Angiotensin II AT1 receptor antagonists. Clinical implications of active metabolites

Suzuki-Miyaura/Mizoroki-Heck coupling cascade to access 2,2'-bifunctionalized biaryls

Biaryl motifs are essential structural features in several drugs and functional molecules. Cyclic diaryliodonium has been scarcely explored as a bifunctional agent compared to ring opening and annulation reactions. Herein, a three-component cascade approach is developed to synthesize bifunctionalized biaryls employing cyclic diaryliodoniums as a biarylating agent. The mild conditions enabled a vast array of biarylated products in good yields in a single step. Furthermore, preliminary mechanistic details and photophysical properties have been investigated.

Role of the Renin-Angiotensin System in Long COVID's Cardiovascular Injuries

The renin-angiotensin system (RAS) is one of the biggest challenges of cardiovascular medicine. The significance of the RAS in the chronic progression of SARS-CoV-2 infection and its consequences is one of the topics that are currently being mostly discussed. SARS-CoV-2 undermines the balance between beneficial and harmful RAS pathways. The level of soluble ACE2 and membrane-bound ACE2 are both upregulated by the endocytosis of the SARS-CoV-2/ACE2 complex and the tumor necrosis factor (TNF)-α-converting enzyme (ADAM17)-induced cleavage. Through the link between RAS and the processes of proliferation, the processes of fibrous remodelling of the myocardium are initiated from the acute phase of the disease, continuing into the long COVID stage. In the long term, RAS dysfunction may cause an impairment of its beneficial effects leading to thromboembolic processes and a reduction in perfusion of target organs. The main aspects of ACE2-a key pathogenic role in COVID-19 as well as the mechanisms of RAS involvement in COVID cardiovascular injuries are studied. Therapeutic directions that can be currently anticipated in relation to the various pathogenic pathways of progression of cardiovascular damage in patients with longCOVID have also been outlined.

Palladium-Catalyzed C(sp3)-H Biarylation of 8-Methyl Quinolines with Cyclic Diaryliodonium Salts to Access Functionalized Biaryls and Fluorene Derivatives

Herein, we have developed the cyclic diaryliodonium salts as biarylating agents in the C(sp³)-H functionalization using 8-methyl quinoline as the intrinsic directing group. The oxidant-free reaction produces a vast array of the biarylated products with iodo functionality that can be further functionalized. Additionally, intramolecular C(sp³)-H functionalization in a stepwise manner under palladium-catalyzed conditions produced the fluorene derivatives in excellent yields.

The rationale for the treatment of long-Covid symptoms – A cardiologist's view

The ongoing coronavirus disease 2019 pandemic left us with thousands of patients suffering from neurological, cardiovascular, and psychiatric disorders named post-acute sequelae of COVID-19 or just long-Covid. In parallel, the vaccination campaigns against SARS-CoV-2 spike protein saved millions of lives worldwide but long-Covid symptoms also appeared rarely following vaccination with a strong overlap to the “canonical” long-Covid symptoms. A therapeutic strategy targeting both, post-VAC and post-SARS-CoV-2 long-Covid symptoms is warranted since exposure to the S-protein either by vaccination or SARS-CoV-2 infection may trigger identical immuno-inflammatory cascades resulting in long-Covid symptoms.

The Race for ACE: Targeting Angiotensin-Converting Enzymes (ACE) in SARS-CoV-2 Infection

The SARS-CoV-2 virus is spreading around the world, and its clinical manifestation COVID-19 is challenging medical, economic, and social systems. With more and more scientific and social media reports on the COVID-19 pandemic appearing, differences in geographical presentations and clinical management occur. Since ACE2 (angiotensin-converting enzyme 2) is the gatekeeper receptor for the SARS-CoV-2 virus in the upper bronchial system, we here focus on the central role of the renin-angiotensin aldosterone system (RAAS) in the SARS-CoV-2 virus infection, the role of pharmacological RAAS inhibitors, and specific genetic aspects, i.e., single nucleotide polymorphisms (SNP) for the clinical outcome of COVID-19. We aimed to bring together clinical, epidemiological, molecular, and pathophysiological and pharmacological data/observations on cardiovascular aspects in the actual SARS-CoV-2 virus pandemic. In detail, we will report controversies about the Yin-Yan between ACE2 and ACE1 and potential implications for the treatment of hypertension, coronary artery disease, and heart failure. Here, we summarize the encouraging and dynamic global effort of multiple biomedical disciplines resulted in astonishing fight against COVID-19 targeting the renin-angiotensin-aldosterone system, yet the race for ACE just begun.

