Digoxin treatment is associated with an increased incidence of breast cancer: a population-based case-control study

Drug Repurposing Strategies for Non-Cancer to Cancer Therapeutics

Global efforts invested for the prevention and treatment of cancer need to be repositioned to develop safe, effective, and economic anticancer therapeutics by adopting rational approaches of drug discovery. Drug repurposing is one of the established approaches to reposition old, clinically approved off patent noncancer drugs with known targets into newer indications. The literature review suggests key role of drug repurposing in the development of drugs intended for cancer as well as noncancer therapeutics. A wide category of noncancer drugs namely, drugs acting on CNS, anthelmintics, cardiovascular drugs, antimalarial drugs, anti-inflammatory drugs have come out with interesting outcomes during preclinical and clinical phases. In the present article a comprehensive overview of the current scenario of drug repurposing for the treatment of cancer has been focused. The details of some successful studies along with examples have been included followed by associated challenges.

Cardiac Glycoside Ouabain Exerts Anticancer Activity via Downregulation of STAT3

Cardiac glycosides are plant-derived steroid-like compounds which have been used for the treatment of cardiovascular diseases. Ouabain, a cardiotonic steroid and specific Na⁺/K⁺-ATPase inhibitor, has been rediscovered for its potential use in the treatment of cancer. However, the cellular targets and anticancer mechanism of ouabain in various cancers remain largely unexplored. In this study, we confirmed the cytotoxic effects of ouabain on several cancer cell lines. Further examination revealed the increase of apoptosis, intracellular ROS generation and DNA double-strand breaks induced by ouabain treatment. Besides, ouabain effectively suppressed STAT3 expression as well as phosphorylation in addition to block STAT3-mediated transcription and downstream target proteins. Interestingly, these inhibitory activities seemed to be independent of the Na⁺/K⁺-ATPase. Furthermore, we found that ouabain inhibited protein synthesis through regulation of the eukaryotic initiation factor 4E (eIF4E) and eIF4E binding protein 1 (4EBP1). Taken together, our study provided a novel molecular insight of anticancer activities of ouabain in human cancer cells, which could raise the hope of using cardiac glycosides for cancer therapeutics more rational.

Association Between Digoxin Use and Cancer Incidence: A Propensity Score-Matched Cohort Study With Competing Risk Analysis

Background: Previous studies neglected death as a critical competing risk while estimating the cancer risk for digoxin users. Therefore, the current study aims to assess the effectiveness of digoxin on cancer prevention by competing risk analysis. Methods: We performed a population-based retrospective cohort study using the Taiwan National Health Insurance Research database between 1998 and 2010. After one-to-one propensity score-matching from 36,160 patients with defined criteria, we enrolled 758 patients both in digoxin and β-blocker group for further analysis. Results: The results showed that the digoxin group had higher all-cause mortality than the β-blocker group in the 4- year (10.4 vs. 4.9%) and 8 years (13.6 vs. 7.0%) follow-up. The subdistribution HR of cancer incidence in the digoxin group compared to the β-blocker group was 1.99 (95% confidence interval [CI]: 1.22-3.01) and 1.46 (95% CI: 1.01-2.15) in the 4 years and 8 years follow-up, respectively. Conclusions: The result of our study showed the usage of digoxin has no benefit in cancer prevention compared with β-blocker. The possibility of β-blocker as a new drug candidate for cancer prevention needs further clinical evaluation. The current study also emphasized the necessity of competing risk analysis applying to similar clinical researches.

Digoxin use is associated with pancreatic cancer risk but does not affect survival

PURPOSE

Digoxin affects several cellular pathways involved in tumorigenesis. We sought to determine the association between digoxin use and pancreatic cancer risk and survival.

METHODS

A nested case-control study using The Health Improvement Network (THIN), a population-representative database from the United Kingdom (UK). Cases included all individuals with incident diagnosis of pancreatic cancer. Each case was matched to up to four controls using incidence density sampling based on age, sex, practice site, calendar time, and duration of follow-up. Exposure of interest was digoxin therapy before cancer diagnosis. Odds ratios (ORs) and 95% confidence intervals (CIs) for the association between digoxin use and pancreatic cancer risk were estimated using conditional logistic regression. We further conducted a retrospective cohort study among pancreatic cancer cases using Cox regression model in order to evaluate the association between digoxin use and overall survival.

RESULTS

We identified 4,113 cases with incident pancreatic cancer and 16,072 matched controls. The adjusted OR for diagnosis of pancreatic cancer among active digoxin users was 1.41 (95% CI 1.16-1.72). The risk did not change among active users with duration of therapy of more than 1 year (adjusted OR of 1.39, 95% CI 1.11-1.76). Digoxin was not associated with change in overall survival with an adjusted hazard ratio of 0.97 (95% CI 0.81-1.18).

CONCLUSIONS

Digoxin use was associated with modestly increased pancreatic cancer risk but did not affect overall survival.

The Association of New-Onset Atrial Fibrillation and Risk of Cancer: A Systematic Review and Meta-Analysis

Background

There are distinct results for the relationship between new-onset atrial fibrillation (NOAF) and subsequent incident cancer. To date, no systematic analysis has been conducted on this issue. This study aims to explore the relationship between NOAF and the risk of developing cancer through a meta-analysis with a large sample size.

Methods

Electronic databases, such as PubMed and EMBASE, were searched for published relevant studies on NOAF patients diagnosed with cancer after and during follow-ups, including reported records of baseline information and the statistical result of morbidity. Two investigators independently reviewed the articles and extracted the data using uniform standards and definitions. The meta-analysis was conducted using the Cochrane Program Review Manager.

Results

This meta-analysis consisted of five cohort studies and one case-control study, which comprised 533,514 participants. The pooled relative risk (RR) for incident cancer was 1.24 (95% CI: 1.10–1.39, P=0.0003). The temporal trend analysis demonstrated that an increased risk of cancer was observed during the initial 90 days (RR: 3.44, 95% CI: 2.29–5.57, P < 0.00001), but not after that. Lung cancer (RR: 1.51, 95% CI: 1.47–1.55, P < 0.00001) was associated with NOAF, but not colorectal cancer and breast cancer.

Conclusion

This meta-analysis provides evidence that NOAF is associated with increased risk of cancer. The risk of incident cancer particularly increases within 90 days after NOAF diagnosis, but not after that.

Differential risk of incident cancer in patients with heart failure: A nationwide population-based cohort study

BACKGROUND

Heart failure (HF) and cancer are currently two leading causes of mortality, and sometimes coexist. However, the relationship between them is not completely elucidated. We aimed to investigate whether patients with HF are predisposed to cancer development using the large Korean National Health Insurance claims database.

METHODS

This study included 128,441 HF patients without a history of cancer and 642,205 age- and sex-matched individuals with no history of cancer and HF between 1 January 2010 and 31 December 2015.

