Abstract

Aims

Mutations in A-type nuclear lamins gene, LMNA, lead to a dilated cardiomyopathy. We have reported abnormal activation of the extracellular signal-regulated kinase1/2 (ERK1/2) signalling in hearts from LmnaH222P/H222P mice, which develop dilated cardiomyopathy. We therefore determined whether an inhibitor of ERK1/2 signalling that has been investigated in clinical trials for cancer has the potential to be translated to humans with LMNA cardiomyopathy.

Methods and results

To evaluate the relevance of this finding in mice to patients, we analysed the ERK1/2 signalling in heart tissue from human subjects with LMNA cardiomyopathy and showed that it was abnormally activated. To determine whether pharmacological inhibitors of the ERK1/2 signalling pathway could potentially be used to treat LMNA cardiomyopathy, we administered selumetinib to male LmnaH222P/H222P mice starting at 16 weeks of age, after they show signs of cardiac deterioration, up to 20 weeks of age. Selumetinib is an inhibitor of ERK1/2 signalling and has been given safely to human subjects in clinical trials for cancer. Systemic treatment with selumetinib inhibited cardiac ERK1/2 phosphorylation and blocked increased expression of RNAs encoding natriuretic peptide precursors and proteins involved in sarcomere architecture that occurred in placebo-treated mice. Echocardiography and histological analysis demonstrated that treatment increases cardiac fractional shortening, prevents myocardial fibrosis, and prolongs survival. Selumetinib treatment did not induce biochemical abnormalities suggestive of renal or hepatic toxicity.

Conclusion

Our results suggest that selumetinib or other related inhibitors that have been safely administered to humans in clinical trials could potentially be used to treat LMNA cardiomyopathy.

Introduction

The lamin A/C gene, LMNA, encodes A-type nuclear lamins, intermediate filament proteins comprising the nuclear lamina of most differential mammalian somatic cells. Mutations in LMNA cause more than a dozen previously defined clinical entities primarily, often referred to as laminopathies, affecting either striated muscle, adipose tissue, peripheral nerve, or multiple systems with an accelerated ageing phenotype.1 Most disease-causing LMNA mutations affect the heart, particularly as a dilated cardiomyopathy, which occurs with or without concurrent skeletal muscle involvement, usually Emery–Dreifuss muscular dystrophy or limb-girdle muscular dystrophy type 1B.2–4

Cardiomyopathy caused by LMNA mutation is characterized by chamber enlargement and systolic dysfunction of one or both ventricles. A key feature of LMNA cardiomyopathy is early atrioventricular conduction block and other conduction system defects.2–4LMNA mutations have been found in up to 7.5% of cases of dilated cardiomyopathy with a positive family history and in 3.6–11% of sporadic cases.5,6 In one study of familial dilated cardiomyopathy with conduction block as prominent feature, 33% were found to have LMNA mutations.7 Timely insertion of a pacemaker and/or intracardiac cardioverter defibrillator can decrease the risk of death from arrhythmias but most patients ultimately develop advanced heart failure. Approximately 55% of the patients with LMNA cardiomyopathy die of cardiovascular death or receive a heart transplant by 60 years of age.5,8,9 While drugs such as angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, β-blockers, diuretics, and aldosterone antagonists may be of some benefit to patients with LMNA cardiomyopathy, there is no specific therapeutic intervention that improves cardiac function or prevents heart muscle deterioration.

Several genetically modified mouse lines have been created to help understand the pathogenic mechanisms of how alterations in A-type lamins cause disease.10LmnaH222P/H222P mice contain a mutation corresponding to one that causes Emery–Dreifuss muscular dystrophy in humans and develop cardiomyopathy with skeletal muscle involvement.11 We have discovered abnormal activation of the Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK1/2) branches of the mitogen-activated protein kinase (MAPK) signalling cascade in hearts of these mice, which occurs prior to the onset of significant cardiomyopathy.12 This finding has linked a cardiac disease-causing A-type lamin alteration to signal transduction pathways implicated in heart function and cardiomyopathy. Based on this discovery, we hypothesized that pharmacological inhibitors of these signalling pathways could improve heart function and prevent LMNA cardiomyopathy and have shown beneficial effects of treatment with such drugs in LmnaH222P/H222P mice.13–15

Our preclinical research showing abnormal activation of MAPK signalling pathways in hearts of LmnaH222P/H222P mice and that inhibitors of enzymes in these pathways have beneficial therapeutic effects has the potential to be translated to humans with LMNA cardiomyopathy. However, there are several limitations. First, it is not clear whether the same cell signalling abnormalities occur in hearts of human subjects with LMNA mutations. Secondly, JNK inhibitors have not advanced significantly in human clinical trials and the MAPK/ERK1/2 kinase (MEK1/2) inhibitor we previously used to block activation of ERK1/2, PD98059, is unsuitable for human use because of its poor pharmacokinetic profile and off-target toxicities. However, several biotechnology and pharmaceutical companies have MEK1/2 inhibitors in clinical development for cancer.16 Among these MEK1/2 inhibitors, selumetinib (AZD6244/ARRY-142886)17 has shown a high selectivity for its target by without activity against more than 40 other kinases.18 Selumetinib has been studied in Phase I and Phase II clinical trials in patients with biliary cancers, colorectal cancer, myeloma, and hepatocellular carcinoma.19–21 Thirdly, although often difficult to demonstrate in small animal studies, we have not yet reported a survival benefit of MAPK signalling inhibitors in LmnaH222P/H222P mice. Fourthly, a preliminary analysis of potential hepatic and renal toxicity in mice with cardiomyopathy has not been performed. We therefore carried out the current study to overcome these shortcomings.

