Background Nucleoside Diphosphate Kinase (NDPK), described as NM23 a metastasis suppressor, is found in the culture medium of cancer cells lines suggesting that the kinase may have an extracellular role. We propose that extracellular NM23 released from breast cancers in vivo stimulates tumor cell migration, proliferation and endothelial cell angiogenesis in support of metastasis development. Methods NM23 in the bloodstream of immunocompromised mice carrying human triple-negative breast cancers or in breast cancer patients was measured by ELISA. Primary and metastatic tumor development, the impact of blockade of NM23 and/or its stimulation of nucleotide receptors were measured using in vivo imaging. NM23 expression data in the Curtis breast dataset was examined to test our hypothesis that NM23 may play a mechanistic role in breast cancer development. Results SCID mice carrying metastatic MDA-MB-231Luc+ triple-negative human breast tumor cells elaborate NM23 into the circulation correlated with primary tumor growth. Treatment of mice with the NM23 inhibitor ellagic acid (EA) or the purinergic receptor antagonist MRS2179 slowed primary tumor growth. At 16 weeks following implantation, lung metastases were reduced in mice treated with EA, MRS2179 or the combination. Expression of NM23 in the Curtis breast dataset confirmed a likely role for NM23 in tumor metastasis. Conclusions Extracellular NM23 may constitute both a biomarker and a therapeutic target in the management of breast cancer.

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Metastasis accounts for over 90% of cancer-related deaths, yet the mechanisms guiding this process remain unclear. Secreted nucleoside diphosphate kinase A and B (NDPK) support breast cancer metastasis. Proteomic evidence confirms their presence in breast cancer-derived extracellular vesicles (EVs). We investigated the role of EV-associated NDPK in modulating the host microenvironment in favor of pre-metastatic niche formation. We measured NDPK expression and activity in EVs isolated from triple-negative breast cancer (MDA-MB-231) and non-tumorigenic mammary epithelial (HME1) cells using flow cytometry, western blot, and ATP assay. We evaluated the effects of EV-associated NDPK on endothelial cell migration, vascular remodeling, and metastasis. We further assessed MDA-MB-231 EV-induced proteomic changes in support of pre-metastatic lung niche formation. NDPK-B expression and phosphotransferase activity were enriched in MDA-MB-231 EVs that promote vascular endothelial cell migration and disrupt monolayer integrity. MDA-MB-231 EV-treated mice demonstrate pulmonary vascular leakage and enhanced experimental lung metastasis, whereas treatment with an NDPK inhibitor or a P2Y1 purinoreceptor antagonist blunts these effects. We identified perturbations to the purinergic signaling pathway in experimental lungs, lending evidence to support a role for EV-associated NDPK-B in lung pre-metastatic niche formation and metastatic outgrowth. These studies prompt further evaluation of NDPK-mediated EV signaling using targeted genetic silencing approaches.

Metastasis accounts for over 90% of cancer-related deaths. The mechanisms guiding this process remain unclear. Secreted nucleoside diphosphate kinase A and B (NDPK) support breast cancer metastasis. Proteomic evidence confirms their presence in breast cancer-derived extracellular vesicles (EVs). We investigated the role of EV-associated NDPK in modulating the host microenvironment in favor of pre-metastatic niche formation. We measured NDPK expression and activity in EVs isolated from triple-negative breast cancer (MDA-MB-231) and non-tumorigenic mammary epithelial (HME1) cells using flow cytometry, western blot, and ATP assay. We evaluated the effects of EV-associated NDPK on endothelial cell migration, vascular remodeling, and metastasis. We further assessed MDA-MB-231 EV induced-proteomic changes in support of pre-metastatic lung niche formation. NDPK-B expression and phosphotransferase activity were enriched in MDA-MB-231 EVs that promote vascular endothelial cell migration and disrupt monolayer integrity. MDA-MB-231 EV-treated mice demonstrate pulmonary vascular leakage and enhanced experimental lung metastasis, whereas treatment with an NDPK inhibitor or a P2Y1 purinoreceptor antagonist blunts these effects. We identified perturbations to the purinergic signaling pathway in experimental lungs, lending evidence to support a role for EV-associated NDPK-B in lung pre-metastatic niche formation and metastatic outgrowth.