RESULTS

During a median follow-up of 4.06 years, 11,808 patients from the HF group and 40,805 participants from the control were newly diagnosed with cancer (cumulative incidence, 9.2% vs. 6.4%, p < 0.0001). Patients with HF presented a higher risk for cancer development compared to controls in multivariable Cox analysis [hazard ratio (HR) 1.64, 95% confidence interval (CI) 1.61-1.68]. The increased risk was consistent for all site-specific cancers. To minimize potential surveillance bias, additional analysis was performed by eliminating participants who developed cancer within the initial 2 years of HF diagnosis (i.e. 2-year lag analysis). In the 2-year lag analysis, the higher risk of overall cancer remained significant in patients with HF (HR 1.09, 95% CI 1.05-1.13), although the association was weaker. Among the site-specific cancers, three types of cancer (lung, liver/biliary/pancreas, and hematologic malignancy) were consistently at higher risk in patients with HF. An exploratory analysis showed that patients with repeated HF hospitalization had a higher risk of cancer development compared to those without, in a pattern of stepwise increases across the three groups [controls vs. HF without re-hospitalization vs. HF with re-hospitalization ≥1; HR (95% CI), 1.00 (reference) vs. 1.55 (1.51-1.59) vs. 1.96 (1.89-2.03), respectively].

CONCLUSIONS

Cancer incidence is higher in patients with HF than the general population. Active surveillance of coexisting malignancy needs to be considered in these patients.

Cinobufagin Triggers Defects in Spindle Formation and Cap-Dependent Translation in Liver Cancer Cells by Inhibiting the AURKA-mTOR-eIF4E Axis

Cinobufagin is a Na+/K+-ATPase (NKA) inhibitor with excellent anticancer effects to prolong the survival of patients. The purpose of the present study was to clarify the underlying mechanism of the anticancer effects of cinobufagin using overexpression or inhibition of aurora kinase A (AURKA) signaling. First, high expression of Na+/K+-ATPase alpha 1 subunit (ATP1A1) and AURAK resulted in increased malignant transformation in hepatocellular carcinoma (HCC) patients using the cancer genome atlas (TCGA) data and tissue samples. After treatment with cinobufagin, we successfully screened 202, 249, and 335 changing expression proteins in Huh-7 cells under normal, overexpression, and inhibition of AURKA using tandem mass tags (TMT)-labeled quantitative proteomics coupled to 2D liquid chromatography-tandem mass spectrometry (LC-MS/MS). Bioinformatics analysis revealed that these molecules were closely associated with chromosome segregation, DNA damage, and regulation of translation processes. We further confirmed that cinobufagin induced DNA damage and chromosome segregation disorders and suppresses translational processing in oncogenes by decreasing the expression of AURKA, mechanistic target of rapamycin kinase (mTOR), p-mTOR, p-extracellular regulated protein kinases (ERK), eukaryotic translation initiation factor 4E (eIF4E), and p-eIF4E, while increasing the expression of p-eukaryotic translation initiation factor 4E binding protein 1 (4E-BP1) (S65, T37, T46, T45) and increasing the interaction between eIF4 and 4E-BP1. Our results suggested that cinobufagin performed an antitumor effects in liver cancer cells by inhibiting the AURKA-mTOR-eIF4E axis.

Cardiac glycosides with target at direct and indirect interactions with nuclear receptors

Cardiac glycosides are compounds isolated from plants and animals and have been known since ancient times. These compounds inhibit the activity of the sodium potassium pump in eukaryotic cells. Cardiac glycosides were used as drugs in heart ailments to increase myocardial contraction force and, at the same time, to lower frequency of this contraction. An increasing number of studies have indicated that the biological effects of these compounds are not limited to inhibition of sodium-potassium pump activity. Furthermore, an increasing number of data have shown that they are synthesized in tissues of mammals, where they may act as a new class of steroid hormones or other hormones by mimicry to modulate various signaling pathways and influence whole organisms. Thus, we discuss the interactions of cardiac glycosides with the nuclear receptor superfamily of transcription factors activated by low-weight molecular ligands (including hormones) that regulate many functions of cells and organisms. Cardiac glycosides of endogenous and exogenous origin by interacting with nuclear receptors can affect the processes regulated by these transcription factors, including hormonal management, immune system, body defense, and carcinogenesis. They can also be treated as initial structures for combinatorial chemistry to produce new compounds (including drugs) with the desired properties.

Digoxin use and following risk of psoriasis: A population-based cohort study in Taiwan

This study examined the association between digoxin use and subsequent psoriasis risk using a population-based database in Taiwan. This cohort study enrolled 15 545 digoxin users and 15 545 propensity score-matched non-users from the Taiwan National Health Insurance Research Database. Each patient was independently followed up for 5 years to confirm whether they had been diagnosed with psoriasis. Cox proportional hazard regression was used to estimate psoriasis risk among digoxin users. Subgroup and sensitivity analyses were also performed. The psoriasis incidence rates were 3.02 and 2.27 per 1000 person-years among digoxin users and non-users, respectively. After adjustment for confounders, psoriasis risk was significantly higher among digoxin users than among non-users. Notably, in most subgroup analyses, digoxin use tended to increase psoriasis risk, particularly among patients with heart failure, diabetes, hypertension and hyperlipidaemia. Moreover, significantly increased psoriasis risk was noted over 2, 3, 4 and 5 years of digoxin use. In conclusion, our findings confirm that digoxin use increases subsequent psoriasis risk. Thus, physicians should be aware of this association and accordingly estimate the risks and benefits of digoxin use. Nevertheless, some patient variables, such as body mass index and obesity, were unavailable in this study. The findings in this study should be elucidated carefully because the potential effects of these factors could not be considered.

Integrative analysis of clinical and bioinformatics databases to identify anticancer properties of digoxin

Cardiac glycosides, such as digoxin, inhibit Na⁺/K⁺-ATPases and cause secondary activation of Na⁺/Ca²⁺ exchangers. Preclinical investigations have suggested that digoxin may have anticancer properties. In order to clarify the functional mechanisms of digoxin in cancer, we performed an integrative analysis of clinical and bioinformatics databases. The US Food and Drug Administration Adverse Event Reporting System and the Japan Medical Data Center claims database were used as clinical databases to evaluate reporting odds ratios and adjusted sequence ratios, respectively. The BaseSpace Correlation Engine and Connectivity Map bioinformatics databases were used to investigate molecular pathways related to digoxin anticancer mechanisms. Clinical database analyses suggested an inverse association between digoxin and four cancers: gastric, colon, prostate and haematological malignancy. The bioinformatics database analysis suggested digoxin may exert an anticancer effect via peroxisome proliferator-activated receptor α and apoptotic caspase cascade pathways. Our integrative analysis revealed the possibility of digoxin as a drug repositioning candidate for cancers.

