The benefits, limitations and opportunities of preclinical models for neonatal drug development

Increased research to improve preclinical models to inform the development of therapeutics for neonatal diseases is an area of great need. This article reviews five common neonatal diseases – bronchopulmonary dysplasia, retinopathy of prematurity, necrotizing enterocolitis, perinatal hypoxic–ischemic encephalopathy and neonatal sepsis – and the available in vivo, in vitro and in silico preclinical models for studying these diseases. Better understanding of the strengths and weaknesses of specialized neonatal disease models will help to improve their utility, may add to the understanding of the mode of action and efficacy of a therapeutic, and/or may improve the understanding of the disease pathology to aid in identification of new therapeutic targets. Although the diseases covered in this article are diverse and require specific approaches, several high-level, overarching key lessons can be learned by evaluating the strengths, weaknesses and gaps in the available models. This Review is intended to help guide current and future researchers toward successful development of therapeutics in these areas of high unmet medical need.

Summary: This article reviews and analyzes the available preclinical models for five common neonatal diseases to direct therapeutic development in these areas of high unmet medical need.

An Industry Survey With Focus on Cardiovascular Safety Pharmacology Study Design and Data Interpretation

Introduction:

The Safety Pharmacology Society (SPS) conducted a membership survey to examine industry practices related mainly to cardiovascular (CV) safety pharmacology (SP).

Methods:

Questions addressed nonclinical study design, data analysis methods, drug-induced effects, and conventional and novel CV assays.

Results:

The most frequent therapeutic area targeted by drugs developed by the companies/institutions that employ survey responders was oncology. The most frequently observed drug-mediated effects included an increased heart rate, increased arterial blood pressure, hERG (IKr) block, decreased arterial blood pressure, decreased heart rate, QTc prolongation, and changes in body temperature. Broadly implemented study practices included Latin square crossover study design with n = 4 for nonrodent CV studies, statistical analysis of data (eg, analysis of variance), use of arrhythmia detection software, and the inclusion of data from all study animals when integrating SP studies into toxicology studies. Most responders frequently used individual animal housing conditions. Responders commonly evaluated drug effects on multiple ion channels, but in silico modeling methods were used much less frequently. Most responders rarely measured the J-Tpeak interval in CV studies. Uncertainties relative to Standard for Exchange of Nonclinical Data applications for data derived from CV SP studies were common. Although available, the use of human induced pluripotent stem cell cardiomyocytes remains rare. The respiratory SP study was rarely involved with identifying drug-induced functional issues. Responders indicated that the study-derived no observed effect level was more frequently determined than the no observed adverse effect level in CV SP studies; however, a large proportion of survey responders used neither.

A multidimensional sight on cardiac failure: uncovered from structural to molecular level

Heart failure is one of the leading causes of death, with high mortality rate within 5 years after diagnosis. Treatment and prognosis options for heart failure primarily targeted on hemodynamic and neurohumoral components that drive progressive deterioration of the heart. However, given the multifactorial background that eventually leads to the "phenotype" named heart failure, better insight into the various components may lead to personalized treatment opportunities. Indeed, currently used criteria to diagnose and/or classify heart failure are possibly too focused on phenotypic improvement rather than the molecular driver of the disease and could therefore be further refined by integrating the leap of molecular and cellular knowledge. The ambiguity of the ejection fraction-based classification criteria became evident with development of advanced molecular techniques and the dawn of omics disciplines which introduced the idea that disease is caused by a myriad of cellular and molecular processes rather than a single event or pathway. The fact that different signaling pathways may underlie similar clinical manifestations calls for a more holistic study of heart failure. In this context, the systems biology approach can offer a better understanding of how different components of a system are altered during disease and how they interact with each other, potentially leading to improved diagnosis and classification of this condition. This review is aimed at addressing heart failure through a multilayer approach that covers individually some of the anatomical, morphological, functional, and tissue aspects, with focus on cellular and subcellular features as an alternative insight into new therapeutic opportunities.

Identification and Optimization of Pyrrolo[3,2-d]pyrimidine Toll-like Receptor 7 (TLR7) Selective Agonists for the Treatment of Hepatitis B

Pyrrolo[3,2-d]pyrimidines were identified as a new series of potent and selective TLR7 agonists. Compounds were optimized for their activity and selectivity over TLR8. This presents an advantage over recently described scaffolds that have residual TLR8 activity, which may be detrimental to the tolerability of the candidate drug. Oral administration of the lead compound 54 effectively induced a transient interferon stimulated gene (ISG) response in mice and cynomolgus monkeys. We aimed for a high first pass effect, limiting cytokine induction systemically, and demonstrated the potential for the immunotherapy of viral hepatitis.

Single Dose Caffeine Protects the Neonatal Mouse Brain against Hypoxia Ischemia

In this randomized blinded study, we investigated caffeine 5 mg/kg treatment given directly after neonatal brain hypoxia ischemia. Brain morphology, behavior and key brain infiltrating immune populations were examined. Caffeine treatment significantly improves outcome when compared to phosphate buffered saline. Flow cytometric analysis of immune responses revealed no persistent immunological alterations. Given its safety caffeine emerges as a candidate for neuroprotective intervention after neonatal brain injury.

HCN channelopathy and cardiac electrophysiologic dysfunction in genetic and acquired rat epilepsy models

OBJECTIVE

Evidence from animal and human studies indicates that epilepsy can affect cardiac function, although the molecular basis of this remains poorly understood. Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels generate pacemaker activity and modulate cellular excitability in the brain and heart, with altered expression and function associated with epilepsy and cardiomyopathies. Whether HCN expression is altered in the heart in association with epilepsy has not been investigated previously. We studied cardiac electrophysiologic properties and HCN channel subunit expression in rat models of genetic generalized epilepsy (Genetic Absence Epilepsy Rats from Strasbourg, GAERS) and acquired temporal lobe epilepsy (post-status epilepticus SE). We hypothesized that the development of epilepsy is associated with altered cardiac electrophysiologic function and altered cardiac HCN channel expression.

