Synthesis of novel 5-substituted indirubins as protein kinases inhibitors

cAMP-guanine exchange factor protection from bile acid-induced hepatocyte apoptosis involves glycogen synthase kinase regulation of c-Jun NH2-terminal kinase

Cholestatic liver disorders are accompanied by the hepatic accumulation of cytotoxic bile acids that induce cell death. Increases in cAMP protect hepatocytes from bile acid-induced apoptosis by a cAMP-guanine exchange factor (cAMP-GEF)/phosphoinositide-3-kinase (PI3K)/Akt pathway. The aim of these studies was to identify the downstream substrate in this pathway and to determine at what level in the apoptotic cascade cytoprotection occurs. Since inhibitory phosphorylation of glycogen synthase kinase-3 (GSK) occurs downstream of PI3K/Akt and this phosphorylation has been implicated in cell survival, we conducted studies to determine whether GSK was downstream in cAMP-GEF/PI3K/Akt-mediated cytoprotection. Our results show that treatment of hepatocytes with the cAMP-GEF-specific analog, 4-(4-chlorophenylthio)-2'-O-methyladenosine-3',5'-cAMP, results in PI3K-dependent phosphorylation of GSK. Direct chemical inhibition of GSK in rat hepatocytes or human HUH7-NTCP cells with several structurally and functionally distinct inhibitors including bromoindirubin-3'-oxime (BIO), maleimides (SB216763, SB415286), thiadiazolidine derivatives, and LiCl attenuates apoptosis induced by glycochenodeoxycholate (GCDC). In addition, genetic silencing of the GSK β isoform with small interfering RNA attenuates GCDC apoptosis in HUH7-NTCP cells. Adenoviral inhibition of the Rap1 blocks both cAMP-GEF-mediated cytoprotection against GCDC-induced apoptosis and Akt/GSK3β phosphorylation. GCDC-induced phosphorylation of the proapoptotic kinase, c-Jun NH(2)-terminal kinase (JNK) is inhibited by GSK inhibition or cAMP-GEF activation. GCDC-induced apoptosis is accompanied by phosphorylation of the endoplasmic reticulum stress markers pIEF2α and IRE-1, and pretreatment with the cAMP-GEF analog or GSK inhibitors prevents this phosphorylation. Collectively, our results support the presence of a cAMP/cAMP-GEF/Rap1/PI3K/Akt/GSKβ survival pathway in hepatocytes that inhibits bile acid-induced JNK phosphorylation.

Synthesis and Toxicity Evaluation of Some N4-Aryl Substituted 5-Trifluoromethoxyisatin-3-thiosemicarbazones

A series of twenty one N4-aryl substituted 5-trifluoromethoxyisatin-3-thiosemicarbazones 3a-3u was synthesized by the reaction of trifluoromethoxyisatin 1 with different arylthiosemicarbazides 2 in aqueous ethanol (50%), containing a few drops of acetic acid. Their structures were established on the basis of analytical (CHN) and spectral (IR, 1H-NMR, EIMS) data. All the synthesized compounds were evaluated for their toxicity potential by a brine shrimp lethality bioassay. Ten compounds i.e., 3a, 3e, 3i-3l and 3n-3q proved to be active in this assay, displaying promising toxicity (LD50 = 1.11 × 10-5 M - 1.80 × 10-4 M). Amongst these, 3k, 3n and 3o were found to be the most active ones (LD50 = 1.11 × 10-5 M - 1.43 × 10-5 M). Compound 3k showed the highest activity with a LD50 value of 1.11 × 10-5 M and can, therefore, be used as a lead for further studies. Structure-activity relationship (SAR) studies revealed that the presence of strong inductively electron-attracting trifluoromethoxy substituent at position-5 of the isatin moiety played an important role in inducing or enhancing toxic potentiality of some of the synthesized compounds.

5,5'-substituted indirubin-3'-oxime derivatives as potent cyclin-dependent kinase inhibitors with anticancer activity

To enhance the ability of indirubin derivatives to inhibit CDK2/cyclin E, a target of anticancer agents, we designed and synthesized a new series of indirubin-3'-oxime derivatives with combined substitutions at the 5 and 5' positions. A molecular docking study predicted the binding of derivatives with OH or halogen substitutions at the 5' position to the ATP binding site of CDK2, revealing the critical interactions that may explain the improved CDK2 inhibitory activity of these derivatives. Among the synthesized derivatives, the 5-nitro-5'-hydroxy analogue 3a and the 5-nitro-5'-fluoro analogue 5a displayed potent inhibitory activity against CDK2, with IC(50) values of 1.9 and 1.7 nM, respectively. These derivatives also showed antiproliferative activity against several human cancer cell lines, with IC(50) values of 0.2-3.3 microM. A representative analogue, 3a, showed greater than 500-fold selectivity for CDK relative to selected kinase panel and potent in vivo anticancer activity.

