Ink4a/Arf(-/-) and HRAS(G12V) transform mouse mammary cells into triple-negative breast cancer containing tumorigenic CD49f(-) quiescent cells

In vivo genome-wide CRISPR screen reveals breast cancer vulnerabilities and synergistic mTOR/Hippo targeted combination therapy

Triple negative breast cancer (TNBC) patients exhibit poor survival outcomes and lack effective targeted therapies. Using unbiased in vivo genome-wide CRISPR screening, we interrogated cancer vulnerabilities in TNBC and identified an interplay between oncogenic and tumor suppressor pathways. This study reveals tumor regulatory functions for essential components of the mTOR and Hippo pathways in TNBC. Using in vitro drug matrix synergy models and in vivo patient-derived xenografts, we further establish the therapeutic relevance of our findings and show that pharmacological inhibition of mTORC1/2 and oncoprotein YAP efficiently reduces tumorigenesis in TNBC. At the molecular level, we find that while verteporfin-induced YAP inhibition leads to apoptosis, torin1-mediated mTORC1/2 inhibition promotes macropinocytosis. Torin1-induced macropinocytosis further facilitates verteporfin uptake, thereby greatly enhancing its pro-apoptotic effects in cancer cells. Overall, our study underscores the power and robustness of in vivo CRISPR genome-wide screens in identifying clinically relevant and innovative therapeutic modalities in cancer.

Triple negative breast cancer (TNBC) lack effective therapies. Here, through an in vivo genome-wide CRISPR screen in TNBCs, the authors identify tumorigenic functions for components of the mTORC1/2 complex and of the YAP/Hippo pathway, and demonstrate that pharmacological inhibition of mTOR and YAP reduces tumour growth in vivo.

CSF-1/CSF-1R axis is associated with epithelial/mesenchymal hybrid phenotype in epithelial-like inflammatory breast cancer

Inflammatory breast cancer (IBC) is a rare subtype of breast cancer, accounting for 8–10% of breast cancer-associated deaths in the US. Clinical hallmarks of IBC include tumor emboli in lymphatic vessels and E-cadherin overexpression, which supports a type of metastasis referred to as cell cluster-based metastasis, prevalent in IBC. In contrast, we previously reported epithelial-to-mesenchymal transition (EMT)-based progression of IBC, utilizing in vivo xenografts and in vitro Matrigel culture models. To address these two contradictory concepts of IBC metastasis, we used Matrigel culture to induce EMT in a panel of IBC cells. Results revealed Matrigel culture induced vimentin expression in SUM149 and SUM190 IBC cells at the transcriptional and protein levels while maintaining the expression of E-cadherin, a phenomenon referred to as partial EMT. Transcriptional profiling revealed that expression of colony-stimulating factor 1 (CSF-1) was induced in Matrigel culture. When the receptor tyrosine kinase of CSF-1 (CSF-1R) was inhibited by CSF-1R inhibitor BLZ945, the partial EMT was reversed in a dose-dependent manner, indicating that the CSF-1/CSF-1R axis plays a key role in controlling partial EMT. This observation may help reconcile the two contradictory theories of IBC metastasis, EMT vs cell cluster-based metastasis.

Llgl1 prevents metaplastic survival driven by epidermal growth factor dependent migration

We have previously demonstrated that Llgl1 loss results in a gain of mesenchymal phenotypes and a loss of apicobasal and planar polarity. We now demonstrate that these changes represent a fundamental shift in cellular phenotype. Llgl1 regulates the expression of multiple cell identity markers, including CD44, CD49f, and CD24, and the nuclear translocation of TAZ and Slug. Cells lacking Llgl1 form mammospheres, where survival and transplantability is dependent upon the Epidermal Growth Factor Receptor (EGFR). Additionally, Llgl1 loss allows cells to grow in soft-agar and maintain prolonged survival as orthotopic transplants in NOD-SCIDmice. Lineage tracing and wound healing experiments demonstrate that mammosphere survival is due to enhanced EGF-dependent migration. The loss of Llgl1 drives EGFR mislocalization and an EGFR mislocalization point mutation (P667A) drives these same phenotypes, including activation of AKT and TAZ nuclear translocation. Together, these data indicate that the loss of Llgl1 results in EGFR mislocalization, promoting pre-neoplastic changes.

