Quercetin Inhibits Angiogenesis Mediated Human Prostate Tumor Growth by Targeting VEGFR- 2 Regulated AKT/mTOR/P70S6K Signaling Pathways

Angiogenesis is a crucial step in the growth and metastasis of cancers, since it enables the growing tumor to receive oxygen and nutrients. Cancer prevention using natural products has become an integral part of cancer control. We studied the antiangiogenic activity of quercetin using ex vivo, in vivo and in vitro models. Rat aortic ring assay showed that quercetin at non-toxic concentrations significantly inhibited microvessel sprouting and exhibited a significant inhibition in the proliferation, migration, invasion and tube formation of endothelial cells, which are key events in the process of angiogenesis. Most importantly, quercetin treatment inhibited ex vivo angiogenesis as revealed by chicken egg chorioallantoic membrane assay (CAM) and matrigel plug assay. Western blot analysis showed that quercetin suppressed VEGF induced phosphorylation of VEGF receptor 2 and their downstream protein kinases AKT, mTOR, and ribosomal protein S6 kinase in HUVECs. Quercetin (20 mg/kg/d) significantly reduced the volume and the weight of solid tumors in prostate xenograft mouse model, indicating that quercetin inhibited tumorigenesis by targeting angiogenesis. Furthermore, quercetin reduced the cell viability and induced apoptosis in prostate cancer cells, which were correlated with the downregulation of AKT, mTOR and P70S6K expressions. Collectively the findings in the present study suggest that quercetin inhibits tumor growth and angiogenesis by targeting VEGF-R2 regulated AKT/mTOR/P70S6K signaling pathway, and could be used as a potential drug candidate for cancer therapy.     

Luteolin downregulates IL-1β-induced MMP-9 and -13 expressions in osteoblasts via inhibition of ERK signalling pathway

The inhibitory effect of four structurally related flavonoids, apigenin, baicalein, luteolin and quercetin on the matrix metalloproteinase (MMP)-9 and -13 expressions in osteoblasts was investigated. Treatment with IL-1β induced both MMP-9 and -13 mRNA expressions as measured by quantitative real-time PCR. Luteolin and apigenin decreased IL-1β-induced MMP-9 and -13 mRNA expressions, whereas baicalein and quercetin showed little effects. Related to signalling, treatment with IL-1β induced ERK phosphorylation as measured by Western blotting. Further studies showed that transfection with a constitutively active form of the Ras protein (Ras(V12)) induced stronger ERK phosphorylation and upregulated MMP-9 and -13 mRNA expressions. However, transfection with a dominant-negative form of the Ras protein (Ras(N17)) inhibited the ERK activation and MMP-9 and -13 mRNA expressions induced by IL-1β, which supported the involvement of ERK signalling in IL-1β-induced MMP-9 and -13 expressions. Treatment with luteolin effectively inhibited the IL-1β-induced ERK activation in dose-dependent manner. Taken together, luteolin might inhibit IL-1β-induced MMP-9 and -13 expressions, in part, via inhibition of ERK signalling.     

Luteolin suppresses androgen receptor-positive triple-negative breast cancer cell proliferation and metastasis by epigenetic regulation of MMP9 expression via the AKT/mTOR signaling pathway

BackgroundTriple-negative breast cancer (TNBC) represents up to 20% of all breast cancers. This cancer lacks the expression of the estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2. The current therapeutic strategy for patients with this subtype is the use of cytotoxic chemotherapy and surgery. Luteolin is a natural herbal flavonoid and a potential therapeutic candidate for multiple diseases. The use of a treatment that combines Chinese herbal medicine and western medicine is rising in Asia.PurposeThe present study evaluates the effects and molecular mechanisms involved with luteolin treatment and evaluates whether this herb affects androgen receptor-positive breast cancer cell proliferation or metastasis.Study DesignIn vitro evaluation of the effect of luteolin on androgen receptor-positive TNBC cell proliferation and metastasisMethodsCell viability analysis was used for the cytotoxicity test. Colony formation and Bromodeoxyuridine (BrdU) staining-based proliferation experiments were used for cell proliferation. Wound healing and transwell assays were used for in vitro migration/invasion. The RT-qPCR analysis was used for gene expression. Furthermore, ChIP-qPCR analysis was used for epigenetic modification of gene promoters.ResultsLuteolin significantly inhibited the proliferation and metastasis of androgen receptor-positive TNBC. Furthermore, luteolin inactivated the AKT/mTOR signaling pathway and reversed the epithelial-mesenchymal transition (EMT). The combination of luteolin and inhibitors of AKT/mTOR synergistically repressed an androgen receptor-positive TNBC cell proliferation and metastasis. Luteolin also downregulated MMP9 expression by decreasing the levels of the AKT/mTOR promoting H3K27Ac and H3K56A on the MMP9 promoter region.ConclusionOur findings indicate that luteolin inhibited the proliferation and metastasis of androgen receptor-positive TNBC by regulating MMP9 expression through a reduction in the levels of AKT/mTOR-inducing H3K27Ac and H3K56Ac.     

