SBT6050, a HER2-directed TLR8 therapeutic, as a systemically administered, tumor-targeted human myeloid cell agonist.

2020 ◽  
Vol 38 (15_suppl) ◽  
pp. 3110-3110
Author(s):  
Heather Metz ◽  
Monica Childs ◽  
Jamie Brevik ◽  
Damion Winship ◽  
Ty Brender ◽  
...  
Keyword(s):  
Tumor Cells ◽  
Cytokine Production ◽  
Single Agent ◽  
Myeloid Cells ◽  
Myeloid Cell ◽  
Clinical Development ◽  
Innate Immune ◽  
Mouse Tumor ◽  
Systemic Delivery ◽  
Mouse Tumor Models

3110 Background: Solid tumors are replete with myeloid cells which, when activated, drive potent anti-tumor responses. Clinical development of systemically administered myeloid cell agonists, however, has been hindered by acute toxicities due to peripheral activation of the targeted cell types. Intratumoral administration, the route of delivery typically used for innate immune/myeloid cell agonists, is limited by tumor accessibility and a dependence on abscopal responses. A systemically delivered myeloid cell agonist with tumor-localized activity has the potential to overcome challenges encountered with other innate immune/myeloid cell agonists in clinical development. Methods: SBT6050 is a novel therapeutic comprised of a potent toll-like receptor (TLR) 8 agonist payload conjugated to a HER2-directed monoclonal antibody. Delivery of the payload into the endosome of human myeloid cells, where TLR8 resides, requires the co-engagement of HER2 on tumor cells and Fc gamma receptor on human myeloid cells. Thus, SBT6050 is designed for systemic delivery and tumor-targeted activation of human myeloid cells. Results: Studies with human immune cells show that SBT6050 potently induces, in a HER2-dependent manner, multiple anti-tumor immune activities due to its direct activation of myeloid cells and the subsequent induction of T and NK cell cytolytic activity. SBT6050 is designed to activate human myeloid cells only in the presence of HER2-positive tumor cells with moderate (2+ by IHC) or high (3+ by IHC) expression levels. Tumor-localized activity has been demonstrated in mouse models using a SBT6050 mouse surrogate. Systemic delivery results in robust single agent efficacy in multiple mouse tumor models, even those engineered to lack T cells, without accompanying peripheral cytokine production. Trastuzumab and SBT6050 bind to distinct epitopes on HER2 and enhanced activity is observed when the two agents are combined. Conclusions: SBT6050 is a systemically administered, tumor-targeted myeloid cell agonist that demonstrates single agent efficacy in multiple mouse tumor models without peripheral cytokine production. A first-in-human study with SBT6050 is expected to begin this year for patients with HER2-expressing solid tumors.

scholarly journals 859 Tuning the tumor microenvironment by reprogramming TREM1+ myeloid cells to unleash anti-tumor immunity in solid tumors

2021 ◽  
Vol 9 (Suppl 3) ◽  
pp. A900-A900
Author(s):  
Nadine Jahchan ◽  
Hanna Ramoth ◽  
Vladi Juric ◽  
Erin Mayes ◽  
Shilpa Mankikar ◽  
...  
Keyword(s):  
Flow Cytometry ◽  
Tumor Microenvironment ◽  
Tumor Immunity ◽  
Single Agent ◽  
Myeloid Cells ◽  
Mouse Tumor ◽  
Syngeneic Mouse ◽  
Tumor Tissues ◽  
Mouse Tumor Models

