Potential Efficacy of a Delta 5-Aminolevulinic Acid Bioadhesive Gel Formulation for the Photodynamic Treatment of Lesions of the Gastrointestinal Tract in Mice

A delta 5‐aminolevulinic acid (ALA) bioadhesive gel has been developed and evaluated in an in‐vivo mouse model for photodynamic treatment of gastric cancer or Barrett's oesophagus. Four gels were tested: noveon AA‐1, keltrol T, lutrol and blanose. An initial in‐vitro study of gel adhesion showed that noveon and keltrol had longer polyethylene transit times than lutrol and blanose. In‐vivo assays indicated that protoporphyrin IX was synthesized by gastric mucosa when ALA‐noveon and ALA‐lutrol were used (preferable results for noveon). Keltrol was eliminated from the study after these investigations. Only ALA‐noveon gel was retained for studies of the relationship between ALA dose and fluorescence. Fluorescence measurements in‐vivo showed that ALA concentration and application time had an influence on protoporphyrin IX synthesis. Maximum intensity (2091 counts s−) was found with 2 mg mL− ALA, and fluorescence intensities differed with application time, reaching 1805 counts s− after 240 min. ALA‐noveon, showing good adhesion and enabling efficient diffusion of ALA at a pH < 6, was considered the best formulation for maintaining ALA stability.