A PDK-1 allosteric agonist neutralizes insulin signaling derangements and beta-amyloid toxicity in neuronal cells and in vitro.

The Alzheimer's brain is affected by multiple pathophysiological processes, which include a unique, organ-specific form of insulin resistance that begins early in its course. An additional complexity arises from the four-fold risk of Alzheimer's Disease (AD) in type 2 diabetics, however there is no definitive proof of causation. Several strategies to improve brain insulin signaling have been proposed and some have been clinically tested. We report findings on a small allosteric molecule that reverses several indices of insulin insensitivity in both cell culture and in vitro models of AD that emphasize the intracellular accumulation of ß-amyloid (Aßi). PS48, a chlorophenyl pentenoic acid, is an allosteric activator of PDK-1, which is an Akt-kinase in the insulin/PI3K pathway. PS48 was active at 10 nM to 1 µM in restoring normal insulin-dependent Akt activation and in mitigating Aßi peptide toxicity. Synaptic plasticity (LTP) in prefrontal cortical slices from normal rat exposed to Aß oligomers also benefited from PS48. During these experiments, neither overstimulation of PI3K/Akt signaling nor toxic effects on cells was observed. Another neurotoxicity model producing insulin insensitivity, utilizing palmitic acid, also responded to PS48 treatment, thus validating the target and indicating that its therapeutic potential may extend outside of ß-amyloid reliance. The described in vitro and cell based-in vitro coupled enzymatic assay systems proved suitable platforms to screen a preliminary library of new analogs.

Rosmarinic Acid Regulates Microglial M1/M2 Polarization via the PDPK1/Akt/HIF Pathway Under Conditions of Neuroinflammation.

Microglia are resident macrophage-like cells in the central nervous system (CNS). The induction of microglial activation dampens neuroinflammation-related diseases by promoting microglial (re)polarization to the anti-inflammatory (M2) phenotype and can serve as a potential therapeutic approach. Mitochondrial respiration and metabolic reprogramming are required for the anti-inflammatory response of M2 macrophages. However, whether these mitochondrial-dependent pathways are involved in microglial (re)polarization to the anti-inflammatory (M2) phenotype under conditions of lipopolysaccharide (LPS)-induced neuroinflammation remains unclear. Moreover, the mechanisms that coordinate mitochondrial respiration and the functional reprogramming of microglial cells have not been fully elucidated. Rosmarinic acid (RA) possesses antioxidative and anti-inflammatory activities, and we previously reported that RA markedly suppresses LPS-stimulated M1 microglial activation in mice. In this study, we found that RA suppresses M1 microglial polarization and promotes microglial polarization to the M2 phenotype under conditions of neuroinflammation. We identified an increase in mitochondrial respiration and found that metabolic reprogramming is required for the RA-mediated promotion of microglial polarization to the M2 phenotype under LPS-induced neuroinflammation conditions. Hypoxia-inducible factor (HIF) subunits are the key effector molecules responsible for the effects of RA on the restoration of mitochondrial function, metabolic reprogramming, and phenotypic polarization to M2 microglia. The phosphoinositide-dependent protein kinase 1 (PDPK1)/Akt/mTOR pathway is involved in the RA-mediated regulation of HIF expression and increase in M2 marker expression. We propose that the inhibition of PDPK1/Akt/HIFs by RA might be a potential therapeutic approach for inhibiting neuroinflammation through the regulation of microglial M1/M2 polarization. Graphical abstract Schematic of the mechanism through which RA suppresses LPS-induced neuroinflammation by promoting microglial polarization to the M2 phenotype via PDPK1/Akt/HIFs. The bold arrows indicate the direction of the effects of RA (i.e., inhibitory or promoting effects on cytokines or mediators).

Effects of inhibiting PDK­1 expression in bone marrow mesenchymal stem cells on osteoblast differentiation in vitro.

