A new peucemycin derivative and impacts of peuR and bldA on peucemycin biosynthesis in Streptomyces peucetius

Streptomyces peucetius ATCC 27952 is known to produce a variety of secondary metabolites, including two important antitumor anthracyclines: daunorubicin and doxorubicin. Identification of peucemycin and 25-hydroxy peucemycin (peucemycin A), as well as their biosynthetic pathway, has expanded its biosynthetic potential. In this study, we isolated a new peucemycin derivative and identified it as 19-hydroxy peucemycin (peucemycin B). Its antibacterial activity was lower than those of peucemycin and peucemycin A. On the other hand, this newly identified peucemycin derivative had higher anticancer activity than the other two compounds for MKN45, NCI-H1650, and MDA-MB-231 cancer cell lines with IC50 values of 76.97 µM, 99.68 µM, and 135.2 µM, respectively. Peucemycin biosynthetic gene cluster revealed the presence of a SARP regulator named PeuR whose role was unknown. The presence of the TTA codon in the peuR and the absence of global regulator BldA in S. peucetius reduced its ability to regulate the peucemycin biosynthetic gene cluster. Hence, different mutants harboring these genes were prepared. S. peucetius bldA25 harboring bldA produced 1.75 times and 1.77 times more peucemycin A (11.8 mg/L) and peucemycin B (21.2 mg/L), respectively, than the wild type. On the other hand, S. peucetius R25 harboring peuR produced 1.86 and 1.79 times more peucemycin A (12.5 mg/L) and peucemycin B (21.5 mg/L), respectively, than the wild type. Finally, strain S. peucetius bldAR25 carrying bldA and peuR produced roughly 3.52 and 2.63 times more peucemycin A (23.8 mg/L) and peucemycin B (31.5 mg/L), respectively, than the wild type. KEY POINTS: • This study identifies a new peucemycin derivative, 19-hydroxy peucemycin (peucemycin B). • The SARP regulator (PeuR) acts as a positive regulator of the peucemycin biosynthetic gene cluster. • The overexpression of peuR and heterologous expression of bldA increase the production of peucemycin derivatives.

Streptomyces extracellular vesicles are a broad and permissive antimicrobial packaging and delivery system

Streptomyces are the primary source of bioactive specialized metabolites used in research and medicine, including many antimicrobials. These are presumed to be secreted and function as freely soluble compounds. However, increasing evidence suggests that extracellular vesicles are an alternative secretion system. We assessed environmental and lab-adapted Streptomyces (sporulating filamentous actinomycetes) and found frequent production of antimicrobial vesicles. The molecular cargo included actinomycins, anthracyclines, candicidin, and actinorhodin, reflecting both diverse chemical properties and diverse antibacterial and antifungal activity. The levels of packaged antimicrobials correlated with the level of inhibitory activity of the vesicles, and a strain knocked out for the production of anthracyclines produced vesicles that lacked antimicrobial activity. We demonstrated that antimicrobial containing vesicles achieve direct delivery of the cargo to other microbes. Notably, this delivery via membrane fusion occurred to a broad range of microbes, including pathogenic bacteria and yeast. Vesicle encapsulation offers a broad and permissive packaging and delivery system for antimicrobial specialized metabolites, with important implications for ecology and translation.IMPORTANCEExtracellular vesicle encapsulation changes our picture of how antimicrobial metabolites function in the environment and provides an alternative translational approach for the delivery of antimicrobials. We find many Streptomyces strains are capable of releasing antimicrobial vesicles, and at least four distinct classes of compounds can be packaged, suggesting this is widespread in nature. This is a striking departure from the primary paradigm of the secretion and action of specialized metabolites as soluble compounds. Importantly, the vesicles deliver antimicrobial metabolites directly to other microbes via membrane fusion, including pathogenic bacteria and yeast. This suggests future applications in which lipid-encapsulated natural product antibiotics and antifungals could be used to solve some of the most pressing problems in drug resistance.

Anthracyclines induce cardiotoxicity through a shared gene expression response signature

TOP2 inhibitors (TOP2i) are effective drugs for breast cancer treatment. However, they can cause cardiotoxicity in some women. The most widely used TOP2i include anthracyclines (AC) Doxorubicin (DOX), Daunorubicin (DNR), Epirubicin (EPI), and the anthraquinone Mitoxantrone (MTX). It is unclear whether women would experience the same adverse effects from all drugs in this class, or if specific drugs would be preferable for certain individuals based on their cardiotoxicity risk profile. To investigate this, we studied the effects of treatment of DOX, DNR, EPI, MTX, and an unrelated monoclonal antibody Trastuzumab (TRZ) on iPSC-derived cardiomyocytes (iPSC-CMs) from six healthy females. All TOP2i induce cell death at concentrations observed in cancer patient serum, while TRZ does not. A sub-lethal dose of all TOP2i induces limited cellular stress but affects calcium handling, a function critical for cardiomyocyte contraction. TOP2i induce thousands of gene expression changes over time, giving rise to four distinct gene expression response signatures, denoted as TOP2i early-acute, early-sustained, and late response genes, and non-response genes. There is no drug- or AC-specific signature. TOP2i early response genes are enriched in chromatin regulators, which mediate AC sensitivity across breast cancer patients. However, there is increased transcriptional variability between individuals following AC treatments. To investigate potential genetic effects on response variability, we first identified a reported set of expression quantitative trait loci (eQTLs) uncovered following DOX treatment in iPSC-CMs. Indeed, DOX response eQTLs are enriched in genes that respond to all TOP2i. Next, we identified 38 genes in loci associated with AC toxicity by GWAS or TWAS. Two thirds of the genes that respond to at least one TOP2i, respond to all ACs with the same direction of effect. Our data demonstrate that TOP2i induce thousands of shared gene expression changes in cardiomyocytes, including genes near SNPs associated with inter-individual variation in response to DOX treatment and AC-induced cardiotoxicity.

Hypoxia-Responsive Golgi-Targeted Prodrug Assembled with Anthracycline for Improved Antitumor and Antimetastasis Efficacy

Tumor metastasis is an intricate multistep process regulated via various proteins and enzymes modified and secreted by swollen Golgi apparatus in tumor cells. Thus, Golgi complex is considered as an important target for the remedy of metastasis. Currently, Golgi targeting technologies are mostly employed in Golgi-specific fluorescent probes for diagnosis, but their applications in therapy are rarely reported. Herein, we proposed a prodrug (INR) that can target and destroy the Golgi apparatus, which consisted of indomethacin (IMC) as the Golgi targeting moiety and retinoic acid (RA), a Golgi disrupting agent. The linker between IMC and RA was designed as a hypoxia-responsive nitroaromatic structure, which ensured the release of the prototype drugs in the hypoxic tumor microenvironment. Furthermore, INR could be assembled with pirarubicin (THP), an anthracycline, to form a carrier-free nanoparticle (NP) by emulsion-solvent evaporation method. A small amount of mPEG2000-DSPE was added to shield the positive charges and improve the stability of the nanoparticle to obtain PEG-modified nanoparticle (PNP). It was proved that INR released the prototype drugs in tumor cells and hypoxia promoted the release. The Golgi destructive effect of RA in INR was amplified owing to the Golgi targeting ability of IMC, and IMC also inhibited the protumor COX-2/PGE2 signaling. Finally, PNP exhibited excellent curative efficacy on 4T1 primary tumor and its pulmonary and hepatic metastasis. The small molecular therapeutic prodrug targeting Golgi apparatus could be adapted to multifarious drug delivery systems and disease models, which expanded the application of Golgi targeting tactics in disease treatment.

Targeting autophagy with SAR405 alleviates doxorubicin-induced cardiotoxicity

Anthracycline antitumor agents, such as doxorubicin (DOX), are effective in the treatment of solid tumors and hematological malignancies, but anthracycline-induced cardiotoxicity (AIC) limits their application as chemotherapeutics. Dexrazoxane (DEX) has been adopted to prevent AIC. Using a chronic AIC mouse model, we demonstrated that DEX is insufficient to reverse DOX-induced cardiotoxicity. Although therapies targeting autophagy have been explored to prevent AIC, but whether novel autophagy inhibitors could alleviate or prevent AIC in clinically relevant models needs further investigation. Here, we show that genetic ablation of Atg7, a key regulator in the early phase of autophagy, protected mice against AIC. We further demonstrated that SAR405, a novel autophagy inhibitor, attenuated DOX-induced cytotoxicity. Intriguingly, the combination of DEX and SAR405 protected cells against DOX-induced cardiotoxicity in vivo. Using the cardiomyocyte cell lines AC16 and H9c2, we determined that autophagy was initiated during AIC. Our results suggest that inhibition of autophagy at its early phase with SAR405 combined with DEX represents an effective therapeutic strategy to prevent AIC.

