Of microneedles and ultrasound: Physical modes of gastrointestinal macromolecule delivery

Biodegradable polymeric insulin microneedles - a design and materials perspective review

Microneedle (MN) delivery devices are more accepted by people than regular traditional needle injections (e.g. vaccination) due to their simplicity and adaptability. Thus, patients of chronic diseases like diabetes look for alternative pain-free treatment regimens circumventing regular subcutaneous injections. Insulin microneedles (INS-MNs) are a thoughtfully researched topic (1) to overcome needle phobia in patients, (2) for controlled delivery of the peptide, (3) decreasing the frequency of drug administration, (4) to ease the drug administration procedure, and (5) thus increasing patient adherence to the treatment dosage regimes. MNs physically disrupt the hard outer skin layer to create minuscule pores for insulin (INS) to pass through the dermal capillaries into the systemic circulation. Biodegradable polymeric MNs are of greater significance for INS and vaccine delivery than silicon, metal, glass, or non-biodegradable polymeric MNs due to their ease of fabrication, mass production, cost-effectiveness, and bioerodability. In recent years, INS-MNs have been researched to deliver INS through the transdermal implants, buccal mucosa, stomach wall, intestinal mucosal layers, and colonic mucosa apart from the usual transdermal delivery. This review focuses on the design characteristics and the applications of biodegradable/dissolvable polymeric INS-MNs in transdermal, intra-oral, gastrointestinal (GI), and implantable delivery. The prospective approaches to formulate safe, controlled-release INS-MNs were highlighted. Biodegradable/dissolvable polymers, their significance, their impact on MN morphology, and INS release characteristics were outlined. The developments in biodegradable polymeric INS-MN technology were briefly discussed. Bio-erodible polymer selection, MN fabrication and evaluation factors, and other design aspects were elaborated.

Sonosensitive Cavitation Nuclei-A Customisable Platform Technology for Enhanced Therapeutic Delivery

Ultrasound-mediated cavitation shows great promise for improving targeted drug delivery across a range of clinical applications. Cavitation nuclei-sound-sensitive constructs that enhance cavitation activity at lower pressures-have become a powerful adjuvant to ultrasound-based treatments, and more recently emerged as a drug delivery vehicle in their own right. The unique combination of physical, biological, and chemical effects that occur around these structures, as well as their varied compositions and morphologies, make cavitation nuclei an attractive platform for creating delivery systems tuned to particular therapeutics. In this review, we describe the structure and function of cavitation nuclei, approaches to their functionalization and customization, various clinical applications, progress toward real-world translation, and future directions for the field.

Challenges and Opportunities in the Oral Delivery of Recombinant Biologics

Recombinant biological molecules are at the cutting-edge of biomedical research thanks to the significant progress made in biotechnology and a better understanding of subcellular processes implicated in several diseases. Given their ability to induce a potent response, these molecules are becoming the drugs of choice for multiple pathologies. However, unlike conventional drugs which are mostly ingested, the majority of biologics are currently administered parenterally. Therefore, to improve their limited bioavailability when delivered orally, the scientific community has devoted tremendous efforts to develop accurate cell- and tissue-based models that allow for the determination of their capacity to cross the intestinal mucosa. Furthermore, several promising approaches have been imagined to enhance the intestinal permeability and stability of recombinant biological molecules. This review summarizes the main physiological barriers to the oral delivery of biologics. Several preclinical in vitro and ex vivo models currently used to assess permeability are also presented. Finally, the multiple strategies explored to address the challenges of administering biotherapeutics orally are described.

An insight into gastrointestinal macromolecule delivery using physical oral devices

Oral delivery is preferred over other routes of drug administration by both patients and physicians. The bioavailability of some therapeutics that are delivered via the oral route is restricted due to the protease- and bacteria-rich environment in the gastrointestinal tract, and by the pH variability along the delivery route. Given these harsh environments, the oral delivery of therapeutic macromolecules is complicated and remains challenging. Various formulation approaches, including the use of permeation enhancers and nanosized carriers, as well as chemical alteration of the drug structure, have been studied as ways to improve the oral absorption of macromolecular drugs. Nevertheless, the bioavailability of marketed oral peptide medicines is often relatively poor. This review highlights the most recent and promising physical methods for improving the oral bioavailability of macromolecules such as peptides. These methods include microneedle injections, high-speed stream injectors, magnetic drug targeting, expandable hydrogels, and iontophoresis. We highlight the potential and challenges of these new technologies, which may impact the future approaches used by pharmaceutical companies to create more efficient and safer orally administered macromolecules. Teaser: Despite substantial effort, the oral delivery of macromolecules remains challenging due to their low bioavailability. This review discusses the potential, challenges, and safety concerns associated with new technologies and devices for oral macromolecule delivery.

