Synthesis, kinase inhibitory potencies, and in vitro antiproliferative evaluation of new Pim kinase inhibitors

Synthesis of biscarbazole derivative, detection of the "on-off" sensor property of Cu2+ by fluorimetry, and anti-cancer evaluation

Biscarbazole derivative probe (6) (Z)-2-(3-(((9-heptyl-9H-carbazol-3-yl)methylene)amino)-9H-carbazol-9-yl)ethan-1-ol containing an imine group, which is a sensitive and selective fluorescence chemosensor, was designed and synthesized for the effective evaluation of Cu2+ metal ion levels. The synthesized compounds were characterized using 1H NMR, 13C NMR, FT-IR, and MALDI-TOF MS (for compound 6) spectroscopic data. The interaction model between probe 6 and Cu2+ was determined by combining fluorescence methods, 1H NMR titration, Job's plot, and theoretical calculations. For probe 6, the fluorogenic recognition of Cu2+ was investigated by fluorescence spectroscopy, and the optical changes caused by Cu2+ ions were carried out in ACN/H2O (50:50) solution at pH 7.0. Fluorescence probe 6 was found to "turn-off" its fluorescence in the presence of paramagnetic Cu2+ ions. Probe 6 was determined to have a rapid response within 40s and showed a fluorescence response to Cu2+ with a low detection limit of 0.16 μM. Additionally, in vitro anticancer activity and cell imaging studies of probe 6 against the prostate cell line (PC-3) were performed.

Reactivity of ethyl nitrosoacrylate toward pyrrole, indole and pyrrolo[3,2-c]carbazole: an experimental and theoretical study

Nitrosoalkenes react with 8-methyl-1,6-dihydropyrrolo[3,2-c]carbazole to give both 2- and 3-alkylated products via hetero-Diels-Alder reaction followed by the cycloadduct ring-opening. Quantum chemical calculations, at DFT level of theory, were carried out to investigate the regioselectivity of the cycloaddition of ethyl nitrosoacrylate with 1,6-dihydropyrrolo[3,2-c]carbazoles as well as with pyrrole and indole, allowing a more comprehensive analysis of the reactivity pattern of nitrosoalkenes with five-membered heterocycles. Furthermore, theoretical calculations confirmed that ethyl nitrosoacrylate reacts with these heterocycles via a LUMOheterodiene-HOMOdienophile controlled cycloaddition. The reactivity of one of the oxime-functionalized 1,6-dihydropyrrolo[3,2-c]carbazole was explored and a new hexahydropyrido[4',3':4,5]pyrrolo[3,2-c]carbazole system was obtained in high yield via a one-pot, two-step procedure.

Designing of kinase hinge binders: A medicinal chemistry perspective

Protein kinases are key regulators of cellular signaling and play a critical role in oncogenesis. Inhibitors of protein kinases are pursued by both industry and academia as a promising target for cancer therapy. Within the protein kinases, the ATP site has produced more than 40 FDA-approved drugs. The ATP site is broadly composed of a hinge region, gatekeeper residues, DFG-loop, ribose pocket, and other hydrophobic regions. The hinge region in the ATP site can be used for designing potent inhibitors. In this review, we discuss some representative studies that will highlight the interactions of heterocyclic compounds with hinge regions of different kinases like BRAF kinase, EGRF kinase, MAP kinase, and Mps1 kinase.

Stereoselective synthesis of 3,4-dihydropyrrolo[1,2-a]pyrazin-1(2H)-one derivatives as PIM kinase inhibitors inspired from marine alkaloids

We previously demonstrated that natural product-inspired 3,4-dihydropyrrolo[1,2-a]pyrazin-1(2H)-ones derivatives delivered potent and selective PIM kinases inhibitors however with non-optimal ADME/PK properties and modest oral bioavailability. Herein, we describe a structure-based scaffold decoration and a stereoselective approach to this chemical class. The synthesis, structure-activity relationship studies, chiral analysis, and pharmacokinetic data of compounds from this inhibitor class are presented herein. Compound 20c demonstrated excellent potency on PIM1 and PIM2 with exquisite kinases selectivity and PK properties that efficiently and dose-dependently promoted c-Myc degradation and appear to be promising lead compounds for further development.

Choosing Kinase Inhibitors for Androgen Deprivation Therapy-Resistant Prostate Cancer

Androgen deprivation therapy (ADT) is a systemic therapy for advanced prostate cancer (PCa). Although most patients initially respond to ADT, almost all cancers eventually develop castration resistance. Castration-resistant PCa (CRPC) is associated with a very poor prognosis, and the treatment of which is a serious clinical challenge. Accumulating evidence suggests that abnormal expression and activation of various kinases are associated with the emergence and maintenance of CRPC. Many efforts have been made to develop small molecule inhibitors to target the key kinases in CRPC. These inhibitors are designed to suppress the kinase activity or interrupt kinase-mediated signal pathways that are associated with PCa androgen-independent (AI) growth and CRPC development. In this review, we briefly summarize the roles of the kinases that are abnormally expressed and/or activated in CRPC and the recent advances in the development of small molecule inhibitors that target kinases for the treatment of CRPC.

