Abstract 5415: Fibroblast mediated head and neck tumor cell invasion in 3D culture is independent of partial epithelial to mesenchymal transition

Abstract Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide, with a five-year-survival of 61-64%. Recent studies have demonstrated tumor keratinocytes with features of a partial transition from epithelial to a mesenchymal phenotype, also known as partial-EMT (pEMT), at the edge of invading tumor islands associates with metastatic disease. As such, pEMT likely results from direct interactions between tumor cells and their surrounding microenvironment. To test if specific secreted factors or cell interactions drive the acquisition of pEMT, we first analyzed a series of primary and established HNSCC cell populations to determine TGF-β1 responsiveness since TGF-β1 is a known driver of pEMT. Of the eight populations tested, six displayed an increased level of pSMAD3 upon incubation with 5 ng/mL of TGF-β1 (p < 0.0001). To determine if this TGF-β1 response leads to an increase in pEMT phenotype, a pEMT-score (derived from mRNA expression of 9 pEMT markers) for each HNSCC population was determined following TGF-β1 treatment. As expected, the two non-responsive HNSCC populations showed no increase in pEMT-score, whilst five of the six TGF-β1-responsive HNSCC populations demonstrated a significant increase in pEMT-score (p = 0.006). To assess if TGF-β induced pEMT phenotype correlates with increased invasive potential, we produced 3D skin equivalent models using the eight HNSCC keratinocyte populations, in the presence or absence of primary fibroblasts and/or TGF-β1 treatment. TGF-β1 treatment alone caused a significant increase in invasion of all five TGF-β1-induced pEMT HNSCC populations (r2 = 0.449, p = 0.0045), whilst the three populations previously shown to be pEMT unresponsive to TGF-β1 treatment showed no increase. Interestingly, addition of primary fibroblasts without TGF-β1 treatment caused a universal dramatic increase in invasion in 3D organ culture (p = 0.0064, 34-fold increase), regardless of the previously determined TGF-β1-induced pEMT status. Unexpectedly, TGF-β1 treatment in the presence of fibroblasts caused no significant increase in invasion in 3D cultures (r2 = 0.00001, p = 0.9906). We next compared levels of pEMT markers in 3D cultures using immunofluorescence and observed a significant increase in PDPN in six of the eight HNSCC populations (p = 0.0136) with the addition of fibroblasts suggesting that factors independent of TGF-β1 contributes to pEMT marker expression and invasion in 3D culture. Overall, these data demonstrate fibroblasts induce HNSCC keratinocyte invasion regardless of the population’s ability to respond to TGF-β1-induced pEMT and that pEMT may be driven by factors independent of TGF-β1 in 3D culture. Citation Format: Pyung Hun Park, Michael M. Alexander, Joseph M. Curry, Adam J. Luginbuhl, Andrew P. South. Fibroblast mediated head and neck tumor cell invasion in 3D culture is independent of partial epithelial to mesenchymal transition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5415.