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1.  Physical Approaches for Nucleic Acid Delivery to Liver 
The AAPS Journal  2008;10(4):589-595.
The liver is a key organ for numerous metabolic pathways and involves many inherited diseases that, although being different in their pathology, are often caused by lack or overproduction of a critical gene product in the diseased cells. In principle, a straightforward method to fix such problem is to introduce into these cells with a gene-coding sequence to provide the missing gene product or with the nucleic acid sequence to inhibit production of the excessive gene product. Practically, however, success of nucleic acid-based pharmaceutics is dependent on the availability of a method capable of delivering nucleic acid sequence in the form of DNA or RNA to liver cells. In this review, we will summarize the progress toward the development of physical methods for nucleic acid delivery to the liver. Emphasis is placed on the mechanism of action, pros, and cons of each method developed so far. We hope the information provided will encourage new endeavor to improve the current methodologies or develop new strategies that will lead to safe and effective delivery of nucleic acids to the liver.
doi:10.1208/s12248-008-9067-y
PMCID: PMC2628207  PMID: 19083101
gene delivery; liver; nonviral vectors; physical method; transfection
2.  Physical Approaches for Nucleic Acid Delivery to Liver 
The AAPS journal  2008;10(4):589-595.
Liver is a key organ for numerous metabolic pathways and involves many inherited diseases that, although being different in their pathology, are often caused by lack or overproduction of a critical gene product in the diseased cells. In principle, a straightforward method to fix such problem is to introduce into these cells with a gene-coding sequence to provide the missing gene product, or with the nucleic acid sequence to inhibit production of the excessive gene product. Practically, however, success of nucleic acid-based pharmaceutics is dependent on availability of a method capable of delivering nucleic acid sequence in the form of DNA or RNA to liver cells. In this review, we will summarize the progress toward development of physical methods for nucleic acid delivery to liver. Emphasis is placed on the mechanism of action, pros and cons of each method developed so far. We hope the information provided will encourage new endeavor to improve the current methodologies or develop new strategies that will lead to safe and effective delivery of nucleic acids to liver.
doi:10.1208/s12248-008-9067-y
PMCID: PMC2628207  PMID: 19083101
Gene delivery; non-viral vectors; physical method; liver; transfection
3.  A Bayesian Approach for Quantifying Trace Amounts of Antibody Aggregates by Sedimentation Velocity Analytical Ultracentrifugation 
The AAPS Journal  2008;10(3):481-493.
Sedimentation velocity analytical ultracentrifugation (SV-AUC) has become an important tool for the characterization of the purity of protein therapeutics. The work presented here addresses a need for methods orthogonal to size-exclusion chromatography for ensuring the reliable quantitation of immunogenic oligomers, for example, in antibody preparations. Currently the most commonly used approach for SV-AUC analysis is the diffusion-deconvoluted sedimentation coefficient distribution c(s) method, previously developed by us as a general purpose technique and implemented in the software SEDFIT. In both practical and theoretical studies, different groups have reported a sensitivity of c(s) for trace oligomeric fractions well below the 1% level. In the present work we present a variant of c(s) designed for the purpose of trace detection, with customized Bayesian regularization. The original c(s) method relies on maximum entropy regularization providing the most parsimonious distribution consistent with the data. In the present paper, we use computer simulations of an antibody system as example to demonstrate that the standard maximum entropy regularization, due to its design, leads to a theoretical lower limit for the detection of oligomeric traces and a consistent underestimate of the trace populations by ∼0.1% (dependent on the level of regularization). This can be overcome with a recently developed Bayesian extension of c(s) (Brown et al., Biomacromolecules, 8:2011–2024, 2007), utilizing the known regions of sedimentation coefficients for the monomer and oligomers of interest as prior expectation for the peak positions in the distribution. We show that this leads to more clearly identifiable and consistent peaks and lower theoretical limits of quantization by approximately an order of magnitude for some experimental conditions. Implications for the experimental design of SV-AUC and practical detection limits are discussed.
doi:10.1208/s12248-008-9058-z
PMCID: PMC2696691  PMID: 18814037
analytical ultracentrifugation; Bayesian analysis; hydrodynamic separation; sedimentation velocity; size-distribution; trace aggregates
4.  Pharmacogenetic and Metabolic Differences Between Dog Breeds: Their Impact on Canine Medicine and the Use of the Dog as a Preclinical Animal Model 
The AAPS journal  2008;10(1):110-119.
