Inhibition of ILK in PTEN-mutant human glioblastomas inhibits PKB/Akt activation, induces apoptosis, and delays tumor growth

Abstract

The tumor suppressor gene phosphatase and tensin homologue (PTEN) regulates the phosphatidylinositol-3 0 -kinase (PI3K) signaling pathway and has been shown to correlate with poor prognosis in high-grade astrocytomas when mutational inactivation or loss of the PTEN gene occurs. PTEN mutation leads to constitutive activation of protein kinase B (PKB)/Akt with phosphorylation at the PKB/Akt sites Thr-308 and Ser-473. Integrin-linked kinase (ILK) has been shown to regulate PKB/Akt activity with the loss of PTEN in prostate cancer. We now demonstrate that ILK activity regulates PKB/Akt activity in glioblastoma cells. The activity of ILK is constitutively elevated in a serum-independent manner in PTEN mutant cells, and transfection of wild-type PTEN under the control of an inducible promoter into mutant PTEN cells inhibits ILK activity. Transfection of ILK antisense (ILKAS) or exposure to a small-molecule ILK inhibitor suppresses the constitutive phosphorylation of PKB/Akt on Ser-473 in PTEN-mutant glioblastoma cell lines. In addition, the delivery of ILKAS to PTENnegative glioblastoma cells resulted in apoptosis. Rag-2M mice bearing established (B100 mg) human U87MG glioblastoma tumors, treated QD Â 5 for 3 consecutive weeks with ILKAS (i.p. 5 mg/kg), exhibited stable disease with p7% increase in tumor volume over the 3-week course of treatment. In contrast, animals treated with an oligonucleotide control or saline exhibited a >100% increase in tumor volume over the same time period. Our initial results indicate that therapeutic strategies targeting ILK may be beneficial in the treatment of glioblastomas.

The phosphatidyl inositol 3-kinase signaling network: implications for human breast cancer

“…For example, the inhibition of ILK kinase activity in PTEN-mutant prostate and glioblastoma cells results in apoptosis and reduced tumor growth in vivo (Persad et al, 2000;Edwards et al, 2005;Koul et al, 2005). The impact of ILK inhibition in these cells was due to downregulation of Akt phosphorylation, and is consistent with reports that ILK suppresses anoikis through activation of Akt .…”

Targeting integrin-linked kinase inhibits Akt signaling pathways and decreases tumor progression of human glioblastoma

“…For example, the inhibition of ILK by antisense ILK suppressed the constitutive phosphorylation of Akt on Ser 473 , resulting in apoptosis in a U87 glioma cell model (27). Similarly, ILK suppression by antisense ILK caused a tumor growth delay in Rag-2M mice bearing established human U87 glioblastoma tumors (27), suggesting that ILK is an important therapeutic target.…”

Integrin signalling adaptors: not only figurants in the cancer story

“…The use of RNAi and antisense oligonucleotides to downregulate ILK expression and small molecule inhibitors to abrogate its kinase activity, has been shown to reverse ILK oncogenic effects in a variety of cancers. Indeed inhibition of either ILK expression or its activity results in decreased cell migration and invasion, metastasis formation, induction of apoptosis in vitro 30,129,130 and in vivo [131][132][133] . In addition, on the basis of the new role of ILK in mitosis 103,104 , the potential targeting of ILK as an anti-mitotic chemotherapeutic might provide a promising alternative to the chemotherapeutics avoiding severe toxic side effects and drug resistance.…”