Comparing the efficacy of nanocarriers for cutaneous and follicular delivery of poorly water-soluble molecules: A case study with ciclosporin A

Abstract

Therapeutic agents approved for the topical treatment of dermatological diseases have diverse physicochemical properties, but they are frequently poorly water-soluble, which makes it a challenge to prepare stable aqueous formulations with good delivery characteristics. Several types of nanocarrier have been reported to facilitate formulation and to enhance cutaneous delivery but there are few direct comparisons of nanocarriers in terms of their ability to deliver a specific molecule to the skin under the same controlled conditions. The present study aimed to address this by developing, optimizing, and comparing different nanocarriers with respect to their ability to deliver ciclosporin A (CsA) to the skin and the hair follicle. Nanoconstructs were categorized as vesicular carriers (micelles and liposomes), emulsion-based systems (microemulsions and nanoemulsions), and nanoparticle systems (e.g. polymeric nanoparticles, solid lipid nanoparticles, nanostructured lipid carriers). Formulations were optimized using a design of experiments approach and were characterized with respect to size, morphology and incorporation efficiency. Cutaneous and follicular delivery experiments were performed using porcine skin. CsA deposition, cutaneous biodistribution, follicular delivery and targeting potential (ratio of delivery to skin with and without pilosebaceous units) were assessed. Nanoemulsions, kinetically stable systems with high thermodynamic activity, showed the highest cutaneous delivery of CsA among the nanosystems tested followed by solid lipid nanoparticles and mPEG-dihexPLA micelles – i.e. three different types of nanocarrier. The results confirmed the pivotal role of thermodynamic activity in determining delivery efficiency of a nanocarrier and its greater importance than other routinely studied morphological parameters such as nanocarrier size: the smallest nanocarriers did not yield the highest delivery.

Introduction

Ciclosporin A (CsA) is a neutral lipophilic cyclic undecapeptide having a molecular weight of 1202 Da (Gupta et al., 1989). It was approved in 1983 (Sandimmune®) for the prevention of organ transplant rejection and an oral formulation (Neoral®) was approved in 1997 for the treatment of psoriasis and rheumatoid arthritis (Rosmarin et al., 2010). CsA freely diffuses into the cytoplasm of T cells, binds to cyclophilin; the resulting complex binds to and inhibits calcineurin, a Ca2+/calmodulin-dependent phosphatase, which dephosphorylates nuclear factor of activated T cells (NFAT) allowing it to translocate to the nucleus and so facilitate the transcription of proinflammatory genes coding for IL-2, IL-4, interferon-gamma, transforming growth factor-beta, and up-regulation of the IL-2 receptor. CsA also down-regulates intercellular adhesion molecule-1 on keratinocytes and endothelial cells as well as prevents the recruitment of inflammatory cells into the skin (Gottlieb et al., 1992; Prens et al., 1995; Horrocks et al., 1991).

Currently, CsA is given orally in cases of moderate to severe psoriasis where the disease affects a more significant surface area or plaques are recalcitrant to topical treatments. To-date, and despite its known therapeutic efficacy, there are no approved topical formulations of CsA for cutaneous applications. CsA has a large of volume of distribution and systemic administration results in its “untargeted and nonselective” delivery. Although systemic administration of CsA is clearly justified for indications where the benefits to the patient outweigh the risks of the adverse effects (Sternthal et al., 2008; Marienhagen et al., 2019), long-term systemic CsA exposure is associated with hepatotoxicity, nephrotoxicity, neurotoxicity, hypertension, hypertrichosis, and hyperpigmentation (Marienhagen et al., 2019; Wysocki and Daley, 1987; Wu et al., 2018; Kassianides et al., 1990; Serkova et al., 2004; Sharma et al., n.d.; Abikhair et al., n.d.). In the case of psoriasis where the disease is localized, it would be advantageous to apply CsA directly to the diseased skin; topical delivery would be more targeted and would obviously diminish the risk of off-site effects.

CsA is poorly water-soluble (log P 4.12) (Goyal et al., 2015); its solubility in PBS (pH 7) at room temperature is 5.2 μg/mL (Lallemand et al., 2005). This makes it very difficult to prepare aqueous topical preparations of CsA. Many different nanocarriers – e.g. nanosuspensions (Romero et al., 2016), polymeric nanoparticles (Jain et al., 2011), liposomes (Kumar et al., 2016), nanoemulsion (Musa et al., 2017). microemulsion (Pandey et al., 2020), solid lipid nanoparticle (SLN) and nanostructured lipid carrier (NLC) (Arora et al., 2017) – have been studied using skin from different species, with the aim to improve the cutaneous delivery of CsA. Lapteva et al. developed a micelle-based formulation of CsA and demonstrated its ability to deliver CsA to porcine and human skin at supra-therapeutic concentrations (Lapteva et al., 2014).

