Tumor Endothelial Cells Express Epidermal Growth Factor Receptor (EGFR) but not ErbB3 and Are Responsive to EGF and to EGFR Kinase Inhibitors

Heterogeneity of tumor endothelial cells: comparison between tumor endothelial cells isolated from high- and low-metastatic tumors

An important concept in tumor angiogenesis is that tumor endothelial cells (TECs) are genetically normal and homogeneous. However, we previously reported that TECs differ from normal ECs. Whether the characteristics of TECs derived from different tumors differ remains unknown. To elucidate this, in this study, we isolated two types of TECs from high-metastatic (HM) and low-metastatic (LM) tumors and compared their characteristics. HM tumor-derived TECs (HM-TECs) showed higher proliferative activity and invasive activity than LM tumor-derived TECs (LM-TECs). Moreover, the mRNA expression levels of pro-angiogenic genes, such as vascular endothelial growth factor (VEGF) receptors 1 and 2, VEGF, and hypoxia-inducible factor-1α, were higher in HM-TECs than in LM-TECs. The tumor blood vessels themselves and the surrounding area in HM tumors were exposed to hypoxia. Furthermore, HM-TECs showed higher mRNA expression levels of the stemness-related gene stem cell antigen and the mesenchymal marker CD90 compared with LM-TECs. HM-TECs were spheroid, with a smoother surface and higher circularity in the stem cell spheroid assay. HM-TECs differentiated into osteogenic cells, expressing activated alkaline phosphatase in an osteogenic medium at a higher rate than either LM-TECs or normal ECs. Furthermore, HM-TECs contained more aneuploid cells than LM-TECs. These results indicate that TECs from HM tumors have a more pro-angiogenic phenotype than those from LM tumors.

Impact of immunization technology and assay application on antibody performance--a systematic comparative evaluation

Antibodies are quintessential affinity reagents for the investigation and determination of a protein's expression patterns, localization, quantitation, modifications, purification, and functional understanding. Antibodies are typically used in techniques such as Western blot, immunohistochemistry (IHC), and enzyme-linked immunosorbent assays (ELISA), among others. The methods employed to generate antibodies can have a profound impact on their success in any of these applications. We raised antibodies against 10 serum proteins using 3 immunization methods: peptide antigens (3 per protein), DNA prime/protein fragment-boost ("DNA immunization"; 3 per protein), and full length protein. Antibodies thus generated were systematically evaluated using several different assay technologies (ELISA, IHC, and Western blot). Antibodies raised against peptides worked predominantly in applications where the target protein was denatured (57% success in Western blot, 66% success in immunohistochemistry), although 37% of the antibodies thus generated did not work in any of these applications. In contrast, antibodies produced by DNA immunization performed well against both denatured and native targets with a high level of success: 93% success in Western blots, 100% success in immunohistochemistry, and 79% success in ELISA. Importantly, success in one assay method was not predictive of success in another. Immunization with full length protein consistently yielded the best results; however, this method is not typically available for new targets, due to the difficulty of generating full length protein. We conclude that DNA immunization strategies which are not encumbered by the limitations of efficacy (peptides) or requirements for full length proteins can be quite successful, particularly when multiple constructs for each protein are used.

Differential contribution to neuroendocrine tumorigenesis of parallel egfr signaling in cancer cells and pericytes

Factors associated with tumor sensitivity to epidermal growth factor receptor (EGFR) inhibitors in the context of wild-type EGFR remain elusive. This study investigates the mechanistic basis of responsiveness to EGFR inhibitors in the RIP1-Tag2 (RT2) mouse model of pancreatic neuroendocrine tumorigenesis (PNET). Upon treatment of RT2 mice with EGFR inhibitors, PNET tumors harboring wild-type, nonamplified alleles of Egfr grow at a markedly reduced rate and display a significant increase in tumor cell apoptosis, as well as reduced neovascularization. The authors identify Tgf-α and Hb-egf as key limiting mediators of separable pathological functions of Egfr in neuroendocrine tumor progression: Tgf-α mutant tumors present with an elevated apoptotic index, whereas Hb-egf mutant lesions exhibit decreased angiogenic switching and neovascularization. This study not only associates Tgf-α and Hb-egf expression with wild-type Egfr oncogenicity but also ascribes the proangiogenic activity of Egfr in this tumor model to a novel mesenchymal Hb-egf/Egfr signaling axis, whereby endothelial and pericyte-derived Hb-egf activates Egfr specifically in tumor-associated perivascular cells, leading to increased pericyte coverage of the tumor endothelium and enhanced angiogenesis.

Altered angiogenesis in the tumor microenvironment

Tumor blood vessels play an important role in tumor progression and metastasis. Thus, targeting the tumor blood vessels is an important strategy in cancer therapy. Tumor blood vessels generally arise from pre-existing vessels and have been thought to be genetically normal. However, they have been shown to differ from their normal counterparts, e.g. with regard to the morphological changes. We isolated tumor endothelial cells (TEC) from mouse tumor xenografts and showed that they were abnormal. TEC up-regulate many genes, proliferate more rapidly and migrate more than normal endothelial cells (NEC). Furthermore, the TEC in our study were cytogenetically abnormal. We concluded that TEC can acquire cytogenetic abnormalities while in the tumor microenvironment. In order to develop ideal antiangiogenic therapies, understanding the crosstalk between blood vessels and the tumor microenvironment is important. This review considers the current studies on TEC abnormalities and discusses the possible mechanism by which the tumor microenvironment produces abnormal TEC.

Anti-angiogenic effects of two cystine-knot miniproteins from tomato fruit

BACKGROUND AND PURPOSE

Cystine-knot miniproteins are characterized by a similar molecular structure. Some cystine-knot miniproteins display therapeutically useful biological activities, as antithrombotic agents or tumour growth inhibitors. A critical event in the progression of tumours is the formation of new blood vessels. The aim of this work was to test two tomato cystine-knot miniproteins for their effects on endothelial cell proliferation and angiogenesis in vitro.

EXPERIMENTAL APPROACH

Two tomato cystine-knot miniproteins (TCMPs) were expressed and purified either as recombinant or as native proteins from tomato fruits. The Matrigel assay was used to investigate the effects of TCMPs on in vitro angiogenesis. Viability and proliferation of endothelial cells were tested. Extracellular signal-regulated kinase (ERK)1/2 phosphorylation was assayed in either HUVEC or A431 epidermal growth factor receptor (EGFR)-overexpressing cells treated with TCMPs. EGFR phosphorylation was tested in A431 cells.

KEY RESULTS

Both recombinant and native TCMPs inhibited in vitro angiogenesis of HUVEC cells at concentrations of 15-100 nM. The anti-angiogenic effect of TCMPs was associated with the inhibition of ERK phosphorylation. The two miniproteins did not alter the viability and proliferation of the endothelial cells.

CONCLUSIONS AND IMPLICATIONS

The anti-angiogenetic properties of TCMPs are of potential pharmacological interest because they are common and natural components of the human diet, they possess low toxicity, they are active at submicromolar concentrations, they share a common molecular structure that can be used as a molecular platform for the design of molecules with enhanced biological activity.

