Activity of the mTOR inhibitor RAD001, the dual mTOR and PI3-kinase inhibitor BEZ235 and the PI3-kinase inhibitor BKM120 in hepatocellular carcinoma

Signaling pathways in liver cancer: pathogenesis and targeted therapy

Liver cancer remains one of the most prevalent malignancies worldwide with high incidence and mortality rates. Due to its subtle onset, liver cancer is commonly diagnosed at a late stage when surgical interventions are no longer feasible. This situation highlights the critical role of systemic treatments, including targeted therapies, in bettering patient outcomes. Despite numerous studies on the mechanisms underlying liver cancer, tyrosine kinase inhibitors (TKIs) are the only widely used clinical inhibitors, represented by sorafenib, whose clinical application is greatly limited by the phenomenon of drug resistance. Here we show an in-depth discussion of the signaling pathways frequently implicated in liver cancer pathogenesis and the inhibitors targeting these pathways under investigation or already in use in the management of advanced liver cancer. We elucidate the oncogenic roles of these pathways in liver cancer especially hepatocellular carcinoma (HCC), as well as the current state of research on inhibitors respectively. Given that TKIs represent the sole class of targeted therapeutics for liver cancer employed in clinical practice, we have particularly focused on TKIs and the mechanisms of the commonly encountered phenomena of its resistance during HCC treatment. This necessitates the imperative development of innovative targeted strategies and the urgency of overcoming the existing limitations. This review endeavors to shed light on the utilization of targeted therapy in advanced liver cancer, with a vision to improve the unsatisfactory prognostic outlook for those patients.

Hepatocellular carcinoma: signaling pathways, targeted therapy, and immunotherapy

Hepatocellular carcinoma (HCC) is the most common primary liver cancer with a high mortality rate. It is regarded as a significant public health issue because of its complicated pathophysiology, high metastasis, and recurrence rates. There are no obvious symptoms in the early stage of HCC, which often leads to delays in diagnosis. Traditional treatment methods such as surgical resection, radiotherapy, chemotherapy, and interventional therapies have limited therapeutic effects for HCC patients with recurrence or metastasis. With the development of molecular biology and immunology, molecular signaling pathways and immune checkpoint were identified as the main mechanism of HCC progression. Targeting these molecules has become a new direction for the treatment of HCC. At present, the combination of targeted drugs and immune checkpoint inhibitors is the first choice for advanced HCC patients. In this review, we mainly focus on the cutting-edge research of signaling pathways and corresponding targeted therapy and immunotherapy in HCC. It is of great significance to comprehensively understand the pathogenesis of HCC, search for potential therapeutic targets, and optimize the treatment strategies of HCC.

The synergistic antitumor effect of IL-6 neutralization with NVP-BEZ235 in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) still ranks among the top cancers worldwide with high incidence and mortality. Due to abnormal activation of the PI3K/AKT/mTOR signalling pathway in HCC, targeting this pathway represents a potential therapeutic strategy. NVP-BEZ235 is a novel dual-targeted ATP-competitive PI3K/mTOR inhibitor that has shown effective antitumor effects. In this study, we found that interleukin-6 (IL-6) was significantly increased after exposure to NVP-BEZ235, and we proposed a treatment in which an anti-IL-6 antibody was combined with NVP-BEZ235 for HCC. In vitro results revealed that targeted inhibition of IL-6 potentiated the antitumor effects of NVP-BEZ235 in HCC cells. The mechanism might be attributed to their synergistic inhibitory activity on the PI3K/AKT/mTOR signalling pathway. Furthermore, an in vivo study demonstrated that combined administration of NVP-BEZ235 and anti-IL-6 Ab reduced HCC tumour load more effectively than either NVP-BEZ235 or anti-IL-6 Ab treatment alone. These findings add guidance value to the analysis of HCC and provide a reference for clinical treatment.

Advances of Tumorigenesis, Diagnosis at Early Stage, and Cellular Immunotherapy in Gastrointestinal Malignancies

Globally, in 2018, 4.8 million new patients have a diagnosis of gastrointestinal (GI) cancers, while 3.4 million people died of such disorders. GI malignancies are tightly relevant to 26% of the world-wide cancer incidence and occupies 35% of all cancer-associated deaths. In this article, we principally investigated molecular and cellular mechanisms of tumorigenesis in five major GI cancers occurring at esophagus, stomach, liver, pancreas, and colorectal region that illustrate high morbidity in Eastern and Western countries. Moreover, through this investigation, we not only emphasize importance of the tumor microenvironment in development and treatment of malignant tumors but also identify significance of M2PK, miRNAs, ctDNAs, circRNAs, and CTCs in early detection of GI cancers, as well as systematically evaluate contribution of personalized precision medicine including cellular immunotherapy, new antigen and vaccine therapy, and oncolytic virotherapy in treatment of GI cancers.

The Synergistic Anti-Cancer Effects of NVP-BEZ235 and Regorafenib in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the most common type of liver cancer worldwide. Regorafenib is a multi-kinase inhibitor and the second-line treatment for HCC. Since the PI3K/Akt/mTOR signaling pathway is dysregulated in HCC, we evaluated the therapeutic effects of regorafenib combined with a dual PI3K/mTOR inhibitor BEZ235 in the human HCC cell lines (n = 3). The combined treatment with BEZ235 and regorafenib enhanced the inhibition of cell proliferation and increased the expression of cleaved caspase-3 and cleaved PARP in HCC cells. Moreover, the combined treatment suppressed HCC cell migration and invasion in the transwell assay. Further, the Western blot analyses confirmed the involvement of epithelial-mesenchymal transition (EMT)-related genes such as slug, vimentin, and matrix metalloproteinase (MMP)-9/-2. Additionally, the proteinase activity of MMP-9/-2 was analyzed using gelatin zymography. Furthermore, the inhibition of phosphorylation of the Akt, mTOR, p70S6K, and 4EBP1 after combined treatment was validated using Western blot analysis. Therefore, these results suggest that the combined treatment with BEZ235 and regorafenib benefits patients with HCC.

