Molecular determinants of lung cancer metastasis to the central nervous system

AKT1 Transcriptomic Landscape in Breast Cancer Cells

Overexpression and hyperactivation of the serine/threonine protein kinase B (AKT) pathway is one of the most common cellular events in breast cancer progression. However, the nature of AKT1-specific genome-wide transcriptomic alterations in breast cancer cells and breast cancer remains unknown to this point. Here, we delineate the impact of selective AKT1 knock down using gene-specific siRNAs or inhibiting the AKT activity with a pan-AKT inhibitor VIII on the nature of transcriptomic changes in breast cancer cells using the genome-wide RNA-sequencing analysis. We found that changes in the cellular levels of AKT1 lead to changes in the levels of a set of differentially expressed genes and, in turn, imply resulting AKT1 cellular functions. In addition to an expected positive relationship between the status of AKT1 and co-expressed cellular genes, our study unexpectedly discovered an inherent role of AKT1 in inhibiting the expression of a subset of genes in both unstimulated and growth factor stimulated breast cancer cells. We found that depletion of AKT1 leads to upregulation of a subset of genes—many of which are also found to be downregulated in breast tumors with elevated high AKT1 as well as upregulated in breast tumors with no detectable AKT expression. Representative experimental validation studies in two breast cancer cell lines showed a reasonable concurrence between the expression data from the RNA-sequencing and qRT-PCR or data from ex vivo inhibition of AKT1 activity in cancer patient-derived cells. In brief, findings presented here provide a resource for further understanding of AKT1-dependent modulation of gene expression in breast cancer cells and broaden the scope and significance of AKT1 targets and their functions.

The structure of blood-tumor barrier and distribution of chemotherapeutic drugs in non-small cell lung cancer brain metastases

Background

Brain metastasis is an important cause of increased mortality in patients with non-small cell lung cancer (NSCLC). In brain metastasis, the blood–brain barrier (BBB) is frequently impaired, forming blood–tumor barrier (BTB). The efficacy of chemotherapy is usually very poor. However, the characteristics of BTB and the impacts of BTB on chemotherapeutic drug delivery remain unclear. The present study investigated the structure of BTB, as well as the distribution of routine clinical chemotherapeutic drugs in both brain and peripheral tumors.

Methods

Bioluminescent image was used to monitor the tumor load after intracranial injection of lung cancer Lewis cells in mice. The permeability of BBB and BTB was measured by fluorescent tracers of evans blue and fluorescein sodium. Transmission electron microscopy (TEM), immunohistochemistry and immunofluorescence were performed to analyze structural differences between BBB and BTB. The concentrations of chemotherapeutic drugs (gemcitabine, paclitaxel and pemetrexed) in tissues were assayed by liquid chromatography with tandem mass spectrometry (LC-MS/MS).

Results

Brain metastases exhibited increased BTB permeability compared with normal BBB detected by fluorescence tracers. TEM showed abnormal blood vessels, damaged endothelial cells, thick basement membranes, impaired intercellular endothelial tight junctions, as well as increased fenestrae and pinocytotic vesicles in metastatic lesions. Immunohistochemistry and immunofluorescence revealed that astrocytes were distributed surrounded the blood vessels both in normal brain and the tumor border, but no astrocytes were found in the inner metastatic lesions. By LC-MS/MS analysis, gemcitabine showed higher permeability in brain metastases.

Conclusions

Brain metastases of lung cancer disrupted the structure of BBB, and this disruption was heterogeneous. Chemotherapeutic drugs can cross the BTB of brain metastases of lung cancer but have difficulty crossing the normal BBB. Among the three commonly used chemotherapy drugs, gemcitabine has the highest distribution in brain metastases. The permeability of chemotherapeutic agents is related to their molecular weight and liposolubility.

In vivo Tumor Growth and Spontaneous Metastasis Assays Using A549 Lung Cancer Cells

Metastasis accounts for the majority of cancer related deaths. The genetically engineered mouse (GEM) models and cell line-based subcutaneous and orthotopic mouse xenografts have been developed to study the metastatic process. By using lung cancer cell line A549 as an example, we present a modified protocol to establish the cell line-based xenograft. Our protocol ensures sufficient establishment of the mouse xenografts and allows us to monitor tumor growth and spontaneous metastasis. This protocol could be adapted to other types of established cancer cell lines or primary cancer cells to study the mechanism of metastatic process as well as to test the effect of the potential anti-cancer agents on tumor growth and metastatic capacity.

