Studies on agents with mixed NO-dependent vasodilating and beta-blocking activities

Anti-Proliferative Properties of the Novel Hybrid Drug Met-ITC, Composed of the Native Drug Metformin with the Addition of an Isothiocyanate H2S Donor Moiety, in Different Cancer Cell Lines

Metformin (Met) is the first-line therapy in type 2 diabetes mellitus but, in last few years, it has also been evaluated as anti-cancer agent. Several pathways, such as AMPK or PI3K/Akt/mTOR, are likely to be involved in the anti-cancer Met activity. In addition, hydrogen sulfide (H2S) and H2S donors have been described as anti-cancer agents affecting cell-cycle and inducing apoptosis. Among H2S donors, isothiocyanates are endowed with a further anti-cancer mechanism: the inhibition of the histone deacetylase enzymes. On this basis, a hybrid molecule (Met-ITC) obtained through the addition of an isothiocyanate moiety to the Met molecule was designed and its ability to release Met has been demonstrated. Met-ITC exhibited more efficacy and potency than Met in inhibiting cancer cells (AsPC-1, MIA PaCa-2, MCF-7) viability and it was less effective on non-tumorigenic cells (MCF 10-A). The ability of Met-ITC to release H2S has been recorded both in cell-free and in cancer cells assays. Finally, its ability to affect the cell cycle and to induce both early and late apoptosis has been demonstrated on the most sensitive cell line (MCF-7). These results confirmed that Met-ITC is a new hybrid molecule endowed with potential anti-cancer properties derived both from Met and H2S.

Structure-Activity Relationship Studies on Tetrahydroisoquinoline Derivatives: [4'-(6,7-Dimethoxy-3,4-dihydro-1H-isoquinolin-2-ylmethyl)biphenyl-4-ol] (MC70) Conjugated through Flexible Alkyl Chains with Furazan Moieties Gives Rise to Potent and Selective Ligands of P-glycoprotein

P-glycoprotein (P-gp) is a well-known membrane transporter expressed in a number of strategic biological barriers, where it exerts a protective effect of paramount importance. Conversely it is one of the main causes of multidrug resistance (MDR), being capable of effluxing many chemotherapeutics. In a development of previous research, a small library of compounds was created conjugating diversely substituted furazan rings with MC70, a well-known P-gp inhibitor. These compounds were assessed for their potency against P-gp and another transporter (MRP1), for their apparent permeability (Papp) and for their ability to induce ATPase activity, thus delineating a complete functional profile. They displayed a substrate mechanism of action and high selectivity toward P-gp, unlike the lead compound. Data relating to their activity range from low micromolar to sub-nanomolar EC50, the most interesting compounds being 15 (0.97 nM), 19 (1.3 nM), 25 (0.60 nM), and 27 (0.90 nM).

Heterocyclic ring cleavage upon collision-induced dissociation of deprotonated 3-hydroxy-1,2,5-oxadiazoles (3-hydroxyfurazans)

A series of 4-substituted 3-hydroxyfurazans were subjected to electrospray ionization tandem mass spectrometry. At low collision energy, oxyisocyanate ([O=C=N-O](-), m/z 58) was formed as the predominant product ion from each deprotonated 3-hydroxyfurazan, indicating cleavage of the heterocyclic ring. The facile energetics of this characteristic fragmentation process was confirmed by density functional computations.

New praziquantel derivatives containing NO-donor furoxans and related furazans as active agents against Schistosoma mansoni

A series of NO-donor praziquantel hybrid compounds was obtained by combining praziquantel (PZQ) and furoxan moieties in a single entity. NO-donor properties of the furoxan derivatives were evaluated by detecting nitrite after incubation of the products in 7.4 pH buffered solution in the presence of L-cysteine. Structurally-related furazans, devoid of NO release capacity, were also synthesized for control purposes. All products were studied for their ability to inhibit recombinant Schistosoma mansoni thioredoxin glutathione reductase (TGR). Mobility and death of adult Schistosoma mansoni worms cultured in the presence of the products were evaluated versus PZQ. Analysis of the results showed that some products were endowed with both PZQ and NO-dependent antiparasitic properties. Compounds 6, 7, 18, and 24 emerged as the most interesting balanced hybrids, worthy of additional study on PZQ-resistant parasites.

