Refocussing therapeutic strategies for cardiac arrhythmias: defining viable molecular targets to restore cardiac ion flux

Pleiotropic mechanisms of action of perhexiline in heart failure

INTRODUCTION

The re-purposing of the anti-anginal drug perhexiline (PHX) has resulted in symptomatic improvements in heart failure (HF) patients. The inhibition of carnitine palmitoyltransferase-1 (CPT-1) has been proposed as the primary mechanism underlying the therapeutic benefit of PHX. This hypothesis is contentious.

AREAS COVERED

We reviewed the primary literature and patent landscape of PHX from its initial development in the 1960s through to its emergence as a drug beneficial for HF. We focused on its physico-chemistry, molecular targets, tissue accumulation and clinical dosing.

EXPERT OPINION

Dogma that the beneficial effects of PHX are due primarily to potent myocardial CPT-1 inhibition is not supported by the literature and all available evidence point to it being extremely unlikely that the major effects of PHX occur via this mechanism. In vivo PHX is much more likely to be an inhibitor of surface membrane ion channels and also to have effects on other components of cellular metabolism and reactive oxygen species (ROS) generation across the cardiovascular system. However, the possibility that minor effects of PHX on CPT-1 underpin disproportionately large effects on myocardial function cannot be entirely excluded, especially given the massive accumulation of the drug in heart tissue.

AP-1 Transcription Factor Serves as a Molecular Switch between Chlamydia pneumoniae Replication and Persistence

Chlamydia pneumoniae is a Gram-negative bacterium that causes acute or chronic respiratory infections. As obligate intracellular pathogens, chlamydiae efficiently manipulate host cell processes to ensure their intracellular development. Here we focused on the interaction of chlamydiae with the host cell transcription factor activator protein 1 (AP-1) and its consequence on chlamydial development. During Chlamydia pneumoniae infection, the expression and activity of AP-1 family proteins c-Jun, c-Fos, and ATF-2 were regulated in a time- and dose-dependent manner. We observed that the c-Jun protein and its phosphorylation level significantly increased during C. pneumoniae development. Small interfering RNA knockdown of the c-Jun protein in HEp-2 cells reduced the chlamydial load, resulting in smaller inclusions and significantly lower chlamydial recovery. Furthermore, inhibition of the c-Jun-containing AP-1 complexes using tanshinone IIA changed the replicative infection phenotype into a persistent one. Tanshinone IIA-dependent persistence was characterized by smaller, aberrant inclusions, a strong decrease in the chlamydial load, and significantly reduced chlamydial recovery, as well as by the reversibility of the reduced recovery after the removal of tanshinone IIA. Interestingly, not only was tanshinone IIA treatment accompanied by a significant decrease of ATP levels, but fluorescence live cell imaging analysis by two-photon microscopy revealed that tanshinone IIA treatment also resulted in a decreased fluorescence lifetime of protein-bound NAD(P)H inside the chlamydial inclusion, indicating that chlamydial reticulate bodies have decreased metabolic activity. In all, these data demonstrate that the AP-1 transcription factor is involved in C. pneumoniae development, with tanshinone IIA treatment resulting in persistence.

A new system for profiling drug-induced calcium signal perturbation in human embryonic stem cell-derived cardiomyocytes

The emergence of human stem cell–derived cardiomyocyte (hSCCM)–based assays in the cardiovascular (CV) drug discovery sphere requires the development of improved systems for interrogating the rich information that these cell models have the potential to yield. We developed a new analytical framework termed SALVO (synchronization, amplitude, length, and variability of oscillation) to profile the amplitude and temporal patterning of intra- and intercellular calcium signals in hSCCM. SALVO quantified drug-induced perturbations in the calcium signaling “fingerprint” in spontaneously contractile hSCCM. Multiparametric SALVO outputs were integrated into a single index of in vitro cytotoxicity that confirmed the rank order of perturbation as astemizole > thioridazine > cisapride > flecainide > valdecoxib > sotalol > nadolol ≈ control. This rank order of drug-induced Ca²⁺ signal disruption is in close agreement with the known arrhythmogenic liabilities of these compounds in humans. Validation of the system using a second set of compounds and hierarchical cluster analysis demonstrated the utility of SALVO to discriminate drugs based on their mechanisms of action. We discuss the utility of this new mechanistically agnostic system for the evaluation of in vitro drug cytotoxicity in hSCCM syncytia and the potential placement of SALVO in the early stage drug screening framework.

