Anthracycline antitumour agents. A review of physicochemical, analytical and stability properties

pH-Responsive Hybrid Nanoassemblies for Cancer Treatment: Formulation Development, Optimization, and In Vitro Therapeutic Performance

Current needs for increased drug delivery carrier efficacy and specificity in cancer necessitate the adoption of intelligent materials that respond to environmental stimuli. Therefore, we developed and optimized pH-triggered drug delivery nanoassemblies that exhibit an increased release of doxorubicin (DOX) in acidic conditions typical of cancer tissues and endosomal vesicles (pH 5.5) while exhibiting significantly lower release under normal physiological conditions (pH 7.5), indicating the potential to reduce cytotoxicity in healthy cells. The hybrid (polymeric/lipid) composition of the lyotropic non-lamellar liquid crystalline (LNLCs) nanoassemblies demonstrated high encapsulation efficiency of the drug (>90%) and high drug loading content (>7%) with colloidal stability lasting at least 4 weeks. Confocal microscopy revealed cancer cellular uptake and DOX-loaded LNLCs accumulation near the nucleus of human hepatocellular carcinoma cells, with a large number of cells appearing to be in apoptosis. DOX-loaded LNLCs have also shown higher citotoxicity in cancer cell lines (MDA-MB 231 and HepG2 cell lines after 24 h and in NCI-H1299 cell line after 48 h) when compared to free drug. After 24 h, free DOX was found to have higher cytotoxicity than DOX-loaded LNLCs and empty LNLCs in the normal cell line. Overall, the results demonstrate that DOX-loaded LNLCs have the potential to be explored in cancer therapy.

Advanced Electrodegradation of Doxorubicin in Water Using a 3-D Ti/SnO2 Anode

This study investigated the application of an advanced electrooxidation process with three-dimensional tin oxide deposited onto a titanium plate anode, named 3-D Ti/SnO2, for the degradation and mineralization of one of the most important emerging contaminants with cytostatic properties, doxorubicin (DOX). The anode was synthesized using a commercial Ti plate, with corrosion control in acidic medium, used as a substrate for SnO2 deposition by the spin-coating method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that porous SnO2 was obtained, and the rutile phase of TiO2 was identified as an intermediary substrate onto the Ti plate. The results of CV analysis allowed us to determine the optimal operating conditions for the electrooxidation process conducted under a constant potential regime, controlled by the electron transfer or the diffusion mechanisms, involving hydroxyl radicals. The determination of UV–VIS spectra, total organic carbon (TOC), and chemical oxygen demand (COD) allowed us to identify the degradation mechanism and pathway of DOX onto the 3-D Ti/SnO2 anode. The effective degradation and mineralization of DOX contained in water by the electrooxidation process with this new 3-D dimensionally stable anode (DSA) was demonstrated in this study.

Investigation of Adsorption Behavior of Anticancer Drug on Zinc Oxide Nanoparticles: A Solid State NMR and Cyclic Voltammetry (CV) Analysis

The present study aims to comprehend the adsorption behavior of a set of anticancer drugs namely 5-fluorouracil (5-FU), doxorubicin and daunorubicin on ZnO nanoparticles (ZnO NPs) proposed as drug delivery systems employing solid state (ss) NMR, FTIR and Cyclic Voltammetry (CV) analysis. FTIR and ¹H MAS ssNMR data recorded for bare ZnO nanoparticle confirmed the presence of adsorbed -OH groups on the surface. ¹³C CP-MAS NMR spectra recorded for free and ZnO surface adsorbed drug samples exhibited considerable line broadening and chemical shift changes that complemented our earlier report on UV-DRS and XRD data of surface adsorption in case of 5-FU. Moreover, a remarkable enhancement of ¹³C signal intensity in case of loaded 5-FU was observed. This clearly indicated rigid nature of the drug on the surface allowing efficient transfer of ¹H polarization from the hetero nitrogen of 5-FU to ZnO to form surface hydroxyl (-OH) groups and the same has been observed in the quantum chemical calculations. To further analyze the motional dynamics of the surface adsorbed 5-FU, longitudinal relaxation times (T₁) were quantified employing Torchia method that revealed significant enhancement of ¹³C relaxation rate of adsorbed 5-FU. The enhanced rate suggested an effective role of quadrupolar contribution from ⁶⁷Zn to the ¹³C relaxation mechanism of ZnO_5-FU. The heterogeneous rate constant (k_het), average free energy of activation (∆G^≠) and point of zero charge (PZC) measured for free and drug loaded ZnO NPs samples using CV further support the SS-NMR results.

Synergistic effect of photodynamic treatment and doxorubicin on triple negative breast cancer cells

Breast cancer is a metastatic cancer that can spread to other organs, such as the bone, liver, and brain. There are many treatments for breast cancer, such as surgery and chemotherapy, but they lead to resistance and side effects. Therefore, the discovery of new therapies with high efficacy and low toxicity that selectively affect cancer cells is of great importance. Of late, the combination therapy has been suggested as a novel approach compared to existing treatments. In the present study, the effect of the combined treatment of doxorubicin (DOX) and methylene blue activated in the presence of laser irradiation (PDT) on triple-negative breast cancer cells has been investigated. Human breast cancer cell line MDA-MB-231 was exposed to different concentrations of DOX, methylene blue (MB) and DOX-methylene blue (MB-DOX) combination therapy in two different conditions: first the treatment with DOX and then with MB-PDT, and another treatment first with MB-PDT and then with DOX. Cell viability was evaluated using the MTT assay. Morphological and colonization changes were observed by light microscopy. The occurrence of apoptotic cell death was assessed by double-staining ethidium bromide-acridine orange using fluorescence microscopy and flow cytometry. The results showed that the combination of using MB-PDT, followed by DOX (even at low concentrations), has a better effect on inducing cancer cell death in comparison to DOX alone. The result of this study suggests that the combination therapy of MB-PDT-DOX can be used as a potential strategy for the treatment of triple-negative breast cancer cells.

