Studies of the potential of 5-aminolevulinic acid in photodynamic therapy of skin cancer: obtaining and evaluating liposomes with release system (phase II)

Abstract

The 5-aminolevulinic acid (5-ALA) as well as other photosensitizer agent (as m-THPC clorines (Foscan) and other) have been studied in the leveI of topical application as a prodrug or associated drug specific for Photodynamic therapy (PDT) (DE ROSA, F.S. et al., 2003); (GARCIA, F.S. et al., 2003); (TEDESCO, A.C. et al., 2003); (PIERRE, M.B. et al., 2001); (PIERRE, M.B. et al., 2001); (DE ROSA, F.S. et al., 2000); (DE ROSA, F.S. et al., 2000). For 5-ALA and its ester derivatives compounds, after its topical application, the incidence of visible light in an appropriated wavelength, induces the formation of a fluorescent and highly photodynamic active substance, Protoporphyrin IX (PpIX). The use of the 5-ALA as precursory in biosynthesis of Protoporphyrin IX, and consequent use in Photodynamic therapy, has limited until the moment to skin cancer with great difficulties to expand its utilization for other types of cancer. The 5-ALA or its ester derivatives topically applied can permeate easily the abnormal straum corneum (with neoplastic chacaterisitic), but not through the normal epidermis, allowing then to present highly selective to skin tumors. The proposal of utilization of specifics drug delivery systems that provide an increase in the penetration and, consequently, the concentration of ALA in tumor tissues, constitutes a way to optimize the therapy. The activity of the photosensitizer is dependent of its concentration in the target tissues. The theoretical and clinical results obtained until now comprove the efficiency of the original proposal presented in the phase I of their project (FAPESP 98/12654-3), with more than 40 clinical cases of cancer eradication from baso and spino cellular skin cancer and Bowen' s diseases. The use of liposome as drug delivery systems for topical appIication has been considered for some authors (FOLDIVARI, M., 1991; BONINA, F.P. et al., 1995; VEMURI, S. and RHODES, C.T., 1995). Beyond these innumerable other systems have been studied with excellent properties of delivery systems. During the development of the project (phase I), much time were invested in the synthesis of new esters derived from the 5-ALA (butil, hexil, octil and decil) leading to molecules more hydrophobic maximizing its spectroscopic properties with reduction of the total amounts of active principIe in the final formulation. Preliminary studies in human beings with actinic keratosiss, had indicated an exceIIent incorporation of the gel formularizations prepared with the new esters derivatives. The work proposed for these new phase, of the thematic project (phase II) it is based in an new and higher basic and clinical proposal... (AU)