Modified chitosan-zeolite supported Pd nanoparticles: A reusable catalyst for the synthesis of 5-substituted-1H-tetrazoles from aryl halides

A novel heterogeneous catalyst has been developed using chitosan-zeolite supported Pd nanoparticles (PdNPs@CS-Zeo) and used in an efficient synthesis of 5-substituted-1H-tetrazoles from aryl halides with high yields for relatively short reaction times with an easy work-up procedure. In this method, highly effective and reusable PdNPs@CS-Zeo catalyst was used in the reaction of various aryl iodides/bromides with K₄[Fe(CN)₆] as a non-toxic cyanide source to catalyze the [2 + 3] cycloaddition of the corresponding aryl nitriles with NaN₃ in the sequential one-pot preparation of 5-substituted-1H-tetrazoles. The synthesized PdNPs@CS-Zeo nanocatalyst was characterized using XRD, FTIR, TEM, HRTEM, XPS, Raman, TG-DTG, ICP-OES, BET, and EDS mapping. Additionally, the nanocatalyst could be effectively separated by filtration and reused for multiple times without significant decrease of catalytic activity.

The emergence of the C-H functionalization strategy in medicinal chemistry and drug discovery

Owing to the market competitiveness and urgent societal need, an optimum speed of drug discovery is an important criterion for successful implementation. Despite the rapid ascent of artificial intelligence and computational and bioanalytical techniques to accelerate drug discovery in big pharma, organic synthesis of privileged scaffolds predicted in silico for in vitro and in vivo studies is still considered as the rate-limiting step. C-H activation is the latest technology added into an organic chemist's toolbox for the rapid construction and late-stage modification of functional molecules to achieve the desired chemical and physical properties. Particularly, elimination of prefunctionalization steps, exceptional functional group tolerance, complexity-to-diversity oriented synthesis, and late-stage functionalization of privileged medicinal scaffolds expand the chemical space. It has immense potential for the rapid synthesis of a library of molecules, structural modification to achieve the required pharmacological properties such as absorption, distribution, metabolism, excretion, toxicology (ADMET) and attachment of chemical reporters for proteome profiling, metabolite synthesis, etc. for preclinical studies. Although heterocycle synthesis, late-stage drug modification, ¹⁸F labelling, methylation, etc. via C-H functionalization have been reviewed from the synthetic standpoint, a general overview of these protocols from medicinal and drug discovery aspects has not been reviewed. In this feature article, we will discuss the recent trends of C-H activation methodologies such as synthesis of medicinal scaffolds through C-H activation/annulation cascade; C-H arylation for sp²-sp² and sp²-sp³ cross-coupling; C-H borylation/silylation to introduce a functional linchpin for further manipulation; C-H amination for N-heterocycles and hydrogen bond acceptors; C-H fluorination/fluoroalkylation to tune polarity and lipophilicity; C-H methylation: methyl magic in drug discovery; peptide modification and macrocyclization for therapeutics and biologics; fluorescent labelling and radiolabelling for bioimaging; bioconjugation for chemical biology studies; drug-metabolite synthesis for biodistribution and excretion studies; late-stage diversification of drug-molecules to increase efficacy and safety; cutting-edge DNA encoded library synthesis and improved synthesis of drug molecules via C-H activation in medicinal chemistry and drug discovery.

Degradation of Losartan in Fresh Urine by Sonochemical and Photochemical Advanced Oxidation Processes

In this work, the degradation of the pharmaceutical losartan, in simulated fresh urine (which was considered because urine is the main excretion route for this compound) by sonochemistry and UVC/H2O2 individually, was studied. Initially, special attention was paid to the degrading action of the processes. Then, theoretical analyses on Fukui function indices, to determine electron-rich regions on the pharmaceutical susceptible to attacks by the hydroxyl radical, were performed. Afterward, the ability of the processes to mineralize losartan and remove the phyto-toxicity was tested. It was found that in the sonochemical treatment, hydroxyl radicals played the main degrading role. In turn, in UVC/H2O2, both the light and hydroxyl radical eliminated the target contaminant. The sonochemical system showed the lowest interference for the elimination of losartan in the fresh urine. It was established that atoms in the imidazole of the contaminant were the moieties most prone to primary transformations by radicals. This was coincident with the initial degradation products coming from the processes action. Although both processes exhibited low mineralizing ability toward losartan, the sonochemical treatment converted losartan into nonphytotoxic products. This research presents relevant results on the elimination of a representative pharmaceutical in fresh urine by two advanced oxidation processes.

