An approach to a cold chain free oral cholera vaccine: in vitro and in vivo characterization of Vibrio cholerae gastro-resistant microparticles

Co-spray Drying Drugs with Aqueous Polymer Dispersions (APDs)-a Systematic Review

Aqueous colloidal dispersions of water-insoluble polymers (APDs) avoid hassles associated with the use of organic solvents and offer processing advantages related to their low viscosity and short processing times. Therefore, they became the main vehicle for pharmaceutical coating of tablets and multiparticulates, a process commonly employed using pan and fluidized-bed machinery. Another interesting although less common processing approach is co-spray drying APDs with drugs in aqueous systems. It enables the manufacture of capsule- and matrix-type microspheres with controllable size and improved processing characteristics in a single step. These microspheres can be further formulated into different dosage forms. This systematic review is based on published research articles and aims to highlight the applicability and opportunities of co-spray drying drugs with APDs in drug delivery.

Spray Drying and Particle Engineering in Dosage Form Design for Global Vaccines

Vaccines are a very important tool in the effort to reduce the global burden of infectious diseases. Modern vaccines can be formulated in several ways to induce specific immunity, including through the use of live bacteria, subunit antigens, and even genetic material. However, vaccines typically need to be transported and stored under controlled refrigerated or frozen conditions to maintain potency. This strict temperature control is incompatible with the available infrastructure in many developing countries. One method of improving the thermostability of a vaccine is through drying of a liquid presentation into a dry dosage form. In addition to enhancing the capability for distribution in resource-poor settings, these dry vaccine forms are more suitable for long-term stockpiling. Spray drying is a drying method that has been successfully used to stabilize many experimental vaccines into a dry form for storage above refrigerated temperatures. Additionally, the use of spray drying allows for the production of engineered particles suitable for respiratory administration. These particles can be further designed for increased out-of-package robustness against high humidity. Furthermore, there are already commercial dry powder delivery devices available that can be used to safely deliver vaccines to the respiratory system. The research in this field demonstrates that the resources to develop highly stable vaccines in flexible dosage forms are available and that these presentations offer many advantages for global vaccination campaigns.

Demystifying particle-based oral vaccines

Introduction: The oral route of vaccination is pain- and needle-free and can induce systemic and mucosal immunity. However, gastrointestinal barriers and antigen degradation impose significant hurdles in the development of oral vaccines. Live attenuated viruses and bacteria can overcome these barriers but at the risk of introducing safety concerns. As an alternative, particles have been investigated for antigen protection and delivery, yet there are no FDA-approved oral vaccines based on particle-based delivery systems. Our objective was to discover underlying determinants that can explain the current inadequacies and identify paradigms that can be implemented in future for successful development of oral vaccines relying on particle-based delivery systems.Areas covered: We reviewed literature related to the use of particles for oral vaccination and placed special emphasis on formulation characteristics and administration schedules to gain an insight into how these parameters impact production of antigen-specific antibodies in systemic and mucosal compartments.Expert opinion: Despite the long history of vaccines, particle-based oral vaccination is a relative new field with the first study published in 1989. Substantial variability exists between different studies with respect to dosing schedules, number of doses, and the amount of vaccine per dose. Most studies have not used adjuvants in the formulations. Better standardization in vaccination parameters is required to improve comparison between experiments, and adjuvants should be used to enhance the systemic and mucosal immune responses and to reduce the number of doses, which will make oral vaccines more attractive.

Recent advances in nano/microparticle-based oral vaccines

Background

Vaccines are often recognized as one of the most cost-effective public health interventions in controlling infectious diseases. Most pathogens infiltrate the body from mucosal sites, primarily from the oral and pulmonary region and reach the systemic circulation where disease manifestation starts. Traditional needle-based vaccines are usually not capable of inducing immunity at the mucosal sites where pathogen infiltrates start, but induces systemic immunity. In contrast to needle-based vaccines, mucosally administered vaccines induce immunity at both the mucosal sites and systemically. The oral route of immunization is the most convenient way to administer the vaccines. However, due to the complicated and hostile gastrointestinal structure and environment, vaccines need to overcome major hurdles while retaining their stability and immunogenicity.

Area covered

This review will briefly discuss different barriers to oral vaccine development. It gives a brief overview of different types of nano/microparticle-based oral vaccines and discusses how physicochemical characteristics of the particles influence overall immunity after oral immunization.

