Accumulation of degradation products of doxorubicin and pirarubicin formed in cell culture medium within sensitive and resistant cells

Multiscale and Translational Quantitative Systems Toxicology, Pharmacokinetic-Toxicodynamic Modeling Analysis for Assessment of Doxorubicin-Induced Cardiotoxicity

Dose-dependent life-threatening doxorubicin-induced cardiotoxicity (DIC) is a major clinical challenge that needs to be addressed. Here, we developed an integrated multiscale and translational quantitative systems toxicology and pharmacokinetic-toxicodynamic (QST-PK/TD) model for optimization of doxorubicin dosing regimens for early monitoring and minimization of DIC. A QST model was established by exposing human cardiomyocytes, AC16 cells, to doxorubicin over a time course, and measuring the dynamics of intracellular signaling proteins, AC16 cell viability and released biomarkers of cardiomyocyte injury such as the B-type natriuretic peptide (BNP). Experiments were scaled up to a three-dimensional and dynamic (3DD) cell culture system to evaluate DIC under various dosing regimens. The PK determinants of doxorubicin influencing DIC were identified in vitro and then translated to the in vivo setting through hybrid physiologically based PK (PBPK)/TD models using preclinical- and clinical-level data extracted from literature. The developed cellular-level QST model captured well the observed dynamics of intracellular proteins, AC16 cell viability and BNP kinetics. In the 3DD setting, dose fractionation of doxorubicin displayed a significant reduction in cardiotoxicity compared to single intravenous doses with equal exposure, implying doxorubicin peak concentrations as the PK determinant for DIC. The in vivo hybrid PBPK/TD models captured well doxorubicin PK and DIC. Peak doxorubicin concentrations correlated well with acute DIC for dose-fractionated regimens, while maximum 48-h moving average concentrations correlated with DIC for dose-fractionated and long-term infusion regimens in vivo. The developed multiscale and translational QST-PK/TD modeling platform may serve as an in silico tool for assessment of early toxicity and/or efficacy of developmental drugs in vitro.

A Ratiometric Fluorescent Bioprobe Based on Carbon Dots and Acridone Derivate for Signal Amplification Detection Exosomal microRNA

Recently, sensitive and selective detection of exosomal microRNAs (miRNAs) has been garnering significant attention, because it is related to many complex diseases, including cancer. Herein, we report a ratiometric fluorescent bioprobe based on DNA-labeled carbon dots (DNA-CDs) and 5,7-dinitro-2-sulfo-acridone (DSA) coupling with the target-catalyzing signal amplification for the detection of exosomal miRNA-21. There was high fluorescence resonance energy transfer (FRET) efficiency between carbon dots (CDs) and DSA when the bioprobe was assembled. However, in the presence of the target, with disassembling of the fluorescent bioprobe, the fluorescence intensities of CDs and DSA were changed simultaneously. Because of the ratio of dual fluorescence intensities, this ratiometric fluorescent bioprobe was able to cancel out environmental fluctuations by calculating emission intensity ratio at two different wavelengths, being robust and stable enough for detection of exosomal miRNA-21. In addition, we displayed that a single miRNA-21 can catalyze the disassembly of multiple CDs with DSA theoretically, yielding significant change in the fluorescence ratio for the detection of miRNA-21. With this signal amplification strategy, the limit of detection was as low as 3.0 fM. Furthermore, because of the introduction of lock nucleic acid to mediate the strand displacement reaction, the selectivity of this strategy was improved remarkably, even against single base mismatch sequence. More importantly, our strategy could monitor the dynamic change of exosomal miRNA-21, which maybe becomes a potential tool to distinguish cancer exosomes and nontumorigenic exosomes. In a short, this ratiometric fluorescence bioprobe possessed high stability, sensitivity and selectivity coupling with ease of operation and cost efficiency, leading to great potential for wide application.

Tumor targeting with pH-responsive poly(2-oxazoline)-based nanogels for metronomic doxorubicin treatment

The synthesis of a new nanogel drug carrier system loaded with the anti-cancer drug doxorubicin (DOX) is presented. Poly(2-oxazoline) (POx) based nanogels from block copolymer micelles were cross-linked and covalently loaded with DOX using pH-sensitive Schiff' base chemistry. DOX loaded POx based nanogels showed a toxicity profile comparable to the free drug, while unloaded drug carriers showed no toxicity. Hemolytic activity and erythrocyte aggregation of the drug delivery system was found to be low and cellular uptake was investigated by flow cytometry and fluorescence microscopy. While the amount of internalized drug was enhanced when incorporated into a nanogel, the release of the drug into the nucleus was delayed. For in vivo investigations the nanogel drug delivery system was combined with a metronomic treatment of DOX. Low doses of free DOX were compared to equivalent DOX loaded nanogels in a xenograft mouse model. Treatment with POx based nanogels revealed a significant tumor growth inhibition and increase in survival time, while pure DOX alone had no effect on tumor progression. The biodistribution was investigated by microscopy of organs of mice and revealed a predominant localization of DOX within tumorous tissue. Thus, the POx based nanogel system revealed a therapeutic efficiency despite the low DOX concentrations and could be a promising strategy to control tumor growth with fewer side effects.

