is a targetable pathway that promotes breast cancer tumorigenesis, is associated with basal-like breast cancer, and is differentially expressed by race. This study assessed whether a 38-gene HGF expression signature is associated with recurrence and survival in Black and non-Black women.

METHODS

Study participants included 1957 invasive breast cancer cases from the Carolina Breast Cancer Study. The HGF signature was evaluated in association with recurrence (n = 1251, 171 recurrences), overall, and breast cancer-specific mortality (n = 706, 190/328 breast cancer/overall deaths) using Cox proportional hazard models.

RESULTS

Women with HGF-positive tumors had higher recurrence rates [HR 1.88, 95% CI (1.19, 2.98)], breast cancer-specific mortality [HR 1.90, 95% CI (1.26, 2.85)], and overall mortality [HR 1.69; 95% CI (1.17, 2.43)]. Among Black women, HGF positivity was significantly associated with higher 5-year rate of recurrence [HR 1.73; 95% CI (1.01, 2.99)], but this association was not significant in non-Black women [HR 1.68; 95% CI (0.72, 3.90)]. Among Black women, HGF-positive tumors had elevated breast cancer-specific mortality [HR 1.80, 95% CI (1.05, 3.09)], which was not significant in non-Black women [HR 1.52; 95% CI (0.78, 2.99)].

CONCLUSION

This multi-gene HGF signature is a poor-prognosis feature for breast cancer and may identify patients who could benefit from HGF-targeted treatments, an unmet need for Black and triple-negative patients.

Therapeutic Targeting of Stromal-Tumor HGF-cMET Signaling in an Organotypic Triple Negative Breast Tumor Model

The tumor microenvironment (TME) promotes proliferation, drug resistance, and invasiveness of cancer cells. Therapeutic targeting of the TME is an attractive strategy to improve outcomes for patients, particularly in aggressive cancers such as triple negative breast cancer (TNBC) that have a rich stroma and limited targeted therapies. However, lack of preclinical human tumor models for mechanistic understanding of tumor-stromal interactions has been an impediment to identify effective treatments against the TME. To address this need, we developed a three-dimensional (3D) organotypic tumor model to study interactions of patient-derived cancer-associated fibroblasts (CAFs) with TNBC cells and explore potential therapy targets. We found that CAFs predominantly secreted hepatocyte growth factor (HGF) and activated MET receptor tyrosine kinase in TNBC cells. This tumor-stromal interaction promoted invasiveness, epithelial-to-mesenchymal transition, and activities of multiple oncogenic pathways in TNBC cells. Importantly, we established that TNBC cells become resistant to monotherapy and demonstrated a design-driven approach to select drug combinations that effectively inhibit pro-metastatic functions of TNBC cells. Our study also showed that HGF-MET from lung fibroblasts promotes colony formation by TNBC cells, suggesting that blocking HGF-MET signaling potentially could target both primary TNBC tumorigenesis and lung metastasis. Overall, we established the utility of our organotypic tumor model to identify and therapeutically target specific mechanisms of tumor-stromal interactions in TNBC toward the goal of developing targeted therapies against the TME. Implications: Leveraging a state-of-the-art organotypic tumor model, we demonstrated that CAFs-mediated HGF-MET signaling drive tumorigenic activities in TNBC and presents a therapeutic target.

Effects of Pubertal Exposure to Butyl Benzyl Phthalate, Perfluorooctanoic Acid, and Zeranol on Mammary Gland Development and Tumorigenesis in Rats

Endocrine-disrupting chemicals (EDCs)—including butyl benzyl phthalate (BBP), perfluorooctanoic acid (PFOA), and zeranol (α-ZAL, referred to as ZAL hereafter)—can interfere with the endocrine system and produce adverse effects. It remains unclear whether pubertal exposure to low doses of BBP, PFOA, and ZAL has an impact on breast development and tumorigenesis. We exposed female Sprague Dawley rats to BBP, PFOA, or ZAL through gavage for 21 days, starting on day 21, and analyzed their endocrine organs, serum hormones, mammary glands, and transcriptomic profiles of the mammary glands at days 50 and 100. We also conducted a tumorigenesis study for rats treated with PFOA and ZAL using a 7,12-dimethylbenz[a]anthracene (DMBA) model. Our results demonstrated that pubertal exposure to BBP, PFOA, and ZAL affected endocrine organs and serum hormones, and induced phenotypic and transcriptomic changes. The exposure to PFOA + ZAL induced the most phenotypic and transcriptomic changes in the mammary gland. PFOA + ZAL downregulated the expression of genes related to development at day 50, whereas it upregulated genes associated with tumorigenesis at day 100. PFOA + ZAL exposure also decreased rat mammary tumor latency, reduced the overall survival of rats after DMBA challenge, and affected the histopathology of mammary tumors. Therefore, our study suggests that exposure to low doses of EDCs during the pubertal period could induce changes in the endocrine system and mammary gland development in rats. The inhibition of mammary gland development by PFOA + ZAL might increase the risk of developing mammary tumors through activation of signaling pathways associated with tumorigenesis.

Evidence That the Etiology of Congenital Hypopituitarism Has a Major Genetic Component but Is Infrequently Monogenic

Purpose

Congenital hypopituitarism usually occurs sporadically. In most patients, the etiology remains unknown.

Methods

We studied 13 children with sporadic congenital hypopituitarism. Children with non-endocrine, non-familial idiopathic short stature (NFSS) (n = 19) served as a control group. Exome sequencing was performed in probands and both unaffected parents. A burden testing approach was used to compare the number of candidate variants in the two groups.

Results

First, we assessed the frequency of rare, predicted-pathogenic variants in 42 genes previously reported to be associated with pituitary gland development. The average number of variants per individual was greater in probands with congenital hypopituitarism than those with NFSS (1.1 vs. 0.21, mean variants/proband, P = 0.03). The number of probands with at least 1 variant in a pituitary-associated gene was greater in congenital hypopituitarism than in NFSS (62% vs. 21%, P = 0.03). Second, we assessed the frequency of rare, predicted-pathogenic variants in the exome (to capture undiscovered causes) that were inherited in a fashion that could explain the sporadic occurrence of the proband's condition with a monogenic etiology (de novo mutation, autosomal recessive, or X-linked recessive) with complete penetrance. There were fewer monogenic candidates in the probands with congenital hypopituitarism than those with NFSS (1.3 vs. 2.5 candidate variants/proband, P = 0.024). We did not find any candidate variants (0 of 13 probands) in genes previously reported to explain the phenotype in congenital hypopituitarism, unlike NFSS (8 of 19 probands, P = 0.01).

Conclusion

Our findings provide evidence that the etiology of sporadic congenital hypopituitarism has a major genetic component but may be infrequently monogenic with full penetrance, suggesting a more complex etiology.

Quantitative Tyrosine Phosphoproteome Profiling of AXL Receptor Tyrosine Kinase Signaling Network

Simple Summary

AXL is a receptor tyrosine kinase belonging to the TAM (Tyro3, Axl and Mer) family. The AXL protein plays an important role in promoting cancer development, such as proliferation, migration, invasion and survival of cancer cells. In this study, we used mass spectrometry-based proteomics to quantify the cancer signaling regulated by AXL activation. Our study identified more than 1000 phosphotyrosine sites and discovered that activation of AXL can upregulate multiple cancer-promoting and cell migration/invasion-related signaling pathways. We also observed significant crosstalk as evidenced by rapid phosphorylation of multiple receptor tyrosine kinases and protein tyrosine phosphatases, including PTPN11 and PTPRA, upon GAS6 stimulation. These discoveries should serve as a potentially useful resource for studying AXL functions as well as for the development of effective therapeutic options to target AXL.

Abstract

Overexpression and amplification of AXL receptor tyrosine kinase (RTK) has been found in several hematologic and solid malignancies. Activation of AXL can enhance tumor-promoting processes such as cancer cell proliferation, migration, invasion and survival. Despite the important role of AXL in cancer development, a deep and quantitative mapping of its temporal dynamic signaling transduction has not yet been reported. Here, we used a TMT labeling-based quantitative proteomics approach to characterize the temporal dynamics of the phosphotyrosine proteome induced by AXL activation. We identified >1100 phosphotyrosine sites and observed a widespread upregulation of tyrosine phosphorylation induced by GAS6 stimulation. We also detected several tyrosine sites whose phosphorylation levels were reduced upon AXL activation. Gene set enrichment-based pathway analysis indicated the activation of several cancer-promoting and cell migration/invasion-related signaling pathways, including RAS, EGFR, focal adhesion, VEGFR and cytoskeletal rearrangement pathways. We also observed a rapid induction of phosphorylation of protein tyrosine phosphatases, including PTPN11 and PTPRA, upon GAS6 stimulation. The novel molecules downstream of AXL identified in this study along with the detailed global quantitative map elucidating the temporal dynamics of AXL activation should not only help understand the oncogenic role of AXL, but also aid in developing therapeutic options to effectively target AXL.

Hepatocyte growth factor pathway expression in breast cancer by race and subtype

BACKGROUND

African American women have the highest risk of breast cancer mortality compared to other racial groups. Differences in tumor characteristics have been implicated as a possible cause; however, the tumor microenvironment may also contribute to this disparity in mortality. Hepatocyte growth factor (HGF) is a stroma-derived marker of the tumor microenvironment that may affect tumor progression differentially by race.

OBJECTIVE

To examine whether an HGF gene expression signature is differentially expressed by race and tumor characteristics.

METHODS

Invasive breast tumors from 1957 patients were assessed for a 38-gene RNA-based HGF gene expression signature. Participants were black (n = 1033) and non-black (n = 924) women from the population-based Carolina Breast Cancer Study (1993-2013). Generalized linear models were used to estimate the relative frequency differences (RFD) in HGF status by race, clinical, and demographic factors.