BackgroundThe tumor microenvironment (TME) often contains high levels of suppressive myeloid cells that contribute to innate checkpoint inhibitor (CPI) resistance. Pionyr’s Myeloid Tuning approach involves altering the composition and/or the function of myeloid cells in the TME. Myeloid reprogramming alters the function of immunosuppressive myeloid cells to acquire an immunostimulatory phenotype. Triggering receptor expressed on myeloid cells-1 (TREM1) is an immunoglobulin superfamily cell surface receptor enriched on tumor-associated myeloid cells. To investigate the potential of TREM1 modulation as an anti-cancer therapeutic strategy, Pionyr developed an afucosylated humanized anti-TREM1 monoclonal antibody termed PY159 and characterized it in pre-clinical and translational biomarker assays described below.MethodsPY159 responses in human whole blood and dissociated primary tumor cells in vitro were evaluated by flow cytometry and measurement of secreted cytokines and chemokines by MSD. TREM1 expression in human tumors was validated by scRNAseq, flow cytometry, and immunohistochemistry (IHC). In vivo efficacy and pharmacodynamic studies of a surrogate anti-mouse TREM1 antibody, termed PY159m, were evaluated using syngeneic mouse tumor models, either as a single-agent or in combination with anti-PD-1. To select tumor types and patients most likely to benefit from PY159 therapy, Pionyr developed qualitative and quantitative monoplex and multiplex IHC assays that detect TREM1 expression levels in human tumor tissues.ResultsPY159 treatment in vitro induced signaling, upregulated monocyte activation markers, and induced proinflammatory cytokines. In human tumors, TREM1 was detected on tumor-associated neutrophils, tumor-associated macrophages, and monocytic myeloid-derived suppressive cells. The surrogate PY159m anti-mouse TREM1 antibody exhibited anti-tumor efficacy in several syngeneic mouse tumor models, both as single-agent and in combination with anti-PD-1. Screening for TREM1 expression in tumor tissues demonstrated that TREM1+ tumor associated myeloid cells were highly enriched in the TME of multiple solid tumor indications. The monoplex and multiplex IHC assays offered insights into the localization of TREM1+ myeloid cells and their spatial relationship with other immune cells present in the TME to determine what immune composition will be more favorable for response to PY159 therapy.ConclusionsCollectively, the available nonclinical data support PY159 as a TREM1 agonist that reprograms myeloid cells and unleashes anti-tumor immunity. PY159 safety and efficacy are currently being evaluated in first-in-human clinical trial (NCT04682431) involving select advanced solid tumors patients resistant and refractory to standard of care therapies alone and in combination with a CPI. The TREM1 IHC assay is successfully being used on FFPE archival tumor tissues from enrolled patients to determine TREM1 expression levels.

712 SBT6290, a systemically administered Nectin-4-directed TLR8 ImmunoTAC (TM) therapeutic, is a potent human myeloid cell agonist for the treatment of Nectin-4-expressing tumors

2020 ◽  
Vol 8 (Suppl 3) ◽  
pp. A754-A754
Author(s):  
Heather Metz ◽  
Ty Brender ◽  
Brenda Stevens ◽  
Damion Winship ◽  
Jamie Brevik ◽  
...  
Keyword(s):  
Tumor Cells ◽  
Immune Cells ◽  
Proinflammatory Cytokine ◽  
Single Agent ◽  
Myeloid Cells ◽  
Myeloid Cell ◽  
Dependent Manner ◽  
Tumor Models ◽  
Chemokine Production ◽  
Human Immune

