Cyclic AMP induces IPC leukemia cell apoptosis via CRE-and CDK-dependent Bim transcription.

The IPC-81 cell line is derived from the transplantable BNML model of acute myelogenic leukemia (AML), known to be a reliable predictor of the clinical efficiency of antileukemic agents, like the first-line AML anthracycline drug daunorubicin (DNR). We show here that cAMP acted synergistically with DNR to induce IPC cell death. The DNR-induced death differed from that induced by cAMP by (1) not involving Bim induction, (2) being abrogated by GSK3ß inhibitors, (3) by being promoted by the HSP90/p23 antagonist geldanamycin and truncated p23 and (4) by being insensitive to the CRE binding protein (CREB) antagonist ICER and to cyclin-dependent protein kinase (CDK) inhibitors. In contrast, the apoptosis induced by cAMP correlated tightly with Bim protein expression. It was abrogated by Bim (BCL2L11) downregulation, whether achieved by the CREB antagonist ICER, by CDK inhibitors, by Bim-directed RNAi, or by protein synthesis inhibitor. The forced expression of BimL killed IPC-81(WT) cells rapidly, Bcl2-overexpressing cells being partially resistant. The pivotal role of CREB and CDK activity for Bim transcription is unprecedented. It is also noteworthy that newly developed cAMP analogs specifically activating PKA isozyme I (PKA-I) were able to induce IPC cell apoptosis. Our findings support the notion that AML cells may possess targetable death pathways not exploited by common anti-cancer agents.

Aryl rings are part of the darpone pharmacophore.

In order to investigate structure-activity relationships in the antiproliferative darpone series, the derivatives 8a and 8b lacking the aryl substituents in either 2- or 4-position were synthesized and evaluated for cancer cell growth inhibition. Since both 8a and 8b were devoid of noteworthy antiproliferative activity, both aryl substituents can be considered as part of the darpone pharmacophore.

Biotin labelling of amines by polymer-assisted solution-phase synthesis.

An efficient and simple polymer-assisted approach has been developed to biotinylate multifunctional compounds bearing an amino functionality. Biotin was immobilized on aminomethylated polystyrene via the Kenner safety catch linker, activated and subsequently transferred to the amino function of the target compounds chemoselectively, thus avoiding protecting group operations. This approach holds potential for the introduction of spacer-modified biotin derivatives.

Paullones are potent inhibitors of glycogen synthase kinase-3beta and cyclin-dependent kinase 5/p25.

Paullones constitute a new family of benzazepinones with promising antitumoral properties. They were recently described as potent, ATP-competitive, inhibitors of the cell cycle regulating cyclin-dependent kinases (CDKs). We here report that paullones also act as very potent inhibitors of glycogen synthase kinase-3beta (GSK-3beta) (IC50: 4-80 nM) and the neuronal CDK5/p25 (IC50: 20-200 nM). These two enzymes are responsible for most of the hyperphosphorylation of the microtubule-binding protein tau, a feature observed in the brains of patients with Alzheimer's disease and other neurodegenerative 'taupathies'. Alsterpaullone, the most active paullone, was demonstrated to act by competing with ATP for binding to GSK-3beta. Alsterpaullone inhibits the phosphorylation of tau in vivo at sites which are typically phosphorylated by GSK-3beta in Alzheimer's disease. Alsterpaullone also inhibits the CDK5/p25-dependent phosphorylation of DARPP-32 in mouse striatum slices in vitro. This dual specificity of paullones may turn these compounds into very useful tools for the study and possibly treatment of neurodegenerative and proliferative disorders.

Structure-based design modifications of the paullone molecular scaffold for cyclin-dependent kinase inhibition.