There is strong evidence implicating exosomes, cell-derived nanoscale vesicles, and their protein cargo in facilitating dialogue between primary tumor cells and the premetastatic niche. Identified by our lab as one such protein, secreted nucleoside diphosphate kinase (NM23/NDPK) has been shown to activate endothelial remodeling in support of proangiogenic and prometastatic events. We have previously demonstrated that triple-negative breast cancer (MDA-MB-231) cells elaborate exosomes enriched with NDPK transphosphorylase activity and target the lung as a future site of metastasis. Using in vitro and in vivo approaches, we interrogate the functional role of NDPK in exosome-mediated lung remodeling. In cell-based assays, we demonstrate that MDA-MB-231 exosomes stimulate migration of pulmonary vascular endothelial cells and enhance monolayer permeability. These effects are reversed following treatment with an inhibitor of NDPK activity or an antagonist to the purinergic P2Y1 receptor. Further, we show that immune-compromised mice receiving intravenous injections of MDA-MB-231 exosomes exhibit enhanced pulmonary vascular leakage, whereas treatment with an inhibitor of NDPK attenuates this effect. Using tandem mass tag labeling and mass spectrometry, we profiled proteomic changes to the lung and identified the purinergic signaling pathway as among those significantly affected by exosome treatment. These results elucidate the functional role of exosomal NDPK in compromising vascular integrity and transforming the pulmonary landscape to support colonization by circulating breast cancer cells. Citation Format: Suzann Duan, Senny Nordmeier, Aidan E. Byrnes, Miles A. Brown, Iain L. Buxton. Triple-negative breast cancer cells alter the pulmonary landscape to favor metastasis via exosome-mediated release of NM23 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 35.

Decades of research has established the idea that cancer cells of the primary tumor prime the metastatic microenvironment prior to establishing metastases at distant sites in the body. While this process is thought to facilitate neocolonization of dislodged primary tumor cells, the mechanisms by which cancer cells communicate to their remote targets remain largely unknown. Our lab has previously shown that triple negative breast cancer cells release exosomes carrying NM23, a nucleoside diphosphate kinase (eNDPK) implicated in promoting angiogenesis and pro-metastatic events extracellularly. To further elucidate the role of eNDPK in breast cancer signaling, we are developing a novel murine model that will allow us to examine its effects in vivo, as well as establish a timeline for the occurrence of metastases. To establish our metastasis model in mice, we first showed that injecting human MDA-MB-231 cells into the mammary fat pad results in the formation of a primary tumor and subsequent development of metastases in the lung. Treating mice with inhibitors of NDPK activity reduces the size of the primary tumor and prevents secondary tumor formation in the lung. To mimic the pulmonary tumor microenvironment, we have isolated endothelial cells from the lungs of 6-8 day old mouse pups using magnetic beads conjugated to the endothelial cell markers CD54, CD102, or CD106. Purity of endothelial cells was confirmed by immunofluorescence staining. In preparation for in vivo experiments that demonstrate eNDPK targeting to lung endothelial cells, we have 3D printed biocompatible polylactic acid (PLA) tubular inserts that are capable of supporting lung endothelial cells encompassed in a gelatinous cell scaffold. Inserts containing lung endothelial cells are surgically introduced into the subcutaneous tissue of adult SCID mice. Human MDA-MB-231 cells expressing GFP-tagged tetraspanin are then injected orthotopically into the mammary fat pads of mice. After a period of 7-21 days, the inserts are excised and analyzed for the presence of GFP-labeled exosomes containing eNDPK and reorganization of the insert microenvironment. Using this model for metastasis, we will be able to confirm the involvement of eNDPK in cell-cell communication between primary tumor cells and their targets in vivo. The significance of uncovering the mechanism(s) by which cancer cells metastasize is emphasized by the fact that recurrence of cancer at distant sites is associated with the most negative outcome in women diagnosed with breast cancer. Implication of eNDPK signaling in metastasis will lead to future research in developing novel small molecule inhibitors. Further, eNDPK can be used as a biomarker for the beginning stages of metastatic breast cancer, replacing current unreliable early detection methods and improving long-term survival outcomes. Citation Format: Suzann Duan, Senny Nordmeier, Iain L.O. Buxton. Exploring the metastatic potential of exosomal NM23 signaling using a triple negative breast cancer model in mice. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4275.