The studies described above were performed using a variety of experimental conditions and parameters. There are few systematic studies comparing the abilities of different nanocarriers to deliver poorly water-soluble molecules to the skin under the same controlled conditions. Furthermore, each nanocarrier has its own strengths and weaknesses, posing different challenges and technical hurdles during development and eventual scale up and there is also the question of cost.

Therefore, it was of interest to compare the abilities of different nanocarriers to deliver CsA to the skin under standardized conditions, and to investigate parameters that might affect cutaneous bioavailability and delivery efficiency. Furthermore, determination of the cutaneous biodistribution, and the amounts of CsA present in the pilosebaceous unit (PSU), enabled delivery to the different anatomical layers to be quantified and the ability of the nanocarriers to target specific skin structures to be evaluated. This approach not only allowed the development of the most efficient and robust aqueous “nanocarrier” formulation for cutaneous topical delivery of CsA but also provided insight into differences between the nanocarriers with respect to possible penetration pathways. Of course, the observations made during the study would also have potential applications in the development of nanocarrier-based formulations for the delivery of other poorly water-soluble moleculesto the skin.

The specific objectives of the present study were: (i) to develop and to optimize a series of nanocarrier formulations of CsA using a design of experiments (DoE) approach, (ii) to characterize them with respect to their morphology and CsA incorporation efficiency, (iii) to investigate the cutaneous delivery of CsA from the different nanocarrier formulations, (iv) to assess the cutaneous biodistribution, i.e. CsA delivery as a function of depth, in the skin, (v) to quantify follicular delivery of CsA using a punch biopsy method that enabled the extraction of an intact PSU. In conclusion, the results would enable a systematic comparison of the ability of the nanocarriers to deliver CsA to the skin and the different anatomical regions and to assess the potential for selective/preferential delivery to the PSU.

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Materials

CsA was kindly provided by Apidel SA (Geneva, Switzerland). mPEG-dihexPLA copolymer (methoxy-poly(ethylene glycol) di-(hexyl-substituted polylactide)) was synthesized in-house as described previously (Trimaille et al., 2006). D-α-Tocopherol polyethylene glycol 1000 succinate (TPGS), formic acid (FA; MS grade), Tween 20, Tween 80, isopentane, and Dulbecco’s phosphate-buffered saline (DPBS), Resomer® RG 503H (PLGA; MW: 24–38 kDa), polyvinylpyrrolidone (PVP; MW: 360 kDa), castor oil, Kolliphor® EL, oleic acid, palmitic acid, myristic acid, chloroform were purchased from Sigma-Aldrich (Buchs, Switzerland). Lipoid S100 was kindly provided as a gift by Lipoid GmbH (Ludwigshafen, Germany). Stearic acid was purchased from Hänseler AG (Herisau, Switzerland). Bovine serum albumin (BSA), polyethylene glycol 400 were purchased from Axon Lab (Baden-Dättwil, Switzerland). Acetone (analytical grade), lauric acid, and Nile Red were obtained from Acros Organics (Geel, Belgium). Glycerol monostearate (GMS) was procured from BASF (Ludwigshafen, Germany). Transcutol® P, Labrafac™ WL 1349, Labrasol® were procured from Gattefosse (Saint Priest, France). Miglyol® 840 was obtained from Cremer Oleo GmbH (Hamburg, Germany). Methanol and acetonitrile (LC-MS grade), dichloromethane (DCM) were purchased from Fisher Scientific (Reinach, Switzerland). PTFE membrane filters (0.22 μm), Amicon Ultra 0.5 mL (5 kDa) filtration units were purchased from VWR (Nyon, Switzerland). Ultrapure water (Millipore Milli-Q Gard 1 Purification Pack resistivity >18 MΩ.cm; Zug, Switzerland) was used for formulation development and analysis. All other chemicals were at least of analytical grade.

Aditya R. Darade, Maria Lapteva, Yogeshvar N. Kalia, Comparing the efficacy of nanocarriers for cutaneous and follicular delivery of poorly water-soluble molecules: A case study with ciclosporin A, International Journal of Pharmaceutics: X, Volume 11, 2026, 100505, ISSN 2590-1567, https://doi.org/10.1016/j.ijpx.2026.100505.

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