BackgroundSBT6290 is a novel therapeutic comprised of a selective TLR8 agonist conjugated to a Nectin-4-specific monoclonal antibody, designed for systemic delivery and tumor-localized activation of myeloid cells. Nectin-4 is a cell surface adhesion molecule that is overexpressed in multiple solid tumor types including triple negative breast, head and neck, lung, and urothelial cancers, with limited expression in normal tissues. Many solid tumors, including those expressing Nectin-4, are resistant to immunotherapy due to immune-suppressive mechanisms, loss of HLA, low neoantigen availability, and/or minimal T cell infiltrates. These tumors, however, are often replete with myeloid cells. Activation of these cells has emerged as a promising approach in overcoming resistance mechanisms to current cancer immunotherapies. TLR8 is highly expressed in myeloid cell types prevalent in human tumors, including conventional DCs and macrophages. Agonism of TLR8 in human myeloid cells activates a broad spectrum of anti-tumor immune mechanisms, including proinflammatory cytokine production, repolarization of suppressive myeloid cells, and the priming of CTL responses. Here, we show that SBT6290 potently activates human myeloid cells in a Nectin-4-dependent manner and that a mouse surrogate confers single agent anti-tumor activity in preclinical studies. These data support the development of SBT6290 for the treatment of patients with Nectin-4-expressing tumors.MethodsSBT6290 activity was characterized in vitro using co-culture systems consisting of human immune cells and Nectin-4-expressing tumor cells. The in vivo efficacy of the SBT6290 surrogate was evaluated as a single agent in mouse tumor models expressing Nectin-4.ResultsStudies with human immune cells show that SBT6290 potently induces multiple anti-tumor immune activities including proinflammatory cytokine and chemokine production, inflammasome activation, direct activation of DCs and indirect T and NK cell cytolytic activity. This activity requires the presence of Nectin-4 expressing tumor cells and the engagement of Fc gamma receptors on the surface of the myeloid cells by the conjugate to facilitate delivery of SBT6290 into myeloid cells. Notably, SBT6290 is >100 fold more potent than the free, unconjugated TLR8 agonist. Systemic administration of a SBT6290 surrogate in mice results in robust single agent efficacy in tumor models intrinsically resistant to checkpoint blockade, including the EMT6 model engineered to express human Nectin-4.ConclusionsThe preclinical data described here show the potential for SBT6290 to drive robust, single agent anti-tumor responses and support the clinical development of SBT6290 for patients with Nectin-4 expressing tumors.

scholarly journals 843 Development and engineering of human sialidase for degradation of immunosuppressive sialoglycans to treat cancer

2021 ◽  
Vol 9 (Suppl 3) ◽  
pp. A884-A884
Author(s):  
Li Peng ◽  
Lizhi Cao ◽  
Sujata Nerle ◽  
Robert LeBlanc ◽  
Abhishek Das ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Immune Cells ◽  
First Generation ◽  
Single Agent ◽  
Mouse Tumor ◽  
Cytokine Release ◽  
Tumor Models ◽  
Cell Immunity ◽  
Mouse Tumor Models

BackgroundSialoglycans, a type of glycans with a terminal sialic acid, have emerged as a critical glyco-immune checkpoint that impairs antitumor response by inhibiting innate and adaptive immunity. Upregulation of sialoglycans on tumors has been observed for decades and correlates with poor clinical outcomes across many tumor types. We previously showed that targeted desialylation of tumors using a bifunctional sialidase x antibody molecule, consisting of sialidase and a tumor-associated antigen (TAA)-targeting antibody, has led to robust single-agent efficacy in mouse tumor models. In addition to tumor cells, most immune cells present substantially more abundant sialoglycans than non-hematological healthy cells, which may also contribute to immunosuppression. Therefore, we studied the impact of immune cell desialylation and evaluated the therapeutic potential of a newly developed sialidase-Fc fusion (Bi-Sialidase), which lacks a TAA-targeting moiety and consists of engineered human neuraminidase 2 (Neu2) and human IgG1 Fc region, in preclinical mouse tumor models.MethodsThe first generation Neu2 variant was further optimized to improve titers and stability to constructed Bi-Sialidase. Bi-Sialidase’s desialylation potency and impact on immune responses were studied in vitro using various human immune functional assays, including T-cell activation, allogeneic mixed lymphocyte reaction, antibody-dependent cellular cytotoxicity, macrophages polarization/activation, neutrophil activation, and peripheral blood mononuclear cell (PBMC) cytokine release assays. We evaluated its antitumor efficacy in mouse tumor models. Bi-Sialidase’s safety profile was characterized by conducting rat and non-human primate (NHP) toxicology studies.ResultsThe optimized Bi-Sialidase achieved a titer of 2.5 g/L from a 15-day fed-batch Chinese hamster ovary cell culture; in contrast, the wild-type and first-generation Neu2 had no production or a low titer (<0.1 g/L) under similar conditions, respectively. We demonstrated that Bi-Sialidase led to dose-dependent desialylation of immune cells and potentiated T-cell immunity, without impacting NK, macrophage, or neutrophil activation by desialylating immune cells. Activated and exhausted T cells upregulated surface sialoglycans and Bi-Sialidase-mediated desialylation reinvigorated exhausted-like T cells as measured by IFNg production. Bi-Sialidase treatment also enhanced DC priming and activation of naïve T cells by desialylating both T cells and DCs. Furthermore, Bi-Sialidase showed single-agent antitumor activity in multiple mouse tumor models, including MC38, CT26, A20, and B16F10. Importantly, Bi-Sialidase did not cause cytokine release in human PBMC assays and was tolerated to up to 100 mg/kg in rats and NHPs, demonstrating a wide safety margin.ConclusionsBi-Sialidase with an optimized Neu2 offers a novel immunomodulatory approach to enhancing T-cell immunity by desialylating immunosuppressive sialoglycans for cancer treatment.

