Perturbations of the AKT signaling pathway in human cancer

HIV protease inhibitors decrease VEGF/HIF-1alpha expression and angiogenesis in glioblastoma cells

Glioblastomas are malignant brain tumors that are rarely curable, even with aggressive therapy (surgery, chemotherapy, and radiation). Glioblastomas frequently display loss of PTEN and/or epidermal growth factor receptor activation, both of which activate the PI3K pathway. This pathway can increase vascular endothelial growth factor (VEGF) and hypoxia-inducible factor (HIF)-1alpha expression. We examined the effects of two human immunodeficiency virus protease inhibitors, nelfinavir and amprenavir, which inhibit Akt signaling, on VEGF and HIF-1alpha expression and on angiogenesis. Nelfinavir decreased VEGF mRNA expression and VEGF secretion under normoxia. Downregulation of P-Akt decreased VEGF secretion in a manner similar to that of nelfinavir, but the combination of the two had no greater effect, consistent with the idea that nelfinavir decreases VEGF through the PI3K/Akt pathway. Nelfinavir also decreased the hypoxic induction of VEGF and the hypoxic induction of HIF-1alpha, which regulates VEGF promoter. The effect of nelfinavir on HIF-1alpha was most likely mediated by decreased protein translation. Nelfinavir's effect on VEGF expression had the functional consequence of decreasing angiogenesis in in vivo Matrigel plug assays. Similar effects on VEGF and HIF-1alpha expression were seen with a different protease inhibitor, amprenavir. Our results support further research into these protease inhibitors for use in future clinical trials for patients with glioblastoma multiformes.

Sanguinarine inhibits VEGF-induced angiogenesis in a fibrin gel matrix

BACKGROUND

The identification of possible ways to block blood vessels formation has become a major scientific objective of the last decade and several phytochemicals are currently being exploited to target tumour angiogenesis.

AIM

The effects of Sanguinarine (SA), an alkaloid from the root of Sanguinaria Canadensis, were evaluated in an in vitro angiogenesis model; moreover the effects on Akt phosphorylation in porcine aortic endothelial cell line (AOC) were also examined.

METHODS

SA (300 nM) was tested in the presence or absence of VEGF (100 ng/ml) in a three dimensional angiogenesis bioassay obtained pipetting a suspension of AOC on microcarrier beads in a fibrinogen solution before the addition of thrombine. Endothelial cell proliferation was measured at 48, 96, 144, 192 h. The phosphorylation of Akt was measured by ELISA in 2 x 10(5) AOC treated as described above.

RESULTS

The addition of SA abolished (p< 0.001) VEGF stimulatory effect on AOC growth at all the examined times. In addition, the stimulatory effect induced by VEGF on Akt phosphorylation was significantly (p< 0.001) inhibited by SA.

CONCLUSION

SA appear to be an antiangiogenic natural product by directly suppressing the proliferative effect of VEGF on endothelial cell line: this effect could be mediated by blocking the VEGF-induced Akt activation.

Antitumor activity of suberoylanilide hydroxamic acid against thyroid cancer cell lines in vitro and in vivo

PURPOSE

The histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), has multiple antitumor effects against a variety of human cancers.

EXPERIMENTAL DESIGN

We treated several anaplastic and papillary thyroid cancer cell lines with SAHA to determine if it could inhibit the growth of these cells in vitro and in vivo.

RESULTS

SAHA effectively inhibited 50% clonal growth of the anaplastic thyroid cancer cell lines, ARO and FRO, and the papillary thyroid cancer cell line, BHP 7-13, at 1.3x10(-7) to 5x10(-7) mol/L, doses that are achievable in patients. In concert with growth inhibition, SAHA down-regulated the expression of cyclin D1 and up-regulated levels of p21WAF1. Annexin V and cleavage of poly(ADP)ribose polymerase were both increased by exposure of the thyroid cancer cells to SAHA. Expression of the death receptor 5 (DR5) gene was also increased by SAHA, but the combination of the DR5 ligand, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), with SAHA had little effect compared with SAHA alone. Of note, the combination of paclitaxel, doxorubicin, or paraplatin with SAHA enhanced cell killing of the thyroid cancer cells. In addition, murine studies showed that SAHA administered daily by i.p. injection at 100 mg/kg inhibited the growth of human thyroid tumor cells.

