Neuroprotective effect of Myo/Nog cells in the stressed retina

Myo/Nog cells are essential for eye development in the chick embryo and respond to injury in adult tissues. These cells express mRNA for the skeletal muscle specific transcription factor MyoD, the bone morphogenetic protein (BMP) inhibitor Noggin and the cell surface protein recognized by the G8 monoclonal antibody (mAb). In this study, we determined that Myo/Nog cells are present in low numbers in the retina of the mouse eye. G8-positive Myo/Nog cells were distinguished from neuronal, Müller and microglial cells that were identified with antibodies to calretinin, Chx10, glial fibrillary acidic protein and ionized calcium binding adaptor molecule 1, respectively. In the neonatal retina, the number of Myo/Nog cells increased in parallel with cell death induced by transient exposure to hyperoxia. In this model of retinopathy of prematurity, depletion of Myo/Nog cells by intravitreal injection of the G8 mAb and complement increased cell death. These findings demonstrate that Myo/Nog cells are a distinct population of cells, not previously described in the retina, which increases in response to retinal damage and mitigate hypoxia-induced cell death.

Abstract 5223: A novel pro-angiogenic role for IDO1 in inflammatory tumor promotion

Chronic inflammation is a major contributing factor in cancer, but, due to the complex multifactorial nature of inflammation, there remains limited understanding of specific pathogenic determinants that might be targeted therapeutically. The tryptophan-catabolizing enzyme IDO1 (indoleamine 2,3-dioxygenase) has emerged as an intriguing, pro-tumorigenic regulator of immune function in this regard. Because IDO1 can be elevated in chronic inflammatory states even prior to the initiation of cancer, it may represent one of the earliest determinants directing the immune response towards supporting rather than eliminating tumors. Genetic studies in mice have clearly established the tumor-promoting role of IDO1, but what this actually entails remains uncertain. Here we present evidence to support the novel hypothesis that a principle means by which IDO1 facilitates tumorigenesis is by mitigating immune-based angiostasis.

Tumor angiogenesis is characterized by excessive and disorganized blood vessel growth much like that induced by ischemia where immune cells have been shown to be important for limiting neovascularization. Likewise, an anti-angiogenic response may be a factor in tumor immunity. In particular, IFNγ, an inflammatory cytokine, long recognized as a major inducer of IDO1, has been shown to exert angiostatic activity against developing tumors, which was implicated in these studies as the primary mechanism for both CD4 and CD8 T cell dependent tumor rejection. Our recently reported finding that the loss of IDO1 resulted in diminished pulmonary vascularization (Smith, Cancer Discovery 2012) suggested the possibility that IDO1 might be working at cross purposes to limit IFNγ-mediated angiostasis. In this same study IDO1 loss was also associated with the attenuated induction of the pro-angiogenic inflammatory cytokine IL6.

To directly investigate the role of IDO1 in pathologic angiogenesis, we have utilized an oxygen-induced retinopathy (OIR) model. As predicted, neovascularization in the OIR model was significantly reduced in Ido1-/- mice. Consistent with the hypothesis that IDO1 supports neovascularization primarily by counteracting the angiostatic activity of IFNγ, neovascularization in double knockout Ifng-/- Ido1-/- mice reverted back to wild type levels. Il6-/- mice, on the other hand, exhibited reduced neovascularization which was likewise reversed by the concurrent elimination of IFNγ. In conjunction with these angiogenesis studies, we have also examined pulmonary metastasis development by 4T1 breast carcinoma isografts. Loss of either IDO1 or IL6 resulted in resistance to pulmonary metastases that, in both cases, was abrogated by the concurrent loss of IFNγ. Taken together, these findings have led us to propose a conceptually novel working hypothesis that, in the context of an inflammatory cytokine milieu, IDO1 plays a key role in supporting tumor angiogenesis.

Citation Format: Arpita Mondal, James B. DuHadaway, Erika Sutanto-Ward, Courtney Smith, George C. Prendergast, Arturo Bravo-Nuevo, Alexander J. Muller. A novel pro-angiogenic role for IDO1 in inflammatory tumor promotion. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5223. doi:10.1158/1538-7445.AM2015-5223

Classification of current anticancer immunotherapies

During the past decades, anticancer immunotherapy has evolved from a promising therapeutic option to a robust clinical reality. Many immunotherapeutic regimens are now approved by the US Food and Drug Administration and the European Medicines Agency for use in cancer patients, and many others are being investigated as standalone therapeutic interventions or combined with conventional treatments in clinical studies. Immunotherapies may be subdivided into "passive" and "active" based on their ability to engage the host immune system against cancer. Since the anticancer activity of most passive immunotherapeutics (including tumor-targeting monoclonal antibodies) also relies on the host immune system, this classification does not properly reflect the complexity of the drug-host-tumor interaction. Alternatively, anticancer immunotherapeutics can be classified according to their antigen specificity. While some immunotherapies specifically target one (or a few) defined tumor-associated antigen(s), others operate in a relatively non-specific manner and boost natural or therapy-elicited anticancer immune responses of unknown and often broad specificity. Here, we propose a critical, integrated classification of anticancer immunotherapies and discuss the clinical relevance of these approaches.

IDO2 in Immunomodulation and Autoimmune Disease

IDO2 is a relative of IDO1 implicated in tryptophan catabolism and immune modulation but its specific contributions to normal physiology and pathophysiology are not known. Evolutionary genetic studies suggest that IDO2 has a unique function ancestral to IDO1. In mice, IDO2 gene deletion does not appreciably affect embryonic development or hematopoiesis, but it leads to defects in allergic or autoimmune responses and in the ability of IDO1 to influence the generation of T regulatory cells. Gene expression studies indicate that IDO2 is a basally and more narrowly expressed gene than IDO1 and that IDO2 is uniquely regulated by AhR, which serves as a physiological receptor for the tryptophan catabolite kynurenine. In the established KRN transgenic mouse model of rheumatoid arthritis, where IDO1 gene deletion has no effect, IDO2 deletion selectively blunts responses to autoantigen but has no effect on responses to neoantigen challenge. In human populations, natural variations in IDO2 gene sequence that attenuate enzymatic activity have been reported to influence brain cancer control and adaptive immune responses to the IDO2 protein itself, consistent with the concept that IDO2 is involved in shaping immune tolerance in human beings. Biochemical and pharmacological studies provide further evidence of differences in IDO2 enzymology and function relative to IDO1. We suggest that IDO2 may act in a distinct manner from IDO1 as a set-point for tolerance to "altered-self" antigens along the self-non-self continuum where immune challenges from cancer and autoimmunity may arise.

Bin1 Interacts with and Restrains the DNA End-Binding Protein Complex Ku

The Bin1 gene encodes a BAR adapter protein that suppresses cancer by poorly defined mechanisms. In an effort to gain insights, we identified cellular proteins that form biochemical complexes with Bin1 protein. Here we report that Bin1 physically binds to Ku, a DNA end-binding protein that functions in telomere maintenance, apoptosis, and DNA repair. Both Ku70 and Ku80 were purified from human and murine cell extracts using the Bin1 BAR domain as an affinity matrix. A BAR domain mutation that destroys antioncogenic activity completely abolished Ku binding, supporting functional relevance. To further evaluate meaning, we investigated interactions between the Bin1 homolog hob1+ and the Ku homologs pku70+ and pku80+ in fission yeast. Notably, deleting pku70+ or pku80+ relieved the survival defect displayed by hob1delta cells after treatment with the DNA damaging agent phleomycin, suggesting that hob1+ may restrain Ku. Consistent with this notion, telomere length was altered in hob1delta cells. The potential relevance of Bin1-Ku interaction to cancer are discussed in light of these findings.

