Current trends in β-lactam based β-lactamases inhibitors

The introduction of antibiotics to treat bacterial infections either by killing or blocking their growth has been accompanied by the development of resistance mechanism that allows the bacteria to survive and proliferate. In particular the successive series of β-lactams have selected several generations of β-lactamases including ESBLs, AmpC β-lactamases, KPC carbapenamases in Enterobacteriaceae, the metallo β-lactamases VIMs and IMPs, and very recently the threatening NDM-1 that confers resistance to virtually any clinically used antibiotic. The increasing use of carbapenems due to the spread of resistance to other existing antibacterial agents has facilitated the spread of resistance, especially in Acinetobacter spp. due to OXA- and metallo-carbapenemases. The pharmaceutical industry, that abandoned this field at the end of the nineties, is now trying to recover by developing some novel β-lactam antibiotics and novel β-lactamase-inhibitors, the latter to be used in combination with new as well as seasoned β-lactam antibiotics. This article provides a survey of patent and scientific literature for β-lactamase inhibitors discovered in the period 2006-2010.     

The lead structure in cardiac glycosides is 5 β,14 β-androstane-3 β,14-diol

The purpose of the present study was to determine the lead structure in cardiac glycosides at the receptor level, i.e. the minimal structural requirement for specific and powerful receptor recognition. Accordingly 73 digitalis-like acting steroids were characterized as to the concentration effecting half-maximum inhibition of Na,K-ATPase from human cardiac muscle under standardized turnover conditions. Since the Ki value equaled the apparent KD value, K'D was expressed in terms of the apparent standard Gibbs energy change delta G degrees' of steroid interaction with Na,K-ATPase. This allowed the use of the extrathermodynamic approach as a rational way of correlating in a quantitative manner, the potency and structure of the various steroidal compounds. The results of the present analysis taken in conjunction with relevant findings reported in the literature, favour the following conclusions. Cassaine, canrenone, prednisolone- and progesterone-3,20-bisguanylhydrazone, and chlormadinol acetate are compounds that are not congeneric with digitalis. The butenolide ring of cardenolides or the analogous side-chains at C17 beta of 5 beta, 14 beta-androstane-3 beta, 14-diol are not pharmacophoric substructures, but merely amplifiers of the interaction energy of the steroid lead. All modifications of the structure, geometry and spatial relationship between the steroid nucleus and butenolide side chain of digitoxigenin all at once weaken the close fit interaction with the steroid and butenolide binding subsites of the enzyme in such way that the cardenolide derivatives interact with the receptor binding site area in whatever orientation that will minimize the Gibbs energy of the steroid-receptor-solvent system. The "butenolide carbonyl oxygen distance model" (Ahmed et al. 1983) for the interpretation of the differences in potency of the cardenolide derivatives describes the change in interaction energy through structural modification as a function of the entire molecule. 5 beta, 14 beta-androstane-3 beta, 14-diol, the steroid nucleus of cardiac glycosides of the digitalis type, is the minimum structure for specific receptor recognition and the key structure for inducing protein conformational change and thus Na,K-ATPase inhibition. It is also the structural requirement for maximum contributions of the butenolide substituent at C17 beta and the sugar substituent at C3 beta-OH to the overall interaction energy, i.e. this steroid nucleus is the lead structure.(ABSTRACT TRUNCATED AT 400 WORDS)     

Different steric characteristics of β1- and β2-adrenoceptors

Summary -Adrenoceptors of lung (75% ₂) and heart (95% ₁) of calf were labelled with ³H-(–)-propranolol. The stereoisomers of 10 ligands were used to inhibit the binding of ³H-(–)-propranolol to membrane particles. The affinity ratio of sereoisomers is consistently greater for ₁-adrenoceptors than for ₂-adrenoceptors, regardless of whether the ligands are agonists, partial agonists or antagonists. The ₁-adrenoceptor appears to possess stricter steric requirements than the ₂-adrenoceptor. This property may prove helpful in differentiating the -adrenoceptor subtypes during receptor solubilization and purification.     

