Synthesis and biological evaluation of some novel N-aryl-1,4-dihydropyridines as potential antitubercular agents

1,4-Dihydropyridines are the emerging class of antitubercular agent. Recently, studies have revealed that 1,4-dihydropyridine-3,5-dicarbamoyl derivatives with lipophilic groups have demonstrated excellent antitubercular activity. We have synthesized new N-aryl-1,4-dihydropyridines bearing carbethoxy and acetyl group at C-3 and C-5 of the DHP ring. In addition, 1H-pyrazole ring is substituted at C-4 position. The lowest minimum inhibitory concentration value, 0.02 μg/mL, was found for diethyl 1-(2-chlorophenyl)-1,4-dihydro-2,6-dimethyl-4-(1,3-diphenyl-1H-pyrazol-4-yl)pyridine-3,5-dicarboxylate 4e making it more potent than first line antitubercular drug isoniazid. In addition, this compound exhibited relatively low cytotoxicity.     

Synthesis and biological activity of the calcium modulator (R) and (S)-3-methyl 5-pentyl 2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate

An efficient total synthesis of (R) and (S)-3-methyl 5-pentyl 2,6-dimethyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate in high optical purities is reported. The useful step is the resolution of racemic 2, 6-dimethyl-5-methoxycarbonyl-4-(3-nitrophenyl)-1,4-dihydropyridine-3-carboxylic acid by using commercially available Cinchona alkaloids cinchonidine and quinidine as the resolving agents. Under the optimum conditions, the optical purities for R- and S-enantiomers are extremely high (ee >99.5%). The further dihydropyridine receptor binding activity assay shows that the S-enantiomer is more potent than R-enantiomer both in rat cardiac (approximately 19 times) and cerebral cortex membrane (12 times).     

Sensitive and specific liquid chromatographic–tandem mass spectrometric assay for barnidipine in human plasma

A sensitive and specific LC–MS–MS assay has been developed and validated for barnidipine (1-benzyl-3-pyrrolidinyl)methyl-2,6-dimethyl-4(m-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate). The assay involves a simple and rapid solid-phase extraction procedure. Sample analysis was on a Spherisorb S3ODS2 100 mm×2 mm I.D. column, with a Finnigan TSQ 7000 mass spectrometer, using an electrospray interface and selective reaction monitoring (SRM). The intra- and inter-day precision and accuracy, determined as the coefficient of variation and relative error, respectively, were 11.8% or less. The limit of quantitation was 0.03 ng/ml, and the calibration was linear between 0.03 and 3.0 ng/ml. The method has been used successfully for the measurement of over two thousand human plasma samples from pharmacokinetic clinical trials.     

Microwave-assisted synthesis of antimicrobial dihydropyridines and tetrahydropyrimidin-2-ones: novel compounds against aspergillosis

Ten 4-aryl-1,4-dihydropyridine and three 4-aryl-1,2,3,4-tetrahydropyrimidin-2-one derivatives have been synthesized and examined for their activity against pathogenic strains of Aspergillus fumigatus and Candida albicans. Although none of the three compounds belonging to pyrimidin-2-one series showed any activity against two pathogens, two of the compounds of the dihydropyridine series, that is, diethyl 4-(4-methoxyphenyl)-2,6-dimethyl-1,4-dihydropyridin-3,5-dicarboxylate and dimethyl 4-(4-methoxyphenyl)-2,6-dimethyl-1,4-dihydropyridin-3,5-dicarboxylate, exhibited significant activity against A. fumigatus in disc diffusion, microbroth dilution and percent spore germination inhibition assays. The most active diethyl dihydropyridine derivative exhibited a MIC value of 2.92 microg/disc in disc diffusion and 15.62 microg/ml in microbroth dilution assays. The MIC(90) value of the most active compound by percent germination inhibition assay was found to be 15.62 microg/ml. The diethyl dicarboxylate derivative of dihydropyridine also exhibited appreciable activity against C. albicans. The in vitro toxicity of the most active diethyl dihydropyridine derivative was evaluated using haemolytic assay, in which the compound was found to be non-toxic to human erythrocytes even at a concentration of 625 microg/ml. The standard drug amphotericin B exhibited 100% lysis of erythrocytes at a concentration almost 16 times less than the safer concentration of the most active dihydropyridine derivative.     

