The effect of mTOR inhibition alone or combined with MEK inhibitors on brain metastasis: an in vivo analysis in triple-negative breast cancer models

The murine metastatic microenvironment of experimental brain metastases of breast cancer differs by host age in vivo: a proteomic study

Breast cancer in young patients is known to exhibit more aggressive biological behavior and is associated with a less favorable prognosis than the same disease in older patients, owing in part to an increased incidence of brain metastases. The mechanistic explanations behind these findings remain poorly understood. We recently reported that young mice, in comparison to older mice, developed significantly greater brain metastases in four mouse models of triple-negative and luminal B breast cancer. Here we have performed a quantitative mass spectrometry-based proteomic analysis to identify proteins potentially contributing to age-related disparities in the development of breast cancer brain metastases. Using a mouse hematogenous model of brain-tropic triple-negative breast cancer (MDA-MB-231BR), we harvested subpopulations of tumor metastases, the tumor-adjacent metastatic microenvironment, and uninvolved brain tissues via laser microdissection followed by quantitative proteomic analysis using high resolution mass spectrometry to characterize differentially abundant proteins potentially contributing to age-dependent rates of brain metastasis. Pathway analysis revealed significant alterations in signaling pathways, particularly in the metastatic microenvironment, modulating tumorigenesis, metabolic processes, inflammation, and neuronal signaling. Tenascin C (TNC) was significantly elevated in all laser microdissection (LMD) enriched compartments harvested from young mice relative to older hosts, which was validated and confirmed by immunoblot analysis of whole brain lysates. Additional in vitro studies including migration and wound-healing assays demonstrated TNC as a positive regulator of tumor cell migration. These results provide important new insights regarding microenvironmental factors, including TNC, as mechanisms contributing to the increased brain cancer metastatic phenotype observed in young breast cancer patients.

Excitatory neuron-specific suppression of the integrated stress response contributes to autism-related phenotypes in fragile X syndrome

Dysregulation of protein synthesis is one of the key mechanisms underlying autism spectrum disorder (ASD). However, the role of a major pathway controlling protein synthesis, the integrated stress response (ISR), in ASD remains poorly understood. Here, we demonstrate that the main arm of the ISR, eIF2α phosphorylation (p-eIF2α), is suppressed in excitatory, but not inhibitory, neurons in a mouse model of fragile X syndrome (FXS; Fmr1-/y). We further show that the decrease in p-eIF2α is mediated via activation of mTORC1. Genetic reduction of p-eIF2α only in excitatory neurons is sufficient to increase general protein synthesis and cause autism-like behavior. In Fmr1-/y mice, restoration of p-eIF2α solely in excitatory neurons reverses elevated protein synthesis and rescues autism-related phenotypes. Thus, we reveal a previously unknown causal relationship between excitatory neuron-specific translational control via the ISR pathway, general protein synthesis, and core phenotypes reminiscent of autism in a mouse model of FXS.

An Overview of Systemic Targeted Therapy in Renal Cell Carcinoma, with a Focus on Metastatic Renal Cell Carcinoma and Brain Metastases

The most commonly diagnosed malignancy of the urinary system is represented by renal cell carcinoma. Various subvariants of RCC were described, with a clear-cell type prevailing in about 85% of all RCC tumors. Patients with metastases from renal cell carcinoma did not have many effective therapies until the end of the 1980s, as long as hormonal therapy and chemotherapy were the only options available. The outcomes were unsatisfactory due to the poor effectiveness of the available therapeutic options, but then interferon-alpha and interleukin-2 showed treatment effectiveness, providing benefits but only for less than half of the patients. However, it was not until 2004 that targeted therapies emerged, prolonging the survival rate. Currently, new technologies and strategies are being developed to improve the actual efficacy of available treatments and their prognostic aspects. This article summarizes the mechanisms of action, importance, benefits, adverse events of special interest, and efficacy of immunotherapy in metastatic renal cell carcinoma, with a focus on brain metastases.

A scientometric analysis of research trends on targeting mTOR in breast cancer from 2012 to 2022

Over the past decade, thousands of articles have been published on the mechanistic target of rapamycin (mTOR) and its role in breast cancer. However, the variability and heterogeneity of academic data may impact the acquisition of published research information. Due to the large number, heterogeneity, and varying quality of publications related to mTOR and breast cancer, sorting out the present state of the research in this area is critical for both researchers and clinicians. Therefore, scientometric techniques and visualization tools were employed to analyze the large number of bibliographic metadata related to the research area of mTOR and breast cancer. The features of relevant publications were searched from 2012 to 2022 to evaluate the present status of research and the evolution of research hotspots in this particular field. Web of Science was utilized to extract all relevant publications from 2012 to 2022. Subsequently, Biblioshiny and VOSviewer were utilized to obtain data on the most productive countries, authors, and institutions, annual publications and citations, the most influential journals and articles, and the most frequently occurring keywords. In total, 1,471 publications were retrieved, comprising 1,167 original articles and 304 reviews. There was a significant rise in publications between 2015 and 2018, followed by a sharp decline in 2019 and a rebound since then. The publication with the highest number of citations was a 2012 review authored by Baselga et al. The United States had the highest number of publications, citations and connections among all countries. Oncotarget had the highest number of published articles among all the journals, and José Baselga had the strongest links with other authors. Excluding the search topics, the most frequently used words were "expression" (n = 297), "growth" (n = 228), "activation" (n = 223), "pathway" (n = 205), and "apoptosis" (n = 195). mTOR is crucially involved in breast cancer pathogenesis, but its exact mechanism of action remains controversial and warrants further investigation. The scientometric analysis provides a distinct overview of the existing state of research and highlights the topical issues that deserve further exploration.

