Differential modulation of signaling pathways and apoptosis of ras-transformed 10T1/2 cells by the depsipeptide FR901228

(E)-(1S,4S,10S,21R)-7-[(Z)-ethylidene]-4,21-diisopropyl-2-oxa-12,13-dithia-5,8,20,23-tetraazabicyclo[8,7,6]-tricos-16-ene-3,6,9,19,22-pentanone (FR901228), a natural anticancer depsipeptide, induces apoptosis of ras-transformed 10T1/2 cells whereas it induces growth arrest of nontransformed counterpart cells in G0/G1 phase of the cell cycle. Our study of the effect of FR901228 treatment on intracellular signaling pathways reveals a discriminating activity of FR901228 to regulate signaling cascades differently in ras-transformed 10T1/2 cells and nontransformed counterpart cells. Induction of apoptosis of ras-transformed cells by FR901228 correlates with suppression of the extracellular signal-regulated kinase (ERK) signaling pathway through reduction of Raf expression and deactivation of Mek and Erk, inhibition of the phosphoinositide-3 kinase (PI3-K) pathway indexed by suppression of Akt activity, suppression of p38 activity, and activation of caspase-3. Expression of p21(Cip1) is not induced in ras-transformed cultures undergoing apoptosis induced by FR901228. In contrast, FR901228 induces p21(Cip1) expression in nontransformed counterpart cultures growth-arrested in G0/G1 that is also accompanied by moderate induction of the kinase activities of Raf, Mek, Erk, and Akt, but not accompanied by activation of caspase-3 or changes in p38 activity. Our study indicates a potential value of FR901228 in the treatment of cancer cells involving aberrant regulation of Ras through preferential induction of the caspase cascade and suppression of the ERK, PI3-K, and p38 pathways.     

An NF-κB pathway-mediated positive feedback loop amplifies Ras activity to pathological levels in mice

Genetic mutations that give rise to active mutant forms of Ras are oncogenic and found in several types of tumor. However, such mutations are not clear biomarkers for disease, since they are frequently detected in healthy individuals. Instead, it has become clear that elevated levels of Ras activity are critical for Ras-induced tumorigenesis. However, the mechanisms underlying the production of pathological levels of Ras activity are unclear. Here, we show that in the presence of oncogenic Ras, inflammatory stimuli initiate a positive feedback loop involving NF-κB that further amplifies Ras activity to pathological levels. Stimulation of Ras signaling by typical inflammatory stimuli was transient and had no long-term sequelae in wild-type mice. In contrast, these stimuli generated prolonged Ras signaling and led to chronic inflammation and precancerous pancreatic lesions (PanINs) in mice expressing physiological levels of oncogenic K-Ras. These effects of inflammatory stimuli were disrupted by deletion of inhibitor of NF-κB kinase 2 (IKK2) or inhibition of Cox-2. Likewise, expression of active IKK2 or Cox-2 or treatment with LPS generated chronic inflammation and PanINs only in mice expressing oncogenic K-Ras. The data support the hypothesis that in the presence of oncogenic Ras, inflammatory stimuli trigger an NF-κB-mediated positive feedback mechanism involving Cox-2 that amplifies Ras activity to pathological levels. Because a large proportion of the adult human population possesses Ras mutations in tissues including colon, pancreas, and lung, disruption of this positive feedback loop may be an important strategy for cancer prevention.     

Specific inhibition of the Akt1 pleckstrin homology domain by D-3-deoxy-phosphatidyl-myo-inositol analogues

Activation of Akt (protein kinase B), a Ser/Thr protein kinase that promotes cell survival, has been linked to tumorigenesis. Akt is activated by phosphorylation after binding of its pleckstrin homology (PH) domain to plasma membrane phosphatidyl-myo-inositol-3-phosphates, formed by phosphoinositide-3-kinase. We report a novel strategy to inhibit Akt activation based on the use of D-3-deoxy-phosphatidyl-myo-inositols (DPIs) that cannot be phosphorylated on the 3-position of the myo-inositol ring. We have studied the DPIs, DPI 1-[(R)-2,3-bis(hexadecanoyloxy)propyl hydrogen phosphate], its ether lipid derivative DPI 1-[(R)-2-methoxy-3-octadecyloxypropyl hydrogen phosphate] (DPIEL), and its carbonate derivative DPI 1-[(R)-2-methoxy-3-octadecyloxypropyl carbonate]. We demonstrate in platelet-derived growth factor-stimulated mouse NIH3T3 cells that the DPIs bind to the PH domain of Akt, trapping it in the cytoplasm and thus preventing Akt activation. DPIEL did not inhibit myristylated-Akt, a constitutively active membrane-bound Akt expressed in NIH3T3 cells, and cell growth was not inhibited, unlike in wild-type NIH3T3 cells. Molecular modeling and docking studies show that DPIEL binds with much higher affinity to Akt's PH domain as compared with DPI and DPI 1-[(R)-2-methoxy-3-octadecyloxypropyl carbonate]. This study shows that the DPIs are a novel class of growth inhibitory agents with a novel mechanism of action through binding to the PH domain of Akt and inhibition of Akt activation.     