METHODS

Electrocardiography studies were recorded in vivo in rats and in vitro in isolated hearts. Cardiac HCN channel messenger RNA (mRNA) and protein expression were measured using quantitative PCR and Western blotting respectively.

RESULTS

Cardiac electrophysiology was significantly altered in adult GAERS, with slower heart rate, shorter QRS duration, longer QTc interval, and greater standard deviation of RR intervals compared to control rats. In the post-SE model, we observed similar interictal changes in several of these parameters, and we also observed consistent and striking bradycardia associated with the onset of ictal activity. Molecular analysis demonstrated significant reductions in cardiac HCN2 mRNA and protein expression in both models, providing a molecular correlate of these electrophysiologic abnormalities.

SIGNIFICANCE

These results demonstrate that ion channelopathies and cardiac dysfunction can develop as a secondary consequence of chronic epilepsy, which may have relevance for the pathophysiology of cardiac dysfunction in patients with epilepsy.

Abstract P300: A Novel Highly Selective Adenosine A 1 Receptor Agonist (VCP28) Reduces Ischemia/Reperfusion Injury at Concentrations that Do Not Affect Heart Rate

Whilst adenosine A1 receptor agonists have repeatedly been shown to protect the ischaemic myocardium, the clinical use of these agents is limited by strong cardiodepressant effects. The cardioprotective effects of a novel adenosine A1 receptor agonist N6-(2,2,5,5-tetramethylpyrrolidin-1-yloxyl-3-ylmethyl) adenosine (VCP28) were compared with the selective adenosine A1receptor agonist N6-cyclopentyladenosine (CPA) in a H9c2(2–1) cardiac cell line-simulated ischemia (SI) model (12 hours) and a global ischemia (30 minutes) and reperfusion (60 minutes) model in isolated rat heart model. H9c2(2–1) cells were treated with CPA and VCP28 at the start of ischemia for entire ischemic duration, whereas isolated rat hearts were treated at the onset of reperfusion for 15 minutes. In a H9c2(2–1) cell SI model, CPA and VCP28 (100 nM) significantly (P , 0.05, n = 5–6) reduced the proportion of nonviable cells (30.88% 6 2.49% and 16.17% 6 3.77% of SI group, respectively) and lactate dehydrogenase efflux. In isolated rat hearts, CPA and VCP28 significantly (n = 6–8, P , 0.05) improved postischemic contractility (dP/dtmax, 81.69% 6 10.96%, 91.07% 6 19.87% of baseline, respectively), left ventricular developed pressure, and end diastolic pressure and reduced infarct size. The adenosine A1 receptor antagonist DPCPX abolished the cardioprotective effects of CPA and VCP28 in both models. At the concentrations used in the ischaemia models, VCP28 had no effect on heart rate, unlike CPA. In conclusion, the adenosine A1 receptor agonist VCP28 has cardioprotective equal effects to the prototype A1 agonist CPA at concentrations that have no effect on heart rate.

Synthesis and evaluation of new N6-substituted adenosine-5'-N-methylcarboxamides as A3 adenosine receptor agonists

A number of N(6)-substituted adenosine-5'-N-methylcarboxamides were synthesised and their pharmacology, in terms of their receptor affinity, selectivity and cardioprotective effects, were explored. The first series of compounds, 4a-4f and 5a-5f, showed modest receptor affinity for the A(3)AR with K(i) values in the low to mid muM range. However, the incorporation of a 4-(2-aminoethyl)-2,6-di-tert-butylphenol group in the N(6)-position (in compounds 4g and 5g) significantly improved the affinity with K(i) values of 30 and 9 nM, respectively. Improvements in affinity, as well as selectivity were seen when a functionalized linker was introduced. The N(6)-phenyl series, compounds 7a-7d, demonstrated low to mid nanomolar receptor affinities (K(i)=2.3-45.0 nM), with 7b displaying 109-fold selectivity for the A(3)AR (vs A(1)). The N(6)-benzyl series 9a-9c also proved to be potent and selective A(3)AR agonists and the longer chain length linker 13 was tolerated at the A(3)AR without abrogation of affinity or selectivity. Cardioprotection was demonstrated by a simulated ischaemia cell culture assay, whereby 7b, 7c, 9a, 9b and 9c all showed cardioprotective effects at 100 nM comparable or better than the benchmark A(3)AR agonist IB-MECA, but which were indistinguishable by statistical analysis. For example, compound 9c reduced cell death by 68.0+/-3.6%.

Dual acting antioxidant A1 adenosine receptor agonists

Herein we report the synthesis and biological evaluation of some potent and selective A(1) adenosine receptor agonists, which incorporate a functionalised linker attached to an antioxidant moiety. N(6)-(2,2,5,5-Tetramethylpyrrolidin-1-yloxyl-3-ylmethyl)adenosine (VCP28, 2e) proved to be an agonist with high affinity (K(i)=50nM) and good selectivity (A(3)/A(1) > or = 400) for the A(1) adenosine receptor. N(6)-[4-[2-[1,1,3,3-Tetramethylisoindolin-2-yloxyl-5-amido]ethyl]phenyl]adenosine (VCP102, 5a) has higher binding affinity (K(i)=7 nM), but lower selectivity (A(3)/A(1)= approximately 3). All compounds bind weakly (K(i)>1 microM) to A(2A) and A(2B) receptors. The combination of A(1) agonist activity and antioxidant activity has the potential to produce cardioprotective effects.