Breast cancer brain metastasis: from etiology to state-of-the-art modeling

Currently, breast carcinoma is the most common form of malignancy and the main cause of cancer mortality in women worldwide. The metastasis of cancer cells from the primary tumor site to other organs in the body, notably the lungs, bones, brain, and liver, is what causes breast cancer to ultimately be fatal. Brain metastases occur in as many as 30% of patients with advanced breast cancer, and the 1-year survival rate of these patients is around 20%. Many researchers have focused on brain metastasis, but due to its complexities, many aspects of this process are still relatively unclear. To develop and test novel therapies for this fatal condition, pre-clinical models are required that can mimic the biological processes involved in breast cancer brain metastasis (BCBM). The application of many breakthroughs in the area of tissue engineering has resulted in the development of scaffold or matrix-based culture methods that more accurately imitate the original extracellular matrix (ECM) of metastatic tumors. Furthermore, specific cell lines are now being used to create three-dimensional (3D) cultures that can be used to model metastasis. These 3D cultures satisfy the requirement for in vitro methodologies that allow for a more accurate investigation of the molecular pathways as well as a more in-depth examination of the effects of the medication being tested. In this review, we talk about the latest advances in modeling BCBM using cell lines, animals, and tissue engineering methods.

Evidence for Bell-Shaped Dose-Response Emetic Effects of Temsirolimus and Analogs: The Broad-Spectrum Antiemetic Efficacy of a Large Dose of Temsirolimus Against Diverse Emetogens in the Least Shrew (Cryptotis parva)

Temsirolimus is a prodrug form of sirolimus (rapamycin). With its analogs (everolimus, ridaforolimus, and rapamycin), it forms a group of anticancer agents that block the activity of one of the two mammalian targets of rapamycin (mTOR) complexes, mTORC1. We investigated the emetic potential of varying doses (0, 0.5, 1, 2.5, 5, 10, 20, and 40 mg/kg, i.p.) of temsirolimus in the least shrew. Temsirolimus caused a bell-shaped and dose-dependent increase in both the mean vomit frequency and the number of shrews vomiting with maximal efficacy at 10 mg/kg (p < 0.05 and p < 0.02, respectively). Its larger doses (20 or 40 mg/kg) had no significant emetic effect. We also evaluated the emetic potential of its analogs (5, 10, and 20 mg/kg, i.p.), all of which exhibited a similar emetic profile. Our observational studies indicated that temsirolimus can reduce the shrew motor activity at 40 mg/kg, and subsequently, we examined the motor effects of its lower doses. At 10 and 20 mg/kg, it did not affect the spontaneous locomotor activity (distance moved) but attenuated the mean rearing frequency in a U-shaped manner at 10 mg/kg (p < 0.05). We then determined the broad-spectrum antiemetic potential of a 20 mg/kg (i.p.) dose of temsirolimus against diverse emetogens, including selective and nonselective agonists of 1) dopaminergic D2/3 receptors (apomorphine and quinpirole); 2) serotonergic 5-HT3 receptors [5-HT (serotonin) and 2-methyl-5-HT]; 3) cholinergic M1 receptors (pilocarpine and McN-A-343); 4) substance P neurokinin NK1 receptors (GR73632); 5) the L-type calcium (Ca2+) channel (LTCC) (FPL64176); 6) the sarcoplasmic endoplasmic reticulum Ca2+ ATPase inhibitor, thapsigargin; 7) the CB1 receptor inverse agonist/antagonist, SR141716A; and 8) the chemotherapeutic cisplatin. Temsirolimus prevented vomiting evoked by the aforementioned emetogens with varying degrees. The mechanisms underlying the pro- and antiemetic effects of temsirolimus evaluated by immunochemistry for c-fos expression demonstrated a c-fos induction in the AP and NTS, but not DMNX with the 10 mg/kg emetic dose of temsirolimus, whereas its larger antiemetic dose (20 mg/kg) had no significant effect. Our study is the first to provide preclinical evidence demonstrating the promising antiemetic potential of high doses of temsirolimus and possibly its analogs in least shrews.

Preclinical Models of Brain Metastases in Breast Cancer

Breast cancer remains a leading cause of mortality among women worldwide. Brain metastases confer extremely poor prognosis due to a lack of understanding of their specific biology, unique physiologic and anatomic features of the brain, and limited treatment strategies. A major roadblock in advancing the treatment of breast cancer brain metastases (BCBM) is the scarcity of representative experimental preclinical models. Current models are predominantly based on the use of animal xenograft models with immortalized breast cancer cell lines that poorly capture the disease’s heterogeneity. Recent years have witnessed the development of patient-derived in vitro and in vivo breast cancer culturing systems that more closely recapitulate the biology from individual patients. These advances led to the development of modern patient-tissue-based experimental models for BCBM. The success of preclinical models is also based on the imaging technologies used to detect metastases. Advances in animal brain imaging, including cellular MRI and multimodality imaging, allow sensitive and specific detection of brain metastases and monitoring treatment responses. These imaging technologies, together with novel translational breast cancer models based on patient-derived cancer tissues, represent a unique opportunity to advance our understanding of brain metastases biology and develop novel treatment approaches. This review discusses the state-of-the-art knowledge in preclinical models of this disease.

