Abstract 1410: An effect of Phenylalanine hydroxylase (PAH) deficiency on cancer development in kidney
Authors: Kim Seojeong , Park Jihyun , Park Jeongmin , Kang Chaelin , Moon Kyung Chul , Han Seung Seok , Koh Youngil , Yoon Sung-Soo 
Published: March 2024

Abstract
Several studies have noted the importance of amino acid metabolism in cancer progression. Preliminary research using public cancer multi-omics data has revealed associations between heterozygous germline mutations in genes associated with amino acid metabolism and cancer development. In particular, the heterozygous status of the PAH gene enhances the risk of developing kidney cancer by more than three times. Phenylalanine hydroxylase (PAH) is an enzyme that converts phenylalanine to tyrosine. It is highly expressed in the liver and kidneys. Analysis of the blood metabolome in prospectively collected PAH heterozygous carriers indicates that heterozygous status causes metabolome fluctuations in the body. By the way, renal cell carcinoma (RCC) is an immunogenic tumor mainly infiltrated by T cells. Accordingly, we suggest that defects in the PAH gene change the metabolites in the body, leading to a reduction in immune function and an increased risk of developing kidney cancer. First, the expression of the PAH protein was confirmed through immunohistochemistry in a tissue microarray from RCC patients, and the results were then compared with clinical information. Next, we simulated the environment of PAH deficiency in vitro by treating the cells with phenylalanine (Phe) and its metabolite, phenylpyruvate (PRA), which accumulates during PAH dysfunction. The cytotoxicity of Phe and PPA was investigated using the WST assay. The Jurkat T cell line was cultured long-term in a medium containing Phe or PPA and then stimulated with PHA/PMA. Cytokine secretion was confirmed in these supernatants. In addition, purified primary human pan T cells were stimulated with Anti-CD3/CD28 in the medium containing either Phe or PPA. Proliferation was evaluated using CFSE staining. The IHC was performed on 467 tissues from RCC patients aged 29 to 101 years. We classified the cases into three scale scores based on the percentage of PAH intensity. Approximately 73% of cases were PAH-negative, and only 27% were positive (score 1+ or 2+). A comparison of IHC results with clinical information showed that lower PAH expression was associated with a lower relapse-free survival rate. Next, Phe and PPA exhibited minimal cytotoxicity. The secretion of representative proinflammatory cytokines IL-2 and TNF- α were dose-dependent and significantly decreased with Phe and PPA treatment. Additionally, cell proliferation, a critical step in acquiring effector functions of T cells, was inhibited by treatment with Phe and PPA, particularly in the CD8+ T cell population compared to CD4+ T cells. These results suggest that metabolite changes within the tissue microenvironment of the kidney, caused by Pah defects, may suppress anti-tumor immunity by impairing the function of immune cells. This novel discovery may contribute to the importance of the PAH gene as a new biomarker for diagnosing kidney cancer and to the development of kidney cancer therapy.
Citation Format: Seojeong Kim, Jihyun Park, Jeongmin Park, Chaelin Kang, Kyung Chul Moon, Seung Seok Han, Youngil Koh, Sung-Soo Yoon. An effect of Phenylalanine hydroxylase (PAH) deficiency on cancer development in kidney [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1410.