Matthew J. Grimshaw

Endothelin-2 is a macrophage chemoattractant: implications for macrophage distribution in tumors

Endothelins (ET‐1, ET‐2 and ET‐3) are 21‐amino acid vasoactive peptides that bind to G‐protein‐linked transmembrane receptors, ET‐RA and ET‐RB. As well as modulating vasoconstriction, endothelins regulate growth in several cell types and may also affect differentiation, inflammation and angiogenesis. Both macrophages and endothelins are found in areas of hypoxia in solid tumors and ET‐2 expression may be modulated by hypoxia in some tumors. As the peptide structure of mature endothelins is similar to that of CXC chemokines, we asked if endothelins contribute to control of macrophage distribution in tumors. We found that ET‐2 is a chemoattractant for macrophages and THP‐1 monocytic cells, but not for freshly isolated monocytes. The chemotactic response to ET‐2 shows a typical bell‐shaped response curve. Experiments with endothelin receptor antagonists showed that migration to ET‐2 is mediated via the ET‐RB receptor. Moreover, monocytes do not express ET‐RB. Chemotaxis towards ET‐2 is via the MAPK pathway: p44 and p42 are phosphorylated when THP‐1 cells are stimulated with ET‐2, and the MAPKK inhibitor PD98059 stops chemotaxis. As with ‘classical’ chemokines, migration toET‐2 is also inhibited by hypoxia and by pertussis toxin. As well as its chemotactic properties, ET‐2 leads to activation of macrophages. In human breast tumors that express ET‐2, endothelins and ET‐RB expressing macrophages often co‐localized. While shorter than ‘classical’ chemokines, ET‐2 shares a similar peptide sequence with chemokines and may signal via a similar receptor and MAPK‐mediated pathway. Furthermore, ET‐2 expression by tumors may modulate the behavior of macrophages such that activated cells accumulate in areas of hypoxia.

Expression and regulation of tumor necrosis factor alpha in normal and malignant ovarian epithelium.

Epidemiologic studies implicate inflammatory stimuli in the development of ovarian cancer. The proinflammatory cytokine tumor necrosis factor α (TNF-α) and both its receptors (TNFRI and TNFRII) are expressed in biopsies of this malignancy. Here, we tested the hypothesis that TNF-α is a regulator of the proinflammatory microenvironment of ovarian cancer. A cancer profiling array showed higher expression of TNF-α in ovarian tumors compared with normal ovarian tissue, and cultured ovarian cancer cells expressed up to 1,000 times more TNF-α mRNA than cultured normal ovarian surface epithelial cells; TNF-α protein was only detected in the supernatant of tumor cell cultures. Treatment with TNF-α induced TNF-α mRNA via TNFRI in both malignant and normal cells with evidence for enhanced TNF-α mRNA stability in tumor cells. TNF-α induced TNF-α protein in an autocrine fashion in tumor but not in normal ovarian surface epithelial cells. The TNF-α neutralizing antibody infliximab reduced the constitutive levels of TNF-α mRNA in tumor cell lines capable of autocrine TNF-α production. Apart from TNF-α mRNA expression, several other proinflammatory cytokines were constitutively expressed in malignant and normal ovarian surface epithelial cells, including interleukin (IL)-1α, IL-6, CCL2, CXCL8, and M-CSF. TNF-α treatment further induced these cytokines with de novo transcription of IL-6 mRNA contrasting with the increased stability of CCL2 mRNA. RNA interference directed against TNF-α was highly effective in abolishing constitutive IL-6 production by ovarian tumor cells. In summary, we show that TNF-α is differentially regulated in ovarian cancer cells compared with untransformed cells and modulates production of several cytokines that may promote ovarian tumorigenesis. Infliximab treatment may have a role in suppressing the TNF-α-driven inflammatory response associated with ovarian cancer. [Mol Cancer Ther 2006;5(2):382-90]

In vivo Loss of Expression of Argininosuccinate Synthetase in Malignant Pleural Mesothelioma Is a Biomarker for Susceptibility to Arginine Depletion

