Effects of Integrin-Linked Kinase (ILK) Inhibitor QLT0267 on Multiple Myeloma Cells and Evaluation of ILK as a Therapeutic Target in Multiple Myeloma.

Multiple myeloma (MM) is a fatal plasma cell tumor that accounts for about 1% of cancers. A hallmark of the disease is its location in the bone marrow where the tumor cells receive prosurvival support from the microenvironment and cause extensive osteolytic damage. Novel drugs are currently being developed into a range of new treatment options. However, because the problems of cancer relapse and eventual selection of therapy-resistant offspring remain, additional therapeutic targets should still be investigated. ILK is a multifunctional protein that, as an adaptor and/or as a kinase, may relay adhesion- and growth factor receptor-mediated signals to downstream signaling cascades that promote growth and survival. We have analysed the expression of ILK in MM cells and have tested the effects of a novel small molecule ILK-inhibitor (QLT0267; QLT Inc., Vancouver, Canada) in MM cell lines, primary MM tumor cells and healthy cells, respectively. ILK expression at either cDNA or protein level was detectable in virtually every MM sample tested. Treatment with QLT0267 for up to 3 days resulted in extensive apoptotic death in MM cell lines (EC50 values below 10 microM in 8/9 MM cell lines tested) and in a majority of primary (anti-CD138-purified) MM samples (EC50 values below 10 microM in 8/14 primary MM samples tested). Drug treatment led to rapid decreases in the levels of phospho-STAT3, phospho-GSK3beta and total Akt protein, whereas levels of ILK and of phospho-ERK were unaffected or, in the latter case, showed a slight increase. Similar to other current pharmacologic approaches, targeting ILK may have several detrimental impacts on the signaling network that sustains MM cells. Such pleiotropic effects could prove valuable for combination treatments. The survival of peripheral blood mononuclear cells and of bone marrow stromal cells (BMSCs) at 20 microM QLT0267 was just slightly affected, indicating that the scope for establishment of a therapeutic window in MM might exist. High (20 microM) concentrations of QLT0267 gradually (and reversibly) promoted detachment of BMSCs from the culture dish, indicating that the drug might be useful to temporarily impair their effectiveness to support myeloma cells. Taken together, these experiments provide a rationale to further explore the utility of ILK-inhibition for the treatment of MM.