Indirubins deplete striatal monoamines in the Intact and MPTP-treated mouse brain and block kainate-induced striatal astrogliosis

The indirubins long have been used in Chinese medicine for treatment of myelocytic leukemia. Among the many more recently described biological activities of the indirubins, attention has been directed toward the ability of these compounds to inhibit GSK-3 and CDKs, kinases implicated in neurodegenerative conditions. Little information is available on effects of indirubins on chemically-induced neurodegeneration. Here we examined the influence of three indirubins on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)- and kainic acid (KA)-induced neurotoxicity in the mouse. The three indirubins examined were 6-bromoindirubin-3'-oxime (6BIO), 5-bromoindirubin-3'-oxime (5BIO) and 5-amino-6-bromoindirubin (5A6BI). The first two derivatives were previously described indirubins with low nanomolar inhibitory activity against GSK-3 and CDKs. The third compound was synthesized by the dimerization of 5-amino-6-bromoisatin with 3-acetoxyindol. The synthesis of the key compound 5-amino-6-bromoisatin was based on the bromination of the ketal of 5-amino-isatin. All indirubins examined decreased various measures associated with dopaminergic neurotransmission in striatum. These effects occurred alone or over and above the decrements seen following administration of the dopaminergic neurotoxicant, MPTP. Striatal serotonin and serotonin turnover were decreased by the indirubins in MPTP-treated mice. None of these striatal effects of the indirubins alone were associated with evidence of astrogliosis, an indicator of underlying neuropathology, nor did they potentiate the astrogliosis accompanying administration of MPTP. In general, the indirubins reduced KA-associated mortality and striatal but not hippocampal astrogliosis due to this toxicant. The data suggest that indirubins affect striatal biogenic amine levels and turnover in intact mice. The data do not indicate a neuroprotective action of indirubins in mice treated with MPTP but that they do suggest that they may be neuroprotective against KA-induced injury of the neostriatum.

(Z)-4-Hexyl-1-(5-nitro-2-oxo-2,3-dihydro-1H-indol-3-yl-idene)thio-semicarbazide

In the title compound, C(15)H(19)N(5)O(3)S, intra-molecular N-H⋯O, N-H⋯N and C-H⋯S inter-actions occur and the three terminal C atoms of the hexyl group are disordered over two sites with an occupancy ratio of 0.664 (12):0.336 (12). In the crystal, inversion dimers linked by pairs of N-H⋯O hydrogen bonds occur and C-H⋯O bonds link the dimers into chains. A short C=O⋯π contact is also present.

Synthesis, activity, and pharmacophore development for isatin-beta-thiosemicarbazones with selective activity toward multidrug-resistant cells

We have recently identified a new class of compounds that selectively kill cells that express P-glycoprotein (P-gp, MDR1), the ATPase efflux pump that confers multidrug resistance on cancer cells. Several isatin-beta-thiosemicarbazones from our initial study have been validated and a range of analogues synthesized and tested. A number demonstrated improved MDR1-selective activity over the lead, NSC73306 (1). Pharmacophores for cytotoxicity and MDR1 selectivity were generated to delineate the structural features required for activity. The MDR1-selective pharmacophore highlights the importance of aromatic/hydrophobic features at the N4 position of the thiosemicarbazone and the reliance on the isatin moiety as key bioisosteric contributors. Additionally, a quantitative structure-activity relationship (QSAR) model that yielded a cross-validated correlation coefficient of 0.85 effectively predicts the cytotoxicity of untested thiosemicarbazones. Together, the models serve as effective approaches for predicting structures with MDR1-selective activity and aid in directing the search for the mechanism of action of 1.

Glycogen synthase kinase 3: more than a namesake

Glycogen synthase kinase 3 (GSK3), a constitutively acting multi-functional serine threonine kinase is involved in diverse physiological pathways ranging from metabolism, cell cycle, gene expression, development and oncogenesis to neuroprotection. These diverse multiple functions attributed to GSK3 can be explained by variety of substrates like glycogen synthase, tau protein and beta catenin that are phosphorylated leading to their inactivation. GSK3 has been implicated in various diseases such as diabetes, inflammation, cancer, Alzheimer's and bipolar disorder. GSK3 negatively regulates insulin-mediated glycogen synthesis and glucose homeostasis, and increased expression and activity of GSK3 has been reported in type II diabetics and obese animal models. Consequently, inhibitors of GSK3 have been demonstrated to have anti-diabetic effects in vitro and in animal models. However, inhibition of GSK3 poses a challenge as achieving selectivity of an over achieving kinase involved in various pathways with multiple substrates may lead to side effects and toxicity. The primary concern is developing inhibitors of GSK3 that are anti-diabetic but do not lead to up-regulation of oncogenes. The focus of this review is the recent advances and the challenges surrounding GSK3 as an anti-diabetic therapeutic target.

