Modeling vancomycin release kinetics from microporous calcium phosphate ceramics comparing static and dynamic immersion conditions

The release kinetics of vancomycin from calcium phosphate dihydrate (brushite) matrices and polymer/brushite composites were compared using different fluid replacement regimes, a regular replacement (static conditions) and a continuous flow technique (dynamic conditions). The use of a constantly refreshed flowing resulted in a faster drug release due to a constantly high diffusion gradient between drug loaded matrix and the eluting medium. Drug release was modeled using the Weibull, Peppas and Higuchi equations. The results showed that drug liberation was diffusion controlled for the ceramics matrices, whereas ceramics/polymer composites led to a mixed diffusion and degradation controlled release mechanism. The continuous flow technique was for these materials responsible for a faster release due to an accelerated polymer degradation rate compared with the regular fluid replacement technique.

Chemical, biological and microbiological evaluation of cyclodextrin finished polyamide inguinal meshes

This study describes the use of cyclodextrins (CDs) as a finishing agent of polyamide (PA) fibers used in order to obtain inguinal meshes with improved antibiotic delivery properties. The finishing process involved polymerization between citric acid and CDs, which yielded a cross-linked polymer that physically adhered to the surface of PA fibers. This permanent functionalization was characterized by evaluating the damping property with a polar liquid (glycerol) via the drop contact angle method for various rates of modification of the fabrics. The biological and microbiological effects of the PA, which were functionalized with hydroxypropylated derivate of gamma-CD (HP-gamma-CDs) and charged with ciprofloxacin (CFX), were evaluated by cell culture assays. We observed a good adhesion and proliferation of fibroblastic cells (NIH3T3) after 3 and 6 days and no detectable toxicity of the modified substrate. The in vitro antibacterial activity of the HP-gamma-CD grafted PA fabrics charged with CFX against the bacteria Staphylococcus aureus, Staphylococcus epidermidis and Escherichia coli was greatly superior to that of the virgin sample within a 24h batch experiment in human blood plasma medium. In conclusion, these results from our study offer an insight into the efficient performance of CDs as drug delivery systems for multiple applications in the fields of biomaterials and medical textiles.

Selective drug delivery to the colon using pectin-coated pellets

A combination of ethylcellulose and pectin, when applied as a film coat, has a potential value as a colon-specific delivery system. Dispersions of pectin in ethylcellulose were used as the film former for coating of 5-aminosalicylic acid (5-ASA) pellet cores. Drug release behavior was assessed, in vitro, under simulating conditions in term of pH and time in vivo during transit to the colon. Negligible drug release occurred during first 5 h, when the coated pellets were in the simulated gastric and small intestinal conditions. After that, rat cecal contents were added into the pH 6.8 medium to simulate the in vivo condition where there is the digestion of bacteria in the colon. Drug release depended on the composition of the mixed film, as well as the ratio of ethylcellulose to pectin. Drug release profiles seemed to conform to the mechanism involving the osmotically driven release and formation of channels in the film caused by dissolution of pectin. Channel formation was, in most cases, activated by the presence of rat cecal contents, showing that the pectin in the mixed film was subjected to enzymic breakdown. In conclusion, pectin could be used as an additive in ethylcellulose films to control the release of colonic delivery system. In addition, the mechanism of the hydrophilic drug release from pellets coated with ethylcellulose aqueous dispersions containing an aqueous gel-forming polymer (pectin) is also discussed.

Generating elastic, biodegradable polyurethane/poly(lactide-co-glycolide) fibrous sheets with controlled antibiotic release via two-stream electrospinning

