Effects of JAK/STAT inhibitors in cutaneous T-cell lymphoma cells

Summary: Abstract Body: Mycosis fungoides (MF) and Sézary syndrome (SS) are the most common types of cutaneous T-cell lymphoma (CTCL), characterized by defective apoptosis and uncontrolled proliferation of malignant T-cells. Current treatments alleviate symptoms but lack a definitive cure. Dysregulation of the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway is a key driver of CTCL pathogenesis, making it a promising yet understudied therapeutic target. This study evaluates the effects of JAK/STAT inhibitors on MF-derived MJ cells and SS-derived HuT 78 cells in vitro. Four JAK inhibitors were tested: Abrocitinib (JAK1), Tofacitinib (pan-JAK, potent JAK3 inhibition), Ritlecitinib (JAK3), and Brepocitinib (pan-JAK, potent TYK2/JAK1 inhibition). Two STAT inhibitors targeted STAT3 (TTI-101) and STAT6 (AS1517499). Cell proliferation was assessed using the MTS assay, and apoptosis was analyzed by flow cytometry. For proliferation inhibition, all inhibitors demonstrated inhibitory effects in both cell lines. Among JAK inhibitors, HuT 78 cells were most sensitive to Abrocitinib (IC50: 1.71 µM), followed by Brepocitinib (2.30 µM), Tofacitinib (7.42 µM), and Ritlecitinib (14.30 µM) at 48 hours. MJ cells were most sensitive to Tofacitinib (IC50: 4.35 µM), followed by Brepocitinib (6.97 µM), Ritlecitinib (13.77 µM), and least sensitive to Abrocitinib (24.83 µM). STAT inhibitors showed strong effects, with HuT 78 cells sensitive to both AS1517499 (2.19 µM) and TTI-101 (1.23 µM). MJ cells were more sensitive to AS1517499 (1.23 µM) than TTI-101 (5.75 µM). For apoptosis induction, STAT inhibitors exhibited stronger effects than JAK inhibitors in both cell lines. AS1517499 induced greater apoptosis than TTI-101. Notably, Tofacitinib combined with AS1517499 or TTI-101 showed synergistic apoptotic effects, as did the combination of the two STAT inhibitors. These findings underscore the efficacy of JAK/STAT inhibitors in MJ and HuT 78 cells, highlight differential sensitivities between the cell lines, and support ongoing investigations into the underlying mechanisms. Xiaoying Zhang¹, Xiaohong Wang¹, Madeleine Duvic¹, Julia Dai¹, Xiao Ni¹ 1. Dept. of Dermatology, The University of Texas MD Anderson Cancer Center, Houston, TX, United States. Translational Studies: Preclinical