Bin1 Homolog Hob1 Supports a Rad6-Set1 Pathway of Transcriptional Repression in Fission Yeast

Bin1 encodes a mammalian BAR adapter protein with a nuclear anti-oncogenic function that is poorly understood. To gain functional insights, we investigated the role of the fission yeast homolog hob1+ in growth arrest and survival of cells treated with phleomycin, a DNA damaging drug. Unlike wild-type cells, hob1delta cells treated with phleomycin displayed a defective growth arrest phenotype, elongating abnormally without septation or cytokinesis and eventually losing viability. Genetic investigations suggested that the survival defect in hob1delta cells reflected a deficiency in a Rad6 pathway involving histone methyltransferase Set1 that leads to transcriptional repression. In support of this connection, transcription of telomeric and centromeric heterochromatin that is normally silenced by a Rad6/Set1-dependent mechanism was aberrantly activated in hob1delta cells. Taken together, these findings suggest that hob1+ may support a mechanism of transcriptional repression possibly relevant to the role of Bin1 in cancer suppression.

Genetic response to DNA damage: Proapoptotic targets of RhoB include modules for p53 response and susceptibility to alzheimer’s disease

Knockout mouse studies indicate that the small GTPase RhoB is critical for apoptosis triggered by genotoxic stress in transformed mouse cells. However, the mechanisms used by RhoB to sensitize cells to cell death are obscure. To gain insight into this question, we compared the genetic response of cells with different rhoB genotypes to the DNA damaging anticancer drug doxorubicin (DOX). The microarray hybridization strategy focused on events occurring by 6 hr of DOX treatment, preceding the execution phase of RhoB-dependent apoptosis by 12-16 hr. Genes controlling cytoskeletal organization, adhesion, transcription, trafficking, apoptosis, and protein turnover were represented prominently. Gene clustering revealed a module of p53 target genes, suggesting that RhoB may modify the p53 response, and a module for susceptibility to Alzheimer's disease, suggesting a link between RhoB and age-associated dementia. The findings of this study suggest mechanisms by which RhoB may act to elevate the sensitivity of cells to apoptosis following genotoxic stress.

Abstract 3665: IDO1 is an integrative determinant of tumor-promoting, pathogenic inflammation

The tryptophan-catabolizing enzyme IDO1 (indoleamine 2,3-dioxygenase 1) has been implicated as a mediator of immune tolerance in the reproductively essential process of shielding the ‘foreign’ fetus from maternal immunity. By extrapolation, we and others hypothesized that tumors might elevate IDO1 under selective pressure by the immune system. Our finding that loss of the Bin1 tumor suppressor gene potentiates the superinduction of IDO1 provided the first discreet example of a molecular pathway through which this immune escape process can occur. However, the involvement of IDO1 in tumorigenesis has turned out to be far more complex. Tumors that inherently lack IDO1 expression have been demonstrated to induce IDO1 expression in antigen presenting cells of the host, providing an alternative mechanism for immune escape. We have also found from studies in the classical DMBA/TPA skin carcinogenesis model that IDO1 can be induced by the inflammatory tumor-promoting process itself independent of the presence of an initiated tumor. Thus, IDO1 can be a factor in tumor promotion throughout the entire immunoediting process. With the rapid pace of development of IDO inhibitors, which are currently being evaluated in clinical trials, we are interested in determining whether mouse tumor models might provide additional insight into the optimal therapeutic application of these agents based on the underlying biology. In current studies, we have found that IDO1-nullizygous mice are resistant to both KRAS-induced lung adenocarcinomas and pulmonary breast carcinoma metastases. Micro-computed tomographic imaging confirmed that lung tumor burden was correspondingly lower in IDO1-nullizygous mice. Surprisingly, this analysis also revealed a significantly reduced pulmonary blood vessel density in IDO1-nullizygous mice. Elevation of the inflammatory cytokine IL6 (interleukin 6) was greatly attenuated in conjunction with the loss of IDO1, consistent with in vitro evidence that IDO1 potentiates IL6 production. MDSCs (myeloid derived suppressor cells) from IDO1-nullizygous animals exhibited reduced T cell suppressive activity that could be rescued by IL6. IL6 could likewise reverse the pulmonary metastasis resistance exhibited by IDO1-nullizygous mice. Together, our findings provide support for the emerging concept of IDO1 as a prototypical, integrative immune modifier that bridges inflammation, vascularization and immune escape to foster the establishment of a pathogenic, tumor-promoting environment.

Citation Format: Alexander J. Muller, Courtney Smith, Mee Young Chang, James DuHadaway, Arpita Mondal, Hollie Flick, Katherine Parker, Daniel Beury, Suzanne Ostrand-Rosenberg, George C. Prendergast. IDO1 is an integrative determinant of tumor-promoting, pathogenic inflammation. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3665. doi:10.1158/1538-7445.AM2014-3665

Aryl hydrocarbon receptor control of a disease tolerance defence pathway

Disease tolerance is the ability of the host to reduce the effect of infection on host fitness. Analysis of disease tolerance pathways could provide new approaches for treating infections and other inflammatory diseases. Typically, an initial exposure to bacterial lipopolysaccharide (LPS) induces a state of refractoriness to further LPS challenge (endotoxin tolerance). We found that a first exposure of mice to LPS activated the ligand-operated transcription factor aryl hydrocarbon receptor (AhR) and the hepatic enzyme tryptophan 2,3-dioxygenase, which provided an activating ligand to the former, to downregulate early inflammatory gene expression. However, on LPS rechallenge, AhR engaged in long-term regulation of systemic inflammation only in the presence of indoleamine 2,3-dioxygenase 1 (IDO1). AhR-complex-associated Src kinase activity promoted IDO1 phosphorylation and signalling ability. The resulting endotoxin-tolerant state was found to protect mice against immunopathology in Gram-negative and Gram-positive infections, pointing to a role for AhR in contributing to host fitness.

Specific in situ detection of murine indoleamine 2, 3-dioxygenase

Indoleamine 2,3-dioxygenase-1 (IDO1) catabolizes the essential amino acid tryptophan, acting as a modifier of inflammation and immune tolerance. Recent work has implicated IDO1 in many human diseases, including in cancer, chronic infection, autoimmune disorders, and neurodegenerative disease, stimulating a major surge in preclinical and clinical studies of its pathogenic functions. In the mouse, IDO1 is expressed widely but in situ detection of the enzyme in murine tissues has been unreliable due to the lack of specific antibodies that do not also react with tissues from animals that are genetically deficient in IDO1. Such probes are crucial to establish cellular mechanisms since IDO1 appears to act in different cell types depending on disease context, but reliable probes have been elusive in the field. In this report, we address this issue with the development of IDO1 monoclonal antibody 4B7 which specifically recognizes the murine enzyme in tissue sections, offering a reliable tool for immunohistology in preclinical disease models.

RhoB controls coordination of adult angiogenesis and lymphangiogenesis following injury by regulating VEZF1-mediated transcription

Mechanisms governing the distinct temporal dynamics that characterize post-natal angiogenesis and lymphangiogenesis elicited by cutaneous wounds and inflammation remain unclear. RhoB, a stress-induced small GTPase, modulates cellular responses to growth factors, genotoxic stress and neoplastic transformation. Here we show, using RhoB null mice, that loss of RhoB decreases pathological angiogenesis in the ischaemic retina and reduces angiogenesis in response to cutaneous wounding, but enhances lymphangiogenesis following both dermal wounding and inflammatory challenge. We link these unique and opposing roles of RhoB in blood versus lymphatic vasculatures to the RhoB-mediated differential regulation of sprouting and proliferation in primary human blood versus lymphatic endothelial cells. We demonstrate that nuclear RhoB-GTP controls expression of distinct gene sets in each endothelial lineage by regulating VEZF1-mediated transcription. Finally, we identify a small-molecule inhibitor of VEZF1-DNA interaction that recapitulates RhoB loss in ischaemic retinopathy. Our findings establish the first intra-endothelial molecular pathway governing the phased response of angiogenesis and lymphangiogenesis following injury.

