The Ewing Family of Tumors Relies on BCL-2 and BCL-XL to Escape PARP Inhibitor Toxicity

Abstract

Purpose: It was recently demonstrated that the EWSR1-FLI1 t(11;22)(q24;12) translocation contributes to the hypersensitivity of Ewing sarcoma to PARP inhibitors, prompting clinical evaluation of olaparib in a cohort of heavily pretreated Ewing sarcoma tumors. Unfortunately, olaparib activity was disappointing, suggesting an underappreciated resistance mechanism to PARP inhibition in patients with Ewing sarcoma. We sought to elucidate the resistance factors to PARP inhibitor therapy in Ewing sarcoma and identify a rational drug combination capable of rescuing PARP inhibitor activity. Experimental Design: We employed a pair of cell lines derived from the same patient with Ewing sarcoma prior to and following chemotherapy, a panel of Ewing sarcoma cell lines, and several patient-derived xenograft (PDX) and cell line xenograft models. Results: We found olaparib sensitivity was diminished following chemotherapy. The matched cell line pair revealed increased expression of the antiapoptotic protein BCL-2 in the chemotherapy-resistant cells, conferring apoptotic resistance to olaparib. Resistance to olaparib was maintained in this chemotherapy-resistant model in vivo, whereas the addition of the BCL-2/X L inhibitor navitoclax led to tumor growth inhibition. In 2 PDXs, olaparib and navitoclax were minimally effective as monotherapy, yet induced dramatic tumor growth inhibition when dosed in combination. We found that EWS-FLI1 increases BCL-2 expression; however, inhibition of BCL-2 alone by venetoclax is insufficient to sensitize Ewing sarcoma cells to olaparib, revealing a dual necessity for BCL-2 and BCL-X L in Ewing sarcoma survival. Conclusions: These data reveal BCL-2 and BCL-X L act together to drive olaparib resistance in Ewing sarcoma and reveal a novel, rational combination therapy that may be put forward for clinical trial testing.

<p>Identification of key genes and pathways in Ewing’s sarcoma patients associated with metastasis and poor prognosis</p>

“…On the other hand, microsatellite instability (MSI) is closely related to DNA MMR deficiency (dMMR). To date, MSI has been identified to affect cancer response to chemotherapies and could regulate PD-1 blockade response in the solid tumor 29,30. Gryfe et al reported that dMMR tumors had significantly more favorable prognosis,31 and this result was supported by other researchers 32.…”

“…EWSR/FLI1 protein regulates multiple target gene expression, which acts as a critical in ES. Heisey et al found that EWSR/FLI1 fusion would increase BCL-2 expression, and thereby induce drug resistant to PARP inhibitors, and BCL-2 and BCL-XL inhibition could significantly reverse the drug resistance in ES. 30 FOXO1 is a cancer suppressor in multiple cancer types,45–47 which significantly inhibited cell proliferation and clone formation ability in ES cell 48.…”

Comprehensive Analysis of Key Genes and Regulatory Elements in Ewing Sarcoma With Prognostic Values

“…Some of them have been stated involved in the tumorigenesis and progression of ES. A previous study revealed that BCL2 interacted with BCLXL to escape PARP inhibitor toxicity in ES [33]. The density of CD68-positive Tumor-associated macrophages was found in ES tissue samples and statistically correlated with clinical parameters [34].…”

Interrogation of SLFN11 in pediatric sarcomas uncovers an unexpected biological role and a novel therapeutic approach to overcoming resistance to replicative stress

“…During this project, it was reported that resistance to the PARPi olaparib in ES cell lines could be overcome with the pan-BCL2 inhibitor navitoclax [41]. Motivated by that work and by our own findings, we screened small molecules inhibitors that were selective for individual BCL2 family members: venetoclax (BCL2), S63845 (MCL), and A-1331852 (BCL-XL).…”