Anthracycline derivatives inhibit cardiac CYP2J2

Anthracycline chemotherapeutics are highly effective, but their clinical usefulness is hampered by adverse side effects such as cardiotoxicity. Cytochrome P450 2J2 (CYP2J2) is a cytochrome P450 epoxygenase in human cardiomyocytes that converts arachidonic acid (AA) to cardioprotective epoxyeicosatrienoic acid (EET) regioisomers. Herein, we performed biochemical studies to understand the interaction of anthracycline derivatives (daunorubicin, doxorubicin, epirubicin, idarubicin, 5-iminodaunorubicin, zorubicin, valrubicin, and aclarubicin) with CYP2J2. We utilized fluorescence polarization (FP) to assess whether anthracyclines bind to CYP2J2. We found that aclarubicin bound the strongest to CYP2J2 despite it having large bulky groups. We determined that ebastine competitively inhibits anthracycline binding, suggesting that ebastine and anthracyclines may share the same binding site. Molecular dynamics and ensemble docking revealed electrostatic interactions between the anthracyclines and CYP2J2, contributing to binding stability. In particular, the glycosamine groups in anthracyclines are stabilized by binding to glutamate and aspartate residues in CYP2J2 forming salt bridge interactions. Furthermore, we used iterative ensemble docking schemes to gauge anthracycline influence on EET regioisomer production and anthracycline inhibition on AA metabolism. This was followed by experimental validation of CYP2J2-mediated metabolism of anthracycline derivatives using liquid chromatography tandem mass spectrometry fragmentation analysis and inhibition of CYP2J2-mediated AA metabolism by these derivatives. Taken together, we use both experimental and theoretical methodologies to unveil the interactions of anthracycline derivatives with CYP2J2. These studies will help identify alternative mechanisms of how anthracycline cardiotoxicity may be mediated through the inhibition of cardiac P450, which will aid in the design of new anthracycline derivatives with lower toxicity.

Natural Products Counteracting Cardiotoxicity during Cancer Chemotherapy: The Special Case of Doxorubicin, a Comprehensive Review

Cardiotoxicity is a frequent undesirable phenomenon observed during oncological treatment that limits the therapeutic dose of antitumor drugs and thus may decrease the effectiveness of cancer eradication. Almost all antitumor drugs exhibit toxic properties towards cardiac muscle. One of the underlying causes of cardiotoxicity is the stimulation of oxidative stress by chemotherapy. This suggests that an appropriately designed diet or dietary supplements based on edible plants rich in antioxidants could decrease the toxicity of antitumor drugs and diminish the risk of cardiac failure. This comprehensive review compares the cardioprotective efficacy of edible plant extracts and foodborne phytochemicals whose beneficial activity was demonstrated in various models in vivo and in vitro. The studies selected for this review concentrated on a therapy frequently applied in cancer, anthracycline antibiotic-doxorubicin-as the oxidative stress- and cardiotoxicity-inducing agent.

Streptomyces griseus KJ623766: A Natural Producer of Two Anthracycline Cytotoxic Metabolites β- and γ-Rhodomycinone

Background: This study aimed to produce, purify, structurally elucidate, and explore the biological activities of metabolites produced by Streptomyces (S.) griseus isolate KJ623766, a recovered soil bacterium previously screened in our lab that showed promising cytotoxic activities against various cancer cell lines. Methods: Production of cytotoxic metabolites from S. griseus isolate KJ623766 was carried out in a 14L laboratory fermenter under specified optimum conditions. Using a 3-(4,5-dimethylthazol-2-yl)-2,5-diphenyl tetrazolium-bromide assay, the cytotoxic activity of the ethyl acetate extract against Caco2 and Hela cancer cell lines was determined. Bioassay-guided fractionation of the ethyl acetate extract using different chromatographic techniques was used for cytotoxic metabolite purification. Chemical structures of the purified metabolites were identified using mass, 1D, and 2D NMR spectroscopic analysis. Results: Bioassay-guided fractionation of the ethyl acetate extract led to the purification of two cytotoxic metabolites, R1 and R2, of reproducible amounts of 5 and 1.5 mg/L, respectively. The structures of R1 and R2 metabolites were identified as β- and γ-rhodomycinone with CD₅₀ of 6.3, 9.45, 64.8 and 9.11, 9.35, 67.3 µg/mL against Caco2, Hela and Vero cell lines, respectively. Values were comparable to those of the positive control doxorubicin. Conclusions: This is the first report about the production of β- and γ-rhodomycinone, two important scaffolds for synthesis of anticancer drugs, from S. griseus.

Actinobacteria from Antarctica as a source for anticancer discovery

Although many advances have been achieved to treat aggressive tumours, cancer remains a leading cause of death and a public health problem worldwide. Among the main approaches for the discovery of new bioactive agents, the prospect of microbial secondary metabolites represents an effective source for the development of drug leads. In this study, we investigated the actinobacterial diversity associated with an endemic Antarctic species, Deschampsia antarctica, by integrated culture-dependent and culture-independent methods and acknowledged this niche as a reservoir of bioactive strains for the production of antitumour compounds. The 16S rRNA-based analysis showed the predominance of the Actinomycetales order, a well-known group of bioactive metabolite producers belonging to the Actinobacteria phylum. Cultivation techniques were applied, and 72 psychrotolerant Actinobacteria strains belonging to the genera Actinoplanes, Arthrobacter, Kribbella, Mycobacterium, Nocardia, Pilimelia, Pseudarthrobacter, Rhodococcus, Streptacidiphilus, Streptomyces and Tsukamurella were identified. The secondary metabolites were screened, and 17 isolates were identified as promising antitumour compound producers. However, the bio-guided assay showed a pronounced antiproliferative activity for the crude extracts of Streptomyces sp. CMAA 1527 and Streptomyces sp. CMAA 1653. The TGI and LC50 values revealed the potential of these natural products to control the proliferation of breast (MCF-7), glioblastoma (U251), lung/non-small (NCI-H460) and kidney (786-0) human cancer cell lines. Cinerubin B and actinomycin V were the predominant compounds identified in Streptomyces sp. CMAA 1527 and Streptomyces sp. CMAA 1653, respectively. Our results suggest that the rhizosphere of D. antarctica represents a prominent reservoir of bioactive actinobacteria strains and reveals it as an important environment for potential antitumour agents.

CytA, a reductase in the cytorhodin biosynthesis pathway, inactivates anthracycline drugs in Streptomyces

Antibiotic-producing microorganism can develop strategies to deal with self-toxicity. Cytorhodins X and Y, cosmomycins A and B, and iremycin, are produced as final products from a marine-derived Streptomyces sp. SCSIO 1666. These C-7 reduced metabolites show reduced antimicrobial and comparable cytotoxic activities relative to their C-7 glycosylated counterparts. However, the biosynthetic mechanisms and relevant enzymes that drive C-7 reduction in cytorhodin biosynthesis have not yet been characterized. Here we report the discovery and characterization of a reductase, CytA, that mediates C-7 reduction of this anthracycline scaffold; CytA endows the producer Streptomyces sp. SCSIO 1666 with a means of protecting itself from the effects of its anthracycline products. Additionally, we identified cosmomycins C and D as two intermediates involved in cytorhodin biosynthesis and we also broadened the substrate specificity of CytA to clinically used anthracycline drugs.

