Structural reengineering of imatinib to decrease cardiac risk in cancer therapy

Mitochondrial Dysfunction in Cardiotoxicity Induced by BCR-ABL1 Tyrosine Kinase Inhibitors -Underlying Mechanisms, Detection, Potential Therapies

The advent of BCR-ABL tyrosine kinase inhibitors (TKIs) targeted therapy revolutionized the treatment of chronic myeloid leukemia (CML) patients. Mitochondria are the key organelles for the maintenance of myocardial tissue homeostasis. However, cardiotoxicity associated with BCR-ABL1 TKIs can directly or indirectly cause mitochondrial damage and dysfunction, playing a pivotal role in cardiomyocytes homeostatic system and putting the cancer survivors at higher risk. In this review, we summarize the cardiotoxicity caused by BCR-ABL1 TKIs and the underlying mechanisms, which contribute dominantly to the damage of mitochondrial structure and dysfunction: endoplasmic reticulum (ER) stress, mitochondrial stress, damage of myocardial cell mitochondrial respiratory chain, increased production of mitochondrial reactive oxygen species (ROS), and other kinases and other potential mechanisms of cardiotoxicity induced by BCR-ABL1 TKIs. Furthermore, detection and management of BCR-ABL1 TKIs will promote our rational use, and cardioprotection strategies based on mitochondria will improve our understanding of the cardiotoxicity from a mitochondrial perspective. Ultimately, we hope shed light on clinical decision-making. By integrate and learn from both research and practice, we will endeavor to minimize the mitochondria-mediated cardiotoxicity and reduce the adverse sequelae associated with BCR-ABL1 TKIs.

Validating the pharmacogenomics of chemotherapy-induced cardiotoxicity: What is missing?

The cardiotoxicity of certain chemotherapeutic agents is now well-established, and has led to the development of the field of cardio-oncology, increased cardiac screening of cancer patients, and limitation of patients' maximum cumulative chemotherapeutic dose. The effect of chemotherapeutic regimes on the heart largely involves cardiomyocyte death, leading to cardiomyopathy and heart failure, or the induction of arrhythmias. Of these cardiotoxic drugs, those resulting in clinical cardiotoxicity can range from 8 to 26% for doxorubicin, 7-28% for trastuzumab, or 5-30% for paclitaxel. For tyrosine kinase inhibitors, QT prolongation and arrhythmia, ischemia and hypertension have been reported in 2-35% of patients. Furthermore, newly introduced chemotherapeutic agents are commonly used as part of changed combinational regimens with significantly increased incidence of cardiotoxicity. It is widely believed that the mechanism of action of these drugs is often independent of their cardiotoxicity, and the basis for why these drugs specifically affect the heart has yet to be established. The genetic rationale for why certain patients experience cardiotoxicity whilst other patients can tolerate high chemotherapy doses has proven highly illusive. This has led to significant genomic efforts using targeted and genome-wide association studies (GWAS) to divine the pharmacogenomic cause of this predilection. With the advent of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), the putative risk and protective role of single nucleotide polymorphisms (SNPs) can now be validated in a human model. Here we review the state of the art knowledge of the genetic predilection to chemotherapy-induced cardiotoxicity and discuss the future for establishing and validating the role of the genome in this disease.

Cardiotoxicity associated with targeted cancer therapies

Compared with traditional chemotherapy, targeted cancer therapy is a novel strategy in which key molecules in signaling pathways involved in carcinogenesis and tumor spread are inhibited. Targeted cancer therapy has fewer adverse effects on normal cells and is considered to be the future of chemotherapy. However, targeted cancer therapy-induced cardiovascular toxicities are occasionally critical issues in patients who receive novel anticancer agents, such as trastuzumab, bevacizumab, sunitinib and imatinib. The aim of this review was to discuss these most commonly used drugs and associated incidence of cardiotoxicities, including left ventricular dysfunction, heart failure, hypertension and thromboembolic events, as well as summarize their respective molecular mechanisms of cardiovascular adverse effects.

