Carbocyclic Analogues of Distamycin and Netropsin.

The DNA as the depository of genetic information is a natural target for chemotherapy. A lot of anticancer and antimicrobial agents derive their biological activity from their selective interaction with DNA in the minor groove and from their ability to interfere with biological processes such as enzyme catalysis, replication and transcription. The discovery of the details of minor groove binding drugs, such as netropsin and distamycin A, oligoamides built of 4-amino-1-methylpyrrole-2-carboxylic acid residues, allowed to develop various DNA sequence-reading molecules, named lexitropsins, capable of interacting with DNA precisely, strongly and with a high specificity, and at the same time exhibiting significant cytotoxic potential. Among such compounds, lexitropsins built of carbocyclic sixmembered aromatic rings occupy a quite prominent place in drug research. This work is an attempt to present current findings in the study of carbocyclic lexitropins, their structures, syntheses and biological investigations such as DNA-binding and antiproliferative activity.

An evaluation of Minor Groove Binders as anti-fungal and anti-mycobacterial therapeutics.

This study details the synthesis and biological evaluation of a collection of 19 structurally related Minor Groove Binders (MGBs), derived from the natural product distamycin, which were designed to probe antifungal and antimycobacterial activity. From this initial set, we report several MGBs that are worth more detailed investigation and optimisation. MGB-4, MGB-317 and MGB-325 have promising MIC80s of 2, 4 and 0.25 µg/mL, respectively, against the fungus C. neoformans.MGB-353 and MGB-354 have MIC99s of 3.1 µM against the mycobacterium M. tuberculosis. The selectivity and activity of these compounds is related to their physicochemical properties and the cell wall/membrane characteristics of the infective agents.

Synthesis, anti-mycobacterial activity and DNA sequence-selectivity of a library of biaryl-motifs containing polyamides.

The alarming rise of extensively drug-resistant tuberculosis (XDR-TB) strains, compel the development of new molecules with novel modes of action to control this world health emergency. Distamycin analogues containing N-terminal biaryl-motifs 2(1-5)(1-7) were synthesised using a solution-phase approach and evaluated for their anti-mycobacterial activity and DNA-sequence selectivity. Thiophene dimer motif-containing polyamide 2(2,6) exhibited 10-fold higher inhibitory activity against Mycobacterium tuberculosis compared to distamycin and library member 2(5,7) showed high binding affinity for the 5'-ACATAT-3' sequence.

New solid phase synthesis of distamycin analogues.

A novel and straightforward solid phase synthesis of distamycin analogues containing benzene units has been developed.

Distamycins: strategies for possible enhancement of activity and specificity.

The present review focused on the strategies aimed to possibly solve toxicity problems of distamycins. Distamycins are compounds characterized by an oligopeptidic pyrrolocarbamoyl frame ending with an amidino moiety. This class of compounds displays antiviral and antibiotic activity and shows interesting antiprotozoal activity related to the ability to reversibly bind to the minor groove of DNA with a high selectivity for TA-rich sequences. In consideration of their potential therapeutic properties, the synthesis of new distamycin derivatives and especially the development of controlled delivery strategies, could lead to important advantages in the clinical use of these molecules, possibly overcoming or mitigating the low solubility, specificity and toxicity problems associated with their use. To these aims an ensemble of the main synthetic distamycin derived compounds and of the potential drug delivery systems for distamycins described in literature is reviewed.

Efficient solid-phase synthesis of a library of distamycin analogs containing novel biaryl motifs on SynPhase Lanterns.

Distamycin is a naturally occurring antibiotic that binds to AT-rich sequences in the minor groove of DNA in a noncovalent manner. It continues to be of interest as a "building block" for more-complex small-molecule ligands capable of targeting specific DNA sequences for gene regulation purposes (i.e., transcription factor inhibitors). We report here a convenient and efficient synthesis of a library of 72 novel analogs (3a-f) of the parent distamycin on SynPhase Lanterns. To investigate structure-activity relationships including DNA-binding affinity and sequence-selectivity, two previously unexplored points of diversification have been introduced into the distamycin structure by replacing one of its pyrrole rings with novel biaryl motifs. The key aspects of the synthetic approach include the development of an efficient protocol for preparation of the heterocyclic polyamide chain, optimization of the Suzuki-Miyaura cross-coupling reaction and application of a split-and-mix technique based on radiofrequency encoding. In addition, a series of biaryl carboxamide derivatives (4a-f) has been synthesized utilizing the title library diversity reagents.

