Solar Simulated Light Induces Cutaneous Squamous Cell Carcinoma in Inbred Mice: A Clinically Relevant Model to Investigate T-Cell Responses

FGFR2 in the Development and Progression of Cutaneous Squamous Cell Cancer

Cutaneous squamous cell carcinoma (cSCC) is an increasingly common malignancy of the skin and the leading cause of death from skin cancer in adults over the age of 85. Fibroblast growth factor receptor 2 (FGFR2) has been identified as an important effector of signaling pathways that lead to the growth and development of cSCC. In recent years, there have been numerous studies evaluating the role FGFR2 plays in multiple cancers, its contribution to resistance to anticancer therapy, and new drugs that may be used to inhibit FGFR2. This review will provide an overview of our current understanding of FGFR2 and potential mechanisms in which we can target FGFR2 in cSCC. The goals of this review are the following: (1) to highlight our current knowledge of the role of FGFR2 in healthy skin and contrast this with its role in the development of cancer; (2) to further explain the specific molecular mechanisms that FGFR2 uses to promote tumorigenesis; (3) to describe how FGFR2 contributes to more invasive disease; (4) to describe its immunosuppressive effects in skin; and (5) to evaluate its effect on current anticancer therapy and discuss therapies on the horizon to target FGFR2 related malignancy.

Tumor immune microenvironment permissive to metastatic progression of ING4-deficient breast cancer

Deficiencies in the ING4 tumor suppressor are associated with advanced stage tumors and poor patient survival in cancer. ING4 was shown to inhibit NF-kB in several cancers. As NF-kB is a key mediator of immune response, the ING4/NF-kB axis is likely to manifest in tumor-immune modulation but has not been investigated. To characterize the tumor immune microenvironment associated with ING4-deficient tumors, three approaches were employed in this study: First, tissue microarrays composed of 246 primary breast tumors including 97 ING4-deficient tumors were evaluated for the presence of selective immune markers, CD68, CD4, CD8, and PD-1, using immunohistochemical staining. Second, an immune-competent mouse model of ING4-deficient breast cancer was devised utilizing CRISPR-mediated deletion of Ing4 in a Tp53 deletion-derived mammary tumor cell line; mammary tumors were evaluated for immune markers using flow cytometry. Lastly, the METABRIC gene expression dataset was evaluated for patient survival related to the immune markers associated with Ing4-deleted tumors. The results showed that CD68, CD4, CD8, or PD-1, was not significantly associated with ING4-deficient breast tumors, indicating no enrichment of macrophages, T cells, or exhausted T cell types. In mice, Ing4-deleted mammary tumors had a growth rate comparable to Ing4-intact tumors but showed increased tumor penetrance and metastasis. Immune marker analyses of Ing4-deleted tumors revealed a significant increase in tumor-associated macrophages (Gr-1loCD11b+F4/80+) and a decrease in granzyme B-positive (GzmB+) CD4+ T cells, indicating a suppressive and/or less tumoricidal immune microenvironment. The METABRIC data analyses showed that low expression of GZMB was significantly associated with poor patient survival, as was ING4-low expression, in the basal subtype of breast cancer. Patients with GZMB-low/ING4-low tumors had the worst survival outcomes (HR = 2.80, 95% CI 1.36-5.75, p = 0.0004), supportive of the idea that the GZMB-low immune environment contributes to ING4-deficient tumor progression. Collectively, the study results demonstrate that ING4-deficient tumors harbor a microenvironment that contributes to immune evasion and metastasis.

Distinct sets of molecular characteristics define tumor-rejecting neoantigens

Challenges in identifying tumor-rejecting neoantigens limit the efficacy of neoantigen vaccines to treat cancers, including cutaneous squamous cell carcinoma (cSCC). A minority of human cSCC tumors shared neoantigens, supporting the need for personalized vaccines. Using a UV-induced mouse cSCC model which recapitulated the mutational signature and driver mutations found in human disease, we found that CD8 T cells constrain cSCC. Two MHC class I neoantigens were identified that constrained cSCC growth. Compared to the wild-type peptides, one tumor-rejecting neoantigen exhibited improved MHC binding and the other had increased solvent accessibility of the mutated residue. Across known neoantigens that do not impact MHC binding, structural modeling of the peptide/MHC complexes indicated that increased solvent accessibility, which will facilitate TCR recognition of the neoantigen, distinguished tumor-rejecting from non-immunogenic neoantigens. This work reveals characteristics of tumor-rejecting neoantigens that may be of considerable importance in identifying optimal vaccine candidates in cSCC and other cancers.

Inducible Keratinocyte Specific FGFR2 Deficiency Inhibits UVB-Induced Signaling, Proliferation, Inflammation, and Skin Carcinogenesis

A potential role for fibroblast growth factor receptor 2 (FGFR2) in cutaneous squamous cell carcinoma (cSCC) has been reported. To demonstrate the specific role of FGFR2 in UVB-induced skin carcinogenesis and development of cSCC, we generated a keratinocyte specific, tamoxifen inducible mouse model of FGFR2 deficiency. In this mouse model, topical application of 4-hydroxy tamoxifen led to the induction of Cre recombinase to delete FGFR2 in epidermal keratinocytes of both male and female transgenic mice. Analysis of epidermal protein lysates isolated from FGFR2 deficient mice exposed to UVB showed significant reductions of phospho-FGFR (pFGFR; Y653/654) and phospho-fibroblast growth factor receptor substrate 2α as well as downstream effectors of mTORC1 signaling. Phosphorylation of signal transducer and activators of transcription 1/3 was significantly reduced as well as levels of IRF-1, DUSP6, early growth response 1, and PD-L1 compared to the control groups. Keratinocyte-specific ablation of FGFR2 also significantly inhibited epidermal hyperproliferation, hyperplasia, and inflammation after exposure to UVB. Finally, keratinocyte-specific deletion of FGFR2 significantly inhibited UVB-induced cSCC formation. Collectively, the current data demonstrate an important role of FGFR2 in UVB-induced oncogenic signaling as well as development of cSCC. In addition, the current preclinical findings suggest that inhibition of FGFR2 signaling may provide a previously unreported strategy to prevent and/or treat UVB-induced cSCC.