Damage control laparotomy is commonly applied to prevent compartment syndrome following trauma but is associated with new risks to the tissue, including infection. To address the need for biomaterials to improve abdominal laparotomy management, we fabricated an elastic, fibrous composite sheet with two distinct submicrometer fiber populations: biodegradable poly(ester urethane) urea (PEUU) and poly(lactide-co-glycolide) (PLGA), where the PLGA was loaded with the antibiotic tetracycline hydrochloride (PLGA-tet). A two-stream electrospinning setup was developed to create a uniform blend of PEUU and PLGA-tet fibers. Composite sheets were flexible with breaking strains exceeding 200%, tensile strengths of 5-7 MPa, and high suture retention capacity. The blending of PEUU fibers markedly reduced the shrinkage ratio observed for PLGA-tet sheets in buffer from 50% to 15%, while imparting elastomeric properties to the composites. Antibacterial activity was maintained for composite sheets following incubation in buffer for 7 days at 37 degrees C. In vivo studies demonstrated prevention of abscess formation in a contaminated rat abdominal wall model with the implanted material. These results demonstrate the benefits derivable from a two-stream electrospinning approach wherein mechanical and controlled-release properties are contributed by independent fiber populations and the applicability of this composite material to abdominal wall closure.

Recent advances in ceramic implants as drug delivery systems for biomedical applications

Research in the development of new bioceramics with local drug delivery capability for bone regeneration technologies is receiving great interest by the scientific biomedical community. Among bioceramics, silica-based ordered mesoporous materials are excellent candidates as bone implants due to two main reasons: first, the bioactive behavior of such materials in contact with simulated body fluids, ie, a carbonate hydroxyapatite similar to the mineral phase of bone is formed onto the materials surfaces. Second, their capability of acting as delivery systems of a large variety of biologically active molecules, including drugs to treat bone infection, inflammation or diseases, and molecules that promote bone tissue regeneration, such as peptides, proteins, growth factors, and other osteogenic agents. The recent chemical and technological advances in the nanometer scale has allowed the design of mesoporous silicas with tailored structural and textural properties aimed at achieving a better control over molecule loading and release kinetics. Moreover organic modification of mesoporous silica walls has been revealed as a key strategy to modulate molecule adsorption and delivery rates.

Cell apoptosis control using BMP4 and noggin embedded in a polyelectrolyte multilayer film

Programmed cell death (apoptosis) is a genetically regulated process of cell elimination essential during development. During development, programmed cell death is involved in the specific shaping of organs, in the elimination of cells having achieved their program, and in regulating the number of cells to differentiate. Tooth development includes these three aspects and was used here as a model to study the control of apoptosis. Bone morphogenetic proteins (BMPs) are currently considered as playing a major role in signaling apoptosis. This apoptosis could be stopped by treatments with a BMP antagonist ("Noggin"). We selected a model system made by a layer-by-layer approach using poly-L-glutamic acid (PlGA) and poly-L-lysine (PlL) films into which BMP4 and/or Noggin have been embedded. Our results indicate that in situ control of apoptosis during tooth differentiation mediated by both BMP4 and Noggin embedded in a polyelectrolyte multilayer film is possible. We show here for the first time that in the presence of BMP4 and Noggin embedded in a multilayered film, we can induce or inhibit cell death in tooth differentiation, and conserve their biological effects.

The Application of Ink-Jet Technology for the Coating and Loading of Drug-Eluting Stents

The combination of drugs with devices, where locally delivered drugs elute from the device, has demonstrated distinct advantages over therapies involving systemic or local drugs and devices administered separately. Drug-eluting stents are most notable. Ink jet technology offers unique advantages for the coating of very small medical devices with drugs and drug-coating combinations, especially in cases where the active pharmaceutical agent is very expensive to produce and wastage is to be minimized. For medical devices such as drug-containing stents, the advantages of ink-jet technology result from the controllable and reproducible nature of the droplets in the jet stream and the ability to direct the stream to exact locations on the device surfaces. Programmed target deliveries of 100 microg drug, a typical dose for a small stent, into cuvettes gave a standard deviation (SD) of dose of 0.6 microg. Jetting on coated, uncut stent tubes exhibited 100% capture efficiency with a 1.8 microg SD for a 137 microg dose. In preliminary studies, continuous jetting on stents can yield efficiencies up to 91% and coefficients of variation as low as 2%. These results indicate that ink-jet technology may provide significant improvement in drug loading efficiency over conventional coating methods.

