Metabotropic glutamate receptor-1 as a novel target for the antiangiogenic treatment of breast cancer

Metabotropic glutamate receptors (mGluRs) are normally expressed in the central nervous system, where they mediate neuronal excitability and neurotransmitter release. Certain cancers, including melanoma and gliomas, express various mGluR subtypes that have been implicated as playing a role in disease progression. Recently, we detected metabotropic glutamate receptor-1 (gene: GRM1; protein: mGluR1) in breast cancer and found that it plays a role in the regulation of cell proliferation and tumor growth. In addition to cancer cells, brain endothelial cells express mGluR1. In light of these studies, and because angiogenesis is both a prognostic indicator in cancer correlating with a poorer prognosis and a potential therapeutic target, we explored a potential role for mGluR1 in mediating endothelial cell (EC) proliferation and tumor-induced angiogenesis. GRM1 and mGluR1 were detected in various types of human ECs and, using mGluR1-specific inhibitors or shRNA silencing, we demonstrated that EC growth and Matrigel tube formation are dependent on mGluR1 signaling. In addition, loss of mGluR1 activity leads to reduced angiogenesis in a murine Matrigel sponge implant model as well as a murine tumor model. These results suggest a role for mGluR1 in breast cancer as a pro-angiogenic factor as well as a mediator of tumor progression. They also suggest mGluR1 as a potential new molecular target for the anti-angiogenic therapy of breast cancer.

Next-generation sequencing: a powerful tool for the discovery of molecular markers in breast ductal carcinoma in situ

Mammographic screening leads to frequent biopsies and concomitant overdiagnosis of breast cancer, particularly ductal carcinoma in situ (DCIS). Some DCIS lesions rapidly progress to invasive carcinoma, whereas others remain indolent. Because we cannot yet predict which lesions will not progress, all DCIS is regarded as malignant, and many women are overtreated. Thus, there is a pressing need for a panel of molecular markers in addition to the current clinical and pathological factors to provide prognostic information. Genomic technologies such as microarrays have made major contributions to defining subtypes of breast cancer. Next-generation sequencing (NGS) modalities offer unprecedented depth of expression analysis through revealing transcriptional boundaries, mutations, rare transcripts and alternative splice variants. NGS approaches are just beginning to be applied to DCIS. Here, the authors review the applications and challenges of NGS in discovering novel potential therapeutic targets and candidate biomarkers in the premalignant progression of breast cancer.

Abstract 3895: Metabotropic glutamate receptor-1 as a novel target for the anti-angiogenic treatment of breast cancer

Introduction: Metabotropic glutamate receptors (mGluRs) are normally expressed in the central nervous system where they mediate neuronal excitability and neurotransmitter release. However, certain cancers including melanoma and gliomas, have been shown to express various mGluR subtypes. Recently, we detected the metabotropic glutamate receptor-1 subtype (gene: GRM1; protein: mGluR1) in breast cancer and have demonstrated its role in the regulation of cell proliferation and tumor growth. In addition to cancer cells, brain endothelial cells have been shown to express mGluR1. In light of these studies and since angiogenesis is a known prognostic indicator of early relapse in cancer correlating with a poorer prognosis, we wished to examine a potential role for mGluR1 in mediating endothelial cell proliferation and angiogenesis in breast cancer.

Methods: To do this, we analyzed several primary endothelial cells for mGluR1 protein and mRNA expression and looked at their potential role in mediating cell proliferation and angiogenesis using various mGluR1 inhibitors or by silencing the gene for mGluR1 (GRM1). Cell proliferation was determined by MTT analysis or by cell counting and angiogenesis was determined in vitro using the matrigel tube formation assay. Angiogenesis was also determined in vivo using human dermal micro-endothelial cells (HDMEC) embedded in a matrigel sponge and implanted into the flanks of nude mice treated with the mGluR1 inhibitors, BAY36-7620 or Riluzole. The role of mGluR1 in mediating tumor-induced angiogenesis was also examined using the 4T1 tumor model in the presence of these same inhibitors.

Results: We detected mRNA and protein expression of mGluR1 in various human endothelial cells and, using mGluR1-specific inhibitors, have demonstrated its ability to regulate cell growth as well as matrigel tube formation. Both BAY36-7620 and Riluzole inhibited cell growth and matrigel tube formation in a dose-response manner. BAY36-7620, which is a more specific-inhibitor than Riluzole, inhibited tube formation by almost 90% compared to 50% by Riluzole, at the highest doses tested. These results were confirmed using mGluR1-silenced cells. In addition, both BAY36-7620 and Riluzole inhibited angiogenesis in the in vivo matrigel sponge model by approximately 50% each, compared to vehicle treated mice.

Conclusion: These results suggest a role for mGluR1 in the development and progression of breast cancer and thus, provide a potential new molecular target for the anti-angiogenic treatment of breast cancer.

