Expression profiling reveals genes associated with transendothelial migration of tumor cells: a functional role for alphavbeta3 integrin

ITGAV Promotes the Progression of Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinoma (HNSCC) refers to the malignancy of squamous cells in the head and neck region. Ranked as the seventh most common cancer worldwide, HNSCC has a very low survival rate, highlighting the importance of finding therapeutic targets for the disease. Integrins are cell surface receptors that play a crucial role in mediating cellular interactions with the extracellular matrix (ECM). Within this protein family, Integrin αV (ITGAV) has received attention for its important functional role in cancer progression. In this study, we first demonstrated the upregulation of ITGAV expression in HNSCC, with higher ITGAV expression levels correlating with significantly lower overall survival, based on TCGA (the Cancer Genome Atlas) and GEO datasets. Subsequent in vitro analyses revealed an overexpression of ITGAV in highly invasive HNSCC cell lines UM1 and UMSCC-5 in comparison to low invasive HNSCC cell lines UM2 and UMSCC-6. In addition, knockdown of ITGAV significantly inhibited the migration, invasion, viability, and colony formation of HNSCC cells. In addition, chromatin immunoprecipitation (ChIP) assays indicated that SOX11 bound to the promoter of ITGAV gene, and SOX11 knockdown resulted in decreased ITGAV expression in HNSCC cells. In conclusion, our studies suggest that ITGAV promotes the progression of HNSCC cells and may be regulated by SOX11 in HNSCC cells.

Liposome-Encapsulated Tiancimycin A Is Active against Melanoma and Metastatic Breast Tumors: The Effect of cRGD Modification of the Liposomal Carrier and Tiancimycin A Dose on Drug Activity and Toxicity

Enediyne natural products, including neocarzinostatin and calicheamicin γ¹, are used in the form of a copolymer or antibody-drug conjugate to treat hepatomas and leukemia. Tiancimycin (TNM) A is a novel anthraquinone-fused enediyne that can rapidly and completely kill tumor cells. Herein, we encapsulated TNM A in liposomes (Lip-TNM A) and cyclic arginine-glycine-aspartate (cRGD)-functionalized liposomes (cRGD-Lip-TNM A) and demonstrated its antitumor activity using mouse xenografts. Because TNM A causes rapid DNA damage, cell cycle arrest, and apoptosis, these nanoparticles exhibited potent cytotoxicity against multiple tumor cells for 8 h. In B16-F10 and KPL-4 xenografts, both nanoparticles showed superior potency over doxorubicin and trastuzumab. However, cRGD-Lip-TNM A reduced the tumor weight more significantly than Lip-TNM A in B16-F10 xenografts, in which the α_vβ₃-integrin receptors are significantly overexpressed in this melanoma. Lip-TNM A was slightly more active than cRGD-Lip-TNM A against KPL-4 xenografts, which probably reflected the difference of their in vivo fate in this mouse model. In a highly metastatic 4T1 tumor model, cRGD-Lip-TNM A reduced tumor metastasis induced by losartan, a tumor microenvironment-remodeling agent. These findings suggest that targeted delivery of enediynes with unique modes of action may enable more effective translation of anticancer nanomedicines.

A narrative review on tumor microenvironment in oligometastatic and oligoprogressive non-small cell lung cancer: a lot remains to be done

Objective

In this review, we aim to collect and discuss available data about the role and composition of tumor microenvironment (TME) in oligometastatic (OMD) and oligoprogressive (OPD) non-small cell lung cancer (NSCLC). Furthermore, we aim to summarize the ongoing clinical trials evaluating as exploratory objective the TME composition, through tissue and/or blood samples, in order to clarify whether TME and its components could explain, at least partially, the oligometastatic/oligoprogressive process and could unravel the existence of predictive and/or prognostic factors for local ablative therapy (LAT).

Background

OMD/OPD NSCLC represent a heterogeneous group of diseases. Several data have shown that TME plays an important role in tumor progression and therefore in treatment response. The crucial role of several types of cells and molecules such as immune cells, cytokines, integrins, protease and adhesion molecules, tumor-associated macrophages (TAMs) and mesenchymal stem cells (MSCs) has been widely established. Due to the peculiar activation of specific pathways and expression of adhesion molecules, metastatic cells seem to show a tropism for specific anatomic sites (the so-called “seed and soil” hypothesis). Based on this theory, metastases appear as a biologically driven process rather than a random release of cancer cells. Although the role and the function of TME at the time of progression in patients with NSCLC treated with tyrosine-kinase inhibitors and immune checkpoint inhibitors (ICIs) have been investigated, limited data about the role and the biological meaning of TME are available in the specific OMD/OPD setting.

Methods

Through a comprehensive PubMed and ClinicalTrials.gov search, we identified available and ongoing studies exploring the role of TME in oligometastatic/oligoprogressive NSCLC.

Conclusions

Deepening the knowledge on TME composition and function in OMD/OPD may provide innovative implications in terms of both prognosis and prediction of outcome in particular from local treatments, paving the way for future investigations of personalized approaches in both advanced and early disease settings.

Triple negative breast cancer and non-small cell lung cancer: Clinical challenges and nano-formulation approaches

Triple negative breast cancer (TNBC) and non-small cell lung cancer (NSCLC) are amongst the most aggressive forms of solid tumors. TNBC is highlighted by absence of genetic components of progesterone receptor, HER2/neu and estrogen receptor in breast cancer. NSCLC is characterized by integration of malignant carcinoma into respiratory system. Both cancers are associated with poor median and overall survival rates with low progression free survival with high incidences of relapse. These cancers are characterized by tumor heterogeneity, genetic mutations, generation of cancer-stem cells, immune-resistance and chemoresistance. Further, these neoplasms have been reported for tumor cross-talk into second primary cancers for each other. Current chemotherapeutic regimens include usage of multiple agents in tandem to affect tumor cells through multiple mechanisms with various such combinations being clinically tested. However, lack of controlled delivery and effective temporospatial presence of chemotherapeutics has resulted in suboptimal therapeutic response. Consequently, passive targeted albumin bound paclitaxel and PEGylated liposomal doxorubicin have been clinically used and tested with newer drugs for improved therapeutic efficacy in these cancers. Active targeting of nanocarriers against surface overexpressed proteins in both neoplasms have been explored. However, use of single agent nanoparticulate formulations against both cancers have failed to elicit desired outcomes. This review aims to identify clinical unmet need in these cancers while establishing a correlation with tested nano-formulation approaches and issues with preclinical to clinical translation. Lipid and polymer-based drug-drug and drug-gene combinatorial nanocarriers delivering multiple chemotherapeutics simultaneously to desired site of action have been detailed. Finally, emerging opportunities such as pharmacological targets (immune check point and epigentic modulators) as well as gene-based modulation (siRNA/CRISPR/Cas9) and the nano-formulation challenges for effective treatment of both cancers have been explored.