PIM1 Inhibition Affects Glioblastoma Stem Cell Behavior and Kills Glioblastoma Stem-like Cells

Despite comprehensive therapy and extensive research, glioblastoma (GBM) still represents the most aggressive brain tumor in adults. Glioma stem cells (GSCs) are thought to play a major role in tumor progression and resistance of GBM cells to radiochemotherapy. The PIM1 kinase has become a focus in cancer research. We have previously demonstrated that PIM1 is involved in survival of GBM cells and in GBM growth in a mouse model. However, little is known about the importance of PIM1 in cancer stem cells. Here, we report on the role of PIM1 in GBM stem cell behavior and killing. PIM1 inhibition negatively regulates the protein expression of the stem cell markers CD133 and Nestin in GBM cells (LN-18, U-87 MG). In contrast, CD44 and the astrocytic differentiation marker GFAP were up-regulated. Furthermore, PIM1 expression was increased in neurospheres as a model of GBM stem-like cells. Treatment of neurospheres with PIM1 inhibitors (TCS PIM1-1, Quercetagetin, and LY294002) diminished the cell viability associated with reduced DNA synthesis rate, increased caspase 3 activity, decreased PCNA protein expression, and reduced neurosphere formation. Our results indicate that PIM1 affects the glioblastoma stem cell behavior, and its inhibition kills glioblastoma stem-like cells, pointing to PIM1 targeting as a potential anti-glioblastoma therapy.

Therapeutic targeting of PIM KINASE signaling in cancer therapy: Structural and clinical prospects

BACKGROUND

PIM kinases are well-studied drug targets for cancer, belonging to Serine/Threonine kinases family. They are the downstream target of various signaling pathways, and their up/down-regulation affects various physiological processes. PIM family comprises three isoforms, namely, PIM-1, PIM-2, and PIM-3, on alternative initiation of translation and they have different levels of expression in different types of cancers. Its structure shows a unique ATP-binding site in the hinge region which makes it unique among other kinases.

SCOPE OF REVIEW

PIM kinases are widely reported in hematological malignancies along with prostate and breast cancers. Currently, many drugs are used as inhibitors of PIM kinases. In this review, we highlighted the physiological significance of PIM kinases in the context of disease progression and therapeutic targeting. We comprehensively reviewed the PIM kinases in terms of their expression and regulation of different physiological roles. We further predicted functional partners of PIM kinases to elucidate their role in the cellular physiology of different cancer and mapped their interaction network.

MAJOR CONCLUSIONS

A deeper mechanistic insight into the PIM signaling involved in regulating different cellular processes, including transcription, apoptosis, cell cycle regulation, cell proliferation, cell migration and senescence, is provided. Furthermore, structural features of PIM have been dissected to understand the mechanism of inhibition and subsequent implication of designed inhibitors towards therapeutic management of prostate, breast and other cancers.

GENERAL SIGNIFICANCE

Being a potential drug target for cancer therapy, available drugs and PIM inhibitors at different stages of clinical trials are discussed in detail.

4,5,6,7-Tetrahydroindol-4-Ones as a Valuable Starting Point for the Synthesis of Polyheterocyclic Structures

This review focuses on the synthesis of polyheterocyclic structures with a variety of medicinal and optoelectronic applications, starting from readily available 4,5,6,7-tetrahydroindol-4-one analogs. First, routes toward the 4,5,6,7-tetrahydroindol-4-one starting materials are summarized, followed by synthetic pathways towards polyheterocyclic structures which are categorized based on the size and attachment point of the newly formed (hetero)cyclic ring.

PIM kinases inhibit AMPK activation and promote tumorigenicity by phosphorylating LKB1

BACKGROUND

The oncogenic PIM kinases and the tumor-suppressive LKB1 kinase have both been implicated in the regulation of cell growth and metabolism, albeit in opposite directions. Here we investigated whether these kinases interact with each other to influence AMPK activation and tumorigenic growth of prostate and breast cancer cells.

METHODS

We first determined how PIM and LKB1 kinases affect AMPK phosphorylation levels. We then used in vitro kinase assays to demonstrate that LKB1 is phosphorylated by PIM kinases, and site-directed mutagenesis to identify the PIM target sites in LKB1. The cellular functions of PIM and LKB1 kinases were evaluated using either pan-PIM inhibitors or CRISPR/Cas9 genomic editing, with which all three PIM family members and/or LKB1 were knocked out from PC3 prostate and MCF7 breast cancer cell lines. In addition to cell proliferation assays, we examined the effects of PIM and/or LKB1 loss on tumor growth using the chick embryo chorioallantoic membrane (CAM) xenograft model.

RESULTS

We provide both genetic and pharmacological evidence to demonstrate that inhibition of PIM expression or activity increases phosphorylation of AMPK at Thr172 in both PC3 and MCF7 cells, but not in their derivatives lacking LKB1. This is explained by our observation that all three PIM family kinases can phosphorylate LKB1 at Ser334. Wild-type LKB1, but not its phosphodeficient derivative, can restore PIM inhibitor-induced AMPK phosphorylation in LKB1 knock-out cells. In the CAM model, loss of LKB1 enhances tumorigenicity of PC3 xenografts, while cells lacking both LKB1 and PIMs exhibit slower proliferation rates and form smaller tumors.

CONCLUSION

PIM kinases are novel negative regulators of LKB1 that affect AMPK activity in an LKB1-dependent fashion. The impairment of cell proliferation and tumor growth in cells lacking both LKB1 and PIMs indicates that these kinases possess a shared signaling role in the context of cancer. These data also suggest that PIM inhibitors may be a rational therapeutic option for LKB1-deficient tumors. Video Abstract.

