Chromatographic analysis and pharmacokinetics of liposome-encapsulated doxorubicin in non-small-cell lung cancer patients

From Conventional to Stealth Liposomes a new Frontier in Cancer Chemotherapy

Many attempts have been made to achieve good selectivity to targeted tumor cells by preparing specialized carrier agents that are therapeutically profitable for anticancer therapy. Among these, liposomes are the most studied colloidal particles thus far applied in medicine and in particular in antitumor therapy. Although they were first described in the 1960s, only at the beginning of 1990s did the first therapeutic liposomes appear on the market. The first-generation liposomes (conventional liposomes) comprised a liposome-containing amphotericin B, Ambisome (Nexstar, Boulder, CO, USA), used as an antifungal drug, and Myocet (Elan Pharma Int, Princeton, NJ, USA), a doxorubicin-containing liposome, used in clinical trials to treat metastatic breast cancer. The second-generation liposomes (“pure lipid approach”) were long-circulating liposomes, such as Daunoxome, a daunorubicin-containing liposome approved in the US and Europe to treat AIDS-related Kaposi's sarcoma. The third-generation liposomes were surface-modified liposomes with gangliosides or sialic acid, which can evade the immune system responsible for removing liposomes from circulation. The fourth-generation liposomes, pegylated liposomal doxorubicin, were called “stealth liposomes” because of their ability to evade interception by the immune system, in the same way as the stealth bomber was able to evade radar. Actually, the only stealth liposome on the market is Caelyx/Doxil (Schering-Plough, Madison NJ, USA), used to cure AIDS-related Kaposi's sarcoma, resistant ovarian cancer and metastatic breast cancer. Pegylated liposomal doxorubicin is characterized by a very long-circulation half-life, favorable pharmacokinetic behavior and specific accumulation in tumor tissues. These features account for the much lower toxicity shown by Caelyx in comparison to free doxorubicin, in terms of cardiotoxicity, vesicant effects, nausea, vomiting and alopecia. Pegylated liposomal doxorubicin also appeared to be less myelotoxic than doxorubicin. Typical forms of toxicity associated to it are acute infusion reaction, mucositis and palmar plantar erythrodysesthesia, which occur especially at high doses or short dosing intervals. Active and cell targeted liposomes can be obtained by attaching some antigen-directed monoclonal antibodies (Moab or Moab fragments) or small proteins and molecules (folate, epidermal growth factor, transferrin) to the distal end of polyethylene glycol in pegylated liposomal doxorubicin. The most promising therapeutic application of liposomes is as non-viral vector agents in gene therapy, characterized by the use of cationic phospholipids complexed with the negatively charged DNA plasmid. The use of liposome formulations in local-regional anticancer therapy is also discussed. Finally, pegylated liposomal doxorubicin containing radionuclides are used in clinical trials as tumor-imaging agents or in positron emission tomography.

Pharmacokinetics and Urinary Excretion of Vincristine Sulfate Liposomes Injection in Metastatic Melanoma Patients

Vincristine sulfate liposomes injection (VSLI) is a liposomal formulation of vincristine encapsulated in sphingosomes composed of sphinogomyelin and cholesterol (58/42; mol/mol). The pharmacokinetics and urinary excretion of VSLI were evaluated in 12 patients with metastatic melanoma after single-dose (2.0 mg/m2 every 2 weeks = 1 cycle) and multiple-dose (cycle 3, pharmacokinetics only) administrations (intravenous infusion over 1 hour). After VSLI infusion, total (released and encapsulated) vincristine concentrations in plasma remained relatively constant for 3 to 12 hours and thereafter declined, with interpatient variability seen in the rate of decline resulting in monoexponential or biexponential profiles. The area under the plasma concentration-time curve from time zero to infinity of total vincristine in plasma ranged from 4933 to 40495 h.ng/mL and total clearance ranged from 131 to 445 mL/h. The volume of distribution at steady state was 2650 +/- 731 mL, indicating VSLI was mainly confined within the plasma. The released vincristine concentrations in plasma were below the level of quantitation in 95% of samples. The pharmacokinetic parameters were similar between cycles 1 and 3, and trough plasma levels of total vincristine were below the level of quantitation of 1 ng/mL. Approximately 8% of the injected dose was excreted in the urine as unchanged vincristine (7%) or N-desformylvincristine (0.8%). Overall, VSLI exhibited a longer circulation half-life and higher area under the plasma concentration-time curve compared to conventional vincristine, whereas its route of elimination remained unchanged.

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.

Active methods of drug loading into liposomes: recent strategies for stable drug entrapment and increased in vivo activity

INTRODUCTION

The use of liposomes increases the therapeutic index of many drugs, and also offers drug targeting and controlled release. The commercial impact of liposomes is strengthened by the invention of several active drug encapsulation methods, allowing the encapsulation of several weak base or weak acid drugs with very high drug-to-lipid ratios.