Synthesis and biological evaluation of distamycin analogues - new potential anticancer agents.

Eight of analogues of distamycin, potential minor-groove binders, were synthesized and tested for in-vitro cytotoxicity towards human breast cancer cells MCF-7 and MDA-MB-231. The method of synthesis is simple and convenient. All of the compounds 1-8 showed antiproliferative and cytotoxic effects against both cell lines in the range 3.47 to 12.53 microM for MDA-MB-231 and 4.35 to 12.66 microM for MCF-7. All compounds demonstrated activity against DNA topoisomerases I and II at a concentration of 50 microM. The ethidium bromide assay showed that these compounds bind to plasmid pBR322, yet weaker than distamycin. Further investigations concerning the mechanism of cytotoxicity are now in progress, but the IC(50) values suggest that synthetic distamycin analogues with a free amino group, 3-4 and 7-8, can serve as potential carriers of strong acting elements, e. g. alkylating groups.

Analogues of distamycin--synthesis and biological evaluation of new aromatic oligopeptides, potential anticancer agents.

Six new aromatic oligopeptides were synthesized and evaluated for their activity in the standard cell line of the mammalian tumor MCF-7 as well as in a cell-free system employing the topoisomerase I/II inhibition assay.

Bis-epoxyethyl derivatives of distamycin A modified on the amidino moiety: induction of production of fetal hemoglobin in human erythroid precursor cells.

Derivatives of distamycin A modified at the C-terminal amidine moiety and tethered to bis-epoxyethyl moieties at the N-terminal position were tested for their ability to induce erythroid differentiation in the human erythroleukemic cell line K562. None of the compounds without bis-epoxyethyl moiety were active. A comparison of the biological activity of diepoxy compounds containing different non-basic amidine-modified moieties, showed low activity of amidoxime, carbamoyl and N-methyl carbamoyl derivatives as differentiation agents. In contrast, a cyanamidine derivative, compound 3, was able to induce erythroid differentiation of K562 cells. In addition, the cyanamidine derivative 3 was able to induce HbF accumulation following treatment of cultures of erythroid precursor cells isolated from the peripheral blood of normal subjects.

Design, synthesis, and DNA binding properties of photoisomerizable azobenzene-distamycin conjugates: an experimental and computational study.

Here, we present the synthesis, photochemical, and DNA binding properties of three photoisomerizable azobenzene-distamycin conjugates in which two distamycin units were linked via electron-rich alkoxy or electron-withdrawing carboxamido moieties with the azobenzene core. Like parent distamycin A, these molecules also demonstrated AT-specific DNA binding. Duplex DNA binding abilities of these conjugates were found to depend upon the nature and length of the spacer, the location of protonatable residues, and the isomeric state of the conjugate. The changes in the duplex DNA binding efficiency of the individual conjugates in the dark and with their respective photoirradiated forms were examined by circular dichroism, thermal denaturation of DNA, and Hoechst displacement assay with poly[d(A-T).d(T-A)] DNA in 150 mM NaCl buffer. Computational structural analyses of the uncomplexed ligands using ab initio HF and MP2 theory and molecular docking studies involving the conjugates with duplex d[(GC(AT)10CG)]2 DNA were performed to rationalize the nature of binding of these conjugates.

Small-molecule based delivery systems for alkylating antineoplastic compounds.

Alkylating agents are a major class of anticancer drugs for the treatment of various cancers including hematological malignancies. Targeting alkylating moieties to DNA by attachment of a DNA minor groove binding carrier such as distamycin, netropsin, or Hoechst 33252 reduces the loss of active drug due to reaction with other cell components and makes it possible to direct the alkylation both sequence specifically and regiospecifically. We reported the synthesis and structure-activity studies of amidine analogues of alkylating antineoplastic compounds, which appeared to be a new class of cytotoxic minor groove binders and topoisomerase II inhibitors. Another approach to overcome the toxicity of alkylating agents to normal tissue is to construct a prodrug with lower hydrophobicity and cytotoxicity but is preferentially activated in cancer cells. Overexpression of prolidase in some neoplastic cells suggests that the proline analogue of alkylating agents may serve as a prolidase convertible prodrugs. We have compared several aspects of pharmacological actions of proline analogues of chlorambucil and melphalan in breast cancer cells. The results suggest that prolidase could serve as a target enzyme for the selective action of anticancer agents.