1-Methyl-tryptophan synergizes with methotrexate to alleviate arthritis in a mouse model of arthritis

Rheumatoid arthritis (RA) is an inflammatory autoimmune disease with no known cure. Current strategies to treat RA, including methotrexate (MTX), target the later inflammatory stage of disease. Recently, we showed that inhibiting indoleamine-2,3-dioxygenase (IDO) with 1-methyl-tryptophan (1MT) targets autoantibodies and cytokines that drive the initiation of the autoimmune response. Therefore, we hypothesized that combining 1MT with MTX would target both the initiation and chronic inflammatory phases of the autoimmune response and be an effective co-therapeutic strategy for arthritis. To test this, we used K/BxN mice, a pre-clinical model of arthritis that develops joint-specific inflammation with many characteristics of human RA. Mice were treated with 1MT, MTX, alone or in combination, and followed for arthritis, autoantibodies, and inflammatory cytokines. Both 1MT and MTX were able to partially inhibit arthritis when used individually; however, combining MTX + 1MT was significantly more effective than either treatment alone at delaying the onset and alleviating the severity of joint inflammation. We went on to show that combination of MTX + 1MT did not lower inflammatory cytokine or autoantibody levels, nor could the synergistic co-therapeutic effect be reversed by the adenosine receptor antagonist theophylline or be mimicked by inhibition of polyamine synthesis. However, supplementation with folinic acid did reverse the synergistic co-therapeutic effect, demonstrating that, in the K/BxN model, MTX synergizes with 1MT by blocking folate metabolism. These data suggest that pharmacological inhibition of IDO with 1MT is a potential candidate for use in combination with MTX to increase its efficacy in the treatment of RA.

Indoleamine 2,3-dioxygenase pathways of pathogenic inflammation and immune escape in cancer

Genetic and pharmacological studies of indoleamine 2,3-dioxygenase (IDO) have established this tryptophan catabolic enzyme as a central driver of malignant development and progression. IDO acts in tumor, stromal and immune cells to support pathogenic inflammatory processes that engender immune tolerance to tumor antigens. The multifaceted effects of IDO activation in cancer include the suppression of T and NK cells, the generation and activation of T regulatory cells and myeloid-derived suppressor cells, and the promotion of tumor angiogenesis. Mechanistic investigations have defined the aryl hydrocarbon receptor, the master metabolic regulator mTORC1 and the stress kinase Gcn2 as key effector signaling elements for IDO, which also exerts a non-catalytic role in TGF-β signaling. Small-molecule inhibitors of IDO exhibit anticancer activity and cooperate with immunotherapy, radiotherapy or chemotherapy to trigger rapid regression of aggressive tumors otherwise resistant to treatment. Notably, the dramatic antitumor activity of certain targeted therapeutics such as imatinib (Gleevec) in gastrointestinal stromal tumors has been traced in part to IDO downregulation. Further, antitumor responses to immune checkpoint inhibitors can be heightened safely by a clinical lead inhibitor of the IDO pathway that relieves IDO-mediated suppression of mTORC1 in T cells. In this personal perspective on IDO as a nodal mediator of pathogenic inflammation and immune escape in cancer, we provide a conceptual foundation for the clinical development of IDO inhibitors as a novel class of immunomodulators with broad application in the treatment of advanced human cancer.

Meglumine exerts protective effects against features of metabolic syndrome and type II diabetes

Metabolic syndrome, diabetes and diabetes complications pose a growing medical challenge worldwide, accentuating the need of safe and effective strategies for their clinical management. Here we present preclinical evidence that the sorbitol derivative meglumine (N-methyl-D-glucamine) can safely protect against several features of metabolic syndrome and diabetes, as well as elicit enhancement in muscle stamina. Meglumine is a compound routinely used as an approved excipient to improve drug absorption that has not been ascribed any direct biological effects in vivo. Normal mice (SV129) administered 18 mM meglumine orally for six weeks did not display any gastrointestinal or other observable adverse effects, but had a marked effect on enhancing muscle stamina and at longer times in limiting weight gain. In the established KK.Cg-Ay/J model of non-insulin dependent diabetes, oral administration of meglumine significantly improved glycemic control and significantly lowered levels of plasma and liver triglycerides. Compared to untreated control animals, meglumine reduced apparent diabetic nephropathy. Sorbitol can improve blood glucose uptake by liver and muscle in a manner associated with upregulation of the AMPK-related enzyme SNARK, but with undesirable gastrointestinal side effects not seen with meglumine. In murine myoblasts, we found that meglumine increased steady-state SNARK levels in a dose-dependent manner more potently than sorbitol. Taken together, these findings provide support for the clinical evaluation of meglumine as a low-cost, safe supplement offering the potential to improve muscle function, limit metabolic syndrome and reduce diabetic complications.

IDO2 is a critical mediator of autoantibody production and inflammatory pathogenesis in a mouse model of autoimmune arthritis

Rheumatoid arthritis and other autoimmune disorders are associated with altered activity of the immunomodulatory enzyme IDO. However, the precise contributions of IDO function to autoimmunity remain unclear. In this article, we examine the effect of two different IDO enzymes, IDO1 and IDO2, on the development of autoimmune arthritis in the KRN preclinical model of rheumatoid arthritis. We find that IDO2, not IDO1, is critical for arthritis development, providing direct evidence of separate in vivo functions for IDO1 and IDO2. Mice null for Ido2 display decreased joint inflammation relative to wild-type mice owing to a reduction in pathogenic autoantibodies and Ab-secreting cells. Notably, IDO2 appears to specifically mediate autoreactive responses, but not normal B cell responses, as total serum Ig levels are not altered and IDO2 knockout mice are able to mount productive Ab responses to model Ags in vitro and in vivo. Reciprocal adoptive transfer studies confirm that autoantibody production and arthritis are modulated by IDO2 expression in a cell type extrinsic to the T cell. Taken together, our results, provide important insights into IDO2 function by defining its pathogenic contributions to autoantibody-mediated autoimmunity.

IDO2 is critical for IDO1-mediated T-cell regulation and exerts a non-redundant function in inflammation

IDO2 is implicated in tryptophan catabolism and immunity but its physiological functions are not well established. Here we report the characterization of mice genetically deficient in IDO2, which develop normally but exhibit defects in IDO-mediated T-cell regulation and inflammatory responses. Construction of this strain was prompted in part by our discovery that IDO2 function is attenuated in macrophages from Ido1 (-/-) mice due to altered message splicing, generating a functional mosaic with implications for interpreting findings in Ido1 (-/-) mice. No apparent defects were observed in Ido2 (-/-) mice in embryonic development or hematopoietic differentiation, with wild-type profiles documented for kynurenine in blood serum and for immune cells in spleen, lymph nodes, peritoneum, thymus and bone marrow of naive mice. In contrast, upon immune stimulation we determined that IDO1-dependent T regulatory cell generation was defective in Ido2 (-/-) mice, supporting Ido1-Ido2 genetic interaction and establishing a functional role for Ido2 in immune modulation. Pathophysiologically, both Ido1 (-/-) and Ido2 (-/-) mice displayed reduced skin contact hypersensitivity responses, but mechanistic distinctions were apparent, with only Ido2 deficiency associated with a suppression of immune regulatory cytokines that included GM-CSF, G-CSF, IFN-γ, TNF-α, IL-6 and MCP-1/CCL2. Different contributions to inflammation were likewise indicated by the finding that Ido2 (-/-) mice did not phenocopy Ido1 (-/-) mice in the reduced susceptibility of the latter to inflammatory skin cancer. Taken together, our results offer an initial glimpse into immune modulation by IDO2, revealing its genetic interaction with IDO1 and distinguishing its non-redundant contributions to inflammation.

The SOCS3-independent expression of IDO2 supports the homeostatic generation of T regulatory cells by human dendritic cells

Dendritic cells (DCs) are professional APCs that have a role in the initiation of adaptive immune responses and tolerance. Among the tolerogenic mechanisms, the expression of the enzyme IDO1 represents an effective tool to generate T regulatory cells. In humans, different DC subsets express IDO1, but less is known about the IDO1-related enzyme IDO2. In this study, we found a different pattern of expression and regulation between IDO1 and IDO2 in human circulating DCs. At the protein level, IDO1 is expressed only in circulating myeloid DCs (mDCs) and is modulated by PGE2, whereas IDO2 is expressed in both mDCs and plasmacytoid DCs and is not modulated by PGE2. In healthy subjects, IDO1 expression requires the presence of PGE2 and needs continuous transcription and translation, whereas IDO2 expression is constitutive, independent from suppressor of cytokine signaling 3 activity. Conversely, in patients suffering from inflammatory arthritis, circulating DCs express both IDO1 and IDO2. At the functional level, both mDCs and plasmacytoid DCs generate T regulatory cells through an IDO1/IDO2-dependent mechanism. We conclude that, in humans, whereas IDO1 provides an additional mechanism of tolerance induced by proinflammatory mediators, IDO2 is stably expressed in steady-state conditions and may contribute to the homeostatic tolerogenic capacity of DCs.