Insulin-like growth factor 1 receptor activation promotes mammary gland tumor development by increasing glycolysis and promoting biomass production

Background

The insulin-like growth factor 1 (IGF1) signaling axis plays a major role in tumorigenesis. In a previous experiment, we chronically treated mice with several agonists of the IGF1 receptor (IGF1R). We found that chronic treatment with insulin analogues with high affinity towards the IGF1R (IGF1 and X10) decreased the mammary gland tumor latency time in a p53^R270H/+WAPCre mouse model. Frequent injections with insulin analogues that only mildly activated the IGF1R in vivo (glargine and insulin) did not significantly decrease the tumor latency time in this mouse model.

Methods

Here, we performed next-generation RNA sequencing (40 million, 100 bp reads) on 50 mammary gland tumors to unravel the underlying mechanisms of IGF1R-promoted tumorigenesis. Mutational profiling of the individual tumors was performed to screen for treatment-specific mutations. The transcriptomic data were used to construct a support vector machine (SVM) classifier so that the phenotypic characteristics of tumors exposed to the different insulin analogue treatments could be predicted. For translational purposes, we ran the same classifiers on transcriptomic (micro-array) data of insulin analogue-exposed human breast cancer cell lines. Genome-scale metabolic modeling was performed with iMAT.

Results

We found that chronic X10 and IGF1 treatment resulted in tumors with an increased and sustained proliferative and invasive transcriptomic profile. Furthermore, a Warburg-like effect with increased glycolysis was observed in tumors of the X10/IGF1 groups and, to a lesser extent, also in glargine-induced tumors. A metabolic flux analysis revealed that this enhanced glycolysis programming in X10/IGF1 tumors was associated with increased biomass production programs. Although none of the treatments induced genetic instability or enhanced mutagenesis, mutations in Ezh2 and Hras were enriched in X10/IGF1 treatment tumors.

Conclusions

Overall, these data suggest that the decreased mammary gland tumor latency time caused by chronic IGF1R activation is related to modulation of tumor progression rather than increased tumor initiation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-017-0802-0) contains supplementary material, which is available to authorized users.

Development of mouse models of malignant phyllodes tumors by transplantation of syngeneic mammary gland cells expressing mutant H-Ras

Phyllodes tumors (PTs) are rare fibroepithelial tumors of the breast with epithelial and stromal components, and surgical resection is the standard and only available treatment for malignant PTs. To provide a better understanding of these tumors, we developed mouse models that recapitulate the pathological and clinical properties of human malignant PTs. Mouse undifferentiated mammary gland cells were infected with a retrovirus encoding the human oncoprotein H-Ras^G12V , and the infected cells were transplanted orthotopically into the mammary fat pads of syngeneic mice. The transplanted cells showed a high tumorigenic activity, with the resulting tumors manifesting pathological characteristics including stromal overgrowth similar to those of human malignant PTs. The tumors also showed high rates of both local recurrence and lung metastasis. Our models may prove useful for studies of the pathophysiology of malignant PTs as well as facilitate the development of new treatments.

Antitumor Activity of KW-2450 against Triple-Negative Breast Cancer by Inhibiting Aurora A and B Kinases

Currently, no targeted drug is available for triple-negative breast cancer (TNBC), an aggressive breast cancer that does not express estrogen receptor, progesterone receptor, or HER2. TNBC has high mitotic activity, and, because Aurora A and B mitotic kinases drive cell division and are overexpressed in tumors with a high mitotic index, we hypothesized that inhibiting Aurora A and B produces a significant antitumor effect in TNBC. We tested this hypothesis by determining the antitumor effects of KW-2450, a multikinase inhibitor of both Aurora A and B kinases. We observed significant inhibitory activities of KW-2450 on cell viability, apoptosis, colony formation in agar, and mammosphere formation in TNBC cells. The growth of TNBC xenografts was significantly inhibited with KW-2450. In cell-cycle analysis, KW-2450 induced tetraploid accumulation followed by apoptosis or surviving octaploid (8N) cells, depending on dose. These phenotypes resembled those of Aurora B knockdown and complete pharmaceutical inhibition of Aurora A. We demonstrated that 8N cells resulting from KW-2450 treatment depended on the activation of mitogen-activated protein kinase kinase (MEK) for their survival. When treated with the MEK inhibitor selumetinib combined with KW-2450, compared with KW-2450 alone, the 8N cell population was significantly reduced and apoptosis was increased. Indeed, this combination showed synergistic antitumor effect in SUM149 TNBC xenografts. Collectively, Aurora A and B inhibition had a significant antitumor effect against TNBC, and this antitumor effect was maximized by the combination of selumetinib with Aurora A and B inhibition.