Simple and precise detection of lipid compounds present within liposomal formulations using a charged aerosol detector

Simultaneous Chromatographic Quantitation of Drug Substance and Excipients in Nanoformulations Using a Combination of Evaporative Light Scattering and Absorbance Detectors

Nanomedicines including lipid- and polymer-based nanoparticles and polymer-drug conjugates enable targeted drug delivery for the treatment of numerous diseases. Quantitative analysis of components in nanomedicines is routinely performed to characterize the products to ensure quality and property consistency but has been mainly focused on the active pharmaceutical ingredients (APIs) in academic publications. It has been increasingly recognized that excipients in nanomedicines are critical in determining the product quality, stability, consistency, and safety. APIs are often analyzed by high-performance liquid chromatography (HPLC), and it would be convenient if the same method can be applied to excipients to robustly quantify all components in nanomedicines. Here, we report the development of a HPLC method that combined an evaporative light scattering (ELS) detector with an UV-vis detector to simultaneously analyze drugs and excipients in nanomedicines. This method was tested on diverse nanodrug delivery systems, including a niosomal nanoparticle encapsulating a phytotherapeutic, a liposome encapsulating an immune boosting agent, and a PEGylated peptide. This method can be utilized for a variety of applications, such as monitoring drug loading, studying drug release, and storage stability. The information obtained from the analyses is of importance for nanomedicine formulation development.

HPLC-DAD-CAD-based approach for the simultaneous analysis of hydrophobic drugs and lipid compounds in liposomes and for cyclodextrin/drug inclusion complexes

In recent decades liposomes have become attractive carriers for hydrophobic drugs to enhance their solubility and improve their therapeutic application. For liposomal drug products, both drug and lipid quantification are required by regulatory authorities, making the implementation of precise quantification methods a step of crucial importance in formulation development and quality control. Therefore, the present study is focused on the development and validation of a simple and time-saving method for the simultaneous analysis of hydrophobic drugs and conventional liposomal components. The new HPLC method was established with a combined detection by a diode array detector (DAD) and a corona charged aerosol detector (CAD). As a wide calibration range of the liposomal components can be achieved (10-1000 μg/mL), the analysis of samples with different drug to lipid ratios is enabled. Moreover, an excellent precision including repeatability and low limits of detection (≤ 1.8 μg/mL) and limits of quantification (≤ 5.9 μg/mL) were accomplished for all analytes. The method was successfully applied to liposomes incorporating mitotane. Everolimus was additionally analyzed as hydrophobic model drug. Furthermore, cyclodextrin/mitotane inclusion complexes were investigated to proof a broad range of applications for the developed method.

Evaluation of size-based distribution of drug and excipient in amphotericin B liposomal formulation

Conventional quantitation of drug content in the liposome formulation involves the breakdown of bulk liposomes, which ignores details on the distribution of the active pharmaceutical ingredient (API) and excipients in liposomes of different sizes. The objective of this study is to develop an analytical method which can separate the liposomes into different sizes and obtain information of the drug and excipient distribution in the different sized liposomes. We developed an asymmetric flow field-flow fractionation (AF4) method for size-based separation of AmBisome, an amphotericin B liposomal formulation, and a high-performance liquid chromatography ultraviolet-visible and charged aerosol detection (HPLC-UV-CAD) method for simultaneous quantitation of the API (Amphotericin B) and the lipid excipients [1,2-Distearoyl-sn-glycero-3-phosphoglycerol (DSPG), hydrogenated soy phosphatidylcholine (HSPC), and cholesterol]. The measured drug content in the bulk liposome formulation was consistent with the drug product labeling. Liposomes were separated using AF4 into eleven size fractions and the liposomes particles sizes of each fraction were measured with nanoparticle tracking analysis. The drug to total lipid ratios in fractionated liposomes increased from 0.1 to 0.45 when the liposome size increased from 75 nm to 124 nm, while the lipid composition remained constant throughout the fractioned size range (cholesterol:DSPG, 0.7 and HSPC:DSPG, 0.3). These study results suggest that, for liposomal formulations of Amphotericin B in liposomes, the drug to lipid ratio increases with the size of the liposomes. This new analytical method provided a more in-depth characterization of liposomes, i.e., determining drug and excipient distributions in different sizes of liposomes, in a more efficient manner with more specific size-based composition information.