Osteoblasts are the main functional cells in bone formation, which are responsible for the synthesis, secretion and mineralization of bone matrix. The PI3K/AKT signaling pathway is strongly associated with the differentiation and survival of osteoblasts. The 3­phosphoinositide­dependent protein kinase­1 (PDK­1) protein is considered the master upstream lipid kinase of the PI3K/AKT cascade. The present study aimed to investigate the role of PDK­1 in the process of mouse osteoblast differentiation in vitro. In the BX­912 group, BX­912, a specific inhibitor of PDK­1, was added to osteoblast induction medium (OBM) to treat bone marrow mesenchymal stem cells (BMSCs), whereas the control group was treated with OBM alone. Homozygote PDK1flox/flox mice were designed and generated, and were used to obtain BMSCsPDK1flox/flox. Subsequently, an adenovirus containing Cre recombinase enzyme (pHBAd­cre­EGFP) was used to disrupt the PDK­1 gene in BMSCsPDK1flox/flox; this served as the pHBAd­cre­EGFP group and the efficiency of the disruption was verified. Western blot analysis demonstrated that the protein expression levels of phosphorylated (p)­PDK1 and p­AKT were gradually increased during the osteoblast differentiation process. Notably, BX­912 treatment and disruption of the PDK­1 gene with pHBAd­cre­EGFP effectively reduced the number of alkaline phosphatase (ALP)­positive cells and the optical density value of ALP activity, as well as the formation of cell mineralization. The mRNA expression levels of PDK­1 in the pHBAd­cre­EGFP group were significantly downregulated compared with those in the empty vector virus group on days 3­7. The mRNA expression levels of the osteoblast­related genes RUNX2, osteocalcin and collagen I were significantly decreased in the BX­912 and pHBAd­cre­EGFP groups on days 7 and 21 compared with those in the control and empty vector virus groups. Overall, the results indicated that BX­912 and disruption of the PDK­1 gene in vitro significantly inhibited the differentiation and maturation of osteoblasts. These experimental results provided an experimental and theoretical basis for the role of PDK­1 in osteoblasts.

Inhibition of 3-phosphoinositide-dependent protein kinase 1 (PDK1) can revert cellular senescence in human dermal fibroblasts.

Cellular senescence is defined as a stable, persistent arrest of cell proliferation. Here, we examine whether senescent cells can lose senescence hallmarks and reenter a reversible state of cell-cycle arrest (quiescence). We constructed a molecular regulatory network of cellular senescence based on previous experimental evidence. To infer the regulatory logic of the network, we performed phosphoprotein array experiments with normal human dermal fibroblasts and used the data to optimize the regulatory relationships between molecules with an evolutionary algorithm. From ensemble analysis of network models, we identified 3-phosphoinositide-dependent protein kinase 1 (PDK1) as a promising target for inhibitors to convert the senescent state to the quiescent state. We showed that inhibition of PDK1 in senescent human dermal fibroblasts eradicates senescence hallmarks and restores entry into the cell cycle by suppressing both nuclear factor κB and mTOR signaling, resulting in restored skin regeneration capacity. Our findings provide insight into a potential therapeutic strategy to treat age-related diseases associated with the accumulation of senescent cells.

Phosphoinositide-dependent Kinase-1 (PDPK1) regulates serum/glucocorticoid-regulated Kinase 3 (SGK3) for prostate cancer cell survival.

Prostate cancer (PCa) is the most common malignancy and is the second leading cause of cancer among men globally. Using a kinome-wide lentiviral small-hairpin RNA (shRNA) library screen, we identified phosphoinositide-dependent kinase-1 (PDPK1) as a potential mediator of cell survival in PCa cells. We showed that knock-down of endogenous human PDPK1 induced significant tumour-specific cell death in PCa cells (DU145 and PC3) but not in the normal prostate epithelial cells (RWPE-1). Further analyses revealed that PDPK1 mediates cancer cell survival predominantly via activation of serum/glucocorticoid-regulated kinase 3 (SGK3). Knock-down of endogenous PDPK1 in DU145 and PC3 cells significantly reduced SGK3 phosphorylation while ectopic expression of a constitutively active SGK3 completely abrogated the apoptosis induced by PDPK1. In contrast, no such effect was observed in SGK1 and AKT phosphorylation following PDPK1 knock-down. Importantly, PDPK1 inhibitors (GSK2334470 and BX-795) significantly reduced tumour-specific cell growth and synergized docetaxel sensitivity in PCa cells. In summary, our results demonstrated that PDPK1 mediates PCa cells' survival through SGK3 signalling and suggest that inactivation of this PDPK1-SGK3 axis may potentially serve as a novel therapeutic intervention for future treatment of PCa.

