Endoxifen, the active metabolite of tamoxifen, inhibits cloned hERG potassium channels

Aromatase Inhibitor Therapy Increases the Risk of New-Onset Atrial Fibrillation in Patients With Breast Cancer

Background

Previous studies suggest that aromatase inhibitors (AIs) increase the risk of adverse cardiovascular events and cardiac arrhythmias in patients with breast cancer, but it is unclear whether AIs also increase the risk of new-onset atrial fibrillation (AF).

Objectives

The purpose of this study was to investigate whether the use of AIs was associated with an increased risk of new-onset AF in patients with breast cancer.

Methods

We performed a retrospective analysis involving 5,707 patients with breast cancer (mean age 63.9 ± 11.2 years and 99.9% women) who received adjunctive hormone therapy with an AI (AI group, n = 4,878) or tamoxifen (tamoxifen group, n = 829) in Hong Kong between January 1, 1999, and December 31, 2020. After propensity score matching, there were 1,658 and 829 patients with balanced characteristics in the AI group and tamoxifen group, respectively.

Results

After 8,863 patient-years of follow-up, patients who were prescribed AI had a trend toward more new-onset arrhythmias compared with those prescribed tamoxifen (0.62 vs 0.30 per 100 patient-years; crude HR: 2.05; P = 0.053). The difference in arrhythmic risk was mainly driven by a higher incidence rate of new-onset AF in the AI group (0.59 vs 0.27 per 100 patient-years; crude HR: 2.18; P = 0.046). The use of AIs was confirmed to be an independent risk factor for new-onset AF on multivariate analysis (adjusted HR: 2.75; P = 0.01).

Conclusions

Among breast cancer patients prescribed adjunctive hormonal therapy, AI was associated with an increased risk of new-onset AF. Regular surveillance for new-onset AF should be considered in breast cancer patients treated with an AI.

Ion Channels in Gliomas-From Molecular Basis to Treatment

Ion channels provide the basis for the nervous system's intrinsic electrical activity. Neuronal excitability is a characteristic property of neurons and is critical for all functions of the nervous system. Glia cells fulfill essential supportive roles, but unlike neurons, they also retain the ability to divide. This can lead to uncontrolled growth and the formation of gliomas. Ion channels are involved in the unique biology of gliomas pertaining to peritumoral pathology and seizures, diffuse invasion, and treatment resistance. The emerging picture shows ion channels in the brain at the crossroads of neurophysiology and fundamental pathophysiological processes of specific cancer behaviors as reflected by uncontrolled proliferation, infiltration, resistance to apoptosis, metabolism, and angiogenesis. Ion channels are highly druggable, making them an enticing therapeutic target. Targeting ion channels in difficult-to-treat brain tumors such as gliomas requires an understanding of their extremely heterogenous tumor microenvironment and highly diverse molecular profiles, both representing major causes of recurrence and treatment resistance. In this review, we survey the current knowledge on ion channels with oncogenic behavior within the heterogeneous group of gliomas, review ion channel gene expression as genomic biomarkers for glioma prognosis and provide an update on therapeutic perspectives for repurposed and novel ion channel inhibitors and electrotherapy.

New Insights into Ion Channels: Predicting hERG-Drug Interactions

Drug-induced long QT syndrome can be a very dangerous side effect of existing and developmental drugs. In this work, a model proposed two decades ago addressing the ion specificity of potassium channels is extended to the human ether-à-gogo gene (hERG). hERG encodes the protein that assembles into the potassium channel responsible for the delayed rectifier current in ventricular cardiac myocytes that is often targeted by drugs associated with QT prolongation. The predictive value of this model can guide a rational drug design decision early in the drug development process and enhance NCE (New Chemical Entity) retention. Small molecule drugs containing a nitrogen that can be protonated to afford a formal +1 charge can interact with hERG to prevent the repolarization of outward rectifier currents. Low-level ab initio calculations are employed to generate electronic features of the drug molecules that are known to interact with hERG. These calculations were employed to generate structure–activity relationships (SAR) that predict whether a small molecule drug containing a protonated nitrogen has the potential to interact with and inhibit the activity of the hERG potassium channels of the heart. The model of the mechanism underlying the ion specificity of potassium channels offers predictive value toward optimizing drug design and, therefore, minimizes the effort and expense invested in compounds with the potential for life-threatening inhibitory activity of the hERG potassium channel.

Flavonoids and hERG channels: Friends or foes?