PIM-induced phosphorylation of Notch3 promotes breast cancer tumorigenicity in a CSL-independent fashion

Dysregulation of the developmentally important Notch signaling pathway is implicated in several types of cancer, including breast cancer. However, the specific roles and regulation of the four different Notch receptors have remained elusive. We have previously reported that the oncogenic PIM kinases phosphorylate Notch1 and Notch3. Phosphorylation of Notch1 within the second nuclear localization sequence of its intracellular domain (ICD) enhances its transcriptional activity and tumorigenicity. In this study, we analyzed Notch3 phosphorylation and its functional impact. Unexpectedly, we observed that the PIM target sites are not conserved between Notch1 and Notch3. Notch3 ICD (N3ICD) is phosphorylated within a domain, which is essential for formation of a transcriptionally active complex with the DNA-binding protein CSL. Through molecular modeling, X-ray crystallography, and isothermal titration calorimetry, we demonstrate that phosphorylation of N3ICD sterically hinders its interaction with CSL and thereby inhibits its CSL-dependent transcriptional activity. Surprisingly however, phosphorylated N3ICD still maintains tumorigenic potential in breast cancer cells under estrogenic conditions, which support PIM expression. Taken together, our data indicate that PIM kinases modulate the signaling output of different Notch paralogs by targeting distinct protein domains and thereby promote breast cancer tumorigenesis via both CSL-dependent and CSL-independent mechanisms.

Carbazole Derivatives as Kinase-Targeting Inhibitors for Cancer Treatment

Protein Kinases (PKs) are a heterogeneous family of enzymes that modulate several biological pathways, including cell division, cytoskeletal rearrangement, differentiation and apoptosis. In particular, due to their crucial role during human tumorigenesis and cancer progression, PKs are ideal targets for the design and development of effective and low toxic chemotherapeutics and represent the second group of drug targets after G-protein-coupled receptors. Nowadays, several compounds have been claimed to be PKs inhibitors, and some of them, such as imatinib, erlotinib and gefitinib, have already been approved for clinical use, whereas more than 30 others are in various phases of clinical trials. Among them, some natural or synthetic carbazole-based molecules represent promising PKs inhibitors due to their capability to interfere with PK activity by different mechanisms of action including the ability to act as DNA intercalating agents, interfere with the activity of enzymes involved in DNA duplication, such as topoisomerases and telomerases, and inhibit other proteins such as cyclindependent kinases or antagonize estrogen receptors. Thus, carbazoles can be considered a promising this class of compounds to be adopted in targeted therapy of different types of cancer.

PIM1 accelerates prostate cancer cell motility by phosphorylating actin capping proteins

Background

The PIM family kinases promote cancer cell survival and motility as well as metastatic growth in various types of cancer. We have previously identified several PIM substrates, which support cancer cell migration and invasiveness. However, none of them are known to regulate cellular movements by directly interacting with the actin cytoskeleton. Here we have studied the phosphorylation-dependent effects of PIM1 on actin capping proteins, which bind as heterodimers to the fast-growing actin filament ends and stabilize them.

Methods

Based on a phosphoproteomics screen for novel PIM substrates, we have used kinase assays and fluorescence-based imaging techniques to validate actin capping proteins as PIM1 substrates and interaction partners. We have analysed the functional consequences of capping protein phosphorylation on cell migration and adhesion by using wound healing and real-time impedance-based assays. We have also investigated phosphorylation-dependent effects on actin polymerization by analysing the protective role of capping protein phosphomutants in actin disassembly assays.

Results

We have identified capping proteins CAPZA1 and CAPZB2 as PIM1 substrates, and shown that phosphorylation of either of them leads to increased adhesion and migration of human prostate cancer cells. Phosphorylation also reduces the ability of the capping proteins to protect polymerized actin from disassembly.

Conclusions

Our data suggest that PIM kinases are able to induce changes in actin dynamics to support cell adhesion and movement. Thus, we have identified a novel mechanism through which PIM kinases enhance motility and metastatic behaviour of cancer cells.

Structural insights for rational design of new PIM-1 kinase inhibitors based on 3,5-disubstituted indole derivatives: An integrative computational approach

Proviral integration Moloney virus (PIM) 1, 2, and 3 kinases are a family of constitutively active serine/threonine kinases that are involved in a number of signaling pathways important to cancer cells. Their overexpression in a variety of human hematopoietic malignancies and solid tumors suggest that inhibition of PIM signaling could provide patients with therapeutic benefit. In this study, a series of 3,5-disubstituted indole derivatives have been systematically studied using three-dimensional quantitative structure-activity relationship (3D-QSAR) analysis, molecular docking simulation, and partial least-squares (PLS) analysis methods to explore the influence of the structural characteristics on the inhibitory activity and use them to propose novel bioactive molecules. The comparative molecular field and comparative molecular similarity indices analyses (CoMFA and CoMSIA) models exhibited a good correlation between the predicted and experimental activities with excellent predictive capability and yielded statistically reliable value (CoMFA: Q² = 0.535, R² = 0.987, r²_pred = 0.909; CoMSIA: Q² = 0.785, R² = 0.989, r²_pred = 0.969). Based on the CoMFA and CoMSIA models and docking results, ten novel potent PIM-1 inhibitors (N1-N10) have been designed and the molecular models have validated their inhibitory activities. These results provided strong theoretical guidance for the development of novel PIM-1 inhibitors.

