Reduced angiotensin II levels cause generalized vascular dysfunction via oxidant stress in hamster cheek pouch arterioles.

OBJECTIVES: We investigated the effect of suppressing plasma angiotensin II (ANG II) levels on arteriolar relaxation in the hamster cheek pouch. METHODS: Arteriolar diameters were measured via television microscopy during short-term (3-6days) high salt (HS; 4% NaCl) diet and angiotensin converting enzyme (ACE) inhibition with captopril (100mg/kg/day). RESULTS: ACE inhibition and/or HS diet eliminated endothelium-dependent arteriolar dilation to acetylcholine, endothelium-independent dilation to the NO donor sodium nitroprusside, the prostacyclin analogs carbacyclin and iloprost, and the KATP channel opener cromakalim; and eliminated arteriolar constriction during KATP channel blockade with glibenclamide. Scavenging of superoxide radicals and low dose ANG II infusion (25ng/kg/min, subcutaneous) reduced oxidant stress and restored arteriolar dilation in arterioles of HS-fed hamsters. Vasoconstriction to topically-applied ANG II was unaffected by HS diet while arteriolar responses to elevation of superfusion solution PO2 were unaffected (5% O2, 10% O2) or reduced (21% O2) by HS diet. CONCLUSIONS: These findings indicate that sustained exposure to low levels of circulating ANG II leads to widespread dysfunction in endothelium-dependent and independent vascular relaxation mechanisms in cheek pouch arterioles by increasing vascular oxidant stress, but does not potentiate O2- or ANG II-induced constriction of arterioles in the distal microcirculation of normotensive hamsters.

Modulation of the 6-position of benzopyran derivatives and inhibitory effects on the insulin releasing process.

The synthesis of different series of 4- and 6-substituted R/S-3,4-dihydro-2,2-dimethyl-2H-1-benzopyrans is described. All of these new benzopyran derivatives were bearing, at the 4-position, a phenylthiourea moiety substituted on the phenyl ring by a meta or a para-electron-withdrawing group such as Cl or CN. The study aimed at exploring the influence of the nature of the substituent at the 6-position in order to develop new benzopyran-type K(ATP) channel activators exhibiting an improved selectivity towards the insulin secreting cells. The original compounds were examined in vitro on rat pancreatic islets (inhibition of insulin release) as well as on rat aorta rings (vasorelaxant effect) and their activity was compared to that of the reference K(ATP) channel activators (±)-cromakalim, (±)-pinacidil, diazoxide and to previously synthesized cromakalim analogues. Structure-activity relationships indicated that the inhibitory effect on the insulin secreting cells was related to the lipophilicity of the molecules and to the size of the substituent located at the 6-position. A marked inhibitory activity on the insulin secretory process was obtained with molecules bearing a bulky tert-butyloxycarbonylamino group at the 6-position (20-23). The latter compounds were found to have the same efficacy on the pancreatic endocrine tissue than some previously described molecules. Lastly, radioisotopic experiments further identified R/S-N-4-chlorophenyl-N'-(6-tert-butyloxycarbonylamino-3,4-dihydro-2,2-dimethyl-2H-1-benzopyran-4-yl)thiourea (23) as a K(ATP) channel opener.

New R/S-3,4-dihydro-2,2-dimethyl-2H-1-benzopyrans as K(ATP) channel openers: modulation of the 4-position.

The present work aimed at exploring a series of diversely 4-arylthiourea-substituted R/S-3,4-dihydro-2,2-dimethyl-6-halo-2H-1-benzopyrans structurally related to (+/-)-cromakalim. These new compounds were examined in vitro as putative potassium channel openers (PCOs) on rat pancreatic islets (inhibition of insulin release) as well as on rat aorta rings (relaxation of aorta ring) and their activity was compared to that of the reference K(ATP) channel activators (+/-)-cromakalim, (+/-)-pinacidil, diazoxide and of previously reported cromakalim analogues. Structure-activity relationships indicated that the most pronounced inhibitory activity on the insulin secretory process was obtained with molecules bearing a strong meta- or para-electron-withdrawing group (CN or NO(2)) on the phenyl ring of the arylthiourea moiety at the 4-position of the benzopyran nucleus (compounds 12-23). Among those, R/S-6-chloro-4-(4-cyanophenylaminothiocarbonylamino)-3,4-dihydro-2,2-dimethyl-2H-1-benzopyran (16) was found to be the most potent benzopyran-type inhibitor of insulin release ever described. Most of these original benzopyran derivatives show increased selectivity for pancreatic versus vascular tissue. Radioisotopic investigations indicated that these new compounds activated pancreatic K(ATP) channels.