CONCLUSION

Our data indicate that SAHA is a plausible adjuvant therapy for thyroid cancers.

Isoform-specific requirement for Akt1 in the developmental regulation of cellular metabolism during lactation

The metabolic demands and synthetic capacity of the lactating mammary gland exceed that of any other tissue, thereby providing a useful paradigm for understanding the developmental regulation of cellular metabolism. By evaluating mice bearing targeted deletions in Akt1 or Akt2, we demonstrate that Akt1 is specifically required for lactating mice to synthesize sufficient quantities of milk to support their offspring. Whereas cellular proliferation, differentiation, and apoptosis are unaffected, loss of Akt1 disrupts the coordinate regulation of metabolic pathways that normally occurs at the onset of lactation. This results in a failure to upregulate glucose uptake, Glut1 surface localization, lipid synthesis, and multiple lipogenic enzymes, as well as a failure to downregulate lipid catabolic enzymes. These findings demonstrate that Akt1 is required in an isoform-specific manner for orchestrating many of the developmental changes in cellular metabolism that occur at the onset of lactation and establish a role for Akt1 in glucose metabolism.

Nelfinavir down-regulates hypoxia-inducible factor 1alpha and VEGF expression and increases tumor oxygenation: implications for radiotherapy

The phosphatidylinositol 3-kinase (PI3K)/Akt pathway can increase vascular endothelial growth factor (VEGF) and hypoxia-inducible factor 1alpha (HIF-1alpha) expression. We examined the effect of nelfinavir, an HIV protease inhibitor that inhibits Akt signaling, on VEGF and HIF-1alpha expression and on angiogenesis, tumor oxygenation, and radiosensitization. Nelfinavir decreases VEGF expression under normoxia via the transcription factor Sp1, which regulates the proximal core VEGF promoter. Nelfinavir decreased Sp1 phosphorylation and decreased Sp1 binding to a probe corresponding to the proximal VEGF promoter in a gel shift assay. Nelfinavir also decreased the hypoxic induction of HIF-1alpha, which also regulates the VEGF promoter, most likely by decreasing its translation. The effect of nelfinavir on VEGF expression had the functional consequence of decreasing angiogenesis in an in vivo Matrigel plug assay. To determine the effect this might have on tumor radiosensitization, we did tumor regrowth assays with xenografts in nude mice. The combination of nelfinavir and radiation increased time to regrowth compared with radiation alone whereas nelfinavir alone had little effect on tumor regrowth. This radiosensitizing effect was greater than suggested by in vitro clonogenic survival assays. One possible explanation for the discordance is that nelfinavir has an effect on tumor oxygenation. Therefore, we examined this with the hypoxia marker EF5 and found that nelfinavir leads to increased oxygenation within tumor xenografts. Our results suggest that nelfinavir decreases HIF-1alpha/VEGF expression and tumor hypoxia, which could play a role in its in vivo radiosensitizing effect. These data support the use of nelfinavir in combination with radiation in future clinical trials.

Prognostic significance of clinical factors and Akt activation in patients with bronchioloalveolar carcinoma

PURPOSE

Lung cancer is the leading cause of cancer related mortality in the world. Bronchioloalveolar carcinoma (BAC) is a subset of NSCLC that has recently gained attention because of distinct biological and clinical features, increased incidence, and enhanced responsiveness to new therapies such as epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs). However, prognostic features for BAC have not been well defined. Because activation of Akt is highly prevalent and a poor prognostic factor for other types of NSCLC, we assessed the prognostic significance of clinical features and Akt activation in patients with BAC.

METHODS

Forty-six cases of BAC in Iceland were classified according to WHO 1999 criteria. Akt activation was assessed using two phospho-specific antibodies against Akt (S473 and T308) in immunohistochemical (IHC) analysis. Associations between ordered Akt levels and other dichotomous parameters were evaluated using an exact Cochran-Armitage test for trend. Survival was analyzed by the Kaplan-Meier method and log-rank test, with hazard ratios (HR) determined by Cox proportional hazard models. The Cox model was also used to assess the joint effect of multiple factors on survival when they are considered simultaneously.