Phosphorylation of NFATC1 at PIM1 target sites is essential for its ability to promote prostate cancer cell migration and invasion

Background

Progression of prostate cancer from benign local tumors to metastatic carcinomas is a multistep process. Here we have investigated the signaling pathways that support migration and invasion of prostate cancer cells, focusing on the role of the NFATC1 transcription factor and its post-translational modifications. We have previously identified NFATC1 as a substrate for the PIM1 kinase and shown that PIM1-dependent phosphorylation increases NFATC1 activity without affecting its subcellular localization. Both PIM kinases and NFATC1 have been reported to promote cancer cell migration, invasion and angiogenesis, but it has remained unclear whether the effects of NFATC1 are phosphorylation-dependent and which downstream targets are involved.

Methods

We used mass spectrometry to identify PIM1 phosphorylation target sites in NFATC1, and analysed their functional roles in three prostate cancer cell lines by comparing phosphodeficient mutants to wild-type NFATC1. We used luciferase assays to determine effects of phosphorylation on NFAT-dependent transcriptional activity, and migration and invasion assays to evaluate effects on cell motility. We also performed a microarray analysis to identify novel PIM1/NFATC1 targets, and validated one of them with both cellular expression analyses and in silico in clinical prostate cancer data sets.

Results

Here we have identified ten PIM1 target sites in NFATC1 and found that prevention of their phosphorylation significantly decreases the transcriptional activity as well as the pro-migratory and pro-invasive effects of NFATC1 in prostate cancer cells. We observed that also PIM2 and PIM3 can phosphorylate NFATC1, and identified several novel putative PIM1/NFATC1 target genes. These include the ITGA5 integrin, which is differentially expressed in the presence of wild-type versus phosphorylation-deficient NFATC1, and which is coexpressed with PIM1 and NFATC1 in clinical prostate cancer specimens.

Conclusions

Based on our data, phosphorylation of PIM1 target sites stimulates NFATC1 activity and enhances its ability to promote prostate cancer cell migration and invasion. Therefore, inhibition of the interplay between PIM kinases and NFATC1 may have therapeutic implications for patients with metastatic forms of cancer.

Graphical abstract

Functionalization of 9-thioxanthone at the 1-position: From arylamino derivatives to [1]benzo(thio)pyrano[4,3,2-de]benzothieno[2,3-b]quinolines of biological interest

Original 1-amino substituted thioxanthone derivatives were easily prepared from the bare heterocycle by a deprotometalation-iodolysis-copper-catalyzed CN bond formation sequence. This last reaction delivered mono- or/and diarylated products depending on the aniline involved. 1-Amino-9-thioxanthone was also prepared and reacted with 2-iodoheterocycles. Interestingly, while 1-(arylamino)-9-thioxanthones could be isolated, their subsequent cyclization was found to deliver original hexacyclic derivatives of helicoidal nature. Evaluation of their photophysical properties revealed high fluorescence in polar media, indicating potential applications for biological imaging. These compounds being able to inhibit PIM1 kinase, their putative binding mode was examined through molecular modeling experiments. Altogether, these results tend to suggest the discovery of a new family of fluorescent PIM inhibitors and pave the way for their future rational optimization.

PIM-Related Kinases Selectively Regulate Olfactory Sensations in Caenorhabditis elegans

The mammalian PIM family of serine/threonine kinases regulate several cellular functions, such as cell survival and motility. Because PIM expression is observed in sensory organs, such as olfactory epithelium, we now wanted to explore the physiological roles of PIM kinases there. As our model organism, we used the Caenorhabditis elegans nematodes, which express two PIM-related kinases, PRK-1 and PRK-2. We demonstrated PRKs to be true PIM orthologs with similar substrate specificity as well as sensitivity to PIM-inhibitory compounds. When we analyzed the effects of pan-PIM inhibitors on C. elegans sensory functions, we observed that PRK activity is selectively required to support olfactory sensations to volatile repellents and attractants sensed by AWB and AWC^ON neurons, respectively, but is dispensable for gustatory sensations. Analyses of prk-deficient mutant strains confirmed these findings and suggested that PRK-1, but not PRK-2 is responsible for the observed effects on olfaction. This regulatory role of PRK-1 is further supported by its observed expression in the head and tail neurons, including AWB and AWC neurons. Based on the evolutionary conservation of PIM-related kinases, our data may have implications in regulation of also mammalian olfaction.

A review on PIM kinases in tumors

The Proviral Integration site for Moloney murine leukemia virus (PIM) kinases is serine/threonine kinases that promote growth and survival in multiple cell types, implicated in the pathogenesis of various diseases. Over expression of Pim-1 experimentally leads to tumor formation in mice, whereas there is no observable phenotype concerning the complete knockout of the protein. When it is over expressed it may lead to cancer development by three major ways; by inhibiting apoptosis, by promoting cell proliferation and also through promoting genomic instability. Expression in normal tissues is nearly undetectable. Recent improvements in the development of novel inhibitors of PIMs have been reviewed. Significant progress in the design of PIMs inhibitors, in which it displays selectivity versus other kinases, has been achieved within the last years. However, the development of isoform-selective PIM inhibitors is still an open task. As Pim-1 possesses oncogenic functions and is over expressed in various kinds of cancer diseases, its inhibition provides a new option in cancer therapy. A PubMed literature search was performed to review the currently available data on Pim-1 expression, regulation, and targets; its implication in different types of cancer and its impact on prognosis is described. Consequently, designing new inhibitors of PIMs is now a very active area of research in academic and industrial laboratories.

