Photodynamic therapy (PDT) is a promising modality for the
treatment of solid tumors that combines a photosensitizing
agent and light to produce cytotoxic reactive oxygen species that
lead to tumor cell death. The recent introduction of bio-
luminescence imaging (BLI), involving the use of the luciferase
gene (luc) transferred into target tumor cells, followed by
systemic administration of luciferin and detection of the emitted
visible chemiluminescence photons, offers the potential for
longitudinal imaging of tumor growth and therapeutic response
in single animals. We demonstrate in this study the first results
of the use of BLI to assess the response of an intracranial brain
tumor model (9L rat gliosarcoma) to aminolevulinic acid
(ALA)–mediated PDT. Complementary in vitro experiments
with the luciferase-transfected 9L cells show that the decrease in
the luminescent signal after PDT correlates with cell kill.In vivo
imaging shows a decrease in the BLI signal from the tumor after
ALA-PDT treatment, followed by tumor regrowth. Further-
more, preliminary studies using cells transfected with a hypoxia-
responsive vector show an increase in bioluminescence within
4 h after Photofrin-mediated PDT, demonstrating the ability to
observe stress-gene responses. These results suggest that BLI
can be used to provide spatiotemporal information of in-
tracranial brain tumor responses after PDT and may serve as
a valuable response-endpoint measure.