Cutaneous biodistribution of ionizable, biolabile aciclovir prodrugs after short duration topical iontophoresis: Targeted intraepidermal drug delivery

Development of an UHPLC-MS/MS method to determine cutaneous biodistribution of cannabidiol after topical application of cannabidiol gel assisted by iontophoresis

Cannabidiol has potential for use in skin disease therapy, so it is important to know the cutaneous biodistribution of cannabidiol after topical application of cannabidiol formulations. However, currently existing quantification methods for the investigation of cannabidiol skin distribution are not optimal. This study aimed to establish a method for the determination of cannabidiol in skin samples by UHPLC-MS/MS. A BEH C18 (50.0 × 2.1 mm, 2.5 μm) column was used; the mobile phase consisted of acetonitrile-0.1% formic acid (70:30, v/v), the flow rate was 0.2 μl·min-1 and the column temperature was 30°C. Positive-ion mode with multiple reaction monitoring detection was used to quantify cannabidiol (m/z 315.1 → 193.1) while diphenhydramine (m/z 256.3 → 167.08) served as the internal standard. Good linearity was shown in the range of 1-200 ng·ml-1 for cannabidiol with correlation coefficients of >0.999. The LLOQ was 1 ng·ml-1 . The intra-day and inter-day RSDs of cannabidiol were all <2%. A cryo-sectioning technique combined with the UHPLC-MS/MS method was used to successfully determine cannabidiol levels in a series of very thin skin layers.

Detailed pharmacokinetic characterization of advanced topical acyclovir formulations with IVPT and in vivo Open Flow Microperfusion

Successful treatment of herpes simplex viruses is currently limited by a lack of effective topical drugs. Commonly used topical acyclovir products only reduce the duration of lesions by a few days. Optimizing topical formulations to achieve an enhanced acyclovir solubility and penetration could increase the efficacy of topically applied acyclovir, but new formulations need to show reliable acyclovir delivery into at least the epidermis/dermis and need to provide sustained acyclovir release for extended time periods. The aim of this study was to compare pharmacokinetic data from in vitro permeation testing (IVPT) and preclinical dermal open flow microperfusion (dOFM) experiments regarding the penetration behavior of different acyclovir formulations relative to the reference product Zovirax® 5% cream. Four test formulations that delivered the best penetration data in IVPT were further tested using continuous dOFM in vivo dermal sampling. The use of dOFM identified one of the four tested formulations to perform significantly better than the other three tested formulations and the reference product. In vivo dOFM data showed differences in the dermal acyclovir concentration that had not been detected by using IVPT. Improved acyclovir delivery to the dermis was likely achieved by the new formulation that uses a much lower drug load compared to the reference product. This optimized formulation was able to achieve a dermal concentration similar to oral application and can thus provide the opportunity of more efficacious topical HSV-1 treatment with less side effects than oral systemic treatment.

Advance and Challenges in the Treatment of Skin Diseases with the Transdermal Drug Delivery System

Skin diseases are among the most prevalent non-fatal conditions worldwide. The transdermal drug delivery system (TDDS) has emerged as a promising approach for treating skin diseases, owing to its numerous advantages such as high bioavailability, low systemic toxicity, and improved patient compliance. However, the effectiveness of the TDDS is hindered by several factors, including the barrier properties of the stratum corneum, the nature of the drug and carrier, and delivery conditions. In this paper, we provide an overview of the development of the TDDS from first-generation to fourth-generation systems, highlighting the characteristics of each carrier in terms of mechanism composition, penetration method, mechanism of action, and recent preclinical studies. We further investigated the significant challenges encountered in the development of the TDDS and the crucial significance of clinical trials.

Polymeric micelle formulations for the cutaneous delivery of sirolimus: A new approach for the treatment of facial angiofibromas in tuberous sclerosis complex

Facial angiofibromas are benign tumors characteristic of tuberous sclerosis complex. The disease involves the mTOR pathway and the cutaneous manifestation responds to topical treatment with sirolimus (SIR). However, there are no approved topical SIR products and extemporaneous formulations have been sub-optimal. The aims of this study were (i) to develop aqueous formulations of SIR loaded in polymeric micelles prepared using D-α-tocopherol polyethylene glycol 1000 succinate (TPGS) and (ii) to use the cutaneous biodistribution method, in conjunction with a new statistical approach, to investigate the feasibility of SIR delivery to the viable epidermis. Optimized micelle solutions and hydrogels (0.2%) were developed and stable at 4 °C for at least 6 and 3 months, respectively. Cutaneous delivery experiments (infinite and finite dose) using porcine skin demonstrated that both formulations increased SIR cutaneous bioavailability as compared to the control (ointment 0.2%). Moreover, studies with the micellar hydrogel 0.2% demonstrated SIR deposition in the viable epidermis with no transdermal permeation. These encouraging results confirmed that polymeric micelles enabled development of aqueous SIR formulations capable of targeted epidermal delivery. Furthermore, the cutaneous biodistribution provided a detailed insight into drug bioavailability in the different skin compartments that could complement/explain clinical observations of formulation efficacy.

