Flexible Organic Framework-Based Anthracycline Prodrugs for Enhanced Tumor Growth Inhibition.

A water-soluble flexible organic framework FOF-hz of low cytotoxicity has been synthesized from a pyridinium-derived tetracationic tetraaldehyde and a citric acid-derived tritopic acylhydrazine (1:2) through the formation of a hydrazone bond. Dynamic light-scattering experiments reveal that FOF-hz has a hydrodynamic diameter of 79 nm at 0.1 mM concentration of the tetrahedral precursor. Dialysis experiments show that the free acylhydrazine units of FOF-hz can react with the C-13 ketone units of anthracycle drugs, including doxorubicin (DOX), daunorubicin, epirubicin, and pirarubicin, at pH = 3.0 to conjugate the drugs in 78-85% yields. The resulting FOF-prodrugs exhibit remarkable acid-responsive deconjugation of the conjugated active agents. Laser confocal scanning microscopy and flow cytometric analysis support that FOF-hz displays enhanced permeability and retention effect, which helps to overcome the multidrug resistance of MCF-7/ADR tumor cells and leads to enhanced cytotoxicity for MCF-7/ADR cells. In vivo studies reveal a considerable improvement of the efficacy of the prodrug FOF-DOX for the inhibition of the growth of the MCF-7/ADR tumor.

Development of New Innovative Synthetic Organic Chemistry Using Lone Pairs of Oxygen Atoms.

Oxygen atoms have a lone pair of electrons, so they have high chelation ability, high nucleophilic ability, stabilizing ability of adjacent cations, and take a chelate or oxocarbenium ion structure with Lewis acids and metals. I took advantage of these properties to develop three new reactions, 1) asymmetric synthesis of chiral quaternary carbon centers, 2) asymmetric synthesis using acetal functions, and 3) organic chemistry using acetal-type reactive salt chemical species, and applied them to biologically active natural products synthesis. New reactions described here are all innovative and useful for natural products synthesis. In particular, the first asymmetric synthesis of fredericamycin A, and concise asymmetric synthesis of anthracycline antibiotics, scyphostatin, (+)-Sch 642305, (-)-stenine, clavolonine, (+)-rubrenolide, (+)-rubrynolide, (+)-centrolobine, and decytospolide A and B, etc., are noteworthy. Furthermore, since reactions using acetal-type reactive salt chemical species allow the coexistence of functional groups that normally cannot coexist, the reactions using reactive salts have potential to change the retrosynthesis planned based on conventional reactions.

Antitumour Anthracyclines: Progress and Perspectives.

Anthracyclines are ranked among the most effective chemotherapeutics against cancer. They are glycoside drugs comprising the amino sugar daunosamine linked to a hydroxy anthraquinone aglycone, and act by DNA intercalation, oxidative stress generation and topoisomerase II poisoning. Regardless of their therapeutic value, multidrug resistance and severe cardiotoxicity are important limitations of anthracycline treatment that have prompted the discovery of novel analogues. This review covers the most clinically relevant anthracyclines and their development over decades, since the first discovered natural prototypes to recent semisynthetic and synthetic derivatives. These include registered drugs, drug candidates undergoing clinical trials, and compounds under pre-clinical investigation. The impact of the structural modifications on antitumour activity, toxicity and resistance profile is addressed.

Reagent-Controlled α-Selective Dehydrative Glycosylation of 2,6-Dideoxy Sugars: Construction of the Arugomycin Tetrasaccharide.

The first synthesis of the tetrasaccharide fragment of the anthracycline natural product Arugomycin is described. A reagent controlled dehydrative glycosylation method involving cyclopropenium activation was utilized to synthesize the α-linkages with complete anomeric selectivity. The synthesis was completed in 20 total steps, and in 2.5% overall yield with a longest linear sequence of 15 steps.

Synthetic routes to nanoconjugates of anthracyclines.

Anthracyclines (Anth) are widely used in the treatment of various types of cancer. Unfortunately, they exhibit serious adverse effects, such as hematopoietic depression and cardiotoxicity, leading to heart failure. In this review, we focus on recently developed conjugates of anthracyclines with a range of nanocarriers, such as polymers, peptides, DNA or inorganic systems. Manipulation of the composition, size and shape of chemical entities at the nanometer scale makes possible the design and development of a range of prodrugs. In this review we concentrate on synthetic chemistry in the long process leading to the introduction of novel therapeutic products.