Molecular Interpretation of Pharmaceuticals’ Adsorption on Carbon Nanomaterials: Theory Meets Experiments

The ability of carbon-based nanomaterials (CNM) to interact with a variety of pharmaceutical drugs can be exploited in many applications. In particular, they have been studied both as carriers for in vivo drug delivery and as sorbents for the treatment of water polluted by pharmaceuticals. In recent years, the large number of experimental studies was also assisted by computational work as a tool to provide understanding at molecular level of structural and thermodynamic aspects of adsorption processes. Quantum mechanical methods, especially based on density functional theory (DFT) and classical molecular dynamics (MD) simulations were mainly applied to study adsorption/release of various drugs. This review aims to compare results obtained by theory and experiments, focusing on the adsorption of three classes of compounds: (i) simple organic model molecules; (ii) antimicrobials; (iii) cytostatics. Generally, a good agreement between experimental data (e.g. energies of adsorption, spectroscopic properties, adsorption isotherms, type of interactions, emerged from this review) and theoretical results can be reached, provided that a selection of the correct level of theory is performed. Computational studies are shown to be a valuable tool for investigating such systems and ultimately provide useful insights to guide CNMs materials development and design.

Newly Synthesized Doxorubicin Complexes with Selected Metals-Synthesis, Structure and Anti-Breast Cancer Activity

Doxorubicin (DOX) is very effective chemotherapeutic agent, however it has several major drawbacks. Therefore the motivation for developing novel drug complexes as anticancer agents with different mechanism of action has arisen. The aim of the present study was to evaluate the influence of newly synthesized DOX complexes with selected metals (Mg, Mn, Co, Ni, Fe, Cu, Zn) on apoptosis, cell cycle, viability, proliferation and cytotoxicity in the breast cancer cell line MCF-7. Complexation of DOX with metals has likewise been the subject of our research. The current work showed that the tested bivalent metals at a given pH condition formed metal:DOX complexes in a ratio of 2:1, while iron complexes with DOX in a ratio of 3:1. The studies also showed that selected metal-DOX complexes (Mg-DOX, Mn-DOX, Ni-DOX) at 0.5 µM concentration significantly decreased cell viability and proliferation, however they increased caspase 7 activity. Results also indicated that studied metal-DOX complexes showed high cytotoxicity in MCF-7 cells. Therefore they were chosen for cell cycle check-points and apoptosis/necrosis analysis studied by flow cytometry. Obtained results suggest that doxorubicin complexed by specified metals can be considered as a potential anti-breast cancer agent, which is characterized by a higher efficacy than a parent drug.

Fabrication and in vitro characterization of gadolinium-based nanoclusters for simultaneous drug delivery and radiation enhancement

We report the synthesis of a gadolinium hydroxide (Gd(OH)3) nanorod based doxorubicin (Dox) delivery system that can enhance both magnetic resonance imaging contrast and radiation sensitivity. A simple and cost effective wet-chemical method was utilized in the presence of manganese (Mn) ions and Dox to produce the Gd(OH)3:Mn·Dox nanocluster structure. The Gd(OH)3:Mn·Dox nanocluster was composed of Mn-doped Gd(OH)3 nanorods arranged in parallel with Dox as a linker molecule between the adjacent nanorods. No other studies have utilized Dox as both the linker and therapeutic molecule in a nanostructure to date. The Gd(OH)3 nanorod is reported to have no significant cellular or in vivo toxicity, which makes it an ideal base material for this biomedical application. The Gd(OH)3:Mn·Dox nanocluster exhibited paramagnetic behavior and was stable in a colloidal solution. The nanocluster also enabled high Dox loading capacity and specifically released Dox in a sustained and pH-dependent manner. The positively charged Gd(OH)3:Mn·Dox nanoclusters were readily internalized into MDA-MB-231 breast cancer cells via endocytosis, which resulted in intracellular release of Dox. The released Dox in cells was effective in conferring cytotoxicity and inhibiting proliferation of cancer cells. Furthermore, a synergistic anticancer effect could be observed with radiation treatment. Overall, the Gd(OH)3:Mn·Dox nanocluster drug delivery system described herein may have potential utility in clinics as a multifunctional theranostic nanoparticle with combined benefits in both diagnosis and therapy in the management of cancer.

Interaction of doxorubicin with polynucleotides. A spectroscopic study

The interaction of doxorubicin (DX) with model polynucleotides poly(dG-dC)·poly(dG-dC) (polyGC), poly(dA-dT)·poly(dA-dT) (polyAT), and calf thymus DNA has been studied by several spectroscopic techniques in phosphate buffer aqueous solutions. UV-vis, circular dichroism, and fluorescence spectroscopic data confirm that intercalation is the prevailing mode of interaction, and also reveal that the interaction with AT-rich regions leads to the transfer of excitation energy to DX not previously documented in the literature. Moreover, the DX affinity for AT sites has been found to be on the same order of magnitude as that reported for GC sites.

