Topical iontophoretic delivery of ionizable, biolabile aciclovir prodrugs: A rational approach to improve cutaneous bioavailability

Intracorneal iontophoretic delivery of triamcinolone acetonide prodrugs: Physicochemical parameters guiding electrotransport

Intracorneal delivery of ten amino acid (alanine, arginine, asparagine, glutamine, glycine, histidine, isoleucine, lysine, methionine and valine) ester prodrugs of triamcinolone acetonide (TA-AA) was investigated in vitro, using a corneal iontophoresis device (IONTOFOR-CXL; SOOFT Italia S.p.A.) approved for clinical use in the treatment of keratoconus. Short duration iontophoresis (1 mA for 5 min) was performed and intracorneal deposition of TA was quantified by HPLC-UV and UHPLC-MS/MS. The data evidenced the clear advantage of TA-AA prodrug iontophoresis compared to passive delivery and revealed unexpected and prodrug dependent deposition profiles. Despite their superior electrical mobility, intracorneal delivery of dications, TA-Arg and TA-Lys, did not outperform that of TA-Ala and TA-Gly. In silico investigations to relate the TA-AA prodrugs' physicochemical properties to their electrotransport confirmed that increased lipophilicity potential did not favour iontophoretic transport. For TA-Ala and TA-Gly, it was hypothesized that the greater charge distribution and decreased tendency to interact with the corneal tissue via electrostatic and H-bonds contributed to their successful iontophoretic delivery. Intracorneal biodistribution of TA confirmed that TA-Gly iontophoresis resulted in supratherapeutic concentrations in deep corneal stroma, exceeding TA IC50 by ∼ 104-fold. The results clearly demonstrated the successful combination of the clinically approved SOOFT iontophoretic device and the TA-AA prodrugs for targeted corneal iontophoretic delivery.

An Injectable Oil-Based Depot Formulation of N-Acyloxymethyl Prodrug of Ropivacaine for Long-Acting Local Analgesia: Formulation Development and In Vitro/In Vivo Evaluation

Objectives: The development of novel long-acting injectables for local anesthetics is necessary to effectively manage the acute postoperative pain. The aim of this study was to prepare an injectable oil-based formulation of ropivacaine (ROP) prodrug (ropivacaine stearoxil, ROP-ST) and to investigate the pharmacokinetics and pharmacodynamics after injectable administration. Methods: A novel N-acyloxymethyl prodrug of ROP, i.e., ROP-ST, was synthesized and its physicochemical properties such as log P, solubility and stability characterized. A soybean oil-based depot of ROP-ST was prepared, and the in-vitro release of ROP-ST was evaluated using an "inverted-cup" method. Pharmacokinetic profiles and tissue retention properties were investigated after intramuscular administration of the formulation in rats. The analgesic efficacy was assessed via a von Frey monofilaments test by measuring the paw withdrawal thresholds. Results: The structure of ROP-ST was ascertained with clear 1H NMR assignment and accurate mass-to-charge ratio. The high Log P value of ROP-ST (9.16) demonstrated extremely low aqueous solubility, but the prodrug is biolabile when in contact with plasma or liver esterase. Intramuscular injection of ROP-ST oil solution in rats provided a significantly higher mean residence time without a very clear plasma peak of ROP. In a postoperative pain model of rats, the injection of ROP-ST oil solution into the vicinity of the sciatic nerve in the right ankle effectively controlled the postoperative pain for at least 72 h. Conclusions: The injectable oil-based depot formulation of N-acyloxymethyl prodrug of ROP may provide a new opportunity of long-acting local analgesia for postoperative pain.

Development and Assessment of Acyclovir Gel Plaster Containing Sponge Spicules

Acyclovir is an acyclic purine nucleoside analog that is highly effective in inhibiting the herpes simplex virus. However, topical acyclovir has poor efficacy because of its low skin permeability. This study aimed to develop an acyclovir gel plaster containing sponge spicules (AGP-SS) to achieve synergistic improvements in skin absorption and deposition of acyclovir. The process of preparing the gel plaster was optimized by orthogonal experiments, while the composition of the formulation was optimized using the Plackett-Burman and Box-Behnken experimental designs. The selected formula was tested for physical properties, in vitro release, stability, ex vivo permeation, skin irritation, and pharmacokinetics. The optimized formulation exhibited good physical characteristics. In vitro release and ex vivo permeation studies showed that acyclovir release from AGP-SS was dominated by diffusion with significantly higher skin permeation (20.00 ± 1.07 μg/cm2) than that of the controls (p < 0.05). Dermatopharmacokinetic analyses revealed that the maximum concentration (78.74 ± 11.12 μg/g), area under the curve (1091.81 ± 29.05 μg/g/h) and relative bioavailability (197.12) of AGP-SS were higher than those of the controls. Therefore, gel plaster containing sponge spicules show potential for development as transdermal delivery systems to achieve higher skin absorption and deposition of acyclovir, especially in deep skin layers.

Iontosomes: Electroresponsive Liposomes for Topical Iontophoretic Delivery of Chemotherapeutics to the Buccal Mucosa

The targeted local delivery of anticancer therapeutics offers an alternative to systemic chemotherapy for oral cancers not amenable to surgical excision. However, epithelial barrier function can pose a challenge to their passive topical delivery. The charged, deformable liposomes—“iontosomes”—described here are able to overcome the buccal mucosal barrier via a combination of the electrical potential gradient imposed by iontophoresis and their shape-deforming characteristics. Two chemotherapeutic agents with very different physicochemical properties, cisplatin (CDDP) and docetaxel (DTX), were co-encapsulated in cationic iontosomes comprising 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) and Lipoid-S75. The entrapment of CDDP was improved by formulating it in anionic reverse micelles of dipalmitoyl-sn-glycero-3-phospho-rac-glycerol sodium (DPPG) prior to loading in the iontosomes. Cryo-TEM imaging clearly demonstrated the iontosomes’ electroresponsive shape-deformable properties. The in vitro transport study using porcine mucosa indicated that iontosomes did not enter the mucosa without an external driving force. However, anodal iontophoresis resulted in significant amounts of co-encapsulated CDDP and DTX being deposited in the buccal mucosa; e.g., after current application for 10 min, the deposition of CDDP and DTX was 13.54 ± 1.78 and 10.75 ± 1.75 μg/cm² cf. 0.20 ± 0.07 and 0.19 ± 0.09 μg/cm² for the passive controls—i.e., 67.7- and 56.6-fold increases—without any noticeable increase in their transmucosal permeation. Confocal microscopy confirmed that the iontosomes penetrated the mucosa through the intercellular spaces and that the penetration depth could be controlled by varying the duration of current application. Overall, the results suggest that the combination of topical iontophoresis with a suitable nanocarrier system can be used to deliver multiple “physicochemically incompatible” chemotherapeutics selectively to oral cancers while decreasing the extent of systemic absorption and the associated risk of side effects.

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.

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.