β₁Integrin/FAK/cortactin signaling is essential for human head and neck cancer resistance to radiotherapy

Report on the International Workshop 'Cancer stem cells: the mechanisms of radioresistance and biomarker discovery'

The aim of the Workshop "Cancer stem cells: The mechanisms of radioresistance and biomarker discovery", which was held on 23-24 September 2013 at OncoRay - National Center for Radiation Research in Oncology in Dresden, Germany, was to bring together the most recent viewpoints and insights about: (i) the molecular characterization and regulation of CSC, (ii) the mechanisms of CSC radioresistance, and (iii) the discovery of new CSC targeting therapeutics and biomarkers. In this report some research aspects presented in these three topics are highlighted.

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.

Targeted drugs in combination with radiotherapy for the treatment of solid tumors: current state and future developments

The continuously rising use of novel drugs, especially of molecules belonging to the group of targeted drugs is now shaping the therapeutic landscape. However, treatment combinations of targeted drugs with radiotherapy are still rare. Only the monoclonal antibody cetuximab (Erbitux®) has been approved for the treatment of locally advanced squamous cell cancer of the head and neck in combination with radiotherapy. Several targeted compounds are in advanced stages of clinical development for combination treatments with radiotherapy, of which substances with either anti-EGFR or anti-angiogenic mechanisms, such as trastuzumab, panitumumab, erlotinib, cilengitide and bevacizumab are the most promising. Aim of this article is to provide, mainly from a radio-oncological point of view, an overview about the current state as well as to give an outlook on the near future of the most advanced targeted combined treatment concepts for solid tumors.

Nanoparticle-formulated siRNA targeting integrins inhibits hepatocellular carcinoma progression in mice

Integrins play an important role during development, regulating cell differentiation, proliferation and survival. Here we show that knockdown of integrin subunits slows down the progression of hepatocellular carcinoma (HCC). Using nanoparticulate delivery of short interfering RNAs targeting β1 and αv integrin subunits we downregulate all integrin receptors in hepatocytes. Short-term integrin knockdown (two weeks) does not cause apparent structural or functional perturbations of normal liver tissue. Alterations in liver morphology accumulate upon sustained integrin downregulation (seven weeks). The integrin knockdown leads to significant retardation of HCC progression, reducing proliferation and increasing tumour cell death. This tumour retardation is accompanied by reduced activation of MET oncogene as well as expression of its mature form on the cell surface. Our data suggest that transformed proliferating cells from HCC are more sensitive to knockdown of integrins than normal quiescent hepatocytes, highlighting the potential of siRNA-mediated inhibition of integrins as an anti-cancer therapeutic approach.

APPL proteins modulate DNA repair and radiation survival of pancreatic carcinoma cells by regulating ATM

Despite intensive multimodal therapies, the overall survival rate of patients with ductal adenocarcinoma of the pancreas is still poor. The chemo- and radioresistance mechanisms of this tumor entity remain to be determined in order to develop novel treatment strategies. In cancer, endocytosis and membrane trafficking proteins are known to be utilized and they also critically regulate essential cell functions like survival and proliferation. On the basis of these data, we evaluated the role of the endosomal proteins adaptor proteins containing pleckstrin homology domain, phosphotyrosine binding domain and a leucine zipper motif (APPL)1 and 2 for the radioresistance of pancreatic carcinoma cells. Here, we show that APPL2 expression in pancreatic cancer cells is upregulated after irradiation and that depletion of APPL proteins by small interfering RNA (siRNA) significantly reduced radiation survival in parallel to impairing DNA double strand break (DSB) repair. In addition, APPL knockdown diminished radiogenic hyperphosphorylation of ataxia telangiectasia mutated (ATM). Activated ATM and APPL1 were also shown to interact after irradiation, suggesting that APPL has a more direct role in the phosphorylation of ATM. Double targeting of APPL proteins and ATM caused similar radiosensitization and concomitant DSB repair perturbation to that observed after depletion of single proteins, indicating that ATM is the central modulator of APPL-mediated effects on radiosensitivity and DNA repair. These data strongly suggest that endosomal APPL proteins contribute to the DNA damage response. Whether targeting of APPL proteins is beneficial for the survival of patients with pancreatic adenocarcinoma remains to be elucidated.