Spectroscopic and cytotoxicity studies on the combined interaction of (-)-epigallocatechin-3-gallate and anthracycline drugs with human serum albumin

The interactions of (-)-epigallocatechin-3-Gallate (EGCG) and anthracycline drugs (doxorubicin, DOX and epirubicin, EPI) alone or in combination with human serum albumin (HSA) under physiological condition were studied by fluorescence spectroscopy, UV-vis absorption spectroscopy, circular dichroism (CD) spectroscopy, and dynamic light scattering (DLS). The cytotoxic activity of the single drug, combined drugs, and their complexes with HSA against human cervical cancer HeLa cell line was determined by MTT assay. Fluorescence quenching result and difference spectra of UV absorption revealed the formation of static complex between EGCG, DOX, or EPI and HSA. The binding of EGCG with HSA was driven by both enthalpy and entropy while the binding of DOX or EPI was mainly entropy driven. The nature of binding was expounded based on the effect of sodium chloride, tetrabutylammonium bromide, and sucrose which interfere in electrostatic, hydrophobic, and hydrogen bonding interactions, respectively. Site marker competitive experiments combined with synchronous fluorescence spectra showed that these three ligands mainly bound to subdomain IIA of HSA and were closer to tryptophan residues. In EGCG + DOX/EPI + HSA ternary system, the effect of one drug on the binding ability of another drug was discussed. The influences of the individual and combined binding of EGCG and DOX/EPI on the secondary structure and particle size of HSA were investigated by CD spectroscopy and DLS, respectively. Moreover, the synergistic cytotoxicity of EGCG and DOX/EPI as well as their complexes with HSA were discussed. Obtained results would provide beneficial information on the combination of EGCG and anthracyclines in clinic.

Cardiotoxicity among adult survivors suffered from childhood malignancies

Late cardiotoxicity following treatment of malignancy diseases has been long established. Cancer therapeutics-related cardiac dysfunction (CTRCD), acute arrhythmias, pericardial disease, valvopathies and early atherosclerotic Cardiovascular Disease (CVD), are the clinical presentations of cardiotoxicity. Although these clinical modalities can affect adults treated for malignancies, they are more common to present in the pediatric survivors as improvement of prognosis, nowadays exists. Studies have shown that CVD can present earlier than thirty years, post treatment. If adding on this the early and late effect of cardiotoxicity on the developing in childhood cardiovascular system, we are then faced with a new Risk Factor (RF) for CVD. Anthracyclines and its derivatives have served for over fifty years as the road model of studding early, mid and late term cardiotoxicity. Today a vast number of chemical agents are used, many of them with very good results in treating the existing malignancies. Unfortunate, little or even less are known on their potential mechanism of derived cardiotoxicity when used by their own or combined with others and/or radiotherapy (RT). The 2013 existing guidelines by ACC/AHA on surveillance of the cardiovascular health of oncology survivors, are mostly addressing early cardiac adverse effects and CTRCD. Little is mentioned about the development of early CVD, its subclinical diagnosis, prevention and the need of early intervention before clinical events are present. The aim of this paper is to review the exist knowledge and practice on this condition with growing numbers of survivors facing the risk of early atherosclerotic CVD.

Metabolic and non-metabolic pathways that control cancer resistance to anthracyclines

Anthracyclines Doxorubicin, Epirubicin, Daunorubicin and Idarubicin are used to treat a variety of tumor types in the clinics, either alone or, most often, in combination therapies. While their cardiotoxicity is well known, the emergence of chemoresistance is also a major issue accounting for treatment discontinuation. Resistance to anthracyclines is associated to the acquisition of multidrug resistance conferred by overexpression of permeability glycoprotein-1 or other efflux pumps, by altered DNA repair, changes in topoisomerase II activity, cancer stemness and metabolic adaptations. This review further details the metabolic aspects of resistance to anthracyclines, emphasizing the contributions of glycolysis, the pentose phosphate pathway and nucleotide biosynthesis, glutathione, lipid metabolism and autophagy to the chemoresistant phenotype.

Evaluation of the impact of single-nucleotide polymorphisms on treatment response, survival and toxicity with cytarabine and anthracyclines in patients with acute myeloid leukaemia: a systematic review protocol

INTRODUCTION

Acute myeloid leukaemia is the most common type of acute leukaemia in the world. Thus, the study of genetic alterations, such as single-nucleotide polymorphisms (SNPs), has contributed to a better understanding of the mechanisms underlying leukaemogenesis, to improve the prognosis and to increase the survival of these patients. However, there is no synthesis of evidence in the literature evaluating the quality of evidence and the risk of bias in the studies such that the results can be translated. Thus, this systematic review protocol aims to assess the impact of SNPs on genes involved in the metabolism of cytarabine and anthracyclines with respect to survival, treatment response and toxicity in patients with AML.

METHODS

This systematic review protocol is based on PRISMA guidelines and includes searches in six electronic databases, contact with authors, repositories of clinical trials, and cancer research. Studies published in peer-reviewed journals will be included if they meet the eligibility criteria: (a) samples composed of individuals of any age, of both sexes, with a diagnosis of AML, regardless of the time of diagnosis of disease; (b) participants who have undergone or are undergoing cytarabine- and anthracycline-associated chemotherapy or cytarabine-only chemotherapy; and (c) in vivo studies. Studies that include patients with promyelocytic leukaemia (Fab type 3) will be excluded because this disease has different treatment. The process of study selection, data extraction, and evaluation/synthesis will be performed in duplicate. Assessment of methodological quality and risk of bias will be performed using the Cochrane Risk of Bias Tool for randomized clinical studies and the Downs-Black Checklist for cohort and case-control studies. The synthesis of evidence will include the level of evidence based on the GRADE protocol. A meta-analysis of the association between SNPs and outcomes may be performed based on Cochrane guidelines.

DISCUSSION

It is expected that clinical decisions for AML patients will consider evidence-based practices to contribute to better patient management. In this way, we will be able to define how to treat patients with AML to improve their survival and quality of life.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42018100750.

Cytotoxic Anthracycline Metabolites from a Recombinant Streptomyces

The C7 (C9 or C10)- O-l-rhodosamine-bearing anthracycline antibiotic cytorhodins and their biosynthetic intermediates were recently isolated from Streptomyces sp. SCSIO 1666. Cosmid p17C4 from the Streptomyces lydicus genomic library, which harbors both the biosynthetic genes for l-rhodinose (or 2-deoxy-l-fucose) and its glycosyltransferase (encoded by slgG), was introduced into SCSIO 1666 to yield the recombinant strain Streptomyces sp. SCSIO 1666/17C4. Chemical investigations of this strain's secondary metabolic potential revealed the production of different anthracyclines featuring C7- O-l-rhodinose (or 2-deoxy-l-fucose) instead of the typically observed l-rhodosamine. Purification of the fermentation broth yielded 12 new anthracycline antibiotics including three new ε-rhodomycinone derivatives, 1, 4, and 8, nine new β-rhodomycinone derivatives, 2, 3, 5-7, and 9-12, and three known compounds, l-rhodinose-l-rhodinose-l-rhodinoserhodomycinone (13), ε-rhodomycinone (14), and γ-rhodomycinone (15). All compounds were characterized on the basis of detailed spectroscopic analyses and comparisons with previously reported data. These compounds exhibited cytotoxicity against a panel of human cancer cell lines. Significantly, compounds 4 and 13 displayed pronounced activity against HCT-116 as characterized by IC₅₀ values of 0.3 and 0.2 μM, respectively; these IC₅₀ values are comparable to that of the positive control epirubicin.

Divergent evolution of an atypical S-adenosyl-l-methionine-dependent monooxygenase involved in anthracycline biosynthesis

Bacterial secondary metabolic pathways are responsible for the biosynthesis of thousands of bioactive natural products. Many enzymes residing in these pathways have evolved to catalyze unusual chemical transformations, which is facilitated by an evolutionary pressure promoting chemical diversity. Such divergent enzyme evolution has been observed in S-adenosyl-L-methionine (SAM)-dependent methyltransferases involved in the biosynthesis of anthracycline anticancer antibiotics; whereas DnrK from the daunorubicin pathway is a canonical 4-O-methyltransferase, the closely related RdmB (52% sequence identity) from the rhodomycin pathways is an atypical 10-hydroxylase that requires SAM, a thiol reducing agent, and molecular oxygen for activity. Here, we have used extensive chimeragenesis to gain insight into the functional differentiation of RdmB and show that insertion of a single serine residue to DnrK is sufficient for introduction of the monooxygenation activity. The crystal structure of DnrK-Ser in complex with aclacinomycin T and S-adenosyl-L-homocysteine refined to 1.9-Å resolution revealed that the inserted serine S297 resides in an α-helical segment adjacent to the substrate, but in a manner where the side chain points away from the active site. Further experimental work indicated that the shift in activity is mediated by rotation of a preceding phenylalanine F296 toward the active site, which blocks a channel to the surface of the protein that is present in native DnrK. The channel is also closed in RdmB and may be important for monooxygenation in a solvent-free environment. Finally, we postulate that the hydroxylation ability of RdmB originates from a previously undetected 10-decarboxylation activity of DnrK.