Atrial Fibrillation and Heart Failure in Women

Atrial fibrillation often occurs as a cause or consequence of heart failure. Clinical outcomes are worse when atrial fibrillation and heart failure coexist. There are important sex-related differences in the incidence, prevalence, pathophysiology, treatment, and outcomes of these patients. Women with heart failure are at greater risk of developing atrial fibrillation than men, and more women with atrial fibrillation develop heart failure. More women die of atrial fibrillation-related strokes. Despite significant morbidity and mortality, current treatments for women are inadequate. This review explores sex differences in atrial fibrillation and heart failure, emphasizing risk stratification and treatments to improve clinical outcomes.

Cardenolides: Insights from chemical structure and pharmacological utility

Cardiac glycosides (CGs) are a class of naturally occurring steroid-like compounds, and members of this class have been in clinical use for more than 1500 years. They have been used in folk medicine as arrow poisons, abortifacients, heart tonics, emetics, and diuretics as well as in other applications. The major use of CGs today is based on their ability to inhibit the membrane-bound Na⁺/K⁺-ATPase enzyme, and they are regarded as an effective treatment for congestive heart failure (CHF), cardiac arrhythmia and atrial fibrillation. Furthermore, increasing evidence has indicated the potential cytotoxic effects of CGs against various types of cancer. In this review, we highlight some of the structural features of this class of natural products that are crucial for their efficacy, some methods of isolating these compounds from natural resources, and the structural elucidation tools that have been used. We also describe their physicochemical properties and several modern biotechnological approaches for preparing CGs that do not require plant sources.

Risk of cancer in patients with heart failure who use digoxin: a 10-year follow-up study and cell-based verification

Heart failure (HF) is the leading cause of death in the world and digoxin remains one of the oldest therapies for HF. However, its safety and efficacy have been controversial since its initial use and there is uncertainty about its long-term efficacy and safety. Recently, the repositioning of cardiac glycosides is to function in anti-tumor activity via multiple working pathways. It is interesting to compare the potential effects of digoxin in clinical patients and cell lines. First, we analyze patient information retrieved from the National Health Insurance Research database of Taiwan between January 1, 2000 and December 31, 2000. This retrospective study included a study cohort (1,219 patients) and a comparison cohort. Our analytical data suggested that patients taking digoxin are at an increased risk of cancers, including breast, liver, and lung cancers, during the 10-year follow-up period. In contrast to the anti-tumor function of digoxin, we further examined the potential pathway of digoxin via the cell-based strategy using several breast cancer cell lines, including MCF-7, BT-474, MAD-MB-231, and ZR-75-1. Digoxin consistently exerted its cytotoxicity to these four cell lines with various range of concentration. However, the proliferation of ZR-75-1 cells was the only cell lines induced by digoxin and the others were dramatically suppressed by digoxin. The responsiveness of SRSF3 to digoxin might be involved with cell-type differences. In summary, we combined a cohort study for digoxin treatment for HF patients with a cell-based strategy that addresses the translation issue, which revealed the complexity of personalized medicine.

Concurrent new drug prescriptions and prognosis of early breast cancer: studies using the Danish Breast Cancer Group clinical database

BACKGROUND

Myriad reports suggest that frequently used prescription drugs alter the viability of breast cancer cells in pre-clinical studies. Routine use of these drugs, therefore, may impact breast cancer prognosis, and could have important implications for public health.

METHODS

The Danish Breast Cancer Group (DBCG) clinical database provides high-quality prospectively collected data on breast cancer diagnosis, treatment, and routine follow-up for breast cancer recurrence. Individual-level linkage of DBCG data to other population-based and medical registries in Denmark, including the Danish National Prescription Registry, has facilitated large population-based pharmacoepidemiology studies. A unique advantage of using DBCG data for such studies is the ability to investigate the association of drugs with breast cancer recurrence rather than breast cancer mortality - which may be misclassified - or all-cause mortality. Here we summarize findings from pharmacoepidemiological studies, based on DBCG data, on the association between routinely used prescription drugs and risk of breast cancer recurrence.

RESULTS

Our findings suggest that concurrent use of glucocorticoids, ACE inhibitors, aspirin, NSAIDs, selective COX-2 inhibitors, digoxin, and opioids has little impact on breast cancer recurrence. Similarly, patients who use SSRIs concurrently with tamoxifen treatment are not at increased risk of recurrence. In contrast, post-diagnostic use of simvastatin, a lipophilic statin, correlates with a decreased risk of breast cancer recurrence, providing a rationale for a prospective randomized clinical trial investigating simvastatin as an adjuvant therapy for breast cancer.

CONCLUSION

As a whole, findings of pharmacoepidemiological studies based on DBCG data provide reassurance to physicians and healthcare personnel who provide supportive care during and after cancer (including prescriptions for comedications) and to breast cancer survivors for whom the risk of breast cancer recurrence is a major concern.

Digitalis Use and the Risk of Breast Cancer: A Systematic Review and Meta-Analysis

INTRODUCTION

Previous epidemiological studies have indicated an increased risk of breast cancer associated with digitalis medication, though results are inconsistent. We performed this systematic review of available epidemiological studies to clarify the association between digitalis use and the risk of breast cancer.

METHODS

A search of studies published through May 2016 in MEDLINE and EMBASE databases was performed, supplemented by manual searches of reference lists. The quality of the included studies was assessed, and relative risks were pooled using both random- and fixed-effect models.

RESULTS

Three case-control studies and six cohort studies were identified. Meta-analysis generated a pooled relative risk of 1.35 (95% confidence interval 1.24-1.46) in both fixed- and random-effect models. The heterogeneity test suggested low heterogeneity across studies. The funnel plot suggested no existence of publication bias. Subgroup analysis by study design revealed an increased risk of breast cancer associated with digitalis use from cohort studies only (relative risk = 1.39, 95% confidence interval 1.27-1.52), rather than from case-control studies. Studies with adjustment for tobacco smoking or body mass index generated lower overall estimates than those not adjusted.

CONCLUSIONS

Existing epidemiological evidence regarding the association between digitalis use and the risk of breast cancer remains inconclusive and more well-designed studies are still needed.

Management of Heart Failure in Cancer Patients and Cancer Survivors

The number of cancer survivors increases annually, because of advances in detection and treatment, and the aging and growth of the population. This increase has brought a concomitant increase in morbidity and mortality from other conditions related to the adverse effects of cancer treatments. Cardiovascular diseases, and in particular left ventricular dysfunction and heart failure, are among the most significant of these. There are no unified and universally accepted evidence-based practice guidelines on the management of heartfailure in this population. This article discusses the epidemiologic impact of cancer therapeutics-related cardiac dysfunction, and reviews its most significant mediators and provides a condensed but comprehensive synopsis on its evaluation and management.

Cardiac glycosides use and the risk and mortality of cancer; systematic review and meta-analysis of observational studies

BACKGROUND

Cardiac glycosides (CGs) including digitalis, digoxin and digitoxin are used in the treatment of congestive heart failure and atrial fibrillation. Pre-clinical studies have investigated the anti-neoplastic properties of CGs since 1960s. Epidemiological studies concerning the association between CGs use and cancer risk yielded inconsistent results. We have performed a systematic review and meta-analysis to summarize the effects of CGs on cancer risk and mortality.

