Arginine metabolism is a key parameter of tumor immunology and availability of this specific amino acid for both cancer and immune cells is a potentially decisive factor for tumor growth versus cancer elimination. A recurrent finding in cancer patients is the depletion of the amino acid arginine in the tumor micromilieu. This arginine consumption is due to the enzyme arginase, which can be expressed by tumor cells themselves or by tumor-invading myeloid cells (myeloid-derived suppressor cells, MDSC) of the patient’s immune system. We have first described the specific and constitutive expression of arginase I in human neutrophil granulocytes. Upon liberation of the enzyme and consecutive arginine depletion, human T lymphocytes and NK cells are severely suppressed in their effector functions. MDSC-induced arginine depletion has emerged as a key tumor immune escape mechanism and inhibition of this pathway is associated with tumor control or eradication in a variety of murine tumor models. Arginine availability, on the other hand, is also necessary for cancer cell proliferation and tumor growth. Arginine depletion is therefore emerging as a novel metabolically-oriented treatment strategy that aims to deprive cancer cells of this crucial nutrient.
Our laboratory therefore works on (i) a better understanding of intracellular arginine metabolism and ways to preserve immune function in the context of arginine deprivation, (ii) analyses of the membrane transport proteins, which are necessary to provide arginine to cells and (iii) novel therapeutic strategies to maximize arginine deprivation as efficient anti-tumor effector pathway.
Project 1: Tumor – T cell interactions in the context of arginine deficiency
Nadine Leuchtner, Jose Hadi Sutanto, Janine Tappe
Arginine deficiency impairs both important immune cell functions as well as tumor growth itself. We hypothesize that the outcome of tumor-immune cell interactions in the context of arginine deficiency (reflecting the in vivo situation of the tumor micromilieu) depends on the balance of preserved antitumor immunity versus tumor cell growth under arginine limitation. Arginine can be recycled in certain mammalian tissues from citrulline via the enzymes argininosuccinate synthase (ASS) and argininosuccinate lyase (ASL). We are analysing the expression pattern and regulation of this bypass pathway both in human immune and tumor cells. The goal of this project is to endow immune cells with the ability to synthesize endogenous arginine from external precursors in order to regain their full functional immune competence. This strategy – possibly in conjunction with pharmacological MDSC-associated arginase inhibition – is a promising approach to overcome tumor-associated immune suppression. We are currently testing this hypothesis in complex 3D tumor cell spheroid models with p53 as tumor antigen and genetically engineered p53 reactive human primary T cells (in collaboration with the group of Prof. Dr. Matthias Theobald).
Funding 2010-2012: Else Kröner-Fresenius-Stiftung (P13/10 // A05/10)
Funding 2013-2015: MAIFOR 2013, University Medicine Mainz
Project 2: Regulation and function of arginine transport in human immune cells
Nadine Leuchtner, Elena Rohleder, Vanessa Schnitzius, Rebecca Seidl, Anke Werner
Since arginine availability is crucial for full T cell activation, we have started to analyse how this amino acid is transported into human T lymphocytes and other immune cells. While the complexity and diversity of Cationic Amino Acid Transporters (CATs) and Heteromeric Amino Acid Transporters (HATs) is well appreciated in various mammalian tissues, practically nothing is known about the expression and regulation of potential arginine transport proteins in primary human immune cells. We have joined forces with the group of Prof. Dr. Ellen Closs (Institute of Pharmacology) here in Mainz in order to bring light into this black box. We recently demonstrated that the human cationic amino acid transporter-1 (hCAT-1) is necessary for arginine import and efficient human T cell activation. The identification of the relevant arginine transport proteins in human immune cells will not only lead to a better understanding of the regulation of adaptive immune responses but will also potentially identify novel target structures for immunosuppressive pharmacological interference with immune cell function.
Funding 2012-2015: German Science Foundation (DFG; MU 1547/4-1)
Project 3: Induction of arginine deficiency as novel metabolic treatment strategy for multiple myeloma
Björn Jacobi, Lara Kürzer, Lilli Sester, Lea Ströher, Anke Werner, Johannes Windschmitt
Multiple myeloma is the second most prevalent hematological cancer. The disease is due to malignant expansion of antibody-secreting plasma cells, is characterised by a high degree of morbidity (e.g. anemia, bone fractures and pain, kidney failure, infections) and is still largely incurable. Due their high immunoglobulin synthesis and secretion, myeloma cells are especially dependent on a proper protein metabolism with degradation and disposal of misfolded proteins. To cope with misfolded proteins, myeloma cells rely on a cellular stress response program (Unfolded Protein Response, UPR), which preserves cellular viability under physiological conditions but induces cell death upon prolonged or exaggerated induction via misfolded intracellular proteins. Since availability of arginine is necessary for unimpaired protein synthesis, we are currently analysing the role of therapeutic arginine deprivation as potential UPR inducer. This strategy is also tested in combination with (i) the anti-myeloma drug class of proteasome inhibitors, which interfere with proper protein degradation and (ii) the arginine analogue canavanine, which by itself can induce massive protein misfolding due to incorporation into nascent protein chains instead of arginine. We also characterize the arginine transporters in myeloma cells as potential novel target structures for pharmacological interference with arginine supply for these cancer cells.
Funding 2016-2018: Stiftung Rheinland-Pfalz für Innovation
Project 4: A novel immuno-metabolic anti-tumor strategy: T-cell receptor (TCR) and chimeric antigen receptor (CAR) gene therapy in combination with therapeutic arginine depletion
This is a joint project together with Prof. Dr. Matthias Theobald and Prof. Dr. Winfried Wels (Georg-Speyer-Haus, Frankfurt). It aims to improve cancer immunotherapy by combining adoptive innovative cellular therapeutics with targeted inhibition of tumor metabolism by systemic depletion of arginine. We target multiple myeloma (MM) and melanoma tumor cells by (i) T cells redirected with an optimized MDM2-specific TCR and (ii) a CAR-engineered variant of the human NK cell line NK-92 recognizing the ErbB2/HER2 antigens. Arginine depletion will be induced in vivo by two pharmacologically optimized variants of the enzymes arginine deiminase (ADI) or arginase, which are both in clinical development for various cancer entities. The potential synergistic effect of the combined immuno-metabolic approach could directly be translated into a clinical treatment protocol, since the Arg-depleting drug ADI-PEG20 is already in phase III clinical trials and ErbB2-specific NK CAR cells are available in GMP format.
Funding 2016: Deutsches Konsortium für Translationale Krebsforschung (DKTK)
Project 5: Identification and characterisation of human myeloid-derived suppressor cells (MDSC) in colorectal cancer patients upon immunisation with L-BLP25 (MUC-1; LICC Study)
While we could clarify the physiological expression of arginase in human peripheral blood leukocytes (Munder 2005), the identity and regulation of tumor-associated, arginase-expressing MDSC is largely unknown in human cancer entities. We are responsible for the immunomonitoring of human MDSC within a large multicenter study placebo-controlled study in which patients with colorectal cancer are vaccinated with L-BLP25 (antigen MUC-1) after surgical removal of liver metastases (LICC study). Within our MDSC immunomonitoring workpackage we longitudinally analyse the phenotype and potential tumor immune escape mechanisms of MDSC in patients before and at various time points after L-BLP25 vacination. This analysis should provide valuable information on MDSC analysis as potential biomarker and / or to finally interfere with tumor-induced MDSC in cancer patients. The LICC study as a whole and our immunomonitoring project are co-financed by the Federal Ministry of Education and Research as part of the successful Cluster of Excellence competition.