Purpose: Malignant pleural mesothelioma (MPM) is an increasing health burden on many societies worldwide and, being generally resistant to conventional treatment, has a poor prognosis with a median survival of <1 year. Novel therapies based on the biology of this tumor seek to activate a proapoptotic cellular pathway. In this study, we investigated the expression and biological significance of argininosuccinate synthetase (AS), a rate-limiting enzyme in arginine production. Experimental Design: Initially, we documented down-regulation of AS mRNA in three of seven MPM cell lines and absence of AS protein in four of seven MPM cell lines. We confirmed that the 9q34 locus, the site of the AS gene, was intact using a 1-Mb comparative genomic hybridization array; however, there was aberrant promoter CpG methylation in cell lines lacking AS expression, consistent with epigenetic regulation of transcription. To investigate the use of AS negativity as a therapeutic target, arginine was removed from the culture medium of the MPM cell lines. Results: In keeping with the cell line data, 63% (52 of 82) of patients had tumors displaying reduced or absent AS protein, as assessed using a tissue microarray. Cell viability declined markedly in the AS-negative cell lines 2591 and MSTO but not in the AS-positive cell line, 28. This response was apparent by day 4 and maintained by day 9 in vitro. Arginine depletion induced BAX conformation change and mitochondrial inner membrane depolarization selectively in AS-negative MPM cells. Conclusions: In summary, we have identified AS negativity as a frequent event in MPM in vivo, leading to susceptibility to cytotoxicity following restriction of arginine. A phase II clinical trial is planned to evaluate the role of arginine depletion in patients with AS-negative MPM.

A role for endothelin-2 and its receptors in breast tumor cell invasion.

We have studied the role of endothelins (ET-1, ET-2 and ET-3) and ET receptors (ET-RA and ET-RB) in the invasive capacity of breast tumor cells, which express ET-1 and ET-2 as well as ET-RA and ET-RB. Of five human breast tumor cell lines tested, all expressed mRNAs for ET-1, ET-2, and ET-RB. ET-RA mRNA was expressed by four of five tumor cell lines. Breast tumor cells migrated toward ET-1 and ET-2 but not toward ET-3. Chemotaxis involved signaling via both receptors, and a pertussis toxin-sensitive p42/p44 mitogen-activated protein kinase (MAPK)-mediated pathway that could be inhibited by MAPK kinase (MEK)1/2 antagonists. Chemotaxis toward ETs did not involve p38 or stress-activated protein kinase (SAPK)/Jun N-terminal kinase (JNK) and was not inhibited by hypoxia. Incubation of tumor cells with ET-2 also increased chemotaxis toward the chemokines CXCL12 and CCL21. As well as inducing chemotaxis of tumor cells, ET-1 and ET-2 increased tumor cell invasion through Matrigel. Furthermore, stimulation of macrophage/tumor cell cocultures with ETs led to increased matrix metalloproteinase (MMP)-2 and -9 production by macrophages and a marked increase in invasion of tumor cells. Antagonism of either ET-RA or ET-RB decreased the invasion seen in ET-stimulated cocultures, as did a broad-spectrum MMP inhibitor. Immunohistochemical staining of human breast tumor sections showed increased ET and ET receptor protein expression by tumor cells in invasive ductal carcinoma compared with normal breast tissue or ductal carcinoma in situ. Furthermore, tumor cell ET and receptor expression was stronger at the invasive margin of invasive ductal carcinomas, in the lymphovascular space, and in lymph node metastases. ET expression often colocalized with ET-RB expression in all neoplastic tissue indicating a possible autocrine action of ETs. We suggest that expression of ETs and their receptors by human breast tumors, particularly in conjunction with a high macrophage infiltrate, may have a role in the progression of breast cancer and the invasion of tumor cells.