METHODS

PubMed, Scopus, Cochrane library, Medline and Web of Knowledge were searched for identifying relevant studies. Summary relative risks (RR) and 95% confidence intervals (CI) were calculated using random-effects model.

RESULTS

We included 14 case-control studies and 15 cohort studies published between 1976 and 2016 including 13 cancer types. Twenty-four studies reported the association between CGs and cancer risk and six reported the association between CGs and mortality of cancer patients. Using CGs was associated with a higher risk of breast cancer (RR = 1.330, 95% CI: 1.247-1.419). Subgroup analysis showed that using CGs increased the risk of ER+ve breast cancer but not ER-ve. Using CGs wasn't associated with prostate cancer risk (RR = 1.015, 95% CI: 0.868-1.87). However, CGs decreased the risk in long term users and showed a protective role in decreasing the risk of advanced stages. CGs use was associated with increased all-cause mortality (HR = 1.35, 95% CI: 1.248-1.46) but not cancer-specific mortality (HR = 1.075, 95% CI: 0.968-1.194).

CONCLUSION

The anti-tumor activity of CGs observed in pre-clinical studies requires high concentrations which can't be normally tolerated in humans. However, the estrogen-like activity of CGs could be responsible for increasing the risk of certain types of tumors.

Digoxin Plus Trametinib Therapy Achieves Disease Control in BRAF Wild-Type Metastatic Melanoma Patients

This is the first prospective study of a combination therapy involving a cardenolide and a MEK inhibitor for metastatic melanoma. Whereas BRAF mutant melanomas can exhibit profound responses to treatment with BRAF and MEK inhibitors, there are fewer options for BRAF wild-type melanomas. In preclinical studies, we discovered that cardenolides synergize with MEK inhibitor to promote the regression of patient-derived xenografts irrespective of BRAF mutation status. We therefore conducted a phase 1B study of digoxin 0.25 mg and trametinib 2 mg given orally once daily in 20 patients with advanced, refractory, BRAF wild-type melanomas. The most common adverse events were rash, diarrhea, nausea, and fatigue. The response rate was 4/20 or 20% with response durations of 2, 4, 6, and 8 months. The disease control rate (including partial responses and stable disease) was 13/20 or 65% of patients, including 5/6 or 83% of patients with NRAS mutant melanomas and 8/14 or 57% of NRAS wild-type melanomas. Patients with stable disease had disease control for 2, 2, 2, 4, 5, 6, 7, 10, and 10 months. Xenografts from four patients recapitulated the treatment responses observed in patients. Based on these pilot results, an expansion arm of digoxin plus MEK inhibitor is warranted for NRAS mutant metastatic melanoma patients who are refractory or intolerant of immunotherapy.

KEY POINTS

Digoxin plus trametinib is well tolerated and achieves a high rate of disease control in BRAF wild-type metastatic melanoma patients.

Digoxin reduces the mutagenic effects of Mitomycin C in human and rodent cell lines

Digoxin is a drug widely used to treat heart failure and studies have demonstrated its potential as anticancer agent. In addition, digoxin presents the potential to interact with a series of other compounds used in medicine. The aim of the present study was to evaluate in vitro the cytotoxicity, genotoxicity and mutagenicity of digoxin and its potential to interact with the mutagen Mitomycin C (MMC). The cytotoxicity of digoxin was assessed by employing the MTT method and the comet assay was performed to assess the genotoxicity of this medicine in CHO-K1 and HeLa cell lines. Besides, the cytokinesis-block micronucleus assay was performed to assess the mutagenicity and the antimutagenicity of this drug. The Ames assay was also performed with TA98 and TA100 strains of S. typhimurium. Results showed that digoxin was cytotoxic, genotoxic and mutagenic for HeLa and CHO-K1 cell lines at concentrations many times higher than those observed in human therapeutic conditions. Nevertheless, an antimutagenic effect against the mutagen MMC was observed on both cell lines in concentrations near those used therapeutically in humans. This chemoprotective effect observed is an interesting finding that should be better explored regarding its impact in anticancer chemotherapy.

The Associations of Atrial Fibrillation With the Risks of Incident Invasive Breast and Colorectal Cancer

Atrial fibrillation (AF) is a common arrhythmia that poses a significant risk of stroke. Cross-sectional and case-control studies have shown evidence of associations between AF and breast or colorectal cancer, but there have been no longitudinal studies in which this has been assessed. We prospectively examined a cohort of 93,676 postmenopausal women enrolled in the Women's Health Initiative from 1994 to 1998 to determine whether there are relationships between baseline AF and the development of invasive breast or colorectal cancer. The prevalence of self-reported physician diagnosis of AF at baseline was 5.1%. Over approximately 15 years of follow-up, the incidence of invasive breast cancer was 5.7%, and the incidence of colorectal cancer was 1.6%. Adjusted hazard ratios and 95% confidence intervals were obtained using Cox proportional hazards models. We found no significant association between AF and incident colorectal cancer, but we did see a 19% excess risk of invasive breast cancer among those with AF (adjusted hazard ratio (HR) = 1.19, 95% confidence interval (CI): 1.03, 1.38). Additional adjustment for baseline use of cardiac glycosides attenuated the association between AF and invasive breast cancer (HR = 1.01, 95% CI: 0.85, 1.20). Cardiac glycoside use was strongly associated with incident invasive breast cancer (HR = 1.68, 95% CI: 1.33, 2.12) independent of AF and other confounders. Mechanisms of the associations among breast cancer, AF, and cardiac glycosides need further investigation.

Cardiac glycosides and breast cancer risk: A systematic review and meta-analysis of observational studies

Cardiac glycosides are phytoestrogens and have been linked to the risk of estrogen sensitive cancers such as uterus cancer. However, the association between use of cardiac glycosides and risk of breast cancer remains unclear. We investigated the association between cardiac glycosides use and the risk of breast cancer by systematically reviewing the published literature and performing meta-analyses. A comprehensive literature search was performed using MEDLINE, EMBASE, Web of Science and SCOPUS to identify all relevant articles published up to November 2015. Risk estimates, and accompanying standard errors, for the association between cardiac glycoside use and breast cancer were extracted from identified studies. Meta-analysis models were used to calculate a combined hazard ratio (HR), and 95% confidence interval (CI), and to investigate heterogeneity between studies. In total, nine studies were identified investigating cardiac glycosides use and risk of developing breast cancer. Overall, there was evidence to suggest an association between cardiac glycosides use and breast cancer risk (HR = 1.34; 95% CI 1.25, 1.44; p < 0.001) with little variation in the association between studies (I²  = 16%, p for heterogeneity = 0.30). Results were little altered when analysis was restricted to studies with high quality scores or cohort studies. Overall, there was a 34% increase in breast risk with use of cardiac glycosides but it is unclear whether this association reflects confounding or is causal. Further observational studies are required to examine this association particularly for estrogen receptor positive breast cancer and to explore the role of potential confounding variables.

