Effects of Imipramine on Ion Channels and Proliferation of IGR1 Melanoma Cells

Abstract

Human IGR1 cells are a model for malignant melanoma. Since progression through the cell cycle is accompanied by transient cell hyperpolarization, we studied the properties of potassium and chloride ion channels and their impact on cell growth. The major potassium current components were mediated by outward rectifying ether à go-go (hEAG) channels and Ca2+-activated channels (KCa) of the IK/SK type. The major chloride channel component was activated by osmotic cell swelling (Clvol). To infer about the contribution of these channels to proliferation, specific inhibitors are required. Since there is no specific blocker for hEAG available, we used the tricyclic antidepressant imipramine, which blocked all channels mentioned, in combination with blockers for KCa (charybdotoxin) and Clvol (DIDS and pamoic acid). Incubation of IGR1 cells for 48 hr in 10-15 mM imipramine reduced DNA synthesis and metabolism without significant effects on apoptosis. hEAG channels were most sensitive to imipramine (IC50: 3.4 microM at +50 mV), followed by KCa (13.8 microM at +50 mV) and Clvol (12 microM at -100 mV), indicating that hEAG expression may be of importance for proliferation of melanoma cells. The contribution of KCa channels could be excluded, as 500 nM charybdotoxin, which completely blocked KCa, had no effect on proliferation. The impact of Clvol also seems to be minor, because 500 microM pamoic acid, which completely blocked Clvol, did not affect proliferation either.

Silencing the Activity and Proliferative Properties of the Human EagI Potassium Channel by RNA Interference

“…EagI has also been proposed to be important for cell growth in several cell lines (6,13,14), and we therefore investigated the possible effect that EagI knock down could have on the proliferation of cells. Because maximal knock down of the protein levels occurs at 48 h, we expected to detect an impact on proliferation relatively late after transfection.…”

“…These data suggest that EagI may not only represent a potential marker for the diagnosis and prognosis of cancer but also that it may contribute to the formation and progression of cancers. Indeed, it has been shown for breast cancer cells (13) and for melanoma cells (14) that the use of EagI blockers leads to a reduction in proliferation. In those reports, the antihistamine astemizole and the tricyclic antidepressant imipramine were used, respectively.…”

Aberrant expression of ether à go-go potassium channel in colorectal cancer patients and cell lines

“…On the other hand, eag1 is expressed in several cell lines derived from human malignant tumors, such as neuroblastoma [5,6] , melanoma [7] , breast [5] , and cervical carcinoma [5] . In these cell lines, Eag1 enhances the proliferation of the cells, and is required for the maintenance of growth.…”

“…Similarly, aberrant expression of the channel has also been detected in sarcomas [9] and other tumors from diverse origins [12] , while the surrounding tissues are devoid of Eag1 expression. Moreover, specific inhibition of Eag1 expression by antisense technique [5] , siRNA [9,10] or by non-specific blockers [7,11] leads to a reduction in tumor cell proliferation in vitro.…”

Risco de câncer associado ao uso de antidepressivos

“…Um outro mecanismo que fundamenta essa idéia é o bloqueio dose-reversível e voltagem-dependente dos canais hEag1 causado pela imipramina e pelo astemizol. Esses canais foram detectados em várias linhagens de células tumorais, influenciando a sua taxa de proliferação 11,13 . Outro canal bloqueado pela imipramina e pela desipramina é o SK3 presente nas células TE671 do meduloblastoma humano, que também influencia na divisão das células cancerígenas 12 .…”