Dependence on the MUC1-C oncoprotein in non-small cell lung cancer cells

Non-small cell lung cancer (NSCLC) cells are often associated with constitutive activation of the phosphoinositide 3-kinase (PI3K) → Akt → mTOR pathway. The mucin 1 (MUC1) heterodimeric glycoprotein is aberrantly overexpressed in NSCLC cells and induces gene signatures that are associated with poor survival of NSCLC patients. The present results show that the MUC1 C-terminal subunit (MUC1-C) cytoplasmic domain associates with PI3K p85 in NSCLC cells. We show that inhibition of MUC1-C with cell-penetrating peptides blocks this interaction with PI3K p85 and suppresses constitutive phosphorylation of Akt and its downstream effector, mTOR. In concert with these results, treatment of NSCLC cells with the MUC1-C peptide inhibitor GO-203 was associated with downregulation of PI3K → Akt signaling and inhibition of growth. GO-203 treatment was also associated with increases in reactive oxygen species (ROS) and induction of necrosis by a ROS-dependent mechanism. Moreover, GO-203 treatment of H1975 (EGFR L858R/T790M) and A549 (K-Ras G12S) xenografts growing in nude mice resulted in tumor regressions. These findings indicate that NSCLC cells are dependent on MUC1-C both for activation of the PI3K → Akt pathway and for survival.     

Akt or phosphoinositide-3-kinase inhibition reverses cardio-protection in Toll-like receptor 2 deficient mice

Aim

Absence or inhibition of Toll-like receptor 2 (TLR2) signalling during murine myocardial ischaemia/reperfusion (MI/R) decreases myocardial necrosis and inflammation, thereby ameliorating cardiac dysfunction and improving survival. In the present study, we provide evidence for the involvement of the phosphoinositide-3-kinase/Akt pathway in TLR2-dependent reperfusion injury.

Methods

Adult male wild-type (WT) and TLR2^−/− mice were subjected to myocardial ischaemia (30 min) and reperfusion (4 h). Animals were treated with phosphoinositide-3-kinase inhibitor wortmannin, Akt inhibitor V (triciribine), or vehicle 1 h prior to MI/R. Protein expression levels of Akt1 and phosphoinositide-3-kinase and their respective phosphorylated forms were determined by Western blot analysis. Myocardial necrosis was quantified after staining with the tetrazolium method and by troponin T plasma levels.

Results

TLR2^−/− mice displayed significantly increased Akt and phospho-Akt levels compared to WT mice, whilst no significant difference in phosphoinositide-3-kinase expression and phosphorylation could be observed. TLR2^−/− mice also showed a blunted myocardial necrosis, the extent of which inversely correlated with Akt expression and degree of phosphorylation. Pharmacological inhibition of both, phosphoinositide-3-kinase or Akt, reversed the cardioprotection observed in TLR2^−/− mice, whilst no effect could be observed in WT mice.

Conclusion

Akt is an important mediator of cardioprotection in TLR2^−/− animals during MI/R. The effect is, however, likely mediated by its genomic overexpression in the heart of TLR2^−/− animals whilst Akt activation by phosphoinositide-3-kinase is unaltered.     

