Photodynamic therapy (PDT) shows good promise as an adjuvant therapy for the treatment of gliomas. PDT
requires the use of a photosensitizer but there have been few studies in which they have been directly compared.
Two rat brain glioma cell lines, BT4C and F98 were used to study the effects of Photofrin (PF) and aminolevulinic
acid (ALA) as photosensitizers. Both compounds were able to sensitize cells to red light (635nm) however, PF
treated (2.5 &mgr;g/ml) cells displayed more cell death than ALA treated (1 mM) cells. ALA-PDT treated cells did not
have a block in the cell cycle while PF-PDT treated cells had a fluence dependent G1 block 24 hrs after treatment.
The BT4C cell line also displayed a G2 cell cycle block. Both photosensitizers were able to induce apoptosis as
measured by flow cytometry but only PF-PDT was able to induce necrosis at the fluence rates investigated (1-20
J/cm<sup>2</sup>). These differences in cellular responses to ALA and
A significant contributory factor to the poor prognosis of patients with glioblastoma multiforme is the inability of conventional treatments to eradicate infiltrating glioma cells. A syngeneic rat brain tumor model is used to investigate the effects of aminolevulinic acid (ALA)-mediated photodynamic therapy (PDT) on small clusters of tumor cells sequestered in normal brain. The intrinsic sensitivity of rat glioma cells to PDT was investigated by exposing ALA-incubated cells to a range of radiant exposures and irradiances using 635 nm light. Biodistribution studies were undertaken on tumor-bearing animals in order to determine the tumor selectivity of the photosensitizer following systemic administration (i.p.) of ALA. Effects of ALA-PDT on normal brain and gross tumor were evaluated using histopathology. Effects of PDT on isolated glioma cells in normal brain were investigated by treating animals 48 h after tumor cell implantation: a time when the micro-clusters of cells are protected by an intact blood-brain-barrier (BBB). Rat glioma cells in monolayer are susceptible to ALA-PDT - lower irradiances are more effective than higher ones. Fluorescence microscopy of frozen tissue sections showed that photosensitizer is produced with better than 200:1 tumor-to-normal tissue selectivity following i.p. ALA administration. ALA-PDT resulted in significant damage to both gross tumor and normal brain, however, the treatment failed to prolong survival of animals with newly implanted glioma cells compared to non-treated controls if the drug was delivered either i.p. or directly into the brain. In contrast, animals inoculated with tumor cells pre-incubated in vitro with ALA showed a significant survival advantage in response to PDT.
Introduction: Failure of treatment for high grade gliomas is usually due to local recurrence at the site of surgical resec-tion indicating that a more aggressive form of local therapy could be of benefit. Photodynamic therapy (PDT) is a local form of treatment involving the administration of a tumor-localizing photosensitizing drug that is activated by light of a specific wavelength The results of in vitro experiments indicated that PDT, given at low fluence rates was substantially more effective at inhibiting glioma spheroid growth than short term high fluence rate regimes. This prompted the initia-tion of in vivo studies of low fluence rate 5-aminolevulinic acid (ALA) PDT in a rat glioma model.
Methods:BT4C cell line tumors were established in the brains of inbred BD- IX rats. Eighteen days following tumor induction the animals were injected with 125 mg/kg ALA ip. and four hours later light treatment at various fluences and fluence rates were given after the introduction of an optical fiber. Tumor histology and animal survival were examined.
Results: In vitro experiments verified that the cell line was sensitive to ALA PDT. Microfluorometry of frozen tissue sections showed that PpIX is produced with a greater than 20:1 tumor to normal tissue selectivity ratio four hours after ALA injection. Histological examination demonstrated neutrophil infiltration and tumor central necrosis in low fluence rate treated tumors.
Conclusions: Low fluence rate long term ALA mediated PDT had a more pronounced effect on tumor histology than single shot short duration treatments at similar total fluence levels.