RESULTS

Age and histology (mucinous versus non-mucinous) were not associated with survival. Activation of Akt was highly prevalent in BAC, with only 2 out of 46 patients exhibiting negative staining with either antibody. Moderate to high Akt activation was observed in 63% of cases and was associated with non-mucinous histology. Akt activation was not associated with differences in survival or smoking status. In contrast, Cox model analysis revealed that male gender (HR 2.24, 95% CI, 1.07-4.71, p=0.032), advanced stage (III or IV) (HR 2.17, 95% CI, 1.004-4.71, p=0.049) and smoking status (HR 6.89, 95% CI, 1.49-31.88, p=0.013) were associated with a worse prognosis.

CONCLUSIONS

Male gender, advanced stage, and especially smoking status (but not Akt activation) are potentially important prognostic features for BAC. These features should be considered in the design and interpretation of clinical trials that enroll BAC patients.

Inhibition of c-Met as a therapeutic strategy for esophageal adenocarcinoma

The hepatocyte growth factor (HGF) receptor c-Met is a tyrosine kinase receptor with established oncogenic properties. We have previously shown that c-Met is usually overexpressed in esophageal adenocarcinoma (EA), yet the implications of c-Met inhibition in EA remain unknown. Three c-Met-overexpressing EA cell lines (Seg-1, Bic-1, and Flo-1) were used to examine the effects of a c-Met-specific small molecule inhibitor (PHA665752) on cell viability, apoptosis, motility, invasion, and downstream signaling pathways. PHA665752 demonstrated dose-dependent inhibition of constitutive and/or HGF-induced phosphorylation of c-Met, which correlated with reduced cell viability and inhibition of extracellular regulated kinase 1/2 phosphorylation in all three EA cell lines. In contrast, PHA665752 induced apoptosis and reduced motility and invasion in only one EA cell line, Flo-1. Interestingly, Flo-1 was the only cell line in which phosphatidylinositol 3-kinase (PI3K)/Akt was induced following HGF stimulation. The PI3K inhibitor LY294002 produced effects equivalent to those of PHA665752 in these cells. We conclude that inhibition of c-Met may be a useful therapeutic strategy for EA. Factors other than receptor overexpression, such as c-Met-dependent PI3K/Akt signaling, may be predictive of an individual tumor's response to c-Met inhibition.

Isoginkgetin inhibits tumor cell invasion by regulating phosphatidylinositol 3-kinase/Akt-dependent matrix metalloproteinase-9 expression

Matrix metalloproteinase (MMP)-9 plays a key role in tumor invasion. Inhibitors of MMP-9 were screened from Metasequoia glyptostroboides (Dawn redwood) and one potent inhibitor, isoginkgetin, a biflavonoid, was identified. Noncytotoxic levels of isoginkgetin decreased MMP-9 production profoundly, but up-regulated the level of tissue inhibitor of metalloproteinase (TIMP)-1, an inhibitor of MMP-9, in HT1080 human fibrosarcoma cells. The major mechanism of Ras-dependent MMP-9 production in HT1080 cells was phosphatidylinositol 3-kinase (PI3K)/Akt/nuclear factor-kappaB (NF-kappaB) activation. Expression of dominant-active H-Ras and p85 (a subunit of PI3K) increased MMP-9 activity, whereas dominant-negative forms of these molecules decreased the level of MMP-9. H-Ras did not increase MMP-9 in the presence of a PI3K inhibitor, LY294002, and a NF-kappaB inhibitor, SN50. Further studies showed that isoginkgetin regulated MMP-9 production via PI3K/Akt/NF-kappaB pathway, as evidenced by the findings that isoginkgetin inhibited activities of both Akt and NF-kappaB. PI3K/Akt is a well-known key pathway for cell invasion, and isoginkgetin inhibited HT1080 tumor cell invasion substantially. Isoginkgetin was also quite effective in inhibiting the activities of Akt and MMP-9 in MDA-MB-231 breast carcinomas and B16F10 melanoma. Moreover, isoginkgetin treatment resulted in marked decrease in invasion of these cells. In summary, PI3K/Akt is a major pathway for MMP-9 expression and isoginkgetin markedly decreased MMP-9 expression and invasion through inhibition of this pathway. This suggests that isoginkgetin could be a potential candidate as a therapeutic agent against tumor invasion.