Tissue Levels of Flurbiprofen in the Rat Plantar Heel after Short-Duration Topical Iontophoresis Are Sufficient to Induce Pharmacodynamic Responses to Local Pain Stimuli

The objective of this study was to investigate the topical iontophoresis of flurbiprofen (FBF) as a means to enhance its local bioavailability and thereby provide an improved and targeted treatment of plantar heel pain. Initial in vitro experiments using porcine ear skin investigated iontophoretic transport of FBF under different conditions. Local FBF biodistribution in the rat paw in vivo was compared after topical or oral administration. Efficacy of pain management was investigated using a plantar incisional model by evaluating pharmacodynamic responses to local pain stimuli. The results demonstrated that iontophoresis of FBF significantly increased cutaneous deposition and transdermal permeation of FBF as compared to passive delivery—it also enabled drug input to be controlled by modulation of current density and drug concentration (r2 > 0.99). Topical iontophoresis of FBF in vivo enabled higher drug levels in skin and muscle in rat plantar aspect and superior pharmacodynamic responses to local pain stimuli, in comparison to oral and passive delivery. In conclusion, short-duration topical iontophoresis of FBF may better help to relieve plantar heel pain than oral or passive administration, which should be of clinical interest.

Cutaneous Biodistribution: A High-Resolution Methodology to Assess Bioequivalence in Topical Skin Delivery

A draft guideline from the European Medicines Agency (EMA) highlights the need for methods to assess the quality/equivalence of topical drug formulations. The “cutaneous biodistribution method”, which provides insight into a drug’s spatial distribution in the epidermis/dermis, was used to compare cutaneous bioavailability of econazole nitrate (ECZ) from a reference medicinal product (RMP) and two approved bioequivalent generic creams under finite dose conditions. Statistically significant differences between the ECZ biodistributions from the RMP/Generics were determined and used with acceptance criteria based on those from the EMA to evaluate bioequivalence. In porcine skin, ECZ deposition in total skin, epidermis, upper and lower dermis from Generic 1 was within the acceptance interval, contrary to Generic 2, which was marginally below it. For human skin, Generic 1 deposition was marginally above the acceptance interval and not bioequivalent. The results were consistent with those using the EMA’s acceptance intervals using the ratio of the mean ECZ depositions of Generic 1 and the RMP. Differences identified using this data-rich technique may not translate to observable differences in clinical efficacy; however, generics with non-statistically different biodistributions to the RMP should have a comparable clinical effect. The cutaneous biodistribution method could benchmark the development of topical generic products.

Using ordered mesoporous silica SBA-15 to limit cutaneous penetration and transdermal permeation of organic UV filters

Avobenzone (AVO), oxybenzone (OXY), and octyl methoxycinnamate (OMC), are widely used UV filters. The aim of this study was to investigate the effect of incorporation in mesoporous silica (SBA-15) on their cutaneous deposition and permeation. Stick formulations containing "free" and "incorporated" UV filters (SF1 and SF2, respectively) were prepared and characterized with respect to their physicochemical, thermal, and functional properties. Cutaneous delivery experiments using porcine skin with quantification by UHPLC-MS/MS, demonstrated that skin deposition of AVO and OXY after application of SF2 for 6 and 12 h was significantly lower than that from SF1 at each time-point (Student t-test, p < 0.05): e.g. OXY permeation across the skin was 30-, 12- and 1.5-fold lower after 6, 12 and 24 h, respectively, following application of SF2. Cutaneous biodistribution profiles of AVO and OXY to 800 µm evidenced a significant decrease in the amounts in the viable epidermis and dermis. In contrast, deposition of the more lipophilic OMC was not significantly different (p ˃ 0.05). In vitro photoprotective efficacy results demonstrated that adsorption/entrapment of UV filters enhanced the sun protection factor by 94%. In conclusion, SBA-15, an innovative mesoporous material, increased photoprotection by UV filters while reducing their cutaneous penetration and transdermal permeation.