Physical biology in cancer. 3. The role of cell glycocalyx in vascular transport of circulating tumor cells

Circulating tumor cells (CTCs) in blood are known to adhere to the luminal surface of the microvasculature via receptor-mediated adhesion, which contributes to the spread of cancer metastasis to anatomically distant organs. Such interactions between ligands on CTCs and endothelial cell-bound surface receptors are sensitive to receptor-ligand distances at the nanoscale. The sugar-rich coating expressed on the surface of CTCs and endothelial cells, known as the glycocalyx, serves as a physical structure that can control the spacing and, thus, the availability of such receptor-ligand interactions. The cancer cell glycocalyx can also regulate the ability of therapeutic ligands to bind to CTCs in the bloodstream. Here, we review the role of cell glycocalyx on the adhesion and therapeutic treatment of CTCs in the bloodstream.

Lyophilisomes as a new generation of drug delivery capsules

Nanoparticulate drug delivery systems are currently explored to overcome critical challenges associated with classical administration forms. In this study, we present a drug delivery system based on a novel class of proteinaceous biodegradable nano/micro capsules, lyophilisomes. Lyophilisomes can be prepared from biomolecules without the need for amphiphilicity. Albumin-based lyophilisomes were prepared by freezing, annealing and lyophilizing, resulting in capsules ranging from 100 to 3000 nm. Lyophilisomes were loaded with the anti-tumor drugs doxorubicin and curcumin using different concentrations and time/temperature regimes. Incubation in 0.1 mg/ml doxorubicin or 1.0 mg/ml curcumin resulted in an entrapment efficiency of 95±1% and 4±1%, respectively. This corresponds to a drug loading of 0.24 mg doxorubicin per milligram albumin and 0.10 mg curcumin per milligram albumin. Drug release profiles from doxorubicin and curcumin-loaded lyophilisomes were studied in culture medium and showed slow release for doxorubicin (2.7% after 72 h), and rapid release for curcumin (55% after 72 h). When applied to cells, non-loaded lyophilisomes did not influence cell viability, even at high concentrations (1 mg/ml). Lyophilisomes were internalized by cells. When loaded with doxorubicin and curcumin, lyophilisomes strongly reduced cell proliferation and viability of SKOV-3 and HeLa cells, respectively, to a level similar or better compared to an equal amount of free drugs. In conclusion, albumin lyophilisomes show potential as (nano)carriers of drugs for tumor cell elimination.

E-selectin liposomal and nanotube-targeted delivery of doxorubicin to circulating tumor cells

The presence of circulating tumor cells (CTCs) is believed to lead to the formation of secondary tumors via an adhesion cascade involving interaction between adhesion receptors of endothelial cells and ligands on CTCs. Many CTCs express sialylated carbohydrate ligands on their surfaces that adhere to selectin protein found on inflamed endothelial cells. We have investigated the feasibility of using immobilized selectin proteins as a targeting mechanism for CTCs under flow. Herein, targeted liposomal doxorubicin (L-DXR) was functionalized with recombinant human E-selectin (ES) and polyethylene glycol (PEG) to target and kill cancer cells under shear flow, both when immobilized along a microtube device or sheared in a cone-and-plate viscometer in a dilute suspension. Healthy circulating cells such as red blood cells were not targeted by this mechanism and were left to freely circulate, and minimal leukocyte death was observed. Halloysite nanotube (HNT)-coated microtube devices immobilized with nanoscale liposomes significantly enhanced the targeting, capture, and killing of cancer cells. This work demonstrates that E-selectin functionalized L-DXR, sheared in suspension or immobilized onto microtube devices, provides a novel approach to selectively target and deliver chemotherapeutics to CTCs in the bloodstream.

Analysis of anticancer drugs: a review

In the last decades, the number of patients receiving chemotherapy has considerably increased. Given the toxicity of cytotoxic agents to humans (not only for patients but also for healthcare professionals), the development of reliable analytical methods to analyse these compounds became necessary. From the discovery of new substances to patient administration, all pharmaceutical fields are concerned with the analysis of cytotoxic drugs. In this review, the use of methods to analyse cytotoxic agents in various matrices, such as pharmaceutical formulations and biological and environmental samples, is discussed. Thus, an overview of reported analytical methods for the determination of the most commonly used anticancer drugs is given.

Quantitative liquid chromatographic analysis of anthracyclines in biological fluids

Anthracyclines are amongst the most widely used drugs in oncology, being part of the treatment regimen in most patients receiving systemic chemotherapy. This review provides a comprehensive summary of the sample preparation techniques and chromatographic methods that have been developed during the last two decades for the analysis of the 4 most administered anthracyclines, doxorubicin, epirubicin, daunorubicin and idarubicin in plasma, serum, saliva or urine, within the context of clinical and pharmacokinetic studies or for assessing occupational exposure. Following deproteinization, liquid-liquid extraction, solid phase extraction or a combination of these techniques, the vast majority of methods utilizes reversed-phase C18 stationary phases for liquid chromatographic separation, followed by fluorescence detection, or, more recently, tandem mass spectrometric detection. Some pros and cons of the different techniques are addressed, in addition to potential pitfalls that may be encountered in the analysis of this class of compounds.

Optimization of doxorubicin loading for superabsorbent polymer microspheres: in vitro analysis

PURPOSE

This study was designed to establish the ability of super-absorbent polymer microspheres (SAP) to actively uptake doxorubicin and to establish the proof of principle of SAP's ability to phase transfer doxorubicin onto the polymer matrix and to elute into buffer with a loading method that optimizes physical handling and elution characteristics.

