Comparative molecular field analysis of flavonoid inhibitors of the PIM-1 kinase

In silico-guided synthesis of a new, highly soluble, and anti-melanoma flavone glucoside: Skullcapflavone II-6'-O-β-glucoside

Guided by in silico analysis tools and biotransformation technology, new derivatives of natural compounds with heightened bioactivities can be explored and synthesized efficiently. In this study, in silico data mining and molecular docking analysis predicted that glucosides of skullcapflavone II (SKII) were new flavonoid compounds and had higher binding potential to oncogenic proteins than SKII. These benefits guided us to perform glycosylation of SKII by utilizing four glycoside hydrolases and five glycosyltransferases (GTs). Findings unveiled that exclusive glycosylation of SKII was achieved solely through the action of GTs, with Bacillus subtilis BsUGT489 exhibiting the highest catalytic glycosylation efficacy. Structure analysis determined the glycosylated product as a novel compound, skullcapflavone II-6'-O-β-glucoside (SKII-G). Significantly, the aqueous solubility of SKII-G exceeded its precursor, SKII, by 272-fold. Furthermore, SKII-G demonstrated noteworthy anti-melanoma activity against human A2058 cells, exhibiting an IC50 value surpassing that of SKII by 1.4-fold. Intriguingly, no substantial cytotoxic effects were observed in a murine macrophage cell line, RAW 264.7. This promising anti-melanoma activity without adverse effects on macrophages suggests that SKII-G could be a potential candidate for further preclinical and clinical studies. The in silico tool-guided synthesis of a new, highly soluble, and potent anti-melanoma glucoside, SKII-G, provides a rational design to facilitate the future discovery of new and bioactive compounds.

Mur ligase F as a new target for the flavonoids quercitrin, myricetin, and (-)-epicatechin

MurC, D, E, and F are ATP-dependent ligases involved in the stepwise assembly of the tetrapeptide stem of forming peptidoglycan. As highly conserved targets found exclusively in bacterial cells, they are of significant interest for antibacterial drug discovery. In this study, we employed a computer-aided molecular design approach to identify potential inhibitors of MurF. A biochemical inhibition assay was conducted, screening twenty-four flavonoids and related compounds against MurC-F, resulting in the identification of quercitrin, myricetin, and (-)-epicatechin as MurF inhibitors with IC50 values of 143 µM, 139 µM, and 92 µM, respectively. Notably, (-)-epicatechin demonstrated mixed type inhibition with ATP and uncompetitive inhibition with D-Ala-D-Ala dipeptide and UM3DAP substrates. Furthermore, in silico analysis using Sitemap and subsequent docking analysis using Glide revealed two plausible binding sites for (-)-epicatechin. The study also investigated the crucial structural features required for activity, with a particular focus on the substitution pattern and hydroxyl group positions, which were found to be important for the activity. The study highlights the significance of computational approaches in targeting essential enzymes involved in bacterial peptidoglycan synthesis.

Discovery of Isojacareubin as a covalent inhibitor of SARS-CoV-2 main protease using structural and experimental approaches

The ongoing pandemic with the emergence of immune evasion potential and, particularly, the current omicron subvariants intensified the situation further. Although vaccines are available, the immune evasion capabilities of the recent variants demand further efficient therapeutic choices to control the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. Hence, considering the necessity of the small molecule inhibitor, we target the main protease (3CLpro), which is an appealing target for the development of antiviral drugs against SARS-CoV-2. High-throughput molecular in silico screening of South African natural compounds database reported Isojacareubin and Glabranin as the potential inhibitors for the main protease. The calculated docking scores were reported to be -8.47 and -8.03 kcal/mol, respectively. Moreover, the structural dynamic assessment reported that Isojacareubin in complex with 3CLpro exhibit a more stable dynamic behavior than Glabranin. Inhibition assay indicated that Isojacareubin could inhibit SARS-CoV-2 3CLpro in a time- and dose-dependent manner, with half maximal inhibitory concentration values of 16.00 ± 1.35 μM (60 min incubation). Next, the covalent binding sites of Isojacareubin on SARS-CoV-2 3CLpro was identified by biomass spectrometry, which reported that Isojacareubin can covalently bind to thiols or Cysteine through Michael addition. To evaluate the inactivation potency of Isojacareubin, the inactivation kinetics was further investigated. The inactivation kinetic curves were plotted according to various concentrations with gradient-ascending incubation times. The KI value of Isojacareubin was determined as 30.71 μM, whereas the Kinact value was calculated as 0.054 min-1 . These results suggest that Isojacareubin is a covalent inhibitor of SARS-CoV-2 3CLpro .