Ageing is a risk factor in imatinib mesylate cardiotoxicity

AIMS

Chemotherapy-induced heart failure is increasingly recognized as a major clinical challenge. Cardiotoxicity of imatinib mesylate, a highly selective and effective anticancer drug belonging to the new class of tyrosine kinase inhibitors, is being reported in patients, some progressing to congestive heart failure. This represents an unanticipated challenge that could limit effective drug use. Understanding the mechanisms and risk factors of imatinib mesylate cardiotoxicity is crucial for prevention of cardiovascular complications in cancer patients.

METHODS AND RESULTS

We used genetically engineered mice and primary rat neonatal cardiomyocytes to analyse the action of imatinib on the heart. We found that treatment with imatinib (200 mg/kg/day for 5 weeks) leads to mitochondrial-dependent myocyte loss and cardiac dysfunction, as confirmed by electron microscopy, RNA analysis, and echocardiography. Imatinib cardiotoxicity was more severe in older mice, in part due to an age-dependent increase in oxidative stress. Mechanistically, depletion of the transcription factor GATA4 resulting in decreased levels of its prosurvival targets Bcl-2 and Bcl-XL was an underlying cause of imatinib toxicity. Consistent with this, GATA4 haploinsufficient mice were more susceptible to imatinib, and myocyte-specific up-regulation of GATA4 or Bcl-2 protected against drug-induced cardiotoxicity.

CONCLUSION

The results indicate that imatinib action on the heart targets cardiomyocytes and involves mitochondrial impairment and cell death that can be further aggravated by oxidative stress. This in turn offers a possible explanation for the current conflicting data regarding imatinib cardiotoxicity in cancer patients and suggests that cardiac monitoring of older patients receiving imatinib therapy may be especially warranted.

Synergizing immunotherapy with molecular-targeted anticancer treatment

The therapeutic opportunity for anticancer kinase inhibitors (KIs) that block cell-signaling pathways is materializing. Yet, these molecular-targeted therapies are not tailored to be allies of the immune system, and often antagonize it despite generating antigenic activity. KIs usually offer an incomplete cure and one culprit is the lack of synergy between the drug and the immune system, a problem that is magnified when the therapeutic context involves HIV-1-induced immunosuppression (AIDS). We outline a strategy to fulfill the therapeutic imperative of recruiting cooperative immune responses. Accordingly, we propose a method to redesign anticancer drugs to harness the antigenic products of drug-induced apoptosis of tumor cells, thus eliciting an adjuvant immune response.

Daunorubicin induces cell death via activation of apoptotic signalling pathway and inactivation of survival pathway in muscle-derived stem cells

Daunorubicin (as well as other anthracyclines) is known to be toxic to heart cells and other cells in organism thus limiting its applicability in human cancer therapy. To investigate possible mechanisms of daunorubicin cytotoxicity, we used stem cell lines derived from adult rabbit skeletal muscle. Recently, we have shown that daunorubicin induces apoptotic cell death in our cell model system and distinctly influences the activity of MAP kinases. Here, we demonstrate that two widely accepted antagonistic signalling pathways namely proapoptotic JNK and prosurvival PI3K/AKT participate in apoptosis. Using the Western blot method, we observed the activation of JNK and phosphorylation of its direct target c-Jun along with inactivation of AKT and its direct target GSK in the course of programmed cell death. By means of small-molecule kinase inhibitors and transfection of cells with the genes of the components of these pathways, c-Jun and AKT, we confirm that JNK signalling pathway is proapoptotic, whereas AKT is antiapoptotic in daunorubicin-induced muscle cells. These findings could contribute to new approaches which will result in less toxicity and fewer side effects that are currently associated with the use of daunorubicin in cancer therapies.

Predicting adverse side effects of drugs

Background

Studies of toxicity and unintended side effects can lead to improved drug safety and efficacy. One promising form of study comes from molecular systems biology in the form of "systems pharmacology". Systems pharmacology combines data from clinical observation and molecular biology. This approach is new, however, and there are few examples of how it can practically predict adverse reactions (ADRs) from an experimental drug with acceptable accuracy.

