Antitumor activity of NVP-BKM120--a selective pan class I PI3 kinase inhibitor showed differential forms of cell death based on p53 status of glioma cells.

PURPOSE: The aim of this study was to show preclinical efficacy and clinical development potential of NVP-BKM120, a selective pan class I phosphatidylinositol-3 kinase (PI3K) inhibitor in human glioblastoma (GBM) cells in vitro and in vivo. EXPERIMENTAL DESIGN: The effect of NVP-BKM120 on cellular growth was assessed by CellTiter-Blue assay. Flow cytometric analyses were carried out to measure the cell-cycle, apoptosis, and mitotic index. Mitotic catastrophe was detected by immunofluorescence. The efficacy of NVP-BKM120 was tested using intracranial U87 glioma model. RESULTS: We tested the biologic effects of a selective PI3K inhibitor NVP-BKM120 in a set of glioma cell lines. NVP-BKM120 treatment for 72 hours resulted in a dose-dependent growth inhibition and effectively blocked the PI3K/Akt signaling cascade. Although we found no obvious relationship between the cell line's sensitivity to NVP-BKM120 and the phosphatase and tensin homolog (PTEN) and epidermal growth factor receptor (EGFR) statuses, we did observe a differential sensitivity pattern with respect to p53 status, with glioma cells containing wild-type p53 more sensitive than cells with mutated or deleted p53. NVP-BKM120 showed differential forms of cell death on the basis of p53 status of the cells with p53 wild-type cells undergoing apoptotic cell death and p53 mutant/deleted cells having a mitotic catastrophe cell death. NVP-BKM120 mediates mitotic catastrophe mainly through Aurora B kinase. Knockdown of p53 in p53 wild-type U87 glioma cells displayed microtubule misalignment, multiple centrosomes, and mitotic catastrophe cell death. Parallel to the assessment of the compound in in vitro settings, in vivo efficacy studies using an intracranial U87 tumor model showed an increased median survival from 26 days (control cohort) to 38 and 48 days (treated cohorts). CONCLUSION: Our present findings establish that NVP-BKM120 inhibits the PI3K signaling pathways, leading to different forms of cell death on the basis of p53 statuses. Further studies are warranted to determine if NVP-BKM120 has potential as a glioma treatment.

Silencing kinase-interacting stathmin gene enhances erlotinib sensitivity by inhibiting Ser¹° p27 phosphorylation in epidermal growth factor receptor-expressing breast cancer.

The epidermal growth factor receptor (EGFR) signaling pathway has emerged as a promising target for cancer therapy. EGFR tyrosine kinase inhibitors (TKI) such as erlotinib have been approved for cancer treatment but have shown very limited activity in breast cancer patients. Clarifying the molecular mechanism underlying resistance to EGFR TKIs could lead to more effective treatment against breast cancer. We previously reported that the sensitivity of breast cancer cells to erlotinib is partially dependent on p27 and that cytoplasmic localization of p27 is associated with erlotinib resistance. In the present study, we found that erlotinib induces p27 phosphorylation at Ser¹° (S10), and S10 p27 phosphorylation leads to erlotinib resistance in EGFR-expressing breast cancer. Inhibiting S10 phosphorylation of p27 by knocking down human kinase-interacting stathmin (KIS), a nuclear protein that can phosphorylate p27 at S10, led to p27 accumulation in the nucleus and enhanced erlotinib-mediated cytotoxicity. Further, in vivo KIS gene silencing enhanced the antitumor activity of erlotinib in an orthotopic breast cancer xenograft model. KIS depletion also enhanced erlotinib sensitivity in erlotinib-resistant EGFR-expressing triple-negative breast cancer cells. Our study provides a rationale for the development of combinations of erlotinib with KIS inhibition to overcome EGFR TKI resistance in EGFR-expressing breast cancer.

Epidermal growth factor receptor tyrosine kinase inhibitor reverses mesenchymal to epithelial phenotype and inhibits metastasis in inflammatory breast cancer.

