Antitumor activity of the combination of an HSP90 inhibitor and a PI3K/mTOR dual inhibitor against cholangiocarcinoma

The PI3K/Akt/mTOR pathway is overactivated and heat shock protein (HSP) 90 is overexpressed in common cancers. We hypothesized that targeting both pathways can kill intrahepatic cholangiocarcinoma (CCA) cells. HSP90 and PTEN protein expression was evaluated by immunohistochemical staining of samples from 78 patients with intrahepatic CCA. CCA cell lines and a thioacetamide (TAA)-induced CCA animal model were treated with NVP-AUY922 (an HSP90 inhibitor) and NVP-BEZ235 (a PI3K/mTOR inhibitor) alone or in combination.Both HSP90 overexpression and loss of PTEN were poor prognostic factors in patients with intrahepatic CCA. The combination of the HSP90 inhibitor NVP-AUY922 and the PI3K/mTOR inhibitor NVP-BEZ235 was synergistic in inducing cell death in CCA cells. A combination of NVP-AUY922 and NVP-BEZ235 caused tumor regression in CCA rat animal model. This combination not only inhibited the PI3K/Akt/mTOR pathway but also induced ROS, which may exacerbate the vicious cycle of ER stress. Our data suggest simultaneous targeting of the PI3K/mTOR and HSP pathways for CCA treatment.     

PI3K/AKT/MTOR信号通路对肾癌A498细胞增殖、迁移及侵袭的影响研究

目的 探讨PI3K/AKT/MTOR信号通路对肾癌A498细胞增殖、迁移及侵袭的影响.方法 选用PI3K/MTOR双重阻断剂NVP-BEZ235体外处理肾癌A498细胞,浓度分别为0、100、250、500 nmol/L.48 h后采用蛋白质印迹法(Western blot)检测肾癌A498细胞中AKT和MTOR蛋白磷酸化情况;MTT法检测细胞增殖情况;细胞划痕实验检测细胞迁移能力;Transwell小室检测细胞侵袭能力;Western blot法检测细胞中E-Cadherin和PTEN蛋白表达变化.结果 肾癌A498细胞中p-AKT、MTOR、p-MTOR、E-Cadherin、PTEN的表达及细胞增殖率、迁移率、穿膜细胞数量各自在不同NVP-BEZ235浓度下比较,差异均有统计学意义(P﹤0.01).与0 nmol/L组比较,100、250、500 nmol/L的NVP-BEZ235处理肾癌A498细胞后,细胞中磷酸化蛋白p-AKT和p-MTOR的表达均下调,细胞增殖率下降,细胞迁移率下降,穿膜细胞数量减少,细胞中E-Cadherin和PTEN蛋白表达均上调,差异均有统计学意义(P﹤0.05).结论 通过阻断PI3K/AKT/MTOR信号通路可以抑制肾癌A498细胞的增殖、迁移和侵袭,可能与上调细胞中E-Cadherin和PTEN蛋白表达有关.     

Effect of BRAF-mediated PI3K/Akt/mTOR pathway on biological characteristics and chemosensitivity of NSCLC A549/DDP cells