Expert opinion

Formulation strategies using novel lipid and polymer-based nano/microparticle platforms retain stability and antigenicity of vaccines against the harsh gastrointestinal condition. The physicochemical properties of particles can be uniquely tailored to prolong the release of antigens, and attached ligands (M-cells and APC-ligands) can precisely target uptake by immune cells. These represent viable strategies for efficient delivery of oral vaccines.

Stability of lyophilized and spray dried vaccine formulations

Liquid formulations of vaccines are subject to instabilities that result from degradation processes that proceed via a variety of physical and chemical pathways. In dried formulations, such as those prepared by lyophilization or spray drying, many of these degradation pathways may be avoided or inhibited. Thus, the stability of vaccine formulations can be enhanced significantly in the absence of bulk water. Potential advantages of dry vaccine formulations include extended shelf lives and less stringent cold-chain storage requirements, both of which offer possibilities of reduced vaccine wastage and facilitated distribution to resource-poor areas. Lyophilization and spray drying represent the most common methods of stabilizing vaccines through drying. This article reviews several lyophilized and spray dried vaccines that address a diverse set of pathogens, as well as some of the assays used to quantify their stability. Recent dry vaccine trends include needle-free delivery of dry powder via non-parenteral routes of administration and the incorporation of advanced vaccine adjuvants into formulations, which further contribute to the goal of increasing vaccine distribution to resource-poor areas. Challenges associated with development of these newer technologies are also discussed.

Current and New Approaches for Mucosal Vaccine Delivery

Mucosal surfaces are the interface between the host’s internal milieu and the external environment, and they have dual functions, serving as physical barriers to foreign antigens and as accepting sites for vital materials. Mucosal vaccines are more favored to prevent mucosal infections from the portal of entry. Although mucosal vaccination has many advantages, licensed mucosal vaccines are scarce. The most widely studied mucosal routes are oral and intranasal. Licensed oral and intranasal vaccines are composed mostly of whole cell killed or live attenuated microorganisms serving as both delivery systems and built-in adjuvants. Future mucosal vaccines should be made with more purified antigen components, which will be relatively less immunogenic. To induce robust protective immune responses against well-purified vaccine antigens, an effective mucosal delivery system is an essential requisite. Recent developments in biomaterials and nanotechnology have enabled many innovative mucosal vaccine trials. For oral vaccination, the vaccine delivery system should be able to stably carry antigens and adjuvants and resist harsh physicochemical conditions in the stomach and intestinal tract. Besides many nano/microcarrier tools generated by using natural and chemical materials, the development of oral vaccine delivery systems using food materials should be more robustly researched to expand vaccine coverage of gastrointestinal infections in developing countries. For intranasal vaccination, the vaccine delivery system should survive the very active mucociliary clearance mechanisms and prove safety because of the anatomical location of nasal cavity separated by a thin barrier. Future mucosal vaccine carriers, regardless of administration routes, should have certain common characteristics. They should maintain stability in given environments, be mucoadhesive, and have the ability to target specific tissues and cells.

Spray-dried pH-sensitive microparticles: effectual methodology to ameliorate the bioavailability of acid labile pravastatin

Pravastatin is a promising drug utilized in the treatment of hyperlipidemia, yet, its main clinical limitation is due to gastric liability which fractions its oral bioavailability to less than 18%. The purpose of the current study is to encapsulate pravastatin into Eudragit^®-based spray-dried microparticles aspiring to overcome its acid liability. With the aim to optimize the microparticles, formulation and process parameters were studied through acid resistance challenging test. Physicochemical characterization of the optimized spray-dried pH-sensitive microparticles namely; in-vitro dissolution, surface morphology, compatibility, and solid-state studies were performed. Moreover, in-vivo evaluation of the microparticles and accelerated stability studies were carried out. The results outlined that polymer to drug ratio at 5:1 and pravastatin concentration at 1%w/w in spray-drying feed solution showed 38.55% and 53.97% encapsulation efficiency, respectively. The significance of process parameters specifically; the flow rate and the inlet temperature on microparticles surface integrity were observed, and optimized until encapsulating efficiency reached 72.37%. The scanning electron microscopical examination of the optimized microparticles illustrate uniform smooth surface spheres entrapping the drug in an amorphous state as proved through Differential Scanning Calorimetry (DSC) and Fourier Transfer Infrared (FTIR) studies. The in-vivo evaluation demonstrated a 5-fold enhancement in pravastatin bioavailability compared to the marketed product. The results provided evidence for the significance of spray-dried pH-sensitive microparticles as a promising carrier for pravastatin, decreasing its acid liability, and improving its bioavailability.