A Flow Cytometric Clonogenic Assay Reveals the Single-Cell Potency of Doxorubicin

Standard cell proliferation assays use bulk media drug concentration to ascertain the potency of chemotherapeutic drugs; however, the relevant quantity is clearly the amount of drug actually taken up by the cell. To address this discrepancy, we have developed a flow cytometric clonogenic assay to correlate the amount of drug in a single cell with the cell's ability to proliferate using a cell tracing dye and doxorubicin, a naturally fluorescent chemotherapeutic drug. By varying doxorubicin concentration in the media, length of treatment time, and treatment with verapamil, an efflux pump inhibitor, we introduced 10(5) -10(10) doxorubicin molecules per cell; then used a dye-dilution assay to simultaneously assess the number of cell divisions. We find that a cell's ability to proliferate is a surprisingly conserved function of the number of intracellular doxorubicin molecules, resulting in single-cell IC50 values of 4-12 million intracellular doxorubicin molecules. The developed assay is a straightforward method for understanding a drug's single-cell potency and can be used for any fluorescent or fluorescently labeled drug, including nanoparticles or antibody-drug conjugates.

Targeting of multidrug-resistant human ovarian carcinoma cells with anti-P-glycoprotein antibody conjugates

A monoclonal antibody (mAb) to P-glycoprotein (Pgp), UIC2, is used as a targeting moiety for N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer/drug [(meso chlorin e(6) mono(N-2-aminoethylamide) (Mce(6)) or doxorubicin (DOX)] conjugates to investigate their cytotoxicity towards the Pgp-expressing human ovarian carcinoma cell line A2780/AD. The binding, internalization, and subcellular trafficking of a fluorescein labeled UIC2 targeted HPMA copolymer are studied and show localization to the plasma membrane with limited internalization. The specificity of the UIC2-targeted HPMA copolymer/drug conjugates are confirmed using the sensitive cell line A2780 that does not express Pgp.

Spectral analysis of doxorubicin accumulation and the indirect quantification of its DNA intercalation

There is a wide range of techniques utilizing fluorescence of doxorubicin (Dox) commonly used for analysis of intracellular accumulation and destiny of various drug delivery systems containing this anthracycline antibiotic. Unfortunately, results of these studies can be significantly influenced by doxorubicin degradation product, 7,8-dehydro-9,10-desacetyldoxorubicinone (D*) forming spontaneously in aqueous environment, whose fluorescence strongly interfere with that of doxorubicin. Here, we define two microscopy techniques enabling to distinguish and separate Dox and D* emission based either on its spectral properties or on fluorescence lifetime analysis. To analyze influx and nuclear accumulation of Dox (free or polymer-bound) by flow cytometry, we propose using an indirect method based on its DNA intercalation competition with Hoechst 33342 rather than a direct measurement of doxorubicin fluorescence inside the cells.

One-pot conversion of RAFT-generated multifunctional block copolymers of HPMA to doxorubicin conjugated acid- and reductant-sensitive crosslinked micelles

N-(2-Hydroxypropyl)methacrylamide (HPMA) containing polymers that are widely used as anticancer drug carriers. We have synthesized new amphiphilic block copolymers of HPMA with a functional monomer 2-(2-pyridyldisulfide)ethylmethacrylate (PDSM) via reversible addition-fragmentation chain transfer (RAFT) polymerization. In a one-pot reaction, the versatility of PDS groups on poly(PDSM)- b-poly(HPMA) was used to conjugate an anticancer drug, doxorubicin (DOX), and also simultaneously crosslink the micellar assemblies via acid-cleavable hydrazone bonds and reducible disulfide bonds. DOX-conjugated crosslinked micelles with an average diameter of approximately 60 nm were observed to be formed in aqueous medium. Disintegration of the micelles into unimers in the presence of a disulfide reducing agent confirmed the crosslinking via disulfide bonds. While the release of DOX from the crosslinked micelles at pH 5.0 was faster compared to the release at pH 7.4, a high proportion of released DOX was found to retain the original active structure. Overall results demonstrate the simplicity and the versatility of the poly(PDSM)- b-poly(HPMA) system, which are potentially important in the design of new generation of polymer therapeutics.