Proliferation-associated long noncoding RNA, TMPO-AS1, is a potential therapeutic target for triple-negative breast cancer

Triple‐negative breast cancer (TNBC) is an aggressive subtype of breast cancer compared with luminal or epidermal growth factor receptor 2 subtypes, thus effective therapeutic options for TNBC are yet to be developed. Nowadays, oncogenic long noncoding RNAs (lncRNAs) are applied to cancer management as a new class of therapeutic targets. We previously showed that thymopoietin antisense transcript 1 (TMPO‐AS1) is a proliferation‐associated lncRNA that contributes to hormone‐dependent breast cancer progression by stabilizing estrogen receptor‐α mRNA. We here showed that TMPO‐AS1 is abundantly expressed in basal‐like breast cancer subtype based on the transcriptomic data in The Cancer Genome Atlas as well as in TNBC cell lines and patient‐derived cells. Small interfering RNA‐based loss‐of‐function analyses showed that TMPO‐AS1 knockdown substantially represses the proliferation and migration of TNBC cells. Expression microarray analysis showed that TMPO‐AS1 alters gene signatures related to transforming growth factor‐β signaling in addition to proliferative E2F signaling pathways. TMPO‐AS1‐targeted siRNA treatment through engineered drug delivery systems using cancer‐targeted polyion complex micelle or nanoball technology significantly impaired the in vivo growth of primary and metastatic TNBC xenograft tumors. Our findings suggest that TMPO‐AS1 plays a key role in TNBC pathophysiology and could be a potential therapeutic target for TNBC.

A Multifunctional Peptide-Conjugated AIEgen for Efficient and Sequential Targeted Gene Delivery into the Nucleus

Gene therapy has immense potential as a therapeutic approach to serious diseases. However, efficient delivery and real-time tracking of gene therapeutic agents have not been solved well for successful gene-based therapeutics. Herein we present a versatile gene-delivery strategy for efficient and visualized delivery of therapeutic genes into the targeted nucleus. We developed an integrin-targeted, cell-permeable, and nucleocytoplasmic trafficking peptide-conjugated AIEgen named T_D NCP for the efficient and sequential targeted delivery of an antisense single-stranded DNA oligonucleotide (ASO) and tracking of the delivery process into the nucleus. As compared with T_D NCP/siRNA-NPs (siRNA functions mainly in the cytoplasm), T_D NCP/ASO-NPs (ASO functions mainly in the nucleus) exhibited a better interference effect, which further indicates that T_D NCP is a nucleus-targeting vector. Moreover, T_D NCP/ASO-NPs showed a favorable tumor-suppressive effect in vivo.

Improved anticancer effects of epigallocatechin gallate using RGD-containing nanostructured lipid carriers

The global burden of cancer have encouraged oncologists to develop novel strategies for treatment. Present study was proposed to develop Arginyl-glycyl-aspartic acid (RGD)-containing nanostructured lipid carriers (NLC) as a delivery system for improving the anticancer capability of epigallocatechin gallate (EGCG) on breast cancer cell line by attaching to integrin superfamily on cancer cells. For this purpose, RGD-containing EGCG-loaded NLC were prepared by hot homogenization technique and characterized by different techniques. Then, cytotoxic and apoptotic effects of prepared nanoparticles and their uptake into cells was evaluated. As results, the nanoparticles with particle size of 85 nm, zeta potential of -21 mV, encapsulation of 83% were prepared. Cytotoxicity and apoptosis experiments demonstrated that EGCG-loaded NLC-RGD possessed greatest apoptotic activity. Furthermore, it has been shown that, EGCG-loaded NLC-RGD causes cell cycle arresting more effective than EGCG. Therefore, loading EGCG into NLC-RGD make it more effective in both targeting and accumulation into tumour cells, which results from specialized uptake mechanism by adhesion to αvβ3 integrin. The results strengthen our hope that loading EGCG into RGD-containing NLC could possibly overcome the therapeutic limitations of EGCG and make it more effective in cancer therapy.

Rare-Earth-Doped Nanoparticles for Short-Wave Infrared Fluorescence Bioimaging and Molecular Targeting of αVβ3-Expressing Tumors

The use of short-wave infrared (SWIR) light for fluorescence bioimaging offers the advantage of reduced photon scattering and improved tissue penetration compared to traditional shorter wavelength imaging approaches. While several nanomaterials have been shown capable of generating SWIR emissions, rare-earth-doped nanoparticles (REs) have emerged as an exceptionally bright and biocompatible class of SWIR emitters. Here, we demonstrate SWIR imaging of REs for several applications, including lymphatic mapping, real-time monitoring of probe biodistribution, and molecular targeting of the αvβ3 integrin in a tumor model. We further quantified the resolution and depth penetration limits of SWIR light emitted by REs in a customized imaging unit engineered for SWIR imaging of live small animals. Our results indicate that SWIR light has broad utility for preclinical biomedical imaging and demonstrates the potential for molecular imaging using targeted REs.

Transcription factor c-Myb inhibits breast cancer lung metastasis by suppression of tumor cell seeding

Metastasis accounts for most of cancer-related deaths. Paracrine signaling between tumor cells and the stroma induces changes in the tumor microenvironment required for metastasis. Transcription factor c-Myb was associated with breast cancer (BC) progression but its role in metastasis remains unclear. Here we show that increased c-Myb expression in BC cells inhibits spontaneous lung metastasis through impaired tumor cell extravasation. On contrary, BC cells with increased lung metastatic capacity exhibited low c-Myb levels. We identified a specific inflammatory signature, including Ccl2 chemokine, that was expressed in lung metastatic cells but was suppressed in tumor cells with higher c-Myb levels. Tumor cell-derived Ccl2 expression facilitated lung metastasis and rescued trans-endothelial migration of c-Myb overexpressing cells. Clinical data show that the identified inflammatory signature, together with a MYB expression, predicts lung metastasis relapse in BC patients. These results demonstrate that the c-Myb-regulated transcriptional program in BCs results in a blunted inflammatory response and consequently suppresses lung metastasis.

Dual-targeted hybrid nanoparticles of synergistic drugs for treating lung metastases of triple negative breast cancer in mice

Lung metastasis is the major cause of death in patients with triple negative breast cancer (TNBC), an aggressive subtype of breast cancer with no effective therapy at present. It has been proposed that dual-targeted therapy, ie, targeting chemotherapeutic agents to both tumor vasculature and cancer cells, may offer some advantages. The present work was aimed to develop a dual-targeted synergistic drug combination nanomedicine for the treatment of lung metastases of TNBC. Thus, Arg-Gly-Asp peptide (RGD)-conjugated, doxorubicin (DOX) and mitomycin C (MMC) co-loaded polymer-lipid hybrid nanoparticles (RGD-DMPLN) were prepared and characterized. The synergism between DOX and MMC and the effect of RGD-DMPLN on cell morphology and cell viability were evaluated in human MDA-MB-231 cells in vitro. The optimal RGD density on nanoparticles (NPs) was identified based on the biodistribution and tumor accumulation of the NPs in a murine lung metastatic model of MDA-MB-231 cells. The microscopic distribution of RGD-conjugated NPs in lung metastases was examined using confocal microscopy. The anticancer efficacy of RGD-DMPLN was investigated in the lung metastatic model. A synergistic ratio of DOX and MMC was found in the MDA-MB-231 human TNBC cells. RGD-DMPLN induced morphological changes and enhanced cytotoxicity in vitro. NPs with a median RGD density showed the highest accumulation in lung metastases by targeting both tumor vasculature and cancer cells. Compared to free drugs, RGD-DMPLN exhibited significantly low toxicity to the host, liver and heart. Compared to non-targeted DMPLN or free drugs, administration of RGD-DMPLN (10 mg/kg, iv) resulted in a 4.7-fold and 31-fold reduction in the burden of lung metastases measured by bioluminescence imaging, a 2.4-fold and 4.0-fold reduction in the lung metastasis area index, and a 35% and 57% longer median survival time, respectively. Dual-targeted RGD-DMPLN, with optimal RGD density, significantly inhibited the progression of lung metastasis and extended host survival.

