Abstract 178: Adipose tissue upregulates expression of RANKL in B-cell acute lymphoblastic leukemia through prostaglandin E2 signaling
Authors: Cohen Michael , Tan Jia , Kuk Tyler , Nadeak Blesscamal , Ahn In Sook , Yang Xia , Orgel Etan , Mittelman Steven D. 
Published: March 2024

Abstract
Obesity increases the risk of developing cancer and worsens treatment outcome. Our lab has shown that adipose tissue contributes to B-cell acute lymphoblastic leukemia (B-ALL) resistance to chemotherapy both in vitro and in vivo. However, the mechanisms by which adipose tissue causes ALL cell resistance are complex and not completely understood. We therefore implanted obese mice (n=3) with syngeneic BCR/ABL B-ALL cells and performed single-cell RNA sequencing (scRNAseq) of ALL collected from epididymal adipose tissue vs. bone marrow. Our data uncovered a strong adipose microenvironment effect on the ALL transcriptome, identifying 577 differentially expressed genes using a log2 fold threshold of 0.25 and Bonferroni corrected p-values &lt;0.05. Notably, we found that ALL cells in adipose tissue upregulate expression of Tnfsf11, the gene that encodes receptor activator of nuclear factor kappa beta ligand (RANKL). 93% of ALL cells in adipose tissue express RANKL compared to 33% in marrow, along with a log2 fold expression increase of 2.12 (p&lt;1 × 10−100, Wilcoxon test). Because ALL expression of RANKL has been linked to bone resorption and CNS invasion, both of which have increased incidence in obese patients, we elected to explore this further. Ex vivo culture with human visceral adipose tissue validated ALL cell RANKL upregulation, demonstrating a 1.63 and 17.5-fold increase in gene expression after 48 hours in BV173 and RS4;11 B-ALL cell lines, respectively (n=4-6, both p&lt;0.01, paired t test). Soluble RANKL was not detected in media from ALL cells cultured alone, detectable in media conditioned by human adipose tissue (0.018 pM), but increased in media from adipose-ALL cocultures (RS4;11: 0.065 pM, BV173: 0.317 pM, n=1). One potential candidate signal to stimulate ALL cell RANKL expression is the inflammatory mediator prostaglandin E2 (PGE2), which is known to be released by adipose tissue. Physiological concentrations of PGE2 (200 ng/mL) caused a similar increase in ALL cell RANKL gene expression as adipose tissue in both cell lines (n=6). PGE2 treatment also caused a mild resistance of ALL cells to daunorubicin chemotherapy in vitro, increasing the EC50 from 27±4 to 53±12 nM in RS4;11 (n=6, p&lt;0.05), and from 39±11 to 62±19 nM in BV173 (n=6, p=0.06). Adipose tissue induction of RANKL expression was partially blocked by the addition of PGE2 receptor EP2 and EP4 blockers. Taken together, our results suggest that PGE2 produced by the adipose microenvironment activates ALL cell RANKL expression, which could potentially contribute to CNS invasion, bone breakdown, and chemoresistance.
Citation Format: Michael Cohen, Jia Tan, Tyler Kuk, Blesscamal Nadeak, In Sook Ahn, Xia Yang, Etan Orgel, Steven D. Mittelman. Adipose tissue upregulates expression of RANKL in B-cell acute lymphoblastic leukemia through prostaglandin E2 signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 178.