METHODS

Phase I: 50-100 μm SAP subject to various prehydration methods (normal saline 10 cc, hypertonic saline 4 cc, iodinated contrast 10 cc) or left in their dry state, and combined with 50 mg of clinical grade lyophilized doxorubicin reconstituted with various methods (normal saline 10 cc and 25 cc, sterile water 4 cc, iodinated contrast 5 cc) were placed in buffer and assessed based on loading, handling, and elution utilizing high-performance liquid chromatography (HPLC). Phase II: top two performing methods were subject to loading of doxorubicin (50, 75, 100 mg) in a single bolus (group A) or as a serial loading method (group B) followed by measurement of loading vs. time and elution vs. time.

RESULTS

Phase I revealed the most effective loading mechanisms and easiest handling to be dry (group A) vs. normal saline prehydrated (group B) SAP with normal saline reconstituted doxorubicin (10 mg/mL) with loading efficiencies of 83.1% and 88.4%. Phase II results revealed unstable behavior of SAP with 100 mg of doxorubicin and similar loading/elution profiles of dry and prehydrated SAP, with superior handling characteristics of group B SAP at 50 and 75 mg.

CONCLUSIONS

SAP demonstrates the ability to load and bulk phase transfer doxorubicin at 50 and 75 mg with ease of handling and optimal efficiency through dry loading of SAP.

Daunomycin interaction with DNA: microcalorimetric studies of the thermodynamics and binding mechanism

Nucleic acids are an important target for many therapeutics. Small molecules that bind to nucleic acids are important in many aspects of medicines, particularly in cancer chemotherapy. In recent years, many studies have utilized polynucleic acids with various sequences to demonstrate the binding mechanism of daunomycin, a potent anticancer drug. This study describes that isothermal titration calorimetry is a useful tool for studying the fundamental binding mechanism systemically. The results suggest that the binding free energy is more favorable when the temperature is increased. The binding entropy contributes to this effect. Furthermore, the amine group on daunomycin contributes electrostatic interaction that induces the binding process. In addition, enthalpy-entropy compensation is also exhibited in the daunomycin-DNA binding mechanism. This study used an easy, convenient method of performing a systemic study in a recognition system. The results from this study provide additional information about microscopic mechanisms for molecular design and molecular recognition.

Nanaomycin A selectively inhibits DNMT3B and reactivates silenced tumor suppressor genes in human cancer cells

Enzymes involved in the epigenetic regulation of the genome represent promising starting points for therapeutic intervention by small molecules, and DNA methyltransferases (DNMT) are emerging targets for the development of a new class of cancer therapeutics. In this work, we present nanaomycin A, initially identified by a virtual screening for inhibitors against DNMT1, as a compound inducing antiproliferative effects in three different tumor cell lines originating from different tissues. Nanaomycin A treatment reduced the global methylation levels in all three cell lines and reactivated transcription of the RASSF1A tumor suppressor gene. In biochemical assays, nanaomycin A revealed selectivity toward DNMT3B. To the best of our knowledge, this is the first DNMT3B-selective inhibitor identified to induce genomic demethylation. Our study thus establishes the possibility of selectively inhibiting individual DNMT enzymes.

Pharmacokinetics of daunorubicin and daunorubicinol in infants with leukemia treated in the interfant 99 protocol

BACKGROUND

There is an extreme paucity of pharmacokinetic data for anticancer agents in infants. Therefore, we aimed at characterizing the pharmacokinetics for daunorubicin in infants and examined their relationship to age, body weight, and body surface area.

PROCEDURE

Leukemia patients treated according to the Interfant 99 protocol received 30 mg/m(2) daunorubicin, with dose reduction to 3/4 for patients 6-12 months old and 2/3 for patients <6 months, respectively. Plasma samples from 21 patients (aged 0.05-1.88 years) were collected and analyzed for daunorubicin and daunorubicinol. Samples from 12 children (age 1.6-18.8 years), who received daunorubicin in an earlier investigation, were used for pharmacokinetic model building using the software NONMEM.

RESULTS

Plasma concentration time profiles could be described using a two compartment model. Daunorubicin clearance was 43.9 L hr(-1) m(-2) +/- 65% and central volume of distribution 16.4 L m(-2) +/- 46%, whereas apparent clearance of daunorubicinol was 19.1 L hr(-1) m(-2) +/- 32% and apparent volume of distribution 228 L m(-2) +/- 80% (mean +/- interindividual variability). No age-dependency in any of the BSA-normalized pharmacokinetic parameters was observed. Consequently, due to the empirical dose reduction in infants the overall exposure to daunorubicinol in infants was smaller than would be expected from older children. Patients aged <6 months experienced more infections in the induction phase than the group aged 6-12 months at diagnosis. Other toxicities were similar in both groups.

CONCLUSION

We observed no indication of an age-dependency in the pharmacokinetics of daunorubicin. Pediatr Blood Cancer 2010;54:355-360.

The reduction of doxorubicin at a mercury electrode and monitoring its interaction with DNA using constant current chronopotentiometry

In this report, voltammetry with linear scan and chronopotentiometric stripping (CPS) with constant current were used for the analysis of doxorubicin (DOX) at a hanging mercury drop electrode (HMDE). CPS was used for the study of DOX in situ electrochemical reduction in adsorbed state and for ex situ (adsorptive transfer) analysis of the drug. For the first time, CPS was used to study the reversible reduction of the DOX quinine moiety at –0.45 V (vs Ag|AgCl|3 M KCl) as well as electrode processes giving rise to an irreversible signal around –1.45 V at the HMDE in 0.2 M acetate or Britton–Robinson buffers at different pH values. The dependence of the latter signal on pH revealed involvement of protonation equilibria; however, neither CV nor CPS data confirmed the catalytic character of the electrode reaction previously suggested by other authors. The CPS method was also applied to monitor the DOX interaction with double- (ds) and single-stranded (ss) DNA. In the presence of dsDNA, more pronounced changes in DOX signal intensity were observed, in agreement with a strong intercalation of the DOX redox centre into the DNA double helix.