Dual-targeted peptide-conjugated multifunctional fluorescent probe with AIEgen for efficient nucleus-specific imaging and long-term tracing of cancer cells

Precisely targeted transportation of a long-term tracing regent to a nucleus with low toxicity is one of the most challenging concerns in revealing cancer cell behaviors. Here, we report a dual-targeted peptide-conjugated multifunctional fluorescent probe (cNGR-CPP-NLS-RGD-PyTPE, TCNTP) with aggregation-induced emission (AIE) characteristic, for efficient nucleus-specific imaging and long-term and low-toxicity tracing of cancer cells. TCNTP mainly consists of two components: one is a functionalized combinatorial peptide (TCNT) containing two targeted peptides (cNGR and RGD), a cell-penetrating peptide (CPP) and a nuclear localization signal (NLS), which can specifically bind to a cell surface and effectively enter into the nucleus; the other one is an AIE-active tetraphenylethene derivative (PyTPE, a typical AIEgen) as fluorescence imaging reagent. In the presence of aminopeptidase N (CD13) and integrin αvβ3, TCNTP can specifically bind to both of them using cNGR and RGD, respectively, lighting up its yellow fluorescence. Because it contains CPP, TCNTP can be effectively integrated into the cytoplasm, and then be delivered into the nucleus with the help of NLS. TCNTP exhibited strong fluorescence in the nucleus of CD13 and integrin αvβ3 overexpression cells due to the specific targeting ability, efficient transport capacity and AIE characteristic in a more crowded space. Furthermore, TCNTP can be applied for long-term tracing in living cells, scarcely affecting normal cells with negligible toxicity in more than ten passages.

Prostaglandin E2 receptor 4 mediates renal cell carcinoma intravasation and metastasis

Treatment options for metastatic renal cell carcinoma (RCC) are limited. In this study, we investigated impact of prostaglandin E2 (PGE2) receptor 4 (EP4) on RCC metastasis. We found that knockdown of EP4 in two RCC cell lines, ACHN and SN12C, does not affect xenograft tumor take or growth rate in mice, but reduces metastasis by decreasing tumor intravasation. Using chick chorioallantoic membrane (CAM) assay, we confirmed that blockade of EP4 signaling inhibits tumor intravasation. In vitro studies associated EP4 expression and activity with RCC cell transendothelial migration (TEM). Gene expression analysis and validation assays showed that EP4 knockdown decreases expression of CD24, a ligand to the adhesion molecule P-selectin. Forced expression of CD24 in EP4 knockdown RCC rescues TEM capacity of the cells. Pharmacologic inhibition or knockdown of endothelial P-selectin blocks EP4-mediated cancer cell TEM, and inhibition of P-selectin prevents RCC tumor intravasation in CAM assay. Our results demonstrate that inhibition of EP4 attenuates the RCC intravasation and metastasis by downregulating CD24 and that P-selectin participates in tumor intravasation, implying a potential for these molecules as therapeutic targets for advanced RCC treatment.

Functional characterization of six aspartate (D) recombinant mojastin mutants (r-Moj): A second aspartate amino acid carboxyl to the RGD in r-Moj-D_ peptides is not sufficient to induce apoptosis of SK-Mel-28 cells

Disintegrins are small peptides produced in viper venom that act as integrin antagonists. When bound to integrins, disintegrins induce altered cellular behaviors, such as apoptotic induction. Disintegrins with RGDDL or RGDDM motifs induce apoptosis of normal and cancer cells. We hypothesized that a second aspartate (D) carboxyl to the RGD is sufficient to induce apoptosis. Five recombinant mojastin D mutants were produced by site-directed mutagenesis (r-Moj-DA, r-Moj-DG, r-Moj-DL, r-Moj-DN, and r-Moj-DV). Stable αv integrin knockdown and shRNA scrambled control SK-Mel-28 cell lines were produced to test a second hypothesis: r-Moj-D_ peptides bind to αv integrin. Only r-Moj-DL, r-Moj-DM, and r-Moj-DN induced apoptosis of SK-Mel-28 cells (at 29.4%, 25.6%, and 36.2%, respectively). Apoptotic induction was significantly reduced in SK-Mel-28 cells with a stable αv integrin knockdown (to 2%, 17%, and 2%, respectively), but not in SK-Mel-28 cells with a stable scrambled shRNA. All six r-Moj-D_ peptides inhibited cell proliferation; ranging from 49.56% (r-Moj-DN) to 75.6% (r-Moj-DA). Cell proliferation inhibition by r-Moj-D_ peptides was significantly reduced in SK-Mel-28 cells with a stable αv integrin knockdown. All six r-Moj-D_ peptides inhibited SK-Mel-28 cell migration at high levels (69%-100%). As a consequence, rac-1 mRNA expression levels were significantly reduced as early as 1 h after treatment, suggesting that rac-1 is involved in the cell migration activity of SK-Mel-28.

RGD-conjugated solid lipid nanoparticles inhibit adhesion and invasion of αvβ3 integrin-overexpressing breast cancer cells

αvβ3 integrin receptors expressed on cancer cell surfaces play a crucial role in promoting tumor angiogenesis and cancer cell metastasis. Thus, cyclic arginyl-glycyl-aspartic acid (cRGD) peptides have been explored as a αvβ3 integrin receptor-specific targeting moiety for the targeted delivery of nanoparticle-loaded therapeutics. However, our previous study showed that cyclic RGD could act as a double-edged sword that, on one hand, extended the retention of cRGD-modified solid lipid nanoparticles (RGD-SLNs) at αvβ3 integrin receptor overexpressing breast carcinoma, and yet on the other hand, decreased the amount of tumor accumulation of RGD-SLNs attributable to the greater uptake by the mononuclear phagocyte system (MPS). Therefore, we aimed to optimize the RGD-decorated nanoparticle systems for (1) inhibiting αvβ3 integrin receptor overexpressing tumor cell metastasis and (2) increasing nanoparticle accumulation to tumor site. SLNs with cRGD content ranging from 0 to 10 % mol of total polyethyleneglycol (PEG) chains were synthesized. The binding of RGD-SLNs with αvβ3 integrin receptors increased with increasing cRGD concentration on the nanoparticles. RGD-SLNs were demonstrated to inhibit MDA-MB-231 cell adhesion to fibronectin and invasion through Matrigel. In vivo whole-body fluorescence imaging revealed that 1 % cRGD on the SLNs' surface had maximum tumor accumulation with extended tumor retention among all formulations tested in an orthotopic MDA-MB-231/EGFP breast tumor model. This work has laid a foundation for further development of anticancer drug-loaded optimized cRGD nanoparticle formulations for the treatment of breast cancer metastasis.

cRGD-installed polymeric micelles loading platinum anticancer drugs enable cooperative treatment against lymph node metastasis

