Co‐administration of 2’3’-cGAMP STING activator and CpG-C adjuvants with a mutated form of HPV 16 E7 protein leads to tumor growth inhibition in the mouse model

Abstract

Persistent infection with high-risk genotypes of human papillomavirus (HPV) is the leading cause of cervical cancer. The HPV oncoprotein E7 is constitutively expressed in cervical cancer and considered as an essential target for tumor-specific immunity. The goal of this study was to develop a candidate therapeutic vaccine based on the mutated E7 protein that had possibly reduced transformation capacity while was able to elicit a robust immune response. Therefore, the mutant type of HPV 16 E7 (E7GRG) protein was recombinantly expressed in E. coli. The protein was then purified and formulated with 2’-3’cGAMP CDN and/or CpG-C ODN adjuvants and subcutaneously injected to female C57BL/6 mice. To evaluate the immunogenic response, lymphocyte proliferation, secretion levels of IFN-γ and IL-4 cytokines, granzyme B level, and total IgG and subclasses of IgG antibody were measured. The anti-tumor activity was evaluated in tumor-harboring C57BL/6 mice. The highest rate of cell proliferation, IFN-γ and granzyme B levels, and amount of IgG antibody were found in mice group that were injected by E7GRG + 2′-3′cGAMP + CpG-C. Therapeutic immunization with E7GRG + 2′-3′cGAMP + CpG-C also significantly suppressed TC-1 tumor growth in mice. In conclusion, the results demonstrated that E7GRG + 2′-3′cGAMP + CpG-C induced strong cell-mediated and humoral immune responses that resulted in inhibition of tumor in mouse model.

Molecular mechanisms of mitochondrial DNA release and activation of the cGAS-STING pathway

“…Interestingly, cGAMP in the extracellular space can propagate the intercellular immune response. For example, direct administration of cGAMP to mice induced an innate immune response by upregulating IFN expression, which did not occur in STINGdeficient mice [39][40][41] . On the other hand, ecto-nucleotide pyrophosphatase phosphodiesterase 1 (ENPP1) degraded extracellular cGAMP and blunted the host immune response 42,43 .…”

The cGAS/STING Pathway: A Novel Target for Cancer Therapy

“…A study using a model of mouse cervical cancer demonstrated that the use of the mutant type of HPV 16 E7 protein (E7GRG) as a therapeutic vaccine candidate antigen-stimulated the cell-mediated and humoral immune response and inhibited tumor growth. The co-administration of 2’,3’-cGAMP, E7GRG and CpG-C adjuvant exerted a synergistic effect, establishing a shift towards the Th1 type immune response and decreasing tumor growth ( 80 ). In malignant B-cell tumors, 3’3’-cGAMP induces the prolonged presence of STING in the endoplasmic reticulum or Golgi apparatus to form protein complexes to activate apoptosis, without any significant association with activated IFN.…”

Activation of Stimulation of Interferon Genes (STING) Signal and Cancer Immunotherapy

“…Co-injection of cGAMP with PD-1 or CTLA-4 inhibitor exhibited an enhanced anti-tumor effect and increased tumor-infiltrating CD8+ T cell responses in a mouse model of melanoma and an ex vivo model of cultured human melanoma explants [ 52 , 53 ]. Co-administration of 2′,3′-cGAMP, E7GRG (HPV 16 E7 protein), and CpG-C adjuvant in a mouse model of cervical cancer led to an enhanced suppression of tumor growth and metastasis [ 54 ]. In addition, treatment of 3′3′-cGAMP in mice with lymphocytic leukemia or myeloma caused significant cancer cell apoptosis and tumor inhibition, indicating the potential of 3′3′-cGAMP in immunomodulation [ 55 ].…”