Developments in the formulation and delivery of spray dried vaccines

Spray drying is a promising method for the stabilization of vaccines, which are usually formulated as liquids. Usually, vaccine stability is improved by spray drying in the presence of a range of excipients. Unlike freeze drying, there is no freezing step involved, thus the damage related to this step is avoided. The edge of spray drying resides in its ability for particles to be engineered to desired requirements, which can be used in various vaccine delivery methods and routes. Although several spray dried vaccines have shown encouraging preclinical results, the number of vaccines that have been tested in clinical trials is limited, indicating a relatively new area of vaccine stabilization and delivery. This article reviews the current status of spray dried vaccine formulations and delivery methods. In particular it discusses the impact of process stresses on vaccine integrity, the application of excipients in spray drying of vaccines, process and formulation optimization strategies based on Design of Experiment approaches as well as opportunities for future application of spray dried vaccine powders for vaccine delivery.

Thermostability of the coating, antigen and immunostimulator in an adjuvanted oral capsule vaccine formulation

Oral vaccines present an attractive alternative to injectable vaccines for enteric diseases due to ease of delivery and the induction of intestinal immunity at the site of infection. However, susceptibility to gastrointestinal proteolysis, limited transepithelial uptake and a lack of clinically acceptable adjuvants present significant challenges. A further challenge to mass vaccination in developing countries is the very expensive requirement to maintain the cold chain. We recently described the effectiveness of a Single Multiple Pill^® (SmPill^®) adjuvanted capsule approach to enhance the effectiveness of a candidate enterotoxigenic Escherichia coli (ETEC) oral vaccine. Here it was demonstrated that this delivery system maintains the antigenicity of ETEC colonisation factor antigen I (CFA/I) and the immunostimulatory activity of the orally active α-Galactosylceramide (α-GalCer) adjuvant after storage of SmPill^® minispheres under room temperature and extreme storage conditions for several months. In addition, the internal structure of the cores of SmPill^® minispheres and antigen release features at intestinal pH were found to be preserved under all these conditions. However, changes in the surface morphology of SmPill^® minispheres leading to the antigen release at gastric pH were observed after a few weeks of storage under extreme conditions. Those modifications were prevented by the introduction of an Opadry^® White film coating layer between the core of SmPill^® minispheres and the enteric coating. Under these conditions, protection against antigen release at gastric pH was maintained even under high temperature and humidity conditions. These results support the potential of the SmPill^® minisphere approach to maintain the stability of an adjuvanted whole cell killed oral vaccine formulation.

Evaluation of microparticulate ovarian cancer vaccine via transdermal route of delivery

Ovarian cancer is the fifth most commonly occurring malignancy in women, with the highest mortality rate among all the gynecological tumors. Microparticulate vaccine can serve as an immunotherapeutic approach with a promising antigenic delivery system without a need for conventional adjuvants. In this study, a microparticulate vaccine using whole cell lysate of a murine ovarian cancer cell line, ID8 was prepared by spray drying. Further, the effect of interleukins (ILs) such as IL-2 and IL-12 was evaluated in a separate study group by administering them with vaccine particles to enhance the immune response. The vaccine microparticles were administered to C57BL/6 female mice via transdermal alone and in combination with the oral route. The transdermal vaccine was delivered using a metallic microneedle device, AdminPen™. Orally administered microparticles also included an M-cell targeting ligand, Aleuria aurantia lectin, to enhance the targeted uptake from microfold cells (M-cells) in Peyer's patches of small intestine. In case of combination of routes, mice were given 5 transdermal doses and 5 oral doses administered alternatively, beginning with transdermal dose. At the end of vaccination, mice were challenged with live tumor cells. Vaccine alone resulted in around 1.5 times tumor suppression in case of transdermal and combination of routes at the end of 15th week when compared to controls. Inclusion of interleukins resulted in 3 times tumor suppression when administered with transdermal vaccine and around 9 times tumor suppression for the combination route of delivery in comparison to controls. These results were further potentiated by serum IgG, IgG1 and IgG2a titers. Moreover, CD8+ T-cell, CD4+ T-cell and NK (natural killer) cell populations in splenocytes were elevated in case of vaccinated mice. Thus, vaccine microparticles could trigger humoral as well as cellular immune response when administered transdermally and via combination of route of delivery. However overall, vaccine administered with interleukins, via combination of route, was found to be the most efficacious to suppress the tumor growth and lead to a protective immune response.