There is limited information describing species related pharmacogenetic differences in animals. Despite the lack of genetic information in veterinary medicine, breed specific responses to endogenous and exogenous substances have been reported across many species. This finding underscores the importance of obtaining insight into the genotypic and phenotypic variation present across breeds. This article provides a summary of the literature pertaining to canine breed differences in physiology, drug response, drug pharmacokinetics, and metabolic idiosyncrasies. The existing knowledge of pedigrees and the known phenotypes and genotypes of dogs provides important information for determining mode of inheritance, penetration, and other major characteristics of heritable traits. Understanding these breed differences will improve canine population predictions (for canine drug products) and may be of value when extrapolating toxicology data from dogs to humans.
doi:10.1208/s12248-008-9011-1
PMCID: PMC2747081  PMID: 18446511
bioavailability; breed-related differences; canine pharmacodynamics; canine pharmacogenetics; canine pharmacokinetics; drug response; population diversity
5.  A Bayesian Approach for Quantifying Trace Amounts of Antibody Aggregates by Sedimentation Velocity Analytical Ultracentrifugation 
The AAPS journal  2008;10(3):481-493.
Sedimentation velocity analytical ultracentrifugation (SV-AUC) has become an important tool for the characterization of the purity of protein therapeutics. The work presented here addresses a need for methods orthogonal to size-exclusion chromatography for ensuring the reliable quantitation of immunogenic oligomers, for example, in antibody preparations. Currently the most commonly used approach for SV-AUC analysis is the diffusion-deconvoluted sedimentation coefficient distribution c(s) method, previously developed by us as a general purpose technique and implemented in the software SEDFIT. In both practical and theoretical studies, different groups have reported a sensitivity of c(s) for trace oligomeric fractions well below the 1% level. In the present work we present a variant of c(s) designed for the purpose of trace detection, with customized Bayesian regularization. The original c(s) method relies on maximum entropy regularization providing the most parsimonious distribution consistent with the data. In the present paper, we use computer simulations of an antibody system as example to demonstrate that the standard maximum entropy regularization, due to its design, leads to a theoretical lower limit for the detection of oligomeric traces and a consistent underestimate of the trace populations by ∼0.1% (dependent on the level of regularization). This can be overcome with a recently developed Bayesian extension of c(s) (Biomacromolecules (2007), 8, 2011-2024), utilizing the known regions of sedimentation coefficients for the monomer and oligomers of interest as prior expectation for the peak positions in the distribution. We show that this leads to more clearly identifiable and consistent peaks and lower theoretical limits of quantization by approximately an order of magnitude for some experimental conditions. Implications for the experimental design of SV-AUC and practical detection limits are discussed.
doi:10.1208/s12248-008-9058-z
PMCID: PMC2696691  PMID: 18814037
sedimentation velocity; analytical ultracentrifugation; trace aggregates; hydrodynamic separation; size-distribution; Bayesian analysis
6.  Overview of the Proton-coupled MCT (SLC16A) Family of Transporters 
The AAPS journal  2008;10(2):311-321.
