Ibrutinib Displays Atrial-Specific Toxicity in Human Stem Cell-Derived Cardiomyocytes

Atrial fibrillation in cancer, anticancer therapies, and underlying mechanisms

Atrial fibrillation (AF) is a common arrhythmic complication in cancer patients and can be exacerbated by traditional cytotoxic and targeted anticancer therapies. Increased incidence of AF in cancer patients is independent of confounding factors, including preexisting myocardial arrhythmogenic substrates, type of cancer, or cancer stage. Mechanistically, AF is characterized by fast unsynchronized atrial contractions with rapid ventricular response, which impairs ventricular filling and results in various symptoms such as fatigue, chest pain, and shortness of breath. Due to increased blood stasis, a consequence of both cancer and AF, concern for stroke increases in this patient population. To compound matters, cardiotoxic anticancer therapies themselves promote AF; thereby exacerbating AF morbidity and mortality in cancer patients. In this review, we examine the relationship between AF, cancer, and anticancer therapies with a focus on the shared molecular and electrophysiological mechanisms linking these disease processes. We also explore the potential role of sodium-glucose co-transporter 2 inhibitors (SGLT2i) in the management of anticancer-therapy induced AF.

Intercellular pathways of cancer treatment-related cardiotoxicity and their therapeutic implications: the paradigm of radiotherapy

Advances in cancer therapeutics have improved patient survival rates. However, cancer survivors may suffer from adverse events either at the time of therapy or later in life. Cardiovascular diseases (CVD) represent a clinically important, but mechanistically understudied complication, which interfere with the continuation of best-possible care, induce life-threatening risks, and/or lead to long-term morbidity. These concerns are exacerbated by the fact that targeted therapies and immunotherapies are frequently combined with radiotherapy, which induces durable inflammatory and immunogenic responses, thereby providing a fertile ground for the development of CVDs. Stressed and dying irradiated cells produce 'danger' signals including, but not limited to, major histocompatibility complexes, cell-adhesion molecules, proinflammatory cytokines, and damage-associated molecular patterns. These factors activate intercellular signaling pathways which have potentially detrimental effects on the heart tissue homeostasis. Herein, we present the clinical crosstalk between cancer and heart diseases, describe how it is potentiated by cancer therapies, and highlight the multifactorial nature of the underlying mechanisms. We particularly focus on radiotherapy, as a case known to often induce cardiovascular complications even decades after treatment. We provide evidence that the secretome of irradiated tumors entails factors that exert systemic, remote effects on the cardiac tissue, potentially predisposing it to CVDs. We suggest how diverse disciplines can utilize pertinent state-of-the-art methods in feasible experimental workflows, to shed light on the molecular mechanisms of radiotherapy-related cardiotoxicity at the organismal level and untangle the desirable immunogenic properties of cancer therapies from their detrimental effects on heart tissue. Results of such highly collaborative efforts hold promise to be translated to next-generation regimens that maximize tumor control, minimize cardiovascular complications, and support quality of life in cancer survivors.

Metabolic and toxicological considerations of Bruton's tyrosine kinase inhibitors for the treatment of chronic lymphocytic leukemia/small lymphocytic lymphoma

INTRODUCTION

Bruton tyrosine kinase inhibitors (BTKi) have been used for the management of human diseases since the approval of the first-in class agent, ibrutinib, by the Food and Drug Administration in 2013 for the treatment of patients with mantle cell lymphoma (MCL). Ibrutinib is a covalent inhibitor along with second-class BTKis: acalabrutinib and zanubrutinib. These well-tolerated agents have transformed the treatment landscape of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL). A new class of these inhibitors, non-covalent, might become an answer to the emerging resistance by avoiding the sustained contact with the kinase binding domain.

AREAS COVERED

This article examines the chemical composition, mechanism of action, metabolic characteristics, and potential toxicity of inhibitors targeting Bruton tyrosine kinase. A comprehensive search was conducted across English-language articles in PubMed, Web of Science, and Google Scholar.

EXPERT OPINION

Bruton tyrosine kinase inhibitors have greatly enhanced the armamentarium against lymphoid malignancies including CLL/SLL. Their future lies in the choice of appropriate patients who will benefit from the treatment without significant adverse reaction. Combination chemotherapy-free fixed-duration regimens with targeted molecules will allow for MRD-driven approach in patients with CLL/SLL in the near future.

hiPSC-derived cardiomyocytes as a model to study the role of small-conductance Ca2+-activated K+ (SK) ion channel variants associated with atrial fibrillation

Atrial fibrillation (AF), the most common arrhythmia, has been associated with different electrophysiological, molecular, and structural alterations in atrial cardiomyocytes. Therefore, more studies are required to elucidate the genetic and molecular basis of AF. Various genome-wide association studies (GWAS) have strongly associated different single nucleotide polymorphisms (SNPs) with AF. One of these GWAS identified the rs13376333 risk SNP as the most significant one from the 1q21 chromosomal region. The rs13376333 risk SNP is intronic to the KCNN3 gene that encodes for small conductance calcium-activated potassium channels type 3 (SK3). However, the functional electrophysiological effects of this variant are not known. SK channels represent a unique family of K+ channels, primarily regulated by cytosolic Ca2+ concentration, and different studies support their critical role in the regulation of atrial excitability and consequently in the development of arrhythmias like AF. Since different studies have shown that both upregulation and downregulation of SK3 channels can lead to arrhythmias by different mechanisms, an important goal is to elucidate whether the rs13376333 risk SNP is a gain-of-function (GoF) or a loss-of-function (LoF) variant. A better understanding of the functional consequences associated with these SNPs could influence clinical practice guidelines by improving genotype-based risk stratification and personalized treatment. Although research using native human atrial cardiomyocytes and animal models has provided useful insights, each model has its limitations. Therefore, there is a critical need to develop a human-derived model that represents human physiology more accurately than existing animal models. In this context, research with human induced pluripotent stem cells (hiPSC) and subsequent generation of cardiomyocytes derived from hiPSC (hiPSC-CMs) has revealed the underlying causes of various cardiovascular diseases and identified treatment opportunities that were not possible using in vitro or in vivo studies with animal models. Thus, the ability to generate atrial cardiomyocytes and atrial tissue derived from hiPSCs from human/patients with specific genetic diseases, incorporating novel genetic editing tools to generate isogenic controls and organelle-specific reporters, and 3D bioprinting of atrial tissue could be essential to study AF pathophysiological mechanisms. In this review, we will first give an overview of SK-channel function, its role in atrial fibrillation and outline pathophysiological mechanisms of KCNN3 risk SNPs. We will then highlight the advantages of using the hiPSC-CM model to investigate SNPs associated with AF, while addressing limitations and best practices for rigorous hiPSC studies.