Methods

Human heart tissue

Sections of explanted hearts from human subjects with LMNA mutations were obtained from Myobank-AFM de l'lnstitut de Myologie (Paris, France). Myobank-AFM is a non-profit service dealing with the collection, preparation, storage, and distribution of human tissue samples. The Myobank-AFM has received authorization to preserve and prepare tissues and cells of human origin for scientific purposes (French Ministry of Research—April 2008—authorization no. 2008-87), use computerized data files for sample tracking and banking activities (Commission Nationale Informatique et Libertés, CNIL—law no. 94-548), and import and export tissues and cells of human origin for scientific purposes in the context of international collaborations (French Ministry of Health, 2008—law no. 96-327). Myobank-AFM received the authorizations from the French Ministry of Health and from the Comity for Protection of Patient to share tissues and cells of human origin for scientific purposes, ensuring the donors the maintenance of anonymity, respect of their volition, and consent according to the legislation (http://www.institut-myologie.org/anglais/ewb_pages/r/recherche_banquetissus_activites2003.php). Control human heart samples were obtained from the National Disease Research Interchange (Philadelphia, PA, USA); information regarding donor confidentiality and consent can be found at http://www.ndriresource.org. Tissue samples received from either autopsy or transplanted consent donors were not obtained specifically for this study and provided by Myobank-AFM or the National Disease Research Interchange without patient identifiers; therefore, Institutional Review Board approval at Columbia University Medical Center was required. This study conforms to the Declaration of Helsinki for ethical principles for medical research involving research on identifiable human material and data.

Mice and treatment protocols

LmnaH222P/H222P mice were bred and genotyped as described previously.11,13 Mice were fed chow and housed in a disease-free barrier facility with 12 h/12 h light/dark cycles. The study conforms to the Guide for the Care and Use of Laboratory Animals published by the United States National Institutes of Health (NIH Publication No. 85-53, revised 1996). The Institutional Animal Care and Use Committee at Columbia University Medical Center approved the use of animals and the study protocol. Selumetinib (Selleck Chemicals) was dissolved in dimethyl sulfoxide (DMSO; Sigma) at a concentration of 0.5 mg/mL. The placebo control consisted of the same volume of DMSO. Selumetinib was delivered at a dose of 1 mg/kg/day.22 For biochemical analysis, echocardiographic analysis, and toxicity studies, selumetinib and DMSO were administered by ip injection using a 27 G 5/8 syringe starting when mice were 16 weeks of age and continuing until 20 weeks of age. For survival analysis, selumetinib and DMSO were diluted in the drinking water starting when mice were 16 weeks of age and continued until they suffered from significant distress or died. Specific signs of significant distress included (i) difficulty with normal ambulatory movement, (ii) failure to eat or drink, (iii) weight loss of more than 20%, (iv) depression, (v) rough or unkempt hair coat, and (vi) significant respiratory distress and were confirmed by consulting with veterinarians at the Institute of Comparative Medicine, Columbia University Medical Center. For most of these experiments, euthanasia of the animals was performed in a CO2 chamber followed by cervical dislocation, according to the protocol of the Institute of Comparative Medicine. Euthanasia was confirmed by checking for lack of response to limb and tail pinch. Mouse hearts were then quickly excised by cutting the aorta.

Protein extraction and immunoblotting

Human or mouse heart tissue was homogenized in extraction buffer as described previously.12,13 Extracted proteins were separated by SDS–polyacrylamide gel electrophoresis, transferred to nitrocellulose membranes, and blotted with primary antibodies against total ERK1/2 (no. Sc-94, Santa-Cruz) and phosphorylated ERK1/2 (no. 9101, Cell Signaling). Secondary antibodies were horseradish peroxidase-conjugated (GE Healthcare). Recognized proteins were visualized by enhanced chemiluminescence (ECL, GE Healthcare). For quantification of phosphorylated ERK1/2 compared with total ERK1/2, immunoblots were scanned and analysed using ImageJ64 software.

Quantitative real-time RT–PCR analysis

Total RNA was extracted using the Rneasy isolation kit (Qiagen). Complementary DNA was synthesized using Superscript first-strand synthesis system according to the manufacturer's instructions (Invitrogen) on total RNA. For each replicate in each experiment, RNA from tissue samples of different animals was used. Primers were designed corresponding to mouse RNA sequences using Primer3 (http://frodo.wi.mit.edu/cgi-bin/primer3/primer3_www.cgi) for Nppa (forward 5′-gcttccaggccatattggag-3′, reverse 5′-ccctgcttcctcagtctgct-3′), Mlc-1a (forward 5′-cccaagcctgaagagatgag-3′, reverse 5′-agacaacagctgctccacct-3′) and Mlc-2a (forward 5′-tcaaggaagccttcagctgc-3′, reverse 5′-cggaacacttaccctcccg-3′). Real-time RT–PCRs contained HotStart-IT SYBR green qPCR Master Mix (Usb, Affymetrix), 200 nM of each primer, and 0.2 µL of template in a 25 µL reaction volume. Amplification was carried out using the ABI 7300 Real-Time PCR System (Applied Biosystems) with an initial denaturation at 95°C for 2 min followed by 50 cycles at 95°C for 30 s and 62°C for 30 s. Relative levels of mRNA expression were calculated using the ΔΔCT method.23 Individual expression values were normalized by comparison with Gapdh mRNA (forward 5′-tgcaccaccaactgcttag-3′, reverse 5′-ggatgcagggatgatgttc-3′) and Hprt mRNA (forward 5′-agttgagagatcatctccac-3′, reverse 5′-ttgctgacctgctggatttac-3′).

Natriuretic peptide A ELISA

Natriuretic peptide A in serum was detected using a commercially available kit (EIA-ANP-1, RayBiotech) as per the manufacturer's recommendations.

Transthoracic echocardiography

LmnaH222P/H222P mice were anaesthetized with 1.5% isoflurane inhalation and placed on a heating pad (37°C). Echocardiography was performed using a Visualsonics Vevo 770 ultrasound with a 30 MHz transducer applied to the chest wall. Cardiac ventricular dimensions were measured in two-dimensional mode and M-mode three times for the number of animals indicated. Fractional shortening (FS) was calculated using the following formula: FS (%) = [(LVEDD – LVESD)/LVEDD] × 100.

Histopathological analysis

Hearts from LmnaH222P/H222P mice were fixed in 4% formaldehyde for 48 h, embedded in paraffin, sectioned at 5 µM, and stained with haematoxylin and eosin and Gomori's trichrome. Representative stained sections were photographed using a Microphot SA (Nikon) light microscope attached to a Spot RT Slide camera (Diagnostic Instruments). Images were processed using Adobe Photoshop CS (Adobe Systems). To quantify myocardial fibrosis, micrographs of sections stained with Gomori's trichrome from each heart were processed (JMicroVision software) and blue-stained fibrotic tissue measured (ImageJ64 software). For quantification of nuclear length, cardiomyocyte nuclei were measured along the longitudinal length of a given cell (ImageJ64) in micrographs of sections of heart stained with haematoxylin and eosin.