Endothelins and hypoxia-inducible factor in cancer

The endothelin system is a family of three similar small peptides, two G-protein-coupled receptors and two proteinases. Endothelins have several physiological roles, notably in embryonic differentiation and vascular homeostasis. Numerous types of tumour express endothelins and their regulation is often aberrant when compared with the normal tissue from which the tumour arose. However, endothelin expression is tumour-type specific, and in some instances, expression of individual members of the endothelin system will be upregulated, while in other tumour types, they may be downregulated. Endothelins have numerous potential roles in tumours including modulating angiogenesis, inducing mitogenesis and invasion of tumour cells, and protecting cells from apoptosis. Expression of endothelins is controlled by the tumour microenvironment, whilst the endothelins themselves modify that environment; a case in point is that hypoxia stimulates endothelin expression via hypoxia-inducible factor (HIF)-1, while endothelins stabilise HIF-1 leading to expression of, for instance, vascular endothelial growth factor. This review highlights the potential roles of endothelins in various cancers and describes the pre-clinical and clinical progress that has been made in several tumour types - notably prostate, ovary, melanoma and breast cancer. The interactions between the endothelin network and HIF-1 are highlighted.

Endothelins Induce CCR7 Expression by Breast Tumor Cells via Endothelin Receptor A and Hypoxia-Inducible Factor-1

Endothelin expression is increased in breast tumors and is associated with invasion and metastasis, whereas CCR7 expression by breast tumor cells may have a role in the organ specificity of breast cancer spread. In this article, we have analyzed whether endothelins influence breast tumor cell expression of the chemokine receptor CCR7. Stimulation of human breast tumor cell lines with endothelins increased cell surface expression of CCR7 via endothelin receptor A. The iron chelators desferrioxamine and cobalt chloride, which induce hypoxia-inducible factor (HIF)-mediated transcription, also increased CCR7 expression; transfection of a dominant-negative version of the HIF regulatory subunit, HIF-1alpha, into MCF-7 cells abolished CCR7 induction by endothelins, indicating that increased expression is due to HIF-1 stabilization. Endothelin stimulation promoted invasion toward the CCR7 ligands CCL19 and CCL21. Endothelin-mediated chemokine-independent invasion itself is dependent on CCR7 activity and could be abolished using a CCR7-neutralizing monoclonal antibody. In human breast carcinomas, mRNA expression of endothelins correlated with the level of CCR7 expression, both of which were associated with the presence of lymph node metastases. Expression of the CCR7 ligands CCL19 and CCL21 was also higher in breast cancer patients with lymph node involvement compared with those without, but expression of these chemokines did not correlate with endothelin expression. These data show that CCR7 may be regulated by the breast tumor microenvironment and further support the use of endothelin receptor antagonists in the treatment of invasive and metastatic breast cancer.

Sialyl-Lewisx on P-Selectin Glycoprotein Ligand-1 Is Regulated during Differentiation and Maturation of Dendritic Cells: A Mechanism Involving the Glycosyltransferases C2GnT1 and ST3Gal I

To fulfil their function as APCs, dendritic cells (DC) and their precursors need to travel from blood to the peripheral tissues and, upon activation, migrate from tissues to draining lymph nodes. Because O-glycans play a role in T cell trafficking, we investigated the O-glycosylation profile of human monocyte-derived DC. Sialyl-Lewisx (sLex), a glycan involved in extravasation via selectin binding, was found to be expressed exclusively on P-selectin glycoprotein ligand-1 in monocytes and immature DC. However, sLex was lost from mature DC even though these cells retained expression of P-selectin glycoprotein ligand-1. Maturation of DC led to a rapid change in the expression of glycosyltransferases involved in O-linked glycosylation. A down-regulation of C2GnT1 mRNA and enzymatic activity was observed with a concurrent up-regulation of ST3Gal I and ST6GalNAc II mRNA resulting in a loss of the core 2 structures required for sLex expression as a P-selectin ligand. Interestingly, the early regulation of these glycosyltransferases was mediated by PGE2, which is known to be required for human DC migration. The pattern of O-glycosylation seen in mature cells was very similar to that expressed by naive T cells, which home to lymph nodes. Our data show that the regulation of O-glycosylation controls sLex expression, and also suggest that O-glycans may have a function in DC migration.