A Polyvinyl Alcohol Core Coil Containing Basic Fibroblast Growth Factor Evaluated in Rabbits with Aneurysms Induced by Elastase

OBJECTIVE

The present study evaluates the effect of a novel coil with a polyvinyl alcohol (PVA) core that delivered basic fibroblast growth factor (bFGF) to aneurysms in rabbits induced by elastase.

METHODS

PVA was processed to form small threads and inserted into the central core of a primary coil (PVA-core coil). After immersion in saline or bFGF (500 or 2000 mug/ml), PVA-core coils were implanted into elastase-induced aneurysms in rabbits in vivo. Follow-up angiography was performed 4 and 8 weeks after embolization, and the effects were histologically semiquantified according to a grading scale.

RESULTS

Follow-up angiography showed that the coils did not compact or protrude and that clots did not form in any group. The score of gross neck healing was significantly higher in the 8-week 2000 bFGF group than in the 8-week PVA coil group (2.7 +/- 0.6 versus 0.0 +/- 0.0, P < 0.05). The dome healing score was significantly higher in the 4-week 2000 bFGF group than that of the 4-week PVA coil group (4.0 +/- 0.0 versus 2.7 +/- 0.6, P < 0.05). Cells positive for alpha-smooth muscle actin densely accumulated in the dome of the aneurysm embolized with PVA-core coils containing bFGF.

CONCLUSION

Implantation of the PVA-core coil containing bFGF accelerated tissue growth at the neck as well as in the dome of aneurysms induced by elastase in rabbits. These results suggested that PVA-core coils could prevent the recanalization of embolized aneurysms.

Konduktives Knochenersatzmaterial mit variabler Antibiotikaversetzung

BACKGROUND

A new bone substitute, consisting of hydroxylapatite and calcium sulphate, was prepared in two formulations and analysed for its mechanical strength and antibiotic elution.

MATERIAL AND METHODS

The bone substitute PerOssal has osteoconductive and degradable properties. The material has a built-in capillary structure, which results in an immediate fluid uptake. Antibiotics absorbed to the bone substitute resulted in a prolonged release rate. Mechanical strength was investigated by an unconfined compression test up to failure under both wet and dry conditions for both formulations of the bone substitute. Antibiotic release was analysed microbiologically for two antibiotics, vancomycin and gentamicin, over an elution period of 10 days using the agar diffusion method.

RESULTS

The drug release analysis resulted in a prolonged release rate of both antibiotics over 10 days. In vitro the amount of gentamicin and vancomycin eluted at day 10. From one pellet still exceeded the minimal inhibitory concentration of most aetiologically important pathogens. Formulation two of the present bone substitute is significantly harder in both wet and dry conditions when compared to formulation one. Both formulations lose strength in the wet condition relative to their performance in the dry condition. However, formulation two is as hard under wet conditions as formulation one is when dry.

CONCLUSION

PerOssal is a suitable new degradable osteoconductive bone substitute that can be loaded with antibiotic solutions, which are released in effective doses over 10 days. The mechanical strength of PerOssal is sufficient to support cancellous bone defects in non-weight-bearing areas or in combination with osteosynthesis.

A 'biorelevant' system to investigate in vitro drug released from a naltrexone implant

This research is based on the recognized need for an in vitro release method for drug implants that better simulate physiological conditions at the site of implantation ('biorelevance'). In this paper, we describe the evaluation of a 'biorelevant' approach for in vitro drug release testing of a biodegradable implant of naltrexone in a pre-clinical stage of development. A miniature, capillary cell culture device was modified and tested as a biorelevant alternative for a standard commercially available flow-through cell. The real-time data generated through 90 days indicated a 48% lower rate of release for the capillary system. The profiles using both systems followed zero-order kinetics after an initial period of burst release. In vitro release data from the capillary device resulted in a 1-to-1 correlation with dog plasma pharmacokinetic data, and furthermore, the capillary device potentially simulated the lag-time in absorption more effectively than the flow-through cell. Scanning electron micrographs revealed that the sheath was continuous with no signs of cracks at the end of in vitro and in vivo studies. However, at the interface of the sheath and the core, intercalating, "finger-like" projections were observed consistent with penetration of the medium. No macroscopic or clinical toxicity signs were observed during the in vivo implantation study.