Microvesicles Derived from Human Wharton's Jelly Mesenchymal Stem Cells Promote Human Renal Cancer Cell Growth and Aggressiveness through Induction of Hepatocyte Growth Factor

In our previous study, microvesicles (MVs) released from human Wharton''s jelly mesenchymal stem cells (hWJ-MSCs) retard the growth of bladder cancer cells. We would like to know if MVs have a similar effect on human renal cell carcinoma (RCC). By use of cell culture and the BALB/c nu/nu mice xeno-graft model, the influence of MVs upon the growth and aggressiveness of RCC (786-0) was assessed. Cell counting kit-8 (CCK-8) assay, incidence of tumor, tumor size, Ki-67 or TUNEL staining was used to evaluate tumor cell growth in vitro or in vivo. Flow cytometry assay (in vitro) or examination of cyclin D1 expression (in vivo) was carried out to determine the alteration of cell cycle. The aggressiveness was analyzed by Wound Healing Assay (in vitro) or MMP-2 and MMP-9 expression (in vivo). AKT/p-AKT, ERK1/2/p-ERK1/2 or HGF/c-MET expression was detected by real-time PCR or western blot. Our data demonstrated that MVs promote the growth and aggressiveness of RCC both in vitro and in vivo. In addition, MVs facilitated the progression of cell cycle from G_0/1 to S. HGF expression in RCC was greatly induced by MVs, associated with activation of AKT and ERK1/2 signaling pathways. RNase pre-treatment abrogated all effects of MVs. In summary, induction of HGF synthesis via RNA transferred by MVs activating AKT and ERK1/2 signaling is one of crucial contributors to the pro-tumor effect.     

Anti-Cancer Activity of an Osthole Derivative,NBM-T-BMX-OS01: Targeting Vascular Endothelial Growth Factor Receptor Signaling and Angiogenesis

Angiogenesis occurs during tissue growth, development and wound healing. It is also required for tumor progression and represents a rational target for therapeutic intervention. NBM-T-BMX-OS01 (BMX), derived from the semisynthesis of osthole, an active ingredient isolated from Chinese herb Cnidium monnieri (L.) Cuss., was recently shown to enhance learning and memory in rats. In this study, we characterized the anti-angiogenic activities of NBM-T-BMX-OS01 (BMX) in an effort to develop novel inhibitors to suppress angiogenesis and tumor growth. BMX inhibited vascular endothelial growth factor (VEGF)-induced proliferation, migration and endothelial tube formation in human umbilical endothelial cells (HUVECs). BMX also attenuated VEGF-induced microvessel sprouting from aortic rings ex vivo and reduced HCT116 colorectal cancer cells-induced angiogenesis in vivo. Moreover, BMX inhibited the phosphorylation of VEGFR2, FAK, Akt and ERK in HUVECs exposed to VEGF. BMX was also shown to inhibit HCT116 cell proliferation and to suppress the growth of subcutaneous xenografts of HCT116 cells in vivo. Taken together, this study provides evidence that BMX modulates vascular endothelial cell remodeling and leads to the inhibition of tumor angiogenesis. These results also support the role of BMX as a potential drug candidate and warrant the clinical development in the treatment of cancer.     

Interleukin-6 triggers human cerebral endothelial cells proliferation and migration: the role for KDR and MMP-9

Interleukin-6 (IL-6) is involved in angiogenesis. However, the underlying mechanisms are unknown. Using human cerebral endothelial cell (HCEC), we report for the first time that IL-6 triggers HCEC proliferation and migration in a dose-dependent manner, specifically associated with enhancement of VEGF expression, up-regulated and phosphorylated VEGF receptor-2 (KDR), and stimulated MMP-9 secretion. We investigated the signal pathway of IL-6/IL-6R responsible for KDR's regulation. Pharmacological inhibitor of PI3K failed to inhibit IL-6-mediated VEGF overexpression, while blocking ERK1/2 with PD98059 could abolish IL-6-induced KDR overexpression. Further, neutralizing endogenous VEGF attenuated KDR expression and phosphorylation, suggesting that IL-6-induced KDR activation is independent of VEGF stimulation. MMP-9 inhibitor GM6001 significantly decreases HCEC proliferation and migration (p<0.05), indicating the crucial function of MMP-9 in promoting angiogenic changes in HCECs. We conclude that IL-6 triggers VEGF-induced angiogenic activity through increasing VEGF release, up-regulates KDR expression and phosphorylation through activating ERK1/2 signaling, and stimulates MMP-9 overexpression.     

