Mucoadhesive fenretinide patches for site-specific chemoprevention of oral cancer: enhancement of oral mucosal permeation of fenretinide by coincorporation of propylene glycol and menthol

Abstract

The objective of this study was to enhance oral mucosal permeation of fenretinide by coincorporation of propylene glycol (PG) and menthol in fenretinide/Eudragit RL PO mucoadhesive patches. Fenretinide is an extremely hydrophobic chemopreventive compound with poor tissue permeability. Coincorporation of 5-10 wt % PG (mean J(s) = 16-23 μg cm⁻² h⁻¹; 158-171 μg of fenretinide/g of tissue) or 1-10 wt % PG + 5 wt % menthol (mean J(s) = 18-40 μg cm⁻² h⁻¹; 172-241 μg of fenretinide/g of tissue) in fenretinide/Eudragit RL PO patches led to significant ex vivo fenretinide permeation enhancement (p < 0.001). Addition of PG above 2.5 wt % in the patch resulted in significant cellular swelling in the buccal mucosal tissues. These alterations were ameliorated by combining both enhancers and reducing PG level. After buccal administration of patches in rabbits, in vivo permeation of fenretinide across the oral mucosa was greater (∼43 μg fenretinide/g tissue) from patches that contained optimized permeation enhancer content (2.5 wt % PG + 5 wt % menthol) relative to permeation obtained from enhancer-free patch (∼17 μg fenretinide/g tissue) (p < 0.001). In vitro and in vivo release of fenretinide from patch was not significantly increased by coincorporation of permeation enhancers, indicating that mass transfer across the tissue, and not the patch, largely determined the permeation rate control in vivo. As a result of its improved permeation and its lack of deleterious local effects, the mucoadhesive fenretinide patch coincorporated with 2.5 wt % PG + 5 wt % menthol represents an important step in the further preclinical evaluation of oral site-specific chemoprevention strategies with fenretinide.

Figure 1

Solubilization of fenretinide in bovine serum. The effect of quantity (0.9 (•), 2.26 (○), 3.97 (▼), 8.03 (△), and 20.05 (■)) of fenretinide added in 15-mL bovine serum and incubation time on the solubility of fenretinide (A) and the relationship between the quantity of fenretinide added and time required to reach equilibration (B). Solubility study was conducted at 37 °C under the protection from light.

Figure 2

Co-incorporation of propylene glycol (PG) or PG + menthol in fenretinide/Eudragit® RL PO patches significantly enhance fenretinide permeation across porcine buccal mucosa. The effect of co-incorporation of 0 (•), 5 (○) and 10 (▼) wt% PG (A), 5 (▲) and 10 (□) wt% menthol (B), and 1 wt% PG + 5 wt% menthol (■), 2.5 wt% PG + 5 wt% menthol (◇) and 10 wt% PG + 5 wt% menthol (◆) (C) in patches on ex vivo permeation of fenretinide across porcine buccal mucosa. Ex vivo permeation studies were conducted using side-by-side flow-through diffusion cells at 37 °C. Permeation enhancer-free patch comprised of 5 wt% fenretinide, 20 wt% Tween® 80, and 40 wt% sodium deoxycholate. Symbols represent mean ± SE, n = 5.

Figure 3

Histological examination of porcine buccal tissue after 8 h buccal mucosal attachment of permeation enhancer-free and permeation enhancers-loaded fenretinide mucoadhesive patches. The effect of co-incorporation of 0 (A), 5 (B) or 10 (C) wt% propylene glycol (PG), 5 (D) or 10 (E) wt% menthol, and 1 wt% PG + 5 wt% menthol (F) or 2.5 wt% PG + 5 wt% menthol (G) or 10 wt% PG + 5 wt% menthol (H) in fenretinide/Eudragit RL PO mucoadhesive patches on histological changes of porcine buccal tissue. As is apparent from these photomicrographs, patch application (with or without permeation enhancers) did not dramatically perturb porcine buccal mucosa. All sections demonstrate a preserved basement membrane and basal cell layer, an intact stratified squamous surface epithelium with an overlying parakeratotic layer. Notably, no evidence of changes consistent with extensive epithelial damage e.g. hydropic degeneration of the basal cell layer or acantholysis were observed in multiple sections. The evidence of increased intracellular and intercellular edema observed in epithelia exposed to increased levels PG (C and H.) likely reflects diffusion of PG into individual keratinocytes as well as the intercellular spaces. Images were taken by a light microscope. Permeation enhancer-free patch comprised of 5 wt% fenretinide, 20 wt% Tween® 80, and 40 wt% sodium deoxycholate.

Figure 4

In vitro and in vivo release characteristics of permeation enhancers-free and permeation enhancers-loaded fenretinide/Eudragit® RL PO mucoadhesive patches. Cumulative amount of fenretinide released in vitro/in vivo from permeation enhancers-free (○: in vitro; △: in vivo) and permeation enhancers (2.5 wt% propylene glycol + 5 wt% menthol)-loaded (•: in vitro; ▲: in vivo) patches as a function of time. In vitro and in vivo release studies were conducted in simulated saliva containing 5% w/v sodium deoxycholate (pH 6.8) at 37 °C and rabbits, respectively. Permeation enhancer-free patch comprised of 5 wt% fenretinide, 20 wt% Tween® 80, and 40 wt% sodium deoxycholate. Symbols represent mean ± SE, n = 4 (in vitro) or 6 (in vivo).

Figure 5

Co-incorporation of permeation enhancers (2.5 wt% propylene glycol + 5 wt% menthol) in fenretinide/Eudragit® RL PO patch enhances in vivo buccal mucosal permeation of fenretinide. Tissue levels of fenretinide as a function of buccal administration time of permeation enhancer-free (filled bars) and permeation enhancers-loaded (open bars) patches in rabbits. Permeation enhancer-free patch comprised of 5 wt% fenretinide, 20 wt% Tween® 80, and 40 wt% sodium deoxycholate. Bars represent mean ± SE, n = 6).

Figure 6