Furazan and furoxan sulfonamides are strong α-carbonic anhydrase inhibitors and potential antiglaucoma agents

A series of furazan and furoxan sulfonamides were prepared and studied for their ability to inhibit human carbonic anhydrase (CA, EC 4.2.1.1) isoforms hCA I, hCA II, hCA IX, and hCA XII. The simple methyl substituted products 3-5 were potent inhibitors. Differing structural modifications of these leads had differing effects on potency and selectivity. In particular, products in which the sulfonamide group is separated from the hetero ring by a phenylene bridge retained high potency only on the hCA XII isoform. The sulfonamides 3-5 exerted intraocular pressure (IOP) lowering effects in vivo in hypertensive rabbits more efficiently than dorzolamide. Some other products (39-42), although less effective in vitro hCA II/XII inhibitors, also effectively lowered IOP in two different animal models of glaucoma.

Furoxans (1,2,5-oxadiazole-N-oxides) as novel NO mimetic neuroprotective and procognitive agents

Furoxans (1,2,5-oxadiazole-N-oxides) are thiol-bioactivated NO-mimetics that have not hitherto been studied in the CNS. Incorporation of varied substituents adjacent to the furoxan ring system led to modulation of reactivity toward bioactivation, studied by HPLC-MS/MS analysis of reaction products. Attenuated reactivity unmasked the cytoprotective actions of NO in contrast to the cytotoxic actions of higher NO fluxes reported previously for furoxans. Neuroprotection was observed in primary neuronal cell cultures following oxygen glucose deprivation (OGD). Neuroprotective activity was observed to correlate with thiol-dependent bioactivation to produce NO(2)(-), but not with depletion of free thiol itself. Neuroprotection was abrogated upon cotreatment with a sGC inhibitor, ODQ, thus supporting activation of the NO/sGC/CREB signaling cascade by furoxans. Long-term potentiation (LTP), essential for learning and memory, has been shown to be potentiated by NO signaling, therefore, a peptidomimetic furoxan was tested in hippocampal slices treated with oligomeric amyloid-β peptide (Aβ) and was shown to restore synaptic function. The novel observation of furoxan activity of potential therapeutic use in the CNS warrants further studies.

Synthesis and preliminary pharmacological characterisation of a new class of nitrogen-containing bisphosphonates (N-BPs)

A new series of bisphosphonates bearing either the nitrogen-containing NO-donor furoxan (1,2,5-oxadiazole 2-oxide) system or the related furazan (1,2,5-oxadiazole) in lateral chain has been developed. pK(a) values and affinity for hydroxyapatite were determined for all the compounds. The products were able to inhibit osteoclastogenesis on RAW 246.7 cells at 10microM concentration. The most active compounds were further assayed on human PBMC cells and on rat microsomes. Unlike most nitrogen-containing bisphosphonates which target farnesyl pyrophosphate synthase, experimental and theoretical investigations suggest that the activity of our derivatives may be related to different mechanisms. The furoxan derivatives were also tested for their ability to relax rat aorta strips in view of their potential NO-dependent vasodilator properties.

Nitric Oxide Donor β2-Agonists: Furoxan Derivatives Containing the Fenoterol Moiety and Related Furazans

The structure of fenoterol, a beta2-adrenoceptor agonist used in therapy, has been joined with furoxan NO-donor moieties to give new NO-donor beta2-agonists. The furazan analogues, devoid of the property to release NO, were also synthesized for comparison. All the compounds retained beta2-agonistic activity at micromolar or submicromolar concentration when tested on guinea pig tracheal rings precontracted with carbachol. Among the furoxan derivatives, the NO contribution to trachea relaxation was evident with product 15b at micromolar concentrations. All the new NO-donor hybrids were able to dilate rat aortic strips precontracted with phenylephrine. Both furoxan and furazan derivatives displayed antioxidant activity greater than that of fenoterol.

Recent developments in nitric oxide donor drugs

During the 1980s, the free radical, nitric oxide (NO), was discovered to be a crucial signalling molecule, with wide-ranging functions in the cardiovascular, nervous and immune systems. Aside from providing a credible explanation for the actions of organic nitrates and sodium nitroprusside that have long been used in the treatment of angina and hypertensive crises respectively, the discovery generated great hopes for new NO-based treatments for a wide variety of ailments. Decades later, however, we are still awaiting novel licensed agents in this arena, despite an enormous research effort to this end. This review explores some of the most promising recent advances in NO donor drug development and addresses the challenges associated with NO as a therapeutic agent.