Ligand Based Pharmacophore Modeling Followed by Biological Screening Lead to Discovery of Novel PDK1 Inhibitors as Anticancer Agents.

BACKGROUND: Phosphoinositide-Dependent Kinase-1 (PDK1) is a serine/threonine kinase, which belongs to AGC kinase family required by cancer cells. METHODS: Pharmacophoric space of 86 PDK1 inhibitors using six diverse sets of inhibitors was explored to identify high-quality pharmacophores. The best combination of pharmacophoric models and physicochemical descriptors was selected by genetic algorithm-based QSAR analysis that can elucidate the variation of bioactivity within the training inhibitors. Two successful orthogonal pharmacophores emerged in the optimum QSAR equation (r2 69 = 0.90, r2 LOO= 0.86, F= 51.92, r2 PRESS against 17 test inhibitors = 0.79). Receiver Operating Characteristic (ROC) curve analyses were used to estimate the QSAR-selected pharmacophores. RESULTS: 5 out of 11 compounds tested had shown potential intracellular PDK1 inhibition with the highest inhibition percent for compounds 92 and 93 as follows; 90 and 92% PDK1 inhibition, respectively. CONCLUSION: PDK1 inhibitors are potential anticancer agents that can be discovered by combination method of ligand based design with QSAR and ROC analysis.

Novel reciprocal interaction of lncRNA HOTAIR and miR-214-3p contribute to the solamargine-inhibited PDPK1 gene expression in human lung cancer.

Solamargine (SM) has been shown to have anti-cancer properties. However, the underlying mechanism involved remains undetermined. We showed that SM inhibited the growth of non-small cell lung cancer (NSCLC) cells, which was enhanced in cells with silencing of long non-coding RNA (lncRNA) HOX transcript antisense RNA (HOTAIR), while it overcame by overexpression of HOTAIR. In addition, SM increased the expression of miR-214-3p and inhibited 3-phosphoinositide-dependent protein kinase-1 (PDPK1) gene expression, which was strengthened by miR-214-3p mimics. Intriguingly, HOTAIR could directly bind to miR-214-3p and sequestered miR-214-3p from the target gene PDPK1. Intriguingly, overexpression of PDPK1 overcame the effects of SM on miR-214-3p expressions and neutralized the SM-inhibited cell growth. Similar results were observed in vivo. In summary, our results showed that SM-inhibited NSCLC cell growth through the reciprocal interaction between HOTAIR and miR-214-3p, which ultimately suppressed PDPK1 gene expression. HOTAIR effectively acted as a competing endogenous RNA (ceRNA) to stimulate the expression of target gene PDPK1. These complex interactions and feedback mechanisms contribute to the overall effect of SM. This unveils a novel molecular mechanism underlying the anti-cancer effect of SM in human lung cancer.

Discovery of SBF1 as an allosteric inhibitor targeting the PIF-pocket of 3-phosphoinositide-dependent protein kinase-1.

3-phosphoinositide-dependent protein kinase-1 (PDK1) plays a crucial role in the signal transduction of massive growth-related protein kinases. In this work, a computational study has been performed to investigate the binding pose of the hydrolyzed product of SBF1 (SBF1-) with PDK1. The binding pose was predicted by Vina and was further refined in a molecular dynamics simulation. For comparison, four published low molecular weight compounds (PS48, PS171, PS182, and PS210) binding with PDK1 were also studied. SBF1- was anchored in the PIF-pocket of PDK1 with salt bridge interaction using its carboxylate moiety, which is a common feature among the known ligands. Hydrogen bonds to THR148 and vdW interactions with GLN150 also have contributions to the association affinity. The allosteric regulation on PDK1 via the binding of SBF1- was further addressed. The binding affinity of SBF1- in complex with PDK1 is comparable to those of PS171 and PS182, with an estimated IC50 in a range from 2.0 to 10.0 µ molar. Comparison between the free energy profiles with the presence or absence of SBF1- in the binding pocket indicates that the binding of SBF1- enhances the hinge motion and suppresses the fluctuation of the end-to-end distance in α B of PDK1. These results demonstrate that SBF1- is a promising allosteric regulator of PDK1 targeting the PIF-binding pocket and can serve as a new scaffold template for the design of new drugs targeting PDK1.