MiR-21 induced angiogenesis through AKT and ERK activation and HIF-1α expression

MicroRNAs (miRNAs) are endogenous, small noncoding RNAs that play important roles in various cellular functions and tumor development. Recent studies have indicated that miR-21 is one of the important miRNAs associated with tumor growth and metastasis, but the role and molecular mechanism of miR-21 in regulating tumor angiogenesis remain to be elucidated. In this study, miR-21 was overexpressed by transfecting pre-miR-21 into human prostate cancer cells and tumor angiogenesis was assayed using chicken chorioallantoic membrane (CAM). We found that overexpression of miR-21 in DU145 cells increased the expression of HIF-1α and VEGF, and induced tumor angiogenesis. AKT and extracellular regulated kinases (ERK) 1/2 are activated by miR-21. Inhibition of miR-21 by the antigomir blocked this process. Overexpression of the miR-21 target, PTEN, also inhibited tumor angiogenesis by partially inactivating AKT and ERK and decreasing the expression of HIF-1 and VEGF. The AKT and ERK inhibitors, LY294002 and U0126, suppressed HIF-1α and VEGF expression and angiogenesis. Moreover, inhibition of HIF-1α expression alone abolished miR-21-inducing tumor angiogenesis, indicating that HIF-1α is required for miR-21-upregulated angiogenesis. Therefore, we demonstrate that miR-21 induces tumor angiogenesis through targeting PTEN, leading to activate AKT and ERK1/2 signaling pathways, and thereby enhancing HIF-1α and VEGF expression; HIF-1α is a key downstream target of miR-21 in regulating tumor angiogenesis.     

Dietary compound glycyrrhetinic acid suppresses tumor angiogenesis and growth by modulating antiangiogenic and proapoptotic pathways in vitro and in vivo

Glycyrrhetinic acid (GA) is a major bioactive compound of licorice. The objective of this study was to investigate the effects of GA on ovarian cancer, particularly those related to angiogenesis and apoptosis, and to elucidate the underlying mechanisms of action. In vitro studies showed that GA significantly inhibited proliferation, migration, invasion and tube formation in human umbilical vein endothelial cells (HUVECs) in a concentration-dependent manner. GA inhibited the phosphorylation of major receptors and enzymes involved in angiogenesis, such as VEGFR2, mTOR, Akt, ERK1/2, MEK1/2, p38 and JNK1/2 in HUVECs. In addition, GA induced apoptosis, loss of mitochondrial membrane potential and cell cycle arrest in G1 phase in A2780 ovarian cancer cells. The proapoptotic effect of GA involved the increased phosphorylation of p38 and JNK1/2; increased cleavage of caspase 3, caspase 9 and PARP; reduced phosphorylation of mTOR, Akt and ERK1/2; and reduced expressions of survivin and cyclin D1. Ex vivo studies showed that GA significantly inhibited microvessel sprouting in rat aortic ring model. In vivo studies showed that GA inhibited the formation of new blood vessels in zebrafish and mouse Matrigel plug. GA also significantly reduced the size of ovarian cancer xenograft tumors in nude mice. Taken together, GA possesses potential antitumor effects, and the underlying mechanisms may involve the inhibition of signaling pathways related to angiogenesis and the activation of apoptotic pathways in cancer cells. Our findings suggest that GA could serve as an effective regimen in the prevention or treatment of cancer.     