Tuning the allosteric sequestration of anticancer drugs for developing cooperative nano-antidotes.

A dual-cavity basket 16-, holding six γ-aminobutyric acids at its termini, encapsulates variously sized aromatics 2-7+, including four anthracyclines (8+-11+), driven by the hydrophobic effect and hydrogen bonding (HB). In particular, the formation of stable (K = 1012 M-2) anthracycline complexes [(8+-11+)2⊂16-], assembled into nanoparticles, occurred with positive homotropic cooperativity (α = 4K2/K1 = 1.1 ± 0.3 × 102-1.3 ± 0.7 × 103) in PBS medium. Importantly, weakening the first binding event (K1, i.e. by removing HBs) turned the second one (K2) more favorable. The finding is of interest for developing cooperative nano-antidotes acting as biodetoxifying agents.

Cytotoxic activity of some glycoconjugates including saponins and anthracyclines.

Many different glycoconjugates, including saponins (e.g., hellebrin) and anthracyclines (e.g., doxorubicin), are known to display cytotoxic activities. In recent work, we have developed synthetic protocols for the synthesis of various glycoconjugates, focusing on glycosylation methods for different classes of biomolecules. Simultaneously a number of saponins and anthracyclines have been generated. In this note, the cytotoxic activities of these synthesized compounds are briefly addressed.

Design, synthesis, and biological evaluation of a novel series of bisintercalating DNA-binding piperazine-linked bisanthrapyrazole compounds as anticancer agents.

A series of bisintercalating DNA binding bisanthrapyrazole compounds containing piperazine linkers were designed by molecular modeling and docking techniques. Because the anthrapyrazoles are not quinones they are unable to be reductively activated like doxorubicin and other anthracyclines and thus they should not be cardiotoxic. The concentration dependent increase in DNA melting temperature was used to determine the strength of DNA binding and the bisintercalation potential of the compounds. Compounds with more than a three-carbon linker that could span four DNA base pairs achieved bisintercalation. All of the bisanthrapyrazoles inhibited human erythroleukemic K562 cell growth in the low to submicromolar concentration range. They also strongly inhibited the decatenation activity of topoisomerase IIα and the relaxation activity of topoisomerase I. However, as measured by their ability to induce double strand breaks in plasmid DNA, the bisanthrapyrazole compounds did not act as topoisomerase IIα poisons. In conclusion, a novel group of bisanthrapyrazole compounds were designed, synthesized, and biologically evaluated as potential anticancer agents.

Inhibitory activity of four demethoxy fluorinated anthracycline analogs against five human-tumor cell lines.

Four anthracycline analogs synthesized in our laboratory were evaluated in comparison with adriamycin (doxorubicin) for their growth-inhibitory effect against five human-tumor cell lines, including lung carcinoma, colon adenocarcinoma, breast adenocarcinoma, melanoma, and glioblastoma. The compounds included 4-demethoxy-7-O-(2,6-dideoxy-2-fluoro--l-talopyranosyl)daunomycinone (2), its 3',4'-diacetate (1), its 14-bromo derivative 3, and its 14-hydroxy analog, namely 4-demethoxy-7-O-(2,6-dideoxy-2-fluoro-α-l-talopyranosyl)adriamycinone (4). Compounds 1, 2, and 3 showed moderate cytotoxic effect in most of the cell lines, while compound 4 had a strong effect, comparable to or better than that of adriamycin in most of the cell lines.

Design, synthesis and biological evaluation of a novel series of anthrapyrazoles linked with netropsin-like oligopyrrole carboxamides as anticancer agents.

Anticancer drugs that bind to DNA and inhibit DNA-processing enzymes represent an important class of anticancer drugs. Combilexin molecules, which combine DNA minor groove binding and intercalating functionalities, have the potential for increased DNA binding affinity and increased selectivity due to their dual mode of DNA binding. This study describes the synthesis of DNA minor groove binder netropsin analogs containing either one or two N-methylpyrrole carboxamide groups linked to DNA-intercalating anthrapyrazoles. Those hybrid molecules which had both two N-methylpyrrole groups and terminal (dimethylamino)alkyl side chains displayed submicromolar cytotoxicity towards K562 human leukemia cells. The combilexins were also evaluated for DNA binding by measuring the increase in DNA melting temperature, for DNA topoisomerase IIalpha-mediated double strand cleavage of DNA, for inhibition of DNA topoisomerase IIalpha decatenation activity, and for inhibition of DNA topoisomerase I relaxation of DNA. Several of the compounds stabilized the DNA-topoisomerase IIalpha covalent complex indicating that they acted as topoisomerase IIalpha poisons. Some of the combilexins had higher affinity for DNA than their parent anthrapyrazoles. In conclusion, a novel group of compounds combining DNA intercalating anthrapyrazole groups and minor groove binding netropsin analogs have been designed, synthesized and biologically evaluated as possible novel anticancer agents.