Transdermal delivery of β-blockers

β-Adrenoceptor blocking drugs (β-blockers) are one of the most frequently used class of cardiovascular drugs that are mainly used in conventional dosage forms., which have their own limitations including hepatic first-pass metabolism, high incidence of adverse effects due to variable absorption profiles, higher frequency of administration and poor patient compliance. Essentially, attempts have been made to develop novel drug delivery systems for β-blockers, including transdermal delivery systems, to circumvent the drawbacks of conventional drug delivery. However, so far none of the β-blocker drugs have been marketed as transdermal delivery systems. Nevertheless, there have been noteworthy research endeavours worldwide at the laboratory level to investigate the skin permeation and to develop transdermal formulations of β-blockers including: propranolol, metoprolol, atenolol, timolol, levobunolol, bupranolol, bopindolol, mepindolol, sotalol, labetolol, pindolol, acebutolol and oxprenolol. Innovative research exploiting penetration-enhancing strategies, such as iontophoresis, electroporation, microneedles and sonophoresis, holds promise for the successful use of these drugs as consumer-friendly transdermal dosage forms in clinical practice. This paper presents an overview of the transdermal research on this important class of drugs.     

Ligand-directed signalling at β-adrenoceptors

β-Adrenoceptors (ARs) classically mediate responses to the endogenous ligands adrenaline and noradrenaline by coupling to Gsα and stimulating cAMP production; however, drugs designed as β-AR agonists or antagonists can activate alternative cell signalling pathways, with the potential to influence clinical efficacy. Furthermore, drugs acting at β-ARs have differential capacity for pathway activation, described as stimulus trafficking, biased agonism, functional selectivity or ligand-directed signalling. These terms refer to responses where drug A has higher efficacy than drug B for one signalling pathway, but a lower efficacy than drug B for a second pathway. The accepted explanation for such responses is that drugs A and B have the capacity to induce or stabilize distinct active conformations of the receptor that in turn display altered coupling efficiency to different effectors. This is consistent with biophysical studies showing that drugs can indeed promote distinct conformational states. Agonists acting at β-ARs display ligand-directed signalling, but many drugs acting as cAMP antagonists are also able to activate signalling pathways central to cell survival and proliferation or cell death. The observed complexity of drug activity at β-ARs, prototypical G protein-coupled receptors, necessitates rethinking of the approaches used for screening and characterization of novel therapeutic agents. Most studies of ligand-directed signalling employ recombinant cell systems with high receptor abundance. While such systems are valid for examining upstream signalling events, such as receptor conformational changes and G protein activation, they are less robust when comparing downstream signalling outputs as these are likely to be affected by complex pathway interactions.This article is part of a themed section on Molecular Pharmacology of GPCR. To view the editorial for this themed section visit http://dx.doi.org/10.1111/j.1476-5381.2010.00695.x     

The Development of β-Lactam Antibiotics in Response to the Evolution of β-Lactamases

beta-Lactam antibiotics, viz., penicillin, penicillin derivatives, cephalosporins, cephamycins, carbapenems, monobactams. and monocarbams, are the most widely used of all antimicrobial classes by virtue of their high efficacy and specificity and the availability of several derivatives. The expression of one or several beta-lactamases (beta-lactam antibiotic-inactivating enzymes) represents the most widespread and the most clinically relevant resistance mechanism to these antibiotics. The development of beta-lactam antibiotics has thus been a continuous battle of the design of new compounds to withstand inactivation by the ever-increasing diversity of beta-lactamases. This article traces antibiotic development in response to the evolution of beta-lactamases.     

A set of multiplex PCRs for genotypic detection of extended-spectrum β-lactamases, carbapenemases, plasmid-mediated AmpC β-lactamases and OXA β-lactamases

Worldwide, resistance of Gram-negative micro-organisms to third-generation cephalosporins and carbapenems owing to β-lactamases is an increasing problem. Although the CTX-M, TEM and SHV extended-spectrum β-lactamases (ESBLs) are most widely disseminated, other β-lactamase families have also recently emerged, such as plasmid-mediated AmpC β-lactamases and carbapenemases. Here we describe a new set of multiplex polymerase chain reactions (PCRs) with one amplification protocol enabling detection of 25 prevalent β-lactamase families, including ESBLs, carbapenemases, plasmid-mediated AmpC β-lactamases and OXA β-lactamases.     

