An Automated Capillary Electrophoresis Based Method for Drug Release Profiling of Liposomal Doxorubicin

Liposomal doxorubicin hydrochloride is an antineoplastic agent widely used against human cancers. The data from in vitro drug release test (IVRT) is essential for quality and/or bioequivalence evaluation in drug approval and post-approval regulation of liposomal drug products. However, most of the currently available IVRT methods for liposomal doxorubicin hydrochloride have experimental deficiencies associated with liposomal rupture during the separation process which is needed for selective quantification of released drug from liposomal-bound drug. In addition, many of the methods are time consuming, requiring bulk quantities of liposomal drug product, and lack of automation. We have developed a selective, sensitive, and automated capillary electrophoresis (CE)-based IVRT method, measuring released doxorubicin without additional sampling and separation steps. This method requires a small volume of sample compared to currently available methods. The IVRT release study with liposomal doxorubicin was conducted at different temperatures and pH conditions. It was observed that the release profiles obtained for five formulations including the reference listed drug were similar at pH 6.50 and 47.0 °C. The drug release increased with the increase of media pH and temperature. Complete doxorubicin release (100 %) was obtained in 7 h at pH 6.50 and 47.0 °C, and in less than 3 h at pH 6.50 and 52.0 °C. This CE-based method can be extended for determination of the IVRT profiling of other liposomal drug products.

Folded, undulating, and fibrous doxorubicin sulfate crystals in liposomes

High-resolution cryogenic transmission electron microscopy (cryo-TEM) evidenced that doxorubicin sulfate crystals in liposomes (prepared by remote loading with ammonium sulfate) form folded, undulating, and fibrous crystals with a diameter of approximately 2.4 nm. An undulating, fibrous crystal considered to be undergrowth, in addition to bundles of fibrous crystals, was also observed in doxorubicin-loaded liposomes. This explains the validity of the formation of doxorubicin sulfate crystals of various shapes, e.g., curved, U-shaped, or circular, in addition to cylinder and/or rod-like crystals reported in the literature. Liposomes that do not contain crystals have inner aqueous phases with high electron density, suggesting that the doxorubicin is remotely loaded and remains as a solute without precipitation.

Regulatory Science Approach in Pharmaceutical Development of Follow-On Versions of Non-Biological Complex Drug Products

Scientific and technological breakthroughs in the field of Nanotechnology have been a driving force throughout the development and approval of Non-Biological Complex Drugs (NBCDs). However, the fast-growing expansion of NBCDs and the emergence of their follow-on versions have brought with them several scientific, technological, and regulatory challenges. The definition of NBCDs is still not officially recognized by the regulatory authorities, and there is no dedicated regulatory pathway addressing the particular features of NBCDs and their follow-on versions. The lack of clear and consistent regulatory guidance documents in this field, as well as, the inconsistency across different regulatory agencies, impact negatively on the acceptance and enormous potential of these drug products. Patient access to high-quality NBCDs follow-on versions may be compromised by regulatory uncertainty resulting from the use of different regulatory approaches across the globe, as well as within the same class of products. Accordingly, there is a real need to develop a specific regulatory pathway compliant with the complexity of NBCDs and their follow-on versions or, alternatively, make better use of available regulatory pathways. The main goal of the review is to deeply investigate and provide a critical overview of the regulatory landscape of NBCDs and follow-on versions currently adopted by the regulatory authorities. The dissemination of knowledge and discussion in this field can contribute to clarifying regulations, policies, and regulatory approaches to complex generics, thereby filling regulatory and scientific gaps in the establishment of therapeutic equivalence.

