Synthesis, DNA binding, and cleaving properties of an ellipticine-salen.copper conjugate.

The synthesis of a DNA-cutting agent that conjugates an ellipticine chromophore and a copper complex of bis(salicylidene)ethylenediamine, referred to as a salen, is reported. The presence of the salen.Cu complex allows cleavage of DNA via oxygen-based radicals, and the ellipticine moiety serves as a DNA anchor. Spectroscopic measurements indicate that the intercalation geometry of the ellipticine chromophore is preserved with the hybrid. The cleavage is much more efficient with the conjugate than with the Schiff base copper complex alone.

Complementary advantages of fluorescence and SIMS microscopies in the study of cellular localization of two new antitumor drugs.

Low light level fluorescence microscopy studies have been carried out on MCF7-P human mammary tumor cells to localize the intracellular distribution of two new anticancer drugs, Pazelliptine and Intoplicine, which are currently under clinical evaluation. These two molecules are thought to act at the nuclear level, through DNA topoisomerase interactions. Because fluorescence of these compounds appears strongly quenched by intercalation in double strand DNA, secondary ion mass spectrometry (SIMS) imaging was used to check the presence of the drugs in the nuclear compartment. In spite of chemical structure similitudes, pazelliptine and intoplicine appear to be distributed in quite different ways within the cells. Incubation for 1 and 24 hours also allowed us to bring to light strong differences in the distribution kinetics. Pazelliptine quickly enters into the nucleoli but is no longer present in the nucleus after 24 hours incubation. Intoplicine was not detected by fluorescence in the nucleus, however SIMS microscopy allowed us to show its accumulation within this cellular compartment as a function of time of exposure. This study shows the complementarity of fluorescence and SIMS microscopies.

Reaction of a biscationic distamycin-ellipticine hybrid ligand with DNA. Mode and sequence specificity of binding.

Molecular modeling of complexes between the octanucleotide d(CGATATCG)2 and either a monocationic or biscationic distamycin-ellipticine hybrid molecule predicted that the extra positive charge on the latter conjugate ligand should ensure tight fitting into the minor groove of the duplex without affecting intercalation of the ellipticine chromophore. To test this prediction, we have synthesized a biscationic compound Distel (2+) and investigated its interaction with DNA using various optical and gel electrophoresis techniques. Viscosity, fluorescence lifetime, and circular and linear dichroism measurements bear out the validity of the calculations and show that Distel (2+) does indeed come to lie with its distamycin moiety in the minor groove of DNA and its ellipticine ring intercalated nearby. Linear dichroism experiments with a range of polynucleotides indicate that, unlike its monocationic homologue, the biscationic ligand engages in bidentate binding to AT sequences but not to GC sequences. Footprinting studies employing DNase I and methidiumpropyl-EDTA.FeII as DNA cleaving agents reveal that the biscationic hybrid is notably selective for AT-rich sequences in DNA. The concentrations required to detect a clear footprint at AT sites with Distel (2+) are 4- to 10-fold lower than those required to produce comparable DNase I footprints with distamycin alone. Also, in accord with the energy-minimized model of the hybrid-oligonucleotide complex, chemical probing experiments using diethyl pyrocarbonate and osmium tetroxide reveal that the hybrid causes significant distortion of the DNA helix, explicable in terms of bending of the duplex toward the minor groove, which greatly enhances the reactivity toward probes in the major groove of the DNA. The experimental results help to identify the determinant factors, predominantly steric and electrostatic interactions, which shape the DNA-binding reaction. Thus, molecular modeling has correctly predicted the DNA-binding properties of a doubly charged ligand and shown that appending an auxiliary basic group onto the distamycin moiety was the right way to proceed in order to convert a nonspecific conjugate into a highly specific DNA reader.

Two-photon ionisation of the antitumor drug pazelliptine (BD40) by 355 nm laser photolysis.

