STING inhibition in myocardial remodelling following myocardial infarction

Background

Myocardial infarction (MI) is one of the prevalent causes of death in the world, with some patients developing heart failure from myocardial remodelling after infarction. Inflammatory processes trigger remodelling post-MI. One inflammatory factor is Type 1 Interferon which can be released by cytosolic dsDNA, sensed via the STING-receptor. The aim of this study was to reduce this inflammatory response by inhibiting the STING-receptor and thus reduce post-infarctional remodelling.

Methods

Surgery was performed to trigger infarction for 30 minutes by ligating of the proximal LAD in 22 wildtype male mice (C57BL6/J), another 10 mice have undergone sham operation. Echocardiographic assessment of the endocardial systolic fractional area change (FAC) was carried out before, one day after and three weeks after surgery. The mice with ligation were separated into two groups with eleven individuals each, as well as the sham operated mice in five each group. One group was treated with the STING-Inhibitor while the other received a control substance. Treatment was applied intraperitoneally once per day for three weeks.

Results

– Procedural success was good as evidenced by immediate FAC decline in MI animals.

– One day post-op no significant difference in FAC and infarct size can be seen between the two groups of MI mice

– Three weeks post-op a highly significant difference in FAC can be observed in the group treated with STING-Inhibitor compared to the control group in the MI mice

– The sham operated mice never showed any difference between the groups at any time.

– Fibrosis and Cross sectinal area significantly reduced in treated MI group compared to control

– Ifi44 and Cxcl10 expression levels in the infarct area showed significant reduction in the inhibitor MI group compared to the control MI group after three weeks

Conclusion

STING-Inhibitor potentially improves outcome after a myocardial infarction.

Funding Acknowledgement

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): European Research Area Network on Cardiovasczlar Diseases (ERA-CVD) PhD-Program Molecular Medicine - Medical Unviersity of Graz

Dextran-coated superparamagnetic iron oxide nanoparticles for magnetic resonance imaging: evaluation of size-dependent imaging properties, storage stability and safety

BACKGROUND

Rising criticism of currently available contrast agents for magnetic resonance imaging, either due to their side effects or limited possibilities in terms of functional imaging, evoked the need for safer and more versatile agents. We previously demonstrated the suitability of novel dextran-coated superparamagnetic iron oxide nanoparticles (SPIONDex) for biomedical applications in terms of safety and biocompatibility.

METHODS

In the present study, we investigated the size-dependent cross-linking process of these particles as well as the size dependency of their imaging properties. For the latter purpose, we adopted a simple and easy-to-perform experiment to estimate the relaxivity of the particles. Furthermore, we performed an extensive analysis of the particles' storage stability under different temperature conditions, showing their superb stability and the lack of any signs of agglomeration or sedimentation during a 12 week period.

RESULTS

Independent of their size, SPIONDex displayed no irritation potential in a chick chorioallantoic membrane assay. Cell uptake studies of ultra-small (30 nm) SPIONDex confirmed their internalization by macrophages, but not by non-phagocytic cells. Additionally, complement activation-related pseudoallergy (CARPA) experiments in pigs treated with ultra-small SPIONDex indicated the absence of hypersensitivity reactions.

CONCLUSION

These results emphasize the exceptional safety of SPIONDex, setting them apart from the existing SPION-based contrast agents and making them a very promising candidate for further clinical development.

Toxicity of Mitoxantrone-loaded Superparamagnetic Iron Oxide Nanoparticles in a HT-29 Tumour Spheroid Model

BACKGROUND/AIM

Cancer research is commonly carried out in two-dimensional (2D) cell cultures, which poorly reflect in vivo settings where the growing tumours are exposed to mechanical forces and biochemical gradients. In this study we established a HF-29 colon carcinoma tumor spheroid model to investigate the effect of free mitoxantrone (MTO) and its nanoparticle-bound form (SPION(MTO)) under 3D cell culture conditions.

MATERIALS AND METHODS

Tumour spheroids were generated by seeding HT-29 colon carcinoma cells on agarose-coated cell culture wells. Growth of the spheroids was monitored daily by transmission microscopy upon treatment with free MTO, SPION(MTO) or unloaded SPION.

RESULTS AND CONCLUSION

Unloaded SPION did not affect the spheroid size compared to untreated controls, while both free MTO and SPION(MTO) inhibited growth of the spheroids in a dose- and time-dependent manner. In comparison to free MTO, the effect of SPION(MTO) on spheroid growth was slightly delayed. Further analyses are necessary to investigate if MTO infiltrates spheroids in its nanoparticle-bound form or whether it is released from SPION before infiltration.