Lymph node metastasis (LNM) is correlated with decreased survival, indicating high tumor malignancy and being a potential source for subsequent fatal metastases. Targeted therapies inhibiting the formation of LNM, while eliminating established metastatic foci, could provide synergistic effects by reducing the incidence and growth of metastasis. Based on the inhibitory activity of cRGD peptide against the development of metastasis, and the LNM targeting ability of systemically injected drug-loaded polymeric micelles, herein, we studied the capability of cRGD-installed polymeric micelles incorporating the platinum anticancer drug (1,2-diaminocylohexane)platinum(II) (DACHPt) for cooperatively inhibiting the formation and progression of LNM. As cRGD-installed DACHPt-loaded micelles (cRGD-DACHPt/m) presented similar size, drug loading and surface charge to non-conjugated micelles (MeO-DACHPt/m), the differences in the biological performance of the micelles were endorsed to the effect of the ligand. In a syngeneic melanoma model, both MeO-DACHPt/m and cRGD-DACHPt/m showed comparable antitumor activity against the primary tumors and the established metastatic foci in lymph nodes. However, cRGD-DACHPt/m significantly enhanced the efficacy against LNM draining from primary tumors through the effective inhibition of the spreading of cancer cells. This improved inhibition was associated with the ability of cRGD-DACHPt/m to reduce the migration of melanoma cells, which was higher than that of MeO-DACHPt/m, free cRGD and their combination. These results support our strategy of using cRGD-installed micelles for attaining cooperative therapies against LNM exploiting the inhibitory function of the peptide and the cytotoxic effect of the micelles.

SUV420H2 suppresses breast cancer cell invasion through down regulation of the SH2 domain-containing focal adhesion protein tensin-3

The genome-wide loss of histone H4 lysine 20 tri-methylation (H4K20me3) is observed in multiple types of cancer, including breast tumors. Since H4K20me3 is preferentially targeted to repetitive elements in the pericentromeric and telomeric heterochromatin and plays a role in chromatin integrity, the pathological effects of disrupted H4K20me3 in tumors have been attributed to genomic instability. However, in this report, we show that loss of H4K20me3 modulates gene expression profiles, leading to increased cell invasion. Reduced H4K20me3 levels in tumor cells are often accompanied by a decrease in the expression of the H4K20-specific methyltransferase, SUV420H2. Exogenous delivery of SUV420H2 into MDA-MB-231 human breast cancer cells induced selective and specific changes in the expression of cancer-related genes. One of the most downregulated genes in response to SUV420H2 expression was the Src substrate, tensin-3, a focal adhesion protein that contributes to cancer cell migration. Depletion of tensin-3 suppressed breast cancer cell invasiveness. Furthermore, silencing of tensin-3 was associated with enrichment of H4K20me3 immediately upstream of the tensin-3 transcription start site, suggesting that the loss of H4K20me3 in tumor cells induced the expression of cancer-promoting genes. These findings connect the loss of H4K20me3 with tumor progression, through the transcriptional activation of cancer-promoting genes.

Resistance to the mTOR inhibitor temsirolimus alters adhesion and migration behavior of renal cell carcinoma cells through an integrin α5- and integrin β3-dependent mechanism

Inhibitors of the mammalian target of rapamycin (mTOR) have improved the treatment of renal cell carcinoma (RCC). However, chronic drug exposure may trigger resistance, limiting the utility of these agents. The metastatic behavior of RCC cells, susceptible (RCC(par)) or resistant (RCC(res)) to the mTOR inhibitor temsirolimus, was investigated. Adhesion to vascular endothelium or immobilized collagen and fibronectin was quantified. Chemotactic motility was evaluated with a modified Boyden chamber assay. Integrin α and β subtype receptors were analyzed by flow cytometry and Western blot analysis. The physiological relevance of the integrins was then determined by blocking studies and small interfering RNA knockdown. Adhesion to endothelial cells and to fibronectin (not to collagen) and chemotaxis were enhanced in RCC(res) compared to RCC(par). RCC(res) detached from fibronectin and motile activity further increased under retreatment with low-dosed temsirolimus. α5 integrin was diminished inside the cell and at the cell surface, whereas the β3 subtype was reduced intracellularly but elevated at the plasma membrane. In RCC(par), blocking α5 surface receptors enhanced RCC-collagen but reduced RCC-fibronectin interaction, whereas the opposite was true for RCC(res). Chemotaxis of RCC(par) but not of RCC(res) was strongly diminished by the α5 antibody. Blocking β3 significantly lowered chemotaxis with stronger effects on RCC(res), compared to RCC(par). Importantly, β3 knockdown reduced chemotaxis of RCC(par) but upregulated the motile behavior of RCC(res). Temsirolimus resistance is characterized by quantitative alterations of integrin α5 and β3 expression, coupled to functional changes of the integrin molecules, and forces a switch from RCC adhesion to RCC migration.

The fundamental role of mechanical properties in the progression of cancer disease and inflammation

The role of mechanical properties in cancer disease and inflammation is still underinvestigated and even ignored in many oncological and immunological reviews. In particular, eight classical hallmarks of cancer have been proposed, but they still ignore the mechanics behind the processes that facilitate cancer progression. To define the malignant transformation of neoplasms and finally reveal the functional pathway that enables cancer cells to promote cancer progression, these classical hallmarks of cancer require the inclusion of specific mechanical properties of cancer cells and their microenvironment such as the extracellular matrix as well as embedded cells such as fibroblasts, macrophages or endothelial cells. Thus, this review will present current cancer research from a biophysical point of view and will therefore focus on novel physical aspects and biophysical methods to investigate the aggressiveness of cancer cells and the process of inflammation. As cancer or immune cells are embedded in a certain microenvironment such as the extracellular matrix, the mechanical properties of this microenvironment cannot be neglected, and alterations of the microenvironment may have an impact on the mechanical properties of the cancer or immune cells. Here, it is highlighted how biophysical approaches, both experimental and theoretical, have an impact on the classical hallmarks of cancer and inflammation. It is even pointed out how these biophysical approaches contribute to the understanding of the regulation of cancer disease and inflammatory responses after tissue injury through physical microenvironmental property sensing mechanisms. The recognized physical signals are transduced into biochemical signaling events that guide cellular responses, such as malignant tumor progression, after the transition of cancer cells from an epithelial to a mesenchymal phenotype or an inflammatory response due to tissue injury. Moreover, cell adaptation to mechanical alterations, in particular the understanding of mechano-coupling and mechano-regulating functions in cell invasion, appears as an important step in cancer progression and inflammatory response to injuries. This may lead to novel insights into cancer disease and inflammatory diseases and will overcome classical views on cancer and inflammation. In addition, this review will discuss how the physics of cancer and inflammation can help to reveal whether cancer cells will invade connective tissue and metastasize or how leukocytes extravasate and migrate through the tissue. In this review, the physical concepts of cancer progression, including the tissue basement membrane a cancer cell is crossing, its invasion and transendothelial migration as well as the basic physical concepts of inflammatory processes and the cellular responses to the mechanical stress of the microenvironment such as external forces and matrix stiffness, are presented and discussed. In conclusion, this review will finally show how physical measurements can improve classical approaches that investigate cancer and inflammatory diseases, and how these physical insights can be integrated into classical tumor biological approaches.