Targeting the phosphatidylinositol 3-kinase/Akt pathway for enhancing breast cancer cells to radiotherapy

The phosphatidylinositol 3-kinase (PI-3K)/Akt pathway, regulated by its upstream growth factor receptor tyrosine kinases, plays a critical role in promoting cell proliferation and inhibiting cell death. The aim of this study was to determine whether the PI-3K/Akt activity contributes to the resistance of human breast cancer cells to ionizing radiation and whether inhibition of the PI-3K/Akt pathway could sensitize human breast cancer cells to radiotherapy. To determine a causal relationship between the activity of Akt and radioresistance in human breast cancer cells, MCF7 cells, transfected with constitutively active H-Ras (RadG12V) or constitutively active Akt, were chosen for analysis of the cell clonogenic survival fraction and induction of apoptosis after ionizing radiation. The PI-3K-specific inhibitor LY294002 was used to examine whether inhibition of PI-3K could sensitize these cells to radiation treatment. Our results indicate that the expression of constitutively active Ras (which activated Akt in a PI-3K-dependent manner) and the expression of constitutively active Akt (which caused a PI-3K-independent activation of Akt) each increased cellular resistance to radiation. Inhibition of PI-3K with LY294002 reverted the constitutively active Ras-mediated radioresistance but not the constitutively active Akt-mediated radioresistance. Our data suggest that Akt may be a potential target for enhancing the response to radiotherapy in patients with breast cancer.     

Flavopiridol and trastuzumab synergistically inhibit proliferation of breast cancer cells: association with selective cooperative inhibition of cyclin D1-dependent kinase and Akt signaling pathways

Cyclin D1 is essential for Neu-induced cell growth and is induced by growth factors through Ras-dependent and Ras-independent signaling pathways (1). Because flavopiridol, a novel flavanoid cyclin-cyclin-dependent kinase inhibitor, may function through Ras-dependent and/or -independent pathways, we hypothesized that treatment of breast cancer cells with inhibitors of Neu signaling and flavopiridol might synergize to inhibit proliferation. Human breast cancer cell lines, which express high levels of endogenous Neu receptor, were treated with the anti-Neu antibody, trastuzumab, together with flavopiridol and subject to MTT assay. Cell lines were assayed for alterations in cell cycle by fluorescence-activated cell sorter and signaling proteins by Western blot. Flavopiridol and trastuzumab synergistically inhibited DNA synthesis, cellular proliferation, and contact-dependent growth. Cytotoxic synergy was observed independent of the sequence of addition of the two drugs to cultured cells. In SKBR3 cells, a combination of trastuzumab and flavopiridol inhibited the Ras-MAPK-Akt pathway, decreased cyclin D1 abundance, and kinase activity to a greater extent than either drug alone. Compared with single-agent treatment, combination treatment selectively inhibited Akt and pRB phosphorylation. Cytotoxic synergy was observed with flavopiridol plus LY294002 (selective phosphatidylinositol 3-kinase inhibitor) but not with PD98059 (selective mitogen-activated protein kinase kinase 1 inhibitor) suggesting that Akt inhibition may be important in synergy. Zinc-induced overexpression of cyclin D1 in T-47D deltaMTcycD1 cells were more resistant to drug-induced cell death when compared with vector-transfected T-47D deltaMT cells. Cyclin D1 overexpression reverses drug treatment induced cell cycle arrest in SKBR3 cells. Flavopiridol and trastuzumab yield cytotoxic synergy in human breast cancer cells overexpressing Neu. Cyclin D1 overexpression results in combination drug resistance. In addition, inhibition of Akt may prove to be a useful therapeutic strategy in combination with flavopiridol.     

Delivery of PTEN via a novel gene microcapsule sensitizes prostate cancer cells to irradiation

The tumor suppressor gene MMAC/PTEN located on chromosome10q23.3 has dual phosphatase activity in the phosphoinositide-3-kinase signaling pathway and inhibits Akt activation, a serine-threonine kinase, which is involved in proliferative and antiapoptotic pathways. Furthermore, MMAC/PTEN is frequently inactivated in a variety of tumors including prostate cancer. In this study, we generated a new type of gene transfer drug, GelaTen, which is a microsphere of cationized gelatin hydrogels incorporating PTEN plasmid DNA. Using our previously reported radiation-resistant PC3-Bcl-2 human prostate cancer cells (PTEN deleted), we examined the efficacy of GelaTen to force the expression of PTEN in vivo to inhibit tumor growth after intratumoral injection alone or with irradiation. Combinational therapy with GelaTen and irradiation improved both the in vitro and in vivo efficacy of growth inhibition compared with GelaTen or irradiation alone. These data show that GelaTen gene therapy, enabling radiosensitization, can potentially treat prostate cancers that have MMAC/PTEN gene alterations associated with radioresistance.     