Abstract 3071: Size-based isolation of circulating tumor cells (CTCs) in mouse tumor models

2014 ◽  
Author(s):  
Katarina Kolostova ◽  
Robert M. Hoffman ◽  
Ali Maawy ◽  
Yong Zhang ◽  
Vladimir Bobek
Keyword(s):  
Tumor Cells ◽  
Circulating Tumor Cells ◽  
Mouse Tumor ◽  
Tumor Models ◽  
Mouse Tumor Models

Vaccination during myeloid cell depletion by cancer chemotherapy fosters robust T cell responses

2016 ◽  
Vol 8 (334) ◽  
pp. 334ra52-334ra52 ◽  
Author(s):  
Marij J. Welters ◽  
Tetje C. van der Sluis ◽  
Hélène van Meir ◽  
Nikki M. Loof ◽  
Vanessa J. van Ham ◽  
...  
Keyword(s):  
Cervical Cancer ◽  
T Cell ◽  
Myeloid Cells ◽  
Myeloid Cell ◽  
T Cell Responses ◽  
Mouse Tumor ◽  
Therapeutic Vaccination ◽  
Advanced Cervical Cancer ◽  
Hpv16 E6 ◽  
Cell Responses

Therapeutic vaccination with human papillomavirus type 16 synthetic long peptides (HPV16-SLPs) results in T cell–mediated regression of HPV16-induced premalignant lesions but fails to install clinically effective immunity in patients with HPV16-positive cervical cancer. We explored whether HPV16-SLP vaccination can be combined with standard carboplatin and paclitaxel chemotherapy to improve immunity and which time point would be optimal for vaccination. This was studied in the HPV16 E6/E7–positive TC-1 mouse tumor model and in patients with advanced cervical cancer. In mice and patients, the presence of a progressing tumor was associated with abnormal frequencies of circulating myeloid cells. Treatment of TC-1–bearing mice with chemotherapy and therapeutic vaccination resulted in superior survival and was directly related to a chemotherapy-mediated altered composition of the myeloid cell population in the blood and tumor. Chemotherapy had no effect on tumor-specific T cell responses. In advanced cervical cancer patients, carboplatin-paclitaxel also normalized the abnormal numbers of circulating myeloid cells, and this was associated with increased T cell reactivity to recall antigens. The effect was most pronounced starting 2 weeks after the second cycle of chemotherapy, providing an optimal immunological window for vaccination. This was validated with a single dose of HPV16-SLP vaccine given in this time window. The resulting proliferative HPV16-specific T cell responses were unusually strong and were retained after all cycles of chemotherapy. In conclusion, carboplatin-paclitaxel therapy fosters vigorous vaccine-induced T cell responses when vaccination is given after chemotherapy and has reset the tumor-induced abnormal myeloid cell composition to normal values.

scholarly journals Krüppel like factor 2 - deficient myeloid cells promote skeletal muscle regeneration after injury