Utilizing human induced pluripotent stem cells to study atrial arrhythmias in the short QT syndrome

BACKGROUND

Among the monogenic inherited causes of atrial fibrillation is the short QT syndrome (SQTS), a rare channelopathy causing atrial and ventricular arrhythmias. One of the limitations in studying the mechanisms and optimizing treatment of SQTS-related atrial arrhythmias has been the lack of relevant human atrial tissues models.

OBJECTIVE

To generate a unique model to study SQTS-related atrial arrhythmias by combining the use of patient-specific human induced pluripotent stem cells (hiPSCs), atrial-specific differentiation schemes, two-dimensional tissue modeling, optical mapping, and drug testing.

METHODS AND RESULTS

SQTS (N588K KCNH2 mutation), isogenic-control, and healthy-control hiPSCs were coaxed to differentiate into atrial cardiomyocytes using a retinoic-acid based differentiation protocol. The atrial identity of the cells was confirmed by a distinctive pattern of MLC2v downregulation, connexin 40 upregulation, shorter and triangular-shaped action potentials (APs), and expression of the atrial-specific acetylcholine-sensitive potassium current. In comparison to the healthy- and isogenic control cells, the SQTS-hiPSC atrial cardiomyocytes displayed abbreviated APs and refractory periods along with an augmented rapidly activating delayed-rectifier potassium current (IKr). Optical mapping of a hiPSC-based atrial tissue model of the SQTS displayed shortened APD and altered biophysical properties of spiral waves induced in this model, manifested by accelerated spiral-wave frequency and increased rotor curvature. Both AP shortening and arrhythmia irregularities were reversed by quinidine and vernakalant treatment, but not by sotalol.

CONCLUSIONS

Patient-specific hiPSC-based atrial cellular and tissue models of the SQTS were established, which provide examples on how this type of modeling can shed light on the pathogenesis and pharmacological treatment of inherited atrial arrhythmias.

Mechanisms of Pathogenicity of Hypertrophic Cardiomyopathy-Associated Troponin T (TNNT2) Variant R278C+/- During Development

Hypertrophic cardiomyopathy (HCM) is one of the most common heritable cardiovascular diseases and variants of TNNT2 (cardiac troponin T) are linked to increased risk of sudden cardiac arrest despite causing limited hypertrophy. In this study, a TNNT2 variant, R278C+/-, was generated in both human cardiac recombinant/reconstituted thin filaments (hcRTF) and human- induced pluripotent stem cells (hiPSCs) to investigate the mechanisms by which the R278C+/- variant affects cardiomyocytes at the proteomic and functional levels. The results of proteomics analysis showed a significant upregulation of markers of cardiac hypertrophy and remodeling in R278C+/- vs. the isogenic control. Functional measurements showed that R278C+/- variant enhances the myofilament sensitivity to Ca2+, increases the kinetics of contraction, and causes arrhythmia at frequencies >75 bpm. This study uniquely shows the profound impact of the TNNT2 R278C+/- variant on the cardiomyocyte proteomic profile, cardiac electrical and contractile function in the early stages of cardiac development.

Predictors of ibrutinib-associated atrial fibrillation: 5-year follow-up of a prospective study

Ibrutinib-associated atrial fibrillation (IRAF) emerged among the adverse events of major interests in ibrutinib-treated patients as real-world studies showed a higher incidence compared to clinical trials. We prospectively analyzed predictors of IRAF in 43 single-center consecutive patients affected by chronic lymphocytic leukemia that started therapy with ibrutinib between 2015 and 2017. Key secondary endpoints were to describe the management of IRAF and survival outcomes. During a median follow-up period of 52 months, we registered 45 CV events, with a total of 23 AF events in 13 patients (CI 30.0% (95% CI: 16.5-43.9)). Pre-existent cardiovascular risk factors, in particular hypertension, a previous history of AF and a high Shanafelt risk score emerged as predictors of IRAF. Baseline echocardiographic evaluation of left atrial (LA) dimensions confirmed to predict IRAF occurrence and cut-off values were identified in our cohort: 32 mm for LA diameter and 18 cm2 for LA area. No difference in progression free survival and overall survival emerged in patients experiencing IRAF. Following AF, anticoagulation was started in all eligible patients, and cardioactive therapy was accordingly modified. Echocardiography represents a highly reproducible and widespread tool to be included in the work-up of ibrutinib candidates; the identification of IRAF predictors represents a useful guide to clinical practice.

3D bioprinting for organ and organoid models and disease modeling

INTRODUCTION

3D printing, a versatile additive manufacturing technique, has diverse applications ranging from transportation, rapid prototyping, clean energy, and medical devices.