Tumor exploits alternative strategies to achieve vascularization

Neoangiogenesis is crucial for solid tumor growth and invasion, as the vasculature provides metabolic support and access to the circulation. Current antiangiogenic therapies have been designed on the assumption that endothelial cells forming the tumor vasculature exhibit genetic stability. Recent studies demonstrate that this is not the case. Tumor endothelial cells possess a distinct phenotype, differing from normal endothelial cells at both molecular and functional levels. This challenges the concept that tumor angiogenesis exclusively depends on normal endothelial cell recruitment from the surrounding vascular network. Indeed, recent data suggest alternative strategies for tumor vascularization. It has been reported that tumor vessels may derive from an intratumor embryonic-like vasculogenesis. This condition might be due to differentiation of normal stem and progenitor cells of hematopoietic origin or resident in tissues. Cancer stem cells may also participate in tumor vasculogenesis by virtue of their stem and progenitor cell properties. Finally, normal endothelial cells might be reprogrammed to a proangiogenic or dedifferentiated phenotype by genetic information transmitted from the tumor trough apoptotic bodies, or following mRNA and microRNA transfer by exosomes and microvesicles. In this review, we discuss the different aspects of intratumor angiogenesis and vasculogenesis, the known mechanisms involved, and the possible implications for the response to antiangiogenic therapy.

Upregulated stromal EGFR and vascular remodeling in mouse xenograft models of angiogenesis inhibitor-resistant human lung adenocarcinoma

Angiogenesis is critical for tumor growth and metastasis, and several inhibitors of angiogenesis are currently in clinical use for the treatment of cancer. However, not all patients benefit from antiangiogenic therapy, and those tumors that initially respond to treatment ultimately become resistant. The mechanisms underlying this, and the relative contributions of tumor cells and stroma to resistance, are not completely understood. Here, using species-specific profiling of mouse xenograft models of human lung adenocarcinoma, we have shown that gene expression changes associated with acquired resistance to the VEGF inhibitor bevacizumab occurred predominantly in stromal and not tumor cells. In particular, components of the EGFR and FGFR pathways were upregulated in stroma, but not in tumor cells. Increased activated EGFR was detected on pericytes of xenografts that acquired resistance and on endothelium of tumors with relative primary resistance. Acquired resistance was associated with a pattern of pericyte-covered, normalized revascularization, whereas tortuous, uncovered vessels were observed in relative primary resistance. Importantly, dual targeting of the VEGF and EGFR pathways reduced pericyte coverage and increased progression-free survival. These findings demonstrated that alterations in tumor stromal pathways, including the EGFR and FGFR pathways, are associated with, and may contribute to, resistance to VEGF inhibitors and that targeting these pathways may improve therapeutic efficacy. Understanding stromal signaling may be critical for developing biomarkers for angiogenesis inhibitors and improving combination regimens.

Resiliency and vulnerability in the HER2-HER3 tumorigenic driver

About 25% of breast cancers harbor the amplified oncogene human epidermal growth factor receptor 2 (HER2) and are dependent on HER2 kinase function, identifying HER2 as a vulnerable target for therapy. However, HER2-HER3 signaling is buffered so that it is protected against a nearly two-log inhibition of HER2 catalytic activity; this buffering is driven by the negative regulation of HER3 by Akt. We have now further characterized HER2-HER3 signaling activity and have shown that the compensatory buffering prevents apoptotic tumor cell death from occurring as a result of the combined loss of mitogen-activated protein kinase (MAPK) and Akt signaling. To overcome the cancer cells' compensatory mechanisms, we coadministered a phosphoinositide 3-kinase-mammalian target of rapamycin inhibitor and a HER2 tyrosine kinase inhibitor (TKI). This treatment strategy proved equivocal because it induced both TKI-sensitizing and TKI-desensitizing effects and robust cross-compensation of MAPK and Akt signaling pathways. Noting that HER2-HER3 activity was completely inhibited by higher, fully inactivating doses of TKI, we then attempted to overcome the cells' compensatory buffering with this higher dose. This treatment crippled all downstream signaling and induced tumor apoptosis. Although such high doses of TKI are toxic in vivo when given continuously, we found that intermittent doses of TKI administered to mice produced sequential cycles of tumor apoptosis and ultimately complete tumor regression in mouse models, with little toxicity. This strategy for inactivation of HER2-HER3 tumorigenic activity is proposed for clinical testing.

Neuregulin signaling and heart failure

Neuregulin-1 (NRG-1), a ligand of receptor tyrosine kinases of the ErbB family, plays a critical role in cardiovascular development and maintenance of adult heart function. Results from cellular, animal, and clinical experiments have shown NRG-1 to be a promising drug candidate for restoring cardiac function after cardiac injury. Various mechanisms have been suggested to be involved in this process, such as improving sarcomeric structure or cell-cell adhesion, promoting proliferation and survival of cardiac myocytes, balancing Ca(2+) homeostasis, modulating inotropic effects, promoting angiogenesis, and preventing atherosclerosis. However, the contribution of these effects to the restoration of cardiac function remains to be estimated, and it may depend on the specific events that led to heart failure. Meanwhile, distinct and crossed signaling pathways downstream of NRG-1 may play a role in these underlying mechanisms, resulting in a complicated network of signaling mediating the function of NRG-1.

Parenteral administration of recombinant human neuregulin-1 to patients with stable chronic heart failure produces favourable acute and chronic haemodynamic responses

AIMS

Neuregulin-1 (NRG-1) plays a critical role in the adaptation of the heart to injury, inhibiting apoptosis and inducing cardiomyocyte proliferation. We have shown previously that rhNRG-1 improves cardiac function and survival in animal models of cardiomyopathy. Here we report the first human study aimed at exploring the acute and chronic haemodynamic responses to recombinant human NRG-1 (beta(2a) isoform; rhNRG-1) in patients with stable chronic heart failure (CHF).

METHODS AND RESULTS

Fifteen patients (age, 60 ± 2; NYHA II:III, 9:6; left ventricular ejection fraction (LVEF) <40%) on optimal medical therapy for CHF, received a rhNRG-1 infusion daily for 11 days. Acute and chronic haemodynamic, structural and biochemical effects were determined by serial right heart catheterization, cardiac magnetic resonance (CMR), echocardiography and measurement of neurohumoral indices. Acutely, cardiac output increased by 30% during a 6 h rhNRG-1 infusion (P < 0.01). Pulmonary artery wedge pressure and systemic vascular resistance decreased 30 and 20%, respectively, at 2 h (P < 0.01). A 47% reduction in serum noradrenaline, a 55% reduction in serum aldosterone and a 3.6-fold increase in N-terminal prohormone brain natriuretic peptide levels were concurrently observed (P < 0.001). These acute haemodynamic effects were sustained, as demonstrated by the 12% increase in LVEF from 32.2 ± 2.0% (baseline) to 36.1 ± 2.3% (mean ± SE, P < 0.001) at 12 weeks. The therapy was well tolerated.

CONCLUSION

rhNRG-1 appears to produce favourable acute and chronic haemodynamic effects in patients with stable CHF on optimal medical therapy. Randomized controlled trials of rhNRG-1 in cardiac disease are thus warranted. Clinical Trial Registration Information The trial was registered with the Australian New Zealand Clinical Trials Registry, anzctr.org.au Identifier: ACTRN12607000330448.