2018 ◽  
Author(s):  
Palanikumar Manoharan ◽  
Taejeong Song ◽  
Tatiana L Radzyukevich ◽  
Sakthivel Sadayappan ◽  
Jerry B Lingrel ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Muscle Regeneration ◽  
Cell Activation ◽  
Myeloid Cells ◽  
Myeloid Cell ◽  
Innate Immune ◽  
Skeletal Muscle Regeneration ◽  
Adult Skeletal Muscle ◽  
Complex Interactions ◽  
Elevated Expression

Regeneration of adult skeletal muscle after injury is coordinated by complex interactions between the injured muscle and the innate immune system. Myeloid lineage cells predominate in this process. This study examined the role of Krüppel like factor 2 (KLF2), a zinc-finger transcription factor that regulates myeloid cell activation state, in muscle regeneration. Gastrocnemius muscles of wild-type and myeKlf2-/- mice, which lack KLF2 in all myeloid cells, were subjected to cardiotoxin injury and followed for 21 days. Injured muscles of myeKlf2-/- contained more infiltrating, inflammatory Ly6C+ monocytes, with elevated expression of inflammatory mediators. Infiltrating monocytes matured earlier into pro-inflammatory macrophages with phenotype Ly6C+, CD11b+, F4/80+. Inflammation resolved earlier and progressed to myogenesis, marked by an earlier decline of Ly6C+ macrophages and their replacement with anti-inflammatory Ly6C- populations, in association with elevated expression of factors that resolve inflammation and promote myogenesis. Overall, regeneration was completed earlier. These findings identify myeloid KLF2 as a central regulator of the innate immune response to acute skeletal muscle injury. Manipulating myeloid KLF2 levels may be a useful strategy for accelerating regeneration.

scholarly journals FRI0016 R835, A NOVEL IRAK1/4 DUAL INHIBITOR IN CLINICAL DEVELOPMENT, BLOCKS TOLL-LIKE RECEPTOR 4 (TLR4) SIGNALING IN HUMAN AND MOUSE

2020 ◽  
Vol 79 (Suppl 1) ◽  
pp. 579.1-579
Author(s):  
C. Lamagna ◽  
C. Gundel ◽  
M. Chan ◽  
C. Young ◽  
S. Braselmann ◽  
...  
Keyword(s):  
Whole Blood ◽  
Cytokine Production ◽  
Interleukin 1 ◽  
Clinical Development ◽  
Innate Immune ◽  
Toll Like Receptor ◽  
Serum Cytokine ◽  
Tlr4 Signaling ◽  
Molecule Inhibitor ◽  
Human And Mouse

