Selective 3-Phosphoinositide-Dependent Kinase 1 (PDK1) Inhibitors: Dissecting the Function and Pharmacology of PDK1

3-Phosphoinositide-Dependent Kinase 1 as a Therapeutic Target for Treating Diabetes

The role of 3-phosphoinositide-dependent kinase 1 (PDK1) has been welldocumented in the development of diabetes. This review offers a thorough examination of its composition and associated routes, specifically focusing on insulin signaling and glucose processing. By examining the precise connection between PDK1 and diabetes, various strategies specifically targeting PDK1 were also investigated. Additionally, recent discoveries from mouse models were compiled where PDK1 was knocked out in certain tissues, which demonstrated encouraging outcomes for focused treatments despite the absence of any currently approved clinical PDK1 activators. Moreover, the dual nature of PDK1 activation was discussed, encompassing both anti-diabetic and pro-oncogenic effects. Hence, the development of a PDK1 modifier is of utmost importance, as it can activate anti-diabetic pathways while inhibiting pro-oncogenic pathways, thus aiding in the treatment of diabetes. In general, PDK1 presents a noteworthy opportunity for future therapeutic strategies in the treatment of diabetes.

FTO activates PD-L1 promotes immunosuppression in breast cancer via the m6A/YTHDF3/PDK1 axis under hypoxic conditions

INTRODUCTION

Altered epigenetic reprogramming enables breast cancer cells to adapt to hypoxic stress. Hypoxic microenvironment can alter immune cell infiltration and function, limiting the effectiveness of immunotherapy.

OBJECTIVES

The study aimed to identify how fat mass and obesity-associated protein (FTO) helps breast cancer cells cope with the hypoxic microenvironment and the mechanisms behind breast cancer cell resistance to tumor immunity.

METHODS

Clinical samples were utilized to analyze the impact of FTO on breast cancer progression and the effect of programmed cell death protein 1/ programmed cell death 1 ligand 1(PD-1/PD-L1) immune checkpoint inhibitor treatment. Utilized MeRIP-seq and mRNA-seq to analyze the downstream genes regulated by FTO under hypoxia. Methylation modification regulation of PDK1 by FTO was clarified using RIP. Then mouse models were utilized to analyze the efficacy of inhibiting FTO and 3-Phosphoinositide-dependent protein kinase 1(PDK1) in combination with PD-1/PD-L1 immune checkpoint inhibitor treatment.

RESULT

N6-Methyladenosine(m6A) demethylase FTO was transcriptionally activated by hypoxia inducible factor 1α(HIF-1α). PDK1 was identified as a potential target of FTO under hypoxic conditions through high-throughput sequencing. Mechanistically, overexpression of FTO decreases m6A modification sites on PDK1 mRNA, preventing YTH domain family 3(YTHDF3) from recognizing and binding to these sites, thereby inhibiting the degradation of PDK1 mRNA. Overexpression of PDK1 activates the AKT/STAT3 pathway, leading to enhanced PD-L1 expression. Targeting the FTO and PDK1-AKT pathways with FB23 and BX-912 inhibit breast cancer growth, enhance cytotoxic T lymphocyte (CTL) activity, and enhance the effectiveness of the PD-1/PD-L1 checkpoint inhibitor Atezolizumab.

CONCLUSION

This study reveals that HIF-1α promotes FTO transcription under hypoxic conditions, thereby increasing PD-L1 expression through the PDK1/AKT/STAT3 axis. Inhibition of FTO and PDK1 under hypoxic conditions could serve as a promising immunotherapeutic strategy for breast cancer.

Capturing Autoinhibited PDK1 Reveals the Linker's Regulatory Role, Informing Innovative Inhibitor Design