RESULTS

Thirty-two percent of tumors were positive for the HGF signature. Black women were more likely [42% vs. 21%; RFD = + 19.93% (95% CI 16.00, 23.87)] to have HGF-positive tumors compared to non-black women. Triple-negative patients had a higher frequency of HGF positivity [82% vs. 13% in non-triple-negative; RFD = + 65.85% (95% CI 61.71, 69.98)], and HGF positivity was a defining feature of basal-like subtype [92% vs. 8% in non-basal; RFD = + 81.84% (95% CI 78.84, 84.83)]. HGF positivity was associated with younger age, stage, higher grade, and high genomic risk of recurrence (ROR-PT) score.

CONCLUSION

HGF expression is a defining feature of basal-like tumors, and its association with black race and young women suggests it may be a candidate pathway for understanding breast cancer disparities.

Phospho-Ser784-VCP Is Required for DNA Damage Response and Is Associated with Poor Prognosis of Chemotherapy-Treated Breast Cancer

Spatiotemporal protein reorganization at DNA damage sites induced by genotoxic chemotherapies is crucial for DNA damage response (DDR), which influences treatment response by directing cancer cell fate. This process is orchestrated by valosin-containing protein (VCP), an AAA+ ATPase that extracts polyubiquinated chromatin proteins and facilitates their turnover. However, because of the essential and pleiotropic effects of VCP in global proteostasis, it remains challenging practically to understand and target its DDR-specific functions. We describe a DNA-damage-induced phosphorylation event (Ser⁷⁸⁴), which selectively enhances chromatin-associated protein degradation mediated by VCP and is required for DNA repair, signaling, and cell survival. These functional effects of Ser⁷⁸⁴ phosphorylation on DDR correlate with a decrease in VCP association with chromatin, cofactors NPL4/UFD1, and polyubiquitinated substrates. Clinically, high phospho-Ser⁷⁸⁴-VCP levels are significantly associated with poor outcome among chemotherapy-treated breast cancer patients. Thus, Ser⁷⁸⁴ phosphorylation is a DDR-specific enhancer of VCP function and a potential predictive biomarker for chemotherapy treatments.

Modeling Heterogeneity of Triple-Negative Breast Cancer Uncovers a Novel Combinatorial Treatment Overcoming Primary Drug Resistance

Triple-negative breast cancer (TNBC) is a highly aggressive breast cancer subtype characterized by a remarkable molecular heterogeneity. Currently, there are no effective druggable targets and advanced preclinical models of the human disease. Here, a unique mouse model (MMTV-R26Met mice) of mammary tumors driven by a subtle increase in the expression of the wild-type MET receptor is generated. MMTV-R26Met mice develop spontaneous, exclusive TNBC tumors, recapitulating primary resistance to treatment of patients. Proteomic profiling of MMTV-R26Met tumors and machine learning approach show that the model faithfully recapitulates intertumoral heterogeneity of human TNBC. Further signaling network analysis highlights potential druggable targets, of which cotargeting of WEE1 and BCL-XL synergistically kills TNBC cells and efficiently induces tumor regression. Mechanistically, BCL-XL inhibition exacerbates the dependency of TNBC cells on WEE1 function, leading to Histone H3 and phosphoS33RPA32 upregulation, RRM2 downregulation, cell cycle perturbation, mitotic catastrophe, and apoptosis. This study introduces a unique, powerful mouse model for studying TNBC formation and evolution, its heterogeneity, and for identifying efficient therapeutic targets.

Overexpression of HGF/MET axis along with p53 inhibition induces de novo glioma formation in mice

Background

Aberrant MET receptor tyrosine kinase (RTK) activation leads to invasive tumor growth in different types of cancer. Overexpression of MET and its ligand hepatocyte growth factor (HGF) occurs more frequently in glioblastoma (GBM) than in low-grade gliomas. Although we have shown previously that HGF-autocrine activation predicts sensitivity to MET tyrosine kinase inhibitors (TKIs) in GBM, whether it initiates tumorigenesis remains elusive.

Methods

Using a well-established Sleeping Beauty (SB) transposon strategy, we injected human HGF and MET cDNA together with a short hairpin siRNA against Trp53 (SB-hHgf.Met.ShP53) into the lateral ventricle of neonatal mice to induce spontaneous glioma initiation and characterized the tumors with H&E and immunohistochemistry analysis. Glioma sphere cells also were isolated for measuring the sensitivity to specific MET TKIs.

Results

Mixed injection of SB-hHgf.Met.ShP53 plasmids induced de novo glioma formation with invasive tumor growth accompanied by HGF and MET overexpression. While glioma stem cells (GSCs) are considered as the tumor-initiating cells in GBM, both SB-hHgf.Met.ShP53 tumor sections and glioma spheres harvested from these tumors expressed GSC markers nestin, GFAP, and Sox 2. Moreover, specific MET TKIs significantly inhibited tumor spheres' proliferation and MET/MAPK/AKT signaling.

Conclusions

Overexpression of the HGF/MET axis along with p53 attenuation may transform neural stem cells into GSCs, resulting in GBM formation in mice. These tumors are primarily driven by the MET RTK pathway activation and are sensitive to MET TKIs. The SB-hHgf.Met.ShP53 spontaneous mouse glioma model provides a useful tool for studying GBM tumor biology and MET-targeting therapeutics.

Targeting c-Met in triple negative breast cancer: preclinical studies using the c-Met inhibitor, Cpd A

Introduction Triple negative breast cancer (TNBC) represents a heterogeneous subtype of breast cancer that carries a poorer prognosis. There remains a need to identify novel drivers of TNBC, which may represent targets to treat the disease. c-Met overexpression is linked with decreased survival and is associated with the basal subtype of breast cancer. Cpd A, a kinase inhibitor selective/specific for Met kinase has demonstrated preclinical anti-cancer efficacy in TNBC. We aimed to assess the anti-cancer efficacy of Cpd A when combined with Src kinase, ErbB-family or hepatocyte growth factor (HGF) inhibitors in TNBC cell lines. Methods We determined the anti-proliferative effects of Cpd A, rilotumumab, neratinib and saracatinib tested alone and in combination in a panel of TNBC cells by acid phosphatase assays. We performed reverse phase protein array analysis of c-Met and IGF1Rβ expression and phosphorylation of c-Met (Y1234/1235) in TNBC cells and correlated their expression/phosphorylation with Cpd A sensitivity. We examined the impact of Cpd A, neratinib and saracatinib tested alone and in combination on invasive potential and colony formation.Results TNBC cells are not inherently sensitive to Cpd A, and neither c-Met expression nor phosphorylation are biomarkers of sensitivity to Cpd A. Cpd A enhanced the anti-proliferative effects of neratinib in vitro; however, this effect was limited to cell lines with innate sensitivity to Cpd A. Cpd A had limited anti-invasive effects but it reduced colony formation in the TNBC cell line panel.Conclusions Despite Cpd A having a potential role in reducing cancer cell metastasis, identification of strong predictive biomarkers of c-Met sensitivity would be essential to the development of a c-Met targeted treatment for an appropriately selected cohort of TNBC patients.

RON and MET Co-overexpression Are Significant Pathological Characteristics of Poor Survival and Therapeutic Targets of Tyrosine Kinase Inhibitors in Triple-Negative Breast Cancer

Purpose

Triple-negative breast cancer (TNBC) is highly malignant and has poor prognosis and a high mortality rate. The lack of effective therapy has spurred our investigation of new targets for treating this malignant cancer. Here, we identified RON (macrophage-stimulating 1 receptor) and MET (MET proto-oncogene, receptor tyrosine kinase) as a prognostic biomarker and therapeutic targets for potential TNBC treatment.

Materials and Methods

We analyzed RON and MET expression in 187 primary TNBC clinical samples with immunohistochemistry. We validated the targeted therapeutic effects of RON and MET in TNBC using three tyrosine kinase inhibitors (TKIs): BMS-777607, INCB28060, and tivantinib. The preclinical therapeutic efficacy of the TKIs was mainly estimated using a TNBC xenograft model.

Results

Patients with TNBC had widespread, abnormal expression of RON and MET. There was RON overexpression, MET overexpression, and RON and MET co-overexpression in 63 (33.7%), 63 (33.7%), and 43 cases (23.0%), respectively, which had poor prognosis and short survival. In vivo, the TKI targeting RON ant MET inhibited the activation of the downstream signaling molecules, inhibited TNBC cell migration and proliferation, and increased TNBC cell apoptosis; in the xenograft model, they significantly inhibited tumor growth and shrank tumor volumes. The TKI targeting RON and Met, such as BMS-777607 and tivantinib, yielded stronger anti-tumor effects than INCB28060.

Conclusion

RON and MET co-overexpression can be significant pathological characteristics in TNBC for poor prognosis. TKIs targeting RON and MET have stronger drug development potential for treating TNBC.

A Phase Ib/II Study of Ramucirumab in Combination with Emibetuzumab in Patients with Advanced Cancer

PURPOSE

Inhibition of the VEGFR-2 blocks angiogenesis and attenuates tumor growth, but cancers may evade this effect through activation of the hepatocyte growth factor receptor MET. Here we report results of the phase Ib/II study of ramucirumab, a monoclonal anti-VEGFR-2 antibody, plus the anti-MET mAb emibetuzumab.

PATIENTS AND METHODS

A 3+3 dose escalation of emibetuzumab plus ramucirumab (phase Ib) was followed by tumor-specific expansion cohorts. Primary objectives were to determine the recommended phase II dose and to evaluate antitumor activity. Secondary objectives included safety, pharmacokinetics, and immunogenicity. Tumoral MET expression was explored by immunohistochemistry (IHC).