AREAS COVERED

In recent years, there have been reports on several new approaches to retain more hydrophobic drugs inside liposomes, in the circulation. Most of these methods apply drug precipitation inside preformed liposomes, as low soluble complexes with ions or chemicals. In some cases, drug derivatization was applied to enable active encapsulation of hydrophobic drugs, previously not reported to encapsulate, by active or remote loading. This review presents and compares most of the existing methods of active drug encapsulation and outlines recent strategies to achieve stable drug encapsulation in vivo.

EXPERT OPINION

At present, there is no single universal encapsulation method that offers stable encapsulation of most drugs; each drug requires a different approach to manage all of its properties. Now is the time to combine all these strategies to achieve the goal of a complex, but successful, anticancer therapy.

Traces of phosgene in chloroform: Consequences for extraction of anthracyclines

Chloroform is commonly used to extract anthracyclines from various biological matrices. However, their determination can be seriously compromised by phosgene traces present as a result of failing stabilization of chloroform. Out of the three varieties in which chloroform exists (not stabilized, stabilized with an alcohol and stabilized with a hydrocarbon) only the ethanol stabilized type minimizes chances on creating artifacts. Chromatographic separation after extraction of four anthracyclines (doxorubicin, epirubicin, daunorubicin and idarubicin) and two metabolites (13-S-dihydrodoxorubicin and 13-S-dihydroepirubicin) with chloroform under various conditions indicate that the appropriate choice of stabilizer in this extraction solvent is highly relevant.

Enhanced efficacy of anti-tumor liposomal doxorubicin by hyperthermia

The efficiency of novel tumor chemotherapeutics could be increased using targeted drug delivery by hyperthermia. In this paper, the 3D liposomal doxorubicin distribution in the tumor tissue enhanced by local hyperthermia was quantitatively studied in real time using laser confocal microscopy. Results showed that the thermally induced liposomal doxorubicin extravasation was non-uniform and more excessive in the peripheral region than that in the tumor center. The effect of the thermally targeted drug delivery was also investigated. On the 1st, 3rd day after the thermally targeted drug treatment, histological examination showed that many nucleolus were condensed and collapsed in the peripheral region. But, in the tumor center, there were no such changes found until the 3rd day. While on the 6th day, tumor cells in both the peripheral and center region were found necrotic. The enhancement of the nanoparticle anti-tumor drug effect was significant. A theoretical analysis of liposomal doxorubicin diffusion to the tumor cells in vivo was performed. Results showed that it took more than 40 hrs for the doxorubicin to get into the tumor cells in the center region from the periphery region. The theoretical results well explained the experimental observations.

Trastuzumab and liposomal Doxorubicin in the treatment of mcf-7 xenograft tumor-bearing mice: combination does not affect drug serum levels

PURPOSE

We assessed the combination of doxorubicin or liposomal doxorubicin with trastuzumab for alterations in peak serum drug levels, as these agents are increasingly being paired in the treatment of aggressive breast cancer. We hypothesized that trastuzumab would exhibit a slower rate of elimination from the serum when in combination with liposomal doxorubicin based on the known effects of liposomal doxorubicin on phagocytic cells of the mononuclear phagocyte system (MPS), which are responsible in part for the uptake and degradation of antibodies.

METHODS

Doxorubicin and trastuzumab serum levels were assessed following injection of free doxorubicin, liposomal doxorubicin, or trastuzumab into female RAG2-M mice bearing subcutaneous MCF-7(HER-2) tumors. The effects of combination drug treatment on tumor growth were compared to single-agent treatment.

RESULTS

Peak serum trastuzumab levels were not altered as a result of addition of doxorubicin therapy, nor were doxorubicin levels altered over 24 h as a result of coadministration of trastuzumab. Liposomal doxorubicin administration did result in serum doxorubicin levels 200- to 1000-fold higher than with injection of free doxorubicin.

CONCLUSIONS

For the specific combination of trastuzumab with doxorubicin, either in free or liposomal form, coadministered in mice, there was no impact of one drug on the other in terms of peak serum drug levels or efficacy.