PDK1 is crucial for PI3K/AKT/mTOR and Ras/MAPK cancer signaling. It phosphorylates AKT in a PIP3-dependent but S6K, SGK, and RSK kinases in a PIP3-independent manner. Unlike its substrates, its autoinhibited monomeric state has been unclear, likely due to its low population time, and phosphorylation in the absence of PIP3 has been puzzling too. Here, guided by experimental data, we constructed models and performed all-atom molecular dynamics simulations. In the autoinhibited PDK1 conformation that resembles autoinhibited AKT, binding of the linker between the kinase and PH domains to the PIF-binding pocket promotes the formation of the Glu130-Lys111 salt bridge and weakens the association of the kinase domain with the PH domain, shifting the population from the autoinhibited state to states accessible to the membrane and its kinase substrates. The interaction of the substrates' hydrophobic motif and the PDK1 PIF-binding pocket facilitates the release of the autoinhibition even in the absence of PIP3. Phosphorylation of the serine-rich motif within the linker further attenuates the association of the PH domain with the kinase domain. These suggest that while the monomeric autoinhibited state is relatively stable, it can readily shift to its active, catalysis-prone state to phosphorylate its diverse substrates. Our findings reveal the PDK1 activation mechanism and discover the regulatory role of PDK1's linker, which lead to two innovative linker-based inhibitor strategies: (i) locking the autoinhibited PDK1 through optimization of the interactions of AKT inhibitors with the PH domain of PDK1 and (ii) analogs (small molecules or peptidomimetics) that mimic the linker interactions with the PIF-binding pocket.

A novel small molecule, CU05-1189, targeting the pleckstrin homology domain of PDK1 suppresses VEGF-mediated angiogenesis and tumor growth by blocking the Akt signaling pathway

Inhibition of angiogenesis is considered a promising therapeutic approach for cancer treatment. Our previous genetic research showed that the use of a cell-penetrating peptide to inhibit the pleckstrin homology (PH) domain of 3-phosphoinositide-dependent kinase 1 (PDK1) was a viable approach to suppress pathological angiogenesis. Herein, we synthesized and characterized a novel small molecule, CU05-1189, based on our prior study and present evidence for the first time that this compound possesses antiangiogenic properties both in vitro and in vivo. The computational analysis showed that CU05-1189 can interact with the PH domain of PDK1, and it significantly inhibited vascular endothelial growth factor (VEGF)-induced proliferation, migration, invasion, and tube formation in human umbilical vein endothelial cells without apparent toxicity. Western blot analysis revealed that the Akt signaling pathway was specifically inhibited by CU05-1189 upon VEGF stimulation, without affecting other VEGF receptor 2 downstream molecules or cytosolic substrates of PDK1, by preventing translocation of PDK1 to the plasma membrane. We also found that CU05-1189 suppressed VEGF-mediated vascular network formation in a Matrigel plug assay. More importantly, CU05-1189 had a good pharmacokinetic profile with a bioavailability of 68%. These results led to the oral administration of CU05-1189, which resulted in reduced tumor microvessel density and growth in a xenograft mouse model. Taken together, our data suggest that CU05-1189 may have great potential and be a promising lead as a novel antiangiogenic agent for cancer treatment.

The 3-phosphoinositide-dependent protein kinase 1 is an essential upstream activator of protein kinase A in malaria parasites

Cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) signalling is essential for the proliferation of Plasmodium falciparum malaria blood stage parasites. The mechanisms regulating the activity of the catalytic subunit PfPKAc, however, are only partially understood, and PfPKAc function has not been investigated in gametocytes, the sexual blood stage forms that are essential for malaria transmission. By studying a conditional PfPKAc knockdown (cKD) mutant, we confirm the essential role for PfPKAc in erythrocyte invasion by merozoites and show that PfPKAc is involved in regulating gametocyte deformability. We furthermore demonstrate that overexpression of PfPKAc is lethal and kills parasites at the early phase of schizogony. Strikingly, whole genome sequencing (WGS) of parasite mutants selected to tolerate increased PfPKAc expression levels identified missense mutations exclusively in the gene encoding the parasite orthologue of 3-phosphoinositide-dependent protein kinase-1 (PfPDK1). Using targeted mutagenesis, we demonstrate that PfPDK1 is required to activate PfPKAc and that T189 in the PfPKAc activation loop is the crucial target residue in this process. In summary, our results corroborate the importance of tight regulation of PfPKA signalling for parasite survival and imply that PfPDK1 acts as a crucial upstream regulator in this pathway and potential new drug target.

Investigation of Binding Characteristics of Phosphoinositide-dependent Kinase-1 (PDK1) Co-crystallized Ligands Through Virtual Pharmacophore Modeling Leading to Novel Anti-PDK1 Hits

BACKGROUND

3-Phosphoinositide Dependent Protein Kinase-1 (PDK1) is being lately considered as an attractive and forthcoming anticancer target. A Protein Data Bank (PDB) cocrystallized crystal provides not only rigid theoretical data but also a realistic molecular recognition data that can be explored and used to discover new hits.

OBJECTIVE

This incited us to investigate the co-crystallized ligands' contacts inside the PDK1 binding pocket via a structure-based receptor-ligand pharmacophore generation technique in Discovery Studio 4.5 (DS 4.5).

