New Insight into the Role of Polyethylene Glycol Acting as Protein Release Modifier in Lipidic Implants

Spray congealed solid lipid microparticles as a sustained release delivery system for Gonadorelin [6-D-Phe]: Production, optimization and in vitro release behavior

Sustained release lipid microparticles for a potential veterinary application were produced by the means of spray congealing using saturated triglycerides with respective surfactants. The spray congealing process was optimized using unloaded and loaded microparticles, revealing the highest impact of the spray flow on material loss. Yield could be optimized by increasing the spray flow as well as a reduction of the melt temperature from 90 to 75 °C. For the delivery system developed in this study, a release of around 15 days was targeted. The release profile was in first hand determined with the use of model substances (aspartame and tryptophan), before incorporating the decapeptide Gonadorelin [6-D-Phe]. Release could be controlled between 2 and 28 d, which was dependent on stability of microparticles upon incubation, type and concentration of emulsifier, as well as the used triglyceride. Differential scanning calorimetry and X-ray powder diffraction confirmed the crystallization behavior of C14 and C16-triglycerides in combination with various emulsifiers in different modification without impact on release.

New insights into process understanding of solid lipid extrusion (SLE) of extruded lipid implants for sustained protein delivery

The aim of this work is a better understanding of solid lipid extrusion (SLE) for protein depot production using a lab-scale twin-screw (tsc)-extruder. In this context, little is known about the relationship of process parameters such as extrusion temperature, screw speed, or formulation on implant characteristics. It is difficult to attribute release characteristics to only one parameter, since the release will always be influenced by a combination of parameters. In this study, we describe the use of an online pressure measurement tool which allows to characterize pressure profiles during an extrusion run. We systematically investigated the impact of various process parameters on implant properties as well as release patterns using a monoclonal antibody (mAb). Solid lipid implants (SLIs) were produced by tsc-extrusion using the low melting triglyceride H12 and the high melting triglyceride Dynasan® D118. A mAb available in a freeze-dried matrix containing hydroxypropyl-β-cyclodextrine (HP-β-CD) was used as incorporated active pharmaceutical ingredient. Extrusion temperature (33-37 °C), screw speed (40-80 rpm) and the lipid composition (30-70% of each triglyceride) were modified. Additionally, freshly extruded SLIs were ground and extruded again as a preparation technique to optimize properties of SLIs. Using the pressure monitoring tool, four characteristic phases were defined for an extrusion run. We found that both, sufficient pressure and adequately molten material, is needed to form a suitable implant. Using the double extrusion technique, release rates could substantially be slowed down without changing formulation.

Impact of change of matrix crystallinity and polymorphism on ovalbumin release from lipid-based implants

The objectives of this study were to prepare lipid-based implants by hot melt extrusion (HME) for the prolonged release of ovalbumin (OVA), and to relate protein release to crystallinity and polymorphic changes of the lipid matrix. Two lipids, glycerol tristearate and hydrogenated palm oil, with different composition and degree of crystallinity were studied. Solid OVA was dispersed within the lipid matrixes, which preserved its stability during extrusion. This was partially attributed to a protective effect of the lipidic matrix. The incorporation of OVA decreased the mechanical strength of the implants prepared with the more crystalline matrix, glycerol tristearate, whereas it remained comparable for the hydrogenated palm oil because of stronger physical and non-covalent interactions between the protein and this lipid. This was also the reason for the faster release of OVA from the glycerol tristearate matrix when compared to the hydrogenated palm oil (8 vs. 28 weeks). Curing induced and increased crystallinity, and changes in the release rate, especially for the more crystalline matrix. In this case, both an increase and a decrease in release, were observed depending on the tempering condition. Curing at higher temperatures induced a melt-mediated crystallization and solid state transformation of the glycerol tristearate matrix and led to rearrangements of the inner structure with the formation of larger pores, which accelerated the release. In contrast, changes in the hydrogenated palm oil under the same curing conditions were less noticeable leading to a more robust formulation, because of less polymorphic changes over time. This study helps to understand the effect of lipid matrix composition and crystallinity degree on the performance of protein-loaded implants, and to establish criteria for the selection of a lipid carrier depending on the release profile desired.

