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 pri mary 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 muc osa from noncancer patients. In the primary localization of the tumor, calc ium-independent NOS activity is maximal at early stages of tumor growth, wh ereas calcium-dependent activity increases from early to advanced stages. C onclusions: These data suggest that tumor growth and malignancy is associat ed with a change in the enzymatic source of NO from calcium-independent NOS to calcium-dependent NOS isoform in primary localization, These data sugge st that the inhibition of calcium-independent NOS activity in early stages and/or inhibition of calcium-dependent NOS activity in later stages could d elay growth of solid tumors.