PEGylated PLGA nanoparticles for the improved delivery of doxorubicin

We hypothesize that the efficacy of doxorubicin (DOX) can be maximized and dose-limiting cardiotoxicity minimized by controlled release from PEGylated nanoparticles. To test this hypothesis, a unique surface modification technique was used to create PEGylated poly(lactic-co-glycolic acid) (PLGA) nanoparticles encapsulating DOX. An avidin-biotin coupling system was used to control poly(ethylene glycol) conjugation to the surface of PLGA nanoparticles, of diameter approximately 130 nm, loaded with DOX to 5% (wt/wt). Encapsulation in nanoparticles did not compromise the efficacy of DOX; drug-loaded nanoparticles were found to be at least as potent as free DOX against A20 murine B-cell lymphoma cells in culture and of comparable efficacy against subcutaneously implanted tumors. Cardiotoxicity in mice as measured by echocardiography, serum creatine phosphokinase (CPK), and histopathology was reduced for DOX-loaded nanoparticles as compared with free DOX. Administration of 18 mg/kg of free DOX induced a sevenfold increase in CPK levels and significant decreases in left ventricular fractional shortening over control animals, whereas nanoparticle-encapsulated DOX produced none of these pathological changes.

FROM THE CLINICAL EDITOR

The efficacy of doxorubicin (DOX) may be maximized and dose-limiting cardiotoxicity minimized by controlled release from PEGylated nanoparticles. Administration of 18 mg/kg of free DOX induced a sevenfold increase in CPK levels and significant decreases in left ventricular fractional shortening in mice, whereas nanoparticle-encapsulated DOX produced none of these pathological changes.

Remote loading of doxorubicin into liposomes driven by a transmembrane phosphate gradient

This study examines a new method for the remote loading of doxorubicin into liposomes. It was shown that doxorubicin can be loaded to a level of up to 98% into large unilamellar vesicles composed of egg phosphatidylcholine/cholesterol (7/3 mol/mol) with a transmembrane phosphate gradient. The different encapsulation efficiencies which were achieved with ammonium salts (citrate 100%, phosphate 98%, sulfate 95%, acetate 77%) were significantly higher as compared to the loading via sodium salts (citrate 54%, phosphate 52%, sulfate 44%, acetate 16%). Various factors, including pH-value, buffer capacity, solubility of doxorubicin in different salt solutions and base counter-flow, which likely has an influence on drug accumulation in the intraliposomal interior are taken into account. In contrast to other methods, the newly developed remote loading method exhibits a pH-dependent drug release property which may be effective in tumor tissues. At physiological pH-value doxorubicin is retained in the liposomes, whereas drug release is achieved by lowering the pH to 5.5 (approximately 25% release at 25 degrees C or 30% at 37 degrees C within two h). The DXR release of liposomes which were loaded via a sulfate gradient showed a maximum of 3% at pH 5.5.

Pharmacokinetics of low-dose doxorubicin and metabolites in patients with AIDS-related Kaposi sarcoma

PURPOSE

Systemic chemotherapy is the treatment of choice for AIDS-related advanced Kaposi sarcoma. One principal schedule combines adriamycin (doxorubicin), bleomycin, and vincristine (ABV). We analysed the plasma concentrations of low-dose doxorubicin (Dx) and its metabolites doxorubicinol, 7-deoxydoxorubicinone, doxorubicinone, doxorubicinolone, and 7-deoxydoxorubicinolone in AIDS-patients to define patient-group and dose-specific pharmacokinetic parameters.

MATERIALS AND METHODS

A previously described high-performance liquid chromatographic (HPLC) method and a population approach with non-linear mixed effects modelling (NONMEM) were used for analysis and subsequent modelling of the time-concentration data of low-dose Dx and metabolites in seven patients with AIDS-related advanced Kaposi sarcoma. Patients received Dx 20 mg m(-2), bleomycin 15 U m(-2) and vincristine 2 mg as a 30-min intravenous infusion each. Blood samples were collected up to 72 h after the start of Dx treatment. WinNonlin software version 4.1 was used for non-compartmental analysis and NONMEM software version V for compartmental analysis. Covariate analysis was performed for various clinical and laboratory parameters.

RESULTS

Non-compartmental analysis yielded an area under the plasma concentration-time curve (AUC) for Dx of 566 mug h L(-1), a maximum plasma concentration (c(max)) of 599 mug L(-1) and an elimination half-life (t(1/2)) of 30.8 h. Compartmental analysis resulted in a two-compartment model with first-order elimination, which best fitted the concentration-time data. Model estimate for Dx clearance was 61.8 L h(-1), for intercompartmental clearance (Q) 112 L h(-1), for the volume of the central compartment (V(1)) 23.3 L, and for the volume of the peripheral compartment (V(2)) 1,130 L. Metabolite data could adequately be estimated by NONMEM using single-compartment models. Graphical plots of residuals versus time for all metabolites yielded no evidence of non-linear pharmacokinetic behaviour. Laboratory parameters of liver and renal function were all in the normal range and their inclusion in the pharmacokinetic model did not improve data fit. A final jack-knife analysis was performed.