Signaling of ERBB receptor tyrosine kinases promotes neuroblastoma growth in vitro and in vivo

BACKGROUND

ERBB receptor tyrosine kinases can mediate proliferation, migration, adhesion, differentiation, and survival in many types of cells and play critical roles in many malignancies. Recent reports suggest a role for EGFR signaling in proliferation and survival of neuroblastoma, a common form of pediatric cancer that often has an extremely poor outcome.

METHODS

The authors examined ERBB family expression in neuroblastoma cell lines and patient samples by flow cytometry, western blot, and quantitative real time polymerase chain reaction (Q-PCR). Response to ERBB inhibition was assessed in vitro by cell-cycle analysis and western blot and in vivo by serial tumor-size measurements.

RESULTS

A panel of neuroblastoma cell lines and primary patient tumors expressed EGFR, HER-3, and HER-4, with HER-2 in some tumors. HER-4 mRNA was expressed predominantly in cleavable isoforms. Whereas EGFR inhibition with erlotinib and pan-ERBB inhibition with CI-1033 inhibited EGF-induced phosphorylation of EGFR, AKT, and ERK1/2, only CI-1033 induced growth inhibition and dose-dependent apoptosis in vitro. Both CI-1033 and erlotinib treatment of neuroblastoma xenograft tumors resulted in decreased tumor growth in vivo, although CI-1033 was more effective. In vivo expression of EGFR was observed predominantly in vascular endothelial cells.

CONCLUSIONS

Pan-ERBB inhibition is required for ERBB-related neuroblastoma apoptosis in vitro, although EGFR contributes indirectly to tumor growth in vivo. Inhibition of EGFR in endothelial cells may be an important aspect of erlotinib's impact on neuroblastoma growth in vivo. Our results suggest that non-EGFR ERBB family members contribute directly to neuroblastoma growth and survival, and pan-ERBB inhibition represents a potential therapeutic target for treating neuroblastoma.

Alteration of angiogenic patterns on B16BL6 melanoma development promoted in Matrigel

Because the progression and metastasis of solid tumors depend on their local microcirculation, we sought to characterize tumor angiogenesis three dimensionally in a highly metastatic mouse melanoma model, B16BL6 (B16), injected with Matrigel into the subcutis in the skin on the back of syngeneic C57BL/6 mice. We found that B16 with Matrigel grew significantly faster than B16 alone and had altered tumor angiogenesis. Tumor vessels apparently grew vigorously in the opposite direction of the tumor without invading the tumor mass until at least day 10 of injection. In addition, vascular branching resulted not only from sprouting as was seen in B16 without Matrigel but also from vascular splitting, either because of compression from outside the vessels or from septum formation by endothelial cells. This phenomenon was characteristic of B16 cells, but not of other tumor cells, including Lewis lung carcinoma and ASH-1 hybridoma cell lines, both of which were tested under the same conditions. The reduction in various angiogenic factors in Matrigel did not affect the angiogenic patterns and tumor growth. We hypothesize that tumor vessels may vigorously alter their angiogenic patterns in response to the local microenvironment.

HDL-mimicking peptide-lipid nanoparticles with improved tumor targeting

Targeted delivery of intracellularly active diagnostics and therapeutics in vivo is a major challenge in cancer nanomedicine. A nanocarrier should possess long circulation time yet be small and stable enough to freely navigate through interstitial space to deliver its cargo to targeted cells. Herein, it is shown that by adding targeting ligands to nanoparticles that mimic high-density lipoprotein (HDL), tumor-targeted sub-30-nm peptide-lipid nanocarriers are created with controllable size, cargo loading, and shielding properties. The size of the nanocarrier is tunable between 10 and 30 nm, which correlates with a payload of 15-100 molecules of fluorescent dye. Ligand-directed nanocarriers targeting epidermal growth factor receptor (EGFR) are confirmed both in vitro and in vivo. The nanocarriers show favorable circulation time, tumor accumulation, and biodistribution with or without the targeting ligand. The EGFR targeting ligand is proved to be essential for the EGFR-mediated tumor cell uptake of the nanocarriers, a prerequisite of intracellular delivery. The results demonstrate that targeted HDL-mimetic nanocarriers are useful delivery vehicles that could open new avenues for the development of clinically viable targeted nanomedicine.

Evading tumor evasion: current concepts and perspectives of anti-angiogenic cancer therapy

Within three decades, anti-angiogenic therapy has rapidly evolved into an integral component of current standard anti-cancer treatment. Anti-angiogenic therapy has fulfilled a number of its earlier proposed promises. The universality of this approach is demonstrated by the broad spectrum of malignant and benign tumor entities, as well as non-neoplastic diseases, that are currently treated with anti-angiogenic agents. In contrast to tumor cell targeting therapies, the development of acquired drug resistance (e.g., via mutations in growth factor receptor signaling genes) has not been described yet for the principal target of anti-angiogenic therapy--the tumor endothelium. Moreover, the tumor endothelium has emerged as a critical target of conventional cancer therapies, such as chemotherapy and radiotherapy. The presumption that tumor growth and metastasis are angiogenesis-dependent implies that the number of potential targets of an anti-cancer therapy could be reduced to those that stimulate the angiogenesis process. Therefore, the set of endogenous angiogenesis stimulants might constitute an "Achilles heel" of cancer. Direct targeting of tumor endothelium via, e.g., endogenous angiogenesis inhibitors poses another promising but clinically less explored therapeutic strategy. Indeed, the majority of current anti-angiogenic approaches block the activity of a single or at most a few pro-angiogenic proteins secreted by tumor cells or the tumor stroma. Based on our systems biology work on the angiogenic switch, we predicted that the redundancy of angiogenic signals might limit the efficacy of anti-angiogenic monotherapies. In support of this hypothesis, emerging experimental evidence suggests that tumors may become refractory or even evade the inhibition of a single pro-angiogenic pathway via compensatory upregulation of alternative angiogenic factors. Here, we discuss current concepts and propose novel strategies to overcome tumor evasion of anti-angiogenic therapy. We believe that early detection of tumors, prediction of tumor evasive mechanisms and rational design of anti-angiogenic combinations will direct anti-angiogenic therapy towards its ultimate goal--the conversion of cancer to a dormant, chronic, manageable disease.

Epidermal growth factor receptor inhibitors in cancer treatment: advances, challenges and opportunities

Aberrant expression of the epidermal growth factor receptor (EGFR) system has been reported in a wide range of epithelial cancers. In some studies, this has also been associated with a poor prognosis and resistance to the conventional forms of therapies. These discoveries have led to the strategic development of several kinds of EGFR inhibitors, five of which have gained US Food and Drug Administration approval for the treatment of patients with non-small-cell lung cancer (gefitinib and erlotinib), metastatic colorectal cancer (cetuximab and panitumumab), head and neck (cetuximab), pancreatic cancer (erlotinib) and breast (lapatinib) cancer. Despite these advances and recent studies on the predictive value of activating EGFR mutation and KRAS mutations with response in non-small-cell lung cancer and colon cancer patients, there is currently no reliable predictive marker for response to therapy with the anti-EGFR monoclonal antibodies cetuximab and panitumumab or the small molecule EGFR tyrosine kinase inhibitors gefitinib and erlotinib. In particular, there has been no clear association between the expression of EGFR, determined by the US Food and Drug Administration-approved EGFR PharmDX kit, and response to the EGFR inhibitors. Here, we discuss some of the controversial data and explanatory factors as well as future studies for the establishment of more reliable markers for response to therapy with EGFR inhibitors. Such investigations should lead to the selection of a more specific subpopulation of cancer patients who benefit from therapy with EGFR inhibitors, but equally to spare those who will receive no benefit or a detrimental effect from such biological agents.