Abstract B070: TIMP-4 – prognostic marker and treatment target for triple-negative breast cancers

Background: Tissue inhibitor of metalloproteinase-4 (TIMP-4) is a secreted multi-functional protein associated with poor survival prognosis among early-stage triple-negative breast cancers (TNBC)a. Triple-negative breast cancers (TNBC) represent a highly aggressive form of this disease with few treatment options available. Current standard chemotherapy (CTX) includes taxane or adriamycin based regiments.

Extracellular TIMP-4 binds to the membrane bound tetraspanin CD63 and induces the activation of PI3K/AKT/mTOR survival pathway. Here we report that TIMP-4 induced aggressive tumor growth and metastasis can be adverted by targeting TIMP-4 either directly by sequestering extracellular pools of TIMP-4 or indirectly by blocking the activation of downstream survival pathways.

Methods: Prospectively collected patient samples, in accordance with the IRB approved protocol, were tested for circulating levels of TIMP-4 using a commercially available ELISA assay in samples from time of surgery and at each treatment cycle. The medical oncology staff recommended therapy without knowledge of TIMP-4 status.

The role of elevated TIMP-4 in TNBC cell behavior was tested in cell culture and animal experiments using the human breast cancer line MDA-MB-468. Cells with or without TIMP-4 added to the medium were used to determine the effects on growth, clonogenic survival and response to chemotherapeutic agents such as adriamycin, Taxol, the new anti-TIMP-4 antibodyb and the PI3K/AKT/mTOR inhibitor GDC-0941. The same cell-line was used to induce tumor growth in nude mice with or without TIMP-4 containing slow-release pellets implanted into the mammary fatpad (mfp). Tumor growth and response to therapy was followed over a six-week period.

Results: Results from patient samples demonstrated that circulating TIMP-4 levels in breast cancer patients remain unaffected after surgical removal of the primary tumor. Adriamycin containing regiments was the only CTX to suppress the TIMP-4 levels independent of primary tumor size and nodal status.

Adding TIMP-4 to cell culture medium or the mfp of mice resulted in an 1.5-fold increased tumor growth rate. Elevated TIMP-4 in mice also resulted in liver metastasis in 25% of animals (N=8).

In cell cultures, the TIMP-4 induced effects were completely adverted by addition of GDC-0941. Adding the TIMP-4 antibody, to cell culture medium or i.p. injections to mice, resulted in a decelerated growth rate and no metastasis.

Conclusions: On the basis of these clinical and experimental data we suggest that TIMP-4 may represent a simple prognostic and predictive marker for TNBC patients at highest risk. The presence of TIMP-4 identifies a patient population likely to recur quickly based on the continuous activation of the PI3K/AKT/mTOR pathway. Though adriamycin therapy can reduce the TIMP-4 levels, the toxicity of this agent suggests that targeted therapy of the PI3K/AKT pathway and/or a biological therapeutic approach directed against TIMP-4 may be of benefit in this subset of pts and should be further explored.

a Liss, M et.al. Am. J. Pathol. 2009

b Donover, P et.al. J. Cell. Biochem. 2010

Citation Format: Emily K. Kunkel, James DuHadaway, Erika Sutanto-Ward, Lauren N. Birnhak, Jenny R. Ringqvist, Zonera A. Ali, Paul B. Gilman, George C. Prendergast, U. Margaretha Wallon. TIMP-4 – prognostic marker and treatment target for triple-negative breast cancers. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr B070.

The N-BAR domain protein, Bin3, regulates Rac1- and Cdc42-dependent processes in myogenesis

Actin dynamics are necessary at multiple steps in the formation of multinucleated muscle cells. BAR domain proteins can regulate actin dynamics in several cell types, but have been little studied in skeletal muscle. Here, we identify novel functions for the N-BAR domain protein, Bridging integrator 3 (Bin3), during myogenesis in mice. Bin3 plays an important role in regulating myofiber size in vitro and in vivo. During early myogenesis, Bin3 promotes migration of differentiated muscle cells, where it colocalizes with F-actin in lamellipodia. In addition, Bin3 forms a complex with Rac1 and Cdc42, Rho GTPases involved in actin polymerization, which are known to be essential for myotube formation. Importantly, a Bin3-dependent pathway is a major regulator of Rac1 and Cdc42 activity in differentiated muscle cells. Overall, these data classify N-BAR domain proteins as novel regulators of actin-dependent processes in myogenesis, and further implicate BAR domain proteins in muscle growth and repair.

Amino acid catabolism: a pivotal regulator of innate and adaptive immunity

Enhanced amino acid catabolism is a common response to inflammation, but the immunologic significance of altered amino acid consumption remains unclear. The finding that tryptophan catabolism helped maintain fetal tolerance during pregnancy provided novel insights into the significance of amino acid metabolism in controlling immunity. Recent advances in identifying molecular pathways that enhance amino acid catabolism and downstream mechanisms that affect immune cells in response to inflammatory cues support the notion that amino acid catabolism regulates innate and adaptive immune cells in pathologic settings. Cells expressing enzymes that degrade amino acids modulate antigen-presenting cell and lymphocyte functions and reveal critical roles for amino acid- and catabolite-sensing pathways in controlling gene expression, functions, and survival of immune cells. Basal amino acid catabolism may contribute to immune homeostasis that prevents autoimmunity, whereas elevated amino acid catalytic activity may reinforce immune suppression to promote tumorigenesis and persistence of some pathogens that cause chronic infections. For these reasons, there is considerable interest in generating novel drugs that inhibit or induce amino acid consumption and target downstream molecular pathways that control immunity. In this review, we summarize recent developments and highlight novel concepts and key outstanding questions in this active research field.

RIN3 is a negative regulator of mast cell responses to SCF

Stimulation of the receptor tyrosine kinase KIT by Stem Cell Factor (SCF) triggers activation of RAS and its downstream effectors. Proper KIT activation is essential for the maturation, survival and proliferation of mast cells. In addition, SCF activation of KIT is critical for recruiting mast cells to sites of infection or injury, where they release a mix of pro-inflammatory substances. RIN3, a RAS effector and RAB5-directed guanine nucleotide exchange factor (GEF), is highly expressed and enriched in human mast cells. SCF treatment of mast cells increased the amount of GTP-bound RAB5, and the degree of RAB5 activation correlated with the expression level of RIN3. At the same time, SCF caused the dissociation of a pre-formed complex of RIN3 with BIN2, a membrane bending protein implicated in endocytosis. Silencing of RIN3 increased the rate of SCF-induced KIT internalization, while persistent RIN3 over-expression led to KIT down regulation. These observations strongly support a role for RIN3 in coordinating the early steps of KIT endocytosis. Importantly, RIN3 also functioned as an inhibitor of mast cell migration toward SCF. Finally, we demonstrate that elevated RIN3 levels sensitize mastocytosis cells to treatment with a KIT tyrosine kinase inhibitor, suggesting the value of a two-pronged inhibitor approach for this difficult to treat malignancy. These findings directly connect KIT activation with a mast cell-specific RAS effector that regulates the cellular response to SCF and provide new insight for the development of more effective mastocytosis treatments.

RhoB differentially controls Akt function in tumor cells and stromal endothelial cells during breast tumorigenesis

Tumors are composed of cancer cells but also a larger number of diverse stromal cells in the tumor microenvironment. Stromal cells provide essential supports to tumor pathophysiology but the distinct characteristics of their signaling networks are not usually considered in developing drugs to target tumors. This oversight potentially confounds proof-of-concept studies and increases drug development risks. Here, we show in established murine and human models of breast cancer how differential regulation of Akt by the small GTPase RhoB in cancer cells or stromal endothelial cells determines their dormancy versus outgrowth when angiogenesis becomes critical. In cancer cells in vitro or in vivo, RhoB functions as a tumor suppressor that restricts EGF receptor (EGFR) cell surface occupancy as well as Akt signaling. However, after activation of the angiogenic switch, RhoB functions as a tumor promoter by sustaining endothelial Akt signaling, growth, and survival of stromal endothelial cells that mediate tumor neoangiogenesis. Altogether, the positive impact of RhoB on angiogenesis and progression supercedes its negative impact in cancer cells themselves. Our findings elucidate the dominant positive role of RhoB in cancer. More generally, they illustrate how differential gene function effects on signaling pathways in the tumor stromal component can complicate the challenge of developing therapeutics to target cancer pathophysiology.