The PtdIns 3-Kinase/Akt Pathway Regulates Macrophage-Mediated ADCC against B Cell Lymphoma

Macrophages are important effectors in the clearance of antibody-coated tumor cells. However, the signaling pathways that regulate macrophage-induced ADCC are poorly defined. To understand the regulation of macrophage-mediated ADCC, we used human B cell lymphoma coated with Rituximab as the tumor target and murine macrophages primed with IFNγ as the effectors. Our data demonstrate that the PtdIns 3-kinase/Akt pathway is activated during macrophage-induced ADCC and that the inhibition of PtdIns 3-kinase results in the inhibition of macrophage-mediated cytotoxicity. Interestingly, downstream of PtdIns 3-kinase, expression of constitutively active Akt (Myr-Akt) in macrophages significantly enhanced their ability to mediate ADCC. Further analysis revealed that in this model, macrophage-mediated ADCC is dependent upon the release of nitric oxide (NO). However, the PtdIns 3-kinase/Akt pathway does not appear to regulate NO production. An examination of the role of the PtdIns 3-kinase/Akt pathway in regulating conjugate formation indicated that macrophages treated with an inhibitor of PtdIns 3-kinase fail to polarize the cytoskeleton at the synapse and show a significant reduction in the number of conjugates formed with tumor targets. Further, inhibition of PtdIns 3-kinase also reduced macrophage spreading on Rituximab-coated surfaces. On the other hand, Myr-Akt expressing macrophages displayed a significantly greater ability to form conjugates with tumor cells. Taken together, these findings illustrate that the PtdIns 3-kinase/Akt pathway plays a critical role in macrophage ADCC through its influence on conjugate formation between macrophages and antibody-coated tumor cells.     

Curcumin inhibits Akt/mammalian target of rapamycin signaling through protein phosphatase-dependent mechanism

Akt/mammalian target of rapamycin (mTOR) signaling plays an important role in tumorigenesis and is dysregulated in many tumors, especially metastatic prostate cancers. Curcumin has been shown to effectively prevent or inhibit prostate cancer in vivo and inhibit Akt/mTOR signaling in vitro, but the mechanism(s) remains unclear. Here, we show that curcumin concentration- and time-dependently inhibited the phosphorylation of Akt, mTOR, and their downstream substrates in human prostate cancer PC-3 cells, and this inhibitory effect acts downstream of phosphatidylinositol 3-kinase and phosphatidylinositol-dependent kinase 1. Overexpression of constitutively activated Akt or disruption of TSC1-TSC2 complex by small interfering RNA or gene knockout only partially restored curcumin-mediated inhibition of mTOR and downstream signaling, indicating that they are not the primary effectors of curcumin-mediated inhibition of Akt/mTOR signaling. Curcumin also activated 5'-AMP-activated protein kinase and mitogen-activated protein kinases; however, inhibition of these kinases failed to rescue the inhibition by curcumin. Finally, it was shown that the inhibition of Akt/mTOR signaling by curcumin is resulted from calyculin A-sensitive protein phosphatase-dependent dephosphorylation. Our study reveals the profound effects of curcumin on the Akt/mTOR signaling network in PC-3 cells and provides new mechanisms for the anticancer effects of curcumin. [Mol Cancer Ther 2008;7(9):2609-20].     

Inhibition of phosphatidylinositol-3-kinase and mitogen-activated protein kinase kinase 1/2 prevents melanoma development and promotes melanoma regression in the transgenic TPRas mouse model

A number of human melanomas show hyperactivation of the Ras pathway due to mutations of the molecule or alteration of upstream or downstream effectors. In this study, we evaluated the effect of blocking the two Ras downstream pathways phosphatidylinositol-3-kinase/Akt and Raf/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase on melanoma development and regression in the TPRas mouse model. The inhibition of these two signaling cascades by topically applied Ly294002 and U0126 significantly delayed melanoma development and significantly decreased the tumor incidence, particularly when the drugs were applied in combination. Treatment with the inhibitors of established melanomas resulted in complete remission in 33% of mice and partial regression in 46% of mice when drugs were delivered in combination. These responses correlated with increased apoptosis and decreased proliferation both in vitro and in vivo and reduced tumor angiogenesis. In conclusion, this study strongly supports the role of the phosphatidylinositol-3-kinase/Akt and Raf/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase pathways in the development and maintenance of Ras-dependent melanomas and supports the notion that specific inhibition of these effectors may represent a very promising avenue for the treatment and prevention of the disease.     

