Small-cell lung cancer brain metastasis: From molecular mechanisms to diagnosis and treatment

Lung cancer is the most malignant human cancer worldwide, also with the highest incidence rate. However, small-cell lung cancer (SCLC) accounts for 14 % of all lung cancer cases. Approximately 10 % of patients with SCLC have brain metastasis at the time of diagnosis, which is the leading cause of death of patients with SCLC worldwide. The median overall survival is only 4.9 months, and a long-tern cure exists for patients with SCLC brain metastasis due to limited common therapeutic options. Recent studies have enhanced our understanding of the molecular mechanisms leading to meningeal metastasis, and multimodality treatments have brought new hopes for a better cure for the disease. This review aimed to offer an insight into the cellular processes of different metastatic stages of SCLC revealed by the established animal models, and into the major diagnostic methods of SCLC. Additionally, it provided in-depth information on the recent advances in SCLC treatments, and highlighted several new models and biomarkers with promises to improve the prognosis of SCLC.     

Brain microvascular endothelium induced-annexin A1 secretion contributes to small cell lung cancer brain metastasis

Small cell lung cancer is the most aggressive histologic subtype of lung cancer, with a strong predilection for metastasizing to brain early. However, the cellular and molecular basis is poorly known. Here, we provided evidence to reveal the role of annexin A1 in small cell lung cancer metastasis to brain. Firstly, the elevated annexin A1 serum levels in small cell lung cancer patients were associated with brain metastasis. The levels of annexin A1 were also upregulated in NCI-H446 cells, a small cell lung cancer cell line, upon migration into the mice brain. More interestingly, annexin A1 was secreted by NCI-H446 cells in a time-dependent manner when co-culturing with human brain microvascular endothelial cells, which was identified with the detections of annexin A1 in the co-cultured cellular supernatants by ELISA and western blot. Further results showed that blockage of annexin A1 in the co-cultured cellular supernatants using a neutralized antibody significantly inhibited NCI-H446 cells adhesion to brain endothelium and its transendothelial migration. Conversely, the addition of Ac2-26, an annexin A1 mimic peptide, enhanced these effects. Furthermore, knockdown of annexin A1 in NCI-H446 cells prevented its transendothelial migration in vitro and metastasis to mice brain in vivo. Our data showed that small cell lung cancer cell in brain microvasculature microenvironment could express much more annexin A1 and release it outside, which facilitated small cell lung cancer cell to gain malignant properties of entry into brain. These findings provided a potential target for the management of SCLC brain metastasis.     

The brain microenvironment and cancer metastasis

The process of metastasis consists of a series of sequential, selective steps that few cells can complete. The outcome of cancer metastasis depends on multiple interactions between metastatic cells and homeostatic mechanisms that are unique to one or another organ microenvironment. The specific organ microenvironment determines the extent of cancer cell proliferation, angiogenesis, invasion and survival. Many lung cancer, breast cancer, and melanoma patients develop fatal brain metastases that do not respond to therapy. The blood-brain barrier is intact in and around brain metastases that are smaller than 0.25 mm in diameter. Although the blood-brain barrier is leaky in larger metastases, the lesions are resistant to many chemotherapeutic drugs. Activated astrocytes surround and infiltrate brain metastases. The physiological role of astrocytes is to protect against neurotoxicity. Our current data demonstrate that activated astrocytes also protect tumor cells against chemotherapeutic drugs.     

DJ-1 may contribute to metastasis of non-small cell lung cancer

Lung cancer is a leading cause of cancer-related death, about 40% human non-small cell lung cancer (NSCLC) patients showed lymph node involvements. However, the precise mechanism for the metastasis is still not fully understood. This study was to analyze the potential molecular mechanism for lung cancer metastasis. In the current study, proteomics analysis by two-dimensional electrophoresis (2-DE) was performed first to identify the differentially expressed protein between the higher metastasis lung adenocarcinoma cell line Anip973 and the lower metastasis lung adenocarcinoma cell line AGZY83-a. We confirmed the result by RT-PCR, immunoblotting and immunocytochemistry analyses in these two cell lines. Then we examined the expression of the differentially expressed protein in tumor tissues of NSCLC patients by immunoblotting and immunohistochemistry analyses. Using 2-DE analysis, we have identified DJ-1 was expressed higher in the higher metastasis Anip973 compared to the parental cell line AGZY83-a, that was confirmed by RT-PCR, immunoblotting and immunocytochemistry analyses. In NSCLC patients?? tumor tissues study, immunoblotting data showed that, DJ-1 expression level was significantly higher in 72.2% (13/18) of NSCLC tissue samples compared to that in paired normal lung tissues (P?=?0.044). Immunohistochemistry analysis demonstrated increased DJ-1 expression in 85 NSCLC tumor tissue samples compared with 7 normal lung tissue samples (P?=?0.044). DJ-1 expression was also found to be significantly correlated with cancer lymphatic metastasis (P?=?0.039). DJ-1 might contribute to the metastasis of NSCLC.     

