Abstract 5313: The potential role of cellular iron in head and neck squamous cell carcinoma

Introduction. Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide. Half of the patients present with advanced disease, which despite aggressive treatments, achieves five-year survival rates of only 50%, underscoring a need to better understand the biology of this disease. One approach would be to examine the role of cellular iron in HNSCC. We are interested in the role of iron as a result of: (1) A previous study in our lab in which uroporphyrinogen decarboxylase was identified as a radiosensitizing target for HNSCC. The radiosentization was due to alterations in iron homeostasis which elevated reactive oxygen species (ROS) and enhance tumor oxidative stress and cytotoxicity. (2) The requirement of iron in a rate limiting step with ribonucleotide reductase for DNA synthesis, and hence cell proliferation. (3) The deregulation of iron in many cancers. Experimental design. A list of proteins involved in iron homeostasis was generate from the literature and evaluated using qRT-PCR in 3 HNSCC cells (FaDu, UTSCC 42a, UTSCC 8) compare to a Normal Oral Epithelial (NOE) cell line. The most highly over expressed iron protein across all cell lines compared to the NOE was hemochromatosis (HFE), thus was selected for further evaluation. Knockdown of HFE was achieved using a siRNA based approach and cellular effects were determined using MTS, clonogenic, BRDU and flow cytometry assays with or without 4 Gy of radiation. Iron rescue experiments where preformed using Ferric ammonium citrate (FACs). Iron chelation was accomplished in HNSCC cells lines using ciclopirox olamine (CPX), a clinical approved iron chelating chemotherapeutic. Results. HFE was selected for further evaluation based on the expression in HNSCC cell lines versus the NOE cell line. Mutations in HFE are linked to the genetic condition hemochromatosis, which is characterized by elevated hepcidin levels and iron accumulation in peripheral tissues. Cell proliferation assays (MTS, clonogenic, BRDU assay) after HFE knockdown with or without RT in HNSCC cells demonstrated a significant decrease in proliferation across all cancer cells with negligible effects on NOE cells. Furthermore, we observed a significant decrease in the Labile iron pool and cellular ROS levels, following HFE knockdown. Re-introduction of iron into the cell after HFE knockdown rescued our phenotype, suggesting that this process is indeed mediated by cellular iron levels. Next, we treated HNSCC cell lines