Zeta potential: a case study of cationic, anionic, and neutral liposomes

Zeta potential is often used to approximate a nanoparticle's surface charge, i.e., cationic, anionic, or neutral character, and has become a standard characterization technique to evaluate nanoparticle surfaces. While useful, zeta potential values provide only very general conclusions about surface charge character. Without a thorough understanding of the measurement parameters and limitations of the technique, these values can become meaningless. This case study attempts to explore the sensitivity of zeta potential measurement using specifically formulated cationic, anionic, and neutral liposomes. This study examines zeta potential dependence on pH and ionic strength, resolving power, and highlights the sensitivity of zeta potential to charged liposomes. Liposomes were prepared with cholesterol, 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), and varying amounts of 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) or 1,2-dioleoyl-sn-glycero-3-phospho-L-serine (DOPS). A strong linear relationship was noted between zeta potential values and the mole percentage of charged lipids within a liposome (e.g., cationic DOTAP or anionic DOPS). This finding could be used to formulate similar liposomes to a specific zeta potential, potentially of importance for systems sensitive to highly charged species. In addition, cationic and anionic liposomes were titrated with up to two mole percent of the neutral lipid 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (lipid-PEG; LP). Very small amounts of the lipid-PEG (<0.2 mol%) were found to impart stability to the DOTAP- and DOPS-containing liposomes without significantly affecting other physicochemical properties of the formulation, providing a simple approach to making stable liposomes with cationic and anionic surface charge.

A versatile, quantitative analytical method for pharmaceutical relevant lipids in drug delivery systems

Over the past few years, liposomal formulations as drug carrier systems have markedly advanced in pharmaceutical research and development. Therefore, analytical methods to characterize liposome-based formulations are required. One particular issue in liposome analysis is the imbalance of lipid ratios within the vesicle formulations and the detectability of degradation products such as lysophospholipids and fatty acids caused by hydrolysis, especially in low molar ranges. Here, a highly sensitive and selective reversed-phase high-performance liquid chromatography (rp-HPLC) method is described by the combination of an organic solvent/trifluoroacetic acid (TFA) triggered gradient and the application of an evaporative light scattering detector (ELSD). Gain setting adjustments of the ELSD were applied to obtain an optimal detection profile of the analyzed substances. This optimization provides simultaneous separation and quantification of 16 components, including different phosphatidylcholines, phosphatidylglycerols and their degradation products, as well as cholesterol. Parameters such as limit of detection (LOD) and limit of quantification (LOQ) were determined for each of the components and had ranges from 0.25-1.00mg/mL (LOD) and 0.50-2.50μg/mL (LOQ), respectively. The intra-day precision for all analytes is less than 3% (RSD) and inter-day precision is about 8%. The applicability of the method was verified by analyzing two different liposome formulations consisting of DSPC:DPPC:DSPG:Chol (35:35:20:10) and DSPC:DPPC:DSPG (38:38:24). For degradation studies, both formulations were stored at 4°C and at ambient temperature. Additionally, forced degradation experiments were performed to determine hydrolysis mass balances. A total recovery of 96-102% for phospholipid compounds was found. Analytical data revealed that the sensitivity, selectivity, accuracy, and resolution are appropriate for the detection and quantification of phospholipids and their hydrolysis products. These results as well as additional preliminary analyses of other relevant components used in liposomal formulations indicate that the developed method is suitable for the development, characterization, and stability testing of liposomal based biopharmaceuticals.

Charged aerosol detection to characterize components of dispersed-phase formulations

Colloidal formulations based on biocompatible phospholipids, emulsifiers, and oils are employed in a wide range of applications including medicine, food, and cosmetics. However, characterization of these dispersed-phase components may be difficult to analyze by traditional HPLC with UV, visible, or fluorescence detection modalities due to lack of chromophores or fluorophores. Charged aerosol detection (CAD) is increasingly used for analysis of dispersed-phase components due to its broad applicability and high sensitivity for non-chromophore containing components found in many colloidal systems, such as lipid-based molecules. In this review, we summarize the recent applications of CAD reported in the literature as well as our own laboratory for the analysis of widely used components of dispersed-phase systems. In particular, we discuss the advantages and disadvantages of CAD compared to other HPLC detection methods, as well as the various sample preparation methods suitable for colloidal formulations prior to HPLC-CAD analysis.

Treatment of neuroblastoma and rhabdomyosarcoma using RGD-modified liposomal formulations of patupilone (EPO906)

Background

Patupilone (EPO906) is a microtubule stabilizer with a potent antitumor effect. Integrin αVβ3-binding (RGD) liposomes were loaded with EPO906, and their antitumor efficacy was evaluated in two pediatric tumor models, ie, neuroblastoma and rhabdomyosarcoma.

