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1.  O-Phospho-L-Serine, Multi-functional Excipient for B Domain Deleted Recombinant Factor VIII 
The AAPS journal  2007;9(2):E251-E259.
Factor VIII (FVIII) is an important cofactor in the blood coagulation cascade. A deficiency or dysfunction of FVIII causes hemophilia A, a life-threatening bleeding disorder. FVIII circulates in plasma as a heterodimer comprising 6 domains (heavy chain, A1-A2-B and light chain, A3-C1-C2). Replacement therapy using FVIII is the leading therapy in the management of hemophilia A. However, ∼15% to 30% of patients develop inhibitory antibodies that neutralize the activity of the protein. Neutralizing antibodies to epitopes in the lipid binding region of FVIII are commonly identified in patients’ plasma. In this report, we investigated the effect of O-phospho-L-serine (OPLS), which binds to the lipid binding region, on the immunogenicity of B domain deleted recombinant factor VIII (BDDrFVIII). Sandwich enzyme-linked immunosorbent assay (ELISA) studies showed that OPLS specifically bind to the lipid binding region, localized in the C2 domain of the coagulation factor. Size exclusion chromatography and fluorescence anisotropy studies showed that OPLS interfered with the aggregation of BDDrFVIII. Immunogenicity of free-vs BDDrFVIII-OPLS complex was evaluated in a murine model of hemophilia A. Animals administered subcutaneous (sc) injections of BDDrFVIII-OPLS had lower neutralizing titers compared with animals treated with BDDrFVIII alone. Based on these studies, we hypothesize that specific molecular interactions between OPLS and BDDrFVIII may improve the stability and reduce the immunogenicity of BDDrFVIII formulations.
doi:10.1208/aapsj0902028
PMCID: PMC2573386  PMID: 17907766
B domain deleted recombinant factor VIII; O-phospho-L-serine; protein formulation; excipient; physical stability; immunogenicity; inhibitor development
2.  O-phospho-L-serine, multi-functional excipient for B domain deleted recombinant factor VIII 
The AAPS Journal  2007;9(2):E251-E259.
Factor VIII (FVIII) is an important cofactor in the blood coagulation cascade. A deficiency or dysfunction of FVIII causes hemophilia A, a life-threatening bleeding disorder. FVIII circulates in plasma as a heterodimer comprising 6 domains (heavy chain, A1-A2-B and light chain A3-C1-C2). Replacement therapy using FVIII is the leading therapy in the management of hemophilia A. However, ∼15% to 30% of patients develop inhibitory antibodies that neutralize the activity of the protein. Neutralizing antibodies to epitopes in the lipid binding region of FVIII are commonly identified in patients' plasma. In this report, we investigated the effect of O-phospho-L-serine (OPLS), which binds to the lipid bindinding region, on the immunogenicity of B domain deleted recombinant factor VIII (BDDrFVIII). Sandwich enzyme-linked immunosorbent assay (ELISA) studies showed that OPLS specifically bind to the lipid binding region, localized in the C2 domain of the coagulation factor. Size exclusion chromatography and fluorescence anisotropy studies showed that OPLS interfered with the aggregation of BDDrFVIII. Immunogenicity of free-vs BDDrFVIII-OPLS complex was evaluated in a murine model of hemophilia A. Animals administered subcutaneous (sc) injections of BDDrFVIII-OPLS had lower neutralizing titers compared with animals treated with BDDRFVIII alone. Based on these studies, we hypothesize that specific molecular interactions between OPLS and BDDrFVIII may improve the stability and reduce the immunogenicity of BDDrFVIII formulations.
doi:10.1208/aapsj0902028
PMCID: PMC2573386  PMID: 17907766
B domain deleted recombinant factor VIII; O-phospho-L-serine; protein formulation; excipient; physical stability; immunogenicity; inhibitor development
3.  Pharmacokinetics in mice implanted with xenografted tumors after intravenous administration of tasidotin (ILX651) or its carboxylate metabolite 
The AAPS Journal  2007;9(3):E378-E387.
