Redox-Responsive Nanocarrier for Controlled Release of Drugs in Inflammatory Skin Diseases

Versatile and Controlled Synthesis of Degradable, Water-Soluble Bottlebrush Polymers with Poly(disulfide) Backbones Derived from α-Lipoic Acid

Bottlebrush (BB) polymers, with their densely grafted side chains and unique architecture, are highly advantageous for drug delivery due to their high functional group density for drug conjugation, unimolecular nature, and enhanced biodistribution properties. These attributes enable extended blood circulation half-life, improved tumor tissue penetration, and high tumoral drug accumulation. However, the typically nondegradable, all-carbon backbones of most BB polymers limit their suitability for applications requiring controlled clearance and biodegradability. To address this, we developed degradable BB polymers with poly(disulfide) backbones synthesized via reversible addition-fragmentation chain transfer (RAFT) copolymerization of α-lipoic acid (LA), a renewable and readily available compound, with acrylate-based inimers. These copolymers feature degradable backbones and initiating sites for subsequent BB synthesis. Using an atom transfer radical polymerization (ATRP) grafting-from methodology, we synthesized BB polymers with relatively low dispersities (Đ = 1.30-1.53), high backbone degrees of polymerization (DPbb), and high molar masses (Mn,MALS = 650-2700 kg/mol). The easily cleavable disulfide bonds enabled backbone degradation under mild reducing conditions. Beyond hydrophilic BB with tri(ethylene glycol) methyl ether acrylate (TEGA) side chains, we synthesized BB with cationic, anionic, and zwitterionic side chains, demonstrating broad monomer compatibility. This scalable approach produces water-soluble, degradable BB polymers with tunable architectures and predictable molecular weights. By addressing the need for degradability in BB polymers, this work advances their potential for drug delivery, offering enhanced functionality, biocompatibility, and sustainability.

Biodegradable and Stimuli-Responsive Nanomaterials for Targeted Drug Delivery in Autoimmune Diseases

Autoimmune diseases present complex therapeutic challenges due to their chronic nature, systemic impact, and requirement for precise immunomodulation to avoid adverse side effects. Recent advancements in biodegradable and stimuli-responsive nanomaterials have opened new avenues for targeted drug delivery systems capable of addressing these challenges. This review provides a comprehensive analysis of state-of-the-art biodegradable nanocarriers such as polymeric nanoparticles, liposomes, and hydrogels engineered for targeted delivery in autoimmune therapies. These nanomaterials are designed to degrade safely in the body while releasing therapeutic agents in response to specific stimuli, including pH, temperature, redox conditions, and enzymatic activity. By achieving localized and controlled release of anti-inflammatory and immunosuppressive agents, these systems minimize systemic toxicity and enhance therapeutic efficacy. We discuss the underlying mechanisms of stimuli-responsive nanomaterials, recent applications in treating diseases such as rheumatoid arthritis, multiple sclerosis, and inflammatory bowel disease, and the design considerations essential for clinical translation. Additionally, we address current challenges, including biocompatibility, scalability, and regulatory hurdles, as well as future directions for integrating advanced nanotechnology with personalized medicine in autoimmune treatment. This review highlights the transformative potential of biodegradable and stimuli-responsive nanomaterials, presenting them as a promising strategy to advance precision medicine and improve patient outcomes in autoimmune disease management.

Topical calcineurin and mammalian target of rapamycin inhibitors in inflammatory dermatoses: Current challenges and nanotechnology‑based prospects (Review)

Topical therapy remains a critical component in the management of immune‑mediated inflammatory dermatoses such as psoriasis and atopic dermatitis. In this field, macrolactam immunomodulators, including calcineurin and mammalian target of rapamycin inhibitors, can offer steroid‑free therapeutic alternatives. Despite their potential for skin‑selective treatment compared with topical corticosteroids, the physicochemical properties of these compounds, such as high lipophilicity and large molecular size, do not meet the criteria for efficient penetration into the skin, especially with conventional topical vehicles. Thus, more sophisticated approaches are needed to address the pharmacokinetic limitations of traditional formulations. In this regard, interest has increasingly focused on nanoparticulate systems to optimize penetration kinetics and enhance the efficacy and safety of topical calcineurin and mTOR inhibitors in inflamed skin. Several types of nanovectors have been explored as topical carriers to deliver tacrolimus in both psoriatic and atopic skin, while preclinical data on nanocarrier‑based delivery of topical sirolimus in inflamed skin are also emerging. Given the promising preliminary outcomes and the complexities of drug delivery across inflamed skin, further research is required to translate these nanotherapeutics into clinical settings for inflammatory skin diseases. The present review outlined the dermatokinetic profiles of topical calcineurin and mTOR inhibitors, particularly tacrolimus, pimecrolimus and sirolimus, focusing on their penetration kinetics in psoriatic and atopic skin. It also summarizes the potential anti‑inflammatory benefits of topical sirolimus and explores novel preclinical studies investigating dermally applied nanovehicles to evaluate and optimize the skin delivery, efficacy and safety of these 'hard‑to‑formulate' macromolecules in the context of psoriasis and atopic dermatitis.

