In vivo electrochemical detection of nitric oxide in tumor-bearing mice

Interest in elucidating the mechanisms of action of various classes of anticancer agents and exploring the pathways of the induced-nitric oxide (NO) release provides an impetus to conceive a better designed approach to locally detect NO in tumors, in vivo. We report here on the first use of an electrochemical sensor that allows the in vivo detection of NO in tumor-bearing mice. In a first step, we performed the electrochemical characterization of a stable electroactive probe, K4Fe(CN)(6), directly injected into the liquid microenvironment especially created around the electrode in the tumor. Second, the ability of the inserted electrode system to detect the presence of NO itself in the tumoral tissue was achieved by using the chemically modified Pt/Ir electrode as NO sensor and two NO donor molecules: diethylammonium (Z)-1-(N,N-diethylamino)diazen-1-ium 1,2-diolate (DEA-NONOate) and (Z)-1-[N-(2-aminopropyl)-N-(2-ammonio propyl)amino]diazen-1-ium 1,2-diolate (PAPA-NONOate). These two NO donor molecules allowed proving the electrochemical detection of (i) directly injected exogenous NO phosphate buffer solution into the tumor (decomposed DEA-NONOate) and (ii) biomimetically induced endogeneous release of NO in the tumoral tissue, upon injection of PAPA-NONOate into the tumor. This approach could be applied to the in vivo study of candidate anticancer drugs acting on the NO pathways.