Inhibition of the sodium potassium adenosine triphosphatase pump sensitizes cancer cells to anoikis and prevents distant tumor formation.
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.
Simpson
Craig D
CD
Ontario Cancer Institute, Princess Margaret Hospital, Toronto, ON, Canada.
Mawji
Imtiaz A
IA
Anyiwe
Kika
K
Williams
Moyo A
MA
Wang
Xiaoming
X
Venugopal
Amudha L
AL
Gronda
Marcela
M
Hurren
Rose
R
Cheng
Sonia
S
Serra
Stefano
S
Beheshti Zavareh
Reza
R
Datti
Alessandro
A
Wrana
Jeffrey L
JL
Ezzat
Shereen
S
Schimmer
Aaron D
AD
D000818:Animals; D023102:Anoikis / Q000187:drug effects* / Q000502:physiology; D002301:Cardiac Glycosides / Q000494:pharmacology*; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D004354:Drug Screening Assays, Antitumor; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D008297:Male; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology; D009362:Neoplasm Metastasis; D009369:Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D009997:Osmotic Pressure / Q000187:drug effects; D010042:Ouabain / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*; D023041:Xenograft Model Antitumor Assays
D002301:Cardiac Glycosides; D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D010042:Ouabain; D020169:Caspases; D000254:Sodium-Potassium-Exchanging ATPase