Fast and versatile analysis of liposome encapsulation efficiency by nanoParticle exclusion chromatography

Liposomes are an attractive drug delivery platform for a wide variety of pharmaceutical molecules. Encapsulation efficiency, which refers to the amount of drug contained inside liposomes compared with the total amount of drug, is a critical quality attribute of liposome products, as the free drug in a liposomal formulation may cause toxicity or undesired biodistribution. The determination of encapsulation efficiency requires the measurement of at least two of the three drug populations: total drug, encapsulated drug and free drug. However, direct measurement of the encapsulated drug and free drug remains a challenging analytical task. Nanoparticle exclusion chromatography (nPEC), an emerging high-performance liquid chromatography (HPLC) technique, has shown great potential in separating and quantifying the free drug in liposomal formulations. In this study, nPEC was systematically evaluated for two representative liposomal formulations containing either hydrophilic or hydrophobic small molecule drugs. It is reported for the first time that the insoluble free drug suspended in the aqueous formulation can be directly measured by nPEC. This free drug in the suspension sample was quantified with excellent accuracy and precision. On the other hand, the total drug measurement from dissociated liposomes was confirmed by the benchmark methodology of reversed phase liquid chromatography (RPLC). The facile quantitation of free and total drug in the liposome formulation enables the fast and accurate determination of the encapsulation efficiency, which can be used to guide the formulation development and characterize the product quality.

In Vitro Cell Toxicity and Intracellular Uptake of Doxorubicin Exposed as a Solution or Liposomes: Implications for Treatment of Hepatocellular Carcinoma

Cytostatic effects of doxorubicin in clinically applied doses are often inadequate and limited by systemic toxicity. The main objective of this in vitro study was to determine the anti-tumoral effect (IC₅₀) and intracellular accumulation of free and liposomal doxorubicin (DOX) in four human cancer cell lines (HepG2, Huh7, SNU449 and MCF7). The results of this study showed a correlation between longer DOX exposure time and lower IC₅₀ values, which can be attributed to an increased cellular uptake and intracellular exposure of DOX, ultimately leading to cell death. We found that the total intracellular concentrations of DOX were a median value of 230 times higher than the exposure concentrations after exposure to free DOX. The intracellular uptake of DOX from solution was at least 10 times higher than from liposomal formulation. A physiologically based pharmacokinetic model was developed to translate these novel quantitative findings to a clinical context and to simulate clinically relevant drug concentration-time curves. This showed that a liver tumor resembling the liver cancer cell line SNU449, the most resistant cell line in this study, would not reach therapeutic exposure at a standard clinical parenteral dose of doxorubicin (50 mg/m²), which is serious limitation for this drug. This study emphasizes the importance of in-vitro to in-vivo translations in the assessment of clinical consequence of experimental findings.

Gelation of the internal core of liposomes as a strategy for stabilization and modified drug delivery II. Theoretical analysis and modelling of in-vitro release experiments

PEG-DMA was incorporated in unilamellar liposomes. PEG-DMA crosslinking by photo-induced radical reaction transforms the liquid aqueous core of the liposome into a hydrogel. The molecular weight of PEG-DMA significantly influences both structural and release properties of these hybrid nanosystems, by affecting both membrane permeability and diffusional properties of the inner core. Release studies of 5-(6) carboxyfluorescein from Conventional Liposomes (CL) and Gel-in-Liposome (GiL) systems were carried out in a vertical Franz Diffusion Cell. A detailed transport model is proposed, aimed at describing the entire drug diffusive pathway from the vesicles' inner core, through the double-layer membrane, into the buffer solution in the donor chamber of the Franz Cell and from there to the receptor chamber, where withdrawals are performed to evaluate the released drug concentration. The model permits to give a quantitative estimate of the diffusional resistances offered by the inner core (liquid or gelled) and by the double-layer membrane for CLs and different GiLs systems. The theoretical analysis of experimental release data strongly supports the basic assumption that, by varying the molecular weight of PEG-DMA, a different arrangement of the polymer within the liposomal structure and a different interaction with the membrane occur. PEG₇₅₀-DMA decreases the transport resistance of the double layer membrane with respect to CLs, while PEG₄₀₀₀-DMA plays the opposite role. After gelation of the internal core, the diffusional resistance to drug transport inside GiLs becomes controlling, thus significantly slowing down drug release from these systems. Therefore, the combination of PEG-DMA with phospholipid vesicles appears an interesting strategy to develop sustained drug delivery systems.