Complementation of the Yeast Model System Reveals that Caenorhabditis elegans OCT-1 Is a Functional Transporter of Anthracyclines

The yeast plasma membrane protein Agp2 belongs to the family of amino acid transporters. It acts as a regulator that controls the expression of several uptake transporter genes such as DUR3 and SAM3 encoding two high-affinity polyamine permeases. agp2Δ mutants display extreme resistance to several cationic compounds including polyamines, the anticancer agent bleomycin, and cationic antifungal peptides. We propose that Agp2 might be involved in regulating the uptake of other cationic anticancer drugs. To date, an uptake transporter has not been reported for anthracyclines, a family of chemotherapeutic agents that are used for treating adult patients with acute myeloid leukemia. Herein, we develop assay conditions to monitor the uptake of the anthracycline doxorubicin into yeast cells and demonstrate for the first time that Agp2 is required for the drug uptake. Deletion of both the DUR3 and SAM3 genes reduced doxorubicin uptake, but not the deletion of either gene alone, while the agp2Δ mutant was severely compromised, suggesting that Agp2 controls the drug uptake via Dur3 and Sam3 and at least one additional transporter. Overexpression of DUR3 or SAM3 from the endogenous promoter rescued doxorubicin uptake into the sam3Δdur3Δ double mutant, consistent with a role for these transporters in the uptake of anthracyclines. We further show by cross-species complementation analysis that expression of the Caenorhabditis elegans oct-1 gene encoding an organic cation transporter restored full doxorubicin uptake in the agp2Δ mutant. Four separate variants of CeOCT-1 derived by substituting the amino acid residues Gln15, Cys31, Gln109 and Lys300 with alanine were stably expressed, but did not mediate doxorubicin uptake into the agp2Δ mutant. Moreover, we show that overexpression of CeOCT-1 sensitized parent yeast cells to doxorubicin, suggesting that CeOCT-1 related members might be key transporters to facilitate entry of anthracyclines into human cells.

Synergistic actions of tailoring enzymes in pradimicin biosynthesis

Three key tailoring enzymes in pradimicin biosynthesis: PdmJ, PdmW, and PdmN, were investigated. PdmW was characterized as the C-6 hydroxylase by structural characterization of the corresponding product, 6-hydroxy-G-2A. The efficiencies of the C-5 and C-6 hydroxylations, catalyzed respectively by PdmJ and PdmW, were low when they were expressed individually with the early biosynthetic enzymes that form G-2A. When these two cytochrome P450 enzymes were co-expressed, a dihydroxylated product, 5,6-dihydroxy-G-2A, was efficiently produced, indicating that these two enzymes work synergistically in pradimicin biosynthesis. Heterologously expressed PdmN in Streptomyces coelicolor CH999 converted G-2A to JX137a by ligating a unit of D-alanine to the carboxyl group. PdmN has relaxed substrate specificity toward both amino acid donors and acceptors. Through combinatorial biosynthesis, a series of new pradimicin analogues were produced.

Multiparameter analysis of apoptosis using lab-on-a-chip flow cytometry

The age of microfluidic flow cytometry (µFCM) is fast becoming a reality. One of the most exciting applications of miniaturized chip-based cytometers is multivariate analysis using sampling volumes as small as 10 µl while matching the multiparameter data collection of conventional flow cytometers. We outline several innovative protocols for analyzing caspase-dependent cell death and cell cycle (DNA-content) profile using a fully integrated microfluidic flow cytometry system, Fishman-R. The first protocol describes the use of a new plasma membrane-permeability marker, DRAQ7, and the fluorogenic caspase substrate PhiPhiLux to track caspase activation during programmed cell death. Also outlined is the use of DRAQ7 fluorochrome in conjunction with the mitochondrial membrane potential-sensitive probe TMRM to track dissipation of inner mitochondrial cross-membrane potential. Another protocol adds the ability to measure dissipation of mitochondrial inner membrane potential (using TMRM probe) in relation to the cell cycle profile (using DRAQ5 probe) in living leukemic cells. Finally, we describe the combined use of fluorogenic caspases substrate PhiPhiLux with DRAQ5 probe to measure caspase activation in relation to the cell cycle profile in living tumor cells.

Follow-up of natural products isolation

Follow-up of natural products isolation refers to re-isolation of compound(s) of interest in larger amounts for further pharmacological testing, conclusive structure elucidation, structure modifications to synthesize analogs for structure-activity relationships (SAR) studies, preformulation and formulation studies or clinical trials. In addition to conventional synthetic chemistry approaches, several other methodologies can be applied for following-up natural products isolation. This chapter outlines, with specific examples, various strategies and methods involved in follow-up of natural products isolation.

Expression of the anthracycline-metabolizing enzyme carbonyl reductase 1 in hearts from donors with Down syndrome

Cancer patients with Down syndrome (DS) are susceptible to developing anthracycline-related cardiotoxicity. The pathogenesis of anthracycline-related cardiotoxicity has been linked to the intracardiac synthesis of alcohol metabolites by carbonyl reductase 1 (CBR1). CBR1 is located in the DS critical region (21q22.12). The expression of CBR1 in hearts from individuals with DS has not been characterized. This study documented CBR1 expression in hearts from donors with DS (n = 4) and donors without DS (n = 15). The DS samples showed 1.8-fold higher CBR1 mRNA levels compared to the non-DS samples (levels in DS samples were 3.3-relative fold, and those in non-DS were 1.8-relative fold; p = 0.012). CBR1 protein levels were 1.9-fold higher in DS samples than in non-DS samples (13.5 ± 7.7 versus 7.2 ± 3.9 nmol/g cytosolic protein, respectively; p = 0.029). CBR1 activity for daunorubicin was 1.7-fold higher in DS samples than in non-DS samples (3.8 ± 0.1 versus 2.3 ± 0.2 nmol daunol/min · mg, respectively; p = 0.050). CBR1 1096G>A (rs9024) affects CBR1 activity, and one heart trisomic for the variant A allele (A/A/A) exhibited low enzymatic activity. These findings suggest that increased CBR1 expression in the hearts of individuals with DS may contribute to the risk of anthracycline-related cardiotoxicity.

PSMB7 is associated with anthracycline resistance and is a prognostic biomarker in breast cancer

BACKGROUND

To date individual markers have failed to correctly predict resistance against anticancer agents in breast cancer. We used gene expression patterns attributable to chemotherapy-resistant cells to detect potential new biomarkers related to anthracycline resistance. One of the genes, PSMB7, was selected for further functional studies and clinical validation.

METHODS

We contrasted the expression profiles of four pairs of different human tumour cell lines and of their counterparts resistant to doxorubicin. Observed overexpression of PSMB7 in resistant cell lines was validated by immunohistochemistry. To examine its function in chemoresistance, we silenced the gene by RNA interference (RNAi) in doxorubicin-resistant MCF-7 breast cancer cells, then cell vitality was measured after doxorubicin treatment. Microarray gene expression from GEO raw microarray samples with available progression-free survival data was downloaded, and expression of PSMB7 was used for grouping samples.

RESULTS

After doxorubicin treatment, 79.8+/-13.3% of resistant cells survived. Silencing of PSMB7 in resistant cells decreased survival to 31.8+/-6.4% (P>0.001). A similar effect was observed after paclitaxel treatment. In 1592 microarray samples, the patients with high PSMB7 expression had a significantly shorter survival than the patients with low expression (P<0.001).

CONCLUSION

Our findings suggest that high PSMB7 expression is an unfavourable prognostic marker in breast cancer.