A congeneric series of paullones were characterized using a 3-D QSAR with cyclin-dependent kinase 1 (CDK1) inhibition data. A homology model of CDK1-cyclin B was developed from the crystal structure of CDK2-cyclin A, which subsequently served as the basis for the structure-based design. Paullones were docked into the ATP binding site of the CDK1-cylin B models and were optimized with molecular mechanics. Hydropathic analyses of the paullone-CDK1 complexes were performed after the atom types were assigned based on each ligand's electronic properties calculated from quantum mechanics. Hydropathic descriptors formed a significant multiple regression equation that predicts paullone IC50 data. The results indicate that the combination of hydropathic descriptors with molecular mechanics geometries are sufficient to design overt steric and chemical complementarity of the ligands. However, the electronic properties derived from quantum mechanics helped direct synthetic chemistry efforts to produce ligands that promote better charge transfer and strengthen hydrogen bonding as facilitated by resonance stabilization. Compounds with low affinity for CDK1 were poor charge acceptors and made less than ideal hydrogen bonding arrangements with the receptor. These considerations led to the prediction that structures such as 9-cyanopaullone would be considerably more potent than the parent compound, a finding supported by enzyme inhibition data. Also, 9-nitropaullone emerged as a paullone which also had similar potency in enzyme inhibition as well as a favorable anti-proliferative activity profile in living cells.

2-Substituted paullones: CDK1/cyclin B-inhibiting property and in vitro antiproliferative activity.

9-Trifluoromethyl-paullones with a carbon chain in the 2-position were synthesized by palladium-catalyzed coupling reactions of a 2-iodoprecursor with terminal alkenes or alkynes, respectively. The introduction of a 2-cyanoethyl substituent led to a significant enhancement of CDK1/cyclin B inhibiting property and in vitro antiproliferative activity.

Exploration of the effect of sterically demanding 3'-amido substitution of 3'-deoxyadenosines towards inhibition of cyclin-dependent kinase 1.

With focus on exploring the structural demands of adenosine triphosphate pockets of different target enzymes, the 3'-amido-3'-deoxyadenosines 1-7 were synthesized. The inhibitory activity of these compounds on a selected cyclin-dependent kinase as model target in anticancer research was evaluated in vitro. A starfish oocyte enzyme based assay revealed a decreased inhibitory activity in comparison to adenosine. Consequently, the introduction of spacefilling lipophilic 3'-amido substituents alters the enzyme inhibition in an unfavorable manner.

Naphthannelated azepinones: synthesis and antitumor activity.

5H-Benzo[b]naphth[2,3-e]azepine-6,13-diones 4a, 4b and 4H-naphtho[2,3-e]thieno[3,2-b]azepine-5,12-dione (6) were prepared by aldol condensation of phthalic dialdehyde (3) with the fused azepinediones 2a, 2b and 5, respectively. The Schmidt reaction of naphthacene-5,12-quinone (7) yielded 6H-benzo[e]naphth[2,3-b]azepine-7,12-dione (10). Several derivatives of the heterocyclic basic scaffolds 4, 6 and 10 were prepared by standard procedures, e.g. Grignard reaction, deoxygenation with triethylsilane, and sodium borohydride reduction. Evaluation of the synthesized compounds in the NCI in vitro cell line screening revealed a modest antitumor activity without marked cell line selectivity for the majority of the derivatives. The 2-bromo-5H-benzo[b]naphth[2,3-e]azepin-6(13H)-one (19) was the only representative in this series exhibiting a noteworthy growth inhibitory effect for human tumor cells.

Cyclin-dependent kinases: initial approaches to exploit a novel therapeutic target.