Inhibition of Toxoplasma gondii by indirubin and tryptanthrin analogs

New drugs are needed for treatment of Toxoplasma gondii infections. We tested derivatives of principles found in Isatis indigotica for in vitro efficacy against T. gondii infection. Indirubin-3'-oxime analogs showed modest micromolar activity, while tryptanthrin derivatives displayed 50% inhibitory doses in the low nanomolar range. Tryptanthrins have potential as anti-Toxoplasma infection therapeutics.

Soluble 3',6-substituted indirubins with enhanced selectivity toward glycogen synthase kinase -3 alter circadian period

Glycogen synthase kinase -3 (GSK-3) is a key enzyme involved in numerous physiological events and in major diseases, such as Alzheimer's disease, diabetes, and cardiac hypertrophy. Indirubins are bis-indoles that can be generated from various natural sources or chemically synthesized. While rather potent and selective as GSK-3 inhibitors, most indirubins exhibit low water solubility. To address the issue of solubility, we have designed novel analogues of 6-bromo-indirubin-3'-oxime with increased hydrophilicity based on the GSK-3/indirubins cocrystal structures. The new derivatives with an extended amino side chain attached at position 3' showed potent GSK-3 inhibitory activity, enhanced selectivity, and dramatically increased water solubility. Furthermore, some of them displayed little or no cytotoxicity. The new indirubins inhibit GSK-3 in a cellular reporter model. They alter the circadian period measured in rhythmically expressing cell cultures, suggesting that they might constitute tools to investigate circadian rhythm regulation.

Novel aryl and heteroaryl substituted N-[3-(4-phenylpiperazin-1-yl)propyl]-1,2,4-oxadiazole-5-carboxamides as selective GSK-3 inhibitors

Synthesis, biological evaluation, and SAR dependencies for a series of novel aryl and heteroaryl substituted N-[3-(4-phenylpiperazin-1-yl)propyl]-1,2,4-oxadiazole-5-carboxamide inhibitors of GSK-3beta kinase are described. The inhibitory activity of the synthesized compounds is highly dependent on the character of substituents in the phenyl ring and the nature of terminal heterocyclic fragment of the core molecular scaffold. The most potent compounds from this series contain 3,4-di-methyl or 2-methoxy substituents within the phenyl ring and 3-pyridine fragment connected to the 1,2,4-oxadiazole heterocycle. These compounds selectively inhibit GSK-3beta kinase with IC(50) value of 0.35 and 0.41 microM, respectively.

Quantitative and selective assay of 5-methylindirubine, an inhibitor of cyclin-dependent kinases, in murine plasma using coupled liquid chromatography and electrospray tandem mass spectrometry

A sensitive and rapid LC-MS/MS assay for the quantitative determination of 5-methylindirubine (5-MI) in murine plasma is described. A 50-microL-murine plasma aliquot was spiked with an internal standard, indirubine-3-monoxime (IMO), and extracted with 1.25 mL diethyl ether. Dried extracts were reconstituted in methanol-water (8:2, v/v) and 10 microL-volumes were injected onto the HPLC system. Separation was achieved on a Gemini C18 column (150 mm x 2.1 mm ID, particle size 5 microm) using an alkaline eluent (10 mM ammonium hydroxide-methanol (5:95, v/v)). Detection was performed by negative ion electrospray followed by tandem mass spectrometry. The assay quantifies 5-MI in a range from 1 to 500 ng/mL using 50 microL of murine EDTA plasma samples. Validation results demonstrate that 5-MI concentrations can be accurately and precisely quantified in murine plasma. This assay is used to support pre-clinical pharmacologic studies with 5-MI.

Structure-activity relationships of 3,4-dihydro-1H-quinazolin-2-one derivatives as potential CDK5 inhibitors

Cyclin-dependent kinase 5 (CDK5) is a serine/threonine kinase that plays a critical role in the early development of the nervous system. Deregulation of CDK5 is believed to contribute to the abnormal phosphorylation of various cellular substrates associated with neurodegenerative disorders such as Alzheimer's disease, amyotrophic lateral sclerosis, and ischemic stroke. Acyclic urea 3 was identified as a potent CDK5 inhibitor and co-crystallographic data of urea 3/CDK2 enzyme were used to design a novel series of 3,4-dihydroquinazolin-2(1H)-ones as CDK5 inhibitors. In this investigation we present our synthetic studies toward this series of compounds and discuss their biological relevance as CDK5 inhibitors.