AREAS COVERED

The authors focus on how 3D printing technology can enhance the drug discovery process through automating tissue production that enables high-throughput screening of potential drug candidates. They also discuss how the 3D bioprinting process works and what considerations to address when using this technology to generate cell laden constructs for drug screening as well as the outputs from such assays necessary for determining the efficacy of potential drug candidates. They focus on how bioprinting how has been used to generate cardiac, neural, and testis tissue models, focusing on bio-printed 3D organoids.

EXPERT OPINION

The next generation of 3D bioprinted organ model holds great promises for the field of medicine. In terms of drug discovery, the incorporation of smart cell culture systems and biosensors into 3D bioprinted models could provide highly detailed and functional organ models for drug screening. By addressing current challenges of vascularization, electrophysiological control, and scalability, researchers can obtain more reliable and accurate data for drug development, reducing the risk of drug failures during clinical trials.

Human Stem Cells for Cardiac Disease Modeling and Preclinical and Clinical Applications—Are We on the Road to Success?

Cardiovascular diseases (CVDs) are pointed out by the World Health Organization (WHO) as the leading cause of death, contributing to a significant and growing global health and economic burden. Despite advancements in clinical approaches, there is a critical need for innovative cardiovascular treatments to improve patient outcomes. Therapies based on adult stem cells (ASCs) and embryonic stem cells (ESCs) have emerged as promising strategies to regenerate damaged cardiac tissue and restore cardiac function. Moreover, the generation of human induced pluripotent stem cells (iPSCs) from somatic cells has opened new avenues for disease modeling, drug discovery, and regenerative medicine applications, with fewer ethical concerns than those associated with ESCs. Herein, we provide a state-of-the-art review on the application of human pluripotent stem cells in CVD research and clinics. We describe the types and sources of stem cells that have been tested in preclinical and clinical trials for the treatment of CVDs as well as the applications of pluripotent stem-cell-derived in vitro systems to mimic disease phenotypes. How human stem-cell-based in vitro systems can overcome the limitations of current toxicological studies is also discussed. Finally, the current state of clinical trials involving stem-cell-based approaches to treat CVDs are presented, and the strengths and weaknesses are critically discussed to assess whether researchers and clinicians are getting closer to success.

Human Stem Cells for Cardiac Disease Modeling and Preclinical and Clinical Applications-Are We on the Road to Success?

Cardiovascular diseases (CVDs) are pointed out by the World Health Organization (WHO) as the leading cause of death, contributing to a significant and growing global health and economic burden. Despite advancements in clinical approaches, there is a critical need for innovative cardiovascular treatments to improve patient outcomes. Therapies based on adult stem cells (ASCs) and embryonic stem cells (ESCs) have emerged as promising strategies to regenerate damaged cardiac tissue and restore cardiac function. Moreover, the generation of human induced pluripotent stem cells (iPSCs) from somatic cells has opened new avenues for disease modeling, drug discovery, and regenerative medicine applications, with fewer ethical concerns than those associated with ESCs. Herein, we provide a state-of-the-art review on the application of human pluripotent stem cells in CVD research and clinics. We describe the types and sources of stem cells that have been tested in preclinical and clinical trials for the treatment of CVDs as well as the applications of pluripotent stem-cell-derived in vitro systems to mimic disease phenotypes. How human stem-cell-based in vitro systems can overcome the limitations of current toxicological studies is also discussed. Finally, the current state of clinical trials involving stem-cell-based approaches to treat CVDs are presented, and the strengths and weaknesses are critically discussed to assess whether researchers and clinicians are getting closer to success.

Generation of cardiomyocytes from human-induced pluripotent stem cells resembling atrial cells with ability to respond to adrenoceptor agonists

Atrial fibrillation (AF) is the most common chronic arrhythmia presenting a heavy disease burden. We report a new approach for generating cardiomyocytes (CMs) resembling atrial cells from human-induced pluripotent stem cells (hiPSCs) using a combination of Gremlin 2 and retinoic acid treatment. More than 40% of myocytes showed rod-shaped morphology, expression of CM proteins (including ryanodine receptor 2, α-actinin-2 and F-actin) and striated appearance, all of which were broadly similar to the characteristics of adult atrial myocytes (AMs). Isolated myocytes were electrically quiescent until stimulated to fire action potentials with an AM profile and an amplitude of approximately 100 mV, arising from a resting potential of approximately -70 mV. Single-cell RNA sequence analysis showed a high level of expression of several atrial-specific transcripts including NPPA, MYL7, HOXA3, SLN, KCNJ4, KCNJ5 and KCNA5. Amplitudes of calcium transients recorded from spontaneously beating cultures were increased by the stimulation of α-adrenoceptors (activated by phenylephrine and blocked by prazosin) or β-adrenoceptors (activated by isoproterenol and blocked by CGP20712A). Our new approach provides human AMs with mature characteristics from hiPSCs which will facilitate drug discovery by enabling the study of human atrial cell signalling pathways and AF. This article is part of the theme issue 'The heartbeat: its molecular basis and physiological mechanisms'.

Ibrutinib-Associated Cardiotoxicity: From the Pharmaceutical to the Clinical

Ibrutinib is the first-in-class Bruton tyrosine kinase (BTK) inhibitor that has revolutionized the treatment of B cell malignancies. Unfortunately, increased incidences of cardiotoxicity have limited its use. Despite over a decade of research, the biological mechanisms underlying ibrutinib cardiotoxicity remain unclear. In this review, we discuss the pharmacological properties of ibrutinib, the incidence and mechanisms of ibrutinib-induced cardiotoxicity, and practical management to prevent and treat this condition. We also synopsize and discuss the cardiovascular adverse effects related to other more selective BTK inhibitors, which may guide the selection of appropriate BTK inhibitors.