Repurposing of approved cardiovascular drugs

Research and development of new drugs requires both long time and high costs, whereas safety and tolerability profiles make the success rate of approval very low. Drug repurposing, applying known drugs and compounds to new indications, has been noted recently as a cost-effective and time-unconsuming way in developing new drugs, because they have already been proven safe in humans. In this review, we discuss drug repurposing of approved cardiovascular drugs, such as aspirin, beta-blockers, angiotensin converting enzyme inhibitors, angiotensin II receptor blockers, cardiac glycosides and statins. Regarding anti-tumor activities of these agents, a number of experimental studies have demonstrated promising pleiotropic properties, whereas all clinical trials have not shown expected results. In pathological conditions other than cancer, repurposing of cardiovascular drugs is also expanding. Numerous experimental studies have reported possibilities of drug repurposing in this field and some of them have been tried for new indications ('bench to bedside'), while unexpected results of clinical studies have given hints for drug repurposing and some unknown mechanisms of action have been demonstrated by experimental studies ('bedside to bench'). The future perspective of experimental and clinical studies using cardiovascular drugs are also discussed.

Synergistic effects of ion transporter and MAP kinase pathway inhibitors in melanoma

New therapies are required for melanoma. Here, we report that multiple cardiac glycosides, including digitoxin and digoxin, are significantly more toxic to human melanoma cells than normal human cells. This reflects on-target inhibition of the ATP1A1 Na(+)/K(+) pump, which is highly expressed by melanoma. MEK inhibitor and/or BRAF inhibitor additively or synergistically combined with digitoxin to induce cell death, inhibiting growth of patient-derived melanomas in NSG mice and synergistically extending survival. MEK inhibitor and digitoxin do not induce cell death in human melanocytes or haematopoietic cells in NSG mice. In melanoma, MEK inhibitor reduces ERK phosphorylation, while digitoxin disrupts ion gradients, altering plasma membrane and mitochondrial membrane potentials. MEK inhibitor and digitoxin together cause intracellular acidification, mitochondrial calcium dysregulation and ATP depletion in melanoma cells but not in normal cells. The disruption of ion homoeostasis in cancer cells can thus synergize with targeted agents to promote tumour regression in vivo.

Digoxin use after diagnosis of breast cancer and survival: a population-based cohort study

Digoxin has been shown to have an estrogenic effect and is associated with increased risk of gynecomastia and estrogen-sensitive cancers such as breast and uterus cancer. These findings, particularly recent observations of increased breast cancer risk, raise questions about the safety of digoxin use in breast cancer patients. Therefore, we investigated whether digoxin use after breast cancer diagnosis increased the risk of breast cancer-specific mortality in breast cancer patients. A cohort of 17,842 breast cancer patients newly diagnosed from 1998 to 2009 was identified from English cancer registries (from the National Cancer Data Repository). This cohort was linked to the UK Clinical Practice Research Datalink (to provide digoxin and other prescription records) and to the Office of National Statistics mortality data (to identify breast cancer-specific deaths). Using time-dependent Cox regression models, unadjusted and adjusted hazard ratios (HR) and 95 % confidence intervals (CIs) were calculated for the association between post-diagnostic exposure to digoxin and breast cancer-specific and all-cause mortality. In 17,842 breast cancer patients, there were 2219 breast cancer-specific deaths. Digoxin users appeared to have increased breast cancer-specific mortality compared with non-users (HR 1.73; 95 % CI 1.39-2.15) but this association was entirely attenuated after adjustment for potential confounders (adjusted HR 0.91; 95 % CI 0.72-1.14). In this large population-based breast cancer cohort study, there was little evidence of an increase in breast cancer-specific mortality with digoxin use after diagnosis. These results provide some reassurance that digoxin use is safe in breast cancer patients.

Trial watch: Cardiac glycosides and cancer therapy

Cardiac glycosides (CGs) are natural compounds sharing the ability to operate as potent inhibitors of the plasma membrane Na⁺/K⁺-ATPase, hence promoting—via an indirect mechanism—the intracellular accumulation of Ca²⁺ ions. In cardiomyocytes, increased intracellular Ca²⁺ concentrations exert prominent positive inotropic effects, that is, they increase myocardial contractility. Owing to this feature, two CGs, namely digoxin and digitoxin, have extensively been used in the past for the treatment of several cardiac conditions, including distinct types of arrhythmia as well as contractility disorders. Nowadays, digoxin is approved by the FDA and indicated for the treatment of congestive heart failure, atrial fibrillation and atrial flutter with rapid ventricular response, whereas the use of digitoxin has been discontinued in several Western countries. Recently, CGs have been suggested to exert potent antineoplastic effects, notably as they appear to increase the immunogenicity of dying cancer cells. In this Trial Watch, we summarize the mechanisms that underpin the unsuspected anticancer potential of CGs and discuss the progress of clinical studies that have evaluated/are evaluating the safety and efficacy of CGs for oncological indications.

Digoxin use and the risk for colorectal cancer

PURPOSE

Cardiac glycosides affect several pathways central for tumor formation. We sought to evaluate the association between digoxin use and colorectal cancer (CRC) risk.

METHODS

We conducted a nested case-control study using The Health Improvement Network (THIN), a medical record database representative of the broader UK population. Study cases were defined as those with a diagnostic code for CRC. Each case was matched to up to four eligible controls on age, sex, practice site, and duration of follow-up before index date using incidence density sampling. Exposure of interest was digoxin therapy before index date. The odds ratios (ORs) and 95% confidence intervals (CIs) for CRC associated with digoxin use were estimated using conditional logistic regression analysis, adjusted for BMI, alcoholism, smoking history, diabetes mellitus, heart disease, chronic NSAIDs use and previous screening colonoscopies.

RESULTS

The case-control analysis included 20 990 CRC patients and 82 054 controls whose mean follow-up time before index date was 6.5 years (SD 4.0). The adjusted OR for CRC among current digoxin users was increased compared with non-users with an adjusted ORs of 1.41 (95%CI 1.25-1.59, p < 0.0001), 1.45 (95%CI 1.22-1.72, p < 0.0001) and 1.41 (95%CI 1.00-1.99, p = 0.049) for first prescriptions 1-5 years, 5-10 years and more than 10 years before index date respectively. Similar results were observed when cumulative duration and number of digoxin prescriptions were analyzed. The risk was not elevated for past digoxin users.

CONCLUSIONS

Current digoxin use is associated with increased CRC risk.

Cardiac glycosides use and the risk of lung cancer: a nested case-control study

Background

Two studies have reported statistically significant associations between the use of cardiac glycosides (CGs) and an increased risk of lung cancer. However, these studies had a number of methodological limitations. Thus, the objective of this study was to assess this association in a large population-based cohort of patients.