The transport of monocarboxylates, such as lactate and pyruvate, is mediated by the SLC16A family of proton-linked membrane transport proteins known as monocarboxylate transporters (MCTs). Fourteen MCT-related genes have been identified in mammals and of these seven MCTs have been functionally characterized. Despite their sequence homology, only MCT1-4 have been demonstrated to be proton-dependent transporters of monocarboxylic acids. MCT6, MCT8 and MCT10 have been demonstrated to transport diuretics, thyroid hormones and aromatic amino acids, respectively. MCT1-4 vary in their regulation, tissue distribution and substrate/inhibitor specificity with MCT1 being the most extensively characterized isoform. Emerging evidence suggests that in addition to endogenous substrates, MCTs are involved in the transport of pharmaceutical agents, including γ-hydroxybuytrate (GHB), 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase inhibitors (statins), salicylic acid, and bumetanide. MCTs are expressed in a wide range of tissues including the liver, intestine, kidney and brain, and as such they have the potential to impact a number of processes contributing to the disposition of xenobiotic substrates. GHB has been extensively studied as a pharmaceutical substrate of MCTs; the renal clearance of GHB is dose-dependent with saturation of MCT-mediated reabsorption at high doses. Concomitant administration of GHB and l-lactate to rats results in an approximately two-fold increase in GHB renal clearance suggesting that inhibition of MCT1-mediated reabsorption of GHB may be an effective strategy for increasing renal and total GHB elimination in overdose situations. Further studies are required to more clearly define the role of MCTs on drug disposition and the potential for MCT-mediated detoxification strategies in GHB overdose.
doi:10.1208/s12248-008-9035-6
PMCID: PMC2574616  PMID: 18523892
butyrate; gamma-hydroxybutyrate; lactate; monocarboxylate transporters; SLC16A
7.  Overview of the Proton-coupled MCT (SLC16A) Family of Transporters: Characterization, Function and Role in the Transport of the Drug of Abuse γ-Hydroxybutyric Acid 
The AAPS Journal  2008;10(2):311-321.
The transport of monocarboxylates, such as lactate and pyruvate, is mediated by the SLC16A family of proton-linked membrane transport proteins known as monocarboxylate transporters (MCTs). Fourteen MCT-related genes have been identified in mammals and of these seven MCTs have been functionally characterized. Despite their sequence homology, only MCT1–4 have been demonstrated to be proton-dependent transporters of monocarboxylic acids. MCT6, MCT8 and MCT10 have been demonstrated to transport diuretics, thyroid hormones and aromatic amino acids, respectively. MCT1–4 vary in their regulation, tissue distribution and substrate/inhibitor specificity with MCT1 being the most extensively characterized isoform. Emerging evidence suggests that in addition to endogenous substrates, MCTs are involved in the transport of pharmaceutical agents, including γ-hydroxybuytrate (GHB), 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase inhibitors (statins), salicylic acid, and bumetanide. MCTs are expressed in a wide range of tissues including the liver, intestine, kidney and brain, and as such they have the potential to impact a number of processes contributing to the disposition of xenobiotic substrates. GHB has been extensively studied as a pharmaceutical substrate of MCTs; the renal clearance of GHB is dose-dependent with saturation of MCT-mediated reabsorption at high doses. Concomitant administration of GHB and l-lactate to rats results in an approximately two-fold increase in GHB renal clearance suggesting that inhibition of MCT1-mediated reabsorption of GHB may be an effective strategy for increasing renal and total GHB elimination in overdose situations. Further studies are required to more clearly define the role of MCTs on drug disposition and the potential for MCT-mediated detoxification strategies in GHB overdose.
doi:10.1208/s12248-008-9035-6
PMCID: PMC2574616  PMID: 18523892
butyrate; gamma-hydroxybutyrate; lactate; monocarboxylate transporters; SLC16A
8.  Pharmacogenetic and Metabolic Differences Between Dog Breeds: Their Impact on Canine Medicine and the Use of the Dog as a Preclinical Animal Model 
The AAPS Journal  2008;10(1):110-119.
There is limited information describing species related pharmacogenetic differences in animals. Despite the lack of genetic information in veterinary medicine, breed specific responses to endogenous and exogenous substances have been reported across many species. This finding underscores the importance of obtaining insight into the genotypic and phenotypic variation present across breeds. This article provides a summary of the literature pertaining to canine breed differences in physiology, drug response, drug pharmacokinetics, and metabolic idiosyncrasies. The existing knowledge of pedigrees and the known phenotypes and genotypes of dogs provides important information for determining mode of inheritance, penetration, and other major characteristics of heritable traits. Understanding these breed differences will improve canine population predictions (for canine drug products) and may be of value when extrapolating toxicology data from dogs to humans.
doi:10.1208/s12248-008-9011-1
PMCID: PMC2747081  PMID: 18446511
bioavailability; breed-related differences; canine pharmacodynamics; canine pharmacogenetics; canine pharmacokinetics; drug response; population diversity
9.  PTD-mediated Loading of Tumor-Seeking Lymphocytes with Prodrug-Activating Enzymes 
The AAPS Journal  2008;10(4):614-621.