Identification of potential genes related to breast cancer brain metastasis in breast cancer patients

Brain metastases (BMs) usually develop in breast cancer (BC) patients. Thus, the molecular mechanisms of breast cancer brain metastasis (BCBM) are of great importance in designing therapeutic strategies to treat or prevent BCBM. The present study attempted to identify novel diagnostic and prognostic biomarkers of BCBM. Two datasets ({"type":"entrez-geo","attrs":{"text":"GSE125989","term_id":"125989"}}GSE125989 and {"type":"entrez-geo","attrs":{"text":"GSE100534","term_id":"100534"}}GSE100534) were obtained from the Gene Expression Omnibus (GEO) database to find differentially expressed genes (DEGs) in cases of BC with and without brain metastasis (BM). A total of 146 overlapping DEGs, including 103 up-regulated and 43 down-regulated genes, were identified. Functional enrichment analysis showed that these DEGs were mainly enriched for functions including extracellular matrix (ECM) organization and collagen catabolic fibril organization. Using protein–protein interaction (PPI) and principal component analysis (PCA) analysis, we identified ten key genes, including LAMA4, COL1A1, COL5A2, COL3A1, COL4A1, COL5A1, COL5A3, COL6A3, COL6A2, and COL6A1. Additionally, COL5A1, COL4A1, COL1A1, COL6A1, COL6A2, and COL6A3 were significantly associated with the overall survival of BC patients. Furthermore, COL6A3, COL5A1, and COL4A1 were potentially correlated with BCBM in human epidermal growth factor 2 (HER2) expression. Additionally, the miR-29 family might participate in the process of metastasis by modulating the cancer microenvironment. Based on datasets in the GEO database, several DEGs have been identified as playing potentially important roles in BCBM in BC patients.     

A stochastic Markov chain model to describe lung cancer growth and metastasis

A stochastic Markov chain model for metastatic progression is developed for primary lung cancer based on a network construction of metastatic sites with dynamics modeled as an ensemble of random walkers on the network. We calculate a transition matrix, with entries (transition probabilities) interpreted as random variables, and use it to construct a circular bi-directional network of primary and metastatic locations based on postmortem tissue analysis of 3827 autopsies on untreated patients documenting all primary tumor locations and metastatic sites from this population. The resulting 50 potential metastatic sites are connected by directed edges with distributed weightings, where the site connections and weightings are obtained by calculating the entries of an ensemble of transition matrices so that the steady-state distribution obtained from the long-time limit of the Markov chain dynamical system corresponds to the ensemble metastatic distribution obtained from the autopsy data set. We condition our search for a transition matrix on an initial distribution of metastatic tumors obtained from the data set. Through an iterative numerical search procedure, we adjust the entries of a sequence of approximations until a transition matrix with the correct steady-state is found (up to a numerical threshold). Since this constrained linear optimization problem is underdetermined, we characterize the statistical variance of the ensemble of transition matrices calculated using the means and variances of their singular value distributions as a diagnostic tool. We interpret the ensemble averaged transition probabilities as (approximately) normally distributed random variables. The model allows us to simulate and quantify disease progression pathways and timescales of progression from the lung position to other sites and we highlight several key findings based on the model.     

微RNA调节肺癌转移的分子机制

微RNA(microRNA,miRNA)是一类长约22 nt的非编码小分子RNA,在转录后水平上通过基因沉默调节靶基因的活性。近年来,miRNA与肿瘤转移关系的研究成为探讨肿瘤转移调控机制的热点。越来越多的研究提示miRNA在肿瘤转移过程中发挥着重要作用。肺癌转移是影响肺癌预后的关键,是一种复杂的多因素、多步骤、多基因参与调控的过程。研究miRNA对肺癌转移的作用有助于我们找到阻断肺癌转移的靶点。本文就miRNA和肺癌转移关系的研究进展作一综述。     

MiRNA调控非小细胞肺癌转移的研究进展

微小RNA是内源性的非编码小RNA分子,通过与靶mRNA的结合在转录后水平调控基因的表达,从而参与众多生命活动的调控。NSCLC是严重威胁人类健康的恶性肿瘤,侵袭转移是其主要特征,也是其治疗失败和死亡的主要原因。miRNA可以通过促进上皮-间质转化、金属基质蛋白酶表达,以及血管生成来促进NSCLC转移,而且miRNA在调节肺癌干细胞特性中也发挥着重要作用。转移相关的miRNA已成为肺癌靶向治疗的新靶点。     