Repurposing old drugs to fight multidrug resistant cancers

Overcoming multidrug resistance represents a major challenge for cancer treatment. In the search for new chemotherapeutics to treat malignant diseases, drug repurposing gained a tremendous interest during the past years. Repositioning candidates have often emerged through several stages of clinical drug development, and may even be marketed, thus attracting the attention and interest of pharmaceutical companies as well as regulatory agencies. Typically, drug repositioning has been serendipitous, using undesired side effects of small molecule drugs to exploit new disease indications. As bioinformatics gain increasing popularity as an integral component of drug discovery, more rational approaches are needed. Herein, we show some practical examples of in silico approaches such as pharmacophore modelling, as well as pharmacophore- and docking-based virtual screening for a fast and cost-effective repurposing of small molecule drugs against multidrug resistant cancers. We provide a timely and comprehensive overview of compounds with considerable potential to be repositioned for cancer therapeutics. These drugs are from diverse chemotherapeutic classes. We emphasize the scope and limitations of anthelmintics, antibiotics, antifungals, antivirals, antimalarials, antihypertensives, psychopharmaceuticals and antidiabetics that have shown extensive immunomodulatory, antiproliferative, pro-apoptotic, and antimetastatic potential. These drugs, either used alone or in combination with existing anticancer chemotherapeutics, represent strong candidates to prevent or overcome drug resistance. We particularly focus on outcomes and future perspectives of drug repositioning for the treatment of multidrug resistant tumors and discuss current possibilities and limitations of preclinical and clinical investigations.

Unpuzzling COVID-19: tissue-related signaling pathways associated with SARS-CoV-2 infection and transmission

The highly infective coronavirus disease 19 (COVID-19) is caused by a novel strain of coronaviruses - the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) - discovered in December 2019 in the city of Wuhan (Hubei Province, China). Remarkably, COVID-19 has rapidly spread across all continents and turned into a public health emergency, which was ultimately declared as a pandemic by the World Health Organization (WHO) in early 2020. SARS-CoV-2 presents similar aspects to other members of the coronavirus family, mainly regarding its genome, protein structure and intracellular mechanisms, that may translate into mild (or even asymptomatic) to severe infectious conditions. Although the mechanistic features underlying the COVID-19 progression have not been fully clarified, current evidence have suggested that SARS-CoV-2 may primarily behave as other β-coronavirus members. To better understand the development and transmission of COVID-19, unveiling the signaling pathways that may be impacted by SARS-CoV-2 infection, at the molecular and cellular levels, is of crucial importance. In this review, we present the main aspects related to the origin, classification, etiology and clinical impact of SARS-CoV-2. Specifically, here we describe the potential mechanisms of cellular interaction and signaling pathways, elicited by functional receptors, in major targeted tissues/organs from the respiratory, gastrointestinal (GI), cardiovascular, renal, and nervous systems. Furthermore, the potential involvement of these signaling pathways in evoking the onset and progression of COVID-19 symptoms in these organ systems are presently discussed. A brief description of future perspectives related to potential COVID-19 treatments is also highlighted.

Ethanol-Drop Grinding Approach: Cadmium Oxide Nanoparticles Catalyzed the Synthesis of [1,3]Dioxolo[g][1]benzopyran-6-carboxylic Acids and Pyrido[d]pyrimidine-7-carboxylic Acids

AIM AND OBJECTIVE

In the last decades, it has extensively been verified that nanostructured transition metal oxides emerge as inexpensive, available and extremely efficient heterogeneous catalysts in chemical transformations. The high electrical conductivity, high carrier concentration, and improved reactivity in cadmium oxide nanoparticles (CdO NPs) make it as a potential candidate for applications in the fields of nanocatalysis. [1]Benzopyran and pyridopyrimidine derivatives compose major classes of heterocyclic compounds, which have a wide spectrum of biological activities.

