Abstract 4226: Genome-wide CRISPRi screening identifies histone modification as a synergistic partner with JAK/STAT inhibition for enhancing anti-tumor activity in CTCL, validated in PDX-derived tumor cells

Cutaneous T-cell lymphoma (CTCL) is a subtype of non-Hodgkin lymphoma and a counterpart to the nodal form of T-cell lymphomas, peripheral T-cell lymphoma (PTCL). Patients with advanced-stage CTCL have a median survival of 3-5 years, a result that has not significantly improved for decades, highlighting an unmet medical need. The JAK/STAT pathway is frequently dysregulated in PTCL and CTCL through point mutations and copy number changes. These genetic aberrations lead to uncontrolled signaling, cell proliferation, and disease progression. The JAK/STAT pathway has been established as a suitable therapeutic target in PTCL and CTCL, with several inhibitors, including ruxolitinib, demonstrating clinical activity. However, response rates remain modest, and the clinical benefits are often transient. To identify synergistic partners for ruxolitinib, we conducted a genome-wide CRISPRi screening in CTCL cell lines, HH and Hut78. The screen identified histone modification, particularly acetylation and methylation, as a key mechanism involving the sensitivity of CTCL cells to ruxolitinib. To validate these findings, we assessed the anti-tumor activities of ruxolitinib in combination with histone-modifying agents already in clinical use, such as romidepsin and 5-azacitidine. Combination studies demonstrated that romidepsin and 5-azacitidine synergistically enhanced the growth-inhibitory and apoptotic-inducing effects of ruxolitinib in CTCL cell lines, HH and Hut 78, as well as in primary tumor cells from CTCL patient-derived xenograft (PDX) models. Notably, similar synergy was observed with golidocitinib, a novel JAK1 inhibitor that demonstrated promising clinical activity in PTCL, indicating an on-target class effect of synergy between JAK/STAT inhibition and histone-modifying agents. Using primary human CTCL cells derived from PDX models, we observed synergistic induction of apoptosis with ruxolitinib or golidocitinib in combination with either romidepsin or 5-azacitidine, as demonstrated by caspase activation assays. In conclusion, histone modification agents significantly enhance the anti-tumor activity of JAK/STAT inhibitors, promoting both growth inhibition and apoptosis induction. Synergy was observed with two distinct JAK/STAT inhibitors, ruxolitinib and golidocitinib, both already in clinical use. These findings demonstrated in primary human CTCL cells from the PDX models—a clinically relevant experimental system—highlight the translational significance of this approach. Ongoing therapeutic trials with PDX animals will further investigate these promising findings. Citation Format: Yan-Jin Liu, Haitao Wang, Laura Pincus, Frank McCormick, Weiyun Z. Ai. Genome-wide CRISPRi screening identifies histone modification as a synergistic partner with JAK/STAT inhibition for enhancing anti-tumor activity in CTCL, validated in PDX-derived tumor cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4226.