Hypericin-bearing magnetic iron oxide nanoparticles for selective drug delivery in photodynamic therapy

Combining the concept of magnetic drug targeting and photodynamic therapy is a promising approach for the treatment of cancer. A high selectivity as well as significant fewer side effects can be achieved by this method, since the therapeutic treatment only takes place in the area where accumulation of the particles by an external electromagnet and radiation by a laser system overlap. In this article, a novel hypericin-bearing drug delivery system has been developed by synthesis of superparamagnetic iron oxide nanoparticles (SPIONs) with a hypericin-linked functionalized dextran coating. For that, sterically stabilized dextran-coated SPIONs were produced by coprecipitation and crosslinking with epichlorohydrin to enhance stability. Carboxymethylation of the dextran shell provided a functionalized platform for linking hypericin via glutaraldehyde. Particle sizes obtained by dynamic light scattering were in a range of 55-85 nm, whereas investigation of single magnetite or maghemite particle diameter was performed by transmission electron microscopy and X-ray diffraction and resulted in approximately 4.5-5.0 nm. Surface chemistry of those particles was evaluated by Fourier transform infrared spectroscopy and ζ potential measurements, indicating successful functionalization and dispersal stabilization due to a mixture of steric and electrostatic repulsion. Flow cytometry revealed no toxicity of pure nanoparticles as well as hypericin without exposure to light on Jurkat T-cells, whereas the combination of hypericin, alone or loaded on particles, with light-induced cell death in a concentration and exposure time-dependent manner due to the generation of reactive oxygen species. In conclusion, the combination of SPIONs' targeting abilities with hypericin's phototoxic properties represents a promising approach for merging magnetic drug targeting with photodynamic therapy for the treatment of cancer.

Nanomedical innovation: the SEON-concept for an improved cancer therapy with magnetic nanoparticles

Nanomedicine offers tremendous opportunities for the development of novel therapeutic and diagnostic tools. During the last decades, extensive knowledge was gained about stabilizing and the coating of nanoparticles, their functionalization for drug binding and drug release and possible strategies for therapies and diagnostics of different diseases. Most recently, more and more emphasis has been placed on nanotoxicology and nanosafety aspects. The section of experimental oncology and nanomedicine developed a concept for translating this knowledge into clinical application of magnetic drug targeting for the treatment of cancer and other diseases using superparamagnetic iron oxide nanoparticles. This approach includes reproducible synthesis, detailed characterization, nanotoxicological testing, evaluation in ex vivo models, preclinical animal studies and production of superparamagnetic iron oxide nanoparticles according to good manufacturing practice regulations.

Abstract 406: Effects of an RGD peptide in osteoclast maturation and behavior as a therapeutic option for metastatic bone disease

Metastatic bone disease is a common feature of many types of cancer and has a severe impact on the quality of life of patients. Hence, specific therapeutic strategies inhibiting tumor induced osteolysis are urgently needed. In this study, we aimed to interfere with integrin adhesion receptors, which are central players of the bone resorption process, including osteoclastogenesis as well as osteoclast/bone matrix interaction. For this purpose, we used a cyclic RGD peptide which blocks integrin áVâ3 and áVâ5-ligand binding. Our results revealed that the RGD peptide blocked osteoclast maturation in a dose-dependent manner. In detail, pre-osteoclasts treated with the RGD peptide exhibited reduced cell spreading, migration and adhesion on RGD-containing matrix proteins, such as osteopontin and fibrinogen, which are ligands of integrin áVâ3. The activation of the most upstream signal transduction molecules of the integrin receptor-initiated pathway, such as FAK and c-Src, were consistently blocked by the RGD peptide. First evidence has suggested that the RGD peptide might interfere with metastatic bone disease in vivo and the evidence presented herein describes the underlying mechanisms of the inhibitory effect of the RGD peptide on áV-integrin expressing pre-osteoclasts by blocking integrin ligand binding and interfering with osteoclast maturation and cell behavior. In conclusion, our findings suggest that using an RGD peptide to interfere with áV-integrins on osteoclasts may represent a novel therapeutic strategy in the treatment of malignant bone disease.