Phosphatidylinositol 3-kinase-dependent modulation of carnitine palmitoyltransferase 1A expression regulates lipid metabolism during hematopoietic cell growth

An abundant supply of extracellular nutrients is believed to be sufficient to suppress catabolism of cellular macromolecules. Here we show that, despite abundant extracellular nutrients, interleukin-3-deprived hematopoietic cells begin to catabolize intracellular lipids. Constitutive Akt activation blunts the increased beta-oxidation that accompanies growth factor withdrawal, and in growth factor-replete cells, phosphatidylinositol 3-kinase (PI3K) signaling is required to suppress lipid catabolism. Surprisingly, PI3K and Akt exert these effects by suppressing expression of the beta-oxidation enzyme carnitine palmitoyltransferase 1A (CPT1A). Cells expressing a short hairpin RNA against CPT1A fail to induce beta-oxidation in response to growth factor withdrawal and are unable to survive glucose deprivation. When CPT1A is constitutively expressed, growth factor stimulation fails to repress beta-oxidation. As a result, both net lipid synthesis and cell proliferation are diminished. Together, these results demonstrate that modulation of CPT1A expression by PI3K-dependent signaling is the major mechanism by which cells suppress beta-oxidation during anabolic growth.

Inhibition of Akt by the alkylphospholipid perifosine does not enhance the radiosensitivity of human glioma cells

Akt has been implicated as a molecular determinant of cellular radiosensitivity. Because it is often constitutively activated or overexpressed in malignant gliomas, it has been suggested as a target for brain tumor radiosensitization. To evaluate the role of Akt in glioma radioresponse, we have determined the effects of perifosine, a clinically relevant alkylphospholipid that inhibits Akt activation, on the radiosensitivity of three human glioma cell lines (U87, U251, and LN229). Each of the glioma cell lines expressed clearly detectable levels of phosphorylated Akt indicative of constitutive Akt activity. Exposure to a perifosine concentration that reduced survival by approximately 50% significantly reduced the level of phosphorylated Akt as well as Akt activity. Cell survival analysis using a clonogenic assay, however, revealed that this Akt-inhibiting perifosine treatment did not enhance the radiosensitivity of the glioma cell lines. This evaluation was then extended to an in vivo model using U251 xenografts. Perifosine delivered to mice bearing U251 xenografts substantially reduced tumor phosphorylated Akt levels and inhibited tumor growth rate. However, the combination of perifosine and radiation resulted in a less than additive increase in tumor growth delay. Thus, in vitro and in vivo data indicate that the perifosine-mediated decrease in Akt activity does not enhance the radiosensitivity of three genetically disparate glioma cell lines. These results suggest that, although Akt may influence the radiosensitivity of other tumor types, it does not seem to be a target for glioma cell radiosensitization.

Targeting GSK-3: a promising approach for cancer therapy?

Glycogen synthase kinase (GSK)-3 has emerged as one of the most attractive therapeutic targets for the treatment of multiple neurological diseases, including Alzheimer's, stroke and bipolar disorders, as well as noninsulin-dependent diabetes mellitus and inflammation. Although the prominent role of GSK-3 in the adenomatous polyposis coli (APC)-beta-catenin destruction complex implies that inhibition of GSK-3 could possibly lead to tumor promotion through the activation of beta-catenin, several recent studies have shed new light on the activity of GSK-3 in cancer and provide insight into the molecular mechanisms by which it regulates tumor cell proliferation and survival of multiple human malignancies. In fact, GSK-3beta is a critical regulator of nuclear factor (NF)kappaB nuclear activity, suggesting that inhibition of GSK-3beta could be effective in the treatment of a wide variety of tumors with constitutively active NFkappaB. Herein, the authors will discuss the current understanding of the role of GSK-3 in human cancer and its potential as a therapeutic target.

Investigating mammalian target of rapamycin inhibitors for their anticancer properties

The mammalian target of rapamycin (mTOR) is a key element of the PI3KAkt (protein kinase B) signalling pathway, responsible for the regulation of cell growth and proliferation. There are two main downstream messengers of the mTOR kinase, eukaryotic initiation factor 4E-binding protein-1 and the 40S ribosomal protein S6 kinase 1, that control translation and cell-cycle progression. Abnormal activation of the mTOR pathway occurs frequently in numerous human malignancies; therefore, mTOR represents an attractive target for anticancer drug development. Rapamycin and its analogues CCI-779, RAD-001 and AP-23573 are known specific inhibitors of the mTOR kinase. Several clinical Phase I/II trials showed their activity in solid tumours and haematological malignancies. Moreover, inhibitors of mTOR were found to synergise with some cytostatics or other biological agents, which seems to be a promising direction for future strategies of antitumour treatment.