Using the approach of peptide transduction domain (PTD)-mediated loading of interleukin-2(IL-2)-activated natural killer (A-NK) cells, tumor-seeking lymphocytes, with prodrug-activating enzymes, we primarily aim to generate a cytotoxic drug selectively within tumors and minimize damage to normal tissues. A-NK cells are able to accumulate selectively at tumor sites. While these cells by themselves possess significant antitumor effect in vivo, we suggest that they can also serve as Trojan horses, by bringing anticancer agents, such as prodrug-activating enzymes, selectively to tumors. We have successfully demonstrated in a mouse model that A-NK cells can be rapidly loaded with prodrug-activating enzymes, such as alkaline phosphatase (AP) and beta-galactosidase (beta-gal), in vitro using enzyme-conjugated peptide PTD5. Upon adoptive transfer into lung-tumor-bearing animals, the loaded A-NK cells are able to bring their cargo of the prodrug-activating enzymes selectively to pulmonary metastases. The targeting of the AP to the tumor tissues is highly specific, since more than a fivefold higher concentration of AP was found in the tumor tissues compared to the surrounding normal lung tissue at 24 h after injection. The approach of transporting prodrug-activating enzymes selectively into tumors clearly shows potential for future targeted chemotherapy. Ongoing studies in our laboratory are evaluating the antitumor efficacy of cellular-dependent enzyme prodrug therapy.
doi:10.1208/s12248-008-9066-z
PMCID: PMC2628208  PMID: 19104945
activated natural killer cells; delivery; metastases in vivo; prodrug enzymes; protein transduction domain
10.  Characterization of Cyclodextrin Inclusion Complexes of the Anti-HIV Non-Nucleoside Reverse Transcriptase Inhibitor UC781 
The AAPS Journal  2008;10(4):606-613.
The highly potent anti-HIV agent UC781 is being evaluated for use in topical microbicides to prevent HIV transmission. However, UC781 is extremely hydrophobic with poor water solubility, a property that may complicate appropriate formulation of the drug. In this study, we examined the ability of several cyclodextrins, beta-cyclodextrin (βCD), methyl-beta-cyclodextrin (MβCD), and 2-hydroxylpropyl-beta-cyclodextrin (HPβCD), to enhance the aqueous solubility of UC781. Each of the cyclodextrins provided dramatic increases in UC781 aqueous solubility, the order being MβCD>HPβCD>βCD. The complexation constants (K1:1) of the inclusion complexes were determined via a phase solubility technique using high-performance liquid chromatography and showed that UC781 solubility increased linearly as a function of cyclodextrin concentration. Ultraviolet spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, and 2D 1H ROESY NMR spectroscopy were used to further characterize these UC781/cyclodextrin complexes. The inhibitory potency of UC781 and its HPβCD inclusion complex were evaluated using an in vitro HIV-1 reverse transcriptase inhibition assay The inhibitory potency of the UC781/HPβCD complex was 30-fold greater than that of UC781 alone, showing that the complexed drug is able to provide substantial inhibition of its target. The enhancement of UC781 aqueous solubility is essential for the development of a useful vaginal microbicide dosage form, and our data suggest that UC781/cyclodextrin inclusion complexes may be useful in this context.
doi:10.1208/s12248-008-9070-3
PMCID: PMC2628202  PMID: 19089644
beta-cyclodextrin inclusion complex; DSC; FTIR; HIV-1; NMR; non-nucleoside reverse transcriptase inhibitor; solubility; UC781
11.  Method to Screen Substrates of Apical Sodium-Dependent Bile Acid Transporter 
The AAPS Journal  2008;10(4):596-605.