Δ9 -Tetrahydrocannabinol promotes oligodendrocyte development and CNS myelination in vivo

Δ⁹‐Tetrahydrocannabinol (THC), the main bioactive compound found in the plant Cannabis sativa, exerts its effects by activating cannabinoid receptors present in many neural cells. Cannabinoid receptors are also physiologically engaged by endogenous cannabinoid compounds, the so‐called endocannabinoids. Specifically, the endocannabinoid 2‐arachidonoylglycerol has been highlighted as an important modulator of oligodendrocyte (OL) development at embryonic stages and in animal models of demyelination. However, the potential impact of THC exposure on OL lineage progression during the critical periods of postnatal myelination has never been explored. Here, we show that acute THC administration at early postnatal ages in mice enhanced OL development and CNS myelination in the subcortical white matter by promoting oligodendrocyte precursor cell cycle exit and differentiation. Mechanistically, THC‐induced‐myelination was mediated by CB₁ and CB₂ cannabinoid receptors, as demonstrated by the blockade of THC actions by selective receptor antagonists. Moreover, the THC‐mediated modulation of oligodendroglial differentiation relied on the activation of the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway, as mTORC1 pharmacological inhibition prevented the THC effects. Our study identifies THC as an effective pharmacological strategy to enhance oligodendrogenesis and CNS myelination in vivo.

Inhibition of the mechanistic target of rapamycin induces cell survival via MAPK in tuberous sclerosis complex

Background

Tuberous sclerosis complex (TSC) is a genetic disorder that cause tumors to form in many organs. These lesions may lead to epilepsy, autism, developmental delay, renal, and pulmonary failure. Loss of function mutations in TSC1 and TSC2 genes by aberrant activation of the mechanistic target of rapamycin (mTORC1) signaling pathway are the known causes of TSC. Therefore, targeting mTORC1 becomes a most available therapeutic strategy for TSC. Although mTORC1 inhibitor rapamycin and Rapalogs have demonstrated exciting results in the recent clinical trials, however, tumors rebound and upon the discontinuation of the mTORC1 inhibition. Thus, understanding the underlying molecular mechanisms responsible for rapamycin-induced cell survival becomes an urgent need. Identification of additional molecular targets and development more effective remission-inducing therapeutic strategies are necessary for TSC patients.

Results

We have discovered an Mitogen-activated protein kinase (MAPK)-evoked positive feedback loop that dampens the efficacy of mTORC1 inhibition. Mechanistically, mTORC1 inhibition increased MEK1-dependent activation of MAPK in TSC-deficient cells. Pharmacological inhibition of MAPK abrogated this feedback loop activation. Importantly, the combinatorial inhibition of mTORC1 and MAPK induces the death of TSC2-deficient cells.

Conclusions

Our results provide a rationale for dual targeting of mTORC1 and MAPK pathways in TSC and other mTORC1 hyperactive neoplasm.

The Missing Lnc: The Potential of Targeting Triple-Negative Breast Cancer and Cancer Stem Cells by Inhibiting Long Non-Coding RNAs

Treatment decisions for breast cancer are based on staging and hormone receptor expression and include chemotherapies and endocrine therapy. While effective in many cases, some breast cancers are resistant to therapy, metastasize and recur, leading to eventual death. Higher percentages of tumor-initiating cancer stem cells (CSCs) may contribute to the increased aggressiveness, chemoresistance, and worse outcomes among breast cancer. This may be particularly true in triple-negative breast cancers (TNBCs) which have higher percentages of CSCs and are associated with worse outcomes. In recent years, increasing numbers of long non-coding RNAs (lncRNAs) have been identified as playing an important role in breast cancer progression and some of these have been specifically associated within the CSC populations of breast cancers. LncRNAs are non-protein-coding transcripts greater than 200 nucleotides which can have critical functions in gene expression regulation. The preclinical evidence regarding lncRNA antagonists for the treatment of cancer is promising and therefore, presents a potential novel approach for treating breast cancer and targeting therapy-resistant CSCs within these tumors. Herein, we summarize the lncRNAs that have been identified as functionally relevant in breast CSCs. Furthermore, our review of the literature and analysis of patient datasets has revealed that many of these breast CSC-associated lncRNAs are also enriched in TNBC. Together, this suggests that these lncRNAs may be playing a particularly important role in TNBC. Thus, certain breast cancer-promoting/CSC-associated lncRNAs could be targeted in the treatment of TNBCs and the CSCs within these tumors should be susceptible to anti-lncRNA therapy.

Anti-tumor and anti-metastasis efficacy of E6201, a MEK1 inhibitor, in preclinical models of triple-negative breast cancer

PURPOSE

Triple-negative breast cancer (TNBC) lacks the receptor targets estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2, and thus, it does not respond to receptor-targeted treatments. TNBC has higher recurrence, metastasis, and mortality rates than other subtypes of breast cancer. Mounting data suggest that the MAPK (also known as RAS-RAF-MEK-ERK) pathway is an important therapeutic target in TNBC.

METHODS

To evaluate anti-tumor and anti-metastasis efficacy of E6201, we used cell proliferation assay, soft agar assay, cell cycle assay, Annexin V staining assay, immunoblotting analysis, immunohistochemistry, migration assay, invasion assay, mammary fat pad xenograft, and experimental and spontaneous metastasis xenograft models. We also evaluated the anti-tumor efficacy of E6201 plus CDK4/6 inhibitor, mTOR inhibitor, or ATR inhibitor.