Nanoparticulate drug delivery systems for cancer chemotherapy

Nanoparticles (NPs) are, in general, colloidal particles, less than 1000 nm, that can be used for better drug delivery and prepared either by encapsulating the drug within a vesicle and or by dispersing the drug molecules within a matrix. Nanoparticulate drug delivery systems have been extensively studied in recent years for spatial and temporal delivery, especially in tumour and brain targeting. NPs have great promise for better drug delivery as found in both pharmaceutical and clinical research. As a drug carrier, NPs have significant advantages like better bioavailability, systemic stability, high drug loading, long blood circulation time and selective distribution in the organs/tissues with longer half life. The selective targeting of NPs can be achieved by the enhanced permeability and retention effect (EPR-effect), attaching specific ligands, or by making selective distribution due to change of the physiological conditions of specific systems like nature, pH, temperature, etc. It has been observed that drug-loaded NPs can have selective distribution to organs/tissues using different types of and proportions of polymers. The current aim of researchers is to prepare NPs that are long-lived with and that demonstrate the appropriate selective distribution for better therapy and thus improved clinical outcomes. Nanoparticulate drug delivery systems have the potential to deliver a drug to the target site with specificity and to maintain the desired concentration at the site for the intended time without untoward effects. In this review article, the methods for the preparation of NPs, their characterization, biodistribution, and pharmacokinetic characteristics are discussed.     

Nanoparticulate drug delivery systems for cancer chemotherapy

Abstract

Nanoparticles (NPs) are, in general, colloidal particles, less than 1000 nm, that can be used for better drug delivery and prepared either by encapsulating the drug within a vesicle and or by dispersing the drug molecules within a matrix. Nanoparticulate drug delivery systems have been extensively studied in recent years for spatial and temporal delivery, especially in tumour and brain targeting. NPs have great promise for better drug delivery as found in both pharmaceutical and clinical research. As a drug carrier, NPs have significant advantages like better bioavailability, systemic stability, high drug loading, long blood circulation time and selective distribution in the organs/tissues with longer half life. The selective targeting of NPs can be achieved by the enhanced permeability and retention effect (EPR-effect), attaching specific ligands, or by making selective distribution due to change of the physiological conditions of specific systems like nature, pH, temperature, etc. It has been observed that drug-loaded NPs can have selective distribution to organs/tissues using different types of and proportions of polymers. The current aim of researchers is to prepare NPs that are long-lived with and that demonstrate the appropriate selective distribution for better therapy and thus improved clinical outcomes. Nanoparticulate drug delivery systems have the potential to deliver a drug to the target site with specificity and to maintain the desired concentration at the site for the intended time without untoward effects. In this review article, the methods for the preparation of NPs, their characterization, biodistribution, and pharmacokinetic characteristics are discussed.     

Photoaffinity labelling of a 33-35,000 dalton protein in cardiac, skeletal and smooth muscle membranes using a new 125I-labelled 1,4-dihydropyridine calcium channel antagonist

The binding sites for Ca2+ channel antagonists were probed using Bay P 8857 [2-iodoethyl isopropyl 1,4-dihydropyridine-2,6-dimethyl-4-(3-nitrophenyl)-pyridine-3,5-dicarbox ylate] that has been radiolabelled with 125I. This drug was shown to bind with high affinity to cardiac, smooth, and skeletal muscle membranes, with a KD approximately equal to 0.3 nM. A protein of molecular weight 33-35,000 daltons was specifically and irreversibly radiolabelled after irradiation of cardiac, skeletal and aortic smooth muscle membranes, incubated with the [125I]-Bay P 8857. The peptide labelled by 1,4-dihydropyridine binding therefore appears similar in size for cardiac, skeletal, and smooth muscle. This data suggests that of the three peptide subunits which reportedly comprise the skeletal and cardiac muscle 1,4-dihydropyridine receptor complex, the 33-35,000 dalton peptide contains the dihydropyridine binding site.     

脂质体药物传递系统

脂质体已经发展成为一种成熟的传递系统,从脂质体作为载体概念的提出发展到生产制药水平历经了很长的发展阶段,如今脂质体制剂已有效地应用于重要疾病的治疗领域。简述了有关药物传递脂质体的目标和系统,透视了那些正在研究的领域,以及有哪些机会可合理改进脂质体的药物治疗。     