High level expression of AMAP1 protein correlates with poor prognosis and survival after surgery of head and neck squamous cell carcinoma patients

Background

Despite recent advances in cancer therapeutics in general, the survival of patients with head and neck squamous cell carcinomas (HNSCCs) has not improved substantially over the past few decades. HNSCC cells often exhibit invasive and metastatic phenotypes, and expression of epidermal growth factor receptor (EGFR) and cortactin has been highly implicated in the development of malignancy in HNSCCs. We have shown previously that an Arf6 pathway, in which Arf6 is activated by GEP100 and employs AMAP1 (also called DDEF1 or ASAP1) as its downstream effector, is pivotal for the invasion and metastasis of different breast cancer cells. This pathway is activated by receptor tyrosine kinases, including EGFR; and moreover, AMAP1 physically associates with cortactin, in which inhibition of this binding effectively blocks invasion and metastasis. We here investigated whether the expression of Arf6 pathway components correlates with the poor prognosis of HNSCC patients. We have shown previously that AMAP1 protein levels are not correlated with its mRNA levels, and hence we here employed immunohistochemical staining of HNSCC clinical specimens to investigate AMAP1 protein levels.

Results

We found that high levels of AMAP1 protein expression on its own, as well as its co-overexpression with EGFR statistically correlates with poor disease-free survival and poor overall survival, while high levels of cortactin expression or its co-expression with EGFR did not.

Conclusion

Our identification of predictive biomarkers, together with our previous findings on the coherent signaling pathway that these biomarkers ultimately generate should be powerful information for the further development of HNSCC therapeutics.

Focal adhesion kinase antagonizes doxorubicin cardiotoxicity via p21(Cip1.)

Clinical application of potent anthracycline anticancer drugs, especially doxorubicin (DOX), is limited by a toxic cardiac side effect that is not fully understood and preventive strategies are yet to be established. Studies in genetically modified mice have demonstrated that focal adhesion kinase (FAK) plays a key role in regulating adaptive responses of the adult myocardium to pathological stimuli through activation of intracellular signaling cascades that facilitate cardiomyocyte growth and survival. The objective of this study was to determine if targeted myocardial FAK activation could protect the heart from DOX-induced de-compensation and to characterize the underlying mechanisms. To this end, mice with myocyte-restricted FAK knock-out (MFKO) or myocyte-specific expression of an active FAK variant (termed SuperFAK) were subjected to DOX treatment. FAK depletion enhanced susceptibility to DOX-induced myocyte apoptosis and cardiac dysfunction, while elevated FAK activity provided remarkable cardioprotection. Our mec6hanistic studies reveal a heretofore unappreciated role for the protective cyclin-dependent kinase inhibitor p21 in the repression of the pro-apoptotic BH3-only protein Bim and the maintenance of mitochondrial integrity and myocyte survival. DOX treatment induced proteasomal degradation of p21, which exacerbated mitochondrial dysfunction and cardiomyocyte apoptosis. FAK was both necessary and sufficient for maintaining p21 levels following DOX treatment and depletion of p21 compromised FAK-dependent protection from DOX. These findings identify p21 as a key determinant of DOX resistance downstream of FAK in cardiomyocytes and indicate that cardiac-restricted enhancement of the FAK/p21 signaling axis might be an effective strategy to preserve myocardial function in patients receiving anthracycline chemotherapy.

β1 integrins mediate resistance to ionizing radiation in vivo by inhibiting c-Jun amino terminal kinase 1

This study was carried out to dissect the mechanism by which β1 integrins promote resistance to radiation. For this purpose, we conditionally ablated β1 integrins in the prostatic epithelium of transgenic adenocarcinoma of mouse prostate (TRAMP) mice. The ability of β1 to promote resistance to radiation was also analyzed by using an inhibitory antibody to β1 , AIIB2, in a xenograft model. The role of β1 integrins and of a β1 downstream target, c-Jun amino-terminal kinase 1 (JNK1), in regulating radiation-induced apoptosis in vivo and in vitro was studied. We show that β1 integrins promote prostate cancer (PrCa) progression and resistance to radiation in vivo. Mechanistically, β1 integrins are shown here to suppress activation of JNK1 and, consequently apoptosis, in response to irradiation. Downregulation of JNK1 is necessary to preserve the effect of β1 on resistance to radiation in vitro and in vivo. Finally, given the established crosstalk between β1 integrins and type1 insulin-like growth factor receptor (IGF-IR), we analyzed the ability of IGF-IR to modulate β1 integrin levels. We report that IGF-IR regulates the expression of β1 integrins, which in turn confer resistance to radiation in PrCa cells. In conclusion, this study demonstrates that β1 integrins mediate resistance to ionizing radiation through inhibition of JNK1 activation.

SRChing for the substrates of Src

By the mid 1980's, it was clear that the transforming activity of oncogenic Src was linked to the activity of its tyrosine kinase domain and attention turned to identifying substrates, the putative next level of control in the pathway to transformation. Among the first to recognize the potential of phosphotyrosine-specific antibodies, Parsons and colleagues launched a risky shotgun-based approach that led ultimately to the cDNA cloning and functional characterization of many of today's best-known Src substrates (for example, p85-Cortactin, p110-AFAP1, p130Cas, p125FAK and p120-catenin). Two decades and over 6000 citations later, the original goals of the project may be seen as secondary to the enormous impact of these protein substrates in many areas of biology. At the request of the editors, this review is not restricted to the current status of the substrates, but reflects also on the anatomy of the project itself and some of the challenges and decisions encountered along the way.