A Kinase Inhibitor with Anti-Pim Kinase Activity is a Potent and Selective Cytotoxic Agent Toward Acute Myeloid Leukemia

More than 40 years ago, the present standard induction therapy for acute myeloid leukemia (AML) was developed. This consists of the metabolic inhibitor cytarabine (AraC) and the cytostatic topoisomerase 2 inhibitor daunorubucin (DNR). In light of the high chance for relapse, as well as the large heterogeneity, novel therapies are needed to improve patient outcome. We have tested the anti-AML activity of 15 novel compounds based on the scaffolds pyrrolo[2,3-a]carbazole-3-carbaldehyde, pyrazolo[3,4-c]carbazole, pyrazolo[4,3-a]phenanthridine, or pyrrolo[2,3-g]indazole. The compounds were inhibitors of Pim kinases, but could also have inhibitory activity against other protein kinases. Ser/Thr kinases like the Pim kinases have been identified as potential drug targets for AML therapy. The compound VS-II-173 induced AML cell death with EC₅₀ below 5 μmol/L, and was 10 times less potent against nonmalignant cells. It perturbed Pim-kinase-mediated AML cell signaling, such as attenuation of Stat5 or MDM2 phosphorylation, and synergized with DNR to induce AML cell death. VS-II-173 induced cell death also in patients with AML blasts, including blast carrying high-risk FLT3-ITD mutations. Mutation of nucleophosmin-1 was associated with good response to VS-II-173. In conclusion new scaffolds for potential AML drugs have been explored. The selective activity toward patient AML blasts and AML cell lines of the pyrazolo-analogue VS-II-173 make it a promising drug candidate to be further tested in preclinical animal models for AML.

Design, synthesis and biological evaluation of N-arylsulfonyl carbazoles as novel anticancer agents

In this work, a set of structurally diverse synthetic carbazoles was screened for their anticancer activities. According to structure–activity relationship studies, carbazoles with an N-substituted sulfonyl group exhibited better anticancer activity. Moreover, compound 8h was discovered to show the most potent anticancer effects on Capan-2 cells by inducing apoptosis and cell cycle arrest in G2/M phase. Finally, the in vivo study demonstrated that 8h prevented the tumor growth in PANC-1 and Capan-2 xenograft models without apparent toxicity.

In this work, a set of structurally diverse synthetic carbazoles was screened for their anticancer activities.

Phosphorylation of Notch1 by Pim kinases promotes oncogenic signaling in breast and prostate cancer cells

Tumorigenesis is a multistep process involving co-operation between several deregulated oncoproteins. In this study, we unravel previously unrecognized interactions and crosstalk between Pim kinases and the Notch signaling pathway, with implications for both breast and prostate cancer. We identify Notch1 and Notch3, but not Notch2, as novel Pim substrates and demonstrate that for Notch1, the serine residue 2152 is phosphorylated by all three Pim family kinases. This target site is located in the second nuclear localization sequence (NLS) of the Notch1 intracellular domain (N1ICD), and is shown to be important for both nuclear localization and transcriptional activity of N1ICD. Phosphorylation-dependent stimulation of Notch1 signaling promotes migration of prostate cancer cells, balances glucose metabolism in breast cancer cells, and supports in vivo growth of both types of cancer cells on chick embryo chorioallantoic membranes. Furthermore, Pim-induced growth of orthotopic prostate xenografts in mice is associated with enhanced nuclear Notch1 activity. Finally, simultaneous inhibition of Pim and Notch abrogates the cellular responses more efficiently than individual treatments, opening up new vistas for combinatorial cancer therapy.

G9a-mediated methylation of ERα links the PHF20/MOF histone acetyltransferase complex to hormonal gene expression

The euchromatin histone methyltransferase 2 (also known as G9a) methylates histone H3K9 to repress gene expression, but it also acts as a coactivator for some nuclear receptors. The molecular mechanisms underlying this activation remain elusive. Here we show that G9a functions as a coactivator of the endogenous oestrogen receptor α (ERα) in breast cancer cells in a histone methylation-independent manner. G9a dimethylates ERα at K235 both in vitro and in cells. Dimethylation of ERαK235 is recognized by the Tudor domain of PHF20, which recruits the MOF histone acetyltransferase (HAT) complex to ERα target gene promoters to deposit histone H4K16 acetylation promoting active transcription. Together, our data suggest the molecular mechanism by which G9a functions as an ERα coactivator. Along with the PHF20/MOF complex, G9a links the crosstalk between ERα methylation and histone acetylation that governs the epigenetic regulation of hormonal gene expression.

The histone methyltransferase G9a methylates histone H3K9 to repress gene expression, but it also acts as a coactivator for some nuclear receptors. Here, Zhang et al. show that methylation of ERα by G9a recruits the PHF20/MOF complex that deposits histone H4K16 acetylation promoting active transcription.