The synthesis and biological evaluation of a range of novel functionalized benzopyrans as potential potassium channel activators.

A range of novel benzopyrans have been synthesised and biologically evaluated for K(ATP) channel activity employing cromakalim 1 as a benchmark K(ATP) channel opener. Although the compounds that were evaluated demonstrated a reduced ability to relax phenylephrine stimulated rat thoracic tissue, we provide evidence that benzopyrans 7a-h may be operating via an alternative mechanism than ATP-sensitive K(+) channel activity.

New R/S-3,4-dihydro-2,2-dimethyl-6-halo-4-(phenylaminothiocarbonylamino)-2H-1-benzopyrans structurally related to (+/-)-cromakalim as tissue-selective pancreatic beta-cell K(ATP) channel openers.

The present work was aimed at exploring a series of R/S-3,4-dihydro-2,2-dimethyl-6-halo-4-(phenylaminothiocarbonylamino)-2H-1-benzopyrans structurally related to (+/-)-cromakalim and differently substituted at the 4- and 6-positions. The biological effects of these putative activators of ATP-sensitive potassium channels (K(ATP)) were characterized in vitro on the pancreatic endocrine tissue (inhibition of insulin release) and on the vascular smooth muscle tissue (relaxation of aorta rings). The biological activity of these new dimethylchroman derivatives was further compared to that of (+/-)-cromakalim, (+/-)-pinacidil, diazoxide and BPDZ 73. Structure-activity relationships indicated that an improved potency for the pancreatic tissue was obtained by introducing a meta- or a para-electron-withdrawing group such as a chlorine atom on the C-4 phenyl ring, independently of the nature of the halogen atom at the 6-position of the benzopyran nucleus. Most original dimethylchroman thioureas were more potent than their 'urea' homologues and even more potent than diazoxide at inhibiting insulin release. Moreover, and unlike (+/-)-cromakalim or (+/-)-pinacidil, such compounds appeared to be highly selective towards the pancreatic tissue. Radioisotopic and fluorimetric investigations indicated that the new drugs activated pancreatic K(ATP) channels. Lastly, conformational studies suggested that the urea/thiourea dimethylchromans can be regarded as hybrid compounds between cromakalim and pinacidil.

QSAR study about ATP-sensitive potassium channel activation of cromakalim analogues using CP-MLR approach.

The structure-activity models of the myorelaxant activity of the cromakalim analogues have been investigated with nearly 470 topological descriptors from DRAGON software using Combinatorial Protocol in Multiple Linear Regression (CP-MLR). Among the descriptor classes considered in the study, the binding affinity is correlated with simple functional (FUN), topological (TOPO), atom centered fragments (ACF), empirical (EMP), modified Burden eigenvalues (BCUT), Galvez topological charge indices (GVZ), 2D-autocorrelation (2D-AUTO) and constitutional (CONS) descriptors. The models developed, and the participating descriptors suggest that the substituent groups of 4,6-disubstituted-2,2-dimethylchromans hold scope for further modification in the optimization of activity. The higher path lengths rich in polarizability and lower path length rich in atomic mass in addition to the lower charge indices of the molecule are beneficiary to the activity. The participating descriptors also suggested that certain structural features such as carbon atoms attached to the heteroatom by single or multiple bonding, and lesser or 'no' branching in a molecule are helpful to augment the activity.

Design, synthesis and biological evaluation of novel ring-opened cromakalim analogues with relaxant effects on vascular and respiratory smooth muscles and as stimulators of elastin synthesis.

Two new series of ring-opened analogues of cromakalim bearing sulfonylurea moieties (series A: with N-unmethylated sulfonylureas, series B: with N-methylated sulfonylureas) were synthesized and tested as relaxants of vascular and respiratory smooth muscles (rat aorta and trachea, respectively). Ex vivo biological evaluations indicated that the most active compounds, belonging to series B, displayed a marked vasorelaxant activity on endothelium-intact aortic rings and the trachea. A majority of series B compounds exhibited a higher vasorelaxant activity (EC50 < 22 µM) than that of the reference compound diazoxide (EC50 = 24 µM). Interestingly, several tested compounds of series B also presented stronger relaxant effects on the trachea than the reference compound cromakalim (EC50 = 124 µM), in particular compounds B4, B7 and B16 (EC50 < 10 µM). By contrast, series A derivatives were poorly active on aortic rings (EC50 > 57 µM for all, and EC50 > 200 µM for a majority of them), but some of them showed an interesting relaxing effect on trachea (i.e. A15 and A33, EC50 = 30 µM). The most potent compounds of both series, i.e. A15, A33 and B16, tested on aortic rings in the presence of glibenclamide or 80 mM KCl, suggested that they acted as voltage-gated Ca2+ channel blockers, like verapamil, instead of being ATP-potassium channel activators, as is cromakalim, the parent molecule. Further investigations on cultured vascular smooth muscle cells showed a strong stimulating effect on elastin synthesis, especially compound B16, which was more active at 20 µM than diazoxide, a reference ATP-sensitive potassium channel activator. Taken together, our results show that the N-methylation of the sulfonylurea moieties of ring-opened cromakalim analogues led to new compounds blocking calcium-gated channels, which had a major impact on the arterial and tracheal activities as well as selectivity.