MATERIALS AND METHODS

In the present work, we report a facile and highly effective synthesis of 8- aryl-8H-[1,3]dioxolo[4,5-g][1]benzopyran-6-carboxylic acids and 1,3-dimethyl-2,4-dioxo-5- phenyl-1,2,3,4,5,8-hexahydropyrido[2,3-d]pyrimidine-7-carboxylic acids via CdO NPs catalyzed cyclo condensation reaction of 4-substituted phenylmethylidenepyruvic acids with 3,4- methylenedioxyphenol or 6-amino-1,3-dimethyluracil, which was accomplished under ethanoldrop grinding at room temperature. The described catalyst was prepared successfully by a simple precipitation method and characterized by the Fourier transformed infrared absorption (FT-IR) spectroscopy, X-Ray diffraction (XRD) analytical technique, and scanning electron microscopy (SEM).

RESULTS

A number of [1,3]dioxolo[g][1]benzopyran-6-carboxylic acids and pyrido[d]pyrimidine- 7-carboxylic acids were effectively synthesized in high yields (96-98%) within short reaction times (10-15 min). All synthesized compounds were well-characterized by IR, 1H and 13C NMR spectroscopy, and also by elemental analyses.

CONCLUSION

In summary, we have developed a very simple and impressive procedure for the synthesis of 8-aryl-8H-[1,3]dioxolo[4,5-g][1]benzopyran-6-carboxylic acids and 1,3-dimethyl- 2,4-dioxo-5-phenyl-1,2,3,4,5,8-hexahydropyrido[2,3-d]pyrimidine-7-carboxylic acids as biologically interesting structures in the presence of CdO NPs as an efficient recyclable heterogeneous catalyst. The remarkable advantages for the offered protocol compared with traditional methods are short reaction time, good yields of the products, and the ease of operation with simple work-up procedure.

Systematic characterization of AT1 receptor antagonists with label-free dynamic mass redistribution assays

INTRODUCTION

In the drug discovery field, the binding affinities and binding kinetics of drug candidates are very important. Angiotensin II type 1 (AT1) receptor antagonists, e.g., candesartan, telmisartan, irbesartan, losartan and valsartan, show high affinities and long-lasting bindings to the receptor, making them preferred medications for hypertension treatment. However, the molecular binding properties of AT1 receptor antagonists are controversial.

METHODS

In this work, we established a profile to study the phenotypic properties of AT1 receptor antagonists with label-free dynamic mass redistribution (DMR) assays in native human cells. With noninvasive features, DMR assay were conducted in multiple formats. Eleven antagonists were systematically evaluated with angiotensin II as an agonist probe in the Hep G2 cell line, which endogenously expresses the AT1 receptor.

RESULTS

The IC₅₀ values to the AT1 receptor of individual antagonist varied with different incubation times. The antagonists showed competitive behavior with angiotensin II. Schild analysis was used to analyze the competitive behavior of the antagonist. All of the antagonist showed long-lasting possession of the AT1 receptor, except telmisartan. The systematic evaluation of the antagonists implied that 11 antagonists showed high binding affinity but distinct binding modes to AT1 receptor.

DISCUSSION

This study demonstrated that the DMR assay has great potential for determining the pharmacological parameters of ligands. This work may serve as guidance for other receptor and ligand assays.

Magnetic chitosan-copper nanocomposite: A plant assembled catalyst for the synthesis of amino- and N-sulfonyl tetrazoles in eco-friendly media

A greener, cost efficient and simple method is described to prepare copper nanoparticles (NPs) immobilized on the magnetic chitosan (one of the more versatile polysaccharides) using Euphorbia falcata leaf extract as reducing/stabilizing agent. The prepared catalyst (Cu NPs@Fe₃O₄-chitosan) was authenticated by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), Scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDS), thermogravimetry/derivative thermogravimetry (TG/DTG), Vibrating sample magnetometer (VSM), and elemental mapping. TEM analysis indicates that Cu NPs with average sizes in 5-10 nm range is formed on magnetic chitosan with the spherical morphology. The Cu NPs@Fe₃O₄-chitosan was employed as a new catalyst for the synthesis of different tetrazoles by the reaction of various secondary or tertiary cyanamides with sodium azide in water under reflux conditions. Easy separation by external magnetic field, mild reaction conditions, low cost and the reusability are some of the beneficial features of this catalyst.