METHODS

Accordingly, 35 crystals for PDK1 were collected and studied. Every single receptorligand interaction was validated and the significant ones were converted into their corresponding pharmacophoric features. The generated pharmacophores were scored by the Receiver Operating Characteristic (ROC) curve analysis.

RESULTS

Consequently, 169 pharmacophores were generated and sorted, 11 pharmacophores acquired good ROC-AUC results of 0.8 and a selectivity value above 8. Pharmacophore 1UU3_2_01 was used in particular as a searching filter to screen NCI database because of its acceptable validity criteria and its distinctive positive ionizable feature. Several low micromolar PDK1 inhibitors were revealed. The most potent hit illustrated anti-PDK1 IC50 values of 200 nM with 70% inhibition against SW480 cell lines.

CONCLUSION

Eventually, the active hits were docked inside the PDK1 binding pocket and the recognition points between the active hits and the receptor were analyzed that led to the discovery of new scaffolds as potential PDK1 inhibitors.

The chemical diversity and structure-based discovery of allosteric modulators for the PIF-pocket of protein kinase PDK1

Phosphoinositide-dependent protein kinase-1 (PDK1) is an important protein in mediating the PI3K-AKT pathway and is thus identified as a promising target. The catalytic activity of PDK1 is tightly regulated by allosteric modulators, which bind to the PDK1 Interacting Fragment (PIF) pocket of the kinase domain that is topographically distinct from the orthosteric, ATP binding site. Allosteric modulators by attaching to the less conserved PIF-pocket have remarkable advantages such as higher selectivity, less side effect, and lower toxicity. Targeting allosteric PIF-pocket of PDK1 has become the focus of recent attention. In this review, we summarise the current advances in the structure-based discovery of PDK1 allosteric modulators. We will first present the three-dimensional structure of PDK1 and illustrate the allosteric regulatory mechanism of PDK1 through the modulation of the PIF-pocket. Then, the recent advances of PDK1 allosteric modulators targeting the PIF-pocket will be recapitulated detailly according to the structural similarity of allosteric modulators.

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.

Design, Synthesis and Biological Activity Evaluation of S-Substituted 1H-5-Mercapto-1,2,4-Triazole Derivatives as Antiproliferative Agents in Colorectal Cancer

Colon cancer is a widespread pathology with complex biochemical etiology based on a significant number of intracellular signaling pathways that play important roles in carcinogenesis, tumor proliferation and metastasis. These pathways function due to the action of key enzymes that can be used as targets for new anticancer drug development. Herein we report the synthesis and biological antiproliferative evaluation of a series of novel S-substituted 1H-3-R-5-mercapto-1,2,4-triazoles, on a colorectal cancer cell line, HT-29. Synthesized compounds were designed by docking based virtual screening (DBVS) of a previous constructed compound library against protein targets, known for their important role in colorectal cancer signaling: MEK1, ERK2, PDK1, VEGFR2. Among all synthesized structures, TZ55.7, which was retained as a possible PDK1 (phospholipid-dependent kinase 1) inhibitor, exhibited the most significant cytotoxic activity against HT-29 tumor cell line. The same compound alongside other two, TZ53.7 and TZ3a.7, led to a significant cell cycle arrest in both sub G0/G1 and G0/G1 phase. This study provides future perspectives for the development of new agents containing the 1,2,4-mercapto triazole scaffold with antiproliferative activities in colorectal cancer.

Kinome-Wide RNA Interference Screen Reveals a Role for PDK1 in Acquired Resistance to CDK4/6 Inhibition in ER-Positive Breast Cancer