Methods

We used the United Kingdom Clinical Practice Research Datalink (CPRD) to identify a cohort of patients, at least 40 years of age, newly-diagnosed with heart failure, or supra-ventricular arrhythmia. A nested case–control analysis was conducted where each incident case of lung cancer identified during follow-up was randomly matched with up to 10 controls. Exposure to CGs was assessed in terms of ever use, cumulative duration of use and cumulative dose. Rate ratios (RRs) with 95% confidence intervals (CIs) were estimated using conditional logistic regression after adjusting for potential confounders.

Results

A total of 129,002 patients were included, and followed for a mean (SD) of 4.7 (3.8) years. During follow-up, 1237 patients were newly-diagnosed with lung cancer. Overall, ever use of CGs was not associated with an increased risk of lung cancer when compared to never use (RR = 1.09, 95% CI: 0.94-1.26). In addition, no dose–response relationship was observed in terms of cumulative duration of use and cumulative dose with all RRs around the null value across quartile categories.

Conclusion

The results of this large population-based study indicate that the use of CGs is not associated with an increased risk of lung cancer.

Cardiac glycosides and the risk of breast cancer in women with chronic heart failure and supraventricular arrhythmia

The aim of this study is to determine whether the use of cardiac glycosides (CGs), drugs used in the treatment of congestive heart failure (CHF) and supra-ventricular arrhythmia, is associated with an increased risk of breast cancer. A cohort of 53,454 women newly diagnosed with CHF or supra-ventricular arrhythmia between January 1, 1988 and December 31, 2010, followed until December 31, 2012, was identified using the United Kingdom Clinical Practice Research Datalink. A nested case-control analysis was performed, where all incident cases of breast cancer occurring during follow-up were identified and matched with up to 10 controls on age, cohort entry date, and duration of follow-up. Conditional logistic regression models were used to estimate adjusted odds ratios (ORs) with 95 % confidence intervals (CIs) of incident breast cancer associated with the use of CGs, along with measures of cumulative duration of use and dose. All analyses considered a one year lag period prior to the event, necessary for latency considerations and to minimize detection bias. The 898 breast cancer cases diagnosed beyond one year of follow-up were matched to 8,940 controls. Overall, use of CGs was not associated with an increased risk of breast cancer when compared to non-use (OR 1.07, 95 % CI 0.90-1.26). Furthermore, the risk did not vary with cumulative duration of use or cumulative dose. The findings of this large population-based study indicate that the use of CGs is not associated with an increased risk of breast cancer. This should provide reassurance to physicians and patients using these drugs.

Lifestyle changes for prevention of breast cancer

Breast cancer is the second most common cause of death from cancer among women. Lifestyle changes are shown to be important in the prevention of breast cancer. Diet, physical activity, smoking, alcohol use, and vitamin and mineral use are key factors influencing the risk of breast cancer among women. Because these factors are related to each other, it is difficult to assess their individual roles in breast cancer. Some of these factors are alterable, meaning that women can decrease their risk for breast cancer by changing their behavior. Breast cancer is associated with a high rate of mortality and morbidity among women. Therefore, it is logical to try to find ways to decrease the risk of developing breast cancer. Lifestyle changes seem to be an easy, effective, and economical way to help prevention breast cancer. In women with a confirmed breast cancer diagnosis who are under radiotherapy treatment after undergoing a mastectomy, lifestyle changes are still very important. Some factors, such as smoking cessation and prevention of weight gain, may improve the long-term survival chances of these patients. Therefore, ways to increase women’s knowledge about the role of lifestyle changes in the prevention of breast cancer and in the survival of patients with diagnosed breast cancer should be considered and studied.

Digoxin use and risk of invasive breast cancer: evidence from the Nurses' Health Study and meta-analysis

Despite preclinical evidence supporting anti-cancer effects of cardiac glycosides, epidemiologic studies consistently show elevated breast cancer risk in digoxin users. We studied this association in the Nurses' Health Study cohort to evaluate influences of screening mammography and lifestyle-related risk factors. We followed 90,202 postmenopausal women from 1994 to 2010. Self-reported breast cancers were confirmed by medical record review. We fit Cox regression models to estimate associations between time-varying digoxin use and breast cancer incidence, overall and by tumor ER status, accounting for mammography screening and established breast cancer risk factors. There were 5,004 digoxin users over 1.05 million person-years of observation, among whom 144 breast cancer cases occurred. Digoxin users were more likely to undergo mammographic screening, to be former users of postmenopausal hormones, and to take other medications than never-users; the groups were similar on reproductive history and alcohol consumption. Current digoxin use of >4-year duration was associated with a 45 % increased rate of breast cancer compared with never use (HRadj = 1.45, 95 % CI 1.13-1.86). The association appeared stronger for ER-positive disease (HRadj = 1.46, 95 % CI 1.10-1.95) than for ER-negative disease (HRadj = 1.12, 95 % CI 0.52-2.37). Associations were robust to restriction on regular mammography use and to adjustment for established breast cancer risk factors, including lifestyle-related exposures. The positive association between digoxin use and breast cancer occurrence was not attenuated when lifestyle-related breast cancer risk factors and screening practices were accounted for. Digoxin, a common cardiac drug worldwide, may promote breast carcinogenesis.

Recent advances in drug repositioning for the discovery of new anticancer drugs

Drug repositioning (also referred to as drug repurposing), the process of finding new uses of existing drugs, has been gaining popularity in recent years. The availability of several established clinical drug libraries and rapid advances in disease biology, genomics and bioinformatics has accelerated the pace of both activity-based and in silico drug repositioning. Drug repositioning has attracted particular attention from the communities engaged in anticancer drug discovery due to the combination of great demand for new anticancer drugs and the availability of a wide variety of cell- and target-based screening assays. With the successful clinical introduction of a number of non-cancer drugs for cancer treatment, drug repositioning now became a powerful alternative strategy to discover and develop novel anticancer drug candidates from the existing drug space. In this review, recent successful examples of drug repositioning for anticancer drug discovery from non-cancer drugs will be discussed.

Human breast tumor cells are more resistant to cardiac glycoside toxicity than non-tumorigenic breast cells

Cardiotonic steroids (CTS), specific inhibitors of Na,K-ATPase activity, have been widely used for treating cardiac insufficiency. Recent studies suggest that low levels of endogenous CTS do not inhibit Na,K-ATPase activity but play a role in regulating blood pressure, inducing cellular kinase activity, and promoting cell viability. Higher CTS concentrations inhibit Na,K-ATPase activity and can induce reactive oxygen species, growth arrest, and cell death. CTS are being considered as potential novel therapies in cancer treatment, as they have been shown to limit tumor cell growth. However, there is a lack of information on the relative toxicity of tumor cells and comparable non-tumor cells. We have investigated the effects of CTS compounds, ouabain, digitoxin, and bufalin, on cell growth and survival in cell lines exhibiting the full spectrum of non-cancerous to malignant phenotypes. We show that CTS inhibit membrane Na,K-ATPase activity equally well in all cell lines tested regardless of metastatic potential. In contrast, the cellular responses to the drugs are different in non-tumor and tumor cells. Ouabain causes greater inhibition of proliferation and more extensive apoptosis in non-tumor breast cells compared to malignant or oncogene-transfected cells. In tumor cells, the effects of ouabain are accompanied by activation of anti-apoptotic ERK1/2. However, ERK1/2 or Src inhibition does not sensitize tumor cells to CTS cytotoxicity, suggesting that other mechanisms provide protection to the tumor cells. Reduced CTS-sensitivity in breast tumor cells compared to non-tumor cells indicates that CTS are not good candidates as cancer therapies.