The cardiac action potential is regulated by several ion channels. Drugs capable to block these channels, in particular the human ether-à-go-go-related gene (hERG) channel, also known as K_V11.1 channel, may lead to a potentially lethal ventricular tachyarrhythmia called "Torsades de Pointes". Thus, evaluation of the hERG channel off-target activity of novel chemical entities is nowadays required to safeguard patients as well as to avoid attrition in drug development. Flavonoids, a large class of natural compounds abundantly present in food, beverages, herbal medicines, and dietary food supplements, generally escape this assessment, though consumed in consistent amounts. Continuously growing evidence indicates that these compounds may interact with the hERG channel and block it. The present review, by examining numerous studies, summarizes the state-of-the-art in this field, describing the most significant examples of direct and indirect inhibition of the hERG channel current operated by flavonoids. A description of the molecular interactions between a few of these natural molecules and the Rattus norvegicus channel protein, achieved by an in silico approach, is also presented.

Ion Channels as Therapeutic Targets in High Grade Gliomas

Simple Summary

Glioblastoma multiforme is an aggressive grade IV lethal brain tumour with a median survival of 14 months. Despite surgery to remove the tumour, and subsequent concurrent chemotherapy and radiotherapy, there is little in terms of effective treatment options. Because of this, exploring new treatment avenues is vital. Brain tumours are intrinsically electrically active; expressing unique patterns of ion channels, and this is a characteristic we can exploit. Ion channels are specialised proteins in the cell’s membrane that allow for the passage of positive and negatively charged ions in and out of the cell, controlling membrane potential. Membrane potential is a crucial biophysical signal in normal and cancerous cells. Research has identified that specific classes of ion channels not only move the cell through its cell cycle, thus encouraging growth and proliferation, but may also be essential in the development of brain tumours. Inhibition of sodium, potassium, calcium, and chloride channels has been shown to reduce the capacity of glioblastoma cells to grow and invade. Therefore, we propose that targeting ion channels and repurposing commercially available ion channel inhibitors may hold the key to new therapeutic avenues in high grade gliomas.

Abstract

Glioblastoma multiforme (GBM) is a lethal brain cancer with an average survival of 14–15 months even with exhaustive treatment. High grade gliomas (HGG) represent the leading cause of CNS cancer-related death in children and adults due to the aggressive nature of the tumour and limited treatment options. The scarcity of treatment available for GBM has opened the field to new modalities such as electrotherapy. Previous studies have identified the clinical benefit of electrotherapy in combination with chemotherapeutics, however the mechanistic action is unclear. Increasing evidence indicates that not only are ion channels key in regulating electrical signaling and membrane potential of excitable cells, they perform a crucial role in the development and neoplastic progression of brain tumours. Unlike other tissue types, neural tissue is intrinsically electrically active and reliant on ion channels and their function. Ion channels are essential in cell cycle control, invasion and migration of cancer cells and therefore present as valuable therapeutic targets. This review aims to discuss the role that ion channels hold in gliomagenesis and whether we can target and exploit these channels to provide new therapeutic targets and whether ion channels hold the mechanistic key to the newfound success of electrotherapies.

Focus on Triple-Negative Breast Cancer: Potassium Channel Expression and Clinical Correlates

Despite improvements in early diagnosis and treatment, breast cancer is still a major health problem worldwide. Among breast cancer subtypes, the most challenging and harder to treat is represented by triple-negative molecular subtype. Due to its intrinsic features this subtype cannot be treated neither with hormonal therapy (since it does not express estrogen or progesterone receptors) nor with epidermal growth factor receptor 2 (HER2) inhibitors (as it does not express high levels of this protein). For these reasons, the standard of care for these patients is represented by a combination of surgery, radiation therapy and chemotherapy. In this scenario, searching for novel biomarkers that might help both in diagnosis and therapy is mandatory. In the last years, it was shown that different families of potassium channels are overexpressed in primary breast cancers. The altered ion channel expression may be useful for diagnostic and therapeutic purposes due to some peculiar characteristics of this class of molecules. Ion channels are defined as pore-forming transmembrane proteins regulating passive ion fluxes in the cells. Ion channels represent good potential markers since, being localized at the plasma membrane level, their detection and block with specific drugs and antibodies might be fast and tunable. This review focuses on triple-negative breast cancers and recapitulates the current knowledge about potassium channels' clinical relevance and their potential use in the clinical setting, for triple-negative breast cancer diagnosis and therapy.