The pharmacokinetics of tasidotin (ILX651), a depsipeptide currently in phase II for the treatment of advanced solid tumors, and tasidotin-C-carboxylate, the main metabolite, were characterized in male nude mice implanted with LOX tumors, which are sensitive to tasidotin, or H460 tumors, which are resistant to tasidotin. The pharmacokinetics of tasidotin and its metabolites were characterized after singledose administration of tasidotin (20 and 120 mg/kg), tasidotin-C-carboxylate (150 mg/kg), or tasidotin (53 mg/kg) in the presence and absence of Z-prolyl prolinal (5 mg/kg administered 1 hour prior to tasidotin administration), a competitive antagonist of prolyl oligopeptidase, the enzyme responsible for the metabolism of tasidotin to tasidotin-C-carboxylate. A secondary study was done comparing tumor growth in tasidotin-treated mice with implanted LOX tumors in the presence and absence of Z-prolyl-prolinal. After tasidotin administration, the pharmacokinetics of tasidotin and tasidotin-C-carboxylate were similar in plasma and tumors in LOX- and H460-implanted mice, indicating the resistance was not due to pharmacokinetic factors. Tumor carboxylate concentrations were much higher than in plasma after tasidotin administration. The metabolite appeared to contribute ∼17% to 33% to the total exposure in LOX tumors and 20% to 49% in H460 tumors but <5% in plasma. Less than 5% of the administered tasidotin dose was converted to tasidotin-C-carboxylate, with no apparent differences between LOX- and H460-treated animals. The presence of Z-prolyl-prolinal decreased the amount of tasidotin converted to tasidotin-C-carboxylate from 5.5% to 0.90%, a reduction of almost 80%. After tasidotin-C-carboxylate administration, the half-life was on the order of minutes compared with hours when observed after tasidotin administration. Tasidotin-C-carboxylate elimination was not dependent on tasidotin pharmacokinetics, suggesting that the rate of efflux from cells into plasma was the rate-limiting step in its elimination. Tasidotin-C-carboxylate was also further metabolized to desprolyl-tasidotin-C-carboxylate, although the metabolite ratios were <10%. Pretreatment with Z-prolyl-prolinal completely abolished the antitumor activity of tasidotin, indicating that the metabolite is the main moiety responsible for activity and that, despite tasidotin itself having activity in vitro, tasidotin is acting mainly as a prodrug.
doi:10.1208/aapsj0903045
PMCID: PMC2751490  PMID: 18170985
Depsipeptide; solid tumors; metabolite kinetics; ILX651; prolyl oligopeptidase
4.  Preparation and ocular pharmacokinetics of ganciclovir liposomes 
The AAPS Journal  2007;9(3):E371-E377.
Ophthalmic liposomes of ganciclovir (GCV) were prepared by the reverse phase evaporation method, and their ocular pharmacokinetics in albino rabbits were compared with those obtained after dosing with GCV solution. The in vitro transcorneal permeability of GCV liposomes was found to be 3.9-fold higher than that of the solution. After in vivo instillation in albino rabbits, no difference was found in the precorneal elimination rate of GCV from liposome vs solution dosing. The aqueous humor concentration-time profiles of both liposomes and solution were well described by 2-compartmental pharmacokinetics with first-order absorption. The area under the curve of the aqueous humor concentration-time profiles of GCV liposomes was found to be 1.7-fold higher than that of GCV solution. Ocular tissue distribution of GCV from liposomes was 2 to 10 times higher in the sclera, cornea, iris, lens, and vitreous humor when compared with those observed after solution dosing. These results suggested that liposomes may hold some promise in ocular GCV delivery.
doi:10.1208/aapsj0903044
PMCID: PMC2751489  PMID: 18170984
Ganciclovir; liposomes; precorneal clearance; ocular pharmacokinetics
5.  Characterization of the distribution, polymorphism, and stability of nimodipine in its solid dispersions in polyethylene glycol by micro-Raman spectroscopy and powder x-ray diffraction 
The AAPS Journal  2007;9(3):E361-E370.