Human apical sodium-dependent bile acid transporter (hASBT) is a potential prodrug target under study. Development of prodrugs that target hASBT may yield compounds with low solubility and/or susceptibility to hydrolysis. A transport uptake method is needed that increases compound solubility and avoids NaOH for cell lysis during postexperimental cell sample preparation. The overall goal was to develop an assay method to screen for hASBT uptake of novel compounds. The first objective was to determine the maximum cosolvent concentrations that are compatible with an hASBT active transport assay. The second objective was to develop a NaOH-free cell lysis method to process cell samples from these uptake studies. The following cosolvents were studied: dimethylacetamide (DMAC), dimethylformamide (DMF), dimethylsulfoxide (DMSO), ethanol, methanol, polyethylene glycol-400, propylene glycol, and dioxane. Initial studies included taurocholate flux studies across hASBT-Madin–Darby canine kidney monolayers using up to 10% cosolvent, as well as cytotoxicity studies. The effect of selected cosolvent concentrations on the hASBT Michaelis–Menten kinetic parameters was evaluated. Additionally, two acetonitrile-based cell lysis methods that do not use NaOH were evaluated in terms of percent sample recovery and hASBT kinetic parameters. Results showed that the maximum permissible cosolvent concentrations for hASBT uptake studies, without compromising assay results or causing cytotoxicity, are 1% DMAC, 1% DMF, 2.5% DMSO, 2.5% methanol, and 2.5% ethanol. Additionally, both NaOH-free, acetonitrile-based cell lysis methods provided similar recovery and hASBT results, compared to NaOH method. Hence, an assay method was developed to screen for active transport, allowing for cosolvents that can solubilize compounds and avoid NaOH sample treatment, which can otherwise degrade compound.
doi:10.1208/s12248-008-9069-9
PMCID: PMC2628203  PMID: 19085111
apical sodium-dependent bile acid transporter; bile acid; screen; solvent; transporter
12.  Commentary: Current Advances and Future Directions for CNS Delivery 
The AAPS Journal  2008;10(4):587-588.
doi:10.1208/s12248-008-9064-1
PMCID: PMC2628206  PMID: 19082900
blood–brain barrier; CNS; drug delivery
13.  P-gp Inhibition Potential in Cell-Based Models: Which “Calculation” Method is the Most Accurate? 
The AAPS Journal  2008;10(4):577-586.
The objective was to directly compare the four different “calculation” methods of assessing P-gp inhibition potential using experimental data obtained from ~60 structurally diverse internal research and marketed compounds. Bidirectional studies for digoxin (probe for P-gp substrate) were performed with and without test compounds (at 10 μM). Four different calculation methods were applied to the same dataset (raw bidirectional permeability values) to obtain the “percent inhibition of P-gp” for these compounds using the different methods. Significantly different inhibition potential was obtained with the “exact” same experimental dataset depending on the calculation method used. Subsequently, entirely different conclusions regarding the “inhibition potential” of test compound was reached due to the different calculation methods. Based on the direct comparison of these methods, method no. 3 (i.e., inhibition of B to A permeability of digoxin) is recommended as the calculation method ideal during screening stages due to its high throughput amenability. The methodology is capable of rapidly screening compounds with adequate reliability for early stage drug discovery. Method no. 3 provides an abridged version of a bidirectional study that is fully capable of identifying all non-inhibitors (0–20%), moderate inhibitors (20–60%), and potent inhibitors (>60%) and demonstrates high correlation with method no. 1 (inhibition based on both A to B and B to A permeability of digoxin). Nevertheless, method no. 1 might be appropriate for more detailed mechanistic studies required in late stage discovery and development.
doi:10.1208/s12248-008-9068-x
PMCID: PMC2628205  PMID: 19082742
drug–drug interactions; efflux ratio; in vitro models; P-gp inhibition; permeability
14.  Epidermal Growth Factor Receptor-Targeted Gelatin-Based Engineered Nanocarriers for DNA Delivery and Transfection in Human Pancreatic Cancer Cells 
The AAPS Journal  2008;10(4):565-576.