Citation Format: Cecilia L. Speyer, Ali H. Hachem, Ali Assi, John A. DeVries, David H. Gorski. Metabotropic glutamate receptor-1 as a novel target for the anti-angiogenic treatment of breast cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3895. doi:10.1158/1538-7445.AM2013-3895

Abstract 1206: Metabotropic glutamate receptor 1 functions as an oncogene in the progression of triple negative breast cancer

Introduction: L-glutamate is the major excitatory neurotransmitter in the central nervous system and activates both ionotropic and metabotropic glutamate receptors. The metabotropic glutamate receptors (mGluRs) are a family of G protein-coupled receptors. mGluR1 (gene: GRM1) is included in Group I of these receptors and have been shown to activate phosphatidylinositol-calcium second messenger system. Aberrant extracellular glutamate signaling has been implicated in carcinogenesis; specifically, the aberrant expression of mGluR1 in melanocytes plays a critical role in the development of melanoma. Previously in our laboratory, we detected mGRM1 expression in triple negative breast cancer cells. We therefore evaluated its role in regulating the phenotype of these cells and found that mGluR1 expression is oncogenic in triple negative breast cancer (TNBC) progression. Methods: We determined the role of mGluR1 in TNBC progression using the MCF-10 triple negative series of cell lines, which represent the progression from normal mammary epithelium (MCF10A) to atypical hyperplasia (MCF10AT1) to ductal carcinoma in situ (MCF10.DCIS.com), and finally to malignant (MCF10.CA1D). GRM1 was overexpressed in MCF10A and MCF10AT1 and silenced MCF10.DCIS.com and MCF10.CA1D. We then determined whether mGRM1 has a transforming role through in vitro studies of proliferation, invasion, migration and anchorage-independent growth. We also inhibited mGluR1 signaling using two pharmacologic inhibitors: Riluzole, which is FDA-approved for amyotropic lateral sclerosis, and BAY36-7620, which is a specific noncompetitive inhibitor of mGluR1. Effects were evaluated on proliferation and anchorage independent growth. Finally, MCF10AT1 cells were transduced with a lentiviral construct driving mGluR1 expression and injected into athymic nude mice. The growth and histology of the resultant xenografts were compared with control LacZ transduced cells. Results: mGluR1 overexpression increased proliferation, anchorage-independent growth, and invasiveness in MCF10AT1 and not in MCF10A cells, while knockdown of mGluR1 expression resulted in a decrease in proliferation, anchorage independent growth and invasiveness in MCF10.CA1D cells. Pharmacologic inhibition of mGluR1 signaling in MCF10.CA1D cells resulted in a decrease in proliferation and anchorage independent growth. Transduction of MCF10AT1 cells with GRM1 resulted in transformation to carcinoma in 10/11 of the resultant xenografts compared to 2/9 for wild type and 3/11 for LacZ controls. Conclusions: mGluR1 expression and activity increases cell proliferation, anchorage independent growth, and invasion in vitro. In vivo, mGluR1 drives progression of MCF10AT1 cells from hyperplastic lesions to frank carcinoma. We therefore conclude that mGRM1 plays a role of an oncogene in the progression of TNBC and represents a therapeutic target.

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 1206. doi:1538-7445.AM2012-1206

Metabotropic glutamate receptor-1: a potential therapeutic target for the treatment of breast cancer

Metabotropic glutamate receptors are G-protein-coupled receptors normally expressed in the central nervous system where they mediate neuronal excitability, synaptic plasticity, and feedback inhibition of neurotransmitter release. However, recent data suggest that these receptors are also expressed and functional in some cancers, most notably melanoma. We detected the expression of metabotropic glutamate receptor-1 (gene: GRM1; protein: mGluR1) in triple negative breast cancer cells and evaluated its role in regulating the pro-proliferative phenotype of these cells. mGluR1 inhibitors (Riluzole or BAY36-7620) inhibited the proliferation of triple negative breast cancer cells in a time- and dose-dependent manner and this inhibition correlated with increased apoptosis as demonstrated by increase in PARP cleavage products and Annexin V staining. mGluR1 knockdown using Lentiviral constructs expressing shRNA targeting GRM1 also inhibited proliferation compared to non-silencing controls. In addition, treatment of mice bearing MDA-MB-231 xenografts with Riluzole or BAY36-7620, by intraperitoneal injection, resulted in a significant reduction in tumor volume of up to 80%. Moreover, Riluzole was effective against triple negative breast cancer xenografts in mice at doses equivalent to those currently being used in humans for the treatment of amyotrophic lateral sclerosis. Our observations implicate mGluR1 and glutamate signaling as a promising new molecular target for the treatment of breast cancer. Even more promising, Riluzole, because it is an oral drug that can be administered with low toxicity, represents a promising approach in the treatment of triple negative breast cancer.