Cytogenetic abnormalities of tumor-associated endothelial cells in human malignant tumors

Tumor blood vessels are thought to contain genetically normal and stable endothelial cells (ECs), unlike tumor cells, which typically display genetic instability. Yet, chromosomal aberration in human tumor-associated ECs (hTECs) in carcinoma has not yet been investigated. Here we isolated TECs from 20 human renal cell carcinomas and analyzed their cytogenetic abnormalities. The degree of aneuploidy was analyzed by fluorescence in situ hybridization using chromosome 7 and chromosome 8 DNA probes in isolated hTECs. In human renal cell carcinomas, 22-58% (median, 33%) of uncultured hTECs were aneuploid, whereas normal ECs were diploid. The mechanisms governing TEC aneuploidy were then studied using mouse TECs (mTECs) isolated from xenografts of human epithelial tumors. To investigate the contribution of progenitor cells to aneuploidy in mTECs, CD133(+) and CD133(-) mTECs were compared for aneuploidy. CD133(+) mTECs showed aneuploidy more frequently than CD133(-) mTECs. This is the first report showing cytogenetic abnormality of hTECs in carcinoma, contrary to traditional belief. Cytogenetic alterations in tumor vessels of carcinoma therefore can occur and may play a significant role in modifying tumor- stromal interactions.

Inhibitory effects of epigallocatechin-3 gallate, a polyphenol in green tea, on tumor-associated endothelial cells and endothelial progenitor cells

The polyphenol epigallocatechin-3 gallate (EGCG) in green tea suppresses tumor growth by direct action on tumor cells and by inhibition of angiogenesis, but it is not known whether it specifically inhibits tumor angiogenesis. We examined the anti-angiogenic effect of EGCG on tumor-associated endothelial cells (TEC), endothelial progenitor cells (EPC), and normal endothelial cells (NEC). EGCG suppressed the migration of TEC and EPC but not NEC. EGCG also inhibited the phosphorylation of Akt in TEC but not in NEC. Furthermore, vascular endothelial growth factor-induced mobilization of EPC into circulation was inhibited by EGCG. MMP-9 in the bone marrow plasma plays key roles in EPC mobilization into circulation. We observed that expression of MMP-9 mRNA was downregulated by EGCG in mouse bone marrow stromal cells. In an in vivo model, EGCG suppressed growth of melanoma and reduced microvessel density. Our study showed that EGCG has selective anti-angiogenic effects on TEC and EPC. It is suggested that EGCG could be a promising angiogenesis inhibitor for cancer therapy.

Enhanced adhesion of early endothelial progenitor cells to radiation-induced senescence-like vascular endothelial cells in vitro

The effects of ionizing radiation (IR) on tumor neovascularization are still unclear. We previously reported that vascular endothelial cells (ECs) expressing the IR-induced senescence-like (IRSL) phenotype exhibit a significant decrease in angiogenic activity in vitro. In this study, we examined the effects of the IRSL phenotype on adhesion to early endothelial progenitor cells (early EPCs). Adhesion of human peripheral blood-derived early EPCs to human umbilical vein endothelial cells (HUVECs) expressing the IRSL phenotype was evaluated by an adhesion assay under static conditions. It was revealed that the IRSL HUVECs supported significantly more adhesion of early EPCs than normal HUVECs. Expressions of ICAM-1, VCAM-1 and E-selectin were up-regulated in IRSL HUVECs. Pre-treatment of IRSL HUVECs with adhesion-blocking monoclonal antibodies against E-selectin and VCAM-1 significantly reduced early EPC adhesion to IRSL HUVECs, suggesting a potential role for the E-selectin and VCAM-1 in the adhesion between IRSL ECs and early EPCs. Therefore, the IRSL phenotype expressed in ECs may enhance neovascularization via increased homing of early EPCs. Our findings are first to implicate the complex effects of this phenotype on tumor neovascularization following irradiation.

A novel magnetic crystal-lipid nanostructure for magnetically guided in vivo gene delivery

Cancer gene therapy requires a safe and effective gene delivery system. Polymer- and lipid-coated magnetic nanocrystals have been used to deliver silencing RNA, but synthesizing these magnetic vectors is difficult. Here, we show that a new nanoparticle formulation can be magnetically guided to deliver and silence genes in cells and tumours in mice. This formulation, termed LipoMag, consists of an oleic acid-coated magnetic nanocrystal core and a cationic lipid shell. When compared with the commercially available PolyMag formulation, LipoMag displayed more efficient gene silencing in 9 of 13 cell lines, and better anti-tumour effects when systemically administered to mice bearing gastric tumours. By delivering an optimized sequence of a silencing RNA that targets the epidermal growth factor receptor of tumour vessels, the intended therapeutic benefit was achieved with no evident adverse immune reaction or untoward side effects.

A phase I study of a 2-day lapatinib chemosensitization pulse preceding nanoparticle albumin-bound Paclitaxel for advanced solid malignancies

PURPOSE

Systemic chemotherapy fails to access much of the tumor burden in patients with advanced cancer, significantly limiting its efficacy. In preclinical studies, brief high doses of tyrosine kinase inhibitors (TKI) targeting the human epidermal growth factor receptor (HER) family can prime tumor vasculature for optimal chemotherapeutic delivery and efficacy. This study investigates the clinical relevance of this approach.

EXPERIMENTAL DESIGN

A phase I clinical study of escalating doses of the HER TKI lapatinib given as a 2-day pulse before a weekly infusion of nab-paclitaxel (100 mg/m(2)) was conducted in patients with advanced solid tumors.

RESULTS

Twenty-five patients were treated. Treatment was associated with grade 1 to 2 toxicities including diarrhea, nausea, rash, neutropenia, neuropathy, fatigue, alopecia, and anemia. The two dose-limiting toxicities were grade 3 vomiting and grade 4 neutropenia, and the maximum tolerated dose of lapatinib was defined as 5250 mg/day in divided doses. Lapatinib concentrations increased with increasing dose. Dynamic Contrast Enhanced Magnetic Resonance Imaging studies in a subset of patients confirmed a decrease in tumor vascular permeability immediately following a lapatinib pulse. Sixty-five percent of evaluable patients experienced a partial or stable response on this therapy, 72% of whom were previously taxane-refractory.

CONCLUSION

A 2-day pulse of high-dose lapatinib given before weekly nab-paclitaxel is a feasible and tolerable clinical regimen, suitable for testing this novel vascular-priming chemosensitization hypothesis developed in preclinical models.

