Reactive species promotion of head and neck squamous cell carcinoma

by 1977- Bradburn, Jennifer Elizabeth

Head and neck squamous cell carcinoma (HNSCC), which comprises 3% of all of the cancers in the U.S., is the most common form of oral cancer. The overall 5 year survival rate is 59%, however, this disease is associated with high morbidity. Current standard therapy involves surgical resection of the primary tumor followed by radiotherapy and/or chemotherapy. Many of these tumors involve structures essential for speech, taste, smell, breathing and eating. Surgical resection can compromise these functions as well as leave the patient horribly disfigured. In addition, 3-7% patients per year succumb to a second primary tumor at a related site as a complication of treatment. While in the US this disease is regarded as a preventable cancer with low prevalence it is the 8th most common cancer diagnosed in the world. Clinical evidence supports a contribution of sustained inflammation, reactive species (RS) and their sequelae in carcinogenesis. Studies in Chapter 2 focused on elucidating mechanisms by which RS facilitate HNSCC tumorigenesis and included evaluation of RS effects on sustained cell proliferation, induction of a proangiogenic environment and increased growth factor production. Proinflammatory and protumorigenic enzymes upregulated during inflammation include the RS-generating enzymes inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2. While ii clinical data show upregulation of iNOS and COX-2 in HNSCC development, mechanisms by which these cellular processes occur and downstream consequences have not been characterized. The purpose of this investigation was to assess the effects of reactive oxygen and nitrogen species on selected parameters of the HNSCC tumorigenic phenotype i.e. nuclear factor (NF)?B activation, sustained cell proliferation, and production of proinflammatory and proangiogenic proteins. RS donors included TNF, H2O2, NOC18 and SIN1. NF?B activation was determined by in situ immunostaining and reporter assay. Protein levels of VEGF, IL-8 and EGFR (determined by ELISA and immunoblot) assessed downstream effects of NF?B activation. Results showed that reactive oxygen (H2O2) and for the first time reactive nitrogen (SIN1) activated NF?B in HNSCC cells. Notably, TNF, H2O2, NOC18 and SIN1 increased IL-8, VEGF and EGFR protein levels. Our results indicate RS mediate HNSCC development by activation of NF?B followed by increased growth factor production. Much of cancer research focus is now directed towards the development of a new generation of chemotherapeutics in an effort to prevent cancer. Chemoprevention refers to the use of pharmacologic or natural compounds to either inhibit the invasive phenotype of cancer by blocking progression of initiated cells, or by blocking or reversing immortalization of cancer cells. Goals of chemoprevention therapy must address changes at all levels of disease from clinical presentation to cellular and tissue levels. N-acetyl-cysteine (NAC) has previously been identified as a potentially effective chemopreventative agent. As a precursor to L-cysteine, the rate limiting reactant in glutathione (GSH) synthesis, it possesses the innate ability to increase cellular stores of the powerful antioxidant GSH, and inhibit consequences of RS. Matrix iii metalloproteinases (MMPs) are a family of enzymes noted for their ability to degrade the extracellular matrix, which are activated by RS. Our laboratory recently determined a mechanism by which NAC can inhibit the extracellular activation of MMP-9 by preventing the cysteine switch step of activation. Their overexpression has been linked to the ability of tumors to invade, metastasize and release growth factors bound to proteins in the ECM.