Synthesis and DNA-binding affinity studies of glycosylated intercalators designed as functional mimics of the anthracycline antibiotics

Anthracycline antibiotics such as daunomycin (Dauno) and doxorubicin (Dox) are well-known clinically used cancer chemotherapeutics, which, among other mechanisms, bind to DNA, thereby triggering a cascade of biological responses leading to cell death. However, anthracyclines are cardiotoxic, and drug resistance develops rapidly, thus limiting their clinical use. We report here the synthesis and DNA-binding affinity of a novel class of functional anthracycline mimetics consisting of an aromatic moiety linked to a carbohydrate (1-12). In the targets, the aromatic core consists of a 2-phenylbenzo[b]furan-3-yl, 2-phenylbenzo[b]thiophen-3-yl, 1-tosyl-2-phenylindol-3-yl, or 2-phenylindol-3-yl group that is bound to one of three aminosugars (daunosamine, acosamine, or 4-amino-2,3,4,6-tetradeoxy-alpha-l-hexopyranoside) via a propargyl linker. The DNA binding affinity of these twelve compounds has been evaluated by using both direct and indirect fluorescence measurements. Compared to Dauno and Dox, the DNA binding affinity of these analogues is weaker. However, both aromatic and aminosugar motifs are critical to DNA binding, with more influence coming from the structural features of the aromatic portion.

Structural basis for substrate recognition and specificity in aklavinone-11-hydroxylase from rhodomycin biosynthesis

In the biosynthesis of several anthracyclines, aromatic polyketides produced by many Streptomyces species, the aglycone core is modified by a specific flavin adenine dinucleotide (FAD)- and NAD(P)H-dependent aklavinone-11-hydroxylase. Here, we report the crystal structure of a ternary complex of this enzyme from Streptomyces purpurascens, RdmE, with FAD and the substrate aklavinone. The enzyme is built up of three domains, a FAD-binding domain, a domain involved in substrate binding, and a C-terminal thioredoxin-like domain of unknown function. RdmE exhibits structural similarity to aromatic hydroxylases from the p-hydroxybenzoate hydroxylase family, but unlike most other related enzymes, RdmE is a monomer. The substrate is bound in a hydrophobic pocket in the interior of the enzyme, and access to this pocket is provided through a different route than for the isoalloxazine ring of FAD-the backside of the ligand binding cleft. The architecture of the substrate binding pocket and the observed enzyme-aklavinone interactions provide a structural explanation for the specificity of the enzyme for non-glycosylated substrates with C9-R stereochemistry. The isoalloxazine ring of the flavin cofactor is bound in the "out" conformation but can be modeled in the "in" conformation without invoking large conformational changes of the enzyme. This model places the flavin ring in a position suitable for catalysis, almost perpendicular to the tetracyclic ring system of the substrate and with a distance of the C4a carbon atom of the isoalloxazine ring to the C-11 carbon atom of the substrate of 4.8 A. The structure suggested that a Tyr224-Arg373 pair might be involved in proton abstraction at the C-6 hydroxyl group, thereby increasing the nucleophilicity of the aromatic ring system and facilitating electrophilic attack by the perhydroxy-flavin intermediate. Replacement of Tyr224 by phenylalanine results in inactive enzyme, whereas mutants at position Arg373 retain catalytic activity close to wild-type level. These data establish an essential role of residue Tyr224 in catalysis, possibly in aligning the substrate in a position suitable for catalysis.

Amidinoanthracyclines – a new group of potential anti-hepatitis C virus compounds

Hepatitis C virus (HCV) infections represent one of the major and still unresolved health problems because current therapy is effective in only 50–80% of cases, depending on viral genotype. A large group of amidinoanthracyclines, with decreased acute toxicity and cardiotoxicity compared to the parent antibiotics, was tested in a high-throughput fluorometric HCV helicase assay. Here, we report the selection of more than 50 potent inhibitors of helicase activity that inhibit the enzyme with IC50 values in the range of 0.03–10 μm; four of these compounds are the most potent inhibitors of helicase activity described in the literature. The activity of these inhibitors is highly dependent on their chemical structure, mainly on the substituent at the amidino carbon atom and on the orientation of the hydroxyl group at the 4′ position of the daunosamine moiety. The most effective compounds act not solely via intercalation into the double-stranded DNA substrate, but also compete with the enzyme for access to the substrate, impeding formation of the active helicase complex. Selected amidinoanthracyclines were tested in the subgenomic HCV replicon system. These experiments confirmed the antiviral activity of two selected inhibitors (EC50 values below 0.2 μm with selectivity indices of 19 and 33) and proved that they may be considered as potential anti-HCV drugs.

Characterization of the enzymes involved in thein vitrometabolism of amrubicin hydrochloride

The in vitro metabolism of amrubicin by rat and human liver microsomes and cytosol was examined. The main metabolic routes in both species were reductive deglycosylation and carbonyl group reduction in the side-chain. In vitro metabolism of amrubicinol by rat and human liver microsomes and cytosol was also examined and the main metabolic route of this active metabolite was reductive deglycosylation. Metabolism of amrubicin in human liver microsomes was inhibited by TlCl(3) and that in human liver cytosol was inhibited by dicumarol and quercetin. Generation of amrubicinol was inhibited only by quercetin. The results indicate that metabolism of amrubicin is mediated by NADPH-cytochrome P450 reductase, NADPH:quinone oxidoreductase and carbonyl reductase. In addition, generation of amrubicinol is mediated by carbonyl reductase. Metabolism of amrubicinol in human liver microsomes was inhibited by TlCl(3) and that in human liver cytosol was inhibited by dicumarol. The results indicate that metabolism of amrubicinol is mediated by NADPH-cytochrome P450 reductase and NADPH:quinone oxidoreductase. To investigate the influence of cisplatin on the metabolism of amrubicin and amrubicinol, human liver microsomes and cytosol were pre-incubated with cisplatin. This did not change the rates of amrubicin and amrubicinol metabolism in either human liver microsomes or cytosol.

Sensitization by docosahexaenoic acid (DHA) of breast cancer cells to anthracyclines through loss of glutathione peroxidase (GPx1) response

Docosahexaenoic acid (DHA, a lipid of marine origin) has been found to enhance the activity of several anticancer drugs through an oxidative mechanism. To examine the relation between chemosensitization by DHA and tumor cells antioxidant status, we used two breast cancer cell lines: MDA-MB-231, in which DHA increases sensitivity to doxorubicin, and MCF-7, which does not respond to DHA. Under these conditions, reactive oxygen species (ROS) level increased on anthracycline treatment only in MDA-MB-231. This was concomitant with a decreased cytosolic glutathione peroxidase (GPx1) activity, a crucial enzyme for protection against hydrogen and lipid peroxides, while major antioxidant enzyme activities increased in both cell lines in response to ROS. GPx-decreased activity was accompanied by an accumulation of glutathione, the GPx cosubstrate, and resulted from a decreased amount of GPx protein. In rat mammary tumors, when a DHA dietary supplementation led to an increased tumor sensitivity to anthracyclines, GPx1 activity was similarly decreased. Furthermore, vitamin E abolished both DHA effects on chemotherapy efficacy enhancement and on GPx1 inhibition. Thus, loss of GPx response to an oxidative stress in transformed cells may account for the ability of peroxidizable targets such as DHA to enhance tumor sensitivity to ROS-generating anticancer drugs.

DNA topoisomerase II structures and anthracycline activity: insights into ternary complex formation

DNA Topoisomerase II (Top2) is an essential nuclear enzyme that regulates the topological state of the DNA, and a target of very effective anticancer drugs including anthracycline antibiotics. Even though several aspects of drug activity against Top2 are understood, the drug receptor site is not yet known. Several Top2 mutants have altered drug sensitivity and have provided information of structural features determining drug action. Here, we have revised the published crystal structures of eukaryotic and prokaryotic Top2s and relevant biochemical investigations of enzyme activity and anthracycline action. In particular, we have considered Top2 mutations conferring resistance to anthracyclines and related agents. Following a previous study (Moro et al, Biochemistry, 2004; 43: 7503-13), we have then re-built a molecular model of the entire enzyme in complex with DNA after the cleavage reaction, and used it to define the receptor site of anthracyclines. The results suggest a model wherein the drug specifically contacts the cleaved DNA as well as amino acid residues of the enzyme CAP-like domain. The findings can explain several established structure-activity relationships of antitumour anthracyclines, and provide a framework for further developments of effective Top2 poison.