Exogenous nucleoside diphosphate kinase (eNDPK or NM23) has been shown to promote endothelial cell proliferation and migration and tumor-mediated angiogenesis. This is facilitated by its transphosphorylase activity, in which a gamma terminal phosphate group from a triphosphate nucleoside is transferred to a diphosphate nucleoside, resulting in elevated ATP levels. Increased levels of ATP in the tumor microenvironment can activate purinergic receptors (P2Y1) on adjacent endothelial cells to promote angiogenesis, independent of VEGF stimulation. Triple negative human breast cancer (MDA-MB-231) cells have been shown to elaborate exosomes that contain NM23. These exosomes have implications in targeting specific tissues/cells to promote angiogenesis and tumorigenesis. Our lab has shown that inhibition of eNDPK and the P2Y1 receptor reduces endothelial cell tubulogenesis (Rumjahn, et al., 2007) and breast cancer metastasis (Yokdang, et al., 2015). Therefore, targeted inhibition of eNDPK may have implications as a treatment for early tumor-mediated angiogenesis. For this study, we utilized a transphosphorylation activity assay to perform a drug screen on compounds from the Prestwick chemical library. Recombinant NDPK-B was added to FDA-approved drug compounds along with ADP and UTP substrates. Subsequent ATP generation was detected with a luciferase luciferin reaction. Decreased luminescence signal/inhibition of NDPK was compared to ellagic acid control, a known inhibitor of NDPK. From our initial screen, we identified eight potential compounds that inhibited NDPK at comparable levels to ellagic acid. These eight compounds were further examined to determine the dose response curve. We found that Chicago Sky Blue 6B inhibited NDPK at an IC50 value of 1.88µM. The results from this study demonstrate a drug screening method to discover alternative small molecule inhibitors of NDPK as a potential treatment of angiogenesis and breast cancer metastasis. Citation Format: Senny Nordmeier, Jon Evasovic, Suzann Duan, Ryan Wuebbles, Dean J. Burkin, Iain L. Buxton. Identification of novel NM23 inhibitors as potential anti-angiogenic agents [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1804. doi:10.1158/1538-7445.AM2017-1804

Functional interactions between primary tumor cells and their vascular targets orchestrate the formation of a metastatic milieu enriched with oxygen and metabolic substrates. These interactions have been largely attributed to the activation of VEGF receptor pathways through localized tumor-mediated release of VEGF, in addition to indirect receptor phosphorylation. However, pro-angiogenic events are known to occur in the absence of VEGF and alternative pathways resulting in dual activation of neovascularization and enhanced vascular permeability are of growing interest. Our lab has previously shown that triple-negative human breast cancer (MDA-MB-231) cells elaborate exosomes carrying NM23, a nucleoside diphosphate kinase (eNDPK) that is suggested to act as an upstream mediator of vasodilation and pro-angiogenic activity through its action of elevating extracellular ADP/ATP levels. To further elucidate the role of eNDPK in breast cancer signaling and metastasis, we show that 231-exosomes induce a pro-angiogenic phenotype in both human umbilical vein and murine pulmonary endothelial cells. Treatment with an NDPK-specific inhibitor and an antagonist to the ADP/ATP-activated P2Y1 receptor results in amelioration of pro-angiogenic characteristics. Further, we report the development and application of a novel murine implant model to demonstrate increased specificity of 231 exosome targeting to pulmonary endothelial cells over unrelated cell lines. These results suggest the involvement of exosomes and eNDPK in pro-angiogenic communication between metastatic breast cancer cells and their vascular targets. Exosomes elaborated by these cells specifically target pulmonary endothelium in vivo, mirroring the organotropic nature of breast cancer metastasis. Implication of eNDPK in angiogenesis and metastasis may challenge current and invasive treatment methods in favor of developing novel small molecule inhibitors of eNDPK signaling. Lastly, eNDPK can be explored as a potential biomarker for early detection of metastatic breast cancer as it uniquely appears in the serum of patients with breast cancer and not in the serum of individuals with unrelated pathologies. Citation Format: Suzann Duan, Senny Nordmeier, Iain L. Buxton. Exosomal NM23 facilitates pro-angiogenic communication between triple-negative breast cancer cells and their vascular targets [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1807. doi:10.1158/1538-7445.AM2017-1807