Phosphorylated-Akt overexpression is associated with a higher risk of brain metastasis in patients with non-small cell lung cancer

Brain metastasis (BM) of non-small cell lung cancer (NSCLC) is relatively common and has a poor prognosis. Moreover, identifying which patients are more likely to develop BM is challenging. Akt, a serine/threonine-specific protein kinase, can be activated in various tumors, including lung cancer, and may be associated with poor prognosis. Here, we used immunohistochemistry to evaluate phosphorylated-Akt (p-Akt) expression in tumor tissues of 99 NSCLC patients. We also analyzed the genotype of the patients for two single nucleotide polymorphisms (SNPs) of the AKT1 gene, rs2498804 and rs2494732. We found that p-Akt expression differs between NSCLC patients and correlates with the risk of BM. Indeed, patients exhibiting medium to high p-Akt expression had a higher incidence of BM than those exhibiting low to no p-Akt expression (39% vs 16%). Our data also show that patients with the rs2498804 GT/GG and rs2494732 CT/TT variant genotypes were more likely to exhibit higher levels of p-Akt expression than those with the rs2498804 TT and rs2494732 CC variant genotypes (35% vs. 24% and 37% vs. 25%, respectively). Our results suggest that the level of expression of p-Akt, which may be affected by the AKT1 genotype, is correlated with the risk of BM. However, further studies are needed to establish p-Akt as a predictive marker for BM in NSCLC patients.     

Cyclin D1 regulates lung cancer invasion and metastasis

Cyclin D1, as a regulatory factor in cell cycle, is highly expressed in many tumors, such as lung cancer, breast cancer and thyroid cancer. The aim of the present study was to study the role of Cyclin D1 in invasion and metastasis of lung cancer cells. Lung adenocarcinoma cell line A549 and squamous cell line SK-MES-1 were selected as the objects, because A549 expresses Cyclin D1 highly, and SK-MES-1 expresses lowly. Nude mice were injected with A549 or SK-MES-1 via tail vein, and were sacrificed after 4 weeks for cancer tissue isolation. The harvested cancer cells were reinjected into another nude mouse. After one more time of such seeding, highly metastatic lung cancer model was established. After A549 and SK-MES-1 were transfected with Cyclin D1 RNAi and expression vector respectively, transwell migration assay was used to analyze transferring capacity of lung cancer cells. Western blot was used to detect Cyclin D1 and WNT/TCF pathway proteins expressions in parental cell lines and cancer tissue from metastasis model animals. The results showed that, along with the increase of seeding times, lung cancer cells from model animals, no matter A549 or SK-MES-1, exhibited augmented metastasis activity and up-regulated Cyclin D1 expression. The transferring capacity was weakened significantly in A549 cells where the Cyclin D1 was interfered by RNAi, and it was enhanced significantly in SK-MES-1 cells which were transfected with the expression vector of Cyclin D1. The expressions of WNT/TCF pathway proteins, including β-catenin, lymphoid enhancer-binding factor (LEF) and T cell factor (TCF), increased significantly in highly metastatic model animals. The parental cell lines showed lower expressions of WNT/TCF pathway proteins compared with cancer tissue from metastasis model animals. These results suggest that Cyclin D1 is closely related with the invasion and metastasis of lung cancer cells, and the WNT/TCF signal pathway may promote the expression of Cyclin D1.     

Differential protein expression on the cell surface of colorectal cancer cells associated to tumor metastasis

Progression to metastasis is the critical point in colorectal cancer (CRC) survival. However, the proteome associated to CRC metastasis is very poorly understood at the moment. In this study, we used stable isotope labeling by amino acids in cell culture to compare two CRC cell lines: KM12C and KM12SM, representing poorly versus highly metastatic potential, to find and quantify the differences in protein expression, mostly at the cell surface level. After biotinylation followed by affinity purification, membrane proteins were separated by SDS‐PAGE and analyzed using nanoflow LC‐ESI‐LTQ. A total of 291 membrane and membrane‐associated proteins were identified with a p value<0.01, from which 60 proteins were found to be differentially expressed by more than 1.5‐fold. We identified a number of cell signaling, CDs, integrins and other cell adhesion molecules (cadherin 17, junction plakoglobin (JUP)) among the most deregulated proteins. They were validated by Western blot, confocal microscopy and flow cytometry analysis. Immunohistochemical analysis of paired tumoral samples confirmed that these differentially expressed proteins were also altered in human tumoral tissues. A good correlation with a major abundance in late tumor stages was observed for JUP and 17‐β‐hydroxysteroid dehydrogenase type 8 (HSD17B8). Moreover, the combined increase in JUP, occludin and F11 receptor expression together with cadherin 17 expression could suggest a reversion to a more epithelial phenotype in highly metastatic cells. Relevant changes were observed also at the metabolic level in the pentose phosphate pathway and several amino acid transporters. In summary, the identified proteins provide us with a better understanding of the events involved in liver colonization and CRC metastasis.     