Phagocytized beads reduce the α5β1 integrin facilitated invasiveness of cancer cells by regulating cellular stiffness

Cell invasion through the extracellular matrix (ECM) of connective tissue is an important biomechanical process, which plays a prominent role in tumor progression. The malignancy of tumors depends mainly on the capacity of cancer cells to migrate and metastasize. A prerequisite for metastasis is the invasion of cancer cells through connective tissue to targeted organs. Cellular stiffness and cytoskeletal remodeling dynamics have been proposed to affect the invasiveness of cancer cells. Here, this study investigated whether highly invasive cancer cells are capable of invading into dense 3D-ECMs with an average pore-size of 1.3 or 3.0 μm when phagocytized beads (2.7 and 4.5 μm diameter) increased their cellular stiffness and reduced their cytoskeletal remodeling dynamics compared to weakly invasive cancer cells. The phagocytized beads decreased the invasiveness of the α5β1(high) cancer cells into 3D-ECMs, whereas the invasiveness of the α5β1(low) cancer cells was not affected. The effect of phagocytized beads on the highly invasive α5β1(high) cells was abolished by specific knock-down of the α5 integrin subunit or addition of an anti-α5 integrin blocking antibody. Furthermore, the reduction of contractile forces using MLCK and ROCK inhibitors abolished the effect of phagocytized beads on the invasiveness of α5β1(high) cells. In addition, the cellular stiffness of α5β1(high) cells was increased after bead phagocytosis, whereas the bead phagocytosis did not alter the stiffness of α5β1(low) cells. Taken together, the α5β1 integrin dependent invasiveness was reduced after bead phagocytosis by altered biomechanical properties, suggesting that the α5β1(high) cells need an appropriate intermediate cellular stiffness to overcome the steric hindrance of 3D-ECMs, whereas the α5β1(low) cells were not affected by phagocytized beads.

Targeting endothelial junctional adhesion molecule-A/ EPAC/ Rap-1 axis as a novel strategy to increase stem cell engraftment in dystrophic muscles

Muscular dystrophies are severe genetic diseases for which no efficacious therapies exist. Experimental clinical treatments include intra-arterial administration of vessel-associated stem cells, called mesoangioblasts (MABs). However, one of the limitations of this approach is the relatively low number of cells that engraft the diseased tissue, due, at least in part, to the sub-optimal efficiency of extravasation, whose mechanisms for MAB are unknown. Leukocytes emigrate into the inflamed tissues by crossing endothelial cell-to-cell junctions and junctional proteins direct and control leukocyte diapedesis. Here, we identify the endothelial junctional protein JAM-A as a key regulator of MAB extravasation. We show that JAM-A gene inactivation and JAM-A blocking antibodies strongly enhance MAB engraftment in dystrophic muscle. In the absence of JAM-A, the exchange factors EPAC-1 and 2 are down-regulated, which prevents the activation of the small GTPase Rap-1. As a consequence, junction tightening is reduced, allowing MAB diapedesis. Notably, pharmacological inhibition of Rap-1 increases MAB engraftment in dystrophic muscle, which results into a significant improvement of muscle function offering a novel strategy for stem cell-based therapies.

Crossing the endothelial barrier during metastasis

During metastasis, cancer cells disseminate to other parts of the body by entering the bloodstream in a process that is called intravasation. They then extravasate at metastatic sites by attaching to endothelial cells that line blood vessels and crossing the vessel walls of tissues or organs. This Review describes how cancer cells cross the endothelial barrier during extravasation and how different receptors, signalling pathways and circulating cells such as leukocytes and platelets contribute to this process. Identification of the mechanisms that underlie cancer cell extravasation could lead to the development of new therapies to reduce metastasis.

The role of the tumor-microenvironment in lung cancer-metastasis and its relationship to potential therapeutic targets

Non-small cell lung cancer (NSCLC) accounts for >80% of lung cancer cases and currently has an overall five-year survival rate of only 15%. Patients presenting with advanced stage NSCLC die within 18-months of diagnosis. Metastatic spread accounts for >70% of these deaths. Thus elucidation of the mechanistic basis of NSCLC-metastasis has potential to impact on patient quality of life and survival. Research on NSCLC metastasis has recently expanded to include non-cancer cell components of tumors-the stromal cellular compartment and extra-cellular matrix components comprising the tumor-microenvironment. Metastasis (from initial primary tumor growth through angiogenesis, intravasation, survival in the bloodstream, extravasation and metastatic growth) is an inefficient process and few released cancer cells complete the entire process. Micro-environmental interactions assist each of these steps and discovery of the mechanisms by which tumor cells co-operate with the micro-environment are uncovering key molecules providing either biomarkers or potential drug targets. The major sites of NSCLC metastasis are brain, bone, adrenal gland and the liver. The mechanistic basis of this tissue-tropism is beginning to be elucidated offering the potential to target stromal components of these tissues thus targeting therapy to the tissues affected. This review covers the principal steps involved in tumor metastasis. The role of cell-cell interactions, ECM remodeling and autocrine/paracrine signaling interactions between tumor cells and the surrounding stroma is discussed. The mechanistic basis of lung cancer metastasis to specific organs is also described. The signaling mechanisms outlined have potential to act as future drug targets minimizing lung cancer metastatic spread and morbidity.

αV integrins in angiogenesis and cancer

During angiogenesis, αv integrins are overexpressed on the endothelial cell surface to facilitate the growth and survival of newly forming vessels. Accordingly, blocking αv integrin function by disrupting ligand binding can produce an antiangiogenic effect. Although the integrin ectodomain regulates ligand binding specificity, the short cytoplasmic tail facilitates intracellular signaling pathways through the recruitment and activation of specific kinases and signaling intermediates. This in turn controls endothelial cell adhesion, morphology, migration, invasion, proliferation, and survival. These same integrin-mediated signaling pathways are exploited in cancer to promote the invasiveness and survival of tumor cells and to manipulate the host microenvironment to provide ample blood vessel and stromal resources to support tumor growth and metastatic spread. Because expression of αv integrins on distinct cell types contributes to cancer growth, αv integrin antagonists have the potential to disrupt multiple aspects of disease progression.

Physical break-down of the classical view on cancer cell invasion and metastasis

Eight classical hallmarks of cancer have been proposed and are well-defined by using biochemical or molecular genetic methods, but are not yet precisely defined by cellular biophysical processes. To define the malignant transformation of neoplasms and finally reveal the functional pathway, which enables cancer cells to promote cancer progression, these classical hallmarks of cancer require the inclusion of specific biomechanical properties of cancer cells and their microenvironment such as the extracellular matrix and embedded cells such as fibroblasts, macrophages or endothelial cells. Nonetheless a main novel ninth hallmark of cancer is still elusive in classical tumor biological reviews, which is the aspect of physics in cancer disease by the natural selection of an aggressive (highly invasive) subtype of cancer cells. The physical aspects can be analyzed by using state-of-the-art biophysical methods. Thus, this review will present current cancer research in a different light and will focus on novel physical methods to investigate the aggressiveness of cancer cells from a biophysicist's point of view. This may lead to novel insights into cancer disease and will overcome classical views on cancer. In addition, this review will discuss how physics of cancer can help to reveal whether cancer cells will invade connective tissue and metastasize. In particular, this review will point out how physics can improve, break-down or support classical approaches to examine tumor growth even across primary tumor boundaries, the invasion of single or collective cancer cells, transendothelial migration of cancer cells and metastasis in targeted organs. Finally, this review will show how physical measurements can be integrated into classical tumor biological analysis approaches. The insights into physical interactions between cancer cells, the primary tumor and the microenvironment may help to solve some "old" questions in cancer disease progression and may finally lead to novel approaches for development and improvement of cancer diagnostics and therapies.