RESULTS

A total of 97 patients with solid tumor [6 phase Ib, 16 gastric or gastroesophageal junction adenocarcinoma, 45 hepatocellular carcinoma (HCC), 15 renal cell carcinoma, and 15 non-small lung cancer] received emibetuzumab at 750 or 2,000 mg flat dosing plus ramucirumab at 8 mg/kg every 2 weeks. No dose-limiting toxicities were observed. Common adverse events were primarily mild or moderate and included fatigue (36.1%), peripheral edema (28.9%), and nausea (14.4%). Emibetuzumab exposures were similar as in previous studies with no apparent drug-drug interactions. Five partial responses (5.2%) were observed across all tumor types. The greatest antitumor activity was noted in HCC with a 6.7% overall response rate, 60% disease control rate, and 5.42 months (95% confidence interval, 1.64-8.12) progression-free survival (PFS). HCC with high MET expression showed improved PFS with approximately 3-fold increase in PFS (8.1 vs. 2.8 months) relative to low MET expression.

CONCLUSIONS

Ramucirumab plus emibetuzumab was safe and exhibited cytostatic antitumor activity. MET expression may help to select patients benefitting most from this combination treatment in select tumor types.

p53 controls the plasticity of mammary luminal progenitor cells downstream of Met signaling

Background

The adult mammary epithelium is composed of basal and luminal cells. The luminal lineage comprises two major cell populations, positive and negative for estrogen and progesterone receptors (ER and PR, respectively), both containing clonogenic progenitor cells. Deregulated ER/PR⁻ luminal progenitor cells are suspected to be at the origin of basal-type triple-negative (TNBC) breast cancers, a subtype frequently associated with loss of P53 function and MET signaling hyperactivation. Using mouse models, we recently reported that p53 restricts luminal progenitor cell amplification whereas paracrine Met activation stimulates their growth and favors a luminal-to-basal switch. Here, we analyzed how these two critical pathways interact to control luminal progenitor function.

Methods

We have (i) established and analyzed the gene expression profile of luminal progenitors isolated by ICAM-1, a robust surface marker we previously identified; (ii) purified luminal progenitors from p53-deficient and p53-proficient mouse mammary epithelium to compare their functional and molecular characteristics; and (iii) analyzed their response to HGF, the major Met ligand, in three-dimensional cultures.

Results

We found that luminal progenitors, compared to non-clonogenic luminal cells, overexpress Trp53 and numerous p53 target genes. In vivo, loss of Trp53 induced the expansion of luminal progenitors, affecting expression of several important p53 target genes including those encoding negative regulators of cell cycle progression. Consistently, p53-deficient luminal progenitors displayed increased proliferative and self-renewal activities in culture. However, they did not exhibit perturbed expression of luminal-specific markers and major regulators, such as Hey1, Elf5, and Gata3. Moreover, although expressing Met at higher level than p53-proficient luminal progenitors, p53-deficient luminal progenitors failed to acquire basal-specific features when stimulated by HGF, showing that p53 promotes the plastic behavior of luminal progenitors downstream of Met activation.

Conclusions

Our study reveals a crosstalk between Met- and p53-mediated signaling pathways in the regulation of luminal progenitor function. In particular, it shows that neither p53 loss alone nor p53 loss combined with Met signaling activation caused an early detectable cell fate alteration in luminal progenitors. Conceivably, additional events are required to confer basal-specific characteristics to luminal-derived TNBCs.

Electronic supplementary material

The online version of this article (10.1186/s13058-019-1101-8) contains supplementary material, which is available to authorized users.

microRNA Regulation in Estrogen Receptor-Positive Breast Cancer and Endocrine Therapy

As de novo and acquired resistance to standard first line endocrine therapies is a growing clinical challenge for estrogen receptor-positive (ER⁺) breast cancer patients, understanding the mechanisms of resistance is critical to develop novel therapeutic strategies to prevent therapeutic resistance and improve patient outcomes. The widespread post-transcriptional regulatory role that microRNAs (miRNAs) can have on various oncogenic pathways has been well-documented. In particular, several miRNAs are reported to suppress ERα expression via direct binding with the 3’ UTR of ESR1 mRNA, which can confer resistance to estrogen/ERα-targeted therapies. In turn, estrogen/ERα activation can modulate miRNA expression, which may contribute to ER⁺ breast carcinogenesis. Given the reported oncogenic and tumor suppressor functions of miRNAs in ER⁺ breast cancer, the targeted regulation of specific miRNAs is emerging as a promising strategy to treat ER⁺ breast cancer and significantly improve patient responsiveness to endocrine therapies. In this review, we highlight the major miRNA-ER regulatory mechanisms in context with ER⁺ breast carcinogenesis, as well as the critical miRNAs that contribute to endocrine therapy resistance or sensitivity. Collectively, this comprehensive review of the current literature sheds light on the clinical applications and challenges associated with miRNA regulatory mechanisms and novel miRNA targets that may have translational value as potential therapeutics for the treatment of ER⁺ breast cancer.

TGFβ1 regulates HGF-induced cell migration and hepatocyte growth factor receptor MET expression via C-ets-1 and miR-128-3p in basal-like breast cancer

Breast cancer is the most common cancer in women worldwide. The tumor microenvironment contributes to tumor progression by inducing cell dissemination from the primary tumor and metastasis. TGFβ signaling is involved in breast cancer progression and is specifically elevated during metastatic transformation in aggressive breast cancer. In this study, we performed genomewide correlation analysis of TGFBR2 expression in a panel of 51 breast cancer cell lines and identified that MET is coregulated with TGFBR2. This correlation was confirmed at the protein level in breast cancer cell lines and human tumor tissues. Flow cytometric analysis of luminal and basal‐like breast cancer cell lines and examination of 801 tumor specimens from a prospective cohort of breast cancer patients using reverse phase protein arrays revealed that expression of TGFBR2 and MET is increased in basal‐like breast cancer cell lines, as well as in triple‐negative breast cancer tumor tissues, compared to other subtypes. Using real‐time cell analysis technology, we demonstrated that TGFβ1 triggered hepatocyte growth factor (HGF)‐induced and MET‐dependent migration in vitro. Bioinformatic analysis predicted that TGFβ1 induces expression of C‐ets‐1 as a candidate transcription factor regulating MET expression. Indeed, TGFβ1‐induced expression of ETS1 and breast cancer cell migration was blocked by knockdown of ETS1. Further, we identified that MET is a direct target of miR‐128‐3p and that this miRNA is negatively regulated by TGFβ1. Overexpression of miR‐128‐3p reduced MET expression and abrogated HGF‐induced cell migration of invasive breast cancer cells. In conclusion, we have identified that TGFβ1 regulates HGF‐induced and MET‐mediated cell migration, through positive regulation of C‐ets‐1 and negative regulation of miR‐128‐3p expression in basal‐like breast cancer cell lines and in triple‐negative breast cancer tissue.

Known and novel roles of the MET oncogene in cancer: a coherent approach to targeted therapy

The MET oncogene encodes an unconventional receptor tyrosine kinase with pleiotropic functions: it initiates and sustains neoplastic transformation when genetically altered ('oncogene addiction') and fosters cancer cell survival and tumour dissemination when transcriptionally activated in the context of an adaptive response to adverse microenvironmental conditions ('oncogene expedience'). Moreover, MET is an intrinsic modulator of the self-renewal and clonogenic ability of cancer stem cells ('oncogene inherence'). Here, we provide the latest findings on MET function in cancer by focusing on newly identified genetic abnormalities in tumour cells and recently described non-mutational MET activities in stromal cells and cancer stem cells. We discuss how MET drives cancer clonal evolution and progression towards metastasis, both ab initio and under therapeutic pressure. We then elaborate on the use of MET inhibitors in the clinic with a critical appraisal of failures and successes. Ultimately, we advocate a rationale to improve the outcome of anti-MET therapies on the basis of thorough consideration of the entire spectrum of MET-mediated biological responses, which implicates adequate patient stratification, meaningful biomarkers and appropriate clinical end points.

Recalling Cohnheim's Theory: Papillary Renal Cell Tumor as a Model of Tumorigenesis from Impaired Embryonal Differentiation to Malignant Tumors in Adults

We have suggested that papillary renal cell tumor (PRCT) of the kidney arises from nephrogenic rest-like lesions. To approve our hypothesis, we worked up 14 kidneys bearing papillary and 14 ones with conventional renal cell carcinoma (CRCC) histologically and found 42 papillary lesions in average per kidney bearing PRCT. PRCTs are characterized by loss of the Y chromosome and trisomy of chromosomes 7 and 17. The MET and HNF1B are localized to chromosome 7q31 and 17q21 and are frequently amplified in PRCT. We have analyzed the expression of the mutant MET in hereditary PRCTs and precursor lesions and found duplication and expression of the mutated allele. Because both genes are involved in early stage of nephron development, we have analyzed the expression of MET and HNF1B by immunohistochemistry in fetal kidneys, precursor lesions and PRCTs. We detected strong expression of MET and HNF1B in distal compartment of S-shaped body of fetal kidneys and in nephrogenic rest-like precursor lesions. Our finding suggests an association between expression of MET and HNF1B in precursor lesions and development of PRCT. We propose a model involving chromosomal clonal evolution and corresponding gene expression for development of PRCTs from embryonic rests due to impaired differentiation. Our model suggests that PRCT have a natural history distinct from that of most common CRCC.

Prognostic Significance of Mesenchymal-Epithelial Transition in Triple-Negative Breast Cancers

INTRODUCTION

The prognostic value of the mesenchymal-epithelial transition (MET) in triple-negative breast cancers (TNBCs) remains controversial. A meta-analysis of the impact of MET in TNBCs was performed by searching published data.