In the present study, a series of solid dispersions of the drug nimodipine using polyethylene glycol as carrier were prepared following the hot-melt method. Micro-Raman spectroscopy in conjunction with X-ray powder diffractometry was used for the characterization of the solid structure, including spatial distribution, physical state, and presence of polymorphs, as well as storage stability of nimodipine in its solid formulations. The effect of storage time on drug stability was investigated by examination of the samples 6 months and 18 months after preparation. Confocal micro-Raman mapping performed on the samples showed that the drug was not uniformly distributed on a microscopic level. The presence of crystals of nimodipine with sizes varying between one and several micrometers was detected, and the crystal size seemed to increase with overall drug content. In samples examined 6 months after preparation it was found that the crystals existed mainly as the racemic compound, whereas after 18 months of storage mainly crystal conglomerates were observed.
doi:10.1208/aapsj0903043
PMCID: PMC2751488  PMID: 18170983
Solid dispersion; nimodipine; Raman spectroscopy; polymorphism
6.  Determination of carryover and contamination for mass spectrometry-based chromatographic assays 
The AAPS Journal  2007;9(3):E353-E360.
The Third American Association of Pharmaceutical Scientists/Food and Drug Administration Bioanalytical Workshop, held in 2006, reviewed and evaluated current practices and proposed that carryover and contamination be assessed not only during the validation of an assay but also during the application of the method in a study. In this article, the potential risks of carryover and contamination in each stage of a bioanalytical method are discussed, to explain to the industry why this recommendation is being made.
doi:10.1208/aapsj0903042
PMCID: PMC2751487  PMID: 18170982
Carryover; contamination; extraction; chromatography; detection; bioanalysis; accuracy; precision; memory effect
7.  Preparation and in vivo evaluation of SMEDDS (self-microemulsifying drug delivery system) containing fenofibrate 
The AAPS Journal  2007;9(3):E344-E352.
The present work was aimed at formulating a SMEDDS (self-microemulsifying drug delivery system) of fenofibrate and evaluating its in vitro and in vivo potential. The solubility of fenofibrate was determined in various vehicles. Pseudoternary phase diagrams were used to evaluate the microemulsification existence area, and the release rate of fenofibrate was investigated using an in vitro dissolution test. SMEDDS formulations were tested for microemulsifying properties, and the resultant microemulsions were evaluated for clarity, precipitation, and particle size distribution. Formulation development and screening was done based on results obtained from phase diagrams and characteristics of resultant microemulsions. The optimized formulation for in vitro dissolution and pharmacodynamic studies was composed of Labrafac CM10 (31.5%), Tween 80 (47.3%), and polyethylene glycol 400 (12.7%). The SMEDDS formulation showed complete release in 15 minutes as compared with the plain drug, which showed a limited dissolution rate. Comparative pharmacodynamic evaluation was investigated in terms of lipid-lowering efficacy, using a Triton-induced hypercholesterolemia model in rats. The SMEDDS formulation significantly reduced serum lipid levels in phases I and II of the Triton test, as compared with plain fenofibrate. The optimized formulation was then subjected to stability studies as per International Conference on Harmonization (ICH) guidelines and was found to be stable over 12 months. Thus, the study confirmed that the SMEDDS formulation can be used as a possible alternative to traditional oral formulations of fenofibrate to improve its bioavailability.
doi:10.1208/aapsj0903041
PMCID: PMC2751486  PMID: 18170981
Fenofibrate; SMEDDS; pseudoternary phase diagrams; Triton-induced hyperlipidemia
8.  Confirmatory reanalysis of incurred bioanalytical samples 
The AAPS Journal  2007;9(3):E336-E343.
