Formulation approaches for improved retinoids delivery in the treatment of several pathologies

Structure-Activity Relationships and Therapeutic Applications of Retinoids in View of Potential Benefits from Drug Repurposing Process

Vitamin A, an essential micronutrient, is integral to various biological processes crucial for organismal development and maintenance. Dietary sources of vitamin A encompass preformed retinol, retinyl esters, and provitamin A carotenoids. Retinoic acid (RA), a key component, plays pivotal roles in vision, cell proliferation, apoptosis, immune function, and gene regulation. Drug repurposing, an effective strategy for identifying new therapeutic applications for existing drugs, has gained prominence in recent years. This review seeks to provide a comprehensive overview of the current research landscape surrounding retinoids and drug repurposing. The scope of this review encompasses a comprehensive examination of retinoids and their potential for repurposing in various therapeutic contexts. Despite their efficacy in treating dermatological conditions, concerns about toxicity persist, driving the search for safer and more potent retinoids. The molecular mechanisms underlying retinoid activity involve binding to retinoic acid receptors (RARs) and retinoid X receptors (RXRs), leading to transcriptional regulation of target genes. This review seeks to shed light on the possibilities for repurposing retinoids to cover a wider spectrum of therapeutic uses by exploring recent scientific progress. It also aims to offer a more comprehensive understanding of the therapeutic prospects of retinoids and the broader impact of drug repositioning in contemporary medicine.

Attempts to Improve Lipophilic Drugs' Solubility and Bioavailability: A Focus on Fenretinide

The development of numerous drugs is often arrested at clinical testing stages, due to their unfavorable biopharmaceutical characteristics. It is the case of fenretinide (4-HPR), a second-generation retinoid, that demonstrated promising in vitro cytotoxic activity against several cancer cell lines. Unfortunately, response rates in early clinical trials with 4-HPR did not confirm the in vitro findings, mainly due to the low bioavailability of the oral capsular formulation that was initially developed. Capsular 4-HPR provided variable and insufficient drug plasma levels attributable to the high hepatic first-pass effect and poor drug water solubility. To improve 4-HPR bioavailability, several approaches have been put forward and tested in preclinical and early-phase clinical trials, demonstrating generally improved plasma levels and minimal systemic toxicities, but also modest antitumor efficacy. The challenge is thus currently still far from being met. To redirect the diminished interest of pharmaceutical companies toward 4-HPR and promote its further clinical development, this manuscript reviewed the attempts made so far by researchers to enhance 4-HPR bioavailability. A comparison of the available data was performed, and future directions were proposed.

In vitro bioaccessibility and intestinal transport of retinoic acid in ethyl cellulose-based microparticles and impact of meal co-ingestion

The development of carrier-based delivery systems for oral administration of retinoic acid (RA), that provides its release and absorption at intestinal level, is of major relevance in the treatment of acute promyelocytic leukemia. The aim of this work was to evaluate RA bioaccessibility and intestinal transport on ethyl cellulose (EC)- and EC + polyethylene glycol (ECP)-based microparticles and to understand the impact of meal co-ingestion by applying in vitro assays. RA-loaded microparticles were produced by spray-drying with an encapsulation efficiency higher than 90 % for both formulations. The gastric bioaccessibility of RA (after in vitro static digestion of RA-loaded particles) was lower than 3 % for both types of microparticles, with and without meal co-ingestion. Whereas after intestinal digestion, RA bioaccessibility was significantly higher and affected by the type of microparticles and the presence of meal. The digestion of EC- and ECP-based microparticles without diet enabled a significantly higher bioaccessibility of RA when compared to the one recorded for the co-digestion of these microparticles with diet. Herein, RA bioaccessibility decreased from 84 ± 1 to 24 ± 6 % (p < 0.0001) for microparticles EC and 54 ± 4 to 25 ± 5 % (p < 0.001) for microparticles ECP. Moreover, comparing both types of microparticles, RA bioaccessibility was significantly higher for EC-based microparticles digested without diet (p < 0.0001). At last, the bioaccessibility of RA was similar among EC- and ECP-based microparticles when co-digested with diet. Intestinal transport experiments performed in Caco-2 monolayers evidenced that after 2 h of transport the amount of RA retained in the apical compartment was higher than the amount that reached the basolateral compartment evidencing a slow transport at intestinal level that was higher when RA is spiked in the blank of digestion and the meal digestion samples compared to RA dissolved in HBSS (44 ± 6 (p < 0.01) and 38 ± 1 (p < 0.05) vs 26 ± 2 %, respectively).