Polymer based cardiovascular gene therapy

Therapeutic angiogenesis is a new potential treatment in cardiovascular disease. It is performed by the delivery of the angiogenic agents (protein, gene). Most important consideration for gene therapy is the construction of an effective therapeutic gene. Currently, VEGF is the most effective therapeutic gene for the neovascularization. We constructed the hypoxia-regulated VEGF plasmid using the Epo enhancer and RTP801 promoter. The efficiency of the pEpo-SV-VEGF and pRTP801-VEGF were evaluated by various methodsin vitro andin vivo. The results suggested that the hypoxia-inducible VEGF gene therapy system is effective and safe, which may be useful for the gene therapy of ischemic heart disease. Development of a safe and efficient gene carrier is another main requirement for successful gene therapy. Although viralbased gene delivery is currently the most effective way to transfer genes to cells, nonviral vectors are increasingly being considered forin vivo gene delivery. The advantages of nonviral gene therapy are lack of specific immunogenecity, simplicity of use, and ease of large-scale production. In addition, the simple conjugation of a targeting moiety to nonviral gene carrier can facilitate tissue-targeting gene delivery. We have developed two new gene carrier systems, TerplexDNA and WSLP (water soluble lipopolymer). These two are efficient carrier to ischemic myocardium and has low toxicity and high transfection efficiency. So it may allow for application ofin vivo gene therapy in the treatment of heart disease.     

Synthesis and evaluation of novel triazoles and mannich bases functionalized 1,4-dihydropyridine as angiotensin converting enzyme (ACE) inhibitors

A series of novel diethyl 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate embedded triazole and mannich bases were synthesized, and evaluated for their angiotensin converting enzyme (ACE) inhibitory activity. Screening of above synthesized compounds for ACE inhibition showed that triazoles functionalized compounds have better ACE inhibitory activity compared to that of mannich bases analogues. Among all triazoles we found 6h, 6i and 6j to have good ACE inhibition activity with IC₅₀ values 0.713 μM, 0.409 μM and 0.653 μM, respectively. Among mannich bases series compounds, only 7c resulted as most active ACE inhibitor with IC₅₀ value of 0.928 μM.     

Drug delivery and nanoparticles:applications and hazards

The use of nanotechnology in medicine and more specifically drug delivery is set to spread rapidly. Currently many substances are under investigation for drug delivery and more specifically for cancer therapy. Interestingly pharmaceutical sciences are using nanoparticles to reduce toxicity and side effects of drugs and up to recently did not realize that carrier systems themselves may impose risks to the patient. The kind of hazards that are introduced by using nanoparticles for drug delivery are beyond that posed by conventional hazards imposed by chemicals in classical delivery matrices. For nanoparticles the knowledge on particle toxicity as obtained in inhalation toxicity shows the way how to investigate the potential hazards of nanoparticles. The toxicology of particulate matter differs from toxicology of substances as the composing chemical(s) may or may not be soluble in biological matrices, thus influencing greatly the potential exposure of various internal organs. This may vary from a rather high local exposure in the lungs and a low or neglectable exposure for other organ systems after inhalation. However, absorbed species may also influence the potential toxicity of the inhaled particles. For nanoparticles the situation is different as their size opens the potential for crossing the various biological barriers within the body. From a positive viewpoint, especially the potential to cross the blood brain barrier may open new ways for drug delivery into the brain. In addition, the nanosize also allows for access into the cell and various cellular compartments including the nucleus. A multitude of substances are currently under investigation for the preparation of nanoparticles for drug delivery, varying from biological substances like albumin, gelatine and phospholipids for liposomes, and more substances of a chemical nature like various polymers and solid metal containing nanoparticles. It is obvious that the potential interaction with tissues and cells, and the potential toxicity, greatly depends on the actual composition of the nanoparticle formulation. This paper provides an overview on some of the currently used systems for drug delivery. Besides the potential beneficial use also attention is drawn to the questions how we should proceed with the safety evaluation of the nanoparticle formulations for drug delivery. For such testing the lessons learned from particle toxicity as applied in inhalation toxicology may be of use. Although for pharmaceutical use the current requirements seem to be adequate to detect most of the adverse effects of nanoparticle formulations, it can not be expected that all aspects of nanoparticle toxicology will be detected. So, probably additional more specific testing would be needed.     

Asymmetric synthesis and biological evaluations of (+)- and (-)-6-dimethoxymethyl-1,4-dihydropyridine-3-carboxylic acid derivatives blocking N-type calcium channels

An efficient asymmetric synthesis of 1,4-dihydropyridine derivatives is described. The key step is the stereoselective Michael addition using t-butyl ester of l-valine as a chiral auxiliary to achieve good ee (>95% for all the tested experiments) and moderate yield. With this method, (+)-4-(3-chlorophenyl)-6-dimethoxymethyl-2-methyl-1,4-dihydropyridine-3,5-dicarboxylic acid cinnamyl ester was obtained and was characterized as a promising N-type calcium channel blocker with improved selectivity over L-type compared to its (−)- and racemic isomers.     