Preventive effects of heregulin-beta1 on macrophage foam cell formation and atherosclerosis

RATIONALE

Human heregulins, neuregulin-1 type I polypeptides that activate proliferation, differentiation, and survival of glial cells, neurons, and myocytes, are expressed in macrophage foam cells within human coronary atherosclerotic lesions. Macrophage foam cell formation, characterized by cholesterol ester accumulation, is modulated by scavenger receptor class A (SR-A), acyl-coenzyme A:cholesterol acyltransferase (ACAT)1, and ATP-binding cassette transporter (ABC)A1.

OBJECTIVE

The present study clarified the roles of heregulins in macrophage foam cell formation and atherosclerosis.

METHODS AND RESULTS

Plasma heregulin-beta(1) levels were significantly decreased in 31 patients with acute coronary syndrome and 33 patients with effort angina pectoris compared with 34 patients with mild hypertension and 40 healthy volunteers (1.3+/-0.3, 2.0+/-0.4 versus 7.6+/-1.4, 8.2+/-1.2 ng/mL; P<0.01). Among all patients with acute coronary syndrome and effort angina pectoris, plasma heregulin-beta(1) levels were further decreased in accordance with the severity of coronary artery lesions. Expression of heregulin-beta(1) was observed at trace levels in intracoronary atherothrombosis obtained by aspiration thrombectomy from acute coronary syndrome patients. Heregulin-beta(1), but not heregulin-alpha, significantly reduced acetylated low-density lipoprotein-induced cholesterol ester accumulation in primary cultured human monocyte-derived macrophages by reducing SR-A and ACAT1 expression and by increasing ABCA1 expression at both mRNA and protein levels. Heregulin-beta(1) significantly decreased endocytic uptake of [(125)I]acetylated low-density lipoprotein and ACAT activity, and increased cholesterol efflux to apolipoprotein (Apo)A-I from human macrophages. Chronic infusion of heregulin-beta(1) into ApoE(-/-) mice significantly suppressed the development of atherosclerotic lesions.

CONCLUSIONS

This study provided the first evidence that heregulin-beta(1) inhibits atherogenesis and suppresses macrophage foam cell formation via SR-A and ACAT1 downregulation and ABCA1 upregulation.

Human hepatocellular carcinoma tumor-derived endothelial cells manifest increased angiogenesis capability and drug resistance compared with normal endothelial cells

PURPOSE

Increasing evidence indicates that tumor-derived endothelial cells (TEC) possess a distinct and unique phenotype compared with endothelial cells (NEC) from adjacent normal tissue and may be able to acquire resistance to drugs. The aim of this study was to investigate the angiogenesis activity and response to drug treatment of TECs and NECs derived from human hepatocellular carcinoma (HCC).

EXPERIMENTAL DESIGN

TECs or NECs were isolated from HCC or adjacent normal liver tissue using anti-CD105 antibody coupled to magnetic beads. The phenotypic and functional properties of endothelial cells were characterized by testing the expression of CD105, CD31, CD144, vascular endothelial growth factor receptor-1, vascular endothelial growth factor receptor-2, and von Willebrand factor, and the ability of DiI-Ac-LDL-uptake and tube formations. CD105(+) TECs were compared with CD105(+) NECs and human umbilical vein endothelial cells (HUVEC) by examining their ability to proliferate, motility, ability to adhere to tumor cells, response to tumor conditioned medium, and reactions to the chemotherapy drugs Adriamycin and 5-fluorouracil and the antiangiogenic drug sorafenib.

RESULTS

Compared with CD105(+) NECs and HUVECs, CD105(+) TECs showed increased apoptosis resistance and motility and proangiogenic properties. Meanwhile, CD105(+) TECs had a greater ability to adhere to tumor cells and survive in the tumor environment. Moreover, CD105(+) TECs acquired more resistance to Adriamycin, 5-fluorouracil, and sorafenib than CD105(+) NECs and HUVECs.

CONCLUSIONS

TECs possessed enhanced angiogenic activity and resistance to chemotherapeutic drugs and an angiogenesis inhibitor, and may provide a better tool for studying tumor angiogenesis and antiangiogenesis drugs in HCC.

Factors underlying sensitivity of cancers to small-molecule kinase inhibitors

Selective small-molecule kinase inhibitors have emerged over the past decade as an important class of anti-cancer agents, and have demonstrated impressive clinical efficacy in several different diseases, including relatively common malignancies such as breast and lung cancer. However, clinical benefit is typically limited to a fraction of treated patients. Genomic features of individual tumours contribute significantly to such clinical responses, and these seem to vary tremendously across patients. Additional factors, including pharmacogenomics, the tumour microenvironment and rapidly acquired drug resistance, also contribute to the clinical sensitivity of various cancers, and should be considered and applied in the development and use of new kinase inhibitors.

Erlotinib and bevacizumab have synergistic activity against melanoma

PURPOSE

Melanoma is one of the most aggressive types of cancer with currently no chance of cure once the disease has spread to distant sites. Therapeutic options for advanced stage III and IV are very limited, mainly palliative, and show response in only approximately 20% of all cases. The presented preclinical study was done to investigate the influence of a combined treatment of the epidermal growth factor receptor inhibitor erlotinib and the vascular endothelial growth factor monoclonal antibody bevacizumab in melanoma.

EXPERIMENTAL DESIGN AND RESULTS

The epidermal growth factor receptor was expressed in all cell lines tested, and treatment with erlotinib did inhibit the activation of the MEK/extracellular signal-regulated kinase and AKT signaling pathways. Whereas in vitro no influence on tumor cell proliferation was seen with erlotinib or bevacizumab monotherapy, a decreased invasive potential on erlotinib treatment in a three-dimensional Matrigel assay was observed. Furthermore, both drugs inhibited proliferation and sprouting of endothelial cells. In vivo, in a severe combined immunodeficient mouse xenotransplantation model, reduction in tumor volume under combined treatment with erlotinib and bevacizumab was superior to the additive effect of both single agents. This was associated with reduced cell proliferation, increased apoptosis, and a reduction in tumor angiogenesis compared with control or single treatment groups. Likewise, the reduction in the extent of lymph node and lung metastasis was most pronounced in animals treated with both drugs.

CONCLUSION

The presented data strongly support the use of a combination of erlotinib and bevacizumab as a novel treatment regimen for metastatic melanoma.

Combined vascular endothelial growth factor receptor and epidermal growth factor receptor (EGFR) blockade inhibits tumor growth in xenograft models of EGFR inhibitor resistance

PURPOSE

The epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKI) gefitinib and erlotinib benefit some non-small cell lung cancer (NSCLC) patients, but most do not respond (primary resistance) and those who initially respond eventually progress (acquired resistance). EGFR TKI resistance is not completely understood and has been associated with certain EGFR and K-RAS mutations and MET amplification.

EXPERIMENTAL DESIGN

We hypothesized that dual inhibition of the vascular endothelial growth factor (VEGF) and EGFR pathways may overcome primary and acquired resistance. We investigated the VEGF receptor/EGFR TKI vandetanib, and the combination of bevacizumab and erlotinib in vivo using xenograft models of EGFR TKI sensitivity, primary resistance, and three models of acquired resistance, including models with mutated K-RAS and secondary EGFR T790M mutation.