Computer-Aided Drug Design Applied to Secondary Metabolites as Anticancer Agents

Computer-Aided Drug Design (CADD) techniques have garnered a great deal of attention in academia and industry because of their great versatility, low costs, possibilities of cost reduction in in vitro screening and in the development of synthetic steps; these techniques are compared with highthroughput screening, in particular for candidate drugs. The secondary metabolism of plants and other organisms provide substantial amounts of new chemical structures, many of which have numerous biological and pharmacological properties for virtually every existing disease, including cancer. In oncology, compounds such as vimblastine, vincristine, taxol, podophyllotoxin, captothecin and cytarabine are examples of how important natural products enhance the cancer-fighting therapeutic arsenal. In this context, this review presents an update of Ligand-Based Drug Design and Structure-Based Drug Design techniques applied to flavonoids, alkaloids and coumarins in the search of new compounds or fragments that can be used in oncology. A systematical search using various databases was performed. The search was limited to articles published in the last 10 years. The great diversity of chemical structures (coumarin, flavonoids and alkaloids) with cancer properties, associated with infinite synthetic possibilities for obtaining analogous compounds, creates a huge chemical environment with potential to be explored, and creates a major difficulty, for screening studies to select compounds with more promising activity for a selected target. CADD techniques appear to be the least expensive and most efficient alternatives to perform virtual screening studies, aiming to selected compounds with better activity profiles and better "drugability".

Structure-Based Virtual Screening and De Novo Design of PIM1 Inhibitors with Anticancer Activity from Natural Products

BACKGROUND

the proviral insertion site of Moloney murine leukemia (PIM) 1 kinase has served as a therapeutic target for various human cancers due to the enhancement of cell proliferation and the inhibition of apoptosis.

METHODS

to identify effective PIM1 kinase inhibitors, structure-based virtual screening of natural products of plant origin and de novo design were carried out using the protein-ligand binding free energy function improved by introducing an adequate dehydration energy term.

RESULTS

as a consequence of subsequent enzyme inhibition assays, four classes of PIM1 kinase inhibitors were discovered, with the biochemical potency ranging from low-micromolar to sub-micromolar levels. The results of extensive docking simulations showed that the inhibitory activity stemmed from the formation of multiple hydrogen bonds in combination with hydrophobic interactions in the ATP-binding site. Optimization of the biochemical potency by chemical modifications of the 2-benzylidenebenzofuran-3(2H)-one scaffold led to the discovery of several nanomolar inhibitors with antiproliferative activities against human breast cancer cell lines.

CONCLUSIONS

these new PIM1 kinase inhibitors are anticipated to serve as a new starting point for the development of anticancer medicine.

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.

Identification of quinones as novel PIM1 kinase inhibitors

PIM1 is a proto-oncogene encoding the serine/threonine PIM1 kinase. PIM1 kinase plays important roles in regulating aspects of cell cycle progression, apoptosis resistance, and has been implicated in the development of such malignancies as prostate cancer and acute myeloid leukemia among others. Knockout of PIM1 kinase in mice has been shown to be non-lethal without any obvious phenotypic changes, making it an attractive therapeutic target. Our investigation of anthraquinones as kinase inhibitors revealed a series of quinone analogs showing high selectivity for inhibition of the PIM kinases. Molecular modeling studies were used to identify key interactions and binding poses of these compounds within the PIM1 binding pocket. Compounds 1, 4, 7 and 9 inhibited the growth of DU-145 prostate cancer cell lines with a potency of 8.21μM, 4.06μM, 3.21μM and 2.02μM.