Type B gelatin-based engineered nanocarrier systems (GENS) have been used over the last several years as a non-condensing systemic and oral DNA delivery system. In this study, we have modified the surface of GENS with epidermal growth factor receptor (EGFR)-targeting peptide for gene delivery and transfection in pancreatic cancer cell lines. GENS were prepared by the solvent displacement method and the EGFR-targeting peptide was grafted on the surface using a hetero-bifunctional poly(ethylene glycol) (PEG) spacer. Plasmid DNA, encoding for enhanced green fluorescent protein (GFP), was efficiently encapsulated and protected from degrading enzymes in the control and surface-modified GENS. Upon incubation with EGFR over-expressing Panc-1 human pancreatic adenocarcinoma cells, the peptide-modified nanoparticles were found to be internalized efficiently by receptor-mediated endocytosis. Both quantitative and qualitative transgene expression efficiencies were significantly enhanced when plasmid DNA was administered with EGFR-targeted GENS relative to the control-unmodified gelatin or PEG-modified gelatin nanoparticle systems. Based on these preliminary results, EGFR-targeted GENS show tremendous promise as a safe and effective gene delivery vector with the potential to treat pancreatic cancer.
doi:10.1208/s12248-008-9065-0
PMCID: PMC2628214  PMID: 19034673
EGFP-N1 plasmid DNA; EGFR-targeted delivery; Panc-1 human pancreatic adenocarcinoma cells; transgene expression; type B gelatin nanoparticles
15.  Microstructural Analysis of Porous Composite Materials: Dynamic Imaging of Drug Dissolution and Diffusion Through Porous Matrices 
The AAPS Journal  2008;10(4):560-564.
doi:10.1208/s12248-008-9063-2
PMCID: PMC2628213  PMID: 19009357
dissolution and diffusion; microstructure; porous matrix; X-ray computerised microtomography
16.  Concepts and Challenges in Quantitative Pharmacology and Model-Based Drug Development 
The AAPS Journal  2008;10(4):552-559.
Model-based drug development (MBDD) has been recognized as a concept to improve the efficiency of drug development. The acceptance of MBDD from regulatory agencies, industry, and academia has been growing, yet today’s drug development practice is still distinctly distant from MBDD. This manuscript is aimed at clarifying the concept of MBDD and proposing practical approaches for implementing MBDD in the pharmaceutical industry. The following concepts are defined and distinguished: PK–PD modeling, exposure–response modeling, pharmacometrics, quantitative pharmacology, and MBDD. MBDD is viewed as a paradigm and a mindset in which models constitute the instruments and aims of drug development efforts. MBDD covers the whole spectrum of the drug development process instead of being limited to a certain type of modeling technique or application area. The implementation of MBDD requires pharmaceutical companies to foster innovation and make changes at three levels: (1) to establish mindsets that are willing to get acquainted with MBDD, (2) to align processes that are adaptive to the requirements of MBDD, and (3) to create a closely collaborating organization in which all members play a role in MBDD. Pharmaceutical companies that are able to embrace the changes MBDD poses will likely be able to improve their success rate in drug development, and the beneficiaries will ultimately be the patients in need.
doi:10.1208/s12248-008-9062-3
PMCID: PMC2628212  PMID: 19003542
drug development; modeling; pharmacodynamics; pharmacokinetics; pharmacometrics; simulation
17.  The International Patent System and Biomedical Research: Reconciling Aspiration, Policy and Practice 
The AAPS Journal  2008;10(4):526-536.
This article reviews how the international environment shapes international patent law and practice with bearing on biomedical innovation. The cluster of issues is encapsulated in two core paradoxes. The first concerns how public goods, such as new pharmaceuticals, may be produced through the deliberate creation of private rights that exclude material from the public domain. The second paradox concerns how “technological neutrality” and overall policy balance in the application of general patent law principles requires technology-specific interventions by regulators. The article illustrates how centrifugal and centripetal trends influence diverse national approaches to applying patentability criteria for pharmaceutical products.
doi:10.1208/s12248-008-9049-0
PMCID: PMC2628210  PMID: 18989789
international patent law; pharmaceutical innovation
18.  Opioid Tolerance Development: A Pharmacokinetic/Pharmacodynamic Perspective 
The AAPS Journal  2008;10(4):537-551.