Febuxostat increases ventricular arrhythmogenesis through calcium handling dysregulation in human induced pluripotent stem cell-derived cardiomyocytes

Febuxostat is a xanthine oxidase inhibitor used to reduce the formation of uric acid and prevent gout attacks. Previous studies have suggested that febuxostat was associated with a higher risk of cardiovascular events, including atrial fibrillation, compared with allopurinol, another anti-hyperuricemia drug. Whereas in our clinical practice, we identified two cases of febuxostat-associated ventricular tachycardia events. The proarrhythmogenic effects of febuxostat on human cardiomyocytes and underlined mechanisms remain poorly understood. In this study, we employed real time cell analysis (RTCA) and calcium transient to investigate the effects of febuxostat on the cytotoxicity and electrophysiology properties of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). Up to 10 μM febuxostat treatment did not show toxicity to cell viability. However, 48-hour febuxostat exposure generated dose-dependent increased irregular calcium transients and decreased calcium transient amplitude. Furthermore, RNA-seq analysis indicated that the MAPK signaling pathway was enriched in the febuxostat-treated group, especially the protein kinases JNK. Western blotting of three main protein kinases demonstrated that JNK activation is related to febuxostat-induced arrythmia rather than ERK or p38. The dysfunctional calcium dynamics of febuxostat-treated hiPSC-CMs could be ameliorated by SP600125, the inhibitor of JNK. In conclusion, our study demonstrated that febuxostat increases the predisposition to ventricular arrythmia by dysregulating calcium dynamics.

hESC derived cardiomyocyte biosensor to detect the different types of arrhythmogenic properties of drugs

In the present work, we introduce a new cell-based biosensor for detecting arrhythmias based on a novel utilization of the combination of the Atomic Force Microscope (AFM) lateral force measurement as a nanosensor with a dual 3D cardiomyocyte syncytium. Two spontaneously coupled clusters of cardiomyocytes form this. The syncytium's functional contraction behavior was assessed using video sequences analyzed with Musclemotion ImageJ/Fiji software, and immunocytochemistry evaluated phenotype composition. The application of caffeine solution induced arrhythmia as a model drug, and its spontaneous resolution was monitored by AFM lateral force recording and interpretation and calcium fluorescence imaging as a reference method describing non-synchronized contractions of cardiomyocytes. The phenotypic analysis revealed the syncytium as a functional contractile and conduction cardiac behavior model. Calcium fluorescence imaging was used to validate that AFM fully enabled to discriminate cardiac arrhythmias in this in vitro cellular model. The described novel 3D hESCs-based cellular biosensor is suitable to detect arrhythmic events on the level of cardiac contractile and conduction tissue cellular model. The resulting biosensor allows for screening of arrhythmogenic properties of tailored drugs enabling its use in precision medicine.

Using hiPSC-CMs to Examine Mechanisms of Catecholaminergic Polymorphic Ventricular Tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a potentially lethal inherited cardiac arrhythmia condition, triggered by physical or acute emotional stress, that predominantly expresses early in life. Gain-of-function mutations in the cardiac ryanodine receptor gene (RYR2) account for the majority of CPVT cases, causing substantial disruption of intracellular calcium (Ca²⁺ ) homeostasis particularly during the periods of β-adrenergic receptor stimulation. However, the highly variable penetrance, patient outcomes, and drug responses observed in clinical practice remain unexplained, even for patients with well-established founder RyR2 mutations. Therefore, investigation of the electrophysiological consequences of CPVT-causing RyR2 mutations is crucial to better understand the pathophysiology of the disease. The development of strategies for reprogramming human somatic cells to human induced pluripotent stem cells (hiPSCs) has provided a unique opportunity to study inherited arrhythmias, due to the ability of hiPSCs to differentiate down a cardiac lineage. Employment of genome editing enables generation of disease-specific cell lines from healthy and diseased patient-derived hiPSCs, which subsequently can be differentiated into cardiomyocytes. This paper describes the means for establishing an hiPSC-based model of CPVT in order to recapitulate the disease phenotype in vitro and investigate underlying pathophysiological mechanisms. The framework of this approach has the potential to contribute to disease modeling and personalized medicine using hiPSC-derived cardiomyocytes. © 2021 Wiley Periodicals LLC.

Distinct Effects of Ibrutinib and Acalabrutinib on Mouse Atrial and Sinoatrial Node Electrophysiology and Arrhythmogenesis

Background

Ibrutinib and acalabrutinib are Bruton tyrosine kinase inhibitors used in the treatment of B‐cell lymphoproliferative disorders. Ibrutinib is associated with new‐onset atrial fibrillation. Cases of sinus bradycardia and sinus arrest have also been reported following ibrutinib treatment. Conversely, acalabrutinib is less arrhythmogenic. The basis for these different effects is unclear.

Methods and Results

The effects of ibrutinib and acalabrutinib on atrial electrophysiology were investigated in anesthetized mice using intracardiac electrophysiology, in isolated atrial preparations using high‐resolution optical mapping, and in isolated atrial and sinoatrial node (SAN) myocytes using patch‐clamping. Acute delivery of acalabrutinib did not affect atrial fibrillation susceptibility or other measures of atrial electrophysiology in mice in vivo. Optical mapping demonstrates that ibrutinib dose‐dependently impaired atrial and SAN conduction and slowed beating rate. Acalabrutinib had no effect on atrial and SAN conduction or beating rate. In isolated atrial myocytes, ibrutinib reduced action potential upstroke velocity and Na⁺ current. In contrast, acalabrutinib had no effects on atrial myocyte upstroke velocity or Na⁺ current. Both drugs increased action potential duration, but these effects were smaller for acalabrutinib compared with ibrutinib and occurred by different mechanisms. In SAN myocytes, ibrutinib impaired spontaneous action potential firing by inhibiting the delayed rectifier K⁺ current, while acalabrutinib had no effects on SAN myocyte action potential firing.