Optically monitoring the microenvironment of a hydrophobic cargo in amphiphilic nanogels: influence of network composition on loading and release

Amphiphilic nanogels (ANGs) are promising carriers for hydrophobic cargos such as drugs, dyes, and catalysts. Loading content and release kinetics of these compounds are controlled by type and number of hydrophobic groups in the amphiphilic copolymer network. Thus, understanding the interactions between cargo and colloidal carrier is mandatory for a tailor-made and cargo-specific ANG design. To systematically explore the influence of the network composition on these interactions, we prepared a set of ANGs of different amphiphilicity and loaded these ANGs with varying concentrations of the solvatochromic dye Nile Red (NR). Here, NR acts as a hydrophobic model cargo to optically probe the polarity of its microenvironment. Analysis of the NR emission spectra as well as measurements of the fluorescence quantum yields and decay kinetics revealed a decrease in the polarity of the NR microenvironment with increasing hydrophobicity of the hydrophobic groups in the ANG network and dye-dye interactions at higher loading concentrations. At low NR concentrations, the hydrophobic cargo NR is encapsulated in the hydrophobic domains. Increasing NR concentrations resulted in probe molecules located in a more hydrophilic environment, i.e., at the nanodomain border, and favored dye-dye interactions and NR aggregation. These results correlate well with release experiments, indicating first NR release from more hydrophilic network locations. Overall, our findings demonstrate the importance to understand carrier-drug interactions for efficient loading and controlled release profiles in amphiphilic nanogels.

Efficacy of topically applied rapamycin-loaded redox-sensitive nanocarriers in a human skin/T cell co-culture model

Rapamycin, also known as Sirolimus, is a promising anti-proliferative drug, but its therapeutic use for the topical treatment of inflammatory, hyperproliferative skin disorders is limited by insufficient penetration rates due to its high molecular weight (MW of 914.172 g/mol) and high lipophilicity. We have shown that core multi-shell (CMS) nanocarriers sensitive to oxidative environment can improve drug delivery to the skin. In this study, we investigated the mTOR inhibitory activity of these oxidation-sensitive CMS (osCMS) nanocarrier formulations in an inflammatory ex vivo human skin model. In this model, features of inflamed skin were introduced by treating the ex vivo tissue with low-dose serine protease (SP) and lipopolysaccharide (LPS), while phorbol 12-myristate 13-acetate and ionomycin were used to stimulate IL-17A production in the co-cultured SeAx cells. Furthermore, we tried to elucidate the effects of rapamycin on single cell populations isolated from skin (keratinocytes, fibroblast) as well as on SeAx cells. Further, we measured possible effects of the rapamycin formulations on dendritic cell (DC) migration and activation. The inflammatory skin model enabled the assessment of biological readouts at both the tissue and T cell level. All investigated formulations successfully delivered rapamycin across the skin as revealed by reduced IL-17A levels. Nevertheless, only the osCMS formulations reached higher anti-inflammatory effects in the skin compared to the control formulations with a significant downregulation of mTOR activity. These results indicate that osCMS formulations could help to establish rapamycin, or even other drugs with similar physico-chemical properties, in topical anti-inflammatory therapy.

Biodegradable core-multishell nanocarrier: Topical tacrolimus delivery for treatment of dermatitis

Two challenges in topical drug delivery to the skin include solubilizing hydrophobic drugs in water-based formulations and increasing drug penetration into the skin. Polymeric core-multishell nanocarrier (CMS), particularly the novel biodegradable CMS (bCMS = hPG-PCL_1.1K-mPEG_2k-CMS) have shown both advantages on excised skin ex vivo. Here, we investigated topical delivery of tacrolimus (TAC; > 500 g/mol) by bCMS in a hydrogel on an oxazolone-induced model of dermatitis in vivo. As expected, bCMS successfully delivered TAC into the skin. However, in vivo they did not increase, but decrease TAC penetration through the stratum corneum compared to ointment. Differences in the resulting mean concentrations were mostly non-significant in the skin (epidermis: 35.7 ± 20.9 ng/cm² for bCMS vs. 92.6 ± 62.7 ng/cm² for ointment; dermis: 76.8 ± 26.8 ng/cm²vs 118.2 ± 50.4 ng/cm²), but highly significant in blood (plasma: 1.1 ± 0.4 ng/ml vs 11.3 ± 9.3 ng/ml; erythrocytes: 0.5 ± 0.2 ng/ml vs 3.4 ± 2.4 ng/ml) and liver (0.01 ± 0.01 ng/mg vs 0.03 ± 0.01 ng/mg). bCMS were detected in the stratum corneum but not in viable skin or beyond. The therapeutic efficacy of TAC delivered by bCMS was equivalent to that of standard TAC ointment. Our results suggest that bCMS may be a promising carrier for the topical delivery of TAC. The quantitative difference to previous results should be interpreted in light of structural differences between murine and human skin, but highlights the need as well as potential methods to develop more a complex ex vivo analysis on human skin to ensure quantitative predictive value.