RESULTS

E6201 inhibited TNBC cell colony formation, migration, and invasion in a dose-dependent manner. E6201 induced G1 cell cycle arrest and apoptosis. E6201 inhibited TNBC xenograft growth and inhibited TNBC lung metastasis and improved mouse survival in experimental metastasis and spontaneous metastasis assays. Immunohistochemical staining demonstrated that E6201 decreased the metastatic burden in the lung and decreased phosphorylated ERK expression in a dose-dependent manner. Combination of E6201 with CDK4/6 inhibitor or mTOR inhibitor enhanced E6201's in vitro anti-tumor efficacy.

CONCLUSION

These results indicate that E6201 exhibits anti-tumor efficacy against TNBC in vitro and anti-metastasis efficacy against TNBC in vivo. These results provide a rationale for further clinical development of E6201 as a MAPK-pathway-targeted therapy for TNBC.

Brain Complete Response to Cabozantinib prior to Radiation Therapy in Metastatic Renal Cell Carcinoma

Cabozantinib represents an established vascular endothelial growth factor- (VEGF-) tyrosine kinase inhibitor (TKI) in the treatment paradigm of metastatic renal cell carcinoma (mRCC). Its activity in mRCC patients with brain metastases (BMs) has been largely underreported in prospective clinical trials. We present the unique case of a heavily pretreated mRCC patient with BMs who achieved a brain complete response to cabozantinib prior to receiving radiation therapy. We end with a literature review and discussion of the biologic rationale and growing evidence supporting the intracranial activity of cabozantinib.

Combined use of CDK4/6 and mTOR inhibitors induce synergistic growth arrest of diffuse intrinsic pontine glioma cells via mutual downregulation of mTORC1 activity

Background

Diffuse intrinsic pontine glioma (DIPG) is a lethal type of pediatric brain tumor that is resistant to conventional chemotherapies. Palbociclib is a putative novel DIPG treatment that restricts the proliferation of rapidly dividing cancer cells via selective inhibition of cyclin-dependent kinase (CDK) 4 and CDK6. However, implementing palbociclib as a monotherapy for DIPG is unfeasible, as CDK4/6 inhibitor resistance is commonplace and palbociclib does not readily cross the blood-brain barrier (BBB) or persist in the central nervous system. To inhibit the growth of DIPG cells, we aimed to use palbociclib in combination with the rapamycin analog temsirolimus, which is known to ameliorate resistance to CDK4/6 inhibitors and inhibit BBB efflux.

Materials and methods

We tested palbociclib and temsirolimus in three patient-derived DIPG cell lines. The expression profiles of key proteins in the CDK4/6 and mammalian target of rapamycin (mTOR) signaling pathways were assessed, respectively, to determine feasibility against DIPG. Moreover, we investigated effects on cell viability and examined in vivo drug toxicity.

Results

Immunoblot analyses revealed palbociclib and temsirolimus inhibited CDK4/6 and mTOR signaling through canonical perturbation of phosphorylation of the retinoblastoma (RB) and mTOR proteins, respectively; however, we observed noncanonical downregulation of mTOR by palbociclib. We demonstrated that palbociclib and temsirolimus inhibited cell proliferation in all three DIPG cell lines, acting synergistically in combination to further restrict cell growth. Flow cytometric analyses revealed both drugs caused G₁ cell cycle arrest, and clonogenic assays showed irreversible effects on cell proliferation. Palbociclib did not elicit neurotoxicity in primary cultures of normal rat hippocampi or when infused into rat brains.

Conclusion

These data illustrate the in vitro antiproliferative effects of CDK4/6 and mTOR inhibitors in DIPG cells. Direct infusion of palbociclib into the brain, in combination with systemic delivery of temsirolimus, represents a promising new approach to developing a much-needed treatment for DIPG.

Targeting Brain-Adaptive Cancer Stem Cells Prohibits Brain Metastatic Colonization of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) exhibits more traits possessed by cancer stem cells (CSC) than other breast cancer subtypes and is more likely to develop brain metastases. TNBC patients usually have shorter survival time after diagnosis of brain metastasis, suggesting an innate ability of TNBC tumor cells in adapting to the brain. In this study, we establish novel animal models to investigate early tumor adaptation in brain metastases by introducing both patient-derived and cell line-derived CSC-enriched brain metastasis tumorsphere cells into mice. We discovered astrocyte-involved tumor activation of protocadherin 7 (PCDH7)-PLCβ-Ca2+-CaMKII/S100A4 signaling as a mediator of brain metastatic tumor outgrowth. We further identified and evaluated the efficacy of a known drug, the selective PLC inhibitor edelfosine, in suppressing the PCDH7 signaling pathway to prohibit brain metastases in the animal models. The results of this study reveal a novel signaling pathway for brain metastases in TNBC and indicate a promising strategy of metastatic breast cancer prevention and treatment by targeting organ-adaptive cancer stem cells.Significance: These findings identify a compound to block adaptive signaling between cancer stem cells and brain astrocytes. Cancer Res; 78(8); 2052-64. ©2018 AACR.

Enhancement of Cancer-Specific Protoporphyrin IX Fluorescence by Targeting Oncogenic Ras/MEK Pathway

Protoporphyrin IX (PpIX) is an endogenous fluorescent molecule that selectively accumulates in cancer cells treated with the heme precursor 5-aminolevulinic acid (5-ALA). This cancer-specific accumulation of PpIX is used to distinguish tumor from normal tissues in fluorescence-guided surgery (FGS) and to destroy cancer cells by photodynamic therapy (PDT). In this study, we demonstrate that oncogenic Ras/mitogen-activated protein kinase kinase (MEK) pathway can modulate PpIX accumulation in cancer cells.