Foundations of gastrointestinal-based drug delivery and future developments

Gastrointestinal-based drug delivery is considered the preferred mode of drug administration owing to its convenience for patients, which improves adherence. However, unique characteristics of the gastrointestinal tract (such as the digestive environment and constraints on transport across the gastrointestinal mucosa) limit the absorption of drugs. As a result, many medications, in particular biologics, still exist only or predominantly in injectable form. In this Review, we examine the fundamentals of gastrointestinal drug delivery to inform clinicians and pharmaceutical scientists. We discuss general principles, including the challenges that need to be overcome for successful drug formulation, and describe the unique features to consider for each gastrointestinal compartment when designing drug formulations for topical and systemic applications. We then discuss emerging technologies that seek to address remaining obstacles to successful gastrointestinal-based drug delivery.

Formulation strategies to improve the efficacy of intestinal permeation enhancers. Adv Drug Deliv Rev 2021;177:113925. [PMID: 34418495 DOI: 10.1016/j.addr.2021.113925]

The use of chemical permeation enhancers (PEs) is the most widely tested approach to improve oral absorption of low permeability active agents, as represented by peptides. Several hundred PEs increase intestinal permeability in preclinical bioassays, yet few have progressed to clinical testing and, of those, only incremental increases in oral bioavailability (BA) have been observed. Still, average BA values of ~1% were sufficient for two recent FDA approvals of semaglutide and octreotide oral formulations. PEs are typically screened in static in vitro and ex-vivo models where co-presentation of active agent and PE in high concentrations allows the PE to alter barrier integrity with sufficient contact time to promote flux across the intestinal epithelium. The capacity to maintain high concentrations of co-presented agents at the epithelium is not reached by standard oral dosage forms in the upper GI tract in vivo due to dilution, interference from luminal components, fast intestinal transit, and possible absorption of the PE per se. The PE-based formulations that have been assessed in clinical trials in either immediate-release or enteric-coated solid dosage forms produce low and variable oral BA due to these uncontrollable physiological factors. For PEs to appreciably increase intestinal permeability from oral dosage forms in vivo, strategies must facilitate co-presentation of PE and active agent at the epithelium for a sustained period at the required concentrations. Focusing on peptides as examples of a macromolecule class, we review physiological impediments to optimal luminal presentation, discuss the efficacy of current PE-based oral dosage forms, and suggest strategies that might be used to improve them.

Devices for drug delivery in the gastrointestinal tract: A review of systems physically interacting with the mucosa for enhanced delivery

The delivery of macromolecules via the gastrointestinal (GI) tract remains a significant challenge. A variety of technologies using physical modes of drug delivery have been developed and investigated to overcome the epithelial cell layer of the GI tract for local and systemic delivery. These technologies include direct injection, jetting, ultrasound, and iontophoresis, which have been largely adapted from transdermal drug delivery. Direct injection of agents using needles through endoscopy has been used clinically for over a century. Jetting, a needle-less method of drug delivery where a high-speed stream of fluid medication penetrates tissue, has been evaluated pre-clinically for delivery of agents into the buccal mucosa. Ultrasound has been shown to be beneficial in enhancing delivery of macromolecules, including nucleic acids, in pre-clinical animal models. The application of an electric field gradient to drive drugs into tissues through the technique of iontophoresis has been shown to deliver highly toxic chemotherapies into GI tissues. Here in, we provide an in-depth overview of these physical modes of drug delivery in the GI tract and their clinical and preclinical uses.

Smart pills for gastrointestinal diagnostics and therapy

Ingestible smart pills have the potential to be a powerful clinical tool in the diagnosis and treatment of gastrointestinal disease. Though examples of this technology, such as capsule endoscopy, have been successfully translated from the lab into clinically used products, there are still numerous challenges that need to be overcome. This review gives an overview of the research being done in the area of ingestible smart pills and reports on the technical challenges in this field.