The effect of 2 ns pulses of 355 nm laser light on aqueous solutions of pazelliptine (PZE) was investigated and biphotonic ionization was observed. The absorption spectrum corresponding to the pazelliptine radical cation (PZE+) and the hydrated electron simultaneously formed in this process was determined. In the absence of oxygen, eaq- reacted with unexcited PZE (k = 1.6 x 10(10) M-1 s-1) to give the pazelliptine radical anion (PZE-). This latter species was identified by separate pulse radiolysis experiments. The radicals cation and anion disappeared by recombination on the millisecond time range. In presence of oxygen, eaq- was scavenged by O2 leading to the formation of the superoxide radical (O2.-) in competition to the formation of the radical PZE.-.PZE+ reacted with O2.- to produce H2O2 (k = 9 x 10(9) M-1 s-1). The spectral analysis revealed that PZE triplet was also formed during the laser pulse. In the absence of oxygen, the triplet-triplet absorption decreased on the microsecond time scale (2k = 1.5 x 10(10) M-1 s-1). In oxygenated solutions, eaq- and the pazelliptine triplet decayed exponentially in the same time range.

Binding to DNA, cellular uptake and biological activity of a distamycin-ellipticine hybrid molecule.

A hybrid molecule which conjugates the minor groove binding agent distamycin and an ellipticine derivative was synthesized and evaluated for cytostatic and cytotoxic activities against L1210 leukaemia cells in vitro. The binding of the hybrid molecule, named 'Distel', to a range of natural DNAs and synthetic polynucleotides with different base pair arrangements was studied by electric linear dichroism. The interaction with DNA simultaneously implicates binding of the distamycin part in the minor groove and intercalation of the ellipticine chromophore. The drug binds to DNA without any apparent preference for AT or GC polynucleotides, and can accommodate both homopolymeric and co-polymeric sequences as a binding site. However, the geometry of the drug-DNA complex varies depending on the targeted sequence. The lower activity of the hybrid as compared to the ellipticine derivative cannot be explained in terms of DNA binding. Taking advantage of the fluorescence of the pyridocarbazole chromophore, fluorescence microscopy was used to map cellular uptake of the hybrid molecule compared to the ellipticine derivative. Both the conjugate and the ellipticine derivative preferentially accumulate in the nuclei of HeLa cells rather than in the cytoplasm. Nuclei of ellipticine derivative-treated cells appear markedly more fluorescent than those of cells treated with the hybrid, which seems to be preferentially located in the nucleoli. Therefore, we consider the possibility that the difference in cytotoxicity between the two ellipticine-containing drugs is due to different intranuclear concentrations of these two compounds.

Binding of a distamycin-ellipticine hybrid molecule to DNA and chromatin: spectroscopic, biochemical, and molecular modeling investigations.

A bifunctional molecule in which an ellipticine chromophore is attached to a distamycin residue via a diaminopropyl tether has been designed and synthesized in the expectation of creating a hybrid molecule capable of bidentate binding to DNA by both intercalation and minor-groove interactions. The strength and mode of binding to DNA of this conjugate have been studied by means of circular and linear dichroism as well as by stopped-flow kinetics and measurements of reactivity toward a chemical probe. The results converge to reveal that the ellipticine moiety of the hybrid largely dominates the binding reaction with DNA. In the presence of chromatin, the hybrid molecule binds preferentially to the internucleosomal DNA, a preference dictated by its intercalating chromophore. Theoretical computations were performed on the comparative complexation energies of distamycin, the ellipticine derivative, and the hybrid ligand with a B-representative octanucleotide, d(GCATATGC)2. The best binding configuration of the ellipticine derivative locates its aminoalkyl side chain in the minor groove where distamycin is also present. The molecular modeling analysis fully supports the involvement of a bimodal binding process for the hybrid and reveals that the binding of the conjugate to DNA favors a pronounced bending toward the minor groove. This effect is attributed to intercalation of the ellipticine chromophore. An interesting link is established between the DEPC reactivity experiments and the theoretical computations, suggesting that DEPC can be used as a probe for drug-induced DNA bending. On the basis of these results, we propose the design of a new hybrid ligand bearing an additional positively-charged amidine side chain to confer higher DNA-binding affinity.

DNA-binding properties of a distamycin-ellipticine hybrid molecule.