Regional differences of β1- and β2-adrenoceptor-mediated functions in feline heart

The effects of (-)-adrenaline and (-)-noradrenaline were studied on isolated preparations of kitten heart. To define the contribution of beta 1-adrenoceptors (beta 1AR) and beta 2-adrenoceptors (beta 2AR) we used as tools the highly beta 1AR-selective antagonist CGP 20,712 A and non-linear analysis of antagonism. The beta 2AR-mediated responses to the catecholamines, disclosed by CGP 20,712 A, were verified by blockade with the beta 2AR-selective ICI 118,551. The relative density and contribution of beta 1AR and beta 2AR to (-)-adrenaline- and (-)-noradrenaline-induced adenylyl cyclase stimulation was also estimated in right ventricular membranes. 1. In the sinoatrial pacemaker (-)-adrenaline caused positive chronotropic effects through both beta 1AR and beta 2AR while (-)-noradrenaline does so predominantly through beta 1AR. During beta 1AR blockade (-)-adrenaline did cause the same maximum effects through beta 2AR as (-)-noradrenaline did through beta 1AR. 2. In left atria (-)-adrenaline caused positive inotropic effects predominantly through beta 1AR. CGP 20,712 A also uncovered a beta 2AR component at high (-)-adrenaline concentrations comprising one third of the maximum beta 1AR-mediated response. 3. Receptor binding assays revealed that 80% of right ventricular beta AR were beta 1AR and 20% beta 2AR. Consistent with this finding, around 80% of the adenylyl cyclase stimulation by both (-)-noradrenaline and (-)-adrenaline was mediated through beta 1AR, around 20% through beta 2AR. The positive inotropic effects of (-)-noradrenaline appeared to be nearly exclusively mediated through beta 1AR in right ventricular papillary muscles. 4. The positive inotropic effects of (-)-adrenaline were quite variable with regard to beta 1AR and beta 2AR in right ventricular papillary muscles. Although beta 1AR-mediated effects are predominant in many muscles with only a small contribution of beta 2AR, in some muscles beta 2AR mediated around 50% of the maximum effect elicited through beta 1AR. In 3 out of 17 muscles beta 2AR mediated the same maximum effect of (-)-adrenaline as beta 1AR. 5. On occasion, we found marked beta AR heterogeneity amongst two muscles from the same right ventricle. One muscle only exhibited beta 1AR-mediated effects of (-)-adrenaline whereas in the other muscle maximal effects could be elicited through beta 2AR.(ABSTRACT TRUNCATED AT 400 WORDS)     

Disposition of β-methyldigoxin in man

Summary The time course of radioactivity in plasma and the excretion in urine and faeces over 7 days were determined in 12 healthy subjects after single oral and intravenous doses of a solution of³H--methyldigoxin. 62.2±2.1 and 29.0±5.2 per cent of the dose were excreted in urine and faeces, respectively, within 7 days of intravenous administration, compared with 55.2±2.8 and 28.6±5.7 per cent after oral administration. This indicates almost complete absorption of the glycoside when given in solution. 12 hours after its administration a pseudo-distribution equilibrium was reached and the average half life of tritiated compounds was 1.3 days. By 48 – 96 hours after treatment the average half life was 2.8 days. O-demethylation was revealed as the main metabolic degradation step in man. The rate of Demethylation was higher after oral than i.v. administration. Thus, only 31% of the radioactivity excreted in the urine consisted of unchanged -methyldigoxin after oral administration compared to 51% after i.v. dosing. Only traces of bis- and monoglycosides were excreted in urine, but there were considerable amounts in faeces, where they accounted for more than 35% of the total excretion. Up to 40% of the radioactivity in plasma and urine consisted of polar conjugates during the first 12 hours after administration of -methyldigoxin. The mono- and bisglycosides were identified as the main products of conjugation. During the 7 days approximately 15% of the administered dose was metabolized by splitting off glycosidic bonds and conjugation to polar compounds.Supported by the Deutsche Forschungsgemeinschaft and by Boehringer Mannheim, Germany     

