Oxidative Inactivation of the Lipid Phosphatase Phosphatase and Tensin Homolog on Chromosome Ten (PTEN) as a Novel Mechanism of Acquired Long QT Syndrome

The most common cause of cardiac side effects of pharmaco-therapy is acquired long QT syndrome, which is characterized by abnormal cardiac repolarization and most often caused by direct blockade of the cardiac potassium channel human ether a-go-go-related gene (hERG). However, little is known about therapeutic compounds that target ion channels other than hERG. We have discovered that arsenic trioxide (As2O3), a very potent antineoplastic compound for the treatment of acute promyelocytic leukemia, is proarrhythmic via two separate mechanisms: a well characterized inhibition of hERG/I-Kr trafficking and a poorly understood increase of cardiac calcium currents. We have analyzed the latter mechanism in the present study using biochemical and electrophysiological methods. We find that oxidative inactivation of the lipid phosphatase PTEN by As2O3 enhances cardiac calcium currents in the therapeutic concentration range via a PI3K alpha-dependent increase in phosphatidylinositol 3,4,5-triphosphate (PIP3) production. In guinea pig ventricular myocytes, even a modest reduction in PTEN activity is sufficient to increase cellular PIP3 levels. Under control conditions, PIP3 levels are kept low by PTEN and do not affect calcium current amplitudes. Based on pharmacological experiments and intracellular infusion of PIP3, we propose that in guinea pig ventricular myocytes, PIP3 regulates calcium currents independently of the protein kinase Akt along a pathway that includes a secondary oxidation-sensitive target. Overall, our report describes a novel form of acquired long QT syndrome where the target modified by As2O3 is an intracellular signaling cascade.