3D-QSAR and docking studies of flavonoids as potent Escherichia coli inhibitors

Flavonoids are potential antibacterial agents. However, key substituents and mechanism for their antibacterial activity have not been fully investigated. The quantitative structure-activity relationship (QSAR) and molecular docking of flavonoids relating to potent anti-Escherichia coli agents were investigated. Comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) were developed by using the pIC50 values of flavonoids. The cross-validated coefficient (q(2)) values for CoMFA (0.743) and for CoMSIA (0.708) were achieved, illustrating high predictive capabilities. Selected descriptors for the CoMFA model were ClogP (logarithm of the octanol/water partition coefficient), steric and electrostatic fields, while, ClogP, electrostatic and hydrogen bond donor fields were used for the CoMSIA model. Molecular docking results confirmed that half of the tested flavonoids inhibited DNA gyrase B (GyrB) by interacting with adenosine-triphosphate (ATP) pocket in a same orientation. Polymethoxyl flavones, flavonoid glycosides, isoflavonoids changed their orientation, resulting in a decrease of inhibitory activity. Moreover, docking results showed that 3-hydroxyl, 5-hydroxyl, 7-hydroxyl and 4-carbonyl groups were found to be crucial active substituents of flavonoids by interacting with key residues of GyrB, which were in agreement with the QSAR study results. These results provide valuable information for structure requirements of flavonoids as antibacterial agents.

Pim-1 kinase as cancer drug target: An update

Proviral integration site for Moloney murine leukemia virus-1 (Pim-1) is a serine/threonine kinase that regulates multiple cellular functions such as cell cycle, cell survival, drug resistance. Aberrant elevation of Pim-1 kinase is associated with numerous types of cancer. Two distinct isoforms of Pim-1 (Pim-1S and Pim-1L) show distinct cellular functions. Pim-1S predominately localizes to the nucleus and Pim-1L localizes to plasma membrane for drug resistance. Recent studies show that mitochondrial Pim-1 maintains mitochondrial integrity. Pim-1 is emerging as a cancer drug target, particularly in prostate cancer. Recently the potent new functions of Pim-1 in immunotherapy, senescence bypass, metastasis and epigenetic dynamics have been found. The aim of the present updated review is to provide brief information regarding networks of Pim-1 kinase and focus on its recent advances as a novel drug target.

Binding site identification and role of permanent water molecule of PIM-3 kinase: A molecular dynamics study

The kinome is a protein kinase complement of the human genome, categorized as serine/threonine and tyrosine kinases. These kinases catalyze phosphorylation reaction by using ATP as phosphoryl donor. Proviral Integration Site for Moloney Murine Leukemia Virus (PIM) kinase encodes serine/threonine protein kinases that recognized as proto-oncogene, responsible for rapid growth of cancerous cells. It is implicated in cell survival and function via cell cycle progression and its metabolism. PIM-3, sub-member of PIM kinases is a proto-oncogene, its overexpression inhibits apoptosis, and results in progression of hepatocellular carcinoma. PIM-3 is considered as a promising drug target but attempts to develop its specific inhibitors is slowed down due to the lack of 3D structure by any experimental technique. In silico techniques generally facilitate scientist to explore hidden structural features in order to improve drug discovery. In the present study, homology modeling, molecular docking and MD simulation techniques were utilized to explore the structure and dynamics of PIM-3 kinase. Induction of water molecules during molecular docking simulation explored differences in the hinge region between PIM-1 and PIM-3 kinases that may be responsible for specificity. Furthermore, role of water molecules in the active site was also explored via radial distribution function (RDF) after a 10 ns molecular dynamics (MD) simulations. Generated RDF plots exhibited the importance of water for inhibitor binding through their bridging capability that links the ligand with binding site residues.

