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Published on: June 6, 2025
Serum-resistant CpG-STAT3 decoy for targeting survival and immune checkpoint signaling in acute myeloid leukemia
Qifang Zhang1, Dewan Md Sakib Hossain2, Priyanka Duttagupta2
1Department of Immuno-Oncology, Beckman Research Institute at City of Hope, Duarte, CA; Key Laboratory of Medical Molecular Biology, Guizhou Medical University, Guiyang, People's Republic of China;
Abstract:
Targeting oncogenic transcription factor signal transducer and activator of transcription 3 (STAT3) in acute myeloid leukemia (AML) can reduce blast survival and tumor immune evasion. Decoy oligodeoxynucleotides (dODNs), which comprise STAT3-specific DNA sequences are competitive inhibition of STAT3 transcriptional activity. To deliver STAT3dODN specifically to myeloid cells, we linked STAT3dODN to the Toll-like receptor 9 (TLR9) ligand, cytosine guanine dinucleotide (CpG). The CpG-STAT3dODN conjugates are quickly internalized by human and mouse TLR9(+)immune cells (dendritic cells, B cells) and the majority of patients' derived AML blasts, including leukemia stem/progenitor cells. Following uptake, CpG-STAT3dODNs are released from endosomes, and bind and sequester cytoplasmic STAT3, thereby inhibiting downstream gene expression in target cells. STAT3 inhibition in patients' AML cells limits their immunosuppressive potential by reduced arginase expression, thereby partly restoring T-cell proliferation. Partly chemically modified CpG-STAT3dODNs have >60 hours serum half-life which allows for IV administration to leukemia-bearing mice (50% effective dose ∼ 2.5 mg/kg). Repeated administration of CpG-STAT3dODN resulted in regression of human MV4-11 AML in mice. The antitumor efficacy of this strategy is further enhanced in immunocompetent mice by combining direct leukemia-specific cytotoxicity with immunogenic effects of STAT3 blocking/TLR9 triggering. CpG-STAT3dODN effectively reducedCbfb/MYH11/MplAML burden in various organs and eliminated leukemia stem/progenitor cells, mainly through CD8/CD4 T-cell-mediated immune responses. In contrast, small-molecule Janus kinase 2/STAT3 inhibitor failed to reproduce therapeutic effects of cell-selective CpG-STAT3dODN strategy. These results demonstrate therapeutic potential of CpG-STAT3dODN inhibitors with broad implications for treatment of AML and potentially other hematologic malignancies.
Insights
This study developed a novel CpG-STAT3dODN conjugate to target acute myeloid leukemia (AML) cells. This conjugate effectively inhibits STAT3, reduces tumor burden, and enhances anti-leukemia immune responses in preclinical models.
Area of Science:
- Oncology
- Immunology
- Molecular Biology
Background:
- Signal transducer and activator of transcription 3 (STAT3) is a key oncogenic driver in acute myeloid leukemia (AML), promoting blast survival and immune evasion.
- Targeting STAT3 offers a potential therapeutic strategy for AML, but effective and specific delivery remains a challenge.
Purpose of the Study:
- To develop and evaluate a novel targeted delivery system for STAT3 decoy oligodeoxynucleotides (dODNs) in AML.
- To assess the efficacy of CpG-STAT3dODN conjugates in inhibiting STAT3 activity, reducing AML burden, and modulating the immune response.
Main Methods:
- STAT3-specific decoy oligodeoxynucleotides (dODNs) were conjugated to a Toll-like receptor 9 (TLR9) ligand, cytosine guanine dinucleotide (CpG).
- The cellular uptake, STAT3 inhibition, and downstream effects of CpG-STAT3dODN conjugates were evaluated in human and mouse AML models.
- Therapeutic efficacy was assessed in vivo following intravenous administration in leukemia-bearing mice, including immunocompetent models.
Main Results:
- CpG-STAT3dODN conjugates were efficiently internalized by AML blasts and immune cells expressing TLR9.
- STAT3 inhibition by CpG-STAT3dODN reduced AML cell immunosuppressive potential and restored T-cell proliferation.
- Intravenous administration of CpG-STAT3dODN led to significant AML regression, elimination of leukemia stem/progenitor cells, and enhanced T-cell-mediated anti-leukemia immunity in mice.
Conclusions:
- CpG-STAT3dODN conjugates represent a promising cell-selective therapeutic strategy for AML by combining direct anti-leukemic effects with immunomodulation.
- This approach demonstrates superior therapeutic outcomes compared to small-molecule STAT3 inhibitors in preclinical AML models.
- CpG-STAT3dODN holds potential for treating AML and other hematologic malignancies.
