Poster Presentation NSW State Cancer Conference 2023

Hiding in plain sight: tryptophan metabolism in hepatocellular carcinoma (#127)

Shivani Krishnamurthy 1 , Seong Beom Ahn 1 , Vincent Lam 1 , Ken Liu 2 3 , Joo-Shik Shin 3 4 , Avik Majumdar 2 3 , Geoff McCaughan 2 3 , Gilles Guillemin 1 , Benjamin Heng 1
  1. Macquarie Medical School , Macquarie University, Sydney , NSW , Australia
  2. AW Morrow Gastroenterology and Liver Centre, Royal Prince Alfred Hospital , Sydney , NSW , Australia
  3. Central Clinical School, Faculty of Medicine and Health, University of Sydney, Sydney , NSW , Australia
  4. Tissue Pathology and Diagnostic Oncology, Royal Prince Alfred Hospital, Sydney , NSW , Australia

Introduction: Hepatocellular carcinoma (HCC) is the third leading cause of cancer mortality globally. Although immune checkpoint inhibitors have shown to be effective in advanced HCC patients, a proportion of HCC patients failed to respond to immune therapy - suggesting HCC cells can evade local immune surveillance by other mechanisms. The kynurenine pathway (KP) of tryptophan metabolism has been proposed to be one of the key mechanisms to mediate tumoral immune evasion. In an inflammatory tumour microenvironment, the KP is highly activated to 1) suppress and trigger death of local immune cells and 2) enhance cancer cell growth and metastasis.

Aim: The objective of this study is to characterize the activity of entire KP and identify key enzymes/metabolites that may have a contributing role in HCC development.

Methods: We studied the entire KP profile in HCC cell lines and sera (n=54) obtained from untreated HCC patients. Expression levels of KP enzymes and their activities were examined by using western blot and analytical techniques including high-performance liquid chromatography (HPLC), ultra-HPLC and gas-chromatography/mass spectrometry, respectively.

Results: KP appeared to be highly activated in HCC as demonstrated by high expression and upregulated activity of the first-rate limiting enzymes, indoleamine-2,3-dioxygenase (IDO-1) and tryptophan-2,3-dioxygenase (TDO). Profiling of KP activities and enzyme expression levels revealed that downstream KP enzymes including kynurenine 3-monooxygenase (KMO) and quinolinate phosphoribosyl transferase (QPRT) were highly activated, and the pathway was skewed towards the production of immune suppressive metabolite, 3-hydroxykynurenine (3-HK). These results suggest that upregulated KP activity may have a role in mediating tumour immune evasion through a double mechanism including TRP depletion and production of KP metabolite such as 3-HK, suppressing the local tumour-targeting immune response.  

Conclusion: KP is highly activated and may potentially be one of the mechanisms used by HCC for tumour immune tolerance facilitating cancer proliferation and metastasis.