A cohort study of digoxin exposure and mortality in men with prostate cancer

OBJECTIVE

To examine the association between digoxin exposure and mortality in men with prostate cancer using linked Irish National Cancer Registry and pharmacy claims data.

PATIENTS AND METHODS

Prostate cancer cases were identified from the database and digoxin exposure at prostate cancer diagnosis was identified from prescription claims. Digoxin users were matched to non-users using a propensity score to identify men with similar cardiovascular comorbidity. Adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated for the association between digoxin exposure and all-cause and prostate cancer-specific mortality (PCSM). Analyses were repeated in the propensity score-matched cohort. Effect modification of treatment with radiation or androgen-deprivation therapy by digoxin exposure was also assessed.

RESULTS

In all, 5732 men with a prostate cancer diagnosis (2001-2006) were identified (digoxin exposed, 391). The median follow-up was 4.3 years. Digoxin exposure was associated with a small non-significant increase in PCSM in the full cohort (HR 1.13, 95% CI 0.91, 1.42) and the propensity. score-matched cohort (HR 1.17, 95% CI 0.88, 1.57). Adjusted HRs for all-cause mortality were increased for digoxin exposed men (HR 1.24, 95% CI 1.07, 1.43). Interactions with treatments received were not significant.

CONCLUSIONS

These results suggest digoxin exposure is not associated with reduced PCSM. Further investigation of other cardiac glycosides that have shown anti-cancer potential may be warranted.

Risk factors of breast cancer: a systematic review and meta-analysis

The etiology of breast cancer might be explained by 2 mechanisms, namely, differentiation and proliferation of breast epithelial cells mediated by hormonal factors. We performed a systematic review and meta-analysis to update effects of risk factors for both mechanisms. MEDLINE and EMBASE were searched up to January 2011. Studies that assessed association between oral contraceptives (OC), hormonal replacement therapy (HRT), diabetes mellitus (DM), or breastfeeding and breast cancer were eligible. Relative risks with their confidence intervals (CIs) were extracted. A random-effects method was applied for pooling the effect size. The pooled odds ratios of OC, HRT, and DM were 1.10 (95% CI = 1.03-1.18), 1.23 (95% CI = 1.21-1.25), and 1.14 (95% CI = 1.09-1.19), respectively, whereas the pooled odds ratio of ever-breastfeeding was 0.72 (95% CI = 0.58-0.89). Our study suggests that OC, HRT, and DM might increase risks, whereas breastfeeding might lower risks of breast cancer.

Breast cancer in women using digoxin: tumor characteristics and relapse risk

Introduction

Digoxin use is associated with increased incidence of breast and uterus cancers. We postulated that digoxin use might affect tumor characteristics and increase relapse risk in women with breast cancer.

Methods

Incident breast cancer cases in Danish women (n = 49,312; 1995 to 2008) were identified. Analyses were conducted in women 20 to 74 years old. Relapse hazard ratios (HR) were compared in women using and not using digoxin, adjusting for age, calendar period, protocol, tumor size, nodal involvement, histology grade, estrogen-receptor (ER) status, and anti-estrogen therapy in Cox regression models.

Results

At diagnosis, tumors in digoxin users were more likely ER+ (85.4% vs. 78.6%: P = 0.002) and have grade 1 ductal histology (37.2% vs. 25.7%; P = 0.004), compared to non-users. 45 relapses occurred in women already using digoxin at breast cancer diagnosis (1,487 person-years); 24 relapses occurred in women later starting digoxin (384 person-years). Overall relapse risk HR in digoxin users was 1.13 (95% confidence interval: 0.88, 1.46) compared to non-users. Relapse risk in digoxin users was significantly increased in the first year (2.19; 1.26, 3.78) but not thereafter (0.99; 0.74, 1.32) (P = 0.02 for difference in HRs). First-year relapse hazard was high in digoxin-using women with ER+ tumors (2.51; 1.39, 4.55) but not ER- tumors (0.72; 0.10, 5.27). Recurrence hazard was not significantly changed among digoxin-using women also using tamoxifen.

Conclusions

Breast cancers arising in digoxin-using women had better prognostic features. After adjustment for markers, overall breast cancer relapse risk in digoxin users was not increased significantly, although recurrence hazards for ER+ tumors were higher in the first year following diagnosis.

A novel two-stage, transdisciplinary study identifies digoxin as a possible drug for prostate cancer treatment

Identification of novel indications for commonly prescribed drugs could accelerate translation of therapies. We investigated whether any clinically-used drugs might have utility for treating prostate cancer by coupling an efficient, high-throughput laboratory-based screen and a large, prospective cohort study. In stage 1, we conducted an in vitro prostate cancer cell cytotoxicity screen of 3,187 compounds. Digoxin emerged as the leading candidate given its potency in inhibiting proliferation in vitro (mean IC₅₀=163 nM) and common use. In stage 2, we evaluated the association between the leading candidate drug from stage 1 and prostate cancer risk in 47,884 men followed 1986-2006. Regular digoxin users (versus nonusers: RR=0.76, 95% CI 0.61-0.95), especially users for ≥ 10 years (RR=0.54, 95% CI 0.37-0.79, P-trend<0.001), had a lower prostate cancer risk. Digoxin was highly potent in inhibiting prostate cancer cell growth in vitro and its use was associated with a 25% lower prostate cancer risk.

SIGNIFICANCE

Our two-stage transdisciplinary approach for drug repositioning provides compelling justification for further mechanistic and possibly clinical testing of the leading nonchemotherapy candidate, digoxin, a cardiac glycoside, as a drug for prostate cancer treatment. Perhaps of equal importance, our study illustrates the power of the transdisciplinary approach in translational cancer research. By coupling laboratory and epidemiologic methods and thinking, we reduced the probability of identifying false-positive candidate drugs for the next steps in testing.