Particulate delivery systems for vaccination against bioterrorism agents and emerging infectious pathogens

Bioterrorism agents that can be easily transmitted with high mortality rates and cause debilitating diseases pose major threats to national security and public health. The recent Ebola virus outbreak in West Africa and ongoing Zika virus outbreak in Brazil, now spreading throughout Latin America, are case examples of emerging infectious pathogens that have incited widespread fear and economic and social disruption on a global scale. Prophylactic vaccines would provide effective countermeasures against infectious pathogens and biological warfare agents. However, traditional approaches relying on attenuated or inactivated vaccines have been hampered by their unacceptable levels of reactogenicity and safety issues, whereas subunit antigen-based vaccines suffer from suboptimal immunogenicity and efficacy. In contrast, particulate vaccine delivery systems offer key advantages, including efficient and stable delivery of subunit antigens, co-delivery of adjuvant molecules to bolster immune responses, low reactogenicity due to the use of biocompatible biomaterials, and robust efficiency to elicit humoral and cellular immunity in systemic and mucosal tissues. Thus, vaccine nanoparticles and microparticles are promising platforms for clinical development of biodefense vaccines. In this review, we summarize the current status of research efforts to develop particulate vaccine delivery systems against bioterrorism agents and emerging infectious pathogens. WIREs Nanomed Nanobiotechnol 2017, 9:e1403. doi: 10.1002/wnan.1403 For further resources related to this article, please visit the WIREs website.

Delivery strategies to enhance oral vaccination against enteric infections

While the majority of human pathogens infect the body through mucosal sites, most licensed vaccines are injectable. In fact the only mucosal vaccine that has been widely used globally for infant and childhood vaccination programs is the oral polio vaccine (OPV) developed by Albert Sabin in the 1950s. While oral vaccines against Cholera, rotavirus and Salmonella typhi have also been licensed, the development of additional non-living oral vaccines against these and other enteric pathogens has been slow and challenging. Mucosal vaccines can elicit protective immunity at the gut mucosa, in part via antigen-specific secretory immunoglobulin A (SIgA). However, despite their advantages over the injectable route, oral vaccines face many hurdles. A key challenge lies in design of delivery strategies that can protect antigens from degradation in the stomach and intestine, incorporate appropriate immune-stimulatory adjuvants and control release at the appropriate gastrointestinal site. A number of systems including micro and nanoparticles, lipid-based strategies and enteric capsules have significant potential either alone or in advanced combined formulations to enhance intestinal immune responses. In this review we will outline the opportunities, challenges and potential delivery solutions to facilitate the development of improved oral vaccines for infectious enteric diseases.

Mannose derivative and lipid A dually decorated cationic liposomes as an effective cold chain free oral mucosal vaccine adjuvant-delivery system

To develop convenient, effective cold chain-free subunit vaccines, a mannose-PEG-cholesterol conjugate (MPC) was synthesized as a lectin binding molecule and anchored onto liposomes which entrapped lipid A and model antigen to form a vaccine adjuvant-delivery system targeting antigen presenting cells. With MPC, soy phosphatidylcholine, stearylamine and monophosphoryl lipid A as emulsifiers dissolved in oil phase (O), and sucrose and BSA in water phase (W), the O/W emulsions were prepared and subsequently lyophilized. The lyophilized product was stable enough to be stored at room temperature and, upon rehydration, formed MPC-/lipid A-liposomes (MLLs) with a size under 300 nm and antigen association rates of around 36%. The MLLs given to mice via oral mucosal (o.m.) administration showed no side effects but induced potent immune responses as evidenced by the high levels of IgG in the sera and IgA in the salivary, intestinal and vaginal secretions of mice. High levels of IgG2a and IFN-γ in treated mice revealed that MLLs via o.m. vaccination induced a mixed Th1/Th2 response against antigens, establishing both humoral and cellular immunity. Thus, the MLLs may be a potent cold chain-free oral mucosal vaccine adjuvant-delivery system.

