Abstract PO-099: Overexpression of proinflammatory chemokines CCL5 and CCL17 after gene electrotransfer to murine tumors modifies their cytokine expression profile and leads to tumor cures in combination with tumor irradiation

Proinflammatory chemokines are small signaling proteins, with the ability to induce migration of different types of immune cells. The degree and type of immune cell infiltrate in the tumor microenvironment often correlates with the outcome of immunotherapies in cancer patients. Therefore, combining chemokines with classical, but immune response activating therapy, such as irradiation presents one of the potential approaches in cancer immunotherapy. Through the use of plasmid DNA encoding either proinflammatory chemokine CCL5 or CCL17 we studied their effects on cytokine expression profile in vitro and in vivo in murine breast (4T1, E0771) and colon (CT26, MC38) cancer models. While in vitro plasmid DNA was introduced in the cells using lipofection, gene electrotransfer was utilized in case of tumors in vivo. Viability of all cell lines 48 h after lipofection remained above 80%. Using qRT-PCR expression of 11 cytokines was determined 48 h after lipofection, which showed significantly increased expression of CCL5, CCL17 demonstrating successful transfection. Moreover, increased levels of IL-6 and CXCL10 were also observed in the surviving cells. Gene electrotransfer after intratumoral injection of plasmid DNA encoding either CCL5 or CCL17 in CT26 and 4T1 murine tumor model (animal license: U34401-1/2015/43) resulted in minor tumor growth delay. Concurrent expression analysis of 7 cytokines after gene electrotransfer in tumors showed overexpression of both chemokines, while levels of proinflammatory cytokines IL-6, IL-12 and IFNγ were modestly increased. Obtained altered expression profile, both in vitro and in vivo, is typical for inflammation. Furthermore, irradiation of CT26 and 4T1 tumors combined with gene electrotransfer of plasmids encoding CCL5 or CCL17 resulted in significant tumor growth delay and even tumor cures. Therefore, based on changes in tumor microenvironment after therapy future experiments will be focused towards elucidating the mechanisms of immune response and determining the optimal time window for combined tumor irradiation and gene electrotransfer of plasmids encoding chemokines CCL5 and CCL17. Citation Format: Gregor Sersa, Tim Bozic, Bostjan Markelc, Maja Cemazar, Simona Kranjc Brezar. Overexpression of proinflammatory chemokines CCL5 and CCL17 after gene electrotransfer to murine tumors modifies their cytokine expression profile and leads to tumor cures in combination with tumor irradiation [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr PO-099.