Targeting integrins and PI3K/Akt-mediated signal transduction pathways enhances radiation-induced anti-angiogenesis

Radiobiological Studies of Microvascular Damage through In Vitro Models: A Methodological Perspective

Ionizing radiation (IR) is used in radiotherapy as a treatment to destroy cancer. Such treatment also affects other tissues, resulting in the so-called normal tissue complications. Endothelial cells (ECs) composing the microvasculature have essential roles in the microenvironment's homeostasis (ME). Thus, detrimental effects induced by irradiation on ECs can influence both the tumor and healthy tissue. In-vitro models can be advantageous to study these phenomena. In this systematic review, we analyzed in-vitro models of ECs subjected to IR. We highlighted the critical issues involved in the production, irradiation, and analysis of such radiobiological in-vitro models to study microvascular endothelial cells damage. For each step, we analyzed common methodologies and critical points required to obtain a reliable model. We identified the generation of a 3D environment for model production and the inclusion of heterogeneous cell populations for a reliable ME recapitulation. Additionally, we highlighted how essential information on the irradiation scheme, crucial to correlate better observed in vitro effects to the clinical scenario, are often neglected in the analyzed studies, limiting the translation of achieved results.

Integrative transcriptomic and proteomic analysis reveals CD9/ITGA4/PI3K-Akt axis mediates trabecular meshwork cell apoptosis in human glaucoma

Glaucoma has been the leading cause of irreversible blindness worldwide. High intraocular pressure (IOP) is a high‐risk factor of glaucoma, repression of which has been the important treatment of glaucoma in clinic. Trabecular meshwork is crucial for maintaining IOP in aqueous humour out‐flow system. It is urgent to reveal the molecular mechanism of trabecular meshwork in glaucoma. Previous studies found that some pathways were related to glaucoma, such as extracellular matrix (ECM)‐receptor interaction, phosphatidylinositol 3‐kinase (PI3K)‐protein kinase B (Akt) and apoptosis. To identify novel molecules in glaucoma, we performed high‐throughput transcriptome and proteome analysis to immortal human trabecular meshwork cells (iHTM) and glaucomatous human trabecular meshwork cells (GTM₃), respectively. Twenty‐six up‐regulated genes/proteins and 59 down‐regulated genes/proteins were identified as the high‐risk factors based on differential analysis, including some known factors of glaucoma. Furthermore, a glaucoma‐related protein‐protein interaction (PPI) network was constructed for investigating the function roles of risk factors. Some genes were identified as potential regulator in the pathogenesis of glaucoma based on the topology analysis and module analysis to the network. Importantly, we identified and demonstrated that CD9 played key roles in glaucoma by biological experiment. CD9 is down‐regulated in glaucoma, overexpression of CD9 can active integrin α4 (ITGA4), PI3K and Akt, which lead to the decreased apoptosis and attenuate glaucoma. All these results provide a novel molecular therapy of glaucoma.

Static Compression Induces ECM Remodeling and Integrin α2β1 Expression and Signaling in a Rat Tail Caudal Intervertebral Disc Degeneration Model

STUDY DESIGN

A three-level rat tail caudal intervertebral disc (IVD) degeneration (IVDD) model was established to study effects of static compression on extracellular matrix (ECM) remodeling and integrin signaling in IVDs during IVDD.

OBJECTIVE

The aim of this study was to investigate the effect of compression force on ECM remodeling and integrin signaling in IVDs during IVDD.

SUMMARY OF BACKGROUND DATA

Integrins sense mechanical environment alteration via binding to ECM ligands and trigger intracellular signaling for pathological ECM remodeling during IVDD. However, the role of compression force in ECM remodeling and integrin signaling during IVDD remains elusive.

METHODS

Compared with the classical one-level rat tail IVDD model that exerts axial stress on the 8th to 9th caudal vertebral bodies, a three-level model was established by using an Ilizarov-type apparatus to exert stress on the 7th to 10th caudal vertebral bodies in rat tails for four weeks. To exclude side effects from surgical stab injury on manipulated discs, intact coccygeal (Co) disc Co8-9 was analyzed.