Methods

Integrin αVβ3 gene expression, RGD-liposome cellular association, and the effect of EPO906 and liposomal formulations of EPO906 on cell viability were assessed in vitro in human umbilical vein endothelial cells (HUVEC), in the RH-30 rhabdomyosarcoma cell line, and in the Kelly neuroblastoma cell line. In vivo, mice bearing neuroblastoma or rhabdomyosarcoma tumors were treated with EPO906, EPO906-liposomes, or EPO906-RGD-liposomes. Tumor growth, cumulative survival, and toxicity were monitored.

Results

Integrin αVβ3 was highly expressed in HUVEC and RH-30, but not in Kelly cells. Accordingly, RGD-liposomes were highly associated with HUVEC and RH-30 cells in vitro, but not with the Kelly cells. EPO906 and its liposomal formulations inhibited HUVEC, RH-30, and Kelly cell viability to the same extent. In vivo, EPO906 1.5 mg/kg and liposomal EPO906 potently inhibited tumor growth in both xenograft models without triggering major toxicity. At this dose, liposomal EPO906 did not enhance the antitumor effect of EPO906 in neuroblastoma, but tended to have an increased antitumor effect in rhabdomyosarcoma. Using a lower dose of EPO906-RGD-liposomes significantly enhanced cumulative survival in rhabdomyosarcoma compared with EPO906 alone.

Conclusion

EPO906 shows a strong antitumor effect in neuroblastoma and rhabdomyosarcoma, without triggering major side effects. Its liposomal encapsulation does not alter its activity, and enhances cumulative survival when EPO906-RGD-liposomes are used at low dose in rhabdomyosarcoma.

Simultaneous determination of polyethylene glycol-conjugated liposome components by using reversed-phase high-performance liquid chromatography with UV and evaporative light scattering detection

Liposomes incorporating polyethylene glycol (PEG)-conjugated lipids (PEGylated liposomes) have attracted attention as drug delivery carriers because they show good in vivo stability. The lipid component of PEGylated liposomal formulations needs to be quantified for quality control. In this study, a simple reversed-phase high-performance liquid chromatography (HPLC) method with an evaporative light-scattering detector (ELSD) was established for simultaneous determination of hydrogenated soy phosphatidylcholine, cholesterol, PEG-conjugated lipid, and hydrolysis products of phospholipid in PEGylated liposomal formulations. These lipids were separated using a C18 column with a gradient mobile phase consisting of ammonium acetate buffer and ammonium acetate in methanol at a flow rate of 1.0 ml/min. This method provided sufficient repeatability, linearity, and recovery rate for all lipids. However, the linearity and recovery rates of cholesterol achieved using a ultraviolet (UV) detector were better than those achieved using an ELSD. This validated method can be applied to assess the composition change during the preparation process of liposomes and to quantify lipid components and hydrolysis products contained in a commercially available liposomal formulation DOXIL®. Taken together, this reversed-phase HPLC-UV/ELSD method may be useful for the rapid or routine analysis of liposomal lipid components in process development and quality control.

Rapid quantification of yeast lipid using microwave-assisted total lipid extraction and HPLC-CAD

We here present simple and rapid methods for fast screening of yeast lipids in Saccharomyces cerevisiae. First we introduced a microwave-assisted technique for fast lipid extraction that allows the extraction of lipids within 10 min. The new method enhances extraction rate by 27 times, while maintaining product yields comparable to conventional methods (n = 14, P > 0.05). The recovery (n = 3) from spiking of synthetic standards were 92 ± 6% for cholesterol, 95 ± 4% for triacylglycerol, and 92 ± 4% for free fatty acids. Additionally, the new extraction method combines cell disruption and extraction in one step, and the approach, therefore, not only greatly simplifies sample handling but also reduces analysis time and minimizes sample loss during sample preparation. Second, we developed a chromatographic separation that allowed separation of neutral and polar lipids from the extracted samples within a single run. The separation was performed based on a three gradient solvent system combined with hydrophilic interaction liquid chromatography-HPLC followed by detection using a charged aerosol detector. The method was shown to be highly reproducible in terms of retention time of the analytes (intraday; 0.002-0.034% RSD; n = 10, interday; 0.04-1.35% RSD; n = 5) and peak area (intraday; 0.63-6% RSD; n = 10, interday; 4-12% RSD; n = 5).

An LC method for the analysis of phosphatidylcholine hydrolysis products and its application to the monitoring of the acyl migration process

An assay for quantitative analysis of phosphatidylcholine (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) and its hydrolysis products: 1-hydroxy-2-palmitoyl-sn-glycero-3-phosphocholine and 1-palmitoyl-2-hydroxy-sn-glycero-3-phosphocholine, sn-glycero-3-phosphocholine and palmitic acid using high-performance liquid chromatography with charge aerosol detector (CAD) was developed. The separation of the compounds of interest was achieved on a reversed-phase/hydrophilic interaction stationary phase with a mobile phase consisting of acetonitrile:methanol:10mM ammonium acetate solution. The method was applied to control the acyl migration process of LPC regioisomers in the most common solvents used in the synthesis or modification of PC.