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

PURPOSE

It has recently been shown that the addition of polyethylene glycol 6000 (PEG) to lipidic implants fundamentally affects the resulting protein release kinetics and moreover, the underlying mass transport mechanisms (Herrmann, Winter, Mohl, F. Siepmann, & J. Siepmann, J. Control. Release, 2007). However, it is yet unclear in which way PEG acts. It was the aim of this study to elucidate the effect of PEG in a mechanistic manner.

MATERIALS AND METHODS

rh-interferon alpha-2a (IFN-alpha)-loaded, tristearin-based implants containing various amounts of PEG were prepared by compression. Protein and PEG release was monitored in phosphate buffer pH 4.0 and pH 7.4. IFN-alpha solubility and stability were assessed by reverse phase and size exclusion HPLC, SDS PAGE, fluorescence and FTIR.

RESULTS

Importantly, in presence of PEG IFN-alpha was drastically precipitated at pH 7.4. In contrast, at pH 4.0 up to a PEG concentration of 20% no precipitation occurred. These fundamental effects of PEG on protein solubility were reflected in the release kinetics of IFN-alpha from the tristearin implants: At pH 7.4 the protein release rates remained nearly constant over prolonged periods of time, whereas at pH 4.0 high initial bursts and continuously decreasing release rates were observed. Interestingly, it could be shown that IFN-alpha release was governed by pure diffusion at pH 4.0, irrespective of the PEG content of the matrices. In contrast, at pH 7.4 both--the limited solubility of the protein as well as diffusion through tortuous liquid-filled pores--are dominating.

CONCLUSIONS

For the first time it is shown that the release of pharmaceutical proteins can be controlled by an in-situ precipitation within inert matrices.

Novel biocompatible intraperitoneal drug delivery system increases tolerability and therapeutic efficacy of paclitaxel in a human ovarian cancer xenograft model

PURPOSE

We compared the safety, toxicity, biocompatibility and anti-tumour efficacy of a novel chitosan-egg phosphatidylcholine (ePC) implantable drug delivery system that provides controlled and sustained release of paclitaxel (PTX(ePC)) versus commercial paclitaxel formulated in Cremophor EL (PTX(CrEL)).

METHODS

Toxicity studies were conducted in healthy CD-1 female mice, whereas efficacy studies were performed in the SKOV-3 xenograft model of ovarian cancer. Treatments consisted of intraperitoneal (IP) implantation of drug-free or PTX(ePC) formulations, IP bolus PTX(CrEL), or Cremophor EL (CrEL) vehicle. Toxicity was assessed as number of deaths, weight loss, serum hepatic enzyme levels and histopathological changes.

RESULTS

Mice implanted with drug-free or PTX(ePC) formulations did not exhibit observable toxicities, local inflammation or fibrous encapsulation of the implant. In contrast, mice receiving PTX(CrEL) or CrEL encountered significant toxicity, lethality, abnormal peritoneal organ morphology and hepatic inflammation. The maximum tolerable dose (MTD) of PTX(CrEL) was 20 mg/kg/week, whereas PTX doses of up to 280 mg/kg/week were well tolerated when administered as PTX(ePC). Enhanced anti-tumour efficacy was achieved with PTX(ePC) in contrast to PTX(CrEL) with the same total dose of 60 mg/kg PTX.

CONCLUSIONS

The novel PTX(ePC) formulation is a safer and better tolerated method for PTX administration, with significant increase in MTD and enhanced anti-tumour efficacy, suggesting improved therapeutic index with possible clinical implications in the treatment of ovarian tumours.