RESULTS

In three-level IVDD model, significant degeneration of the Co8-9 disc was observed. Quantitative real-time polymerase chain reaction (qRT-PCR) showed elevated mRNA expression of collagen types I, III, and V; matrix metalloproteinases (MMPs) 2, 3, 9, 13, 14; and decreased mRNA expression of collagen type II in Co8-9 disc. Compression loading altered the expression of integrin α2β1 (upregulated) and α10β1 (downregulated) in NP cells, and activated integrin downstream signaling. By contrast, one-level model showed more severe disc degeneration and ECM remodeling. Integrin α1, α2, α11, and β1 were upregulated, whereas α10 was downregulated. Similar activation of integrin signaling was observed.

CONCLUSION

Static compression altered collagen and MMP expression, and promoted β1 integrin expression and signaling in IVD. Compared with one-level rat tail IVDD model, three-level model showed milder effects on disc degeneration, ECM remodeling, and integrin expression, suggesting one-level model might involve other causes that induce IVDD via mechanisms independent of compression force.

LEVEL OF EVIDENCE

N/A.

The Transcriptional Landscape of Radiation-Treated Human Prostate Cancer: Analysis of a Prospective Tissue Cohort

PURPOSE

The resistance of prostate cancer to radiation therapy (RT) is a significant clinical issue and still largely unable to be guided by patient-specific molecular characteristics. The present study describes the gene expression changes induced in response to RT in human prostate tissue obtained from a prospective tissue acquisition study designed for radiobiology research.

METHODS AND MATERIALS

A prospective cohort of 5 men with intermediate-risk and clinically localized tumors were treated with high-dose-rate brachytherapy with 2 × 10-Gy fractions. Image-guided transperineal biopsy specimens were taken immediately before and 14 days after the first high-dose-rate brachytherapy fraction. Using genome-wide 3' RNA sequencing on total RNA extracted from 10 biopsy specimens, we obtained quantitative expression data for a median of 13,244 genes. We computed the fold-change information for each gene and extracted high-confidence lists of transcripts with either increased or decreased expression (≥1.5-fold) after radiation in ≥4 of the 5 patients. Several gene ontology analyses were then used to identify functionally enriched pathways.

RESULTS

The predominant change in response to RT was elevation of the transcript levels, including that of DNA damage binding protein 2 and p21, and collagens, laminins, and integrins. We observed strong upregulation of the p53 pathway, without observable dysregulation of p53 itself. Interstitial remodeling, extracellular matrix proteins, and focal adhesion pathways were also strongly upregulated, as was inflammation. Functional network analysis showed clustering of the changes inherent in apoptosis and programmed cell death, extracellular matrix organization, and immune regulation.

CONCLUSIONS

In the present prospective study of matched clinical tissues, we successfully recognized known radiation-sensitive transcriptional pathways and identified numerous other novel and significantly altered genes with no current association with RT. These data could be informative in the development of future personalized therapeutic agents.

HAb18G/CD147 promotes radioresistance in hepatocellular carcinoma cells: a potential role for integrin β1 signaling