Digoxin use and the risk of cancers of the corpus uteri, ovary and cervix

Digoxin is a phyto-estrogen capable of inducing hormonal effects. Use has been associated with increased risk of breast cancer, an estrogen-sensitive malignancy. The incidence of corpus uteri (uterus) cancer is also strongly increased with exposure to estrogens. Therefore, we evaluated whether digoxin use might also increase its incidence. In all women in Denmark, we identified digoxin users from 1995 through 2008 using a nationwide pharmacy registry system. Cancer occurrence was obtained from Danish Cancer Registry. Relative risk was determined using incidence risk ratios (RR) and 95% confidence intervals (CIs) relative to non-users after adjustment for age- and calendar-time. For ovarian and cervical cancers, RRs in users and non-users were similarly evaluated, these cancers representing gynecological cancers with weak or no associations to estrogen exposure. Of 2.1 million women, 104,648 (4.9%) had digoxin exposure and 137,493 6.5% had exposure to angina drugs but not digoxin during the study period. For uterus cancer, the RR was increased in current digoxin users (1.48, 95% CI: 1.32-1.65; N = 350). Incidence was marginally increased in former users. For ovary and cervix cancers, RRs in current digoxin users were 1.06 (95% CI: 0.92-1.22; N = 207) and 1.00 (95% CI: 0.79-1.25; N = 81), respectively. We examined risks in women using angina drugs but not digoxin to determine whether being under cardiac care affected risk. Among women using angina drugs only, RRs for uterus, ovary or cervix cancers were not statistically significant. We conclude that women currently using digoxin, a phyto-estrogen, have an increased risk of developing uterus cancers.

Digoxin - time to take the gloves off?

Digoxin has been used for hundreds of years to aid rate control in atrial fibrillation and as a positive inotrope in heart failure. Our familiarity with digoxin has allowed it to become easily prescribed even though there are data suggesting that use of digoxin may in fact result in increased mortality and pro-arrhythmia. Within this review we explain some of the outcome data associated with digoxin use to determine if it is time to take the gloves off and examine if we should still be using this drug in the 21st century.

Digoxin use and the risk of breast cancer in women

PURPOSE

Digoxin resembles estrogen chemically and may have estrogenic effect. We hypothesized that digoxin use might increase breast cancer incidence and examined if use might be associated with risk of breast cancer, categorized by estrogen receptor (ER) status. To determine if being under care for heart disease biased the findings, rate ratios in users of angina drugs were similarly evaluated as a control exposure group.

PATIENTS AND METHODS

Women using digoxin and angina drugs were identified in the nationwide Danish Prescription Database, available between 1995 and 2008. Incident breast cancers were identified in the Danish Cancer Registry and further classifying by ER status. Relative risks (RR) were compared to nonusers using age- and period-adjusted incidence rate ratios.

RESULTS

Two thousand one hundred forty-four of 104,648 women using digoxin developed breast cancer. Current digoxin users were at increased risk of breast cancer (RR, 1.39; 95% CI, 1.32 to 1.46), but risk was not increased in former users (RR, 0.91; 95% CI, 0.83 to 1.00). The increased risks in digoxin users were marginally higher for ER-positive breast cancers (RR, 1.35; 95% CI, 1.26 to 1.45) and ER unknown breast cancers (RR, 1.51; 95% CI, 1.38 to 1.64) than for ER-negative breast cancers (RR, 1.20; 95% CI, 1.03 to 1.40). Among 137,493 women exposed to angina drugs only (a comparison group with cardiovascular disease; n = 2,658 breast cancers), incidence was not increased in current or former users.

CONCLUSION

Women currently using digoxin had a significantly increased risk of breast cancer. Risk normalized when digoxin was stopped. No risk increases were observed in women using angina drugs only. The higher risk of developing ER-positive breast cancers supports an estrogen-mimicking mechanism.

Digitoxin activates EGR1 and synergizes with paclitaxel on human breast cancer cells

BACKGROUND

Numerous studies have suggested that digitalis derivatives promise to be superior to existing adjuvant therapy for breast cancer as to effects and side-effects. In the present study, we have used gene expression analysis to determine the molecular action of digitoxin on breast cancer cells and assessed digitoxin's ability to synergize with the chemotherapy agent paclitaxel with respect to inhibition of cell proliferation

MATERIALS AND METHODS

We treated (Her2 overexpressing, ER low) MDA-MB-453 human breast cancer cells with digitoxin at four doses {20 ng/ml (26 nM) to 1 μg/ml} and collected RNA at 6 h and 24 h for gene expression analysis. To examine the effects on ER positive cells, we treated MCF7 cells with digitoxin at 1 μg/ml and collected RNA for RT-PCR analysis. In addition, we assayed the growth inhibitory effect of low doses of digitoxin combined with paclitaxel and determined combination index values.

RESULTS

To reveal primary effects, we examined digitoxin's effect 6 h post-treatment with the highest dose, 1μg/ml, and found upregulation of the stress response genes EGR-1 and NAB2, lipid biosynthetic genes and the tumor suppressor gene p21, and downregulation of the mitotic cell cycle gene CDC16 and the replication gene PolR3B. RT-PCR analysis validated effects on stress response, apoptotic and cell cycle genes on MDA-MB-453 and MCF7 cells. Western blot analysis confirmed induction of EGR1 protein at 1 h and ATF3 at 24 h. Paclitaxel, as well as digitoxin, inhibited the in vitro activity of the purified Na(+)-K(+)-ATPase; digitoxin enhanced the growth inhibitory effects of paclitaxel on Her2 overexpressing breast cancer cells.

CONCLUSIONS

Our studies show the potential of digitoxin to prevent and treat breast cancer and indicate that the combination of digitoxin and paclitaxel is a promising treatment for ER negative breast cancer. These findings are the first to alert physicians to the possible dangers to patients who take a combination of digitoxin and paclitaxel. The potential dangers ensuing when paclitaxel and digitoxin are combined are dependent on the dose of digitoxin.

Cardiac glycosides induce cell death in human cells by inhibiting general protein synthesis

BACKGROUND

Cardiac glycosides are Na(+)/K(+)-pump inhibitors widely used to treat heart failure. They are also highly cytotoxic, and studies have suggested specific anti-tumor activity leading to current clinical trials in cancer patients. However, a definitive demonstration of this putative anti-cancer activity and the underlying molecular mechanism has remained elusive.

METHODOLOGY/PRINCIPAL FINDINGS

Using an unbiased transcriptomics approach, we found that cardiac glycosides inhibit general protein synthesis. Protein synthesis inhibition and cytotoxicity were not specific for cancer cells as they were observed in both primary and cancer cell lines. These effects were dependent on the Na(+)/K(+)-pump as they were rescued by expression of a cardiac glycoside-resistant Na(+)/K(+)-pump. Unlike human cells, rodent cells are largely resistant to cardiac glycosides in vitro and mice were found to tolerate extremely high levels.

CONCLUSIONS/SIGNIFICANCE

The physiological difference between human and mouse explains the previously observed sensitivity of human cancer cells in mouse xenograft experiments. Thus, published mouse xenograft models used to support anti-tumor activity for these drugs require reevaluation. Our finding that cardiac glycosides inhibit protein synthesis provides a mechanism for the cytotoxicity of CGs and raises concerns about ongoing clinical trials to test CGs as anti-cancer agents in humans.