Conclusions

Ibrutinib and acalabrutinib have distinct effects on atrial electrophysiology and ion channel function that provide insight into the basis for increased atrial fibrillation susceptibility and SAN dysfunction with ibrutinib, but not with acalabrutinib.

Recent progress of iPSC technology in cardiac diseases

It has been nearly 15 years since the discovery of human-induced pluripotent stem cells (iPSCs). During this time, differentiation methods to targeted cells have dramatically improved, and many types of cells in the human body can be currently generated at high efficiency. In the cardiovascular field, the ability to generate human cardiomyocytes in vitro with the same genetic background as patients has provided a great opportunity to investigate human cardiovascular diseases at the cellular level to clarify the molecular mechanisms underlying the diseases and discover potential therapeutics. Additionally, iPSC-derived cardiomyocytes have provided a powerful platform to study drug-induced cardiotoxicity and identify patients at high risk for the cardiotoxicity; thus, accelerating personalized precision medicine. Moreover, iPSC-derived cardiomyocytes can be sources for cardiac cell therapy. Here, we review these achievements and discuss potential improvements for the future application of iPSC technology in cardiovascular diseases.

Applying Machine Learning to Stem Cell Culture and Differentiation

Machine learning techniques are increasingly becoming incorporated into biological research workflows in a variety of disciplines, most notably cancer research and drug discovery. Efforts in stem cell research comparatively lag behind. We detail key paradigms in machine learning, with a focus on equipping stem cell biologists with the understanding necessary to begin conceptualizing and designing machine learning workflows within their own domain of expertise. Supervised approaches in both regression and classification as well as unsupervised clustering techniques are all covered, with examples from across the biological sciences. High-throughput, high-content, multiplex assays for data acquisition are also discussed in the form of single-cell RNA sequencing and image-based approaches. Lastly, potential applications in stem cell biology, including the development of novel cell types, and improving model maturation are also discussed. Machine learning approaches applied in stem cell biology show promise in accelerating progress in developmental biology, drug screening, disease modeling, and personalized medicine. © 2021 Wiley Periodicals LLC.

Modulated Calcium Homeostasis and Release Events Under Atrial Fibrillation and Its Risk Factors: A Meta-Analysis

Background: Atrial fibrillation (AF) is associated with calcium (Ca²⁺) handling remodeling and increased spontaneous calcium release events (SCaEs). Nevertheless, its exact mechanism remains unclear, resulting in suboptimal primary and secondary preventative strategies.

Methods: We searched the PubMed database for studies that investigated the relationship between SCaEs and AF and/or its risk factors. Meta-analysis was used to examine the Ca²⁺ mechanisms involved in the primary and secondary AF preventative groups.

Results: We included a total of 74 studies, out of the identified 446 publications from inception (1982) until March 31, 2020. Forty-five were primary and 29 were secondary prevention studies for AF. The main Ca²⁺ release events, calcium transient (standardized mean difference (SMD) = 0.49; I² = 35%; confidence interval (CI) = 0.33–0.66; p < 0.0001), and spark amplitude (SMD = 0.48; I² = 0%; CI = −0.98–1.93; p = 0.054) were enhanced in the primary diseased group, while calcium transient frequency was increased in the secondary group. Calcium spark frequency was elevated in both the primary diseased and secondary AF groups. One of the key cardiac currents, the L-type calcium current (I_CaL) was significantly downregulated in primary diseased (SMD = −1.07; I² = 88%; CI = −1.94 to −0.20; p < 0.0001) and secondary AF groups (SMD = −1.28; I² = 91%; CI = −2.04 to −0.52; p < 0.0001). Furthermore, the sodium–calcium exchanger (I_NCX) and NCX1 protein expression were significantly enhanced in the primary diseased group, while only NCX1 protein expression was shown to increase in the secondary AF studies. The phosphorylation of the ryanodine receptor at S2808 (pRyR-S2808) was significantly elevated in both the primary and secondary groups. It was increased in the primary diseased and proarrhythmic subgroups (SMD = 0.95; I² = 64%; CI = 0.12–1.79; p = 0.074) and secondary AF group (SMD = 0.66; I² = 63%; CI = 0.01–1.31; p < 0.0001). Sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) expression was elevated in the primary diseased and proarrhythmic drug subgroups but substantially reduced in the secondary paroxysmal AF subgroup.

Conclusions: Our study identified that I_CaL is reduced in both the primary and secondary diseased groups. Furthermore, pRyR-S2808 and NCX1 protein expression are enhanced. The remodeling leads to elevated Ca²⁺ functional activities, such as increased frequencies or amplitude of Ca²⁺ spark and Ca²⁺ transient. The main difference identified between the primary and secondary diseased groups is SERCA expression, which is elevated in the primary diseased group and substantially reduced in the secondary paroxysmal AF subgroup. We believe our study will add new evidence to AF mechanisms and treatment targets.

Human-induced pluripotent stem cell-derived cardiomyocytes, 3D cardiac structures, and heart-on-a-chip as tools for drug research

Development of new drugs is of high interest for the field of cardiac and cardiovascular diseases, which are a dominant cause of death worldwide. Before being allowed to be used and distributed, every new potentially therapeutic compound must be strictly validated during preclinical and clinical trials. The preclinical studies usually involve the in vitro and in vivo evaluation. Due to the increasing reporting of discrepancy in drug effects in animal and humans and the requirement to reduce the number of animals used in research, improvement of in vitro models based on human cells is indispensable. Primary cardiac cells are difficult to access and maintain in cell culture for extensive experiments; therefore, the human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) became an excellent alternative. This technology enables a production of high number of patient- and disease-specific cardiomyocytes and other cardiac cell types for a large-scale research. The drug effects can be extensively evaluated in the context of electrophysiological responses with a use of well-established tools, such as multielectrode array (MEA), patch clamp, or calcium ion oscillation measurements. Cardiotoxicity, which is a common reason for withdrawing drugs from marketing or rejection at final stages of clinical trials, can be easily verified with a use of hiPSC-CM model providing a prediction of human-specific responses and higher safety of clinical trials involving patient cohort. Abovementioned studies can be performed using two-dimensional cell culture providing a high-throughput and relatively lower costs. On the other hand, more complex structures, such as engineered heart tissue, organoids, or spheroids, frequently applied as co-culture systems, represent more physiological conditions and higher maturation rate of hiPSC-derived cells. Furthermore, heart-on-a-chip technology has recently become an increasingly popular tool, as it implements controllable culture conditions, application of various stimulations and continuous parameters read-out. This paper is an overview of possible use of cardiomyocytes and other cardiac cell types derived from hiPSC as in vitro models of heart in drug research area prepared on the basis of latest scientific reports and providing thorough discussion regarding their advantages and limitations.