Pharmacokinetics of doxorubicin administered i.v. as Myocet (TLC D-99; liposome-encapsulated doxorubicin citrate) compared with conventional doxorubicin when given in combination with cyclophosphamide in patients with metastatic breast cancer

Myocet (TLC D-99) is a liposomal formulation of the anti-neoplastic drug doxorubicin with an improved therapeutic index compared with conventional doxorubicin. The objective of this study was to assess the plasma disposition of doxorubicin when administered i.v. as TLC D-99 and to compare this to conventional drug. Metabolite (doxorubicinol) plasma levels were also quantitated in both treatment groups. Plasma was collected during the first course of treatment from 10 patients receiving TLC D-99 60 mg/m and 10 receiving conventional doxorubicin 60 mg/m2, each with cyclophosphamide 600 mg/m2. Samples were assayed for total doxorubicin (all doxorubicin regardless of whether it is encapsulated or not), encapsulated doxorubicin (TLC D-99 group only) and doxorubicinol using high-performance liquid chromatography. Plasma concentrations of total doxorubicin were higher in patients receiving TLC D-99 than in patients receiving conventional doxorubicin. The clearance of total doxorubicin after administration of TLC D-99 was lower (approximately 9-fold) and the volume of distribution at steady state was less (25-fold) than that of doxorubicin after conventional drug. Doxorubicinol was detected in the plasma of all patients in both treatment groups. The mean AUC(0-infinity) of doxorubicinol for patients receiving TLC D-99 (1.5+/-0.4 M x h) was not statistically different than that in patients receiving conventional doxorubicin (1.8+/-0.4 M x h), although the appearance of the peak doxorubicinol concentration occurred later and was lower in patients receiving TLC D-99. There was a correlation between the plasma AUC(0-infinity) of total doxorubicin and the degree of myelosuppression in patients receiving conventional doxorubicin, but this correlation was not found in patients receiving TLC D-99.

Liposomally targeted cytotoxic drugs for the treatment of cancer

Phospholipid spherules composed of lipid bilayer membranes entrapping a central aqueous core were first described more than 30 years ago (Bangham et al 1965). The term liposome was coined in 1968 (Sessa & Weissmann 1968) and the first suggestions that these vesicles might have potential as vehicles for targeted drug delivery for a range of diseases, including cancer, appeared shortly afterwards (Gregoriades et al 1974; Gregoriades 1976a, b). However, the process of turning this expectation into a clinical reality has suffered a number of setbacks and has taken more than a quarter of a century. In the process, new types of liposomes with favourable in-vivo pharmacokinetics and biodistribution patterns have been generated (Lasic & Papahadjopoulos 1995). Many of these preparations have been subjected to extensive examination and an increasing number of agents have entered clinical trials. In this review, we will trace the development of those liposomes that are currently undergoing (or are about to undergo) clinical evaluation.

High-performance liquid chromatographic methods for the determination of topoisomerase II inhibitors

Various methods for separating eleven different types of topoisomerase II (TOPO-2) inhibitors, including epipodophyllotoxins, anthracyclines, anthracenediones, anthrapyrazoles, anthracenebishydrazones, indole derivatives, aminoacridines, benzisoquinolinediones, isoflavones, bisdioxopiperazines and thiobarbituric acids, are summarized. Proper sample preparation and storage is critical to the successful analysis of some TOPO-2 inhibitors due to difficulties associated with adsorption, instability and complex biological components. Solid-phase and liquid-liquid extractions are widely used to separate TOPO-2 inhibitors from biological samples, although simple deproteinization followed by direct analysis of the supernatant is preferable to extraction based on its speed and simplicity. High-performance liquid chromatography (HPLC) is the favored method for the bioanalysis of TOPO-2 inhibitors. UV or diode array detection is generally employed for early pharmacokinetic studies, while fluorescence or electrochemical detection is used more frequently for analytes with fluorescent or oxidative-reductive properties. For analyses requiring highly sensitive and/or specific detection, electrospray mass spectrometry (ESI-MS or ESI-MS-MS) provides a suitable alternative. A comprehensive compilation of the HPLC techniques currently used to separate TOPO-2 inhibitors will aid the future development of analytical methods for new TOPO-2 inhibitors.

A simple HPLC method using a microbore column for the analysis of doxorubicin

Doxorubicin is one of the most potent anti-tumor agents generally used in the treatment of bone cancer. A simple and sensitive HPLC method was developed and validated for the assay of doxorubicin. The method used a C18 Luna microbore column (50 x 1 mm) with a fluorescent detector (505 nm Ex. and 550 nm Em.). The mobile phase consisted of water-acetonitrile-acetic acid (80:19:1, v/v/v, pH 3.0) and the flow rate was 0.1 ml min(-1). Daunomycin was used as the internal standard. This isocratic system required a 10-min run-time, giving a detection limit of 0.02 ng (0.035 pmol per injection). Standard curves were linear over the concentration range of 0.01-0.1 microg ml(-1). Relative standard deviations (R.S.D.) for the within-day, day-to-day precision, and the accuracy measurement for the assay were less than 4.0, 3.2, and 4.1%, respectively. This HPLC method was used to study the in vitro release characteristics of doxorubicin from implantable drug delivery system.

