Abstract 2064: Targeting Cblb-Notch1 axis as a novel strategy for cancer immunotherapy

Abstract

Abstract Background: Tumor-induced immunosuppression is a way in which cancers evade the host immune response. In recent years, a great effort has been made in designing immunotherapies that can boost the immune system response against cancer. However, not all tumors respond to these therapies. Therefore, there remains an unmet need for immunotherapies that are able to circumvent tumor-induced immunosuppression. Adenosine is an immunosuppressive metabolite which is overproduced in hypoxic tumor microenvironments and dampens T-cell anti-tumor immune responses. Adenosine A2A receptor (A2AR) activation was shown to downregulate Notch1, a key regulator of T-cell functions, in CD8+ T-cells, leading to immunosuppression. Notch1 signaling appears to protect T-cells against immunosuppressive signals, as Notch1 overexpressing T-cells were shown to be resistant to tumor-induced immunosuppression mediated by myeloid-derived suppressor cells (MDSC), as well as adenosine. We hypothesize that rescuing Notch1 from downregulation will make T-cells resistant to tumor-induced immunosuppression. We applied several functional assays in primary CD8+ T-cells and tumor-derived organoids to study how Notch1 is regulated by A2AR and explore strategies to target this pathway for cancer immunotherapy. Results: Our results indicate that the ubiquitin ligase Cbl-b, a negative regulator of T-cell functions, is responsible for the ubiquitination and degradation of Notch1 in CD8+ T-cells. A2AR signaling leads to Notch1 downregulation by promoting Cbl-b-mediated Notch1 degradation. Inhibition of Cbl-b using small molecule compounds restores Notch1 and T-cell functions in CD8+ T-cells in the presence of adenosine, making them resistant to A2AR-mediated immunosuppression. Cbl-b inhibitors show anti-tumor activity in tumor-derived organoids from pre-clinical models and enhance immune-checkpoint immunotherapy, by promoting T-cells anti-cancer responses. Conclusions: Our work suggests that promoting Notch1 signaling by blocking Cbl-b-mediated degradation results in increased T-cell responses and resistance to immunosuppression. Targeting Cbl-b-Notch1 axis represents a promising novel strategy to boost anti-cancer T-cell responses. Citation Format: Giulia Monticone, Fred Csibi, Silvana Leit, Jermaine E. Austin, Deniz A. Ucar, Fokhrul M. Hossain, Samarpan Majumder, Barbara A. Osborne, Christine Loh, Lucio Miele. Targeting Cblb-Notch1 axis as a novel strategy for cancer immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2064.