Development of a new drug delivery system for protein drugs using silicone (II)

Recent advancements in single dose slow-release devices for prophylactic vaccines

Single dose slow-release vaccines herald a new era in vaccine administration. An ideal device for slow-release vaccine delivery would be minimally invasive and self-administered, making these approaches an attractive alternative for mass vaccination programs, particularly during the time of a pandemic. In this review article, we discuss the latest advances in this field, specifically for prophylactic vaccines able to prevent infectious diseases. Recent studies have found that slow-release vaccines elicit better immune responses and often do not require cold chain transportation and storage, thus drastically reducing the cost, streamlining distribution, and improving efficacy. This promise has attracted significant attention, especially when poor patient compliance of the standard multidose vaccine regimes is considered. Single dose slow-release vaccines are the next generation of vaccine tools that could overcome most of the shortcomings of present vaccination programs and be the next platform technology to combat future pandemics. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Implantable Materials and Surgical Technologies > Nanomaterials and Implants Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Vaginal rings with exposed cores for sustained delivery of the HIV CCR5 inhibitor 5P12-RANTES

Antiretroviral-releasing vaginal rings are at the forefront of ongoing efforts to develop microbicide-based strategies for prevention of heterosexual transmission of the human immunodeficiency virus (HIV). However, traditional ring designs are generally only useful for vaginal administration of relatively potent, lipophilic, and small molecular weight drug molecules that have sufficient permeability in the non-biodegradable silicone elastomer or thermoplastic polymers. Here, we report a novel, easy-to-manufacture 'exposed-core' vaginal ring that provides sustained release of the protein microbicide candidate 5P12-RANTES, an experimental chemokine analogue that potently blocks the HIV CCR5 coreceptor. In vitro release, mechanical, and stability testing demonstrated the utility and practicality of this novel ring design. In a sheep pharmacokinetic model, a ring containing two ¼-length excipient-modified silicone elastomer cores - each containing lyophilised 5P12-RANTES and exposed to the external environment by two large windows - provided sustained concentrations of 5P12-RANTES in vaginal fluid and vaginal tissue between 10 and 10,000 ng/g over 28days, at least 50 and up to 50,000 times the reported in vitro IC50 value.

Sustained release of the candidate antiretroviral peptides T-1249 and JNJ54310516-AFP from a rod insert vaginal ring

Administration of biomacromolecular drugs in effective quantities from conventional vaginal rings is hampered by poor drug permeability in the polymers from which rings are commonly constructed. Here, we report the formulation development and testing of rod insert rings for sustained release of the candidate antiretroviral peptides T-1249 and JNJ54310516-AFP (JNJ peptide), both of which have potential as HIV microbicides. Rod inserts were prepared comprising antiviral peptides T-1249 or JNJ peptide in combination with a hydrophilic excipient (sodium chloride, sodium glutamate, lactose or zinc acetate) dispersed at different loadings within a medical grade silicone elastomer. The inserts were tested for weight change and swelling when immersed in simulated vaginal fluid (SVF). Dye migration into the inserts was also assessed visually over 28 days. In vitro release of T-1249 and JNJ peptide from rings containing various insert types was tested. Weight change and degree of swelling of rods immersed in SVF was dependent on the type and concentration of excipient present. The rods displayed the following rank order in terms of weight change: sodium glutamate > zinc acetate ≈ sodium chloride > lactose. The weight change and degree of swelling of the inserts did not correlate with the level of dye uptake observed. In vitro release of T-1249 was improved through addition of lactose, sodium chloride and sodium glutamate, while release of JNJ peptide was improved through addition of sodium chloride or sodium glutamate. Sustained release of hydrophobic peptides can be achieved using a rod insert ring design formulated to include a hydrophilic excipient. Release rates were dependent upon the type of excipient used. The degree of release improvement with different inserts partially reflects their ability to imbibe surrounding fluid and swell in aqueous environments.

Long-term delivery of protein therapeutics

INTRODUCTION

Proteins are effective biotherapeutics with applications in diverse ailments. Despite being specific and potent, their full clinical potential has not yet been realized. This can be attributed to short half-lives, complex structures, poor in vivo stability, low permeability, frequent parenteral administrations and poor adherence to treatment in chronic diseases. A sustained release system, providing controlled release of proteins, may overcome many of these limitations.