Aberrant regulation of argininosuccinate synthetase by TNF‐α in human epithelial ovarian cancer

The pro‐inflammatory cytokine, tumour necrosis factor‐α, TNF‐α, is dysregulated in malignant compared with normal ovarian surface epithelium (OSE). Several epidemiological studies have associated inflammation with ovarian tumorigenesis, with TNF‐α playing a key role in modulating invasion, angiogenesis and metastasis. Here, we show that TNF‐α also induces expression of arate‐limiting enzyme in arginine synthesis, argininosuccinate synthetase (AS), thereby linking inflammation with several arginine‐dependent metabolic pathways, implicated in accelerated carcinogenesis and tumour progression. Having identified AS mRNA induction in TNF‐α‐treated IGROV‐1 ovarian cancer cells, using RNA‐arbitrarily primed‐PCR, we then observed differential regulation of AS mRNA and protein in malignant, compared with normal, OSE cells. A cDNA cancer profiling array with matched normal ovarian and ovarian tumour samples revealed increased expression of AS mRNA in the latter. Moreover, AS protein co‐localised with TNF‐α in ovarian cancer cells, with significantly higher levels of AS in malignant compared with normal ovarian tissue. Increased co‐expression of AS and TNF‐α mRNA was also observed in 2 other epithelial tumours, non‐small cell lung and stomach cancer, compared with normal corresponding tissues. In summary, high levels of AS expression, which may be required for several arginine‐dependent processes in cancer, including the production of nitric oxide, proline, pyrimidines and polyamines, is regulated by TNF‐α and may provide an important molecular pathway linking inflammation and metabolism to ovarian tumorigenesis.

Stromal endothelin B receptor-deficiency inhibits breast cancer growth and metastasis

The endothelin (ET) axis, often deregulated in cancers, is a promising target for anticancer strategies. Whereas previous investigations have focused mostly on ET action in malignant cells, we chose a model allowing separate assessment of the effects of ETs and their receptors ETAR and ETBR in the tumor cells and the stromal compartment, which is increasingly recognized as a key player in cancer progression. In homozygous spotting lethal rats (sl/sl), a model of constitutive ETBR deficiency, we showed significant reduction of growth and metastasis of MAT B III rat mammary adenocarcinoma cells overexpressing ETAR and ET-1 but negative for ETBR. Lack of stromal ETBR expression did not influence angiogenesis. However, it was correlated with diminished infiltration by tumor-associated macrophages and with reduced production of tumor necrosis factor-α, both known as powerful promoters of tumor progression. These effects were almost completely abolished in transgenic sl/sl rats, wherein ETBR function is restored by expression of an intact ETBR transgene. This shows that tumor growth and metastasis are critically dependent on ETBR function in cells of the microenvironment and suggests that successful ETR antagonist therapy should also target the stromal component of ET signaling.[Mol Cancer Ther 2009;8(8):2452–60]

Genetically modified macrophages expressing hypoxia regulated cytochrome P450 and P450 reductase for the treatment of cancer

This study describes a combined gene and cell therapy based on the genetic modification of primary human macrophages, as a treatment for cancer. Here, we have utilised the tumour-infiltrating properties of macrophages as vehicles to deliver a gene encoding a prodrug-activating enzyme such as human cytochrome P450 2B6 (CYP2B6) inside tumours followed by killing the tumour cells with the prodrug cyclophosphamide (CPA). Macrophages were transduced with an adenoviral vector that expresses human cytochrome CYP2B6 via a synthetic hypoxia responsive promoter (OBHRE) and with human P450 reductase (P450R), via the CMV promoter. In the presence of CPA, these genetically modified macrophages showed increased cytotoxicity against various tumour cell lines compared to untransduced macrophages or macrophages transduced with CYP2B6 alone. In human ovarian carcinoma xenograft models, the median survival of mice treated with genetically modified macrophages plus CPA increased up to two-fold compared to the survival of mice treated with untransduced macrophages and CPA. Genetically modified autologous macrophages may be a feasible therapeutic option for the treatment of some solid tumours, such as ovarian cancer.