STAT3 Inhibition Enables TLR9-Driven Differentiation of Cbfb/Myh11 acute Myeloid Leukemia Cells to Antigen-Presenting Cell Phenotype In Vivo

STAT3 transcription factor is persistently activated in cancer cells and in diverse tumor-associated immune cells being an important oncogene and an essential immune checkpoint regulator. It is a highly desirable but challenging therapeutic target for pharmacological intervention. We previously demonstrated that ligand for the intracellular receptor TLR9 (CpG oligonucleotide) allows for the uptake and cytoplasmic delivery of decoy oligodeoxynucleotides (dODNs) to inhibit transcriptional activity of STAT3 in a variety of human and mouse acute myeloid leukemia (AML) cells. Here, we demonstrate that CpG-STAT3dODN injected intravenously to mice engrafted with Cbfb/MYH11 AML, dramatically altered leukemic cell morphology, by reducing nucleus-cytoplasm ratio and increasing mitochondria size, and also resulting in metabolic shift from glycolysis to oxidative phosphorylation, resulting in increased mitochondrial ATP production. The transcriptional profiling of AML cells isolated from spleens of mice treated using CpG-STAT3dODN vs control CpG-scrODN or PBS, revealed the increased expression of genes regulating myeloid cell differentiation (Irf8, Cebpa, Gadd45a) and antigen-presentation (B2m, CIIta, IL-12a, Ifng), with decrease of leukemia-related regulators Runx1and Run1t1. Thein vivodifferentiation of leukemic cells was confirmed using flow cytometry by detecting appearance of the population of AML-derived CD11b⁺/MHCII⁺/CD86⁺myeloid cells after CpG-STAT3dODN but not control treatments. Furthermore, we confirmed that the differentiated AML cells have immunogenic effects, which drive expansion of Th1 effector T cell responses in Cbfb/MYH11 as well as C1498 AML models. Overall, our studies suggest that STAT3-inhibition can unleash immune-stimulatory potential downstream of TLR9 signaling transforming AMLcells into antigen-presenting cells. These findings support development of CpG-STAT3dODN strategy as a new bi-functional agent for AML immunotherapy.

This project described was supported by the National Cancer Institute of the National Institutes of Health under award number R01CA213131 to M.K.