Diverse signaling pathways through the SDF-1/CXCR4 chemokine axis in prostate cancer cell lines leads to altered patterns of cytokine secretion and angiogenesis

The establishment of metastatic bone lesions in prostate cancer (CaP) is a process partially dependent on angiogenesis. Previously we demonstrated that the stromal-derived factor-1 (SDF-1 or CXCL12)/CXCR4 chemokine axis is critical for CaP cell metastasis. In this investigation, cell lines were established in which CXCR4 expression was knocked down using siRNA technology. When CaP cells were co-transplanted with human vascular endothelial cells into SCID mice, significantly fewer human blood vessels were observed paralleling the reductions in CXCR4 levels. Likewise, the invasive behaviors of the CaP cells were inhibited in vitro. From these functional observations we explored angiogenic and signaling mechanisms generated following SDF-1 binding to CXCR4. Differential activation of the MEK/ERK and PI3K/AKT pathways that result in differential secretion IL-6, IL-8, TIMP-2 and VEGF were seen contingent on the cell type examined; VEGF and TIMP-2 expression in PC3 cells are dependent on AKT activation and ERK activation in LNCaP and LNCaP C4-2B cells leads to IL-6 or IL-8 secretion. At the same time, expression of angiostatin levels were inversely related to CXCR4 levels, and inhibited by SDF-1 stimulation. These data link the SDF-1/CXCR4 pathway to changes in angiogenic cytokines by different signaling mechanisms and, suggest that the delicate equilibrium between proangiogenic and antiangiogenic factors may be achieved by different signal transduction pathways to regulate the angiogenic phenotype of prostate cancers. Taken together, our results provide new information regarding expression of functional CXCR4 receptor-an essential role and potential mechanism of angiogenesis upon SDF-1 stimulation.     

The Polyphenols (?)-Epigallocatechin-3-Gallate and Luteolin Synergistically Inhibit TGF-β-Induced Myofibroblast Phenotypes through RhoA and ERK Inhibition

The presence of reactive stroma, predominantly composed of myofibroblasts, is directly associated with and drives prostate cancer progression. We have previously shown that (−)-Epigallocatechin-3-gallate (EGCG), in the form of Polyphenon E, significantly decreases serum levels of HGF and VEGF in prostate cancer patients. Given that HGF and VEGF are secreted from surrounding tumor myofibroblasts, these observations suggested that EGCG may inhibit prostate cancer-associated myofibroblast differentiation. Herein, we demonstrate that micromolar combinations of EGCG and a second polyphenol, luteolin, synergistically inhibit TGF-β-induced myofibroblast phenotypes in prostate fibroblast cell lines, as observed primarily by potentiation of fibronectin expression. Functionally, EGCG and luteolin inhibited TGF-β-induced extracellular matrix contraction, an enhancer of tumor cell invasion. EGCG and luteolin inhibited downstream TGF-β-induced signaling, including activation of ERK and AKT, respectively, but mechanistically, only ERK appeared to be necessary for TGF-β-induced fibronectin expression. Furthermore, neither EGCG nor luteolin affected Smad signaling or nuclear translocation. Rho signaling was found to be necessary for TGF-β-induced fibronectin expression and EGCG and luteolin each reduced RhoA activation. Finally, EGCG and luteolin were shown to reverse TGF-β-induced fibronectin expression, implicating that these natural compounds may be useful not only in preventing but also in treating already activated myofibroblasts and the diseases they cause, including cancer. The ability of EGCG and luteolin to synergistically target myofibroblasts suggests that combined clinical use of these compounds could prevent or reverse cancer progression through targeting the tumor microenvironment, in addition to the tumor itself.     

Luteolin 8-C-β-fucopyranoside inhibits invasion and suppresses TPA-induced MMP-9 and IL-8 via ERK/AP-1 and ERK/NF-κB signaling in MCF-7 breast cancer cells

Matrix metalloproteinase 9 (MMP-9) and interleukin-8 (IL-8) play major roles in tumor progression and invasion of breast cancer cells. The present study was undertaken to investigate the inhibitory mechanism of cell invasion by luteolin 8-C-β-fucopyranoside (named as LU8C-FP), a C-glycosylflavone, in human breast cancer cells. We investigated whether LU8C-FP would inhibit MMP-9 activation and IL-8 expression in 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated MCF-7 breast cancer cells. LU8C-FP suppressed TPA-induced MMP-9 and IL-8 secretion and mRNA expression via inhibition of the MAPK signaling pathway and down-regulation of nuclear AP-1 and NF-κB. TPA-induced phosphorylation of ERK 1/2 was suppressed by LU8C-FP, whereas JNK and p38 MAPK phosphorylation were unaffected. In addition, LU8C-FP blocked the ERK 1/2 pathways following expression of MMP-9 and IL-8. These results suggest LU8C-FP may function to suppress invasion of breast cancer cells through the ERK/AP-1 and ERK/NF-κB signaling cascades.     

