Abstract 4603: Protocol optimization combining activatable nanodelivery with immunotherapy in a murine breast cancer model

Activatable nanotherapeutics provide the opportunity to deliver anthracyclines to a well-controlled region of interest and therefore to locally stimulate immunogenic cell death. Such a strategy can be combined with immunotherapy for both local tumor control and creation of an abscopal effect. Our group previously reported that combining local administration of a CpG oligonucleotide with local release of doxorubicin from a temperature-sensitive liposomal nanoparticle (TSL) led to the elimination of directly treated lesions in a syngeneic murine model of mammary adenocarcinoma.1 While this therapeutic approach increased the numbers of tumor infiltrating CD8+ T lymphocytes in distant lesions and extended survival, distant tumors returned with a growth delay of approximately 14 days and T-regulatory cells were not reduced by treatment. Therefore, checkpoint blockade of the programmed death-1 (PD-1) pathway (anti-PD-1) was incorporated in the protocol. CuDox-TSL were prepared from DPPC:MPPC:DSPE-PEG2k (86:10:4) in the presence of copper (II) gluconate and triethanolamine at 0.2 mg-drug/mg-lipid. A complex between doxorubicin and copper was created to enhance the circulation and stability of TSL and to reduce systemic toxicity. On day 21, mice with bilateral invasive neu deletion (NDL) tumors (~4 mm) were treated with i.v. administration of CuDox-TSL at 6 mg doxorubicin/kg body weight. Ultrasound (US) hyperthermia (1.1 MPa, 1.5 MHz, achieving 42°C for 5 min before and 20 min after drug injection) triggered drug release. Immediately after US, 100 µg of CpG-ODN 1826 was administered intratumorally to the insonified tumor; anti-PD-1 (200 µg, i.p.) was administrated three days later. Flow cytometry and immunohistochemistry were performed on day 28 after one treatment with each component and survival was assessed after treatment was repeated for three weeks. While control mice survived 35 days, 50% of treated mice were tumor-free after 100 days. All primary tumors and 50% of the contralateral tumors regressed and were eliminated by day 63. With the incorporation of immunotherapy, three doses of chemotherapy were sufficient to eliminate all directly treated tumors, as compared with 8 doses without immunotherapy. After a single treatment with each component, a substantial change was observed in systemic immune cells, including a significant increase in natural killer and dendritic cells in distant lymph nodes, in CD8+ T cells in tumors and associated lymph nodes and in IFNγ-secreting CD4+ T cells in the treated tumor and distant lymph nodes. The results demonstrate that activatable chemotherapy can be paired with an immune adjuvant and PD-1 blockade to generate a curative response in primary and distant tumors. Further, local chemotherapy, as potentiated by activatable liposomes does not impede a systemic CD8+ T cell response. [1] Journal of Controlled Release (2015); 220: 253-264. Citation Format: Azadeh Kheirolomoom, Matthew Silvestrini, Lisa Mahakian, Elizabeth Ingham, Josquin Foiret, Spencer Tumbale, Sarah Tam, Neil Hubbard, Alexander Borowsky, Katherine Ferrara. Protocol optimization combining activatable nanodelivery with immunotherapy in a murine breast cancer model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4603. doi:10.1158/1538-7445.AM2017-4603