Inactivation of Icmt inhibits transformation by oncogenic K-Ras and B-Raf

Isoprenylcysteine carboxyl methyltransferase (Icmt) methylates the carboxyl-terminal isoprenylcysteine of CAAX proteins (e.g., Ras and Rho proteins). In the case of the Ras proteins, carboxyl methylation is important for targeting of the proteins to the plasma membrane. We hypothesized that a knockout of Icmt would reduce the ability of cells to be transformed by K-Ras. Fibroblasts harboring a floxed Icmt allele and expressing activated K-Ras (K-Ras-Icmt^flx/flx) were treated with Cre-adenovirus, producing K-Ras-Icmt^Δ/Δ fibroblasts. Inactivation of Icmt inhibited cell growth and K-Ras–induced oncogenic transformation, both in soft agar assays and in a nude mice model. The inactivation of Icmt did not affect growth factor–stimulated phosphorylation of Erk1/2 or Akt1. However, levels of RhoA were greatly reduced as a consequence of accelerated protein turnover. In addition, there was a large Ras/Erk1/2-dependent increase in p21^Cip1, which was probably a consequence of the reduced levels of RhoA. Deletion of p21^Cip1 restored the ability of K-Ras-Icmt^Δ/Δ fibroblasts to grow in soft agar. The effect of inactivating Icmt was not limited to the inhibition of K-Ras–induced transformation: inactivation of Icmt blocked transformation by an oncogenic form of B-Raf (V599E). These studies identify Icmt as a potential target for reducing the growth of K-Ras– and B-Raf–induced malignancies.     

MiR-1 targets PIK3CA and inhibits tumorigenic properties of A549 cells

MicroRNAs are small endogenous RNAs that play important roles in the pathogenesis of human diseases, including malignancy. MicroRNA-1 (miR-1) is downregulated in non-small cell lung cancer (NSCLC); however, the underlying mechanisms by which it suppresses tumorigenesis in NSCLC are largely unknown. We investigated whether phosphoinositide-3-kinase catalytic subunit alpha (PIK3CA) was a novel target of miR-1 in the NSCLC cell line A549, and the mechanism of miR-1 inhibition of the tumorigenic properties of A549 cells is discussed. The influence of miR-1 on A549 cells was studied by transfection with miR-1 mimics or inhibitor. MiR-1 overexpression led to downregulation of PIK3CA protein, but not mRNA by western blot and quantitative real-time PCR, respectively. The dual-luciferase reporter assay confirmed that miR-1 targeted PIK3CA directly. PIK3CA downregulation by miR-1 mimics led to a significant reduction of phosphorylated Akt and survivin protein, the downstream targets of the PI3 K/Akt pathway. Cell proliferation was studied using a cell counting kit. Migration and invasion were evaluated by Transwell and Matrigel assays, respectively. Cell cycle and apoptosis were detected by flow cytometry. The results were that miR-1 upregulation inhibited A549 cell proliferation, migration, and invasion. These findings indicate that miR-1 may play an important role in the pathogenesis of NSCLC by regulating PIK3CA through the PI3 K/Akt pathway. Increasing miR-1 expression may provide a novel approach for NSCLC treatment.     

A genome-wide RNAi screen in mouse embryonic stem cells identifies Mp1 as a key mediator of differentiation

Despite intense investigation of intrinsic and extrinsic factors that regulate pluripotency, the process of initial fate commitment of embryonic stem (ES) cells is still poorly understood. We used a genome-wide short hairpin RNA screen in mouse ES cells to identify genes that are essential for initiation of differentiation. Knockdown of the scaffolding protein Mek binding protein 1 (Mp1, also known as Lamtor3 or Map2k1ip1) stimulated self-renewal of ES cells, blocked differentiation, and promoted proliferation. Fibroblast growth factor 4 (FGF4) signaling is required for initial fate commitment of ES cells. Knockdown of Mp1 inhibited FGF4-induced differentiation but did not alter FGF4-driven proliferation. This uncoupling of differentiation and proliferation was also observed when oncogenic Ras isoforms were overexpressed in ES cells. Knockdown of Mp1 redirected FGF4 signaling from differentiation toward pluripotency and up-regulated the pluripotency-related genes Esrrb, Rex1, Tcl1, and Sox2. We also found that human germ cell tumors (GCTs) express low amounts of Mp1 in the invasive embryonic carcinoma and seminoma histologies and higher amounts of Mp1 in the noninvasive carcinoma in situ precursor and differentiated components. Knockdown of Mp1 in invasive GCT cells resulted in resistance to differentiation, thereby showing a functional role for Mp1 both in normal differentiation of ES cells and in germ cell cancer.     