Acid-labile core cross-linked micelles for pH-triggered release of antitumor drugs

Micelles of a model amphiphilic block copolymer, poly(hydroxyethyl acrylate)-block-poly(n-butyl acrylate) (PHEA-b-PBA), synthesized via the RAFT polymerization were cross-linked by copolymerization of a degradable cross-linker from the living RAFT-end groups of PBA chains, yielding a cross-linked core without affecting significantly the original micelle size. The cross-linker incorporation into the micelles was evidenced via physicochemical analysis of the copolymer unimers formed upon acidic cleavage of the cross-linked micelles. High doxorubicin loading capacities (60 wt %) were obtained. Hydrolysis of less than half of the cross-links in the core was found to be sufficient to release doxorubicin faster at acidic pH compared to neutral pH. The system represents the first example of core-cross-linked micelles that can be destabilized (potentially both above and below CMC) by the pH-dependent cleavage of the cross-links and the subsequent polarity change in the core to enable the release of hydrophobic drugs entrapped inside the micelle.

Targeting MDR1 gene: synthesis and cellular study of modified daunomycin-triplex-forming oligonucleotide conjugates able to inhibit gene expression in resistant cell lines

Reversal of the multidrug-resistant (MDR) phenotype is very important for chemotherapy success. In fact, the expression of the MDR1 gene-encoded P-glycoprotein (P-gp) actively expels antitumor agents such as daunomycin (DNM) out of the cells, resulting in drug resistance. We show that upon conjugation to triplex-forming oligonucleotides, it is possible to address DNM in resistant cells (MCF7-R and NIH-MDR-G185). The oligonucleotide moiety of the conjugate changes the cellular penetration properties of the antitumor agent that is no more the target of P-gp in resistant cells. We observe an accumulation of conjugated DNM in cells up to 72 h. For more efficient delivery in the cells' nuclei, transfectant agents must be used. In addition, the conjugate recognizes a sequence located in exon 3 of MDR1, and it inhibits its gene expression as measured both by Western blot and by reverse transcription-polymerase chain reaction.

Solution structure of iron(III)-anthracycline complexes

The interaction of Fe(3+) with the anthracycline anticancer drug idarubicin (Ida) was studied by absorption, CD, Mössbauer, and EPR spectroscopy. The formation of two major Fe(3+)-Ida complexes, labeled I and II, was observed. In complex I, Fe(3+) ion was bound to anthracycline at the {C(12)=O; C(11)-O(-)} coordination site. In complex II, two Fe(3+) ions were bound at sites {C(5)=O; C(6)-O(-)} and {C(12)=O; C(11)-O(-)}, respectively. Complex I was an equimolar monomeric species with a 1:1 Fe(3+):Ida stoichiometry (beta(1) = 4.8 x 10(11) M(-1)), whereas in complex II the anthracycline ligand was bridging two metal ions, alternatively bound to both anthracycline ring chelating sites with the assumption that the ratio of Fe(3+):Ida in complex II was 2:1 (beta(2) = 5.3 x 10(24) M(-2)). Alternatively, complex II may be oligomeric with Fe(3+):Ida = 1:1 and with each Fe(3+) bridging two Ida molecules. Our findings could be important in understanding the biological effects of the anthracycline-ferric complexes. Thus, providing information about the nature of the Fe(3+)-Ida system, we suggest that the formal 1:3 Fe(3+):anthracycline complexes, reported in the previous literature, could be a mixture of species I, II, and free ligand.

Correlation between the kinetics of anthracycline uptake and the resistance factor in cancer cells expressing the multidrug resistance protein or the P-glycoprotein

Multidrug resistance (MDR) in model systems is known to be conferred by two different integral proteins, the 170-kDa P-glycoprotein (Pgp) and the 190-kDa multidrug resistance-associated protein (MRP1). One possible pharmacological approach to overcome drug resistance is the use of specific inhibitors, which enhance the cytotoxicity of known antineoplastic agents. However, while many compounds have been proven to be very efficient in inhibiting Pgp activity only some of them are able to inhibit MRP1. The other likely approach is based on the design and synthesis of new non-cross-resistant drugs with physicochemical properties favoring the uptake of the drug by the resistant cells. The intracellular drug retention influences its cytotoxic effect. The level of the intracellular drug content is a function of the amount of drug transported inside the cell (influx) and the amount of drug expelled from the cell (efflux). In this work, the kinetics of drug uptake and the kinetics of active efflux of several anthracycline derivatives in both Pgp expressing K562/Adr cells and MRP1 expressing GLC4/Adr cells was determined. Our data have shown that in both cell lines there is no correlation between the resistance factor and the kinetics of drug efflux by these pumping systems. However, a very good correlation between the resistance factor and the kinetics of drug uptake has been established in both cell lines: the resistance factor decreases when the kinetics of drug uptake increases. This work has clearly shown that when the rate of transmembrane transport of anthracycline is high enough, the efflux mediated by the protein transporter is not able to pace with it. The protein transporter essentially operates in a futile cycle and the resistance factor is tending to one. It does not mean, however, that when the resistance factor is close to one the anthracycline is not transported by the pump.

