Injectable silicone implants as vaccine delivery vehicles

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.

Vaccine implants: current status and recent advancements

Implants have long been used in the field of drug delivery as controlled release vehicles and are now being investigated as single-shot vaccine technologies. Implants have shown great promise, minimizing the need for multiple immunizations while stimulating potent immune responses with reduced doses of vaccine. Synchronous release of vaccine components from implants over an appropriate period of time is important in order to avoid issues including immune tolerance, sequestration or deletion. Traditionally, implants require surgical implantation and removal, which can be a barrier to their widespread use. Degradable and in situ implants are now being developed that can be administered using minimally invasive subcutaneous or intramuscular injection techniques. Injectable hydrogels remain the most commonly studied approach for sustained vaccine delivery due to their ease of administration and tunable degradation properties. Despite exciting advancements in the field of vaccine implants, few technologies have progressed to clinical trials. To increase the likelihood of clinical translation of vaccine implants, strategic testing of disease-relevant antigens in appropriate species is essential. In this review, the significance of vaccine implants and the different types of implants being developed to deliver vaccines are discussed.

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.

Numerical modelling and experimental investigation of drug release from layered silicone matrix systems

Medical devices and polymeric matrix systems that release drugs or other bioactive compounds are of interest for a variety of applications. The release of the drug can be dependent on a number of factors such as the solubility, diffusivity, dissolution rate and distribution of the solid drug in the matrix. Achieving the goal of an optimal release profile can be challenging when relying solely on traditional experimental work. Accurate modelling complementing experimentation is therefore desirable. Numerical modelling is increasingly becoming an integral part of research and development due to the significant advances in computer simulation technology. This work focuses on numerical modelling and investigation of multi-layered silicone matrix systems. A numerical model that can be used to model multi-layered systems was constructed and validated by comparison with experimental data. The model could account for the limited dissolution rate and effect of the drug distribution on the release profiles. Parametric study showed how different factors affect the characteristics of drug release. Multi-layered medical silicone matrices were prepared in special moulds, where the quantity of drug in each layer could be varied, and release was investigated with Franz-diffusion cell setup. Data for long-term release was fitted to the model and the full depletion of the system predicted. The numerical model constructed for this study, whose input parameters are the diffusion, effective dissolution rate and dimensional solubility coefficients, does not require any type of steady-state approximation. These results indicate that numerical model can be used as a design tool for development of controlled release systems such as drug-loaded medical devices.

A cationic vaccine adjuvant based on a saturated quaternary ammonium lipid have different in vivo distribution kinetics and display a distinct CD4 T cell-inducing capacity compared to its unsaturated analog

Adjuvants are often composed of different constituents that can be divided into two groups based on their primary activity: the delivery system which carries and presents the vaccine antigen to antigen-presenting cells, and the immunostimulator that activates and modulates the ensuing immune response. Herein, we have investigated the importance of the delivery system and in particular its physical characteristics by comparing the delivery properties of two lipids which differ only in the degree of saturation of the acyl chains, rendering the liposomes either rigid (DDA, dimethyldioctadecylammonium) or highly fluid (DODA, dimethyldioleoylammonium) at physiological temperature. We show that these delivery systems are remarkably different in their ability to prime a Th1-directed immune response with the rigid DDA-based liposomes inducing a response more than 100 times higher compared to that obtained with the fluid DODA-based liposomes. Upon injection with a vaccine antigen, DDA-based liposomes form a vaccine depot that results in a continuous attraction of antigen-presenting cells that engulf a high amount of adjuvant and are subsequently efficiently activated as measured by an elevated expression of the co-stimulatory molecules CD40 and CD86. In contrast, the fluid DODA-based liposomes are more rapidly removed from the site of injection resulting in a lower up-regulation of co-stimulatory CD40 and CD86 molecules on adjuvant-positive antigen-presenting cells. Additionally, the vaccine antigen is readily dissociated from the DODA-based liposomes leading to a population of antigen-presenting cells that are antigen-positive but adjuvant-negative and consequently are not activated. These studies demonstrate the importance of studying in vivo characteristics of the vaccine components and furthermore show that physicochemical properties of the delivery system have a major impact on the vaccine-induced immune response.

Veterinary applications of cytokines

In the recent past a large variety of cytokines have been cloned for most important veterinary species and more is planned with development of a coordinated approach to cytokine reagents production. Application of these cytokines in veterinary species can be found in the development of effective diagnostics, with the IFN-gamma-based detection of tuberculosis as a prime example. In addition, cytokines have been used to determine which immune responses are essential for immune protection with flow-on effects for the development of novel ways to induce these specific immune responses. The realisation that the murine immune system is quite different from the human, together with the increased availability of cytokine reagents for many large animals plus unique experimental approaches only available in these animals, has lead to an explosion in the use of veterinary species as models for human diseases.

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.