23 March 2007 Monitoring Pc 4-mediated photodynamic therapy of U87 tumors with 18F- fluorodeoxy-glucose PET imaging in the Athymic Nude Rat
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Abstract
Introduction: We have previously demonstrated the use of phthalocyanine Pc 4 for the photodynamic therapy (PDT) of ectopic human glial tumors in the athymic nude rat brain. We wish to determine whether 18F-fluorodeoxy-glucose (18F-FDG) Positron Emission Tomography (PET) imaging can detect the reduction in tumor metabolism that must occur after Pc 4-PDT-induced necrosis. Methods: 2.5 x 105 U87 cells were injected into the brains of 12 athymic nude rats. After 7 days of tumor growth, all 12 animals were imaged functionally by 18F-FDG micro-PET (&mgr;PET) and structurally by micro-CT and/or micro-MR. These animals received 0.5 mg/kg b.w. Pc 4 via tail-vein injection. One day later the scalp was re-incised and the tumor illuminated with 30 J/cm2 of 672-nm light from a diode laser. The next day these animals were again 18F-FDG &mgr;PET imaged. Next, the animals were euthanized and their brains were explanted for H&E histology. Results: Histology showed that tumors in the 6 Pc 4-PDT-treated animals demonstrated necrosis ranging from full to frank (severe). Preliminary analysis showed that 18F-FDG &mgr;PET activity in 3 of the 6 non-PDT group (i.e., no tumor necrosis observed) animals was seen to increase 2.28 times following tumor photoirradiation, whereas 18F-FDG &mgr;PET activity in 5 of the 6 PDT group (i.e., tumor necrosis observed) animals was seen to increase 1.15 times following tumor photoirradiation. Discussion: The increased 18F-FDG &mgr;PET activity in the PDT group was unexpected. We had expected this activity to decrease and are presently investigating the cause of this observation.
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Davood Varghai, Nathan Cross, Chandra Spring-Robinson, Rahul Sharma, Denise K. Feyes, Yusra Ahmad, Nancy L. Oleinick, Raymond F. Muzic, David Dean, "Monitoring Pc 4-mediated photodynamic therapy of U87 tumors with 18F- fluorodeoxy-glucose PET imaging in the Athymic Nude Rat", Proc. SPIE 6424, Photonic Therapeutics and Diagnostics III, 64242G (23 March 2007); doi: 10.1117/12.701517; https://doi.org/10.1117/12.701517
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