Regulation of Akt/PKB by phosphatidylinositol 3-kinase-dependent and -independent pathways in B-cell chronic lymphocytic leukemia cells: role of protein kinase Cβ

Apoptosis of B cell chronic lymphocytic leukemia (B-CLL) cells is regulated by the PI-3K-Akt pathway. In the present work, we have analyzed the mechanisms of Akt phosphorylation in B-CLL cells. Freshly isolated cells present basal Akt phosphorylation, which is PI-3K-dependent, as incubation with the PI-3K inhibitor LY294002 decreased Ser-473 and Thr-308 phosphorylation in most samples analyzed (seven out of 10). In three out of 10 cases, inhibition of protein kinase C (PKC) inhibited basal Akt phosphorylation. Stromal cell-derived factor-1alpha, IL-4, and B cell receptor activation induced PI-3K-dependent Akt phosphorylation. PMA induced the phosphorylation of Akt at Ser-473 and Thr-308 and the phosphorylation of Akt substrates, independently of PI-3K in B-CLL cells. In contrast, PKC-mediated phosphorylation of Akt was PI-3K-dependent in normal B cells. Finally, a specific inhibitor of PKCbeta blocked the phosphorylation and activation of Akt by PMA in B-CLL cells. Taken together, these results suggest a model in which Akt could be activated by two different pathways (PI-3K and PKCbeta) in B-CLL cells.

MondoA-Mlx heterodimers are candidate sensors of cellular energy status: mitochondrial localization and direct regulation of glycolysis

Transcription factors can be sequestered at specific organelles and translocate to the nucleus in response to changes in organellar homeostasis. MondoA is a basic helix-loop-helix leucine zipper transcriptional activator similar to Myc in function. However, unlike Myc, MondoA and its binding partner Mlx localize to the cytoplasm, suggesting tight regulation of their nuclear function. We show here that endogenous MondoA and Mlx associate with mitochondria in primary skeletal muscle cells and erythroblast K562 cells. Interaction between MondoA and the mitochondria is salt and protease sensitive, demonstrating that it associates with the outer mitochondrial membrane by binding a protein partner. Further, endogenous MondoA shuttles between the mitochondria and the nucleus, suggesting that it communicates between these two organelles. When nuclear, MondoA activates transcription of a broad spectrum of metabolic genes, including those for the glycolytic enzymes lactate dehydrogenase A, hexokinase II, and 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3. Regulation of these three targets is mediated by direct interaction with CACGTG sites in their promoters. Consistent with its regulation of glycolytic targets, MondoA is both necessary and sufficient for glycolysis. We propose that MondoA communicates information about the intracellular energy state between the mitochondria and the nucleus, resulting in transcriptional activation of glycolytic target genes.

Discovery of 2-pyrimidyl-5-amidothiophenes as potent inhibitors for AKT: Synthesis and SAR studies

A series of 2-pyrimidyl-5-amidothiophenes has been synthesized and evaluated for AKT inhibition. SAR studies resulted in potent inhibitors of AKT with IC(50) values as low as single digit nanomolar as represented by compound 2aa. Compound 2aa showed cellular activity including antiproliferation and downstream target modulation. Selectivity profile is described. A co-crystal of 2aa with PKA is determined and discussed.

Human papillomavirus type 16 E7 up-regulates AKT activity through the retinoblastoma protein

Human papillomaviruses (HPV) are small DNA tumor viruses causally associated with cervical cancer. The early gene product E7 from high-risk HPV is considered the major transforming protein expressed by the virus. Although many functions have been described for E7 in disrupting normal cellular processes, we describe in this study a new cellular target in primary human foreskin keratinocytes (HFK), the serine/threonine kinase AKT. Expression of HPV type 16 E7 in HFK caused inhibition of differentiation, hyperproliferation, and up-regulation of AKT activity in organotypic raft cultures. The ability of E7 to up-regulate AKT activity is dependent on its ability to bind to and inactivate the retinoblastoma (Rb) gene product family of proteins. Furthermore, we show that knocking down Rb alone, with short hairpin RNAs, was sufficient to up-regulate AKT activity in differentiated keratinocytes. Up-regulation of AKT activity and loss of Rb was also observed in HPV-positive cervical high-grade squamous intraepithelial lesions when compared with normal cervical tissue. Together, these data provide evidence linking inactivation of Rb by E7 in the up-regulation of AKT activity during cervical cancer progression.