The novel HDAC inhibitor NDACI054 sensitizes human cancer cells to radiotherapy

BACKGROUND AND PURPOSE

Inhibition of histone deacetylases (HDACs) has preclinically and clinically shown promise to overcome radio- and chemoresistance of tumor cells. NDACI054 is a novel HDAC inhibitor, which has been evaluated here for its effects on cell survival and radiosensitization of human tumor cell lines from different origins cultured under more physiological three-dimensional (3D), extracellular matrix (ECM)-based conditions.

MATERIAL AND METHODS

A549 lung, DLD-1 colorectal, MiaPaCa2 pancreatic and UT-SCC15 head and neck squamous cell carcinoma cells were treated with increasing NDACI054 concentrations (0-50 nM, 24 h) either alone or in combination with X-rays (single dose, 0-6 Gy). Subsequently, 3D clonogenic cell survival, HDAC activity, histone H3 acetylation, apoptosis, residual DNA damage (γH2AX/p53BP1 foci assay 24h post irradiation) and phosphorylation kinetics of Ataxia telangiectasia mutated (ATM), DNA-dependent protein kinase (DNA-PK), Caspase-3 and Poly(ADP-ribose)-Polymerase 1 (PARP 1) cleavage were analyzed.

RESULTS

NDACI054 potently decreased HDAC activity with concomitant increase in acetyl-histone H3 levels, mediated significant cytotoxicity and radiosensitization. These effects were accompanied by a significant increase of residual γH2AX/p53BP1-positive foci, slightly elevated levels of Caspase-3 and PARP 1 cleavage but no induction of apoptosis.

CONCLUSIONS

Our data show potent antisurvival and radiosensitizing effects of the novel HDAC inhibitor NDACI054 encouraging further preclinical examinations on this compound for future clinical use.

Acquired resistance of non-small cell lung cancer to epidermal growth factor receptor tyrosine kinase inhibitors

Activation of epidermal growth factor receptor (EGFR) triggers anti-apoptotic signaling, proliferation, angiogenesis, invasion, metastasis, and drug resistance, which leads to development and progression of human epithelial cancers, including non-small cell lung cancer (NSCLC). Inhibition of EGFR by tyrosine kinase inhibitors such as gefitinib and erlotinib has provided a new hope for the cure of NSCLC patients. However, acquired resistance to gefitinib and erlotinib via EGFR-mutant NSCLC has occurred through various molecular mechanisms such as T790M secondary mutation, MET amplification, hepatocyte growth factor (HGF) overexpression, PTEN downregulation, epithelial-mesenchymal transition (EMT), and other mechanisms. This review will discuss the biology of receptor tyrosine kinase inhibition and focus on the molecular mechanisms of acquired resistance to tyrosine kinase inhibitors of EGFR-mutant NSCLC.

Cetuximab attenuates its cytotoxic and radiosensitizing potential by inducing fibronectin biosynthesis

Inherent and acquired resistance to targeted therapeutics continues to emerge as a major clinical obstacle. For example, resistance to EGF receptor targeting occurs commonly, more so than was expected, on the basis of preclinical work. Given emerging evidence that cancer cell-substrate interactions are important determinants of therapeutic sensitivity, we examined the impact of cell-fibronectin interactions on the efficacy of the EGF receptor antibody cetuximab, which is used widely for lung cancer treatment. Our results revealed the potential for cell-fibronectin interactions to induce radioresistance of human non-small cell lung cancer cells. Cell adhesion to fibronectin enhanced tumor cell radioresistance and attenuated the cytotoxic and radiosensitizing effects of cetuximab. Both in vitro and in vivo, we found that cetuximab treatment led to a remarkable induction of fibronectin biosynthesis. Mechanistic analyses revealed the induction was mediated by a p38-MAPK-ATF2 signaling pathway and that RNAi-mediated inhibition of fibronectin could elevate the cytotoxic and radiosensitizing potential of cetuximab. Taken together, our findings show how cell adhesion blunts cetuximab, which, by inducing fibronectin, generates a self-attenuating mechanism of drug resistance.

Integrin Signaling as a Cancer Drug Target

Integrins are transmembrane receptors that mediate cell adhesion to neighboring cells and to the extracellular matrix. Here, the various modes in which integrin-mediated adhesion regulates intracellular signaling pathways impinging on cell survival, proliferation, and differentiation are considered. Subsequently, evidence that integrins also control crucial signaling cascades in cancer cells is discussed. Lastly, the important role of integrin signaling in tumor cells as well as in stromal cells that support cancer growth, metastasis, and therapy resistance indicates that integrin signaling may be an attractive target for (combined) cancer therapy strategies. Current approaches to target integrins in this context are reviewed.