Background:Toll-Like Receptors (TLR) and Interleukin-1 Receptors (IL-1R) play a critical role in the innate immune response as microbial sensors, providing a bridge between the innate and adaptive immunity (1). Interleukin receptor associated kinases (IRAK) 1 and 4 are serine/threonine kinases that are essential for signaling downstream of most TLRs and IL-1Rs and the resulting production of pro-inflammatory cytokines (2). Suppression of TLR and IL-1R signaling through inhibition of IRAK1/4 kinases is a promising therapeutic approach for the treatment of inflammatory and autoimmune diseases.Objectives:The aim of the study was to characterize the effects of R835, a novel small molecule inhibitor of IRAK1/4, on TLR4 signaling.Methods:R835 was identified in cell-based assays measuring cytokine production induced by LPS (TLR4 ligand). Inhibition of IRAK1 and IRAK4 kinases by R835 was confirmed in biochemical assays and cell lysates. The ability of R835 to inhibit TLR4 signaling was further evaluated in human and mouse whole blood assays. R835 was tested in a mouse model of LPS-induced cytokine release. Mice were pre-treated orally with vehicle or R835 prior to challenge with LPS and serum cytokine levels were monitored over a 24-hour period.Results:We have identified R835, a selective small molecule inhibitor of IRAK1 and IRAK4. R835 blocked LPS/TLR4 signaling and the resulting production of proinflammatory cytokines in both human and mouse cells and whole blood. R835 suppressed serum cytokine elevation in mice challenged with LPS.Conclusion:Our study demonstrates that R835, through inhibition of IRAK1/4 kinase activity, blocks LPS-induced cytokine production in vitro and in vivo. In a recent phase 1 study, R835 substantially reduced the increase of serum cytokines after an intravenous LPS challenge in healthy volunteers. Importantly, this shows that the pharmacological inhibition of IRAK1/4 pathway by R835 in humans mirrors the results obtained in mice. To our knowledge, R835 is the first dual IRAK1/4 inhibitor to enter clinical development and demonstrate inhibition of TLR4-induced cytokines in both mice and humans. R835 is a promising clinical candidate that will allow the exploration of IRAK1/4 inhibition in the treatment of cytokine-driven rheumatic and autoimmune diseases.References:[1]The interleukin-1 receptor/ Toll-like receptor superfamily: 10 years of progress. Luke A. J. O’Neill. Immunological Reviews 2008. Vol. 226: 10–18[2]Flannery S, Bowie A G. The interleukin-1 receptor-associated kinases: Critical regulators of innate immune signaling. Biochemical Pharmacology, Volume 80, Issue 12, 15 December 2010, Pages 1981-1991.Disclosure of Interests:Chrystelle Lamagna Shareholder of: Rigel Pharmaceuticals, Employee of: Rigel Pharmaceuticals, Caroline Gundel Shareholder of: Shareholder of Rigel Pharmaceuticals, Employee of: Employee of Rigel Pharmaceuticals, Meagan Chan Shareholder of: Rigel Pharmaceuticals, Employee of: Rigel Pharmaceuticals, Chi Young Shareholder of: Rigel Pharmaceuticals, Employee of: Rigel Pharmaceuticals, Sylvia Braselmann Shareholder of: Shareholder of Rigel Pharmaceuticals, Employee of: Employee of Rigel Pharmaceuticals, Roy Frances Shareholder of: Rigel Pharmaceuticals, Employee of: Rigel Pharmaceuticals, Sothy Yi Shareholder of: Rigel Pharmaceuticals, Employee of: Rigel Pharmaceuticals, Yan Chen Shareholder of: Rigel Pharmaceuticals, Employee of: Rigel Pharmaceuticals, Gary Park Shareholder of: Rigel Pharmaceuticals, Employee of: Rigel Pharmaceuticals, Lu Chou Shareholder of: Rigel Pharmaceuticals, Employee of: Rigel Pharmaceuticals, Esteban Masuda Shareholder of: Rigel Pharmaceuticals, Employee of: Rigel Pharmaceuticals, Vanessa Taylor Shareholder of: Rigel Pharmaceuticals, Employee of: Rigel Pharmaceuticals

scholarly journals Vpx enhances innate immune responses independently of SAMHD1 during HIV-1 infection

Retrovirology ◽  
2021 ◽  
Vol 18 (1) ◽  
Author(s):  
Oya Cingöz ◽  
Nicolas D. Arnow ◽  
Mireia Puig Torrents ◽  
Norbert Bannert
Keyword(s):  
Immune Responses ◽  
Cell Lines ◽  
Myeloid Cells ◽  
Adaptor Protein ◽  
Myeloid Cell ◽  
Innate Immune ◽  
Innate Immune Responses ◽  
Accessory Gene ◽  
Monocytic Cell ◽  
Hiv 1