Akt signaling and cancer: surviving but not moving on

The frequent deregulation of the phosphoinositide 3-kinase/Akt survival signaling pathway in cancer has prompted significant interest in blocking this pathway to treat cancer. Recently, however, two studies have shown that the Akt isoform Akt1 limits the invasive migration of breast cancer cells. These studies suggest that Akt1 may have a dual role in tumorigenesis, acting not only pro-oncogenically by suppressing apoptosis but also anti-oncogenically by suppressing invasion and metastasis. We discuss the possible implications of these findings for therapeutic development of Akt inhibitors to treat cancer.

Hsp90 recognizes a common surface on client kinases

Hsp90 is a highly abundant chaperone whose clientele includes hundreds of cellular proteins, many of which are central players in key signal transduction pathways and the majority of which are protein kinases. In light of the variety of Hsp90 clientele, the mechanism of selectivity of the chaperone toward its client proteins is a major open question. Focusing on human kinases, we have demonstrated that the chaperone recognizes a common surface in the amino-terminal lobe of kinases from diverse families, including two newly identified clients, NFkappaB-inducing kinase and death-associated protein kinase, and the oncoprotein HER2/ErbB-2. Surface electrostatics determine the interaction with the Hsp90 chaperone complex such that introduction of a negative charge within this region disrupts recognition. Compiling information on the Hsp90 dependence of 105 protein kinases, including 16 kinases whose relationship to Hsp90 is first examined in this study, reveals that surface features, rather than a contiguous amino acid sequence, define the capacity of the Hsp90 chaperone machine to recognize client kinases. Analyzing Hsp90 regulation of two major signaling cascades, the mitogen-activated protein kinase and phosphatidylinositol 3-kinase, leads us to propose that the selectivity of the chaperone to specific kinases is functional, namely that Hsp90 controls kinases that function as hubs integrating multiple inputs. These lessons bear significance to pharmacological attempts to target the chaperone in human pathologies, such as cancer.

Mechanism of Akt1 inhibition of breast cancer cell invasion reveals a protumorigenic role for TSC2

Akt1 is frequently up-regulated in human tumors and has been shown to accelerate cell proliferation and to suppress programmed cell death; consequently, inhibition of the activity of Akt1 has been seen as an attractive target for therapeutic intervention. Paradoxically, hyperactivation of the Akt1 oncogene can also prevent the invasive behavior that underlies progression to metastasis. Here we show that overexpression of activated myr-Akt1 in human breast cancer cells phosphorylates and thereby targets the tumor suppressor tuberous sclerosis complex 2 (TSC2) for degradation, leading to reduced Rho-GTPase activity, decreased actin stress fibers and focal adhesions, and reduced motility and invasion. Overexpression of TSC2 rescues the migration phenotype of myr-Akt1-expressing tumor cells, and high levels of TSC2 in breast cancer patients correlate with increased metastasis and reduced survival. These data indicate that the functional properties of genes designated as oncogenes or tumor suppressor genes depend on the context of the cell type and the tissues studied, and suggest the need for caution in designing therapies targeting the function of individual genes in epithelial tissues.

Protein kinases and phosphatases as therapeutic targets in cancer

Protein phosphorylation plays key roles in many physiological processes and is often deregulated in pathological conditions. Our current understanding of how protein kinases and phosphatases orchestrate the phosphorylation changes that control cellular functions has made these enzymes potential drug targets for the treatment of many diseases. The success of the tyrosine kinase inhibitor Gleevec in the treatment of some cancers has further invigorated the development of kinase inhibitors as anti-cancer drugs. A large number of these compounds are currently undergoing clinical trials and there is much expectation on the therapeutic potential of these molecules, as more specific and less toxic drugs than currently used generic chemotherapeutic agents. In this manuscript, we review the current status of more than 30 protein kinase inhibitors with proven or potential therapeutic value for cancer treatment. These include inhibitors of receptor and cytosolic tyrosine kinases as well as compounds that target different families of serine/threonine kinases involved in signalling and cell cycle regulation. We also briefly touch on the prospects of phosphatase inhibitors. The combination of kinase inhibitors to target different components of signalling pathways that are found deregulated in tumours is also emerging as an interesting approach for cancer therapy.