Pyrido[2,3-d]pyrimidin-7(8H)-ones: Synthesis and Biomedical Applications

Pyrido[2,3-d]pyrimidines (1) are a type of privileged heterocyclic scaffolds capable of providing ligands for several receptors in the body. Among such structures, our group and others have been particularly interested in pyrido[2,3-d]pyrimidine-7(8H)-ones (2) due to the similitude with nitrogen bases present in DNA and RNA. Currently there are more than 20,000 structures 2 described which correspond to around 2900 references (half of them being patents). Furthermore, the number of references containing compounds of general structure 2 have increased almost exponentially in the last 10 years. The present review covers the synthetic methods used for the synthesis of pyrido[2,3-d]pyrimidine-7(8H)-ones (2), both starting from a preformed pyrimidine ring or a pyridine ring, and the biomedical applications of such compounds.

Discovery of thiophene-containing biaryl amide derivatives as novel glucagon receptor antagonists

A novel series of thiophene-containing biaryl amide glucagon receptor (GCGR) antagonists were designed and synthesized. Two compounds of this series, 14f and 14h, exhibited good GCGR binding (IC₅₀  = 6.1 and 4.4 μm, respectively) and cAMP functional activities (IC₅₀  = 4.4 and 14.4 μm, respectively). The possible binding modes of compounds 14f and 14h with GCGR were explored by molecular simulation.

Urinary antihypertensive drug metabolite screening using molecular networking coupled to high-resolution mass spectrometry fragmentation

INTRODUCTION

Mass spectrometry is the current technique of choice in studying drug metabolism. High-resolution mass spectrometry in combination with MS/MS gas-phase experiments has the potential to contribute to rapid advances in this field. However, the data emerging from such fragmentation spectral files pose challenges to downstream analysis, given their complexity and size.

OBJECTIVES

This study aims to detect and visualize antihypertensive drug metabolites in untargeted metabolomics experiments based on the spectral similarity of their fragmentation spectra. Furthermore, spectral clusters of endogenous metabolites were also examined.

METHODS

Here we apply a molecular networking approach to seek drugs and their metabolites, in fragmentation spectra from urine derived from a cohort of 26 patients on antihypertensive therapy. The mass spectrometry data was collected on a Thermo Q-Exactive coupled to pHILIC chromatography using data dependent analysis (DDA) MS/MS gas-phase experiments.

RESULTS

In total, 165 separate drug metabolites were found and structurally annotated (17 by spectral matching and 122 by classification based on a clustered fragmentation pattern). The clusters could be traced to 13 drugs including the known antihypertensives verapamil, losartan and amlodipine. The molecular networking approach also generated clusters of endogenous metabolites, including carnitine derivatives, and conjugates containing glutamine, glutamate and trigonelline.

CONCLUSIONS

The approach offers unprecedented capability in the untargeted identification of drugs and their metabolites at the population level and has great potential to contribute to understanding stratified responses to drugs where differences in drug metabolism may determine treatment outcome.

International Union of Basic and Clinical Pharmacology. XCIX. Angiotensin Receptors: Interpreters of Pathophysiological Angiotensinergic Stimuli [corrected]

The renin angiotensin system (RAS) produced hormone peptides regulate many vital body functions. Dysfunctional signaling by receptors for RAS peptides leads to pathologic states. Nearly half of humanity today would likely benefit from modern drugs targeting these receptors. The receptors for RAS peptides consist of three G-protein-coupled receptors—the angiotensin II type 1 receptor (AT1 receptor), the angiotensin II type 2 receptor (AT2 receptor), the MAS receptor—and a type II trans-membrane zinc protein—the candidate angiotensin IV receptor (AngIV binding site). The prorenin receptor is a relatively new contender for consideration, but is not included here because the role of prorenin receptor as an independent endocrine mediator is presently unclear. The full spectrum of biologic characteristics of these receptors is still evolving, but there is evidence establishing unique roles of each receptor in cardiovascular, hemodynamic, neurologic, renal, and endothelial functions, as well as in cell proliferation, survival, matrix-cell interaction, and inflammation. Therapeutic agents targeted to these receptors are either in active use in clinical intervention of major common diseases or under evaluation for repurposing in many other disorders. Broad-spectrum influence these receptors produce in complex pathophysiological context in our body highlights their role as precise interpreters of distinctive angiotensinergic peptide cues. This review article summarizes findings published in the last 15 years on the structure, pharmacology, signaling, physiology, and disease states related to angiotensin receptors. We also discuss the challenges the pharmacologist presently faces in formally accepting newer members as established angiotensin receptors and emphasize necessary future developments.