Citation Format: Gerald Prager, Daniela Bianconi, Anastasia Chillà, Alexandra Dorda, Nisha Geetha, Matthias Unseld, Despoina Sykoutri, Marina Poettler, Kurt Redlich, Christoph Zielinski. Effects of an RGD peptide in osteoclast maturation and behavior as a therapeutic option for metastatic bone disease. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 406. doi:10.1158/1538-7445.AM2015-406

Flow cytometry for intracellular SPION quantification: specificity and sensitivity in comparison with spectroscopic methods

Due to their special physicochemical properties, iron nanoparticles offer new promising possibilities for biomedical applications. For bench to bedside translation of super-paramagnetic iron oxide nanoparticles (SPIONs), safety issues have to be comprehensively clarified. To understand concentration-dependent nanoparticle-mediated toxicity, the exact quantification of intracellular SPIONs by reliable methods is of great importance. In the present study, we compared three different SPION quantification methods (ultraviolet spectrophotometry, magnetic particle spectroscopy, atomic adsorption spectroscopy) and discussed the shortcomings and advantages of each method. Moreover, we used those results to evaluate the possibility to use flow cytometric technique to determine the cellular SPION content. For this purpose, we correlated the side scatter data received from flow cytometry with the actual cellular SPION amount. We showed that flow cytometry provides a rapid and reliable method to assess the cellular SPION content. Our data also demonstrate that internalization of iron oxide nanoparticles in human umbilical vein endothelial cells is strongly dependent to the SPION type and results in a dose-dependent increase of toxicity. Thus, treatment with lauric acid-coated SPIONs (SEON(LA)) resulted in a significant increase in the intensity of side scatter and toxicity, whereas SEON(LA) with an additional protein corona formed by bovine serum albumin (SEON(LA-BSA)) and commercially available Rienso(®) particles showed only a minimal increase in both side scatter intensity and cellular toxicity. The increase in side scatter was in accordance with the measurements for SPION content by the atomic adsorption spectroscopy reference method. In summary, our data show that flow cytometry analysis can be used for estimation of uptake of SPIONs by mammalian cells and provides a fast tool for scientists to evaluate the safety of nanoparticle products.

CD98hc (SLC3A2) drives integrin-dependent renal cancer cell behavior

Background

Overexpression of CD98hc (SLC3A2) occurs in a variety of cancers and is suspected to contribute to tumor growth. CD98, a heterodimeric transmembrane protein, physically associates with certain integrin β subunit cytoplasmic domains via its heavy chain, CD98hc. CD98hc regulates adhesion-induced intracellular signal transduction via integrins, thereby, affecting cell proliferation and clonal expansion. Disruption of CD98hc led to embryonic lethality in mice (E 3.5 and E 9.5) and CD98hc −/− embryonic stem cell transplantation failed to form teratomas, while CD98hc over-expression in somatic cells resulted in anchorage-independent growth. However, it is unclear whether interference with CD98hc expression tumor cell behavior.

Methods

Renal cell cancer cell lines have been used to determine the effect of CD98hc expression on cancer cell behavior using cell adhesion, cell trans-migration and cell spreading assays. Flow cytometric analysis was performed to study the rate of apoptosis after detachment or serum starvation. shRNA-lentiviral constructs were used to stably knockdown or reconstitute full length or mutated CD98hc. The role of CD98 as a promotor of tumorigenesis was evaluated using an in in vivo tumor transplantation animal model. Immunohistochemical analysis was performed to analyze cell proliferation and CD98 expression in tumors.

Results

This report shows that CD98hc silencing in clear cell renal cancer cells reverts certain characteristics of tumorigenesis, including cell spreading, migration, proliferation and survival in vitro, and tumor growth in vivo. Acquisition of tumorigenic characteristics in clear cell renal cancer cells occurred through the integrin binding domain of CD98hc. A CD98hc/integrin interaction was required for adhesion-induced sustained FAK phosphorylation and activation of the major downstream signaling pathways PI3k/Akt and MEK/ERK, while overexpression of a constitutive active form of FAK rescued the CD98hc deficiency.

Conclusions

In this study we demonstrate that loss of CD98hc blocks tumorigenic potential in renal cell cancer.

Abstract B6: CEA affects tumor- angiogenesis via integrin-dependent activation of endothelial cells

CEA, first identified in 1965 by Phil Gold and Samuel O. Freedman, is aberrantly overexpressed by up to 70% of human cancers. In clinical use as extracellular marker for monitoring adenocarcinoma growth as well as treatment efficacy, CEA has become included into the routine practice of clinical oncology. In addition to its’ clinical relevance, CEA was so far only described to be pro-tumorigenic in an autocrine manner by inducing anti-apoptosis. Any potential paracrine effects of soluble CEA affecting tumor microenvironment including angiogenesis have not been described.