Results

We have developed a new and practical computational framework to accurately predict ADRs of trial drugs. We combine clinical observation data with drug target data, protein-protein interaction (PPI) networks, and gene ontology (GO) annotations. We use cardiotoxicity, one of the major causes for drug withdrawals, as a case study to demonstrate the power of the framework. Our results show that an in silico model built on this framework can achieve a satisfactory cardiotoxicity ADR prediction performance (median AUC = 0.771, Accuracy = 0.675, Sensitivity = 0.632, and Specificity = 0.789). Our results also demonstrate the significance of incorporating prior knowledge, including gene networks and gene annotations, to improve future ADR assessments.

Conclusions

Biomolecular network and gene annotation information can significantly improve the predictive accuracy of ADR of drugs under development. The use of PPI networks can increase prediction specificity and the use of GO annotations can increase prediction sensitivity. Using cardiotoxicity as an example, we are able to further identify cardiotoxicity-related proteins among drug target expanding PPI networks. The systems pharmacology approach that we developed in this study can be generally applicable to all future developmental drug ADR assessments and predictions.

MicroRNA-494 downregulates KIT and inhibits gastrointestinal stromal tumor cell proliferation

PURPOSE

Gain-of-function mutations and KIT overexpression are well-known tumorigenesis mechanisms in gastrointestinal stromal tumors (GIST). This study aimed to discover microRNAs (miRNA) that target KIT and reveal the relationship between the discovered miRNAs and KIT expression in GISTs.

EXPERIMENTAL DESIGN

Fresh-frozen GISTs from 31 patients were used to confirm the relationship between miR-494 and KIT expression using quantitative reverse transcription-PCR to assess miR-494 expression levels and Western blotting to assess KIT protein expression levels. A luciferase assay was conducted for the target evaluation. The functional effects of miR-494 on GIST882 cells (GIST cell line with activating KIT mutation) were validated by a cell proliferation assay and fluoresce-activated cell sorting analysis.

RESULTS

An inverse relationship was found between the expression levels of miR-494 and KIT in GISTs (r = -0.490, P = 0.005). The direct targeting of KIT by miR-494 was shown by the reduction in KIT expression after miR-494 overexpression and the increase in KIT expression after inhibiting endogenous miR-494 expression. We showed that miR-494 regulates KIT by binding two different seed match sites. Induced miR-494 overexpression in GIST882 reduced the expression of downstream molecules in KIT signaling transduction pathways, including phospho-AKT and phospho-STAT3. Finally, miR-494 overexpression provoked apoptosis and inhibited GIST cell growth, which were accompanied by changes in G(1) and S phase content.

CONCLUSION

Our findings indicate that miR-494 is a negative regulator of KIT in GISTs and overexpressing miR-494 in GISTs may be a promising approach to GIST treatment.

Imatinib treatment duration is related to decreased estimated glomerular filtration rate in chronic myeloid leukemia patients

BACKGROUND

We analyzed the incidence of acute kidney injury and chronic renal failure in chronic myeloid leukemia (CML) patients using imatinib and investigated whether there is a relation between duration of imatinib therapy and decrease in estimated glomerular filtration rate (GFR).

PATIENTS AND METHODS

One hundred five CML patients on imatinib therapy were enrolled. Creatinine, urea, uric acid, and potassium measurements from imatinib treatment onset until the end of follow-up (median 4.5 years) were included in the analysis. GFR was estimated using the Chronic Kidney Disease Epidemiology Collaboration equation.

RESULTS

During follow-up, 7% of patients developed acute kidney injury; creatinine levels returned to baseline in only one of them. According to the regression equation, the mean baseline value of the estimated GFR was 88.9 ml/min/1.73 m(2). Estimated GFR decreased significantly with imatinib treatment duration; the mean decrease per year was 2.77 ml/min/1.73 m(2) (P < 0.001); 12% of patients developed chronic renal failure. Age, hypertension, and a history of chronic renal failure or interferon usage were not significantly related to the mean decrease in the estimated GFR over time.