A bioactive probe of the oxidative pentose phosphate cycle: novel strategy to reverse radioresistance in glucose deprived human colon cancer cells

The specific effects of glucose deprivation on oxidative pentose phosphate cycle (OPPC) function, thiol homeostasis, protein function and cell survival remain unclear due to lack of a glucose-sensitive chemical probe. Using p53 wild type and mutant human colon cells, we determined the effects of hydroxyethyl disulfide (HEDS) on NADPH, GSH, GSSG, total glutathione, total non-protein and protein thiol levels, the function of the DNA repair protein Ku, and the susceptibility to radiation-induced free radicals under normal glucose or glucose-deprived conditions. HEDS is rapidly detoxified in normal glucose but triggered a p53-independent metabolic stress in glucose depleted state that caused loss of NADPH, protein and non-protein thiol homeostasis and Ku function, and enhanced sensitivity of both p53 wild type and mutant cells to radiation induced oxidative stress. Additionally, high concentration of HEDS alone induced cell death in p53 wild type cells without significant effect on p53 mutant cells. HEDS offers a useful tool to gain insights into how glucose metabolism affects OPPC dependent stress-induced cellular functions and injury, including in tumor cells, where our findings imply a novel therapeutic approach to target glucose deprived tumor. Our work introduces a novel probe to address cancer metabolism and ischemic pathology.

IDO is a nodal pathogenic driver of lung cancer and metastasis development

Indoleamine 2,3-dioxygenase (IDO) enzyme inhibitors have entered clinical trials for cancer treatment based on preclinical studies, indicating that they can defeat immune escape and broadly enhance other therapeutic modalities. However, clear genetic evidence of the impact of IDO on tumorigenesis in physiologic models of primary or metastatic disease is lacking. Investigating the impact of Ido1 gene disruption in mouse models of oncogenic KRAS-induced lung carcinoma and breast carcinoma-derived pulmonary metastasis, we have found that IDO deficiency resulted in reduced lung tumor burden and improved survival in both models. Micro-computed tomographic (CT) imaging further revealed that the density of the underlying pulmonary blood vessels was significantly reduced in Ido1-nullizygous mice. During lung tumor and metastasis outgrowth, interleukin (IL)-6 induction was greatly attenuated in conjunction with the loss of IDO. Biologically, this resulted in a consequential impairment of protumorigenic myeloid-derived suppressor cells (MDSC), as restoration of IL-6 recovered both MDSC suppressor function and metastasis susceptibility in Ido1-nullizygous mice. Together, our findings define IDO as a prototypical integrative modifier that bridges inflammation, vascularization, and immune escape to license primary and metastatic tumor outgrowth.

SIGNIFICANCE

This study provides preclinical, genetic proof-of-concept that the immunoregulatory enzyme IDO contributes to autochthonous carcinoma progression and to the creation of a metastatic niche. IDO deficiency in vivo negatively impacted both vascularization and IL-6–dependent, MDSC-driven immune escape, establishing IDO as an overarching factor directing the establishment of a protumorigenic environment.

Bin1 attenuation suppresses experimental colitis by enforcing intestinal barrier function

BACKGROUND

Inflammatory bowel disease (IBD) is associated with defects in intestinal barriers that rely upon cellular tight junctions. Thus, identifying genes that could be targeted to enforce tight junctions and improve barrier function may lead to new treatment strategies for IBD.

AIMS

This preclinical study aimed to evaluate an hypothesized role for the tumor suppressor gene Bin1 as a modifier of the severity of experimental colitis.

METHODS

We ablated the Bin1 gene in a mosaic mouse model to evaluate its effects on experimental colitis and intestinal barrier function. Gross pathology, histology and inflammatory cytokine expression patterns were characterized and ex vivo physiology determinations were conducted to evaluate barrier function in intact colon tissue.

RESULTS

Bin1 attenuation limited experimental colitis in a sexually dimorphic manner with stronger protection in female subjects. Colitis suppression was associated with an increase in basal transepithelial electrical resistance (TER) and a decrease in paracellular transepithelial flux, compared to control wild-type animals. In contrast, Bin1 attenuation did not affect short circuit current, nor did it alter the epithelial barrier response to non-inflammatory permeability enhancers in the absence of inflammatory stimuli.

CONCLUSIONS

Bin1 is a genetic modifier of experimental colitis that controls the paracellular pathway of transcellular ion transport regulated by cellular tight junctions. Our findings offer a preclinical validation of Bin1 as a novel therapeutic target for IBD treatment.

Role of RhoB in the regulation of pulmonary endothelial and smooth muscle cell responses to hypoxia

RATIONALE

RhoA and Rho kinase contribute to pulmonary vasoconstriction and vascular remodeling in pulmonary hypertension. RhoB, a protein homologous to RhoA and activated by hypoxia, regulates neoplastic growth and vasoconstriction but its role in the regulation of pulmonary vascular function is not known.

OBJECTIVE

To determine the role of RhoB in pulmonary endothelial and smooth muscle cell responses to hypoxia and in pulmonary vascular remodeling in chronic hypoxia-induced pulmonary hypertension.

METHODS AND RESULTS

Hypoxia increased expression and activity of RhoB in human pulmonary artery endothelial and smooth muscle cells, coincidental with activation of RhoA. Hypoxia or adenoviral overexpression of constitutively activated RhoB increased actomyosin contractility, induced endothelial permeability, and promoted cell growth; dominant negative RhoB or manumycin, a farnesyltransferase inhibitor that targets the vascular function of RhoB, inhibited the effects of hypoxia. Coordinated activation of RhoA and RhoB maximized the hypoxia-induced stress fiber formation caused by RhoB/mammalian homolog of Drosophila diaphanous-induced actin polymerization and RhoA/Rho kinase-induced phosphorylation of myosin light chain on Ser19. Notably, RhoB was specifically required for hypoxia-induced factor-1α stabilization and for hypoxia- and platelet-derived growth factor-induced cell proliferation and migration. RhoB deficiency in mice markedly attenuated development of chronic hypoxia-induced pulmonary hypertension, despite compensatory expression of RhoA in the lung.

CONCLUSIONS

RhoB mediates adaptational changes to acute hypoxia in the vasculature, but its continual activation by chronic hypoxia can accentuate vascular remodeling to promote development of pulmonary hypertension. RhoB is a potential target for novel approaches (eg, farnesyltransferase inhibitors) aimed at regulating pulmonary vascular tone and structure.

Abstract 295: IDO drives tumor-promoting, pathogenic inflammation in lung

First identified as a mediator of acquired immune tolerance of the ‘foreign’ fetus from maternal immunity, the tryptophan-catabolizing enzyme IDO (indoleamine 2,3-dioxygenase) has since been implicated in tumor escape from the host immune system. Insight into the intricate role of IDO in the classical DMBA/TPA skin carcinogenesis model suggested that inflammatory tumor environments can induce IDO production resulting in de novo tumor development. In the genetically deficient model of IDO, mice show resistance to tumor formation. This provided a basis for our current studies exploring the importance of IDO in the microenvironment of the lung. To this end, we have investigated both primary tumor formation and metastatic disease in the lungs of IDO-deficient mice using the KRAS-induced lung adenocarcinoma and the metastatic 4T1 breast cancer models. Elevation of the inflammatory cytokine IL6 was associated with tumor outgrowth in the lungs in both models but was greatly attenuated with the loss of IDO, consistent with the in vitro demonstration that IDO activity markedly potentiates IL6 production. MDSCs (myeloid derived suppressor cells) exhibited reduced T cell suppressive activity when isolated from tumor-bearing, IDO-deficient animals that could be rescued by ectopic production of IL6 in the tumor. IL6 production could likewise reverse the pulmonary metastasis resistance exhibited by IDO-deficient mice. Interestingly, while there is a clear role of the immune system in lung tumor and metastatic outgrowth, IDO-deficient mice appear to have reduced vascularization in the lung which may partly contribute to reduced tumor formation. Together, these findings genetically validate IDO as a therapeutic target in the settings of pulmonary cancer and metastasis and establish the importance of IDO as a driver of IL6 production and MDSC function. Furthermore, the correlation of IDO to angiogenesis may be a new insight into the role of this enzyme in cancer.

