Elevated Levels of Interleukin-9 in Obese Microenvironments Promote Leukemia Progression and Chemoresistance in B-Cell Acute Lymphoblastic Leukemia Cells

Background: The CDC reports that obesity rates in children and adolescents have more than tripled since the 1970's (Ogden et al., 2006; Ogden et al., 2016). Obese pediatric patients with B-cell acute lymphoblastic leukemia (B-ALL) have inferior overall survival compared to lean patients, with obese patients having a 2.5-fold increased risk of an adverse event and an almost 4-fold greater risk of death compared to non-obese patients (Butturini et al., 2007; Eissa et al., 2017; Ethier et al., 2012). Emerging data suggest that factors in the obese microenvironment directly promote chemoresistance in B-ALL cells (Ehsanipour et al., 2013; Sheng et al., 2016). Despite the emerging epidemiological and clinical studies highlighting the negative impact of obesity on cancer outcomes, there remains a lack of understanding of the molecular mechanisms underlying the dismal outcomes of obese patients with B-ALL.

Methods: Using a global cytokine profiling array, we found that multiple cytokines were secreted at low levels in a lean microenvironment compared to the obese microenvironment. We decided to focus solely on cytokines exclusively present at high concentrations in the obese microenvironment relative to the lean microenvironment in order to determine their impact on the function of murine and human B-ALL cell lines. We also utilized the diet-induced murine model of obesity to determine how survival and treatment outcomes differ in lean and obese mice challenged with B-ALL. Furthermore, we determined how obesity altered the function of B-ALL cells in pediatric patients using primary samples obtained through the Aflac Leukemia and Lymphoma Biorepository.

Results: We made the novel finding that Interleukin-9 is elevated in obese microenvironments and alters the function of human B-ALL cells. It has been previously shown that interleukin-9 (IL-9) promotes chemoresistance in diffuse large B-cell lymphoma and is associated with a worse prognosis in patients with B-cell chronic lymphocytic leukemia (Chen, Lv, Li, Lu, & Wang, 2014; Lv, Feng, Ge, Lu, & Wang, 2016); however, the impact of IL-9 on B-ALL development is unknown. We have found that IL-9 levels were significantly increased in adipose-rich microenvironments. Human B-ALL cells exposed to these environments upregulated the IL-9 receptor (IL-9R), which was not observed in stromal-cell rich microenvironments. Stimulating human B-ALL cells with recombinant IL-9 (rIL-9) promoted cell progression and extensive proliferation over 3 days of culture. Furthermore, rIL-9 stimulation of human B-ALL cells activated survival pathways (STAT3) which coincides with the induction of chemoresistance to methotrexate.

Conclusions: We have found that IL-9 levels are elevated in obese microenvironments and alters the function of human B-ALL (increased proliferation, activation of survival pathways, and induction of chemoresistance). In ongoing murine studies, we will determine if the survival of obese mice with B-ALL is prolonged when chemotherapy treatment and IL-9 neutralizing strategies are combined.