1-Amino-substituted 4-methyl-5H-pyrido[4,3-b]indoles (gamma-carbolines) as tricyclic analogues of ellipticines: a new class of antineoplastic agents

Synthesis and Biological Evaluation of Benzo [4,5]- and Naphtho[2',1':4,5]imidazo[1,2-c]pyrimidinone Derivatives

Azacarbazoles have attracted significant interest due to their valuable properties, such as anti-pathogenic and antitumor activity. In this study, a series of structurally related tricyclic benzo[4,5]- and tertacyclic naphtho[2',1':4,5]imidazo[1,2-c]pyrimidinone derivatives with one or two positively charged tethers were synthesized and evaluated for anti-proliferative activity. Lead tetracyclic derivative 5b with two amino-bearing arms inhibited the metabolic activity of A549 lung adenocarcinoma cells with a CC50 value of 3.6 μM, with remarkable selectivity (SI = 17.3) over VA13 immortalized fibroblasts. Cell-cycle assays revealed that 5b triggers G2/M arrest without signs of apoptosis. A study of its interaction with various DNA G4s and duplexes followed by dual luciferase and intercalator displacement assays suggests that intercalation, rather than the modulation of G4-regulated oncogene expression, might contribute to the observed activity. Finally, a water-soluble salt of 5b was shown to cause no acute toxic effects, changes in mice behavior, or any decrease in body weight after a 72 h treatment at concentrations up to 20 mg/kg. Thus, 5b is a promising candidate for studies in vivo; however, further investigations are needed to elucidate its molecular target(s).

Structure-Based Design of γ-Carboline Analogues as Potent and Specific BET Bromodomain Inhibitors

Small-molecule inhibitors of bromodomain and extra terminal proteins (BET), including BRD2, BRD3, and BRD4 proteins have therapeutic potential for the treatment of human cancers and other diseases and conditions. In this paper, we report the design, synthesis, and evaluation of γ-carboline-containing compounds as a new class of small-molecule BET inhibitors. The most potent inhibitor (compound 18, RX-37) obtained from this study binds to BET bromodomain proteins (BRD2, BRD3, and BRD4) with Ki values of 3.2-24.7 nM and demonstrates high selectivity over other non-BET bromodomain-containing proteins. Compound 18 potently and selectively inhibits cell growth in human acute leukemia cell lines harboring the rearranged mixed lineage leukemia 1 gene. We have determined a cocrystal structure of 18 in complex with BRD4 BD2 at 1.4 Å resolution, which provides a solid structural basis for the compound's high binding affinity and for its further structure-based optimization. Compound 18 represents a promising lead compound for the development of a new class of therapeutics for the treatment of human cancer and other conditions.

2,4-Diamino-9H-pyrimido[4,5-b]indol-5-ols: Synthesis, in vitro cytotoxic activity, and QSAR investigations

A series of novel 2,4-diaminopyrimido[4,5-b]indol-6-ols has been synthesized and the in vitro cytotoxic activities were evaluated against four human cancer cell lines originating from solid tumors. An increase in activity was observed when a heteroaromatic ring was annulated on side g of the pyrimido[4,5-b]indole system to give compounds with activities comparable to ellipticine and cisplatin. To understand the experimental cytotoxic activities, QSAR investigations were performed, which showed a very good linearity between the experimental and predicted IC(50).

Design and Synthesis of a C2-Symmetric Self-Complementary Hydrogen-Bonding Cleft Molecule Based on the Bicyclo[3.3.1]nonane and 4-Oxo-5-azaindole Framework. Formation of Channels and Inclusion Complexes in the Solid State

The synthesis of a C2-symmetric cleft molecule 2 based on the fused framework between bicyclo[3.3.1]nonane and 4-oxo-5-azaindole, incorporating a self-complementary hydrogen-bonding motif, in both racemic and enantiomerically pure forms is reported. This cleft molecule is reminiscent of analogues of Tröger's base though with different cleft dimensions and tilt angles. The framework of 2 provides a building block for the construction of self-assembled hydrogen-bonded supramolecular structures. The solid-state structure of 2 is highly influenced by the limited solubility of (+/-)-2 and (-)-2. The solvents interact with the potential hydrogen-bonding motifs of (+/-)-2 and (-)-2, forming different three-dimensional structures as revealed by X-ray diffraction analysis. In the solid state (+/-)-(2)2 x 5DMF forms hydrogen-bonded pleated band structures that build up three-dimensional pens between adjacent bands in which two molecules of DMF are trapped. In contrast, the aggregate obtained from (-)-2, (-)-2 x 2AcOH, showed infinite bands of complex constitution.

Lewis acid-directed cyclocondensation of piperidone enol ethers with 2-methoxy-4-(N-phenylsulfonyl)-1,4-benzoquinoneimine: a new regioselective synthesis of oxygenated carbolines

Lewis acid-directed cyclocondensations of piperidone enol ethers with 2-methoxy-4-(N-phenylsulfonyl)-1,4-benzoquinoneimine are reported. Benzofurans are obtained with BF3.OEt2 as a promoter, whereas use of excess amounts of TiCl4:Ti(OiPr)4 leads to tetrahydrocarbolines. The latter reactions provide expedient routes to oxygen-substituted tetrahydrocarbolines and carbolines. As applications of this new methodology, the preparations of 1-[3-(dimethylamino)propyl]amino-7-methoxy- and 1-[3-(dimethylamino)propyl]amino-7,8-dimethoxy-5H-pyrido[4,3-b]indoles are described.