We have synthesized a distamycin-ellipticine hybrid compound and investigated its interaction with DNA, using various optical and gel electrophoresis techniques. Binding of the hybrid to DNA is evidenced by spectral shifts, fluorescence quenching, and induced linear dichroism. Absorbance measurements have been used to generate Scatchard plots, which reveal that the interaction cannot be described adequately in terms of a single binding mode, probably because of simultaneous intercalation and minor groove binding of the ligand. Competition with added distamycin has been used to verify involvement of the N-methyl-pyrrole portion of the hybrid molecule in the binding reaction. From electric linear dichroism experiments, it is estimated that the orientation of the DNA-bound ellipticine chromophore in the hybrid differs by about 10 degrees from the orientation of the equivalent chromophore lacking a distamycin tail. Topoisomerase assays establish that binding of the hybrid unwinds the DNA helix by a minimum of 11 degrees, which is consistent with intercalation but notably smaller than the unwinding angle of ellipticine. In footprinting experiments, it is found that the AT- and GC-specificity of distamycin and ellipticine, respectively, appear to be merged in the binding of the hybrid, which produces a pattern of protection distinct from the characteristic patterns for either of the parent compounds. The hybrid is an extremely effective inhibitor of cutting by DNase I.

Recognition and photo-induced cleavage and cross-linking of nucleic acids by oligonucleotides covalently linked to ellipticine.

Oligopyrimidines covalently linked to ellipticine derivatives form duplex and triplex structures with target single-stranded oligopurine sequences. They also bind to duplex DNA at homopurine-homopyrimidine sequences where they form local triple helices. Irradiation at wavelengths longer than 300 nm of the complex formed by an oligonucleotide-ellipticine conjugate with its target sequence induced (i) cleavage of the target at bases located in close proximity to the dye and (ii) cross-linking of the target sequence to the derivatized oligonucleotide. Both cross-linking and cleavage reactions decreased when temperature increased with a half-transition corresponding to the dissociation of the oligonucleotide-ellipticine conjugate from its target nucleic acid, demonstrating that the observed photochemical effects are dependent on hybrid formation. When the target was a double-stranded DNA, photochemical reactions were observed on both strands of the duplex. Photo-induced cross-linking was more efficient than cleavage when the target was single-stranded; the reverse was observed when the target was duplex DNA.

Sequence-selective binding of an ellipticine derivative to DNA.

The DNA sequence specificity of an ellipticine derivative bearing an aminoalkyl side chain has been determined by a variety of footprinting methods. The drug exhibits sequence selective binding and discriminates against runs of adenines or thymines. Binding is shown to occur at various sequences with a preference for GC rich regions of DNA. A large enhancement of DNAase I and of hydroxyl radical cleavage in regions rich in A's or T's is observed together with hyperreactivity of adenines towards diethylpyrocarbonate in the presence of drug. This indicates the occurrence of drug-induced changes in critical conformational features of DNA. The total absence of hyperreactivity of guanine residues towards diethylpyrocarbonate appears to be related to the sequence selectivity of drug binding. No alteration of the dimethyl sulphate and methylene blue-induced cleavage of DNA is observed. Irradiation of ellipticine derivative-DNA complexes with UV light followed by alkali treatment leads to selective photocleavage at guanine residues, consistent with the deduced degree of selectivity of the binding reaction.

Sequence-specific artificial photo-induced endonucleases based on triple helix-forming oligonucleotides.

Homopyrimidine oligonucleotides bind to homopurine-homopyrimidine sequences of duplex DNA forming a local triple helix. This binding can be demonstrated either directly by a footprinting technique, gel assays, or indirectly by inducing irreversible reactions in the target sequence, such as photocrosslinking or cleavage. Binding occurs in the major groove with the homopyrimidine oligonucleotide orientated parallel to the homopurine strand. Thymine and protonated cytosine in the oligonucleotide form Hoogsteen-type hydrogen bonds with A.T and G.C Watson-Crick base pairs, respectively. Here we report that an 11-residue homopyrimidine oligonucleotide covalently attached to an ellipticine derivative by its 3' phosphate photo-induces cleavage of the two strands of a target homopurine--homopyrimidine sequence. To our knowledge, this is the first reported case of a sequence-specific artificial photoendonuclease. In addition we show that a strong binding site for a free ellipticine derivative is induced at the junction between the triplex and duplex structures on the 5' side of the bound oligonucleotide. On irradiation, cleavage is observed on both strands of DNA. This opens new possibilities for inducing irreversible reactions on DNA at specific sites by the synergistic action of a triple helix-forming oligonucleotide and an intercalating agent.

Role of the superoxide anion in the oxidative activation of the new antitumor drug BD40: a radiolysis study.