An improved HPLC method for therapeutic drug monitoring of daunorubicin, idarubicin, doxorubicin, epirubicin, and their 13-dihydro metabolites in human plasma

A single high-performance liquid chromatography (HPLC) method, suitable for the analysis of daunorubicin, idarubicin, doxorubicin, epirubicin, and their 13-dihydro metabolites is validated in the present study. Preparation of plasma samples was performed by a first extraction of analytes with a chloroform/1-heptanol mixture (9:1) and reextraction with ortophosphoric acid 0.1 M. The chromatographic analysis was carried out by reversed-phase isocratic elution of anthracyclines with a Supelcosil LC-CN 5 mm column (25 cm x 4.6 mm internal diameter; Supelco) and detection was accomplished by spectrofluorimetry at excitation and emission wavelengths of 480 and 560 nm, respectively. All anthracyclines eluted within 15 minutes of injection and the method appeared to be specific, because the chromatographic assay did not show interferences at the retention time of analytes. The linearity, evaluated over a concentration range of 0.4-10,000 ng/mL, gave regression coefficients better than 0.999, with recoveries of doxorubicin-doxorubicinol and epirubicin-epirubicinol of 67%-109% and 61%-109% respectively, and 93%-109% for the other compounds. The limits of detection and quantification were 0.4 ng/mL in a 50-mL sample (40 pg/injection) for all anthracyclines tested. The method proved to be precise and accurate, as the within-day and between-day coefficients of variation were less than 10% and the accuracy of the assay was in the range of 91%-107%. Overall results indicate that it is feasible to analyze all the anthracyclines used in clinical practice and their major metabolites with a single optimized method, thereby simplifying their monitoring in chemotherapeutic regimens of cancer patients.

Thermosensitive liposomes: extravasation and release of contents in tumor microvascular networks

PURPOSE

The purpose of this study was to determine whether hyperthermic exposure would accelerate drug release from thermosensitive sterically stabilized liposomes and enhance their extravasation in tumor tissues.

MATERIALS AND METHODS

In vivo fluorescence video microscopy was used to measure the extravasation of liposomes, as well as release of their contents, in a rat skin flap window chamber containing a vascularized mammary adenocarcinoma under defined thermal conditions (34 degrees, 42 degrees, and 45 degrees C). Images of tissue areas containing multiple blood vessels were recorded via a SIT camera immediately before, and for up to 2 h after i.v. injection of two liposome populations with identical lipid composition: one liposome preparation was surface labeled with Rhodamine-PE (Rh-PE) and the other contained either Doxorubicin (Dox) or calcein at self-quenching concentrations. The light intensity of the entire tissue area was measured at 34 degrees C (the physiological temperature of the skin) for 1 h, and at 42 degrees or 45 degrees C for a second hour. These measurements were then used to calculate the fluorescent light intensity arising from each tracer (liposome surface label and the released contents) inside the vessel and in the interstitial region.

RESULTS

The calculated intensity of Rh-PE for the thermosensitive liposomes in the interstitial space (which represents the amount of extravasated liposomes) was low during the first hour, while temperature was maintained at 34 degrees C and increased to 47 times its level before heating, when the tumor was heated at 42 degrees or 45 degrees C for 1 h. The calculated intensity of the liposome contents (Dox) in the interstitial space was negligible at 34 degrees C, and increased by 38- and 76-fold, when the tumor was heated at 42 degrees and 45 degrees C for 1 h, respectively. Similar values were obtained when calcein was encapsulated in liposomes instead of Dox. A similar increase in liposome extravasation was seen with nonthermosensitive liposomes, but negligible release of Dox occurred when the window chamber was heated to 45 degrees C for 1 h. Extravasation of liposomes continued after heating was stopped, but content release stopped after removal of heat. Release of Dox from extravasated liposomes was also seen if heating was applied 24 h after liposome administration, but no further enhancement of liposome extravasation occurred in this case.

CONCLUSIONS

Our data suggest that hyperthermia can be used to selectively enhance both the delivery and the rate of release of drugs from thermosensitive liposomes to targeted tissues.

Liposomal doxorubicin

Doxorubicin is a potent antineoplastic agent with activity against numerous human cancers. Encapsulation of doxorubicin inside a liposome alters bioavailability, biodistribution and thus its biological activity significantly. The physical properties of the liposome (size, lipid components and lipid dose) play a major role in determining drug retention and pharmacokinetics. The therapeutic benefits of liposomal doxorubicin will therefore depend on these physical characteristics. Here we review the toxicity and efficacy of liposomal doxorubicin determined for various liposome compositions (size, lipid composition and drug-to-lipid ratio). These physical properties can be independently varied using the transmembrane pH gradient-dependent drug encapsulation procedure. The results show that the toxicity of the formulation is related to drug retention in the circulation. The antitumor activity is more sensitive to the size of the liposomes. By optimizing these parameters, liposomal doxorubicin formulations can be optimized for improved therapeutic activity.