Bioanalytical methods used to support the drug development process are validated to ensure that they function in the manner in which they are intended. “Incurred” or study samples can vary in their composition when compared with the standards and quality control samples used to validate the method and analyze these samples. During the 3rd American Association of Pharmaceutical Scientists(AAPS)/Food and Drug Administration(FDA) Bioanalytical Workshop, it was suggested that the reproducibility in the analysis of incurred samples be evaluated in addition to the usual prestudy validation activities performed. This manuscript provides recommendations concerning the number and types of samples that should be analyzed in such an evaluation, as well as the manner in which the resultant data should be analyzed. Suggestions as to follow-up activities and data reporting are also discussed. This approach is at best a beginning and is offered as a platform for future discussion, comments, and revision.
doi:10.1208/aapsj0903040
PMCID: PMC2751485  PMID: 18170980
Bioanalytical; incurred samples; LC/MS/MS; ELISA; immunoassay; reproducibility
9.  Polyoxyethylene 40 stearate modulates multidrug resistance and enhances antitumor activity of vinblastine sulfate 
The AAPS Journal  2007;9(3):E329-E335.
Multidrug resistance (MDR) is one of the major obstacles limiting the efficacy of cancer chemotherapy. Identification of new and effective MDR reversal agents is needed. In this study, the effects of polyoxyethylene 40 stearate (PS40) on MDR were evaluated via the transport of the P-glycoprotein (P-gp) substrate vinblastine sulfate (VBL) through Caco-2 cell monolayers and rat intestine tissue. The effects of PS40 on the antitumor activity of VBL were examined through 3-(4,5)-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity assay and multidrug-resistant tumor-bearing mice. Results of the transport experiments showed that PS40 reduced VBL efflux. The cytotoxicity of vinblastine to K562/ADR cells was significantly enhanced when the cells were cotreated with 100 or 150 μg/mL PS40. In vivo data revealed that average tumor volume and average tumor weight were significantly less in the VBL+PS40 group than in the VBL group. The inhibition rate for tumor growth was increased from 0.06 (VBL group) to 0.84 (VBL+PS40 group). These results suggest that PS40 may be a potentially useful adjuvant to enhance the therapeutic effects of P-gp substrates.
doi:10.1208/aapsj0903039
PMCID: PMC2751484  PMID: 18170979
Polyoxyethylene 40 stearate; P-glycoprotein; vinblastine sulfate; Caco-2; nude mice; K562/ADR
12.  Fish pharmacokinetics database updated 
The AAPS Journal  2007;9(3):E325.
doi:10.1208/aapsj0903036
PMCID: PMC2751481
13.  Basic of US patents and the patent system 
The AAPS Journal  2007;9(3):E317-E324.
The patent system plays an important role in stimulating the economy and advancing the quality of life in the United States. It serves as an incentive for innovation by giving inventors an exclusive right to their inventions for a limited period of time. It also increases and hastens the publication of useful knowledge by requiring inventors to disclose their invention to the public. Patents are particularly important in the pharmaceutical and biotechnology industries because they provide a mechanism by which the extremely high product development costs may be recouped. The United States Patent and Trademark Office acts as a gatekeeper in the patent system to prevent patents that do not meet the legal requirements from being thrust on the public. The legal requirements for obtaining a patent are discussed, particularly as they related to pharmaceutical and biotechnological inventions. The process of examining an application for a patent is briefly described, along with some of the burdens faced by examiners when deciding the patentability of therapy-related inventions.
doi:10.1208/aapsj0903035
PMCID: PMC2751480  PMID: 17915834
Patent; pharmaceutical; biotechnology; utility; description; obviousness; examiner
14.  The influence of market exclusivity on drug availability and medical innovations 
The AAPS Journal  2007;9(3):E312-E316.