Preclinical validation of 3-phosphoinositide-dependent protein kinase 1 inhibition in pancreatic cancer.

BACKGROUND: The very aggressive nature and low survival rate of pancreatic ductal adenocarcinoma (PDAC) dictates the necessity to find novel efficacious therapies. Recent evidence suggests that phosphoinositide 3-kinase (PI3K) and 3-phosphoinositide-dependent protein kinase 1 (PDK1) are key effectors of oncogenic KRAS in PDAC. Herein, we report the role and mechanism of action of PDK1, a protein kinase of the AGC family, in PDAC. METHODS: PDAC cell lines were treated with selective PDK1 inhibitors or transfected with specific PDK1-targeting siRNAs. In vitro and in vivo assays were performed to investigate the functional role of PDK1 in PDAC. Specifically, anchorage-dependent and anchorage-independent growth was assessed in PDAC cells upon inhibition or downregulation of PDK1. Detailed investigation of the effect of PDK1 inhibition/downregulation on specific signalling pathways was also performed by Western blotting analysis. A xenograft tumour mouse model was used to determine the effect of pharmacological inhibition of PDK1 on PDAC cells growth in vivo. RESULTS: Treatment with specific inhibitors of PDK1 impaired anchorage-dependent and anchorage-independent growth of pancreatic cancer cell lines, as well as pancreatic tumour growth in a xenograft model. Mechanistically, inhibition or downregulation of PDK1 resulted in reduced activation of the serum/glucocorticoid regulated kinase family member 3 and subsequent reduced phosphorylation of its target N-Myc downstream regulated 1. Additionally, we found that combination of sub-optimal concentrations of inhibitors selective for PDK1 and the class IB PI3K isoform p110γ inhibits pancreatic cancer cell growth and colonies formation more potently than each single treatment. CONCLUSIONS: Our data indicate that PDK1 is a suitable target for therapeutic intervention in PDAC and support the clinical development of PDK1 inhibitors for PDAC.

A patent update on PDK1 inhibitors (2015-present).

INTRODUCTION: 3-Phosphoinositide-dependent kinase 1 (PDK1), the 'master kinase of the AGC protein kinase family', plays a key role in cancer development and progression. Although it has been rather overlooked, in the last decades a growing number of molecules have been developed to effectively modulate the PDK1 enzyme. AREAS COVERED: This review collects different PDK1 inhibitors patented from October 2014 to December 2018. The molecules have been classified on the basis of the chemical structure/type of inhibition, and for each general structure, examples have been discussed in extenso. EXPERT OPINION: The role of PDK1 in cancer development and progression as well as in metastasis formation and in chemoresistance has been confirmed by many studies. Therefore, the pharmaceutical discovery in both public and private institutions is still ongoing despite the plentiful molecules already published. The majority of the new molecules synthetized interact with binding sites different from the ATP binding site (i.e. PIF pocket or DFG-out conformation). However, many researchers are still looking for innovative PDK1 modulation strategy such as combination of well-known inhibitory agents or multitarget ligands, aiming to block, together with PDK1, other different critical players in the wide panorama of proteins involved in tumor pathways.

Repression of PDK1- and LncRNA HOTAIR-Mediated EZH2 Gene Expression Contributes to the Enhancement of Atractylenolide 1 and Erlotinib in the Inhibition of Human Lung Cancer Cells.