Abstract 1673: mGluR1 as a potential therapeutic target in the treatment of triple negative breast cancer

Introduction: Metabotropic glutamate receptors are expressed throughout the central nervous system where they initiate a host of signaling events that regulate neuron function. We have identified the presence of metabotropic glutamate receptor 1 (mGluR1) in breast cancer cells and demonstrated a role for these receptors in regulating the pro-proliferative phenotype of these cells, both in vitro and in vivo. In this study, we investigate the signaling mechanism(s) by which mGluR1 mediates this pro-proliferative effect, as well as investigating a potential role for mGluR1 in mediating anti-apoptotic signaling events in triple negative breast cancer.

Methods: We studied the effect of mGluR1 expression on cell growth using MDA-MB-231 cells stably transduced with plasmids expressing shRNA against GRM1, the gene coding for mGluR1 protein. Cell growth was measured by MTT assay and a role for mGluR1 in mediating apoptosis was assessed by measuring PARP cleavage products and Annexin V staining, using Riluzole or BAY36-7620 (BAY), non-competitive inhibitors of mGluR1 activity. To examine potential signaling mechanisms mediating cell growth, MDA-MB-231 cells were grown in glutamate-free media and stimulated with the mGluR1 agonist, L-Quisqualic acid, in the presence or absence of BAY. PKC and phosphorylated Akt levels were examined by Western analysis. Since mGluR1 is known to protect nerve cells from oxidative stress and increased oxidative stress can result in p53-induced apoptosis, we measured the effect of Riluzole on p53 expression and oxidative stress levels in MDA-MB-231 cells. Oxidative stress was measured using immunofluorescent staining with carboxy-H2DCFDA and p53 by Western blot analysis.

Results: MDA-MB-231 cells were transduced with Lentiviral constructs expressing shRNA against GRM1 and cell growth assessed by MTT assay. Growth of these cells was inhibited 50% by shRNA against GRM1 compared to non-silencing scrambled control. In addition, inhibition of mGluR1 activity by BAY in MDA-MB-231 cells prevented signaling through Akt which ultimately resulted in increased p53 expression and superoxide production and apoptosis. Incubation of MDA-MB-231 or BT549 cells with varying doses of Riluzole resulted in increased PARP cleavage by 24 hours. FACS analysis also showed a three- and ten-fold increase in Annexin V staining of MDA-MB-231 cells after 24 and 48 hr incubation with Riluzole, respectively. BAY also induced Annexin V staining of these cells by almost 3-fold at the 48 hr timepoint.

Conclusion: Our results showing that inhibition of mGluR1 inhibits proliferation and increases apoptosis and oxidative stress implicate mGluR1, or one of its downstream signaling molecules, as potential new molecular targets for the treatment of breast cancer. Because it is an FDA-approved oral drug with low toxicity, Riluzole represents a promising approach in the treatment of triple negative breast cancer.

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 1673. doi:10.1158/1538-7445.AM2011-1673

Abstract 3950: The role of microRNA-130a in regulating HOXA5 expression in breast cancer progression

Introduction: Micro RNAs (miRNAs) are key post -transcriptional and translational regulators of gene expression and regulate diverse physiological activities involving development, cell growth, differentiation, apoptosis, and pathological processes such as heart disease and cancer. In tumorigenesis miRNAs function as oncogenes or tumor suppressors. HOXA5 belongs to the family of homeobox (HOX) genes, which encode a highly conserved family of transcription factors that are known to regulate body patterning during embryogenesis. HOXA5 plays a major role in mesenchymal-epithelial interactions during organogenesis. Sukumar et al have demonstrated that HOXA5 loss of function leads to loss of p53 expression in mammary epithelial cells, which in turn contributes to malignant transformation, which is why understanding the mechanisms by which HOXA5 expression is dysregulated in breast cancer is critical. We identified a consensus binding sequence for miR-130a in the 3′-UTR of the HOXA5 coding region. Previous studies in our laboratory have shown that miR-130a downregulates HOXA5 expression in vascular endothelial cells. In this study we characterize the role of miR130a in downregulating HOXA5 expression that in turn can decrease p53 expression and function in breast cancer cells resulting in tumor proliferation, progression and metastasis.

Methods: We determined whether mitogenic factors in serum affect miR130a and HOXA5 mRNA expression in the breast epithelial cell line MCF10A. Correlation between the expression of miR130a and HOXA5 mRNA expression in the MCF-10 breast progression series cell lines that model the progression from normal mammary epithelium (MCF-10A), ductal carcinoma in situ (MCF10.DCIS.com), to fully malignant (MCF10.CA1) was examined. In addition, we silenced miR-130a using a specific 2’-O-methyl-modified inhibitor and determined whether knocking it out increases HOXA5 mRNA expression in MCF10A cells. The expression levels of miR130a and HOXA5 were measured using quantitative reverse transcriptase real time PCR (QRT-PCR).