The interpretation and application of intellectual property laws is enormously complex in the pharmaceutical industry, with companies needing to obtain multiple patents to fully protect their innovations. While patents provide important incentives for biomedical innovation and ecoinomic growth, concern has been expressed over the growing number of patents, the granting of patents on basic research tools (eg, genetically engineered animals), and the possibility that these legal protections may ultimately inhibit scientific advancement.
doi:10.1208/aapsj0903034
PMCID: PMC2751479  PMID: 17915833
Intellectual property; FDA; patents; Hatch-Waxman; market exclusivity; orphan drug exclusivity; pediatric exclusivity; patent term restoration; generic drugs; ANDA
15.  Intellectual property policy in the pharmaceutical sciences: The effect of inappropriate patents and market exclusivity extensions on the health care system 
The AAPS Journal  2007;9(3):E306-E311.
Though patents are effective tools for promoting innovation and protecting intellectual property in the pharmaceutical sciences, there has been growing concern about 2 important ways that patents in this field can have a negative effect on patient care and the practice of medicine. First, inventors can seek and receive patents on pharmaceutical products or research tools that stretch the statutory requirements for patenting. Second, patent holders in the pharmaceutical market can used legal loopholes or aspects of the patent registration system to extend exclusivity for inventions beyond what was anticipated by the Patent Act or subsequent legislation. The monopoly control bestowed by such inappropriate patents or manipulation of the patent system can limit options available to patients, increase the cost of health care delivery, and make cooperative research more difficult. In response, several different government and market-based efforts have emerged to promote more equitable patent policy in health care that encourages dissemination of ideas while still supporting the development of innovative products.
doi:10.1208/aapsj0903033
PMCID: PMC2751478  PMID: 17915832
Patent; intellectual property; health care costs; innovation
16.  Inactivation of hepatic enzymes by inhalant nitrite—In vivo and in vitro studies 
The AAPS Journal  2007;9(3):E298-E305.
We examined the effects of acute isobutyl nitrite (ISBN) exposure on the activity of several hepatic enzymes. Two strains of adult male mice (Balb/c and C57BL/6) were exposed to 900 ppm ISBN or ambient air for 45 minutes. The enzyme activity of hepatic cytochrome P450 (CYP)-mediated deethylation, glutathione S-transferase (GST), and carboxylesterase (CBE) was monitored through the substrates 3-cyano-7-ethoxycoumarin (CEC), 1-chloro-2,4-dinitrobenzene, and p-nitrophenyl acetate, respectively. Acute ISBN exposure led to a significant reduction in hepatic CYP-mediated CEC deethylation, GST, and CBE activity in Balb/c mice (of 81.5%, 74.7%, and 25.2%, respectively, vs control mice, each at P<.05) when livers were harvested immediately after inhalant exposure. The corresponding decreases in C57BL/6 mice were smaller (with reductions of 21.8%, 18.8%, and 13.3%, respectively, each at P<.05). This enzyme activity, tested in C57BL/6 mice only, returned to control values after a 24-hour period of nonexposure. Follow-up mechanistic investigations using rat liver GST indicated that ISBN-mediated enzyme inactivation was not caused by its metabolites: inorganic nitrite ion (NO2−) or nitric oxide. This inactivation could be prevented, but not reversed, by added glutathione, suggesting irreversible protein oxidation. Using different NO donors as comparative agents, we found that GST inactivation by ISBN was not associated with protein S-nitrosylation or disulfide formation, but with tyrosine nitration. Inhalant nitrite exposure, therefore, led to a significant reduction in hepatic enzyme activity in mice, possibly through tyrosine nitration of hepatic proteins. This effect raises the possibility of drug-drug metabolic interactions from inhalant nitrite abuse. However, determining the applicability of these findings to humans will require further study.
doi:10.1208/aapsj0903032
PMCID: PMC2751477  PMID: 17915831
Inhalant nitrite; liver; enzyme; metabolism; glutathione-S-transferase; nitration; S-nitrosylation
17.  Biomarkers, metabonomics, and drug development: Can inborn errors of metabolism help in understanding drug toxicity? 
The AAPS Journal  2007;9(3):E284-E297.