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 295. doi:1538-7445.AM2012-295

Hydroxyethyl disulfide as an efficient metabolic assay for cell viability in vitro

Cell viability assays have a variety of well known practical and technical limitations. All the available approaches have disadvantages, such as non-linearity, high background and cumbersome protocols. Several commonly used tetrazolium chemicals rely upon generation of a colored formazan product formed by mitochondrial reduction of these compounds via phenazine methosulfate (PMS). However, sensitivity is inherently limited because their reduction relies on mitochondrial bioreduction and cellular transport of PMS, as well as accessibility to tetrazolium chemicals. In this study, we identify hydroxethyldisulfide (HEDS) as an inexpensive probe that can measure cellular metabolic activity without the need of PMS. In tissue culture medium, HEDS accurately quantitated metabolically active live cells in a linear manner superior to tetrazolium based and other assays. Cell toxicity produced by chemotherapeutics (cisplatin, etoposide), oxidants (hydrogen peroxide, acetaminophen), toxins (phenyl arsine oxide, arsenite) or ionizing radiation was rapidly determined by the HEDS assay. We found that HEDS was superior to other commonly used assays for cell viability determinations in its solubility, membrane permeability, and intracellular conversion to a metabolic reporter that is readily transported into the extracellular medium. Our findings establish the use of HEDS in a simple, rapid and low cost assay to accurately quantify viable cells.

Cardiac and gastrointestinal liabilities caused by deficiency in the immune modulatory enzyme indoleamine 2,3-dioxygenase

Indoleamine 2,3-dioxygenase (IDO) modifies adaptive immunity, in part by determining the character of inflammatory responses in the tissue microenvironment. Small molecule inhibitors of IDO are being developed to treat cancer, chronic infections and other diseases, so the systemic effects of IDO disruption on inflammatory phenomena may influence the design and conduct of early phase clinical investigations of this new class of therapeutic agents. Here, we report cardiac and gastrointestinal phenotypes observed in IDO deficient mice that warrant consideration in planned assessments of the safety risks involved in clinical development of IDO inhibitors. Calcification of the cardiac endometrium proximal to the right ventricle was a sexually dimorphic strain-specific phenotype with ~30% penetrance in BALB/c mice lacking IDO. Administration of complete Freund's adjuvant containing Toll-like receptor ligands known to induce IDO caused acute pancreatitis in IDO deficient mice, with implications for the design of planned combination studies of IDO inhibitors with cancer vaccines. In an established model of hyperlipidemia, IDO deficiency caused a dramatic elevation in levels of serum triglycerides. In the large intestine, IDO loss only slightly increased sensitivity to induction of acute colitis, but it markedly elevated tumor incidence, multiplicity and staging during inflammatory colon carcinogenesis. Together, our findings suggest potential cardiac and gastrointestinal risks of IDO inhibitors that should be monitored in patients as this new class of drugs enter early clinical development.

P4-09-21: A Novel Prognostic Marker for Triple-Negative Breast Cancers

BACKGROUND: Triple-negative breast cancers (TNBC) represent a highly aggressive form of this disease with few treatment options available. Currently, even the smallest node negative cancers are considered by many to warrant treatment with chemotherapy (CTX). While many recur early (within 2–3 years), there is a subset of long-term survivors illustrating the heterogeneity within this group. Here we report our ongoing effort to establish tissue inhibitor of metalloproteinase-4 (TIMP-4) as a prognostic marker in all early breast cancers a. While the canonical function of TIMPs is to inhibit tissue degradation, numerous reports have established that TIMPs exert tumor promoting activity. In our prospective study, we evaluated TIMP-4 as prognostic marker for TNBC and its role in disease progression.

METHODS: Specimens from our retrospective and prospective cohorts were assessed by immunohistochemical staining using standard techniques and a monoclonal antibody for TIMP-4b in accordance with the IRB approved protocol. Staining intensity was documented on a scale of 0–3. No data was released to the treating physicians at the time of collection. Outcome data from a total of 240 pts was obtained through tumor registry and clinician practices. Staining intensity was then correlated with outcome to calculate sensitivity and specificity of the marker. To determine the role of TIMP-4 in TNBC cell behavior we have performed microarray analyses. The effects of TIMP-4-induced signaling were tested using invasion and clonogenic survival assays under normal growth conditions and after exposure to gamma radiation.

RESULTS: Elevated TIMP-4 expression identified a high risk of relapse and short survival time with 75% sensitivity and 80% specificity. No discernable differences were noted between retrospective and prospective cohorts. Array analyses revealed activation of the PI3K/AKT pathway in the presence of TIMP-4. Furthermore, elevated TIMP-4 increased the invasive behavior of breast cancer cells in Matrigel™-coated invasion chambers and reduced sensitivity to gamma irradiation. These effects were reversible by addition of either a PI3K inhibitor or an anti-TIMP-4 antibody, suggesting their use as potential therapeutic strategies.

CONCLUSIONS: On the basis of these clinical data we suggest that TIMP-4 may offer a simple prognostic marker for TNBC patients at highest risk. The presence of TIMP-4 identifies a patient population likely to recur quickly despite standard CTX treatment. Our research suggests that targeted therapy of the PI3K/AKT pathway and/or a biological therapeutic approach directed against TIMP-4 may be of benefit in this subset of pts and should be explored. Therefore, TIMP-4 testing of TNBC patients could aid in the selection of a treatment regimen to improve survival outcome.

a Liss, M et.al. Am. J. Pathol. 2009

b Donover, P et.al. J. Cell. Biochem. 2010

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-09-21.

Altered apoptotic responses in neurons lacking RhoB GTPase

Caspase 3 activation has been linked to the acute neurotoxic effects of central nervous system damage, as in traumatic brain injury or cerebral ischaemia, and also to the early events leading to long-term neurodegeneration, as in Alzheimer's disease. However, the precise mechanisms activating caspase 3 in neuronal injury are unclear. RhoB is a member of the Rho GTPase family that is dramatically induced by cerebral ischaemia or neurotrauma, both in preclinical models and clinically. In the current study, we tested the hypothesis that RhoB might directly modulate caspase 3 activity and apoptotic or necrotic responses in neurons. Over-expression of RhoB in the NG108-15 neuronal cell line or in cultured corticohippocampal neurons elevated caspase 3 activity without inducing overt toxicity. Cultured corticohippocampal neurons from RhoB knockout mice did not show any differences in sensitivity to a necrotic stimulus - acute calcium ionophore exposure - compared with neurons from wild-type mice. However, corticohippocampal neurons lacking RhoB exhibited a reduction in the degree of DNA fragmentation and caspase 3 activation induced by the apoptotic agent staurosporine, in parallel with increased neuronal survival. Staurosporine induction of caspase 9 activity was also suppressed. RhoB knockout mice showed reduced basal levels of caspase 3 activity in the adult brain. These data directly implicate neuronal RhoB in caspase 3 activation and the initial stages of programmed cell death, and suggest that RhoB may represent an attractive target for therapeutic intervention in conditions involving elevated caspase 3 activity in the central nervous system.