CONCLUSIONS

Concentration-time data for low-dose Dx and metabolites in the ABV-regimen are best described by a two-compartment model with first-order elimination. The results confirm that the aglycones doxorubicinone, 7-deoxydoxorubicinone, and doxorubicinolone can be reliably detected in the studied patient group and implemented into a common metabolic model. Model estimates suggest that pharmacokinetic parameters are similar for low-dose Dx and higher-dosed Dx. As the role of the aglycones is still poorly understood, despite their potential clinical relevance, their analysis should be implemented in future pharmacokinetic and pharmacodynamic studies of Dx.

The Liposomal Formulation of Doxorubicin

Doxorubicin is the best known and most widely used member of the anthracycline antibiotic group of anticancer agents. It was first introduced in the 1970s, and since that time has become one of the most commonly used drugs for the treatment of both hematological and solid tumors. The therapy-limiting toxicity for this drug is cardiomyopathy, which may lead to congestive heart failure and death. Approximately 2% of patients who have received a cumulative (lifetime) doxorubicin dose of 450-500 mg?m(2) will experience this condition. An approach to ameliorating doxorubicin-related toxicity is to use drug carriers, which engender a change in the pharmacological distribution of the drug, resulting in reduced drug levels in the heart. Examples of these carrier systems include lipid-based (liposome) formulations that effect a beneficial change in doxorubicin biodistribution, with two formulations approved for clinical use. Drug approval was based, in part, on data suggesting that beneficial changes in doxorubicin occurred in the absence of decreased therapeutic activity. Preclinical (animal) and clinical (human) studies showing that liposomes can preferentially accumulate in tumors have provided a rationale for improved activity. Liposomes represent ideal drug delivery systems, as the microvasculature in tumors is typically discontinuous, having pore sizes (100-780 nm) large enough for liposomes to move from the blood compartment into the extravascular space surrounding the tumor cells. Liposomes, in the size range of 100-200 nm readily extravasate within the site of tumor growth to provide locally concentrated drug delivery, a primary role of liposomal formulation. Although other liposomal drugs have been prepared and characterized due to the potential for liposomes to improve antitumor potency of the encapsulated drug, the studies on liposomal doxorubicin have been developed primarily to address issues of acute and chronic toxicity that occur as a consequence of using this drug. It is important to recognize that research programs directed toward the development of liposomal doxorubicin occurred concurrently with synthetic chemistry programs attempting to introduce safer and more effective anthracycline analogues. Although many of these drugs are approved for use, and preliminary liposomal formulations of these analogues have been prepared, doxorubicin continues to be a mainstay of drug cocktails used in the management of most solid tumors. It will be of great interest to observe how the approved formulations of liposomal doxorubicin are integrated into combination regimes for treatment of cancer. In the meantime, we have learned a great deal about liposomes as drug carriers from over 20 years of research on different liposomal doxorubicin formulations, the very first of which were identified in the late 1970s. This chapter will discuss the various methods for encapsulation of doxorubicin into liposomes, as well as some of the important interactions between the formulation components of the drug and how this may impact the biological activity of the associated drug. This review of methodology, in turn, will highlight research activities that are being pursued to achieve better performance parameters for liposomal formulations of doxorubicin, as well as other anticancer agents being considered for use with lipid-based carriers.

Membrane effects of the antitumor drugs doxorubicin and thaliblastine: comparison to multidrug resistance modulators verapamil and trans-flupentixol

The interactions of the antitumor drugs doxorubicin and thaliblastine with model membranes composed of neutral (phosphatidylcholine) and negatively charged (phosphatidylserine) phospholipids were studied by differential scanning calorimetry and nuclear magnetic resonance. The membrane activities of doxorubicin and thaliblastine were compared to those of the powerful multidrug resistance (MDR) modulators trans-flupentixol and verapamil. The results point out to the potential role of the drug-membrane interactions for the effects of doxorubicin and thaliblastine in resistant tumor cells. They direct also to the artificial membranes as a suitable tool for screening of compounds with potential ability to modulate MDR.

In Vitro and in Vivo Characterization of Doxorubicin and Vincristine Coencapsulated within Liposomes through Use of Transition Metal Ion Complexation and pH Gradient Loading

PURPOSE

There is an opportunity to augment the therapeutic potential of drug combinations through use of drug delivery technology. This report summarizes data obtained using a novel liposomal formulation with coencapsulated doxorubicin and vincristine. The rationale for selecting these drugs is due in part to the fact that liposomal formulations of doxorubicin and vincristine are being separately evaluated as components of drug combinations.

EXPERIMENTAL DESIGN

Doxorubicin and vincristine were coencapsulated into liposomes using two distinct methods of drug loading. A manganese-based drug loading procedure, which relies on drug complexation with a transition metal, was used to encapsulate doxorubicin. Subsequently the ionophore A23187 was added to induce formation of a pH gradient, which promoted vincristine encapsulation.

RESULTS

Plasma elimination studies in mice indicated that the drug:drug ratio before injection [4:1 doxorubicin:vincristine (wt:wt ratio)] changed to 20:1 at the 24-h time point, indicative of more rapid release of vincristine from the liposomes than doxorubicin. Efficacy studies completed in MDA MB-435/LCC6 tumor-bearing mice suggested that at the maximum tolerated dose, the coencapsulated formulation was therapeutically no better than liposomal vincristine. This result was explained in part by in vitro cytotoxicity studies evaluating doxorubicin and vincristine combinations analyzed using the Chou and Talalay median effect principle. These data clearly indicated that simultaneous addition of vincristine and doxorubicin resulted in pronounced antagonism.