Innovation for Generic Drugs: Science and Research Under the Generic Drug User Fee Amendments of 2012

Regulatory science is science and research intended to improve decision making in a regulatory framework. Improvements in decision making can be in both accuracy (making better decisions) and in efficiency (making faster decisions). Science and research supported by the Generic Drug User Fee Amendments of 2012 (GDUFA) have focused on two innovative methodologies that work together to enable new approaches to development and review of generic drugs: quantitative models and advanced in vitro product characterization. Quantitative models faithfully represent current scientific understanding. They are tools pharmaceutical scientists and clinical pharmacologists use for making better and faster product development decisions. Advances in the in vitro product comparisons provide the measurements of product differences that are the critical input into the models. This paper outlines four areas where science and research funded by GDUFA support synergistic use of models and characterization at critical decision points during generic drug product development and review.

Single bead investigation of a clinical drug delivery system - A novel release mechanism

Microgels, such as polymeric hydrogels, are currently used as drug delivery devices (DDSs) for chemotherapeutics and/or unstable drugs. The clinical DDS DC bead® was studied with respect to loading and release, measured as relative bead-volume, of six amphiphilic molecules in a micropipette-assisted microscopy method. Theoretical models for loading and release was used to increase the mechanistic understanding of the DDS. It was shown that equilibrium loading was independent of amphiphile concentration. The loading model showed that the rate-determining step was diffusion of the molecule from the bulk to the bead surface ('film control'). Calculations with the developed and applied release model on the release kinetics were consistent with the observations, as the amphiphiles distribute unevenly in the bead. The rate determining step of the release was the diffusion of the amphiphile molecule through the developed amphiphile-free depletion layer. The release rate is determined by the diffusivity and the tendency for aggregation of the amphiphile where a weak tendency for aggregation (i.e. a large cac_b) lead to faster release. Salt was necessary for the release to happen, but at physiological concentrations the entry of salt was not rate-determining. This study provides valuable insights into the loading to and release from the DDS. Also, a novel release mechanism of the clinically used DDS is suggested.

Cardinal Role of Intraliposome Doxorubicin-Sulfate Nanorod Crystal in Doxil Properties and Performance

The uniqueness of Doxil can be attributed, to a large extent, to its intraliposomal doxorubicin-sulfate nanorod crystal. We re-examine these nanocrystal features and their mechanism of the formation by studying pegylated liposomal doxorubicins (PLDs) of the same lipid composition, size distribution, and extraliposome medium that were prepared at different ammonium sulfate (AS) concentrations. This study includes a comparison of the thermotropic behavior, morphology, and in vitro ammonia-induced doxorubicin release (relevant to Doxil's in vivo performance) of these PLDs. In this study, we confirm that a transmembrane ammonium gradient is critical for doxorubicin remote loading, and we demonstrate that the intraliposomal concentration of sulfate counteranions and ammonium ions determine to a large extent the physical state and stability of the PLDs' remote loaded doxorubicin. "Fully-developed" intraliposome doxorubicin-sulfate nanorod crystals (as defined by cryogenic transmission electron microscopy imaging) develop only when the ammonium sulfate (AS) concentration used for PLD preparation is ≥150 mM. Less than 10% of PLDs prepared with 100 mM AS show fully developed nanorod crystals. Intraliposomal AS concentration ≥200 mM is required to support the stable nanocrystallization in PLDs. The presence of nanocrystals and their melting enthalpy and phase transition co-operativity strongly affect the ammonia-induced doxorubicin release of PLDs. A quick, biphasic release occurs for PLDs that lack the nanorod crystals or have crystals of poor crystallinity, whereas PLDs prepared with ≥200 mM AS show a monophasic, zero-order slow release. This study also demonstrates that after remote loading, residual intraliposomal ammonium concentration and the transmembrane pH gradient related to it also play an important role in doxorubicin-sulfate intraliposomal crystallization and ammonia-induced doxorubicin release.