Methods: To identify Ras downstream elements involved in PpIX accumulation, chemical inhibitors were used. To demonstrate the increase of PpIX accumulation by MEK inhibition, different human normal and cancer cell lines, BALB/c mice bearing mammary 4T1 tumors and athymic nude mice bearing human tumors were used. To identify the mechanisms of PpIX regulation by MEK, biochemical and molecular biological experiments were conducted.

Results: Inhibition of one of the Ras downstream elements, MEK, promoted PpIX accumulation in cancer cells treated with 5-ALA, while inhibitors against other Ras downstream elements did not. Increased PpIX accumulation with MEK inhibition was observed in different types of human cancer cell lines, but not in normal cell lines. We identified two independent cellular mechanisms that underlie this effect in cancer cells. MEK inhibition reduced PpIX efflux from cancer cells by decreasing the expression level of ATP binding cassette subfamily B member 1 (ABCB1) transporter. In addition, the activity of ferrochelatase (FECH), the enzyme responsible for converting PpIX to heme, was reduced by MEK inhibition. Finally, we found that in vivo treatment with MEK inhibitors increased PpIX accumulation (2.2- to 2.4-fold) within mammary 4T1 tumors in BALB/c mice injected with 5-ALA without any change in normal organs. Similar results were also observed in a human tumor xenograft model.

Conclusion: Our study demonstrates that inhibition of oncogenic Ras/MEK significantly enhances PpIX accumulation in vitro and in vivo in a cancer-specific manner. Thus, suppressing the Ras/MEK pathway may be a viable strategy to selectively intensify PpIX fluorescence in cancer cells and improve its clinical applications in FGS.

Impact of Blood-Brain Barrier Integrity on Tumor Growth and Therapy Response in Brain Metastases

PURPOSE

The role of blood-brain barrier (BBB) integrity for brain tumor biology and therapy is a matter of debate.

EXPERIMENTAL DESIGN

We developed a new experimental approach using in vivo two-photon imaging of mouse brain metastases originating from a melanoma cell line to investigate the growth kinetics of individual tumor cells in response to systemic delivery of two PI3K/mTOR inhibitors over time, and to study the impact of microregional vascular permeability. The two drugs are closely related but differ regarding a minor chemical modification that greatly increases brain penetration of one drug.

RESULTS

Both inhibitors demonstrated a comparable inhibition of downstream targets and melanoma growth in vitro In vivo, increased BBB permeability to sodium fluorescein was associated with accelerated growth of individual brain metastases. Melanoma metastases with permeable microvessels responded similarly to equivalent doses of both inhibitors. In contrast, metastases with an intact BBB showed an exclusive response to the brain-penetrating inhibitor. The latter was true for macro- and micrometastases, and even single dormant melanoma cells. Nuclear morphology changes and single-cell regression patterns implied that both inhibitors, if extravasated, target not only perivascular melanoma cells but also those distant to blood vessels.

CONCLUSIONS

Our study provides the first direct evidence that nonpermeable brain micro- and macrometastases can effectively be targeted by a drug designed to cross the BBB. Small-molecule inhibitors with these optimized properties are promising agents in preventing or treating brain metastases in patients. Clin Cancer Res; 22(24); 6078-87. ©2016 AACRSee related commentary by Steeg et al., p. 5953.

Application of GFP imaging in cancer

Multicolored proteins have allowed the color-coding of cancer cells growing in vivo and enabled the distinction of host from tumor with single-cell resolution. Non-invasive imaging with fluorescent proteins enabled the dynamics of metastatic cancer to be followed in real time in individual animals. Non-invasive imaging of cancer cells expressing fluorescent proteins has allowed the real-time determination of efficacy of candidate antitumor and antimetastatic agents in mouse models. The use of fluorescent proteins to differentially label cancer cells in the nucleus and cytoplasm can visualize the nuclear-cytoplasmic dynamics of cancer cells in vivo including: mitosis, apoptosis, cell-cycle position, and differential behavior of nucleus and cytoplasm that occurs during cancer-cell deformation and extravasation. Recent applications of the technology described here include linking fluorescent proteins with cell-cycle-specific proteins such that the cells change color from red to green as they transit from G1 to S phases. With the macro- and micro-imaging technologies described here, essentially any in vivo process can be imaged, giving rise to the new field of in vivo cell biology using fluorescent proteins.

Enhanced antitumor effects of the BRBP1 compound peptide BRBP1-TAT-KLA on human brain metastatic breast cancer

Novel molecularly targeted agents that block the development and metastasis of human brain metastatic breast cancer hold great promise for their translational value. In this study, we constructed a novel targeting composite peptide BRBP1-TAT-KLA comprising of three elements: a brain metastatic breast carcinoma cell (231-BR)-binding peptide BRBP1, a cell penetrating peptide TAT, and a proapoptotic peptide KLA. This composite peptide efficiently internalized in 231-BR cells and consequently induced mitochondrial damage and cellular apoptosis. Exposure of 231-BR cells to BRBP1-TAT-KLA significantly decreased cell viability and increased apoptosis compared with the cells treated with the control peptides. In vivo relevance of these findings was further corroborated in the 231-BR tumor-bearing mice that demonstrated significantly delayed tumor development and metastasis following administration of BRBP1-TAT-KLA compared with those treated with TAT-KLA alone. Interestingly, BRBP1-TAT-KLA inhibited the formation of both large and micro-metastases, while TAT-KLA alone failed to significantly reduce micro-metastases in the breast cancer brain metastasis mice. BRBP1-TAT-KLA selectively homed to the tumors in vivo where it induced cellular apoptosis without significant toxicity on non-tumor tissues. Our findings therefore demonstrated the enhanced antitumor effects of the BRBP1 compound peptide BRBP1-TAT-KLA, providing insights toward development of a potential therapeutic strategy for brain metastatic breast cancer.