BD40, a new antitumor drug derived from 9-azaellipticine, is thought to have an oxygen-dependent metabolism in vivo. We have investigated the one-electron oxidation of this drug by gamma radiolysis using OH. free radicals as oxidants and the reaction of O2-. with the BD40 oxidized transient(s). The absorption spectrum of the one-electron oxidized free radical was determined by pulse radiolysis using OH. or N.3 as reactant. In the absence of O2 and O2-., the initial yield of disappearance of the drug is equal to 2.5 x 10(-7) mol J-1 independently of the initial concentration of the drug and of the dose rate. When BD40 is oxidized by OH. radicals in the presence of O2 and O2-., the yield is the same. This yield is halved if superoxide dismutase is present during irradiation. Superoxide anions do not react directly with the drug. Thus it is suggested that these radicals oxidize the BD40 free radical produced by oxidation with OH. Biological implications are discussed.

A new series of ellipticine derivatives (1-(alkylamino)-9-methoxyellipticine). Synthesis, DNA binding, and biological properties.

A new series of ellipticine derivatives, 1-(alkylamino)-5,11-dimethyl-9-methoxy-6H-pyrido[4,3-b]carbazoles, were synthesized as potential DNA intercalating antitumor drugs. The structure of these compounds were confirmed by 1H NMR spectroscopy and mass spectrometry. These compounds are able to bind to DNA with an affinity of about 10(6) M-1, and their intercalating characteristics (lengthening and unwinding of DNA) depend upon the length of the chain in position 1. The cytotoxicities of these compounds on L1210 and NIH-3T3 cells are quite similar, and fluorescence techniques showed that the compounds are localized mainly in the cytoplasmic granules of the cells. One of these compounds appears to show a very high antitumor activity (equivalent to the more active known ellipticine analogues: 10-[[gamma-(diethylamino)propyl]amino]-6-methyl-5H- pyrido[3',4':4,5]pyrollo[2,3-g]isoquinoleine (BD40), 1-[[gamma-(diethylamino)propyl]amino]-9-methoxyellipticine (BD84) and 2-[beta-(diethylamino)ethyl]-9-hydroxyellipticinium chloride (DEAE).

Cytochrome P-450-mediated O-demethylation of two ellipticine derivatives. Differential effect of the murine Ah locus phenotype.

The O-demethylation of two antitumor drugs (9-methoxyellipticine and a 1-polyalkylamino-substituted analog) was studied by incubation with liver microsomes from rats and mice. The former drug underwent a cytochrome P1-450-independent biotransformation in mice, as shown by an indiscriminate response from individuals genetically responsive or nonresponsive to induction by 3-methylcholanthrene. On the other hand, the second drug was O-demethylated only by genetically responsive mice after pretreatment by 3-methylcholanthrene. It was also O-demethylated predominantly in rats pretreated with either 3-methylcholanthrene or Aroclor 1254.

Antitumor amino-substituted pyrido[3',4':4,5]pyrrolo[2,3-g]isoquinolines and pyrido[4,3-b]carbazole derivatives: synthesis and evaluation of compounds resulting from new side chain and heterocycle modifications.

New modifications of 10-[[3-(diethylamino)propyl]amino]-6-methyl-5H-pyrido[3',4':4,5]pyrrolo[2,3-g]i sisoquinoline (1b) and 1-[[3-(diethylamino)propyl]amino]-9-methoxy-5,11-dimethyl-6H-pyrido[4,3-b]carba zole (4b), which display important antitumor properties, were performed either on the side chain or on the intercalating heterocycle. Side chains were introduced by direct substitution of the corresponding chloro derivatives and 6-N-methyl-9-hydroxypyrido[4,3-b]carbazoles analogues were prepared via 9-O-benzoyl-1-chloroellipticines. Evaluation of all new compounds shows no significant increase of in vitro cytotoxicity and percent ILS on the L1210 leukemia system by comparison with the model compounds 1b and 4b.

Possible relationship between pyrido-pyrrolo-isoquinoline derivative (BD-40) cell uptake and cell viability.