Erlotinib resistance in lung cancer cells mediated by integrin β1/Src/Akt-driven bypass signaling

EGF receptor (EGFR) kinase inhibitors, including gefitinib and erlotinib, exert potent therapeutic efficacy in non-small cell lung cancers harboring EGFR-activating mutations. However, most patients ultimately develop resistance to these drugs. Here, we report a novel mechanism of acquired resistance to EGFR tyrosine kinase inhibitors and the reversal of which could improve clinical outcomes. In erlotinib-resistant lung cancer cells harboring activating EGFR mutations that we established, there was increased expression of Src, integrin β1, α2, and α5 along with enhanced cell adhesion activity. Interestingly, RNAi-mediated silencing of integrin β1 restored erlotinib sensitivity and reduced activation of Src and Akt after erlotinib treatment. Furthermore, Src silencing inhibited Akt phosphorylation and cell growth, with this inhibitory effect further augmented by erlotinib treatment. Increased expression of integrin β1, α5, and/or α2 was also observed in refractory tumor samples from patients with lung cancer treated with erlotinib and/or gefitinib. Together, our findings identify the integrin β1/Src/Akt signaling pathway as a key mediator of acquired resistance to EGFR-targeted anticancer drugs.

Double targeting of Survivin and XIAP radiosensitizes 3D grown human colorectal tumor cells and decreases migration

BACKGROUND AND PURPOSE

In the present study, we aimed to investigate the effect of single and double knockdown of the inhibitor of apoptosis proteins (IAP) Survivin and X-linked IAP (XIAP) on three-dimensional (3D) clonogenic survival, migration capacity and underlying signaling pathways.

MATERIALS AND METHODS

Colorectal cancer cell lines (HCT-15, SW48, SW480, SW620) were subjected to siRNA-mediated single or Survivin/XIAP double knockdown followed by 3D colony forming assays, cell cycle analysis, Caspase activity assays, migration assays, matrigel transmigration assays and Western blotting (Survivin, XIAP, Focal adhesion kinase (FAK), p-FAK Y397, Akt1, p-Akt1 S473, Extracellular signal-regulated kinase (ERK1/2), p-ERK1/2 T202/Y204, Glycogen synthase kinase (GSK)3β, p-GSK3β S9, nuclear factor (NF)-κB p65).

RESULTS

While basal cell survival was altered cell line-dependently, Survivin or XIAP single and Survivin/XIAP double knockdown enhanced cellular radiosensitivity of all tested cancer cell lines grown in 3D. Particularly double knockdown conditions revealed accumulation of cells in G2/M, increased subG1 fraction, elevated Caspase 3/7 activity, and reduced migration. Intracellular signaling showed dephosphorylation of FAK and Akt1 upon Survivin and/or Survivin/XIAP silencing.

CONCLUSIONS

Our results strengthen the notion of Survivin and XIAP to act as radiation resistance factors and further indicate that these apoptosis-regulating proteins are also functioning in cell cycling and cell migration.

Epigenetic modulation of signal transduction pathways in HPV-associated HNSCC

OBJECTIVE

Human papilloma virus (HPV) positive and HPV negative head and neck squamous cell cancer (HNSCC) are biologically distinct with a prognostic advantage for HPV positive patients compared to HPV negative cases. DNA promoter methylation is central to human diseases such as cancer, including HNSCC, with reported genome-wide hypomethylaton and promoter hypermethylation in HPV positive HNSCC tumors. The goal of this study was to identify differentially methylated genes in HPV positive versus HPV negative primary HNSCC genomes with clues to signaling networks.

STUDY DESIGN

Laboratory-based study.

SETTING

Primary care academic health care system.

SUBJECTS AND METHODS

DNA from 4 HPV positive and 4 HPV negative freshly frozen primary HNSCC were subject to comprehensive genome-wide methylation profiling. Differentially methylated gene lists were examined using the Signal Transduction Pathways (canonical) filter in the Genomatix Pathway System (GePS).

RESULTS

Twofold methylation differences were observed between HPV positive and HPV negative cases for 1168 genes. Pathway analysis applied to investigate the biological role of the 1168 differentially methylated genes revealed 8 signal transduction pathways forming a network of 66 genes, of which 62% are hypermethylated.

CONCLUSION

Our study reveals a predominant hypermethylation profile for genes in signal transduction pathways of HPV positive HNSCC tumor genomes. Because signaling events in the cell play a critical role in the execution of key biological functions, insights into how complex cellular signaling cascades and networks may be programmed in HNSCC are likely to be critical in the development of new biological agents designed to hit multiple targets.