Multifunctional pentacyclic triterpenoids as adjuvants in cancer chemotherapy: a review

The protective adjuvants in chemotherapy.

Adenosine A1 modulators: a patent update (2008 to present)

INTRODUCTION

In 2008, we published our review titled 'Therapeutic potential of A1 adenosine receptor ligands - a survey of recent patent literature' that reported the compounds active on A1 adenosine receptors (ARs) and the applications of A1 AR ligands patented in the period 2005 - 2008.

AREAS COVERED

This article is a discussion of the patents about the same subjects, issued in the period 2008 to present. It is organized similarly to the first one, with a section about new compounds, subdivided on the basis of their functional activity (agonists, antagonists and allosteric modulators) and a section regarding new therapeutic applications.

EXPERT OPINION

The main novelty is represented by the patenting of A1 AR ligands with dual selectivity which may show, in some conditions, better efficacy and fewer side effects. Moreover, while the way to arrive into the market appears full of obstacles for selective A1 ligands that need systemic administration for long-term therapy, better chances are foreseen in applications requiring topical administration.

A network-oriented perspective on cardiac calcium signaling

The normal contractile, electrical, and energetic function of the heart depends on the synchronization of biological oscillators and signal integrators that make up cellular signaling networks. In this review we interpret experimental data from molecular, cellular, and transgenic models of cardiac signaling behavior in the context of established concepts in cell network architecture and organization. Focusing on the cellular Ca(2+) handling machinery, we describe how the plasticity and adaptability of normal Ca(2+) signaling is dependent on dynamic network configurations that operate across a wide range of functional states. We consider how (mal)adaptive changes in signaling pathways restrict the dynamic range of the network such that it cannot respond appropriately to physiologic stimuli or perturbation. Based on these concepts, a model is proposed in which pathologic abnormalities in cardiac rhythm and contractility (e.g., arrhythmias and heart failure) arise as a consequence of progressive desynchronization and reduction in the dynamic range of the Ca(2+) signaling network. We discuss how a systems-level understanding of the network organization, cellular noise, and chaotic behavior may inform the design of new therapeutic modalities that prevent or reverse the disease-linked unraveling of the Ca(2+) signaling network.

Searching for new cardiovascular drugs: towards improved systems for drug screening?

INTRODUCTION

The pharmaceutical industry urgently needs new ways of profiling the safety and efficacy of new cardiovascular (CV) drugs and more effectively transitioning these compounds through the stages of CV drug screening. This article reviews new technologies and methodological innovations and assesses whether these frameworks offer improved solutions to the problems facing the contemporary CV drug development.

AREAS COVERED

The article comprises literature derived from a systematic search (from 2000 onwards) using the US patent office and ESP@CENET search engines as well as through multiple Boolean terms. The article focuses on patents relating to technologies and resources and categorises the patents according to their niche in the CV drug screening landscape.

EXPERT OPINION

The CV drug pipeline is stalling due to the inability of many contemporary drug screening frameworks to discriminate between safe, efficacious therapy and hazardous off-target effect. Given the current limitations of drug screening frameworks, there is little scope for expanding the CV drug portfolio with newer, safer drugs with improved mechanisms of action. New screening modalities are urgently needed. Searches reveal that there are few examples of truly new technologies and systems in the patent literature. This apparent failure to revamp facets of the CV drug screening process can only perpetuate the inability of current platforms to improve the CV drug pipeline. Consequently, with few exceptions, there is stagnation in pre-clinical assay design that limits the pharmaceutical industry's ability to search for new drugs in new and more effective ways.