Development of Mesoporous Silica Rod-Based Immunotherapies for Head and Neck Squamous Cell Carcinoma

Statement of the problem: Oral squamous cell cancer (OSCC) is the sixth most common cancer worldwide and accounts for 2% of all malignancies in the USA. While the past decades have seen advances in ablative/reconstructive surgery, radiation therapy, and chemotherapy, the overall survival rate of OSCC patients has not improved significantly, and there are multiple co-morbidities which arise from treatment which may negatively affect quality of life. Cancer immunotherapy has arisen as a novel treatment modality for several cancers, and implantable, polymeric cancer vaccines have been developed which show impressive tumor killing in melanoma preclinical models (1).

The objective of this preliminary study was to develop a new preclinical mouse model for immunologic targeting of human papilloma virus (HPV)- related head and neck squamous cell carcinoma and use it to investigate the efficacy of an injectable therapeutic cancer vaccine (2).

Materials and methods: Mouse oral cancer (MOC2) cells were obtained from the Uppaluri Lab at Washington University and transduced with the oncogenic human papilloma virus proteins E6 and E7 to create “MOC2-E6E7” cells. RT-PCR was performed on MOC2-E6E7 cell lysates to confirm E6 and E7 gene expression. In vitro proliferation rate of MOC2 versus MOC2-E6E7 cells was determined, then compared in vivoby examining the growth of MOC2 versus MOC2-E6E7 orthotopic tumors. A pilot study examining the efficacy of a injectable therapeutic cancer vaccine based on mesoporous silica rods (MSR) was performed. MSR-based vaccines were produced by combining mesoporous silica rods with MOC2-E6E7 tumor lysate and the long synthetic E7 immunogenic peptide as antigens, the TLR9 agonist CpG oligonucleotide, and the cytokine granulocyte-macrophage colony stimulating factor. Three groups of mice (n=5 per group) were inoculated with MOC2-E6E7 tumors: the first group received the MSR vaccine only (on Day 3 post-inoculation), the second group received the MSR vaccine (Day 3 post-inoculation) plus checkpoint inhibitor antibodies (anti-PD-1 and anti-CTLA-4 both given on Days 3, 6, and 9 post-inoculation) and the third group was an untreated control. Animals were monitored daily for tumor growth and euthanized per IACUC criteria.

Results: RT-PCR showed successful transduction of MOC2 cells with the HPV E6 and E7 genes. While MOC2 and MOC2-E6E7 cells were found to have no significant difference in proliferation rate in vitro, their corresponding tumors grown in immunocompetent C57BL/6 mice revealed a much slower rate of growth of inoculated MOC2-E6E7 cells versus their MOC2 counterparts.

A pilot study utilizing MSR-based therapeutic cancer vaccines was performed next, which showed a statistically significant difference in the survival curves (Log-rank Mantel-Cox test) between untreated, MSR vaccine-treated, and MSR vaccine + immune-modulating antibody-treated groups.

Conclusion: The preliminary results of this study show that the MOC2-E6E7 tumor model expresses well-defined tumor-specific antigens that can be targeted by the immune system, and represents a promising preclinical model for immunologic targeting of HPV-related head and neck squamous cell cancer. Mesoporous silica rod-based cancer vaccines are a novel type of immunotherapy which show the potential to delay tumor growth and increase survival in this preclinical model of HPV-related HNSCC. Further enhancements in efficacy may be realized through the rational combination of these vaccines with checkpoint inhibitor antibodies. Further studies will further characterize the MOC2-E6E7 tumor microenvironment and optimize MSR-based cancer vaccine formulations.

References:

1. Ali OA, Emerich D, Dranoff G, Mooney DJ. In situ regulation of DC subsets and T cells mediates tumor regression in mice. Science Translational medicine. 2009 Nov 25;1(8):8ra19–9. PMCID: PMC2872791

2. Kim J, Li WA, Choi Y, Lewin SA, Verbeke CS, Dranoff G, et al. Injectable, spontaneously assembling, inorganic scaffolds modulate immune cells in vivo and increase vaccine efficacy. Nat Biotechnol. 2014 Dec 8;33(1):64–72.