RESULTS

Vandetanib, gefitinib, and erlotinib had similar profiles of in vitro activity and caused sustained tumor regressions in vivo in the sensitive HCC827 model. In all four resistant models, vandetanib and bevacizumab/erlotinib were significantly more effective than erlotinib or gefitinib alone. Erlotinib resistance was associated with a rise in both host and tumor-derived VEGF but not EGFR secondary mutations in the KRAS mutant-bearing A549 xenografts. Dual inhibition reduced tumor endothelial proliferation compared with VEGF or EGFR blockade alone, suggesting that the enhanced activity of dual inhibition is due at least in part to antiendothelial effects.

CONCLUSION

These studies suggest that erlotinib resistance may be associated with a rise in both tumor cell and host stromal VEGF and that combined blockade of the VEGFR and EGFR pathways can abrogate primary or acquired resistance to EGFR TKIs. This approach merits further evaluation in NSCLC patients.

Neuropilin2 expressed in gastric cancer endothelial cells increases the proliferation and migration of endothelial cells in response to VEGF

The structure and characteristics of the tumor vasculature are known to be different from those of normal vessels. Neuropilin2 (Nrp2), which is expressed in non-endothelial cell types, such as neuronal or cancer cells, functions as a receptor for both semaphorin and vascular endothelial growth factor (VEGF). After isolating tumor and normal endothelial cells from advanced gastric cancer tissue and normal gastric mucosa tissues, respectively, we identified genes that were differentially expressed in gastric tumor endothelial (TEC) and normal endothelial cells (NEC) using DNA oligomer chips. Using reverse transcriptase-PCR, we confirmed the chip results by showing that Nrp2 gene expression is significantly up-regulated in TEC. Genes that were found to be up-regulated in TEC were also observed to be up-regulated in human umbilical vein endothelial cells (HUVECs) that were co-cultured with gastric cancer cells. In addition, HUVECs co-cultured with gastric cancer cells showed an increased reactivity to VEGF-induced proliferation and migration. Moreover, overexpression of Nrp2 in HUVECs significantly enhanced the proliferation and migration induced by VEGF. Observation of an immunohistochemical analysis of various human tumor tissue arrays revealed that Nrp2 is highly expressed in the tumor vessel lining and to a lesser extent in normal tissue microvessels. From these results, we suggest that Nrp2 may function to increase the response to VEGF, which is more significant in TEC than in NEC given the differential expression, leading to gastric TEC with aggressive angiogenesis phenotypes.

The Ape-1/Ref-1 redox antagonist E3330 inhibits the growth of tumor endothelium and endothelial progenitor cells: therapeutic implications in tumor angiogenesis

The apurinic/apyrimidinic endonuclease 1/redox factor-1 (Ape-1/Ref-1) is a multi-functional protein, involved in DNA repair and the activation of redox-sensitive transcription factors. The Ape-1/Ref-1 redox domain acts as a cytoprotective element in normal endothelial cells, mitigating the deleterious effects of apoptotic stimuli through induction of survival signals. We explored the role of the Ape-1/Ref-1 redox domain in the maintenance of tumor-associated endothelium, and of endothelial progenitor cells (EPCs), which contribute to tumor angiogenesis. We demonstrate that E3330, a small molecule inhibitor of the Ape-1/Ref-1 redox domain, blocks the in vitro growth of pancreatic cancer-associated endothelial cells (PCECs) and EPCs, which is recapitulated by stable expression of a dominant-negative redox domain mutant. Further, E3330 blocks the differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) into CD31(+) endothelial progeny. Exposure of PCECs to E3330 results in a reduction of H-ras expression and intracellular nitric oxide (NO) levels, as well as decreased DNA-binding activity of the hypoxia-inducible transcription factor, HIF-1alpha. E3330 also reduces secreted and intracellular vascular endothelial growth factor expression by pancreatic cancer cells, while concomitantly downregulating the cognate receptor Flk-1/KDR on PCECs. Inhibition of the Ape-1/Ref-1 redox domain with E3330 or comparable angiogenesis inhibitors might be a potent therapeutic strategy in solid tumors.

Endothelial expression of autocrine VEGF upon the uptake of tumor-derived microvesicles containing oncogenic EGFR

Activated EGF receptor (EGFR) plays an oncogenic role in several human malignancies. Although the intracellular effects of EGFR are well studied, its ability to induce and modulate tumor angiogenesis is less understood. We found previously that oncogenic EGFR can be shed from cancer cells as cargo of membrane microvesicles (MVs), which can interact with surfaces of other cells. Here we report that MVs produced by human cancer cells harboring activated EGFR (A431, A549, DLD-1) can be taken up by cultured endothelial cells, in which they elicit EGFR-dependent responses, including activation of MAPK and Akt pathways. These responses can be blocked by annexin V and its homodimer, Diannexin, both of which cloak phosphatidylserine residues on the surfaces of MVs. Interestingly, the intercellular EGFR transfer is also accompanied by the onset of VEGF expression in endothelial cells and by autocrine activation of its key signaling receptor (VEGF receptor-2). In A431 human tumor xenografts in mice, angiogenic endothelial cells stain positively for human EGFR and phospho-EGFR, while treatment with Diannexin leads to a reduction of tumor growth rate and microvascular density. Thus, we propose that oncogene-containing tumor cell-derived MVs could act as a unique form of angiogenesis-modulating stimuli and are capable of switching endothelial cells to act in an autocrine mode.

Combination of antiangiogenesis with chemotherapy for more effective cancer treatment

Angiogenesis is a hallmark of tumor development and metastasis and is now a validated target for cancer treatment. However, the survival benefits of antiangiogenic drugs have thus far been rather modest, stimulating interest in developing more effective ways to combine antiangiogenic drugs with established chemotherapies. This review discusses recent progress and emerging challenges in this field; interactions between antiangiogenic drugs and conventional chemotherapeutic agents are examined, and strategies for the optimization of combination therapies are discussed. Antiangiogenic drugs such as the anti-vascular endothelial growth factor antibody bevacizumab can induce a functional normalization of the tumor vasculature that is transient and can potentiate the activity of coadministered chemoradiotherapies. However, chronic angiogenesis inhibition typically reduces tumor uptake of coadministered chemotherapeutics, indicating a need to explore new approaches, including intermittent treatment schedules and provascular strategies to increase chemotherapeutic drug exposure. In cases where antiangiogenesis-induced tumor cell starvation augments the intrinsic cytotoxic effects of a conventional chemotherapeutic drug, combination therapy may increase antitumor activity despite a decrease in cytotoxic drug exposure. As new angiogenesis inhibitors enter the clinic, reliable surrogate markers are needed to monitor the progress of antiangiogenic therapies and to identify responsive patients. New targets for antiangiogenesis continue to be discovered, increasing the opportunities to interdict tumor angiogenesis and circumvent resistance mechanisms that may emerge with chronic use of these drugs.