AREAS COVERED

This review focuses on recent development in approaches, especially polymer-based formulations, which can provide therapeutic levels of proteins over extended periods. Advances in particulate, gel-based formulations and novel approaches for extended protein delivery are discussed. Emphasis is placed on dosage form, method of preparation, mechanism of release and stability of biotherapeutics.

EXPERT OPINION

Substantial advancements have been made in the field of extended protein delivery via various polymer-based formulations over last decade despite the unique delivery-related challenges posed by protein biologics. A number of injectable sustained-release formulations have reached market. However, therapeutic application of proteins is still hampered by delivery-related issues. A large number of protein molecules are under clinical trials, and hence, there is an urgent need to develop new methods to deliver these highly potent biologics.

Controlled release of linear-dendritic hybrids of carbosiloxane dendrimer: the effect of hybrid's amphiphilicity on drug-incorporation; hybrid-drug interactions and hydrolytic behavior of nanocarriers

Dendritic micelles formed from amphiphilic dendritic ABA triblock copolymers based on organic linear poly(ethylene oxide) and inorganic dendritic block containing silicon atoms (OSC-D(Gn)-PEO-D(Gn)-CSO, n=1-3)(1) were evaluated as drug delivery vehicles for a drug in both lipophilic and hydrophilic forms. The physical parameters of the drug-incorporated carriers including the influences of drug:carrier ratio, the release kinetics of the drugs from the micellar solution were measured. The apparent partition constant of drug between the carriers and the external medium was studied as well. It was observed that the loading efficiency and hydrolytic behavior of the hybrids depend on several factors, such as type of interaction between host and guest molecules, generation of the dendritic copolymers and pH. The release profiles of the drugs from the micelle solution were found to be a slow steady release at pH 1, 7.4 and 10. Investigation of the drug release dynamics in buffered media at pH 7.4 showed that the drug released through the carriers with slight deviation follow Fickian and Case II diffusion mechanisms for drugs in lipophilic and hydrophilic forms, respectively.

Sustained release of proteins from a modified vaginal ring device

A new vaginal ring technology, the insert vaginal ring (InVR), is presented. The InVR overcomes the current shortfall of conventional vaginal rings (VRs) that are generally ineffectual for the delivery of hydrophilic and/or macromolecular actives, including peptides, proteins and antibodies, due to their poor permeation characteristics in the hydrophobic polymeric elastomers from which VRs are usually fabricated. Release of the model protein BSA from a variety of insert matrices for the InVR is demonstrated, including modified silicone rods, directly compressed tablets and lyophilised gels, which collectively provided controlled release profiles from several hours to beyond 4 weeks. Furthermore, the InVR was shown to deliver over 1 mg of the monoclonal antibody 2F5 from a single device, offering a potential means of protecting women against the transmission of HIV.

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.

Novel Delivery Systems for Interferons

Interferons, IFNs, are among the most widely studied and clinically used biopharmaceuticals. Despite their invaluable therapeutic roles, the widespread use of IFNs suffers from some inherent limitations, mainly their relatively short circulation lifespan and their unwanted effects on some non-target tissues. Therefore, both these constraints have become the central focus points for the research efforts on the development of a variety of novel delivery systems for these therapeutic agents with the ultimate goal of improving their therapeutic end-points. Generally, the delivery systems currently under investigation for IFNs can be classified as particulate delivery systems, including micro- and nano-particles, liposomes, minipellets, cellular carriers, and non-particulate delivery systems, including PEGylated IFNs, other chemically conjugated IFNs, immunoconjugated IFNs, and genetically conjugated IFNs. All these strategies and techniques have their own possibilities and limitations, which should be taken into account when considering their clinical application. In this article, currently studied delivery systems/techniques for IFN delivery have been reviewed extensively, with the main focus on the pharmacokinetic consequences of each procedure.