Design, synthesis and biological evaluation of new oligopyrrole carboxamides linked with tricyclic DNA-intercalators as potential DNA ligands or topoisomerase inhibitors.

In the context of the design and synthesis of minor groove binding and intercalating DNA ligands some new oligopyrrole carboxamides were synthesized. These hybrid molecules (combilexins) possess a variable and conformatively flexible spacer at the N-terminal end. As intercalating tricyclic systems acridone, acridine, anthraquinones and in a special case iminostilbene terminate the N-terminal end of the pyrrole chain. The cytotoxicity was examined by the NCI antitumor screening, furthermore, biophysical as well as biochemical studies were performed in order to get some information about the DNA binding properties and topoisomerase inhibition effect of this new series of molecules.

Synthesis and biophysical evaluation of minor-groove binding C-terminus modified pyrrole and imidazole triamide analogs of distamycin.

Five polyamide derivatives with rationally modified C-terminus moieties were synthesized and their DNA binding specificity and affinity determined. A convergent approach was employed to synthesize polyamides containing an alkylaminopiperazine (4 and 5), a truncated piperazine (6), or an alkyldiamino-C-terminus moiety (7 and 8) with two specific objectives: to investigate the effects of number of potential cationic centers and steric bulk at the C-terminus. CD studies confirmed that compounds 4, 5, 7, and 8 bind in the minor groove of DNA. The alkylpiperazine containing compounds (4 and 5) showed only moderate binding to DNA with DeltaT(m) values of 2.8 and 8.3 degrees C with their cognate sequence, respectively. The alkyldiamino compounds (7 and 8) were more impressive producing a DeltaT(m) of >17 and >22 degrees C, respectively. Compound 6 (truncated piperazine) did not stabilize its cognate DNA sequence. Footprints were observed for all compounds (except compound 6) with their cognate DNA sequence using DNase I footprinting, with compound 7 producing a footprint of 0.1 microM at the expected 5'-ACGCGT-3' site. SPR analysis of compound 7 binding to 5'-ACGCGT-3', 5'-ACCGGT-3', and 5'-AAATTT-3' produced binding affinities of 2.2x10(6), 3.3x10(5), and 1x10(5)M(-1), respectively, indicating a preference for its cognate sequence of 5'-ACGCGT-3'. These results are in good agreement with the footprinting data. The results indicate that steric crowding at the C-terminus is important with respect to binding. However, the number of cationic centers within the molecule may also play a role. The alkyldiamino-containing compounds (7 and 8) warrant further investigation in the field of polyamide research.

Synthesis of distamycin A polyamides targeting G-quadruplex DNA.

A number of amide-linked oligopyrroles based on distamycin molecules have been synthesized by solid-state methods, and their interactions with a human intramolecular G-quadruplex have been measured by a melting procedure. Several of these molecules show an enhanced ratio of quadruplex vs. duplex DNA binding compared to distamycin itself, including one with a 2,5-disubstituted pyrrole group. Quadruplex affinity increases with the number of pyrrole groups, and it is suggested that this is consistent with a mixed groove/G-quartet stacking binding mode.

DNA binding ligands with improved in vitro and in vivo potency against drug-resistant Staphylococcus aureus.

Potent in vivo activity against methicillin-resistant Staphylococcus aureus (MRSA) has been difficult to achieve with previously reported DNA binding antibacterials. Herein, we describe an efficient access to a focused library of new analogues yielding compounds with improved activity in a mouse peritonitis model. The most potent molecules (14 and 19) exhibit efficacy against MRSA at ED50 values of approximately 1 and approximately 5 mg/kg, respectively, and display excellent in vitro activity against vancomycin-resistant S. aureus.

Liposomes containing distamycins: preparation, characterization and antiproliferative activity.

This article describes the production and characterization of two liposome formulations containing antitumor drugs, namely distamycin A (Dist) and a new alkyl derivative of distamycin A (C16-Dist). Egg-PC/cholesterol liposomes (4:1 mol/mol) were prepared by reverse phase evaporation technique followed by extrusion through polycarbonate filters. The encapsulation efficiency was found to be almost complete for C16-Dist (99.8%), while native distamycin A showed a lower yield (19.0%). The in vitro antiproliferative activity of the distamycins-containing liposomes determined on human leukaemic K562 cells, was 11-fold and 8-fold higher for native and alkyl derivative distamycin A, respectively, compared with that of the corresponding free drugs. Liposomal formulations show an increase in the activity and specificity of distamycins in experimental antitumor therapy.