Radiotherapy has played a limited role in the treatment of hepatocellular carcinoma (HCC) due to the risk of tumor radioresistance. A previous study in our laboratory confirmed that CD147 interacts with integrin β1 and plays an important role in modulating the malignant properties of HCC cells. In this study, we further evaluated the role of CD147 in the radioresistance of HCC and as a potential target for improving radiosensitivity. Upon irradiation, the colony formation, apoptosis, cell-cycle distribution, migration, and invasion of SMMC-7721, CD147-knockout SMMC-7721, HepG2, and CD147-knockdown HepG2 cells were determined. A nude mouse xenograft model and a metastatic model of HCC were used to detect the role of CD147 in radioresistance in vivo. Deletion of HAb18G/CD147 significantly enhanced the radiosensitivity of SMMC-7721 and HepG2 cells, and knocking out HAb18G/CD147 in SMMC-7721 cells attenuated irradiation-enhanced migration and invasion. The knockout and antibody blockade of CD147 decreased the tumor growth and metastatic potentials of HCC cells under irradiation. CD147-deleted SMMC-7721 cells showed diminished levels of calpain, cleaved talin, active integrin β1, and decreased p-FAK (Tyr397) and p-Akt (Ser473) levels. FAK and PI3K inhibitors, as well as integrin β1 antibodies, increased the radiation-induced apoptosis of SMMC-7721 cells. Our data provide evidence for CD147 as an important determinant of radioresistance via the regulation of integrin β1 signaling. Inhibition of the HAb18G/CD147 integrin interaction may improve the efficiency of radiosensitivity and provide a potential new approach for HCC therapy.

TGF β1 mediates epithelial mesenchymal transition via β6 integrin signaling pathway in breast cancer

BACKGROUND

To understand the function of β6 integrin and elucidate its signaling pathways in TGF-β-induced EMT in breast cancer.

METHODS

The interactions between TGF-β1 and β6 integrin were measured by coimmunoprecipitation. The EMT responses, phospherlation of PI3K/Akt and COX-2 expression were determined by real-time PCR, transwell assay, and western blot after the blockage of β6 integrin.

RESULTS

TGF-β1 and β6 integrin could bind with each other. Blockage of β6 integrin rescued TGF-β1-induced EMT phenotype and reduced expression of COX-2 via dephosphorylation of PI3K/Akt.

CONCLUSIONS

β6 integrin plays a critical role in TGF-β1-induced EMT and overexpression of COX-2 in breast cancer.

Radiation sensitization of tumor cells induced by shear stress: the roles of integrins and FAK

Recent studies revealed that the interstitial fluid flow in and around tumor tissue not only played an important role in delivering anticancer agents, but also affected the microenvironment, mostly hypoxia, in modulating tumor radio-sensitivity. The current study investigated the hypoxia-independent mechanisms of flow-induced shear stress in sensitizing tumors to radiation. Colon cancer cells were seeded onto glass slides pre-coated with fibronectin. A parallel-plate flow chamber system was used to impose fluid shear stress. Cell proliferation, apoptosis and colony assays were measured after shear stress and/or radiation. Cell cycle analysis and immunoblots of cell adhesion signal molecules were evaluated. The effect of shear stress was reversed by modulating integrin β1 or FAK. Shear stress of 12dyne/cm(2) for 24h, but not 3h, enhanced the radiation induced cytotoxicity to colon cancer cells. Protein expression of FAK was significantly down-regulated but not transcriptionally suppressed. By modulating integrin β1 and FAK expression, we demonstrated that shear stress enhanced tumor radiosensitivity by regulating integrin β1/FAK/Akt as well as integrin β1/FAK/cortactin pathways. Shear stress in combination with radiation might regulate integrins signaling by recruiting and activating caspases 3/8 for FAK cleavage followed by ubiquitin-mediated proteasomal degradation. Shear stress enhanced the radiation toxicity to colon cancer cells through suppression of integrin signaling and protein degradation of FAK. The results of our study provide a strong rationale for cancer treatment that combines between radiation and strategy in modulating tumor interstitial fluid flow.

Vascular-homing peptides for targeted drug delivery and molecular imaging: meeting the clinical challenges

The vasculature of each organ expresses distinct molecular signatures critically influenced by the pathological status. The heterogeneous profile of the vascular beds has been successfully unveiled by the in vivo phage display, a high-throughput tool for mapping normal, diseased, and tumor vasculature. Specific challenges of this growing field are targeted therapies against cancer and cardiovascular diseases, as well as novel bioimaging diagnostic tools. Tumor vasculature-homing peptides have been extensively evaluated in several preclinical and clinical studies both as targeted-therapy and diagnosis. To date, results from several Phase I and II trials have been reported and many other trials are currently ongoing or recruiting patients. In this review, advances in the identification of novel peptide ligands and their corresponding receptors on tumor endothelium through the in vivo phage display technology are discussed. Emphasis is given to recent findings in the clinical setting of vascular-homing peptides selected by in vivo phage display for the treatment of advanced malignancies and their altered vascular beds.