Candidate genes and pathways associated with brain metastasis from lung cancer compared with lymph node metastasis

Brain metastasis from lung cancer (BMLC) is one of the common types of metastasis associated with poor prognosis. The aim of the present study was to elucidate the underlying molecular mechanisms of BMLC. The mRNA microarray dataset GSE18549 was downloaded from the Gene Expression Omnibus database. The Limma package of R was used to screen the differentially expressed genes (DEGs). Based on the DAVID database, functional and pathway enrichment analyses of DEGs were performed. Furthermore, the protein-protein interaction (PPI) network was predicted using the STRING database and visualized with Cytoscape software. In addition, hub genes and significant modules were selected based on the network. A total of 190 DEGs with log₂|(fold change)|>1, including 129 significantly downregulated DEGs and 61 upregulated DEGs, were obtained. Gene Ontology functional enrichment analysis indicated that downregulated DEGs were mainly associated with ‘immune response’, ‘cell activation’ and ‘leukocyte activation’, while the upregulated DEGs were involved in ‘DNA repair’ and ‘viral process’. Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated that the downregulated DEGs were mainly enriched in ‘chemokine signaling pathway’, whereas the upregulated DEGs were associated with ‘oocyte meiosis’. Based on the PPI network, 9 hub genes were selected, namely tumor necrosis factor, C-C motif chemokine ligand (CCL) 2, CD34, vascular cell adhesion molecule 1, CD48, CD27, CCL19, C-X-C motif chemokine receptor 6 and C-C motif chemokine receptor 2. The present study sheds light on the molecular mechanisms of BMLC and may provide molecular targets and diagnostic biomarkers for BMLC.

Systemic therapy for brain metastases

Metastases from cells outside of the central nervous system are the most common cancer found in the brain and are commonly associated with poor prognosis. Although cancer treatment is improving overall, central nervous system metastases are becoming more prevalent and require finesse to properly treat. Physicians must consider the biology of the primary tumor and the complex neurological environment that the metastasis resides in. This can be further complicated by the fact that the practice of cancer management is constantly evolving and therapy that works outside of the blood-brain barrier may not be effective inside of it. Therefore, this review seeks to update the reader on recent advancements made on the three most common sources of brain metastases: lung cancer, breast cancer, and melanoma. Each of these malignancies has been the subject of intriguing and novel avenues of therapy which are reviewed here.

Efficacy and Safety of Radiotherapy Plus EGFR-TKIs in NSCLC Patients with Brain Metastases: A Meta-Analysis of Published Data

Background: The role of radiotherapy (RT) combined with epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) in non-small cell lung cancer (NSCLC) patients with brain metastasis (BM) remains controversial. Therefore, we conducted a meta-analysis to comprehensively evaluate the efficacy and safety of RT plus EGFR-TKIs in those patients. Materials and Methods: Relevant literatures published between 2012 and 2017 were searched. Objective response rate(ORR), disease control rate (DCR), overall survival (OS), intracranial progression-free survival (I-PFS) and adverse events (AEs) were extracted. The combined hazard ratios (HRs) and relative risks (RRs) were calculated using random effects models. Results: Twenty-four studies (2810 patients) were included in the analysis. Overall, RT plus EGFR-TKIs had higher ORR (RR = 1.32, 95%CI: 1.13–1.55), DCR (RR = 1.12, 95%CI: 1.04–1.22), and longer OS (HR = 0.72, 95%CI: 0.59–0.89), I-PFS (HR = 0.64, 95%CI: 0.50–0.82) than monotherapy, although with higher overall AEs (20.2% vs 11.8%, RR = 1.34, 95% CI: 1.11–1.62). Furthermore, subgroup analyses found concurrent RT plus EGFR-TKIs could prolong OS (HR = 0.69, 95%CI: 0.55–0.86) and I-PFS (HR = 0.57, 95%CI: 0.44–0.75). Asian ethnicity and lung adenocarcinoma (LAC) patients predicted a more favorable prognosis (HR = 0.69,95%CI: 0.54–0.88, HR = 0.66, 95%CI: 0.53–0.83, respectively). Conclusion: RT plus EGFR-TKIs had higher response rate, longer OS and I-PFS than monotherapy in NSCLC patients with BM. Asian LAC patients with EGFR mutation had a better prognosis with concurrent treatment. The AEs of RT plus EGFR-TKIs were tolerated.