A pharmacokinetic and pharmacodynamic drug interaction between rosuvastatin and valsartan in healthy subjects

PURPOSE

Valsartan, an angiotensin-receptor blocker, and rosuvastatin, a competitive inhibitor of the 3-hydroxy-3-methylglutaryl coenzyme A reductase, are frequently coadministered to treat patients with hypertension and dyslipidemia. The study reported here sought to evaluate the pharmacokinetic and pharmacodynamic interactions between rosuvastatin and valsartan in healthy Korean subjects.

SUBJECTS AND METHODS

Thirty healthy male Korean subjects were administered with rosuvastatin (20 mg/day), valsartan (160 mg/day), and both drugs concomitantly for 4 days in a randomized, open-label, multiple-dose, three-treatment, three-period crossover study. Plasma concentrations of rosuvastatin, N-desmethyl rosuvastatin, and valsartan were determined using validated high-performance liquid chromatography with tandem mass spectrometry. Lipid profiles and vital signs (systolic and diastolic blood pressure and pulse rate) were measured for the pharmacodynamic assessment.

RESULTS

For rosuvastatin, the geometric mean ratios (90% confidence intervals [CIs]) of coadministration to mono-administration were 0.8809 (0.7873-0.9857) for maximum plasma concentration at steady state and 0.9151 (0.8632-0.9701) for area under the concentration-time curve (AUC) over a dosing interval at steady state. For valsartan, the geometric mean ratios (90% CIs) of those were 0.9300 (0.7946-1.0884) and 1.0072 (0.8893-1.1406), respectively. There were no significant differences in the metabolic ratio of N-desmethyl rosuvastatin AUC to rosuvastatin AUC between coadministration and rosuvastatin alone. No interaction was found in terms of systolic or diastolic blood pressure or lipid profiles. Combined treatment with valsartan and rosuvastatin was generally well tolerated without serious adverse events.

CONCLUSION

The pharmacokinetic profiles of rosuvastatin and valsartan in combination were comparable with those of rosuvastatin and valsartan administered individually, suggesting that their individual pharmacokinetics were not affected by their coadministration. No dose adjustment was required and the results are supportive of a study in a larger patient population.

In-silico docking based design and synthesis of [1H,3H] imidazo[4,5-b] pyridines as lumazine synthase inhibitors for their effective antimicrobial activity

PURPOSE

The imidazopyridine moiety is important pharmacophore that has proven to be useful for a number of biologically relevant targets, also reported to display antibacterial, antifungal, antiviral properties. Riboflavin biosynthesis involving catalytic step of Lumazine synthase is absent in animals and human, but present in microorganism, one of marked advantage of this study. Still, this path is not exploited as antiinfective target. Here, we proposed different interactions between [1H,3H] imidazo[4,5-b] pyridine test ligands and target protein Lumazine synthase (protein Data Bank 2C92), one-step synthesis of title compounds and further evaluation of them for in vitro antimicrobial activity.

MATERIALS AND METHODS

Active pocket of the target protein involved in the interaction with the test ligands molecules was found using Biopredicta tools in VLifeMDS 4.3 Suite. In-silico docking suggests H-bonding, hydrophobic interaction, charge interaction, aromatic interaction, and Vanderwaal forces responsible for stabilizing enzyme-inhibitor complex. Disc diffusion assay method was used for in vitro antimicrobial screening.

RESULTS AND DISCUSSION

Investigation of possible interaction between test ligands and target lumazine synthase of Mycobacterium tuberculosis suggested 1i and 2f as best fit candidates showing hydrogen bonding, hydrophobic, aromatic and Vanderwaal's forces. Among all derivatives 1g, 1j, 1k, 1l, 2a, 2c, 2d, 2e, 2h, and 2j exhibited potent activities against bacteria and fungi compared to the standard Ciprofloxacin and Fluconazole, respectively. The superiority of 1H imidazo [4,5-b] pyridine compounds having R' = Cl >No2 > NH2 at the phenyl/aliphatic moiety resident on the imidazopyridine, whereas leading 3H imidazo[4,5-b] pyridine compounds containing R/Ar = Cl > No2 > NH2> OCH3 substituents on the 2(nd) position of imidazole.