NADPH oxidase subunit p22phox-mediated reactive oxygen species contribute to angiogenesis and tumor growth through AKT and ERK1/2 signaling pathways in prostate cancer

Excessive generation of reactive oxygen species (ROS) in cancer cells is associated with cancer development, but the underlying mechanisms and therapeutic significance remain elusive. In this study, we reported that levels of ROS and p22^phox expression are greatly increased in human prostate cancer tissues, and knockdown of p22^phox by specific small interfering RNA (siRNA) decreased ROS levels in prostate cancer cells. We also showed that stable downregulation of p22^phox in prostate cancer cells inhibited cell proliferation and colony formation, which was mediated by AKT and extracellular signal-regulated kinase (ERK)1/2 signaling pathways and their downstream molecules hypoxia-inducible factor 1α (HIF-1α) and vascular endothelial growth factor (VEGF). The NADPH oxidase subunit NOX1 was also elevated in prostate cancer cells, and was involved in activation of AKT/ERK/HIF-1/VEGF pathway and regulation of cell proliferation. Knockdown of p22^phox resulted in inhibition of tumor angiogenesis and tumor growth in nude mice. These findings reveal a new function of p22^phox in tumor angiogenesis and tumor growth, and suggest that p22^phox is a potential novel target for prostate cancer treatment.     

Regulation of Endothelial Cell Proliferation and Vascular Assembly through Distinct mTORC2 Signaling Pathways

Mammalian target of rapamycin (mTOR) is a serine/threonine kinase that regulates a diverse array of cellular processes, including cell growth, survival, metabolism, and cytoskeleton dynamics. mTOR functions in two distinct complexes, mTORC1 and mTORC2, whose activities and substrate specificities are regulated by complex specific cofactors, including Raptor and Rictor, respectively. Little is known regarding the relative contribution of mTORC1 versus mTORC2 in vascular endothelial cells. Using mouse models of Raptor or Rictor gene targeting, we discovered that Rictor ablation inhibited vascular endothelial growth factor (VEGF)-induced endothelial cell proliferation and assembly in vitro and angiogenesis in vivo, whereas the loss of Raptor had only a modest effect on endothelial cells (ECs). Mechanistically, the loss of Rictor reduced the phosphorylation of AKT, protein kinase Cα (PKCα), and NDRG1 without affecting the mTORC1 pathway. In contrast, the loss of Raptor increased the phosphorylation of AKT despite inhibiting the phosphorylation of S6K1, a direct target of mTORC1. Reconstitution of Rictor-null cells with myristoylated AKT (Myr-AKT) rescued vascular assembly in Rictor-deficient endothelial cells, whereas PKCα rescued proliferation defects. Furthermore, tumor neovascularization in vivo was significantly decreased upon EC-specific Rictor deletion in mice. These data indicate that mTORC2 is a critical signaling node required for VEGF-mediated angiogenesis through the regulation of AKT and PKCα in vascular endothelial cells.     

Hydrangenol suppresses VEGF-stimulated angiogenesis by targeting p27KIP1-dependent G1-cell cycle arrest,VEGFR-2-mediated signaling,and MMP-2 expression*

We previously reported that hydrangenol has potent antitumor activity against human bladder cancer EJ cells. Here, we investigated the antiangiogenic activity of hydrangenol using in vitro and ex vivo models. Treatment with hydrangenol significantly inhibited the proliferation of vascular endothelial growth factor (VEGF)-induced HUVECs in a concentration-dependent manner (EC_50?=?10?μM). Flow cytometry analysis revealed that hydrangenol suppressed the VEGF-induced inhibition of G1-cell cycle phase and also decreased cyclin D1, cyclin E, CDK2, and CDK4 levels. Hydrangenol-mediated arrest in the G1-cell cycle phase was associated with p27KIP1 level, but not p21WAF1 or p53 level. Hydrangenol also significantly inhibited VEGFR-2-mediated signaling pathways including ERK1/2, AKT, and endothelial nitric oxide synthase. Interestingly, immunoprecipitation assay demonstrated that the inhibition of VEGFR-2 activation was independent of VEGF binding, thereby suggesting an allosteric regulation of hydrangenol against VEGFR-2. Additionally, hydrangenol inhibited migration, invasion, and capillary-like tubular formation in VEGF-stimulated HUVECs. Zymography and immunoblot analyses revealed that these inhibitory activities were partially owing to the VEGF-induced inhibition of matrix metalloproteinase-2 activity. Finally, VEGF-mediated microvessel sprouting was inhibited in the presence of hydrangenol in ex vivo aortic ring assay. Taken together, hydrangenol possesses a potent antiangiogenesis potential; thus we believe that hydrangenol may be developed as a therapeutic reagent to treat angiogenesis-mediated diseases.     