BACKGROUND/AIMS: We previously showed that the major bioactive compound of Atractylodes macrocephula Koidz atractylenolide 1 (ATL-1) inhibited human lung cancer cell growth by suppressing the gene expression of 3-Phosphoinositide dependent protein kinase-1 (PDK1 or PDPK1). However, the potentially associated molecules and downstream effectors of PDK1 underlying this inhibition, particularly the mechanism for enhancing the anti-tumor effects of epidermal growth factor receptor-tyrosine-kinase inhibitors (EGFR-TKIs), remain unknown. METHODS: Cell viability and cell cycle distribution were measured using 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) and flow cytometry assays, respectively. Western blot analyses were performed to examine the protein expressions of PDK1 and of zeste homolog 2 (EZH2). The levels of long non-coding RNA (lncRNA) and HOX transcript antisense RNA (HOTAIR) were examined via qRT-PCR. RNA-binding protein immunoprecipitation assays were used to analyze HOTAIR interaction with EZH2. The promoter activity of the EZH2 gene was determined using Secrete-Pair Dual Luminescence Assay Kit. Exogenous expressions of PDK1, HOTAIR, and EZH2 were conducted via transient transfection assays. A xenografted tumor model was used to further evaluate the effect of ATL-1 in the presence or absence of erlotinib in vivo. RESULTS: We showed that the combination of ATL-1 and EGFR-TKI erlotinib further inhibited growth and induced cell arrest of the human lung cancer cells, determined by both MTT and flow cytometry assays. ATL-1 inhibited the protein expression and the promoter activity of EZH2, which was reversed in cells with PDK1 overexpression. Interestingly, ATL-1 inhibited the expression levels of HOTAIR. While silencing HOTAIR inhibited the expressions of PDK1 and EZH2, overexpression of HOTAIR reduced the ATL-1-reduced PDK1 and EZH2 protein expressions and EZH2 promoter activity. In addition, ATL-1 reduced the HOTAIR binding to the EZH2 protein. Moreover, we found that exogenously expressed EZH2 antagonized the effect of ATL-1 on cell growth inhibition. Consistent with the in vitro results, ATL-1 inhibited tumor growth and the expression levels of HOTAIR, protein expressions of EZH2 and PDK1 in vivo. Importantly, there was synergy of the combination of ATL-1 and erlotinib in this process. CONCLUSION: Here, we provide the first evidence that ATL-1 inhibits lung cancer cell growth through inhibiting not only the PDK1 but also the lncRNA HOTAIR, which results in the reduction of one downstream effector EZH2 expression. The novel interplay between the HOTAIR and EZH2, as well as repressions of the PDK1 and HOTAIR coordinate the overall effects of ATL-1. Importantly, the combination of ATL-1 and EGFR-TKI erlotinib exhibits synergy. Thus, targeting the PDK1- and HOTAIR-mediated downstream molecule EZH2 by the combination of ATL-1 and erlotinib potentially facilitates the development of an additional novel strategy to combat lung cancer.

Long non­coding RNA HR1 participates in the expression of SREBP­1c through phosphorylation of the PDK1/AKT/FoxO1 pathway.

Sterol regulatory element binding protein­1c (SREBP­1c), which serves an essential role in the process of fat synthesis, is a key adjustment factor that regulates the dynamic balance of lipid metabolism. SREBP­1c activates the transcription of multiple genes encoding for enzymes involved in the synthesis of triglycerides (TG) and fatty acids (FA) and accelerates lipid synthesis. Previous analysis indicated that long non­coding RNA HCV regulated 1 (lncHR1) participates in lipid metabolism in vivo and regulates the level of SREBP­1c protein. However, the mechanism of lncHR1 in regulating SREBP­1c levels has not been revealed. In the present study, a fatty degeneration cell model was used to study how lncHR1 regulates the SREBP­1c protein at the cellular level. Furthermore TG accumulation was assessed according to morphological analysis. Reverse transcription­quantitative polymerase chain reaction and western blotting were used to detected the expression of SREBP­1c. An activator and an inhibitor of phosphoinositide 3­kinase/AKT phosphorylation (IGF­1 and LY294002, respectively) were used to study the effect of lncHR1 on this pathway. It was verified that lncHR1 regulated SREBP­1c levels and the phosphorylation of AKT in the steatosis cell model. Detailed molecular mechanisms mediated by lncHR1 were associated with the phosphorylation AKT/FoxO1 in Huh7 cell lines. Simultaneously, lncHR1 affected the location of FoxO1 inside and outside of the nucleus. Furthermore, the phosphorylation of PDK1 upstream of AKT was regulated through overexpression or knockdown lncHR1, as determined by western blotting. Taken together, these data show that lncHR1 inhibits SREBP­1c levels through the phosphorylation of the PDK1/AKT/FoxO1 axis.

