The Importance of Nanocarrier Design and Composition for an Efficient Nanoparticle-Mediated Transdermal Vaccination

The World Health Organization estimates that the pandemic caused by the SARS-CoV-2 virus claimed more than 3 million lives in 2020 alone. This situation has highlighted the importance of vaccination programs and the urgency of working on new technologies that allow an efficient, safe, and effective immunization. From this perspective, nanomedicine has provided novel tools for the design of the new generation of vaccines. Among the challenges of the new vaccine generations is the search for alternative routes of antigen delivery due to costs, risks, need for trained personnel, and low acceptance in the population associated with the parenteral route. Along these lines, transdermal immunization has been raised as a promising alternative for antigen delivery and vaccination based on a large absorption surface and an abundance of immune system cells. These features contribute to a high barrier capacity and high immunological efficiency for transdermal immunization. However, the stratum corneum barrier constitutes a significant challenge for generating new pharmaceutical forms for transdermal antigen delivery. This review addresses the biological bases for transdermal immunomodulation and the technological advances in the field of nanomedicine, from the passage of antigens facilitated by devices to cross the stratum corneum, to the design of nanosystems, with an emphasis on the importance of design and composition towards the new generation of needle-free nanometric transdermal systems.

Critical quality attributes, in vitro release and correlated in vitro skin permeation-in vivo tape stripping collective data for demonstrating therapeutic (non)equivalence of topical semisolids: A case study of "ready-to-use" vehicles

This work aimed to prove the ability of "ready-to-use" topical vehicles based on alkyl polyglucoside-mixed emulsifier (with/without co-solvent modifications) to replace the conventionally used pharmacopoeial bases (e.g., non-ionic hydrophilic cream) in compounding practice. For this purpose, considering the regulatory efforts to establish alternative, scientifically valid methods for evaluating therapeutic equivalence of topical semisolids, we performed a comparative assessment of microstructure, selected critical quality attributes (CQAs) and in vitro/in vivo product performances, by utilizing aceclofenac as a model drug. The differences in composition between investigated samples have imposed remarkable variances in monitored CQAs (particularly in the amount of aceclofenac dissolved, rheological properties and water distribution mode), reflecting the distinct differences in microstructure formed, as partially observed by polarization microscopy and confocal Raman spectral imaging. Although not fully indicative of the in vivo performances, in vitro release data (vertical diffusion vs. immersion cells) proved the microstructure peculiarities, asserting the rheological properties as decisive factor for obtained liberation profiles. Contrary, in vitro permeation results obtained using pig ear epidermis correlated well with in vivo dermatopharmacokinetic data and distinguished unequivocally between tested formulations, emphasizing the importance of skin/vehicle interactions. In summary, suggested multi-faceted approach can provide adequate proof on topical semisolids therapeutic equivalence or lack thereof.

Topical delivery of anthramycin I. Influence of neat solvents

Anthramycin (ANT) was the first pyrrolobenzodiazepine (PBD) molecule to be isolated, and is a potent cytotoxic agent. Although the PBD family has been investigated for use in systemic chemotherapy, their application in the management of actinic keratoses (AK) or skin cancer has not been investigated to date. In the present work, anthramycin (ANT) was selected as a model PBD compound, and the skin penetration of the molecule was investigated using conventional Franz diffusion cells. Finite dose permeation studies of ANT were performed using propylene glycol (PG), 1,3-butanediol (BD), dipropylene glycol (DiPG), Transcutol P® (TC), propylene glycol monocaprylate (PGMC), propylene glycol monolaurate (PGML) and isopropyl myristate (IPM). The skin penetration of BD, DiPG, PG and TC was also measured. Penetration of ANT through human skin was evident for TC, PG and PGML with the active appearing to "track" the permeation of the vehicle in the case of TC and PG. Deposition of ANT in skin could be correlated with skin retention of the vehicle in the case of IPM, PGMC and PGML. These preliminary findings confirm the ability of ANT to penetrate human skin and, given the potency of the molecule, suggest that further investigation is justified. Additionally, the findings emphasise the critical importance of understanding the fate of the excipient for the rational design of topical formulations.