Chemotherapy and biological treatment options in breast cancer patients with brain metastasis: an update

INTRODUCTION

Breast cancer (BC) is the second most common cause of CNS metastasis. Ten to 20% of all, and 38% of human epidermal growth factor-2(+), metastatic BC patients experience brain metastasis (BM). Prolonged survival with better control of systemic disease and limited penetration of drugs to CNS increased the probability of CNS metastasis as a sanctuary site of relapse. Treatment of CNS disease has become an important component of overall disease control and quality of life.

AREAS COVERED

Current standard therapy for BM is whole-brain radiotherapy, surgery, stereotactic body radiation therapy for selected cases, corticosteroids and systemic chemotherapy. Little progress has been made in chemotherapy for the treatment of BM in patients with BC. Nevertheless, new treatment choices have emerged. In this review, we aimed to update current and future treatment options in systemic treatment for BM of BC.

EXPERT OPINION

Cornerstone local treatment options for BM of BC are radiotherapy and surgery in selected cases. Efficacy of cytotoxic chemotherapeutics is limited. Among targeted therapies, lapatinib has activity in systemic treatment of BM particularly when used in combination with capecitabine. Novel agents are currently investigated.

The mTOR signaling pathway as a treatment target for intracranial neoplasms

Inhibition of the mammalian target of rapamycin (mTOR) signaling pathway has become an attractive target for human cancer therapy. Hyperactivation of mTOR has been reported in both sporadic and syndromic (hereditary) brain tumors. In contrast to the large number of successful clinical trials employing mTOR inhibitors in different types of epithelial neoplasms, their use to treat intracranial neoplasms is more limited. In this review, we summarize the role of mTOR activation in brain tumor pathogenesis and growth relevant to new human brain tumor trials currently under way using mTOR inhibitors.

Role of MAPK in oncolytic herpes viral therapy in triple-negative breast cancer

Triple-negative breast cancers (TNBCs) have poor clinical outcomes owing to a lack of targeted therapies. Activation of the MEK/MAPK pathway in TNBC has been associated with resistance to conventional chemotherapy and biologic agents and has a significant role in poor clinical outcomes. NV1066, a replication-competent herpes virus, infected, replicated in and killed all TNBC cell lines (MDA-MB-231, HCC1806, HCC38, HCC1937, HCC1143) tested. Greater than 90% cell kill was achieved in more-sensitive lines (MDA-MB-231, HCC1806, HCC38) by day 6 at a multiplicity of infection (MOI) of 0.1. In less-sensitive lines (HCC1937, HCC1143), NV1066 still achieved >70% cell kill by day 7 (MOI 1.0). In vivo, mean volume of flank tumors 14 days after treatment with NV1066 was 57 versus 438 mm(3) in controls (P=0.002). NV1066 significantly downregulated p-MAPK activation by 48 h in all cell lines in vitro and in MDA-MB-231 xenografts in vivo. NV1066 demonstrated synergistic effects with a MEK inhibitor, PD98059 in vitro. We demonstrate that oncolytic viral therapy (NV1066) effectively treats TNBC with correlation to decreased MEK/MAPK signaling. These findings merit future studies investigating the potential role of NV1066 as a sensitizing agent for conventional chemotherapeutic and biologic agents by downregulating the MAPK signaling pathway.

Tailoring mTOR-based therapy: molecular evidence and clinical challenges

The mTOR signaling pathway integrates inputs from a variety of upstream stimuli to regulate diverse cellular processes including proliferation, growth, survival, motility, autophagy, protein synthesis and metabolism. The mTOR pathway is dysregulated in a number of human pathologies including cancer, diabetes, obesity, autoimmune disorders, neurological disease and aging. Ongoing clinical trials testing mTOR-targeted treatments number in the hundreds and underscore its therapeutic potential. To date mTOR inhibitors are clinically approved to prevent organ rejection, to inhibit restenosis after angioplasty, and to treat several advanced cancers. In this review we discuss the continuously evolving field of mTOR pharmacogenomics, as well as highlight the emerging efforts in identifying diagnostic and prognostic markers, including miRNAs, in order to assess successful therapeutic responses.

PI3K pathway inhibitors for the treatment of brain metastases with a focus on HER2+ breast cancer

The incidence of breast cancer brain metastases has increased in recent years, largely due to improved control of systemic disease with human epidermal growth factor receptor 2 (HER2)-targeted agents and the inability of most of these agents to efficiently cross the blood-blood barrier (BBB) and control central nervous system disease. There is, therefore, an urgent unmet need for treatments to prevent and treat HER2+ breast cancer brain metastases (BCBMs). Aberrant activation of the phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signaling pathway is frequently observed in many cancers, including primary breast tumors and BCBMs. Agents targeting key components of this pathway have demonstrated antitumor activity in diverse cancers, and may represent a new treatment strategy for BCBMs. In preclinical studies, several inhibitors of PI3K and mTOR have demonstrated an ability to penetrate the BBB and down-regulate PI3K signaling, indicating that these agents may be potential therapies for brain metastatic disease. The PI3K inhibitor buparlisib (BKM120) and the mTOR inhibitor everolimus (RAD001) are currently under evaluation in combination with trastuzumab in patients with HER2+ BCBMs.