Abstract Background The genomes of HIV-2 and some SIV strains contain the accessory gene vpx, which carries out several functions during infection, including the downregulation of SAMHD1. Vpx is also commonly used in experiments to increase HIV-1 infection efficiency in myeloid cells, particularly in studies that investigate the activation of antiviral pathways. However, the potential effects of Vpx on cellular innate immune signaling is not completely understood. We investigated whether and how Vpx affects ISG responses in monocytic cell lines and MDMs during HIV-1 infection. Results HIV-1 infection at excessively high virus doses can induce ISG activation, although at the expense of high levels of cell death. At equal infection levels, the ISG response is potentiated by the presence of Vpx and requires the initiation of reverse transcription. The interaction of Vpx with the DCAF1 adaptor protein is important for the enhanced response, implicating Vpx-mediated degradation of a host factor. Cells lacking SAMHD1 show similarly augmented responses, suggesting an effect that is independent of SAMHD1 degradation. Overcoming SAMHD1 restriction in MDMs to reach equal infection levels with viruses containing and lacking Vpx reveals a novel function of Vpx in elevating innate immune responses. Conclusions Vpx likely has as yet undefined roles in infected cells. Our results demonstrate that Vpx enhances ISG responses in myeloid cell lines and primary cells independently of its ability to degrade SAMHD1. These findings have implications for innate immunity studies in myeloid cells that use Vpx delivery with HIV-1 infection.

scholarly journals Amino acid transporter LAT1 in tumor-associated vascular endothelium promotes angiogenesis by regulating cell proliferation and VEGF-A-dependent mTORC1 activation

2020 ◽  
Vol 39 (1) ◽  
Author(s):  
Lili Quan ◽  
Ryuichi Ohgaki ◽  
Saori Hara ◽  
Suguru Okuda ◽  
Ling Wei ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
Endothelial Cells ◽  
Amino Acid ◽  
Tumor Cells ◽  
Tumor Angiogenesis ◽  
Amino Acid Transporter ◽  
Mouse Tumor ◽  
Tumor Models ◽  
Mouse Tumor Models

Abstract Background Tumor angiogenesis is regarded as a rational anti-cancer target. The efficacy and indications of anti-angiogenic therapies in clinical practice, however, are relatively limited. Therefore, there still exists a demand for revealing the distinct characteristics of tumor endothelium that is crucial for the pathological angiogenesis. L-type amino acid transporter 1 (LAT1) is well known to be highly and broadly upregulated in tumor cells to support their growth and proliferation. In this study, we aimed to establish the upregulation of LAT1 as a novel general characteristic of tumor-associated endothelial cells as well, and to explore the functional relevance in tumor angiogenesis. Methods Expression of LAT1 in tumor-associated endothelial cells was immunohistologically investigated in human pancreatic ductal adenocarcinoma (PDA) and xenograft- and syngeneic mouse tumor models. The effects of pharmacological and genetic ablation of endothelial LAT1 were examined in aortic ring assay, Matrigel plug assay, and mouse tumor models. The effects of LAT1 inhibitors and gene knockdown on cell proliferation, regulation of translation, as well as on the VEGF-A-dependent angiogenic processes and intracellular signaling were investigated in in vitro by using human umbilical vein endothelial cells. Results LAT1 was highly expressed in vascular endothelial cells of human PDA but not in normal pancreas. Similarly, high endothelial LAT1 expression was observed in mouse tumor models. The angiogenesis in ex/in vivo assays was suppressed by abrogating the function or expression of LAT1. Tumor growth in mice was significantly impaired through the inhibition of angiogenesis by targeting endothelial LAT1. LAT1-mediated amino acid transport was fundamental to support endothelial cell proliferation and translation initiation in vitro. Furthermore, LAT1 was required for the VEGF-A-dependent migration, invasion, tube formation, and activation of mTORC1, suggesting a novel cross-talk between pro-angiogenic signaling and nutrient-sensing in endothelial cells. Conclusions These results demonstrate that the endothelial LAT1 is a novel key player in tumor angiogenesis, which regulates proliferation, translation, and pro-angiogenic VEGF-A signaling. This study furthermore indicates a new insight into the dual functioning of LAT1 in tumor progression both in tumor cells and stromal endothelium. Therapeutic inhibition of LAT1 may offer an ideal option to potentiate anti-angiogenic therapies.

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