A network flow approach to predict protein targets and flavonoid backbones to treat respiratory syncytial virus infection

BACKGROUND

Respiratory syncytial virus (RSV) infection is the major cause of respiratory disease in lower respiratory tract in infants and young children. Attempts to develop effective vaccines or pharmacological treatments to inhibit RSV infection without undesired effects on human health have been unsuccessful. However, RSV infection has been reported to be affected by flavonoids. The mechanisms underlying viral inhibition induced by these compounds are largely unknown, making the development of new drugs difficult.

METHODS

To understand the mechanisms induced by flavonoids to inhibit RSV infection, a systems pharmacology-based study was performed using microarray data from primary culture of human bronchial cells infected by RSV, together with compound-proteomic interaction data available for Homo sapiens.

RESULTS

After an initial evaluation of 26 flavonoids, 5 compounds (resveratrol, quercetin, myricetin, apigenin, and tricetin) were identified through topological analysis of a major chemical-protein (CP) and protein-protein interacting (PPI) network. In a nonclustered form, these flavonoids regulate directly the activity of two protein bottlenecks involved in inflammation and apoptosis.

CONCLUSIONS

Our findings may potentially help uncovering mechanisms of action of early RSV infection and provide chemical backbones and their protein targets in the difficult quest to develop new effective drugs.

The PIM kinases in hematological cancers

The PIM genes represent a family of proto-oncogenes that encode three different serine/threonine protein kinases (PIM1, PIM2 and PIM3) with essential roles in the regulation of signal transduction cascades, which promote cell survival, proliferation and drug resistance. PIM kinases are overexpressed in several hematopoietic tumors and support in vitro and in vivo malignant cell growth and survival, through cell cycle regulation and inhibition of apoptosis. PIM kinases do not have an identified regulatory domain, which means that these proteins are constitutively active once transcribed. They appear to be critical downstream effectors of important oncoproteins and, when overexpressed, can mediate drug resistance to available agents, such as rapamycin. Recent crystallography studies reveal that, unlike other kinases, they possess a hinge region, which creates a unique binding pocket for ATP, offering a target for an increasing number of potent small-molecule PIM kinase inhibitors. Preclinical studies in models of various hematologic cancers indicate that these novel agents show promising activity and some of them are currently being evaluated in a clinical setting. In this review, we profile the PIM kinases as targets for therapeutics in hematologic malignancies.

7,8-dichloro-1-oxo-β-carbolines as a versatile scaffold for the development of potent and selective kinase inhibitors with unusual binding modes

Development of both potent and selective kinase inhibitors is a challenging task in modern drug discovery. The innate promiscuity of kinase inhibitors largely results from ATP-mimetic binding to the kinase hinge region. We present a novel class of substituted 7,8-dichloro-1-oxo-β-carbolines based on the distinct structural features of the alkaloid bauerine C whose kinase inhibitory activity does not rely on canonical ATP-mimetic hinge interactions. Intriguingly, cocrystal structures revealed an unexpected inverted binding mode and the presence of halogen bonds with kinase backbone residues. The compounds exhibit excellent selectivity over a comprehensive panel of human protein kinases while inhibiting selected kinases such as the oncogenic PIM1 at low nanomolar concentrations. Together, our biochemical and structural data suggest that this scaffold may serve as a valuable template for the design and development of specific inhibitors of various kinases including the PIM family of kinases, CLKs, DAPK3 (ZIPK), BMP2K (BIKE), and others.