An introduction to the metabolic determinants of anthracycline cardiotoxicity

Antitumor therapy with doxorubicin and other anthracyclines is limited by the possible development of cardiomyopathy upon chronic administration. Several lines of evidence suggest that a close link exists between cardiotoxicity and the amount of anthracycline that accumulates in the heart and then undergoes one- or two- electron reduction to toxic metabolites or by-products. Alternative metabolic pathways lead to an oxidative degradation of anthracyclines, possibly counteracting anthracycline accumulation and reductive bioactivation; unfortunately, however, the actual role of anthracycline oxidation is only partially characterized. Here, we briefly review the biochemical foundations of reductive versus oxidative anthracycline metabolism. We show that multiple links exist between one pathway of toxic biactivation and another, limiting the search and clinical development of "better anthracyclines" that retain antitumor activity but induce less cardiotoxicity than the available analogues.

Anthracycline cardiotoxicity in breast cancer patients: synergism with trastuzumab and taxanes

Doxorubicin is known to cause cardiomyopathy and congestive heart failure (CHF) upon chronic administration. A major obstacle to doxorubicin-containing multiagent therapies pertains to the possible development of cardiomyopathy and CHF at lower than expected cumulative doses of doxorubicin. For example, the cardiac toxicity of doxorubicin is aggravated by the anti-HER2 antibody Trastuzumab or by the tubulin-active taxane paclitaxel; however, the mechanisms by which Trastuzumab and paclitaxel aggravate doxorubicin-induced cardiotoxicity are mechanistically distinct: Trastuzumab interferes with cardiac-specific survival factors that help the heart to withstand stressor agents like anthracyclines, while paclitaxel acts by stimulating the formation of anthracycline metabolites that play a key role in the mechanism of cardiac failure. Here, we briefly review the molecular mechanisms of the cardiotoxic synergism of Trastuzumab or paclitaxel with doxorubicin, and we attempt to briefly outline how the mechanistic know-how translates into the clinical strategies for improving the safety of anthracycline-based multiagent therapies.

A DNA aptamer with high affinity and specificity for therapeutic anthracyclines

We describe the characterization of a DNA aptamer that displays high affinity and specificity for the anthracyclines daunomycin and doxorubicin, both of which are frequently used in chemotherapy. Aptamers were isolated from a pool of random sequences using a semiautomated procedure for magnetic beads. All selected aptamers displayed high affinity for the target molecule daunomycin. One aptamer was further characterized and exhibited a dissociation constant (KD) of 20 nM. To examine the aptamer's binding properties and clarify its applicability for diagnostic assays, its performance under various buffer conditions was evaluated. The aptamer proved to be very robust and not dependent on the presence of specific ions. It also tolerated a wide pH range and immobilization via 5'-biotinylation. Furthermore, a competition assay for sensitive daunomycin detection was established. This not only allows the determination of the aptamer's specificity but also allows the quantification of as little as 8.4 microg/L daunomycin and doxorubicin.

Spectroscopic studies of DNA binding modes of cation-substituted anthrapyrazoles derived from emodin

The DNA binding properties of three cation-substituted anthrapyrazole derivatives of emodin with calf thymus DNA were characterized by spectroscopic methods and the specific binding modes were elucidated. At low drug and high DNA concentrations, compound 1 with a mono-cationic amino side chain exhibited an intercalative binding mode, 2 with a much longer and more flexible di-cationic side chain exhibited an external binding mode, and 3 with a rigid di-cationic side chain exhibited both intercalative and external binding modes. The DNA binding mode of compounds was altered after structural modification. The molecular structure-DNA binding relationships found from this study may be useful for the design of anthrapyrazole derivatives with desired binding characteristics.

The carbohydrate-binding plant lectins and the non-peptidic antibiotic pradimicin A target the glycans of the coronavirus envelope glycoproteins

Objectives

Many enveloped viruses carry carbohydrate-containing proteins on their surface. These glycoproteins are key to the infection process as they are mediators of the receptor binding and membrane fusion of the virion with the host cell. Therefore, they are attractive therapeutic targets for the development of novel antiviral therapies. Recently, carbohydrate-binding agents (CBA) were shown to possess antiviral activity towards coronaviruses. The current study further elucidates the inhibitory mode of action of CBA.

Methods

Different strains of two coronaviruses, mouse hepatitis virus and feline infectious peritonitis virus, were exposed to CBA: the plant lectins Galanthus nivalis agglutinin, Hippeastrum hybrid agglutinin and Urtica dioica agglutinin (UDA) and the non-peptidic mannose-binding antibiotic pradimicin A.

Results and conclusions

Our results indicate that CBA target the two glycosylated envelope glycoproteins, the spike (S) and membrane (M) protein, of mouse hepatitis virus and feline infectious peritonitis virus. Furthermore, CBA did not inhibit virus–cell attachment, but rather affected virus entry at a post-binding stage. The sensitivity of coronaviruses towards CBA was shown to be dependent on the processing of the N-linked carbohydrates. Inhibition of mannosidases in host cells rendered the progeny viruses more sensitive to the mannose-binding agents and even to the N-acetylglucosamine-binding UDA. In addition, inhibition of coronaviruses was shown to be dependent on the cell-type used to grow the virus stocks. All together, these results show that CBA exhibit promising capabilities to inhibit coronavirus infections.

Inactivation of anthracyclines by serum heme proteins

We have previously shown that the anticancer agent doxorubicin undergoes oxidation and inactivation when exposed to myeloperoxidase-containing human leukemia HL-60 cells, or to isolated myeloperoxidase, in the presence of hydrogen peroxide and nitrite. In the current study we report that commercial fetal bovine serum (FBS) alone oxidizes doxorubicin in the presence of hydrogen peroxide and that nitrite accelerates this oxidation. The efficacy of inactivation was dependent on the concentration of serum present; no reaction was observed when hydrogen peroxide or serum was omitted. Peroxidase activity assays, based on oxidation of 3,3',5,5'-tetramethylbenzidine, confirmed the presence of a peroxidase in the sera from several suppliers. The peroxidative activity was contained in the >10000 MW fraction. We also found that hemoglobin, a heme protein likely to be present in commercial FBS, is capable of oxidizing doxorubicin in the presence of hydrogen peroxide and that nitrite further stimulates the reaction. In contrast to intact doxorubicin, the serum + hydrogen peroxide + nitrite treated drug appeared to be nontoxic for PC3 human prostate cancer cells. Together, this study shows that (pseudo)peroxidases present in sera catalyze oxidation of doxorubicin by hydrogen peroxide and that this diminishes the tumoricidal activity of the anthracycline, at least in in vitro settings. Finally, this study also points out that addition of H2O2 to media containing FBS will stimulate peroxidase-type of reactions, which may affect cytotoxic properties of studied compounds.

Cloning, sequencing, and characterization of the pradimicin biosynthetic gene cluster of Actinomadura hibisca P157-2

Pradimicins are potent antifungal antibiotics having an unusual dihydrobenzo[alpha]naphthacenequinone aglycone substituted with D-alanine and sugars. Pradimicins are polyketide antibiotics produced by Actinomadura hibisca P157-2. The gene cluster involved in the biosynthesis of pradimicins was cloned and sequenced. The pradimicin gene cluster was localized to a 39-kb DNA segment and its involvement in the biosynthesis of pradimicin was proven by gene inactivation of prmA and prmB (ketosynthases alpha and beta). The pradimicin gene cluster consists of 28 open reading frames (ORFs), encoding a type II polyketide synthase (PKS), the enzymes involved in sugar biosynthesis and tailoring enzymes as well as two resistance proteins. The deduced proteins showed strong similarities to the previously validated gene clusters of angucyclic polyketides such as rubromycin, griseorhodin, and fredericamycin. From the pradimicin gene cluster, prmP3 encoding a component of the acetyl-CoA carboxylase complex was disrupted. The production levels of pradimicins of the resulting mutants decreased to 62% of the level produced by the wild-type strain, which indicate that the acetyl-CoA carboxylase gene would have a significant role in the production of pradimicins through supplying the extender unit precursor, malonyl-CoA.

