Potential efficacy of a delta 5-aminolevulinic acid bioadhesive gel formulation for the photodynamic treatment of lesions of the gastrointestinal tract in mice

Evaluation of bioadhesive gels for local action in the esophagus

Direct drug administration to the esophagus faces several obstacles, including continuous salivary dilution and removal of the dosage form from the tissue surface due to esophageal peristalsis. These actions often result in short exposure times and reduced concentrations of drug at the esophageal surface, providing limited opportunities for drug absorption into or across the esophageal mucosa. A variety of bioadhesive polymers were investigated for their ability to resist removal by salivary washings using an ex vivo porcine esophageal tissue model. Hydroxypropylmethylcellulose and carboxymethylcellulose both have reported bioadhesive properties, but neither was able to withstand repeated exposure to saliva, and the gels formulated with these polymers were quickly removed from the esophageal surface. Two polyacrylic polymers, carbomer and polycarbophil, also showed limited esophageal surface retention when exposed to salivary washing, likely due to the ionic composition of saliva affecting the inter-polymer interactions necessary for these polymers to maintain their increased viscosities. In situ gel forming polysaccharide gels (ion-triggered), including xanthan gum, gellan gum, and sodium alginate, showed superior tissue surface retention, and formulations containing these bioadhesive polymers along with ciclesonide, an anti-inflammatory soft prodrug, were investigated as potential, locally-acting esophageal delivery systems. Exposure of a segment of esophagus to the ciclesonide-containing gels resulted in therapeutic concentrations of des-ciclesonide, the active drug metabolite, in the tissues within 30 min. Increasing des-CIC concentrations were also observed over a 3-hour exposure interval suggesting continued release and absorption of ciclesonide into the esophageal tissues. These results demonstrate the ability to achieve therapeutic drug concentrations in the esophageal tissues using in situ gel-forming bioadhesive polymer delivery systems, and these systems provide promising opportunities for the local treatment of esophageal disease.

Clinical evaluation of bioadhesive hydrogels for topical delivery of hexylaminolevulinate to Barrett's esophagus

Fluorescence diagnosis following oral administration of 5-aminolevulinic acid (5-ALA) has shown to enable the sensitive visualization of intestinal metaplasia, dysplasia and early carcinoma in Barrett's esophagus. Once being established, this technique will be a potential alternative to today's standard diagnosis, i.e. four-quadrant random biopsies which are taken every 1-2 cm of the esophagus for histopathological analysis. In order to further improve this methodology, topical application of lipophilic 5-ALA esters to the esophagus could be advantageous in terms of fluorescence contrast and fluorescence intensity in the target tissue, adverse side effects, as well as application time. Therefore, the aim of this study was to develop a bioadhesive formulation loaded with hexylaminolevulinate (HAL) targeting the esophageal lining. In the present study, different mucoadhesive gels including poloxamer 407, cross-linked polyacrylic acid, hydroxypropylmethylcellulose, sodium carboxymethylcellulose and chitosan have been evaluated with respect to bioadhesion to the esophagus using an ex vivo rat model and a clinical study on healthy volunteers. In order to visualize the mucoadhesive properties of the formulations, a blue dye was incorporated as contrast agent. Chitosan has shown the best esophageal adhesion both in vitro and in vivo. Furthermore, using the in vitro release profiles from chitosan loaded with 40 mM of HAL, one can estimate that after a residence time of 10 min on the esophageal wall, the amount of HAL delivered to the epithelium will be sufficient to perform fluorescence diagnosis of Barrett's esophagus following swallowing of this formulation.

Bioadhesive Dosage Forms for Esophageal Drug Delivery

The esophagus as a site for drug delivery has been much overlooked in comparison to the remainder of the gastrointestinal tract. The low permeability and transient nature of the esophagus means that it is unsuitable for delivery of drugs for systemic action. However, esophageal disorders including fungal infection, cancers, motility dysfunction, and damage due to gastric reflux may be treated using locally acting agents that offer benefits of reduced dosage and decreased side effects. Bioadhesive dosage forms that adhere to the esophageal mucosa and prolong contact have been investigated to improve the efficacy of locally acting agents. The rationale for local esophageal drug delivery and its limitations, the factors that determine adhesion to this organ, and the experimental models used in esophageal drug delivery research are reviewed.