Regulation of hormone biosynthesis in guinea pig adrenal glands by potassium ions as affected by dihydropyridines. 1. Analysis of changes in steroidogenesis evoked by dihydropyridines]

Influence of Ca2+ channel modulators BAY K 8644, nitrendipine and newly synthesized derivative of 1,4-dihydropyridine: 4-(3', 4'-dimethoxyphenyl)-2,6-dimethyl-3,5- diethoxy-carbonyl-1,4-dihydropyridine-(DHP-51) on aldosterone production by adrenocortical slices depends on K+ content in the incubation medium. The modulators only slightly influence the hormone output at low K+ level in the medium. Intensive synthesis of aldosterone at high level of potassium in the medium was prevented in the presence of DHP-51 and low concentration of BAY K 8644. DHP-51 inhibited [3H]-cholesterol incorporation into all main corticosteroids in the high-potassium medium.     

A new degradable hydroxamate linkage for pH-controlled drug delivery

A new drug delivery system based on a hydrodegradable hydroxamate linkage was evaluated. The carrier support system was poly(N-hydroxyacrylamide), which was synthesized via free radical polymerization of acryloyl chloride in 1,4-dioxane, initiated with 2,2'-azobisisobutyronitrile. The poly(acryloyl chloride) was modified in two steps. First, N-hydroxysuccinimide was added to give the imide ester of poly(acryloyl). In the second step, the imide ester of poly(acryloyl) was reacted with either hydroxylamine or N-methylhydroxylamine to give the corresponding hydroxamic acid. The hydroxamide functionality was then used to link the model drug ketoprofen. All products and intermediates were characterized by elemental analysis and FTIR and 1H NMR spectra. In vitro drug release was performed under specific conditions to elucidate the influence of the pH, polymer microstructure, and temperature on the hydrolysis rate of the amido-ester bond that linked the drug to the macromolecule. The drug release rate from N-methylhydroxamic acid polymers was faster than from hydroxamic acid polymers. All polymers showed higher rates of drug release at higher pH values (9.0 > 7.4 > 2.0) and at higher temperatures (37 degrees C > 20 degrees C).     

Balance of purines may determine life or death of retinal ganglion cells as A3 adenosine receptors prevent loss following P2X7 receptor stimulation

The purines ATP and adenosine can act as a coordinated team of transmitters. As extracellular adenosine is frequently derived from the enzymatic dephosphorylation of released ATP, the distinct actions of the two purines can be synchronized. In retinal ganglion cells (RGCs), stimulation of the P2X7 receptor for ATP leads to increased intracellular Ca2+ and death. Here we define the contrasting effects of adenosine and identify protective actions mediated by the A3 receptor. Adenosine attenuated the rise in Ca2+ produced by the P2X7 agonist 3'-O-(4-benzoylbenzoyl)ATP (BzATP). Adenosine was also neuroprotective, increasing the survival of ganglion cells exposed to BzATP. The A3 adenosine receptor agonist 2-chloro-N6-(3-iodobenzyl)-adenosine-5'-N-methyluronimide (Cl-IB-MECA) mimicked the inhibition of the Ca2+ rise, whereas the A3 antagonist 3-Ethyl-5-benzyl-2-methyl-4-phenylethynyl-6-phenyl-1,4-(+/-)-dihydropyridine-3,5-dicarboxylate (MRS-1191) reduced the protective effects of adenosine. Both Cl-IB-MECA and a second A3 receptor agonist IB-MECA reduced the cell loss triggered by BzATP. The actions of BzATP were mimicked by ATPgammaS, but not by ATP. In summary, adenosine can stop the rise in Ca2+ and cell death resulting from stimulation of the P2X7 receptor on RGCs, with the A3 adenosine receptor contributing to this protection. Hydrolysis of ATP into adenosine and perhaps inosine shifts the balance of purinergic action from that of death to the preservation of life.     