Three-dimensional quantitative structure-activity relationship studies on UGT1A9-mediated 3-O-glucuronidation of natural flavonols using a pharmacophore-based comparative molecular field analysis model

Glucuronidation is often recognized as one of the rate-determining factors that limit the bioavailability of flavonols. Hence, design and synthesis of more bioavailable flavonols would benefit from the establishment of predictive models of glucuronidation using kinetic parameters [e.g., K(m), V(max), intrinsic clearance (CL(int)) = V(max)/K(m)] derived for flavonols. This article aims to construct position (3-OH)-specific comparative molecular field analysis (CoMFA) models to describe UDP-glucuronosyltransferase (UGT) 1A9-mediated glucuronidation of flavonols, which can be used to design poor UGT1A9 substrates. The kinetics of recombinant UGT1A9-mediated 3-O-glucuronidation of 30 flavonols was characterized, and kinetic parameters (K(m), V(max), CL(int)) were obtained. The observed K(m), V(max), and CL(int) values of 3-O-glucuronidation ranged from 0.04 to 0.68 μM, 0.04 to 12.95 nmol/mg/min, and 0.06 to 109.60 ml/mg/min, respectively. To model UGT1A9-mediated glucuronidation, 30 flavonols were split into the training (23 compounds) and test (7 compounds) sets. These flavonols were then aligned by mapping the flavonols to specific common feature pharmacophores, which were used to construct CoMFA models of V(max) and CL(int), respectively. The derived CoMFA models possessed good internal and external consistency and showed statistical significance and substantive predictive abilities (V(max) model: q(2) = 0.738, r(2) = 0.976, r(pred)(2) = 0.735; CL(int) model: q(2) = 0.561, r(2) = 0.938, r(pred)(2) = 0.630). The contour maps derived from CoMFA modeling clearly indicate structural characteristics associated with rapid or slow 3-O-glucuronidation. In conclusion, the approach of coupling CoMFA analysis with a pharmacophore-based structural alignment is viable for constructing a predictive model for regiospecific glucuronidation rates of flavonols by UGT1A9.

Why target PIM1 for cancer diagnosis and treatment?

The highly conserved proto-oncogenic protein PIM1 is an unusual serine or threonine kinase, in part because it is constitutively active. Overexpression of PIM1 experimentally leads to tumor formation in mice, while complete knockout of the protein has no observable phenotype. It appears to contribute to cancer development in three major ways when it is overexpressed; by inhibiting apoptosis, by promoting cell proliferation and by promoting genomic instability. Expression in normal tissues is nearly undetectable. However, in hematopoietic malignancies and in a variety of solid tumors, increased PIM1 expression has been shown to correlate with the stage of disease. This characteristic suggests it can serve as a useful biomarker for cancer diagnosis and prognosis. Several specific and potent inhibitors of PIM1’s kinase activity have also been shown to induce apoptotic death of cancer cells, to sensitize cancer cells to chemotherapy and to synergize with other anti-tumor agents, thus making it an attractive therapeutic target.

Cell-permeable carboxyl-terminal p27(Kip1) peptide exhibits anti-tumor activity by inhibiting Pim-1 kinase

The incidence and death rate of prostate cancer is increasing rapidly. In addition, the low sensitivity of prostate cancer to chemotherapy makes it difficult to treat this condition. The serine/threonine kinase Pim-1 plays an important role in cell cycle progression and apoptosis inhibition, resulting in prostate tumorigenesis. Therefore, Pim-1 inhibition has been expected to be an attractive target for developing new anti-cancer drugs. However, no small compounds targeting Pim-1 have progressed to clinical use because of their lack of specificity. Here, we have reported a new cell-permeable Pim-1 inhibitory p27^Kip1 peptide that could interfere with the binding of Pim-1 to its substrates and act as an anti-cancer drug. The peptide could bind to Pim-1 and inhibit phosphorylation of endogenous p27^Kip1 and Bad by Pim-1. Treatment of prostate cancer with the peptide induces G₁ arrest and subsequently apoptosis in vitro. However, the peptide showed almost no growth inhibitory or apoptosis-inducing effects in normal cells. The peptide could inhibit tumor growth in in vivo prostate cancer xenograft models. Moreover, the peptide treatment could overcome resistance to taxol, one of the first line chemotherapeutic agents for prostate cancer, and a combination of the peptide with taxol synergistically inhibited prostate cancer growth in vivo. These results indicate that a Pim-1 inhibitory p27^Kip1 peptide could be developed as an anti-cancer drug against prostate cancer.