The present study aimed to explore the biological characteristics of non-small cell lung cancer (NSCLC) cells and the mechanism of chemosensitivity through the role of the PI3K/Akt/mTOR signaling pathway mediated by BRAF gene silencing. Following cell transfection and grouping, an MTT assay detected the activity of NSCLC cells, a scratch wound test assessed the migration ability, flow cytometry using PI staining detected the cell cycle phase, TUNEL and flow cytometry through Annexin V-PI staining assessed the apoptosis, and colony formation was used to detect the sensitivity of lung cancer cells to cisplatin chemotherapy. Furthermore, the relative expression levels of BRAF, PTEN, PI3K, mTOR mRNA were assessed by RT-qPCR, and the protein expression levels of BRAF, PTEN, PI3K, phosphorylated (p)-PI3K, Akt, p-Akt, mTOR, p-mTOR, cisplatin resistance-related enzymes ERCC1 and BRCA1, apoptotic proteins Bax and Bcl-2 were assessed by western blotting. Compared with the control group and NC group, there were differences in decreased BRAF mRNA expression levels in the small interfering (si)BRAF group and siBRAF + IGF-1 group (both P<0.05). In addition, compared with the control group, the siBRAF, NVP-BEZ235 and siBRAF + NVP-BEZ235 groups had significant decreased cell viability at 2–6 days, decreased migration ability, shortened proportion of S-phase cells, increased proportion of G₁/G₀-phase cells, increased apoptosis rate, decreased number of colony-forming cells, decreased mRNA expression of PI3K, Akt and mTOR, increased PTEN mRNA expression, decreased protein expression levels of PI3K, p-PI3K, Akt, p-Akt, mTOR, p-mTOR, ERCC1, BRCA1 and Bcl-2, and increased protein expression levels of PTEN and Bax (all P<0.05); and more obvious trends were revealed in the siBRAF + NVP-BEZ235 group (all P<0.05); whereas opposite results were detected in the siBRAF + IGF-1 group when compared with the siBRAF group and NVP-BEZ235 group (all P<0.05). Silencing of BRAF gene expression to inhibit the activation of the PI3K/Akt/mTOR signaling pathway exerted a synergistic effect decreasing cell viability, inhibiting the cell cycle and migration, increasing the apoptosis rate, decreasing the number of colony-forming cells and increasing chemosensitivity of NSCLC. Activation of the PI3K/Akt/mTOR signaling pathway may reverse the role of silencing of BRAF gene expression, providing a potential approach for improving the chemosensitivity of NSCLC. The present study for the first time, to the best of our knowledge, clarified the possible mechanism of NSCLC cell biological characteristic changes and chemosensitivity from the perspective of BRAF gene silencing and PI3K/Akt/mTOR signaling pathway activation, providing a potential reference for suppressing tumor aggravation and improving the therapeutic outcomes of NSCLC at the genetic level.     

Comparison of the effects of the PI3K/mTOR inhibitors NVP-BEZ235 and GSK2126458 on tamoxifen-resistant breast cancer cells

Background

Treatment with anti-estrogens or aromatase inhibitors is commonly used for patients with estrogen receptor-positive (ER⁺) breast cancers; however resistant disease develops almost inevitably, requiring a choice of secondary therapy. One possibility is to use inhibitors of the PI3K/mTOR pathway and several candidate drugs are in development. We examined the in vitro effects of two inhibitors of the PI3K/mTOR pathway on resistant MCF-7 cells.

Results

The derived sub-lines showed increased resistance to tamoxifen but none exhibited concomitantly increased sensitivity to the PI3K inhibitors. NVP-BEZ235 and GSK2126458 acted mainly by induction of cell cycle arrest, particularly in G₁-phase, rather than by induction of apoptosis. The lines varied considerably in their utilization of the AKT, p70S6K and ERK pathways. NVP-BEZ235 and GSK2126458 inhibited AKT signaling but NVP-BEZ235 showed greater effects than GSK2126458 on p70S6K and rpS6 signaling with effects resembling those of rapamycin.

Methods

We cultured MCF-7 cells for prolonged periods either in the presence of the anti-estrogen tamoxifen (three sub-lines) or in estrogen free medium (two sub-lines) to mimic the effects of clinical treatment. We then analyzed the effects of two dual PI3K/mTOR phosphoinositide-3-kinase inhibitors, NVP-BEZ235 and GSK2126458, on the growth and signaling pathways of these MCF-7 sub-lines. The functional status of the PI3K, mTOR and ERK pathways was analyzed by measuring phosphorylation of AKT, p70S6K, rpS6 and ERK.

Conclusion

Increased resistance to tamoxifen in these MCF-7 sub-lines is not associated with hypersensitivity to PI3K inhibitors. While both drugs inhibited AKT signaling, NVP-BEZ235 resembled rapamycin in inhibiting the mTOR pathway.Key words: breast cancer, PI3K, mTOR, BEZ235, GSK2126458, estrogen receptor, MCF-7     

NVP-BEZ235, a dual PI3K/mTOR inhibitor, prevents PI3K signaling and inhibits the growth of cancer cells with activating PI3K mutations