Other uses of dexrazoxane: savene, the first proven antidote against anthracycline extravasation injuries

Dexrazoxane has been in clinical use for more than 25 years for prevention of cardiotoxicity in anthracycline based anticancer therapy. However, we discovered another property of the compound, i.e. the ability to prevent the devastating tissue necrosis after accidental extravasation of anthracyclines. The preclinical and clinical studies leading to the clinical implementation of Savene (dexrazoxane) as the first and only proven antidote in anthracycline extravasation are described in short.

Activation of clinically used anthracyclines by the formaldehyde-releasing prodrug pivaloyloxymethyl butyrate

The anthracycline group of compounds is extensively used in current cancer chemotherapy regimens and is classified as topoisomerase II inhibitor. However, previous work has shown that doxorubicin can be activated to form DNA adducts in the presence of formaldehyde-releasing prodrugs and that this leads to apoptosis independently of topoisomerase II-mediated damage. To determine which anthracyclines would be useful in combination with formaldehyde-releasing prodrugs, a series of clinically relevant anthracyclines (doxorubicin, daunorubicin, idarubicin, and epirubicin) were examined for their capacity to form DNA adducts in MCF7 and MCF7/Dx (P-glycoprotein overexpressing) cells in the presence of the formaldehyde-releasing drug pivaloyloxymethyl butyrate (AN-9). All anthracyclines, with the exception of epirubicin, efficiently yielded adducts in both sensitive and resistant cell lines, and levels of adducts were similar in mitochondrial and nuclear genomes. Idarubicin was the most active compound in both sensitive and resistant cell lines, whereas adducts formed by doxorubicin and daunorubicin were consistently lower in the resistant compared with sensitive cells. The adducts formed by doxorubicin, daunorubicin, and idarubicin showed the same DNA sequence specificity in sensitive and resistant cells as assessed by lambda-exonuclease-based sequencing of alpha-satellite DNA extracted from drug-treated cells. Growth inhibition assays were used to show that doxorubicin, daunorubicin, and idarubicin were all synergistic in combination with AN-9, whereas the combination of epirubicin with AN-9 was additive. Although apoptosis assays indicated a greater than additive effect for epirubicin/AN-9 combinations, this effect was much more pronounced for doxorubicin/AN-9 combinations.

Semisolid formulations containing dimethyl sulfoxide and α-tocopherol for the treatment of extravasation of antiblastic agents

The topical treatment with dimethyl sulfoxide (DMSO) and/or alpha-tocopherol (alpha-T) is widely used in order to prevent the local complications of extravasation of cytostatic drugs and protect patients against skin ulceration. Till now, DMSO and alpha-T have been mainly used in solution. The goal of this study was to formulate semisolid preparations for cutaneous application differing in the hydrophilic and lipophilic properties and containing DMSO and alpha-T in combination. With respect to solutions, the use of semisolid preparations containing DMSO and alpha-T could be advantageous in patients having extravasation as DMSO and alpha-T can remain in contact with the skin over an extended period of time. As a consequence, the action of the active principles can be limited specifically on the injured skin area, reducing the cutaneous irritative effects of DMSO. The following types of semisolid formulations containing 50% m/m DMSO and 2.5% m/m alpha-T were prepared: hydrophilic ointment, o/w emulsion, hydrophilic gel and lipophilic gel. The ex vivo skin permeation of DMSO and alpha-T was evaluated by using modified Franz's diffusion cells and human stratum corneum and epidermis (SCE) as a membrane. The permeated and retained amounts of DMSO and alpha-T were determined. The oleogel preparation, the hydrophilic gel and the o/w emulsion were uniform in colour and aspect, without any evidences of phase separation over the period of the study. Hydrophilic ointments were discarded as they showed phase separation after 12 h. All formulations had a different behaviour in terms of skin permeability. In particular, hydrogel and o/w emulsion showed the best control on the drug release considering the interactions of the vehicle components with the SCE and the drugs partition between the vehicle and the SCE. The DMSO permeated amount after 24 h was 4.1 mg/cm(2) for hydrogel and 2.5 mg/cm(2) for emulsion while the permeated amount of pure DMSO after 24 h was 47.5 mg/cm(2). Therefore, aiming to reduce side effects after the topical application of the antidotes DMSO and alpha-T, these results suggested that hydrogel and o/w emulsion could be considered the most promising formulations for further clinical evaluations in managing of extravasation of anthracyclines.

Coenzyme Q10 in cardiovascular disease

In this review we summarise the current state of knowledge of the therapeutic efficacy and mechanisms of action of CoQ(10) in cardiovascular disease. Our conclusions are: 1. There is promising evidence of a beneficial effect of CoQ(10) when given alone or in addition to standard therapies in hypertension and in heart failure, but less extensive evidence in ischemic heart disease. 2. Large scale multi-centre prospective randomised trials are indicated in all these areas but there are difficulties in funding such trials. 3. Presently, due to the notable absence of clinically significant side effects and likely therapeutic benefit, CoQ(10) can be considered a safe adjunct to standard therapies in cardiovascular disease.

A chemostat study of Streptomyces peucetius var. caesius N47

The behavior of Streptomyces peucetius var. caesius N47 was studied in a glucose limited chemostat with a complex cultivation medium. The steady-state study yielded the characteristic constants mu (max) over 0.10 h(-1), Y (XS) 0.536 g g(-1), and m(S) 0.54 mg g(-1) h(-1). The product of secondary metabolism, epsilon-rhodomycinone, was produced with characteristics Y (PX) 12.99 mg g(-1) and m (P) 1.20 mg g(-1) h(-1). Significant correlations were found for phosphate and glucose consumption with biomass and epsilon-rhodomycinone production. Metabolic flux analysis was conducted to estimate intracellular fluxes at different dilution rates. TCA, PPP, and shikimate pathway fluxes exhibited bigger values with production than with growth. Environmental perturbation experiments with temperature, airflow, and pH changes on a steady-state chemostat implied that an elevation of pH could be the most effective way to shift the cells from growing to producing, as the pH change induced the biggest transient increase to the calculated epsilon-rhodomycinone flux.

Biophysical characterization of MDR breast cancer cell lines reveals the cytoplasm is critical in determining drug sensitivity

Dielectrophoresis (DEP) was used to examine a panel of MCF-7 cell lines comprising parental MCF-7 cells and MDR derivatives: MCF-7TaxR (paclitaxel-resistant, P-glycoprotein (P-gp) positive), MCF-7DoxR (doxorubicin-resistant MRP2 positive) plus MCF-7MDR1 (MDR1 transfected, P-gp positive). MCF-7DoxR and MCF-7MDR1 were broadly cross-resistant to natural product anticancer agents, whereas MCF-7TaxR cells were not, contrary to P-gp expression. Whilst DEP revealed modest membrane changes in MDR sub-lines, we saw significant changes in their cytoplasmic conductivity: MCF-7TaxR<MCF-7<MCF-7MDR1<MCF-7DoxR (range 0.14-0.40 S/m). Cytoplasmic conductivity is affected by the movement of molecules e.g. as in intracellular trafficking MCF-7TaxR showed a reduced membrane potential, whereas MCF-7DoxR and MCF-7MDR1 showed an increase. Thus, altered membrane potential is associated with an MDR phenotype, but in a complex manner. DEP data suggest a model whereby relative increases in cytoplasmic conductivity are correlated with MDR, whilst relative decreases equate with a sensitised phenotype e.g. MCF-7TaxR. Moreover, extent of anthracycline accumulation was inversely related to cytoplasmic conductivity. These data are representative of a model where drug sensitivity is associated with low ionic conductance (reduced cellular trafficking and ion transport) and substantial anthracycline accumulation. For classical MDR i.e. MCF-7MDR1, we saw the reverse picture. Thus, the drug resistance phenotypes of this panel of MCF-7 lines can be delineated by assessment of cytoplasmic biophysical properties using DEP.