Serum biochemical analysis

Serum was separated from blood drawn from mice and stored at –80°C until analysed. Routine clinical chemistry analysis was performed on an AutoAnalyzer at the Comparative Pathology Laboratory at Columbia University Medical Center.

Statistics

Values for scanned immunoblots, real-time RT–PCR, ELISA, fibrosis quantification, nuclear length, and blood chemistry were compared using an unpaired Student's t-test. Comparisons of the echocardiographic parameters between selumetinib- and DMSO-treated LmnaH222P/H222P were performed using a Welch's t-test; to validate these results, a non-parametric test (Mann–Whitney) was performed and concordance checked. Mouse survival was analysed using the Kaplan–Meier estimator followed by a log-rank test with P< 0.05 considered to be statistically significant.24 Statistical analyses were performed using GraphPad Prism software.

Results

Abnormal activation of ERK1/2 signalling in hearts from human subjects with LMNA cardiomyopathy

We have previously shown abnormal activation of ERK1/2 signalling in hearts from LmnaH222P/+ and LmnaH222P/H222P mice that develop cardiomyopathy.12 Reduced expression of A-type lamins and expression of variants that cause cardiomyopathy in transfected cultured cells also activate ERK1/2 signalling.12,16 However, no data on ERK1/2 signalling in hearts from human subjects with LMNA cardiomyopathy have been published previously. We therefore obtained samples of heart tissues from two human subjects with LMNA cardiomyopathy obtained after cardiac transplantation. One sample was from a 47-year-old woman with Emery–Dreifuss muscular dystrophy with an LMNA ▵K261 mutation and the other from a 62-year-old woman with limb-girdle muscular dystrophy type 1B carrying an LMNA IVS9 + 1g > a mutation. Control heart samples were obtained from a 57-year-old man who died from an intracranial bleed, a 15-year-old woman who died from a drug overdose, and a 46-year-old man who died from end-stage liver disease. Immunoblotting using antibodies against phosphorylated ERK1/2 and total ERK1/2 showed obvious increases in phosphorylated (activated) ERK1/2 in heart tissue of the patients with LMNA mutations compared with controls (Figure 1).

Figure 1

ERK1/2 activation in hearts from human subjects with LMNA cardiomyopathy. Immunoblots are shown using antibodies against phosphorylated ERK1/2 (pERK1/2) and total ERK1/2 (ERK1/2) to probe proteins extracted from human heart tissue from controls and individuals with LMNA cardiomyopathy.

Figure 1

ERK1/2 activation in hearts from human subjects with LMNA cardiomyopathy. Immunoblots are shown using antibodies against phosphorylated ERK1/2 (pERK1/2) and total ERK1/2 (ERK1/2) to probe proteins extracted from human heart tissue from controls and individuals with LMNA cardiomyopathy.

Selumetinib inhibits cardiac ERK1/2 activation, improves cardiac function and prevents fibrosis in LmnaH222P/H222P mice with cardiomyopathy

Selumetinib (Figure 2A) is a potent, highly specific allosteric MEK1/2 inhibitor, which does not bind to the ATP-binding site and compete with endogenous ATP.18,19 We therefore assessed the efficacy of selumetinib in the treatment of cardiomyopathy in LmnaH222P/H22P mice. We administered selumetinib systemically (1 mg/kg by ip injection, daily) to male LmnaH222P/H222P mice starting at 16 weeks of age, when they have left ventricular dilatation and decreased cardiac FS,11 and analysed them at 20 weeks of age. Systemic administration of selumetinib blocked the phosphorylation of ERK1/2 in hearts, decreasing it by ∼50% compared with mice treated with DMSO placebo (Figure 2B).

Figure 2

Selumetinib inhibits ERK1/2 signalling in hearts from male LmnaH222P/H222P mice. (A) Chemical structure of selumetinib. (B) Representative immunoblots using antibodies against phosphorylated ERK1/2 (pERK1/2) and total ERK1/2 (ERK1/2) to probe proteins extracted from hearts from LmnaH222P/H222P mice treated with selumetinib or DMSO. The bar graph shows means ± SEM signals pERK1/2/total ERK1/2 (relative expression from immunoblots of n= 5 mice treated with selumetinib and n = 5 mice treated with DMSO) of pERK1/2/total ERK1/2. *P< 0.05.

Figure 2

Selumetinib inhibits ERK1/2 signalling in hearts from male LmnaH222P/H222P mice. (A) Chemical structure of selumetinib. (B) Representative immunoblots using antibodies against phosphorylated ERK1/2 (pERK1/2) and total ERK1/2 (ERK1/2) to probe proteins extracted from hearts from LmnaH222P/H222P mice treated with selumetinib or DMSO. The bar graph shows means ± SEM signals pERK1/2/total ERK1/2 (relative expression from immunoblots of n= 5 mice treated with selumetinib and n = 5 mice treated with DMSO) of pERK1/2/total ERK1/2. *P< 0.05.

We previously reported an up-regulation of genes involved in sarcomere organization in the hearts of LmnaH222P/H222P mice.12–15 We therefore assayed expression of Mlc-1a and Mlc-2a mRNAs, encoding cardiac isoforms of myosin light chains, in hearts from DMSO- and selumetinib-treated LmnaH222P/H222P mice. After treatment with selumetinib from 16 to 20 weeks of age, cardiac expression of both Mlc-1a and Mlc-2a mRNAs was significantly decreased compared with DMSO-treated LmnaH222P/H222P mice (Figure 3A). Cardiac expression of Nppa mRNA encoding natriuretic peptide A, the synthesis of which is increased in dilated hearts, was also significantly decreased in the hearts from selumetinib-treated LmnaH222P/H222P mice compared with hearts from those treated with DMSO (Figure 3B). The concentration of natriuretic peptide A in serum was also decreased by ∼50% in selumetinib-treated LmnaH222P/H222P mice compared with DMSO-treated LmnaH222P/H222P mice (Figure 3B). We further investigated the effects of selumetinib treatment on cardiac chamber diameters and contractility in LmnaH222P/H222P mice using M-mode transthoracic echocardiography (Figure 3C). Left ventricular end-diastolic diameter and left ventricular end-systolic diameter in LmnaH222P/H222P mice treated with selumetinib were significantly smaller than in mice treated with DMSO (Figure 3D). FS was significantly increased in LmnaH222P/H222P mice treated with selumetinib compared with the DMSO-treated mice (Figure 3D). Overall, these results showed that selumetinib had positive effects when administered after cardiac dysfunction occurred in LmnaH222P/H222P mice (Table 1). As treatment with selumetinib could induce changes in biological parameters at their baseline, we also treated Lmna+/+ mice with selumetinib using the same dosing schedule and did not detect any differences in echocardiographic results compared with untreated mice (see Supplementary material online, Table S1).