Targeted DNA sequencing of non-small cell lung cancer identifies mutations associated with brain metastases

Introduction

This study explores the hypothesis that dominant molecular oncogenes in non-small cell lung cancer (NSCLC) are associated with metastatic spread to the brain.

Methods

NSCLC patient groups with no evidence of metastasis, with metastatic disease to a non-CNS site, who developed brain metastasis after diagnosis, and patients with simultaneous diagnosis of NSCLC and metastatic brain lesions were studied using targeted sequencing.

Results

In patients with brain metastasis versus those without, only 2 variants (one each in BCL6 and NOTHC2) were identified that occurred in ≥ 4 NSCLC of patients with brain metastases but ≤ 1 of the NSCLC samples without brain metastases. At the gene level, 20 genes were found to have unique variants in more than 33% of the patients with brain metastases. When analyzed at the patient level, these 20 genes formed the basis of a predictive test to discriminate those with brain metastasis. Further analysis showed that PI3K/AKT signaling is altered in both the primary and metastases of NSCLC patients with brain lesions.

Conclusion

While no single variant was associated with brain metastasis, this study describes a potential gene panel for the identification of patients at risk and implicates PI3K/AKT signaling as a therapeutic target.

Radiotherapy plus EGFR TKIs in non-small cell lung cancer patients with brain metastases: an update meta-analysis

Brain metastasis (BM) is the common complication of non‐small cell lung cancer (NSCLC) with a poor prognosis and dismal survival rate. This update meta‐analysis aimed to derive a more precise estimation of radiotherapy plus epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) in NSCLC patients with BM. PubMed, EMBASE, Web of Science, Google Scholar, and Cochrane Library were searched to identify any relevant publications. After screening the literature and undertaking quality assessment and data extraction, the meta‐analysis was performed using STATA Version 12.0. In total, 15 studies involving 1552 participants were included. The results indicated that radiotherapy plus EGFR TKIs was more effective at improving response rate and disease control rate (DCR) (risk ratio (RR) = 1.48, 95% confidence interval [CI]: 1.12–1.96, P = 0.005; RR = 1.29, 95% CI: 1.02–1.60, P = 0.035; respectively) than radiotherapy alone or plus chemotherapy. Moreover, radiotherapy plus EGFR TKIs significantly prolonged the time to central nervous system progression (CNS‐TTP) (HR = 0.56, 95% CI [0.33, 0.80]; P = 0.000) and median overall survival (OS) (HR = 0.58, 95% CI [0.42, 0.74]; P = 0.000) but significantly increased adverse events (any grade) (RR = 1.25, 95% CI [1.01, 1.57]; P = 0.009), especially rash and dry skin. These results suggested that radiotherapy plus EGFR TKIs produced superior response rate and DCR and markedly prolonged the CNS‐TTP and OS of NSCLC patients with BM. However, combined groups had the higher rate of incidence of overall adverse effects, especially rash and dry skin.

FN14 and GRP94 expression are prognostic/predictive biomarkers of brain metastasis outcome that open up new therapeutic strategies

Brain metastasis is a devastating problem in patients with breast, lung and melanoma tumors. GRP94 and FN14 are predictive biomarkers over-expressed in primary breast carcinomas that metastasized in brain. To further validate these brain metastasis biomarkers, we performed a multicenter study including 318 patients with breast carcinomas. Among these patients, there were 138 patients with metastasis, of whom 84 had brain metastasis. The likelihood of developing brain metastasis increased by 5.24-fold (95%CI 2.83-9.71) and 2.55- (95%CI 1.52-4.3) in the presence of FN14 and GRP94, respectively. Moreover, FN14 was more sensitive than ErbB2 (38.27 vs. 24.68) with similar specificity (89.43 vs. 89.55) to predict brain metastasis and had identical prognostic value than triple negative patients (p < 0.0001). Furthermore, we used GRP94 and FN14 pathways and GUILD, a network-based disease-gene prioritization program, to pinpoint the genes likely to be therapeutic targets, which resulted in FN14 as the main modulator and thalidomide as the best scored drug. The treatment of mice with brain metastasis improves survival decreasing reactive astrocytes and angiogenesis, and down-regulate FN14 and its ligand TWEAK. In conclusion our results indicate that FN14 and GRP94 are prediction/prognosis markers which open up new possibilities for preventing/treating brain metastasis.