Cinnamoyl nitrogen mustard derivatives of pyrazole analogues of tallimustine modified at the amidino moiety: design, synthesis, molecular modeling and antitumor activity studies.

The design, synthesis and in vitro activities of a series of cinnamoyl nitrogen mustard pyrazole analogues of tallimustine 8-13, in which the amidino moiety has been replaced by moieties of different physico-chemical features are described, and the structure-activity relationships are discussed. In spite of the relevance of these modifications on the amidino moiety, these derivatives showed significant growth inhibitory activity against mouse leukemia L1210 cells. A selected series of compounds have been evaluated for their sequence selective alkylating properties and cytotoxicity against human K562 leukemia cells. Therefore, the presence of the amidino moiety, and in general of a basic moiety, is not an absolute requirement for biological activity. Our preliminary results indicated that the compounds of this series have a pattern of alkylation similar to that of tallimustine, but they seem to be less reactive overall in alkylating naked DNA.

Cytotoxic alpha-halogenoacrylic derivatives of distamycin A and congeners.

The mechanism of action of many antitumor agents involves DNA damage, either by direct binding of the drug to DNA or to DNA-binding proteins. However, most of the DNA-interacting agents have only a limited degree of sequence specificity, which implies that they may hit all the cellular genes. DNA minor groove binders, among which the derivatives of distamycin A play an important role, could provide significant improvement in cancer management, increasing gene specificity, due to high selectivity of interaction with thymine-adenine (TA) rich sequences. We now report and discuss the synthesis, the in vitro and in vivo activities, and some mechanistic features of alpha-halogenoacrylamido derivatives of distamycin A. The final result of this work was the selection of brostallicin 17 (PNU-166196). Brostallicin, presently in phase II clinical trials, shows a broad spectrum of antitumor activity and an apoptotic effect higher than distamycin derivative tallimustine. An important in vitro toxicological feature of brostallicin is the very good ratio between myelotoxicity on human haematopoietic progenitor cells and cytotoxicity on tumor cells, in comparison with clinically tested DNA minor groove binders. A peculiarity of brostallicin is its in vitro reactivity in the DNA alkylation assays only in the presence of glutathione. Moreover brostallicin's antitumor activity, both in in vitro and in vivo tumor models, is higher in the presence of increased levels of glutathione/glutathione-S-tranferases. These findings contribute to the definition of brostallicin as a novel anticancer agent that differs from other minor groove binders and alkylating agents for both the profile of activity and the mechanism of action and to classify the alpha-bromoacrylamido derivatives of distamycin as a new class of cytotoxics. Moreover, due to its interaction with glutathione, brostallicin may have a role for the tailored treatment of tumors characterized by constitutive or therapy-induced overexpression of glutathione/glutathione-S-tranferase levels.

Distamycin analogues with enhanced lipophilicity: synthesis and antimicrobial activity.

Forty-eight heterocyclic amino acid trimers, analogues of distamycin, with a number of features that enhance lipophilicity are described. They contain alkyl or cycloalkyl groups larger than methyl; some are N-terminated by acetamide or methoxybenzamide and are C-terminated by dimethylaminopropyl or aliphatic heterocylic aminopropyl substituents. The ability of these compounds to bind principally to AT tracts of DNA has been evaluated using capillary zone electrophoresis. Significant antimicrobial activity against key organisms such as MRSA and Candida albicans is shown by several compounds, especially those containing a thiazole. Moreover, these compounds have low toxicity with respect to several mammalian cell lines.

DNA binding ligands targeting drug-resistant bacteria: structure, activity, and pharmacology.

We describe the lead optimization and structure-activity relationship of DNA minor-groove binding ligands, a novel class of antibacterial molecules. These compounds have been shown to target A/T-rich sites within the bacterial genome and, as a result, inhibit DNA replication and RNA transcription. The optimization was focused on N-terminal aromatic heterocycles and C-terminal amines and resulted in compounds with improved in vivo tolerability and excellent in vitro antibacterial potency (MIC >/= 0.031 microg/mL) against a broad range of Gram-positive pathogens, including drug-resistant strains such as methicillin-resistant Stapylococcus aureus (MRSA), penicillin-resistant Streptococcus pneumoniae (PRSP), and vancomycin-resistant Enterococcus faecalis (VRE). In a first proof-of-concept study, a selected compound (35) showed in vivo efficacy in a mouse peritonitis model against methicillin-sensitive S. aureus infection with an ED(50) value of 30 mg/kg.