Inhibitors of PIM-1 kinase: a computational analysis of the binding free energies of a range of imidazo [1,2-b] pyridazines

The binding of a selection of competitive imidazo [1,2-b] pyridazine inhibitors of PIM-1 kinase with nanomolar activity has been analyzed using computational methods. Molecular dynamics simulations using umbrella sampling to determine a potential of mean force have been used to accurately predict the relative free energies of binding of these inhibitors, from -4.3 to -9.5 kcal mol(-1), in excellent agreement with the trends observed in previous experimental assays. The relative activity of the inhibitors could not be accounted for by any single effect or interaction within the active site and could only be fully reproduced when the overall free energies were considered, including important contributions from interactions outside the hinge region and using explicit solvent in the active site. The potential of mean force for the displacement of the glycine-rich phosphate binding loop (P-loop) has also been estimated and shown to be an important feature in the binding of these ligands.

Discovery of 3H-benzo[4,5]thieno[3,2-d]pyrimidin-4-ones as potent, highly selective, and orally bioavailable inhibitors of the human protooncogene proviral insertion site in moloney murine leukemia virus (PIM) kinases

Pim-1, Pim-2, and Pim-3 are a family of serine/threonine kinases which have been found to be overexpressed in a variety of hematopoietic malignancies and solid tumors. Benzothienopyrimidinones were discovered as a novel class of Pim inhibitors that potently inhibit all three Pim kinases with subnanomolar to low single-digit nanomolar K(i) values and exhibit excellent selectivity against a panel of diverse kinases. Protein crystal structures of the bound Pim-1 complexes of benzothienopyrimidinones 3b (PDB code 3JYA), 6e (PDB code 3JYO), and 12b (PDB code 3JXW) were determined and used to guide SAR studies. Multiple compounds exhibited potent antiproliferative activity in K562 and MV4-11 cells with submicromolar EC(50) values. For example, compound 14j inhibited the growth of K562 cells with an EC(50) value of 1.7 muM and showed K(i) values of 2, 3, and 0.5 nM against Pim-1, Pim-2, and Pim-3, respectively. These novel Pim kinase inhibitors efficiently interrupted the phosphorylation of Bad in both K562 and LnCaP-Bad cell lines, indicating that their potent biological activities are mechanism-based. The pharmacokinetics of 14j was studied in CD-1 mice and shown to exhibit bioavailability of 76% after oral dosing. ADME profiling of 14j suggested a long half-life in both human and mouse liver microsomes, good permeability, modest protein binding, and no CYP inhibition below 20 muM concentration.

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

Members of the Pim kinase family have been identified as promising targets for the development of antitumor agents. After a screening of pyrrolo[2,3-a]- and [3,2-a]carbazole derivatives toward 66 protein kinases, we identified pyrrolo[2,3-a]carbazole as a new scaffold to design potent Pim kinase inhibitors. In particular, compound 9 was identified as a low nM selective Pim inhibitor. Additionally, several pyrrolo[2,3-a]carbazole derivatives showed selectivity for Pim-1 and Pim-3 over Pim-2. In vitro antiproliferative activities of 9 and 28, the most potent Pim inhibitors identified, were evaluated toward three human solid cancer cell lines (PA1, PC3, and DU145) and one human fibroblast primary culture, revealing IC50 values in the micromolar range. Finally, the crystal structure of Pim-1 complexed with lead compound 9 was determined. The structure revealed a non-ATP mimetic binding mode with no hydrogen bonds formed with the kinase hinge region and explained the selectivity of pyrrolo[2,3-a]carbazole derivatives for Pim kinases.