Phosphatidylinositol-3-kinase (PI3K) pathway deregulation is a common event in human cancer, either through inactivation of the tumor suppressor phosphatase and tensin homologue deleted from chromosome 10 or activating mutations of p110-alpha. These hotspot mutations result in oncogenic activity of the enzyme and contribute to therapeutic resistance to the anti-HER2 antibody trastuzumab. The PI3K pathway is, therefore, an attractive target for cancer therapy. We have studied NVP-BEZ235, a dual inhibitor of the PI3K and the downstream mammalian target of rapamycin (mTOR). NVP-BEZ235 inhibited the activation of the downstream effectors Akt, S6 ribosomal protein, and 4EBP1 in breast cancer cells. The antiproliferative activity of NVP-BEZ235 was superior to the allosteric selective mTOR complex inhibitor everolimus in a panel of 21 cancer cell lines of different origin and mutation status. The described Akt activation due to mTOR inhibition was prevented by higher doses of NVP-BEZ235. NVP-BEZ235 reversed the hyperactivation of the PI3K/mTOR pathway caused by the oncogenic mutations of p110-alpha, E545K, and H1047R, and inhibited the proliferation of HER2-amplified BT474 cells exogenously expressing these mutations that render them resistant to trastuzumab. In trastuzumab-resistant BT474 H1047R breast cancer xenografts, NVP-BEZ235 inhibited PI3K signaling and had potent antitumor activity. In treated animals, there was complete inhibition of PI3K signaling in the skin at pharmacologically active doses, suggesting that skin may serve as surrogate tissue for pharmacodynamic studies. In summary, NVP-BEZ235 inhibits the PI3K/mTOR axis and results in antiproliferative and antitumoral activity in cancer cells with both wild-type and mutated p110-alpha.     

Dual PI3K/mTOR inhibition is required to effectively impair microenvironment survival signals in mantle cell lymphoma

Phosphatidylinositol-3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway activation contributes to mantle cell lymphoma (MCL) pathogenesis and drug resistance. Antitumor activity has been observed with mTOR inhibitors. However, they have shown limited clinical efficacy in relation to drug activation of feedback loops. Selective PI3K inhibition or dual PI3K/mTOR catalytic inhibition are different therapeutic approaches developed to achieve effective pathway blockage. Here, we have performed a comparative analysis of the mTOR inhibitor everolimus, the pan-PI3K inhibitor NVP-BKM120 and the dual PI3K/mTOR inhibitor NVP-BEZ235 in primary MCL cells. We found NVP-BEZ235 to be more powerful than everolimus or NVP-BKM120 in PI3K/Akt/mTOR signaling inhibition, indicating that targeting the PI3K/Akt/mTOR pathway at multiple levels is likely to be a more effective strategy for the treatment of MCL than single inhibition of these kinases. Among the three drugs, NVP-BEZ235 induced the highest change in gene expression profile. Functional validation demonstrated that NVP-BEZ235 inhibited angiogenesis, migration and tumor invasiveness in MCL cells. NVP-BEZ235 was the only drug able to block IL4 and IL6/STAT3 signaling which compromise the therapeutic effect of chemotherapy in MCL. Our findings support the use of the dual PI3K/mTOR inhibitor NVP-BEZ235 as a promising approach to interfere with the microenvironment-related processes in MCL.     

Growth inhibition by NVP-BEZ235, a dual PI3K/mTOR inhibitor, in hepatocellular carcinoma cell lines

Dysregulation of the phosphatidylinositol-3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway frequently occurs in human tumors, and is therefore considered to be a good molecular target for treatment. In hepatocellular carcinoma (HCC), overexpression of p-Akt and decrease of PTEN expression have been reported. NVP-BEZ235 is a novel dual inhibitor of PI3K and mTOR; however, its effect on HCC has not been documented. Consequently, we investigated the effects of NVP-BEZ235 on the PLC/PRF/5, HLE, JHH7 and HepG2 HCC cell lines in vitro and in vivo. NVP-BEZ235 decreased the levels of p-Akt and p-p70S6K and inhibited cell proliferation in all HCC cell lines in a dose-dependent manner. Flow cytometric analysis revealed that inhibition of cell proliferation by NVP-BEZ235 was accompanied by G1 arrest in all cell lines, and that NVP-BEZ235 induced apoptosis in PLC/PRF/5 and HLE cells. Tumor growth was suppressed without body weight loss when NVP-BEZ235 was orally administered to JHH-7 tumor-bearing mice for 11 days. These results suggest that NVP-BEZ235 is a potential new candidate for targeted HCC therapy.     