Lactoferrin-endothelin-1 axis contributes to the development and invasiveness of triple-negative breast cancer phenotypes

Triple-negative breast cancer (TNBC) is characterized by the lack of expression of estrogen receptor-α (ER-α), progesterone receptor (PR), and human epidermal growth factor receptor-2 (HER-2). However, pathways responsible for downregulation of therapeutic receptors, as well as subsequent aggressiveness, remain unknown. In this study, we discovered that lactoferrin (Lf) efficiently downregulates levels of ER-α, PR, and HER-2 in a proteasome-dependent manner in breast cancer cells, and it accounts for the loss of responsiveness to ER- or HER-2-targeted therapies. Furthermore, we found that lactoferrin increases migration and invasiveness of both non-TNBC and TNBC cell lines. We discovered that lactoferrin directly stimulates the transcription of endothelin-1 (ET-1), a secreted proinvasive polypeptide that acts through a specific receptor, ET(A)R, leading to secretion of the bioactive ET-1 peptide. Interestingly, a therapeutic ET-1 receptor-antagonist blocked lactoferrin-dependent motility and invasiveness of breast cancer cells. The physiologic significance of this newly discovered Lf-ET-1 axis in the manifestation of TNBC phenotypes is revealed by elevated plasma and tissue lactoferrin and ET-1 levels in patients with TNBC compared with those in ER(+) cases. These findings describe the first physiologically relevant polypeptide as a functional determinant in downregulating all three therapeutic receptors in breast cancer, which uses another secreted ET-1 system to confer invasiveness. Results presented in this article provide proof-of-principle evidence in support of the therapeutic effectiveness of ET-1 receptor antagonist to completely block the lactoferrin-induced motility and invasiveness of the TNBC as well as non-TNBC cells, and thus, open a remarkable opportunity to treat TNBC by targeting the Lf-ET-1 axis using an approved developmental drug.

Opposing biological functions of tryptophan catabolizing enzymes during intracellular infection

Recent studies have underscored physiological and pathophysiological roles for the tryptophan-degrading enzyme indolamine 2,3-dioxygenase (IDO) in immune counterregulation. However, IDO was first recognized as an antimicrobial effector, restricting tryptophan availability to Toxoplasma gondii and other pathogens in vitro. The biological relevance of these findings came under question when infectious phenotypes were not forthcoming in IDO-deficient mice. The recent discovery of an IDO homolog, IDO-2, suggested that the issue deserved reexamination. IDO inhibition during murine toxoplasmosis led to 100% mortality, with increased parasite burdens and no evident effects on the immune response. Similar studies revealed a counterregulatory role for IDO during leishmaniasis (restraining effector immune responses and parasite clearance), and no evident role for IDO in herpes simplex virus type 1 (HSV-1) infection. Thus, IDO plays biologically important roles in the host response to diverse intracellular infections, but the dominant nature of this role--antimicrobial or immunoregulatory--is pathogen-specific.

RhoB links PDGF signaling to cell migration by coordinating activation and localization of Cdc42 and Rac

The small GTPase RhoB regulates endocytic trafficking of receptor tyrosine kinases (RTKs) and the non-receptor kinases Src and Akt. While receptor-mediated endocytosis is critical for signaling processes driving cell migration, mechanisms that coordinate endocytosis with the propagation of migratory signals remain relatively poorly understood. In this study, we show that RhoB is essential for activation and trafficking of the key migratory effectors Cdc42 and Rac in mediating the ability of platelet-derived growth factor (PDGF) to stimulate cell movement. Stimulation of the PDGF receptor-β on primary vascular smooth muscle cells (VSMCs) results in RhoB-dependent trafficking of endosome-bound Cdc42 from the perinuclear region to the cell periphery, where the RhoGEF Vav2 and Rac are also recruited to drive formation of circular dorsal and peripheral ruffles necessary for cell migration. Our findings identify a novel RhoB-dependent endosomal trafficking pathway that integrates RTK endocytosis with Cdc42/Rac localization and cell movement.

Indoleamine 2,3-dioxygenase as a modifier of pathogenic inflammation in cancer and other inflammation-associated diseases

Chronic inflammation underlies the basis for development and progression of cancers and a variety of other disorders, but what specifically defines its pathogenic nature remains largely undefined. Recent genetic and pharmacological studies in the mouse suggest that the immune modulatory enzyme indoleamine 2,3-dioxygenase (IDO), identified as an important mediator of immune escape in cancer, can also contribute to the development of pathology in the context of chronic inflammatory models of arthritis and allergic airway disease. IDO-deficient mice do not display spontaneous disorders of classical inflammation and small molecule inhibitors of IDO do not elicit generalized inflammatory reactions. Rather, in the context of a classical model of skin cancer that is promoted by chronic inflammation, or in models of inflammation-associated arthritis and allergic airway disease, IDO impairment can alleviate disease severity. Here we offer a survey of preclinical literature suggesting that IDO functions as a modifier of inflammatory states rather than simply as a suppressor of immune function. We propose that IDO induction in a chronically inflamed tissue may shape the inflammatory state to support, or in some cases retard, pathogenesis and disease severity.

Perspectives on emerging trends in cancer research

Cancer poses enormous personal, clinical, and societal challenges, but it is exciting to consider prospects for historic progress in treatment this decade based on developments emerging in many areas of the field. Here, I offer a personal perspective on core problems, emerging developments, and responses which investigators and their advocates may benefit from considering. This is the first of a series of editorials which will delve into the issues introduced below.

Expression signatures of the lipid-based Akt inhibitors phosphatidylinositol ether lipid analogues in NSCLC cells

Activation of the serine/threonine kinase Akt contributes to the formation, maintenance, and therapeutic resistance of cancer, which is driving development of compounds that inhibit Akt. Phosphatidylinositol ether lipid analogues (PIA) are analogues of the products of phosphoinositide-3-kinase (PI3K) that inhibit Akt activation, translocation, and the proliferation of a broad spectrum of cancer cell types. To gain insight into the mechanism of PIAs, time-dependent transcriptional profiling of five active PIAs and the PI3K inhibitor LY294002 (LY) was conducted in non-small cell lung carcinoma cells using high-density oligonucleotide arrays. Gene ontology analysis revealed that genes involved in apoptosis, wounding response, and angiogenesis were upregulated by PIAs, whereas genes involved in DNA replication, repair, and mitosis were suppressed. Genes that exhibited early differential expression were partitioned into three groups; those induced by PIAs only (DUSP1, KLF6, CENTD2, BHLHB2, and PREX1), those commonly induced by PIAs and LY (TRIB1, KLF2, RHOB, and CDKN1A), and those commonly suppressed by PIAs and LY (IGFBP3, PCNA, PRIM1, MCM3, and HSPA1B). Increased expression of the tumor suppressors RHOB (RhoB), KLF6 (COPEB), and CDKN1A (p21Cip1/Waf1) was validated as an Akt-independent effect that contributed to PIA-induced cytotoxicity. Despite some overlap with LY, active PIAs have a distinct expression signature that contributes to their enhanced cytotoxicity.

RhoB loss prevents streptozotocin-induced diabetes and ameliorates diabetic complications in mice

RhoB is an early-response gene whose expression is elevated by multiple cellular stresses; this gene plays an important role in cancer, macrophage motility, and apoptosis. These factors are essential for the onset of type 1 diabetes mellitus and related complications. This study explores the role of RhoB in β-cell depletion and hyperglycemia-associated complications and tests whether the pleiotropic effect of statins on glycemic control is RhoB dependent. We induced β-cell depletion in RhoB(+/+), RhoB(+/-), and RhoB(-/-) mice with streptozotocin (STZ). Diabetic status was assessed by glucose tolerance and pancreatic islet loss. RhoB(-/-) mice showed a significant reduction in the severity of STZ-induced diabetes; only 13% of the STZ-treated RhoB-null animals became hyperglycemic, as opposed to 61% of the wild-type controls. Diabetes-related complications, such as wound healing rate and onset of nephropathy, were also assessed. Hyperglycemic RhoB(-/-) mice had fewer signs of nephropathy and showed faster wound healing than RhoB(+/+) animals. After assessing the diabetic status of mice treated simultaneously with STZ and simvastatin, we conclude that the effect of statins in improving glycemic control is RhoB independent. We propose that RhoB is a modifier of diabetes, important for the induction of β-cell loss. Suppression of RhoB expression may have potential application in the treatment of diabetes and associated complications.