Evaluation of the binding effect of human serum albumin on the properties of granules

The main objective of this study was the application of a solution of human serum albumin as a granulating fluid. The properties of the granules formed were evaluated and compared with those when a conventional binder was applied in the same concentration. The powder mixture contained a soluble (mannitol) and an insoluble component (different types of cellulose). The protein solution applied exerted an appropriate aggregating effect if the system contained microcrystalline celluloses. Powdered cellulose was not suitable for the granulation with human serum albumin solution. As compared with the same concentration of the conventionally applied cellulose ethers as binder, the prepared granules exhibited a larger particle size, a significantly better compressibility, a higher breaking hardness and a favourable deformation process. These findings mainly reflect the good adhesive properties of the protein. The best compressibility and mechanical behaviour were attained on the application of the microcrystalline cellulose Vivapur type 105. This favourable behaviour may be connected with the wettability of cellulose. These results suggest that the formulation of tablets may be easier from an active agent in the serum that binds to albumin (e.g. interferon) since the amount of additives (binder) can be reduced.

Preparation and in vitro evaluation of carrier erythrocytes for RES-targeted delivery of interferon-alpha 2b

Carrier erythrocytes is one of the most promising systemic drug delivery systems investigated in recent decades. In this study, human erythrocytes have been loaded with interferon-alpha 2b (IFN) with the aim to benefit the reticuloendothelial system (RES) targeting potential of the carrier cells. Hypotonic preswelling method was used for drug loading in erythrocytes and the entire loading procedure was evaluated and validated. The loaded amount, entrapment efficiency and cell recovery of the loading procedure were 2906.33+/-588.35IU/0.1ml, 14.53+/-2.94%, and 83.61+/-0.49%, respectively, all being practically feasible. The carrier erythrocytes were characterized in vitro in terms of their drug release kinetics, hematological indices, particle size distribution, SEM analysis, and osmotic and turbulence fragility. IFN release from carrier cells was a relatively rapid process in comparison to the cell lysis kinetics, which is unusual considering the whole body of data published on this delivery system and other protein drugs, so far. All the tested in vitro characteristics showed significant, sometimes notable changes upon drug loading procedure, both with and without the drug.

Evaluation of a covered-rod silicone implant containing ivermectin for long-term prevention of heartworm infection in dogs

OBJECTIVE

To evaluate use of covered-rod (CR) silicone implants containing ivermectin for long-term prevention of infection with Dirofilaria immitisin dogs.

ANIMALS

145 adult male and female dogs.

PROCEDURES

Dogs received implants of different sizes, and ivermectin concentrations and serum ivermectin concentrations were monitored for 16, 57, and 56 weeks, respectively, in 3 preclinical dose selection studies. Ability of implants to prevent infection with D immitis was evaluated in 2 further studies; dogs were challenged with 50 infective third-stage larvae 52 weeks after implant administration and necropsied 145 days after challenge, and the total number of adult heartworms was counted. A field study was then undertaken in which client-owned dogs received an implant and plasma samples were collected at intervals until week 52 for ivermectin analysis and heartworm antigen determination.

RESULTS

Use of the implants resulted in maintenance of an ivermectin concentration > or = 0.2 ng/mL for 12 months. In challenge studies, no treated dogs had adult heartworms, in contrast to untreated dogs, which all had adult heartworms at necropsy. In the field study, dogs treated with an implant had negative results of heartworm antigen testing for 12 months.

CONCLUSIONS AND CLINICAL RELEVANCE

The CR silicone implant containing 7.3 mg of ivermectin was 100% effective in preventing experimental infection with D immitislarvae and resulted in negative results for heartworm antigen in a field trial. This product has the potential to alleviate poor owner compliance with monthly prevention regimens.

A novel method for the preparation of biodegradable microspheres for protein drug delivery

Microspheres are potential candidates for the protein drug delivery. In this work, we prepared polymer-coated starch/bovine serum albumin (BSA) microspheres using co-axial electrohydrodynamic atomization (CEHDA). First, starch solution in dimethyl sulphoxide (DMSO) was prepared and then an aqueous solution of BSA was added to it to make a starch-BSA solution. Subsequently, this solution was made to flow through the inner capillary, while the polymer, polydimethylsiloxane (PDMS), flowed through the outer capillary. On collection, filtration and subsequent drying, near-monodisperse microspheres of 5-6microm in size were obtained. The microspheres were characterized by Fourier-transform infrared (FT-IR) spectroscopy and scanning electron microscopy. Cumulative BSA release was investigated by UV spectroscopy. BSA structure and activity was preserved in the microspheres and its release in 0.01M phosphate buffered saline (PBS) was studied over a period of 8 days. There was an initial burst with 32wt% of total BSA released in 2h. Overall 75wt% of BSA was released over a 7 day period.