Interaction of anthracycline disaccharide with human serum albumin: investigation by fluorescence spectroscopic technique and modeling studies.

Anthracyclines are considered to be some of the most effective anticancer drugs for cancer therapy. However, drug resistance and cardiotoxicity of anthracyclines limit their clinical application. An 3'-azido disaccharide analogue of daunorubicin, 7-[4-O-(2,6-dideoxy-3-O-methyl-alpha-l-arabino-hexopyranosyl)-3-azido-2,3,6-trideoxy-alpha-l-lyxo-hexopyranosyl]daunorubicinone (ADNR-3), was shown to exhibit 10-fold better activity than parent compound daunorubicin against the drug-resistant cells and completely overcomes the drug resistance with same IC(50) in both drug-resistant and drug-sensitive cells. In this paper, the interactions between ADNR-3 and human serum albumin (HSA) have been studied by spectroscopic techniques. By the analysis of fluorescence spectrum and fluorescence intensity, it was observed that the ADNR-3 has a strong ability to quench the intrinsic fluorescence of HSA through a static quenching procedure. The association constants of ADNR-3 with HSA were determined at different temperatures based on fluorescence quenching results. The negative DeltaH and positive DeltaS values in case of ADNR-3-HSA complexes showed that both hydrogen bonds and hydrophobic interactions play a role in the binding of ADNR-3 to HSA. Furthermore, synchronous fluorescence spectroscopy data and UV-vis absorbance spectra have suggested that the association between ADNR-3 and HSA changed the molecular conformation of HSA and the hydrophobic interactions play a major role in ADNR-3-HSA association. Moreover, the study of computational modeling indicated that ADNR-3 could bind to the site I of HSA and hydrophobic interaction was the major acting force for the second type of binding site, which was in agreement with the thermodynamic analysis. The distance, r, between donor (HSA) and acceptor (ADNR-3) was obtained according to the Förster's theory of non-radiation energy transfer. In addition, the effects of common ions on the binding constants of ADNR-3-HSA complexes were also investigated.

Synthesis of an advanced intermediate for (+)-pillaromycinone. Staunton-Weinreb annulation revisited.

Condensation of an orsellinate anion with a 2-cyclohexenone (Staunton-Weinreb annulation) afforded a linear tetracycle which was converted to a protected derivative of 12a-epipillaromycinone. Methodology for introducing a 12a-hydroxyl substituent into the tetracycle with correct (R) configuration is described.

The structure-based design, synthesis and biological evaluation of DNA-binding bisintercalating bisanthrapyrazole anticancer compounds.

Anticancer drugs that bind to DNA and inhibit DNA-processing enzymes represent an important class of anticancer drugs. In order to find stronger DNA binding and more potent cytotoxic compounds, a series of ester-coupled bisanthrapyrazole derivatives of 7-chloro-2-[2-[(2-hydroxyethyl)methylamino]ethyl]anthra[1,9-cd]pyrazol-6(2H)-one (AP9) were designed and evaluated by molecular docking techniques. Because the anthrapyrazoles are unable to be reductively activated like doxorubicin and other anthracyclines, they should not be cardiotoxic like the anthracyclines. Based on the docking scores of a series of bisanthrapyrazoles with different numbers of methylene linkers (n) that were docked into an X-ray structure of double-stranded DNA, five bisanthrapyrazoles (n=1-5) were selected for synthesis and physical and biological evaluation. The synthesized compounds were evaluated for DNA binding and bisintercalation by measuring the DNA melting temperature increase, for growth inhibitory effects on the human erythroleukemic K562 cell line, and for DNA topoisomerase IIalpha-mediated cleavage of DNA and inhibition of DNA topoisomerase IIalpha decatenation activities. The results suggest that the bisanthrapyrazoles with n=2-5 formed bisintercalation complexes with DNA. In conclusion, a novel group of bisintercalating anthrapyrazole compounds have been designed, synthesized and biologically evaluated as possible anticancer agents.

General synthesis route to benanomicin-pradimicin antibiotics.