Development of a monoclonal antibody that specifically detects tissue inhibitor of metalloproteinase-4 (TIMP-4) in formalin-fixed, paraffin-embedded human tissues

Overexpression of the extracellular metalloproteinase inhibitor TIMP-4 in estrogen receptor-negative breast cancers was found recently to be associated with a poor prognosis for survival. To pursue exploration of the theranostic applications of TIMP-4, specific antibodies with favorable properties for immunohistochemical use and other clinical assays are needed. Here we report the characterization of a monoclonal antibody (clone 9:4-7) specific for full-length human TIMP-4 with suitable qualities. The antibody was determined to be an IgG(2b) immunoglobulin. In enzyme-linked immunosorbent assay (ELISA) and immunoblotting assays, it did not exhibit any detectable crossreactivity with recombinant forms of the other human TIMPs 1, 2, and 3. In contrast, the antibody displayed high specificity and sensitivity for TIMP-4 including in formalin-fixed and paraffin-embedded specimens of human breast specimens. An analysis of tissue microarrays of human cancer and corresponding normal tissues revealed specific staining patterns with excellent signal-to-noise ratios. This study documents TIMP-4 monoclonal antibody clone 9:4-7 as an effective tool for preclinical and clinical investigations.

Non-hematopoietic expression of IDO is integrally required for inflammatory tumor promotion

Indoleamine 2,3-dioxygenase (IDO) is generally considered to be immunosuppressive but recent findings suggest this characterization oversimplifies its role in disease pathogenesis. Recently, we showed that IDO is essential for tumor outgrowth in the classical two-stage model of inflammatory skin carcinogenesis. Here, we report that IDO loss did not exacerbate classical inflammatory responses. Rather, IDO induction could be elicited by environmental signals and tumor promoters as an integral component of the inflammatory tissue microenvironment even in the absence of cancer. IDO loss had limited impact on tumor outgrowth in carcinogenesis models that lacked an explicit inflammatory tumor promoter. In the context of inflammatory carcinogenesis where IDO was critical to tumor development, the most important source of IDO was radiation-resistant non-hematopoietic cells, consistent with evidence that loss of the IDO regulatory tumor suppressor gene Bin1 in transformed skin cells facilitates IDO-mediated immune escape by a cell autonomous mechanism. Taken together, our results identify IDO as an integral component of 'cancer-associated' inflammation that tilts the immune system toward tumor support. More generally, they promote the concept that mediators of immune escape and cancer-associated inflammation may be genetically synonymous.

Zinc protoporphyrin IX stimulates tumor immunity by disrupting the immunosuppressive enzyme indoleamine 2,3-dioxygenase

The tryptophan catabolic enzyme indoleamine 2,3-dioxygenase (IDO) has emerged as an important driver of immune escape in a growing number of cancers and cancer-associated chronic infections. In this study, we define novel immunotherapeutic applications for the heme precursor compound zinc protoporphyrin IX (ZnPP) based on our discovery that it is a potent small-molecule inhibitor of IDO. Inhibitory activity was determined using in vitro and in-cell enzyme assays as well as a novel in vivo pharmacodynamic system. An irreversible mechanism of inhibition was documented, consistent with competition for heme binding in newly synthesized cellular protein. siRNA methodology and an IDO-deficient mouse strain were used to verify the specificity of ZnPP as an IDO inhibitor. In a preclinical model of melanoma, ZnPP displayed antitumor properties that relied on T-cell function and IDO integrity. ZnPP also phenocopied the known antitumor properties of IDO inhibitors in preclinical models of skin and breast carcinoma. Our results suggest clinical evaluation of ZnPP as an adjuvant immunochemotherapy in chronic infections and cancers in which there is emerging recognition of a pathophysiologic role for IDO dysregulation.

Abstract 1347: Immune escape mediator IDO is a crucial defining element of ‘cancer-associated’ inflammation in the tumor microenvironment

Chronic inflammation promotes cancer susceptibility and progression but a precise genetic definition of ‘cancer-associated’ inflammation’ has been elusive. We report that dysregulation of the immune escape mediator indoleamine 2,3-dioxygenase (IDO) is selectively required for carcinogenesis driven by chronic inflammatory stimuli, but not tumor formation per se, thereby linking IDO relatively more tightly to chronic inflammatory disease. IDO is a tryptophan catabolic enzyme that mediates immune tolerance in physiological processes such as pregnancy and pathophysiological processes such as cancer. Here our findings define IDO as a component of the peculiar inflammatory state that contributes to a supportive tumor microenvironment. In the well-established two-stage model of inflammatory skin carcinogenesis, initiated by ras-activating carcinogen DMBA and promoted by pro-inflammatory phorbol ester TPA, we found that genetic deletion of IDO abolished papilloma formation and progression to carcinoma. IDO deletion did not alter the histological phenotype elicited by TPA in skin, but it did abolish generation of a class of IDO+ regulatory antigen-presenting cells within skin-draining lymph nodes as previously reported (1). Intriguingly, carcinogenesis studies conducted in bone marrow chimeras in wild-type or IDO null animals argued that the supportive action of IDO was required mainly in non-immune host cells. In stark contrast to these findings, IDO deletion had no discernable effect on the efficiency of complete skin carcinogenesis (chronic DMBA treatment alone), or on induction and progression of breast carcinomas that were initiated by i.p. DMBA treatment and promoted by progesterone delivery. Thus, IDO contributed to carcinogenesis chiefly through its ability to support a peculiar inflammatory state engendered by TPA that is associated with tumor formation and progression. Two other lines of evidence furthered these findings. First, mice that were deficient in the IDO regulatory tumor suppressor gene Bin1 exhibited a greater susceptibility to two-stage inflammatory skin carcinogenesis, as expected, and the benefits of Bin1 loss to tumor formation relied on IDO dysregulation, based on their reversal by IDO inhibition. Second, we determined that ethyl pyruvate, a simple anti-inflammatory agent known to dampen ‘danger signaling’ and sepsis-like conditions in inflammed tissues, could mediate profound antitumor effects that relied upon an inhibition of IDO expression. Together, our results offered multiple lines of genetic and pharmacological evidence that IDO function is integral to establishing the peculiar inflammatory state that drives cancer, and that genetic pathways of immune escape and ‘cancer-associated’ inflammation may closely overlap.

(1) Muller et al. PNAS 105, 17073 (2008).

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

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1347.

Abstract 1392: HEDS selectively radiosensitizes human cancer cells in glucose-deprived environments via inhibition of Ku protein function

There remains great interest in strategies to increase the efficacy of radiation therapy in cancer patients. Glucose depletion occurs commonly in certain regions of bulky solid tumors, owing to high glucose metabolism combined with poor perfusion caused by a disorganized blood vasculature. Evidence suggests that cancer cells located in glucose-deprived regions are resistant to therapeutic killing. Agents that sensitize glucose-deprived cancer cells might offer useful adjuvants for tumor radiotherapy. In an earlier study, we demonstrated that rodent cells which are genetically deficient in the oxidative pentose phosphate cycle (OPPC) display a heightened response to hydroxyethyldisulfide (HEDS), a thiol-specific oxidant that can radiosensitize cells by blocking the redox-dependent function of DNA repair protein Ku. Since glucose is the chief substrate of the OPPC, and the OPPC is responsible for detoxifying HEDS, we reasoned that glucose deprivation should phenocopy the effects of OPPC deficiency in enhancing radiosensitization by HEDS. To test this prediction, we compared the effects of HEDS treatment in human colon cancer cell lines HCT116 or HT29, which are radiation sensitive or resistant, respectively. In both cell lines, HEDS was detoxified by OPPC-mediated conversion to mercaptoethanol (ME) in high-glucose media but not in low-glucose media. Consistent with the decrease in cellular bioreductant activity by glucose depletion, HEDS greatly decreased free glutathione levels under low-glucose conditions. Similarly, HEDS greatly decreased the free thiol content of total proteins and impaired the Ku DNA binding activity in low-glucose conditions. Most significantly, in clonogenic cell growth assay, the cytotoxic effects of HEDS were greatly increased under low glucose conditions, when added by itself to HCT116 cells but particularly when added in combination with irradiation to HCT116 or HT29 cells. Together, our findings indicate that glucose depletion enhances the ability of HEDS to radiosensitize cancer cells. More broadly, our findings suggest the potential to use HEDS in a novel strategy to enhance killing of radioresistant regions of tumors that are characterized by a glucose-depleted state.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1392.