Concurrent inhibition of PI3-Kinase and mTOR induces cell death in diffuse large B cell lymphomas,a mechanism involving down regulation of Mcl-1

Phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signaling is frequently dysregulated in diffuse large B cell lymphoma (DLBCL) including the favorable germinal centre B-cell (GCB) and the unfavorable activated B-cell (ABC) subtypes. mTOR promotes cap-dependent translation of proteins, like Mcl-1, through inhibitory phosphorylation of the eukaryotic translation initiation factor 4E binding protein 1 (4EBP1). Inhibition of mTOR by RAD001 reduces proliferation but fails to dephosphorylate 4EBP1 and to induce cell death in either DLBCL subtype. In contrast, concurrent inhibition of PI3K and mTOR with NVP-BEZ235 inhibits proliferation, dephosphorylates 4EBP1, and induces cells death, notably more pronounced in CGB cells. Small RNA interference identifies Mcl-1 as a crucial cell death mediator of both DLBCL subtypes. Inhibition of the PI3K/mTOR/4EBP1 by NVP-BEZ235 results in suppression of the cap-dependent translation initiation complex and concomitant downregulation of Mcl-1 in GCB cell lines. In ABC cell lines, this suppression is possibly compensated by NF-κB- or Pim kinase-mediated signaling.     

PI3K／Akt／mTOR在表阿霉素抑制Jurkat细胞增殖和诱导凋亡中的作用

目的 探讨PI3K／Akt／mTOR信号通路在表阿霉素抑制人T细胞淋巴瘤细胞株Jurkat细胞增殖和诱导凋亡中的作用。方法 用0、1.25、2.5、5、10μmol／L表阿霉素和0、0.25、0.5、1、2μmol／L PI3K／mTOR双重抑制剂（NVP-BEZ235）对Jurkat细胞作用48h后,CCK-8试剂盒检测Jurkat细胞株增殖抑制情况;采用AnnexinⅤ／PE双染法流式细胞术检测上述药物作用Jurkat细胞48h的凋亡率以及5μmol／L表阿霉素和2μmol／L NVP BEZ235单独及联合作用Jurkat细胞0、12、24、36、48h的凋亡率;Western blotting法检测5、10μmol/L的表阿霉素作用Jurkat细胞0、6、12、24、48h,以及5μmol/L表阿霉素与2μmol/L NVP BEZ235单独及联合作用Jurkat细胞24、48h的PI3K／Akt／mTOR信号通路中Akt、mTOR、p70s6k等表达变化。结果 表阿霉素能够抑制Jurkat细胞增殖并诱导其凋亡,且凋亡作用呈浓度依赖性,5μmol／L表阿霉素作用Jurkat细胞48h的凋亡率为57.72％。在表阿霉素诱导Jurkat细胞凋亡过程中伴随Akt、mTOR、p70s6k的表达变化, NVP-BEZ235能够降低Jurkat细胞Akt、p70s6k的磷酸化水平,显著提高表阿霉素诱导Jurkat细胞凋亡的作用,5μmol／L表阿霉素和2μmol／L NVP-BEZ235联合作用Jurkat细胞48h的凋亡率达78.31％,明显高于5μmol／L表阿霉素的57.72％。结论 表阿霉素抑制Jurkat细胞增殖和诱导凋亡与PI3K／Akt／mTOR信号通路有关,当该通路抑制剂与表阿霉素联用时,Jurkat细胞对于表阿霉素敏感性有一定程度的提高。     

Effects of 2-dodecyl-6-methoxycyclohexa-2,5-diene-1,4-dione on autophagy and the PI3K/AKT/mTOR signaling pathway in human cholangiocarcinoma QBC939 cells