Combining molecular targeted agents with radiation therapy for malignant gliomas

The expansion in understanding the molecular biology that characterizes cancer cells has led to the rapid development of new agents to target important molecular pathways associated with aberrant activation or suppression of cellular signal transduction pathways involved in gliomagenesis, including epidermal growth factor receptor, vascular endothelial growth factor receptor, mammalian target of rapamycin, and integrins signaling pathways. The use of antiangiogenic agent bevacizumab, epidermal growth factor receptor tyrosine kinase inhibitors gefitinib and erlotinib, mammalian target of rapamycin inhibitors temsirolimus and everolimus, and integrin inhibitor cilengitide, in combination with radiation therapy, has been supported by encouraging preclinical data, resulting in a rapid translation into clinical trials. Currently, the majority of published clinical studies on the use of these agents in combination with radiation and cytotoxic therapies have shown only modest survival benefits at best. Tumor heterogeneity and genetic instability may, at least in part, explain the poor results observed with a single-target approach. Much remains to be learned regarding the optimal combination of targeted agents with conventional chemoradiation, including the use of multipathways-targeted therapies, the selection of patients who may benefit from combined treatments based on molecular biomarkers, and the verification of effective blockade of signaling pathways.

Short term effects of gamma radiation on endothelial barrier function: uncoupling of PECAM-1

A limiting factor in the treatment of cancer with radiotherapy is the damage to surrounding normal tissue, particularly the vasculature. Vessel pathologies are a major feature of the side effects of radiotherapy and little is known about early events that could initiate subsequent diseases. We tested the hypothesis that gamma radiation has early damaging effects on the human endothelial barrier. Two models were used; Human Brain Microcapillary Endothelial Cells (HBMEC), and Human Umbilical Vein Endothelial Cells (HUVEC). Endpoints included Trans-Endothelial Electrical Resistance (TEER), barrier permeability to 10 kDa and 70 kDa tracer molecules, and the localization of F-actin, and junction proteins and the Platelet Endothelial Cell Adhesion Molecule (PECAM-1). Radiation induced a rapid and transient decrease in TEER at 3 h, with effects also seen at the radiotherapy doses. This dip in resistance correlated to the transient loss of PECAM-1 in discrete areas where cells often detached from the monolayer leaving gaps. Redistribution of PECAM-1 was also seen in 3-D human tissue models. By 6 h, the remaining cells had migrated to reseal the barrier, coincident with TEER returning to control levels. Resealed monolayers contained fewer cells per unit area and their barrier function was weakened as evidenced by an increased permeability over 24 h. This is the first demonstration of a transient and rapid effect of gamma radiation on human endothelial barriers that involves cell detachment and the loss of PECAM-1. Considering the association of cell adhesion molecules with vasculopathies, such an effect has the potential to be clinically relevant to the longer-term effects of radiotherapy.

The role of ROS in ionizing radiation-induced VLA-4 mediated adhesion of RAW264.7 cells to VCAM-1 under flow conditions