Absence of Atg7 in the liver disturbed hepatic regeneration after liver injury

BACKGROUND AND AIMS

Autophagy is a critical process in cell survival and the maintenance of homeostasis. However, the implementation of therapeutic approaches based on autophagy mechanisms after liver damage is still challenging.

METHODS

We used a hepatospecific Atg7-deficient murine model to address this question.

RESULTS

We showed that the proliferation and regeneration capacity of Atg7-deficient hepatocytes was impaired. On the one hand, Atg7-deficient hepatocytes showed steady-state hyperproliferation. On the other hand, external triggers such as partial hepatectomy (PHx) or cell transplantation did not induce hepatocellular proliferation or liver repopulation. After PHx, hepatocyte proliferation was strongly decreased, accompanied by high mortality. This increase in mortality could be overcome by pharmacological mTOR inhibition. In accordance with hepatocyte hypoproliferation after damage, Atg7-deficient hepatocytes failed to repopulate the liver in a hepatic injury model. Atg7-deficient mice showed hepatic hypertrophy, transient cellular hypertrophy, and high transaminase levels followed by strong perisinusoidal/pericellular fibrosis with age. Their elevated modified hepatic activity index (mHAI) was almost exclusively due to apoptosis without any inflammation. These parameters were associated with variations in the triglyceride content and compromised lipid droplet formation after PHx. Mechanistically, we also observed a modulation of HGF, PAK4, NOTCH3 and YES1, which are proteins involved in cell cycle regulation.

CONCLUSION

We demonstrated the important role of autophagy in the regeneration capacity of hepatocytes. We showed the causative relationship between autophagy and triglycerides that is essential for promoting liver recovery. Finally, pharmacological mTOR inhibition overcame the impact of autophagy deficiency after liver damage and prevented mortality.

The PI3K/mTOR dual inhibitor BEZ235 nanoparticles improve radiosensitization of hepatoma cells through apoptosis and regulation DNA repair pathway

Polymer materials encapsulating drugs have broad prospects for drug delivery. We evaluated the effectiveness of polyethylene glycol-poly (lactic-co-glycolic acid) (PLGA-PEG) encapsulation and release characteristics of PI3K/mTOR inhibitor NVP-BEZ235 (BEZ235). We proposed a strategy for targeting radiosensitization of liver cancer cells. The biocompatibility, cell interaction, and internalization of Glypican-3 (GPC3) antibody-modified, BEZ235-loaded PLGA-PEG nanoparticles (NP-BEZ235-Ab) in hepatoma cells in vitro were studied. Also, the cell killing effect of NP-BEZ235-Ab combined with γ-ray cell was evaluated. We used confocal microscopy to monitor nanoparticle-cell interactions and cellular uptake, conducted focus-formation experiments to analyze the synergistic biological effects of NP-BEZ235-Ab and priming, and studied synergy in liver cancer cells using molecular biological methods such as western blotting. We found that PLGA-PEG has good loading efficiency for BEZ235 and high selectivity to GPC3-positive HepG2 liver cancer cells, thus documenting that NP-BEZ235-Ab acts as a small-molecule drug delivery nanocarrier. At the nominal concentration, the NP-BEZ235-Ab nanoformulation synergistically kills liver cancer cells with significantly higher efficiency than does the free drug. Thus, NP-BEZ235-Ab is a potential radiosensitizer.

A Newly Established Murine Cell Line as a Model for Hepatocellular Cancer in Non-Alcoholic Steatohepatitis

Non-alcoholic steatohepatitis (NASH) has become a major risk factor for hepatocellular cancer (HCC) due to the worldwide increasing prevalence of obesity. However, the pathophysiology of NASH and its progression to HCC is incompletely understood. Thus, the aim of this study was to generate a model specific NASH-derived HCC cell line. A murine NASH-HCC model was conducted and the obtained cancer cells (N-HCC25) were investigated towards chromosomal aberrations, the expression of cell type-specific markers, dependency on nutrients, and functional importance of mTOR. N-HCC25 exhibited several chromosomal aberrations as compared to healthy hepatocytes. Hepatocytic (HNF4), EMT (Twist, Snail), and cancer stem cell markers (CD44, EpCAM, CK19, Sox9) were simultaneously expressed in these cells. Proliferation highly depended on the supply of glucose and FBS, but not glutamine. Treatment with a second generation mTOR inhibitor (KU-0063794) resulted in a strong decrease of cell growth in a dose-dependent manner. In contrast, a first generation mTOR inhibitor (Everolimus) only slightly reduced cell proliferation. Cell cycle analyses revealed that the observed growth reduction was most likely due to G₁/G₀ cell cycle arrest. These results indicate that N-HCC25 is a highly proliferative HCC cell line from a NASH background, which might serve as a suitable in vitro model for future investigations of NASH-derived HCC.

Abnormal regulation of non-coding RNAs plays a role in development and progression of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is an aggressive tumor with a poor prognosis. Non-coding RNAs (ncRNAs) are RNAs transcribed from the genome but not translated into protein. In recent years, ncRNAs have been recognized to be key factors in tumorigenesis because of their ability to regulate multiple targets, cell proliferation, differentiation, apoptosis, and development. In this review, we discuss the pathological significance of ncRNAs (microRNAs, long-chain non-coding RNAs, and cyclic RNAs) in the development and progression of HCC. We also discuss the potential role of ncRNAs in the diagnosis and treatment of HCC.

Inhibition of PI3K/mTOR increased the sensitivity of hepatocellular carcinoma cells to cisplatin via interference with mitochondrial-lysosomal crosstalk

OBJECTIVES

The genotoxicity of cisplatin towards nuclear DNA is not sufficient to explain the cisplatin resistance of hepatocellular carcinoma (HCC) cells; cisplatin interacts with many organelles, which can influence the sensitivity. Here, we explored the role of mitochondrial-lysosomal crosstalk in the cisplatin resistance of HCC cells.

MATERIALS AND METHODS

Huh7 and HepG2 cells were subjected to different treatments. Flow cytometry was conducted to detect mitochondrial reactive oxygen species, mitochondrial mass, lysosomal function, mitochondrial membrane potential and apoptosis. Western blotting was performed to evaluate protein levels. The oxygen consumption rate was measured to evaluate mitochondrial function.