Vascular delivery of c-myc antisense from cationically modified phosphorylcholine coated stents

c-Myc is involved in the formation of neointimal hyperplasia. We investigated in vitro, ex vivo and in vivo release of antisense c-myc from cationically modified phosphorylcholine-coated stents, as well as the effects on c-Myc expression and neointima formation in a porcine coronary stent model. In vitro experiments were performed to determine optimal loading of stents with antisense. Stents loaded with labelled antisense were deployed in porcine arteries ex vivo and in vivo. Antisense was detected in the vessel wall directly surrounding the stent of pig carotid and coronary artery up to 48 h after stent deployment. Nuclear uptake was observed in endothelial and vascular smooth muscle cells. Labelled antisense within peripheral tissues in vivo was <1.0% of that within stented arterial segments. Control and antisense loaded stents implanted into 10 pig coronary arteries and analysed at 28 days post-stenting showed that lumen area within the antisense stents was significantly increased (i.e. 30.5% greater, P<0.01), whilst both neointimal area and neointimal thickness were significantly reduced (17.5% and 19.5%, respectively, P<0.01) compared to control stents. Cationically modified phosphorylcholine coated stent-based delivery of c-myc antisense is feasible with minimal systemic delivery and is associated with a reduction of in-stent neointimal hyperplasia in pig coronary arteries.

Controlled Delivery of Peptides and Proteins

The final aim/target of Pharmaceutical Sciences is to design successful dosage forms for effective therapy, considering individual patient needs and compliance. Development of new drug entities, particularly using peptides and proteins, is growing in importance and attracting increased interest, as they are specifically effective at a comparably low dose. These very potent and specific peptides and proteins can now be produced in large quantities due to increased knowledge and advancements in biotechnological and pharmaceutical applications. A number of peptide and protein products are now available on the market, and numerous studies investigating them have been published in the literature. Although many peptide/protein like products are generally designed for parenteral administration, some other noninvasive routes have also been used. For example, desmopressin is delivered nasally and deoxyribonuclease by inhalation. Although peptides and proteins are generally orally inactive, cyclosporine is an exception. In order to design and develop long-acting, more effective peptide/protein drugs, the controlled release mechanisms and effective parameters need to be understood and clarified. Therefore, we review herein various peptide/protein delivery systems, including biodegradable and nondegradable microspheres, microcapsules, nanocapsules, injectable implants, diffusion-controlled hydrogels and other hydrophilic systems, microemulsions and multiple emulsions, and the use of iontophoresis or electroporation, and discuss the results of recent researches.

Development of self-expandable covered stents

We newly developed self-expandable covered stents by combining two of our original technologies. Of these, the first is the dip-coating covering method that was developed previously for balloon-expandable stents; the other is the newly developed self-expandable Nitinol stents, namely, Sendai stents. The three types of covered stents with the expansion diameter of 4.5, 5.0, or 6.0 mm thus obtained had a laser-processed microporous elastomeric cover film (pore diameter: 100 microm, interpore distance: 250 microm). Although the film was extremely thin (approximately 15 microm), the film could be expanded without causing any damage, the strut was completely embedded within the film, and the luminal surface of the film was smooth and flat. Mechanical properties such as ideal flexibility to follow the shapes of arteries were almost retained even after covering. As appropriate drugs, the blood-contacting inner and tissue-contacting outer surfaces of the film were differentially coated with argatroban for antithrombogenicity or FK506 for anti-inflammation, respectively. The preliminary in vivo study indicated that the covered stents mounted in the delivery catheter were navigated and placed to appropriate position in the arteries, and permissible neointimal thickening after 1-month implantation was observed similarly in noncovered stents.

[Application of computer image analysis for characterization of pellets]

The morphological characteristics of pellets are critical parameters, because of their physico-chemical features depend on the size, shape and surface geometric of the particles. To ensure the spherical shape and required particle of pharmaceutical pellets size is a prerequisite. The detailed technology is basic requirement for the successful and cost efficient production of particles of acceptable quality. Since the determination of the particle size is influenced by the particle shape, therefore microscopic examination is always suggested, which together with image analysis is suitable for the assesment of the most typical parameters. The method of the microscopic image analysis is useful not only for particle size measurement, but also for particle shape and texture evaluation, with a high sensitivity. Using the microscopic method particle shape may be defined either qualitatively and quantitatively. Reviewing the related articles and results on the investigation of sugar pellets demonstrate that roundness characterization is strongly influenced by the applied statistical shape parameters.