Here, we report that CEA released by tumor cells induced angiogenesis by directly inducing pro-angiogenic endothelial cells behavior. As shown by gain and loss of function in vivo tumor transplant models, CEA directly stimulated endothelial cell proliferation and migration in vitro and endothelial cell invasion and functional active capillary-tube formation in directed in vivo angiogenesis assays. Thereby, CEA activated endothelial cells via integrin beta-3, leading to FAK phosphorylation and c-src activation as well as induction of MEK/ERK- and PI3kinase/Akt- pathways. Interfering with this chain of events at different steps, such as downregulation of its putative receptor for CEA (CEAR) by shRNA bearing lentivirus or blockage of integrin activity, abrogated CEA-induced endothelial cell activation and tumor-angiogenesis leading to tumor growth arrest. Notably, CEA acted independently and partially additive to the VEGF / VEGFR-2 (KDR or flk-1) system. The biological relevance was further verified by analysis of paraffin-embedded tumor-tissue samples derived from colon cancer patients, whereas vascularization of the tumor microenvironment was significantly higher whenever CEA plasma levels were high.

Thus, our data indicate that the tumor marker CEA acts as a novel angiogenic molecule and might offer a potential therapeutic target in the treatment of tumor-angiogenesis.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B6.

Citation Format: Gerald W. Prager, Kira Braemswig, Marina Poettler, Christoph Zieleinski. CEA affects tumor- angiogenesis via integrin-dependent activation of endothelial cells. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B6.

Abstract C195: CD98hc (SLC3A2) is a central regulator of renal cancer cell behavior

CD98, a heterodimeric transmembrane protein, physically associates with certain integrin β subunit cytoplasmic domains via its heavy chain, CD98hc (SLC3A2). Thereby CD98hc regulates adhesion-induced intracellular signal transduction via integrins, thus, affecting cell proliferation and clonal expansion. Disruption of CD98hc led to embryonic lethality in mice (E3.5 and E 9.5) and CD98hc -/- embryonic stem cell transplantation failed to form teratomas, while over-expression of CD98hc in somatic cells resulted in anchorage-independent growth. Although, we and others identified CD98hc to be highly overexpressed in various cancer types, a functional role of CD98hc in tumor cell behavior is so far unknown. Here we demosntarte that the disruption of CD98hc interaction with integrins in clear cell renal cell cancer (ccRCC) leads to impaired tumor cell behavior such as cell spreading, migration, proliferation and survival in vitro and of tumor growth in vivo. CD98hc/integrin interaction was required for adhesion-induced sustained FAK phosphorylation and activation of the major downstream signaling pathways PI3k/Akt and MEK/ERK, while overexpression of a constitutive active form of FAK rescued for the CD98hc deficiency. Thus, we have identified the cell surface protein CD98hc as a critical mediator of integrin-dependent tumor cell functions. These studies suggest that interference with CD98hc might lead to a novel therapeutic strategy in renal cell cancer.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C195.

Citation Format: Gerald W. Prager, Marina Poettler, Matthias Unseld, Christoph Zielinski. CD98hc (SLC3A2) is a central regulator of renal cancer cell behavior. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C195.

Abstract C3: Tumor-derived soluble uPAR regulates tumor angiogenesis via PTEN

The urokinase receptor uPAR (CD87), a GPI-anchored protein, is frequently over-expressed in tumor cells. uPAR provokes numerous cellular functions by focusing proteolytic activity on the cell surface, but also by inducing intracellular signal transduction via transmembrane interaction partners, thus inducing cell migration and invasion as well as cell survival. Soluble tumor-derived uPAR has recently been described to activate endothelial cells and was suggested to promote angiogenesis. Consistently, high uPAR expression in tumor cells or high serum levels of circulating uPAR predict worse prognosis of breast, lung or colorectal cancer patients. In this study, we found that tumor-derived soluble uPAR is a key regulator of PTEN expression in endothelial cells. HEK cells deficient in endogenous uPAR or uPAR deficient endothelial cells derived from uPAR -/- mice had high PTEN mRNA as well as protein levels, while reconstitution of endogenous as well as addition of soluble exogenous uPAR decreased PTEN levels. uPAR, thereby, led to an integrin-dependent activation of the NFkB pathway, a known transcription pathway inhibitor of PTEN. As a consequence of PTEN downregulation, the downstream PKB/Akt signalling pathway became activated, which led to an enhanced migratory as well as cell survival activity in endothelial cells. Cross-breeding of uPAR -/- mice with endothelial cell-specific PTEN +/- mice, thereby led to a rescue of the high migratory phenotype of PTEN heterozygous endothelial cells in vitro and angiogenesis formation in a directed in vivo angiogenesis assay (DIVAA). From our date we conclude that tumor-derived uPAR is a major regulator of PTEN expression in endothelial cells, which leads to the induction of the PI3K/Akt-pathway and an enhanced angiogenic phenotype.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C3.