RESULTS

Cisplatin activated mitophagy and lysosomal biogenesis, resulting in crosstalk between mitochondria and lysosomes and cisplatin resistance in HCC cells. Furthermore, a combination of cisplatin with the phosphatidylinositol-3-kinase/mammalian target of rapamycin (PI3K/mTOR) inhibitor PKI-402 induced lysosomal membrane permeabilization. This effect changed the role of the lysosome from a protective one to that of a cell death promoter, completely destroying the mitochondrial-lysosomal crosstalk and significantly enhancing the sensitivity of HCC cells to cisplatin.

CONCLUSIONS

This is the first evidence of the importance of mitochondrial-lysosomal crosstalk in the cisplatin resistance of HCC cells and of the destruction of this crosstalk by a PI3K/mTOR inhibitor to increase the sensitivity of HCC cells to cisplatin. This mechanism could be developed as a novel target for treatment of HCC in the future.

Role of non-coding RNAs in liver disease progression to hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a tumor with poor prognosis and frequently aggressive. The development of HCC is associated with fibrosis and cirrhosis, which mainly results from nonalcoholic fatty liver disease, excessive alcohol consumption, and viral infections. Non-coding RNAs (ncRNAs) are RNAs transcribed from the genome, but are not translated into proteins. Recently, ncRNAs emerged as key contributors to tumor development and progression because of their abilities to regulate various targets and modulate cell proliferation, differentiation, apoptosis, and development. In this review, we summarize the frequently activated pathways in HCC and discuss the pathological implications of ncRNAs in the context of human liver disease progression, in particular HCC development and progression. This review aims to summarize the role of ncRNA dysregulation in the diseases and discuss the diagnostic and therapeutic potentials of ncRNAs.

Natural product pectolinarigenin inhibits proliferation, induces apoptosis, and causes G2/M phase arrest of HCC via PI3K/AKT/mTOR/ERK signaling pathway

Background

Hepatocellular carcinoma (HCC) is characterized by considerable phenotypic and molecular heterogeneity, but the overall survival of HCC patients remains extremely poor. Thus, novel and efficient alternatives to antitumor agents are urgently needed. Pectolinarigenin, a flavonoid compound extract, has been previously reported for the treatment of nasopharyngeal cancer. However, the potential antitumor roles of pectolinarigenin in HCC have not been clearly elaborated. In the present study, we investigated its role in HCC treatment and explored the potential molecular mechanism(s).

Materials and methods

HCC cell lines SMMC7721 and PLC5 were cultured and treated with indicated concentrations of pectolinarigenin. For the HCC cell proliferation, after HCC cells were stimulated with indicated concentrations of pectolinarigenin, the cell viability was detected in CCK-8 and colony-forming assays. HCC cell invasion/migration assay was performed by Transwell and wound scratch methods. Additionally, cellular apoptosis and cell cycle arrest analysis was performed with flow cytometric analysis. Finally, the involved underlying signaling pathway, the PI3K/AKT/mTOR/ERK signaling-related molecular markers were detected through Western blot methods with indicated antibodies. Meanwhile, antitumor activity of pectolinarigenin was also assessed in tumor-bearing mice.

Results

The results indicated that the treatment with pectolinarigenin significantly inhibited cell proliferation and migratory and invasive abilities of SMMC7721 and PLC5 cells in concentration- and time-dependent manner. Meanwhile, pectolinarigenin markedly induced cell apoptosis and G2/M phase arrest in SMMC7721 and PLC5 cells, which was associated with apoptosis- and cell cycle-related protein levels, respectively. Furthermore, pectolinarigenin inhibited PI3K/AKT/mTOR/ERK signaling pathway. It also significantly suppressed HCC tumor growth in vivo.

Conclusion

Pectolinarigenin could suppress the viability and motility and cause apoptosis and G2/M phase arrest in HCC cell lines by inhibiting the PI3K/AKT/mTOR/ERK signaling pathway. This might be an appealing potential therapeutic agent for HCC treatment.

NVP-BEZ235 Attenuated Cell Proliferation and Migration in the Squamous Cell Carcinoma of Oral Cavities and p70S6K Inhibition Mimics its Effect

NVP-BEZ235 or BEZ235 is a dual inhibitor of adenosine triphosphate (ATP)-competitive phosphoinositide 3-kinase (PI3K)/mammalian-target-of-rapamycin (mTOR) and is promising for cancer treatment. Because it targets more than one downstream effector, a dual approach is promising for cancer treatment. The aim of this study was to evaluate the efficacy of NVP-BEZ235 in treating oral cavity squamous cell carcinoma (OSCC). Two human OSCC cell lines, SCC-4 and SCC-25, were used in this study. PI3K-AKT signaling, proliferation, and cell migratory and invasion capabilities of OSCC cells were examined. In NVP-BEZ235-treated SCC-4 and SCC-25 cells, the phosphorylation of 70-kDa ribosomal S6 kinase (p70S6K), but not mTOR, decreased within 24 h. NVP-BEZ235 inhibited OSCC-cell proliferation, migration, and invasion possibly by directly deregulating the phosphorylation of p70S6K. The phospho-p70S6K inhibitor mimicked the effects of NVP-BEZ235 for preventing proliferation and weakening the migratory and invasion abilities of SCC-4 and SCC-25 cells. This study further confirmed the effect of NVP-BEZ235 on OSCC cells and provided a new strategy for controlling the proliferation, migration, and invasion of OSCC cells using the phopho-p70S6K inhibitor.