Intracellular trafficking of integrins in cancer cells

Integrins are heterodimeric cell surface receptors, which principally mediate the interaction between cells and their extracellular microenvironments. Because of their pivotal roles in cancer proliferation, survival, invasion and metastasis, integrins have been recognized as promising targets for cancer treatment. As is the case with other receptors, the localization of integrins on the cell surface has provided opportunities to block their functions by various inhibitory monoclonal antibodies. A number of small molecule agents blocking integrin-ligand binding have also been established, and some such agents are currently on the market or in clinical trials for some diseases including cancer. This review exclusively focuses on another strategy for cancer therapy, which comes from the obligate localization of integrins on the cell surface; targeting the intracellular trafficking of integrins. A number of studies have shown the essential roles of integrin trafficking in hallmarks of cancer, such as activation of oncogenic signaling pathways as well as acquisition of invasiveness. Recent findings have shown that increased integrin recycling activity is associated with some types of gain-of-function mutations of p53, a common feature of diverse types of cancers, which also indicates that targeting integrin recycling could be widely applicable and effective against many cancers. We also discuss possible therapeutic contexts where integrin trafficking can be effectively targeted, and what molecular interfaces may hopefully be druggable.

Mechanosensitivity and compositional dynamics of cell-matrix adhesions

Cells perceive information about the biochemical and biophysical properties of their tissue microenvironment through integrin-mediated cell-matrix adhesions, which connect the cytoskeleton with the extracellular matrix and thereby allow cohesion and long-range mechanical connections within tissues. The formation of cell-matrix adhesions and integrin signalling involves the dynamic recruitment and assembly of an inventory of proteins, collectively termed the 'adhesome', at the adhesive site. The recruitment of some adhesome proteins, most notably the Lin11-, Isl1- and Mec3-domain-containing proteins, depends on mechanical tension generated by myosin II-mediated contractile forces exerted on cell-matrix adhesions. When exposed to force, mechanosensitive adhesome proteins can change their conformation or expose cryptic-binding sites leading to the recruitment of proteins, rearrangement of the cytoskeleton, reinforcement of the adhesive site and signal transduction. Biophysical methods and proteomics revealed force ranges within the adhesome and cytoskeleton, and also force-dependent changes in adhesome composition. In this review, we provide an overview of the compositional dynamics of cell-matrix adhesions, discuss the most prevalent functional domains in adhesome proteins and review literature and concepts about mechanosensing mechanisms that operate at the adhesion site.

CDK2 knockdown enhances head and neck cancer cell radiosensitivity

PURPOSE

Cyclin-dependent kinase 2 (CDK2) is critically involved in cell cycling and has been proposed as a potential cancer target. It remains largely elusive whether CDK2 targeting alters the tumor cell radiosensitivity.

MATERIALS AND METHODS

CDK2(-/-) and wild type (WT) mouse embryonic fibroblasts (MEF) as well as six human head and neck squamous cell carcinoma (HNSCC) cell lines (SAS, FaDu, Cal-33, HSC-4, UTSCC-5, UTSCC-8) were used. Upon CDK2 knockdown using small interfering technology, colony formation, DNA double-strand breaks (DSB), cell cycle distribution and expression and phosphorylation of major proteins regulating cell cycle and DNA damage repair were examined.

RESULTS

CDK2(-/-) MEF and CDK2 HNSCC knockdown cell cultures were more radiosensitive than the corresponding controls. Repair of DSB was attenuated under CDK2 knockout or knockdown. In contrast to data in MEF, combined CDK2 knockdown with irradiation showed no cell cycling alterations in SAS and FaDu cultures. Importantly, CDK2 knockdown failed to radiosensitize SAS and FaDu when cultured in a more physiological three-dimensional (3D) extracellular matrix environment.

CONCLUSIONS

Our findings suggest that targeting of CDK2 radiosensitizes HNSCC cells growing as monolayer. Additional studies performed under more physiological conditions are warranted to clarify the potential of CDK2 as target in radiotherapy.

NF-κB regulates radioresistance mediated by β1-integrin in three-dimensional culture of breast cancer cells

β1-integrin induction enhances breast cancer cell survival after exposure to ionizing radiation (IR), but the mechanisms of this effect remain unclear. Although NF-κB initiates prosurvival signaling pathways post-IR, the molecular function of NF-κB with other key elements in radioresistance, particularly with respect to extracellular matrix-induced signaling, is not known. We discovered a typical NF-κB-binding site in the β1-integrin promoter region, indicating a possible regulatory role for NF-κB. Using three-dimensional laminin-rich extracellular matrix (3D lrECM) culture, we show that NF-κB is required for β1-integrin transactivation in T4-2 breast cancer cells post-IR. Inhibition of NF-κB reduced clonogenic survival and induced apoptosis and cytostasis in formed tumor colonies. In addition, T4-2 tumors with inhibition of NF-κB activity exhibit decreased growth in athymic mice, which was further reduced by IR with downregulated β1-integrin expression. Direct interactions between β1-integrin and NF-κB p65 were induced in nonmalignant breast epithelial cells, but not in malignant cells, indicating context-specific regulation. As β1-integrin also activates NF-κB, our findings reveal a novel forward feedback pathway that could be targeted to enhance therapy.