Background2-dodecyl-6-methoxycyclohexa-2,5-diene-1,4-dione (DMDD) has been reported to have good antitumor effects. The aim of this study was to investigate whether DMDD induces apoptosis and autophagy in human cholangiocarcinoma (CCA) QBC939 cells and determine its effect on the PI3K/AKT/mTOR signaling pathway.MethodsQBC939 cells were cultured in vitro and changes in cell viability were detected by the Cell Counting Kit (CCK8) assay after treatment with different concentrations of DMDD for 24, 48, and 72 h. The cells were divided into control and DMDD-treated groups (treated concentrations were 10, 15, and 20 µM/L), and the cell cycle, apoptosis, and autophagic vesicles were assessed. The expression levels of PI3K, AKT, mTOR, microtubule-associated protein 1 light chain 3 beta (LC3-II)/I, Beclin-1, and P62 were detected by Western blot. A xenograft mouse model was constructed to detect the effect of DMDD on CCA.ResultsThe experimental results showed that DMDD was able to inhibit proliferation, migration, and invasion and induce cell cycle arrest and autophagy of QBC939 cells. In addition, DMDD decreased the protein expression of PI3K, AKT, and mTOR and increased the expression of LC3-II/I, Beclin-1, and P62. In mice, DMDD was able to inhibit the growth of tumors.ConclusionsDMDD inhibits CCA cell viability and induces cell cycle arrest and autophagy by a mechanism that may be related to the downregulation of the PI3K/AKT/mTOR signaling pathway.     

Inhibiting PI3K reduces mammary tumor growth and induces hyperglycemia in a mouse model of insulin resistance and hyperinsulinemia

Women with type 2 diabetes mellitus (T2DM) are at a greater risk of developing and dying from breast cancer than women without T2DM. Insulin resistance and hyperinsulinemia underlie the pathogenesis of T2DM. In the MKR mouse model of insulin resistance, we have previously shown increased activation of the phosphatidylinositol 3-kinase (PI3K)/Akt/mTOR pathway in association with accelerated mammary tumor growth. In this study, we demonstrate that inhibiting PI3K with the oral pan-class I PI3K inhibitor, NVP-BKM120 reduced the growth of Met-1 and MCNeuA mammary tumor orthografts in the MKR mouse. NVP-BKM120 treatment decreased phosphorylation of Akt and S6 ribosomal protein (S6rp); no change in Erk1/2 phosphorylation was seen. Hyperglycemia, hypertriglyceridemia and greater hyperinsulinemia developed in the MKR mice treated with NVP-BKM120. We previously reported reduced tumor growth using intraperitoneal rapamycin in the MKR mouse, with the development of hyperglycemia and hypertriglyceridemia. Therefore, we examined whether the oral PI3K/mTOR inhibitor NVP-BEZ235 augmented the tumor suppressing effects of PI3K inhibition. We also investigated the effect of targeted PI3K/mTOR inhibition on PI3K/Akt/mTOR and Erk1/2 signaling, and the potential effects on glycemia. NVP-BEZ235 suppressed the growth of Met-1 and MCNeuA tumor orthografts, and decreased Akt and S6rp phosphorylation, despite increased Erk1/2 phosphorylation in Met-1 orthografts of MKR mice. Less marked hyperglycemia and hyperinsulinemia developed with NVP-BEZ235 than NVP-BKM120. Overall, the results of this study demonstrated that inhibiting PI3K/Akt/mTOR signaling with the oral agents NVP-BKM120 and NVP-BEZ235 decreased mammary tumor growth in the hyperinsulinemic MKR mouse. Inhibiting PI3K alone led to more severe metabolic derangement than inhibiting both PI3K and mTOR. Therefore, PI3K may be an important target for the treatment of breast cancer in women with insulin resistance. Monitoring for hyperglycemia and dyslipidemia should be considered when using these agents in humans, given the metabolic changes detected in this study.     

Overcoming acquired resistance to letrozole by targeting the PI3K/AKT/mTOR pathway in breast cancer cell clones

Development of resistance to endocrine therapy is a clinical issue in estrogen receptor (ER)-positive breast cancer. Here we show that persistent activation of AKT/mTOR signaling is crucial to the acquisition of letrozole resistance in cell clones generated from MCF-7/AROM-1 aromatase-expressing breast cancer cells after prolonged letrozole exposure. ERα plays a marginal role in this context. As a proof of concept, the association between PI3K/AKT/mTOR signaling and insensitivity to endocrine therapies was confirmed in breast cancer patients who developed early letrozole resistance in neoadjuvant setting. In addition our results suggest that, regardless of the mechanism mediating the activation of AKT/mTOR pathway, either RAD001 or NVP-BEZ235 treatment may represent a promising strategy to overcome acquired resistance to letrozole in breast cancers dependent on AKT/mTOR signaling.     