Application of “omics” technology during drug discovery and development is rapidly evolving. This review evaluates the current status and future role of “metabonomics” as a tool in the drug development process to reduce the safety-related attrition rates and bridge the gaps between preclinical and clinical, and clinical and market. Particularly, the review looks at the knowledge gap between the pharmaceutical industry and pediatric hospitals, where metabonomics has been successfully applied to screen and treat newborn babies with inborn errors of metabolism. An attempt has been made to relate the clinical pathology associated with inborn errors of metabolism with those of drug-induced pathology. It is proposed that extending the metabonomic biomarkers used in pediatric hospitals, as “advanced clinical chemistry” for preclinical and clinical drug development, is immediately warranted for better safety assessment of drug candidates. The latest advances in mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy should help replace the traditional approaches of laboratory clinical chemistry and move the safety evaluation of drug candidates into the new millennium.
doi:10.1208/aapsj0903031
PMCID: PMC2751476  PMID: 17915830
Biomarkers; clinical chemistry; drug develoment; inborn errors of metabolism; metabonomics; toxicity
18.  Advanced pharmacokinetic models based on organ clearance, circulatory, and fractal concepts 
The AAPS Journal  2007;9(2):E268-E283.
Three advanced models of pharmacokinetics are described. In the first class are physiologically based pharmacokinetic models based on in vitro data on transport and metabolism. The information is translated as transporter and enzyme activities and their attendant heterogeneities into liver and intestine models. Second are circulatory models based on transit time distribution and plasma concentration time curves. The third are fractal models for nonhomogeneous systems and non-Fickian processes are presented. The usefulness of these pharmacokinetic models, with examples. is compared.
doi:10.1208/aapsj0902030
PMCID: PMC2751417  PMID: 17907768
Pharmacokinetic models; physiologically based pharmacokinetic; PBPK; models; liver; kidney; circulatory models; distribution; fractal models; homogeneous; nonhomogeneous
19.  Appropriate calibration curve fitting in ligand binding assays 
The AAPS Journal  2007;9(2):E260-E267.
Calibration curves for ligand binding assays are generally characterized by a nonlinear relationship between the mean response and the analyte concentration. Typically, the response exhibits a sigmoidal relationship with concentration. The currently accepted reference model for these calibration curves is the 4-parameter logistic (4-PL) model, which optimizes accuracy and precision over the maximum usable calibration range. Incorporation of weighting into the model requires additional effort but generally results in improved calibration curve performance. For calibration curves with some asymmetry, introduction of a fifth parameter (5-PL) may further improve the goodness of fit of the experimental data to the algorithm. Alternative models should be used with caution and with knowledge of the accuracy and precision performance of the model across the entire calibration range, but particularly at upper and lower analyte concentration areas, where the 4-and 5-PL algorithms generally outperform alternative models. Several assay design parameters, such as placement of calibrator concentrations across the selected range and assay layout on multiwell plates, should be considered, to enable optimal application of the 4- or 5-PL model. The fit of the experimental data to the model should be evaluated by assessment of agreement of nominal and model-predicted data for calibrators.
doi:10.1208/aapsj0902029
PMCID: PMC2751416  PMID: 17907767
Ligand-binding assay; nonlinear calibration; 4/5-parameter logistic models; assay design parameters
20.  Biodegradable intraprostatic doxorubicin implants 
The AAPS Journal  2007;9(2):E241-E250.
Systemic chemotherapy is not effective in the treatment of prostate-confined cancer. We developed biodegradable, doxorubicin-loaded cylinders for intraprostatic implantation and evaluated the feasibility of using regional intraprostatic drug therapy to treat prostate-confined cancer. Cylinders were prepared using poly(lactide-co-glycolide) (PLG) or PLG copolymers. The in vitro and in vivo drug release, intraprostatic pharmacokinetics, and histopathology in dogs implanted with the cylinders were studied. The doxorubicin-loaded cylinders made of PLG polymers of 7.9 to 54 kDa molecular weight (MW) had a diameter of ∼800 μm, drug loading of 10% to 30% (wt/wt), and even distribution of crystalline drug throughout the matrix. Burst release varied from 3% to 73%, and 7-day cumulative release from 4% to 90%. Decreasing polymer MW and increasing drug loading were associated with higher initial burst release and overall release rates. The in vivo drug release from cylinders (33-kDa PLG, 30% drug loading) in dog prostates was rapid (∼80% in 48 hours). Spatial drug distribution, visualized using confocal fluorescence microscopy, showed high concentrations confined to the lobule containing the implant (referred to as the implanted lobule), with steep concentration gradients over the septa separating the lobules. Concentrations in the implanted lobule were about 8 times higher than concentrations delivered by an intravenous injection. The implants caused necrotic cell death in the implanted lobule, without damage to prostatic nerve bundles or the urethra. These results indicate the feasibility of using biodegradable PLG cylinders as intraprostatic implants to selectively deliver high drug concentrations to prostate tissue.
