SAT-345 High levels of circulating and monocyte-derived IL-6 in anaplastic thyroid carcinoma

Abstract Disclosure: P. van Houten: None. P. Changoer: None. M. Jaeger: None. L. van Emst: None. M.G. Netea: None. H.J. Bonenkamp: None. H.H. de Wilt: None. P.B. Ottevanger: None. J.E. Walraven: None. R.T. Netea-Maier: None. Objectives: Anaplastic thyroid cancer (ATC) is the most aggressive malignancy with no curative treatment options. The ATC tumor-microenvironment is characterized by pro-tumoral immune cells but circulating immune cells of ATC patients have not yet been immunophenotyped. Here, we aimed to compare the functional phenotype of circulating immune cells and the inflammatory proteome of patients with ATC, other subtypes of TC and healthy controls, to provide new pathogenetic insights in search for therapeutic targets. Methods: Patients with ATC (n=10), poorly differentiated thyroid cancer (PDTC, n=5), radio-iodine refractory TC (RAIR-TC, n=13) differentiated thyroid cancer (DTC, n=19) and healthy controls (n=14) donated blood. Individuals with inflammatory, infectious comorbidities or using immune modulators were excluded. Circulating immune cell counts were assessed. Peripheral blood mononuclear cells (PBMCs) were isolated and stimulated for 24 hours or 7 days with different stimuli to assess cytokine production capacity by ELISA. Circulating inflammatory proteins were assessed in plasma by ELISA and OLINK proteomics. To validate our findings, ATC cell lines (8505C, 8305C & CAL62) were treated with several inhibitors after which the viability was assessed by an ATP-based assay. Results: Circulating absolute numbers of neutrophils and monocytes were higher in ATC patients than in the other subgroups. After 7 days of PBMC stimulation, lymphocytes of ATC and PDTC patients produced less interferon-γ and interleukin- (IL)-22 than the other subgroups. In contrast, 24 hours of stimulation resulted in increased concentrations of monocyte-derived cytokines IL-6 and IL-8 in the ATC and PDTC subgroups. In plasma, IL-6, IL-1RA and granulocyte-colony stimulating factor were higher in the ATC and PDTC subgroups than in the other subgroups, which could explain the increased myelopoiesis in these patients. Assessment of the inflammatory proteome in plasma by OLINK proteomics validated these findings; circulating proteins from the IL-6 family were higher in the ATC subgroup than in the other subgroups. 48 hours of treatment of ATC cell lines with inhibitors of the IL-6/JAK/STAT3-axis resulted in decreased viability, underlining the important role of IL-6 in ATC tumors. Conclusion: PBMCs of ATC and PDTC patients have a reduced capacity to produce lymphocyte-derived cytokines while this is increased for the monocyte-derived pro-tumoral cytokines IL-6 and IL-8 compared to other TC groups and healthy controls. Plasma concentrations of IL-6 and IL-8 are higher in ATC patients compared to other TC groups. Inhibiting the IL-6/JAK/STAT3-axis results in decreased survival of ATC cell lines, emphasizing the major role of IL-6 in ATC tumor cells. Future research in other preclinical models should further elucidate the therapeutic potential of these findings. Presentation: Saturday, July 12, 2025