Results: First, we observed that miR130a expression increases by 2.2 fold and HOXA5 mRNA levels decreases by 0.2 fold following treatment with 5% horse serum in MCF10A cells. Next, we noted that miR-130a expression increases and HOXA5 mRNA expression decreases as tumorigenicity increases in MCF10A progression series cell lines. Finally, knocking out miR-130a activity increased HOXA5 mRNA expression in MCF10A cells, demonstrating that HOXA5 is regulated by miR130a in these cells.

Conclusion: Overall our results indicate that miR130a regulates HOXA5 in breast cancer cells and thus may have a role in breast tumor progression. This study will enable us to decipher the role of mir130a in breast tumor progression and metastasis.

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 3950. doi:10.1158/1538-7445.AM2011-3950

MEOX2 regulates nuclear factor-kappaB activity in vascular endothelial cells through interactions with p65 and IkappaBbeta

AIMS

Tumours secrete proangiogenic factors to induce the ingrowth of blood vessels, the end targets of which are vascular endothelial cells (ECs). The MEOX2 homeoprotein inhibits nuclear factor-kappaB (NF-kappaB) signalling and EC activation in response to serum and proangiogenic factors. We hypothesize that MEOX2 interacts with components of this pathway in vascular ECs to modulate NF-kappaB activity and EC activation and that these interactions depend upon specific domains within the MEOX2 protein.

METHODS AND RESULTS

To test our hypothesis, we transduced ECs with MEOX2 expression constructs. MEOX2 protein localized to the nuclear fraction, as did IkappaBbeta and p65. By co-immunoprecipitation, MEOX2 bound to both p65 and IkappaBbeta. Immunofluorescence demonstrated that MEOX2 colocalizes in the nucleus with both p65 and IkappaBbeta and that this colocalization requires the MEOX2 homeodomain and N-terminal domain. Finally, promoter assays revealed that MEOX2 expression has a biphasic effect on NF-kappaB-dependent promoters. At low levels, MEOX2 stimulates NF-kappaB activity, whereas at high levels, it represses, effects that also depend upon the homeodomain and the N-terminal domain.

CONCLUSION

Our results represent the first report of an interaction between a homeobox protein and IkappaBbeta and suggest that MEOX2 modulates the activity of the RelA complex through direct interaction with its components. These observations implicate MEOX2 as a potentially important regulatory gene inhibiting not only the angiogenic response of ECs to proangiogenic factors, but also their response to chronic inflammatory stimulation that normally activates NF-kappaB, suggesting MEOX2 as a possible molecular target for the therapy of angiogenesis-dependent diseases such as cancer.

The homeobox gene GAX activates p21WAF1/CIP1 expression in vascular endothelial cells through direct interaction with upstream AT-rich sequences

Tumors secrete pro-angiogenic factors to induce the ingrowth of blood vessels from the surrounding stroma, the end targets of which are vascular endothelial cells (ECs). The homeobox gene GAX inhibits angiogenesis and induces p21(WAF1/CIP1) expression in vascular ECs. To elucidate the mechanism through which GAX activates p21(WAF1/CIP1) expression, we constructed GAX cDNAs with deletions of the N-terminal domain, the homeodomain, or the C-terminal domain and then assessed these constructs for their ability to activate p21(WAF1/CIP1). There was an absolute requirement for the homeodomain, whereas deleting the C-terminal domain decreased but did not abolish transactivation of the p21(WAF1/CIP1) promoter by GAX. Deleting the N-terminal domain did abolish transactivation. Next, we performed chromatin immunoprecipitation and found, approximately 15 kb upstream of the p21(WAF1/CIP1) ATG codon, an ATTA-containing GAX-binding site (designated A6) with a sequence similar to that of other homeodomain-binding sites. GAX was able to bind to A6 in a homeodomain-dependent manner and thereby activate the expression of a reporter gene coupled to this sequence, and this activation was abolished by mutating specific residues in this sequence. On the basis of the sequence of A6, we were then able to locate other ATTA-containing sequences that also bound GAX and activated transcription in reporter constructs. Finally, we found that the ability of these GAX deletions to induce G(0)/G(1) arrest correlates with their ability to transactivate the p21(WAF1/CIP1) promoter. We conclude that GAX activates p21(WAF1/CIP1) through multiple upstream AT-rich sequences. Given the multiple biological activities of GAX in regulating EC function, identification of a putative GAX-binding site will allow the study of how GAX activates or represses other downstream targets to inhibit angiogenesis.