Cardiac arrhythmia considerations of hormone cancer therapies

Breast and prostate cancers are among the most prevalent cancers worldwide. Oestradiol and progesterone are major drivers for breast cancer proliferation, and androgens for prostate cancer. Endocrine therapies are drugs that interfere with hormone-activated pathways to slow cancer progression. Multiple new breakthrough drugs improving overall survival have recently been developed within this class. As the use of these latter drugs grows, incidence of cardiac arrhythmias has emerged as an unappreciated complication. These changes are not surprising given that sex hormones alter ventricular repolarization. Testosterone shortens action potential duration and QT interval duration, while oestradiol has an opposite effect. In patients with breast cancer, selective oestrogen receptor modulators are associated with more reports for long QT and torsade de pointes (TdP) than aromatase inhibitors, likely through an oestradiol-like effect on the heart. Cyclin-dependent kinase 4/6 inhibitors, a new class of anticancer drugs used in combination with endocrine therapies in hormone receptor positive breast cancer, are also variably associated with drug-induced long QT, particularly with ribociclib. In prostate cancer, androgen deprivation therapy is associated with long QT and TdP, and possibly atrial fibrillation for abiraterone. In this review, we have summarized the clinical and preclinical data focusing on cardiac arrhythmia considerations of hormone cancer therapies.

Usefulness of Bnet, a Simple Linear Metric in Discerning Torsades De Pointes Risks in 28 CiPA Drugs

The Comprehensive in vitro Proarrhythmia Assay (CiPA) project suggested the torsade metric score (TMS) which requires substantial computing resources as a useful biomarker to predict proarrhythmic risk from human ether-à-go-go-related gene (hERG) and a few other ion channel block data. The TMS was useful to predict low TdP risks of drugs blocking Na+ (ranolazine) and Ca2+ (verapamil) channels as well as the hERG channel. However, Mistry asserted that the simple linear metric, Bnet reflecting net blockade of a few influential ion channels has similar predictive power. Here we compared the predictability of Bnet and TMS for the 12 training and 16 validation CiPA drugs which were pre-classified into three categories according to the known TdP risks (low, intermediate, and high risk) by CiPA. Bnet at 5×Cmax (Bnet5×Cmax) was calculated using the ion-channel IC50 and Hill coefficients of CiPA drugs collected from previous reports by the CiPA team and others. The receiver operating characteristic curve area under curve (ROC AUC) values for TMS and Bnet5×Cmax as performance metrics in discerning low versus intermediate/high risk categories for the 28 CiPA drugs were similar. However, Bnet5×Cmax was much inferior to TMS at discerning between intermediate- and high-risk drugs. Dynamic Bnet, which used in silico hERG dynamic parameters unlike conventional Bnet, improved the misspecification. Thus, we propose that Bnet5×Cmax is used for quick screening of TdP risks of drug candidates and if the "intermediate/high" risk is predicted by Bnet5×Cmax, in silico approaches, such as dynamic Bnet or TMS, may be further considered.

Deep Learning-Based Prediction of Drug-Induced Cardiotoxicity

Blockade of the human ether-à-go-go-related gene (hERG) channel by small molecules induces the prolongation of the QT interval which leads to fatal cardiotoxicity and accounts for the withdrawal or severe restrictions on the use of many approved drugs. In this study, we develop a deep learning approach, termed deephERG, for prediction of hERG blockers of small molecules in drug discovery and postmarketing surveillance. In total, we assemble 7,889 compounds with well-defined experimental data on the hERG and with diverse chemical structures. We find that deephERG models built by a multitask deep neural network (DNN) algorithm outperform those built by single-task DNN, naı̈ve Bayes (NB), support vector machine (SVM), random forest (RF), and graph convolutional neural network (GCNN). Specifically, the area under the receiver operating characteristic curve (AUC) value for the best model of deephERG is 0.967 on the validation set. Furthermore, based on 1,824 U.S. Food and Drug Administration (FDA) approved drugs, 29.6% drugs are computationally identified to have potential hERG inhibitory activities by deephERG, highlighting the importance of hERG risk assessment in early drug discovery. Finally, we showcase several novel predicted hERG blockers on approved antineoplastic agents, which are validated by clinical case reports, experimental evidence, and the literature. In summary, this study presents a powerful deep learning-based tool for risk assessment of hERG-mediated cardiotoxicities in drug discovery and postmarketing surveillance.

Increased long QT and torsade de pointes reporting on tamoxifen compared with aromatase inhibitors

OBJECTIVE

A prolonged QTc (LQT) is a surrogate for the risk of torsade de pointes (TdP). QTc interval duration is influenced by sex hormones: oestradiol prolongs and testosterone shortens QTc. Drugs used in the treatment of breast cancer have divergent effects on hormonal status.