Adverse reactions to β-lactam antimicrobials

INTRODUCTION: Beta-lactam antibiotics are among the most clinically useful antimicrobials used in medicine. Unfortunately, adverse events related to their use remain poorly understood by many clinicians and, in particular, the misdiagnosis of β-lactam allergy and misunderstanding of crossreactivity among members of the β-lactam antibiotics may effectively eliminate a whole class of antimicrobials from use and require the use of broader spectrum agents with less well-established safety profiles. AREAS COVERED: This review describes the range, diagnosis and management of adverse events associated with β-lactam antimicrobials, particularly focusing on recognition, diagnosis and management of true allergy and risk of cross-sensitivity between β-lactam antibiotics. A literature review was undertaken using PubMed, focusing primarily on literature published in the past 10 years relating to β-lactam adverse events and allergy. EXPERT OPINION: Beta-lactams are generally safe drugs and serious adverse events are rare and allergy is overdiagnosed. Accurate diagnosis can usually be achieved through careful history and in some instances skin or in vitro testing is required. Even among individuals with true immediate-type allergy to penicillin, most cephalosporins are readily tolerated and desensitization is usually an option in cases where no alternate antimicrobials are available. Other allergic reactions (Type II, III and IV) are rare and avoidance of the culprit agent is generally recommended. Nonallergic or morbilliform rashes are generally not allergic in nature and should not prompt drug or class avoidance. Other adverse events are frequently dose-related and can be avoided by appropriate dosing and consideration of renal function.     

Tools to study β3-adrenoceptors

Beta(3)-adrenoceptors mediate some of the effects of catecholamines on tissues such as blood vessels or the urinary bladder and are putative targets for the treatment of diseases such as the overactive bladder syndrome. Progress in the understanding of the presence, function, and regulation of beta(3)-adrenoceptors has been hampered by a lack of highly specific tools. "Classical" beta(3)-adrenoceptor agonists such as BRL 37,344 [(R*, R*)-(+/-)-4[2-[(3-chlorophenyl)-2-hydroxyethyl) amino] propyl] phenoxyacetic acid] and CGP 12,177 [(+/-)-4-(3-t-butylamino-2-hydroxypropoxy)benzimidazol-2-one] are only partial agonists in many settings, have limited selectivity over other beta-adrenoceptor subtypes, and may additionally act on receptors other than beta-adrenoceptors. More efficacious and more selective agonists have been reported and, in some cases, are in clinical development but are not widely available for experimental studies. The widely used antagonist SR 59,230 [3-(2-ethylphenoxy)-1-[(1,S)-1,2,3,4-tetrahydronapth-1-ylamino]-2S-2-propanoloxalate] is not selective for beta(3)-adrenoceptors, at least in humans, and may actually be a partial agonist. Radioligands, which are suitable either for the selective labeling of beta(3)-adrenoceptors or for the nonselective labeling of all beta-adrenoceptor subtypes, are also missing. beta(3)- and beta(1)/beta(2) double knockout mice have been reported, but their usefulness for extrapolations in humans is questionable based upon major differences between humans and rodents with regard to the ligand recognition and expression profiles of beta(3)-adrenoceptors. While the common availability of more selective agonists and antagonists at the beta(3)-adrenoceptor is urgently awaited, the limitations of the currently available tools need to be considered in studies of beta(3)-adrenoceptor for the time being.     

Blockade of putative β4- and β1-adrenoceptors by carvedilol in ferret myocardium

The putative β₄-adrenoceptor mediates positive inotropic effects, action potential shortening and arrhythmias in ferret ventricle. Here we compared the affinity of carvedilol at the putative β₄-adrenoceptor and β₁-adrenoceptor, activated by (±)-CGP 12177 and (–)-isoprenaline, respectively. In paced right ventricular preparations, carvedilol (0.01–10 μmol/l) was a simple competitive antagonist of the positive inotropic effects of (±)-CGP 12177 (slope of Schild-plot = 1.02, pK _B = 6.8) and (–)-isoprenaline (slope of Schild-plot = 0.98, pK _B = 8.1). Carvedilol also blocked putative β₄- and β₁-adrenoceptors of left ventricle, left atrium and sino-atrial pacemaker. Carvedilol therefore interacts with the putative β₄-adrenoceptor according to the law of mass action and may provide a lead in the development of putative β₄-adrenoceptor-selective antagonists. Received: 25 January 1999 / Accepted: 2 March 1999     

Statine-derived tetrapeptide inhibitors of β-secretase

Alzheimer’s disease (AD) is characterised by the accumulation of amyloid β-peptide (Aβ) within senile plaques in the brain. β-secretase is one of the enzymes necessary for the production of amyloid β-peptide from the amyloid precursor protein (APP), the other being γ-secretase. β-Secretase was recently characterised as a novel aspartyl protease. Statine-derived tetrapeptide inhibitors of this enzyme, described in this patent, may have therapeutic applications in AD.     