The homeobox gene Gax inhibits angiogenesis through inhibition of nuclear factor-kappaB-dependent endothelial cell gene expression

The growth and metastasis of tumors are heavily dependent on angiogenesis, but much of the transcriptional regulation of vascular endothelial cell gene expression responsible for angiogenesis remains to be elucidated. The homeobox gene Gax is expressed in vascular endothelial cells and inhibits proliferation and tube formation in vitro. We hypothesized that Gax is a negative transcriptional regulator of the endothelial cell angiogenic phenotype and studied its regulation and activity in vascular endothelial cells. Several proangiogenic factors caused a rapid down-regulation of Gax mRNA in human vascular endothelial cells, as did conditioned media from breast cancer cell lines. In addition, Gax expression using a replication-deficient adenoviral vector inhibited human umbilical vein endothelial cell migration toward proangiogenic factors in vitro and inhibited angiogenesis in vivo in Matrigel plugs. To identify putative downstream targets of Gax, we examined changes in global gene expression in endothelial cells due to Gax activity. Gax expression resulted in changes in global gene expression consistent with a quiescent, nonangiogenic phenotype, with increased expression of cyclin kinase inhibitors and decreased expression of genes implicated in endothelial cell activation and angiogenesis. Further analysis revealed that Gax down-regulated numerous nuclear factor-kappaB (NF-kappaB) target genes and decreased the binding of NF-kappaB to its target sequence in electrophoretic mobility shift assays. To our knowledge, Gax is the first homeobox gene described that inhibits NF-kappaB activity in vascular endothelial cells. Because NF-kappaB has been implicated in endothelial cell activation and angiogenesis, the down-regulation of NF-kappaB-dependent genes by Gax suggests one potential mechanism by which Gax inhibits the angiogenic phenotype.

Detection of B-RAF and N-RAS mutations in human melanoma

BACKGROUND

It is now known that activating point mutations in components of the mitogen-activated protein kinase pathway commonly occur in melanoma. We previously described a method to detect point mutations in heterogenous tissues containing both wild-type and mutant B-RAF and N-RAS genes by using site-directed mutagenesis to introduce new restrictions sites in the cDNA sequence when the specific point mutations are present. We modified this technique to improve sensitivity and used it to determine the incidence of B-RAF and N-RAS mutations in human melanoma.

STUDY DESIGN

We screened 115 melanoma samples for the most common B-RAF and N-RAS mutations found in melanoma using a site-directed mutagenesis-based detection technique. Southern blotting was used to increase sensitivity of the basic system. We also tested this method of genetic mutation detection in fine-needle aspiration specimens and paraffin-embedded tissues.

RESULTS

Sixty-eight samples (20 of 36 primaries, 18 of 27 regional metastases, 16 of 40 nodal metastases, and 9 of 12 distant metastases) harbored the V599E B-RAF mutation (59%), 17 contained a Q61R N-RAS mutation, and 4 contained a Q61K N-RAS mutation. We were able to detect the V599E mutation in genomic DNA from paraffin-embedded melanoma samples and could routinely detect this mutation in fine-needle aspirations of melanoma tumors. This method of detection was sensitive and specific with no false positives.

CONCLUSIONS

Activating mutations of B-RAF and N-RAS were present in approximately 60% and 18%, respectively, of samples tested. The site-directed mutagenesis system of mutation detection was both sensitive and specific in detecting these mutations and will likely prove very clinically useful in future studies.

Vascular endothelial growth factor C mRNA expression correlates with stage of progression in patients with melanoma

PURPOSE

Vascular endothelial growth factor (VEGF)-C promotes the ingrowth and invasion of lymphatics in many different tumor types, including melanoma. To determine whether expression of VEGF-C correlates with stage of progression, we measured VEGF-C mRNA levels in melanomas representing different stages of progression and from the vertical and horizontal growth-phase of individual primary melanomas.

EXPERIMENTAL DESIGN

Total RNA was extracted from human melanoma specimens taken from operative specimens and subjected to quantitative real-time PCR. VEGF-C levels were determined for 54 melanoma samples, including primary melanomas (n=15), local recurrences (n=6), regional dermal metastases (n=11), nodal metastases (n=12), and distant metastases (n=10). As a surrogate for lymphatic density, we also measured the expression of the lymphatic endothelial marker LYVE-1 and correlated its expression with previously measured VEGF-C levels.

RESULTS

Vertical growth phase melanomas expressed significantly higher levels of VEGF-C than horizontal growth phase melanomas. Nodal metastases expressed the highest level of VEGF-C, followed by regional dermal metastases. Primary and local recurrences expressed a relatively low level of VEGF-C, as did negative lymph nodes and distant metastases. In addition, VEGF-C expression correlated well with LYVE-1 expression (r=0.611; P<0.0001).

CONCLUSIONS

These data suggest that high levels of VEGF-C may be important in regional lymphatic disease in melanoma and that VEGF-C and LYVE-1 levels may identify tumors with a high risk for nodal metastases, for which antilymphangiogenic therapy may be more effective.