Vascular endothelial growth factor signaling in VE-cadherin expression and tube-like formation by rheumatoid arthritic synovial fibroblast-like cells

An increase in the vasculature is one of most representative changes in the synovial tissue of joints in rheumatoid arthritis (RA) and is closely associated with disease progression. Although the vasculatures are believed to be a result of VE-cadherin-dependent angiogenesis and a possible therapeutic target of the disease, synovial fibroblastic cells express VE-cadherin and form tube-like structures, suggesting that vasculatures in RA synovium may not simply result from angiogenesis. This paper analyzes a mechanism of VE-cadherin expression by rheumatoid arthritic synovial fibroblast-like cells (RSFLs) and their involvement in the tube-like formation. A representative angiogenic factor, vascular endothelial growth factor (VEGF), and its binding to a predominant receptor (VEGFR2) activated VE-cadherin expression and the signaling pathways of ERK/MAPK and PI3K/AKT/mTOR. Treatment of RSFLs with signaling pathway inhibitors, VEGFR2 siRNA and a VEGF-antagonizing mimicking peptide inhibited VE-cadherin expression dose-dependently. VEGF-stimulated tube-like formation by RSFLs on Matrigel was hindered by the mimicking peptide and inhibitor treatment. This data demonstrates that RSFLs activated by VEGF binding of VEGFR2 express VE-cadherin and formed tube-like structure under the control of ERK/MAPK and PI3K/AKT/mTOR pathways suggesting that the inhibition suppresses vascular development in RA synovium.     

MicroRNA-382 induced by HIF-1α is an angiogenic miR targeting the tumor suppressor phosphatase and tensin homolog

Recent studies have revealed that microRNAs (miRs) play important roles in the regulation of angiogenesis. In this study, we have characterized miR-382 upregulation by hypoxia and the functional relevance of miR-382 in tumor angiogenesis. miRs induced by hypoxia in MKN1 human gastric cancer cells were investigated using miRNA microarrays. We selected miR-382 and found that the expression of miR-382 was regulated by HIF-1α. Conditioned media (CM) from MKN1 cells transfected with a miR-382 inhibitor (antagomiR-382) under hypoxic conditions significantly decreased vascular endothelial cell (EC) proliferation, migration and tube formation. Algorithmic programs (Target Scan, miRanda and cbio) predicted that phosphatase and tensin homolog (PTEN) is a target gene of miR-382. Deletion of miR382-binding sequences in the PTEN mRNA 3′-untranslated region (UTR) diminished the luciferase reporter activity. Subsequent study showed that the overexpression of miR-382 or antagomiR-382 down- or upregulated PTEN and its downstream target AKT/mTOR signaling pathway, indicating that PTEN is a functional target gene of miR-382. In addition, PTEN inhibited miR-382-induced in vitro and in vivo angiogenesis as well as VEGF secretion, and the inhibition of miR-382 expression reduced xenograft tumor growth and microvessel density in tumors. Taken together, these results suggest that miR-382 induced by hypoxia promotes angiogenesis and acts as an angiogenic oncogene by repressing PTEN.     

Evidence of mTOR Activation by an AKT-Independent Mechanism Provides Support for the Combined Treatment of PTEN-Deficient Prostate Tumors with mTOR and AKT Inhibitors

Activation of the phosphoinositide 3-kinase pathway is commonly observed in human prostate cancer. Loss of function of phosphatase and tensin homolog (PTEN) is associated with the activation of AKT and mammalian target of rapamycin (mTOR) in many cancer cell lines as well as in other model systems. However, activation of mTOR is also dependent of kinases other than AKT. Here, we show that activation of mTOR is not dependent on AKT in a prostate-specific PTEN-deficient mouse model of prostate cancer. Pathway bifurcation of AKT and mTOR was noted in both mouse and human prostate tumors. We demonstrated for the first time that cotargeting mTOR and AKT with ridaforolimus/MK-8669 and M1K-2206, respectively, delivers additive antitumor effects in vivo when compared to single agents. Our preclinical data suggest that the combination of AKT and mTOR inhibitors might be more effective in treating prostate cancer patients than current treatment regimens or either treatment alone.