A general approach to the regio- and stereoselective total synthesis of the benanomicin-pradimicin antibiotics (BpAs) is described. Construction of the aglycon has been achieved by 1) the diastereoselective ring-opening of a biaryl lactone by using (R)-valinol as a chiral nucleophile and 2) the stereocontrolled semi-pinacol cyclization of the aldehyde acetal by using SmI(2) in the presence of BF(3)OEt(2) and a proton source to afford the ABCD tetracyclic monoprotected diol. This strategy enabled us to control the two stereogenic sites in the B ring (C-5 and C-6) and the regioselective introduction of the carbohydrate moiety. The ABCD tetracycle could serve as an ideal platform for the divergent access to various BpAs. The amino acid (D-alanine) was introduced onto the ABCD tetracycle. Glycosylation was promoted by the combination of Cp(2)HfCl(2) and AgOTf (1:2 ratio). Construction of the E ring followed by deprotection completed the first total synthesis of benanomicin A (2 a), benanomicin B (2 b), and pradimicin A (1 a). The route is flexible enough to allow the synthesis of other congeners differing in their amino acid and carbohydrate moieties.

Anthracycline glycosides of 2,6-dideoxy-2-fluoro-alpha-L-talopyranose.

The methyl beta-glycoside of the title sugar, obtained from 2-deoxy-2-fluoro-beta-D-glucopyranose tetraacetate by a sequence with detailed characterization of all intermediates, was converted by acetolysis-bromination into 3,4-di-O-acetyl-2,6-dideoxy-2-fluoro-alpha-L-talopyranosyl bromide, coupling of which with (7S,9S)-4-demethoxydaunomycinone afforded the 3,4-diacetate of 4-demethoxy-9-O-(2,6-dideoxy-2-fluoro-alpha-L-talopyranosyl)daunomycinone (19). The antitumor-active 19 was converted by way of its 14-bromo derivative into the 14-hydroxy analogue, the antitumor-active 4-demethoxyadriamycinone glycoside 21.

Prodrugs of anthracyclines in cancer chemotherapy.

Designing and developing truly tumor-specific prodrugs remains a challenge in the field of cancer chemotherapy. Active targeting strategies, on the one hand, aim at exploiting membrane-associated receptors or antigens for drug delivery; on the other hand, the enhanced vascular permeability and retention of macromolecules in tumor tissue substantiates the concept of passive targeting. Consequently, research efforts have concentrated on conjugating anticancer agents with a wide spectrum of carriers including antibodies, peptides, serum proteins, and synthetic polymers. Conversely, low-molecular weight prodrugs of anticancer agents have been developed that do not bear an active or passive targeting moiety, but are activated by tumor-associated enzymes at the tumor site. Anthracyclines probably represent the class of anticancer agents that has been most widely used for the development of prodrugs. This overview gives an update of the various low- and high-molecular weight prodrugs of anthracyclines, e.g. with antibodies, peptides, carbohydrates, serum proteins or synthetic polymers, that have been developed over the past 20 years and that exemplify the salient features of a respective drug delivery system. A detailed description will be dedicated to anthracycline prodrugs that have reached an advanced stage of preclinical testing or that have entered clinical trials.

Enzymes in the biosynthesis of aromatic polyketide antibiotics.

Aromatic polyketides are secondary metabolites that afford some of the most common antibiotics and anti-cancer drugs currently in clinical use. Not least because of their medical importance, the biosynthesis of these compounds has attracted considerable interest during the past few years; important advances have been made in the structural and mechanistic characterisation of the enzymes involved. These studies are expected to have implications for the production of novel therapeutic agents by combinatorial biosynthesis.

Influence of the structure of new anthracycline antibiotics on their biological properties.

In the search for new derivatives of anthracycline antibiotics with advantageous biological properties, particularly with lower toxicity and/or higher activity, a series of new analogs of antibiotics applied in therapy such as daunorubicin, doxorubicin, as well as epidoxorubicin and, for comparison, analogs of epidaunorubicin, have been synthesized. Our results show that the new derivatives have antiproliferative activities similar to or higher than the parent antibiotics. The toxicities of these analogs were significantly lower, with LD50 values from 1.8- to 18.4-fold higher than the referential drugs. Cardiotoxicity determinations, using male mice treated with a single dose of 75% of the LD50 values of all tested compounds, indicated that the cardiotoxicity of the new analogs is significantly lower than that of the parent drugs.