Differential expression of vascular endothelial growth factor-A isoforms at different stages of melanoma progression

Vascular endothelial growth factor-A (VEGF-A) is an important mediator of angiogenesis in normal and neoplastic tissues. Total VEGF-A levels have been associated with melanoma progression, but the relative contributions of each isoform is unknown. To determine whether differences in the production of any or all of the major VEGF-A isoforms are related to stage of progression, we compared message levels for the three major isoforms of VEGF in melanoma specimens from different stages of progression.Primary melanomas (N = 18), primary recurrences (N = 5), regional dermal metastases (N = 11), nodal metastases (N = 12), normal lymph nodes (N = 18), and distant metastases (N = 9) were prospectively collected. Samples from the horizontal and vertical growth phases of primary tumors were also collected from five additional patients. Message levels for the three major VEGF-A isoforms were measured using real-time quantitative reverse-transcriptase polymerase chain reaction and normalized to beta-actin mRNA levels. There was a marked increase in the expression of all three VEGF-A isoforms from the vertical growth phase tissue as compared with the horizontal growth phase tissue. Primary tumors, local recurrences, regional dermal metastases, nodal metastases, and distant metastases all produced more VEGF(121) and VEGF(165) than negative nodes. Nodal metastases produced the highest level of these two isoforms, higher even than distant metastases. There was no significant difference in VEGF(189) message among the groups. Melanomas in the vertical growth phase produce more VEGF-A (all isoforms) than in the horizontal growth phase. Nodal metastases produce the highest levels of VEGF(121) and VEGF(165), but not VEGF(189) as compared with other stages of progression. These data suggest that the soluble forms of VEGF-A might be an important factor in melanoma metastasis to regional lymph nodes.

Control of vascular cell differentiation by homeobox transcription factors

Homeobox genes are a family of transcription factors with a highly conserved DNA-binding domain that regulate cell proliferation, differentiation, and migration in many cell types in diverse organisms. These properties are responsible for their critical roles in regulating pattern formation and organogenesis during embryogenesis. The cardiovascular system undergoes extensive remodeling during embryogenesis, and cardiovascular remodeling in the adult is associated with normal physiologic processes such as wound healing and the menstrual cycle, and disease states such as atherosclerosis, tumor-induced angiogenesis, and lymphedema. Aside from their roles in the formation of the embryonic vascular system, homeobox genes recently have been implicated in both physiologic and pathologic processes involving vascular remodeling in the adult, such as arterial restenosis after balloon angioplasty, physiologic and tumor-induced angiogenesis, and lymphangiogenesis. Understanding how homeobox genes regulate the phenotype of smooth muscle and endothelium in the vasculature will improve insight into the molecular mechanisms behind vascular cell differentiation and may suggest therapeutic interventions in human disease.

Inhibition of endothelial cell activation by the homeobox gene Gax

BACKGROUND

cardiovascular system, strongly inhibits growth factor-stimulated phenotypic modulation of vascular smooth muscle cells in vitro and in vivo. The function of Gax in vascular endothelium is unknown, but we hypothesized that it may play a similar role there. We therefore studied Gax expression in vascular endothelial cells and its effects on proliferation and tube formation.

MATERIALS AND METHODS

Gax expression in normal endothelial cells was examined in vitro by Northern blot and reverse transcriptase polymerase chain reaction and in vivo by immunohistochemistry. A replication-deficient adenovirus was then used to express Gax in human umbilical vein endothelial cells (HUVECs). HUVEC proliferation, 3H-thymidine uptake, p21 expression, and tube formation on reconstituted basement membrane were measured at different viral multiplicities of infection.

RESULTS

Gax mRNA was detected in HUVECs by reverse transcriptase polymerase chain reaction and Northern blot analysis and in normal vascular endothelium by immunohistochemistry. Compared with controls transduced with a virus expressing beta-galactosidase, Gax strongly inhibited HUVEC proliferation and mitogen-stimulated 3H-thymidine uptake. p21 expression in HUVECs transduced with Gax was increased up to 5-fold as measured by Northern blot, and p21 promoter activity was activated by 4- to 5-fold. Tube formation on Matrigel was strongly inhibited by Gax expression.

CONCLUSIONS

Gax is expressed in vascular endothelium and strongly inhibits endothelial cell activation in response to growth factors and tube formation in vitro. These observations suggest that Gax inhibits endothelial cell transition to the angiogenic phenotype in response to proangiogenic growth factors and, as a negative regulator of angiogenesis, may represent a target for the antiangiogenic therapy of cancer.

