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.