In situ recognition of cell-surface glycans and targeted imaging of cancer cells

Fluorescent sensors capable of recognizing cancer-associated glycans, such as sialyl Lewis X (sLe(x)) tetrasaccharide, have great potential for cancer diagnosis and therapy. Studies on water-soluble and biocompatible sensors for in situ recognition of cancer-associated glycans in live cells and targeted imaging of cancer cells are very limited at present. Here we report boronic acid-functionalized peptide-based fluorescent sensors (BPFSs) for in situ recognition and differentiation of cancer-associated glycans, as well as targeted imaging of cancer cells. By screening BPFSs with different structures, it was demonstrated that BPFS₁ with a FRGDF peptide could recognize cell-surface glycan of sLe(x) with high specificity and thereafter fluorescently label and discriminate cancer cells through the cooperation with the specific recognition between RGD and integrins. The newly developed peptide-based sensor will find great potential as a fluorescent probe for cancer diagnosis.

Targeting nuclear factor-κB suppresses the negative effect of toll-like receptor 4 signaling on antimetastasis therapy based on targeting αvβ3

The targeting of αvβ3 is a promising therapeutic strategy for suppressing tumor metastasis. However, it is unclear whether the therapeutic efficacy could be influenced by metastasis-promoting factor(s) in vivo. Here we report that Toll-like receptor 4 (TLR4) ligand released from damaged tumor cells or bacteria had a negative effect on the therapeutic effect of a recombinant CBD-HepII polypeptide of fibronectin (CH50) that suppresses tumor metastasis by targeting αvβ3. The TLR4 ligand could antagonize the inhibitory effect of CH50 on tumor cell adhesion and invasion by promoting the expression and activity of αvβ3 in tumor cells. The TLR4 ligand also reduced the antimetastasis effect of CH50 by promoting tumor cell survival in circulation. Moreover, TLR4 ligands released by tumor cells in circulation could increase the survival and proliferation capacity of tumor cells after extravasation, resulting in the formation of more metastatic nodules. The effect of TLR4 signaling was mainly mediated by nuclear factor-κB (NF-κB). Inhibiting NF-κB could abrogate the negative effect of TLR4 ligand, and augment the inhibitory effect of CH50 on tumor metastasis. Consistently, the combination of NF-κB inhibitor and CH50 significantly inhibited metastasis of tumor cells in vivo and prolonged the survival of mice. The findings in this study suggest that the combination of NF-κB inhibitor and αvβ3 antagonist would be a novel therapeutic option for the prevention of tumor metastasis.

MYC suppresses cancer metastasis by direct transcriptional silencing of αv and β3 integrin subunits

Over-expression of MYC transforms cells in culture, elicits malignant tumors in experimental animals and is found in many human tumors. We now report the paradoxical finding that this powerful oncogene can also act as a suppressor of cell motility, invasiveness and metastasis. Overexpression of MYC stimulated proliferation of breast cancer cells both in culture and in vivo as expected, but inhibited motility and invasiveness in culture, and lung and liver metastases in xenografted tumors. We show further that MYC represses transcription of both subunits of αvβ3 integrin, and that exogenous expression of β3 integrin in human breast cancer cells that do not express this integrin rescues invasiveness and migration when MYC is downregulated. These data uncover an unexpected function of MYC, provide an explanation for the hitherto puzzling literature on the relationship between MYC and metastasis and reveal a variable that should influence the development of therapeutics that target MYC.

Endothelial cell's biomechanical properties are regulated by invasive cancer cells

Most cancer-related deaths are caused by the ability of cancer cells to metastasize. This process includes the dissemination of cancer cells from the primary tumor side and their migration to targeted organ sites. During the migration of cancer cells through the connective tissue microenvironment, which consists of endothelial cells and extracellular matrix components, biomechanical properties are crucial for the efficiency and speed of cancer cell invasion and subsequently, metastases formation. Biomechanics can enable cancer cells to migrate through tissue, transmigrate through basement membranes as well as endothelial monolayers and form metastases in targeted organs. The current focus of cancer research still lies on the investigation of cancer cell's biochemical and molecular capabilities such as molecular genetics and gene signaling, but these approaches ignore the mechanical nature of the invasion process of cancer cells. Moreover, even the role of the endothelium during the transmigration and invasion of cells is not clear, it has been seen as a passive barrier, but this could not explain all novel findings. This review discusses how cancer cells alter the structural, biochemical and mechanical properties of the endothelium to regulate their own invasiveness through extracellular matrices and hence, through the tissue microenvironment. Finally, this review sheds light on the mechanical properties of cancer cells and the interacting endothelium and points out the importance of the mechanical properties as a critical determinant for the efficiency of cancer cell invasion and the overall progression of cancer. In conclusion, the regulation of the endothelial cell's biomechanical properties by cancer cells is a critical determinant of cancer cell invasiveness and may affect the future development of new cancer treatments.

The biomechanical properties of 3d extracellular matrices and embedded cells regulate the invasiveness of cancer cells

The malignancy of tumors depends on the biomechanical properties of cancer cells and their microenvironment, which enable cancer cells to migrate through the connective tissue, transmigrate through basement membranes and endothelial monolayers and form metastases in targeted organs. The current focus of cancer research is still based on biological capabilities such as molecular genetics and gene signaling, but these approaches ignore the mechanical nature of the invasion process of cancer cells. This review will focus on how structural, biochemical and mechanical properties of extracellular matrices (ECMs), and adjacent cells regulate the invasiveness of cancer cells. In addition, it presents how cancer cells create their own microenvironment by restructuring of the ECM and by interaction with stromal cells, which then further contribute to the progression of cancer disease. Finally, this review will point out that mechanical properties are a critical determinant for the efficiency of cancer cell invasion and the progression of cancer which might affect the future development of new cancer treatments.

Matched rabbit monoclonal antibodies against αv-series integrins reveal a novel αvβ3-LIBS epitope, and permit routine staining of archival paraffin samples of human tumors

The relationship between integrin expression and function in pathologies is often contentious as comparisons between human pathological expression and expression in cell lines is difficult. In addition, the expression of even integrins αvβ6 and αvβ8 in tumor cell lines is not comprehensively documented. Here, we describe rabbit monoclonal antibodies (RabMabs) against the extracellular domains of αv integrins that react with both native integrins and formalin fixed, paraffin embedded (FFPE) human tissues. These RabMabs, against αvβ3 (EM22703), αvβ5 (EM09902), αvβ6 (EM05201), αvβ8 (EM13309), and pan-αv (EM01309), recognize individual integrin chains in Western blots and in flow cytometry. EM22703 detected a ligand-induced binding site (LIBS), reporting an epitope enhanced by the binding of an RGD-peptide to αvβ3. αvβ8 was rarely expressed in human tumor specimens, and weakly expressed in non-small-cell lung carcinoma (NSCLC). However, ovarian carcinoma cell lines expressed αvβ8, as did some melanoma cells, whereas U87MG glioma lacked αvβ8 expression. We observed an unexpected strong expression of αvβ6 in tumor samples of invasive ductal breast adenoma, colorectal carcinoma (CRC), and NSCLC. αvβ3 was strongly expressed in some invasive NSCLC cohorts. Interestingly, PC3 prostate cell and human prostate tumors did not express αvβ3. The RabMabs stained plasma membranes in FFPE-immunohistochemistry (IHC) samples of tumor cell lines from lung, ovary, colon, prostate, squamous cell carcinoma of head and neck (SCCHN), breast, and pancreas carcinomas. The RabMabs are unique tools for probing αv integrin biology, and suggest that especially αvβ6 and αvβ8 biologies still have much to reveal.