A Brief Review on the Electrohydrodynamic Techniques Used to Build Antioxidant Delivery Systems from Natural Sources

Extracts from plants have been one of the main sources of antioxidants, namely polyphenols. The associated drawbacks, such as instability against environmental factors, low bioavailability, and loss of activity, must be considered during microencapsulation for a better application. Electrohydrodynamic processes have been investigated as promising tools to fabricate crucial vectors to minimize these limitations. The developed microstructures present high potential to encapsulate active compounds and for controlling their release. The fabricated electrospun/electrosprayed structures present different benefits when compared with structures developed by other techniques; they present a high surface-area-to-volume ratio as well as porosity, great materials handling, and scalable production-among other advantages-which make them able to be widely applied in different fields, namely in the food industry. This review presents a summary of the electrohydrodynamic processes, main studies, and their application.

Application of Ethyl Cellulose and Ethyl Cellulose + Polyethylene Glycol for the Development of Polymer-Based Formulations using Spray-Drying Technology for Retinoic Acid Encapsulation

Ethyl cellulose (EC)-based microparticles, with and without the incorporation of polyethylene glycol (PEG) as a second encapsulating agent, were prepared using the spray-drying process for the encapsulation of retinoic acid (RA). The production of a suitable controlled delivery system for this retinoid will promote its antitumor efficiency against acute promyelocytic leukemia (APL) due to the possibility of increasing the bioavailability of RA. Product yield ranged from 12 to 28% in all the microparticle formulations, including unloaded microparticles and RA-loaded microparticles. Microparticles with a mean diameter between 0.090 ± 0.002 and 0.54 ± 0.02 µm (number size distribution) and with an irregular form and rough surface were obtained. Furthermore, regarding RA-loaded microparticles, both polymer-based formulations exhibited an encapsulation efficiency of around 100%. A rapid and complete RA release was reached in 40 min from EC− and EC + PEG-based microparticles.

Development of Inhalable ATRA-Loaded PLGA Nanoparticles as Host-Directed Immunotherapy against Tuberculosis

Developing new effective treatment strategies to overcome the rise in multi-drug resistant tuberculosis cases (MDR-TB) represents a global challenge. A host-directed therapy (HDT), acting on the host immune response rather than Mtb directly, could address these resistance issues. We developed an HDT for targeted TB treatment, using All Trans Retinoic Acid (ATRA)-loaded nanoparticles (NPs) that are suitable for nebulization. Efficacy studies conducted on THP-1 differentiated cells infected with the H37Ra avirulent Mycobacterium tuberculosis (Mtb) strain, have shown a dose-dependent reduction in H37Ra growth as determined by the BACT/ALERT^® system. Confocal microscopy images showed efficient and extensive cellular delivery of ATRA-PLGA NPs into THP-1-derived macrophages. A commercially available vibrating mesh nebulizer was used to generate nanoparticle-loaded droplets with a mass median aerodynamic diameter of 2.13 μm as measured by cascade impaction, and a volumetric median diameter of 4.09 μm as measured by laser diffraction. In an adult breathing simulation experiment, 65.1% of the ATRA PLGA-NP dose was inhaled. This targeted inhaled HDT could offer a new adjunctive TB treatment option that could enhance current dosage regimens leading to better patient prognosis and a decreasing incidence of MDR-TB.