Atrial-specific hiPSC-derived cardiomyocytes in drug discovery and disease modeling

The discovery and application of human-induced pluripotent stem cells (hiPSCs) have been instrumental in the investigation of the pathophysiology of cardiovascular diseases. Patient-specific hiPSCs can now be generated, genome-edited, and subsequently differentiated into various cell types and used for regenerative medicine, disease modeling, drug testing, toxicity screening, and 3D tissue generation. Modulation of the retinoic acid signaling pathway has been shown to direct cardiomyocyte differentiation towards an atrial lineage. A variety of studies have successfully differentiated patient-specific atrial cardiac myocytes (hiPSC-aCM) and atrial engineered heart tissue (aEHT) that express atrial specific genes (e.g., sarcolipin and ANP) and exhibit atrial electrophysiological and contractility profiles. Identification of protocols to differentiate atrial cells from patients with atrial fibrillation and other inherited diseases or creating disease models using genetic mutation studies has shed light on the mechanisms of atrial-specific diseases and identified the efficacy of atrial-selective pharmacological compounds. hiPSC-aCMs and aEHTs can be used in drug discovery and drug screening studies to investigate the efficacy of atrial selective drugs on atrial fibrillation models. Furthermore, hiPSC-aCMs can be effective tools in studying the mechanism, pathophysiology and treatment options of atrial fibrillation and its genetic underpinnings. The main limitation of using hiPSC-CMs is their immature phenotype compared to adult CMs. A wide range of approaches and protocols are used by various laboratories to optimize and enhance CM maturation, including electrical stimulation, culture time, biophysical cues and changes in metabolic factors.

Myosin light chain 2 marks differentiating ventricular cardiomyocytes derived from human embryonic stem cells

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) have great value for studies of human cardiac development, drug discovery, disease modeling, and cell therapy. However, the mixed cardiomyocyte subtypes (ventricular-, atrial-, and nodal-like myocytes) and the maturation heterogeneity of hPSC-CMs restrain their application in vitro and in vivo. Myosin light chain 2 (MYL2, encoding the ventricular/cardiac muscle isoform MLC2v protein) is regarded as a ventricular-specific marker of cardiac myocardium; however, its restricted localization to ventricles during human heart development has been questioned. Consequently, it is currently unclear whether MYL2 definitively marks ventricular hESC-CMs. Here, by using a MYL2-Venus hESC reporter line, we characterized a time-dependent increase of the MYL2-Venus positive (MLC2v-Venus⁺) hESC-CMs during differentiation. We also compared the molecular, cellular, and functional properties between the MLC2v-Venus⁺ and MYL2-Venus negative (MLC2v-Venus^-) hESC-CMs. At early differentiation stages of hESC-CMs, we reported that both MLC2v-Venus^- and MLC2v-Venus⁺ CMs displayed ventricular-like traits but the ventricular-like cells from MLC2v-Venus⁺ hESC-CMs displayed more developed action potential (AP) properties than that from MLC2v-Venus^- hESC-CMs. Meanwhile, about a half MLC2v-Venus^- hESC-CM population displayed atrial-like AP properties, and a half showed ventricular-like AP properties, whereas only ~ 20% of the MLC2v-Venus^- hESC-CMs expressed the atrial marker nuclear receptor subfamily 2 group F member 2 (NR2F2, also named as COUPTFII). At late time points, almost all MLC2v-Venus⁺ hESC-CMs exhibited ventricular-like AP properties. Further analysis demonstrates that the MLC2v-Venus⁺ hESC-CMs had enhanced Ca²⁺ transients upon increase of the MLC2v level during cultivation. Concomitantly, the MLC2v-Venus⁺ hESC-CMs showed more defined sarcomeric structures and better mitochondrial function than those in the MLC2v-Venus^- hESC-CMs. Moreover, the MLC2v-Venus⁺ hESC-CMs were more sensitive to hypoxic stimulus than the MLC2v-Venus^- hESC-CMs. These results provide new insights into the development of human ventricular myocytes and reveal a direct correlation between the expression profile of MLC2v and ventricular hESC-CM development. Our findings that MLC2v is predominantly a ventricular marker in developmentally immature hESC-CMs have implications for human development, drug screening, and disease modeling, and this marker should prove useful in overcoming issues associated with hESC-CM heterogeneity.

Cancer and atrial fibrillation: Epidemiology, mechanisms, and anticoagulation treatment

Cancer patients are at an increased risk of developing atrial fibrillation (AF) and thrombosis. However, the management of anticoagulation in patients with both diseases may be challenging, and data on these patients are lacking. We summarize the current evidence on the incidence and prevalence of cancer in AF and vice versa and provide some practical considerations on the management of oral anticoagulation in specific clinical situations. Low-molecular weight heparins are not approved for thromboprophylaxis in AF, and management of warfarin can be difficult. The use of direct oral anticoagulants may be particularly attractive for their rapid onset/offset action and lower bleeding risk.

