alpha-Bisabolol improves 5-aminolevulinic acid retention in buccal tissues: Potential application in the photodynamic therapy of oral cancer.

CONTEXT: 5-Aminolevulinic acid (5-ALA) is a prodrug used in photodynamic therapy (PDT) of tumors, including cancer of the oral mucosa. 5-ALA poorly penetrates oral tissues due to its high hydrophilicity, which impairs its local effects in PDT. OBJECTIVES: To examine whether alpha-bisabolol (alpha-Bis) influences the 5-ALA permeability in the porcine buccal mucosa, to an extent that improves its application in PDT (which requires low permeation and high retention in the buccal mucosa). METHODS: In vitro permeability studies with 5-ALA (1% and 10% w/w) associated with alpha-Bis (1% to 20% w/w) in propylene glycol were carried out at 4h and 24h using porcine buccal mucosa in a modified Franz cell system. The in vitro release profiles (0.5 to 48h) of the selected formulation and its respective control were determined using artificial membranes. Samples of buccal mucosa treated with the formulation were submitted to histopathological analysis, using a routine optical microscopy technique. RESULTS: The association of 1% 5-ALA and 5% alpha-Bis provided the best results; after 4h of treatment with this formulation, the 5-ALA permeation was low and its retention in the mucosa was six-fold higher than that promoted by the control formulation (5-ALA alone). Histological analysis of the porcine buccal mucosa evidenced that 5% alpha-Bis altered the tissue morphology, which probably promoted 5-ALA retention. We concluded that 5% alpha-Bis is a potential adjuvant in formulations containing 5-ALA that could improve its retention after topical oral administration for the PDT treatment of cancer.