Varsha G. Desai

Anthracycline-induced cardiotoxicity remains a major clinical challenge, often progressing to heart failure years after therapy. Conventional cardioprotective agents, including angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and beta-blockers, are widely used to preserve cardiac function; however, their effectiveness is limited by their inability to comprehensively address the complex, multifactorial pathophysiology of anthracycline-induced cardiotoxicity. This underscores the critical need for more effective and mechanism-based cardioprotective strategies that directly target the underlying molecular mechanisms, particularly oxidative stress and mitochondrial dysfunction. In recent years, the apelin-APJ signalling axis has attracted increasing attention as a potential therapeutic target in cardiovascular diseases owing to its multifaceted biological actions, including positive inotropy, vasodilation, anti-inflammatory, anti-fibrotic, anti-apoptotic, antioxidant, and pro-angiogenic effects. These pleiotropic actions are primarily mediated through the activation of key signalling pathways such as phosphoinositide 3-kinase/protein kinase B, extracellular signal-regulated kinases 1/2, and AMP-activated protein kinase. Given that these signalling cascades are disrupted during anthracycline-induced cardiotoxicity, pharmacological activation of the apelin-APJ axis may represent a promising avenue to mitigate anthracycline-associated cardiac injury with greater efficacy than conventional therapies. While native apelin isoforms (apelin-12, -13, -17, and [Pyr¹]apelin-13) are limited by their short half-lives, chemically modified analogues such as LIT01-196 and apelin-17(A2) exhibit enhanced stability and efficacy, with demonstrated cardioprotective effects in preclinical cardiovascular models and patients with chronic heart failure. However, their therapeutic potential in anthracycline-induced cardiotoxicity remains largely unexplored. This review highlights its promise as a novel cardioprotective strategy for mitigating anthracycline-induced cardiotoxicity.

Anthracycline-induced cardiotoxicity poses a threat to the long-term heart health of childhood cancer survivors; however, early risk assessment remains challenging due to limited predictive tools. While risk prediction models have been developed for chemotherapy-related hematological toxicity in pediatric cancer patients, research efforts addressing anthracycline-induced cardiotoxicity in this population remain limited. To fill this gap, we conducted a pilot study to develop a risk prediction model for anthracycline-induced cardiotoxicity in children. Using a paired-sample design, we analyzed data collected throughout treatment from 18 children receiving anthracycline-based chemotherapy. Patient demographics, clinical features, and treatment regimen served as input (explanatory) variables, while plasma concentration of high-sensitivity cardiac troponin T was used as the outcome (response), representing anthracycline-induced myocardial injury. Of the initial 33 potential variables, the top 18 were selected based on their importance scores in relation to myocardial injury. This set was further refined to 13 by removing redundancies using the caret package in R to develop a preliminary logistic regression model. A Leave-One-Patient-Out Cross-Validation identified four key predictors for the final model: sex, age at diagnosis, total cyclophosphamide dose (mg), and days since the first anthracycline dose. All were significantly associated with myocardial injury. The final logistic regression model achieved an accuracy of 85%, a sensitivity of 80%, a specificity of 88%, an area under the curve of 0.89, and a Youden’s index of 0.68 for predicting myocardial injury risk. These preliminary findings suggest the potential of our predictive model to stratify risk of anthracycline-induced myocardial injury in the pediatric population. Graphical Abstract

Preclinical and clinical findings suggest sexual dimorphism in cardiotoxicity induced by a chemotherapeutic drug, doxorubicin (DOX). However, molecular alterations leading to sex‐related differential vulnerability of heart to DOX toxicity are not fully explored. In the present study, RNA sequencing in hearts of B6C3F₁ mice indicated more differentially expressed genes in males than females (224 vs. 19; ≥1.5‐fold, False Discovery Rate [FDR] < 0.05) at 1 week after receiving 24 mg/kg total cumulative DOX dose that induced cardiac lesions only in males. Pathway analysis further revealed probable inactivation of cardiac apelin fibroblast signaling pathway (p = 0.00004) only in DOX‐treated male mice that showed ≥1.25‐fold downregulation in the transcript and protein levels of the apelin receptor, APJ. In hearts of DOX‐treated females, the transcript levels of apelin (1.24‐fold) and APJ (1.47‐fold) were significantly (p < 0.05) increased compared to saline‐treated controls. Sex‐related differential DOX effect was also observed on molecular targets downstream of the apelin‐APJ pathway in cardiac fibroblasts and cardiomyocytes. In cardiac fibroblasts, upregulation of Tgf‐β2, Ctgf, Sphk1, Serpine1, and Timp1 (fibrosis; FDR < 0.05) in DOX‐treated males and upregulation of only Tgf‐β2 and Timp1 (p < 0.05) in females suggested a greater DOX toxicity in hearts of males than females. Additionally, Ryr2 and Serca2 (calcium handling; FDR < 0.05) were downregulated in conjunction with 1.35‐fold upregulation of Casp12 (sarcoplasmic reticulum‐mediated apoptosis; FDR < 0.05) in DOX‐treated male mice. Drug effect on the transcript level of these genes was less severe in female hearts. Collectively, these data suggest a likely role of the apelin‐APJ axis in sex‐related differential DOX‐induced cardiotoxicity in our mouse model.