New NO-Releasing Pharmacodynamic Hybrids of Losartan and Its Active Metabolite: Design, Synthesis, and Biopharmacological Properties

In a preliminary work, we reported two NO-sartans, possessing the characteristics of an AT(1) antagonist and a "slow NO donor", obtained by adding NO-donor side chains to losartan 1. The NO release from an NO-sartan should be modulated in order to strengthen the antihypertensive activity of the native drug and to ensure additional effects, such as the antiplatelet and anti-ischemic ones. To obtain a collection of prototypical NO-sartans, showing different rates of NO release, new NO-donor moieties have been linked to 1 or its active metabolite 2 (EXP 3174). Almost all the synthesized compounds exhibited both AT(1)-antagonist and NO-mediated vasorelaxing properties, with a wide range of NO-releasing rates. Further pharmacological investigation on compound 4a showed that it possessed antihypertensive and cardiac antihypertrophic effects similar to those of the reference AT(1)-blocking or ACE-inhibiting drugs. Furthermore, the additional anti-ischemic cardio-protective properties and antiplatelet effects of 4a have been preliminarily investigated.

Inactivation of parasite cysteine proteinases by the NO-donor 4-(phenylsulfonyl)-3-((2-(dimethylamino)ethyl)thio)-furoxan oxalate

NO-donors block Plasmodium, Trypanosoma, and Leishmania life cycle by inactivating parasite enzymes, e.g., cysteine proteinases. In this study, the inactivation of falcipain, cruzipain, and Leishmania infantum cysteine proteinase by the NO-donor 4-(phenylsulfonyl)-3-((2-(dimethylamino)ethyl)thio)-furoxan oxalate (SNO-102) is reported. SNO-102 inactivates dose- and time-dependently parasite cysteine proteinases; one equivalent of NO, released from SNO-102, inactivates one equivalent of L. infantum cysteine proteinase. With SNO-102 in excess over the parasite cysteine proteinase, the time course of enzyme inhibition corresponds to a pseudo-first-order reaction for more than 90% of its course. The concentration dependence of the pseudo-first-order rate constant is second-order at low SNO-102 concentration but tends to first-order at high NO-donor concentration. This behavior may be explained by a relatively fast pre-equilibrium followed by a limiting pseudo-first order process. Kinetic parameters of L. infantum cysteine proteinase inactivation by SNO-102 are affected by the acidic pK shift of one apparent ionizing group (from pK(unl)=5.8 to pK(lig)=4.7) upon enzyme inhibition. Falcipain, cruzipain and L. infantum cysteine proteinase inactivation is prevented and reversed by dithiothreitol and L-ascorbic acid. Furthermore, the fluorogenic substrate N-alpha-benzyloxycarbonyl-Phe-Arg-(7-amino-4-methylcoumarin) protects parasite cysteine proteinases from inactivation by SNO-102. The absorption spectrum of the inactive S-nitrosylated SNO-102-treated L. infantum cysteine proteinase displays a maximum at about 340 nm. These results indicate that the parasite cysteine proteinase inactivation by SNO-102 occurs via the NO-mediated S-nitrosylation of the Cys25 catalytic residue.

NO-Sartans: A New Class of Pharmacodynamic Hybrids as Cardiovascular Drugs

The aim of this work was to develop lead pharmacodynamic hybrids, NO-sartans, possessing the characteristics of a typical AT1-antagonist and of a "slow NO donor", by adding NO-donor side chains to losartan. These new compounds, 2a and 2b, displayed vasorelaxing effects, due to the release of NO, and antagonized the vasocontractile effects of angiotensin II, with potency values similar to that of losartan. In vivo, the antihypertensive effects of 2a were similar to those of losartan and captopril.

Synthesis and vasorelaxant properties of hybrid molecules out of NO-donors and the β-receptor blocking drug propranolol

S-Nitroso-N-acetylpenicillamine (SNAP) and 3-nitrooxypivaloyl acid were combined in the form of the respective amides with propranolol, in order to obtain prodrugs (NO-propranololes) with beta-receptor blocking properties of the latter compound with nitric oxide releasing properties of the former compounds. A respective nitratoester could not be synthesized, because it immediately rearranges to the amide after deprotection of the amino group. In vitro tests on porcine pulmonary arteries showed that both types of hybrid molecules (6, 12) elicited vasorelaxation, but the nitratoamide was less potent by more than one order of magnitude. The vasorelaxant effect of SNAP was more pronounced than that of the SNAP-hybrid (12), on the other hand the nitratoamide 6 was more potent than 3-nitrooxypivaloyl acid.