The Molecular Mechanisms of Cardiotoxicity Induced by HER2, VEGF, and Tyrosine Kinase Inhibitors: an Updated Review

AIM

In recent decades, there has been a revolutionary decrease in cancer-related mortality and an increase in survival due to the introduction of novel targeted drugs. Nevertheless, drugs targeting human epidermal growth factor receptor 2 (HER-2), angiogenesis, and other tyrosine kinases also come with unexpected cardiac side effects, including heart failure, hypertension, arterial thrombosis, and arrhythmias, and have mechanisms that are unlike those of classic chemotherapeutic agents. In addition, it is challenging to address some problems, as the existing guidelines need to be more specific, and further large-scale clinical trials and experimental studies are required to confirm the benefit of administering cardioprotective agents to patients treated with targeted therapies. Therefore, an improved understanding of cardiotoxicity becomes increasingly important to minimize the pernicious effects and maximize the beneficial effects of targeted agents.

METHODS

"Cardiotoxicity", "targeted drugs", "HER2", "trastuzumab", "angiogenesis inhibitor", "VEGF inhibitor" and "tyrosine kinase inhibitors" are used as keywords for article searches.

RESULTS

In this article, we report several targeted therapies that induce cardiotoxicity and update knowledge of the clinical evidence, molecular mechanisms, and management measures.

A randomized phase 3 trial of zanubrutinib vs ibrutinib in symptomatic Waldenström macroglobulinemia: the ASPEN study

Bruton tyrosine kinase (BTK) inhibition is an effective treatment approach for patients with Waldenström macroglobulinemia (WM). The phase 3 ASPEN study compared the efficacy and safety of ibrutinib, a first-generation BTK inhibitor, with zanubrutinib, a novel highly selective BTK inhibitor, in patients with WM. Patients with MYD88L265P disease were randomly assigned 1:1 to treatment with ibrutinib or zanubrutinib. The primary end point was the proportion of patients achieving a complete response (CR) or a very good partial response (VGPR) by independent review. Key secondary end points included major response rate (MRR), progression-free survival (PFS), duration of response (DOR), disease burden, and safety. A total of 201 patients were randomized, and 199 received ≥1 dose of study treatment. No patient achieved a CR. Twenty-nine (28%) zanubrutinib patients and 19 (19%) ibrutinib patients achieved a VGPR, a nonstatistically significant difference (P = .09). MRRs were 77% and 78%, respectively. Median DOR and PFS were not reached; 84% and 85% of ibrutinib and zanubrutinib patients were progression free at 18 months. Atrial fibrillation, contusion, diarrhea, peripheral edema, hemorrhage, muscle spasms, and pneumonia, as well as adverse events leading to treatment discontinuation, were less common among zanubrutinib recipients. Incidence of neutropenia was higher with zanubrutinib, although grade ≥3 infection rates were similar in both arms (1.2 and 1.1 events per 100 person-months). These results demonstrate that zanubrutinib and ibrutinib are highly effective in the treatment of WM, but zanubrutinib treatment was associated with a trend toward better response quality and less toxicity, particularly cardiovascular toxicity.

Use of hiPSC to explicate genomic predisposition to anthracycline-induced cardiotoxicity

The anticancer agents of the anthracycline family are commonly associated with the potential to cause severe toxicity to the heart. To solve the question of why particular a patient is predisposed to anthracycline-induced cardiotoxicity (AIC), researchers have conducted numerous pharmacogenomic studies and identified more than 60 loci associated with AIC. To date, none of these identified loci have been developed into US FDA-approved biomarkers for use in routine clinical practice. With advances in the application of human-induced pluripotent stem cell-derived cardiomyocytes, sequencing technologies and genomic editing techniques, variants associated with AIC can now be validated in a human model. Here, we provide a comprehensive overview of known genetic variants associated with AIC from the perspective of how human-induced pluripotent stem cell-derived cardiomyocytes can be used to help better explain the genomic predilection to AIC.

Melphalan induces cardiotoxicity through oxidative stress in cardiomyocytes derived from human induced pluripotent stem cells

BACKGROUND

Treatment-induced cardiotoxicity is a leading noncancer-related cause of acute and late onset morbidity and mortality in cancer patients on antineoplastic drugs such as melphalan-increasing clinical case reports have documented that it could induce cardiotoxicity including severe arrhythmias and heart failure. As the mechanism by which melphalan impairs cardiac cells remains poorly understood, here, we aimed to use cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CMs) to investigate the cellular and molecular mechanisms of melphalan-induced cardiotoxicity.

METHODS

hiPSC-CMs were generated and treated with clinically relevant doses of melphalan. To characterize melphalan-induced cardiotoxicity, cell viability and apoptosis were quantified at various treatment durations. Ca2+ transient and contractility analyses were used to examine the alterations of hiPSC-CM function. Proteomic analysis, reactive oxygen species detection, and RNA-Sequencing were conducted to investigate underlying mechanisms.

RESULTS

Melphalan treatment of hiPSC-CMs induced oxidative stress, caused Ca2+ handling defects and dysfunctional contractility, altered global transcriptomic and proteomic profiles, and resulted in apoptosis and cell death. The antioxidant N-acetyl-L-cysteine attenuated these genomic, cellular, and functional alterations. In addition, several other signaling pathways including the p53 and transforming growth factor-β signaling pathways were also implicated in melphalan-induced cardiotoxicity according to the proteomic and transcriptomic analyses.

CONCLUSIONS

Melphalan induces cardiotoxicity through the oxidative stress pathway. This study provides a unique resource of the global transcriptomic and proteomic datasets for melphalan-induced cardiotoxicity and can potentially open up new clinical mechanism-based targets to prevent and treat melphalan-induced cardiotoxicity.