Physical methods for enhancing drug absorption from the gastrointestinal tract

Overcoming the gastrointestinal (GI) barriers is a formidable challenge in the oral delivery of active macromolecules such as peptide- and protein- based drugs. In the past four decades, a plethora of formulation strategies ranging from permeation enhancers, nanosized carriers, and chemical modifications of the drug's structure has been investigated to increase the oral absorption of these macromolecular compounds. However, only limited successes have been achieved so far, with the bioavailability of marketed oral peptide drugs remaining generally very low. Recently, a few approaches that are based on physical interactions, such as magnetic, acoustic, and mechanical forces, have been explored in order to control and improve the drug permeability across the GI mucosa. Although in the early stages, some of these methods have shown great potential both in terms of improved bioavailability and spatiotemporal delivery of drugs. Here, we offer a concise, yet critical overview of these rather unconventional technologies with a particular focus on their potential and possible challenges for further clinical translation.

Oral Delivery of Biologics in Inflammatory Bowel Disease Treatment

Inflammatory bowel disease (IBD) has been posed as a great worldwide health threat. Having an onset during early adulthood, IBD is a chronic inflammatory disease characterized by remission and relapse. Due to its enigmatic etiology, no cure has been developed at the moment. Conventionally, steroids, 5-aminosalicylic acid, and immunosuppressants have been applied clinically to relieve patients’ syndrome which, unfavorably, causes severe adverse drug reactions including diarrhea, anemia, and glaucoma. Insufficient therapeutic effects also loom, and surgical resection is mandatory in half of the patients within 10 years after diagnosis. Biologics demonstrated unique and differentiative therapeutic mechanism which can alleviate the inflammation more effectively. However, their application in IBD has been hindered considering their stability and toxicity. Scientists have brought up with the concept of nanomedicine to achieve the targeted drug delivery of biologics for IBD. Here, we provide an overview of biologics for IBD treatment and we review existing formulation strategies for different biological categories including antibodies, gene therapy, and peptides. This review highlights the current trends in oral delivery of biologics with an emphasis on the important role of nanomedicine in the development of reliable methods for biologic delivery in IBD treatment.

Reactive oxygen species responsive nanoplatforms as smart drug delivery systems for gastrointestinal tract targeting

The pharmacological therapy for gastrointestinal (GI) diseases, such as inflammatory bowel diseases, continues to present challenges in targeting efficacy. The need for maximal local drug exposure at the inflamed regions of the GI tract has led research to focus on a disease-targeted drug delivery approach. Smart nanomaterials responsive to the reactive oxygen species (ROS) concentrated in the inflamed areas, can be formulated into nanoplatforms to selectively release the active compounds, avoiding unspecific drug delivery to healthy tissues and limiting systemic absorption. Recent developments of ROS-responsive nanoplatforms include combination with other materials to obtain multi-responsive systems and modifications/derivatization to increase the interactions with biological tissues, cell uptake and targeting. This review describes the applications of ROS-responsive nanosystems for on-demand drug delivery to the GI tract.

Quantifying the Value of Orally Delivered Biologic Therapies: A Cost-Effectiveness Analysis of Oral Semaglutide

Oral semaglutide, which has undergone multiple phase 3 clinical trials, represents the first oral biologic medication for type 2 diabetes in the form of a daily capsule. It provides similar efficacy compared with its weekly injection counterpart, but it demands a dose on the order of 100 times as high and requires more frequent administration. We perform a cost effectiveness analysis using a first and second order Monte Carlo simulation to estimate quality-adjusted life expectancies associated with an oral daily capsule, oral weekly capsule, daily injection, and weekly injection of semaglutide. We conclude that the additional costs incurred to produce extra semaglutide for the oral formulation are cost effective, given the greater quality of life experienced when taking a capsule over a weekly injection. We also demonstrate that the potency of semaglutide allows the formulation to be cost effective, and less potent drugs will require increased oral bioavailability to make a cost effective oral formulation.

Ultrasound-Stimulated Phase-Change Contrast Agents for Transepithelial Delivery of Macromolecules, Toward Gastrointestinal Drug Delivery

The gastrointestinal (GI) tract presents a notoriously difficult barrier for macromolecular drug delivery, especially for biologics. Herein, we demonstrate that ultrasound-stimulated phase change contrast agents (PCCAs) can transiently disrupt confluent colorectal adenocarcinoma monolayers and improve the transepithelial transport of a macromolecular model drug. With ultrasound treatment in the presence of PCCAs, we achieved a maximum of 44 ± 15% transepithelial delivery of 70-kDa fluorescein isothiocyanate-dextran, compared with negligible delivery through sham control monolayers. Among all tested rarefactional pressures (300-600 kPa), dextran delivery efficiency was consistently greatest at 300 kPa. To explore this unexpected finding, we quantified stable and inertial cavitation energy generated by various ultrasound exposure conditions. In general, lower pressures resulted in more persistent cavitation activity during the 30-s ultrasound exposures, which may explain the enhanced dextran delivery efficiency. Thus, a unique advantage of using low boiling point PCCAs for this application is that the same low-pressure pulses can be used to induce vaporization and provide maximal delivery.