CONCLUSION

The introduction of imatinib therapy in nonclinical trial CML patients is associated with potentially irreversible acute renal injury, and the long-term treatment may cause a clinically relevant decrease in the estimated GFR.

Why do kinase inhibitors cause cardiotoxicity and what can be done about it?

Cancer growth and metastasis are often driven by activating mutations in, or gene amplications of, specific tyrosine or serine/threonine kinases. Kinase inhibitors (KIs) promised to provide targeted therapy-specifically inhibiting the causal or contributory kinases driving tumor progression while leaving function of other kinases intact. These inhibitors are of 2 general classes: (1) monoclonal antibodies that are typically directed against receptor tyrosine kinases or their ligands and (2) small molecules targeting specific kinases. The latter will be the focus of this review. This class of therapeutics has had some remarkable successes, including revolutionizing the treatment of some malignancies (eg, imatinib [Gleevec] in the management of chronic myeloid leukemia) and adding significantly to the management of other difficult to treat cancers (eg, sunitinib [Sutent] and sorafenib [Nexavar] in the management of renal cell carcinoma). But in some instances, cardiotoxicity, often manifest as left ventricular dysfunction and/or heart failure, has ensued after the use of KIs in patients. Herein we will explore the mechanisms underlying the cardiotoxicity of small-molecule KIs, hoping to explain how and why this happens, and will further examine strategies to deal with the problem.

Collateral damage: toxic effects of targeted antiangiogenic therapies in ovarian cancer

First-line chemotherapy fails in more than 20% of patients with epithelial ovarian cancer and about 40-50% of women who respond to initial treatment relapse within 2 years. In the recurrent setting, second-line chemotherapeutic agents have a 15-20% response rate with no cures. Fortunately, clinical investigations that have assessed the efficacy of new, biologically targeted therapies have reinvigorated therapeutic options for patients living with ovarian and other malignancies. In view of the fact that ovarian cancer is one of the most angiogenic neoplasms, there is great hope that implementing targeted agents with antiangiogenic properties will improve outcomes. However, as experience grows with the antitumour activity of these drugs, new toxic effects are emerging. The effects of antiangiogenic agents on molecules and processes that also have physiologically important roles in healthy tissues are at the crux of these toxic effects, or "collateral damage". This review discusses the leading toxic effects encountered and anticipated in clinical investigation and practice with antiangiogenic agents in patients with ovarian cancer, with particular focus on potential management strategies.

Molecular mechanisms of cardiovascular toxicity of targeted cancer therapeutics

In 2002, Hoshijima and Chien drew largely theoretical parallels between the dysregulation of the signaling pathways driving cancer and those driving cardiac hypertrophy (Hoshijima M, Chien KR. J Clin Invest. 2002;109:849-855). On the surface, this statement appeared to stretch the limits of reason, given the fact that cancer cells are known for their proliferative capacity, and adult cardiomyocytes are, except under unusual circumstances, terminally differentiated and incapable of re-entering the cell cycle. However, on closer examination, there are numerous parallels between signaling pathways that drive tumorigenesis and signaling pathways that regulate hypertrophic responses and survival in cardiomyocytes. Indeed, this issue appears to be at the core of the cardiotoxicity (often manifest as a dilated cardiomyopathy) that can result from treatment with agents typically referred to as "targeted therapeutics," which target specific protein kinases that are dysregulated in cancer. Herein, we examine the cardiotoxicity of targeted therapeutics, focusing on the underlying molecular mechanisms, thereby allowing an understanding of the problem but also allowing the identification of novel, and sometimes surprising, roles played by protein kinases in the heart.