Table 1

Echocardiographic parameters in LmnaH222P/H222P mice treated with selumetinib or placebo (DMSO)

 Heart rate (b.p.m.) LVEDD (mm) LVESD (mm) FS (%) PW (mm) Relative WT 
DMSO (n = 17) 506.4 ± 4.7 4.4 ± 0.1 3.5 ± 0.1 20.7 ± 1.6 0.61 ± 0.01 0.26 ± 0.01 
Selumetinib (n = 21) 511.6 ± 3.8 4.1 ± 0.1*** 3.0 ± 0.1** 25.2 ± 1.2* 0.58 ± 0.01 0.28 ± 0.01 
 Heart rate (b.p.m.) LVEDD (mm) LVESD (mm) FS (%) PW (mm) Relative WT 
DMSO (n = 17) 506.4 ± 4.7 4.4 ± 0.1 3.5 ± 0.1 20.7 ± 1.6 0.61 ± 0.01 0.26 ± 0.01 
Selumetinib (n = 21) 511.6 ± 3.8 4.1 ± 0.1*** 3.0 ± 0.1** 25.2 ± 1.2* 0.58 ± 0.01 0.28 ± 0.01 

Values are means ± SEM. LVEDD, left ventricular end diastolic diameter; LVESD, left ventricular end systolic diameter; FS, fractional shortening; PW, posterior wall thickness dimension; relative WT, relative wall thickness. *P< 0.05, **P< 0.005, ***P< 0.0005.

Figure 3

Selumetinib decreased expression of cardiac myosin light chains and natriuretic peptides and prevents left ventricular dilatation and deterioration of FS in LmnaH222P/H222P mice. Bar graphs indicate the expression levels of (A) Mlc-1a and Mlc-2a mRNAs encoding the cardiac isoforms of myosin light chains and (B) Nppa mRNA encoding the atrial natriuretic peptide A (ANP) and ANP expression in hearts LmnaH222P/H222P mice treated with selumetinib (n = 7) or DMSO (n = 8). Values for the real-time RT–PCR were obtained using the ΔΔCT method using Gapdh as a housekeeping gene (similar values were obtained using Hprt as a housekeeping gene). Values for ELISA are the ratio of ANP expression at the end of the treatment/ANP expression before the treatment. Values for each individual mouse and means ± SEM are shown. **P < 0.005. (C) Representative M-mode transthoracic echocardiographic tracings from 20-week only male LmnaH222P/H222P mice treated with DMSO or selumetinib. (D) Graphs showing mean left ventricular end-diastolic diameter (LVEDD), left ventricular end-systolic diameter (LVESD), and FS in 20-week-old male LmnaH222P/H222P mice treated with selumetinib (n = 21) or DMSO (n = 17). Values for each individual mouse as well as means ± SEM are shown. *P< 0.05, **P< 0.005, ***P< 0.0005.

Figure 3

Selumetinib decreased expression of cardiac myosin light chains and natriuretic peptides and prevents left ventricular dilatation and deterioration of FS in LmnaH222P/H222P mice. Bar graphs indicate the expression levels of (A) Mlc-1a and Mlc-2a mRNAs encoding the cardiac isoforms of myosin light chains and (B) Nppa mRNA encoding the atrial natriuretic peptide A (ANP) and ANP expression in hearts LmnaH222P/H222P mice treated with selumetinib (n = 7) or DMSO (n = 8). Values for the real-time RT–PCR were obtained using the ΔΔCT method using Gapdh as a housekeeping gene (similar values were obtained using Hprt as a housekeeping gene). Values for ELISA are the ratio of ANP expression at the end of the treatment/ANP expression before the treatment. Values for each individual mouse and means ± SEM are shown. **P < 0.005. (C) Representative M-mode transthoracic echocardiographic tracings from 20-week only male LmnaH222P/H222P mice treated with DMSO or selumetinib. (D) Graphs showing mean left ventricular end-diastolic diameter (LVEDD), left ventricular end-systolic diameter (LVESD), and FS in 20-week-old male LmnaH222P/H222P mice treated with selumetinib (n = 21) or DMSO (n = 17). Values for each individual mouse as well as means ± SEM are shown. *P< 0.05, **P< 0.005, ***P< 0.0005.

Later stages cardiomyopathy caused by LMNA mutations are characterized by myocardial fibrosis. Gomori's trichrome staining of hearts from LmnaH222P/H222P mice at 20 weeks of age after treatment with selumetinib showed a significant reduction in fibrosis compared with hearts from DMSO-treated mice (Figure 4A). Hearts from DMSO-treated LmnaH222P/H222P mice had 20.93 ± 2.45% fibrotic tissue per total surface area examined compared with 11.90 ± 1.97% (P< 0.05) in mice treated with selumetinib. At the end of the treatment, hearts from selumetinib-treated LmnaH222P/H222P mice also had a two-fold reduction in expression of Col1a1 and a four-fold decrease in Co1a2 mRNAs that encode collagens compared with DMSO-treated mice (Figure 4B). These results demonstrated that selumetinib decreases progression of myocardial fibrosis in LmnaH222P/H222P mice, an end-stage irreversible pathology.