Drug confinement and delivery in ceramic implants

Ordered silica-based mesoporous materials could be specially designed and chemically modified for the adsorption of drugs that would be locally released. The drug adsorption and release kinetics are controlled by several factors such as pore size, volume, architecture and chemistry of the silica walls.

Coronary stents: a materials perspective

The objective of this review is to describe the suitability of different biomaterials as coronary stents. This review focuses on the following topics: (1) different materials used for stents, (2) surface characteristics that influence stent-biology interactions, (3) the use of polymers in stents, and (4) drug-eluting stents, especially those that are commercially available.

Controlled in vivo degradation of genipin crosslinked polyethylene glycol hydrogels within osteochondral defects

Polyethylene glycol (PEG) hydrogels show promise as scaffolds for growth factor delivery to enhance cartilage repair. However, methods to control growth factor release in vivo are needed. We have recently shown that in vitro polymer degradation and in vitro growth factor release kinetics can be altered using PEG crosslinked with different concentrations of genipin. However, the degradation and behavior of PEG-genipin in vivo within the cartilage repair site are unknown. This study was conducted to test the hypotheses that the degradation of PEG-genipin can be altered in vivo within osteochondral defects by changing the concentration of genipin, and that PEG-genipin is biocompatible within the mammalian diarthrodial environment. PEG-genipin cylindrical polymers crosslinked using 8mM, 17.6 mM, or 35.2 mM of genipin were implanted into osteochondral defects made in the trochlea of 24 male Sprague- Dawley rats (48 knees). Rats were sacrificed at 5 weeks and gross, cross-sectional, and histologic assessments were performed. Altering the genipin concentration changed the in vivo degradation properties of the hydrogel ( p < 0.01). Consistent with in vitro findings, polymer degradation was inversely related to the concentration of genipin. Near-complete degradation was seen at 8 mM, intermediate degradation at 17.6 mM, and minimal degradation at 35.2 mM. The results of this study show the degradation of PEGgenipin can be altered in vivo within osteochondral defects by changing the concentration of genipin and that PEG-genipin is biocompatible within osteochondral defects. This new in vivo data support potential use of PEG-genipin polymer as an innovative delivery system to control in vivo release of growth factors for improving articular cartilage repair.

Acellular biological tissues containing inherent glycosaminoglycans for loading basic fibroblast growth factor promote angiogenesis and tissue regeneration

It was found in our previous study that acellular tissues derived from bovine pericardia consist primarily of insoluble collagen, elastin, and tightly bound glycosaminoglycans (GAGs). It is speculated that the inherent GAGs in acellular tissues may serve as a reservoir for loading basic fibroblast growth factor (bFGF) and promote angiogenesis and tissue regeneration. This study was therefore designed to investigate effects of the content of GAGs in acellular bovine pericardia on the binding of bFGF and its release profile in vitro while its stimulation in angiogenesis and tissue regeneration in vivo were evaluated subcutaneously in a rat model. To control the content of GAGs, acellular tissues were treated additionally with hyaluronidase for 1 (Hase-D1), 3 (Hase-D3), or 5 days (Hase-D5). The in vitro results indicated that a higher content of GAGs in the acellular tissue resulted in an increase in bFGF binding and in a more gradual and sustained release of the growth factor. The in vivo results obtained at 1 week postoperatively showed that the density and the depth of neo-vessels infiltrated into the acellular tissue loaded with bFGF (acellular/bFGF) were significantly greater than the other test samples. At 1 month postoperatively, vascularized neo-connective tissues were found to fill the pores within each test sample, particularly for the acellular/bFGF tissue. These results suggested that the sustained release of bFGF from the acellular/ bFGF tissue continued to be effective in enhancing angiogenesis and generation of new tissues. In conclusion, the inherent GAGs present in acellular tissues may be used for binding and sustained release of bFGF to enhance angiogenesis and tissue regeneration.

