hERG K+ Channels Promote Survival of Irradiated Leukemia Cells

Abstract

Many tumor cells express highly elevated activities of voltage-gated K + channels in the plasma membrane which are indispensable for tumor growth. To test for K + channel function during DNA damage response, we subjected human chronic myeloid leukemia (CML) cells to sub-lethal doses of ionizing radiation (0-8 Gy, 6 MV photons) and determined K + channel activity, K + channel-dependent Ca 2+ signaling, cell cycle progression, DNA repair, and clonogenic survival by whole-cell patch clamp recording, fura-2 Ca 2+ imaging, Western blotting, flow cytometry, immunofluorescence microscopy, and pre-plating colony formation assay, respectively. As a result, the human erythroid CML cell line K562 and primary human CML cells functionally expressed hERG1. Irradiation stimulated in both cell types an increase in the activity of hERG1 K + channels which became apparent 1-2 h post-irradiation. This increase in K + channel activity was paralleled by an accumulation in S phase of cell cycle followed by a G 2 /M cell cycle arrest as analyzed between 8 and 72 h post-irradiation. Attenuating the K + channel function by applying the hERG1 channel inhibitor E4031 modulated Ca 2+ signaling, impaired inhibition of the mitosis promoting subunit cdc2, overrode cell cycle arrest, and decreased clonogenic survival of the irradiated cells but did not affect repair of DNA double strand breaks suggesting a critical role of the hERG1 K + channels for the Ca 2+ signaling and the cell cycle control during DNA damage response.

Against Repurposing Methadone for Glioblastoma Therapy

“…As endpoints, the percentage of cells residing in G 1 , S, and G 2 phase of cell cycle was calculated. Ionizing radiation (4 Gy) induced an increase in G 1 population and a decrease in S and G 2 population at 24 and 48 h after radiation in A172 cells (Figure 3B We have previously shown that experimental interference with electrosignaling and cell cycle control decreases the clonogenic survival of irradiated tumor cells [95,[99][100][101][102][103]. We, therefore, tested whether the observed methadone (20 µM)-mediated modulation of cell cycle control was associated with an impairment of clonogenic survival and radioresistance.…”

“…We, therefore, performed further in vitro experiments that addressed the effect of “supratherapeutic” and clinically relevant concentrations of methadone alone and in combination with ionizing radiation on clonogenic survival in different human glioblastoma cell lines. Since our previous work suggests that blockage of putative methadone targets may decrease clonogenic survival of irradiated tumor cells by impairment of cell cycle arrest [ 95 ], we also tested the effect of methadone and ionizing radiation on cell cycle regulation. Prior to that, we analyzed the expression of putative methadone target molecules in glioblastoma, as described in the following paragraphs.…”

“…Reportedly, electrosignaling and interdependent Ca 2+ signaling contribute to the stress response of cancer cells by regulating cell cycle progression and promoting their clonogenic survival (forreview, see [ 98 ]). Since methadone has been proposed to target hERG1 K + channels and ionotropic receptors (see Table 2 ) and since hERG1 reportedly [ 95 ] and NMDA- as well as nicotinic acetylcholine receptors most probably interfere with electrosignaling, we studied the effect of methadone on cell cycle progression in control and irradiated T98G, A172 and U251 cells by flow cytometry. In particular, we monitored the effect of a “supratherapeutic” methadone concentration (20 µM) in order to modulate the ionotropic nicotinic α 3 β 4 acetylcholine and NMDA receptors, as well as hERG1 and L- and T-type Ca 2+ channels (IC 50 s in Table 2 ) in addition to the µ-opioid receptor.…”

“…We have previously shown that experimental interference with electrosignaling and cell cycle control decreases the clonogenic survival of irradiated tumor cells [ 95 , 99 , 100 , 101 , 102 , 103 ]. We, therefore, tested whether the observed methadone (20 µM)-mediated modulation of cell cycle control was associated with an impairment of clonogenic survival and radioresistance.…”

Potassium Ion Channels in Glioma: From Basic Knowledge into Therapeutic Applications

“…Numerous studies have identified dysregulated potassium channel expression across many tumor types, including breast, prostate, lung, endometrium, pancreas, and others, and were extensively reviewed elsewhere [35]. In summary, the increased expression of potassium channels in cancer is associated with metastasis and tumorigenesis [38,39], higher-grade tumors [40,41], severe cancer phenotypes [42,43], cancer cell migration [44,45], proliferation through calcium regulation [46][47][48], and lower overall survival [49,50], among other effects. As such, the altered potassium ion channel expression serves central roles in neoplastic transformation and provides a toolkit that diverges from the healthy counterparts and warrants thorough investigation as a prevailing focus in cancer biology and therapeutics.…”