NVP-BEZ235, a dual PI3K-mTOR inhibitor, suppresses the growth of FaDu hypopharyngeal squamous cell carcinoma and has a synergistic effect with Cisplatin

NVP-BEZ235 is a dual phosphoinositide 3-kinase (PI3K)-mammalian target of rapamycin (mTOR) inhibitor. A dual approach targeting more than one downstream effector is a promising strategy for treating cancers. The aim of this study was to evaluate the effect of NVP-BEZ235 in treating FaDu hypopharyngeal squamous cell carcinoma (HSCC), either alone or in combination with cisplatin. We found mTOR expression was higher in patients with HSCC. In the in vitro study, treatment with NVP-BEZ235 alone attenuated cell proliferation and suppressed p-p70S6K and p-4E-BP1 expression in FaDu cells. When NVP-BEZ235 was combined with Cisplatin, apoptosis was induced more effectively than with either drug alone. In mice with a FaDu xenograft, cotreatment with NVP-BEZ235 and Cisplatin engendered synergistic effects and produced a greater antitumor response than did treatment with either drug alone. Resected tumor samples also showed decreased p-p70S6K expression. Collectively, these data demonstrate that NVP-BEZ235 inhibits HSCC growth through phospho-p70S6K suppression and has a synergistic effect with Cisplatin in treating HSCC. The data also provide a strategy for more effective HSCC treatment.

An autophagy-related gene expression signature for survival prediction in multiple cohorts of hepatocellular carcinoma patients

Prognostic signatures have been proposed as clinical tools to estimate prognosis in hepatocellular carcinoma (HCC), which is the second most common contributor to cancer-related death at present globally. Autophagy-related genes play a dynamic and fundamental role in HCC, but knowledge of their utility as prognostic markers is limited. Here, we facilitated univariate and multivariate Cox proportional hazards regression analyses to reveal that 3 autophagy-related genes (BIRC5, FOXO1 and SQSTM1) were closely related to the survival of HCC. Then, we generated a prognosis index (PI) for predicting overall survival (OS) based on the three genes, which was an independent prognostic indicator for the OS of HCC (HR = 1.930, 95% CI: 1.200-3.104, P = 0.007). The PI showed moderate performance for predicting the survival of HCC patients and its efficacy was validated by data from three microarrays (GSE10143, GSE10186 and GSE17856). Furthermore, we deeply mined the integrated large-scale datasets from public microarrays and immunohistochemistry to validate the overexpression of BIRC5 and SQSTM1 while down-regulated FOXO1 expression in HCC. Bioinformatic analysis offered the hypothesis that proliferative signals in high-risk HCC patients were disturbing and thereby facilitated inferior clinical outcomes. Collectively, the prognostic signature we proposed is a promising biomarker for monitoring outcome of HCC. Nevertheless, prospective experimental studies are needed to validate the clinical utility.

mTOR inhibition reduces growth and adhesion of hepatocellular carcinoma cells in vitro

Mechanistic target of rapamycin (mTOR) signaling is typically increased in hepatocellular carcinoma (HCC). A panel of HCC cell lines (HepG2, Hep3B and HuH6) was exposed to various concentrations of the mTOR inhibitors, everolimus and temsirolimus, in order to investigate their effects on cell growth, clonal formation, cell cycle progression, and adhesion and chemotactic migration using MTT and clonal cell growth assays, fluorometric detection of cell cycle phases and a Boyden chamber assay. In addition, integrin α and β adhesion receptors were analyzed by flow cytometry and blocking studies using function blocking monoclonal antibodies were conducted to explore functional relevance. The results demonstrated that everolimus and temsirolimus significantly suppressed HCC cell growth and clonal formation, at 0.1 or 1 nM (depending on the cell line). In addition, the number of cells in G0/G1 phase was increased in response to drug treatment, whereas the number of G2/M phase cells was decreased. Drug treatment also considerably suppressed HCC cell adhesion to immobilized collagen. Integrin profiling revealed strong expression of integrin α1, α2, α6 and β1 subtypes; and integrin α1 was upregulated in response to mTOR inhibition. Suppression of integrin α1 did not affect cell growth; however, it did significantly decrease adhesion and chemotaxis, with the influence on adhesion being greater than that on motility. Due to a positive association between integrin α1 expression and the extent of adhesion, whereby reduced receptor expression was correlated to decreased cell adhesion, it may be hypothesized that the adhesion‑blocking effects of mTOR inhibitors are not associated with mechanical contact inhibition of the α1 receptor but with integrin α1‑dependent suppression of oncogenic signaling, thus preventing tumor cell‑matrix interaction.

A functional mammalian target of rapamycin complex 1 signaling is indispensable for c-Myc-driven hepatocarcinogenesis

Amplification and/or activation of the c-Myc proto-oncogene is one of the leading genetic events along hepatocarcinogenesis. The oncogenic potential of c-Myc has been proven experimentally by the finding that its overexpression in the mouse liver triggers tumor formation. However, the molecular mechanism whereby c-Myc exerts its oncogenic activity in the liver remains poorly understood. Here, we demonstrate that the mammalian target of rapamycin complex 1 (mTORC1) cascade is activated and necessary for c-Myc-dependent hepatocarcinogenesis. Specifically, we found that ablation of Raptor, the unique member of mTORC1, strongly inhibits c-Myc liver tumor formation. Also, the p70 ribosomal S6 kinase/ribosomal protein S6 and eukaryotic translation initiation factor 4E-binding protein 1/eukaryotic translation initiation factor 4E signaling cascades downstream of mTORC1 are required for c-Myc-driven tumorigenesis. Intriguingly, microarray expression analysis revealed up-regulation of multiple amino acid transporters, including solute carrier family 1 member A5 (SLC1A5) and SLC7A6, leading to robust uptake of amino acids, including glutamine, into c-Myc tumor cells. Subsequent functional studies showed that amino acids are critical for activation of mTORC1 as their inhibition suppressed mTORC1 in c-Myc tumor cells. In human hepatocellular carcinoma specimens, levels of c-Myc directly correlate with those of mTORC1 activation as well as of SLC1A5 and SLC7A6.

CONCLUSION

Our current study indicates that an intact mTORC1 axis is required for c-Myc-driven hepatocarcinogenesis; thus, targeting the mTOR pathway or amino acid transporters may be an effective and novel therapeutic option for the treatment of hepatocellular carcinoma with activated c-Myc signaling. (Hepatology 2017;66:167-181).

Anti-tumor effects of everolimus and metformin are complementary and glucose-dependent in breast cancer cells

Background

Clinical efficacy of the mTOR inhibitor everolimus is limited in breast cancer and regularly leads to side-effects including hyperglycemia. The AMPK inhibitor and anti-diabetic drug metformin may counteract everolimus-induced hyperglycemia, as well as enhancing anti-cancer efficacy. We investigated the glucose-dependent growth-inhibitory properties of everolimus, metformin and the combination in breast cancer cell lines.