Simple chromatographic method for simultaneous analyses of phosphatidylcholine, lysophosphatidylcholine, and free fatty acids

This study describes a simple chromatographic method for the simultaneous analyses of phosphatidylcholine (PC) and its hydrolytic degradation products: lysophosphatidylcholine (LPC) and free fatty acids (FFA). Quantitative determination of PC, LPC, and FFA is essential in order to assure safety and to accurately assess the shelf life of phospholipid-containing products. A single-run normal-phase high-performance liquid chromatography (HPLC) with evaporative light scattering detector has been developed. The method utilizes an Allsphere silica analytical column and a gradient elution with mobile phases consisting of chloroform: chloroform-methanol (70:30%, v/v) and chloroform-methanol-water-ammonia (45:45:9.5:0.5%, v/v/v/v). The method adequately resolves PC, LPC, and FFA within a run time of 25 min. The quantitative analysis of PC and LPC has been achieved with external standard method. The free fatty acids were analyzed as a group using linoleic acid as representative standard. Linear calibration curves were obtained for PC (1.64-16.3 μg, r(2) = 0.9991) and LPC (0.6-5.0 μg, r(2) = 0.9966), while a logarithmic calibration curve was obtained for linoleic acid (1.1-5.8 μg, r(2) = 0.9967). The detection and quantification limits of LPC and FFA were 0.04 and 0.1 μg, respectively. As a means of validating the applicability of the assay to pharmaceutical products, PC liposome was subjected to alkaline hydrolytic degradation. Quantitative HPLC analysis showed that 97% of the total mass balance for PC could be accounted for in liposome formulation. The overall results show that the HPLC method could be a useful tool for chromatographic analysis, stability studies, and formulation characterization of phospholipid-based pharmaceuticals.

Review of operating principle and applications of the charged aerosol detector

Recently a new detection method, based upon aerosol charging (the charged aerosol detector (CAD)) has been introduced as an alternative to evaporative light-scattering detector (ELSD), chemiluminescent nitrogen detector and refractive index detector for detection of non-ultraviolet and weakly ultraviolet active compounds and for UV-absorbing compounds in the absence of standards. The content of this review article includes description of operation principle, advantages and disadvantages of CAD system, and short reports of selected applications of this detector. The main advantages of CAD detector are unique performance characteristics: better sensitivity than ELSD system, a dynamic range of up to 4 orders of magnitude, ease of use and constancy of response factors. Both detectors are mass dependent and the response generated does not depend on the spectral or physicochemical properties of the analyte. This attractive feature of a detection technique generating universal response factors is the potential use of a single, universal standard for calibration against which all other compounds or impurities can be qualified. CAD also has the same limitation as ELSD, namely, the response is affected by mobile-phase composition. This problem has been resolved by using inverse gradient compensation as is done for high pressure liquid chromatography and supercritical fluid chromatography. CAD has been applied for the analysis of structurally diverse compounds used in the pharmaceutical, chemical, food, and consumer products industries and in life science research. They include nonvolatile and semivolatile neutral, acidic, basic, and zwitterionic compounds, both polar and nonpolar (e.g. lipids, proteins, steroids, polymers, carbohydrates, peptides).

Comparison of ultraviolet detection, evaporative light scattering detection and charged aerosol detection methods for liquid-chromatographic determination of anti-diabetic drugs

Recently, charged aerosol detection (CAD), a new kind of universal detection method, has been widely employed in the HPLC system. In the present study, four kinds of anti-diabetic drug standards, glipizide, gliclazide, glibenclamide and glimepiride were determined by ultraviolet (UV) detection, evaporative light scattering detection (ELSD) and the aforementioned CAD. The results were compared with reference to linearity, accuracy, precision and limit of detection (LOD). All of the experiments were performed on a reverse phase column with water and acetonitrile as the mobile phase. Separations were achieved under the same chromatographic conditions for each detection method. As a result, CAD generated nearly uniform responses compared with UV detection and ELSD. It showed the best accuracy and LOD among 3 detectors and had similar precision with UV detection at higher concentrations while UV detection showed a better precision at lower concentrations than did CAD or ELSD. The LOD of CAD, in fact, can be up to two times higher than that of ELSD. The UV and ELSD linearity was satisfactory at R(2)>0.99, though in the case of CAD, a log-log transformation was needed. The proposed methods were also applied to the real anti-diabetic drugs and diabetes-related dietary supplements.