Cyclin-dependent kinases (CDKs) have been recognized as key regulators of cell cycle progression. Alteration and deregulation of CDK activity are pathogenic hallmarks of neoplasia. Therefore, inhibitors or modulators would be of interest to explore as novel therapeutic agents in cancer, as well as other hyperproliferative disorders. Flavopiridol is a semisynthetic flavonoid that emerged from an empirical screening program as a potent antiproliferative agent that mechanistic studies demonstrated to directly inhibit CDKs 1, 2, and 4 as a competitive ATP site antagonist. Initial clinical trials have shown that concentrations that inhibit cell proliferation and CDK activity in vitro can be safely achieved in humans, and additional clinical trials will establish its clinical potential. To address the need for additional chemotypes that may serve as lead structures for drugs that would not have the toxicities associated with flavopiridol, compounds with a similar pattern of cell growth inhibitory activity in the National Cancer Institute's in vitro anticancer drug screen have been recognized by the computer-assisted pattern recognition algorithm COMPARE and then screened for anti-CDK activity in a biochemical screen. The benzodiazepine derivative NSC 664704 (7,12-dihydro-indolo[3,2-d][1]benzazepin-6(5H)-one) was revealed by that approach as a moderately potent (IC50 0.4 microM) inhibitor of CDK2, which in initial experiments shows evidence of causing cell cycle redistribution in living cells. NSC 664704 is, therefore, a candidate for further structural optimization, guided in part by understanding of the ATP-binding site in CDK2. This approach represents one way of combining empirical screening information with structure-based design to derive novel candidate therapeutic agents directed against an important cellular target.

Paullones, a series of cyclin-dependent kinase inhibitors: synthesis, evaluation of CDK1/cyclin B inhibition, and in vitro antitumor activity.

The paullones represent a novel class of small molecule cyclin-dependent kinase (CDK) inhibitors. To investigate structure-activity relationships and to develop paullones with antitumor activity, derivatives of the lead structure kenpaullone (9-bromo-7,12-dihydroindolo[3,2-d][1]benzazepin-6(5H)-one, 4a) were synthesized. Paullones with different substituents in the 2-, 3-, 4-, 9-, and 11-positions were prepared by a Fischer indole reaction starting from 1H-[1]benzazepine-2,5(3H,4H)-diones 5. Selective substitutions at either the lactam or the indole nitrogen atom were accomplished by treating kenpaullone with alkyl halides in the presence of sodium hydride/THF or potassium hydroxide/acetone, respectively. S-Methylation of the kenpaullone-derived thiolactam 18 yielded the methylthioimidate 19, which gave the hydroxyamidine 20 upon reaction with hydroxylamine. The new paullones were tested both in a CDK1/cyclin B inhibition assay and in the in vitro antitumor cell line-screening program of the National Cancer Institute (NCI). With respect to the CDK1/cyclin B inhibition, electron-withdrawing substituents in the 9-position as well as a 2,3-dimethoxy substitution on the paullone basic scaffold turned out to be favorable. A 9-trifluoromethyl substituent was found to be equivalent to the 9-bromo substituent of kenpaullone. Replacement of the 9-bromo substituent of kenpaullone by a 9-cyano or 9-nitro group produced a substantial increase in enzyme-inhibiting potency. Substitutions in other positions or the replacement of the lactam moiety led to decreased CDK1 inhibition. Noteworthy in vitro antitumor activities (GI(50) values between 1 and 10 microM) were found with the 9-bromo-2,3-dimethoxy-7,12-dihydroindolo[3, 2-d][1]benzazepin-6(5H)-one (4t), its 9-trifluoromethyl analogue 4u, the 12-Boc-substituted paullone15, and the methylthioimidate 19, respectively. The 9-nitro-7,12-dihydroindolo[3, 2-d][1]benzazepin-6(5H)-one (4j, named alsterpaullone) showed a high CDK1/cyclin B inhibitory activity (IC(50) = 0.035 microM) and exceeded the in vitro antitumor potency of the other paullones by 1 order of magnitude (log GI(50) mean graph midpoint = -6.4 M).

Discovery and initial characterization of the paullones, a novel class of small-molecule inhibitors of cyclin-dependent kinases.