Biodistribution Study of Nanoparticle Encapsulated Photodynamic Therapy Drugs Using Multispectral Imaging

Photodynamictherapy (PDT) uses a drug called a photosensitizer that is excited by irradiation with a laser light of a particular wavelength, which generates reactive singlet oxygen that damages the tumor cells. The photosensitizer and light are inert; therefore, systemic toxicities are minimized in PDT. The synthesis of novel PDT drugs and the use of nanosized carriers for photosensitizers may improve the efficiency of the therapy and the delivery of the drug. In this study, we formulated two nanoparticles with and without a targeting ligand to encapsulate phthalocyanines 4 (Pc 4) molecule and compared their biodistributions. Metastatic human head and neck cancer cells (M4e) were transplanted into nude mice. After 2-3 weeks, the mice were injected with Pc 4, Pc 4 encapsulated into surface coated iron oxide (IO-Pc 4), and IO-Pc 4 conjugated with a fibronectin-mimetic peptide (FMP-IO-Pc 4) which binds specifically to integrin β1. The mice were imaged using a multispectral camera. Using multispectral images, a library of spectral signatures was created and the signal per pixel of each tumor was calculated, in a grayscale representation of the unmixed signal of each drug. An enhanced biodistribution of nanoparticle encapsulated PDT drugs compared to non-formulated Pc 4 was observed. Furthermore, specific targeted nanoparticles encapsulated Pc 4 has a quicker delivery time and accumulation in tumor tissue than the non-targeted nanoparticles. The nanoparticle-encapsulated PDT drug can have a variety of potential applications in cancer imaging and treatment.

Integrin signaling in control of tumor growth and progression

Interactions with the extracellular matrix (ECM) provide cells with physical and chemical cues that act in concert with growth factors to support survival and proliferation. Transmembrane receptors of the integrin family mediate ECM attachment and play important roles in sensing and responding to ECM properties. Integrin signaling involves large integrin-associated intracellular protein complexes that act as anchors for the cytoskeleton and as signaling hotspots where enzymes and substrates are concentrated. Moreover, many different growth factor signaling cascades are amplified when cells are attached to the ECM. Integrins are involved in many pathologies; here we focus on their roles in cancer. Although "anchorage-independence" is a hallmark of cancer cells, genetic studies clearly show that integrins and associated proteins provide essential support for early tumor development and growth. Integrins also provide support during later stages of tumor progression but in some scenarios they appear to have suppressive activity, which is currently not understood.

Association of integrin beta1 and c-MET in mediating EGFR TKI gefitinib resistance in non-small cell lung cancer

Although some patients are initially sensitive to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR TKIs), resistance invariably develops. Therefore, it’s very important to study the molecular mechanism of this resistance. In our previous study we found that integrin beta1 can induce EGFR TKIs resistance in non-small cell lung cancer (NSCLC) cells. Here we analyzed the association of integrin beta1 and c-MET that is a recognized mechanism of EGFR TKIs resistance in NSCLC to demonstrate the mechanism of integrin beta1 related EGFR TKIs resistance. We found that the ligands of integrin beta1 and c-MET could synergistically promote cell proliferation and their inhibitors could synergistically improve the sensitivity to gfitinib, increase apoptosis, and inhibit the downstream signal transduction: focal adhesion kinase (FAK) and AKT. On the other hand, ligand-dependent activation of integrin beta1 could induce EGFR TKIs resistance through activating c-MET and its downstream signals. Thus, it can be concluded that there is crosstalk between integrin beta1 and c-MET and integrin beta1 mediates EGFR TKI resistance associating with c-MET signaling pathway in non-small cell lung cancer.

[Molecular signaling pathways. Mechanisms and clinical use]

This brief summary on the role of experimental radiation oncology highlights several new research topics and research approaches that offer great potential for the optimization of modern radiation oncology. In addition, many areas of research, such as hypoxia, angiogenesis, the immune system, and metabolism, to name a few, comprise a substantial part of our current knowledge of tumor and radiation biology. Which new insights and therapeutic possibilities via the Human Cancer Genome Project or new processes, such as next generation sequencing may offer, cannot be easily foreseen at present. However, we do know for certain: radiation biology has and will continue to contribute to improvements in radiation oncology.