Acquired resistance to cyclin-dependent kinases 4 and 6 (CDK4/6) small-molecule inhibitors in breast cancer arises through mechanisms that are yet uncharacterized. In this study, we used a kinome-wide siRNA screen to identify kinases that, when downregulated, yield sensitivity to the CDK4/6 inhibitor ribociclib. In this manner, we identified 3-phosphoinositide-dependent protein kinase 1 (PDK1) as a key modifier of ribociclib sensitivity in estrogen receptor-positive MCF-7 breast cancer cells. Pharmacologic inhibition of PDK1 with GSK2334470 in combination with ribociclib or palbociclib, another CDK4/6 inhibitor, synergistically inhibited proliferation and increased apoptosis in a panel of ER-positive breast cancer cell lines. Ribociclib-resistant breast cancer cells selected by chronic drug exposure displayed a relative increase in the levels of PDK1 and activation of the AKT pathway. Analysis of these cells revealed that CDK4/6 inhibition failed to induce cell-cycle arrest or senescence. Mechanistic investigations showed that resistant cells coordinately upregulated expression of cyclins A, E, and D1, activated phospho-CDK2, and phospho-S477/T479 AKT. Treatment with GSK2334470 or the CDK2 inhibitor dinaciclib was sufficient to reverse these events and to restore the sensitivity of ribociclib-resistant cells to CDK4/6 inhibitors. Ribociclib, in combination with GSK2334470 or the PI3Kα inhibitor alpelisib, decreased xenograft tumor growth more potently than each drug alone. Taken together, our results highlight a role for the PI3K-PDK1 signaling pathway in mediating acquired resistance to CDK4/6 inhibitors. Cancer Res; 77(9); 2488-99. ©2017 AACR.

Locking PDK1 in DFG-out conformation through 2-oxo-indole containing molecules: Another tools to fight glioblastoma

The phosphoinositide-dependent kinase-1 (PDK1) is one of the main components of the PI3K/Akt pathway. Also named the "master kinase" of the AGC family, PDK1 plays a critical role in tumorigenesis, by enhancing cell proliferation and inhibiting apoptosis, as well as in cell invasion and metastasis formation. Although there have been done huge efforts in discovering specific compounds targeting PDK1, nowadays no PDK1 inhibitor has yet entered the clinic. With the aim to pick out novel and potent PDK1 inhibitors, herein we report the design and synthesis of a new class of molecules obtained by merging the 2-oxo-indole nucleus with the 2-oxo-pyridonyl fragment, two moieties with high affinity for the PDK1 hinge region and its DFG-out binding site, respectively. To this purpose, a small series of compounds were synthesised and a tandem application of docking and Molecular Dynamic (MD) was employed to get insight into their mode of binding. The OXID-pyridonyl hybrid 8, possessing the lower IC50 (IC50 = 112 nM), was also tested against recombinant kinases involved in the PI3K/PDK1/Akt pathway and was subjected to vitro studies to evaluate the cytotoxicity and the inhibition of tumour cell migration. All together the results let us to consider 8, as a lead compound of a new generation of PDK1 inhibitors and encourage us to further studies in this direction.

Small-Molecule Allosteric Modulators of the Protein Kinase PDK1 from Structure-Based Docking

Finding small molecules that target allosteric sites remains a grand challenge for ligand discovery. In the protein kinase field, only a handful of highly selective allosteric modulators have been found. Thus, more general methods are needed to discover allosteric modulators for additional kinases. Here, we use virtual screening against an ensemble of both crystal structures and comparative models to identify ligands for an allosteric peptide-binding site on the protein kinase PDK1 (the PIF pocket). We optimized these ligands through an analog-by-catalog search that yielded compound 4, which binds to PDK1 with 8 μM affinity. We confirmed the docking poses by determining a crystal structure of PDK1 in complex with 4. Because the PIF pocket appears to be a recurring structural feature of the kinase fold, known generally as the helix αC patch, this approach may enable the discovery of allosteric modulators for other kinases.

Discovery and optimization of a novel series of Dyrk1B kinase inhibitors to explore a MEK resistance hypothesis

Potent and selective inhibitors of Dyrk1B kinase were developed to explore the hypothesis, based on siRNA studies, that Dyrk1B may be a resistance mechanism in cells undergoing a stress response.

Copper-catalyzed O-arylation of N-protected 1,2-aminoalcohols using functionalized trivalent organobismuth reagents

The O-arylation of 1,2-aminoalcohols using functionalized triarylbismuth reagents is reported.

A small-molecule mimic of a peptide docking motif inhibits the protein kinase PDK1