A new class of NO-donor H3-antagonists

Synthesis and pharmacological characterisation of a series of compounds obtained by joining, through appropriate spacers, NO-donor furoxan and nitrooxy moieties to the imidazole ring, as well as their structurally related analogues devoid of NO-donating properties are described. All the products were studied for their capacity to interact with H3-receptors present on the guinea-pig ileum and with H2-receptors present on guinea-pig right atrium. The whole series of products displayed reversible H3-antagonistic activity. No activity on H2-receptors was observed when the products were tested at 10 microM concentration. Many of the products were also able to induce partial relaxation when added to the bath after electrical contraction of the guinea-pig ileum during the study of their H3-antagonism. This phenomenon seems to be dependent on various factors; for some compounds it proved to be dependent on NO-mediated sGC activation, for other products it could be due to their weak M3-antagonism. The investigation of the lipophilic-hydrophilic balance of all the products indicates, for many of them, an ideal value to cross the blood-brain barrier.

[3-(1H-imidazol-4-yl)propyl]guanidines containing furoxan moieties: a new class of H3-antagonists endowed with NO-donor properties

Synthesis and pharmacological characterisation of a series of products obtained by coupling the H(3)-antagonist SKF 91486 through appropriate spacers with the NO-donor 3-phenylfuroxan-4-yloxy and 3-benzenesulfonylfuroxan-4-yloxy moieties, as well as with the corresponding furazan substructures, devoid of NO-donating properties, are reported. All the products were tested for their H(3)-antagonistic and H(2)-agonistic properties on electrically-stimulated guinea-pig ileum segments and guinea-pig papillary muscle, respectively. The whole series of compounds displayed good H(3)-antagonist behaviour and feeble partial H(2)-agonist activity. Among furoxan derivatives, the benzenesulfonyl hybrid 28, a good NO-donor, triggered a dual NO-dependent muscle relaxation and H(3)-antagonistic effect on guinea-pig intestine.

A new class of ibuprofen derivatives with reduced gastrotoxicity

A new series of nonsteroidal antiinflammatory drugs (NSAIDs) obtained by linking ibuprofen to selected furoxan moieties and to related furazans were synthesized and tested for their antiinflammatory, antiaggregatory, and ulcerogenic properties. All the derivatives are endowed with antiinflammatory activity comparable to that of ibuprofen, but, unlike this drug, they display reduced acute gastrotoxicity. The masking of the ibuprofen-free carboxylic group seems to be principally at the basis of this reduced topical irritant action. The two furoxan derivatives 8 and 9 also trigger potent antiaggregatory effects, principally as a consequence of their NO-donor ability.

Nicorandil analogues containing NO-donor furoxans and related furazans

The synthesis and in vitro vasodilating properties of hybrid compounds in which furoxan (1,2,5-oxadiazole 2-oxide) moieties, endowed with different NO-donor properties, were substituted for the nitroxy function of Nicorandil are reported. The corresponding cyanoguanidine analogues are also considered. This approach has led to a series of vasorelaxing compounds devoid of affinity for K(ATP) channels, whose activity is prevalently due to their ability to activate sGC, at the concentrations of the experiments. Related furazan (1,2,5-oxadiazole) derivatives, unable to release nitric oxide were also prepared and studied for control. The amide analogues of Nicorandil display feeble vasorelaxing action not involving the activation of K+ channels, while in the guanidine analogues, this mechanism seems to underlie this action.

New 1,4-dihydropyridines conjugated to furoxanyl moieties, endowed with both nitric oxide-like and calcium channel antagonist vasodilator activities

A series of 4-phenyl-1,4-dihydropyridines substituted at the ortho and meta positions of the phenyl ring with NO-donating furoxan moieties and their non-NO-releasing furazan analogues were synthesized and pharmacologically characterized. The vasodilator activities of these compounds were evaluated on rat aorta and expressed as EC50 values or as EC50iGC values when obtained in the presence of inhibitors of guanylate cyclase methylene blue (MB) and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). Affinities to 1, 4-DHP receptors on Ca2+ channels, expressed as IC50 values, were determined through displacement experiments of [3H]nitrendipine on rat cortex homogenates. A linear correlation between IC50 and EC50 values was found for compounds unable to release NO. EC50calcd values for derivatives containing NO-donor moieties, expression of the Ca2+-blocking component of their vasodilator activity, were interpolated on this linear regression. They showed a good correspondence with EC50iGC values determined in the presence of soluble guanylate cyclase inhibitors. Analysis of EC50iGC/EC50 ratios provided a useful tool to distinguish well-balanced hybrids from derivatives biased toward Ca2+-blocking or NO-dependent vasodilator activity. A detrimental effect on affinity to the 1, 4-DHP receptor, due to substitution at the ortho and meta positions of the 4-phenyl ring, was observed. SAR to explain this effect is proposed.