Inhibition of Integrin-Linked Kinase by a Selective Small Molecule Inhibitor, QLT0254, Inhibits the PI3K/PKB/mTOR, Stat3, and FKHR Pathways and Tumor Growth, and Enhances Gemcitabine-Induced Apoptosis in Human Orthotopic Primary Pancreatic Cancer Xenografts

Abstract

Integrin-linked kinase (ILK) couples integrins and growth factors to downstream signaling pathways involving phosphatidylinositol 3-kinase, protein kinase B/Akt (PKB/Akt), and glycogen synthase kinase-3β. The anticancer effects of ILK inhibitor QLT0254 were tested in an orthotopic primary xenograft model of pancreatic cancer. The pharmacodynamic effects of a single dose of QLT0254 on the phosphorylation of PKB/Akt were measured by immunohistochemistry and Western blotting, and showed a decrease of >80% after 2 hours, followed by recovery over 24 hours, consistent with the pharmacokinetic profile of this compound in mice. There was also suppression in phosphorylated PKB Thr³⁰⁸, forkhead in rhabdomyosarcoma, S6K1, S6, 4E-BP1, and signal transducers and activators of transcription 3 Tyr⁷⁰⁵ and Ser⁷²⁷ protein levels with ILK inhibition by QLT0254. However, we did not observe an effect on phosphoinositide-dependent kinase 1, glycogen synthase kinase-3β, and extracellular signal-regulated kinase phosphorylation or on total PKB and ILK protein expression levels with QLT0254 treatment. In tumor growth inhibition experiments, daily treatment with QLT0254 for 3 weeks was well tolerated and produced significant tumor growth inhibition compared with vehicle control (P = 0.001). When a single dose of QLT0254 and chemotherapy agent gemcitabine was administered, there was a significant 5.4-fold increase in acute apoptosis in the combination therapy group compared with vehicle controls (P = 0.002). However, the acute effects of QLT0254 on proliferation were not statistically significant. These results show in vivo evidence that ILK plays a prominent role in oncogenic phosphatidylinositol 3-kinase/PKB signaling in vivo with major impact on the mammalian target of rapamycin, signal transducers and activators of transcription 3, and forkhead in rhadomyosarcoma signaling pathways, suggesting that ILK inhibitors might show activity in pancreatic cancer patients.