Effect of Oil-in-Water Emulsions on 5-Aminolevulinic Acid Uptake and Metabolism to PpIX in Cultured MCF-7 Cells

PURPOSE

To identify the optimal vehicle for fast and efficient cellular production of the photosensitizer, protoporphyrin IX (PpIX), upon administration of 5-aminolevulinic acid (ALA).

METHODS

ALA in various oil/water o/w emulsions was applied to the human mammary epithelial cell line (MCF-7) cultured in microplates. Upon incubation for 14 h, the accumulated amount of PpIX was determined by fluorescence spectroscopy. Variables such as the pH and concentration of the emulsions, the temperature and duration of incubation were examined along with the importance of ALA concentration and the presence of endocytosis inhibitors.

RESULTS

An increase in the amount of produced PpIX was observed with an increase in extracellular pH, incubation temperature, and ALA concentration. A saturable mechanism of PpIX accumulation was evident, mainly as a result of the uptake mechanism for ALA. Some of the o/w emulsions increased the amount of intracellular PpIX, and the results indicated that this was not due to an increased k(m) of the extracellular ALA to intracellular PpIX conversion, but to the increased endocytotic uptake in the presence of the emulsions. In general, the increase in PpIX in the presence of emulsions relative to the control was more pronounced after 1 h as compared to after 2-4 h.

CONCLUSIONS

The formation of PpIX in MCF-7 cells exposed to ALA is improved by the presence of certain o/w emulsions, which could be explained by endocytosis.

Timing of 5-aminolaevulinic acid-induced photodynamic therapy for the treatment of patients with Barrett's oesophagus

5-Aminolaevulinic acid-induced photodynamic therapy (ALA-PDT) is being used as an experimental treatment of Barrett's oesophagus (BE), a pre-malignant disorder in the distal oesophagus. The present study aims to acquire detailed knowledge on the pharmacokinetics of ALA and the photosensitizer protoporphyin IX (PPIX) in tissues and plasma of patients with BE to provide a rationale for the conditions used in ALA-PDT. A total of 26 patients with BE were randomized to varying time intervals between ingesting 60 mg/kg ALA and undergoing an endoscopy with biopsies of BE, normal oesophageal and gastric mucosa. At 1, 2, 7, 8 and 24 h, two patients at each time, and at 3, 4, 5 and 6 h, four patients at each time after ALA ingestion were included. ALA, porphyrin intermediates and PPIX were determined in all biopsy and plasma samples. The maximum concentration of PPIX was found earlier in BE (4.6+/-0.5 h) than in squamous epithelium (SQ) (6.6+/-2.2 h) (P<0.05). PPIX concentrations were higher in SQ than in BE especially at longer time intervals. In addition, tissue ALA concentrations were found to be 20-fold higher than the plasma concentrations at 1 h after ALA ingestion, suggesting uptake from the oesophageal lumen. Skin photosensitivity was short-lasting but often debilitating. Our results provide a rationale for the use of ALA-PDT for the treatment of BE at 4-5 h after ALA ingestion and for local application of ALA in the oesophagus. Patients undergoing ALA-PDT must be strongly advised to avoid sunlight for at least 24-36 h.

Potential efficacy of a delta 5-aminolevulinic acid thermosetting gel formulation for use in photodynamic therapy of lesions of the gastrointestinal tract

Photodynamic therapy (PDT) using 5-aminolevulinic acid (ALA)-induced protoporphyrin IX may play a role in the treatment of dysplastic Barrett's oesophagus. An ALA thermosetting gel Pluronic F-127) was developed and evaluated in an in vivo mouse model for potential use in PDT of Barrett's mucosa. In vitro studies of the influence of Pluronic F-127 percentage on thermosetting gel temperature, followed by the influence of ALA concentration on thermosetting temperature and ALA-gel stability as a function of time or temperature were studied. In vivo relationships between ALA doses and fluorescence were studied to determine the optimal concentration. Fluorescence measurement in vivo showed that ALA concentration and time had a nonlinear influence on protoporphyrin IX synthesis. For ALA-gel applications longer than 30 min a plateau fluorescence was reached, the maximum fluorescence being obtained after 4 h whatever the time of contact. The maximum intensity (2824 counts s(-1)) was found with 40 mg mL(-1) ALA-gel, and fluorescence intensities differed with time, reaching a maximum after 3-4 h. ALA-Pluronic F-127 is a suitable formulation for treatment of Barrett's oesophagus, allowing easy application in liquid form at 4 degrees C and good adhesion in the oesophagus in gel form, with efficient diffusion of ALA into treated mucosa.

