Pharmacologic inhibition of beta-adrenergic receptors decreases PD-L1 mediated immunosuppression and improves anti-tumor immune signature in ovarian cancer (126)

Abstract

<b>Objectives:</b> The immune system is affected by stress hormones, but also plays an important role in activating and suppressing mechanisms controlling epithelial ovarian cancer (EOC). Although EOC is a "cold tumor" the trafficking of tumor infiltrating lymphocytes in the tumor mass and the expression of programmed cell death ligand (PD-L1) are prognostic indicators in EOC. To date PD-1/PD-L1 inhibitors have had limited benefit as single agents or in combination with chemotherapy. This study aimed to explore the impact of adrenergic stress and its blockade with propranolol in both <i>in vitro</i> and <i>in vivo</i> EOC models. <b>Methods:</b> Two high grade serous cell lines SKOV3ip1 and OVCAR8 were used in co-culture experiments and exosome experiments. Western blot was used to detect changes in PD-L1 protein expression in exosomes treated with noradrenaline, propranolol, and interferon-gamma (IFN-g). C57bl/6 mice were injected with ID8 cells and exposed to chronic behavioral stress to activate the beta-adrenergic signalling pathway. Mice were treated with the following combinations: control (saline), propranolol (2mg/Kg/d via Alzet pump for 6 weeks), PD-1/PD-L1 inhibitor (200μg/mouse IP, three times a week for two weeks) or a combination of propranolol and PD-1/PD-L1 inhibitor. CD3, CD4, CD8 and CXCL10 mRNA expression were evaluated in the tumors with qPCR. GraphPad Prism v.7 was used as well as one-way ANOVA with Bonferroni multiple comparison test correction. <b>Results:</b> EOC cell lines were treated with noradrenaline (NA), propranolol, IFN-g or in combination (NA+ IFN-g). NA+IFN-g caused an increase in PD-L1 mRNA and protein expression (p<0.05). IFN-g causes a statistically significant increase in the production of PD-L1 carrying exosomes (p<0.05) while propranolol does not. Combination of propranolol and PD-1/PD-L1 inhibitor significantly reduced tumour weight compared to the cancer control group (p<0.05). Chronic behavioural stress significantly increased the number of organs with metastatic nodules (p<0.05) while propranolol monotherapy and the combined therapy showed a significant decrease in the number of organs affected by metastatic nodules (p<0.001). VEGF expression was significantly reduced in the combined therapy group compared to the propranolol and PD-1/PD-L1 monotherapy (p<0.001). CD8 CD3, CD4 mRNA expression increased significantly in the combined therapy group compared to PD-1/PD-L1 inhibitor monotherapy and the control group (p<0.05). Propranolol also decreased IDO1 and CXCL10 mRNA as well. <b>Conclusions:</b> Propranolol decreases upstream production of IFN-g and the IFN-g-mediated PD-L1 expression on cancer cells. Therefore the combination of propranolol with PD-L1 inhibitors is a promising therapy in this preclinical EOC model.