A comparison of 5-aminolaevulinic acid- and its heptyl ester: dark cytotoxicity and protoporphyrin IX synthesis in human adenocarcinoma WiDr cells and in athymic nude mice healthy skin

5-aminolevulinic acid heptyl ester was investigated in human adenocarcinoma WiDr cells and in healthy skin of athymic nude mice in comparison with 5-aminolevulinic acid (ALA). Incubation of WiDr cells with ALA and ALA heptyl ester resulted in production of protoporphyrin IX (PpIX). Concentrations higher than 0.01 mm of ALA heptyl ester and higher than 1 mm of ALA were cytotoxic. The dark cytotoxicity was not related to PpIX. Intracellular localization, photocytoxicity and photobleaching rate of PpIX were the same for both drugs, although a 100 times lower concentration of ALA heptyl ester (0.01 mm) was needed in comparison with ALA (1 mm) to induce the same level of PpIX. ALA heptyl ester, topically (but not systemically) applied, is a promising candidate for fluorescence diagnosis and photodynamic therapy. Special attention must be focused on the concentrations of ALA heptyl ester; as excess may lead to cytotoxicity and inefficient PpIX generation.