EGFR/JIP-4/JNK2 signaling attenuates cetuximab-mediated radiosensitization of squamous cell carcinoma cells

EGF receptor (EGFR) promotes tumor growth as well as radio- and chemoresistance in various human malignancies including squamous cell carcinomas (SCC). In addition to deactivation of prosurvival signaling, cetuximab-mediated EGFR targeting might concomitantly induce self-attenuating signaling bypasses. Identification of such bypass mechanisms is key to improve the efficacy of targeted approaches. Here, we show great similarity of EGFR signaling and radiation survival in cetuximab-treated SCC cells grown in a more physiologic three-dimensional extracellular matrix and as tumor xenografts in contrast to conventional monolayer cell cultures. Using phosphoproteome arrays, we observed strong induction of JNK2 phosphorylation potentially resulting from cetuximab-inhibited EGFR through c-jun-NH(2)-kinase (JNK)-interacting protein-4 (JIP-4), which was identified using an immunoprecipitation-mass spectrometric approach. Inhibition of this signaling bypass by JIP-4 or JNK2 knockdown or pharmacologic JNK2 inhibition enhanced cetuximab efficacy and tumor cell radiosensitivity. Our findings add new facets to EGFR signaling and indicate signaling bypass possibilities of cancer cells to improve their survival on cetuximab treatment. By deactivation of cetuximab-self-attenuating JNK2-dependent signaling, the cytotoxicity, and radiosensitizing potential of cetuximab can be augmented.

Cortactin as a target for FAK in the regulation of focal adhesion dynamics

Background

Efficient cell movement requires the dynamic regulation of focal adhesion (FA) formation and turnover. FAs are integrin-associated sites of cell attachment and establish linkages to the cellular actin cytoskeleton. Cells without focal adhesion kinase (FAK), an integrin-activated tyrosine kinase, exhibit defects in FA turnover and cell motility. Cortactin is an actin binding adaptor protein that can influence FA dynamics. FAK and cortactin interact, but the cellular role of this complex remains unclear.

Principal Findings

Using FAK-null fibroblasts stably reconstituted with green fluorescent protein (GFP) tagged FAK constructs, we find that FAK activity and FAK C-terminal proline-rich region 2 (PRR2) and PRR3 are required for FA turnover and cell motility. Cortactin binds directly to FAK PRR2 and PRR3 sites via its SH3 domain and cortactin expression is important in promoting FA turnover and GFP-FAK release from FAs. FAK-cortactin binding is negatively-regulated by FAK activity and associated with cortactin tyrosine phosphorylation. FAK directly phosphorylates cortactin at Y421 and Y466 and over-expression of cortactin Y421, Y466, and Y482 mutated to phenylalanine (3YF) prevented FAK-enhanced FA turnover and cell motility. However, phospho-mimetic cortactin mutated to glutamic acid (3YE) did not affect FA dynamics and did not rescue FA turnover defects in cells with inhibited FAK activity or with PRR2-mutated FAK that does not bind cortactin.

Conclusions

Our results support a model whereby FAK-mediated FA remodeling may occur through the formation of a FAK-cortactin signaling complex. This involves a cycle of cortactin binding to FAK, cortactin tyrosine phosphorylation, and subsequent cortactin-FAK dissociation accompanied by FA turnover and cell movement.

Focal adhesion kinases in adhesion structures and disease

Cell adhesion to the extracellular matrix (ECM) is essential for cell migration, proliferation, and embryonic development. Cells can contact the ECM through a wide range of matrix contact structures such as focal adhesions, podosomes, and invadopodia. Although they are different in structural design and basic function, they share common remodeling proteins such as integrins, talin, paxillin, and the tyrosine kinases FAK, Pyk2, and Src. In this paper, we compare and contrast the basic organization and role of focal adhesions, podosomes, and invadopodia in different cells. In addition, we discuss the role of the tyrosine kinases, FAK, Pyk2, and Src, which are critical for the function of the different adhesion structures. Finally, we discuss the essential role of these tyrosine kinases from the perspective of human diseases.

Resistance to the mTOR-inhibitor RAD001 elevates integrin α2- and β1-triggered motility, migration and invasion of prostate cancer cells

Background:

Inhibitors of the mammalian target of rapamycin (mTOR) might become a novel tool to treat advanced prostate cancer. However, chronic drug exposure may trigger resistance, limiting the utility of mTOR inhibitors.

Methods:

Metastatic potential of PC3 prostate cancer cells, susceptible (PC3^par) or resistant (PC3^res) to the mTOR-inhibitor RAD001 was investigated. Adhesion to vascular endothelium or immobilised collagen, fibronectin and laminin was quantified. Motility, migration and invasion were explored by modified Boyden chamber assay. Integrin α and β subtypes were analysed by flow cytometry, western blotting and real-time PCR. Integrin-related signalling, EGFr, Akt, p70S6kinase and ERK1/2 activation were determined.

