Nitric oxide synthase activity in human squamous cell carcinoma of the head and neck.

OBJECTIVES: To test whether nitric oxide synthase (NOS) is expressed in primary otolaryngologic tumors and whether this expression is associated with the degree of malignancy. STUDY DESIGN: Twenty-six samples from the primary localization of human pharyngolaryngeal squamous cell carcinoma. MATERIALS AND METHODS: the activity of calcium-dependent and calcium-independent NOS was analyzed by the conversion of L-[14C]-arginine into L-[14C]-citrulline. RESULTS: NOS activity is below detectable levels in pharyngolaryngeal mucosa from noncancer patients. In the primary localization of the tumor, calcium-independent NOS activity is maximal at early stages of tumor growth, whereas calcium-dependent activity increases from early to advanced stages. CONCLUSIONS: These data suggest that tumor growth and malignancy is associated with a change in the enzymatic source of NO from calcium-independent NOS to calcium-dependent NOS isoform in primary localization. These data suggest that the inhibition of calcium-independent NOS activity in early stages and/or inhibition of calcium-dependent NOS activity in later stages could delay growth of solid tumors.