Cardiomyocyte PDGFR-beta signaling is an essential component of the mouse cardiac response to load-induced stress

PDGFR is an important target for novel anticancer therapeutics because it is overexpressed in a wide variety of malignancies. Recently, however, several anticancer drugs that inhibit PDGFR signaling have been associated with clinical heart failure. Understanding this effect of PDGFR inhibitors has been difficult because the role of PDGFR signaling in the heart remains largely unexplored. As described herein, we have found that PDGFR-beta expression and activation increase dramatically in the hearts of mice exposed to load-induced cardiac stress. In mice in which Pdgfrb was knocked out in the heart in development or in adulthood, exposure to load-induced stress resulted in cardiac dysfunction and heart failure. Mechanistically, we showed that cardiomyocyte PDGFR-beta signaling plays a vital role in stress-induced cardiac angiogenesis. Specifically, we demonstrated that cardiomyocyte PDGFR-beta was an essential upstream regulator of the stress-induced paracrine angiogenic capacity (the angiogenic potential) of cardiomyocytes. These results demonstrate that cardiomyocyte PDGFR-beta is a regulator of the compensatory cardiac response to pressure overload-induced stress. Furthermore, our findings may provide insights into the mechanism of cardiotoxicity due to anticancer PDGFR inhibitors.

Protein wrapping: a molecular marker for association, aggregation and drug design

In this tutorial review we survey the concept of protein wrapping from a physico-chemical perspective. Wrapping is introduced as an indicator of the packing quality of protein structure. Thus, while a well-wrapped protein is sustainable in isolation, a poorly wrapped protein is reliant on binding partnerships to maintain its structural integrity. At a local level, wrapping is indicative of the extent of solvent exposure of the amide-carbonyl hydrogen bonds of the protein backbone. Poorly wrapped hydrogen bonds, the so-called dehydrons, are shown to represent structural vulnerabilities. These singularities are sticky, hence promoters of protein associations. We also focus on severely under-wrapped protein structures that belong to an order/disorder twilight. Such proteins are shown to be prone to aggregate. Finally, we survey the recent exploitation of dehydrons as targetable features to promote specificity in drug-based cancer therapy. Dehydrons prove to be valuable targets to reduce side effects and enhance drug safety.

Redesigning kinase inhibitors to enhance specificity

Kinases are important targets in molecular cancer therapy. However, the evolutionary relatedness and structural conservation of these proteins often lead to unforeseen cross reactivity, yielding unexpected side effects. Thus, the use of promiscuous drugs is likely to introduce dangerous clinical uncertainties. Here, we show how to rationally redesign two promiscuous kinase inhibitors, staurosporine (7) and EKB-569 (8), with the goal of turning them into more selective ligands. This problem is addressed by exploiting a structure-based selectivity filter for specificity: the pattern of packing defects in the target. These singularities, called dehydrons, are solvent-exposed intramolecular hydrogen bonds that may be protected by drugs upon association and are not conserved across protein families. Our redesigned compounds possess a significantly focused activity, as experimentally corroborated in high-throughput screening assays. Thus, our design strategy proves to be operative to reduce the inhibitory impact of promiscuous kinase ligands, enhancing their safety as therapeutic agents.

Mast cells and cancer--no longer just basic science

The incorporation of new anti-cancer kinase inhibitors within cancer management is rapidly increasing. Mast cells are sensitive to several of these new anti-cancer agents most notably to c-Kit inhibitors. As a result, studies investigating the role of mast cells in tumors may have direct clinical relevance and consequently, important clinical implications. Here we review some of the basic attributes of mast cells, especially those related to the new "targeted" drugs. Mast cell roles such as modulators of regulatory T-cells, inducers of angiogenesis and promoters of clot formation are discussed. We also review recent mouse tumor models and human pathological data which implicate mast cells as having both pro- and anti-tumor growth properties. These studies expose a complex, emerging picture of mast cell involvement in tumor biology. It seems that mast cell modulator drugs may improve the efficacy of anti-tumor therapy under certain circumstances, whilst under others, may negatively affect drug efficacy.