Peptide conjugates of therapeutically used antitubercular isoniazid—design,synthesis and antimycobacterial effect

Tuberculosis (TB) is a bacterial infectious disease caused by Mycobacterium tuberculosis, a slow‐growing, powerful human pathogen which can survive in the host macrophages. In the chemotherapy of such intracellular pathogens it is necessary to achieve relatively high level of the drug in blood to attain therapeutically effective concentration in infected cells, which presumably has several serious side effects on healthy tissues. The elimination of M. tuberculosis from infected phagocytes could be more efficient with target cell‐directed delivery of antituberculars. A particularly promising approach is to conjugate a drug moiety to a peptide based carrier. The conjugates are chemically constructed to target release by hydrolysis (enzymatic and/or chemical) to liberate the active compound. Here we report the synthesis, characterisation and antimycobacterial evaluation of isoniazid (INH) peptide conjugates. As carrier moiety T‐cell epitope of immundominant 16‐kDa protein of M. tuberculosis and tuftsin‐derived peptides were used. To conjugate INH two synthetic methods were developed, where INH was coupled directly to the peptides or through a heterobifunctional reagent. We found that all of the INH conjugates were effective against M. tuberculosis and the minimal inhibitory concentration (MIC) values were comparable to the free INH moiety. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd.     

外泌体靶向递药在肿瘤治疗中的进展

外泌体是由细胞分泌、粒径为30～ 150 nm的纳米囊泡.外泌体具有优越的生物相容性、良好的载药功能以及便于修饰的膜表面,是一种具有潜力的药物递送载体.在肿瘤治疗研究中,可利用具有靶向识别功能的外泌体来降低脱靶效应,减少不良反应,达到增强治疗效果的目的 .归纳了用不同修饰方法增强外泌体靶向性的研究进展,总结了近五年来利...     

Fluorenone 1,4-dihydropyridine derivatives with cardiodepressant activity: Enantiomeric separation by chiral HPLC and conformational aspects

The direct HPLC enantiomeric separation of five fluorenone-1,4-dihydropyridine-3,5-dicarboxylic diesters has been achieved using a Chiralpak AD stationary phase obtaining simultaneously good enantioselectivities, resolution factors, and elution times. CD spectra of the individual enantiomers for two compounds were measured. Thermodynamic parameters associated with the adsorption equilibria of the enantiomers with the chiral stationary phase were obtained from HPLC runs at various temperatures. The conformational preferences of the synperiplanar fluorenone group and of the cis/cis ester groups were obtained by ¹H NMR spectra, including NOE experiments. © 1996 Wiley-Liss, Inc.     

Targeting of herbal bioactives through folate receptors: a novel concept to enhance intracellular drug delivery in cancer therapy

Targeted drug delivery through folate receptor (FR) has emerged as a most biocompatible, target oriented, and non-immunogenic cargoes for the delivery of anticancer drugs. FRs are highly overexpressed in many tumor cells (like ovarian, lung, breast, kidney, brain, endometrial, and colon cancer), and targeting them through conjugates bearing specific ligand with encapsulated nanodrug moiety is undoubtedly, a promising approach toward tumor targeting. Folate, being an endogenous ligand, can be exploited well to affect various cellular events occurring during the progress of tumor, in a more natural and definite way. Thus, the aim of the review lies in summarizing the advancements taken place in the drug delivery system of different therapeutics through FRs and to refine its role as an endogenous ligand, in targeting of synthetic as well as natural bioactives. The review also provides an update on the patents received on the folate-based drug delivery system.     

Polyketal microparticles: a new delivery vehicle for superoxide dismutase

There is currently great interest in developing microparticles that can enhance the delivery of proteins to macrophages. In this communication, we present a new acid-sensitive polymer for drug delivery, poly(cyclohexane-1,4-diyl acetone dimethylene ketal) (PCADK). PCADK is designed to hydrolyze, after phagocytosis by macrophages, in the acidic environment of the phagosome and enhance the intracellular delivery of phagocytosed therapeutics. Other key attributes of PCADK for drug delivery are its well-characterized degradation products and straightforward synthesis. PCADK hydrolyzes into 1,4-cyclohexanedimethanol, a compound used in food packaging, and acetone, a compound on the FDA GRAS list. PCADK was synthesized using the acetal exchange reaction between 1,4-cyclohexanedimethanol and 2,2-dimethoxypropane, and could be obtained on a multigram scale in one step. The hydrolysis kinetics of the ketal linkages in PCADK were measured by 1H NMR and were determined to be pH-sensitive, having a half-life of 24.1 days at pH 4.5 and over 4 years at pH 7.4. The therapeutic enzyme superoxide dismutase (SOD), which scavenges reactive oxygen species, was encapsulated into PCADK-based microparticles using a double emulsion procedure. Cell culture experiments demonstrated that PCADK-based microparticles dramatically improved the ability of SOD to scavenge reactive oxygen species produced by macrophages. We anticipate numerous applications of PCADK in drug delivery, based on its acid sensitivity, well-characterized degradation products, and straightforward synthesis.