Preparation of nanoparticles composed of chitosan/poly-gamma-glutamic acid and evaluation of their permeability through Caco-2 cells

In this study, a novel nanoparticle system for paracellular transport was prepared using a simple and mild ionic-gelation method upon addition of a poly-gamma-glutamic acid (gamma-PGA) solution into a low-molecular-weight chitosan (low-MW CS) solution. The particle size and the zeta potential value of the prepared nanoparticles can be controlled by their constituted compositions. The results obtained by the TEM and AFM examinations showed that the morphology of the prepared nanoparticles was spherical in shape. Evaluation of the prepared nanoparticles in enhancing intestinal paracellular transport was investigated in vitro in Caco-2 cell monolayers. It was found that the nanoparticles with CS dominated on the surfaces could effectively reduce the transepithelial electrical resistance (TEER) of Caco-2 cell monolayers. After removal of the incubated nanoparticles, a gradual increase in TEER was noticed. The confocal laser scanning microscopy observations confirmed that the nanoparticles with CS dominated on the surface were able to open the tight junctions between Caco-2 cells and allowed transport of the nanoparticles via the paracellular pathways.

Physically crosslinked alginate/N,O-carboxymethyl chitosan hydrogels with calcium for oral delivery of protein drugs

In the study, a complex composed of alginate blended with a water-soluble chitosan (N,O-carboxymethyl chitosan, NOCC) was prepared to form microencapsulated beads by dropping aqueous alginate-NOCC into a Ca(2+) solution. These microencapsulated beads were evaluated as a pH-sensitive system for delivery of a model protein drug (bovine serum albumin, BSA). The main advantage of this system is that all procedures used were performed in aqueous medium at neutral environment, which may preserve the bioactivity of protein drugs. The swelling characteristics of these hydrogel beads at distinct compositions as a function of pH values were investigated. It was found that the test beads with an alginate-to-NOCC weight ratio of 1:1 had a better swelling characteristic among all studied groups. With increasing the total concentration of alginate-NOCC, the effective crosslinking density of test beads increased significantly and a greater amount of drug was entrapped in the polymer chains (up to 77%). The swelling ratios of all test groups were approximately the same ( approximately 3.0) at pH 1.2. At pH 7.4, with increasing the total concentration of alginate-NOCC, the swelling ratios of test beads increased significantly (20.0-40.0), due to a larger swelling force created by the electrostatic repulsion between the ionized acid groups (-COO(-)). It was shown that BSA was uniformly distributed in all test beads. At pH 1.2, retention of BSA in hydrogels may be improved by rinsing test beads with acetone (the amount of BSA released was below 15%). At pH 7.4, the amounts of BSA released increased significantly ( approximately 80%) as compared to those released at pH 1.2. With increasing the total concentration of alginate-NOCC, the release of encapsulated proteins was slower. Thus, the calcium-alginate-NOCC beads with distinct total concentrations developed in the study may be used as a potential system for oral delivery of protein drugs to different regions of the intestinal tract.

Sustained interferon-γ delivery from a photocrosslinked biodegradable elastomer

The application of protein therapeutics for long-term, localized delivery has been hindered by a lack of a delivery device that releases active protein at a concentration within their therapeutic window. A protein delivery system that uses an osmotic pressure delivery mechanism and a photocrosslinked biodegradable elastomer has been designed in an attempt to overcome this limitation. The elastomer is prepared through the UV initiated crosslinking of end terminal acrylated star-poly(epsilon-caprolactone-co-D,L-lactide). Interferon-gamma (IFN-gamma) was released from the optimum formulation at a constant rate of 23 ng/day over 21 days. A cell-based assay showed that over 83% of released IFN-gamma was bioactive. Furthermore, it was demonstrated that bovine serum albumin co-lyophilized with IFN-gamma was released at the same rate as IFN-gamma. This delivery formulation may be clinically useful for sustained, local protein drug delivery applications.

A model for osmotic pressure driven release from cylindrical rubbery polymer matrices

Osmotic pressure-driven drug release from rubbery polymer matrices in a cylindrical geometry has been shown to produce a period of nearly constant release. In order to explain this behavior and in an effort to produce a tool for device design, a mathematical model of the release was developed. The model was tested by application to literature data of the release of NaI from poly(dimethylsiloxane) cylinders and found to provide good agreement with the data. The model demonstrates that, although there is a decrease in solute concentration as one moves from the exterior to the center of the cylinder, a period of nearly constant release is produced, lasting until about 60% of the initial drug load has been released.

