Cardiotoxicity of kinase inhibitors: the prediction and translation of preclinical models to clinical outcomes

Mitochondria death/survival signaling pathways in cardiotoxicity induced by anthracyclines and anticancer-targeted therapies

Anthracyclines remain the cornerstone of treatment in many malignancies but these agents have a cumulative dose relationship with cardiotoxicity. Development of cardiomyopathy and congestive heart failure induced by anthracyclines are typically dose-dependent, irreversible, and cumulative. Although past studies of cardiotoxicity have focused on anthracyclines, more recently interest has turned to anticancer drugs that target many proteins kinases, such as tyrosine kinases. An attractive model to explain the mechanism of this cardiotoxicity could be myocyte loss through cell death pathways. Inhibition of mitochondrial transition permeability is a valuable tool to prevent doxorubicin-induced cardiotoxicity. In response to anthracycline treatment, activation of several protein kinases, neuregulin/ErbB2 signaling, and transcriptional factors modify mitochondrial functions that determine cell death or survival through the modulation of mitochondrial membrane permeability. Cellular response to anthracyclines is also modulated by a myriad of transcriptional factors that influence cell fate. Several novel targeted chemotherapeutic agents have been associated with a small but worrying risk of left ventricular dysfunction. Agents such as trastuzumab and tyrosine kinase inhibitors can lead to cardiotoxicity that is fundamentally different from that caused by anthracyclines, whereas biological effects converge to the mitochondria as a critical target.

EPO and super-EPO: erythropoietins direct neoangiogenesis by cardiac progenitor cells

Erythropoietin, the red blood cell-making cytokine, is also a potential cytoprotective agent in heart disease. In this issue of Cell Stem Cell, Hoch et al. (2011) use two heart failure models, including chemotherapeutic cardiotoxicity, to reveal a mechanistic connection between reduced cardiomyocyte production of erythropoietin and neoangiogenesis by cardiac progenitors.

Testing the promiscuity of commercial kinase inhibitors against the AGC kinase group using a split-luciferase screen

Using a newly developed competitive binding assay dependent upon the reassembly of a split reporter protein, we have tested the promiscuity of a panel of reported kinase inhibitors against the AGC group. Many non-AGC targeted kinase inhibitors target multiple members of the AGC group. In general, structurally similar inhibitors consistently exhibited activity toward the same target as well as toward closely related kinases. The inhibition data was analyzed to test the predictive value of either using identity scores derived from residues within 6 Å of the active site or identity scores derived from the entire kinase domain. The results suggest that the active site identity in certain cases may be a stronger predictor of inhibitor promiscuity. The overall results provide general guidelines for establishing inhibitor selectivity as well as for the future design of inhibitors that either target or avoid AGC kinases.

Animal models in an age of personalized medicine

Personalized medicine is based on intraspecies differences. It is axiomatic that small differences in genetic make-up can result in dramatic differences in response to drugs or disease. To express this in more general terms: in any given complex system, small changes in initial conditions can result in dramatically different outcomes. Despite human variability and intraspecies variation in other species, nonhuman species are still the primary model for ascertaining data for humans. We call this practice into question and conclude that human-based research should be the primary means for obtaining data about human diseases and responses to drugs.

A decade of the human genome sequence--how does the medicinal chemist benefit?

Many have claimed that the sequencing of the human genome has failed to deliver the promised new era of drug discovery and development. Here, we argue that in fact, the availability of the human genome sequence and the genomics technologies that resulted from those research efforts have had a major impact on drug discovery. Medicinal chemists are actively using the data gleaned from structural genomics projects over the past decade to design more selective and more effective drug candidates. For example, large superfamilies of related enzymes, such as the kinome, proteome, proteasome, transportome, identified because of the sequencing of the human genome represent a huge number of potential drug targets. Ten years on, we're able to design multitarget drugs where the selectivity for a certain subgroup of receptors can lead to increased efficacy rather than the side effects traditionally associated with "off-targets". New trends and discoveries in biomedical research are notoriously slow to show their value, and this is also true for genomics technologies. However, the examples we've selected show that these are firmly set in the drug-discovery process, and without the human genome sequence, a number of current clinical candidates and promising drug leads would not have been possible.

A snapshot of chemoresistance to PARP inhibitors

The exploitation of synthetic lethality in BRCA-deficient tumor carriers using potent inhibitors of the enzyme poly(ADP-ribose) polymerase (PARP)-1 has led to an enthusiastic response among basic scientists, oncologists and pharmaceutical companies. However, accumulating evidence demonstrates that resistance to these drugs develops in tumors in both preclinical and clinical settings. Here, I focus on literature dealing with resistance to these drugs and discuss the molecular mechanisms involved, such as restoration of BRCA function, upregulation of nonhomologous end-joining-dependent DNA repair, induction of P-glycoprotein expression and epigenetic deregulation. Clinical implications of resistance to PARP1 inhibitors are also discussed.

Use of human stem cell derived cardiomyocytes to examine sunitinib mediated cardiotoxicity and electrophysiological alterations

Sunitinib, an oral tyrosine kinase inhibitor approved to treat advanced renal cell carcinoma and gastrointestinal stroma tumor, is associated with clinical cardiac toxicity. Although the precise mechanism of sunitinib cardiotoxicity is not known, both the key metabolic energy regulator, AMP-activated protein kinase (AMPK), and ribosomal S 6 kinase (RSK) have been hypothesized as causative, albeit based on rodent models. To study the mechanism of sunitinib-mediated cardiotoxicity in a human model, induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) having electrophysiological and contractile properties of native cardiac tissue were investigated. Sunitinib was cardiotoxic in a dose-dependent manner with an IC₅₀ in the low micromolar range, observed by a loss of cellular ATP, an increase in oxidized glutathione, and induction of apoptosis in iPSC-CMs. Pretreatment of iPSC-CMs with AMPK activators AICAR or metformin, increased the phosphorylation of pAMPK-T172 and pACC-S79, but only marginally attenuated sunitinib mediated cell death. Furthermore, additional inhibitors of AMPK were not directly cytotoxic to iPSC-CMs up to 250 μM concentrations. Inhibition of RSK with a highly specific, irreversible, small molecule inhibitor (RSK-FMK-MEA) did not induce cytotoxicity in iPSC-CMs below 250 μM. Extensive electrophysiological analysis of sunitinib and RSK-FMK-MEA mediated conduction effects were performed. Taken together, these findings suggest that inhibition of AMPK and RSK are not a major component of sunitinib-induced cardiotoxicity. Although the exact mechanism of cardiotoxicity of sunitinib is not known, it is likely due to inhibition of multiple kinases simultaneously. These data highlight the utility of human iPSC-CMs in investigating the potential molecular mechanisms underlying drug-induced cardiotoxicity.

Harnessing synthetic lethal interactions in anticancer drug discovery

Unique features of tumours that can be exploited by targeted therapies are a key focus of current cancer research. One such approach is known as synthetic lethality screening, which involves searching for genetic interactions of two mutations whereby the presence of either mutation alone has no effect on cell viability but the combination of the two mutations results in cell death. The presence of one of these mutations in cancer cells but not in normal cells can therefore create opportunities to selectively kill cancer cells by mimicking the effect of the second genetic mutation with targeted therapy. Here, we summarize strategies that can be used to identify synthetic lethal interactions for anticancer drug discovery, describe examples of such interactions that are currently being investigated in preclinical and clinical studies of targeted anticancer therapies, and discuss the challenges of realizing the full potential of such therapies.