Muscular metastasis, a rare presentation of non-small-cell lung cancer

A 71-year-old man presented with a 2-week history of pain and swelling of his left arm. Subsequent investigations revealed an intramuscular lesion, suggestive of soft tissue sarcoma. Histologic analysis was surprisingly consistent with metastasis from a primary squamous cell lung cancer. Skeletal muscle metastasis as a mode of presentation of primary lung cancer is an unusual phenomenon. A brief literature review accompanies this report.     

肺癌转移抑制相关基因研究进展

肺癌是发病率和死亡率增长最快、对人类健康威胁最大的恶性肿瘤之一。侵袭转移是肺癌患者死亡的首要原因。研究表明,在肺癌中发挥转移抑制作用的相关基因主要有nm23、KAI1、TIMP、Cadherin以及MRP-1等。本文对近年来这些基因的研究进展及其对肺癌侵袭转移的抑制作用作一综述     

肺癌患者外周血血小板在肺癌血行转移中的作用研究

目的：观察肺癌患者外周血血小板对肺癌分期和血行转移的影响。方法：选择在我院呼吸科初诊的原发性肺癌患168例,分析其外周血小板计数与肺癌病理类型和分期的关系,并在模拟流体状态下,体外研究活化血小板对培养的肺癌细胞和内皮细胞相互作用的影响。结果：肺腺癌中外周血血小板计数增高现象最为明显,占37.09%（23/62）（P〈0.05）,鳞癌占22.64%,小细胞癌占22.70%,其他占14.20%。其中有远处血行转移者血小板增多（20.24%）较无明显转移者（7.14%）相差显著（P〈0.01）。同时体外研究显示流体状态对肺癌细胞粘附存在影响,而活化血小板增强了肺癌细胞与内皮细胞的相互作用。结论：血小板活化与肺癌尤其是肺腺癌的血行转移密切相关;活化血小板增强了肺癌细胞与内皮细胞的相互作用是血小板促进肺癌血行转移的重要机制之一。     

Inhibition of checkpoint kinase 1 sensitizes lung cancer brain metastases to radiotherapy

The most important therapeutic tool in brain metastasis is radiation therapy. However, resistance to radiation is a possible cause of recurrence or treatment failure. Recently, signal pathways about DNA damage checkpoints after irradiation have been noticed. We investigated the radiosensitivity can be enhanced with treatment of Chk1 inhibitor, AZD7762 in lung cancer cell lines and xenograft models of lung cancer brain metastasis. Clonogenic survival assays showed enhancement of radiosensitivity with AZD7762 after irradiation of various doses. AZD7762 increased ATR/ATM-mediated Chk1 phosphorylation and stabilized Cdc25A, suppressed cyclin A expression in lung cancer cell lines. In xenograft models of lung cancer (PC14PE6) brain metastasis, AZD7762 significantly prolonged the median survival time in response to radiation. Depletion of Chk1 using shRNA also showed an enhancement of sensitivity to radiation in PC14PE6 cells. The results of this study support that Chk1 can be a good target for enhancement of radiosensitivity.     

Gangliosides activate cultured rat brain microglia

Microglia, brain resident macrophages, are activated in brain injuries and several neurodegenerative diseases. However, microglial activators that are produced in the brain are not yet defined. In this study, we showed that gangliosides, sialic acid-containing glycosphingolipids, could be a microglial activator. Gangliosides induced production of nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) and expression of cyclooxygenase-2 (COX-2). The effect of gangliosides on NO release increased dose-dependently in the range of 10-100 microgram/ml; however, the effect decreased at concentrations higher than 200 microgram/ml. Specific types of gangliosides showed differential effects on microglial activation. Similar to gangliosides, GT1b induced production of NO and TNF-alpha and expression of COX-2. However, GM1 and GD1a induced expression of COX-2 but had little effect on NO and TNF-alpha release. The effect of gangliosides and GT1b on NO release was reduced in the presence of neuraminidase, which removes sialic acid residues from gangliosides and GT1b. Gangliosides activated extracellular signal-regulated kinase significantly but activated c-jun N-terminal kinase/stress-activated protein kinase and p38 relatively weakly. The inhibition of extracellular signal-regulated kinase by PD98059 reduced NO release from both gangliosides- and GT1b-treated microglia whereas inhibition of p38 by SB203580 increased it rather slightly. Gangliosides activated NF-kappaB, and N-acetyl cystein, an inhibitor of NF-kappaB, reduced NO release. These results suggest that gangliosides could be a microglial activator that functions via activation of mitogen-activated protein kinase and NF-kappaB.