Figure 4

Selumetinib prevents cardiac fibrosis in LmnaH222P/H222P mice. (A) Representative heart tissue sections from male LmnaH222P/H222P mice treated with selumetinib or DMSO stained with Gomori's trichrome are shown. Fibrosis appears blue. Scale bar: 50 μm. Values (means ± SEM) reflect the myocardial fibrosis for each group (see Section 2). (B) Bar graphs showing expression levels of Col1a1 and Col1a2 mRNAs encoding collagens in hearts LmnaH222P/H222P mice treated with selumetinib (n = 5) or DMSO (n = 5). Values (means ± SEM) were obtained using the ΔΔCT method using Gapdh as a housekeeping gene (similar values were obtained using Hprt as a housekeeping gene). *P< 0.05, ***P< 0.005.

Figure 4

Selumetinib prevents cardiac fibrosis in LmnaH222P/H222P mice. (A) Representative heart tissue sections from male LmnaH222P/H222P mice treated with selumetinib or DMSO stained with Gomori's trichrome are shown. Fibrosis appears blue. Scale bar: 50 μm. Values (means ± SEM) reflect the myocardial fibrosis for each group (see Section 2). (B) Bar graphs showing expression levels of Col1a1 and Col1a2 mRNAs encoding collagens in hearts LmnaH222P/H222P mice treated with selumetinib (n = 5) or DMSO (n = 5). Values (means ± SEM) were obtained using the ΔΔCT method using Gapdh as a housekeeping gene (similar values were obtained using Hprt as a housekeeping gene). *P< 0.05, ***P< 0.005.

We have previously reported abnormal elongation of nuclei in cardiomyocytes of LmnaH222P/H222P mice.13–15 Nuclei in cardiomyocytes of LmnaH222P/H222P mice treated with selumetinib LmnaH222P/H222P mice had an overall shape that was less elongated and more oval than those in cardiomyocytes of mice treated with DMSO (Figure 5A). The mean lengths of nuclei in cardiomyocytes in LmnaH222P/H222P mice treated with selumetinib were significantly shorter than those in hearts of mice in the DMSO-treated group (P< 0.0005) (Figure 5B). While other abnormalities in nuclear morphology have been observed in hearts of LmnaH222P/H222P mice when cardiac tissue was examined by electron microscopy,11 we could not assess such ultrastructural alterations with the light microscopic methods we used.

Figure 5

Selumetinib prevents abnormal elongation of cardiomyocyte nuclei in LmnaH222P/H222P mice. (A) Histological analysis of cross-sections of hearts from LmnaH222P/H222P mice treated with selumetinib or DMSO. Sections were stained with haematoxylin and eosin. Yellow lines with arrowheads demonstrate the measurement of nuclear length. Scale bar: 10 μm. (B) Quantification of nuclear elongation in cardiomyocytes from mice. Cardiomyocyte nuclei were measured along the yellow lines with arrowheads. Bars indicate the length of cardiomyocyte nuclei in the indicated hearts. Values are means ± SEM for n = 200 cardiomyocytes. ***P< 0.0005.

Figure 5

Selumetinib prevents abnormal elongation of cardiomyocyte nuclei in LmnaH222P/H222P mice. (A) Histological analysis of cross-sections of hearts from LmnaH222P/H222P mice treated with selumetinib or DMSO. Sections were stained with haematoxylin and eosin. Yellow lines with arrowheads demonstrate the measurement of nuclear length. Scale bar: 10 μm. (B) Quantification of nuclear elongation in cardiomyocytes from mice. Cardiomyocyte nuclei were measured along the yellow lines with arrowheads. Bars indicate the length of cardiomyocyte nuclei in the indicated hearts. Values are means ± SEM for n = 200 cardiomyocytes. ***P< 0.0005.

Effect of selumetinib on survival of LmnaH222P/H222P mice with cardiomyopathy

Male LmnaH222P/H222P mice die between 4 and 9 months of age with a median survival of ∼28 weeks.11 Previous studies of MEK1/2 inhibitors or other interventions have not assessed a survival benefit. We therefore analysed the effect of oral administration of selumetinib, which is a more appropriate dosing for long-term study, on the survival of male LmnaH222P/H222P mice. Selumetinib or DMSO was dissolved in drinking water starting at 16 weeks of age. Cardiac ERK1/2 phosphorylation was inhibited in LmnaH222P/H222P mice drinking water containing selumetinib compared with water containing placebo, after 4 weeks treatment (Figure 6A). The inhibition of ERK1/2 phosphorylation was similar to that observed with ip dosing (Figure 2B). DMSO-treated male LmnaH222P/H222P mice had a maximum survival of 29 weeks and a median survival of 27 weeks. Selumetinib-treated LmnaH222P/H222P mice had a statistically significantly increased median survival of 30 weeks (P< 0.0005), with some mice living up to 32 weeks of age (Figure 6B). Hence, selumetinib treatment prolongs the lifespan of male LmnaH222P/H222P mice, consistent with its beneficial effects on cardiac function.

Figure 6

Oral selumetinib inhibits ERK1/2 activity in heart and prolongs survival of LmnaH222P/H222P mice. (A) Representative immunoblots using antibodies against phosphorylated ERK1/2 (pERK1/2) and total ERK1/2 (ERK1/2) to probe proteins extracted from hearts from LmnaH222P/H222P mice treated with selumetinib or DMSO in the drinking water. The bar graph shows means ± SEM signals pERK1/2/total ERK1/2 (relative expression from immunoblots of n = 5 mice treated with selumetinib and n = 5 mice treated with DMSO). *P< 0.05. (B) The Kaplan–Meier analysis of selumetinib-treated (n = 10) and DMSO-treated (n = 7) LmnaH222P/H222P mice.

Figure 6

Oral selumetinib inhibits ERK1/2 activity in heart and prolongs survival of LmnaH222P/H222P mice. (A) Representative immunoblots using antibodies against phosphorylated ERK1/2 (pERK1/2) and total ERK1/2 (ERK1/2) to probe proteins extracted from hearts from LmnaH222P/H222P mice treated with selumetinib or DMSO in the drinking water. The bar graph shows means ± SEM signals pERK1/2/total ERK1/2 (relative expression from immunoblots of n = 5 mice treated with selumetinib and n = 5 mice treated with DMSO). *P< 0.05. (B) The Kaplan–Meier analysis of selumetinib-treated (n = 10) and DMSO-treated (n = 7) LmnaH222P/H222P mice.

