Harnessing immunomodulation during DNA damage in Ewing sarcoma

Ewing sarcoma is a fusion-oncoprotein-driven primary bone tumor most commonly diagnosed in adolescents. Given the continued poor outcomes for patients with metastatic and relapsed Ewing sarcoma, testing innovative therapeutic approaches is essential. Ewing sarcoma has been categorized as a 'BRCAness' tumor with emerging data characterizing a spectrum of DNA damage repair defects within individual Ewing tumors, including the presence of EWSR1::FLI1 itself, recurrent somatic mutations, and rare germline-based defects. It is critical to understand the cumulative impact of various DNA damage repair defects on an individual Ewing tumor's response to therapy. Further, in addition to DNA-damage-directed therapies, subsets of Ewing tumors may be more susceptible to DNA-damage/immunotherapy combinations given the significant cross-talk between DNA damage and inflammatory pathways in the tumor microenvironment. Here we review potential approaches utilizing DNA-damaging agents as modulators of the Ewing tumor immune microenvironment, with a focus on radiation and opportunities during disease metastasis and relapse.

Abstract A004: Radiation-induced changes to the immune microenvironment in an immunocompetent mouse model of Ewing sarcoma

Background: Ewing sarcoma is a rare, aggressive, fusion oncoprotein-driven pediatric cancer. Patients with upfront metastatic or surgically unresectable disease commonly undergo radiation as part of standard of care therapy. Currently, little is known about the effect of radiation specifically on the immune microenvironment of Ewing tumors, as no routine biopsies or other clinical samples are acquired during radiation. Further, historically, the field has lacked an immunocompetent mouse model of Ewing sarcoma in which to study Ewing tumor-immune cell interactions. Given our interest in understanding the anti-tumor immune response specifically during times of DNA damage, we sought to model Ewing sarcoma in a humanized mouse model (where human immune cell interactions with human tumor cells can be examined) in order to examine the Ewing tumor immune microenvironment (TIME) during radiation. Here, we determine the likeness of our established humanized mouse model of Ewing sarcoma to that of human Ewing tumors at baseline and examine changes in the Ewing TIME upon delivery of radiation. Methods: Blood from humanized NSG mice was analyzed by flow cytometry to confirm human immune cell reconstitution. Human Ewing tumor cells were injected into humanized mice and allowed to grow for approximately three weeks. Tumors were treated with radiation (either single dose or fractioned doses x 5 days) using the MultiRad350 Precision irradiator and lead shields were used to isolate the tumor area in the radiation field. Immune cells infiltrating tumors with/without radiation exposure were subsequently analyzed by multiplexed immunohistochemistry, flow cytometry, PCR, and RNAseq analysis. Ewing tumor immune infiltrates (as baseline/without radiation) from humanized mice models were compared to that of patient Ewing tumors. Results: Ewing tumors from both established and primary cell lines were successfully established in humanized mice. Similar to patient primary Ewing tumor samples, local Ewing tumors in humanized mice demonstrate a proportion of T-cell infiltration, although the overall number of infiltrating immune cells is low. Macrophage populations in Ewing sarcoma are not as predominant as in tumors such as osteosarcoma and are represented in this model. Analyses detailing the spatial localization and transcriptional profiles of Ewing tumor immune infiltrates following radiation are ongoing. Conclusions: In the absence of syngeneic and transgenic models of Ewing sarcoma, the use of humanized mouse models is a feasible alternative to address specific questions regarding the Ewing sarcoma TIME. Understanding the Ewing immune microenvironment during radiation therapy, a commonly used treatment modality in Ewing sarcoma, provides clues as to promising agents that may be worthy of preclinical testing to enhance the anti-tumor immune response during radiation in high-risk patients.

Citation Format: Jessica D. Daley, Elina M. Mukherjee, Anthony R. Cillo, Adriana C. Tufino, Nathanael G. Bailey, Tullia C. Bruno, Linda M. McAllister-Lucas, Dario A. Vignali, Kelly M. Bailey. Radiation-induced changes to the immune microenvironment in an immunocompetent mouse model of Ewing sarcoma [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr A004.

BRCA1-associated RING domain-1 (BARD1) loss and GBP1 expression enhance sensitivity to DNA damage in Ewing sarcoma

Ewing sarcoma is a fusion oncoprotein-driven primary bone tumor. A subset of patients (~10%) with Ewing sarcoma are known to harbor germline variants in a growing number of genes involved in DNA damage repair. We recently reported our discovery of a germline mutation in the DNA damage repair protein BARD1 (BRCA1-associated RING domain-1) in a patient with Ewing sarcoma. BARD1 is recruited to the site of DNA double stranded breaks via the poly(ADP-ribose) polymerase (PARP) protein and plays a critical role in DNA damage response pathways including homologous recombination. We thus questioned the impact of BARD1 loss on Ewing cell sensitivity to DNA damage and the Ewing sarcoma transcriptome. We demonstrate that PSaRC318 cells, a novel patient-derived cell line harboring a pathogenic BARD1 variant, are sensitive to PARP inhibition and by testing the effect of BARD1 depletion in additional Ewing sarcoma cell lines, we confirm that BARD1 loss enhances cell sensitivity to PARP inhibition plus radiation. Additionally, RNA-seq analysis revealed that loss of BARD1 results in the upregulation of GBP1 (guanylate-binding protein 1), a protein whose expression is associated with variable response to therapy depending on the adult carcinoma subtype examined. Here, we demonstrate that GBP1 contributes to the enhanced sensitivity of BARD1 deficient Ewing cells to DNA damage. Together, our findings demonstrate the impact of loss-of function mutations in DNA damage repair genes, such as BARD1, on Ewing sarcoma treatment response.

Central aromatization of testosterone in testicular feminized mice

Aromatization of testosterone was examined in hypothalamic and cerebral cortex tissues from 32 mice--10 normal males, 10 normal females, 2 carrying the testicular feminized gene (Tfm) and 10 Tfm with the modifying (Ohv) gene. Total aromatization was 1.5 times greater in normal males than females. In both forms of Tfm, conversions were equal and similar to normal females.

Synthesis of estrogen methyl ethers by extractive alkylation

A rapid method for the quantitative preparation of a number of estrogen methyl ethers is described. Estrogen in aqueous base is extracted as an ion pair with the tetrahexylammonium oin into methylene chloride where irreversible alkylation (extractive alkylation) by methyl iodide occurs. Gas chromatography (GC) - mass spectrometry (MS) provided the basis for identification of the methylated products. Estrone (1) and estradiol were easily 3-0-methylated whereas estriol gave a dimethylated product. Further experiments suggested that dimethylation of 2-hydroxyestrone in reasonable yield was possible.