Exploiting the DNA Damaging Activity of Liposomal Low Dose Cytarabine for Cancer Immunotherapy.

Perhaps the greatest limitation for the continually advancing developments in cancer immunotherapy remains the immunosuppressive tumor microenvironment (TME). The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) axis is an emerging immunotherapy target, with the resulting type I interferons and transcription factors acting at several levels in both tumor and immune cells for the generation of adaptive T cell responses. The cGAS-STING axis activation by therapeutic agents that induce DNA damage, such as certain chemotherapies, continues to be reported, highlighting the importance of the interplay of this signaling pathway and the DNA damage response in cancer immunity/immunotherapy. We have developed a multi-targeted mannosylated cationic liposomal immunomodulatory system (DS) which contains low doses of the chemotherapeutic cytarabine (Ara-C). In this work, we show that entrapment of non-cytotoxic doses of Ara-C within the DS improves its ability to induce DNA double strand breaks in human ovarian and colorectal cancer cell lines, as well as in various immune cells. Importantly, for the first time we demonstrate that the DNA damage induced by Ara-C/DS translates into cGAS-STING axis activation. We further demonstrate that Ara-C/DS-mediated DNA damage leads to upregulation of surface expression of immune ligands on cancer cells, coinciding with priming of cytotoxic lymphocytes as assessed using an ex vivo model of peripheral blood mononuclear cells from colorectal cancer patients, as well as an in vitro NK cell model. Overall, the results highlight a broad immunotherapeutic potential for Ara-C/DS by enhancing tumor-directed inflammatory responses.