PURPOSE: Inflammatory breast cancer (IBC) is a rare but aggressive type of advanced breast cancer. Epidermal growth factor receptor (EGFR) expression is an independent poor prognostic factor in IBC. The purpose of this study was to determine the effect on IBC tumorigenicity and metastasis of blocking the EGFR pathway. EXPERIMENTAL DESIGN: IBC cell lines, which express high level of EGFR, were treated with EGFR small interfering RNA and with the EGFR tyrosine kinase inhibitor erlotinib. The role of EGFR in IBC cell proliferation, motility, invasiveness, and change of the expression levels of epithelial-mesenchymal transition markers was examined. The role of extracellular signal-regulated kinase (ERK)-1/2 in erlotinib activity was also studied. The activity of erlotinib in tumor growth and metastasis was examined in an orthotopic xenograft model of IBC. RESULTS: Erlotinib inhibited proliferation and anchorage-independent growth of IBC cells, and this inhibition was ERK dependent. Erlotinib inhibited cell motility and invasiveness and reversed the mesenchymal phenotype of IBC cells to epithelial phenotype in three-dimensional culture. Erlotinib dramatically inhibited IBC tumor growth in a xenograft model. Interestingly, erlotinib inhibited spontaneous lung metastasis, even at a low dose that had no significant effect on primary tumor growth. These erlotinib-treated tumors were converted to epithelial phenotype from mesenchymal phenotype. CONCLUSIONS: The EGFR pathway is involved in tumor growth and metastasis of IBC. Targeting EGFR through the ERK pathway may represent an effective therapeutic approach to suppress tumorigenicity and prevent metastasis in EGFR-expressing IBC.

Cell cycle-dependent nuclear export of phosphatase and tensin homologue tumor suppressor is regulated by the phosphoinositide-3-kinase signaling cascade.

The tumor suppressor phosphatase and tensin homologue (PTEN) plays distinct growth-regulatory roles in the cytoplasm and nucleus. It has been shown to be preferentially localized to the nucleus in differentiated or resting cells, and to the cytoplasm in advanced tumor cells. Thus, the regulation of PTEN's subcellular localization seems to be critical to its tumor-suppressing functions. In this study, we showed that activation of the phosphoinositide-3-kinase (PI3K) pathway triggers PTEN's cell cycle-dependent chromosome region maintenance 1-mediated nuclear export, as PTEN was predominantly expressed in the cytoplasm of TSC2(-/-) mouse embryo fibroblasts or activated Akt mutant-transfected NIH3T3 cells. In contrast, dominant-negative mutants of Akt and pharmacologic inhibitors of PI3K, mTOR, and S6K1, but not of MEK, suppressed the nuclear export of PTEN during the G(1)-S transition. The nuclear-cytoplasmic trafficking of exogenous PTEN is likewise regulated by the PI3K cascade in PTEN-null U251MG cells. The nuclear export of PTEN could also be blocked by short interfering RNA to S6K1/2. In addition, PTEN interacts with both S6K1 and S6K2. Taken together, our findings strongly indicate that activation of the PI3K/Akt/mTOR/S6K cascade, specifically S6K1/2, is pivotal in regulating the subcellular localization of PTEN. This scenario exemplifies a reciprocal regulation between PI3K and PTEN that defines a novel negative-feedback loop in cell cycle progression.

Inhibition of Akt survival pathway by a small-molecule inhibitor in human glioblastoma.

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) and Akt are important regulators of the phosphatidylinositol 3-kinase (PI3K) pathway and thus are important to the regulation of a wide spectrum of tumor-related biological processes. Akt regulates several critical cellular functions, including cell cycle progression; cell migration, invasion, and survival; and angiogenesis. Decreased expression of PTEN and overexpression of the Akt proto-oncogene, which is located downstream of PI3K, have been shown in a variety of cancers, including glioblastoma. Novel small-molecule inhibitors of receptors and signaling pathways, including inhibitors of the PI3K pathway, have shown antitumor activity, but inhibitors of Akt have not been examined. In this study, we tested our hypothesis that the pharmacologic inhibition of Akt has an antiproliferative effect on gliomas. We showed that two newly developed Akt inhibitors, KP-372-1 and KP-372-2 (herein called KP-1 and KP-2), effectively inhibited the PI3K/Akt signaling cascade. KP-1 and KP-2 blocked both the basal and epidermal growth factor-induced phosphorylation of Akt Ser473 at 125 and 250 nmol/L, which, in turn, reduced the activation of intracellular downstream targets of Akt, including GSK-3beta and p70s6k. Furthermore, the treatment of U87 and U251 glioma cells with 125 to 250 nmol/L KP-1 and KP2 for 48 hours inhibited cell growth by approximately 50%. This decrease in cell growth stemmed from the induction of apoptosis. Collectively, these results provide a strong rationale for the pharmacologic targeting of Akt for the treatment of gliomas.