Results:

Adhesion was reduced, whereas motility, migration and invasion were enhanced in PC3^res. The α2 and β1 integrin subtypes were dramatically elevated, integrins α1 and α6 were lowered, whereas α5 was nearly lost in PC3^res. Activation of the Akt signalling pathway was strongly upregulated in these cells. Treating PC3^par cells with RAD001 reduced motility, migration and invasion and deactivated Akt signalling. Blocking studies revealed that α2 and β1 integrins significantly trigger the motile behaviour of the tumour cells.

Conclusion:

Chronic RAD001 treatment caused resistance development characterised by distinct modification of the integrin-expression profile, driving prostate cancer cells towards high motility.

Focal adhesion-chromatin linkage controls tumor cell resistance to radio- and chemotherapy

Cancer resistance to therapy presents an ongoing and unsolved obstacle, which has clear impact on patient's survival. In order to address this problem, novel in vitro models have been established and are currently developed that enable data generation in a more physiological context. For example, extracellular-matrix- (ECM-) based scaffolds lead to the identification of integrins and integrin-associated signaling molecules as key promoters of cancer cell resistance to radio- and chemotherapy as well as modern molecular agents. In this paper, we discuss the dynamic nature of the interplay between ECM, integrins, cytoskeleton, nuclear matrix, and chromatin organization and how this affects the response of tumor cells to various kinds of cytotoxic anticancer agents.

Genome-wide gene expression analysis in cancer cells reveals 3D growth to affect ECM and processes associated with cell adhesion but not DNA repair

Cell morphology determines cell behavior, signal transduction, protein-protein interaction, and responsiveness to external stimuli. In cancer, these functions profoundly contribute to resistance mechanisms to radio- and chemotherapy. With regard to this aspect, this study compared the genome wide gene expression in exponentially growing cell lines from different tumor entities, lung carcinoma and squamous cell carcinoma, under more physiological three-dimensional (3D) versus monolayer cell culture conditions. Whole genome cDNA microarray analysis was accomplished using the Affymetrix HG U133 Plus 2.0 gene chip. Significance analysis of microarray (SAM) and t-test analysis revealed significant changes in gene expression profiles of 3D relative to 2D cell culture conditions. These changes affected the extracellular matrix and were mainly associated with biological processes like tissue development, cell adhesion, immune system and defense response in contrast to terms related to DNA repair, which lacked significant alterations. Selected genes were verified by semi-quantitative RT-PCR and Western blotting. Additionally, we show that 3D growth mediates a significant increase in tumor cell radio- and chemoresistance relative to 2D. Our findings show significant gene expression differences between 3D and 2D cell culture systems and indicate that cellular responsiveness to external stress such as ionizing radiation and chemotherapeutics is essentially influenced by differential expression of genes involved in the regulation of integrin signaling, cell shape and cell-cell contact.

Targeting FAK radiosensitizes 3-dimensional grown human HNSCC cells through reduced Akt1 and MEK1/2 signaling

PURPOSE

Focal adhesion kinase (FAK), a main regulator of integrin signaling and cell migration, is frequently overexpressed and hyperphosphorylated in human head-and-neck squamous cell carcinoma (HNSCC). We have previously shown that pharmacologic FAK inhibition leads to radiosensitization of 3-dimensionally grown HNSCC cell lines. To further evaluate the role of FAK in radioresistance and as a potential cancer target, we examined FAK and FAK downstream signaling in HNSCC cell lines grown in more physiologic extracellular matrix-based 3-dimensional cell cultures.

METHODS AND MATERIALS

Seven HNSCC cell lines were grown in 3-dimensional extracellular matrix and the clonogenic radiation survival, expression, and phosphorylation of FAK, paxillin, Akt1, extracellular signal-regulated kinase (ERK)1/2, and MEK1/2 were analyzed after siRNA-mediated knockdown of FAK, Akt1, MEK1, FAK+Akt1, or FAK+MEK1 compared with controls or stable overexpression of FAK. The role of MEK1/2 for clonogenic survival and signaling was investigated using the MEK inhibitor U0126 with or without irradiation.

RESULTS

FAK knockdown moderately or significantly enhanced the cellular radiosensitivity of 3-dimensionally grown HNSCC cells. The FAK downstream targets paxillin, Akt1, and ERK1/2 were substantially dephosphorylated under FAK depletion. FAK overexpression, in contrast, increased radiation survival and paxillin, Akt1, and ERK1/2 phosphorylation. The degree of radiosensitization upon Akt1, ERK1/2, or MEK1 depletion or U0126 was superimposable to FAK knockdown. Combination knockdown conditions (ie, Akt1/FAK, MEK1/FAK, or U0126/FAK) failed to provide additional radiosensitization.

CONCLUSIONS

Our data provide further evidence for FAK as important determinant of radiation survival, which acts in the same signaling axis as Akt1 and ERK1/2. These data strongly support our hypothesis that FAK is a relevant molecular target for HNSCC radiotherapy.