Poloxamer 407 as a thermogelling and adhesive polymer for rectal administration of short-chain fatty acids

OBJECTIVES

The purpose of the study was to gel a rectal solution of short-chain fatty acids to decrease the loss of active materials in the colonic lumen and thereby optimize their absorption.

METHODS

Five thermogels were prepared with poloxamer 407 at concentrations ranging from 17% to 20%. Their viscosities were measured at room temperature and 37 degrees C, and their gelling temperatures were determined. The adhesive properties of each gel were assessed in vitro at 37 degrees C. Short-chain fatty acid release was studied using Guyot cells.

RESULTS

From the threshold concentration of 17.5%, the solutions, Newtonian at room temperature (50-80 mPa x s), gelled at 37 degrees C. The higher the concentration, the higher the viscosity (1750 to 49,000 mPa x s), the lower the gelling temperature (27.6 degrees C to 23.4 degrees C), and the stronger the work of adhesion (2.2 to 4.5 mJ). Short-chain fatty acid release from the 18% polymer gel was decreased by 60% compared to the rectal solution.

CONCLUSION

The 18% poloxamer 407 concentration provided a solution that was liquid at room temperature, that gelled at 37 degrees C, possessed adhesive properties, and controlled short-chain fatty acid release.

Routine experimental system for defining conditions used in photodynamic therapy and fluorescence photodetection of (non-) neoplastic epithelia

A common method to induce enhanced short-term endogenous porphyrin synthesis and accumulation in cell is the topical, systemic application of 5-aminolevulinic acid or one of its derivatives. This circumvents the intravenous administration of photosensitizers normally used for photodynamic therapy (PDT) of fluorescence photodetection. However, in the majority of potential medical indications, optimal conditions with respect to the porphyrin precursor or its pharmaceutical formulation have not yet been found. Due to ethical restrictions and animal right directives, the number of available test objects is limited. Hence, definition and use of nonanimal test methods are needed. Tissue and organ cultures are a promising approach in replacing cost intensive animal models in early stages of drug development. In this paper, we present a tissue culture, which can among others be used routinely to answer specific questions emerging in the field of photodynamic therapy and fluorescence photodetection. This technique uses mucosae excised from sheep paranasal sinuses or pig bladder, which is cultured under controlled conditions. It allows quasiquantitative testing of different protoporphyrin IX precursors with respect to dose-response curves and pharmacokinetics, as well as the evaluation of different incubation conditions and/or different drug formulations. Furthermore, this approach, when combined with the use of electron microscopy and fluorescence-based methods, can be used to quantitatively determine the therapeutic outcome following protoporphyrin IX-mediated PDT.

New diagnostic methods for esophageal carcinoma

The increasingly severe problem of esophageal carcinoma on world public health merits the application of new endoscopic methods to assist in early detection and screening. Older methods, such as tissue staining, combined with magnification endoscopy, have shown promising results, while newer techniques capitalize on measurements that discriminate benign from malignant cells based on a wide array of different attributes, ranging from the molecular to the macroscopic level. Instrumentation based on laser-induced fluorescence spectroscopy, ratio fluorescence imaging, elastic scattering spectroscopy, Raman spectroscopy, and optical coherence tomography is presently being tested and compared with standard endoscopic techniques. Using pathologic interpretation of pinch biopsies as the "gold standard," these techniques have shown the ability to identify dysplastic or malignant regions of tissue that would not be visible to the unassisted endoscopist and offer increased sensitivity for detection compared to rigorous random biopsy protocols. The rapid speed of the instruments allows the provision of information to the endoscopist almost instantaneously, potentially allowing therapeutic decisions to be conducted within the confines of the same endoscopic procedure, thereby achieving gains in efficiency and reductions in overall cost. Large, multicenter trials will be necessary to determine the sensitivity and specificity of individual and combined techniques, as well as their ability to favorably influence the early detection, management, and overall outcome of this disease.