There is great interest in developing selective protein kinase inhibitors by targeting allosteric sites, but these sites often involve protein-protein or protein-peptide interfaces that are very challenging to target with small molecules. Here we present a systematic approach to targeting a functionally conserved allosteric site on the protein kinase PDK1 called the PDK1-interacting fragment (PIF)tide-binding site, or PIF pocket. More than two dozen prosurvival and progrowth kinases dock a conserved peptide tail into this binding site, which recruits them to PDK1 to become activated. Using a site-directed chemical screen, we identified and chemically optimized ligand-efficient, selective, and cell-penetrant small molecules (molecular weight ∼ 380 Da) that compete with the peptide docking motif for binding to PDK1. We solved the first high-resolution structure of a peptide docking motif (PIFtide) bound to PDK1 and mapped binding energy hot spots using mutational analysis. We then solved structures of PDK1 bound to the allosteric small molecules, which revealed a binding mode that remarkably mimics three of five hot-spot residues in PIFtide. These allosteric small molecules are substrate-selective PDK1 inhibitors when used as single agents, but when combined with an ATP-competitive inhibitor, they completely suppress the activation of the downstream kinases. This work provides a promising new scaffold for the development of high-affinity PIF pocket ligands, which may be used to enhance the anticancer activity of existing PDK1 inhibitors. Moreover, our results provide further impetus for exploring the helix αC patches of other protein kinases as potential therapeutic targets even though they involve protein-protein interfaces.

Targeting protein kinase C in sarcoma

Protein kinase C (PKC) is a family of serine/threonine tyrosine kinases that regulate many cellular processes including division, proliferation, survival, anoikis and polarity. PKC is abundant in many human cancers and aberrant PKC signalling has been demonstrated in cancer models. On this basis, PKC has become an attractive target for small molecule inhibition within oncology drug development programmes. Sarcoma is a heterogeneous group of mesenchymal malignancies. Due to their relative insensitivity to conventional chemotherapies and the increasing recognition of the driving molecular events of sarcomagenesis, sarcoma provides an excellent platform to test novel therapeutics. In this review we provide a structure-function overview of the PKC family, the rationale for targeting these kinases in sarcoma and the state of play with regard to PKC inhibition in the clinic.

Receptor proximal kinases in NF-κB signaling as potential therapeutic targets in cancer and inflammation

Many signaling pathways leading to activation of transcription factors and gene expression are characterized by phosphorylation events mediated by specific kinases. The transcription factor NF-κB plays a key role in multiple cellular processes, including immune signaling, inflammation, development, proliferation and survival. Dysregulated NF-κB activation is associated with autoimmunity, chronic inflammation and cancer. Activation of NF-κB requires IκB kinase (IKK)α or β, the activity of which is regulated via phosphorylation by specific IKK kinases and by autophosphorylation. Receptor specificity is further obtained by the use of multiple upstream receptor proximal kinases. We review the identities of several IKK regulatory kinases as well as the proposed molecular mechanisms. In addition, we discuss the potential for therapeutic targeting of some of these kinases in the context of inflammatory diseases and cancer.

Prognostic potential of microRNA-138 and its target mRNA PDK1 in sera for patients with non-small cell lung cancer

microRNA (miR)-138 has been recognized as a potential tumor suppressor via regulating 3-phosphoinositide-dependent protein kinase-1 (PDK1) expression in non-small cell lung cancer (NSCLC) cells. The aim of this study was to investigate miR-138 and PDK1 mRNA expression in serum of NSCLC and their associations with patients' prognosis. miR-138 and PDK1 mRNA expressions in 100 NSCLCs and 100 healthy control sera were detected by quantitative real-time PCR. miR-138 expression level was significantly lower in NSCLC serum samples than in healthy control serum samples (P < 0.001), while PDK1 mRNA expression level was significantly increased in NSCLC serum samples compared to healthy control serum samples (P < 0.001). In addition, miR-138 downregulation and PDK1 upregulation were both significantly associated with advanced tumor-node-metastasis (TNM) stage (both P = 0.002) and positive lymph node metastasis (both P = 0.01) of NSCLC patients. Moreover, the overall survival of NSCLC patients with low miR-138 expression or high PDK1 mRNA expression was obviously shorter than those with high miR-138 expression or low PDK1 mRNA expression (both P < 0.001). Notably, NSCLC patients with combined miR-138 downregulation and PDK1 upregulation (miR-138-low/PDK1-high) had shortest overall survival (P < 0.001). Furthermore, multivariate analysis showed that miR-138 expression (P = 0.01), PDK1 expression (P = 0.01), and combined expression of miR-138 and PDK1 (miR-138/PDK1, P = 0.001) were all independent prognostic factors for overall survival in NSCLC patients. Deregulation of miR-138/PDK1 cascade may be implicated in carcinogenesis and cancer progression of human NSCLC. More importantly, miR-138 and PDK1 may synergistically predict patients' prognosis and their combination may represent a promising prognostic biomarker of human NSCLC.