METHODS

PubMed and Embase databases were searched for eligible literature. The principal outcome measures were hazard ratios (HRs) for recurrence-free survival or overall survival according to MET expression. Combined HRs were calculated using fixed- or random-effects models according to heterogeneity.

RESULTS

Six studies involving 785 patients met our selection criteria. The meta-analysis results showed that MET overexpression was associated with a 1.29-fold increased risk of recurrence (combined HR 1.29; 95% confidence interval, 1.04-1.60; P = .020) in the TNBCs. Three studies provided the related overall survival data (488 cases). The results showed that MET overexpression was associated with a 1.38-fold increased risk of mortality (HR, 1.38; 95% confidence interval, 1.08-1.76; P = .009).

CONCLUSION

MET is an adverse prognostic marker for TNBCs. The results strengthen the rationale for targeted therapy of TNBCs using MET inhibitors in future clinical trials.

Metformin Targets Glucose Metabolism in Triple Negative Breast Cancer

Metformin is the most widely administered anti-diabetic agent worldwide. In patients receiving metformin for metabolic syndrome or diabetes, it reduces the incidence and improves the survival of breast cancer (BC) patients. We have previously shown that metformin is particularly potent against triple negative breast cancer (TNBC), with a reduction of proliferation, oncogenicity and motility, inhibition of pro-oncogenic signaling pathways and induction of apoptosis. These BCs are well recognized to be highly dependent on glucose/glucosamine (metabolized through anaerobic glycolysis) and lipids, which are metabolized for the production of energy and cellular building blocks to sustain a high rate of proliferation. We have previously demonstrated that metformin inhibits lipid metabolism, specifically targeting fatty acid synthase (FASN), cholesterol biosynthesis and GM1 lipid rafts in TNBC. We also reported that glucose promotes phenotypic aggression and reduces metformin efficacy. We now show that metformin inhibits several key enzymes requisite to glucose metabolism in TNBC, providing additional insight into why metformin is especially toxic to this subtype of BC. Our data suggests that the use of metformin to target key metabolic defects in lipid and carbohydrate metabolism in cancer may be broadly applicable, especially against highly aggressive malignant cells.

Microenvironmental control of breast cancer subtype elicited through paracrine platelet-derived growth factor-CC signaling

Breast tumors of the basal-like, hormone receptor-negative, subtype remain an unmet clinical challenge, as patients exhibit a high rate of recurrence and poor survival. Co-evolution of the malignant mammary epithelium and its underlying stroma instigates cancer-associated fibroblasts (CAFs) to endorse most, if not all, hallmarks of cancer progression. Here, we delineate a previously unappreciated role for CAFs as determinants of the molecular subtype of breast cancer. We identified a paracrine cross-talk between cancer cells expressing platelet-derived growth factor (PDGF)-CC and CAFs expressing the cognate receptors in human basal-like mammary carcinomas. Genetic or pharmacological intervention with PDGF-CC activity in mouse models of cancer resulted in conversion of basal-like breast cancers into a hormone receptor-positive state that conferred sensitivity to endocrine therapy in previously impervious tumors. We conclude that specification of the basal-like subtype of breast cancer is under microenvironmental control and therapeutically actionable in order to achieve sensitivity to endocrine therapy.

Identifying and Targeting Sporadic Oncogenic Genetic Aberrations in Mouse Models of Triple-Negative Breast Cancer

Triple-negative breast cancers (TNBC) are genetically characterized by aberrations in TP53 and a low rate of activating point mutations in common oncogenes, rendering it challenging in applying targeted therapies. We performed whole-exome sequencing (WES) and RNA sequencing (RNA-seq) to identify somatic genetic alterations in mouse models of TNBCs driven by loss of Trp53 alone or in combination with Brca1 Amplifications or translocations that resulted in elevated oncoprotein expression or oncoprotein-containing fusions, respectively, as well as frameshift mutations of tumor suppressors were identified in approximately 50% of the tumors evaluated. Although the spectrum of sporadic genetic alterations was diverse, the majority had in common the ability to activate the MAPK/PI3K pathways. Importantly, we demonstrated that approved or experimental drugs efficiently induce tumor regression specifically in tumors harboring somatic aberrations of the drug target. Our study suggests that the combination of WES and RNA-seq on human TNBC will lead to the identification of actionable therapeutic targets for precision medicine-guided TNBC treatment.Significance: Using combined WES and RNA-seq analyses, we identified sporadic oncogenic events in TNBC mouse models that share the capacity to activate the MAPK and/or PI3K pathways. Our data support a treatment tailored to the genetics of individual tumors that parallels the approaches being investigated in the ongoing NCI-MATCH, My Pathway Trial, and ESMART clinical trials. Cancer Discov; 8(3); 354-69. ©2017 AACR.See related commentary by Natrajan et al., p. 272See related article by Matissek et al., p. 336This article is highlighted in the In This Issue feature, p. 253.

Ran GTPase promotes cancer progression via Met recepto-rmediated downstream signaling

It has been shown previously that cancer cells with an activated oncogenic pathway, including Met activation, require Ran for growth and survival.

Here, we show that knockdown of Ran leads to a reduction of Met receptor expression in several breast and lung cancer cell lines. This, in turn suppressed HGF expression and the Met-mediated activation of the Akt pathway, as well as cell adhesion, migration, and invasion. In a cell line model where Met amplification has previously been shown to contribute to gefitinib resistance, Ran knockdown sensitized cells to gefitinib-mediated inhibition of Akt and ERK1/2 phosphorylation and consequently reduced cell proliferation. We further demonstrate that Met reduction-mediated by knockdown of Ran, occurs at the post-transcriptional level, probably via a matrix metalloproteinase. Moreover, the level of immunoreactive Ran and Met are positively associated in human breast cancer specimens, suggesting that a high level of Ran may be a pre-requisite for Met overexpression. Interestingly, a high level of immunoreactive Ran dictates the prognostic significance of Met, indicating that the co-overexpression of Met and Ran may be associated with cancer progression and could be used in combination as a prognostic indicator.

Targeting MET and EGFR crosstalk signaling in triple-negative breast cancers

There is a vital need for improved therapeutic strategies that are effective in both primary and metastatic triple-negative breast cancer (TNBC). Current treatment options for TNBC patients are restricted to chemotherapy; however tyrosine kinases are promising druggable targets due to their high expression in multiple TNBC subtypes. Since coexpression of receptor tyrosine kinases (RTKs) can promote signaling crosstalk and cell survival in the presence of kinase inhibitors, it is likely that multiple RTKs will need to be inhibited to enhance therapeutic benefit and prevent resistance. The MET and EGFR receptors are actionable targets due to their high expression in TNBC; however crosstalk between MET and EGFR has been implicated in therapeutic resistance to single agent use of MET or EGFR inhibitors in several cancer types. Therefore it is likely that dual inhibition of MET and EGFR is required to prevent crosstalk signaling and acquired resistance. In this study, we evaluated the heterogeneity of MET and EGFR expression and activation in primary and metastatic TNBC tumorgrafts and determined the efficacy of MET (MGCD265 or crizotinib) and/or EGFR (erlotinib) inhibition against TNBC progression. Here we demonstrate that combined MET and EGFR inhibition with either MGCD265 and erlotinib treatment or crizotinib and erlotinib treatment were highly effective at abrogating tumor growth and significantly decreased the variability in treatment response compared to monotherapy. These results advance our understanding of the RTK signaling architecture in TNBC and demonstrate that combined MET and EGFR inhibition may be a promising therapeutic strategy for TNBC patients.

Crizotinib, a MET inhibitor, inhibits growth, migration, and invasion of breast cancer cells in vitro and synergizes with chemotherapeutic agents

MET is a receptor tyrosine kinase known for its pleiotropic effects in tumorigenesis. Dysregulations of MET expression and/or signaling have been reported and determined to be associated with inferior outcomes in breast cancer patients rendering MET a versatile candidate for targeted therapeutic intervention. Crizotinib is a multi-targeted small-molecule kinase inhibitor for MET, ALK, and ROS1 kinases. This study evaluated the anti-proliferative, cytotoxic, anti-migratory, and anti-invasive effects of crizotinib in breast cancer cells in vitro. Cell viability was assessed by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) colorimetric assay. In vitro wound-healing assay was used to examine the effect of crizotinib on breast cancer cell migration. The expressions of Ki-67, MET, and phospho-MET receptors were characterized using immunofluorescence staining. Results showed that crizotinib has significant anti-proliferative activity on all mammary tumor cells with IC₅₀ values of 5.16, 1.5, and 3.85 µM in MDA-MB-231, MCF-7, and SK-BR-3 cells, respectively. Crizotinib induced cytotoxic effects in all breast cancer cells examined. Combined treatment of small dose of crizotinib with paclitaxel or doxorubicin exhibited a highly synergistic inhibition of growth of MDA-MB-231 and MCF-7 cells with combination index values <1 while no significant effect was observed in SK-BR-3 cells compared with individual compounds. Treatment with crizotinib demonstrated a remarkable reduction in the expression of Ki-67 protein in all 3 tested cell lines. Crizotinib inhibited migration and invasion of MDA-MB-231 cells in a dose-dependent fashion. Crizotinib reduced MET receptor activation in MDA-MB-231 cells when treated at effective concentrations. In conclusion, crizotinib suppressed proliferation, migration, and invasion of breast cancer cells in vitro. The results of this study demonstrated that combined treatment of crizotinib with chemotherapeutic agents resulted in a synergistic growth inhibition of specific breast cancer cell lines.