Prolonged treatment with angiostatin reduces metastatic burden during radiation therapy

Ionizing radiation (IR) and concomitant angiostatin (AS) produce greater than additive local antitumor effects. We examined whether prolonged AS treatment added to IR reduces proliferation of lung metastases from LLC primary tumors. Flank tumors were treated with 40 Gy with or without AS (25 mg/kg/day). IR plus a 14-day course of AS improved local tumor control and blocked the increase in lung weights observed in the group receiving IR plus a 2-day course of AS group. Animals treated with prolonged AS exhibited no increase in lung weight and no macrometastases. These findings suggest that long-term treatment with antiangiogenic compounds may be effective in preventing metastases from IR-treated tumors as well as increasing the local antitumor effects of radiotherapy.

Dual induction of the Epo-Egr-TNF-alpha- plasmid in hypoxic human colon adenocarcinoma produces tumor growth delay

Gene therapy is a modality for the treatment of solid tumors that involves the introduction of a suicide gene into the tumor cells. Genetic radiotherapy involves the placement of a radiation-sensitive promoter upstream from a suicide gene. Because of their irregular vasculature some solid tumors are chronically hypoxic and hence are resistant to conventional treatment with chemotherapy and ionizing radiation (IR). The purpose of this study was to demonstrate that regional tumor hypoxia could be exploited to improve local tumor control. The cDNA coding the erythropoietin hypoxia-responsive element (EPO) was placed upstream from the Egr-TNF-alpha construct. WIDR human colon adenocarcinoma cells were injected into the right hind limb of nude mice and treated with Epo-Egr-TNF-alpha plasmid with or without IR. Tumor volumes were measured by calipers and tumor necrosis factor (TNF)-alpha content of the tumor was determined by enzyme-linked immunosorbent assay. Treatment with the combined regimen of Epo-Egr-TNF-alpha plasmid + IR resulted in significant tumor growth delay. Tumor TNF-alpha content was increased by 30 per cent in the combined treatment group compared with each treatment alone. Regional tumor hypoxia can be exploited successfully to induce tumor growth delay, enhance local control, and enhance the therapeutic ratio.

Dual Induction of the Epo-Egr-TNF-α Plasmid in Hypoxic Human Colon Adenocarcinoma Produces Tumor Growth Delay

Gene therapy is a modality for the treatment of solid tumors that involves the introduction of a suicide gene into the tumor cells. Genetic radiotherapy involves the placement of a radiation-sensitive promoter upstream from a suicide gene. Because of their irregular vasculature some solid tumors are chronically hypoxic and hence are resistant to conventional treatment with chemotherapy and ionizing radiation (IR). The purpose of this study was to demonstrate that regional tumor hypoxia could be exploited to improve local tumor control. The cDNA coding the erythropoietin hypoxia-responsive element (EPO) was placed upstream from the Egr-TNF-α construct. WIDR human colon adenocarcinoma cells were injected into the right hind limb of nude mice and treated with Epo-Egr-TNF-α plasmid with or without IR. Tumor volumes were measured by calipers and tumor necrosis factor (TNF)-α content of the tumor was determined by enzyme-linked immunosorbent assay. Treatment with the combined regimen of Epo-Egr-TNF-α plasmid + IR resulted in significant tumor growth delay. Tumor TNF-α content was increased by 30 per cent in the combined treatment group compared with each treatment alone. Regional tumor hypoxia can be exploited successfully to induce tumor growth delay, enhance local control, and enhance the therapeutic ratio.

The role of homeobox genes in vascular remodeling and angiogenesis

Homeodomain-containing transcription factors are critical in the regulation of cell proliferation, differentiation, and migration, and they play an important role in organogenesis and pattern formation during embryogenesis. There is evidence that some of them are oncogenes or tumor suppressors. The cardiovascular system undergoes extensive remodeling during embryogenesis and disease states such as atherosclerosis and tumor-induced angiogenesis, and homeobox genes may play an important role in regulating these processes. Recently, homeobox genes have been detected in both vascular smooth muscle and endothelial cells, and they are implicated in pathological processes such as arterial restenosis after balloon angioplasty and tumor-induced angiogenesis. The cellular function of some of these genes is beginning to be elucidated. Therefore, we briefly review what is currently known about the involvement of homeobox transcription factors in both physiological and pathological vascular remodeling and angiogenesis.

Blockage of the vascular endothelial growth factor stress response increases the antitumor effects of ionizing radiation

The family of vascular endothelial growth factor (VEGF) proteins include potent and specific mitogens for vascular endothelial cells that function in the lation of angiogenesis Inhibition of VEGF-induced angiogenesis either by neutralizing antibodies or dominant-negative soluble receptor, blocks the growth of primary and metastatic experimental tumors Here we report that VEGF expression is induced in Lewis lung carcinomas (LLCs) both in vitro and vivo after exposure to ionizing radiation (IR) and in human tumor cell lines (Seg-1 esophageal adenocarcinoma, SQ20B squamous cell carcinoma, T98 and U87 glioblastomas, and U1 melanoma) in vitro. The biological significance of IR-induced VEGF production is supported by our finding that treatment of tumor-bearing mice (LLC, Seg-1, SQ20B, and U87) with a neutralizing antibody to VEGF-165 before irradiation is associated with a greater than additive antitumor effect. In vitro, the addition of VEGF decreases IR-induced killing of human umbilical vein endothelial cells, and the anti-VEGF treatment potentiates IR-induced lethality of human umbilical vein endothelial cells. Neither recombinant VEGF protein nor neutralizing antibody to VEGF affects the radiosensitivity of tumor cells These findings support a model in which induction of VEGF by IR contributes to the protection of tumor blood vessels from radiation-mediated cytotoxicity and thereby to tumor radioresistance.

