ROLE OF NITRIC-OXIDE IN ANGIOGENESIS AND MICROCIRCULATION IN TUMORS

Nitric oxide (NO) is a free radical molecule with high reactivity, a s hort half life and a variety of physiological activities. The role of NO in tumor microcirculation, based on the data collected to date, can be summarized as follows: 1) NO may partially mediate tumor angiogene sis; 2) endogenous NO derived from tumor vascular endothelium and/or t umor cells increases and/or maintains tumor blood flow via dilatation of arteriolar vessels, decreases leukocyte-endothelial interaction, an d increases vascular permeability; 3) exogenous NO can increase tumor blood flow via vessel dilatation, and reduce vessel tone; and 4) NO pr oduction rates and vascular response to NO are heterogeneous and tumor -dependent. Modulation of NO level in tumor vessels can alter tumor he modynamics and thus augment oxygen, drug, gene vector and effector cel l delivery to solid tumors.