CONCLUSION

These results emphasize that in vitro drug combination screens can be used to predict whether a coformulated drug combination will act in an antagonistic or synergistic manner.

Formation of transition metal-doxorubicin complexes inside liposomes

Doxorubicin complexation with the transition metal manganese (Mn(2+)) has been characterized, differentiating between the formation of a doxorubicin-metal complex and doxorubicin fibrous-bundle aggregates typically generated following ion gradient-based loading procedures that rely on liposome encapsulated citrate or sulfate salts. The physical and chemical characteristics of the encapsulated drug were assessed using cryo-electron microscopy, circular dichroism (CD) and absorbance spectrophotometric analysis. In addition, in vitro and in vivo drug loading and release characteristics of the liposomal formulations were investigated. Finally, the internal pH after drug loading was measured with the aim of linking formation of the Mn(2+) complex to the presence or absence of a transmembrane pH gradient. Doxorubicin was encapsulated into either 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)/cholesterol (Chol) or 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)/Chol liposomes, where the entrapped salts were citrate, MnSO(4) or MnCl(2). In response to a pH gradient or a Mn(2+) ion gradient, doxorubicin accumulated inside to achieve a drug-to-lipid ratio of approximately 0.2:1 (wt/wt). Absorbance and CD spectra of doxorubicin in the presence of Mn(2+) suggested that there are two distinct structures captured within the liposomes. In the absence of added ionophore A23187, drug loading is initiated on the basis of an established pH gradient; however, efficient drug uptake is not dependent on maintenance of the pH gradient. Drug release from DMPC/Chol is comparable regardless of whether doxorubicin is entrapped as a citrate-based aggregate or a Mn(2+) complex. However, in vivo drug release from DSPC/Chol liposomes indicate less than 5% or greater than 50% drug loss over a 24-h time course when the drug was encapsulated as an aggregate or a Mn(2+) complex, respectively. These studies define a method for entrapping drugs possessing coordination sites capable of complexing transition metals and suggest that drug release is dependent on lipid composition, internal pH, as well as the nature of the crystalline precipitate, which forms following encapsulation.

Ionophore-mediated uptake of ciprofloxacin and vincristine into large unilamellar vesicles exhibiting transmembrane ion gradients

A new method, based on the ion-translocating properties of the ionophores nigericin and A23187, is described for loading large unilamellar vesicles (LUVs) with the drugs vincristine and ciprofloxacin. LUVs composed of distearoylphosphatidylcholine/cholesterol (DSPC/Chol) (55:45 mol/mol) or sphingomyelin (SPM)/Chol (55:45 mol/mol) exhibiting a transmembrane salt gradient (for example, internal solution 300 mM MnSO4 or K2SO4; external solution 300 mM sucrose) are incubated in the presence of drug and, for experiments involving divalent cations, the chelator EDTA. The addition of ionophore couples the outward movement of the entrapped cation to the inward movement of protons, thus acidifying the vesicle interior. External drugs that are weak bases can be taken up in response to this induced transmembrane pH gradient. It is shown that both nigericin and A23187 facilitate the rapid uptake of vincristine and ciprofloxacin, with entrapment levels approaching 100% and excellent retention in vitro. Following drug loading, the ionophores can be removed by gel exclusion chromatography, dialysis, or treatment with biobeads. In vitro leakage assays (addition of 50% mouse serum) and in vivo pharmacokinetic studies (in mice) reveal that the A23187/Mn2+ system exhibits superior drug retention over the nigericin/K+ system, and compares favorably with vesicles loaded by the standard DeltapH or amine methods. The unique features of this methodology and possible benefits are discussed.

Loading of doxorubicin into liposomes by forming Mn2+-drug complexes

A new procedure for loading doxorubicin into large unilamellar vesicles (LUVs) is characterized. It is shown that doxorubicin can be loaded into LUVs composed of sphingomyelin/cholesterol (55:45 mole/mole) in response to a transmembrane MnSO4 gradient in the absence of a transmembrane pH gradient. Complex formation between doxorubicin and Mn2+ is found to be a driving force for doxorubicin uptake. Uptake levels approaching 100% can be achieved up to a drug-to-lipid molar ratio of 0.5 utilizing an encapsulated MnSO4 concentration of 0.30 M. In vitro leakage assays show excellent retention properties over a 24 h period. The possible advantages of a liposomal formulation of doxorubicin loaded in response to entrapped MnSO4 are discussed.

Enzymatic synthesis of [4-methoxy-11C]daunorubicin for functional imaging of P-glycoprotein with PET

One of the mechanisms for multidrug resistance (MDR) of tumors is an overexpression of the P-glycoprotein (P-gp). The cytostatic agent daunorubicin was labeled with carbon-11 to probe P-gp with PET. An enzymatic route for the conversion of carminomycin to [4-methoxy-11C]daunorubicin ([4-methoxy-11C]DNR) was investigated, since attempts failed to prepare daunorubicin chemically using [11C]methyl iodide. In the enzymatic synthesis methylation was accomplished by S-adenosyl-L-[methyl-11C]methionine ([11C]SAM), which was synthesized from L-[methyl-11C]methionine. This methylation is catalyzed by carminomycin-4-O-methyltransferase (CMT). The overall radiochemical yield of [4-methoxy-11C]DNR is 1% (EOB), with a total synthesis time of 75 min. In conclusion, [4-methoxy-11C]DNR can be successfully prepared from carminomycin and [11C]SAM using enzymes.