Metabolic profiling of triple-negative breast cancer cells reveals metabolic vulnerabilities

Background

Among breast cancers, the triple-negative breast cancer (TNBC) subtype has the worst prognosis with no approved targeted therapies and only standard chemotherapy as the backbone of systemic therapy. Unique metabolic changes in cancer progression provide innovative therapeutic opportunities. The receptor tyrosine kinases (RTKs) epidermal growth factor receptor (EGFR), and MET receptor are highly expressed in TNBC, making both promising therapeutic targets. RTK signaling profoundly alters cellular metabolism by increasing glucose consumption and subsequently diverting glucose carbon sources into metabolic pathways necessary to support the tumorigenesis. Therefore, detailed metabolic profiles of TNBC subtypes and their response to tyrosine kinase inhibitors may identify therapeutic sensitivities.

Methods

We quantified the metabolic profiles of TNBC cell lines representing multiple TNBC subtypes using gas chromatography mass spectrometry. In addition, we subjected MDA-MB-231, MDA-MB-468, Hs578T, and HCC70 cell lines to metabolic flux analysis of basal and maximal glycolytic and mitochondrial oxidative rates. Metabolic pool size and flux measurements were performed in the presence and absence of the MET inhibitor, INC280/capmatinib, and the EGFR inhibitor, erlotinib. Further, the sensitivities of these cells to modulators of core metabolic pathways were determined. In addition, we annotated a rate-limiting metabolic enzymes library and performed a siRNA screen in combination with MET or EGFR inhibitors to validate synergistic effects.

Results

TNBC cell line models displayed significant metabolic heterogeneity with respect to basal and maximal metabolic rates and responses to RTK and metabolic pathway inhibitors. Comprehensive systems biology analysis of metabolic perturbations, combined siRNA and tyrosine kinase inhibitor screens identified a core set of TCA cycle and fatty acid pathways whose perturbation sensitizes TNBC cells to small molecule targeting of receptor tyrosine kinases.

Conclusions

Similar to the genomic heterogeneity observed in TNBC, our results reveal metabolic heterogeneity among TNBC subtypes and demonstrate that understanding metabolic profiles and drug responses may prove valuable in targeting TNBC subtypes and identifying therapeutic susceptibilities in TNBC patients. Perturbation of metabolic pathways sensitizes TNBC to inhibition of receptor tyrosine kinases. Such metabolic vulnerabilities offer promise for effective therapeutic targeting for TNBC patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s40170-017-0168-x) contains supplementary material, which is available to authorized users.

MET in human cancer: germline and somatic mutations

Since the initial discovery of missense MET mutations in hereditary papillary renal carcinoma (HPRC), activating MET mutations have been identified in a diverse range of human cancers. MET mutations have been identified in several functional domains including the kinase, juxtamembrane, and Sema domains. Studies of these mutations have been invaluable for our understanding of the tumor initiating activity of MET, receptor tyrosine kinase (RTK) recycling and regulation, and mechanisms of resistance to kinase inhibition. These studies also demonstrate that mutationally activated MET plays a significant role in a wide range of cancers and RTKs can promote tumor progression through diverse mechanisms. This review will cover the various MET mutations that have been identified, their mechanism of action, and the significant role that mutationally-activated MET plays in tumor initiation, progression, and therapeutic resistance.

Induced p53 loss in mouse luminal cells causes clonal expansion and development of mammary tumours

Most breast cancers may have a luminal origin. TP53 is one of the most frequently mutated genes in breast cancers. However, how p53 deficiency contributes to breast tumorigenesis from luminal cells remains elusive. Here we report that induced p53 loss in Krt8⁺ mammary luminal cells leads to their clonal expansion without directly affecting their luminal identity. All induced mice develop mammary tumours with 9qA1 (Yap1) and/or 6qA2 (Met) amplification(s). These tumours exhibit a mammary stem cell (MaSC)-like expression signature and most closely resemble claudin-low breast cancer. Thus, although p53 does not directly control the luminal fate, its loss facilitates acquisition of MaSC-like properties by luminal cells and predisposes them to development of mammary tumours with loss of luminal identity. Our data also suggest that claudin-low breast cancer can develop from luminal cells, possibly via a basal-like intermediate state, although further study using a different luminal promoter is needed to fully support this conclusion.

Phase II and Biomarker Study of Cabozantinib in Metastatic Triple-Negative Breast Cancer Patients

Currently, no targeted therapies are available for metastatic triplenegative breast cancer (mTNBC). We evaluated the safety, efficacy, and biomarkers of response to cabozantinib, a multikinase inhibitor, in patients with mTNBC. We conducted a single arm phase II and biomarker study that enrolled patients with measurable mTNBC. Patients received cabozantinib (60 mg daily) on a 3-week cycle and were restaged after 6 weeks and then every 9 weeks. The primary endpoint was objective response rate. Predefined secondary endpoints included progression-free survival (PFS), toxicity, and tissue and blood circulating cell and protein biomarkers. Of 35 patients who initiated protocol therapy, 3 (9% [95% confidence interval (CI): 2, 26]) achieved a partial response (PR). Nine patients achieved stable disease (SD) for at least 15 weeks, and thus the clinical benefit rate (PR+SD) was 34% [95% CI: 19, 52]. Median PFS was 2.0 months [95% CI: 1.3, 3.3]. The most common toxicities were fatigue, diarrhea, mucositis, and palmar-plantar erythrodysesthesia. There were no grade 4 toxicities, but 12 patients (34%) required dose reduction. Two patients had TNBCs with MET amplification. During cabozantinib therapy, there were significant and durable increases in plasma placental growth factor, vascular endothelial growth factor (VEGF), VEGF-D, stromal cell-derived factor 1a, and carbonic anhydrase IX, and circulating CD3 + cells and CD8 + T lymphocytes, and decreases in plasma soluble VEGF receptor 2 and CD14+ monocytes (all p < .05). Higher baseline concentrations of soluble MET (sMET) associated with longer PFS (p = .03). In conclusion, cabozantinib showed encouraging safety and efficacy signals but did not meet the primary endpoint in pretreated mTNBC. Exploratory analyses of circulating biomarkers showed that cabozantinib induces systemic changes consistent with activation of the immune system and antiangiogenic activity, and that sMET should be further evaluated a potential biomarker of response.

IMPLICATIONS FOR PRACTICE

Triple-negative breast cancer (TNBC)-a disease with a dearth of effective therapies-often overexpress MET, which is associated with poor clinical outcomes. However, clinical studies of agents targeting MET and VEGF pathways-alone or in combination-have shown disappointing results. This study of cabozantinib (a dual VEGFR2/MET) in metastatic TNBC, while not meeting its prespecified endpoint, showed that treatment is associated with circulating biomarker changes, and is active in a subset of patients. Furthermore, this study demonstrates that cabozantinib therapy induces a systemic increase in cytotoxic lymphocyte populations and a decrease in immunosuppressive myeloid populations. This supports the testing of combinations of cabozantinib with immunotherapy in future studies in breast cancer patients.

p53 deficiency induces cancer stem cell pool expansion in a mouse model of triple-negative breast tumors

Triple-negative breast cancer is a heterogeneous disease characterized by the expression of basal cell markers, no estrogen or progesterone receptor expression and a lack of HER2 overexpression. Triple-negative tumors often display activated Wnt/β-catenin signaling and most have impaired p53 function. We studied the interplay between p53 loss and Wnt/β-catenin signaling in stem cell function and tumorigenesis, by deleting p53 from the mammary epithelium of K5ΔNβcat mice displaying a constitutive activation of Wnt/β-catenin signaling in basal cells. K5ΔNβcat transgenic mice present amplification of the basal stem cell pool and develop triple-negative mammary carcinomas. The loss of p53 in K5ΔNβcat mice led to an early expansion of mammary stem/progenitor cells and accelerated the formation of triple-negative tumors. In particular, p53-deficient tumors expressed high levels of integrins and extracellular matrix components and were enriched in cancer stem cells. They also overexpressed the tyrosine kinase receptor Met, a feature characteristic of human triple-negative breast tumors. The inhibition of Met kinase activity impaired tumorsphere formation, demonstrating the requirement of Met signaling for cancer stem cell growth in this model. Human basal-like breast cancers with predicted mutated p53 status had higher levels of MET expression than tumors with wild-type p53. These results connect p53 loss and β-catenin activation to stem cell regulation and tumorigenesis in triple-negative cancer and highlight the role of Met signaling in maintaining cancer stem cell properties, revealing new cues for targeted therapies.

A phase I trial of cabozantinib and gemcitabine in advanced pancreatic cancer

Background Cabozantinib and gemcitabine improve tumor control in pancreatic ductal adenocarcinoma (PDAC) in preclinical models through c-Met inhibition. We sought to determine the maximum tolerated dose (MTD) of this combination in patients with advanced PDAC. Methods Patients with ≤1 prior treatment and adequate performance status were eligible. Cabozantinib was given orally once daily, beginning day (-)7 and continued with gemcitabine given intravenously on days 1, 8, and 15 every 28 days. Dose level was assigned using Time to Event Continual Reassessment Method (TITE-CRM). Primary endpoint was MTD, defined as the highest dose level at which ≤25 % of patients incurred a dose-limiting toxicity (DLT). Secondary endpoints included response rate, progression-free survival (PFS), overall survival (OS) and urinary biomarker assessment. Results Twelve patients were enrolled and treated with 10 patients evaluable for DLT. The probability of DLT was >25 % for all dose levels tested, and thus an MTD was not determined. DLTs included grade 3 ALT/AST elevations and thrombocytopenia. Three patients had partial responses, but each discontinued therapy due to toxicity. Median PFS and OS were 4.7 (95 % CI: 1.4-9.7) and 10.1 months (95 % CI: 3.6-20.6). Exploratory biomarker analysis showed correlation of c-Met and VEGF levels with response. Conclusions An MTD for the combination was not established. Cabozantinib and gemcitabine appear impractical for further development due to DLT at low doses and continuing toxicities with ongoing therapy. Acknowledging the small sample size, responses were seen suggesting further investigation of c-Met inhibition in PDAC may be warranted.