Transcriptional signaling pathways inversely regulated in Alzheimer's disease and glioblastoma multiform

Convincing epidemiological data suggest an inverse association between cancer and neurodegeneration, including Alzheimer's disease (AD). Since both AD and cancer are characterized by abnormal, but opposing cellular behavior, i.e., increased cell death in AD while excessive cell growth occurs in cancer, this motivates us to initiate the study into unraveling the shared genes and cell signaling pathways linking AD and glioblastoma multiform (GBM). In this study, a comprehensive bioinformatics analysis on clinical microarray datasets of 1,091 GBM and 524 AD cohorts was performed. Significant genes and pathways were identified from the bioinformatics analyses – in particular ERK/MAPK signaling, up-regulated in GBM and Angiopoietin Signaling pathway, reciprocally up-regulated in AD – connecting GBM and AD (P < 0.001), were investigated in details for their roles in GBM growth in an AD environment. Our results showed that suppression of GBM growth in an AD background was mediated by the ERK-AKT-p21-cell cycle pathway and anti-angiogenesis pathway.

Multispectral Imaging

The field of anatomic pathology has changed significantly over the last decades and, as a result of the technological developments in molecular pathology and genetics, has had increasing pressures put on it to become quantitative and to provide more information about protein expression on a cellular level in tissue sections. Multispectral imaging (MSI) has a long history as an advanced imaging modality and has been used for over a decade now in pathology to improve quantitative accuracy, enable the analysis of multicolor immunohistochemistry, and drastically reduce the impact of contrast-robbing tissue autofluorescence common in formalin-fixed, paraffin-embedded tissues. When combined with advanced software for the automated segmentation of different tissue morphologies (eg, tumor vs stroma) and cellular and subcellular segmentation, MSI can enable the per-cell quantitation of many markers simultaneously. This article covers the role that MSI has played in anatomic pathology in the analysis of formalin-fixed, paraffin-embedded tissue sections, discusses the technological aspects of why MSI has been adopted, and provides a review of the literature of the application of MSI in anatomic pathology.

Novel modeling of cancer cell signaling pathways enables systematic drug repositioning for distinct breast cancer metastases

A new type of signaling network element, called cancer signaling bridges (CSB), has been shown to have the potential for systematic and fast-tracked drug repositioning. On the basis of CSBs, we developed a computational model to derive specific downstream signaling pathways that reveal previously unknown target-disease connections and new mechanisms for specific cancer subtypes. The model enables us to reposition drugs based on available patient gene expression data. We applied this model to repurpose known or shelved drugs for brain, lung, and bone metastases of breast cancer with the hypothesis that cancer subtypes have their own specific signaling mechanisms. To test the hypothesis, we addressed specific CSBs for each metastasis that satisfy (i) CSB proteins are activated by the maximal number of enriched signaling pathways specific to a given metastasis, and (ii) CSB proteins are involved in the most differential expressed coding genes specific to each breast cancer metastasis. The identified signaling networks for the three types of breast cancer metastases contain 31, 15, and 18 proteins and are used to reposition 15, 9, and 2 drug candidates for the brain, lung, and bone metastases. We conducted both in vitro and in vivo preclinical experiments as well as analysis on patient tumor specimens to evaluate the targets and repositioned drugs. Of special note, we found that the Food and Drug Administration-approved drugs, sunitinib and dasatinib, prohibit brain metastases derived from breast cancer, addressing one particularly challenging aspect of this disease.

Another review on triple negative breast cancer. Are we on the right way towards the exit from the labyrinth?

Triple negative breast cancer is a heterogeneous group of tumors, lacking the expression of estrogen, progesterone and HER-2 receptors. As frequency, it accounts about 15-20% of all breast cancers. Although in the last years there was a "boom" in publishing over this issue, multiple molecular classifications being elaborated, "the triple negative breast cancer odyssey " is still far away from ending, as the complicated molecular pathways of pathogenesis and drug resistance mechanisms remain yet insufficiently explored. The aim of this review is presentation of molecular signatures that could predict outcome and drug resistance in triple negative breast cancer.

Triple-negative breast cancer: molecular characterization and targeted therapies

SUMMARY Triple-negative breast cancer is an aggressive subtype of breast cancer that does not have targeted therapies available. Recent research has focused on extensive molecular characterization in order to identify therapeutic targets. The Cancer Genome Atlas Network recently published one of the most extensive molecular reviews to date and identified modules of related mutations, some of which have been targeted in clinical trials. Due to tumor heterogeneity, it is unlikely that a single therapy will be effective. Identification of molecular targets and tailored treatments based on the molecular alterations in individual cancers hold the best promise for improving the outcomes of this aggressive breast cancer.

Pazopanib inhibits the activation of PDGFRβ-expressing astrocytes in the brain metastatic microenvironment of breast cancer cells

Brain metastases occur in more than one-third of metastatic breast cancer patients whose tumors overexpress HER2 or are triple negative. Brain colonization of cancer cells occurs in a unique environment, containing microglia, oligodendrocytes, astrocytes, and neurons. Although a neuroinflammatory response has been documented in brain metastasis, its contribution to cancer progression and therapy remains poorly understood. Using an experimental brain metastasis model, we characterized the brain metastatic microenvironment of brain tropic, HER2-transfected MDA-MB-231 human breast carcinoma cells (231-BR-HER2). A previously unidentified subpopulation of metastasis-associated astrocytes expressing phosphorylated platelet-derived growth factor receptor β (at tyrosine 751; p751-PDGFRβ) was identified around perivascular brain micrometastases. p751-PDGFRβ(+) astrocytes were also identified in human brain metastases from eight craniotomy specimens and in primary cultures of astrocyte-enriched glial cells. Previously, we reported that pazopanib, a multispecific tyrosine kinase inhibitor, prevented the outgrowth of 231-BR-HER2 large brain metastases by 73%. Here, we evaluated the effect of pazopanib on the brain neuroinflammatory microenvironment. Pazopanib treatment resulted in 70% (P = 0.023) decrease of the p751-PDGFRβ(+) astrocyte population, at the lowest dose of 30 mg/kg, twice daily. Collectively, the data identify a subpopulation of activated astrocytes in the subclinical perivascular stage of brain metastases and show that they are inhibitable by pazopanib, suggesting its potential to prevent the development of brain micrometastases in breast cancer patients.