Cellulose acetate phthalate microparticles containing Vibrio cholerae: steps toward an oral cholera vaccine

Oral cholera vaccine (OCV) has been recommended in some endemic areas and epidemic situations since 1999. Although safe and effective vaccines are currently on the market, the burden of transport and storage remains an issue. Herein, we report an approach to develop an alternative OCV in the form of a gastro-resistant powder. Heat-killed Vibrio cholerae (VC) was encapsulated with a spray-drying technique at different temperatures. Cellulose acetate phthalate (Aquacoat® CPD) was chosen as the core polymer and the addition of alginate was studied. The microparticles (MPs) produced were characterized by surface morphology, particle size, drug loading, antigenicity and gastro resistance. The MPs obtained were 6 µm in size and had appropriate drug content, ranging from 8.16 to 8.64%. Furthermore, antigenicity was maintained, never dropping below 85%, and enteric properties were achieved for all the formulations. Next, an in vivo study was carried out with Aquacoat® CPD MP prepared at 80 °C with and without alginate. Two different doses were assayed, 30 and 60 mg, and compared to the VC suspension. The evoked immune responses showed that alginate containing MPs, especially at the 30 mg dose, displayed values that were very similar to those of VC. In conclusion, spray-dried alginate VC MPs seem to be a promising step toward a powder-form cholera vaccination.

Using procedure of emulsification-lyophilization to form lipid A-incorporating cochleates as an effective oral mucosal vaccine adjuvant-delivery system (VADS)

Using a procedure of emulsification-lyophilization (PEL), adjuvant lipid A-cochleates (LACs) were prepared as a carrier for model antigen bovine serum albumin (BSA). With phosphatidylserine and lipid A as emulsifiers dissolved in oil phase (O), sucrose and CaCl2 in the inner water phase (W1), and BSA, sucrose and PEG2000 in the outer water phase (W2), the W1/O/W2 emulsions were prepared and subsequently lyophilized to form a dry product which was stable enough to be stored at room temperature. Upon rehydration of the dry products, cochleates formed with a size of 800 nm and antigen association rates of 38%. After vaccination of mice through oral mucosal (o.m.) administration, LACs showed no side effects but induced potent immune responses as evidenced by high levels of IgG in the sera and IgA in the salivary, intestinal and vaginal secretions of mice. In addition, high levels of IgG2a and IFN-γ in the sera or culture supernatants of splenocytes of the immunized mice were also detected. These results revealed that LACs induced a mixed Th1/Th2 response against the loaded antigens. Thus, the LACs prepared by PEL were able to induce both systemic and mucosal immune responses and may act as a potent cold-chain-free oral mucosal vaccine adjuvant delivery system (VADS).

The state-of-the-art of approved and under-development cholera vaccines

Cholera remains a huge public health problem. Although in 1894, the first cholera vaccination was reported, an ideal vaccine that meets all the requirements of the WHO has not yet been produced. Among the different approaches used for cholera vaccination, attenuated vaccines represent a major category; these vaccines are beneficial in being able to induce a strong protective response after a single administration. However, they have possible negative effects on immunocompromised patient populations. Both the licensed CVD103-HgR and other vaccine approaches under development are detailed in this article, such as the Vibrio cholerae 638 vaccine candidate, Peru-15 or CholeraGarde(®) and the VA1.3, VA1.4, IEM 108 VCUSM2 and CVD 112 vaccine candidates. In another strategy, killed V. cholerae vaccines have been developed, including Dukoral(®), mORCAX(®) and Sanchol™. The killed vaccines are already sold, and they have successfully demonstrated their potential to protect populations in endemic areas or after natural disasters. However, these vaccines do not fulfill all the requirements of the WHO because they fail to confer long-term protection, are not suitable for children under two years, require more than a single dose and require a distribution chain with cold storage. Lastly, other vaccine strategies under development are summarized in this review. Among these strategies, vaccine candidates based on alternative drug delivery systems that have been reported lately in the literature are discussed, such as microparticles, proteoliposomes, LPS subunits, DNA vaccines and rice seeds containing toxin subunits. Preliminary results reported by many groups working on alternative delivery systems for cholera vaccines demonstrate the importance of new technologies in addressing old problems such as cholera. Although a fully ideal vaccine has not yet been designed, promising steps have been reported in the literature resulting in hope for the fight against cholera.