The Association between EGFR and cMET Expression and Phosphorylation and Its Prognostic Implication in Patients with Breast Cancer

EGFR and cMET cross-talk is involved in breast cancer (BC) progression and resistance to different targeted therapies, however little is known about the co-expression patterns of EGFR and cMET or its prognostic significance in BC. Protein levels of EGFR, cMET and their phosphorylated proteins were measured in 825 BC samples using reverse phase protein array (RPPA). Given unimodal distribution of proteins, the median was selected as a cut-off after sensitivity analyses. Kaplan-Meier survival curves were used to estimate relapse-free (RFS) and overall survival (OS). Cox-proportional hazards models were utilized to determine associations between EGFR and cMET with outcomes. Mean age was 58 years with 457 (55%) hormone receptor (HR) positive, 211 (26%) triple-negative (TN) and 148 (18%) HER2 positive tumors (HER2+). HER2+ was associated with higher EGFR expression and phosphorylation, compared to HR and TN (p<0.05). High EGFR expression was associated with higher phosphorylated-cMET (p-cMET) but not cMET (ANOVA p-cMET p < 0.001; cMET p = 0.34). The same association was found with high phosphorylated-EGFR (p-EGFR) group at Tyr992 and Tyr1068 (both p < 0.001). High expressions in either of two p-EGFRs were linked with higher cMET as well (all p<0.001). For the TN subtype, high expression in EGFR and p-EGFR at Tyr992 but not at Tyr1068 was associated with higher p-cMET (p<0.00, p = 0.012, p = 0.4 respectively). Only high expression in p-EGFR at Tyr992 was linked with higher expression of cMET (p = 0.02). In contrast, among HER2 subtype, high expression in p-EGFR at Tyr1068 but not at Tyr992 was associated with higher cMET and p-cMET (cMET p = 0.023;p-cMET p<0.001). Four subgroups of patients defined by dichotomized EGFR/p-EGFR and cMET/p-cMET level demonstrated no significant differences in survival. In multivariate analyses, neither cMET nor EGFR expression/activation was found to be an independent prognostic factor in survival outcome.

c-Met and ERβ expression differences in basal-like and non-basal-like triple-negative breast cancer

Basal-like breast cancer (BLBC) and triple-negative breast cancer (TNBC) are two entities of breast cancer that share similar poor prognosis. Even though both cancers have overlaps, there are still some differences between those two types. It has been reported that the c-Met high expression was associated with poor prognosis not only in breast cancer but also in many other cancers. The role of ERβ in pathogenesis and treatment of breast cancer has remained controversial. In this study, we firstly distinguished basal-like from nonbasal-like cancer patients in TNBC patients using CK5/6 and EGFR as markers and next determined the relationship of basal-like breast cancer with c-Met or ERβ expression levels and prognosis in TNBC patients. One hundred twenty-seven patients who had been diagnosed with TNBC were enrolled. The clinical and pathological characteristics of the patients were recorded. The expression of EGFR, CK5/6, ERβ, and c-Met were evaluated with immunohistochemical methods using paraffin blocks. The median age of patients was 50.7 years. CK5/6 immunopositivity was 31.5 % (40/127), and EGFR was 40.2 % (51/127). Of the TNBC cases, 55.1 % (71/127) were positive for either CK5/6 or EGFR and were thus classified as basal-like breast cancer. C-Met (P < 0.001) and ERβ (P = 0.002) overexpression, small tumor sizes, a ductal subtype, and high-grade tumor were significantly correlated with BLBC. High c-Met expression was detected in 43.3 % patients. Metastatic lymph nodes and tumor size (>5 cm), which were both important prognostic predictors, were significantly associated with recurrence and mortality. BLBC typically demonstrates a unique profile. CK5/6 and EGFR expression combination indicates a higher basal-like phenotype possibility. The expression of c-Met and ERβ were significantly related to the basal-like phenotype. The classical markers, lymph node metastasis, and tumor size were found to have important prognostic value. However, high c-Met expression and basal-like phenotypes did not show a direct correlation with poor prognosis.

Roles of c-Met and RON kinases in tumor progression and their potential as therapeutic targets

c-Met and receptor originated from nantes (RON) are structurally related transmembrane phosphotyrosine kinase receptors. c-Met and RON show increased expression or activity in a variety of tumors leading to tumor progression and may play a role in acquired resistance to therapy. Although often co-expressed, the distinct functional roles of c-Met and RON are not fully understood. c-Met and RON form both activated homodimers and heterodimers with themselves and other families of phosphotyrosine kinase receptors. Inhibitors for c-Met and RON including small molecular weigh kinase inhibitors and neutralizing antibodies are in pre-clinical investigation and clinical trials. Several of the tyrosine kinase inhibitors have activity against both c-Met and RON kinases whereas the antibodies generally are target specific. As with many targeted agents used to treat solid tumors, it is likely that c-Met/RON inhibitors will have greater benefit when used in combination with chemotherapy or other targeted agents. A careful analysis of c-Met/RON expression or activity and a better elucidation of how they influence cell signaling will be useful in predicting which tumors respond best to these inhibitors as well as determining which agents can be used with these inhibitors for combined therapy.

Cabozantinib (XL184) Inhibits Growth and Invasion of Preclinical TNBC Models

PURPOSE

Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype that is associated with poor clinical outcome. There is a vital need for effective targeted therapeutics for TNBC patients, yet treatment strategies are challenged by the significant intertumoral heterogeneity within the TNBC subtype and its surrounding microenvironment. Receptor tyrosine kinases (RTK) are highly expressed in several TNBC subtypes and are promising therapeutic targets. In this study, we targeted the MET receptor, which is highly expressed across several TNBC subtypes.

EXPERIMENTAL DESIGN

Using the small-molecule inhibitor cabozantinib (XL184), we examined the efficacy of MET inhibition in preclinical models that recapitulate human TNBC and its microenvironment. To analyze the dynamic interactions between TNBC cells and fibroblasts over time, we utilized a 3D model referred to as MAME (Mammary Architecture and Microenvironment Engineering) with quantitative image analysis. To investigate cabozantinib inhibition in vivo, we used a novel xenograft model that expresses human HGF and supports paracrine MET signaling.

RESULTS

XL184 treatment of MAME cultures of MDA-MB-231 and HCC70 cells (± HGF-expressing fibroblasts) was cytotoxic and significantly reduced multicellular invasive outgrowths, even in cultures with HGF-expressing fibroblasts. Treatment with XL184 had no significant effects on MET(neg) breast cancer cell growth. In vivo assays demonstrated that cabozantinib treatment significantly inhibited TNBC growth and metastasis.

CONCLUSIONS

Using preclinical TNBC models that recapitulate the breast tumor microenvironment, we demonstrate that cabozantinib inhibition is an effective therapeutic strategy in several TNBC subtypes.

Development and verification of the PAM50-based Prosigna breast cancer gene signature assay

BACKGROUND

The four intrinsic subtypes of breast cancer, defined by differential expression of 50 genes (PAM50), have been shown to be predictive of risk of recurrence and benefit of hormonal therapy and chemotherapy. Here we describe the development of Prosigna™, a PAM50-based subtype classifier and risk model on the NanoString nCounter Dx Analysis System intended for decentralized testing in clinical laboratories.

METHODS

514 formalin-fixed, paraffin-embedded (FFPE) breast cancer patient samples were used to train prototypical centroids for each of the intrinsic subtypes of breast cancer on the NanoString platform. Hierarchical cluster analysis of gene expression data was used to identify the prototypical centroids defined in previous PAM50 algorithm training exercises. 304 FFPE patient samples from a well annotated clinical cohort in the absence of adjuvant systemic therapy were then used to train a subtype-based risk model (i.e. Prosigna ROR score). 232 samples from a tamoxifen-treated patient cohort were used to verify the prognostic accuracy of the algorithm prior to initiating clinical validation studies.

RESULTS

The gene expression profiles of each of the four Prosigna subtype centroids were consistent with those previously published using the PCR-based PAM50 method. Similar to previously published classifiers, tumor samples classified as Luminal A by Prosigna had the best prognosis compared to samples classified as one of the three higher-risk tumor subtypes. The Prosigna Risk of Recurrence (ROR) score model was verified to be significantly associated with prognosis as a continuous variable and to add significant information over both commonly available IHC markers and Adjuvant! Online.

CONCLUSIONS

The results from the training and verification data sets show that the FDA-cleared and CE marked Prosigna test provides an accurate estimate of the risk of distant recurrence in hormone receptor positive breast cancer and is also capable of identifying a tumor's intrinsic subtype that is consistent with the previously published PCR-based PAM50 assay. Subsequent analytical and clinical validation studies confirm the clinical accuracy and technical precision of the Prosigna PAM50 assay in a decentralized setting.

Cabozantinib, a Novel c-Met Inhibitor, Inhibits Colorectal Cancer Development in a Xenograft Model

Background

Angiogenesis plays a critical role during tumor development. c-Met has recently been implicated in the angiogenesis of various tumors, leaving its role in colorectal cancer (CRC) unknown. In this study, we aimed to evaluate the effect of a novel c-Met inhibitor, cabozantinib, on the tumor growth and angiogenesis in a CRC mouse model.

Material/Methods

A mouse CRC xenograft model was used to evaluate the effect of cabozantinib on vivo growth of tumors and angiogenesis. The expression of angiogenesis-related factors was evaluated by immunohistochemistry (IHC) and Western blotting. Levels of serum cytokines were detected by ELISA.

