Ligand-induced STAT3 signaling increases at relapse and is associated with outcome in pediatric acute myeloid leukemia: a report from the Children's Oncology Group

Roles of STAT3 in leukemia (Review)

Leukemia is a type of hematopoietic malignancy, and the incidence rate in the United States and European Union increases by an average of 0.6 to 0.7% annually. The incidence rate in China is approximately 5.17/100,000 individuals, and the mortality rate is 3.94/100,000 individuals. Leukemia is the most common tumor affecting children and adults under 35 years of age, and is one of the major diseases leading to the death of adolescents. Signal transducer and activator of transcription 3 (STAT3) is a vital regulatory factor of signal transduction and transcriptional activation, and once activated, the phosphorylated form of STAT3 (p-STAT3) is transferred into the nucleus to regulate the transcription of target genes, and plays important roles in cell proliferation, differentiation, apoptosis and other physiological processes. An increasing number of studies have confirmed that the abnormal activation of STAT3 is involved in the development of tumors. In this review, the roles of STAT3 in the pathogenesis, diagnosis, treatment and prognosis of leukemia are discussed in the aspects of cell proliferation, differentiation and apoptosis, with the aim to further clarify the roles of STAT3 in leukemia, and shed light into possible novel targets and strategies for clinical diagnosis and treatment.

Interleukin-6 levels predict event-free survival in pediatric AML and suggest a mechanism of chemotherapy resistance

The tumor microenvironment can protect cancer cells from conventional anticancer therapies. Thus, targeting these protective mechanisms could eradicate therapy-resistant cancer cells and improve outcomes. Interleukin-6 (IL-6) provides extrinsic protection for several solid tumors and multiple myeloma. In pediatric acute myeloid leukemia (AML), IL-6-induced STAT3 signaling frequently becomes stronger at relapse, and increases in IL-6-induced STAT3 activity are associated with inferior survival after relapse. These findings suggested that the IL-6-induced STAT3 pathway may promote chemotherapy resistance and disease progression. Thus, we investigated the dysregulation of IL-6 levels in the bone marrow niche in pediatric patients with AML and the association between IL-6 levels and outcome. We measured levels of over 40 cytokines and growth factors in plasma from diagnostic bone marrow aspirates of 45 pediatric AML patients and 7 healthy sibling controls. Of the measured cytokines, only IL-6 levels were associated with event-free survival. Importantly, the effect of elevated IL-6 was most striking among children classified as having a low risk of relapse. In these patients, 5-year event-free survival was 82.5% ± 11% for patients with low IL-6 levels at diagnosis (n = 14) compared with 17.3% ± 11% for patients with elevated IL-6 (n = 13, log-rank P = .0003). In vitro, exogenous IL-6 reduced mitoxantrone-induced apoptosis in cell lines and primary pediatric AML samples. These results suggest that IL-6 levels at diagnosis could be used to help identify children at high risk of relapse, particularly those who are otherwise classified as low risk by current algorithms. Moreover, the IL-6 pathway could represent a target for overcoming environment-mediated chemotherapy resistance.