Innovative therapeutic strategies in the treatment of brain metastases

Brain metastases (BM) are the most common intracranial tumors and their incidence is increasing. Untreated brain metastases are associated with a poor prognosis and a poor performance status. Metastasis development involves the migration of a cancer cell from the bulk tumor into the surrounding tissue, extravasation from the blood into tissue elsewhere in the body, and formation of a secondary tumor. In the recent past, important results have been obtained in the management of patients affected by BM, using surgery, radiation therapy, or both. Conventional chemotherapies have generally produced disappointing results, possibly due to their limited ability to penetrate the blood-brain barrier. The advent of new technologies has led to the discovery of novel molecules and pathways that have better depicted the metastatic process. Targeted therapies such as bevacizumab, erlotinib, gefitinib, sunitinib and sorafenib, are all licensed and have demonstrated improved survival in patients with metastatic disease. In this review, we will report current data on targeted therapies. A brief review about brain metastatic process will be also presented.

Induction of cytokines and growth factors by rapamycin in the microenvironment of brain metastases of lung cancer

The association between rapamycin and astrocytes in a tumor-bearing mouse model with brain metastases of non-small cell lung cancer (NSCLC) was investigated. For in vitro experiments, NCI-H358, a human lung adenocarcinoma cell line, was co-cultured with immortalized astrocytes, and treated with rapamycin, an mTOR inhibitor. We evaluated the expression of interleukin-1 (IL-1), interleukin-3 (IL-3), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), transforming growth factor-β (TGF-β), insulin-like growth factor-1 (IGF-1), platelet-derived growth factor (PDGF), chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-1 (MIP-1) in tumor cells in vivo. Rapamycin is cytotoxic in vitro; however, co-culturing tumor cells and astrocytes induced tumor cell survival. IL-1, IL-3, IL-6, TNF-α, TGF-β, PDGF, MCP-1 and MIP-1 expression were higher in rapamycin-treated mice compared to the control group, however, IGF-1 expression was lower. Notably, treatment with rapamycin before inoculating tumor cells affected cytokine expression in the tumor microenvironment. We suggest that growth factors and cytokines in the tumor microenvironment play a role in the survival of cancer cells in brain metastases.

[Systemic treatment of brain metastases from breast cancer: cytotoxic chemotherapy and targeted therapies]

Prevalence of brain metastases is increasing in breast cancer. Brain metastases represent a poor-prognosis disease for which local treatments continue to play a major role. In spite of the presence of a physiological blood-brain barrier limiting their activity, some systemic treatments may display a significant antitumor activity at the central nervous system level. In HER2-positive metastatic breast cancer with brain metastases not previously treated with whole brain radiotherapy, capecitabine and lapatinib combination obtains a volumetric reponse in two thirds of patients (LANDSCAPE study). If confirmed, these results could modify in selected patients the layout of therapeutic strategies. Promoting novel targeted approaches and innovative therapeutic combinations is a critical need to improve survival of breast cancer patients with brain metastases.

Involvement of epidermal growth factor receptor overexpression in the promotion of breast cancer brain metastasis

BACKGROUND

Brain-metastatic breast cancer (BMBC) is increasing and poses a severe clinical problem because of the lack of effective treatments and because the underlying molecular mechanisms are largely unknown. Recent work has demonstrated that deregulation of epidermal growth factor receptor (EGFR) may correlate with BMBC progression. However, the exact contribution that EGFR makes to BMBC remains unclear.

METHODS

The role of EGFR in BMBC was explored by serial analyses in a brain-trophic clone of human MDA-MB-231 breast carcinoma cells (231-BR cells). EGFR expression was inhibited by stable short-hairpin RNA transfection or by the kinase inhibitor erlotinib, and it was activated by heparin-binding epidermal growth factor-like growth factor (HB-EGF). Cell growth and invasion activities also were analyzed in vitro and in vivo.

RESULTS

EGFR inhibition or activation strongly affected 231-BR cell migration/invasion activities as assessed by an adhesion assay, a wound-healing assay, a Boyden chamber invasion assay, and cytoskeleton staining. Also, EGFR inhibition significantly decreased brain metastases of 231-BR cells in vivo. Surprisingly, changes to EGFR expression affected cell proliferation activities less significantly as determined by a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, an anchorage-independent growth assay, and cell cycle analysis. Immunoblot analysis suggested that EGFR drives cells' invasiveness capability mainly through phosphoinositide 3-kinase/protein kinase B and phospholipase C γ downstream pathways. In addition, EGFR was involved less in proliferation because of the insensitivity of the downstream mitogen-activated protein kinase pathway.

CONCLUSIONS

The current results indicated that EGFR plays more important roles in cell migration and invasion to the brain than in cell proliferation progression on 231-BR cells, providing new evidence of the potential value of EGFR inhibition in treating BMBC.