Methods

The breast cancer cell lines MCF-7, MDA-MB-231 and T47D were cultured in media containing 11 mM or 2.75 mM glucose with 21% or 1% oxygen. Everolimus and metformin treated cells were subjected to cytotoxicity and clonogenic assays, western blotting, FACS and metabolic measurements.

Results

Everolimus was less effective in MCF7 cells under low glucose conditions compared to high glucose conditions (IC₅₀ of >50 nM vs 29.1 ± 1.4 nM) in a short-term survival assay, while sensitivity of MDA-MB-231 and T47D cells to everolimus was lost under low glucose conditions. In contrast, metformin was more effective in low than in high glucose conditions in MCF7 (IC₅₀ of 1.8 ± 1.2 mM vs >5 mM) and MDA-MB231 cells (1.5 ± 1.3 mM vs 2.6 ± 1.2 mM). Metformin sensitivity of T47D cells was independent of glucose concentrations. Everolimus combined with metformin additively inhibited cell survival, clonogenicity, mTOR signaling activity and mitochondrial respiration. These effects were not the result of enhanced autophagy or apoptosis induction. Similar results were observed under hypoxic conditions.

Conclusion

Metformin-induced effects are additive to the anti-proliferative and colony inhibitory properties of everolimus through inhibition of mitochondrial respiration and mTOR signaling. These results warrant further in vivo investigation of everolimus combined with metformin as a putative anti-cancer therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3230-8) contains supplementary material, which is available to authorized users.

Deconvolution of Buparlisib's mechanism of action defines specific PI3K and tubulin inhibitors for therapeutic intervention

BKM120 (Buparlisib) is one of the most advanced phosphoinositide 3-kinase (PI3K) inhibitors for the treatment of cancer, but it interferes as an off-target effect with microtubule polymerization. Here, we developed two chemical derivatives that differ from BKM120 by only one atom. We show that these minute changes separate the dual activity of BKM120 into discrete PI3K and tubulin inhibitors. Analysis of the compounds cellular growth arrest phenotypes and microtubule dynamics suggest that the antiproliferative activity of BKM120 is mainly due to microtubule-dependent cytotoxicity rather than through inhibition of PI3K. Crystal structures of BKM120 and derivatives in complex with tubulin and PI3K provide insights into the selective mode of action of this class of drugs. Our results raise concerns over BKM120's generally accepted mode of action, and provide a unique mechanistic basis for next-generation PI3K inhibitors with improved safety profiles and flexibility for use in combination therapies.

Buparlisib/BKM120 is in phase 3 clinical trials as a phosphoinositide 3-kinase (PI3K) inhibitor. Here, Bohnacker et al. combine chemical biology and structural biology approaches to segregate BKM120's biological actions, and suggest that it causes mitotic arrest predominantly by binding microtubules and disrupting their dynamics.

PI3 Kinase Pathway and MET Inhibition is Efficacious in Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive cancer that is commonly associated with prior asbestos exposure. Receptor tyrosine kinases (RTKs) such as MET and its downstream target PI3K are overexpressed and activated in a majority of MPMs. Here, we studied the combinatorial therapeutic efficacy of the MET/ALK inhibitor crizotinib, with either a pan-class I PI3K inhibitor, BKM120, or with a PI3K/mTOR dual inhibitor, GDC-0980, in mesothelioma. Cell viability results showed that MPM cells were highly sensitive to crizotinib, BKM120 and GDC-0980 when used individually and their combination was more effective in suppressing growth. Treatment of MPM cells with these inhibitors also significantly decreased cell migration, and the combination of them was synergistic. Treatment with BKM120 alone or in combination with crizotinib induced G2-M arrest and apoptosis. Both crizotinib and BKM120 strongly inhibited the activity of MET and PI3K as evidenced by the decreased phosphorylation of MET, AKT and ribosomal S6 kinase. Using a PDX mouse model, we showed that a combination of crizotinib with BKM120 was highly synergetic in inhibiting MPM tumor growth. In conclusion our findings suggest that dual inhibition of PI3K and MET pathway is an effective strategy in treating MPM as compared to a single agent.

PI3K/AKT/mTOR inhibition in combination with doxorubicin is an effective therapy for leiomyosarcoma

BACKGROUND

Leiomyosarcoma (LMS) is a common type of soft tissue sarcoma that responds poorly to standard chemotherapy. Thus the goal of this study was to identify novel selective therapies that may be effective in leiomyosarcoma by screening cell lines with a small molecule library comprised of 480 kinase inhibitors to functionally determine which signalling pathways may be critical for LMS growth.

METHODS

LMS cell lines were screened with the OICR kinase library and a cell viability assay was used to identify potentially effective compounds. The top 10 % of hits underwent secondary validation to determine their EC50 and immunoblots were performed to confirm selective drug action. The efficacy of combination drug therapy with doxorubicin (Dox) in vitro was analyzed using the Calcusyn program after treatment with one of three dosing schedules: concurrent treatment, initial treatment with a selective compound followed by Dox, or initial treatment with Dox followed by the selective compound. Single and combination drug therapy were then validated in vivo using LMS xenografts.

RESULTS

Compounds that targeted PI3K/AKT/mTOR pathways (52 %) were most effective. EC50s were determined to validate these initial hits, and of the 11 confirmed hits, 10 targeted PI3K and/or mTOR pathways with EC50 values <1 μM. We therefore examined if BEZ235 and BKM120, two selective compounds in these pathways, would inhibit leiomyosarcoma growth in vitro. Immunoblots confirmed on-target effects of these compounds in the PI3K and/or mTOR pathways. We next investigated if there was synergy with these agents and first line chemotherapy doxorubicin (Dox), which would allow for earlier introduction into patient care. Only combined treatment of BEZ235 and Dox was synergistic in vitro. To validate these findings in pre-clinical models, leiomyosarcoma xenografts were treated with single agent and combination therapy. BEZ235 treated xenografts (n = 8) demonstrated a decrease in tumor volume of 42 % whereas combining BEZ235 with Dox (n = 8) decreased tumor volume 68 % compared to vehicle alone.

