In vitro and in vivo porphyrin accumulation by C6 glioma cells after exposure to 5-aminolevulinic acid

Several malignant tissues synthesize endogenous porphyrins after exposure t o 5-aminolevunic acid (5-ALA). The present experiments have been designed t o elucidate whether the C6 glioma cell, a model cell for human malignant gl ioma, similarly synthesizes porphyrins when exposed to 5-ALA, and whether s pecific synthesis occurs when C6 cells are inoculated into rat brains to fo rm a tumor. In this situation the Mood-brain barrier may interfere with 5-A LA availability, and spreading of porphyrins with edema outside the tumor m ay occur. Flow cytometry is used to determine the course of cell volume and porphyrin fluorescence intensities in cultured C6 cells which are incubate d in 1 mM 5-ALA. For the induction of experimental brain tumors, 10(4) untr eated C6 cells are inoculated into the brains of rats. After 9 days animals receive 100 mg 5-ALA/kg body weight. Brains are removed after 3, 6, or 9 h and frozen coronal sections obtained for H/E staining or fluorescence spec tography. Cultured C6 cells show a linear increase of protoporphyrin IX flu orescence after exposure to 5-ALA, which begins to plateau after 85 min. Ma rked fluorescence is also observed in solid and infiltrating experimental t umor. However, faint fluorescence also occurs in normal tissue, basal pia, choroid plexus, and, more obviously, in white-matter tracts bordering the t umor (maximal. distance: 1.5+/-0.7 mm). The observations demonstrate that C 6 cells synthesize protoporphyrin IX after exposure to 5-ALA in vitro and i n vivo. However, when utilizing 5-ALA for fluorescence detection or photody namic therapy of brain tumors, attention should be paid to the possibility of protoporphyrin IX occurring outside the tumor. (C) 1998 Elsevier Science S.A. All rights reserved.