Analysis of the National Cancer Institute Human Tumor Cell Line Anti-Cancer Drug Screen data using the COMPARE algorithm to detect similarities in the pattern of compound action to flavopiridol, a known inhibitor of cyclin-dependent kinases (CDKs), has suggested several possible novel CDK inhibitors. 9-Bromo-7,12-dihydro-indolo[3,2-d][1]benzazepin-6(5H)-one, NSC-664704 (kenpaullone), is reported here to be a potent inhibitor of CDK1/cyclin B (IC50, 0.4 microM). This compound also inhibited CDK2/cyclin A (IC50, 0.68 microM), CDK2/cyclin E (IC50, 7.5 microM), and CDK5/p25 (IC50, 0.85 microM) but had much less effect on other kinases; only c-src (IC50, 15 microM), casein kinase 2 (IC50, 20 microM), erk 1 (IC50, 20 microM), and erk 2 (IC50, 9 microM) were inhibited with IC50s less than 35 microM. Kenpaullone acts by competitive inhibition of ATP binding. Molecular modeling indicates that kenpaullone can bind in the ATP binding site of CDK2 with residue contacts similar to those observed in the crystal structures of other CDK2-bound inhibitors. Analogues of kenpaullone, in particular 10-bromopaullone (NSC-672234), also inhibited various protein kinases including CDKs. Cells exposed to kenpaullone and 10-bromopaullone display delayed cell cycle progression. Kenpaullone represents a novel chemotype for compounds that preferentially inhibit CDKs.

Antitumor pyrido[3,2-d][1]benzazepines: synthesis and in vitro activity of thiophene analogs.

The bioisosteric replacement of benzene elements in the antitumor lead structures 2 and 3 led to the thienyl substituted 5H-pyrido[3,2-d][1]benzazepin-6(7H)-ones 8a and 8b, the analogous thiolactams 4a and 4b, and the 4H-pyrido[2,3-d]-thieno[3,2-b]azepines 11 and 12 which represent a novel heterocyclic scaffold. The in vitro evaluation of 4a in a cell line based screening revealed a noteworthy antitumor activity and a remarkable selectivity for renal tumor cell lines. The cell line selectivity pattern of 4a differs distinctly from the pattern displayed by standard antitumor agents.

Fused azepinones with antitumor activity.

Based on the observation that some simple [1]benzazepin-2-ones exhibit in vivo antitumor activity, studies directed to several new structure classes with this partial motif have been reported recently, comprising 7,12-dihydro-indolo[3, 2-d][1]benzazepin-6(5H)-ones (paullones), 5H-qui nolino[3, 2-d][1]benzazepin-6(7H)-ones, 2,4-diaryl-5H-pyrido[3, 2-d][1]benzazepin-6(7H)-ones, spiro[1-benzazepine-4,1 -cyclohexane] deriva-tives, and naphthannelated benzazepinones. For the syntheses of these heterocyclic compounds, 1H-[1]benzazepine-2,5(3H,4H)-diones were employed as readily available starting materials. In each of the mentioned series, entities with in vitro antitumor activity have been detected. Considering potency and in vitro cell line selectivity, both the 2,4-diaryl-5H-pyrido[3, 2-d][1]benzazepin-6(7H)-ones and the paullones are apparently suitable for a further development. A biological mechanism probably related to the anti proliferative activity has been established only for the paullones. These compounds represent a novel class of selective inhibitors of cyclin-dependent kinases, a family of enzymes whose function seems to be deregulated in many human tumors.

d-Fused [1]benzazepines with selective in vitro antitumor activity: synthesis and structure-activity relationships.

The synthesis of novel quinolino[3,2-d][1]benzazepines and pyrido[3,2-d][1]benzazepines is described. The in vitro antitumor activity of the compounds has been tested in the antitumor screening of the National Cancer Institute (NCI). Several 2,4-diarylpyrido[3, 2-d][1]benzazepin-6-ones and -thiones turned out to exhibit considerable cytotoxicity for tumor cells. For studies of SAR within these series, substituents were introduced into the aromatic rings of the parent systems. Compounds from the thiolactam series tended to show higher potency than the corresponding lactams. Prominent compounds with noteworthy activity and remarkable selectivity for renal cancer cell lines are the lactams 10c, 10g, and 10h and the corresponding thiolactams 11c, 11g, and 11h. Methylation of the azepine nitrogen leads to complete loss of activity, whereas annelation of a triazolo ring at the lactam site or transformation of the thiolactam function to a thiolactim ether results in decreased antitumor activity and selectivity. Consequently, the secondary lactam or thiolactam structure of the seven-membered ring has to be regarded as essential for selective antitumor activity.