Novel screening assay for Arginase-1 inhibitors published in SLAS Discovery
Oss – May, 18th, 2020 – Arginase-1 is a promising new drug target for cancer immunotherapy. A novel assay technology for high-throughput screening (HTS) of Arginase-1 has been published in SLAS Discovery  by researchers from NTRC in collaboration with Pivot Park Screening Centre (PPSC). The assay technology is known as Arginase Gold™.
The enzyme Arginase-1 has a regulatory role in T cell and natural killer cell-mediated immunity in the tumor microenvironment by decreasing levels of the amino acid L-arginine, which is critical for an effective anti-tumor immune response. Preclinical studies have shown that inhibition of Arginase-1 increases tumor immune cell infiltration and decreases tumor growth in model systems for cancer [2-4]. The first small molecule Arginase-1 inhibitor CB-1158 (INCB001158) is currently being investigated in clinical trials for the treatment of advanced and metastatic tumors as a single agent, and in combination with chemotherapy, immune checkpoint therapy and the IDO1 inhibitor epacadostat .
Arginase Gold™ is a homogenous (mix-and-measure) enzyme activity assay for Arginase-1, making use of a fluorescent probe developed at NTRC. The assay measures the conversion of L-arginine into its substrate L-ornithine by a decrease in fluorescent signal, thus generating a gain of signal in the presence of inhibitors. In the article, which appeared online today in SLAS Discovery , the Arginase Gold™ assay was validated by side-by-side profiling of reference inhibitors in a traditional colorimetric, multi-step urea assay and in the Arginase Gold™ assay. The application in automated HTS was demonstrated by screening a library of small synthetic chemicals at PPSC and deconvolution of active hit compounds. Besides its robustness, easiness to use, and scalability, an appealing characteristic of the Arginase Gold™ assay is that it can be used in a kinetic mode, thus enabling the study of slow-on/slow-off inhibitors, that is, compounds with a long target residence time .
The figure shows dose-response curves of three reference inhibitors in the Arginase Gold™ assay (left) and inhibitory constant (Ki) measured as function of reaction time (right). Adapted from Grobben et al. .
 Steggerda et al. (2017) Inhibition of arginase by CB-1158 blocks myeloid cell-mediated immune suppression in the tumor microenvironment. Journal for Immunotherapy of Cancer 5, 101.
 Czystowska-Kuzmicz et al. (2019) Small extracellular vesicles containing arginase-1 suppress T-cell
responses and promote tumor growth in ovarian carcinoma. Nature Communications 10, 3000.
 Miret et al. (2019) Suppression of myeloid cell arginase activity leads to therapeutic response in a NSCLC mouse model by activating anti-tumor immunity. Journal for Immunotherapy of Cancer 7, 32.
 see www.clinicaltrials.gov for NCT02903914, NCT03314935 and NCT03361228
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