Simulation of Stimuli-Responsive and Stoichiometrically Controlled Release Rate of Doxorubicin from Liposomes in Tumor Interstitial Fluid

PURPOSE

To simulate the stimuli-responsive and stoichiometrically controlled doxorubicin (DOX) release from liposomes in in vivo tumor interstitial fluid (TIF), the effect of ammonia concentration and pH on the DOX release from liposomes in human plasma at 37°C was quantitatively evaluated in vitro and the release rate was calculated as a function of ammonia concentration and pH.

METHODS

Human plasma samples spiked with DOX-loaded PEGylated liposomes (PLD) or Doxil^®, containing ammonia (0.3-50 mM) at different pH values, were incubated at 37°C for 24 h. After incubation, the concentration of encapsulated DOX in the samples was determined by validated solid-phase extraction (SPE)-SPE-high performance liquid chromatography.

RESULTS

Accelerated DOX release (%) from liposomes was observed as the increase of ammonia concentration and pH of the matrix, and the decrease of encapsulated DOX concentration. The release rate was expressed as a function of the ammonia concentration and pH by using Henderson-Hasselbalch equation.

CONCLUSIONS

The DOX release from PLD in TIF was expressed as a function ammonia concentration and pH at various DOX concentrations. Further, it was found that the DOX release from liposomes in a simulated TIF was more than 15 times higher than in normal plasma.

Combination of doxorubicin with harmine-loaded liposomes exerting synergistic antitumor efficacy

CONTEXT

Long-circulation (PEGLip), pH-sensitive (PEOzLip), and active targeted liposomes (PEG-TATLip)-loading doxorubicin (DOX) and harmine (HM) were prepared. Their physicochemical properties and antitumor effect were investigated.

OBJECTIVES

The aims of the present study were to evaluate synergistic antitumor efficacy.

MATERIALS AND METHODS

Liposomes were prepared by using thin-film dispersion, active drug-loading and target post-insertion method. Subsequently physiochemical properties including particle size distribution, zeta potential, entrapment efficiency (EE), drug-loading content and in-vitro release were determined. Besides, the in vitro cytotoxicity of free drugs and drug-loaded liposomes was explored by using a Sulforhodamine-B Staining assay and the combination index values (CI Value) were calculated. Finally, the cellular uptake experiments by MCF-7cells were carried out via flow cytometry.

RESULTS AND DISCUSSION

All liposomes enhanced the antitumor effect significantly compared to free drugs. Among liposomes, PEG-TATLip enhanced the antitumor effect significantly compared to others. DOX and HM had moderate synergism with CI Value 0.85 for free drugs, 0.81 for PEGLip, 0.72 for PEOzLip, and 0.84 for PEG-TATLip respectively when the weight ratio of two drugs was 1:2. Moreover, the similarity between DOX and HM such as physicochemical properties, in vitro release modes and in vitro uptake kinetics characteristics when they were in the same formulations proved it possible for them to be delivered together.

CONCLUSION

Active targeting liposomes were the most effective delivery system as compared with pH-sensitive and long circulation liposomes. Additionally, DOX and HM could be co-delivered in liposomes and they could play moderate synergism effect in antitumor efficacy.

How Has CDER Prepared for the Nano Revolution? A Review of Risk Assessment, Regulatory Research, and Guidance Activities

The Nanotechnology Risk Assessment Working Group in the Center for Drug Evaluation and Research (CDER) within the United States Food and Drug Administration (FDA) was established to assess the potential impact of nanotechnology on drug products. One of the working group's major initiatives has been to conduct a comprehensive risk management exercise regarding the potential impact of nanomaterial pharmaceutical ingredients and excipients on drug product quality, safety, and efficacy. This exercise concluded that current review practices and regulatory guidance are capable of detecting and managing the potential risks to quality, safety, and efficacy when a drug product incorporates a nanomaterial. However, three risk management areas were identified for continued focus during the review of drug products containing nanomaterials: (1) the understanding of how to perform the characterization of nanomaterial properties and the analytical methods used for this characterization, (2) the adequacy of in vitro tests to evaluate drug product performance for drug products containing nanomaterials, and (3) the understanding of properties arising from nanomaterials that may result in different toxicity and biodistribution profiles for drug products containing nanomaterials. CDER continues to actively track the incorporation of nanomaterials in drug products and the methodologies used to characterize them, in order to continuously improve the readiness of our science- and risk-based review approaches. In parallel to the risk management exercise, CDER has also been supporting regulatory research in the area of nanotechnology, specifically focused on characterization, safety, and equivalence (between reference and new product) considerations. This article provides a comprehensive summary of regulatory and research efforts supported by CDER in the area of drug products containing nanomaterials and other activities supporting the development of this emerging technology.