Contractile forces contribute to increased glycosylphosphatidylinositol-anchored receptor CD24-facilitated cancer cell invasion

The malignancy of a tumor depends on the capability of cancer cells to metastasize. The process of metastasis involves cell invasion through connective tissue and transmigration through endothelial monolayers. The expression of the glycosylphosphatidylinositol-anchored receptor CD24 is increased in several tumor types and is consistently associated with increased metastasis formation in patients. Furthermore, the localization of β1-integrins in lipid rafts depends on CD24. Cell invasion is a fundamental biomechanical process and usually requires cell adhesion to the extracellular matrix (ECM) mainly through β1 heterodimeric integrin receptors. Here, we studied the invasion of A125 human lung cancer cells with different CD24 expression levels in three-dimensional ECMs. We hypothesized that CD24 expression increases cancer cell invasion through increased contractile forces. To analyze this, A125 cells (CD24 negative) were stably transfected with CD24 and sorted for high and low CD24 expression. The invasiveness of the CD24(high) and CD24(low) transfectants was determined in three-dimensional ECMs. The percentage of invasive cells and their invasion depth was increased in CD24(high) cells compared with CD24(low) cells. Knockdown of CD24 and of the β1-integrin subunit in CD24(high) cells decreased their invasiveness, indicating that the increased invasiveness is CD24- and β1-integrin subunit-dependent. Fourier transform traction microscopy revealed that the CD24(high) cells generated 5-fold higher contractile forces compared with CD24(low) cells. To analyze whether contractile forces are essential for CD24-facilitated cell invasion, we performed invasion assays in the presence of myosin light chain kinase inhibitor ML-7 as well as Rho kinase inhibitor Y27632. Cell invasiveness was reduced after addition of ML-7 and Y27632 in CD24(high) cells but not in CD24(neg) cells. Moreover, after addition of lysophosphatidic acid or calyculin A, an increase in pre-stress in CD24(neg) cells was observed, which enhanced cellular invasiveness. In addition, inhibition of the Src kinase or STAT3 strongly reduced the invasiveness of CD24(high) cells, slightly reduced that of CD24(low) cells, and did not alter the invasiveness of CD24(neg) cells. Taken together, these results suggest that CD24 enhances cell invasion through increased generation or transmission of contractile forces.

Integrin α5β1 facilitates cancer cell invasion through enhanced contractile forces

Cell migration through connective tissue, or cell invasion, is a fundamental biomechanical process during metastasis formation. Cell invasion usually requires cell adhesion to the extracellular matrix through integrins. In some tumors, increased integrin expression is associated with increased malignancy and metastasis formation. Here, we have studied the invasion of cancer cells with different α5β1 integrin expression levels into loose and dense 3D collagen fiber matrices. Using a cell sorter, we isolated from parental MDA-MB-231 breast cancer cells two subcell lines expressing either high or low amounts of α5β1 integrins (α5β1(high) or α5β1(low) cells, respectively). α5β1(high) cells showed threefold increased cell invasiveness compared to α5β1(low) cells. Similar results were obtained for 786-O kidney and T24 bladder carcinoma cells, and cells in which the α5 integrin subunit was knocked down using specific siRNA. Knockdown of the collagen receptor integrin subunit α2 also reduced invasiveness, but to a lesser degree than knockdown of integrin subunit α5. Fourier transform traction microscopy revealed that the α5β1(high) cells generated sevenfold greater contractile forces than α5β1(low) cells. Cell invasiveness was reduced after addition of the myosin light chain kinase inhibitor ML-7 in α5β1(high) cells, but not in α5β1(low) cells, suggesting that α5β1 integrins enhance cell invasion through enhanced transmission and generation of contractile forces.

Cancer dissemination--lessons from leukocytes

Cancer cells can move through tissues in a variety of different ways. In some cases, an epithelial-to-mesenchymal transition enables cancer cells to acquire fibroblast-like migratory properties. However, it is also becoming apparent that some cancer cells move in an amoeboid way similar to leukocytes. This theme will be the focus of the review, where we will discuss the similarities and differences between the mechanisms used by cancer cells and leukocytes to cross parenchymal basement membranes, move through interstitial tissue, and enter and exit the vasculature. Further, we propose that the ability to switch between different migratory mechanisms is critical for cells to relocate from one tissue to another.

Osteopontin promotes gastric cancer metastasis by augmenting cell survival and invasion through Akt-mediated HIF-1alpha up-regulation and MMP9 activation

Osteopontin (OPN) is a secreted, integrin-binding matrix phosphorylated glycoprotein. OPN has been shown to facilitate the progression and metastasis of malignancies and has prognostic value in several types of cancer, including gastric cancer. However, the functional mechanism of OPN mediated metastatic growth in gastric cancer remains unclear. Here, using multiple in vitro and in vivo models, we report that OPN strongly promoted the progression and metastasis of gastric cancer. Immunohistochemical staining revealed that OPN, matrix metalloproteinase (MMP)9 and hypoxia-inducible factor (HIF)-1alpha have statistically significant different expression patterns between well- and poorly differentiated tissue samples (P < 0.05). Correlations existed between OPN and MMP9, and between OPN and HIF-1 (r(1) = 0.872, p(1) < 0.01 and r(2) = 0.878, p(2) < 0.01). Furthermore, OPN dramatically increased colony formation and invasion of gastric cancer cells in vitro and promoted tumour growth and metastasis in vivo. In addition, OPN potently protected gastric cancer cells from serum depletion-induced apoptosis. Further study shows that OPN activated phosphoinositide 3-kinase/Akt survival pathway and up-regulated HIF-1alpha via binding to v3 integrins in gastric cancer cells. Moreover, we found that OPN could activate MMP9 and upregulate MMP2. Taken together, our results suggest that the survival-promoting function is crucial for OPN to promote the development of gastric cancer, and HIF-1 and MMP9 may play key roles during this process. Thus, targeting OPN and its related signalling network may develop an effective therapeutic approach for the management of gastric cancer.