Potentiation of the antitumor effect of ionizing radiation by brief concomitant exposures to angiostatin

Angiostatin, a proteolytic fragment of plasminogen, inhibits the growth of primary and metastatic tumors by suppressing angiogenesis. When used in combination with ionizing radiation (IR), angiostatin demonstrates potent antitumor synergism, largely caused by inhibition of the tumor microvasculature. We report here the temporal interaction of angiostatin and IR in Lewis lung carcinoma (LLC) tumors growing in the hind limbs of syngeneic mice. Tumors with an initial mean volume of 510 +/- 151 mm3 were treated with IR alone (20 Gy x 2 doses on days 0 and 1), angiostatin alone (25 mg/kg/day divided twice daily) on days 0 through 13, or a combination of the two as follows: (a) IR plus angiostatin (days 0 through 13); (b) IR plus angiostatin (days 0 and 1); and (c) IR followed by angiostatin beginning on the day after IR completion and given daily thereafter (days 2 through 13). By day 14, tumors in untreated control mice had grown to 6110 +/- 582 mm3, whereas in mice treated with: (a) IR alone, tumors had grown to 2854 +/- 338 mm3 (P < 0.05 compared with untreated controls); and (b) angiostatin alone, tumors had grown to 3666 +/- 453 mm3 (P < 0.05 compared with untreated controls). In combined-treatment groups, in mice treated with: (a) IR plus longer-course angiostatin, tumors reached 2022 +/- 282 mm3 (P = 0.036 compared with IR alone); (b) IR followed by angiostatin, tumors reached 2677 +/- 469 mm3 (P > 0.05 compared with IR alone); and (c) IR plus short-course angiostatin, tumors reached 1032 +/- 78 mm3 (P < 0.001 compared with IR alone). These findings demonstrate that the efficacy of experimental radiation therapy is potentiated by brief concomitant exposure of the tumor vasculature to angiostatin.

Combined effects of angiostatin and ionizing radiation in antitumour therapy

Angiogenesis, the formation of new capillaries from pre-existing vessels, is essential for tumour progression. Angiostatin, a proteolytic fragment of plasminogen that was first isolated from the serum and urine of tumour-bearing mice, inhibits angiogenesis and thereby growth of primary and metastatic tumours. Radiotherapy is important in the treatment of many human cancers, but is often unsuccessful because of tumour cell radiation resistance. Here we combine radiation with angiostatin to target tumour vasculature that is genetically stable and therefore less likely to develop resistance. The results show an antitumour interaction between ionizing radiation and angiostatin for four distinct tumour types, at doses of radiation that are used in radiotherapy. The combination produced no increase in toxicity towards normal tissue. In vitro studies show that radiation and angiostatin have combined cytotoxic effects on endothelial cells, but not tumour cells. In vivo studies show that these agents, in combination, target the tumour vasculature. Our results provide support for combining ionizing radiation with angiostatin to improve tumour eradication without increasing deleterious effects.

p21CIP1-mediated inhibition of cell proliferation by overexpression of the gax homeodomain gene

gax, a diverged homeobox gene expressed in vascular smooth muscle cells (VSMCs), is down-regulated in vitro by mitogen stimulation and in vivo in response to vascular injury that leads to cellular proliferation. Recombinant Gax protein microinjected into VSMCs and fibroblasts inhibited the mitogen-induced entry into S-phase when introduced either during quiescence or early stages of G1. Overexpression of gax with a replication-defective adenovirus vector resulted in G0/G1 cell cycle arrest of VSMCs and fibroblasts. The gax-induced growth inhibition correlated with a p53-independent up-regulation of the cyclin-dependent kinase inhibitor p21. Gax overexpression also led to an association of p21 with cdk2 complexes and a decrease in cdk2 activity. Fibroblasts deficient in p21 were not susceptible to a reduction in cdk2 activity or growth inhibition by gax overexpression. Localized delivery of the virus to denuded rat carotid arteries significantly reduced neointima formation and luminal narrowing. These data indicate that gax overexpression can inhibit cell proliferation in a p21-dependent manner and can modulate injury-induced changes in vessel wall morphology that result from excessive cellular proliferation.