The opioids are commonly used to treat acute and severe pain. Long-term opioid administration eventually reaches a dose ceiling that is attributable to the rapid onset of analgesic tolerance coupled with the slow development of tolerance to the untoward side effects of respiratory depression, nausea and decreased gastrointestinal motility. The need for effective-long term analgesia remains. In order to develop new therapeutics and novel strategies for use of current analgesics, the processes that mediate tolerance must be understood. This review highlights potential pharmacokinetic (changes in metabolite production, metabolizing enzyme expression, and transporter function) and pharmacodynamic (receptor type, location and functionality; alterations in signaling pathways and cross-tolerance) aspects of opioid tolerance development, and presents several pharmacodynamic modeling strategies that have been used to characterize time-dependent attenuation of opioid analgesia.
doi:10.1208/s12248-008-9056-1
PMCID: PMC2628209  PMID: 18989788
opioid; pharmacodynamics; pharmacokinetics; tolerance
19.  Understanding the Effect of API Properties on Bioavailability Through Absorption Modeling 
The AAPS Journal  2008;10(4):516-525.
Selection of API phase is one of the first decision points in the formulation development process. Subsequent to phase selection, the focus shifts to the API physical properties such as particle size. Oftentimes, such properties are closely monitored throughout the drug development, as they can have a direct impact on the formulation bioperformance. The purpose of this mini-review was to describe the potential for application of absorption modeling in understanding the effect of API properties on bioavailability. Examples are provided to demonstrate how absorption modeling can be applied both early on to set the formulation strategy as well as during the development process to help with setting of specifications around the API. Limitations of the existing models and areas of possible expansion of such tools are also discussed.
doi:10.1208/s12248-008-9061-4
PMCID: PMC2628211  PMID: 19002590
absorption modeling; API properties; bioavailability; formulation; oral absorption
20.  Preparation of Alendronate Liposomes for Enhanced Stability and Bioactivity: In Vitro and In Vivo Characterization 
The AAPS Journal  2008;10(4):505-515.
Liposomes containing bisphosphonates have been shown to deplete circulating monocytes and reduce experimental restenosis. However, acceptable shelf life was not achieved, and the disruption extent and rate of the vesicles in the circulation has not been examined. Designing an optimal liposomal formulation in general, and for an anti-inflammatory effect in particular, requires careful consideration of the factors that contribute to their in vitro stability and integrity in the blood after injection. An improved liposomal alendronate formulation was prepared by a modified thin lipid film hydration technique followed by extrusion, resulting in relatively smaller size vesicles, narrow size distribution, and low drug to lipid ratio in comparison to the reverse phase evaporation method. In order to rule out premature leakage of the drug, the integrity of the vesicles was examined by means of size-exclusion chromatography in vitro and in vivo, with subsequent analysis of size, drug (fractions of encapsulated and free) and lipid concentrations. Vesicles were found to be stable in serum, with 15 ± 3% leakage of the drug after 10 min in rabbit’s circulation, and intact liposomes were detected in the circulation 24 h following administration. It is concluded that the new formulation results in increased stability (2.5 years) as determined by the insignificant changes in vesicle size, drug leakage, lipid and drug stability, in vitro bioactivity (macrophages inhibition), as well as in vivo in depleting circulating monocytes and inhibition of restenosis in rabbits. Our in vitro stability results regarding dilution in serum paralleled in vivo data. Thus, in vitro assessment may provide a valuable tool in assessing in vivo integrity of liposomal formulations.
doi:10.1208/s12248-008-9060-5
PMCID: PMC2628204  PMID: 18937071
alendronate; formulation; leakage; liposomes; macrophages; monocytes; restenosis; stability; vesicles
21.  Surface Energy of Microcrystalline Cellulose Determined by Capillary Intrusion and Inverse Gas Chromatography 
The AAPS Journal  2008;10(3):494-503.