Effects of intracellular iron overload on cell death and identification of potent cell death inhibitors.

Iron overload causes many diseases, while the underlying etiologies of these diseases are unclear. Cell death processes including apoptosis, necroptosis, cyclophilin D-(CypD)-dependent necrosis and a recently described additional form of regulated cell death called ferroptosis, are dependent on iron or iron-dependent reactive oxygen species (ROS). However, whether the accumulation of intracellular iron itself induces ferroptosis or other forms of cell death is largely elusive. In present study, we study the role of intracellular iron overload itself-induced cell death mechanisms by using ferric ammonium citrate (FAC) and a membrane-permeable Ferric 8-hydroxyquinoline complex (Fe-8HQ) respectively. We show that FAC-induced intracellular iron overload causes ferroptosis. We also identify 3-phosphoinositide-dependent kinase 1 (PDK1) inhibitor GSK2334470 as a potent ferroptosis inhibitor. Whereas, Fe-8HQ-induced intracellular iron overload causes unregulated necrosis, but partially activates PARP-1 dependent parthanatos. Interestingly, we identify many phenolic compounds as potent inhibitors of Fe-8HQ-induced cell death. In conclusion, intracellular iron overload-induced cell death form might be dependent on the intracellular iron accumulation rate, newly identified cell death inhibitors in our study that target ferroptosis and unregulated oxidative cell death represent potential therapeutic strategies against iron overload related diseases.

PDK1 governs thromboxane generation and thrombosis in platelets by regulating activation of Raf1 in the MAPK pathway.

Essentials Phosphoinositide 3-kinase and MAPK pathways crosstalk via PDK1. PDK1 is required for adenosine diphosphate-induced platelet activation and thromboxane generation. PDK1 regulates RAF proto-oncogene Ser/Thr kinase (Raf1) activation in the MAPK pathway. Genetic ablation of PDK1 protects against platelet-dependent thrombosis in vivo. SUMMARY: Background Platelets are dynamic effector cells with functions that span hemostatic, thrombotic and inflammatory continua. Phosphoinositide-dependent protein kinase 1 (PDK1) regulates protease-activated receptor 4-induced platelet activation and thrombus formation through glycogen synthase kinase3ß. However, whether PDK1 also signals through the ADP receptor and its functional importance in vivo remain unknown. Objective To establish the mechanism of PDK1 in ADP-induced platelet activation and thrombosis. Methods We assessed the role of PDK1 on 2MeSADP-induced platelet activation by measuring aggregation, thromboxane generation and phosphorylation events in the presence of BX-795, which inhibits PDK1, or by using platelet-specific PDK1 knockout mice and performing western blot analysis. PDK1 function in thrombus formation was assessed with an in vivo pulmonary embolism model. Results PDK1 inhibition with BX-795 reduced 2-methylthio-ADP (2MeSADP)-induced aggregation of human and murine platelets by abolishing thromboxane generation. Similar results were observed in pdk1-/- mice. PDK1 was also necessary for the phosphorylation of mitogen-activated protein kinase kinase 1/2 (MEK1/2), extracellular signal-regulated kinase 1/2, and cytosolic phospholipase A2, indicating that PDK1 regulates an upstream kinase in the mitogen-activated protein kinase (MAPK) pathway. We next determined that this upstream kinase is Raf-1, a serine/threonine kinase that is necessary for the phosphorylation of MEK1/2, as pharmacological inhibition and genetic ablation of PDK1 were sufficient to prevent Raf1 phosphorylation. Furthermore, in vivo inhibition or genetic ablation of PDK1 protected mice from collagen/epinephrine-induced pulmonary embolism. Conclusion PDK1 governs thromboxane generation and thrombosis in platelets that are stimulated with 2MeSADP by regulating activation of the MAPK pathway.

Chemoresistance in ovarian cancer: exploiting cancer stem cell metabolism.