Alteration of adhesion molecule expression on endothelial cells has a direct connection with ionizing radiation-induced atherosclerosis, which is an adverse effect observed after radiotherapy. However, minimal attention has been given to monocytes/macrophages role in atherosclerosis development, which are exposed to the radiation at the same time. Under flow conditions using a parallel plate flow chamber to mimic physiological shear stress, we demonstrate here that the avidity between very late antigen-4 (VLA-4) of RAW264.7 cells and its ligand vascular cell adhesion molecule-1 (VCAM-1), was increased after low dose (0.5 Gy) irradiation, but was reduced after higher dose (5 Gy) treatment of ionizing radiation despite the fact that the surface expression of VLA-4 was up-regulated at 5 Gy of ionizing radiation. Treating the cells with free radical scavenger N-acetylcysteine had no effect on VLA-4 expression, but did reduce the avidity between RAW264.7 cells and VCAM-1 to a similar level, independent of ionizing radiation dose. The effect of H(2)O(2) treatment (from 1-100 μM) on RAW264.7 cell adhesion to VCAM-1 generated a similar bell-shaped graph as ionizing radiation. These results suggest that ionizing radiation regulates adhesive interactions between VLA-4 and VCAM-1, and that reactive oxygen species might function as a regulator, for this increased adhesiveness but with altered expression of integrin not play a major role.

Anti-alphav integrin monoclonal antibody intetumumab enhances the efficacy of radiation therapy and reduces metastasis of human cancer xenografts in nude rats

We previously reported that intetumumab (CNTO 95), a fully human anti-αv integrin monoclonal antibody, is a radiosensitizer in mice with xenograft tumors. Because intetumumab does not cross-react with mouse integrins, but has cross-reactivity with rat integrins, we next studied the potential combined use of radiation therapy and intetumumab in human cancer xenograft models in nude rats to assess effects on both tumor cells and the tumor microenvironment. Nude rats bearing human head and neck cancer and non-small cell lung cancer (NSCLC) xenografts were treated with intetumumab and fractionated local tumor radiotherapy. Effects on tumor growth and metastasis, blood perfusion, oxygenation, and gastrointestinal toxicity were studied. Intetumumab alone had a moderate effect on tumor growth. When combined with fractionated radiation therapy, intetumumab significantly inhibited tumor growth and produced a tumor response rate that was significantly better than with radiation therapy alone. Treatment with intetumumab also significantly reduced lung metastasis in the A549 NSCLC xenograft model. The oxygenation and blood perfusion in xenograft tumors measured by microbubble-enhanced ultrasound imaging were substantially increased after treatment with intetumumab. The combined use of intetumumab and radiation therapy reduced the microvessel density and increased apoptosis in tumor cells and the tumor microenvironment. Toxicity studies showed that treatment with intetumumab did not cause the histopathologic changes in the lungs and did not sensitize the sensitive gastrointestinal epithelium to the effect of radiation therapy. Intetumumab can potentiate the efficacy of fractionated radiation therapy in human cancer xenograft tumors in nude rats without increased toxicity.

Breast cancer cells in three-dimensional culture display an enhanced radioresponse after coordinate targeting of integrin alpha5beta1 and fibronectin

Tactics to selectively enhance cancer radioresponse are of great interest. Cancer cells actively elaborate and remodel their extracellular matrix (ECM) to aid in survival and progression. Previous work has shown that beta1-integrin inhibitory antibodies can enhance the growth-inhibitory and apoptotic responses of human breast cancer cell lines to ionizing radiation, either when cells are cultured in three-dimensional laminin-rich ECM (3D lrECM) or grown as xenografts in mice. Here, we show that a specific alpha heterodimer of beta1-integrin preferentially mediates a prosurvival signal in human breast cancer cells that can be specifically targeted for therapy. 3D lrECM culture conditions were used to compare alpha-integrin heterodimer expression in malignant and nonmalignant cell lines. Under these conditions, we found that expression of alpha5beta1-integrin was upregulated in malignant cells compared with nonmalignant breast cells. Similarly, we found that normal and oncofetal splice variants of fibronectin, the primary ECM ligand of alpha5beta1-integrin, were also strikingly upregulated in malignant cell lines compared with nonmalignant acini. Cell treatment with a peptide that disrupts the interactions of alpha5beta1-integrin with fibronectin promoted apoptosis in malignant cells and further heightened the apoptotic effects of radiation. In support of these results, an analysis of gene expression array data from breast cancer patients revealed an association of high levels of alpha5-integrin expression with decreased survival. Our findings offer preclinical validation of fibronectin and alpha5beta1-integrin as targets for breast cancer therapy.

