Effect of antiarrhythmic drugs on small conductance calcium - activated potassium channels

Atrial fibrillation (AF) is the most common type of arrhythmia. Current pharmacological treatment for AF is moderately effective and/or increases the risk of serious ventricular adverse effects. To avoid ventricular adverse effects, a new target has been considered, the small conductance calcium-activated K⁺ channels (K_Ca2.X, SK channels). In the heart, K_Ca2.X channels are functionally more important in atria compared to ventricles, and pharmacological inhibition of the channel confers atrial selective prolongation of the cardiac action potential and converts AF to sinus rhythm in animal models of AF. Whether antiarrhythmic drugs (AADs) recommended for treating AF target K_Ca2.X channels is unknown. To this end, we tested a large number of AADs on the human K_Ca2.2 and K_Ca2.3 channels to assess their effect on this new target using automated whole-cell patch clamp. Of the AADs recommended for treatment of AF only dofetilide and propafenone inhibited hK_Ca2.X channels, with no subtype selectivity. The calculated IC₅₀ were 90±10µmol/l vs 60±10µmol/l for dofetilide and 42±4µmol/l vs 80±20µmol/l for propafenone (hK_Ca2.3 vs hK_Ca2.2). Whether this inhibition has clinical importance for their antiarrhythmic effect is unlikely, as the calculated IC₅₀ values are very high compared to the effective free therapeutic plasma concentration of the drugs when used for AF treatment, 40,000-fold for dofetilide and 140-fold higher for propafenone.

Identification of KCa3.1 Channel as a Novel Regulator of Oxidative Phosphorylation in a Subset of Pancreatic Carcinoma Cell Lines

Pancreatic ductal adenocarcinoma (PDAC) represents the most common form of pancreatic cancer with rising incidence in developing countries and overall 5-year survival rates of less than 5%. The most frequent mutations in PDAC are gain-of-function mutations in KRAS as well as loss-of-function mutations in p53. Both mutations have severe impacts on the metabolism of tumor cells. Many of these metabolic changes are mediated by transporters or channels that regulate the exchange of metabolites and ions between the intracellular compartment and the tumor microenvironment. In the study presented here, our goal was to identify novel transporters or channels that regulate oxidative phosphorylation (OxPhos) in PDAC in order to characterize novel potential drug targets for the treatment of these cancers. We set up a Seahorse Analyzer XF based siRNA screen and identified previously described as well as novel regulators of OxPhos. The siRNA that resulted in the greatest change in cellular oxygen consumption was targeting the KCNN4 gene, which encodes for the Ca²⁺-sensitive K⁺ channel K_Ca3.1. This channel has not previously been reported to regulate OxPhos. Knock-down experiments as well as the use of a small molecule inhibitor confirmed its role in regulating oxygen consumption, ATP production and cellular proliferation. Furthermore, PDAC cell lines sensitive to K_Ca3.1 inhibition were shown to express the channel protein in the plasma membrane as well as in the mitochondria. These differences in the localization of K_Ca3.1 channels as well as differences in the regulation of cellular metabolism might offer opportunities for targeted therapy in subsets of PDAC.

ANO1 (TMEM16A) in pancreatic ductal adenocarcinoma (PDAC)

Pancreatic ductal adenocarcinoma (PDAC) has one of the worst survival rates of all cancers. ANO1 (TMEM16A) is a recently identified Ca²⁺-activated Cl⁻ channel (CaCC) that is upregulated in several tumors. Although ANO1 was subject to extensive studies in the recent years, its pathophysiological function has only been poorly understood. The aim of the present study is to establish the significance of ANO1 in PDAC behavior and demarcate its roles in PDAC from those of the volume-regulated anion channel (VRAC). We performed qPCR and Western blot measurements on different PDAC cell lines (Panc-1, Mia PaCa 2, Capan-1, AsPC-1, BxPC-3) and compared the results to those obtained in a human pancreatic ductal epithelium (HPDE) cell line. All cancer cell lines showed an upregulation of ANO1 on mRNA and protein levels. Whole-cell patch-clamp recordings identified large Ca²⁺ and voltage-dependent Cl⁻ currents in PDAC cells. Using siRNA knockdown of ANO1 and three ANO1 inhibitors (T16A_inh-A01, CaCC_inh-A01, and NS3728), we found that ANO1 is the main constituent of CaCC current in PDAC cells. We further characterized these three inhibitors and found that they had unspecific effects on the free intracellular calcium concentration. Functional studies on PDAC behavior showed that surprisingly inhibition of ANO1 did not influence cellular proliferation. On the other hand, we found ANO1 channel to be pivotal in PDAC cell migration as assessed in wound healing experiments.

The role of TMEM16A (ANO1) and TMEM16F (ANO6) in cell migration

Members of the TMEM16 family have recently been described as Ca²⁺-activated Cl⁻ channels. They have been implicated in cancer and appear to be associated with poor patient prognosis. Here, we investigate the role of TMEM16 channels in cell migration, which is largely unknown. We focused on TMEM16A and TMEM16F channels that have the highest expression of TMEM16 channels in Ehrlich Lettre ascites (ELA) cells. Due to the lack of specific pharmacological modulators, we employed a miRNA approach and stably knocked down the expression of TMEM16A and TMEM16F channels, respectively. Migration analysis shows that TMEM16A KD clones are affected in their directional migration, whereas TMEM16F KD clones show a 40 % reduced rate of cell migration. Moreover, TMEM16A KD clones have a smaller projected cell area, and they are rounder than TMEM16F KD clones. The morphological changes are linearly correlated with the directionality of cells. TMEM16A and TMEM16F, thus, have an important function in cell migration—TMEM16A in directional migration, TMEM16F in determination of the speed of migration. We conclude that TMEM16A and TMEM16F channels have a distinct impact on the steering and motor mechanisms of migrating ELA cells.