Rationale-based therapeutic combinations with PI3K inhibitors in cancer treatment

The PI3K/AKT/mTOR signaling is important for cell proliferation, survival, and metabolism. Hyperactivation of this pathway is one of the most common signaling abnormalities observed in cancer and a substantial effort has recently been made to develop molecules targeting this signaling cascade. However, it is becoming evident that PI3K inhibitors used as single agents do not elicit dramatic or durable responses. Given the numerous mechanisms mediating intrinsic and acquired resistance to these agents, hypothesis-based combinatorial strategies are probably needed to fully exploit their antitumor activity. In the first part of this review, we briefly dissect the PI3K/AKT/mTOR axis and list the most advanced compounds targeting different nodes of this cascade. The second part focuses on what we believe to be the most promising rationale-based therapeutic combinations with PI3K/AKT/mTOR inhibitors in solid tumors, with special emphasis on breast cancer.

Combined PDK1 and CHK1 inhibition is required to kill glioblastoma stem-like cells in vitro and in vivo

Glioblastoma (GBM) is the most common and deadly adult brain tumor. Despite aggressive surgery, radiation, and chemotherapy, the life expectancy of patients diagnosed with GBM is ∼14 months. The extremely aggressive nature of GBM results from glioblastoma stem-like cells (GSCs) that sustain GBM growth, survive intensive chemotherapy, and give rise to tumor recurrence. There is accumulating evidence revealing that GSC resilience is because of concomitant activation of multiple survival pathways. In order to decode the signal transduction networks responsible for the malignant properties of GSCs, we analyzed a collection of GSC lines using a dual, but complementary, experimental approach, that is, reverse-phase protein microarrays (RPPMs) and kinase inhibitor library screening. We treated GSCs in vitro with clinically relevant concentrations of temozolomide (TMZ) and performed RPPM to detect changes in phosphorylation patterns that could be associated with resistance. In addition, we screened GSCs in vitro with a library of protein and lipid kinase inhibitors to identify specific targets involved in GSC survival and proliferation. We show that GSCs are relatively insensitive to TMZ treatment in terms of pathway activation and, although displaying heterogeneous individual phospho-proteomic profiles, most GSCs are resistant to specific inhibition of the major signaling pathways involved in cell survival and proliferation. However, simultaneous multipathway inhibition by the staurosporin derivative UCN-01 results in remarkable inhibition of GSC growth in vitro. The activity of UCN-01 on GSCs was confirmed in two in vivo models of GBM growth. Finally, we used RPPM to study the molecular and functional effects of UCN-01 and demonstrated that the sensitivity to UCN-01 correlates with activation of survival signals mediated by PDK1 and the DNA damage response initiated by CHK1. Taken together, our results suggest that a combined inhibition of PDK1 and CHK1 represents a potentially effective therapeutic approach to reduce the growth of human GBM.

3-Phosphoinositide-dependent protein kinase-1 as an emerging target in the management of breast cancer

It should be noted that 3-phosphoinositide-dependent protein kinase-1 (PDK1) is a protein encoded by the PDPK1 gene, which plays a key role in the signaling pathways activated by several growth factors and hormones. PDK1 is a crucial kinase that functions downstream of phosphoinositide 3-kinase activation and activates members of the AGC family of protein kinases, such as protein kinase B (Akt), protein kinase C (PKC), p70 ribosomal protein S6 kinases, and serum glucocorticoid-dependent kinase, by phosphorylating serine/threonine residues in the activation loop. AGC kinases are known to play crucial roles in regulating physiological processes relevant to metabolism, growth, proliferation, and survival. Changes in the expression and activity of PDK1 and several AGC kinases have been linked to human diseases including cancer. Recent data have revealed that the alteration of PDK1 is a critical component of oncogenic phosphoinositide 3-kinase signaling in breast cancer, suggesting that inhibition of PDK1 can inhibit breast cancer progression. Indeed, PDK1 is highly expressed in a majority of human breast cancer cell lines and both PDK1 protein and messenger ribonucleic acid are overexpressed in a majority of human breast cancers. Furthermore, overexpression of PDK1 is sufficient to transform mammary epithelial cells. PDK1 plays an essential role in regulating cell migration, especially in the context of phosphatase and tensin homologue deficiency. More importantly, downregulation of PDK1 levels inhibits migration and experimental metastasis of human breast cancer cells. Thus, targeting PDK1 may be a valuable anticancer strategy that may improve the efficacy of chemotherapeutic strategies in breast cancer patients. In this review, we summarize the evidence that has been reported to support the idea that PDK1 may be a key target in breast cancer management.