Abstract 531: The cGAS-STING pathway as a driver of the immune-reactive microenvironment in small cell carcinoma of the ovary, hypercalcemic type
Authors: Oudenhove Elke Van , Patibandla Jay R. , Misirlioglu Selim , Fernandez Ernesto Arostegui , Jelinic Petar , Levine Douglas A. 
Published: August 2019

Abstract
Introduction: Small cell carcinoma of the ovary, hypercalcemic type (SCCOHT) is a rare and aggressive malignancy affecting young women. The disease is characterized by a monogenic mutation of SMARCA4, a key member of the SWI/SNF complex. The treatment options are limited, and survival rates are poor. We have previously reported clinical responses in patients undergoing treatment with anti-PD1 immunotherapy, despite a low mutational burden. The responses were attributed to elevated PD-L1 expression and T-cell infiltration in SCCOHT. To better understand the mechanisms of the immune reactive microenvironment we sought to determine the role of the innate immune response driven by the STING pathway after radiotherapy.
Methods: The cGAS-STING expression of cell lines with SMARCA4 loss (H1299), SMARCA4 knockdown (293T SMARCA4) and SMARCA4 wild type (CAOV3, OVCAR4) were analyzed following 10 Gy of irradiation. We evaluated the expression of the cGAS-STING cytosolic DNA sensing pathway by measuring time-dependent expression of cGAS dependent interferon stimulated genes CCL5 and CXCL10. Finally, we analyzed the number of micronuclei formed in SCCOHT model cell lines BIN67 and SCCOHT-1 following irradiation using multi-parametric immunofluorescence.
Results: In H1299 (SMARCA4 loss), there was an 1847-fold increase (p=0.02) in CCL5 and 3954-fold increase in CXCL10 (p=0.09) at 6 days post-irradiation in comparison to non-irradiated controls. In 293T cells with stable knockdown of SMARCA4, there was a 2.8-fold increase in expression of CCL5 (p &lt; 0.01) and a 1.6-fold increase CXCL10 (p=0.26), 6 days after irradiation compared to irradiated wild type cells. In the SMARCA4 wild type cell lines CAOV3 and OVCAR4, there was no statistically significant upregulation of CCL5 and CXCL10. There were more micronucleated cells per high power field after irradiation in BIN67 (21.2% vs 9.30%, p=0.1) and SCCOHT-1 (9.4% vs 0.0%, p=0.03) compared to non-irradiated controls.
Conclusion: SCCOHT is a low mutational burden cancer with demonstrated response to immune checkpoint blockade. Our research shows that following irradiation, the innate immune response triggered by cGAS-STING may be driving the immune reactive microenvironment of SCCOHT. The loss of SMARCA4 may play a role in activating the innate immune response. Better characterization of the association between the SWI/SNF complex and immune reactivity should lead to a broader use for immune checkpoint inhibitors.
Citation Format: Elke Van Oudenhove, Jay R. Patibandla, Selim Misirlioglu, Ernesto Arostegui Fernandez, Petar Jelinic, Douglas A. Levine. The cGAS-STING pathway as a driver of the immune-reactive microenvironment in small cell carcinoma of the ovary, hypercalcemic type [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 531.