Cutaneous T-cell lymphoma pathogenesis : extracellular vesicles, syncytin-1, and metabolites

Cutaneous T-cell lymphomas (CTCLs) constitute an incurable, chronic, heterogeneous group of non-Hodgkin lymphomas, characterized by a malignant population of mature T-lymphocytes that infiltrate the skin. The incidence of CTCLs has increased worldwide. Symptoms vary from indolent skin patches to aggressive skin tumors. In addition to the skin, lymph nodes, blood, and other body organs are affected depending on the stage and subtype of the disease. Difficulties in differentiating early symptoms from other skin conditions and complex diagnostic criteria make CTCLs challenging to diagnose, often delaying the diagnosis for years. Despite intensive research, the pathogenesis of CTCLs remains mostly unknown. This study emphasizes the impact of the tumor microenvironment (TME) and the tumor cell-released extracellular vesicles (EVs) on the pathogenesis of CTCLs. Particularly, this study examines the role of the tryptophan pathway-associated enzymes indoleamine 2,3-deoxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase (TDO). IDO induces immune tolerance in the TME by inflammation and T-cell activation. While TDO catabolizes the same metabolic pathway as IDO1, its role in tumors is poorly characterized. We showed that both IDO1 and TDO are expressed in CTCL tissues and cell lines. Interestingly, different CTCL subtypes show unique patterns of expression. In addition, elevated serum kynurenine/ tryptophan ratios observable in plasma samples of mycosis fungoides (the most common subtype of CTCL) patients correlated with advanced disease. Furthermore, four tryptophan catabolic route metabolites were upregulated, and two were downregulated. These observations could be exploited in clinical tests, and therapeutic potential for CTCLs may result from blocking IDO activity. EVs are small membranous vesicles released into the extracellular milieu by most cell types – also by cancer cells. The EVs released from cancer cells contain various proteins, lipids, amino acids, and metabolites and have proven to be an essential form of intercellular communication. Malignant cells can release EVs into TME and the circulation to reprogram target cells or prepare a pre-metastatic niche. Such transfer could occur at a very early stage in tumor progression because the small size of EVs allows them to cross barriers that cells cannot. Consequently, the molecular cargo of EVs reflects the cell of origin, which is also detectable in the circulation by the non-invasive liquid biopsy method. This study shows that human endogenous retrovirus, type W (HERV-W)-coded syncytin-1 in CTCL cells and CTCL cell-derived EVs is upregulated. Functionally, upregulated syncytin-1 can promote cell-to-cell fusion. Cell-to-cell fusion in cancers can induce genomic instability and aneuploidy and contribute to tumor heterogeneity, drug resistance, and metastasis. Although the molecular mechanisms of EVs are not fully characterized, syncytin-1 could be involved in binding EVs to target cells to facilitate the progressing fusion. Our functional study suggested that EV-harbored syncytin-1 promoted giant plasma membrane-surrounding fusion cells in the recipient T-cell leukemia cells. In addition, we studied alterations of EV-derived metabolite cargo in CTCL, prostate carcinoma, and colon carcinoma cell lines and compared these with the cargo of their healthy counterparts. In cancers, the expression of metabolites is commonly reregulated due to oncogenes or tumor suppressor mutations. The enhanced metabolism supports cancer cell proliferation and survival. Previously, numerous cancer-associated metabolites have been detected, but little is known of their role in cancer-derived EVs. This study shows that despite the differences among the studied cancer types, all cell line-derived EVs shared a common metabolomic feature: upregulation of proline and succinate. In addition, in CTCL- and prostate cancer-derived EVs, folate and creatinine were upregulated. This doctoral thesis explores the role of EVs and the kynurenine pathway in the pathogenesis of CTCLs. These observations could impact diagnosis and have therapeutic value for currently incurable, complex CTCLs. In addition, our results from three different cancer cell line-derived EVs show that metabolomic reprogramming of cancer cells influences the EV metabolome. In particular, this finding suggests that proline, succinate, folate, and creatinine could constitute a metabolomic fingerprint of cancer, which could serve as a peripherally detectable cancer marker. Thus, exploring the function of EVs in cancer progression will prove valuable in next-generation cancer diagnosis and treatment.