The emerging paradigm of "
oncogene addiction" has been called an Achilles' heel of
cancer that can be exploited therapeutically. Here, we show that
integrin-linked kinase (ILK), which is either activated or overexpressed in many types of
cancers, is a critical regulator of
breast cancer cell survival through the
protein kinase B (PKB)/Akt pathway but is largely dispensable for the survival of normal breast epithelial cells and mesenchymal cells. We show that inhibition of ILK activity with a pharmacologic ILK inhibitor,
QLT-0267, results in the inhibition of PKB/Akt Ser473 phosphorylation, stimulation of apoptosis, and a decrease in
mammalian target of rapamycin (mTOR) expression in human
breast cancer cells. In contrast,
QLT-0267 treatment has no effect on PKB/Akt Ser473 phosphorylation or apoptosis in normal human breast epithelial, mouse fibroblast, or vascular smooth muscle cells. The inhibition of PKB/Akt Ser473 phosphorylation by
QLT-0267 in
breast cancer cells was rescued by a
kinase-active ILK mutant but not by a
kinase-dead ILK mutant. Furthermore, a dominant-negative ILK mutant increased apoptosis in the MDA-MB-231
breast cancer cell line but not in normal human breast epithelial cells. The inhibitor was active against ILK isolated from all cell types but did not have any effect on cell attachment and spreading. Our data point to an "ILK addiction" of
breast cancer cells whereby they become dependent on ILK for cell survival through the mTOR-PKB/Akt signaling pathway and show that ILK is a promising target for the treatment of
breast cancer.