CONCLUSIONS

In summary, this study supports further investigation into the use of PI3K and mTOR inhibitors alone and in combination with standard treatment in leiomyosarcoma patients.

The pan-class I phosphatidyl-inositol-3 kinase inhibitor NVP-BKM120 demonstrates anti-leukemic activity in acute myeloid leukemia

Aberrant activation of the PI3K/Akt/mTOR pathway is a common feature of acute myeloid leukemia (AML) patients contributing to chemoresistance, disease progression and unfavourable outcome. Therefore, inhibition of this pathway may represent a potential therapeutic approach in AML. The aim of this study was to evaluate the pre-clinical activity of NVP-BKM120 (BKM120), a selective pan-class I PI3K inhibitor, on AML cell lines and primary samples. Our results demonstrate that BKM120 abrogates the activity of the PI3K/Akt/mTOR signaling, promoting cell growth arrest and significant apoptosis in a dose- and time-dependent manner in AML cells but not in the normal counterpart. BKM120-induced cytotoxicity is associated with a profound modulation of metabolic behaviour in both cell lines and primary samples. In addition, BKM120 synergizes with the glycolitic inhibitor dichloroacetate enhancing apoptosis induction at lower doses. Finally, in vivo administration of BKM120 to a xenotransplant mouse model of AML significantly inhibited leukemia progression and improved the overall survival of treated mice. Taken together, our findings indicate that BKM120, alone or in combination with other drugs, has a significant anti-leukemic activity supporting its clinical development as a novel therapeutic agent in AML.

Efficacy of dual PI-3K and mTOR inhibitors in vitro and in vivo in acute lymphoblastic leukemia

The major regulators of human acute lymphoblastic leukemia (ALL) cell growth and survival mediate their effects through the phosphoinositide 3-kinase (PI-3K)/mammalian target of rapamycin (mTOR) pathway. We have shown that the mTOR inhibitor everolimus extended survival in a non-obese diabetic/severe combined immune-deficient (NOD/SCID) mouse xenograft model of human ALL. Since PI-3K has mTOR dependent and independent functions we examined the effect of the dual PI-3K/mTOR inhibitors BEZ235 and BGT226. These agents inhibited the proliferation of ALL cell lines with a three log greater potency than everolimus. However, the induction of cell death differed, with BGT226 being cytotoxic in the low micromolar range while a two log higher concentration of BEZ235 was required to produce the same effect. While all three agents extended the survival of NOD/SCID mice engrafted with human ALL, the responses of individual xenografts varied. Although differential phosphorylation of AKT on Ser⁴⁷³ and Thr³⁰⁸ in response to everolimus exposure was observed, this did not entirely explain the different in vivo responses to the drugs. Our data suggests that while dual PI-3K/mTOR inhibitors may improve therapeutic outcomes for a subset of ALL patients, patient selection will be important, with some patients likely to respond better to single mTOR inhibition.

Potentiation of Growth Inhibitory Responses of the mTOR Inhibitor Everolimus by Dual mTORC1/2 Inhibitors in Cultured Breast Cancer Cell Lines

The mammalian target of rapamycin (mTOR), a vital component of signaling pathways involving PI3K/AKT, is an attractive therapeutic target in breast cancer. Everolimus, an allosteric mTOR inhibitor that inhibits the mTOR functional complex mTORC1, is approved for treatment of estrogen receptor positive (ER+) breast cancer. Other mTOR inhibitors show interesting differences in target specificities: BEZ235 and GSK2126458 are ATP competitive mTOR inhibitors targeting both PI3K and mTORC1/2; AZD8055, AZD2014 and KU-0063794 are ATP competitive mTOR inhibitors targeting both mTORC1 and mTORC2; and GDC-0941 is a pan-PI3K inhibitor. We have addressed the question of whether mTOR inhibitors may be more effective in combination than singly in inhibiting the proliferation of breast cancer cells. We selected a panel of 30 human breast cancer cell lines that included ER and PR positive, HER2 over-expressing, and “triple negative” variants, and determined whether signaling pathway utilization was related to drug-induced inhibition of proliferation. A significant correlation (p = 0.005) was found between everolimus IC₅₀ values and p70S6K phosphorylation, but not with AKT or ERK phosphorylation, consistent with the mTOR pathway being a principal target. We then carried out combination studies with four everolimus resistant triple-negative breast cancer cell lines, and found an unexpectedly high degree of synergy between everolimus and the other inhibitors tested. The level of potentiation of everolimus inhibitory activity (measured by IC₅₀ values) was found to be cell line-specific for all the kinase inhibitors tested. The results suggest that judicious combination of mTOR inhibitors with different modes of action could have beneficial effects in the treatment of breast cancer.

Targeted Inhibition of Phosphoinositide 3-Kinase/Mammalian Target of Rapamycin Sensitizes Pancreatic Cancer Cells to Doxorubicin without Exacerbating Cardiac Toxicity

Pancreatic cancer has the lowest 5-year survival rate of all major cancers despite decades of effort to design and implement novel, more effective treatment options. In this study, we tested whether the dual phosphoinositide 3-kinase/mechanistic target of rapamycin inhibitor BEZ235 (BEZ) potentiates the antitumor effects of doxorubicin (DOX) against pancreatic cancer. Cotreatment of BEZ235 with DOX resulted in dose-dependent inhibition of the phosphoinositide 3-kinase/mechanistic target of rapamycin survival pathway, which corresponded with an increase in poly ADP ribose polymerase cleavage. Moreover, BEZ cotreatment significantly improved the effects of DOX toward both cell viability and cell death in part through reduced Bcl-2 expression and increased expression of the shorter, more cytotoxic forms of BIM. BEZ also facilitated intracellular accumulation of DOX, which led to enhanced DNA damage and reactive oxygen species generation. Furthermore, BEZ in combination with gemcitabine reduced MiaPaca2 cell proliferation but failed to increase reactive oxygen species generation or BIM expression, resulting in reduced necrosis and apoptosis. Treatment with BEZ and DOX in mice bearing tumor xenographs significantly repressed tumor growth as compared with BEZ, DOX, or gemcitabine. Additionally, in contrast to the enhanced expression seen in MiaPaca2 cells, BEZ and DOX cotreatment reduced BIM expression in H9C2 cardiomyocytes. Also, the Bcl-2/Bax ratio was increased, which was associated with a reduction in cell death. In vivo echocardiography showed decreased cardiac function with DOX treatment, which was not improved by combination treatment with BEZ. Thus, we propose that combining BEZ with DOX would be a better option for patients than current standard of care by providing a more effective tumor response without the associated increase in toxicity.