Novel Adhesive Nanocarriers Based on Mussel-Inspired Polyglycerols for the Application onto Mucosal Tissues

A synthetic route for adhesive core-multishell (CMS) nanocarriers for application to the oral mucosa was established using mussel-inspired catechol moieties. The three CMS nanocarriers with 8%, 13%, and 20% catechol functionalization were evaluated for loading capacity using Nile red, showing an overall loading of 1 wt%. The ability of Nile red loaded and functionalized nanocarriers to bind to a moist mucosal surface was tested in two complementary adhesion assays under static and dynamic conditions using monolayers of differentiated gingival keratinocytes. Adhesion properties of functionalized nanocarriers were compared to the adhesion of the non-functionalized nanocarrier. In both assays, the CMS nanocarrier functionalized with 8% catechol exhibited the strongest adhesion compared to its catechol-free counterpart and the CMS nanocarriers functionalized with 13% and 20% catechol.

Topical Delivery of Rapamycin by Means of Microenvironment-Sensitive Core-Multi-Shell Nanocarriers: Assessment of Anti-Inflammatory Activity in an ex vivo Skin/T Cell Co-Culture Model

Introduction

Rapamycin (Rapa) is an immunosuppressive macrolide that inhibits the mechanistic target of rapamycin (mTOR) activity. Thanks to its anti-proliferative effects towards different cell types, including keratinocytes and T cells, Rapa shows promise in the treatment of skin diseases characterized by cell hyperproliferation. However, Rapa skin penetration is limited due to its lipophilic nature (log P = 4.3) and high molecular weight (MW = 914 g/mol). In previous studies, new microenvironment-sensitive core multishell (CMS) nanocarriers capable of sensing the redox state of inflamed skin were developed as more efficient and selective vehicles for macrolide delivery to inflamed skin.

Methods

In this study, we tested such redox-sensitive CMS nanocarriers using an inflammatory skin model based on human skin explants co-cultured with Jurkat T cells. Serine protease (SP) was applied on skin surface to induce skin barrier impairment and oxidative stress, whereas phytohaemagglutinin (PHA), IL-17A, and IL-22 were used to activate Jurkat cells. Activation markers, such as CD45 and CD69, phosphorylated ribosomal protein S6 (pRP-S6), and IL-2 release were monitored in activated T cells, whereas pro-inflammatory cytokines were measured in skin extracts and culture medium.

Results

We found that alteration of skin barrier proteins corneodesmosin (CDSN), occludin (Occl), and zonula occludens-1 (ZO-1) as well as oxidation-induced decrease of free thiol groups occurred upon SP-treatment. All Rapa formulations exerted inhibitory effects on T cells after penetration across ex vivo skin. No effects on skin inflammatory markers were detected. The superiority of the oxidative-sensitive CMS nanocarriers over the other formulations was observed with regard to drug delivery as well as downregulation of IL-2 release.

Conclusion

Overall, our results demonstrate that nanocarriers addressing features of diseased skin are promising approaches to improve the topical delivery of macrolide drugs.

Transfersomes as alternative topical nanodosage forms for the treatment of skin disorders

Topical drug delivery is a promising approach to treat different skin disorders. However, it remains a challenge mainly due to the nature and rigidity of the nanosystems, which limit deep skin penetration, and the unsuccessful demonstration of clinical benefits; greater penetration by itself, does not ensure pharmacological success. In this context, transfersomes have appeared as promising nanosystems; deformability, their unique characteristic, allows them to pass through the epidermal microenvironment, improving the skin drug delivery. This review focuses on the comparison of transfersomes with other nanosystems (e.g., liposomes), discusses recent therapeutic applications for the topical treatment of different skin disorders and highlights the need for further studies to demonstrate significant clinical benefits of transfersomes compared with conventional therapies.

Oxidation-Sensitive Core-Multishell Nanocarriers for the Controlled Delivery of Hydrophobic Drugs

A synthetic route for oxidation-sensitive core-multishell (osCMS) nanocarriers was established, and their drug loading and release properties were analyzed based on their structural variations. The nanocarriers showed a drug loading of 0.3-3 wt % for the anti-inflammatory drugs rapamycin and dexamethasone and the photosensitizer meso-tetra-hydroxyphenyl-porphyrin (mTHPP). Oxidative processes of the nanocarriers were probed in vitro by hydrogen peroxide, and the degradation products were identified by infrared spectroscopy supported by ab initio calculations, yielding mechanistic details on the chemical changes occurring in redox-sensitive nanocarriers. Oxidation-triggered drug release of the model drug Nile Red measured and assessed by time-dependent fluorescence spectroscopy showed a release of up to 80% within 24 h. The drug delivery capacity of the new osCMS nanocarriers was tested in ex vivo human skin with and without pretreatments to induce local oxidative stress. It was found that the delivery of mTHPP was selectively enhanced in skin under oxidative stress. The number and position of the thioether groups influenced the physicochemical as well as drug delivery properties of the carriers.