Inhibition of the Sodium Potassium Adenosine Triphosphatase Pump Sensitizes Cancer Cells to Anoikis and Prevents Distant Tumor Formation

Abstract

Normal epithelial cells undergo apoptosis upon detachment from the extracellular matrix, a process termed ''anoikis.'' However, malignant epithelial cells with metastatic potential resist anoikis and can survive in an anchorage-independent fashion. Molecules that sensitize resistant cells to anoikis will be useful chemical probes to understand this pathway. To identify novel anoikis sensitizers in anoikis-resistant PPC-1 prostate adenocarcinoma cells, a library of 2,000 off-patent drugs and natural products was screened for their ability to preferentially induce cell death in suspension over adherent culture conditions. This screen identified five members of the family of cardiac glycosides as anoikis sensitizers, including ouabain, peruvoside, digoxin, digitoxin, and strophanthidin. We conducted further studies with ouabain to discern the mechanism of cardiac glycoside-induced anoikis sensitization. Ouabain initiated anoikis through the mitochondrial pathway of caspase activation. In addition, ouabain sensitized cells to anoikis by inhibiting its known target, the Na + /K + ATPase pump, and inducing hypoosmotic stress. Resistance to anoikis permits cancer cells to survive in the circulation and facilitates their metastasis to distant organs, so we tested the effects of Na + /K + ATPase inhibition on distant tumor formation in mouse models. In these mouse models, ouabain inhibited tumor metastases but did not alter the growth of subcutaneous tumors. Thus, we have identified a novel mechanism to sensitize resistant cells to anoikis and decrease tumor metastasis. These results suggest a potential mechanism for the observed clinical reduction in metastasis and relapse in breast cancer patients who have undergone treatments with cardiac glycosides.

The antiproliferative effects of ouabain and everolimus on adrenocortical tumor cells

“…One previous study reported that ouabain at very high concentration (1 and 10 µM) showed antiproliferative results on 3 different prostate cancer cell lines [14]. A second study described the effects of ouabain (from 0.01 to 100µM) on viability on a small panel of cancer cell lines with essentially the same results [18]. Furthermore combination strategy seemed to be more successful in H295R cells, at least in cell viability and proliferation assay.…”

Digitoxin-Induced Cytotoxicity in Cancer Cells Is Mediated through Distinct Kinase and Interferon Signaling Networks

“…Recent findings that cancer biopsies express much higher levels of different sodium pump subunits might provide a rational basis for this increased sensitivity of cancer cells to the effects of these drugs. Several mechanisms have been proposed by us and others, to account for their cytotoxic action, including inhibition of HIF-1 synthesis (27), downregulation of c-MYC (28), inhibition of topoisomerase II (29), upregulation of death receptors DR4 and DR5 (30), increased expression of ROS (31), alterations in membrane fluidity (32) and anoikis induction (33). Moreover, Wang and colleagues, recently showed that digoxin and other cardiac glycosides inhibit p53 synthesis by a mechanism relieved by Sarcoma kinase (Src kinase) or mitogen-activated protein kinase (MAPK) inhibition, highlighting a potential benefit for the use of these drugs in human cancers with a gain of function p53 mutation (34).…”

Targeting the Na⁺/K⁺-ATPase α1 Subunit of Hepatoma HepG2 Cell Line to Induce Apoptosis and Cell Cycle Arresting

“…[4][5][6][7][8][9] The main reason was the expression of Na ϩ /K ϩ -ATPase in cancer cells was higher than that in normal cells, and provided more binding sites for CSs. Previous research has shown the Na ϩ /K ϩ -ATPase a1 subunit was highly expressed in malignant cells, including human prostate cancer PC-3, DU-145 cells, human non-small cell lung cancer (NSCLC) A549 cells, 10) glioblastomas Hs683, U373-MG, U87-MG, T98G cells, 11) and breast cancer MCF-7 cells.…”