METHODS

We performed a disproportionality analysis using the European database of suspected adverse drug reaction (ADR) reports to evaluate the reporting OR (ROR χ²) of LQT, TdP and ventricular arrhythmias associated with selective oestrogen receptor modulators (SERMs: tamoxifen and toremifene) as opposed to aromatase inhibitors (AIs: anastrozole, exemestane and letrozole). When the proportion of an ADR is greater in patients exposed to a drug (SERMs) compared with patients exposed to control drug (AIs), this suggests an association between the specific drug and the reaction and is a potential signal for safety. Clinical and demographic characterisation of patients with SERMs-induced LQT and ventricular arrhythmias was performed.

RESULTS

SERMs were associated with higher proportion of LQT reports versus AIs (26/8318 vs 11/14851, ROR: 4.2 (2.11-8.55), p<0.001). SERMs were also associated with higher proportion of TdP and ventricular arrhythmia reports versus AIs (6/8318 vs 2/14851, ROR: 5.4 (1.29-26.15), p:0.02; 16/8318 vs 12/14851, ROR: 2.38 (1.15-4.94), p:0.02, respectively). Mortality was 38% in patients presenting ventricular arrhythmias associated with SERMs.

CONCLUSIONS

SERMs are associated with more reports of drug-induced LQT, TdP and ventricular arrhythmias compared with AIs. This finding is consistent with oestradiol-like properties of SERMs on the heart as opposed to effects of oestrogen deprivation and testosterone increase induced by AIs.

TRIAL REGISTRATION NUMBER

NCT03259711.

Anticancer drug-induced cardiac rhythm disorders: Current knowledge and basic underlying mechanisms

Significant advances in cancer treatment have resulted in decreased cancer related mortality for many malignancies with some cancer types now considered chronic diseases. Despite these improvements, there is increasing recognition that many cancer patients or cancer survivors can develop cardiovascular diseases, either due to the cancer itself or as a result of anticancer therapy. Much attention has focused on heart failure; however, other cardiotoxicities, notably cardiac rhythm disorders, can occur without underlying cardiomyopathy. Supraventricular tachycardias occur in cancer patients treated with cytotoxic chemotherapy (anthracyclines, gemcitabine, cisplatin and alkylating-agents) or kinase-inhibitors (KIs) such as ibrutinib. Ventricular arrhythmias, with a subset of them being torsades-de-pointes (TdP) favored by QTc prolongation have been reported: this may be the result of direct hERG-channel inhibition or a more recently-described mechanism of phosphoinositide-3-kinase inhibition. The major anticancer drugs responsible for QTc prolongation in this context are KIs, arsenic trioxide, anthracyclines, histone deacetylase inhibitors, and selective estrogen receptor modulators. Anticancer drug-induced cardiac rhythm disorders remain an underappreciated complication even by experienced clinicians. Moreover, the causal relationship of a particular anticancer drug with cardiac arrhythmia occurrence remains challenging due in part to patient comorbidities and complex treatment regimens. For example, any cancer patient may also be diagnosed with common diseases such as hypertension, diabetes or heart failure which increase an individual's arrhythmia susceptibility. Further, anticancer drugs are generally usually used in combination, increasing the challenge around establishing causation. Thus, arrhythmias appear to be an underappreciated adverse effect of anticancer agents and the incidence, significance and underlying mechanisms are now being investigated.

Tamoxifen and amphetamine abuse: Are there therapeutic possibilities?

Although best known as a selective estrogen receptor modulator (SERM), tamoxifen is a drug with a wide range of activities. Tamoxifen has demonstrated some efficacy has a therapeutic for bipolar mania and is believed to exert these effects through inhibition of protein kinase C (PKC). As the symptoms of amphetamine treatment in rodents are believed to mimic the symptoms of a manic episode, many of the preclinical studies for this indication have demonstrated that tamoxifen inhibits amphetamine action. The amphetamine-induced increase in extracellular dopamine which gives rise to the 'manic' effects is due to interaction of amphetamine with the dopamine transporter. We and others have demonstrated that PKC reduces amphetamine-induced reverse transport through the dopamine transporter. In this review, we will outline the actions of tamoxifen as a SERM and further detail another known action of tamoxifen-inhibition of PKC. We will summarize the literature showing how tamoxifen affects amphetamine action. Finally, we will present our hypothesis that tamoxifen, or an analog, could be used therapeutically to reduce amphetamine abuse in addition to treating mania.