Antileukemia effects of xanthohumol in Bcr/Abl-transformed cells involve nuclear factor-kappaB and p53 modulation

The oncogenic Bcr-Abl tyrosine kinase activates various signaling pathways including phosphoinositide 3-kinase/Akt and nuclear factor-kappaB that mediate proliferation, transformation, and apoptosis resistance in Bcr-Abl+ myeloid leukemia cells. The hop flavonoid xanthohumol inhibits tumor growth by targeting the nuclear factor-kappaB and Akt pathways and angiogenesis. Here, we show that xanthohumol has in vitro activity against Bcr-Abl+ cells and clinical samples and retained its cytotoxicity when imatinib mesylate-resistant K562 cells were examined. Xanthohumol inhibition of K562 cell viability was associated with induction of apoptosis, increased p21 and p53 expression, and decreased survivin levels. We show that xanthohumol strongly inhibited Bcr-Abl expression at both mRNA and protein levels and show that xanthohumol caused elevation of intracellular reactive oxygen species and that the antioxidant N-acetylcysteine blunted xanthohumol-induced events. Further, we observed that xanthohumol inhibits leukemia cell invasion, metalloprotease production, and adhesion to endothelial cells, potentially preventing in vivo life-threatening complications of leukostasis and tissue infiltration by leukemic cells. As structural mutations and/or gene amplification in Bcr-Abl can circumvent an otherwise potent anticancer drug such as imatinib, targeting Bcr-Abl expression as well as its kinase activity could be a novel additional therapeutic approach for the treatment of Bcr-Abl+ myeloid leukemia.     

CD28-dependent activation of protein kinase B/Akt blocks Fas-mediated apoptosis by preventing death-inducing signaling complex assembly

The T cell costimulatory molecule CD28 is important for T cell survival, yet both the signaling pathways downstream of CD28 and the apoptotic pathways they antagonize remain poorly understood. Here we demonstrate that CD4(+) T cells from CD28-deficient mice show increased susceptibility to Fas-mediated apoptosis via a phosphatidylinositol 3-kinase (PI3K)-dependent pathway. Protein kinase B (PKBalpha/Akt1) is an important serine/threonine kinase that promotes survival downstream of PI3K signals. To understand how PI3K-mediated signals downstream of CD28 contribute to T cell survival, we examined Fas-mediated apoptosis in T cells expressing an active form of PKBalpha. Our data demonstrate that T cells expressing active PKB are resistant to Fas-mediated apoptosis in vivo and in vitro. PKB transgenic T cells show reduced activation of caspase-8, BID, and caspase-3 due to impaired recruitment of procaspase-8 to the death-inducing signaling complex (DISC). Similar alterations are seen in T cells from mice which are haploinsufficient for PTEN, a lipid phosphatase that regulates phosphatidylinositol-3,4,5-trisphosphate (PIP(3)) and influences PKBalpha activity. These findings provide a novel link between CD28 and an important apoptosis pathway in vivo, and demonstrate that PI3K/PKB signaling prevents apoptosis by inhibiting DISC assembly.     

2-Deoxyglucose induces Akt phosphorylation via a mechanism independent of LKB1/AMP-activated protein kinase signaling activation or glycolysis inhibition

The compound 2-deoxyglucose (2-DG) enhances chemotherapy/radiotherapy in cell lines and animal models, prompting two phase I clinical trials with this cancer therapeutic. Although its mechanism of action has not been fully elucidated, it is hypothesized that the molecular basis of 2-DG activity is related to glycolysis inhibition. Here, we report that 2-DG induced Akt phosphorylation at Thr(308) and Ser(473) as early as 15 min post-treatment. These phosphorylation events required phosphatidylinositol-3-kinase activity but were not related to LKB1/AMP-activated protein kinase signaling, the inhibition of glycolysis or epidermal growth factor receptor signaling. The 2-DG-mediated Akt phosphorylation also led to the phosphorylation of Akt downstream targets, such as Foxo3a, GSK3beta, and Chk1. Because the functional consequence of Akt activation includes chemotherapy/radiotherapy resistance, our data suggested that the combination of phosphatidylinositol-3-kinase/Akt inhibitory agents in 2-DG-based chemotherapy/radiotherapy may result in enhanced therapeutic efficacy.     