From cromakalim to different structural classes of K(ATP) channel openers.

ATP-Sensitive potassium channel openers (K(ATP)COs) are a group of compounds with a broad spectrum of potential therapeutic applications, as they constitute efficient tools for dampening cell excitability. Interest in the K(ATP)COs was triggered in the early 1980s by the discovery of the benzopyran-based structure cromakalim (CRK), which is a powerful smooth muscle relaxant. CRK can be considered the archetype of K(ATP)COs and is by far the most mimicked structure. In many structure-activity studies various substitutions have been made at the different positions of the benzopyran ring permitting the optimal activity to be correlated with a specific set of structural characteristics and stereochemical features of the molecule. Thus, many potent benzopyran derivatives have been identified. The benzopyran nucleus itself has also been modified in both the aromatic ring and in the pyran moiety. The intention of this review is to bring together all the different structural classes of K(ATP)COs arising from the replacement of CRK benzopyran-based structure with various ring systems; design, structure-activity relationship, and synthesis will be given.

Design, synthesis, and pharmacological evaluation of R/S-3,4-dihydro-2,2-dimethyl- 6-halo-4-(phenylaminocarbonylamino)-2H-1-benzopyrans: toward tissue-selective pancreatic beta-cell KATP channel openers structurally related to (+/-)-cromakalim.

In the search of a novel series of benzopyrans structurally related to (+/-)-cromakalim and acting as pancreatic beta-cell potassium channel openers, several R/S-3,4-dihydro-2,2-dimethyl-6-halo-4-(phenylaminocarbonylamino)-2H-1-benzopyrans with or without a substituent on the phenyl ring in the 4-position were synthesized. Their activity on rat-insulin-secreting cells and rat aorta rings was compared to that of the K(ATP) channel activators (+/-)-cromakalim, diazoxide, (+/-)-pinacidil, and compound 4. Structure-activity relationships indicated that the most pronounced inhibitory activity on the pancreatic tissue was obtained by introducing a meta- or para-electron-withdrawing group (a chlorine atom) on the C-4 phenyl ring (drugs 37-42). Such molecules, unlike the parent compound (+/-)-cromakalim, also exhibited a high selectivity for the pancreatic tissue versus the vascular tissue. Radioisotopic and electrophysiological investigations performed with R/S-6-chloro-4-(3-chlorophenylaminocarbonylamino)-3,4-dihydro-2,2-dimethyl-2H-1-benzopyran (38) confirmed that the drug activated pancreatic KATP channels.

4,6-Disubstituted 2,2-dimethylchromans structurally related to the K(ATP) channel opener cromakalim: design, synthesis, and effect on insulin release and vascular tone.

Five series (ureas, thioureas, carbamates, sulfonylureas, and amides) of 4,6-disubstituted-2,2-dimethylchromans structurally related to cromakalim were prepared and evaluated, as putative ATP-sensitive potassium channel activators, on rat pancreatic islets and rat aorta rings. The biological data indicate that most compounds were, like the reference molecule cromakalim, more active on the vascular smooth muscle tissue (myorelaxant effect on 30 mM KCl induced contractions of rat aorta rings) than on the pancreatic tissue (inhibition of 16.7 mM glucose induced insulin release from rat pancreatic islets). However, some drugs (8h, 8i, 9f, 9g, 9h, and 9i) markedly inhibited insulin release and exhibited an activity equivalent or greater than that of diazoxide. Compounds 9h and 9i were also found to be more active on pancreatic beta-cells than on vascular smooth muscle cells. Last, the amide 6b was selected in order to examine its mechanism of action on vascular smooth muscle cells. Pharmacological results suggest that the compound acted as a K(ATP) channel opener. In conclusion, the present data indicate that appropriate structural modifications can generate dimethylchromans with pharmacological profiles different from that of cromakalim.

Influence of the alkylsulfonylamino substituent located at the 6-position of 2,2-dimethylchromans structurally related to cromakalim: from potassium channel openers to calcium entry blockers?