Fragrance material review on β-methoxy-benzeneethanol

A toxicologic and dermatologic review of β-methoxy-benzeneethanol when used as a fragrance ingredient is presented. β-methoxy-benzeneethanol is a member of the fragrance structural group Aryl Alkyl Alcohols and is a primary alcohol. The AAAs are a structurally diverse class of fragrance ingredients that includes primary, secondary, and tertiary alkyl alcohols covalently bonded to an aryl (Ar) group, which may be either a substituted or unsubstituted benzene ring. The common structural element for the AAA fragrance ingredients is an alcohol group -C-(R1)(R2)OH and generically the AAA fragrances can be represented as an Ar-C-(R1)(R2)OH or Ar-Alkyl-C-(R1)(R2)OH group. This review contains a detailed summary of all available toxicology and dermatology papers that are related to this individual fragrance ingredient and is not intended as a stand-alone document. Available data for β-methoxy-benzeneethanol were evaluated then summarized and includes physical properties, acute toxicity, skin irritation, mucous membrane (eye) irritation, skin sensitization, phototoxicity, and photoallergy data. A safety assessment of the entire Aryl Alkyl Alcohols will be published simultaneously with this document; please refer to Belsito et al., 2012 for an overall assessment of the safe use of this material and all Aryl Alkyl Alcohols in fragrances.     

Antimicrobial β-peptides and α-peptoids

The field of drug discovery and development has seen tremendous activity over the past decade to better tackle the increasing occurrence of drug-resistant bacterial infections and to alleviate some of the pressure we put on the last-resort drugs on the market. One of the new and promising drug candidates is derived from naturally occurring antimicrobial peptides. However, despite promising results in early-stage clinical trials, these molecules have faced some difficulties securing FDA approval, which can be linked to their poor metabolic stability. Hence, mimetics of these antimicrobial peptides have been suggested as new templates for antibacterial compound design, because these mimetics are resistant against degradation by proteases. This review will discuss the structural features of two different types of mimetics, β-peptides and α-peptoids, in relation to their antibacterial activity and conclude on their potential as new candidates for bacterial intervention.     

Opioid activities of human β-casomorphins

Summary Opioid activities of human -casomorphin-4,-5,-7 and -8 and, for comparison, of the corresponding bovine -casomorphins were studied in the guinea-pig ileum preparation. Binding parameters, i.e. K _d -values and binding site concentrations, for the interaction of human and bovine -casomorphins with opioid receptors in rat brain homogenates were determined in inhibition experiments, using [³H]-(d-Ala², MePhe⁴, Gly-ol⁵)enkephalin, [³H]-(d-Ala², d-Leu⁵)enkephalin and [³H]ethylketazocin as -, - and -opioid receptor ligands. Analysis of binding data was performed using a non-linear curve fitting program. All -casomorphins examined displayed opioid activity. The affinity was highest for -receptors, less so for -receptors and lowest for -receptors. It is suggested that human -casomorphins might play a role as food hormones.     

Genotoxicity assessment of β-caryophyllene oxide

β-caryophyllene oxide is a biciclic sesquiterpene, occurring naturally in essential oils from various medicinal and edible plants and used as a flavouring agent. Due to its potential hazardous chemical structure, the European Food Safety Authority reported to be pending a safety assessment for this compound. Here, this flavouring agent was tested for its mutagenic effect in the Ames test and micronucleus assay. Furthermore, considering that the penetration of a substance through phospholipid bilayers is determinant for its activity, the ability of β-caryophyllene oxide to be absorbed into cells was evaluated by differential scanning calorimetry (DSC) using multilamellar vesicles of dimyristoylphosphatidylcholine as a biomembrane model. β-caryophyllene oxide was found to be devoid of mutagenic effect, both at gene level (frameshift or base-substitution mutations), and on chromosome (clastogenicity and aneuploidogenicity). Results of DSC analysis highlighted that the substance was strongly absorbed through the membrane bilayer. Present results show that β-caryophyllene oxide, although absorbed through cell membranes and in spite of its potentially reactive chemical structure, is devoid of genotoxic effects, inducing neither point mutations nor chromosomal damages. These negative genotoxic findings will be critical to the safety assessment of β-caryophyllene oxide as used as a flavouring/fragrance ingredient.