Signal transducer and activator of transcription 3 (STAT3) is a well-described transcription factor that mediates oxidative phosphorylation and glutamine uptake in bulk acute myeloid leukemia (AML) cells and leukemic stem cells (LSCs). STAT3 has also been shown to translocate to the mitochondria in AML cells, and phosphorylation at the serine 727 (pSTAT3 S727) residue has been shown to be especially important for STAT3's mitochondrial functions. We demonstrate that inhibition of STAT3 results in impaired mitochondrial function and decreased leukemia cell viability. We discovered a novel interaction of STAT3 with voltage-dependent anion channel 1 (VDAC1) in the mitochondria which provides a mechanism through which STAT3 modulates mitochondrial function and cell survival. Through VDAC1, STAT3 regulates calcium and oxidative phosphorylation in the mitochondria. STAT3 and VDAC1 inhibition also result in significantly reduced engraftment potential of LSCs, including primary samples resistant to venetoclax. These results implicate STAT3 as a therapeutic target in AML.

Replication stress exerts an important role in fueling genomic instability characterizing multiple myeloma (MM) evolution and is a leading cause of drug resistance. Normal and malignant plasma cells (PCs) are associated with a high transcriptional stress due to the huge production of immunoglobulins. Transcription-replication conflicts (TRCs), arising from collisions between replication and transcription machineries, can promote tumor progression and represent an Achilles' heel to cancer cells. We reported a gene signature related to TRCs management (TRC score), overexpressed in malignant vs normal PCs. High TRC score identified patients with MM with a poor prognosis who could benefit from a TRC-enhancing therapy, in independent cohorts of patients with MM treated with high-dose melphalan chemotherapy or anti-CD38 immunotherapy. Here, we investigated the therapeutic interest of increasing TRCs to target specifically malignant PCs using the G-quadruplex (G4) stabilizer pyridostatin (PDS). PDS exerted significant toxicity in MM cell lines and primary MM cells, inducing DNA damage, cell cycle arrest, and apoptosis. Importantly, primary myeloma cells are significantly more sensitive to PDS treatment than normal bone marrow cells. Moreover, PDS improved the efficacy of MM treatments such as melphalan and histone deacetylase (HDAC) or bromodomain (BRD) inhibitors. Thus, our study shows that G4 stabilizers could be used to specifically target MM cells that exhibit concomitant replication stress and a high level of transcription, through the increase of TRCs. These molecules could be used to increase the efficacy of other treatments including melphalan, HDAC inhibitors, and BRD inhibitors.
© 2025 American Society of Hematology. Published by Elsevier Inc.

T-cell receptor recognition of cognate peptide-MHC leads to the formation of signalling domains and the immunological synapse. Because of the close membrane apposition, there is rapid exclusion of CD45, and therefore LCK activation. Much less is known about whether spatial regulation of the intracellular face dictates LCK activity and TCR signal transduction. Moreover, as LCK is a driver in T acute lymphocytic leukaemia, it is important to understand its regulation. Here, we demonstrate a direct role of the ciliary protein UNC119 in trafficking LCK to the immunological synapse. Inhibiting UNC119 reduces localisation of LCK without impairing LCK phosphorylation and reduces T-cell receptor signal transduction. Although important for initial LCK reorganisation, activated CD8+ T cells retained their ability to kill target tumour cells when UNC119 was inhibited. UNC119 was also needed to sustain proliferation in patient-derived T-ALL cells. UNC119 may therefore represent a novel therapeutic target in T acute lymphocytic leukaemia, which alters the subcellular localisation of LCK in T acute lymphocytic leukaemia cells but preserves the function of existing cytotoxic lymphocytes.
© 2025 Samarakoon et al.

DHX9 is a multifunctional DExH-box RNA helicase with important roles in the regulation of transcription, translation, and maintenance of genome stability. Elevated expression of DHX9 is evident in multiple cancer types, including colorectal cancer. Microsatellite instable-high (MSI-H) tumors with deficient mismatch repair (dMMR) display a strong dependence on DHX9, making this helicase an attractive target for oncology drug discovery. In this report, we show that DHX9 knockdown increased RNA/DNA secondary structures and replication stress, resulting in cell-cycle arrest and the onset of apoptosis in cancer cells with MSI-H/dMMR. ATX968 was identified as a potent and selective inhibitor of DHX9 helicase activity. Chemical inhibition of DHX9 enzymatic activity elicited similar selective effects on cell proliferation as seen with genetic knockdown. In addition, ATX968 induced robust and durable responses in an MSI-H/dMMR xenograft model but not in a microsatellite stable/proficient MMR model. These preclinical data validate DHX9 as a target for the treatment of patients with MSI-H/dMMR. Additionally, this potent and selective inhibitor of DHX9 provides a valuable tool with which to further explore the effects of inhibition of DHX9 enzymatic activity on the proliferation of cancer cells in vitro and in vivo. Significance: DHX9 is required in cancer cells with deficient mismatch repair and can be inhibited by ATX968, providing a promising strategy for the development of precision cancer therapeutics.
©2024 The Authors; Published by the American Association for Cancer Research.

The reaction of different cell types to prion infections is highly heterogeneous. While neurons experience spine retraction and eventually death, astrocytes and microglia undergo strong activation and proliferation. Here we analyzed the cell-type specific responses to prion diseases by establishing a spatiotemporal transcriptomic atlas of mice infected with RML prion strain. Brain areas with severe neuronal loss, such as thalamus and cerebellum, experienced intense microgliosis. Starting from 30 weeks post-inoculation, we observed the accumulation of a novel microglial subpopulation characterized by strong expression of Gpnmb in these brain regions. The molecular profile of Gpnmb+ microglia reflected a state of enhanced phagocytic activity with upregulation of genes associated with lysosomal function and degradation, including vacuolar ATPase V0 domain subunit d2 (Atp6v0d2) and Galectin-3 (Lgals3). In murine BV2 cells, Gpnmb upregulation was induced by soluble find-me signals released during apoptosis, but not by apoptotic bodies or prion accumulation. Gpnmb ablation in BV2 cells impaired their ability to phagocytose apoptotic cells, underscoring its essential role in maintaining microglial phagocytosis. Our findings define Gpnmb⁺ microglia as a distinct, apoptosis-driven phagocytic state, linking neuronal loss to microglial activation in prion disease. The upregulation of GPNMB in sCJD patients, along with its role in apoptotic clearance and lysosomal function, positions it as both a key regulator of microglial responses and a potential biomarker of disease progression.