Targeting the ABCG2-overexpressing multidrug resistant (MDR) cancer cells by PPARγ agonists

BACKGROUND AND PURPOSE

Multidrug resistance (MDR), usually mediated by overexpression of efflux transporters such as P-gp, ABCG2 and/or MRP1, remains a major obstacle hindering successful cancer chemotherapy. There has been great interest in the development of inhibitors towards these transporters to circumvent resistance. However, since the inhibition of transporter is not specific to cancer cells, a decrease in the cytotoxic drug dosing may be needed to prevent excess toxicity, thus undermining the potential benefit brought about by a drug efflux inhibitor. The design of potent MDR modulators specific towards resistant cancer cells and devoid of drug-drug interactions will be needed to effect MDR reversal.

EXPERIMENTAL APPROACH

Recent evidence suggests that the PTEN/PI3K/Akt pathway may be exploited to alter ABCG2 subcellular localization, thereby circumventing MDR. Three PPARγ agonists (telmisartan, pioglitazone and rosiglitazone) that have been used in the clinics were tested for their effect on the PTEN/PI3K/Akt pathway and possible reversal of ABCG2-mediated drug resistance.

KEY RESULTS

The PPARγ agonists were found to be weak ABCG2 inhibitors by drug efflux assay. They were also shown to elevate the reduced PTEN expression in a resistant and ABCG2-overexpressing cell model, which inhibit the PI3K-Akt pathway and lead to the relocalization of ABCG2 from the plasma membrane to the cytoplasma, thus apparently circumventing the ABCG2-mediated MDR.

CONCLUSIONS AND IMPLICATIONS

Since this PPARγ/PTEN/PI3K/Akt pathway regulating ABCG2 is only functional in drug-resistant cancer cells with PTEN loss, the PPARγ agonists identified may represent promising agents targeting resistant cells for MDR reversal.

Bioactivation potential of thiophene-containing drugs

Thiophene is a five-membered, sulfur-containing heteroaromatic ring commonly used as a building block in drugs. It is considered to be a structural alert, as its metabolism can lead to the formation of reactive metabolites. Thiophene S-oxides and thiophene epoxides are highly reactive electrophilic thiophene metabolites whose formation is cytochrome P450-dependent. These reactive thiophene-based metabolites are quite often responsible for drug-induced hepatotoxicity. Tienilic acid is an example of a thiophene-based drug that was withdrawn from the market after only a few months of use, due to severe cases of immune hepatitis. However, inclusion of the thiophene moiety in drugs does not necessarily result in toxic effects. The presence of other, less toxic metabolic pathways, as well as an effective detoxification system in our body, protects us from the bioactivation potential of the thiophene ring. Thus, the presence of a structural alert itself is insufficient to predict a compound's toxicity. The question therefore arises as to which factors significantly influence the toxicity of thiophene-containing drugs. There is no easy way to answer this question. However, the findings presented here indicate that, for a number of reasons, daily dose and alternative metabolic pathways are important factors when predicting toxicity and will therefore be discussed together with examples.

Intermittent losartan administration triggers cardiac post-conditioning in isolated rat hearts: role of BK2 receptors

INTRODUCTION

The angiotensin (Ang) and bradykinin (BK) tissue-system plays a pivotal role in post-conditioning, but the efficacy of angiotensin type 1 receptor (AT1R) blockers (ARBs) in post-ischemic strategies is still under investigation. We evaluated functional and morphological outcomes, together with activation of cytosolic RISK pathway kinases, in rat hearts subjected to losartan (LOS) or irbesartan (IRB) post-ischemic administration.

METHODS

Isolated rat hearts underwent 30 min ischemia and 120 min reperfusion. Post-conditioning was obtained by intermittent (10 s/each) or continuous drug infusion during the first 3 min of reperfusion. Left ventricular end-diastolic pressure (LVEDP), left ventricular developed pressure (dLVP), coronary flow (CF), and left ventricular infarct mass (IM) were measured together with the activation status of RISK kinases Akt, p42/44 MAPK and GSK3β.

