Research paper Topical glycerol monooleate/propylene glycol formulations enhance 5-aminolevulinic acid in vitro skin delivery and in vivo protophorphyrin IX accumulation in hairless mouse skin Regilene Steluti a , Fernanda Scarmato De Rosa a , John Collett b , Anto ˆnio Cla ´udio Tedesco c , Maria Vito ´ria Lopes Badra Bentley a, * a Department of Pharmaceutical Sciences, Faculty of Pharmaceutical Sciences of Ribeira ˜o Preto, University of Sa ˜o Paulo, Ribeira ˜o Preto, SP, Brazil b Department of Pharmacy, University of Manchester, Manchester, UK c Department of Chemistry, Faculdade de Filosofia, Cie ˆncias e Letras de Ribeira ˜o Preto, University of Sa ˜o Paulo, Ribeira ˜o Preto, Brazil Received 8 March 2004; accepted in revised form 3 January 2005 Available online 7 April 2005 Abstract Photodynamic therapy (PDT), a potential therapy for cancer treatment, utilizes exogenously applied or endogenously formed photosensitizers, further activated by light in an appropriate wavelength and dose to induce cell death through free radical formation. 5-Aminolevulinic acid (5-ALA) is a pro-drug which can be converted to the effective photosensitizer, protoporphyrin IX (PpIX). However, the use of 5-ALA in PDT is limited by the low penetration capacity of this highly hydrophilic molecule into appropriate skin layers. In the present study, we propose to increase 5-ALA penetration by using formulations containing glycerol monooleate (GMO), an interesting and useful component of pharmaceutical formulations. Propylene glycol solutions containing different concentrations of GMO significantly increased the in vitro skin permeation/retention of 5-ALA in comparison to control solutions. In vivo studies also showed increased PpIX accumulation in mouse hairless skin, after the use of topical 5-ALA formulations containing GMO in a concentration-dependent manner. The results show that skin 5-ALA penetration and PpIX accumulation, important factors for the success of topical 5-ALA-PDT in skin cancer, are optimized by GMO/propylene glycol formulations. q 2005 Elsevier B.V. All rights reserved. Keywords: 5-Aminolevulinic acid; Monoolein; Photodynamic therapy; Protoporphyrin IX; Skin cancer 1. Introduction Photodynamic therapy (PDT) is a relatively new approach for the treatment of some kinds of cancer and non-malignant conditions [1,2]. The therapy involves topical or systemic administration of photosensitizers, followed by local application of adequate doses of light of appropriate wavelength in the presence of oxygen to induce tissue or cell destruction, presumably via formation of reactive oxygen species [3–5]. Conventional photosensitizers (hematoporphyrin derivatives) have a prolonged photosensitive effect after the treatment, due to the relatively slow clearance rate of these compounds from skin and certain other normal tissues. Thus, patients receiving standard dosages of these compounds must avoid exposure to sunlight for at least 2 weeks following administration. The inconvenience could be alleviated by the search for alternative compounds to be used in PDT [1]. Endogenous induction of photosensitizers is a recent development in tumor destruction through the topical or systemic application of 5-aminolevulinic acid (5-ALA) [1] a metabolic precursor of protoporphyrin IX (PpIX) in the biosynthetic pathway of heme [6]. The photodynamically active PplX can act as an endogenous photosensitizer [7] and it is almost completely cleared from the body within 24 h, reducing the risks of a general photosensitization for longer periods of time [4]. Systemically administered photosensi- tizers like hematoprophyrin or its more purified form European Journal of Pharmaceutics and Biopharmaceutics 60 (2005) 439–444 www.elsevier.com/locate/ejpb 0939-6411/$ - see front matter q 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.ejpb.2005.01.011 * Corresponding author. Department of Pharmaceutical Sciences, Faculty of Pharmaceutical Sciences of Ribeira ˜o Preto, University of Sa ˜o Paulo, Av. do. Cafe ´ s/n, 14040-903, Ribeira ˜o Preto, Sa ˜o Paulo, Brazil. Tel./fax: C55 16 602 4301. E-mail address: vbentley@usp.br (M.V.L.B. Bentley).