Self-assembled mPEG-hexPLA polymeric nanocarriers for the targeted cutaneous delivery of imiquimod

mPEG-hexPLA micelles have shown their ability to improve delivery and cutaneous bioavailability of a wide range of poorly water soluble and lipophilic molecules. Although poorly water soluble, imiquimod (IMQ) is only moderately lipophilic and it was decided to investigate whether mPEG-hexPLA polymeric micelles could be used as a drug delivery system for this "less than ideal" candidate for encapsulation. Nanosized IMQ micelles (d_n = 27 nm) were formulated and characterized. Moreover, the innovative use of size exclusion chromatography allowed the exact drug localization inside the formulation to be determined; it appeared that the use of acetic acid to solubilize IMQ led to a higher IMQ content outside the micelle than inside. IMQ micelles (0.05%) were formulated in a gel using carboxymethyl cellulose (CMC). In vitro application of this formulation to porcine and human skin led to promising delivery results. IMQ deposition in human skin was 1.4 ± 0.4 µg/cm² while transdermal permeation was only 79 ± 19 ng/cm²: the formulation displayed >17-fold selectivity for cutaneous deposition over transdermal permeation. The optimized 0.05% gel significantly outperformed Aldara® cream (containing 5% IMQ) formulation in terms of delivery efficiency to human skin (2.85 ± 0.74% vs 0.04 ± 0.01%). Despite IMQ being only partially incorporated in the micelles, the biodistribution profile showed that the optimized 0.05% gel delivered as much as 518.2 ± 173.3 ng/cm² (1.04 ± 0.35% of the applied dose) to the viable epidermis and 236.4 ± 88.2 ng/cm² (0.47 ± 0.18% of the applied dose) to the upper dermis where the target antigen presenting cells reside. In contrast, for Aldara® cream, the delivery efficiencies in those layers were less than 0.02%. The optimal 0.05% gel thus allowed therapeutically relevant drug levels to be achieved in target tissues despite a 100-fold dose reduction.

Controlled non-invasive iontophoretic delivery of triamcinolone acetonide amino acid ester prodrugs into the posterior segment of the eye

This study investigated short duration transscleral iontophoretic delivery of four triamcinolone acetonide (TA) amino acid ester prodrugs (TA-AA) (alanine, Ala; arginine, Arg; isoleucine, Ile and lysine, Lys) using whole porcine eyes globes in vitro. Post-iontophoretic biodistribution of TA was quantified by UHPLC-MS/MS in the different ocular compartments (cornea, aqueous humor, sclera, ciliary body, choroid and retinal pigmented epithelium (RPE), neural retina and vitreous humor). Transscleral iontophoresis (3 mA/cm² for 10 min) increased total drug delivery of the TA-AA prodrugs by 14-30-fold as compared to passive diffusion. The TA-AA prodrugs had distinct biodistribution profiles - the penetration depth achieved was dependent on their physicochemical properties (e.g. lipophilicity for TA-Ile) and susceptibility to hydrolysis (e.g. TA-Arg). Intraocular drug distribution was also influenced by prodrug binding to melanin (TA-Lys). Interestingly, under conditions of equivalent charge (6 mA/cm² for 5 min vs. 1.5 mA/cm² for 20 min, i.e. 1.44 C respectively) the longer duration (20 min) at lower current density resulted in ∼6 times more TA delivery into the vitreous humor. Overall, the study provided further evidence of the potential of transscleral iontophoresis for the non-invasive treatment of posterior segment inflammatory diseases.

Targeted intracorneal delivery-Biodistribution of triamcinolone acetonide following topical iontophoresis of cationic amino acid ester prodrugs

The aim was to investigate intracorneal iontophoresis of biolabile triamcinolone acetonide (TA) amino acid ester prodrugs (TA-AA). Arginine and lysine esters of TA (TA-Arg and TA-Lys, respectively) were synthesized and characterized; quantification was performed by HPLC-UV and UHPLC-MS/MS. The aqueous solubility of the prodrugs (at pH 5.5) was ∼1000-fold greater than TA. Anodal iontophoresis (10min at 3mA/cm²) of TA-AA was investigated using isolated porcine cornea. Although no statistically significant difference was observed in total intracorneal delivery of TA (468.25±59.70 and 540.85±79.16nmol_TA/cm², for TA-Arg and TA-Lys, respectively), the different susceptibilities of the prodrugs to hydrolysis influenced intracorneal biodistribution. Quantification of TA in twenty-five 40μm thick corneal lamellae revealed significantly deeper penetration of TA following TA-Lys iontophoresis. Its superior resistance to hydrolysis enabled sustained electromigration into the deeper cornea suggesting judicious prodrug selection might enable targeted regioselective drug delivery. The intracorneal biodistribution following anodal iontophoresis of TA-Arg (2.3mM; 10min, 3mA/cm²) was visualized by full field optical coherence tomography providing qualitative confirmation of the extensive intracorneal penetration of TA. Short duration iontophoresis of TA-AA prodrugs may improve deep corneal bioavailability and efficacy in vivo, constituting a "single-shot" treatment option for corneal allograft rejection.