Ovarian cancer is most deadly gynecologic malignancies worldwide. Chemotherapy is the mainstay treatment for ovarian cancer. Despite the initial response is promising, frequent recurrence in patients with advanced diseases remains a therapeutic challenge. Thus, understanding the biology of chemoresistance is of great importance to overcome this challenge and will conceivably benefit the survival of ovarian cancer patients. Although mechanisms underlying the development of chemoresistance are still ambiguous, accumulating evidence has supported an integral role of cancer stem cells (CSCs) in recurrence following chemotherapy. Recently, tumor metabolism has gained interest as a reason of chemoresistance in tumors and chemotherapeutic drugs in combination with metabolism targeting approaches has been found promising in overcoming therapeutic resistance. In this review, we will summarize recent studies on CSCs and metabolism in ovarian cancer and discuss possible role of CSCs metabolism in chemoresistance.

Suppression of Fatty Acid and Triglyceride Synthesis by the Flavonoid Orientin through Decrease of C/EBPδ Expression and Inhibition of PI3K/Akt-FOXO1 Signaling in Adipocytes.

Plant flavonoids have a variety of biological properties. In a previous study, we found that the tea of the Asian dayflower, Commelina communis L., decreased the body weight gain in high-fat diet-fed mice. In this study, we studied the anti-adipogenic ability of a flavonoid orientin that is found in abundance in C. communis. Orientin repressed the accumulation of intracellular triglyceride (TG) in mouse adipocyte 3T3-L1 cells. The treatment with orientin also decreased the mRNA levels of the genes involved in adipogenesis, lipogenesis, lipolysis, and TG synthesis, and reduced the release of glycerol. Orientin lowered the expression of CCAAT/enhancer binding protein (C/EBP) δ in the early stage of adipogenesis, leading to a decrease in the expression of the adipogenic master transcription factors such as peroxisome proliferator-activated receptor (PPAR) γ and C/EBPα. Moreover, the anti-adipogenic effect of orientin repressed the phosphorylation of Akt and subsequent phosphorylation of forkhead box protein O1 (FOXO1), which inhibits the transcription of the Ppar gene. These results indicate that a plant flavonoid orientin suppressed the expression of the Pparγ gene through repression of C/ebpδ expression and inhibition of the phosphoinositide 3-kinase /Akt-FOXO1 signaling in adipocytes.

Phosphoinositide-dependent protein kinase 1 is a potential novel therapeutic target in mantle cell lymphoma.

Mantle cell lymphoma (MCL) is a relatively rare subtype of B-cell non-Hodgkin lymphoma (NHL) that has a poor prognosis despite recent advances in immunochemotherapy and molecular targeted therapeutics against NHL. Therefore, the development of a new therapeutic strategy for MCL is urgently needed. In this study, we show for the first time that 3-phosphoinositide-dependent protein kinase 1 (PDPK1), an oncogenic serine-threonine protein kinase, is commonly expressed in its phosphorylated active form in patient-derived tumor cells of various types of B-cell NHL cells, including diffuse large B-cell lymphoma, follicular lymphoma, and MCL. Blockade of PDPK1 activity by small-molecule inhibitors specific for PDPK1 (BX-912 and GSK2334470) or by RNA interference exerted antiproliferative effects in all four MCL-derived cell lines examined and these growth-inhibitory effects were mediated by both induction of apoptosis and G2/M cell cycle blockade. In addition, blockade of PDPK1 led to inactivation of its downstream effector kinase RSK2, but not AKT, suggesting the importance of the PDPK1/RSK2 signaling pathway in the proliferation and survival of MCL cells. Finally, when combined with anticancer agents, including genotoxic agents, a proteasome inhibitor, and a BH3 mimetic in vitro, the PDPK1 inhibitor BX-912 showed additive growth-inhibitory effects against MCL-derived cell lines in most settings. In particular, the combination of BX-912 and ABT-263, a BH3 mimetic, resulted in the enhancement of the induction of apoptosis. In conclusion, our results suggest that PDPK1 is a potential novel therapeutic target in MCL and indicate that clinical development of PDPK1-targeted therapy for MCL is desirable.