Citation Format: Gerald W. Prager, Matthias Unseld, Marina Poettler, Christoph Zielinski. Tumor-derived soluble uPAR regulates tumor angiogenesis via PTEN. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C3.

Soluble carcinoembryonic antigen activates endothelial cells and tumor angiogenesis

Carcinoembryonic antigen (CEA, CD66e, CEACAM-5) is a cell-surface-bound glycoprotein overexpressed and released by many solid tumors that has an autocrine function in cancer cell survival and differentiation. Soluble CEA released by tumors is present in the circulation of patients with cancer, where it is used as a marker for cancer progression, but whether this form of CEA exerts any effects in the tumor microenvironment is unknown. Here, we present evidence that soluble CEA is sufficient to induce proangiogenic endothelial cell behaviors, including adhesion, spreading, proliferation, and migration in vitro and tumor microvascularization in vivo. CEA-induced activation of endothelial cells was dependent on integrin β-3 signals that activate the focal-adhesion kinase and c-Src kinase and their downstream MAP-ERK kinase/extracellular signal regulated kinase and phosphoinositide 3-kinase/Akt effector pathways. Notably, while interference with VEGF signaling had no effect on CEA-induced endothelial cell activation, downregulation with the CEA receptor in endothelial cells attenuated CEA-induced signaling and tumor angiogenesis. Corroborating these results clinically, we found that tumor microvascularization was higher in patients with colorectal cancer exhibiting higher serum levels of soluble CEA. Together, our results elucidate a novel function for soluble CEA in tumor angiogenesis.

CD98hc expression to predict prognosis in renal cell cancer

26

Background: CD98, a transmembrane protein, has a heteromeric structure, consisting of a heavy subunit (CD98hc) and a light subunit, extracellular linked together via disulfid bounds. A genetic knockout of CD98hc is embryonic lethal and overexpression of CD98hc in somatic cells led to malignant transformation. CD98hc is highly expressed in low differentiated papillary, clear cell and chromophobe RCC, but not in benign tumors. Notably, CD98hc expression directly correlated with grade of differentiation. Methods: To evaluate a potential functional role of CD98hc in renal cancer cell metastatic behavior, we generated a stable low CD98hc clear cell RCC cell line (Caki2) via lentiviral shRNA infection and compared tumor cell behavior with a high expressing mock transfected control. Results: We found that tumor cell behavior such as proliferation (52 ± 3% less 3[H] thymidin – incorporation in low CD98hc/Caki2 cells), cell survival upon anoikis (46% late and 45% early apoptosis in low CD98hc/Caki2 cells compared to high/CD98hc/Caki2 cells with 18% late apoptosis and 64% early apoptosis) and invasion/transmigration (520 ± 67 cells / field after 24h in low CD98hc/ Caki2 cells and 1257 ± 346 cells / field in high CD98hc/Caki2 cells analyzed in a modified boyden chamber) were considerably impaired whenever CD98hc expression was downregulated. To examine the mechanism by which CD98hc affected metastatic tumor cell behavior, we introduced two mutations in a reconstitution (silent mutation). A truncation mutant interfered with integrin interaction and a two point mutations (Cys109Ser and Cys330Ser) mutant affected amino acid transporter activity. Whenever integrin/CD98hc interaction was impaired tumor cell behavior including cell proliferation, cell survival, invasio/transmigration, and cell spreading as well as signal transduction pathways including FAK, c-src, MEK/ERK pathways were significantly compromised resembling the low CD98hc phenotype. Conclusions: For these data we conclude that metastatic tumor cell behavior such as cell survival, invasion and proliferation are dependent on CD98hc expression in renal cancer cells.