Long-term release and stability of pharmaceutical proteins delivered from solid lipid implants

Solid lipid implants (SLIs) prepared by twin-screw (tsc) extrusion represent a promising technology platform for the sustained release of pharmaceutical proteins. In this work, we report on two aspects, long-term release and stability of released protein. First, SLIs were produced by tsc-extrusion containing the low melting triglyceride H12 and the high melting triglyceride Dynasan D118. Two different proteins available in a freeze-dried matrix containing hydroxypropyl-β-cyclodextrine (HP-β-CD) were incorporated into the lipid matrix: a monoclonal antibody (mAb) from the IgG₁ class and the f_ab-fragment Ranibizumab (Lucentis®). SLIs, composed of 10% protein lyophilizate and both triglycerides, were extruded at 35°C and 40rpm. Sustained release of both proteins was observed in a sustained manner for approximately 120days. Protein load per implant was increased by three different approaches resulting in a protein load of 3.00mg per implant without affecting the release profiles. The incubation medium containing the released protein was collected, concentrated and analyzed including liquid chromatography (SE-HPLC, IEX, HIC), electrophoresis (SDS-PAGE, on-chip gel electrophoresis) and FT-IR spectroscopy. The mAb showed a monomer loss of up to 7% (SE-HPLC) and IEX analysis revealed the formation of 16% acidic subspecies after 18weeks. FT-IR spectra of mAb indicated the formation of random coil structures towards the end of the release study. Ranibizumab was mainly released in its monomeric form (>95%), and approximately 5% hydrophobic subspecies were formed after 18weeks of release. FT-IR analysis revealed no changes in secondary structure. The release and stability profiles of both proteins underline the potential of SLIs as a delivery system. SLIs provide a promising platform for applications where really long-term release is needed, for example for intraocular delivery of anti-vascular endothelial growth factor (VEGF) drugs for age related macular degeneration (AMD).

Controlled release of an anthrax toxin-neutralizing antibody from hydrolytically degradable polyethylene glycol hydrogels

In this study, hydrophilic and hydrolytically degradable poly (ethylene glycol) (PEG) hydrogels were formed via Michael-type addition and employed for sustained delivery of a monoclonal antibody against the protective antigen of anthrax. Taking advantage of the PEG-induced precipitation of the antibody, burst release from the matrix was avoided. These hydrogels were able to release active antibodies in a controlled manner from 14 days to as long as 56 days in vitro by varying the polymer architectures and molecular weights of the precursors. Analysis of the secondary and tertiary structure and the in vitro activity of the released antibody showed that the encapsulation and release did not affect the protein conformation or functionality. The results suggest the promise for developing PEG-based carriers for sustained release of therapeutic antibodies against toxins in various applications.

Investigation of cenderitide controlled release platforms for potential local treatment of cardiovascular pathology

In this work, we focused on the development and investigation of controlled release matrices for a novel cardiotherapeutic peptide, cenderitide (CD-NP) that has shown to be useful for control of ventricular remodeling. To circumvent the hydrophilicity disparity between CD-NP and hydrophobic polymer matrix, a cosolvent system (water/dichloromethane) was selected for investigation. The effect of emulsification conditions, addition of poly(ethylene glycol) (PEG) and its copolymer on the release mechanism and profile were investigated. To verify the retention of bioactivity of entrapped CD-NP in different formulations, the generation of 3',5' cyclic guanosine monophospate (cGMP) and the inhibition of human cardiac fibroblast (HCF) were evaluated. The results showed that neat poly(ε-caprolactone) matrices carried out via two distinct emulsification conditions had either an unacceptably high burst or incomplete release of CD-NP; and the addition of PEG and its copolymer obtained intermediate profiles. Our confocal laser scanning microscopy and surface morphological investigations showed that the copolymer excipient was superior in playing stabilizer role by colocalizing and redistributing peptide throughout the matrix, making the release less sensitive to emulsification conditions. Furthermore, the released CD-NP is able to generate the cGMP and inhibit the HCF proliferation. Our investigations showed that CD-NP-loaded platforms can be a feasible option to provide sustained antifibrotic moderation of fibrotic scar formation and be potentially used to alleviate the adverse effects of cardiac remodeling.