Membrane-type 1 matrix metalloproteinase modulates focal adhesion stability and cell migration

Membrane-type 1 matrix metalloproteinase (MT1-MMP) plays an important role in extracellular matrix-induced cell migration and the activation of extracellular signal-regulated kinase (ERK). We showed here that transfection of the MT1-MMP gene into HeLa cells promoted fibronectin-induced cell migration, which was accompanied by fibronectin degradation and reduction of stable focal adhesions, which function as anchors for actin-stress fibers. MT1-MMP expression attenuated integrin clustering that was induced by adhesion of cells to fibronectin. The attenuation of integrin clustering was abrogated by MT1-MMP inhibition with a synthetic MMP inhibitor, BB94. When cultured on fibronectin, HT1080 cells, which endogenously express MT1-MMP, showed so-called motile morphology with well-organized focal adhesion formation, well-oriented actin-stress fiber formation, and the lysis of fibronectin through trails of cell migration. Inhibition of endogenous MT1-MMP by BB94 treatment or expression of the MT1-MMP carboxyl-terminal domain, which negatively regulates MT1-MMP activity, resulted in the suppression of fibronectin lysis and cell migration. BB94 treatment promoted stable focal adhesion formation concomitant with enhanced phosphorylation of tyrosine 397 of focal adhesion kinase (FAK) and reduced ERK activation. These results suggest that lysis of the extracellular matrix by MT1-MMP promotes focal adhesion turnover and subsequent ERK activation, which in turn stimulates cell migration.

AKT crystal structure and AKT-specific inhibitors

AKT kinases are attractive targets for small molecule drug discovery because of their key role in tumor cell survival/proliferation and their overexpression/activation in many human cancers. This review summarizes studies that support the rationale for targeting AKT kinases in new drug discovery efforts. Structural features of AKT kinase in its inactive and active states, as determined by crystal structure analysis, are described. Recent efforts in the development and biological evaluation of small molecule inhibitors of AKT, and the challenges remaining are summarized. Inhibitors targeting the ATP binding site, PH domain and protein substrate binding site, as well as isoform selective allosteric inhibitors are reviewed. Structure-based design using PKA mutants as surrogates and computer modeling in the discovery of selective inhibitors is discussed. The issues and challenges facing the development of different classes of inhibitors as therapeutics are also discussed.

Epithelial-mesenchymal transition in development and cancer: role of phosphatidylinositol 3' kinase/AKT pathways

Epithelial-mesenchymal transition (EMT) is an important process during development by which epithelial cells acquire mesenchymal, fibroblast-like properties and show reduced intercellular adhesion and increased motility. Accumulating evidence points to a critical role of EMT-like events during tumor progression and malignant transformation, endowing the incipient cancer cell with invasive and metastatic properties. Several oncogenic pathways (peptide growth factors, Src, Ras, Ets, integrin, Wnt/beta-catenin and Notch) induce EMT and a critical molecular event is the downregulation of the cell adhesion molecule E-cadherin. Recently, activation of the phosphatidylinositol 3' kinase (PI3K)/AKT axis is emerging as a central feature of EMT. In this review, we discuss the role of PI3K/AKT pathways in EMT during development and cancer with a focus on E-cadherin regulation. Interactions between PI3K/AKT and other EMT-inducing pathways are presented, along with a discussion of the therapeutic implications of modulating EMT in order to achieve cancer control.