PI3K independent activation of mTORC1 as a target in lapatinib-resistant ERBB2+ breast cancer cells

Therapies targeting the ERBB2 receptor, including the kinase inhibitor lapatinib (Tykerb, GlaxoSmithKline), have improved clinical outcome for women with ERBB2-amplified breast cancer. However, acquired resistance to lapatinib remains a significant clinical problem, and the mechanisms governing resistance remain poorly understood. We sought to define molecular alterations that confer an acquired lapatinib resistance phenotype in ER?/ERBB2+ human breast cancer cells. ERBB2-amplified SKBR3 breast cancer cells were rendered resistant to lapatinib via culture in increasing concentrations of the drug, and molecular changes associated with a resistant phenotype were interrogated using a collaborative enzyme-enhanced immunoassay platform and immunoblotting techniques for detection of phosphorylated signaling cascade proteins. Interestingly, despite apparent inactivation of the PI3K/AKT signaling pathway, resistant cells exhibited constitutive activation of mammalian target of rapamycin complex 1 (mTORC1) and were highly sensitive to mTOR inhibition with rapamycin and the dual PI3K/mTOR inhibitor NVP-BEZ235. These data demonstrate a role for downstream activation of mTORC1 in the absence of molecular alterations leading to PI3K/AKT hyperactivation as a potential mechanism of lapatinib resistance in this model of ERBB2+ breast cancer and support the rationale of combination or sequential therapy using ERBB2 and mTOR-targeting molecules to prevent or target resistance to lapatinib. Moreover, our data suggest that assessment of mTOR substrate phosphorylation (i.e., S6) may serve as a more robust biomarker to predict sensitivity to mTOR inhibitors in the context of lapatinib resistance than PI3K mutations, loss of PTEN and p-AKT levels.     

The PI3 kinase/mTOR blocker NVP-BEZ235 overrides resistance against irreversible ErbB inhibitors in breast cancer cells

Resistance against first and second generation (irreversible) ErbB inhibitors is an unsolved problem in clinical oncology. The purpose of this study was to examine the effects of the irreversible ErbB inhibitors pelitinib and canertinib on growth of breast and ovarian cancer cells. Although in vitro growth-inhibitory effects of both drugs exceeded by far the effects of all reversible ErbB blockers tested (lapatinib, erlotinib, and gefitinib), complete growth inhibition was usually not reached. To define the mechanism of resistance, we examined downstream signaling pathways in drug-exposed cells by Western blot analysis. Although ErbB phosphorylation was reduced by pelitinib and canertinib, activation of the AKT/mTOR pathway remained essentially unaltered in drug-resistant cells. Correspondingly, transfection of tumor cells with constitutively activated AKT was found to promote resistance against all ErbB inhibitors tested, whereas dominant negative AKT reinstalled sensitivity in drug-resistant cells. In a next step, we applied PI3K/AKT/mTOR blockers including the dual PI3K/mTOR kinase inhibitor NVP-BEZ235. These agents were found to cooperate with pelitinib and canertinib in producing in vitro growth inhibition in cancer cells resistant against ErbB-targeting drugs. In conclusion, our data show that ErbB drug-refractory activation of the PI3K/AKT/mTOR pathway plays a crucial role in resistance against classical and second-generation irreversible ErbB inhibitors, and NVP-BEZ235 can override this form of resistance against pelitinib and canertinib.     

The synergistic interaction of MEK and PI3K inhibitors is modulated by mTOR inhibition

Background:

Combined targeting of MAPK and PI3K signalling pathways may be necessary for optimal therapeutic activity in cancer. This study evaluated the MEK inhibitors AZD6244 and PD0325901, alone and in combination with the dual mTOR/PI3K inhibitor NVP-BEZ235 or the PI3K inhibitor GDC-0941, in three colorectal cancer cell lines.

Methods:

Growth inhibition, survival and signal transduction were measured using the Sulforhodamine B assay, clonogenicity and western blotting, respectively, in HCT116, HT29 and DLD1 cell lines.