Solid-in-oil nanodispersions for transdermal drug delivery systems

Transdermal administration of drugs has advantages over conventional oral administration or administration using injection equipment. The route of administration reduces the opportunity for drug evacuation before systemic circulation, and enables long-lasting drug administration at a modest body concentration. In addition, the skin is an attractive route for vaccination, because there are many immune cells in the skin. Recently, solid-in-oil nanodisperison (S/O) technique has demonstrated to deliver cosmetic and pharmaceutical bioactives efficiently through the skin. S/O nanodispersions are nanosized drug carriers designed to overcome the skin barrier. This review discusses the rationale for preparation of efficient and stable S/O nanodispersions, as well as application examples in cosmetic and pharmaceutical materials including vaccines. Drug administration using a patch is user-friendly, and may improve patient compliance. The technique is a potent transcutaneous immunization method without needles.

Safety Assessment of Alkyl Esters as Used in Cosmetics

The Cosmetic Ingredient Review Expert Panel (Panel) assessed the safety of 237 alkyl esters for use in cosmetics. The alkyl esters included in this assessment have a variety of reported functions in cosmetics, with skin-conditioning agent being the most common function. The Panel reviewed available animal and clinical data in making its determination of safety on these ingredients, and where there were data gaps, similarity in structure, properties, functions, and uses of these ingredients allowed for extrapolation of the available toxicological data to assess the safety of the entire group. The Panel concluded that these ingredients are safe in cosmetic formulations in the present practices of use and concentration when formulated to be nonirritating.

Effect of permeation enhancers on transdermal delivery of fluoxetine: in vitro and in vivo evaluation

The aim of this study was to investigate the feasibility of transdermal fluoxetine (FX) delivery. The effects of chemical forms (base or salt) and permeation enhancers on in vitro skin permeation of FX were assessed using hairless mouse, rat and human cadaver skin. The optimized formulations from the in vitro studies were then evaluated in an in vivo pharmacokinetic study in rats. The in vitro skin permeation studies suggested that the FX base (FXB) and isopropyl myristate (IPM)-limonene mixture could be suitable for transdermal delivery of FX. The permeation parameters of FX through human cadaver skin were well correlated with that through hairless mouse and rat skin, suggesting that these animal models can be used for predicting the permeability of FX through human skin. After transdermal administration of FX with IPM or the IPM-limonene mixture to rats, the mean steady-state plasma concentration (Css) was 66.20 or 77.55 ng/mL, respectively, which was maintained over 36 h and had a good correlation with the predicted Css from the in vitro data. These in vitro and in vivo data demonstrated that permeation enhancers could be a potential strategy for transdermal delivery of FX.

Cell-penetrating peptides as a novel transdermal drug delivery system

In the last decade, almost one-third of the newly discovered drugs approved by the US FDA were biomolecules and biologics. Effective delivery of therapeutic biomolecules to their target is a challenging issue. Innovations in drug delivery systems have improved the efficiency of many of new biopharmaceuticals. Designing of novel transdermal delivery systems has been one of the most important pharmaceutical innovations, which offers a number of advantages. The cell-penetrating peptides have been increasingly used to mediate delivery of bimolecular cargoes such as small molecules, small interfering RNA nucleotides, drug-loaded nanoparticles, proteins, and peptides, both in vitro and in vivo, without using any receptors and without causing any significant membrane damage. Among several different drug delivery routes, application of cell-penetrating peptides in the topical and transdermal delivery systems has recently garnered tremendous attention in both cosmeceutical and pharmaceutical research and industries. In this review, we discuss history of cell-penetrating peptides, cell-penetrating peptide/cargo complex formation, and their mechanisms of cell and skin transduction.