Modeling and simulation of Streptomyces peucetius var. caesius N47 cultivation and ɛ-rhodomycinone production with kinetic equations and neural networks

This study focuses on comparing different kinetic growth models and the use of neural networks in the batch cultivation of Streptomyces peucetius var. caesius producing epsilon-rhodomycinone. Contois, Monod and Teissier microbial growth models were used as well as the logistic growth modeling approach, which was found best in the simulations of growth and glucose consumption in the batch growth phase. The lag phase was included in the kinetic model with a CO2 trigger and a delay factor. Substrate consumption and product formation were included as Luedeking-Piret and logistic type equations, respectively. Biomass formation was modeled successfully with a 6-8-2 network, and the network was capable of biomass prediction with an R2-value of 0.983. Epsilon-rhodomycinone production was successfully modeled with a recursive 8-3-1 network capable of epsilon-rhodomycinone prediction with an R2-value of 0.903. The predictive power of the neural networks was superior to the kinetic models, which could not be used in predictive modeling of arbitrary batch cultivations.

Chalcone Inhibition of Anthracycline Secondary Alcohol Metabolite Formation in Rabbit and Human Heart Cytosol

Antineoplastic therapy with anthracyclines like doxorubicin (DOX) and daunorubicin (DNR) is limited by the possible development of a dose-related cardiomyopathy. Secondary alcohol metabolites like doxorubicinol (DOXol) and daunorubicinol (DNRol), formed by cytoplasmic two-electron reductases, have been implicated as potential mediators of anthracycline-induced cardiomyopathy. In the present study, we characterized the effects of 12 chalcones on the formation of anthracycline secondary alcohol metabolites by rabbit or human heart cytosol and compared them with those of quercetin and other flavonoids. Both chalcones and flavonoids inhibited DOXol or DNRol formation in isolated rabbit heart cytosol. Structure--activity relationships showed that inhibition by chalcones was determined primarily by the position of hydroxyl groups in their phenolic A and B rings. In particular, the presence of a hydroxyl group at C-4' in the A ring was an important determinant of the inhibitory activity of chalcones. Among chalcones, 2',4',2-trihydroxychalcone exhibited the highest inhibition of both DOXol and DRNol formation, but it proved less efficient than quercetin. Different results were obtained with isolated human heart cytosol: in the latter, 2',4',2-trihydroxychalcone and other hydroxychalcones inhibited both DOXol and DNRol formation, whereas quercetin and other flavonoids inhibited DNRol formation but failed to inhibit or slightly stimulated DOXol formation. These results identify chalcones as versatile inhibitors of the cytoplasmic reductases that convert anthracyclines to cardiotoxic secondary alcohol metabolites.

The 4′-O-benzylated doxorubicin analog WP744 overcomes resistance mediated by P-glycoprotein, multidrug resistance protein and breast cancer resistance protein in cell lines and acute myeloid leukemia cells

BACKGROUND

The synthetic 4'-O-benzylated doxorubicin analog WP744 was designed to abrogate transport by the multidrug resistance (MDR)-associated ATP-binding cassette (ABC) proteins P-glycoprotein (Pgp) and multidrug resistance protein (MRP-1). We compared its uptake and cytotoxicity with those of doxorubicin and daunorubicin in cell lines overexpressing Pgp, MRP-1 or breast cancer resistance protein (BCRP) and in acute myeloid leukemia (AML) cells.

METHODS

Cellular uptake was studied by flow cytometry and cytotoxicity in 96-h 96-well cultures in cell lines overexpressing Pgp, MRP-1 or wild type (BCRP(R482)) or mutant (BCRP(R482T), BCRP(R482G)) BCRP and in pre-treatment AML marrow cells.

RESULTS

Uptake and cytotoxicity of WP744 were consistently greater than those of doxorubicin and daunorubicin at equimolar concentrations in all cell lines studied and in AML cells.

CONCLUSION

WP744 overcomes transport by Pgp, MRP-1 and BCRP in cell lines and AML cells and is a promising agent for clinical development in AML and other malignancies with broad-spectrum multidrug resistance.

Feedback regulation of doxorubicin biosynthesis in Streptomyces peucetius

DnrO, one of three DNA binding regulatory proteins involved in daunorubicin biosynthesis in Streptomyces peucetius, has been purified as a maltose-binding protein-DnrO (MBP-DnrO) fusion protein. Gel mobility shift assays showed that it specifically bound to a DNA fragment containing both dnrN and dnrO promoters. In the presence of some low-molecular-weight compounds from the daunorubicin biosynthetic pathway, the DNA binding ability of MBP-DnrO was affected. Melanin production assays showed that both DnrO and DnrN were required for the increased activity of the dnrI promoter. Rhodomycin D (RHOD), one of the intermediates in the DNR and DXR biosynthetic pathways, had a positive effect on dnrI promoter activity only in the presence of both DnrO and DnrN proteins. The promoter activity of dnrO gene decreased in the presence of the DnrO protein, suggesting that dnrO gene was autoregulated. Repression could be relieved when RHOD was present in the culture, indicating that RHOD might directly interact with the DnrO protein.

Isolation, characterization, and heterologous expression of the biosynthesis gene cluster for the antitumor anthracycline steffimycin

The biosynthetic gene cluster for the aromatic polyketide steffimycin of the anthracycline family has been cloned and characterized from "Streptomyces steffisburgensis" NRRL 3193. Sequence analysis of a 42.8-kbp DNA region revealed the presence of 36 open reading frames (ORFs) (one of them incomplete), 24 of which, spanning 26.5 kb, are probably involved in steffimycin biosynthesis. They code for all the activities required for polyketide biosynthesis, tailoring, regulation, and resistance but show no evidence of genes involved in L-rhamnose biosynthesis. The involvement of the cluster in steffimycin biosynthesis was confirmed by expression of a region of about 15 kb containing 15 ORFS, 11 of them forming part of the cluster, in the heterologous host Streptomyces albus, allowing the isolation of a biosynthetic intermediate. In addition, the expression in S. albus of the entire cluster, contained in a region of 34.8 kb, combined with the expression of plasmid pRHAM, directing the biosynthesis of L-rhamnose, led to the production of steffimycin. Inactivation of the stfX gene, coding for a putative cyclase, revealed that this enzymatic activity participates in the cyclization of the fourth ring, making the final steps in the biosynthesis of the steffimycin aglycon similar to those in the biosynthesis of jadomycin or rabelomycin. Inactivation of the stfG gene, coding for a putative glycosyltransferase involved in the attachment of L-rhamnose, allowed the production of a new compound corresponding to the steffimycin aglycon compound also observed in S. albus upon expression of the entire cluster.

Insights in the glycosylation steps during biosynthesis of the antitumor anthracycline cosmomycin: characterization of two glycosyltransferase genes

Glycosylation pattern in cosmomycins is a distinctive feature among anthracyclines. These antitumor compounds possess two trisaccharide chains attached at C-7 and C-10, each of them with structural variability, mainly at the distal deoxysugar moieties. We have characterized a 14-kb chromosomal region from Streptomyces olindensis containing 13 genes involved in cosmomycin biosynthesis. Two of the genes, cosG and cosK, coding for glycosyltransferase were inactivated with the generation of five new derivatives. Structural elucidation of these compounds showed altered glycosylation patterns indicating the capability of both glycosyltransferases of transferring deoxysugars to both sides of the aglycone and the flexibility of CosK with respect to the deoxysugar donor. A model is proposed for the glycosylation steps during cosmomycins biosynthesis.

The role of genetic variability in drug metabolism pathways in breast cancer prognosis

Among patients receiving adjuvant therapy for breast cancer, there is variability in treatment outcomes, and it is unclear which patients will receive the most benefit from treatment and which will have better disease-free survival. To date, most studies of breast cancer prognosis have focused on tumor characteristics, but it is likely that pharmacogenetics, genetic variability in the metabolism of therapeutic agents, also plays a role in the prediction of survival. In this paper, we briefly discuss the metabolic pathways of drugs commonly used for the treatment of breast cancer (cyclophosphamide, doxorubicin, taxanes, tamoxifen and aromatase inhibitors) and describe the known genetic variants that may impact those pathways. Studies that have evaluated potential effects of these genetic variants on treatment outcomes are also discussed. It is likely that the application of pharmacogenetics, particularly in the setting of randomized clinical trials, will contribute to findings that may result in individualized therapeutic dosing.