Results

Cabozantinib effectively reduced tumor size and angiogenesis, and suppressed the expression of vascular endothelial growth factor (VEGF) in tumor tissues, possibly via the inhibition of Sonic Hedgehog (SHH) pathway.

Conclusions

The blockade of c-Met inhibits the tumor growth and angiogenesis via modulating SHH pathway, suggesting a potential strategy in the treatment of CRC.

Randomized, phase II, placebo-controlled trial of onartuzumab and/or bevacizumab in combination with weekly paclitaxel in patients with metastatic triple-negative breast cancer

BACKGROUND

Increased hepatocyte growth factor/MET signaling is associated with an aggressive phenotype and poor prognosis in triple-negative breast cancer (TNBC). We evaluated the benefit of adding onartuzumab, a monoclonal anti-MET antibody, to paclitaxel with/without bevacizumab in patients with TNBC.

PATIENTS AND METHODS

Women with metastatic TNBC were randomized to receive onartuzumab plus placebo plus weekly paclitaxel (OP; n = 60) or onartuzumab plus bevacizumab plus paclitaxel (OBP; n = 63) or placebo plus bevacizumab plus paclitaxel (BP; n = 62). The primary end point was progression-free survival (PFS); additional end points included overall survival (OS), objective response rate (ORR), and safety. This trial was hypothesis generating and did not have power to detect minimum clinically meaningful differences between treatment arms.

RESULTS

There was no improvement in PFS with the addition of onartuzumab to BP [hazard ratio (HR), 1.08; 95% confidence interval (CI) 0.69-1.70]; the risk of a PFS event was higher with OP than with BP (HR, 1.74; 95% CI 1.13-2.68). Most patients had MET-negative tumors (88%); PAM50 subtype analysis showed basal-like tumors in 68% of samples. ORR was higher in the bevacizumab arms (OBP: 42.2%; 95% CI 28.6-57.1; BP: 54.7%; 95% CI 41.0-68.4) compared with OP (27.5%; 95% CI 15.9-40.6). Median OS was shorter with OBP (HR, 1.36; 95% CI 0.75-2.46) and OP (HR, 1.92; 95% CI 1.03-3.59), than with BP. Peripheral edema was more frequent in the onartuzumab arms (OBP, 51.8%; OP, 58.6%) versus BP (17.7%).

CONCLUSION

This study did not show a clinical benefit of the addition of onartuzumab to paclitaxel with/without bevacizumab in patients with predominantly MET-negative TNBC.

CLINICALTRIALSGOV

NCT01186991.

Paracrine Met signaling triggers epithelial-mesenchymal transition in mammary luminal progenitors, affecting their fate

HGF/Met signaling has recently been associated with basal-type breast cancers, which are thought to originate from progenitor cells residing in the luminal compartment of the mammary epithelium. We found that ICAM-1 efficiently marks mammary luminal progenitors comprising hormone receptor-positive and receptor-negative cells, presumably ductal and alveolar progenitors. Both cell populations strongly express Met, while HGF is produced by stromal and basal myoepithelial cells. We show that persistent HGF treatment stimulates the clonogenic activity of ICAM1-positive luminal progenitors, controlling their survival and proliferation, and leads to the expression of basal cell characteristics, including stem cell potential. This is accompanied by the induction of Snai1 and Snai2, two major transcription factors triggering epithelial–mesenchymal transition, the repression of the luminal-regulatory genes Elf5 and Hey1, and claudin down-regulation. Our data strongly indicate that paracrine Met signaling can control the function of luminal progenitors and modulate their fate during mammary development and tumorigenesis.

DOI:http://dx.doi.org/10.7554/eLife.06104.001

Throughout the life of a female mammal, the mammary glands undergo different phases of development to prepare for, and adapt to, feeding offspring. Luminal cells line the inside of branch-like structures throughout the mammary gland and are responsible for producing milk. When the mammary gland grows, new luminal cells develop from a kind of cell called luminal progenitor cells. However, these progenitor cells are also thought to be the source of certain types of breast cancer.

Recently, it has been suggested that luminal progenitor cells display a receptor protein called Met on their surface. When Met and ‘co-receptor’ proteins bind to a molecule called HGF, this triggers a cascade of signals that can cause certain cells to change their properties. This is known as the epithelial–mesenchymal transition. Although this transition is important for new tissues to develop, it can also result in cancerous tumors forming if it is not correctly controlled. Luminal cells do not produce HGF themselves, which suggests that Met signaling in these cells is triggered by the HGF released from neighboring cells. However, neither the mechanisms behind this signaling nor the effects of signaling on the luminal progenitor cells are well understood.

Di-Cicco et al. set out to identify where Met, its co-receptors and HGF are located in the mouse mammary gland during different phases of development. This revealed that one of the co-receptors—called ICAM-1—can be used as a marker to identify certain types of luminal progenitor cell. Di-Cicco et al. found that these progenitor cells display Met on their surface, and other types of mammary cell—called stromal cells and myoepithelial cells—produce HGF.

When exposed to HGF, luminal progenitor cells grown in culture in the laboratory proliferated and went through the epithelial–mesenchymal transition. These findings suggest that myoepithelial and stromal cells regulate luminal progenitor cells by producing HGF to activate Met signaling in these cells. Such interactions could be of great importance during mammary development and tumorigenesis. The next big challenge will be to determine the circumstances under which luminal progenitor cells stimulated by HGF can give rise to breast cancers. This work will allow us to better define the cell population that should be targeted by anti-cancer drugs.

DOI:http://dx.doi.org/10.7554/eLife.06104.002

Phase II study of tivantinib (ARQ 197) in patients with metastatic triple-negative breast cancer

Background MET expression and activation appear to be important for initiation and progression of triple-negative breast cancer. Tivantinib (ARQ 197) is an orally administered agent that targets MET, although recent preclinical data suggests the agent may have mechanisms of action that are independent of MET signaling. We conducted a phase 2 study of tivantinib monotherapy in patients with metastatic triple-negative breast cancer. Methods Patients with metastatic triple-negative breast cancer who had received 1 to 3 prior lines of chemotherapy in the metastatic setting were enrolled into this two-stage, single arm phase 2 study. Treatment consisted of twice daily oral dosing of tivantinib (360 mg po bid) during a 21-day cycle. Patients underwent restaging scans at 6 weeks, and then every 9 weeks. Tumor biomarkers that might predict response to tivantinib were explored. Results 22 patients were enrolled. The overall response rate was 5 % (95 % CI 0–25 %) and the 6-month progression-free survival (PFS) was 5 % (95 % CI 0–25 %), with one patient achieving a partial response (PR). Toxicity was minimal with only 5 grade ≥3 adverse events (one grade 3 anemia, one grade 3 fatigue, and 3 patients with grade 3/4 neutropenia). Conclusion This study represents the first evaluation of tivantinib for the treatment of metastatic triple-negative breast cancer. These results suggest that single agent tivantinib is well tolerated, but did not meet prespecified statistical targets for efficacy.

Whole-exome DNA sequence analysis of Brca2- and Trp53-deficient mouse mammary gland tumours

Germline mutations in the tumour suppressor BRCA2 predispose to breast, ovarian and a number of other human cancers. Brca2-deficient mouse models are used for preclinical studies but the pattern of genomic alterations in these tumours has not yet been described in detail. We have performed whole-exome DNA sequencing analysis of mouse mammary tumours from Blg-Cre Brca2(f/f) Trp53(f/f) animals, a model of BRCA2-deficient human cancer. We also used the sequencing data to estimate DNA copy number alterations in these tumours and identified a recurrent copy number gain in Met, which has been found amplified in other mouse mammary cancer models. Through a comparative genomic analysis, we identified several mouse Blg-Cre Brca2(f/f) Trp53(f/f) mammary tumour somatic mutations in genes that are also mutated in human cancer, but few of these genes have been found frequently mutated in human breast cancer. A more detailed analysis of these somatic mutations revealed a set of genes that are mutated in human BRCA2 mutant breast and ovarian tumours and that are also mutated in mouse Brca2-null, Trp53-null mammary tumours. Finally, a DNA deletion surrounded by microhomology signature found in human BRCA1/2-deficient cancers was not common in the genome of these mouse tumours. Although a useful model, there are some differences in the genomic landscape of tumours arising in Blg-Cre Brca2(f/f) Trp53(f/f) mice compared to human BRCA-mutated breast cancers. Therefore, this needs to be taken into account in the use of this model.

The clinical and functional significance of c-Met in breast cancer: a review

c-Met is a receptor tyrosine kinase that upon binding of its ligand, hepatocyte growth factor (HGF), activates downstream pathways with diverse cellular functions that are important in organ development and cancer progression. Anomalous c-Met signalling has been described in a variety of cancer types, and the receptor is regarded as a novel therapeutic target. In breast cancer there is a need to develop new treatments, particularly for the aggressive subtypes such as triple-negative and basal-like cancer, which currently lack targeted therapy. Over the last two decades, much has been learnt about the functional role of c-Met signalling in different models of breast development and cancer. This work has been complemented by clinical studies, establishing the prognostic significance of c-Met in tissue samples of breast cancer. While the clinical trials of anti-c-Met therapy in advanced breast cancer progress, there is a need to review the existing evidence so that the potential of these treatments can be better appreciated. The aim of this article is to examine the role of HGF/c-Met signalling in in vitro and in vivo models of breast cancer, to describe the mechanisms of aberrant c-Met signalling in human tissues, and to give a brief overview of the anti-c-Met therapies currently being evaluated in breast cancer patients. We will show that the HGF/c-Met pathway is associated with breast cancer progression and suggest that there is a firm basis for continued development of anti-c-Met treatment, particularly for patients with basal-like and triple-negative breast cancer.

