Cancer Biology and Signal Transduction V-ATPase Inhibition Regulates Anoikis Resistance and Metastasis of Cancer Cells

Fightingmetastasis is amajor challenge in cancer therapy andnovel therapeutic targets anddrugs are highly appreciated. Resistance of invasive cells to anoikis, a particular type of apoptosis induced by loss of cell–matrix contact, is a major prerequisite for their metastatic spread. Inducing anoikis in metastatic cancer cells is therefore a promising therapeutic approach. The vacuolar-ATPase (V-ATPase), a proton pump located at the membrane of acidic organelles, has recently come to focus as an antimetastatic cancer target. As V-ATPase inhibitors have shown to prevent invasion of tumor cells and are able to induce apoptosis, we proposed that V-ATPase inhibition induces anoikis-related pathways in invasive cancer cells. We used the V-ATPase inhibitor archazolid to investigate themechanismof anoikis induction in variousmetastatic cancer cells (T24,MDA-MB-231, 4T1, 5637) in vitro. Anoikis induction by archazolidwas characterized by decreased c-FLIP expression and caspase-8 activation as well as reduction of active integrin-b1 and an early increase of the proapoptotic protein BIM.However,we observed that archazolid also inducesmechanisms opposing anoikis such as degradation of BIM mediated by extracellular signal-regulated kinase (ERK), Akt and Src kinases at later time points and induction of reactive oxygen species. Still, intravenous injection of archazolid-treated 4T1-Luc2 mouse breast cancer cells resulted in reducedmetastasis inmouse lungs. Thus, V-ATPase inhibition is not only an interesting option to reduce cancer metastasis, but also to better understand anoikis resistance and to find choices to fight against it. Mol Cancer Ther; 13(4); 926–37. 2014 AACR