Vascular integrins: therapeutic and imaging targets of tumor angiogenesis

Cells, including endothelial cells, continuously sense their surrounding environment and rapidly adapt to changes in order to assure tissues and organs homeostasis. The extracellular matrix (ECM) provides a physical scaffold for cell positioning and represents an instructive interface allowing cells to communicate over short distances. Cell surface receptors of the integrin family emerged through evolution as essential mediators and integrators of ECM-dependent communication. In preclinical studies, pharmacological inhibition of vascular integrins suppressed angiogenesis and inhibited tumor progression. alpha(V)beta(3) and alpha(V)beta(5) were the first integrins targeted to suppress tumor angiogenesis. Subsequently, additional integrins, in particular alpha(1)beta(1), alpha(2)beta(1), alpha(5)beta(1), and alpha(6)beta(4), emerged as potential therapeutic targets. Integrin inhibitors are currently tested in clinical trials for their safety and antiangiogenic/antitumor activity. In this chapter, we review the role of integrins in angiogenesis and present recent advances in the use of integrin antagonists as potential therapeutics in cancer and discuss future perspectives.

beta1 integrin targeting to enhance radiation therapy

PURPOSE

Cell adhesion to extracellular matrix (ECM) proteins is mediated by the integrin family and has been known to modify radiation sensitivity and resistance in several cell types, including cancer cells. In particular, beta1 integrin signaling has been implicated in the progression and metastasis of various cancers and has been shown to facilitate resistance to radiation therapy.

CONCLUSION

In this mini-review, we provide a brief overview of integrin targeting in radiation therapy. We specifically focus on the updated findings of beta1 integrin-mediated signaling pathways after exposure to ionising radiation (IR) using in vitro and in vivo experimental models, which could represent promising therapeutic targets for breast cancer.

Modulating effect of the PI3-kinase inhibitor LY294002 on cisplatin in human pancreatic cancer cells

BACKGROUND

Chemoresistance is a serious problem in pancreatic cancer, but the mechanism of resistance and strategies against the resistance have not been elucidated. We examined the potential of the phosphatidylinositol 3-kinase (PI3K)/Akt inhibitor LY294002 to enhance the anti-tumor effect of cisplatin and investigated the mechanism of chemoresistance in pancreatic cancer cells using a combination therapy of cisplatin and LY294002, both in vitro and in vivo.

METHODS

Cisplatin and LY294002, individually or in combination, were given to AsPC-1 and PANC-1 cell lines. Tumor growth, DNA fragments, and Akt phosphorylation were examined in vitro. To examine the therapeutic effect of cisplatin and LY294002, individually or combination an AsPC-1 tumor xenograft model was prepared for in vivo study.

RESULTS

Cisplatin induced growth inhibition and Akt phosphorylation in pancreatic cancer cells. LY294002 also inhibited cell proliferation but without showing Akt phosphorylation. However, the combination therapy markedly increased cleavage of caspase-3 and cytoplasmic histone-associated DNA fragments compared to the results with cisplatin alone. In the in vivo study, blocking the PI3K/Akt cascade with LY294002 increased the efficacy of cisplatin-induced inhibition of tumor growth in nude mice, suppressing half the tumor growth with cisplatin alone. There were no detectable side effects in mice treated with combination therapy.

CONCLUSION

Our studies suggest that the PI3K/Akt pathway plays an important role in cisplatin resistance of pancreatic cancer cells. The augmentation of cisplatin with PI3K/Akt inhibitor may resolve the chemoresistance problem of cisplatin, and this might be a plausible strategy for achieving tolerance for chemotherapeutic agents in pancreatic cancer therapy.