STING Ligand c-di-GMP Improves Cancer Vaccination against Metastatic Breast Cancer

Abstract

Cancer vaccination may be our best and most benign option for preventing or treating metastatic cancer. However, breakthroughs are hampered by immune suppression in the tumor microenvironment (TME). In this study, we analyzed whether cyclic di-guanylate (c-di-GMP), a ligand for stimulator of interferon genes (STING), could overcome immune suppression and improve vaccination against metastatic breast cancer. Mice with metastatic breast cancer (4T1 model) were therapeutically immunized with an attenuated Listeria monocytogenes (LM)-based vaccine, expressing tumor-associated antigen Mage-b (LM-Mb), followed by multiple low doses of c-di-GMP (0.01 nmol). This resulted in a striking and near elimination of all metastases. Experiments revealed that c-di-GMP targets myeloid-derived suppressor cells (MDSC) and tumor cells. Low doses of c-di-GMP significantly increased the production of IL-12 by MDSCs, in correlation with improved T-cell responses to Mage-b, while high dose of c-di-GMP (range 15–150 nmol) activated caspase-3 in the 4T1 tumor cells and killed the tumor cells directly. Based on these results we tested one administration of high dose c-di-GMP (150 nmol) followed by repeated administrations of low dose c-di-GMP (0.01 nmol) in the 4T1 model, and found equal efficacy compared to the combination of LM-Mb and c-di-GMP. This correlated with a mechanism of improved CD8 T-cell responses to tumor-associated antigens (TAA) Mage-b and Survivin, most likely through cross-presentation of these TAAs from c-di-GMP-killed 4T1 tumor cells, and through c-di-GMP-activated TAA-specific T cells. Our results demonstrate that activation of STING-dependent pathways by c-di-GMP is highly attractive for cancer immunotherapy.

Stimulation of Innate Immunity byIn VivoCyclic di-GMP Synthesis Using Adenovirus

“…Although the results of this study imply that the c-di-GMP produced from adenovirus vectors may not enhance vaccines that rely on antibody production, such as those targeting bacterial toxins, the Ad5-VCA0956-stimulated c-di-GMP innate immune response might enhance protection of vaccines that drive cell-mediated immunity such as those targeting viral infections or cancers. Consistent with this idea, c-di-GMP has been shown to exhibit anticancer properties in a number of studies (20,64,65), which are thought to be mediated through stimulation of a type I interferon response as observed here. Miyabe et al (20) showed that enhancing c-di-GMP entry into cancer cells using liposomes increased its efficacy; adenovirus delivery of DGCs to tumors might function similarly by driving synthesis of c-di-GMP in cancer cells.…”

Cryoablation and Meriva have strong therapeutic effect on triple-negative breast cancer

“…Based on patient's cytokine profile, an optimal adjuvant could be selected for combining with cryoablation. For instance, patients with high IL-6 levels may benefit from cryoablation plus Meriva, while patients with low levels of IL-12 may benefit from cryoablation with cyclic di-guanylate (c-di-GMP) 30 or CpG. 31 During the early stage of cancer development (day 28 after tumor development), we did not find a significant difference between cryoablation plus Meriva or cryoablation alone in our efficacy studies.…”

The host STING pathway at the interface of cancer and immunity

“…STING-activating CDNs may have high translational potential as oncology therapeutics due to their potent antitumor activity as a single agent in aggressive mouse syngeneic tumor models (8,63,(83)(84)(85)(86). Therapeutic antitumor efficacy with CDN-based STING agonists was initially demonstrated with daily i.p.…”

“…Therapeutic antitumor efficacy with CDN-based STING agonists was initially demonstrated with daily i.p. injection of cyclic diguanylate (c-di-GMP) in the 4T1 mammary carcinoma model (85). However, c-di-GMP and other bacterial CDNs that have a canonical structure defined by a phosphate bridge with two 3′-5′ linkages to join the two purine nucleotides into a cyclic molecule (3′,3′ CDNs) likely have limited translational value due to an inability to activate all human STING alleles D (51,87).…”