FOXO transcription factors at the interface between longevity and tumor suppression

A wide range of human diseases, including cancer, has a striking age-dependent onset. However, the molecular mechanisms that connect aging and cancer are just beginning to be unraveled. FOXO transcription factors are promising candidates to serve as molecular links between longevity and tumor suppression. These factors are major substrates of the protein kinase Akt. In the presence of insulin and growth factors, FOXO proteins are relocalized from the nucleus to the cytoplasm and degraded via the ubiquitin-proteasome pathway. In the absence of growth factors, FOXO proteins translocate to the nucleus and upregulate a series of target genes, thereby promoting cell cycle arrest, stress resistance, or apoptosis. Stress stimuli also trigger the relocalization of FOXO factors into the nucleus, thus allowing an adaptive response to stress stimuli. Consistent with the notion that stress resistance is highly coupled with lifespan extension, activation of FOXO transcription factors in worms and flies increases longevity. Emerging evidence also suggests that FOXO factors play a tumor suppressor role in a variety of cancers. Thus, FOXO proteins translate environmental stimuli into changes in gene expression programs that may coordinate organismal longevity and tumor suppression.

Génétique des tumeurs endocrines

Major advances have been made in the understanding of the genetic mechanisms underlying endocrine tumorigenesis, through the study of several syndromes of genetic predisposition and the identification of the genes involved. The syndrome of type 1 multiple endocrine neoplasia (MEN-1) is one of the best known; this autosomal dominant hereditary syndrome predisposes to the development of endocrine tumors of the pituitary, the parathyroids, the foregut and the adrenals. The responsible gene, known as MEN-1, encodes an original protein, menin, involved in several major cellular functions, such as the control of cell proliferation and differentiation. Type 2 multiple endocrine neoplasia (MEN-2) is an autosomal dominant hereditary syndrome associated with the development of medullary carcinomas of the thyroid, pheochromocytomas and hyperparathyroidism; the corresponding gene, RET, encodes a transmembrane receptor with tyrosine kinase activity. Endocrine tumors are also associated with non Hippel-Lindau disease and with phacomatoses, such as type 1 neurofibromatosis and tuberous sclerosis. Finally, isolated familial syndromes of endocrine tumors have been described: isolated familial hyperparathyroidism type II (HRPT2), associated with alterations in a gene coding for an original protein, parafibromin, or isolated familial syndromes of pheochromocytomas and paragangliomas (PRG) associated with mutations in the genes SDHB, SDHC or SDHD, which encode succinate-dehydrogenase subunits. The understanding of the genetic mechanisms underlying these syndromes of predisposition is essential for the diagnosis and management of these patients and their family; it also gives insight on the molecular mechanisms of endocrine tumorigenesis.

The Akt of translational control

The oncogene AKT (also called protein kinase B (PKB)) signals to the translational machinery, and activation of protein synthesis by Akt is associated with cancer formation. Akt directly stimulates the activity of translation initiation factors and upregulates ribosome biogenesis. Activation of protein synthesis by Akt is phylogenetically conserved from Drosophila to humans, and is important for regulating cell growth, proliferation and cell survival. Consequently, translation defects due to aberrant Akt activation may be a crucial mechanism leading to tumorigenesis. However, few in vivo studies have established a causative role for aberrant protein synthesis control in cancer. A major challenge in the future will be to identify the specific mRNAs regulated at the level of translation control directly relevant for cellular transformation. In this review, we highlight and discuss the emerging molecular and genetic evidence that support a model by which deregulation of specific or global protein synthesis contributes to cancer.

The Akt/PKB pathway: molecular target for cancer drug discovery

The serine/threonine kinase Akt/PKB pathway presents an exciting new target for molecular therapeutics, as it functions as a cardinal nodal point for transducing extracellular (growth factor and insulin) and intracellular (receptor tyrosine kinases, Ras and Src) oncogenic signals. In addition, alterations of the Akt pathway have been detected in a number of human malignancies. Ectopic expression of Akt, especially constitutively activated Akt, is sufficient to induce oncogenic transformation of cells and tumor formation in transgenic mice as well as chemoresistance. Akt has a wide range of downstream targets that regulate tumor-associated cell processes such as cell growth, cell cycle progression, survival, migration, epithelial-mesenchymal transition and angiogenesis. Blockage of Akt signaling results in apoptosis and growth inhibition of tumor cells with elevated Akt. The observed dependence of certain tumors on Akt signaling for survival and growth has wide implications for cancer therapy, offering the potential for preferential tumor cell killing. In the last several years, through combinatorial chemistry, high-throughput and virtual screening, and traditional medicinal chemistry, a number of inhibitors of the Akt pathway have been identified. This review focuses on ongoing translational efforts to therapeutically target the Akt pathway.