Expression of GTPase-deficient Ras inhibits vasopressin signaling in cultured cortical collecting duct cells.

Cross-talk between signaling pathways is increasingly recognized as integral to cellular function. We investigated whether the mitogen-activated protein kinase (MAPK) pathway alters vasopressin (AVP) stimulation of protein kinase A (PKA) by specifically studying the role of Ras. Mouse cortical collecting duct cells (M-1) were transfected with a cDNA encoding oncogenic Ras. Transfection was confirmed by Western blot analysis and functionally by enhanced basal MAPK activity. When compared with basal MAPK activity of 26.4 +/- 6.6 pmol/mg/min in controls, basal MAPK activity varied widely in Ras-transfected clones from 29.0 +/- 6.6 to 96.6 +/- 13.4 pmol/mg/min. Clones that functionally expressed activated Ras displayed complete abolition of AVP-stimulated PKA activity, whereas those that failed to express elevated basal MAPK activity showed intact AVP-stimulated PKA. The correlation between expression of high basal MAPK activity and inhibition of AVP-induced PKA yielded a correlation coefficient of -0.92 (P = 0.009). Exposure to 10 microM forskolin or 1 microgram/ml cholera toxin resulted in comparable activation of PKA in all clones. We found no correlation between PKC activity of the clones and PKA inhibition. To assess whether the observed effect was due to one known Ras target, cells were transfected with constitutively activated Raf. M-1 cells expressing activated Raf exhibited elevated MAPK activity. The Raf clones showed no impairment of AVP-stimulated PKA activity. We conclude that expression of activated Ras is inhibitory of AVP-induced PKA activation in the M-1 cortical collecting duct cell line at a site proximal to G alpha s protein. The failure of Raf to influence AVP signaling indicates that the action of Ras is through a pathway independent of this Ras target.     

In vivo activity of combined PI3K/mTOR and MEK inhibition in a Kras(G12D);Pten deletion mouse model of ovarian cancer

The phosphatidylinositol 3-kinase (PI3K)/Akt pathway is commonly dysregulated in human cancer, making it an attractive target for novel anticancer therapeutics. We have used a mouse model of ovarian cancer generated by Kras(G12D) activation and Pten deletion in the ovarian surface epithelium for the preclinical assessment of a novel PI3K/mTOR inhibitor PF-04691502. To enable higher throughput studies, we developed an orthotopic primary transplant model from these mice and evaluated therapeutic response to PF-04691502 using small-animal ultrasound and FDG-PET imaging. PF-04691502 inhibited tumor growth at 7 days by 72% ± 9. FDG-PET imaging revealed that PF-04691502 reduced glucose metabolism dramatically, suggesting FDG-PET may be exploited as an imaging biomarker of target inhibition by PF-04691502. Tissue biomarkers of PI3K/mTOR pathway activity, p-AKT (S473), and p-RPS6 (S240/244), were also dramatically inhibited following PF-04691502 treatment. However, as a single agent, PF-04691502 did not induce tumor regression and the long-term efficacy was limited, with tumor proliferation continuing in the presence of drug treatment. We hypothesized that tumor progression was because of concomitant activation of the mitogen-activated protein kinase pathway downstream of Kras(G12D) expression promoting cell survival and that the therapeutic effect of PF-04691502 would be enhanced by combinatory inhibition of MEK using PD-0325901. This combination induced striking tumor regression, apoptosis associated with upregulation of Bim and downregulation of Mcl-1, and greatly improved duration of survival. These data suggest that contemporaneous MEK inhibition enhances the cytotoxicity associated with abrogation of PI3K/mTOR signaling, converting tumor growth inhibition to tumor regression in a mouse model of ovarian cancer driven by PTEN loss and mutant K-Ras.