Preliminary analysis of potential renal, hepatic, and pancreatic toxicity of selumetinib in LmnaH222P/H222P mice with cardiomyopathy

Selumetinib has been studied in Phase I and Phase II human clinical trials.20–22 However, its potential safety in subjects with cardiomyopathy is unknown. We therefore carried out a preliminary analysis of potential renal, hepatic, and pancreatic toxicity in the male LmnaH222P/H222P mice that were treated with selumetinib from 16 to 20 weeks of age. At the end of 4 weeks of treatment, we measured serum alkaline phosphatase activity, alanine aminotransferase activity, albumin concentration, globulin concentration, and bilirubin concentration to assess liver injury and function. We also measured serum creatinine and blood urea nitrogen concentrations as indicators of renal function and serum amylase activity as a marker of pancreatic injury. There were no statistically significant differences in any of these parameters between male LmnaH222P/H222P mice treated with selumetinib or placebo except for a decrease in serum alanine aminotransferase activity in the selumetinib-treated mice (Table 2). Significant abnormalities in serum chemistries have also not been reported in human clinical trials of selumetinib.19–21

Table 2

Selected serum chemistry values in male LmnaH222P/H222P mice 20 weeks of age treated for 4 weeks with selumetinib or placebo (DMSO)

Treatment Alk Phos (U/L) ALT (U/L) Amylase (U/L) BUN (mg/dL) Albumin (g/dL) Creatinine (mg/dL) Globulin (g/dL) Bilirubin (mg/dL) 
DMSO (n = 8) 74.1 ± 8.0 106.0 ± 22.4 1,244.0 ± 244.7 34.1 ± 8.6 2.8 ± 0.5 0.3 ± 0.1 1.4 ± 0.5 <0.6 
Selumetinib (n = 15) 76.1 ± 5.6 57.0 ± 10.5* 1,295.0 ± 153.8 25.7 ± 2.4 2.7 ± 0.2 0.3 ± 0.1 1.8 ± 0.2 <0.6 
Treatment Alk Phos (U/L) ALT (U/L) Amylase (U/L) BUN (mg/dL) Albumin (g/dL) Creatinine (mg/dL) Globulin (g/dL) Bilirubin (mg/dL) 
DMSO (n = 8) 74.1 ± 8.0 106.0 ± 22.4 1,244.0 ± 244.7 34.1 ± 8.6 2.8 ± 0.5 0.3 ± 0.1 1.4 ± 0.5 <0.6 
Selumetinib (n = 15) 76.1 ± 5.6 57.0 ± 10.5* 1,295.0 ± 153.8 25.7 ± 2.4 2.7 ± 0.2 0.3 ± 0.1 1.8 ± 0.2 <0.6 

Values are means ± SEM. Alk Phos, alkaline phosphatase; ALT, alanine aminotransferase; BUN, blood urea nitrogen. *P< 0.05.

Discussion

Dilated cardiomyopathy caused by LMNA mutation is a particularly aggressive inherited disease often leading to sudden death and heart failure. Despite its aggressive course, there is no specific therapeutic intervention that improves cardiac function or prevents heart muscle deterioration. We have previously reported aberrant activation of ERK1/2 signalling in hearts of LmnaH222P/H222P mice, a small animal model that phenocopies human cardiomyopathy caused by LMNA mutation.12 This abnormal activation of cardiac ERK1/2 occurs prior to the development of significant cardiac muscle damage or fibrosis, suggesting that it is a primary pathogenic process in LMNA cardiomyopathy. We have now shown similar abnormally activated ERK1/2 signalling in hearts of human subjects with LMNA cardiomyopathy. While it was not possible to obtain heart tissue from human subjects prior to the onset of clinical disease, this suggests that the same pathological process that occurs in model mice may occur in humans with the disease.

We have more recently showed that inhibiting ERK1/2 signalling using small molecule inhibitors of MEK1/2 can prevent the development of cardiomyopathy in LmnaH222P/H222P mice as well as improve cardiac function after there has been some deterioration in contractility.13,15 We have now shown that an MEK1/2 inhibitor, selumetinib, which has been safely given to humans for other indications, has beneficial effects on cardiac pathology in LmnaH222P/H222P mice. Selumetinib treatment prevented further left ventricular dilatation and deterioration of cardiac contractility compared with placebo in male LmnaH222P/H222P mice when started at an age when these mice already have chamber dilatation and decreased FS. It also had other beneficial effects, including on the development of cardiac fibrosis, an end-stage and irreversible predominant feature of LMNA cardiomyopathy.

Our results also strongly suggested that selumetinib can prolong survival in male LmnaH222P/H222P mice. We showed that male LmnaH222P/H222P mice treated with DMSO starting at 16 weeks of age had a median survival of 27 weeks, similar to that previously reported,11,25 while the selumetinib-treated mice had a median survival of 30 weeks. While the prolongation of survival induced by selumetinib was modest, it was highly statistically significant (P< 0.0005). In another study using SCH00013, a calcium-sensitizing agent, 50% survival time was significantly prolonged by 0.8 months in male LmnaH222P/H222P mice, although a Kaplan–Meier analysis of the overall mortality showed no statistical difference; in female LmnaH222P/H222P mice, there were significantly prolonged 50% survival time and reduced overall mortality.25 In addition to cardiac disease, male LmnaH222P/H222P mice also develop myopathy of striated muscles other than the heart, including the diaphragm, by 24 weeks of age.11 Hence, the early death of selumetinib-treated male LmnaH222P/H222P mice may very well be secondary to problems such as decreased locomotion or respiratory capacity rather than a complication of cardiomyopathy.

