title: Biological activity of 5-aminolevulinic acid and its methyl ester after storage under different conditions.
abstract: 5-Aminolevulinic acid (ALA) is a natural precursor of protoporphyrin IX (PpIX) and heme in cells. Photodynamic therapy (PDT) utilizes a metabolic imbalance in cancer cells, leading to increased PpIX generation from exogenous ALA. Due to chemical instability of ALA in therapeutic concentrations at pH values larger than 5.0 and at high temperatures, it looses its activity by spontaneous dimerization to 2,5-dicarboxyethyl-3,6-dihydropyrazine (DHPY). ALA esters are now supplementing ALA in PDT, but little is known about their stability. We have studied the stability of ALA and its methyl ester (MAL) stored under different conditions (temperatures, pH values) by measuring their ability to generate PpIX. 100mM solutions of both compounds were found to be stable at pH 4 and at 4 degrees C. However, at pH 5.5 they lost almost 10% of the initial activity during 5days of storage at 4 degrees C. The fastest decay of ALA and MAL was seen at pH 7.4 and at 37 degrees C, and followed first order kinetics. At pH 7.4 and at 4 degrees C MAL lost its PpIX producing ability more slowly than at 37 degrees C. Our work shows that solutions should be prepared immediately before use and stored at low temperatures. The pH of stock solutions should not exceed 5.
authors.affiliation: Department of Radiation Biology, Institute for Cancer Research, 0310 Montebello, Oslo, Norway. mkaliszewski@wat.edu.pl <mkaliszewski@wat.edu.pl>
authors.forename: Miron
authors.initials: M
authors.lastname: Kaliszewski
authors.forename: Miroslaw
authors.initials: M
authors.lastname: Kwasny
authors.forename: Asta
authors.initials: A
authors.lastname: Juzeniene
authors.forename: Petras
authors.initials: P
authors.lastname: Juzenas
authors.forename: Alfreda
authors.initials: A
authors.lastname: Graczyk
authors.forename: Li-Wei
authors.initials: LW
authors.lastname: Ma
authors.forename: Vladimir
authors.initials: V
authors.lastname: Iani
authors.forename: Patrycja
authors.initials: P
authors.lastname: Mikolajewska
authors.forename: Johan
authors.initials: J
authors.lastname: Moan
mesh_terms: D000622:Aminolevulinic Acid / Q000138:chemical synthesis / Q000737:chemistry*; D004355:Drug Stability; D004952:Esters; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010778:Photochemotherapy; D011524:Protoporphyrins; D013696:Temperature
chemical_list: D004952:Esters; D011524:Protoporphyrins; D000622:Aminolevulinic Acid; C028025:protoporphyrin IX