Inhibition of mTORC2 Induces Cell-Cycle Arrest and Enhances the Cytotoxicity of Doxorubicin by Suppressing MDR1 Expression in HCC Cells

mTOR is aberrantly activated in hepatocellular carcinoma (HCC) and plays pivotal roles in tumorigenesis and chemoresistance. Rapamycin has been reported to exert antitumor activity in HCC and sensitizes HCC cells to cytotoxic agents. However, due to feedback activation of AKT after mTOR complex 1 (mTORC1) inhibition, simultaneous targeting of mTORC1/2 may be more effective. In this study, we examined the interaction between the dual mTORC1/2 inhibitor OSI-027 and doxorubicin in vitro and in vivo. OSI-027 was found to reduce phosphorylation of both mTORC1 and mTORC2 substrates, including 4E-BP1, p70S6K, and AKT (Ser473), and inhibit HCC cell proliferation. Similar to OSI-027 treatment, knockdown of mTORC2 induced G0-G1 phase cell-cycle arrest. In contrast, rapamycin or knockdown of mTORC1 increased phosphorylation of AKT (Ser473), yet had little antiproliferative effect. Notably, OSI-027 synergized with doxorubicin for the antiproliferative efficacy in a manner dependent of MDR1 expression in HCC cells. The synergistic antitumor effect of OSI-027 and doxorubicin was also observed in a HCC xenograft mouse model. Moreover, AKT was required for OSI-027-induced cell-cycle arrest and downregulation of MDR1. Our findings provide a rationale for dual mTORC1/mTORC2 inhibitors, such as OSI-027, as monotherapy or in combination with cytotoxic agents to treat HCC. Mol Cancer Ther; 14(8); 1805-15. ©2015 AACR.

Dual blockade of PI3K/AKT/mTOR (NVP-BEZ235) and Ras/Raf/MEK (AZD6244) pathways synergistically inhibit growth of primary endometrioid endometrial carcinoma cultures, whereas NVP-BEZ235 reduces tumor growth in the corresponding xenograft models

OBJECTIVES

Endometrial carcinoma (EC) is the most common gynecological cancer in the Western World. Treatment options are limited for advanced and recurrent disease. Therefore, new treatment options are necessary. Inhibition of the PI3K/AKT/mTOR and/or the Ras/Raf/MEK pathways is suggested to be clinically relevant. However, the knowledge about the effect of combination targeted therapy in EC is limited. The aim of this study was to investigate the effect of these therapies on primary endometrioid EC cell cultures in vitro and in vivo.

METHODS

Primary endometrioid EC cell cultures were incubated with Temsirolimus (mTORC1 inhibitor), NVP-BKM120 (pan-PI3K inhibitor), NVP-BEZ235 (pan-PI3K/mTOR inhibitor), or AZD6244 (MEK1/2 inhibitor) as single treatment. In vitro, the effect of NVP-BEZ235 with or without AZD6244 was determined for cell viability, cell cycle arrest, apoptosis induction, and cell signaling. In vivo, the effect of NVP-BEZ35 was investigated for 2 subcutaneous xenograft models of the corresponding primary cultures.

RESULTS

NVP-BEZ235 was the most potent PI3K/AKT/mTOR pathway inhibitor. NVP-BEZ235 and AZD6244 reduced cell viability and induced cell cycle arrest and apoptosis, by reduction of p-AKT, p-S6, and p-ERK levels. Combination treatment showed a synergistic effect. In vivo, NVP-BEZ235 reduced tumor growth and inhibited p-S6 expression. The effects of the compounds were independent of the mutation profile of the cell cultures used.

CONCLUSIONS

A synergistic antitumor effect was shown for NVP-BEZ235 and AZD6244 in primary endometrioid EC cells in vitro. In addition, NVP-BEZ235 induced reduction of tumor growth in vivo. Therefore, targeted therapies seem an interesting strategy to further evaluate in clinical trials.

The AKT inhibitor MK-2206 is cytotoxic in hepatocarcinoma cells displaying hyperphosphorylated AKT-1 and synergizes with conventional chemotherapy

Hepatocellular carcinoma (HCC) is one of the most common potentially lethal human malignancies worldwide. Advanced or recurrent HCC is frequently resistant to conventional chemotherapeutic agents and radiation. Therefore, targeted agents with tolerable toxicity are mandatory to improve HCC therapy and prognosis. In this neoplasia, the PI3K/Akt signaling network has been frequently shown to be aberrantly up-regulated. To evaluate whether Akt could represent a target for treatment of HCC, we studied the effects of the allosteric Akt inhibitor, MK-2206, on a panel of HCC cell lines characterized by different levels of Akt-1 activation. The inhibitor decreased cell viability and induced cell cycle arrest in the G₀/G₁ phase of the cell cycle, with a higher efficacy in cells with hyperphosphorylated Akt-1. Moreover, MK-2206 induced apoptosis, as documented by Annexin V labeling, and also caused autophagy, as evidenced by increased levels of the autophagy marker LC3A/B. Autophagy was shown to be a protective mechanism against MK-2206 cytotoxicity. MK-2206 down-regulated, in a concentration-dependent manner, the phosphorylation levels of Akt-1 synergizedand its downstream targets, GSK3 α/β and FOXO3A. MK-2206 synergized with doxorubicin, a chemotherapeutic drug widely used for HCC treatment. Our findings suggest that the use of Akt inhibitors, either alone or in combination with doxorubicin, may be considered as an attractive therapeutic regimen for the treatment of HCC.