The PIM1 kinase promotes prostate cancer cell migration and adhesion via multiple signalling pathways

The ability of cells to migrate and form metastases is one of the fatal hallmarks of cancer that can be conquered only with better understanding of the molecules and regulatory mechanisms involved. The oncogenic PIM kinases have been shown to support cancer cell survival and motility, but the PIM-regulated pathways stimulating cell migration and invasion are less well characterized than those affecting cell survival. Here we have identified the glycogen synthase kinase 3β (GSK3B) and the forkhead box P3 (FOXP3) transcription factor as direct PIM targets, whose tumour-suppressive effects in prostate cancer cells are inhibited by PIM-induced phosphorylation, resulting in increased cell migration. Targeting GSK3B is also essential for the observed PIM-enhanced expression of the prostaglandin-endoperoxide synthase 2 (PTGS2), which is an important regulator of both cell migration and adhesion. Accordingly, selective inhibition of PIM activity not only reduces cell migration, but also affects integrin-mediated cell adhesion. Taken together, these data provide novel mechanistic insights on how and why patients with metastatic prostate cancer may benefit from therapies targeting PIM kinases, and how such approaches may also be applicable to inflammatory conditions.

Identification of novel inhibitors for Pim-1 kinase using pharmacophore modeling based on a novel method for selecting pharmacophore generation subsets

Targeting Proviral integration-site of murine Moloney leukemia virus 1 kinase, hereafter called Pim-1 kinase, is a promising strategy for treating different kinds of human cancer. Headed for this a total list of 328 formerly reported Pim-1 kinase inhibitors has been explored and divided based on the pharmacophoric features of the most active molecules into 10 subsets projected to represent potential active binding manners accessible to ligands within the binding pocket of Pim-1 kinase. Discovery Studio 4.1 (DS 4.1) was employed to detect potential pharmacophoric active binding manners anticipated by Pim-1 Kinase inhibitors. The pharmacophoric models were then allowed to compete within Quantitative Structure Activity Relationship (QSAR) framework with other 2D descriptors. Accordingly Genetic algorithm and multiple linear regression investigation were engaged to find the finest QSAR equation that has the best predictive power r262(2) = 0.70, F = 119.14, rLOO(2) = 0.693, rPRESS(2) against 66 external test inhibitors = 0.71 q(2) = 0.55. Three different pharmacophores appeared in the successful QSAR equation this represents three different binding modes for inhibitors within the Pim-1 kinase binding pocket. Pharmacophoric models were later used to screen compounds within the National Cancer Institute database. Several low micromolar Pim-1 Kinase inhibitors were captured. The most potent hits show IC50 values of 0.77 and 1.03 µM. Also, upon analyzing the successful QSAR Equation we found that some polycyclic aromatic electron-rich structures namely 6-Chloro-2-methoxy-acridine can be considered as putative hits for Pim-1 kinase inhibition.

Pim Kinases Promote Migration and Metastatic Growth of Prostate Cancer Xenografts

Background and methods

Pim family proteins are oncogenic kinases implicated in several types of cancer and involved in regulation of cell proliferation, survival as well as motility. Here we have investigated the ability of Pim kinases to promote metastatic growth of prostate cancer cells in two xenograft models for human prostate cancer. We have also evaluated the efficacy of Pim-selective inhibitors to antagonize these effects.

Results

We show here that tumorigenic growth of both subcutaneously and orthotopically inoculated prostate cancer xenografts is enhanced by stable overexpression of either Pim-1 or Pim-3. Moreover, Pim-overexpressing orthotopic prostate tumors are highly invasive and able to migrate not only to the nearby prostate-draining lymph nodes, but also into the lungs to form metastases. When the xenografted mice are daily treated with the Pim-selective inhibitor DHPCC-9, both the volumes as well as the metastatic capacity of the tumors are drastically decreased. Interestingly, the Pim-promoted metastatic growth of the orthotopic xenografts is associated with enhanced angiogenesis and lymphangiogenesis. Furthermore, forced Pim expression also increases phosphorylation of the CXCR4 chemokine receptor, which may enable the tumor cells to migrate towards tissues such as the lungs that express the CXCL12 chemokine ligand.

Conclusions

Our results indicate that Pim overexpression enhances the invasive properties of prostate cancer cells in vivo. These effects can be reduced by the Pim-selective inhibitor DHPCC-9, which can reach tumor tissues without serious side effects. Thus, Pim-targeting therapies with DHPCC-9-like compounds may help to prevent progression of local prostate carcinomas to fatally metastatic malignancies.

New N-1,N-10-bridged pyrrolo[2,3-a]carbazole-3-carbaldehydes: synthesis and biological activities

The synthesis of new pyrrolocarbazoles substituted at N-1/N-10 positions is described. All the compounds tested demonstrated moderate to high Pim-1/Pim-3 kinase inhibitory potency. The most active inhibitors identified in this series (3, 17) have an alkyl chain bridging the N-1 and N-10 positions. These compounds (3, 17) exhibited apoptosis-inducing activity toward acute myeloid leukemia IPC-81 cells, but not toward normal fibroblasts.

Pathophysiological roles of Pim-3 kinase in pancreatic cancer development and progression

Pim-3 is a member of the provirus integration site for Moloney murine leukemia virus (Pim) family proteins that exhibit serine/threonine kinase activity. Similar to the other Pim kinases (Pim-1 and Pim-2), Pim-3 is involved in many cellular processes, including cell proliferation, survival, and protein synthesis. Although Pim-3 is expressed in normal vital organs, it is overexpressed particularly in tumor tissues of endoderm-derived organs, including the liver, pancreas, and colon. Silencing of Pim-3 expression can retard in vitro cell proliferation of hepatocellular, pancreatic, and colon carcinoma cell lines by promoting cell apoptosis. Pim-3 lacks the regulatory domains similarly as Pim-1 and Pim-2 lack, and therefore, Pim-3 can exhibit its kinase activity once it is expressed. Pim-3 expression is regulated at transcriptional and post-transcriptional levels by transcription factors (e.g., Ets-1) and post-translational modifiers (e.g., translationally-controlled tumor protein), respectively. Pim-3 could promote growth and angiogenesis of human pancreatic cancer cells in vivo in an orthotopic nude mouse model. Furthermore, a Pim-3 kinase inhibitor inhibited cell proliferation when human pancreatic cancer cells were injected into nude mice, without inducing any major adverse effects. Thus, Pim-3 kinase may serve as a novel molecular target for developing targeting drugs against pancreatic and other types of cancer.