Results:

All MEK/PI3K inhibitor combinations exhibited marked synergistic growth inhibition; however, GDC-0941 displayed greater synergy in combination with either MEK inhibitor. NVP-BEZ235 exhibited stronger inhibition of 4EBP1 phosphorylation, and similar inhibition of S6 and AKT phosphorylation, compared with GDC-0941. Both PD0325901 and AZD6244 inhibited ERK phosphorylation, and with MEK/PI3K inhibitor combinations inhibition of S6 phosphorylation was increased. The reduced synergy exhibited by NVP-BEZ235 in combination with MEK inhibitors, compared with GDC-0941, may be due to inhibition of mTOR, and the addition of the mTORC1/2 inhibitor KU0063794 compromised the synergy of GDC-0941:PD0325901 combinations.

Conclusion:

These studies confirm that dual targeting of PI3K and MEK can induce synergistic growth inhibition; however, the combination of specific PI3K inhibitors, rather than dual mTOR/PI3K inhibitors, with MEK inhibitors results in greater synergy.     

The PI3K/AKT/mTOR Signaling Pathway: Implications in the Treatment of Breast Cancer

Epidemiologic and experimental studies support a key role of the phosphatidyl inositol 3-kinase/AKT/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway in the biology of human cancers. Alterations resulting in activation of PI3K/Akt/mTOR signaling are perhaps the most frequent events observed in solid tumors, including breast cancer, and contribute to neoplastic transformation. The PI3K/mTOR pathway can be activated by overproduction of growth factors or chemokines, loss of phosphatase and tensin homolog (PTEN) expression, or by mutations in growth factor receptors Ras, PTEN, or PI3K itself. Activation of this pathway contributes to cell cycle proliferation, growth, cell cycle entry, survival, cell motility, protein synthesis, and glucose metabolism, all important aspects of tumorigenesis. The most common genetic aberrations in breast cancer are activating somatic missense mutations in the gene encoding the p110a (PIK3CA) subunit of PI3K. The PTEN gene is often hypermethylated or decreased in expression, through as yet unclear mechanisms, in breast cancer. Studies have shown that PI3K/PTEN/AKT pathway modulation is implicated in HER2/neu-tumorigenesis and in response to the HER2-targeting antibody trastuzumab. Components of the pathway are regulated by feed-back and cross-talk to other signaling cascades and appear to be implicated with drug resistance. Over the past few years, a number of components of this signaling cascade have been the subject of intense drug-discovery activities. Rapamycin analogs have already been shown to have antitumor efficacy in some tumor types. Newer-generation PI3K, AKT, and mTOR inhibitors have shown significant promise preclinically and are now in clinical trials. This article summarizes the progress made in the elucidation of the pathway, clinical implications in pathology of breast cancer, and reviews novel drugs targeting this pathway for cancer treatment, particularly inhibitors of PI3K, AKT, and mTOR, currently undergoing clinical trials. Potential combination strategies, safety concerns, and resistance mechanisms for this new generation of anticancer agents are also discussed.     

PI3K/AKT/mTOR信号通路在Burkitt淋巴瘤中的研究进展

 Burkitt淋巴瘤是一种高度侵袭性的非霍奇金淋巴瘤，是人类生长最快的肿瘤。根据流行病学及miRNA不同，分为地方型、散发型与免疫缺陷相关型。该病主要发生在儿童及青少年，少数发生于成年人。经短期、强效化疗后疗效显著，但成年、晚期、耐药的患者预后较差。PI3K/AKT/mTOR信号通路在细胞的生长、分化、代谢、生存以及增殖等方面发挥重要作用，研究发现，该信号通路在Burkitt淋巴瘤中呈激活状态，且针对该通路的抑制剂对Burkitt淋巴瘤细胞有抑制作用。通过对该信号通路与PTEN、c-Myc、自噬在Burkitt淋巴瘤中作用及相互关系的研究，了解其发病机制，设计该通路抑制剂与其他相关通路抑制剂或与单克隆抗体的联合用药，为晚期、耐药的患者寻找精准、高效、低毒的靶向治疗方案。     

