Protoporphyrin IX distribution in rat brain following administration of 5-aminolevulinic acid or its hexylester

The distribution of protoporphyrin IX (Pp IX) was investigated in a novel animal model following administration of 5-aminolevulinic acid (ALA) or its hexyl ester (h-ALA). Pre-cultured tumor spheroids prepared from cell lines or tumor biopsy fragments were injected into the brains of immunodeficient rats. Approximately 3 months after spheroid implantation, Rowett nude rats were injected intra-cranially with the maximum tolerable ALA or h-ALA dose. Animals were sacrificed 4 hours post-injection and their brains removed for fluorescence microscopy analysis. The primary finding of this study is that, in the tumor biopsy model, the tumor-to-normal brain PpIX fluorescence ratio is approximately 3 times higher following direct in situ h-ALA administration compared to ALA.