RESULTS

When compared to hearts subjected to ischemia/reperfusion (iI/R) alone, continuous IRB or LOS administration did not significantly reduce total infarct mass (cIRB or cLOS vs. iI/R, p = 0.2). Similarly, intermittent IRB (iIRB) was not able to enhance cardioprotection. Conversely, intermittent LOS administration (iLOS) significantly ameliorated cardiac recovery (iLOS vs iI/R, p<0.01). Differences between iLOS and iIRB persisted under continuous blockade of AT2R (iLOS+cPD vs. iIRB+cPD, p<0.05). Interestingly, iLOS cardioprotection was lost when BK2R was simultaneously blocked (iLOS+cHOE vs. iI/R, p = 0.6), whereas concurrent administration of iBK and iIRB replicated iLOS effects (iIRB+iBK vs. iLOS, p = 0.7). At the molecular level, iIRB treatment did not significantly activate RISK kinases, whereas both iLOS and iBK treatments were associated with activation of the Akt/GSK3β branch of the RISK pathways (p<0.05 vs. iI/R, for both).

CONCLUSIONS

Our results suggest that intermittent losartan is effective in mediating post-conditioning cardioprotection, whereas irbesartan is not. The infarct mass reduction by intermittent losartan seem mainly related on its specific ability to modulate BK2R, and only modestly associated on AT1R blocking properties.

A systematic comparison of the properties of clinically used angiotensin II type 1 receptor antagonists

Angiotensin II type 1 receptor antagonists (ARBs) have become an important drug class in the treatment of hypertension and heart failure and the protection from diabetic nephropathy. Eight ARBs are clinically available [azilsartan, candesartan, eprosartan, irbesartan, losartan, olmesartan, telmisartan, valsartan]. Azilsartan (in some countries), candesartan, and olmesartan are orally administered as prodrugs, whereas the blocking action of some is mediated through active metabolites. On the basis of their chemical structures, ARBs use different binding pockets in the receptor, which are associated with differences in dissociation times and, in most cases, apparently insurmountable antagonism. The physicochemical differences between ARBs also manifest in different tissue penetration, including passage through the blood-brain barrier. Differences in binding mode and tissue penetration are also associated with differences in pharmacokinetic profile, particularly duration of action. Although generally highly specific for angiotensin II type 1 receptors, some ARBs, particularly telmisartan, are partial agonists at peroxisome proliferator-activated receptor-γ. All of these properties are comprehensively reviewed in this article. Although there is general consensus that a continuous receptor blockade over a 24-hour period is desirable, the clinical relevance of other pharmacological differences between individual ARBs remains to be assessed.

Evaluation of the relationship between sex, polymorphisms in CYP2C8 and CYP2C9, and pharmacokinetics of angiotensin receptor blockers

Angiotensin II receptor blockers (ARBs) are used to treat hypertension. Most ARBs are metabolized by CYP2C9. The aim of this study is to evaluate the possible association between sex, polymorphisms in the CYP2C8 and CYP2C9 genes, and the pharmacokinetics of losartan, valsartan, candesartan, and telmisartan. The study population comprised 246 healthy volunteers from seven single-dose clinical trials: 64 from two candesartan studies, 43 from a telmisartan study, 36 from a losartan study, and 103 from three valsartan studies. DNA was extracted from blood samples and single-nucleotide polymorphisms in the CYP2C8 (CYP2C8*2, CYP2C8*3, CYP2C8*4, CYP2C8*5) and CYP2C9 (CYP2C9*2, CYP2C9*3) genes were evaluated using real-time polymerase chain reaction. Sex only affected telmisartan pharmacokinetics, since women showed a higher telmisartan C(max) than men (590.5 ± 75.8 ng/ml versus 282.1 ± 30.8 ng/ml; P ≤ 0.01). CYP2C9 variants were associated only with losartan pharmacokinetics: the half-life of losartan was higher in CYP2C9*3 allele carriers (3.1 ± 0.4 hours) than in volunteers with the wild-type genotype (2.3 ± 0.1 hours) (P ≤ 0.05). CYP2C8 polymorphisms were associated only with valsartan pharmacokinetics, since *2 allele carriers showed faster clearance (1.07 ± 0.57 l/h·kg) than those with the wild-type genotype (0.48 ± 0.72 l/h·kg; P ≤ 0.01) and carriers of the *3 allele (0.35 ± 0.49 l/h·kg; P ≤ 0.001). These results suggest that genotypes for CYP2C9 and CYP2C8 are relevant to the pharmacokinetics of losartan and valsartan, respectively, but not the pharmacokinetics of candesartan or telmisartan.