The urokinase receptor (CD87) represents a central mediator of growth factor-induced endothelial cell migration

Angiogenesis, the sprouting of blood vessels form pre-existing vasculature after injury or in neoplastic diseases, is initiated by growth factor-induced endothelial cell migration. Recently, the major angiogenic growth factor VEGF165 has become the target of therapeutic interventions. However, this approach has been clinically proven to be of limited efficacy, which might be due to the fact that tumour angiogenesis is not only induced by VEGF, but also by a variety of other growth factors. Thus, the identification of a common downstream mediator of growth-factor-induced endothelial cell migration is mandatory to effectively interfere with (tumour-) angiogenesis. We found that the urokinase-type plasminogen activator (uPA)-system, which affects proteolytic as well as adhesive capacities, represents an essential regulatory mechanism in growth factor-induced endothelial cell migration and invasion. This mechanism was not limited to VEGF165, but mediated pro-angiogenic endothelial cell behaviour induced by various growth factors. Thus, VEGF165, VEGF-E, FGF-2, EGF as well as HGF induced a PI3k-dependent activation of pro-uPA when bound to uPAR, which led to an increase in cell surface fibrinolytic activity. As a consequence, uPAR became internalised and redistributed via LDLR-proteins. Interference with these events led to a reduced migratory response of endothelial cells towards VEGF in vitro as well as endothelial cell invasion in vivo. These data give first evidence that the uPA-system, which represents the only level-of-evidence-1 cancer biomarker system for prognosis and/or prediction in node negative breast cancer, might directly affect (tumour-) angiogenesis.

Abstract 4360: CD87 is essential for mediating growth-factor induced angiogenesis via distribution of integrin beta-1

CD87 (urokinase-type plasminogen activator receptor, uPAR) expression has been correlated with tumor progression most likely via its functional ole as a central receptor for extracellular proteolysis, but also via its role in initiating intracellular signal transduction. The role of CD87 in angiogenesis has recently been elucidated. Thus, we observed that in VEGF-stimulated ndothelial cells CD87 is essential for endothelial cell survival as well as for n efficient growth factor- induced endothelial cell migration. Thereby, the PI-anchored protein CD87 formed a complex with its ligand urokinase uPA) as well as the inhibitor plasminogen activator inhibitor-1 (PAI-1), which became redistributed to the leading edge via low density lipoprotein receptor- (LDLR-) like proteins. In this study, we analyzed the functional role of CD87 in integrin redistribution during growth factor-induced endothelial cell migration. CD87, thereby, directly interacted with integrin adhesion receptors (a5b1) as well as with LDLR- proteins. Either by interfering with CD87/integrin nteraction or by interfering with CD87/LDLR-protein interaction by using specific interfering peptides, we observed disruption of integrin redistribution to the leading edge in migrating cells. As a consequence diminished focal adhesion formations were observed and endothelial cell migration was diminished. In CD87-deficient HEK 293 cells as well as in endothelial cells derived from CD87 -/- mice, expression of CD87 mutants (mutL3/uPAR), which lacked the binding motif for LDLR, led to an impaired cell spreading as well as a diminished migratory response towards VEGF, while full length CD87 (wt/CD87) reconstituted this phenotype. That CD87 plays a central role in growth factor induced endothelial cell invasion and capillary-like tube formation in vivo was demonstrated by a directed in vivo angiogenesis assay (DIVAA), which was performed either in CD87 deficient or wild type animals in the presence or absence of interfering peptides. Our data give novel insights into the central role of CD87 in pro- angiogenic endothelial cell behavior as well as in its role in angiogenesis. Thus, CD87 might lead to a novel therapeutic strategies in tumor- angiogenesis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4360. doi:1538-7445.AM2012-4360

Angiogenesis in cancer: Anti-VEGF escape mechanisms

It is now widely accepted that tumor-angiogenesis plays a crucial role in tumor growth, tumor propagation and metastasis formation. Among several angiogenic activators, the vascular endothelial growth factor (VEGF) and its receptors represent one of the major inducers of tumor angiogenesis. Thus, this system has become the focus of therapeutic interventions, which led to the approval of the anti-VEGF blocking antibody bevacizumab and the VEGFR-2 pathway inhibitors pazopanib, sorafenib and sunitinib. However, not every cancer patient benefits from such treatment or finally becomes resistant to anti-VEGF approaches; others are suffering from adverse effects. Thus, there is an urgent need for a better understanding of VEGF-independent mechanisms leading to angiogenesis in cancer. This review focuses on anti-VEGF escape mechanisms of tumor cells and its microenvironment.