All trans retinoic acid as a host-directed immunotherapy for tuberculosis

Tuberculosis (TB) is the top bacterial infectious disease killer and one of the top ten causes of death worldwide. The emergence of strains of multiple drug-resistant tuberculosis (MDR-TB) has pushed our available stock of anti-TB agents to the limit of effectiveness. This has increased the urgent need to develop novel treatment strategies using currently available resources. An adjunctive, host-directed therapy (HDT) designed to act on the host, instead of the bacteria, by boosting the host immune response through activation of intracellular pathways could be the answer. The integration of multidisciplinary approaches of repurposing currently FDA-approved drugs, with a targeted drug-delivery platform is a very promising option to reduce the long timeline associated with the approval of new drugs - time that cannot be afforded given the current levels of morbidity and mortality associated with TB infection. The deficiency of vitamin A has been reported to be highly associated with the increased susceptibility of TB. All trans retinoic acid (ATRA), the active metabolite of vitamin A, has proven to be very efficacious against TB both in vitro and in vivo. In this review, we discuss and summarise the importance of vitamin A metabolites in the fight against TB and what is known regarding the molecular mechanisms of ATRA as a host-directed therapy for TB including its effect on macrophages cytokine profile and cellular pathways. Furthermore, we focus on the issues behind why previous clinical trials with vitamin A supplementation have failed, and how these issues might be overcome.

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Tuberculosis deaths and resistance are increasing – novel therapies are needed.

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Vitamin A deficiency is a strong risk factor for active tuberculosis in contacts.

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All Trans Retinoic Acid is a promising host-directed therapy for tuberculosis.

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It has pleiotropic effects on macrophages & other immune cells in vitro and in vivo.

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Inhaled rather than systemic All Trans Retinoic Acid therapy may be most effective.

Retinoids Delivery Systems in Cancer: Liposomal Fenretinide for Neuroectodermal-Derived Tumors

Retinoids are a class of natural and synthetic compounds derived from vitamin A. They are involved in several biological processes like embryogenesis, reproduction, vision, growth, inflammation, differentiation, proliferation, and apoptosis. In light of their important functions, retinoids have been widely investigated for their therapeutic applications. Thus far, their use for the treatment of several types of cancer and skin disorders has been reported. However, these therapeutic agents present several limitations for their widespread clinical translatability, i.e., poor solubility and chemical instability in water, sensitivity to light, heat, and oxygen, and low bioavailability. These characteristics result in internalization into target cells and tissues only at low concentration and, consequently, at an unsatisfactory therapeutic dose. Furthermore, the administration of retinoids causes severe side-effects. Thus, in order to improve their pharmacological properties and circulating half-life, while minimizing their off-target uptake, various retinoids delivery systems have been recently developed. This review intends to provide examples of retinoids-loaded nano-delivery systems for cancer treatment. In particular, the use and the therapeutic results obtained by using fenretinide-loaded liposomes against neuroectodermal-derived tumors, such as melanoma, in adults, and neuroblastoma, the most common extra-cranial solid tumor of childhood, will be discussed.

The Fabrication and in vitro Evaluation of Retinoic Acid-Loaded Electrospun Composite Biomaterials for Tracheal Tissue Regeneration

Although relatively rare, major trauma to the tracheal region of the airways poses a significant clinical challenge with few effective treatments. Bioengineering and regenerative medicine strategies have the potential to create biocompatible, implantable biomaterial scaffolds, with the capacity to restore lost tissue with functional neo-trachea. The main goal of this study was to develop a nanofibrous polycaprolactone-chitosan (PCL-Chitosan) scaffold loaded with a signaling molecule, all-trans retinoic acid (atRA), as a novel biomaterial approach for tracheal tissue engineering. Using the Spraybase® electrospinning platform, polymer concentration, solvent selection, and instrument parameters were optimized to yield a co-polymer with nanofibers of 181-197 nm in diameter that mimicked tracheobronchial tissue architecture. Thereafter, scaffolds were assessed for their biocompatibility and capacity to induce mucociliary functionalization using the Calu-3 cell line. PCL-Chitosan scaffolds were found to be biocompatible in nature and support Calu-3 cell viability over a 14 day time period. Additionally, the inclusion of atRA did not compromise Calu-3 cell viability, while still achieving an efficient encapsulation of the signaling molecule over a range of atRA concentrations. atRA release from scaffolds led to an increase in mucociliary gene expression at high scaffold loading doses, with augmented MUC5AC and FOXJ1 detected by RT-PCR. Overall, this scaffold integrates a synthetic polymer that has been used in human tracheal stents, a natural polymer generally regarded as safe (GRAS), and a drug with decades of use in patients. Coupled with the scalable nature of electrospinning as a fabrication method, all of these characteristics make the biomaterial outlined in this study amenable as an implantable device for an unmet clinical need in tracheal replacement.