For selumetinib to be a useful drug for human subjects with LMNA cardiomyopathy, it would have to be safe for long-term use. In Phase II clinical trials of selumetinib given for 3 weeks for cancer, frequent but manageable adverse events were rash, nausea, and diarrhea.20,21 These clinical trials used a dose of 1.5–2.0 mg/kg orally twice a day, which is three to four times the dose we used in the present mouse studies. In the male LmnaH222P/H222P mice with cardiomyopathy that received 1 mg/kg/day of selumetinib for 4 weeks, serum biochemical analysis did not reveal any evidence of renal, hepatic, or pancreatic toxicity. Renal and hepatic toxicities are common reasons for new drugs to fail in clinical trials and lack of renal toxicity may be of particular significance in subjects with reduced kidney perfusion secondary to heart failure and reduced kidney perfusion. While safety data on long-term administration of MEK1/2 inhibitors are not readily available, sorafenib, an inhibitor of Raf further upstream in the ERK1/2 signalling cascade, has been tolerated for longer than 2 years in human subjects.26 While some studies have associated cardiac toxicity with the use of tyrosine kinase inhibitors, including sorafenib, the biological effects vary widely across the members of this family of drugs and left ventricular dysfunction does not seem to be common to most.27

Our promising preclinical results suggest that selumetinib could potentially be used to treat LMNA cardiomyopathy. The risks associated with this novel therapy would need to be low, particularly as the treatment may be needed for years. Such treatment may also be applicable to other cardiomyopathies in which there appears to be early abnormal activation of ERK1/2 signalling, such as Chagas disease, caveolin-3 gene mutations, and Noonan syndrome.28–30 ERK1/2 hyperactivation also occurs in dilated, late-stage failing hearts resulting from several different aetiologies.31 Ultimately, only prospective clinical trials in human subjects can determine the risks and benefits of selumetinib or other MEK1/2 inhibitors for patients with these cardiomyopathies.

Supplementary material

Supplementary material is available at Cardiovascular Research online.

Conflict of interest: H.J.W. and A.M. are inventors on a pending PCT patent application on methods for treating and/or preventing cardiomyopathies by ERK and JNK inhibition filed by the Trustees of Columbia University in the City of New York.

Funding

This work was supported by a grant (MDA172222) from the Muscular Dystrophy Association and by a BioAccelerate NYC Prize from the New York City Partnership, Inc. A.M. is supported by a grant from Association Française contre les Myopathies.

References

1
Worman
HJ
Fong
LG
Muchir
A
Young
SG
Laminopathies and the long strange trip from basic cell biology to therapy
J Clin Invest
 , 
2009
, vol. 
119
 (pg. 
1825
-
1836
)
2
Bonne
G
Di Barletta
MR
Varnous
S
Becane
HM
Hammouda
EH
Merlini
L
, et al.  . 
Mutations in the gene encoding lamin A/C cause autosomal dominant Emery–Dreifuss muscular dystrophy
Nat Genet
 , 
1999
, vol. 
21
 (pg. 
285
-
288
)
3
Fatkin
D
MacRae
C
Sasaki
T
Wolff
MR
Porcu
M
Frenneaux
M
, et al.  . 
Missense mutations in the rod domain of the lamin A/C gene as causes of dilated cardiomyopathy and conduction-system disease
N Engl J Med
 , 
1999
, vol. 
341
 (pg. 
1715
-
1724
)
4
Muchir
A
Bonne
G
van der Kooi
AJ
van Meegen
M
Baas
F
Bolhuis
PA
, et al.  . 
Identification of mutations in the gene encoding lamins A/C in autosomal dominant limb girdle muscular dystrophy with atrioventricular conduction disturbances (LGMD1B)
Hum Mol Genet
 , 
2000
, vol. 
9
 (pg. 
1453
-
1459
)
5
Taylor
MR
Fain
PR
Sinagra
G
Robinson
ML
Robertson
AD
Carniel
E
, et al.  . 
Familial Dilated Cardiomyopathy Registry Research Group
Natural history of dilated cardiomyopathy due to lamin A/C gene mutations
J Am Coll Cardiol
 , 
2003
, vol. 
41
 (pg. 
771
-
780
)
6
Parks
SB
Kushner
JD
Nauman
D
Burgess
D
Ludwigsen
S
Peterson
A
, et al.  . 
Lamin A/C mutation analysis in a cohort of 324 unrelated patients with idiopathic or familial dilated cardiomyopathy
Am Heart J
 , 
2008
, vol. 
156
 (pg. 
161
-
169
)
7
Arbustini
E
Pilotto
A
Repetto
A
Grasso
M
Negri
A
Diegoli
M
, et al.  . 
Autosomal dominant dilated cardiomyopathy with atrioventricular block: a lamin A/C defect-related disease
J Am Coll Cardiol
 , 
2002
, vol. 
39
 (pg. 
981
-
990
)
8
van Berlo
JH
de Voogt
WG
van der Kooi
AJ
van Tintelen
JP
Bonne
G
Yaou
RB
, et al.  . 
Meta-analysis of clinical characteristics of 299 carriers of LMNA gene mutations: do lamin A/C mutations portend a high risk of sudden death?
J Mol Med
 , 
2005
, vol. 
83
 (pg. 
79
-
83
)
9
Pasotti
M
Klersy
C
Pilotto
A
Marziliano
N
Rapezzi
C
Serio
A
, et al.  . 
Long-term outcome and risk stratification in dilated cardiolaminopathies
J Am Coll Cardiol
 , 
2008
, vol. 
52
 (pg. 
1250
-
1260
)
10
Stewart
CL
Kozlov
S
Fong
LG
Young
SG
Mouse models of the laminopathies
Exp Cell Res
 , 
2007
, vol. 
313
 (pg. 
2144
-
2156
)
11
Arimura
T
Helbling-Leclerc
A
Massart
C
Varnous
S
Niel
F
Lacène
E
, et al.  . 
Mouse model carrying H222P-Lmna mutation develops muscular dystrophy and dilated cardiomyopathy similar to human striated muscle laminopathies
Hum Mol Genet
 , 
2005
, vol. 
14
 (pg. 
155
-
169
)
12
Muchir
A
Pavlidis
P
Decostre
V
Herron
AJ
Arimura
T
Bonne
G
, et al.  . 
Activation of MAPK pathway links LMNA mutations to cardiomyopathy in Emery–Dreifuss muscular dystrophy
J Clin Invest
 , 
2007
, vol. 
117
 (pg. 
1282
-
1293
)
13
Muchir
A
Shan
J
Bonne
G
Lehnart
SE
Worman
HJ
Inhibition of extracellular signal-regulate kinase signaling to prevent cardiomyopathy caused by mutation in the gene encoding A-type lamins
Hum Mol Genet
 , 
2009
, vol. 
18
 (pg. 
241
-
247
)
14
Wu
W
Shan
J
Bonne
G
Worman
HJ
Muchir
A
Pharmacological inhibition of c-Jun N-terminal kinase signaling prevents cardiomyopathy caused by mutation in LMNA gene
Biochim Biophys Acta
 , 
2010
, vol. 
1802
 (pg. 
632
-
638
)
15
Wu
W
Muchir
A
Shan
J
Bonne
G
Worman
HJ
Mitogen activated protein kinase inhibitors improve heart function and prevent fibrosis in cardiomyopathy caused by lamin A/C gene mutation
Circulation
 , 
2011
, vol. 
123
 (pg. 
53
-
61
)
16
Frémin
C
Meloche
S
From basic research to clinical development of MEK1/2 inhibitors for cancer therapy
J Hemat Oncol
 , 
2010
, vol. 
3
 pg. 
8
 
