Abstract 5209: Overexpression of TGF-β in Smad4 deficient head and neck squamous cell carcinomas promotes myeloid cell infiltration associated with metastatic progression

Abstract

Abstract Purpose of study: Transforming growth factor-β (TGF-β) has been shown to promote tumor progression when overexpressed and could be an important biomarker for head and neck squamous cell carcinomas (HNSCC) prognosis and treatment. Overexpression of TGF-β in tumor epithelia and stroma is observed in Smad4 deficient HNSCCs and is known to upregulate inflammation and angiogenesis. Our preliminary studies in Smad4 deficient HNSCC mice have revealed that inhibition of the TGF-β receptor (TGF-βR), specifically of the intracellular kinase domain, did not affect tumor growth in an immune compromised background but significantly decreased the number of metastatic lesions. We aim to elucidate the specific mechanisms by which TGF-β signaling promotes this metastatic phenotype in Smad4 deficient HNSCCs. We hypothesized that Smad4 deficient SCCs overexpress TGF-β to create an inflammatory microenvironment and promote angiogenesis to drive tumor progression in vivo. Methods: Nude mice were injected subcutaneously in the flank with SCC cells derived from keratinocyte-specific Smad4 knockout mice and treated with either a TGF-βR inhibitor (n=5) or a vehicle control (n=6) once primary tumors reached 1mm3. Using immunofluorescence (IF) or immunohistochemistry (IHC), sections of the primary tumor were probed for leukocyte marker CD45, macrophage markers F4/80, iNOS and Arg1, myeloid cell markers CD11b and Ly6G and endothelial cell marker CD31. Results: Smad4 deficient SCCs treated with the TGF-βR inhibitor showed a significant decrease in CD45+ leukocytes, with a specific decrease in CD11b+Ly6G+ cells compared to the vehicle control group. However, there was no difference in the total number of F4/80+ macrophages between TGF-βR inhibitor treated and vehicle control groups. There was also no significant difference in angiogenesis between these two groups as measured by the number of blood vessels/mm2 and the percentage area of the tumor covered by blood vessels. Conclusions: Smad4 deficient SCC tumors treated with the TGF-βR inhibitor showed a significant decrease in myeloid cell populations, suggesting that overexpressed TGF-β plays a role in mediating inflammation in the tumor stromal environment. Treatment of SCC tumors with the TGF-βR inhibitor, however, did not show an affect on angiogenesis compared to the vehicle control. Citation Format: Jingjing Yu, Ariel Hernandez, David Raben, Xiao-Jing Wang. Overexpression of TGF-β in Smad4 deficient head and neck squamous cell carcinomas promotes myeloid cell infiltration associated with metastatic progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5209.