doi:10.1208/aapsj0902027
PMCID: PMC2751414  PMID: 17907765
PLG; doxorubicin; prostate delivery; controlled release; biodegradable implants
21.  Varying polymer architecture to deliver drugs 
The AAPS Journal  2007;9(2):E235-E240.
Variable architecture polymers are of considerable interest for the delivery of therapeutic biopolymers, such as DNA and proteins, to their site of action. Polymers that can respond with a change in conformation to biologically relevant stimuli, such as temperature and pH, are being carefully designed to take advantage of the change in environmental conditions the polymer-drug conjugate encounters upon progression from larger-scale systems in the body to subcellular compartments. Viruses respond to changes in the cellular environment to gain access to their desired region of cells, and much can be learned from the mechanisms they employ in this effort. However, despite the efficiency of therapeutic biopolymers, undersirable immune and inflammatory responses may result from their repeated administration, so synthetic polymers are an attractive alternative. This mini-review examines a range of recently developed variable architecture polymers, mainly focusing on polymers responsive to temperature and pH, covering both synthetic copolymers and derivatives of naturally occurring polymers for advanced drug delivery applications. The polymers discussed in the article have some of the properties that are most important for polymer drug delivery vehicles to be effective, such as biodegradability, specificity, and biocompatibility.
doi:10.1208/aapsj0902026
PMCID: PMC2751413  PMID: 17907764
Smart polymers; drug delivery; biotherapeutics
22.  Reproductible production of a PEGylated dual-acting peptide for diabetes 
The AAPS Journal  2007;9(2):E227-E234.
A pEGylated glucagon-like peptide-1 (GLP-1) agonist and glucagon antagonist hybrid peptide was engineered as a potential treatment for type 2 diabetes. To support preclinical development of this PEGylated dual-acting peptide for diabetes (DAPD), we developed a reproducible method for PEGylation, purification, and analysis. Optimal conditions for site-specific PEGylation with 22 and 43 kDa maleimide-polyethylene glycol (maleimide-PEG) polymers were identified by evaluating pH, reaction time, and reactant molar ratio parameters. A 3-step purification process was developed and successfully implemented to purify PEGylated DAPD and remove excess uncoupled PEG and free peptide. Five lots of 43 kDa PEGylated DAPD with starting peptide amounts of 100 mg were produced with overall yields of 53% to 71%. Analytical characterization by N-terminal sequencing, amino acid analysis, matrix-assisted laser desorption/ionization mass spectrometry, and GLP-1 receptor activation assay confirmed site-specific attachment of PEG at the engineered cysteine residue, expected molecular weight, correct amino acid sequence and composition, and consistent functional activity. Purity and safety analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), analytical ion-exchange chromatography, reversed-phase high-performance liquid chromatography, and limulus amebocyte lysate test showed that the final products contained<1% free peptide, <5% uncoupled PEG, and <0.2 endotoxin units per milligram of peptide. These results demonstrate that the PEGylation and purification process we developed was consistent and effective in producing PEGylated DAPD preclinical materials at the 100 mg (peptide weight basis) or 1.2 g (drug substance weight basis) scale.
doi:10.1208/aapsj0902025
PMCID: PMC2751412  PMID: 17907763
PEGylation; chromatography; GLP-1; glucagon
23.  2007 highlights of advances in the pharmaceutical sciences: An American Association of Pharmaceutical Scientists (AAPS) perspective 
The AAPS Journal  2007;9(2):E219-E226.