PDK1 inhibitor GSK2334470 exerts antitumor activity in multiple myeloma and forms a novel multitargeted combination with dual mTORC1/C2 inhibitor PP242.

A deeper understanding of the complex pathogenesis of multiple myeloma (MM) continues to lead to novel therapeutic approaches. Prior studies suggest that 3-phosphoinositide-dependent kinase 1 (PDK1) is expressed and active, acting as a crucial regulator of molecules that are essential for myelomagenesis. In the present study, we show that GSK2334470 (GSK-470), a novel and highly specific inhibitor of PDK1, induces potent cytotoxicity in MM cell lines including Dexamethasone-resistant cell line, but not in human normal cells. Insulin-like growth factor-1 could not rescue GSK-470-induced cell death. Moreover, GSK-470 down-modulates phosphor-PDK1, thereby inhibiting downstream phosphor-AKT at Thr308 and mTOR complex 1 (mTORC1) activity. However, GSK-470 could not affect mTORC2 activity and phosphor-AKT at Ser473. RPMI 8226 and OPM-2 cells with low expression of PTEN show relative resistant to GSK-470. Knockout of PTEN by shRNA resulted in a partial reversion of GSK-470-mediated growth inhibition, whereas overexpression of PTEN enhanced myeloma cell sensitivity to GSK-470, suggesting that the sensitivity to GSK-470 is correlated with PTEN expression statue in MM cells. Combining PP242, a dual mTORC1/C2 inhibitor, with GSK-470, had greater antimyeloma activity than either one alone in vitro and in MM xenograft model established in immunodeficient mice. In particular, this combination was able to result in a complete inhibition of mTORC1/C2 and full activity of AKT. Together, these findings raise the possibility that combining PDK1 antagonist GSK-470 with mTORC1/C2 inhibitors may represent a novel strategy against MM including drug-resistant myeloma, regardless of PTEN expression status.

PDK1 promotes the inflammatory progress of fibroblast-like synoviocytes by phosphorylating RSK2.

This study investigated the role of PDK1 in inflammatory response which is initiated by TNF-α and analyzed the association between PDK1 and RSK2. TNF-α were added into MH7A cells to induce inflammation condition. Through overexpressing or suppressing PDK1 in MH7A cells, the role of PDK1 in cell invasiveness and inflammatory factors was determined. Levels of MMPs protein and inflammatory cytokines were assessed with PDK1 siRNA and TNF-α treatment. Inhibition of RSK2 was used to investigate the function of RSK2 on PDK1-induced inflammation. The phosphorylation of RSK2 was detected when PDK1 was inhibited. Luciferase reporter assay was performed to detect the transcriptional activity of NF-κB. We found highly expressed PDK1 could promote cell invasion and secretion of IL-1ß and IL-6 in MH7A cells. Inhibition of RSK2 reduced the PDK1-induced cell invasion and cytokines secretion in MH7A cells. In response to TNF-α, PDK1 could phosphorylate RSK2 and activated RSK2, then promoting the activation of NF-κB. This may be a possible therapeutic option of rheumatoid arthritis.

Relationship between PDK1 and contraction in carotid arteries in Goto-Kakizaki rat, a spontaneous type 2 diabetic animal model.

We studied the relationship between 3-phosphoinositide-dependent protein kinase 1 (PDK1) and contractions induced by serotonin, phenylephrine, and thromboxane A2 mimetic (U46619) in the presence of nitric oxide synthase inhibitor in the carotid arteries of Goto-Kakizaki (GK) rats, a spontaneous type 2 diabetic model, in the chronic stage of disease. Serotonin-induced contraction was greater in the GK rats than in the control Wistar rats. A specific PDK1 inhibitor (GSK2334470) decreased the serotonin-induced contraction in the GK rats but not in the Wistar rats, and the difference in such contraction was abolished with this treatment. In GK rats, phenylephrine-induced contraction exhibited a leftward shift and U46619-induced contraction was greater still. Phenylephrine- and U46619-induced contractions were reduced by GSK2334470 in both groups. These results suggest, for the first time, that the contribution of PDK1 is different among 3 vasoconstrictors and that PDK1 contributed to increased serotonin-induced contraction in the carotid arteries of GK rats.