Antitumor agents 201. Cytotoxicity of harmine and beta-carboline analogs

Twenty-six beta-carbolines were evaluated for in vitro cytotoxicity in a human tumor cell line panel. Harmine (3) showed significant activity against several cell lines including three drug-resistant KB sublines with various resistance mechanisms. Alpha-(4-nitrobenzylidine) harmine (16) had a broad cytotoxicity spectrum (ED50 values from 0.3-1.2 microg/mL against 1A9, KB, SaOS-2, A549, SK-MEL-2, U-87-MG, and MCF-7 cells).

Triple helix-specific ligands

A triple helix is formed upon binding of an oligodeoxynucleotide to the major groove of duplex DNA. A benzo[e]pyridoindole derivative (BePI) strongly stabilized this structure and showed preferential binding to a triplex rather than to a duplex. Energy transfer experiments suggest that BePI intercalates within the triple helix. Sequence-specific inhibition of transcription initiation of a specific gene by Escherichia coli RNA polymerase by a triplex-forming oligodeoxynucleotide is strongly enhanced when the triplex is stabilized by BePI. Upon irradiation with ultraviolet light, BePI induces covalent modifications of the target within the triple helix structure.

Stimulation by gamma-carboline derivatives (simplified analogues of antitumor ellipticines) of site specific DNA cleavage by calf DNA topoisomerase II

gamma-Carbolines are tricyclic aromatic compounds which intercalate into DNA base pairs and exhibit significant cytotoxic and antitumor activities. These compounds which are structurally related to ellipticine by deletion of an aromatic ring, induce DNA breaks in cultured L1210 cells. Since the mechanism of cytotoxic activity of ellipticines involves DNA topoisomerase II, this enzyme might also be a target for gamma-Carbolines. We have tested this hypothesis using an in vitro system containing purified enzyme and pBR322 DNA. The ability of nine derivatives to stabilize the DNA-enzyme covalent complex was studied and compared to their cytotoxicity. The four less cytotoxic compounds do not induce cleavable complex to a significant extent. In contrast, the two most cytotoxic gamma-Carbolines are the most efficient stabilizers of the cleavable complex. The last three compounds exhibit an intermediate cytotoxicity and cleavage activity. In the presence of gamma-Carbolines, cleavage occurs predominantly at a single site in pBR322 which is one of the cleavage sites observed with ellipticines. The cleavage position was determined at the nucleotide level. The increased DNA cleavage specificity observed with gamma-Carbolines suggests that a tricyclic system is as efficient as ellipticines for DNA topoisomerase II cleavage at DNA sequences involved specifically in cytotoxic response. The data presented support the hypothesis that DNA topoisomerase II is a target involved in the mechanisms of action of antitumor gamma-Carbolines.

Interrelationship between affinity for DNA, cytotoxicity and induction of DNA-breaks in cultured L1210 cells for two series of tricyclic intercalators. Simplified analogues of ellipticine derivatives

The interrelationship between affinity for DNA, cytotoxicity and induction of single-strand DNA breaks in cultured L1210 cells was studied for 21 compounds belonging to two series of tricyclic intercalators: 1-amino-substituted 4-methyl-5H-pyrido[4,3-b]indoles (gamma CARB) and 1-amino-substituted 4-methyl-5H-pyrido[3',4':4,5]pyrrolo[2,3-c]pyridines (PPP), which are simplified analogues of Ellipticine derivatives obtained by deletion of one cycle. Adriamycin, m-AMSA (4'-(9-acridinylamino) methanesulfon-m-anisidide), PZE (10-[diethylaminopropyl amino]-6-methyl-5H-pyrido[3',4':4,5]-pyrrolo[2,3-g] isoquinoline and RTE [( 1-(3-diethylaminopropylamino)-9-methoxy ellipticine, bimaleate) are used as reference compounds. The intercalation of these compounds into DNA was strongly suggested by three experimental observations: (i) the competitive inhibition of ethidium bromide intercalation, (ii) bathochromic and hypochromic effects on absorption spectra induced by DNA, and (iii) drug-induced increase of the DNA length, measured by viscosimetry. PPP derivatives are generally less cytotoxic and induce DNA breaks less efficiently than the gamma CARB ones, both in terms of maximum breakage frequencies and required drug concentrations. The most active compounds induced SSB in the DNA of L1210 cells, in a bell-shaped manner: the SSB frequency increased, rose to a maximum and then decreased as the drug concentrations increased. The maximum SSB frequencies induced by the most active compounds are of the same order as those of reference compounds Adriamycin and PZE. The structurally important requirements are essentially the same for both DNA breakage activity and cytotoxicity: (i) a N-CH3 in the 5-position, (ii) a CH3 in the 4-position, (iii) a hydroxy in the 8-position and (iv) the presence of an (aminoalkyl)amino side chain with preferentially a 3 carbon unit. There is no direct relationship between DNA affinity in vitro and induction of DNA breaks in cells, although a relatively high affinity seemed to be a necessary condition, since the most active compounds have the highest affinities and compounds having a very low affinity are totally inactive. The close correlation between cytotoxicity and extent of induction of DNA breaks suggests that these breaks may be in fact the lethal lesions responsible for cell death and thereby for the antitumor properties of these tricyclic intercalators.