Anthracycline gels

Gels have been prepared from aqueous solutions of anthracyclines by addition of salts. The gels are thixotropic and thermally reversible. They are stable for several months in the refrigerator and for long times even at room temperature. The gel-solution transition (melting) temperature depends on the concentration of the anthracycline and on the concentration and nature of the added salt. The melting has been followed by 1H-NMR. Only weak intermolecular interactions (stacking and hydrogen bonds) originate the drug network, within which the solvent is entrapped. 1H-NMR and polarimetric data suggest a stacked helical arrangement of the anthracycline molecules. The gelation process is cooperative.

HPLC determination of doxorubicin, doxorubicinol and four aglycone metabolites in plasma of AIDS patients

A high-performance liquid chromatographic (HPLC) assay has been developed for the determination of the anticancer drug doxorubicin and the metabolites doxorubicinol, doxorubicinone, 7-deoxydoxorubicinone, doxorubicinolone and 7-deoxydoxorubicinolone in plasma of AIDS patients. Samples can be heated at 60 degrees C for 30 min to inactivate the human immunodeficiency virus. The sample pre-treatment involves a liquid-liquid extraction of the buffered plasma sample (pH 9) with a chloroform-1-propanol (4:1, v/v) mixture. The chromatographic analysis is performed on a Lichrosorb RP-8 (5 microns) column and by isocratic elution with a mobile phase of acetonitriletetrahydrofuran-phosphate buffer (pH 2.2) (800:5:200, w/w/w) with fluorescence detection (excitation wavelength: 460 nm; emission wavelength: 550 nm). The proposed method has been validated and, subsequently, implemented in a pharmacokinetic study of doxorubicin in AIDS patients with Kaposi's sarcoma who are treated with the combination regimen doxorubicin, vincristine and bleomycin.

Inhibition of mouse skin tumor promotion by adriamycin and daunomycin in combination with verapamil or palmitoylcarnitine

The anti-cancer drugs Adriamycin (ADR) and Daunomycin (DAU) alone were unable to inhibit the promotion of skin papillomas by repeated applications of 8.5 nmol of 12-O-tetradecanoylphorbol-13-acetate (TPA) in 7,12-dimethylbenz(a)anthracene (DMBA)-initiated mice. Pretreatments with 50 micrograms of ADR also failed to alter the tumor-promoting activities of smaller doses of TPA. Therefore, the effects of the anthracycline antibiotics on skin tumor promotion were evaluated in combination with the Ca2+ antagonist verapamil (VRP) and the protein kinase C (PKC) inhibitor palmitoylcarnitine (PC), compounds known to circumvent drug resistance. When applied simultaneously with each promotion treatment with 8.5 nmol of TPA, 2.5 mg of VRP inhibited the number of papillomas/mouse by 26%. But the combination of VRP + 50 micrograms of ADR or DAU inhibited the yields of papillomas by 50 or 47%, respectively, suggesting that VRP was required to reveal the antitumor-promoting activities of otherwise ineffective drugs. Similarly, the promotion of skin tumors by TPA was inhibited synergistically by the combinations of 2 mumol of PC + 50 micrograms of ADR or DAU. For instance, ADR and DAU had no effects alone but inhibited the incidence of skin papillomas by 78 and 86%, respectively, in the presence of PC, a compound which alone inhibited the tumor incidence by only 44%. The results indicate that ADR and DAU are effective against the promoting component of skin carcinogenesis only if they are applied in combination with Ca2+ antagonists or PKC inhibitors at a time when they can inhibit the early biochemical effects induced by TPA.

High performance liquid chromatography determination of doxorubicin and daunorubicin in plasma using UV detection and column switching

A method for the determination of doxorubicin and daunorubicin in plasma is described. The plasma is injected directly into a loop column and then washed with water. After switching the injection valve, the sample is separated on a phenyl column using detection at 254 nm. The detection limit is 10 ng/mL, the coefficient of variation is 7% for 100 ng/mL of doxorubicin and 4% for 200 ng/mL of daunorubicin.

Immobilization of a primary amine-containing drug, adriamycin. Coupling to crosslinked polyvinyl alcohol and mechanistic comparison of hydrolytic stability

Literature reports have described the covalent coupling of the primary amine-containing anticancer drug, adriamycin, to polymeric supports through the amine group on the drug. These reports also have described drug mechanism studies with the immobilized adriamycin, where the release of the drug would undermine the validity of the conclusions. In the present paper, detailed experimental conditions are given for preparation of nonwater-soluble particles of polyvinyl alcohol by crosslinking water-soluble polyvinyl alcohol with 1,4-benzenedicarboxaldehyde, and for activation with cyanuric chloride and covalent attachment of adriamycin. The expected stability of this drug-support linkage against hydrolytic cleavage is compared mechanistically to that expected for less stable coupling through a carbamate linkage or for less stable coupling via an azomethine link.

Potential pitfalls in in vitro antitumor activity testing of free and liposome-entrapped doxorubicin

This paper addresses several potential problems which may play a critical role in the outcome of in vitro studies designed to investigate the antitumor activity of drugs. These problems were demonstrated to exist in in vitro assays developed for the evaluation of antitumor activity of free and liposome-entrapped doxorubicin (DXR). The stability of DXR-containing liposomes against drug leakage into the culture medium, as well as the chemical stability and extent of adsorption to tissue culture plastics of both free and liposomal DXR during the liposome-tumor cell incubation, were investigated. It is concluded that a full understanding of these processes is required for a reliable interpretation of the experimental results.