Immuno-Oncology: A Practical Toolbox for Quantifying Amino Acid Metabolism

Cancer cells aggressively reprogram amino acid metabolism to sustain their rapid proliferation and survival. By doing so, they deplete the tumor microenvironment (TME) of essential nutrients—thereby suppressing immune cell function—and generate immunosuppressive metabolites. Over the past decade, Immusmol has developed ELISA kits and primary antibodies targeting key amino acids involved in cancer metabolism and immune modulation, to support research in immuno-oncology. 

 

Circulating amino acids as biomarkers in immuno-oncology

Fluctuations in amino acids levels in blood or tumor tissues can serve as biomarkers for cancer diagnosis, prognosis or treatment monitoring. To facilitate large-scale studies, we developed a suite of easy-to-use ELISA kits to quantify critical amino acids in plasma and serum samples. Our immunoassays, which were systematically cross-validated by mass-spectrometry, include Glutamine and Glutamate, Tryptophan, Arginine, Serine, Asparagine, Lysine, Histidine, and Phenylalanine.

In a 2022 Annals of Oncology paper titled “Circulating L-arginine predicts the survival of cancer patients treated with immune checkpoint inhibitors”, our L-Arginine ELISA kit was for instance used to process plasma samples from 77 cancer patients treated with immune-checkpoint blockers.

> Explore our amino acid ELISA kits

 

Focus: assessing Tryptophan metabolism along the kynurenine pathway

Enhanced conversion of Tryptophan to Kynurenine by IDO/TDO enzymes is a hallmark of malignant tumors. This metabolic route is crucial for NAD⁺ synthesis—vital for cancer cell metabolism. Simultaneously, the depletion of Tryptophan and the accumulation of Kynurenine in the TME impair T cell function while promoting immunosuppressive Tregs.

To date, over 13 papers have employed Kynurenine-to-Trytpophan ratio ELISA pack to investigate tumor proliferation, immune escape mechanisms, IDO inhibitor efficacy, and the processes underlying primary resistance to immunotherapies. For instance, in 2024, a research team used our Kyn/Trp ELISA to demonstrate that PABPC1L overexpression in renal cell carcinoma is associated with resistance to immune checkpoint inhibition and upregulation of IDO1.

> Learn about the Kyn/Trp ratio ELISA (>50 citations)

 

Focus: monitoring arginine metabolism (urea cycle & nitric oxide production)

Tumor cells commonly deplete arginine in the tumor microenvironment (TME), inhibiting T-cell activation, proliferation, and cytokine production. As a result, plasma arginine levels can serve as an indicator of a patient’s immunological status. Arginine is metabolized in one of two ways: by arginase 1 (ARG1) in the urea cycle—producing urea and ornithine—or by nitric oxide synthase 2 (NOS2) into nitric oxide (NO) and citrulline. Ornithine promotes tumor proliferation and helps maintain DNA stability, while citrulline formation signals the production of NO, which drives angiogenesis and contributes to immunosuppression.

To accurately track arginine metabolism in cancer patients, we developed a Global Arginine Bioavailability ratio (GABR) ELISA pack, enabling simultaneous measurement of arginine, ornithine and citrulline in serum and plasma samples.

> Our immunoassays for arginine metabolism & polyamines

 

Note: if you wish to generate spatial information about amino acids and their metabolites in tumor specimens, check our range of primary antibodies validated for IF/IHC: amino acids, kynurenines and serotonin, arginine & polyamines, and catecholamines.