Tissue inhibitor of metalloproteinase-2 regulates matrix metalloproteinase-2-mediated endothelial barrier dysfunction and breast cancer cell transmigration through lung microvascular endothelial cells

Matrix metalloproteinases (MMP) have been implicated in multiple stages of cancer metastasis. Tissue inhibitor of metalloproteinase-2 (TIMP-2) plays an important role in regulating MMP-2 activity. By forming a ternary complex with pro-MMP-2 and its activator MMP-14 on the cell surface, TIMP-2 can either initiate or restrain the cleavage and subsequent activation of MMP-2. Our recent work has shown that breast cancer cell adhesion to vascular endothelial cells activates endothelial MMP-2, promoting tumor cell transendothelial migration (TEM(E)). However, the mechanism of MMP-2 regulation during TEM(E) remains unclear. In the current study, we present evidence that MMP-14 is expressed in both invasive breast cancer cells (MDA-MB-231 and MDA-MB-436) and lung microvascular endothelial cells (HBMVEC-L), whereas TIMP-2 is exclusively expressed and released from the cancer cells. The tumor cell-derived TIMP-2 was further identified as a major determinant of endothelial MMP-2 activity during tumor cell transmigration in the presence of MMP-14. This response was associated with endothelial barrier dysfunction because coculture of MDA-MB-231 or MDA-MB-436 with HBMVEC-L caused a significant decrease in transendothelial electrical resistance concomitantly with endothelial cell-cell junction disruption and tumor cell transmigration. Knockdown of TIMP-2 or inhibition of TIMP-2/MMP-14 attenuated MMP-2-dependent transendothelial electrical resistance response and TEM(E). These findings suggest a novel interactive role of breast cancer cells and vascular endothelial cells in regulating the TIMP-2/MMP-14/MMP-2 pathway during tumor metastasis.

Role of the endothelium during tumor cell metastasis: is the endothelium a barrier or a promoter for cell invasion and metastasis?

The malignancy of cancer disease depends on the ability of the primary tumor to metastasize to distant organs. The process of the metastasis formation has largely been analyzed, but still main pathways regarding the extravasation step at the end of the metastasis formation process are controversially discussed. An agreement has been reached about the importance of the endothelium to promote metastasis formation either by enhancing the growth of the primary tumor or by homing (targeting) the tumor cells to blood or lymph vessels. The mechanical properties of the invading tumor cells become the focus of several studies, but the endothelial cell mechanical properties are still elusive. This paper describes the different roles of the endothelium in the process of metastasis formation and focuses on a novel role of the endothelium in promoting tumor cell invasion. It discusses how novel biophysical tools and in vivo animal models help to determine the role of the endothelium in the process of tumor cell invasion. Evidence is provided that cell mechanical properties, for example, contractile force generation of tumor cells, are involved in the process of tumor cell invasion.

ZEB1 enhances transendothelial migration and represses the epithelial phenotype of prostate cancer cells

Metastatic colonization involves cancer cell lodgment or adherence in the microvasculature and subsequent migration of those cells across the endothelium into a secondary organ site. To study this process further, we analyzed transendothelial migration of human PC-3 prostate cancer cells in vitro. We isolated a subpopulation of cells, TEM4-18, that crossed an endothelial barrier more efficiently, but surprisingly, were less invasive than parental PC-3 cells in other contexts in vitro. Importantly, TEM4-18 cells were more aggressive than PC-3 cells in a murine metastatic colonization model. Microarray and FACS analysis of these cells showed that the expression of many genes previously associated with leukocyte trafficking and cancer cell extravasation were either unchanged or down-regulated. Instead, TEM4-18 cells exhibited characteristic molecular markers of an epithelial-to-mesenchymal transition (EMT), including frank loss of E-cadherin expression and up-regulation of the E-cadherin repressor ZEB1. Silencing ZEB1 in TEM4-18 cells resulted in increased E-cadherin and reduced transendothelial migration. TEM4-18 cells also express N-cadherin, which was found to be necessary, but not sufficient for increased transendothelial migration. Our results extend the role of EMT in metastasis to transendothelial migration and implicate ZEB1 and N-cadherin in this process in prostate cancer cells.

Integrin beta3 down-regulates invasive features of ovarian cancer cells in SKOV3 cell subclones

PURPOSE

To investigate the role of integrin beta3 in invasive features of ovarian cancer SKOV3 cells, by comparing different metastatic subclones.

METHODS

In the present study, two cell subclones, termed as S1 and S21, which possessed high and low metastatic potential, respectively, were isolated and established from human ovarian cancer parental cell line SKOV3 by the limited dilution method. The expressions of integrin alphav, integrin alphavbeta3, integrin beta3, E-cadherin, FAK and ILK in the two cell subclones were compared by means of real-time RT-PCR or flow cytometry. Subsequently, S21 was transfected with siRNA for integrin beta3 and the effects of transfection were examined by methyl thiazolyl tetrazolium (MTT) assay, colony formation assay, Matrigel invasion assay and cell migration assay.

RESULTS

The expressions of integrin alphavbeta3, integrin beta3 and E-cadherin were markedly down-regulated in S1; however, there were no significant differences in the expressions of integrin alphav, FAK and ILK beta. Of note, more than 70% knockdown of integrin beta3 expression was obtained by siRNA technique. The integrin beta3-siRNA-transfected cells showed significant increases in cell proliferation, cell migration and invasive activity in contrast with the mock-transfected cells. The expressions of integrin alphavbeta3 and E-cadherin were lower in the integrin beta3-siRNA-transfected cells compared to the mock control.

CONCLUSION

Integrin beta3, like E-cadherin, may be also a suppressor gene down-regulating invasive features of ovarian cancer cells in SKOV3 cell subclones.

Osteopontin prevents curcumin-induced apoptosis and promotes survival through Akt activation via alpha v beta 3 integrins in human gastric cancer cells

Osteopontin (OPN) is a secreted, integrin-binding matrix phosphorylated glycoprotein that is overexpressed in many advanced cancers. However, the functional mechanisms by which OPN contributes to gastric cancer development are poorly understood. Here, we report that curcumin inhibited the growth of SGC7901 cell and induced apoptosis in a concentration- and time-dependent manner, while the acquired expression of OPN in SGC7901 cells dramatically promoted cell survival under serum depletion and prevented curcumin-induced apoptosis. Furthermore, PI3-K inhibitor LY294002 attenuated OPN-mediated Akt activation. Moreover, inhibiting the binding of OPN to alpha(v)beta(3) integrins reduced activation of Akt. Taken together, these results demonstrate that the pro-survival and anti-apoptosis activities of OPN in gastric cancer cells are mediated in part through PI3-K/Akt pathway via alpha(v)beta(3) integrins.

Characterization of key mechanisms in transmigration and invasion of mesenchymal stem cells

For successful systemic stem cell therapy, mesenchymal stem cells (MSCs) must transmigrate across the endothelium and invade their target tissue. To date, most of the underlying mechanisms of transmigration and invasion remain to be elucidated. Improving our knowledge on these core processes might elevate the efficiency of stem cell therapy. Our aim was therefore to characterize key mechanisms involved in transmigration and invasion of MSCs. Co-cultivation experiments infer that MSCs integrate into the endothelial monolayer. However, the time course of adhesion, integration and transmigration depends on the endothelial phenotype and is most effective in venous vessels of the myocardium. Thus, a variable capacity for transmigration exists within the vasculature. Additionally, three-dimensional systems reveal that MSCs penetrate the endothelium and invade the surrounding tissue via plasmic podia. Furthermore, transmigration not only requires the interaction of vascular cell adhesion molecule-1 (VCAM-1) and very late antigen-4 (VLA-4) as verified by blocking experiments, but also triggers the clustering of beta1 integrins. In addition, in situ zymographies infer the activation of gelatinases at sites of MSC invasion into myocardial tissue. As evidenced by ELISA, MSCs secrete matrix metalloproteinase (MMP)-2 but not MMP-9. Finally, media containing additional cytokines accelerate the transmigration. Concluding, key players involved in transmigration and invasion of MSCs are the endothelial phenotype, VCAM-1/VLA-4, beta1 integrins, MMP-2 secretion and cytokines.