The present study described the synthesis of original R/S-6-alkylsulfonylamino-3,4-dihydro-2,2-dimethyl-2H-1-benzopyrans bearing a 3- or 4-substituted phenylthiourea or phenylurea moiety at the 4-position. Their biological effects were evaluated both on insulin-secreting and smooth muscle cells and were compared to those of reference KATP channel activators such as (±)-cromakalim, diazoxide and previously synthesized cromakalim analogues. The study aimed at exploring the influence of the introduction of an alkylsulfonylamino substituent at the 6-position of 2,2-dimethylchromans in order to improve biological activity, tissue selectivity but also hydrophilicity of dihydrobenzopyran derivatives. Several compounds were found to be equipotent or even more potent than (±)-cromakalim and diazoxide at inhibiting the insulin releasing process. Most of the newly synthesized and more hydrophilic dihydrobenzopyrans also exhibited a marked vasorelaxant activity although they were less potent than (±)-cromakalim. Additional pharmacological and radioisotopic investigations suggested that R/S-N-3-chlorophenyl-N'-(3,4-dihydro-6-methylsulfonylamino-2,2-dimethyl-2H-1-benzopyran-4-yl)thiourea (21) did not act as a potassium channel opener but rather as a Ca(2+) entry blocker.

A novel cromakalim analogue induces cell cycle arrest and apoptosis in human cervical carcinoma HeLa cells through the caspase- and mitochondria-dependent pathway.

In the present study, a series of seven synthetic croma-kalim analogues were prepared and evaluated for cytotoxic effect on human cervical carcinoma HeLa cells using WST-8 assay. A preliminary screening of these cromakalim analogues showed that 1-[(3S,4R)-4-(2-ethoxy-4-methyl-1H-pyrrol-1-yl)-3-hydroxy- 2,2-dimethylchroman-6-yl-3-phenylurea (compound 6) had the highest cytotoxic effect (IC50 of 138 µM) and significantly inhibited HeLa cell proliferation after 36 h. In an effort to understand the cytotoxic mechanism of compound 6, we examined its effect on apoptosis and cell cycle distribution. Our results showed that compound 6 induced marked changes in apoptotic morphology and significantly increased early apoptosis of HeLa cells after 48 h by using Annexin V-FITC/PI dual staining assay. This apoptotic induction was associated with an increase in Bax expression, a decrease in Bcl-2 expression, release of cytochrome c and subsequent activation of caspase-9 and -3, which indicated that compound 6 induced apoptosis via caspase- and mitochondria-dependent pathway. By DNA content analysis and [3H]thymidine incorporation assay, compound 6 was found to induce an increase in the number of cells in G1 phase, accompanied by a decrease in the S phase to prevent DNA synthesis after 24 h of treatment. In addition, compound 6 caused significant DNA damage, as detected by the alkaline comet assay. Taken together, the data demonstrate that compound 6 induces apoptosis in HeLa cells through caspase- and mitochondria-dependent pathway and this apoptotic effect is associated with cell cycle arrest and DNA damage. These findings provide further understanding of the molecular mechanisms of compound 6 in cervical cancer.

Synthesis and pharmacological evaluation of some N-arylsulfonyl-N-methyl-N'-(2,2-dimethyl-2H-1-benzopyran-4-yl)ureas structurally related to cromakalim.

Some N-arylsulfonyl-N-methyl-N'-(2,2-dimethyl-2H-1-benzopyran-4-yl)ureas were prepared and evaluated as putative potassium channel openers on the vascular and uterine smooth muscle tissue (myorelaxant effect), as well as on insulin-secreting pancreatic islets (inhibition of insulin release). The pharmacological results indicated that these compounds exhibited a marked biological activity on these three tissues.

Novel potassium channel activators. II. Synthesis and pharmacological evaluation of 3,4-dihydro-2H-1,4-benzoxazine derivatives: modification of the aromatic part.

Three new series of analogues related to 3,4-dihydro-2H-1,4-benzoxazine derivative 1a were synthesized and evaluated for their potassium channel activating activity. In the first series I, where the 6,7-positions were disubstituted, it was found that an electron-withdrawing substituent was preferable at the 6 position, but either an electron-withdrawing or releasing substituent without bulkiness was tolerated at the 7 position. In the second series II, where several heterocycles were introduced into the 6,7-positions, the oxadiazole derivative 6 showed more potent activity than cromakalim. In the third series III, where the benzene ring was replaced by a pyridine ring, borane complex 16 had equivalent activity to cromakalim. Especially, compound 6 showed a potent hypotensive effect with a long duration of action in the spontaneous hypertensive rat and had a lesser increasing effect on intracranial pressure in dogs than 1a and levcromakalim, showing a good profile as an antihypertensive agent.