Recent advances in oral delivery of biologics: nanomedicine and physical modes of delivery

INTRODUCTION

Research into oral delivery of biologics has a long and rich history but has not produced technologies used in the clinic. The area has evolved in terms of strategies to promote oral biologics delivery from early chemical absorption enhancers to nanomedicine to devices. Continued activity in this area is justifiable considering the remarkable proliferation of biologics.

AREAS COVERED

The article discusses some physiological barriers to oral delivery of biologics, with a special focus on less characterized barriers such as the basement membrane. Recent progress in oral delivery of biologics via nanomedicine is subsequently covered. Finally, the emerging field of device-mediated gastrointestinal delivery of biotherapeutics is discussed

EXPERT OPINION

Oral delivery of biologics is considered a 'panacea' in drug delivery. Almost century-old approaches of utilizing chemical absorption enhancers have not produced clinically translated technologies. Nanomedicine for oral biologics delivery has demonstrated potential, but the field is relatively new, and technologies have not progressed to the clinic. Device-mediated oral biologics delivery (e.g. ultrasound or microneedles) is in its infancy. However, this space is likely to intensify owing to advances in electronics and materials, as well as the challenges and history related to clinical translation of alternative approaches.

Defining optimal permeant characteristics for ultrasound-mediated gastrointestinal delivery

Ultrasound-mediated drug delivery in the gastrointestinal (GI) tract is a bourgeoning area of study. Localized, low-frequency ultrasound has recently been shown to enable significant enhancement in delivery of a broad set of active pharmaceutical ingredients including small molecules, proteins, and nucleic acids without any formulation or encapsulation of the therapeutic. Traditional chemical formulations are typically required to protect, stabilize, and enable the successful delivery of a given therapeutic. The use of ultrasound, however, may make delivery insensitive to the chemical formulation. This might open the door to chemical formulations being developed to address other properties besides the deliverability of a therapeutic. Instead, chemical formulations could potentially be developed to achieve novel pharmacokinetics, without consideration of that particular formulation's ability to penetrate the mucus barrier passively. Here we investigated the effect of permeant size, charge, and the presence of chemical penetration enhancers on delivery to GI tissue using ultrasound. Short ultrasound treatments enabled delivery of large permeants, including microparticles, deep into colonic tissue ex vivo. Delivery was relatively independent of size and charge but did depend on conformation, with regular, spherical particles being delivered to a greater extent than long-chain polymers. The subsequent residence time of model permeants in tissue after ultrasound-mediated delivery was found to depend on size, with large microparticles demonstrating negligible clearance from the local tissue 24h after delivery ex vivo. The dependence of clearance time on permeant size was further confirmed in vivo in mice using fluorescently labeled 3kDa and 70kDa dextran. The use of low-frequency ultrasound in the GI tract represents a novel tool for the delivery of a wide-range of therapeutics independent of formulation, potentially allowing for the tailoring of formulations to impart novel pharmacokinetic profiles once delivered into tissue.

Introduction for the special issue on recent advances in drug delivery across tissue barriers

This special issue of Tissue Barriers contains a series of reviews with the common theme of how biological barriers established at epithelial tissues limit the uptake of macromolecular therapeutics. By improving our functional understanding of these barriers, the majority of the authors have highlighted potential strategies that might be applied to the non-invasive delivery of biopharmaceuticals that would otherwise require an injection format for administration. Half of the articles focus on the potential of particular technologies to assist oral delivery of peptides, proteins and other macromolecules. These include use of prodrug chemistry to improve molecule stability and permeability, and the related potential for oral delivery of poorly permeable agents by cell-penetrating peptides and dendrimers. Safety aspects of intestinal permeation enhancers are discussed, along with the more recent foray into drug-device combinations as represented by intestinal microneedles and externally-applied ultrasound. Other articles highlight the crossover between food research and oral delivery based on nanoparticle technology, while the final one provides a fascinating interpretation of the physiological problems associated with subcutaneous insulin delivery and how inefficient it is at targeting the liver.