Human Pluripotent Stem Cell-Derived Cardiovascular Cells: From Developmental Biology to Therapeutic Applications

Advances in our understanding of cardiovascular development have provided a roadmap for the directed differentiation of human pluripotent stem cells (hPSCs) to the major cell types found in the heart. In this Perspective, we review the state of the field in generating and maturing cardiovascular cells from hPSCs based on our fundamental understanding of heart development. We then highlight their applications for studying human heart development, modeling disease-performing drug screening, and cell replacement therapy. With the advancements highlighted here, the promise that hPSCs will deliver new treatments for degenerative and debilitating diseases may soon be fulfilled.

Drug screening platform using human induced pluripotent stem cell-derived atrial cardiomyocytes and optical mapping

Current drug development efforts for the treatment of atrial fibrillation are hampered by the fact that many preclinical models have been unsuccessful in reproducing human cardiac physiology and its response to medications. In this study, we demonstrated an approach using human induced pluripotent stem cell-derived atrial and ventricular cardiomyocytes (hiPSC-aCMs and hiPSC-vCMs, respectively) coupled with a sophisticated optical mapping system for drug screening of atrial-selective compounds in vitro. We optimized differentiation of hiPSC-aCMs by modulating the WNT and retinoid signaling pathways. Characterization of the transcriptome and proteome revealed that retinoic acid pushes the differentiation process into the atrial lineage and generated hiPSC-aCMs. Functional characterization using optical mapping showed that hiPSC-aCMs have shorter action potential durations and faster Ca²⁺ handling dynamics compared with hiPSC-vCMs. Furthermore, pharmacological investigation of hiPSC-aCMs captured atrial-selective effects by displaying greater sensitivity to atrial-selective compounds 4-aminopyridine, AVE0118, UCL1684, and vernakalant when compared with hiPSC-vCMs. These results established that a model system incorporating hiPSC-aCMs combined with optical mapping is well-suited for preclinical drug screening of novel and targeted atrial selective compounds.

Human In Vitro Models for Assessing the Genomic Basis of Chemotherapy-Induced Cardiovascular Toxicity

Chemotherapy-induced cardiovascular toxicity (CICT) is a well-established risk for cancer survivors and causes diseases such as heart failure, arrhythmia, vascular dysfunction, and atherosclerosis. As our knowledge of the precise cardiovascular risks of each chemotherapy agent has improved, it has become clear that genomics is one of the most influential predictors of which patients will experience cardiovascular toxicity. Most recently, GWAS-led, top-down approaches have identified novel genetic variants and their related genes that are statistically related to CICT. Importantly, the advent of human-induced pluripotent stem cell (hiPSC) models provides a system to experimentally test the effect of these genomic findings in vitro, query the underlying mechanisms, and develop novel strategies to mitigate the cardiovascular toxicity liabilities due to these mechanisms. Here we review the cardiovascular toxicities of chemotherapy drugs, discuss how these can be modeled in vitro, and suggest how these models can be used to validate genetic variants that predispose patients to these effects.

Multicellular In vitro Models of Cardiac Arrhythmias: Focus on Atrial Fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia in clinical practice with a large socioeconomic impact due to its associated morbidity, mortality, reduction in quality of life and health care costs. Currently, antiarrhythmic drug therapy is the first line of treatment for most symptomatic AF patients, despite its limited efficacy, the risk of inducing potentially life-threating ventricular tachyarrhythmias as well as other side effects. Alternative, in-hospital treatment modalities consisting of electrical cardioversion and invasive catheter ablation improve patients' symptoms, but often have to be repeated and are still associated with serious complications and only suitable for specific subgroups of AF patients. The development and progression of AF generally results from the interplay of multiple disease pathways and is accompanied by structural and functional (e.g., electrical) tissue remodeling. Rational development of novel treatment modalities for AF, with its many different etiologies, requires a comprehensive insight into the complex pathophysiological mechanisms. Monolayers of atrial cells represent a simplified surrogate of atrial tissue well-suited to investigate atrial arrhythmia mechanisms, since they can easily be used in a standardized, systematic and controllable manner to study the role of specific pathways and processes in the genesis, perpetuation and termination of atrial arrhythmias. In this review, we provide an overview of the currently available two- and three-dimensional multicellular in vitro systems for investigating the initiation, maintenance and termination of atrial arrhythmias and AF. This encompasses cultures of primary (animal-derived) atrial cardiomyocytes (CMs), pluripotent stem cell-derived atrial-like CMs and (conditionally) immortalized atrial CMs. The strengths and weaknesses of each of these model systems for studying atrial arrhythmias will be discussed as well as their implications for future studies.

Modulating cardiomyocyte and fibroblast interaction using layer-by-layer deposition facilitates synchronisation of cardiac macro tissues

Maturation and synchronisation of heart cells, including cardiomyocytes and fibroblasts, are essential to develop functional biomimetic cardiac tissues for regenerative medicine and drug discovery. Synchronisation of cells in the biomimetic cardiac tissue requires the structural integrity and functional maturation of cardiomyocytes with other cell types. However, it is challenging to synchronise the beating of macroscale cardiac tissues and induce maturation of cardiomyocytes derived from stem cells. Here, we developed a simple assembly technology to modulate cell-cell interactions by combining layer-by-layer (LBL) deposition and centrifugation of cells with collagen type I to control cell-cell interactions for the preparation of cardiac macro tissues (CMTs). We found that maturation of cardiomyocytes in CMTs was largely enhanced by growth factors FGF-4 and ascorbic acid, but synchronisation of cardiac beating required LBL deposition of cardiomyocytes and cardiac fibroblasts in addition to the growth factors during the maturation process. Our findings have important implications because incorporation of cardiac fibroblasts into the cardiomyocyte layer is a prerequisite for synchronised beating of macroscale cardiac tissues in addition to growth factors to facilitate maturation of stem cell-derived cardiomyocytes.