The anticancer tyrosine kinase inhibitor sunitinib has been shown recently to be cardiotoxic. Using a neonatal rat myocyte model, we investigated various mechanisms that might be responsible for its cardiotoxicity. Sunitinib potently inhibited the enzyme activity of both AMP-activated protein kinase (AMPK) and the ribosomal S6 kinase RSK1 at therapeutically relevant concentrations. Heart tissue with its high energy needs might be particularly sensitive to inhibition of AMPK because of its role as an energy sensor regulating ATP levels. As measured by lactate dehydrogenase release, sunitinib treatment of myocytes caused dose-dependent damage at therapeutic levels. Sunitinib treatment also caused a dose-dependent reduction in myocyte protein levels of the phosphorylated ␣ and ␤ isoforms of the AMPK phosphorylation target acetyl-Coenzyme A carboxylase.However, myocytes were not protected from sunitinib treatment by pretreating them with the AMPK-activating antidiabetic drug metformin. Sunitinib treatment of myocytes also did not affect cellular ATP levels. Together, these last two results do not suggest a major role for inhibition of AMPK in sunitinibinduced myocyte damage. Dexrazoxane, which is a clinically approved doxorubicin cardioprotective agent, also did not protect myocytes from damage, which suggests that sunitinib did not induce oxidative damage. In conclusion, even though sunitinib potently inhibits AMPK and RSK1, given the extreme lack of kinase selectivity that sunitinib exhibits, it is likely that inhibition of other kinases or combinations of kinases are responsible for the cardiotoxic effects of sunitinib. Sunitinib (Fig.

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Examining global effects of toxic metals on gene expression can be useful for elucidating patterns of biological response, discovering underlying mechanisms of toxicity, and identifying candidate metal-specific genetic markers of exposure and response. Using a 1,200 gene nylon array, we examined changes in gene expression following low-dose, acute exposures of cadmium, chromium, arsenic, nickel, or mitomycin C (MMC) in BEAS-2B human bronchial epithelial cells. Total RNA was isolated from cells exposed to 3 M Cd(II) (as cadmium chloride), 10 M Cr(VI) (as sodium dichromate), 3 g/cm2 Ni(II) (as nickel subsulfide), 5 M or 50 M As(III) (as sodium arsenite), or 1 M MMC for 4 hr. Expression changes were verified at the protein level for several genes. Only a small subset of genes was differentially expressed in response to each agent: Cd, Cr, Ni, As (5 M), As (50 M), and MMC each differentially altered the expression of 25, 44, 31, 110, 65, and 16 individual genes, respectively. Few genes were commonly expressed among the various treatments. Only one gene was altered in response to all four metals (hsp90), and no gene overlapped among all five treatments. We also compared low-dose (5 M, noncytotoxic) and high-dose (50 M, cytotoxic) arsenic treatments, which surprisingly, affected expression of almost completely nonoverlapping subsets of genes, suggesting a threshold switch from a survival-based biological response at low doses to a death response at high doses.

The human prostacyclin receptor is a seven-transmembrane ␣-helical G-protein coupled receptor, which plays important roles in both vascular smooth muscle relaxation as well as prevention of blood coagulation. The position of the native ligand-binding pocket for prostacyclin as well as other derivatives of the 20-carbon eicosanoid, arachidonic acid, has yet to be determined. Through the use of prostanoid receptor sequence alignments, site-directed mutagenesis, and the 2.8-Å x-ray crystallographic structure of bovine rhodopsin, we have developed a three-dimensional model of the agonistbinding pocket within the seven-transmembrane (TM) domains of the human prostacyclin receptor. Upon mutation to alanine, 11 of 29 candidate residues within TM domains II, III, IV, V, and VII exhibited a marked decrease in agonist binding. Of this group, four amino acids, Arg-279 (TMVII), Phe-278 (TMVII), Tyr-75 (TMII), and Phe-95 (TMIII), were identified (via receptor amino acid sequence alignment, ligand structural comparison, and computer-assisted homology modeling) as having direct molecular interactions with ligand side-chain constituents. This binding pocket is distinct from that of the biogenic amine receptors and rhodopsin where the native ligands (also composed of a carbon ring and a carbon chain) are accommodated in an opposing direction. These findings should assist in the development of novel and highly specific ligands including selective antagonists for further molecular pharmacogenetic studies of the human prostacyclin receptor.Vascular smooth muscle relaxation and inhibition of platelet aggregation are two key physiological processes mediated by human prostacyclin. Dysfunctional prostacyclin activity has been implicated in the development of a number of cardiovascular diseases including thrombosis, myocardial infarction, stroke, myocardial ischemia, atherosclerosis, and systemic and pulmonary hypertension (1). In contrast to other members of the rhodopsin-like G-protein coupled receptor (GPCR) 1 subfamily such as the adrenergic receptors or other members of the prostanoid family, there are currently no high affinity selective antagonists for the prostacyclin receptor. This finding suggests that the prostacyclin receptor may possess a unique ligandbinding pocket.Receptor activation is contingent upon ligand binding interactions, which initiate a conformational change in protein structure that is subsequently transmitted to the G-protein.Determining the exact nature and location of receptor-ligand binding interactions at the molecular level is essential for understanding the functions of prostanoid receptor physiology. Moreover, such insights would lend to the development of novel and highly specific modes of treatment for prostanoid-related disorders. Based upon the position of the chromophore (covalently bound 11-cis-retinal) within the binding pocket of rhodopsin along with the location of other ligands within similar rhodopsin-type GPCRs (2), the putative binding pocket for GPCRs with small nonpeptide ligands is beli...

Myocardial ischemia/reperfusion (I/R) injury increases the generation of oxidized phosphatidylcholines (OxPCs) which results in cell death. However, the mechanism by which OxPCs mediate cell death is largely unknown. The aim of this study was to determine the mechanisms by which OxPC triggers cardiomyocyte cell death during reperfusion injury. Cardiomyocyte viability, bioenergetic response and calcium transients were determined in the presence of OxPCs. Fragmented OxPCs resulted in a decrease in cell viability with POVPC and PONPC having the most potent cardiotoxic effect in both a concentration and time dependent manner (P<0.05). POVPC and PONPC also caused a significant decrease in Ca2+ transients and net contraction in isolated cardiomyocytes compared to vehicle treated control cells (P<0.05). PONPC depressed maximal respiration rate (p<0.01; 54%) and spare respiratory capacity (p<0.01; 54.5%). Notably, neither caspase 3 activation or TUNEL staining was observed in cells treated with either POVPC or PONPC. Further, cardiac myocytes treated with OxPCs were indistinguishable from vehicle treated control cells with respect to nuclear HMGB1 activity. Glutathione peroxidase 4 activity was markedly suppressed in cardiomyocytes treated with POVPC and PONPC. Importantly, cell death induced by OxPCs could be suppressed E06 Ab, directed against OxPCs or by ferrostatin. The findings of the present study suggest that OxPCs disrupt mitochondrial bioenergetics, calcium transients and provoke wide spread cell death through ferroptosis during I/R. Neutralization of OxPC with E06 or with ferrostatin-1 prevents cell death during reperfusion. Our study demonstrates a novel signaling pathway that operationally links generation of OxPC during cardiac I/R to ferroptosis.