Angiogenesis in cancer. Basic mechanisms and therapeutic advances

Etiological concepts on cancer development, malignant growth and tumour propagation have undergone a revolutionary development during recent years: Among other aspects, the discovery of angiogenesis - the growth of new blood vessels from pre-existing vasculature - as a key element in the pathogenesis of malignancy has opened an abundance of biologic insights and subsequent therapeutic options, which have led to improved prognosis in many cancers including those originating from colon, lung, breast and kidney. Thereby, targeting the major pro-angiogenic stimulus vascular endothelial growth factor (VEGF) became the focus for therapeutic interventions. However, the use of VEGF-targeting drugs has been shown to be of limited efficacy, which might lie in the fact that tumor angiogenesis is mediated by a variety of different subcellular systems. This review focuses on the basic mechanisms involved in angiogenesis, which potentially represent novel targets for pharmacological agents in the treatment of malignancies.

Abstract 424: Interference with alphaVbeta3 integrins via cyclic RGD peptides affects breast cancer cell behavior

Integrin alphavbeta3 is mainly expressed in stimulated endothelial cells, thus it has recently become the focus of intense research mainly to interfere with tumorangiogenesis. However, alphavbeta3 integrins are also expressed in a variety of tumor cells, such as melanoma, prostate cancer, breast cancer, cervix carcinoma or pancreatic cancer.

While inhibition of integrin alphavbeta3 activity in endothelial cells has been studied extensively, any direct effects on integrin alphavbeta3 expressing tumor cells is hitherto unknown.

In this study we examined alphavbeta3 integrin expression in breast cancer cell lines, where by MDA MB 231 revealed high integrin alphavbeta3 as well as VEGFR-2 and VEGF expression.

While adhesion of MDA MB231 cells to an alphavbeta3 specific matrix such as fibrinogen was blocked by the addition of cyclic RGD peptides, sequentially addition of cyclic RGD peptides to already adherent MDA MB231 cells led to a diminished spreading in a time and dose dependent manner, starting at 20nM.

Furthermore, tumor cell migration as well as transmigration through an EC monolayer upon VEGF stimulation was blocked whenever alphavbeta3 integrins were targeted by RGD mimetic peptide.

Our data give first functional insights into the previously described effects of alphavbeta3 targeting small molecules, which led to a reduced breast cancer metastasis in vivo.

Thus interfering with alphavbeta3 integrins on tumor cells might represent a promising therapeutic lead in certain malignancies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 424. doi:10.1158/1538-7445.AM2011-424

Abstract 3189: Aggressive renal cancer cell behavior is partly mediated by CD98hc

CD98, a heteromeric transmembrane protein, consists of a heavy subunit (4F2hc, SLC3A2), extracellular linked to a light subunit. The light chains provide amino acid transport activity of CD98. Recently, we could show that CD98hc directly interacts with a conserved motif in integrin beta subunits, thereby mediating outside - in signaling. A genetic knockout of CD98hc in animals is embryonic lethal, whereas overexpression of CD98hc in somatic cells leads to malignant transformation.

Recently, we reported that high CD98hc expression is a novel and reliable diagnostic marker for the more malignant subtype II papillary renal cell cancer marker (pRCC). Thereby, CD98hc expression directly correlated with grade of differentiation.

In the present study, we identified the functional role of CD98hc in clear cell renal cell cancer (ccRCC) behavior. First, we generated stable low CD98hc ccRCCs by the use of a shRNA lentiviral construct and compared tumor cell behavior with high CD98hc expressing mock infected ccRCCs. We found that downregulation of CD98hc led to an altered tumor cell behavior including tumor cell survival, migration and proliferation. Expression of a silent mutation - lacking shRNA binding motif - reconstituted CD98hc expression in lowCD98hc ccRCC, thereby restoring aggressive tumor cell behavior. By introducing CD98hc mutations either lacking integrin binding capacities or light chain interactions, we could identify the functional role of leucine amino acid transport in tumor cell proliferation, as affected C14-leucine uptake was directly correlated with tumor cell proliferative activity. In contrast, mutants lacking interaction sites for integrins showed defects adhesion-induced FAK phosphorylation and c-src activation, leading to reduced tumor cell adhesion and spreading. A biological relevance of the in vitro finding was confirmed in in vivo tumor xenotransplant assays, whereby stable low CD98hc/ccRCCs either reconstituted with wild type CD98hc or with mutated CD98hc were used. Only wild type reconstitution was capable to restore full aggressiveness of tumor growth and metastasis formation.

From our data we conclude that CD98 partially mediates functional activity of renal cancer cell behavior. Thus, CD98hc-mediated tumor cell behavior may offer a potential novel therapeutic target for the treatment of cancer.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3189.