Cardiotoxicity is a serious adverse effect of an anticancer drug, doxorubicin (DOX), which can occur within a year or decades after completion of therapy. The present study was designed to address a knowledge gap concerning a lack of circulating biomarkers capable of predicting the risk of cardiotoxicity induced by DOX. Profiling of 2083 microRNAs (miRNAs) in mouse plasma revealed 81 differentially expressed miRNAs 1 week after 6, 9, 12, 18, or 24 mg/kg total cumulative DOX doses (early‐onset model) or saline (SAL). Among these, the expression of seven miRNAs was altered prior to the onset of myocardial injury at 12 mg/kg and higher cumulative doses. The expression of only miR‐34a‐5p was significantly (false discovery rate [FDR] < 0.1) elevated at all total cumulative doses compared with concurrent SAL‐treated controls and showed a statistically significant dose‐related response. The trend in plasma miR‐34a‐5p expression levels during DOX exposures also correlated with a significant dose‐related increase in cardiac expression of miR‐34a‐5p in these mice. Administration of a cardioprotective drug, dexrazoxane, to mice before DOX treatment, significantly mitigated miR‐34a‐5p expression in both plasma and heart in conjunction with attenuation of cardiac pathology. This association between plasma and heart may suggest miR‐34a‐5p as a potential early circulating marker of early‐onset DOX cardiotoxicity. In addition, higher expression of miR‐34a‐5p (FDR < 0.1) in plasma and heart compared with SAL‐treated controls 24 weeks after 24 mg/kg total cumulative DOX dose, when cardiac function was altered in our recently established delayed‐onset cardiotoxicity model, indicated its potential as an early biomarker of delayed‐onset cardiotoxicity.

Subclinical cardiotoxicity at low total cumulative doxorubicin (DOX) doses can manifest into cardiomyopathy in long‐term cancer survivors. However, the underlying mechanisms are poorly understood. In male B6C3F₁ mice, assessment of cardiac function by echocardiography was performed at 1, 4, 10, 17, and 24 weeks after exposure to 6, 9, 12, and 24 mg/kg total cumulative DOX doses or saline (SAL) to monitor development of delayed‐onset cardiotoxicity. The 6‐ or 9‐mg/kg total cumulative doses resulted in a significant time‐dependent decline in systolic function (left ventricular ejection fraction (LVEF) and fractional shortening (FS)) during the 24‐week recovery although there was not a significant alteration in % LVEF or % FS at any specific time point during the recovery. A significant decline in systolic function was elicited by the cardiotoxic cumulative DOX dose (24 mg/kg) during the 4‐ to 24‐week period after treatment compared to SAL‐treated counterparts. At 24 weeks after DOX treatment, a significant dose‐related decrease in the expression of genes and proteins involved in sarcoplasmic reticulum (SR) calcium homeostasis (Ryr2 and Serca2) was associated with a dose‐related increase in the transcript level of Casp12 (SR‐specific apoptosis) in hearts. These mice also showed enhanced apoptotic activity in hearts indicated by a significant dose‐related elevation in the number of apoptotic cardiomyocytes compared to SAL‐treated counterparts. These findings collectively suggest that a steady decline in SR calcium handling and apoptosis might be involved in the development of subclinical cardiotoxicity that can evolve into irreversible cardiomyopathy later in life.

Physiological factors such as age and sex have been shown to be risk factors for adverse effects in the liver, including liver diseases and drug-induced liver injury. Previously, we have reported age- and sex-related significant differences in hepatic basal gene expression in rats during the life span that may be related to susceptibility to such adverse effects. However, the underlying mechanisms of the gene expression changes were not fully understood. In recent years, increasing evidence for epigenetic mechanisms of gene regulation has fueled interest in the role of microRNAs (miRNAs) in toxicogenomics and biomarker discovery. We therefore proposed that significant age and sex differences exist in baseline liver miRNA expression, and that comprehensive profiling of miRNAs will provide insights into the epigenetic regulation of gene expression in rat liver. To address this, liver tissues from male and female F344 rats were examined at 2, 5, 6, 8, 15, 21, 52, 78, and 104 weeks of age for the expression of 677 unique miRNAs. Following data processing, predictive pathway analysis was performed on selected miRNAs that exhibited prominent age and/or sex differences in expression. Of the 314 miRNAs found to be expressed, 214 were differentially expressed; 65 and 212 miRNAs showed significant (false discovery rate (FDR) <5% and ≥1.5-fold change) sex- and age-related differences in expression, respectively. Thirty-eight miRNAs showed 2-week-specific expression, of which 31 miRNAs were found to be encoded within the Dlk1-Dio3 cluster located on chromosome 6. This cluster has been associated with tissue proliferation and differentiation, and liver energy homeostasis in postnatal development. Predictive pathway analysis linked sex-biased miRNA expression with sexually dimorphic molecular functions and toxicological functions that may reflect sex differences in hepatic physiology and disease. The expression of miRNAs (miR-18a, miR-99a, and miR-203, miR-451) was also found to associate with specific sexually dimorphic hepatic histopathology. The expression of miRNAs involved in regulating cell death, cell proliferation, and cell cycle was found to change as the rats matured from adult to old age. Overall, significant age- and sex-related differences in liver miRNA expression were identified and linked to histopathological findings and predicted functional pathways that may underlie susceptibilities to liver toxicity and disease.