BD-40 is a pyrido-pyrrolo-isoquinoline derivative which possesses an heterocyclic nucleus very closely related to ellipticine and a diethylaminopropyl amino lateral chain (Rivalle et al., 1979). Cellular effects of the drug have been studied. Viability and morphology of the cells were irreversibly impaired by 24 hours drug treatments at concentrations exceeding 0.10 micro M. Spectrofluorimetric determinations of the drug repartition between cytoplasm and nucleus showed that 10 per cent of BD-40 was found in the nucleus for external drug concentrations lower than 0.10 micro M. On the other hand, for cytotoxic doses exceeding 0.10 micro M, 40 to 50 per cent of the total intracellular BD-40 were found in the nuclear fraction. Although possible exchange phenomena during the course of the cell fractionation cannot be excluded, these results suggest that a direct relationship exists between BD-40 nuclear content and cell lethality. Comparisons of intracellular drug contents in the absence and the presence of a metabolic inhibitor, sodium azide, indicated that drug content of azide-treated cells was approximately twice that of untreated cells. Besides, sodium azide blocked the release of the drug when previously loaded cells were placed in BD-40-free medium. These results are in agreement with the existence of an active outward transport (efflux), which is sodium azide-sensitive.

Structure-activity relationships in a series of newly synthesized 1-amino-substituted ellipticine derivatives.

The synthesis of a series of 1-amino-substituted pyrido[4,3-b]carbazole derivatives, based on the substitution of corresponding 1-chloroellipticines, is reported. The cytotoxic properties on tumor cells grown in vitro, the in vivo acute toxicity of the most potent in vitro cytotoxic compounds, and the antitumor properties toward the L1210 leukemia system are described. No correlation between the apparent association constant to DNA and the in vitro cytotoxicity or the in vito antitumor efficiency could be observed in this series. 9-Hydroxylated derivatives were more cytotoxic in vitro than the corresponding 9-methoxylated compounds. However, their antitumor efficiencies on the in vivo experimental systems do not confirm the advantage of demethylation. The presence of a [(dialkylamino)alkyl]amino side chain at the 1 position of ellipticines increases the antitumor potency: 1-[[3-(diethylamino)propyl]amino]-5,11-dimethyl-6H-pyrido[4,3-b]carbazole (5) is a very potent antitumor compound (% ILS of 134 on the L1210 leukemia system).

Antitumoral activity of dipyrido [4,3-b] [3,4-f] indoles on L 1210 leukemia.

Newly synthesized dipyrido [4,3-b] [3,4-f] indole compounds have a structural similarity with the DNA intercalating agents ellipticines (pyrido-carbazoles). The procedure of synthesis of these compounds allows the addition of a lateral chain in position 1 of the nucleus. Comparison is made between different substitutions and the resulting cytotoxic and antitumoral effects. The most active compound of the serie (1-gamma-diethyl amino propyl amino)-5-methyl-dipyrido [4,3-b] [3,4-f] indole (called here BD40) protects mice against L1210 leukemia. At the non-toxic dose of 20 mg/kg, particularly, a single infection of this compound given one day after inoculation of 10(5) L1210 cells resulted in an increased life span of 69 per cent with one survivor at 60 days. A combination of cyclophosphamide and BD40 had a synergic effect on the life span of L1210 inoculated mice. The antitumoral action of these drugs may be linked to their intercalative action upon biding to DNA.

Intercalative binding to DNA of new antitumoral agents: dipyrido [4,3-b] [3,4-f] indoles.

The study of new intercalating DNA agents has led to the synthesis of dipyrido [4,3-b] [3,4-f] indole derivatives. These compounds bind preferentially to helical DNA and their affinity constants range from 10(6) to 10(7) M-1. The most active derivative against L1210 mouse leukemia produces viscosity changes in sheared fragments of linear DNA and in circular PM2 DNA on binding, indicating an intercalation process. The unwinding angle is estimated to be 18(0). This active derivative binds preferentially to A-T base pairs.

[Cytotoxic and antitumor activity of a new series of heterocyclic compounds: dipyrido (4,3-b) (3,4-f) indoles]. / Actions cytotoxique et antitumorale de dérivés d'une nouvelle série hétérocyclique: les dipyrido [4,3-b] [3,4-f] indoles.

Among newly synthesized compounds derived from the dipyrido [4,3-b] [3,4-f] indole nucleus, two have proved to be particularly active in vitro and in vivo. Their cytotoxic effects on cultured cells have been determined. At non toxic doses, they displayed a pronounced inhibitory effect on experimental L1210 Leukemia. These compounds have a strong affinity for DNA molecules.