17
Denton
CL
Gustafson
DL
Pharmacokinetics and pharmacodynamics of AZD6244 (ARRY-142886) in tumor-bearing nude mice
Cancer Chemother Pharmacol
 , 
2010
, vol. 
67
 (pg. 
349
-
360
)
18
Yeh
T
Marsh
V
Bernat
BA
Ballard
J
Colwell
H
Evans
RJ
, et al.  . 
Biological characterization of ARRY-142886 (AZD6244), a potent, highly selective mitogen-activated protein kinase kinase1/2 inhibitor
Clin Cancer Res
 , 
2001
, vol. 
13
 (pg. 
1576
-
1582
)
19
Adjei
AA
Cohen
RB
Franklin
W
Morris
C
Wilson
D
Molina
JR
, et al.  . 
Phase I pharmacokinetics and pharmacodynamics study of the oral, small-molecule mitogen-activated protein kinase kinase 1/2 inhibitor AZD6244 (ARRY-142886) in patients with advanced cancers
J Clin Oncol
 , 
2008
, vol. 
26
 (pg. 
2139
-
2146
)
20
Bekaii-Saab
T
Phelps
MA
Li
X
Saji
M
Goff
L
Sae
J
, et al.  . 
Multi-institutional phase II study of selumetinib in patients with metastatic biliary cancer
J Clin Oncol
 , 
2011
, vol. 
29
 (pg. 
2357
-
2363
)
21
O'Neil
BH
Goff
LW
Kauh
JS
Strosberg
JR
Bekaii-Saab
TS
Lee
RM
, et al.  . 
Phase II study of the mitogen-activated protein kinase 1/2 inhibitor selumetinib in patients with advanced hepatocellular carcionoma
J Clin Oncol
 , 
2011
, vol. 
29
 (pg. 
2350
-
2356
)
22
Bhalla
S
Gartenhaus
R
Dai
B
Prachand
S
Mukherjee
A
Elstrom
R
, et al.  . 
The novel 2nd generation small molecule MEK inhibitor, AZD-6244, induces cell death in lymphoma cells lines, primary cells, and in a human lymphoma xenograft model
Blood (ASH Annual Meeting Abstracts)
 , 
2009
, vol. 
114
 pg. 
285
  
(Abstract)
23
Ponchel
F
Toomes
C
Bransfield
K
Leong
FT
Douglas
SH
Field
SL
, et al.  . 
Real-time PCR based on SYBR-Green I fluorescence: an alternative to the TaqMan assay for a relative quantification of gene rearrangements, gene amplifications and micro gene deletions
BMC Biotechnol
 , 
2003
, vol. 
3
 pg. 
18
 
24
Kaplan
EL
Meier
P
Nonparametric estimation from incomplete observations
J Am Stat Assn
 , 
1958
, vol. 
53
 (pg. 
457
-
481
)
25
Arimura
T
Sato
R
Machida
N
Bando
H
Zhan
DY
Morimoto
S
, et al.  . 
Improvement of left ventricular dysfunction and of survival prognosis of dilated cardiomyopathy by administration of calcium sensitizer SCH00013 in a mouse model
J Am Coll Cardiol
 , 
2010
, vol. 
55
 (pg. 
1503
-
1505
)
26
Hutson
TE
Bellmunt
J
Porta
C
Szczylik
C
Staehler
M
Nadel
A
, et al.  . 
TARGET Clinical Trial Group
Long-term safety of sorafenib in advanced renal cell carcinoma: follow-up of patients from phase III TARGET
Eur J Cancer
 , 
2010
, vol. 
46
 (pg. 
2432
-
2440
)
27
Woodman
SE
Park
DS
Cohen
AW
Cheung
MW
Chandra
M
Shirani
J
, et al.  . 
Caveolin-3 knock-out mice develop a progressive cardiomyopathy and show hyperactivation of the p42/44 MAPK cascade
J Biol Chem
 , 
2002
, vol. 
277
 (pg. 
38988
-
38997
)
28
Huang
H
Petkova
SB
Pestell
RG
Bouzahzah
B
Chan
J
Magazine
H
, et al.  . 
Trypanosoma cruzi infection (Chagas' disease) of mice causes activation of the mitogen-activated protein kinase cascade and expression of endothelin-1 in the myocardium
J Cardiovasc Pharmacol
 , 
2000
, vol. 
36
 (pg. 
S148
-
S150
)
29
Wu
X
Simpson
J
Hong
JH
Kim
KH
Thavarajah
NK
Backx
PH
, et al.  . 
MEK-ERK pathway modulation ameliorates disease phenotypes in a mouse model of Noonan syndrome associated with the Raf1(L613V) mutation
J Clin Invest
 , 
2011
, vol. 
121
 (pg. 
1009
-
1025
)
30
Haq
S
Choukroun
G
Lim
H
Tymitz
KM
del Monte
F
Gwathmey
J
, et al.  . 
Differential activation of signal transduction pathways in human hearts with hypertrophy versus advanced heart failure
Circulation
 , 
2001
, vol. 
103
 (pg. 
670
-
677
)
31
Chen
MH
Kerkelä
R
Force
T
Mechanisms of cardiac dysfunction associated with tyrosine kinase inhibitor cancer therapeutics
Circulation
 , 
2008
, vol. 
118
 (pg. 
84
-
95
)