Use of regulators and inhibitors of Pim-1, a serine/threonine kinase, for tumour therapy (review)

Pim-1 is a proto-oncogene that encodes a serine/threonine kinase that is overexpressed in a range of haematopoietic malignancies and solid cancers. Pim-1 expression is tightly regulated by multiple biomolecules at different levels. Several lines of evidence have indicated that dysregulation of Pim-1 can interfere with the cell cycle and apoptosis to promote malignant transformation of a number of types of tumour. Thus, investigation of Pim-1 regulation may provide important theoretical guidance for the development of molecular targeting therapies and drug treatments for Pim-1‑associated diseases. Regulators of Pim-1 expression, include microRNAs, oestrogen, inecalcitol, adenosine triphosphate (ATP) mimetic inhibitors and ATP competitive inhibitors of Pim-1. Combinations of inhibitors of Pim-1 expression and Pim-1‑specific inhibitors may provide novel therapies for cancer patients and directions for cancer treatment.

ZMYND11 links histone H3.3K36me3 to transcription elongation and tumour suppression

Recognition of modified histones by 'reader' proteins plays a critical role in the regulation of chromatin. H3K36 trimethylation (H3K36me3) is deposited onto the nucleosomes in the transcribed regions after RNA polymerase II elongation. In yeast, this mark in turn recruits epigenetic regulators to reset the chromatin to a relatively repressive state, thus suppressing cryptic transcription. However, much less is known about the role of H3K36me3 in transcription regulation in mammals. This is further complicated by the transcription-coupled incorporation of the histone variant H3.3 in gene bodies. Here we show that the candidate tumour suppressor ZMYND11 specifically recognizes H3K36me3 on H3.3 (H3.3K36me3) and regulates RNA polymerase II elongation. Structural studies show that in addition to the trimethyl-lysine binding by an aromatic cage within the PWWP domain, the H3.3-dependent recognition is mediated by the encapsulation of the H3.3-specific 'Ser 31' residue in a composite pocket formed by the tandem bromo-PWWP domains of ZMYND11. Chromatin immunoprecipitation followed by sequencing shows a genome-wide co-localization of ZMYND11 with H3K36me3 and H3.3 in gene bodies, and its occupancy requires the pre-deposition of H3.3K36me3. Although ZMYND11 is associated with highly expressed genes, it functions as an unconventional transcription co-repressor by modulating RNA polymerase II at the elongation stage. ZMYND11 is critical for the repression of a transcriptional program that is essential for tumour cell growth; low expression levels of ZMYND11 in breast cancer patients correlate with worse prognosis. Consistently, overexpression of ZMYND11 suppresses cancer cell growth in vitro and tumour formation in mice. Together, this study identifies ZMYND11 as an H3.3-specific reader of H3K36me3 that links the histone-variant-mediated transcription elongation control to tumour suppression.

Small molecule inhibitors of PIM1 kinase: July 2009 to February 2013 patent update

INTRODUCTION

The proviral insertion in murine (PIM) lymphoma proteins for which three isoforms, PIM1, PIM2 and PIM3 have been identified, belonging to the family of serine/threonine kinases has emerged recently as an important therapeutic target for the development of selective inhibitors as the new drugs for treating hematological malignancies and solid tumors. The small molecules developed by academia and the pharmaceutical industry have steadily increased in the last few years. Several drug discovery groups focus on treating disorders, such as cancer mediated by PIM kinase, have provided preclinical evidence suggesting that PIM inhibitor provides anti-apoptotic activity, inhibit cell survival and cell proliferation.

AREAS COVERED

This article discloses recent reviews on research and advances published in the patent literature and scientific publications from July 2009 to February 2013, highlighting discoveries on PIM1 kinase.

EXPERT OPINION

Several PIM1 kinase small molecule inhibitors are now at the pre-clinical research stage, development and testing. Though nearly 40 patents emerged in the last 3 years, greater efforts towards additional designs and medicinal chemistry continues for developing clinically efficacious PIM1 inhibitors, due to the significance of the target for cancer and the potential for novel and diverse inhibitors as drug candidates.

Discovery and optimization of pyrrolo[1,2-a]pyrazinones leads to novel and selective inhibitors of PIM kinases

A novel series of PIM inhibitors was derived from a combined effort in natural product-inspired library generation and screening. The novel pyrrolo[1,2-a]pyrazinones initial hits are inhibitors of PIM isoforms with IC50 values in the low micromolar range. The application of a rational optimization strategy, guided by the determination of the crystal structure of the complex in the kinase domain of PIM1 with compound 1, led to the discovery of compound 15a, which is a potent PIM kinases inhibitor exhibiting excellent selectivity against a large panel of kinases, representative of each family. The synthesis, structure-activity relationship studies, and pharmacokinetic data of compounds from this inhibitor class are presented herein. Furthermore, the cellular activities including inhibition of cell growth and modulation of downstream targets are also described.