Surface energy data for samples of microcrystalline cellulose have been obtained using two techniques: capillary intrusion and inverse gas chromatography. Ten microcrystalline cellulose materials, studied using capillary intrusion, showed significant differences in the measured surface energetics (in terms of total surface energy and the acid–base characteristics of the cellulose surface), with variations noted between the seven different manufacturers who produced the microcrystalline cellulose samples. The surface energy data from capillary intrusion was similar to data obtained using inverse gas chromatography with the column maintained at 44% relative humidity for the three samples of microcrystalline cellulose studied. This suggests that capillary intrusion may be a suitable method to study the surface energy of pharmaceutical samples.
doi:10.1208/s12248-008-9057-0
PMCID: PMC2761700  PMID: 18841480
capillary intrusion; dynamic contact angle; excipient; inverse gas chromatography; microcrystalline cellulose; surface energy
23.  Evaluation of a Scaling Approach for the Bioequivalence of Highly Variable Drugs 
The AAPS Journal  2008;10(3):450-454.
Various approaches for evaluating the bioequivalence (BE) of highly variable drugs (CV ≥ 30%) have been debated for many years. More recently, the FDA conducted research to evaluate one such approach: scaled average BE. A main objective of this study was to determine the impact of scaled average BE on study power, and compare it to the method commonly applied currently (average BE). Three-sequence, three period, two treatment partially replicated cross-over BE studies were simulated in S-Plus. Average BE criteria, using 80–125% limits on the 90% confidence intervals for Cmax and AUC geometric mean ratios, as well as scaled average BE were applied to the results. The percent of studies passing BE was determined under different conditions. Variables tested included within subject variability, point estimate constraint, and different values for σw0, which is a constant set by the regulatory agency. The simulation results demonstrated higher study power with scaled average BE, compared to average BE, as within subject variability increased. At 60% CV, study power was more than 90% for scaled average BE, compared with about 22% for average BE. A σw0 value of 0.25 appears to work best. The results of this research project suggest that scaled average BE, using a partial replicate design, is a good approach for the evaluation of BE of highly variable drugs.
doi:10.1208/s12248-008-9053-4
PMCID: PMC2761698  PMID: 18726698
bioequivalence; highly variable drugs; scaled bioequivalence; simulations
24.  Comparison of Neutralizing Antibody Assays for Receptor Binding and Enzyme Activity of the Enzyme Replacement Therapeutic Naglazyme® (Galsulfase) 
The AAPS Journal  2008;10(3):439-449.
Most patients receiving Naglazyme® (galsulfase, rhASB) enzyme replacement therapy for mucopolysaccharidosis type VI develop an antibody response. To evaluate the impact of this response, two in vitro neutralizing antibody (NAb) assays were developed based on the two steps of the mechanism of action. Neutralization of enzyme activity was detected by inhibition of rhASB cleavage of a fluorogenic substrate. Neutralization of receptor binding was detected by decreased binding of labeled rhASB to immobilized soluble receptor. For the enzyme activity NAb assay, serum pretreatment was required to isolate antibodies from interfering phosphate ions, with sensitivity of ≤5 μg/mL. The receptor binding NAb assay used a five-fold dilution, with sensitivity of ≤40 μg/mL. Cutpoints for percent inhibition were based on 95% confidence intervals from naïve sera. Clinical samples were similarly likely to be positive in both assays than positive for neutralization of only one step in the mechanism of action. The two NAb assays yielded complementary information about potential neutralization of rhASB. Relative estimated sensitivity between neutralization assays did not correlate with the number of positive clinical samples or patients. In vitro NAb assays based on a well-understood mechanism of action provide specific information about the NAb mechanism.
doi:10.1208/s12248-008-9048-1
PMCID: PMC2761696  PMID: 18709516
enzyme replacement therapy; immunogenicity; naglazyme; neutralizing antibody; MPS VI
25.  Evaluation of Nanosuspensions for Absorption Enhancement of Poorly Soluble Drugs: In Vitro Transport Studies Across Intestinal Epithelial Monolayers 
The AAPS Journal  2008;10(3):435-438.
doi:10.1208/s12248-008-9050-7
PMCID: PMC2761697  PMID: 18690542
absorption; bioavailability enhancement; Caco-2 cells; low soluble drugs; nanosuspensions

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