Chemistry and the biological response against immunoisolating alginate–polycation capsules of different composition

Implantation of microencapsulated cells has been proposed as a therapy for a wide variety of diseases. An absolute requirement is that the applied microcapsules have an optimal biocompatibility. The alginate-poly-L-lysine system is the most commonly applied system but is still suffering from tissue responses provoked by the capsule materials. In the present study, we investigate the biocompatibility of microcapsules elaborated with two commonly applied alginates, i.e. an intermediate-G alginate and a high-G alginate. These alginates were coated with poly-L-lysine (PLL), poly-D-lysine (PDL) and poly-L-ornithine (PLO). The main objective of this study is to determine the interaction of each alginate matrix with the different polycations and the potential impact of these interactions in the modulation of the host's immune response. To address these issues the different types of microcapsules were implanted into the peritoneal cavity of rats for I month. After this period the microcapsules were recovered and they were evaluated by different techniques. Monochromatised X-ray photoelectron spectroscopy (XPS) was performance and the degree of capsular recovery, overgrowth on each capsule, and the cellular composition of the overgrowth were evaluated by histology. Our results illustrate that the different observed immune responses are the consequence of the variations in the interactions between the polycations and alginates rather than to the alginates themselves. Our results suggest that PLL is the best option available and that we should avoid using PLO and PDL in its present form since it is our goals to produce capsules that lack overgrowth and do not induce an immunological response as such.

Novel drug delivery system using thermoreversible gelation polymer for malignant glioma

Many approaches to local tumor treatment have been reported and their efficacy demonstrated in patients with malignant glioma. We studied thermoreversible gelation polymer (TGP) as a novel drug delivery system (DDS) for treating this type of tumor. TGP exhibits sol-gel transition i.e., is water-soluble in the sol phase below the chosen sol-gel transiting temperature and water-insoluble in the gel phase above this temperature. We conjugated doxorubicin with TGP to prepare doxorubicin-TGP (DXR-TGP), then studied the kinetics of doxorubicin release from TGP and the antitumor activity of DXR-TGP in vitro and in vivo. The diffusive speed of doxorubicin from TGP was 9.4x10(-7) cm(2)/s and doxorubicin was reliably released from TGP. DXR-TGP showed antitumor activity against the human glioma cell lines T98G and U87MG and in a subcutaneous tumor model in nude mice. Pathologically, detection of the proliferation marker Ki-67 was considerably lower in the DXR-TGP group than in the control group (30-40% vs. 60-70%, respectively). This is to the best of our knowledge the first report of TGP as a novel drug delivery system, and further we provide evidence that TGP exhibits potential for use as a novel DDS for malignant glioma.

Using Dihydropyridine-Release Strategies to Enhance Load Effects in Engineered Human Bone Constructs

We report on the development of a novel biodegradable scaffold capable of enhancing mechanical signals for tissue-engineering applications. It has been shown that mechanotransduction enhances bone formation in vitro and in vivo; in tissue-engineering applications, this phenomenon is exploited through the use of mechanical bioreactors to generate bone tissue. The dihydropyridine agonist Bay K8644 (Bay) acts to increase the opening time of mechanosensitive voltage-operated calcium channels (VOCCs), specifi- cally L-type VOCCs, which are known to play a fundamental role in the early mediation of mechanotransduction. We have produced porous 3-dimensional, Bay-encapsulated biodegradable poly(L-lactide) acid scaffolds using a solvent-casting and salt-leaching technique. The effects of the released Bay on osteoid production and mineralization in human bone cell-seeded constructs following incubation in a perfusion-compression bioreactor in vitro was investigated using Western blotting techniques and a calcium assay protocol developed in our lab. Our newly developed scaffolds act by slowly releasing the calcium channel agonist Bay K8644 as observed using ultraviolet spectroscopy, maintaining the open state of mechanosensitive VOCCs responding to load, which augments the load signal at sites of strain across the scaffold. Our results demonstrate that, in the presence of physiological loading regimes in vitro, release of Bay enhances collagen I protein production and osteoid calcification more than non-Bay control constructs do. Osteopontin and alpha2delta1 VOCC subunit protein levels were also higher as a result of perfusion-compression conditioning. These results indicate that Bay-encapsulated scaffolds can be used in the presence of load to enhance the production of load-bearing engineered tissue.