Abstract 2380: Carcinoembryonic antigen (CEA) directly activates endothelial cells, thereby inducing (tumor)-angiogenesis

Angiogenesis has become a major target in treatment of a varietly of cancers, whereby the major angiogenic growth factor VEGF is currently in focus for therapeutic interventions. Nevertheless, the use of VEGF-targeting drugs has been shown to be of limited efficacy, which might lie in the fact that tumor angiogenesis is not only induced by VEGF, but also by a variety of other factors.

In this study, we report that the human carcinoembryonic antigen (CEA), a GPI-anchored cell surface adhesion molecule, which is shedded by 70% of human cancers, directly binds to endothelial cells, thereby inducing angiogenic endothelial cell behavior in vitro and in vivo:

Overexpressing CEA in endogenous negative renal cell cancer (RCC) cell line or in the sarcoma cell line MethA led to an enhanced tumor angiogenesis and an increase in tumor growth in vivo, effects which were reverted by downregulation of the CEA receptor in endothelial cells via a lentiviral shRNA construct. Furthermore, targeting CEA by CEA mimotope immunized BALB/c mice, led to a breakdown In tumor vascularization, which was reflected by retarded tumor growth. We found that CEA, by binding to its receptor, led to an increase in integrin activation state, leading to enhanced endothelial cell adhesion, followed by amplified adhesion-induced signal transduction, which involved c-src-activation, focal adhesion kinase (FAK) and ERK phosphorylation, as well as PI3kinase/Akt activation. As a consequence, pro-angiogenic endothelial cell behavior, such as migration and invasion or proliferation were induced. Whenever integrin beta-3 were blocked, CEA was effect less in endothelial cells.

These results show that the tumor marker CEA might bear hitherto undescribed biological significance in promoting tumor-angiogenesis. Thus, CEA-mediated signaling may offer a potential novel therapeutic target for the treatment of cancer.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2380.

Targeting of VEGF-dependent transendothelial migration of cancer cells by bevacizumab

Cancer progression is often associated with the formation of malignant effusions. Vascular endothelial growth factor (VEGF) is a major regulator of vascular permeability and has been implicated as mediator of tumor progression. We examined the production and secretion of VEGF(165) in various primary cancer cells derived from malignant effusions, and the role of exogenous VEGF(165) as a mediator of effusion formation. VEGF(165) was constantly secreted by all cultured tumor cells in an mTOR-dependent manner, as it was inhibited by the mTOR inhibitor rapamycin. Secreted VEGF(165) showed functional activity by inducing endothelial leakiness and tumor cell-transendothelial migration in vitro, effects which could be reverted by the anti-VEGF antibody bevacizumab. Thus, mTOR inhibitors as well as bevacizumab should be considered as potential agents in cancer patients suffering from malignant effusions.

CD98hc (SLC3A2), a novel marker in renal cell cancer

BACKGROUND

In a variety of malignant diseases, molecular targeting represents a therapeutic option, whereby, when compared with chemotherapy, fewer side effects are thought to be expected. Especially in renal cell cancer (RCC), tyrosine kinase-inhibitors have been established as useful and highly effective therapy. However, tyrosine kinase-inhibitors currently approved for RCC treatment lack single molecule specificity and bear a variety of side effects of the gastro-intestinal tract, skin, heart and haematopoietic system. Therefore, the identification of novel cell surface markers is sought, which might lead to novel diagnostic and therapeutic strategies in cancer.

MATERIAL AND METHODS

Paraffin-embedded RCCs from a well characterized tissue bank were immunohistochemically quantified for embryonic transmembrane antigen CD98hc (SLC3A2) expression and semi-quantitative analyses were correlated with subtype or grade of differentiation.

RESULTS

We found increased CD98hc expression in different types of malign RCCs, among them clear cell (cc)RCC, papillary (p)RCC and chromophobe (ch)RCC, but lack of expression in the benign renal oncocytoma. Thereby, the extent of CD98hc expression directly complies with grade of malignancy. Furthermore, the more malignant type II pRCC significantly higher expressed CD98hc than the less malignant and more differentiated type I pRCC (type II 83.34%, type I 4.76% CD98hc positive, P < 0.00001; n = 51). The established marker for type I pRCC, Cytokreatin 7, showed 95.24% expression in type I and 26.67% expression in type II pRCC (P < 0.00001, n = 51).

CONCLUSIONS

From these data, we conclude that CD98hc is expressed in RCCs, whereby the extent of expression is likely to correlate directly with grade of malignancy. In pRCCs, CD98hc might represent a novel and reliable marker for type II pRCC.