Study on accelerated evaluation system for release profiles of covered-rod type silicone formulation using indomethacin as a model drug

The purpose of this study was to establish a method allowing rapid evaluation in vitro of the profiles of drug release from covered-rod type silicone formulation (CR silicone formulation), which releases drug for a prolonged period of time. Three CR silicone formulations containing indomethacin (IDM) with different release profiles were used in this study. The release of IDM was accelerated in a mixture of methanol and water (MeOH/water) compared with in phosphate-buffered saline (PBS) added by Tween 20 (PBS-based solvent). The velocity of IDM release varied depending on the composition of the MeOH/water. The change in release velocity was dependent on the solubility of IDM and the permeability of IDM through the silicone membrane. In all the tested formulations, the release rates of IDM estimated in 90% (v/v) MeOH/water were equally 14.6 times faster than those estimated in PBS-based solvent. Release of IDM from the cross-sections and lateral side evaluated by a bi-directional elution cell were accelerated in the MeOH/water in a similar degree. By introducing a common factor to shorten the time axis in all formulations, a fairly good agreement was observed between the two release profiles obtained in the accelerated MeOH/water system and the usual PBS-based solvent system. These results indicate that MeOH/water system enables to reduce the period for evaluation of profiles of drug release from CR silicone formulations in reflecting their release characteristics in usual PBS-based solvent system.

Design of controlled-release formulation for ivermectin using silicone

The purpose of this study was to design a formulation using silicone as carrier, so that release of ivermectin (IVM) can be controlled for a long period of time. The lateral side of a cylindrical matrix-type formulation composed of IVM and silicone was covered with silicone to obtain a covered-rod (CR) formulation. With this formulation, linear release of IVM was obtained. With addition of polyethylene glycol 4000 (PEG), release of IVM was accelerated. In a trial with subcutaneous administration to mice, blood concentration of IVM was maintained within one-order over a period of 3 months. The velocity of release of IVM from CR preparation depended on the change in solubility of IVM by additives, and in the case of a formulation with addition of desoxycholate sodium, linear in vitro release of IVM was observed over a period of 1 year.

Investigation of the release behavior of a covered-rod-type formulation using silicone

The purpose of this study was to investigate the effects of the properties of a drug on its release behavior in a cylindrical sustained-release formulation having a two-component structure, with a silicone matrix containing drug powder as the inner layer component, and with its lateral side covered with an silicone outer layer (CR silicone formulation). In this study, the release profile of a drug from "the lateral side covered with silicone" and from "the cross-sections where the inner layer is exposed to the surface" was examined using a newly designed bi-directional elution cell. The relationships between the release profile and solubility of the drug and its permeability through silicone were also studied. Bovine serum albumin (BSA), antipyrine (ANP), indometacin (IDM) and ketoprofen (KP) were used as model drugs. Each CR silicone formulation containing drug powder consisting of a drug and sucrose (SUC) was investigated, and a satisfactory relationship was observed between drug release from the cross-sections and drug solubility, and between drug release from the lateral side and permeability of the drug through a silicone membrane. For CR silicone formulations containing IDM, the addition of deoxycholate sodium (DOC) improved the solubility of IDM; however, release from the lateral side of the formulation remained unchanged, and IDM release from the cross-sections of the formulation increased. In this study it was found that, for controlled release of a drug from CR silicone formulations, control of drug solubility is effective.

Novel method to control release of lipophilic drugs with high potency from silicone

Silicone has been utilized as a carrier material for sustained release system of lipophilic drugs. Extensive studies revealed that drug release rate is influenced by factors such as physicochemical properties of the drug and additives.(1-5)) When a lipophilic drug is highly potent at low concentrations, the drug release rate should be strictly controlled so as to avoid side effects. In this study, using vitamin D(3) (VD(3)) as an example of such drugs, we investigated novel method to suppress initial burst and to modify drug release rate from silicone matrix. As a result, it was found that (a). addition of human serum albumin (HSA) suppressed initial burst and enhanced release rate in the later stage, resulting constant release of VD(3), (b). covering a matrix formulation with a membrane of low diffusivity (core-rod formulation) suppressed initial burst and released drug in a constant rate, and (3) using materials for which the drug has high affinity as dissolution solvent (reservoir formulation), the drug release rate was reduced.