Erlotinib and bevacizumab in patients with recurrent or metastatic squamous-cell carcinoma of the head and neck: a phase I/II study

BACKGROUND

Epidermal growth factor receptor (EGFR) is a validated target in squamous-cell carcinoma of the head and neck, but in patients with recurrent or metastatic disease, EGFR targeting agents have displayed modest efficacy. Vascular endothelial growth factor (VEGF)-mediated angiogenesis has been implicated as a mechanism of resistance to anti-EGFR therapy. In this multi-institutional phase I/II study we combined an EGFR inhibitor, erlotinib, with an anti-VEGF antibody, bevacizumab.

METHODS

Between April 15, 2003, and Jan 27, 2005, patients with recurrent or metastatic squamous-cell carcinoma of the head and neck were enrolled from seven centres in the USA and were given erlotinib (150 mg daily) and bevacizumab in escalating dose cohorts. The primary objectives in the phase I and II sections, respectively, were to establish the maximum tolerated dose and dose-limiting toxicity of bevacizumab when administered with erlotinib and to establish the proportion of objective responses and time to disease progression. Pretreatment serum and tissues were collected and analysed by enzyme-linked immunosorbent assay and immunofluorescence quantitative laser analysis, respectively. This study was registered with ClinicalTrials.gov, number NCT00055913.

FINDINGS

In the phase I section of the trial, ten patients were enrolled in three successive cohorts with no dose-limiting toxic effects noted. 46 patients were enrolled in the phase II section of the trial (including three patients from the phase I section) on the highest dose of bevacizumab (15 mg/kg every 3 weeks). Two additional patients were accrued beyond the protocol-stipulated 46, leaving a total of 48 patients for the phase II assessment. The most common toxic effects of any grade were rash and diarrhoea (41 and 16 of 48 patients, respectively). Three patients had serious bleeding events of grade 3 or higher. Seven patients had a response, with four showing a complete response allowing rejection of the null hypothesis. Median time of overall survival and progression-free survival (PFS) were 7.1 months (95% CI 5.7-9.0) and 4.1 months (2.8-4.4), respectively. Higher ratios of tumour-cell phosphorylated VEGF receptor-2 (pVEGFR2) over total VEGFR2 and endothelial-cell pEGFR over total EGFR in pretreatment biopsies were associated with complete response (0.704 vs 0.386, p=0.036 and 0.949 vs 0.332, p=0.036, respectively) and tumour shrinkage (p=0.007 and p=0.008, respectively) in a subset of 11 patients with available tissue.

INTERPRETATION

The combination of erlotinib and bevacizumab is well tolerated in recurrent or metastatic squamous-cell carcinoma of the head and neck. A few patients seem to derive a sustained benefit and complete responses were associated with expression of putative targets in pretreatment tumour tissue.

Calcification of multipotent prostate tumor endothelium

Solid tumors require new blood vessels for growth and metastasis, yet the biology of tumor-specific endothelial cells is poorly understood. We have isolated tumor endothelial cells from mice that spontaneously develop prostate tumors. Clonal populations of tumor endothelial cells expressed hematopoietic and mesenchymal stem cell markers and differentiated to form cartilage- and bone-like tissues. Chondrogenic differentiation was accompanied by an upregulation of cartilage-specific col2a1 and sox9, whereas osteocalcin and the metastasis marker osteopontin were upregulated during osteogenic differentiation. In human and mouse prostate tumors, ectopic vascular calcification was predominately luminal and colocalized with the endothelial marker CD31. Thus, prostate tumor endothelial cells are atypically multipotent and can undergo a mesenchymal-like transition.

Tumor-derived endothelial cells exhibit aberrant Rho-mediated mechanosensing and abnormal angiogenesis in vitro

Tumor blood vessels exhibit abnormal structure and function that cause disturbed blood flow and high interstitial pressure, which impair delivery of anti-cancer agents. Past efforts to normalize the tumor vasculature have focused on inhibition of soluble angiogenic factors, such as VEGF; however, capillary endothelial (CE) cell growth and differentiation during angiogenesis are also influenced by mechanical forces conveyed by the extracellular matrix (ECM). Here, we explored the possibility that tumor CE cells form abnormal vessels because they lose their ability to sense and respond to these physical cues. These studies reveal that, in contrast to normal CE cells, tumor-derived CE cells fail to reorient their actin cytoskeleton when exposed to uniaxial cyclic strain, exhibit distinct shape sensitivity to variations in ECM elasticity, exert greater traction force, and display an enhanced ability to retract flexible ECM substrates and reorganize into tubular networks in vitro. These behaviors correlate with a constitutively high level of baseline activity of the small GTPase Rho and its downstream effector, Rho-associated kinase (ROCK). Moreover, decreasing Rho-mediated tension by using the ROCK inhibitor, Y27632, can reprogram the tumor CE cells so that they normalize their reorientation response to uniaxial cyclic strain and their ability to form tubular networks on ECM gels. Abnormal Rho-mediated sensing of mechanical cues in the tumor microenvironment may therefore contribute to the aberrant behaviors of tumor CE cells that result in the development of structural abnormalities in the cancer microvasculature.

Modification of the primary tumor microenvironment by transforming growth factor alpha-epidermal growth factor receptor signaling promotes metastasis in an orthotopic colon cancer model

The transforming growth factor alpha (TGFalpha)/epidermal growth factor receptor (EGFR) signaling pathway appears to play a critical role in colon cancer progression, but the cellular and molecular mechanisms that contribute to metastasis remain unknown. KM12C colon cancer cell clones expressing high (C9) or negligible (C10) levels of TGFalpha were implanted into the cecal walls of nude mice. C9 tumors formed autocrine and paracrine EGFR networks, whereas C10 tumors were unable to signal through EGFR. The tumor microenvironment of C9, but not C10, contained cells enriched in vascular endothelial growth factor (VEGF) A, interleukin-8, and matrix metalloproteinases-2 and -9 and had a high vascular surface area. C9 tumors recruited a macrophage population that co-expressed F4/80 and lymphatic vessel endothelial hyaluronic acid receptor and produced VEGFC. The mean lymphatic density of C9 tumors was threefold higher than that of C10 tumors. C9, but not C10, tumor cells metastasized to regional lymph nodes in all mice and to the liver in 5 of 10 mice. Forced expression of TGFalpha in C10 tumor cells led to the generation of autocrine and paracrine EGFR signaling, macrophage recruitment, enhanced blood and lymphatic vascular surface areas, and increased lymphatic metastasis. Collectively, these data show that activation of TGFalpha-EGFR signaling in colon cancer cells creates a microenvironment that is conducive for metastasis, providing a rationale for efforts to inhibit EGFR signaling in TGFalpha-positive colon cancers.

Vascular changes in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most vascular solid tumors, in which angiogenesis plays an important role. The status of angiogenesis in HCC correlates with the disease progression and prognosis, and thus provides a potential therapeutic target. This review summarizes the vascular changes and molecular and cellular basis of angiogenesis in HCC. Development of HCC is characterized by arterialization of its blood supply and sinusoidal capillarization. Vascular endothelial growth factor (VEGF) is a potent angiogenic factor that plays a critical role in mediating angiogenesis in HCC. The VEGF can function on various types of cells, such as endothelial cells, hepatic stellate cells, endothelial progenitor cells and hemangiocytes, to induce vascular changes in HCC. Therefore, blockade of VEGF-mediated pathways, either by anti-VEGF neutralizing antibody or tyrosine kinase inhibitors that target VEGF receptors, suppresses carcinogenesis and angiogenesis in HCC. In addition to VEGF, several other angiogenic factors in HCC have recently been identified. These factors can also regulate angiogenic processes through interaction with VEGF or VEGF-independent pathways. Despite the fact that treatment of HCC remains a tough task due to lack of effective systemic therapy, antiangiogenic therapy has already entered clinical trials in HCC patients and sheds light on a promising novel treatment for this disease.