PTEN/PI3K突变对肺癌细胞基因表达谱的影响

目的:探讨第10号染色体同源丢失性磷酸酶-张力蛋白(phosphatase and tensin homolog deleted on chromosome ten,PTEN)和磷脂酰肌醇-3激酶(phosphoinositide3-kinase,PI3K)基因突变对肺癌细胞基因表达谱的影响。方法:采用蛋白质印迹法检测19株非小细胞肺癌细胞中PTEN表达情况,测序验证PTEN基因是否发生突变,检测该突变对于PTEN下游分子AKT和mTOR通路产生的影响。利用基因集富集分析(gene set enrichment analysis,GSEA)方法对19株肺癌细胞的基因表达谱数据进行PTEN/PI3K突变的功能分析。结果:19株非小细胞肺癌细胞中有5株PTEN蛋白表达缺失,通过测序发现这5株均存在PTEN突变;文献检索另有2株存在PIK3CA突变。PTEN突变后其下游分子AKT和mTOR通路处于持续活化状态。借助GSEA法对肺癌细胞基因表达谱数据进行分析,发现PTEN(或PI3K)突变对肺癌细胞的线粒体-能量代谢的基因集产生了重要影响。结论:PTEN/PI3K突变对其下游分子AKT和mTOR通路产生明显影响,对肺癌细胞基因表达谱的影响主要体现在线粒体-能量代谢方面的基因集。这一发现提示,有必要重视线粒体-能量代谢在肺癌发生中的作用。     

The Dual PI3K/mTOR Inhibitor NVP-BEZ235 Is a Potent Inhibitor of ATM- and DNA-PKCs-Mediated DNA Damage Responses

Inhibitors of PI3K/Akt signaling are being actively developed for tumor therapy owing to the frequent mutational activation of the PI3K-Akt-mTORC1 pathway in many cancers, including glioblastomas (GBMs). NVP-BEZ235 is a novel and potent dual PI3K/mTOR inhibitor that is currently in phase 1/2 clinical trials for advanced solid tumors. Here, we show that NVP-BEZ235 also potently inhibits ATM and DNA-PKcs, the two major kinases responding to ionizing radiation (IR)-induced DNA double-strand breaks (DSBs). Consequently, NVP-BEZ235 blocks both nonhomologous end joining and homologous recombination DNA repair pathways resulting in significant attenuation of DSB repair. In addition, phosphorylation of ATMtargets and implementation of the G₂/M cell cycle checkpoint are also attenuated by this drug. As a result, NVP-BEZ235 confers an extreme degree of radiosensitization and impairs DSB repair in a panel of GBM cell lines irrespective of their Akt activation status. NVP-BEZ235 also significantly impairs DSB repair in a mouse tumor model thereby validating the efficacy of this drug as a DNA repair inhibitor in vivo. Our results, showing that NVP-BEZ235 is a potent and novel inhibitor of ATM and DNA-PKcs, have important implications for the informed and rational design of clinical trials involving this drug and also reveal the potential utility of NVP-BEZ235 as an effective radiosensitizer for GBMs in the clinic.     

Role of dual PI3/Akt and mTOR inhibition in Waldenstrom's Macroglobulinemia

Tumorigenesis occurs due to synergistic interactions from a complex of signal transduction processes, including multiple onco-proteins and tumor suppressors such as Ras, Myc, PI3K/Akt/mTOR, Her-2/Neu, p53 and PTEN. Specifically, the PI3K/Akt and mTOR pathways have been shown to play a pivotal role on the initiation and progression of malignancies, enhancing cell survival by stimulating cell proliferation, and inhibiting apoptosis. Therefore, it is critical to examine therapeutic agents that explicitly target both the PI3K/Akt and mTOR signaling cascades in diseases, such as Waldenstrom Macroglobulinemia (WM), that harbor activation of the PI3K/Akt pathway. We demonstrated that dual targeting of the PI3K and mTOR pathways by the novel inhibitor NVP-BEZ235, exhibited toxicity on WM cells by directly targeting the tumor clone and indirectly through an effect on the bone marrow milieu. These findings suggest that dual targeting of the PI3K and mTOR pathways is a better modality of targeted therapy for tumors that harbor activation of the PI3K/mTOR pathways, such as in WM.