Scientific and Regulatory Considerations for Generic Complex Drug Products Containing Nanomaterials

In the past few decades, the development of medicine at the nanoscale has been applied to oral and parenteral dosage forms in a wide range of therapeutic areas to enhance drug delivery and reduce toxicity. An obvious response to these benefits is reflected in higher market shares of complex drug products containing nanomaterials than that of conventional formulations containing the same active ingredient. The surging market interest has encouraged the pharmaceutical industry to develop cost-effective generic versions of complex drug products based on nanotechnology when the associated patent and exclusivity on the reference products have expired. Due to their complex nature, nanotechnology-based drugs present unique challenges in determining equivalence standards between generic and innovator products. This manuscript attempts to provide the scientific rationales and regulatory considerations of key equivalence standards (e.g., in vivo studies and in vitro physicochemical characterization) for oral drugs containing nanomaterials, iron-carbohydrate complexes, liposomes, protein-bound drugs, nanotube-forming drugs, and nano emulsions. It also presents active research studies in bridging regulatory and scientific gaps for establishing equivalence of complex products containing nanomaterials. We hope that open communication among industry, academia, and regulatory agencies will accelerate the development and approval processes of generic complex products based on nanotechnology.

IN VITRO RELEASE KINETICS MODEL FITTING OF LIPOSOMES: AN INSIGHT

Liposomes are emerging cargoes for bioactive delivery owing to their widely accepted biocompatible and biodegradable nature. It is always a challenge to control the release of payload for effective delivery to the site of interest. Over the couple of decennia, mathematical modeling of release process is a need of time whether the drug remains in the circulation or reaches at the target site. For establishing a better in vitro - in vivo correlation, release kinetics models viz. Peppas, Higuchi, Weibull, Zero Order and First order including mechanistic models like All-or-None, Toroidal, and Biomembrane models etc. are continuously exploited to predict drug release profile. Most of these models rely on the diffusion equations based on the composition of liposomes and conditions of release. Here, we summarized the crucial reports exploring these models and associated interventions to know the underlying physicochemical release phenomenon. Such mathematical model fitting can be a promising approach to deduce release/delivery process to help in designing the safe and efficacious ("Smart") liposomes.

Mechanistic model and analysis of doxorubicin release from liposomal formulations

Reliable and predictive models of drug release kinetics in vitro and in vivo are still lacking for liposomal formulations. Developing robust, predictive release models requires systematic, quantitative characterization of these complex drug delivery systems with respect to the physicochemical properties governing the driving force for release. These models must also incorporate changes in release due to the dissolution media and methods employed to monitor release. This paper demonstrates the successful development and application of a mathematical mechanistic model capable of predicting doxorubicin (DXR) release kinetics from liposomal formulations resembling the FDA-approved nanoformulation DOXIL® using dynamic dialysis. The model accounts for DXR equilibria (e.g. self-association, precipitation, ionization), the change in intravesicular pH due to ammonia release, and dialysis membrane transport of DXR. The model was tested using a Box-Behnken experimental design in which release conditions including extravesicular pH, ammonia concentration in the release medium, and the dilution of the formulation (i.e. suspension concentration) were varied. Mechanistic model predictions agreed with observed DXR release up to 19h. The predictions were similar to a computer fit of the release data using an empirical model often employed for analyzing data generated from this type of experimental design. Unlike the empirical model, the mechanistic model was also able to provide reasonable predictions of release outside the tested design space. These results illustrate the usefulness of mechanistic modeling to predict drug release from liposomal formulations in vitro and its potential for future development of in vitro - in vivo correlations for complex nanoformulations.