The American Association of Pharmaceutical Scientists (AAPS) covers the full range of areas of expertise associated with the resolution of concerns pertaining to drugs and drug products. This editorial highlights the initiatives, issues, and challenges that are the forefront of the pharmaceutical sciences in 2007. It also provides an overview of how these difficult questions are being addressed through the programs and events associated with the AAPS 2007 Annual Meeting that will be held at the San Diego, California, Convention Center from November 11 to 15, 2007.
doi:10.1208/aapsj0902024
PMCID: PMC2751411
dose predictions; product design; product quality control; population kinetics; dose individualization; regulatory sciences; pharmacostatistics; process analytical technology; medical imagining; quantitative pharmacology; dissolution; biotechnology
24.  Population pharmacokinetics of S(−)-carvedilol in healthy volunteers after administration of the immediate-release (IR) and the new controlled-release (CR) dosage forms of the racemate 
The AAPS Journal  2007;9(2):E208-E218.
Carvedilol is a β1-, β1-, and α1-adrenoreceptor blocker indicated for treatment of hypertension and mild-tosevere congestive heart failure. The objective of this study was to develop and evaluate a single population model that describesS(−)-carvedilol pharmacokinetics from both the immediate-release (IR) and the new controlled-release dosage forms of the racemate. Carvedilol IR data (1270 measurements) were obtained from 2 open-label studies (50 mg/25 mg Q12 hours for 2 doses). Carvedilol CR data (2058 measurements) were obtained from an open-label, nonrandomized, dose-rising (10, 20, 40, and 80 mg), 4-period balanced crossover study. All data were simultaneously analyzed using NONMEM V. Leverage analysis and internal evaluations were conducted for the final model. A 2-compartment model with first-order absorption and elimination provided the best fit. The model included different absorption rates (KAs) for the CR and IR morning (IRAM) and evening (IRPM) doses; incorporating change-points at certain times. Estimates of KAs indicated that the absorption was slower at equivalent times and extended for CR relative to IR carvedilol. Oral clearance ofS(−)-carvedilol was 149 L/h. The IRPM and the CR doses had bioavailability (Frel) of 0.80 and 0.76, respectively, relative to the IRAM dose. The inter-subject variability in KAs was lower for the CR dosage form than the original IR dosage form. Estimation of interoccasion variability on KAs and Frel for the CR dosage form improved the fit. The model performed well in simulation and leverage analysis indicated its robustness. The model will be a useful tool for future simulation studies.
doi:10.1208/aapsj0902023
PMCID: PMC2751410  PMID: 17614362
Carvedilol; controlled-release; NONMEM; relative bioavailability; population analysis
25.  Polymer-drug conjugates as modulators of cellular apoptosis 
The AAPS Journal  2007;9(2):E200-E207.
The successful clinical application of polymer-protein conjugates (PE Gylated enzymes and cytokines) and the promising results arising from clinical trials with polymerbound chemotherapy (eg, doxorubicin or paclitaxel) have established their potential to reduce toxicity and improve activity in chemotherapy-refractory patients. Furthermore, and more important, they have also provided a firm foundation for more sophisticated second-generation constructs that deliver the newly energing target-directed bioactive agents (eg, modulators of apoptosis, cell cycle, anti-angiogenic drugs) in addition to polymer-based drug combinations (eg, endocrine therapy and chemotherapy). This review will focus on polymer-drug conjugate modulators of cellular apoptosis to be used as single pro-poptotic (eg, cancer) or anti-apoptotic (eg, ischemia) agents or as a combination therapy.
doi:10.1208/aapsj0902022
PMCID: PMC2751409  PMID: 17907762
Polymer-drug conjugates; apoptosis modulators; targeted delivery

Results 1-25 (46)