Beyond wavy hairs: the epidermal growth factor receptor and its ligands in skin biology and pathology

The epidermal growth factor receptor (EGFR) network, including its seven ligands and four related receptors, represents one of the most complex signaling systems in biology. In many tissues, including the skin and its appendages (notoriously the hair follicles), its correct function is necessary for proper development and tissue homeostasis, and its deregulation rapidly results in defects in cellular proliferation and differentiation. The consequences are impaired wound healing, development of psoriasis-like lesions, structural and functional defects of the hair follicles, and tumorigenesis. In addition to in vitro experiments and data from clinical studies, several genetically modified mouse models displaying alterations in the interfollicular skin and hair follicles attributable to mutations in components of the EGFR system have been reported. These animals, in many cases representing bona fide models of known human diseases, have been seminal in the study of the role of EGFR and its ligands in the skin and its appendages. In this review, we take the multiple phenotypes of these animal models as a basis to summarize and discuss the effects elicited by members of the EGFR system in diverse aspects of skin biology and pathology, including cellular proliferation and differentiation, wound healing, hair follicle morphogenesis, and tumorigenesis.

Dopamine increases the efficacy of anticancer drugs in breast and colon cancer preclinical models

PURPOSE

Because neurotransmitter dopamine inhibits vascular permeability factor/vascular endothelial growth factor (VEGF)-induced angiogenesis and as anti-VEGF agents act synergistically with anticancer drugs, we therefore investigated whether dopamine can increase the efficacies of these drugs.

EXPERIMENTAL DESIGN

The effect of dopamine was investigated in human breast cancer-(MCF-7) and colon (HT29) cancer-bearing mice. Experimental groups received either dopamine or doxorubicin or dopamine plus doxorubicin in MCF-7 tumor-bearing mice, and either dopamine or 5-fluorouracil or dopamine plus 5-fluorouracil in HT29-bearing mice. Thereafter, tumor growth, angiogenesis, tumor cell apoptosis, life span, and the effect of dopamine on the growth and survival of tumor cells in vitro were determined. Finally, the effects of dopamine on tumor vascular permeability; on VEGF receptor-2, mitogen-activated protein kinase, and focal adhesion kinase phosphorylation; and also on the proliferation and migration of tumor endothelial cells were investigated.

RESULTS

Dopamine, in combination with anticancer drugs, significantly inhibited tumor growth and increased the life span when compared with treatment with dopamine or anticancer drugs alone. Dopamine had no direct effects on the growth and survival of tumor cells. The antiangiogenic action of dopamine was mediated by inhibiting proliferation and migration of tumor endothelial cells through suppression of VEGF receptor-2, mitogen-activated protein kinase, and focal adhesion kinase phosphorylation.

CONCLUSION

Our study shows that dopamine significantly enhances the efficacies of commonly used anticancer drugs and also indicates that an inexpensive drug like dopamine, which is being extensively used in the clinics, might have a role as an antiangiogenic agent for the treatment of breast and colon cancer.

Targeting EGFR activity in blood vessels is sufficient to inhibit tumor growth and is accompanied by an increase in VEGFR-2 dependence in tumor endothelial cells

Epidermal growth factor receptor (EGFR) targeting agents such as kinase inhibitors reduce tumor growth and progression. We have previously reported that EGFR is not only expressed by the tumor cells but by the tumor endothelial cells (EC) as well (Amin, D. N., Hida, K., Bielenberg, D. R., Klagsbrun, M., 2006. Tumor endothelial cells express epidermal growth factor receptor (EGFR) but not ErbB3 and are responsive to EGF and to EGFR kinase inhibitors. Cancer Res. 66, 2173-80). Thus, targeting tumor blood vessel EGFR may be a viable strategy for tumor growth inhibition. We describe here a melanoma xenograft model where the tumor cells express very little or no EGFR but the tumor blood vessels express activated EGFR. The EGFR kinase inhibitor, gefitinib (Iressa), retarded tumor growth with a size decrease of 38% compared to control mice, ostensibly due to targeting of the blood vessels. EC were isolated from tumors of gefitinib-treated mice. These EC were unable to proliferate in response to EGF and displayed relatively weaker activation of MAPK and AKT signaling in response to EGF compared to tumor EC isolated from vehicle-treated mice. In contrast, the tumor EC from gefitinib-treated mice expressed higher levels of VEGFR-2 both at the mRNA and protein level. In addition, these cells were less sensitive to EGFR kinase inhibitors in vitro but more sensitive to a VEGFR-2 kinase inhibitor. These results suggest that in tumor EC from gefitinib-treated mice there is a switch from dependence on EGFR activity to signaling via VEGFR-2. Our data provide a molecular rationale for combination therapies targeting both EGF and VEGF signaling on the tumor vasculature.

Understanding tumor endothelial cell abnormalities to develop ideal anti-angiogenic therapies

Tumor angiogenesis is necessary for solid tumor progression and metastasis. Tumor blood vessels have been shown to differ from their normal counterparts, for example, by changes in morphology. An important concept in tumor angiogenesis is that tumor endothelial cells are assumed to be genetically normal, even though these endothelial cells are structurally and functionally abnormal. To date, many anti-angiogenic drugs have been developed, but, their therapeutic efficacy is not dramatic and they have also been reported to cause toxic side effects. To develop ideal antiangiogenic therapies, understanding tumor endothelial cell abnormalities is important. We have isolated tumor endothelial cells from mouse tumor xenografts and have shown that tumor-associated endothelial cells are abnormal. Tumor-associated endothelial cells upregulate many genes, such as epidermal growth factor receptor (EGFR). Tumor-associated endothelial cells are also more sensitive to EGF. They also have relatively large, heterogeneous nuclei. Unexpectedly, tumor endothelial cells are cytogenetically abnormal. Fluorescence in situ hybridization (FISH) analysis showed that freshly isolated uncultured tumor endothelial cells were aneuploid and had abnormal multiple centrosomes. The degree of aneuploidy was exacerbated by passage in culture. In marked contrast, freshly isolated normal skin and adipose endothelial cells were diploid. They had normal centrosomes and remained cytogenetically stable in culture even up to 20 passages. We conclude that tumor endothelial cells can acquire cytogenetic abnormalities while in the tumor microenvironment. Questions as to whether or not tumor endothelial cells become resistant to antiangiogenic drugs are thus raised. Our preliminary data show that tumor endothelial cells are more resistant to certain chemotherapeutic drugs. Studies to evaluate the mechanism for cytogenetic abnormalities in tumor endothelial cells are underway. It is becoming quite clear that the tumor vasculature is much more complex and unpredictable than initially perceived. Here, we provide an overview of the current studies on tumor endothelial cell abnormalities.