Araguspongine C induces autophagic death in breast cancer cells through suppression of c-Met and HER2 receptor tyrosine kinase signaling

Receptor tyrosine kinases are key regulators of cellular growth and proliferation. Dysregulations of receptor tyrosine kinases in cancer cells may promote tumorigenesis by multiple mechanisms including enhanced cell survival and inhibition of cell death. Araguspongines represent a group of macrocyclic oxaquinolizidine alkaloids isolated from the marine sponge Xestospongia species. This study evaluated the anticancer activity of the known oxaquinolizidine alkaloids araguspongines A, C, K and L, and xestospongin B against breast cancer cells. Araguspongine C inhibited the proliferation of multiple breast cancer cell lines in vitro in a dose-dependent manner. Interestingly, araguspongine C-induced autophagic cell death in HER2-overexpressing BT-474 breast cancer cells was characterized by vacuole formation and upregulation of autophagy markers including LC3A/B, Atg3, Atg7, and Atg16L. Araguspongine C-induced autophagy was associated with suppression of c-Met and HER2 receptor tyrosine kinase activation. Further in-silico docking studies and cell-free Z-LYTE assays indicated the potential of direct interaction between araguspongine C and the receptor tyrosine kinases c-Met and HER2 at their kinase domains. Remarkably, araguspongine C treatment resulted in the suppression of PI3K/Akt/mTOR signaling cascade in breast cancer cells undergoing autophagy. Induction of autophagic death in BT-474 cells was also associated with decreased levels of inositol 1,4,5-trisphosphate receptor upon treatment with effective concentration of araguspongine C. In conclusion, results of this study are the first to reveal the potential of araguspongine C as an inhibitor to receptor tyrosine kinases resulting in the induction of autophagic cell death in breast cancer cells.

Targeting met mediated epithelial-mesenchymal transition in the treatment of breast cancer

Mesenchymal epithelial transition factor receptor (Met) is a receptor tyrosine kinase that plays a critical role in promoting cancer cell malignant progression. Met is activated by its ligand hepatocyte growth factor (HGF). HGF-dependent Met activation plays an important role in stimulating epithelial-mesenchymal transition (EMT) in tumor cells, resulting in increased tumor cell proliferation, survival, motility, angiogenesis, invasion, and metastasis. The HGF/Met axis has thus attracted great interest as a potential target in the development of novel cancer therapies. In an effort to suppress tumor cell malignant progression, efforts have been made to develop agents capable of inhibiting inhibit Met-induced EMT, including specific Met tyrosine kinase inhibitors, HGF antagonists that interfere with HGF binding to Met, and antibodies that prevent Met activation and/or dimerization. Tocotrienols, a subgroup within the vitamin E family of compounds, display potent anticancer activity that results, at least in part, from inhibition of HGF-dependent Met activation and signaling. The present review will provide a brief summary of the increasing importance of the HGF/Met axis as an attractive target for cancer chemotherapy and the role of tocotrienols in suppressing Met activation, signaling and HGF-induced EMT in breast cancer cells. Evidence provided suggests that γ-tocotrienol therapy may afford significant benefit in the treatment of breast cancers characterized by Met dysregulation.

The three-way switch operation of Rac1/RhoA GTPase-based circuit controlling amoeboid-hybrid-mesenchymal transition

Metastatic carcinoma cells exhibit at least two different phenotypes of motility and invasion - amoeboid and mesenchymal. This plasticity poses a major clinical challenge for treating metastasis, while its underlying mechanisms remain enigmatic. Transitions between these phenotypes are mediated by the Rac1/RhoA circuit that responds to external signals such as HGF/SF via c-MET pathway. Using detailed modeling of GTPase-based regulation to study the Rac1/RhoA circuit's dynamics, we found that it can operate as a three-way switch. We propose to associate the circuit's three possible states to the amoeboid, mesenchymal and amoeboid/mesenchymal hybrid phenotype. In particular, we investigated the range of existence of, and the transition between, the three states (phenotypes) in response to Grb2 and Gab1 - two downstream adaptors of c-MET. The results help to explain the regulation of metastatic cells by c-MET pathway and hence can contribute to the assessment of possible clinical interventions.

Profiling the tyrosine phosphoproteome of different mouse mammary tumour models reveals distinct, model-specific signalling networks and conserved oncogenic pathways

INTRODUCTION

Although aberrant tyrosine kinase signalling characterises particular breast cancer subtypes, a global analysis of tyrosine phosphorylation in mouse models of breast cancer has not been undertaken to date. This may identify conserved oncogenic pathways and potential therapeutic targets.

METHODS

We applied an immunoaffinity/mass spectrometry workflow to three mouse models: murine stem cell virus-Neu, expressing truncated Neu, the rat orthologue of human epidermal growth factor receptor 2, Her2 (HER2); mouse mammary tumour virus-polyoma virus middle T antigen (PyMT); and the p53-/- transplant model (p53). Pathways and protein-protein interaction networks were identified by bioinformatics analysis. Molecular mechanisms underpinning differences in tyrosine phosphorylation were characterised by Western blot analysis and array comparative genomic hybridisation. The functional role of mesenchymal-epithelial transition factor (Met) in a subset of p53-null tumours was interrogated using a selective tyrosine kinase inhibitor (TKI), small interfering RNA (siRNA)-mediated knockdown and cell proliferation assays.

RESULTS

The three models could be distinguished on the basis of tyrosine phosphorylation signatures and signalling networks. HER2 tumours exhibited a protein-protein interaction network centred on avian erythroblastic leukaemia viral oncogene homologue 2 (Erbb2), epidermal growth factor receptor and platelet-derived growth factor receptor α, and they displayed enhanced tyrosine phosphorylation of ERBB receptor feedback inhibitor 1. In contrast, the PyMT network displayed significant enrichment for components of the phosphatidylinositol 3-kinase signalling pathway, whereas p53 tumours exhibited increased tyrosine phosphorylation of Met and components or regulators of the cytoskeleton and shared signalling network characteristics with basal and claudin-low breast cancer cells. A subset of p53 tumours displayed markedly elevated cellular tyrosine phosphorylation and Met expression, as well as Met gene amplification. Treatment of cultured p53-null cells exhibiting Met amplification with a selective Met TKI abrogated aberrant tyrosine phosphorylation and blocked cell proliferation. The effects on proliferation were recapitulated when Met was knocked down using siRNA. Additional subtypes of p53 tumours exhibited increased tyrosine phosphorylation of other oncogenes, including Peak1/SgK269 and Prex2.

CONCLUSION

This study provides network-level insights into signalling in the breast cancer models utilised and demonstrates that comparative phosphoproteomics can identify conserved oncogenic signalling pathways. The Met-amplified, p53-null tumours provide a new preclinical model for a subset of triple-negative breast cancers.

cMET in triple-negative breast cancer: is it a therapeutic target for this subset of breast cancer patients?

INTRODUCTION

The identification and validation of a targeted therapy for triple-negative breast cancer (TNBC) is currently one of the most urgent needs in breast cancer therapeutics. The cMET oncogene encodes a membrane-bound tyrosine kinase implicated in the formation and/or progression of several cancer types, including TNBC. Currently, inhibitors targeting cMET are undergoing clinical trials for a variety of cancers, including TNBC. These include anti-cMET and anti-hepatocyte growth factor (HGF) monoclonal antibodies and tyrosine kinase inhibitors.

AREAS COVERED

This article reviews the structure and mode of action of cMET, the role of cMET in cancer formation/development, with particular emphasis on its role in basal/TNBC and its potential as a therapeutic target for this subtype of breast cancer.

EXPERT OPINION

Due to cancer heterogeneity, it is unlikely that all TNBC patients will be responsive to anti-cMET drugs. Therefore, if cMET is to be used as a target for treatment, it will be important to identify predictive biomarkers to select, upfront, those patients likely to benefit. Potential predictive biomarkers for anti-cMET treatments in basal/TNBC include cMET, phospho-cMET, downstream signaling proteins or HGF. These putative predictive biomarkers should be evaluated in a large panel of basal/TNBC cell lines before incorporation into clinical trials involving anti-cMET drugs.

Analysis of MET genetic aberrations in patients with breast cancer at MD Anderson Phase I unit

BACKGROUND

c-MET is a receptor tyrosine kinase whose phosphorylation activates important proliferation pathways. MET amplification and mutation have been described in various malignancies, including breast cancer (BC), and c-MET overexpression is associated with worse survival outcomes in patients with BC. We describe MET mutation and amplification rates in a BC cohort of patients referred to a Phase I Unit.

METHODS

We reviewed the electronic medical records of all patients with advanced BC tested for MET amplification, mutation, or both who were referred to the Department of Investigational Cancer Therapeutics at MD Anderson.

RESULTS

A total of 107 patients with advanced BC were analyzed for MET mutation/variant (88 patients) or amplification (63 patients). Of these, 49 were tested for both genetic abnormalities. Three of 63 patients (4.7%) demonstrated MET gene amplification by fluorescence in situ hybridization (2 in primary tissue; 1 in metastatic site). MET mutation/variant was detected in 8 of 88 patients (9%). High-grade tumors were characteristic of all patients harboring MET amplification and were present in 7 of 8 (87.5%) of those with MET mutation. Metastatic sites were greater in MET-amplified compared with wild-type patients (median of 7 vs. 3 sites). Five of 8 patients (62.5%) with MET mutations had triple negative BC compared with 46% in controls. In addition, patients with positive test results for MET aberrations (n = 11) had inferior overall survival (OS) from Phase I consult compared with wild-type patients (n = 37), although this was not statistically significant (median OS = 9 vs. 15 months, P = .43).

CONCLUSIONS

In this cohort of patients with BC who were referred to our Phase I Department, MET aberrations were associated with higher metastatic burden and high-grade histology. We could not demonstrate differences in survival outcomes because of a small sample size.