Modeling of diffusion controlled drug delivery

Mathematical modeling of drug release can be very helpful to speed up product development and to better understand the mechanisms controlling drug release from advanced delivery systems. Ideally, in silico simulations can quantitatively predict the impact of formulation and processing parameters on the resulting drug release kinetics. The aim of this article is to give an overview on the current state of the art of modeling drug release from delivery systems, which are predominantly controlled by diffusional mass transport. The inner structure of the device, the ratio "initial drug concentration:drug solubility" as well as the device geometry determine which type of mathematical equation must be applied. A straightforward "road map" is given, explaining how to identify the appropriate equation for a particular type of drug delivery system. The respective equations for a broad range of devices are indicated, including reservoir and matrix systems, exhibiting or not an initial excess of drug and the geometry of slabs, spheres and cylinders. The assumptions the models are based on as well as their limitations are pointed out. Practical examples illustrate the usefulness of mathematical modeling of diffusion controlled drug delivery. Due to the advances in information technology the importance of in silico optimization of advanced drug delivery systems can be expected to significantly increase in the future.

Two-step solid lipid extrusion as a process to modify dissolution behavior

Extrudates based on varying ratios of the triglyceride tripalmitin and the hydrophilic polymer polyethylene glycol as matrix formers were produced as oral dosage forms with controlled release characteristics. The extrudates were processed below the melting points of the excipients and contained the hydrophobic model drug chloramphenicol. The influence of the ratio of the matrix formers on drug dissolution was investigated, with an increase in the water-soluble polymer content increasing the drug release rate. In addition, the effect of varying the extrusion process on the extrudate structure and drug dissolution was investigated. Two-step extrusion was performed, which comprised an initial extrusion step of drug and one matrix component followed by milling these extrudates and a second extrusion step for the milled extrudates mixed with the second matrix component. Initial extrusion with polyethylene glycol led to increased dissolution rates, while initial extrusion with tripalmitin led to decreased dissolution rates compared to the dissolution characteristics of extrudates containing the same composition produced by one-step extrusion. Thus, two-step solid lipid extrusion can successfully be used as a process to modify the dissolution behavior of extrudates.

Interferon alpha delivery systems for the treatment of hepatitis C

Hepatitis C virus (HCV) infections are the most common chronic blood-borne viral infections in the world. The prevalence of HCV infections varies significantly by race or ethnicity, with a high prevalence of the disease displayed in the Hispanic population. Additionally, Hispanics with chronic HCV have also more advanced hepatic fibrosis and faster liver fibrosis progression rates than either African Americans or Caucasians. Furthermore, a higher prevalence of cirrhosis and extent of mortality from liver cirrhosis is also observed in the Hispanic population compared with other groups. Current recommendations for treatment of hepatitis C are interferon alpha (IFNalpha)-based monotherapy and combination of IFNalpha preparations with ribavirin. Future treatment regimens will still be based on IFNalpha therapy with or without other effective antiviral agents, currently under investigation. However, there are some inherent limitations, mainly their relative short systemic circulation lifespan, and their unwanted effects on some non-target tissues. New research focuses on the development of novel modified interferon molecules which demonstrate reduced side effects and extended systemic circulation time, which can ultimately provide greater efficacy. Alternative routes for IFNalpha delivery, such as oral delivery, demonstrate challenging but promising areas of research for improving future patient compliance.

Reduced hydrophobic interaction of polystyrene surfaces by spontaneous segregation of block copolymers with oligo (ethylene glycol) methyl ether methacrylate blocks: force measurements in water using atomic force microscope with hydrophobic probes

Reduction of hydrophobic interaction in water is important in biological interfaces. In our previous work, we have found that poly(styrene- b-triethylene glycol methyl ether methacrylate) (PS-PME3MA) segregates the PME3MA block to the surface in hydrophobic environment, such as in air or in a vacuum, and shows remarkable resistance against adsorption or adhesion of proteins, platelets, and cells in water. In this paper, we report that atomic force microscopy (AFM) with hydrophobic probes can directly monitor the reduced hydrophobic interaction of the PS surfaces modified by poly(styrene- b-origoethylene glycol methyl ether methacrylate) (PS-PME NMA), where N is the number of ethylene glycol units. The pull-off forces between the hydrophobic probes that are coated with octyltrichlorosilane (OLTS) and the PS-PME NMA modified polystyrene (PS) surfaces in water were measured. The absolute spring constants and tip-curvatures of the AFM cantilevers were measured to compute the work of adhesion by the Johnson, Kendall, and Roberts (JKR) theory, which relates the pull-off force at which the separation occurs between a hemisphere and a plane to the work of adhesion. The hydrophobic interactions between the hydrophobic tip and polymer surfaces in water were greatly reduced with the segregated PME NMA blocks. The hydrophobic interactions decrease with increasing N of the series of PS-PME NMA and show a correlation with the amount of protein adsorbed.