Novel drug delivery device using silicone: controlled release of insoluble drugs or two kinds of water-soluble drugs

Drug release mechanism from silicone carrier differs depending on physicochemical properties of the drug. So far, there have been few reports on controlled release of insoluble drug and on simultaneous release of two kinds of water-soluble drugs. The purposes of this study are to establish methods for (1). continuous release of insoluble drug, and (2). release of two kinds of water-soluble drugs from silicone carrier. Polystyrene beads (PSTB) and proteins such as interferon (IFN) and human serum albumin (HSA) were used as model drugs. PSTB was released from silicone only when citric acid (CA) and sodium bicarbonate (SB) existed as additives. The release patterns of IFN and HSA were almost same in the case of matrix and covered-rod formulations, but double-layered formulation released them in different patterns. As far as we are aware, this is the first report on the release of insoluble drug from silicone and the controlled release of two kinds of water-soluble drugs.

Sustained release of low-dose ganciclovir from a silicone formulation prolonged the survival of rats with gliosarcomas under herpes simplex virus thymidine kinase suicide gene therapy

A silicone formulation of ganciclovir (GCV-pellet) was developed to enhance the cytotoxic effects of herpes simplex virus thymidine kinase suicide gene therapy. The effectiveness of this drug delivery system was assessed in a rat 9L gliosarcoma model. The GCV-pellets (1 mm in length and in diameter) used in this experiment contained a total amount of 0.15 mg of GCV. In vitro experiments demonstrated that GCV was gradually released over a period of 7 days. Five days after stereotactic tumor inoculation into the right caudate nucleus, a herpes simplex virus type 1 (HSV-1) vector expressing herpes simplex virus thymidine kinase (HSV-tk) (T1, 2x10(6) pfu) was administered at the same location. The survival rate of the group treated with the GCV-pellet was compared with that of the T1 group injected intraperitoneally (IP) with GCV (30 mg/kg/day for 7 days). The GCV-pellet-treated group had a significantly prolonged survival (a median of more than 80 days) compared with the GCV IP group (a median of 65 days) and with control groups (P<0.05). The control groups (untreated or receiving only the virus vector) had a survival of 35-38 days. The survival rate of the GCV-pellet group over 80 days was 75%, and all the rats that survived more than 80 days and did not show tumors upon histological examination of the brain were deemed cured. No toxic effects or immunological reactions were observed histologically around the pellet in brain sections from the rats treated with the GCV-pellet. After GCV-pellet inoculation into the tumor, drug concentrations were kept at 1-10 microg/g tissue for 3-4 days. When the same dose of GCV (0.15 mg) in aqueous solution was injected into the tumor, GCV concentrations reached a peak of 0.5 mg/g tissue after 30 min and decreased below measurable level within 12 h. After IP injections of 3 mg GCV, GCV concentrations in the tumor reached a peak of 5.7 microg/g tissue after 30 min and also decreased below measurable level within 12 h. This sustained release of a low and effective GCV dose with the silicone formulation significantly prolonged survival in combinations with HSV-tk expression if compared to IP administration of GCV. Histological examination suggests that the treatment appears to be safe.

Continuous antigen delivery from controlled release implants induces significant and anamnestic immune responses

Two continuous delivery injectable silicone implants were tested to determine if they were capable of delivering vaccines in a single shot. The Type A implant delivers antigen in vitro over a 1-month-period and the Type B over several months. Vaccination studies in sheep were designed to compare the responses induced by the Type A and B implants, Alzet mini-osmotic pumps and conventional antigen delivery. A model antigen, avidin, was used along with IL-1beta or alum as adjuvants. Sheep were immunised with various formulations and the titre and isotype of the antigen specific antibodies monitored. The Type B implant induced antibody (Ab) titres of greater magnitude and duration than soluble vaccines or the Type A implant with adjuvant, but only if IL-1beta was included in the formulation. Both implants induced antibodies of IgG1 and IgG2 isotype. A memory response to soluble antigen challenge was induced by the Type B+IL-1beta implant, which was predominantly of an IgG1 isotype.