Abstract 4161: Hiding in plain sight: Understanding the role of tryptophan metabolism in hepatocellular carcinoma

Abstract Introduction: Tumour immune suppression has been identified as an emerging hallmark of cancer that facilitates cancer progression, including hepatocellular carcinoma (HCC). Studies suggest that cancer cells can remain undetected and proliferate by evading local immune surveillance. A major pathway in tryptophan metabolism, the kynurenine pathway (KP), has been suggested to be one of the key mechanisms mediating tumoral immune evasion. In a pro-inflammatory tumour microenvironment, the KP is highly activated which can suppress activation of tumour-targeting immune cells and enhance cancer cell growth. To elucidate the mechanisms underlying KP activation and its contribution to tumour progression in HCC, this study aims to characterize the KP profile and tumour secretome, including cytokines and proteins in HCC patients, to examine the relationship between changes in plasma KP activity and the inflammation-associated secretome. Methods: We have acquired plasma samples collected from patients with HCC (n=30), cirrhosis only (n=30), and healthy control (n=30). The KP metabolomic analysis was carried out using high pressure liquid chromatography (HPLC), Ultra-HPLC and Gas-chromatography Mass-spectrometry. The cytokine and proteomics analysis was performed using flow cytometry and data-independent acquisition mass-spectrometry respectively. Results/Discussion: Our findings demonstrate that the KP is highly activated in HCC, as inferred by the elevated enzymatic activities of indoleamine-2, 3-dioxygenase/tryptophan-2, 3-dioxygenase and kynurenine 3-monooxygenase in HCC patients. Activation of these KP enzymes implies that HCC patients have a suppressed immune profile to facilitate the progression of cancer. Cytokine profiling revealed a more inflamed systemic profile in HCC patients compared to controls and cirrhotic patients. Given that the KP is induced by inflammation, this provides a potential explanation for the elevated KP activity measured in HCC patients. Proteomics analysis further identified differentially expressed proteins linked to inflammation and immune system activation, highlighting that the immune system plays a major role in HCC pathophysiology, potentially driving inflammation and the observed KP profile in HCC patients. Conclusion: Collectively, these results suggest that KP activation may potentially be one of the mechanisms used by HCC tumour to create an immune-tolerant environment, facilitating tumour progression and development. Citation Format: Shivani Krishnamurthy, Bavani Gunasegaran, Sharron Chow, Vincent Lam, Ken Liu, Fiona Guan, Joo-Shik Shin, Avik Majumdar, Geoffrey McCaughan, Seong Beom Ahn, Benjamin Heng. Hiding in plain sight: Understanding the role of tryptophan metabolism in hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4161.