How Fe3+ binds anthracycline antitumour compounds. The myth and the reality of a chemical sphinx

The interaction of Fe3+ with several anthracycline antitumour antibiotics has been reinvestigated. Absorption and circular dichroism (CD) measurements were carried out (i) in aqueous solution and (ii) in semi-aqueous MeOH to avoid the stacking of the anthracycline molecules. The Fe3+ binding to anthracycline was dependent on the metal-to-ligand molar ratio, antibiotic concentration, ionic strength, and pH. The formation of two major Fe3(+)-anthracycline complexes, I and II, was observed for all the drugs. These species differed in their coordination modes to the anthracycline ligands. Complex I was a monomeric species, where Fe3+ was bound to the anthracycline through the {C(11)-O-; C(12) = O} chelating site. In complex II, Fe3+ was also bound through the {C(5) = O; C(6)-O-} coordination site. Thus, the antibiotic ligand was acting as a bridge between two metal ions, forming oligomeric (or polymeric) structures. The different degree of association of the anthracyclines could be responsible for the reactivity of the metal ion. In fact, complexes I and II could constitute mononuclear, binuclear or polynuclear Fe3+ species depending on the competitive kinetics of both coordination and hydrolysis of the metal ion.

Modifications of oxido-reductase activities in adriamycin-resistant leukaemia K562 cells

Adriamycin (ADR), a well-known antitumoral drug, interacts with DNA (nuclear and mitochondrial) and cardiolipin. Moreover, ADR induces numerous mitochondrial modifications in sensitive cells. However, no results have yet been obtained as to the repercussions of drug effects on oxido-reductase activities in ADR-resistant cells. To analyze mitochondrial damage induced by ADR treatment, we investigated lactate content, oxygen consumption, respiratory chain activities, and cytochrome content in ADR-sensitive K562 cells and two ADR-resistant variants (K562/R0.2 and K562/R0.5 cells). Biochemical investigations in ADR-resistant cells showed several mitochondrial modifications (in comparison to the parental cell line) according to the variant line and the physiologic state. More particularly, in K562/R0.5 cells cytochrome c (cyt c) oxidase (COX; EC 1.9.3.1) activity and cytochrome aa3 content dramatically decreased since cells enter into the stationary phase. Regardless of the number of multidrug-resistant cell subcultures in ADR-free medium, the cytochrome c oxidase activity in the stationary phase remained unchanged, indicating an irreversible effect of the drug. These alterations could correspond to several modifications of the nuclear and/or mitochondrial genome(s) following acquisition of the ADR resistance phenotype by K562 cells.

Spectral shape modifications of anthracyclines bound to cell nuclei: a microspectrofluorometric study

Anthracyclines remain today the medications of choice against a wide spectrum of human cancers. Anthracyclines are fluorescent molecules and microfluorimetric methods are often used to determine their cellular distribution. The use of microspectrofluorometric techniques yields additional information because not only the fluorescence intensity but also the spectral modifications of the chromophore can be used to assess the intracellular drug concentration, its localisation and also eventually its metabolisation. It is well-documented that the shape of the fluorescence spectrum of anthracyclines changes markedly with the hydrophobicity of their environment. This change can be quantitatively measured by the ratio rho of the fluorescence emission intensities at 560 and 590 nm. We have observed that the shape of the fluorescent spectrum of adriamycin, daunorubicin and 4'-O-tetrahydropyranyladriamycin recorded from a small volume inside the cell nucleus was strongly dependent on the drug concentration and that the rho value decreases as the drug concentration increases. These data were compared with the rho variations when the drugs were either dissolved in different solvents or intercalated between the base pairs of DNA. We arrived at the conclusion that the shape variation of the drug spectra was not due to a change in their hydrophobicity environment but to an excitonic coupling of the electric dipolar transition moments of the pi --> pi* transition.