Novel benzylidene-thiazolidine-2,4-diones inhibit Pim protein kinase activity and induce cell cycle arrest in leukemia and prostate cancer cells

The Pim protein kinases play important roles in cancer development and progression, including prostate tumors and hematologic malignancies. To investigate the potential role of these enzymes as anticancer drug targets, we have synthesized novel benzylidene-thiazolidine-2,4-diones that function as potent Pim protein kinase inhibitors. With IC(50) values in the nanomolar range, these compounds block the ability of Pim to phosphorylate peptides and proteins in vitro and, when added to DU145 prostate cancer cells overexpressing Pim, inhibit the ability of this enzyme to phosphorylate a known substrate, the BH(3) protein BAD. When added to prostate cancer cell lines, including PC3, DU145, and CWR22Rv1, and human leukemic cells, MV4;11, K562, and U937 cells, these compounds induce G(1)-S cell cycle arrest and block the antiapoptotic effect of the Pim protein kinase. The cell cycle arrest induced by these compounds is associated with an inhibition of cyclin-dependent kinase 2 and activity and translocation of the Pim-1 substrate p27(Kip1), a cyclin-dependent kinase 2 inhibitory protein, to the nucleus. Furthermore, when added to leukemic cells, these compounds synergize with the mammalian target of rapamycin inhibitor rapamycin to decrease the phosphorylation level of the translational repressor 4E-BP1 at sites phosphorylated by mammalian target of rapamycin. Combinations of rapamycin and the benzylidene-thiazolidine-2,4-diones synergistically block the growth of leukemic cells. Thus, these agents represent novel Pim inhibitors and point to an important role for the Pim protein kinases in cell cycle control in multiple types of cancer cells.

Synthesis and evaluation of novel inhibitors of Pim-1 and Pim-2 protein kinases

The Pim protein kinases are frequently overexpressed in prostate cancer and certain forms of leukemia and lymphoma. 5-(3-Trifluoromethylbenzylidene)thiazolidine-2,4-dione (4a) was identified by screening to be a Pim-1 inhibitor and was found to attenuate the autophosphorylation of tagged Pim-1 in intact cells. Although 4a is a competitive inhibitor with respect to ATP, a screen of approximately 50 diverse protein kinases demonstrated that it has high selectivity for Pim kinases. Computational docking of 4a to Pim-1 provided a model for lead optimization, and a series of substituted thiazolidine-2,4-dione congeners was synthesized. The most potent new compounds exhibited IC(50)s of 13 nM for Pim-1 and 2.3 microM for Pim-2. Additional compounds in the series demonstrated selectivities of more than 2500-fold and 400-fold for Pim-1 or Pim-2, respectively, while other congeners were essentially equally potent toward the two isozymes. Overall, these compounds are new Pim kinase inhibitors that may provide leads to novel anticancer agents.

The PIM1 kinase is a critical component of a survival pathway activated by docetaxel and promotes survival of docetaxel-treated prostate cancer cells

A defining characteristic of solid tumors is the capacity to divide aggressively and disseminate under conditions of nutrient deprivation, limited oxygen availability, and exposure to cytotoxic drugs or radiation. Survival pathways are activated within tumor cells to cope with these ambient stresses. We here describe a survival pathway activated by the anti-cancer drug docetaxel in prostate cancer cells. Docetaxel activates STAT3 phosphorylation and transcriptional activity, which in turns induces expression of the PIM1 gene, encoding a serine-threonine kinase activated by many cellular stresses. Expression of PIM1 improves survival of docetaxel-treated prostate cancer cells, and PIM1 knockdown or expression of a dominant-negative PIM1 protein sensitize cells to the cytotoxic effects of docetaxel. PIM1 in turn mediates docetaxel-induced activation of NFkappaB transcriptional activity, and PIM1 depends in part on RELA/p65 proteins for its prosurvival effects. The PIM1 kinase plays a critical role in this STAT3 --> PIM1 --> NFkappaB stress response pathway and serves as a target for intervention to enhance the therapeutic effects of cytotoxic drugs such as docetaxel.