Microtubule-targeting agents in oncology and therapeutic potential in hepatocellular carcinoma

In mammalian cells, microtubules are present both in interphase and dividing cells. In the latter, microtubules forming the mitotic spindle are highly dynamic and exquisitely sensitive to therapeutic inhibitors. Developed to alter microtubule function, microtubule-binding agents have been proven to be highly active as an anticancer treatment. Significant development of microtubule-binding agents has taken place in recent years, with newer anti-tubulin agents now showing novel properties of enhanced tumor specificity, reduced neurotoxicity, and insensitivity to chemoresistance mechanisms. Hepatocellular carcinoma remains one of the most difficult cancers to treat, with chemotherapies being relatively ineffective. There is now evidence to suggest that microtubule-binding agents may be effective in the treatment of hepatocellular carcinoma, especially when used in combination with mammalian target of rapamycin inhibitors. Preclinical models have suggested that the latter may be able to overcome resistance to microtubule binding agents. In this review article, recent developments of novel microtubule binding agents and their relevance to the treatment of hepatocellular carcinoma will be discussed.

Targeting the mTOR pathway in hepatocellular carcinoma: current state and future trends

Mechanistic target of rapamycin (mTOR) regulates cell growth, metabolism and aging in response to nutrients, cellular energy stage and growth factors. mTOR is frequently up-regulated in cancer including hepatocellular carcinoma (HCC) and is associated with bad prognosis, poorly differentiated tumors, and earlier recurrence. Blocking mTOR with rapamycin and first generation mTOR inhibitors, called rapalogs, has shown promising reduction of HCC tumor growth in preclinical models. Currently, rapamycin/rapalogs are used in several clinical trials for the treatment of advanced HCC, and as adjuvant therapy in HCC patients after liver transplantation and TACE. A second generation of mTOR pathway inhibitors has been developed recently and is being tested in various clinical trials of solid cancers, and has been used in preclinical HCC models. The results of series of clinical trials using mTOR inhibitors in HCC treatment will emerge in the near future.

Synergistic growth inhibition by acyclic retinoid and phosphatidylinositol 3-kinase inhibitor in human hepatoma cells

BACKGROUND

A malfunction of RXRα due to phosphorylation is associated with liver carcinogenesis, and acyclic retinoid (ACR), which targets RXRα, can prevent the development of hepatocellular carcinoma (HCC). Activation of PI3K/Akt signaling plays a critical role in the proliferation and survival of HCC cells. The present study examined the possible combined effects of ACR and LY294002, a PI3K inhibitor, on the growth of human HCC cells.

METHODS

This study examined the effects of the combination of ACR plus LY294002 on the growth of HLF human HCC cells.

RESULTS

ACR and LY294002 preferentially inhibited the growth of HLF cells in comparison with Hc normal hepatocytes. The combination of 1 μM ACR and 5 μM LY294002, in which the concentrations used are less than the IC₅₀ values of these agents, synergistically inhibited the growth of HLF, Hep3B, and Huh7 human HCC cells. These agents when administered in combination acted cooperatively to induce apoptosis in HLF cells. The phosphorylation of RXRα, Akt, and ERK proteins in HLF cells were markedly inhibited by treatment with ACR plus LY294002. Moreover, this combination also increased RXRE promoter activity and the cellular levels of RARβ and p21(CIP1), while decreasing the levels of cyclin D1.

CONCLUSION

ACR and LY294002 cooperatively increase the expression of RARβ, while inhibiting the phosphorylation of RXRα, and that these effects are associated with the induction of apoptosis and the inhibition of cell growth in human HCC cells. This combination might therefore be effective for the chemoprevention and chemotherapy of HCC.

Cell cycle-dependent activity of the novel dual PI3K-MTORC1/2 inhibitor NVP-BGT226 in acute leukemia

Background

Dysregulation of the PI3Kinase/AKT pathway is involved in the pathogenesis of many human malignancies. In acute leukemia, the AKT pathway is frequently activated, however mutations in the PI3K/AKT pathway are uncommon. In some cases, constitutive AKT activation can be linked to gain-of-function tyrosine kinase (TK) mutations upstream of the PI3K/AKT pathway. Inhibitors of the PI3K/AKT pathway are attractive candidates for cancer drug development, but so far clinical efficacy of PI3K inhibitors against various neoplasms has been moderate. Furthermore, specific MTORC1 inhibitors, acting downstream of AKT, have the disadvantage of activating AKT via feed-back mechanisms. We now evaluated the antitumor efficacy of NVP-BGT226, a novel dual pan-PI3K and MTORC1/2 inhibitor, in acute leukemia.

Methods

Native leukemia blasts were stained to analyze for AKT phosphorylation levels on a flow cytometer. Efficacy of NVP-BGT226 in comparison to a second dual inhibitor, NVP-BEZ235, was determined with regard to cellular proliferation, autophagy, cell cycle regulation and induction of apoptosis in in vitro and ex vivo cellular assays as well as on the protein level. An isogenic AKT-autoactivated Ba/F3 model, different human leukemia cell lines as well as native leukemia patient blasts were studied. Isobologram analyses were set up to calculate for (super) additive or antagonistic effects of two agents.

Results

We show, that phosphorylation of AKT is frequently augmented in acute leukemia. NVP-BGT226 as well as NVP-BEZ235 profoundly and globally suppress AKT signaling pathways, which translates into potent antiproliferative effects. Furthermore, NVP-BGT226 has potent proapoptotic effects in vitro as well as in ex vivo native blasts. Surprisingly and in contrast, NVP-BEZ235 leads to a profound G1/G0 arrest preventing significant induction of apoptosis. Combination with TK inhibitors, which are currently been tested in the treatment of acute leukemia subtypes, overcomes cell cycle arrest and results in (super)additive proapoptotic effects for NVP-BGT226 – but also for NVP-BEZ235. Importantly, mononuclear donor cells show lower phospho-AKT expression levels and consequently, relative insensitivity towards dual PI3K-MTORC1/2 inhibition.

Conclusions

Our data suggest a favorable antileukemic profile for NVP-BGT226 compared to NVP-BEZ235 – which provides a strong rationale for clinical evaluation of the dual PI3K-MTORC1/2 inhibitor NVP-BGT226 in acute leukemia.