A novel necroptosis inhibitor-necrostatin-21 and its SAR study

An initial structure-activity relationship study of the novel necroptosis inhibitor Nec-21 was described. Any changes of the tetracyclic scaffold were detrimental for the activity. Introduction of a substituent to 7 or 8 position (e.g., cyano or methoxy group, respectively), would increase the activity. The 7 and 8-position disubstituted compound 17 b was 35-fold as potent as the lead, while EC50 reached 14 nM.

Effect of single amino acid substitution observed in cancer on Pim-1 kinase thermodynamic stability and structure

Pim-1 kinase, a serine/threonine protein kinase encoded by the pim proto-oncogene, is involved in several signalling pathways such as the regulation of cell cycle progression and apoptosis. Many cancer types show high expression levels of Pim kinases and particularly Pim-1 has been linked to the initiation and progression of the malignant phenotype. In several cancer tissues somatic Pim-1 mutants have been identified. These natural variants are nonsynonymous single nucleotide polymorphisms, variations of a single nucleotide occurring in the coding region and leading to amino acid substitutions. In this study we investigated the effect of amino acid substitution on the structural stability and on the activity of Pim-1 kinase. We expressed and purified some of the mutants of Pim-1 kinase that are expressed in cancer tissues and reported in the single nucleotide polymorphisms database. The point mutations in the variants significantly affect the conformation of the native state of Pim-1. All the mutants, expressed as soluble recombinant proteins, show a decreased thermal and thermodynamic stability and a lower activation energy values for kinase activity. The decreased stability accompanied by an increased flexibility suggests that Pim-1 variants may be involved in a wider network of protein interactions. All mutants bound ATP and ATP mimetic inhibitors with comparable IC50 values suggesting that the studied Pim-1 kinase mutants can be efficiently targeted with inhibitors developed for the wild type protein.

Identification of 1,6-dihydropyrazolo[4,3-c]carbazoles and 3,6-dihydropyrazolo[3,4-c]carbazoles as new Pim kinase inhibitors

New 1,6-dihydropyrazolo[4,3-c]carbazoles and 3,6-dihydropyrazolo[3,4-c]carbazoles were prepared and evaluated for their Pim kinase inhibitory potencies as well as their antiproliferative activities toward two prostatic cancer cell lines. Pyrazolocarbazole 15a was found to be a potent Pim kinase modulator with inhibitory potency toward the three isoforms. Compound 6c strongly inhibited Pim-3 with weaker effect toward Pim-1 and Pim-2, and thus could be used as an interesting molecular tool to study Pim-3 biological functions.

Identification of pyrrolo[2,3-g]indazoles as new Pim kinase inhibitors

The synthesis and Pim kinase inhibition potency of a new series of pyrrolo[2,3-g]indazole derivatives is described. The results obtained in this preliminary structure-activity relationship study pointed out that sub-micromolar Pim-1 and Pim-3 inhibitory potencies could be obtained in this series, more particularly for compounds 10 and 20, showing that pyrrolo[2,3-g]indazole scaffold could be used for the development of new potent Pim kinase inhibitors. Molecular modeling experiments were also performed to study the binding mode of these compounds in Pim-3 ATP-binding pocket.

Tricyclic Benzo[cd]azulenes selectively inhibit activities of Pim kinases and restrict growth of Epstein-Barr virus-transformed cells

Oncogenic Pim family kinases are often overexpressed in human hematopoietic malignancies as well as in solid tumours. These kinases contribute to tumorigenesis by promoting cell survival and by enhancing resistance against chemotherapy and radiation therapy. Furthermore, we have recently shown that they increase the metastatic potential of adherent cancer cells. Here we describe identification of tricyclic benzo[cd]azulenes and their derivatives as effective and selective inhibitors of Pim kinases. These compounds inhibit Pim autophosphorylation and abrogate the anti-apoptotic effects of Pim kinases. They also reduce cancer cell motility and suppress proliferation of lymphoblastoid cell lines infected and immortalized by the Epstein-Barr virus. Thus, these novel Pim-selective inhibitors provide promising compounds for both research and therapeutic purposes.

T-18, a stemonamide synthetic intermediate inhibits Pim kinase activity and induces cell apoptosis, acting as a potent anticancer drug

Pim-3 kinase has been shown to be aberrantly expressed in premalignant and malignant lesions of endoderm-derived organs such as the liver, pancreas, colon and stomach. Pim-3 kinase inactivates the Bad protein, a proapoptotic molecule, and improves the expression of Bcl-xL, an antiapoptotic molecule, to promote cell proliferation. Thus, blocking Pim-3 kinase activity may be a new strategy for the treatment of pancreatic cancer. In this study, we screened low molecular compounds and observed that the stemonamide synthetic intermediate, T-18, potently inhibited Pim kinase activity. Moreover, T-18 inhibited the proliferation of human pancreatic, as well as that of hepatocellular and colon cancer cells in vitro. It also induced the apoptosis of human pancreatic carcinoma cells in vitro by decreasing the levels of phospho-Ser112-Bad; the levels of Pim-3 kinase and total Bad protein were not altered. Furthermore, T-18 inhibited the growth of human pancreatic cancer cells in nude mice without apparent adverse effects when the tumor was palpable. These observations indicate that stemonamide synthetic intermediates may be novel drugs for the treatment of gastrointestinal cancers, particularly pancreatic cancer.