Katrina M Miranda

Diazeniumdiolate-based aspirin prodrugs have previously been shown to retain the anti-inflammatory properties of aspirin while protecting against the common side effect of stomach ulceration. Initial analysis of two new prodrugs of aspirin that also release either nitroxyl (HNO) or nitric oxide (NO) demonstrated increased cytotoxicity toward human lung carcinoma cells compared to either aspirin or the parent nitrogen oxide donor. In addition, cytotoxicity was significantly lower in endothelial cells, suggesting cancer-specific sensitivity. To assess the chemotherapeutic potential of these new prodrugs in breast cancer, we studied their effect both in cultured cells and in a nude mouse model. Both prodrugs reduced growth of breast adenocarcinoma cells more effectively than the parent compounds while not being appreciably cytotoxic in a related non-tumorigenic cell line (MCF-10A). The HNO donor also was more cytotoxic than the related NO donor. The basis for the observed specificity was investigated in terms of impact on metabolism, DNA damage and repair, apoptosis, angiogenesis and metastasis. The results suggest a significant pharmacological potential for treatment of breast cancer.

Nitroxyl (HNO) donors have been shown to elicit a variety of pharmacological responses, ranging from tumoricidal effects to treatment of heart failure. Isopropylamine-based diazeniumdiolates have been shown to produce HNO on decomposition under physiological conditions. Herein, we report the synthesis and HNO release profiles of primary alicyclic amine-based diazeniumdiolates. These compounds extend the range of known diazeniumdiolate-based HNO donors. Acetoxymethyl ester-protected diazeniumdiolates were also synthesized to improve purification and cellular uptake. The acetoxymethyl derivative of cyclopentylamine diazeniumdiolate not only showed higher cytotoxicity toward cancer cells as compared to the parent anion but was also effective in combination with tamoxifen for targeting estrogen receptor α-negative breast cancer cells.

PMID: 18682867;Abstract:

The synthesis of [Ru(NO2)L(bpy)2]⁺ (bpy = 2,2′-bipyridine and L = pyridine (py) and pyrazine (pz)) can be accomplished by addition of [Ru(NO)L(bpy)2](PF6) 3 to aqueous solutions of physiological pH. The electrochemical processes of [Ru(NO2)L(bpy)2]⁺ in aqueous solution were studied by cyclic voltammetry and differential pulse voltammetry. The anodic scan shows a peak around 1.00 V vs. Ag/AgCl attributed to the oxidation process centered on the metal ion. However, in the cathodic scan a second peak around -0.60 V vs. Ag/AgCl was observed and attributed to the reduction process centered on the nitrite ligand. The controlled reduction potential electrolysis at -0.80 V vs. Ag/AgCl shows NO release characteristics as judged by NO measurement with a NO-sensor. This assumption was confirmed by ESI/MS⁺ and spectroelectrochemical experiment where cis-[Ru(bpy) 2L(H2O)]²⁺ was obtained as a product of the reduction of cis-[Ru^II(NO2)L(bpy)2] ⁺. The vasorelaxation observed in denuded aortic rings pre-contracted with 0.1 μmol L^-1 phenylephrine responded with relaxation in the presence of cis-[Ru^II(NO2)L(bpy)2]⁺. The potential of rat aorta cells to metabolize cis-[Ru^II(NO 2)L(bpy)2]⁺ was also followed by confocal analysis. The obtained results suggest that NO release happens by reduction of cis-[Ru^II(NO2)L(bpy)2]⁺ inside the cell. The maximum vasorelaxation was achieved with 1 × 10^-5 mol L^-1 of cis-[Ru^II(NO2)L(bpy)2] ⁺ complex. © 2008 The Royal Society of Chemistry.

Nitroxyl anion (NO-) is the one-electron reduction product of nitric oxide (NO.) and is enzymatically generated by NO synthase in vitro. The physiologic activity and mechanism of action of NO- in vivo remains unknown. The NO- generator Angeli's salt (AS, Na2N2O3) was administered to conscious chronically instrumented dogs, and pressure-dimension analysis was used to discriminate contractile from peripheral vascular responses. AS rapidly enhanced left ventricular contractility and concomitantly lowered cardiac preload volume and diastolic pressure (venodilation) without a change in arterial resistance. There were no associated changes in arterial or venous plasma cGMP. The inotropic response was similar despite reflex blockade with hexamethonium or volume reexpansion, indicating its independence from baroreflex stimulation. However, reflex activation did play a major role in the selective venodilation observed under basal conditions. These data contrasted with the pure NO donor diethylamine/NO, which induced a negligible inotropic response and a more balanced veno/arterial dilation. AS-induced positive inotropy, but not systemic vasodilatation, was highly redox-sensitive, being virtually inhibited by coinfusion of N-acetyl-L-cysteine. Cardiac inotropic signaling by NO- was mediated by calcitonin gene-related peptide (CGRP), as treatment with the selective CGRP-receptor antagonist CGRP-(8-37) prevented this effect but not systemic vasodilation. Thus, NO- is a redox-sensitive positive inotrope with selective venodilator action, whose cardiac effects are mediated by CGRP-receptor stimulation. This fact is evidence linking NO- to redox-sensitive cardiac contractile modulation by nonadrenergic/noncholinergic peptide signaling. Given its cardiac and vascular properties, NO- may prove useful for the treatment of cardiovascular diseases characterized by cardiac depression and elevated venous filling pressures.