Preclinical evaluation of benzoporphyrin derivative combined with a light-emitting diode array for photodynamic therapy of brain tumors.

OBJECTIVE: The aim of this study was to investigate the second-generation photosensitizer benzoporphyrin derivative (BPD) and a novel light source applicator based on light-emitting diode (LED) technology for photodynamic therapy (PDT) of brain tumors. METHODS: We used a canine model to investigate normal brain stem toxicity. Twenty-one canines underwent posterior fossa craniectomies followed by PDT with BPD. These animals were compared to light only and BPD control. In addition, we investigated the ability of BPD and LED to cause inhibition of cell growth in canine glioma and human glioma cell lines, in vitro. The biodistribution of BPD labeled with 111In-BPD in mice with subcutaneous and intracerebral gliomas and canines with brain tumors was studied. RESULTS: The in vivo canine study resulted in a maximal tolerated dose of 0.75 mg/kg of BPD and 100 J/cm(2) of LED light for normal brain tissue. The in vitro study demonstrated 50% growth inhibition for canine and human glioma cell lines of 10 and 4 ng/ml, respectively. The mucine study using 111In-BPD showed a tumor to normal tissue ratio of 12:1 for intracerebral tumors and 3.3:1 for subcutaneous tumors. Nuclear scans of canines with brain tumors showed uptake into tumors to be maximal from 3 to 5 h. CONCLUSION: Our study supports that BPD and LED light sources when used at appropriate drug and light doses limit normal brain tissue toxicity at doses that can cause significant glioma cell toxicity in vitro. In addition, there is higher BPD uptake in brain tumors as compared to normal brain in a mouse glioma model. These findings make BPD a potential new-generation photosensitizer for the treatment of childhood posterior fossa tumors as well as other malignant cerebral pathology.

Light-emitting diodes as a light source for intraoperative photodynamic therapy.

The development of more cost-effective light sources for photodynamic therapy of brain tumors would be of benefit for both research and clinical applications. In this study, the use of light-emitting diode arrays for photodynamic therapy of brain tumors with Photofrin porfimer sodium was investigated. An inflatable balloon device with a light-emitting diode (LED) tip was constructed. These LEDs are based on the new semiconductor aluminum gallium arsenide. They can emit broad-spectrum red light at high power levels with a peak wavelength of 677 nm and a bandwidth of 25 nm. The balloon was inflated with 0.1% intralipid, which served as a light-scattering medium. Measurements of light flux at several points showed a high degree of light dispersion. The spectral emission of this probe was then compared with the absorption spectrum of Photofrin. This analysis showed that the light absorbed by Photofrin with the use of the LED source was 27.5% of that absorbed with the use of the monochromatic 630-nm light. Thus, to achieve an energy light dose equivalent to that of a laser light source, the LED light output must be increased by a factor of 3.63. This need for additional energy is the difference between a 630- and 677-nm absorption of Photofrin. Using the LED probe and the laser balloon adapter, a comparison of brain stem toxicity in canines was conducted. LED and laser light showed the same signs of toxicity at equivalent light energy and Photofrin doses. The maximal tolerated dose of Photofrin was 1.6 mg/kg, using 100 J/cm2 of light energy administered by laser or LED. This study concludes that LEDs are a suitable light source for photodynamic therapy of brain tumors with Photofrin. In addition, LEDs have the potential to be highly efficient light sources for second-generation photosensitizers with absorption wavelengths closer to the LED peak emission.

Gallium nitrate delays the progression of microscopic disease in a human medulloblastoma murine model.

The goal of adjuvant chemotherapy is to treat postoperative microscopic disease in the hope of preventing tumor recurrence and/or metastasis. Since the introduction of chemotherapeutic agents, the disease-free survival of children with medulloblastoma has improved only modestly. Therefore, there is a need to develop and investigate new chemotherapeutic agents for this malignancy. Gallium nitrate has demonstrated significant antineoplastic activity toward human medulloblastoma in vitro and in vivo and may prove to be an optimal chemotherapeutic agent in treating medulloblastoma microscopic disease. The present study consisted of injecting medulloblastoma Daoy intradermally into both flanks of nude mice. A 15-day 50-mg/kg/day regimen was implemented the day after tumor inoculation. All treated and control mice received saline hyperhydration during the treatment period. The interval between tumor cell inoculation and first measurable tumor detection, tumor occurrence, growth rate, and size were recorded. Results indicated that gallium nitrate significantly prolonged the interval between tumor cell inoculation and measurable tumor detection.

Prevention of gallium toxicity by hyperhydration in treatment of medulloblastoma.

In vitro and in vivo studies have established gallium nitrate as an effective chemotherapeutic agent against human medulloblastoma. In vitro, gallium nitrate reduced cell proliferation and DNA synthesis of medulloblastoma Daoy. Gallium inhibits the availability of 59Fe to ribonucleotide reductase and has a direct effect on the enzyme itself. In vivo, gallium demonstrated similar effects on the medulloblastoma Daoy cell line in nude mice. Tumor growth rate and actual size were decreased; however, severe nephrotoxicity and mortality were observed. In our study, intradermal injections of medulloblastoma Daoy cells were given to nude mice and then tumors were allowed to grow. Tumor-bearing mice received a 15-day gallium (50 mg/kg/day) regimen, 20-day rest, 7-day gallium (66.5 mg/kg/day) dose escalation regimen beginning when tumor size exceeded 8-10 mm in diameter. All treated and control mice received saline hyperhydration during both treatment sessions. Our study resulted in the prevention of severe toxicity and an inhibition of tumor growth. No toxicity occurred with gallium nitrate at 50 mg/kg/day. Severe morbidity and mortality were observed at the higher gallium dose level (66.5 mg/kg/day), suggesting that the 50 mg/kg/day dose is the appropriate level when investigating gallium nitrate as a chemotherapy agent in nude mice.

The role of photodynamic therapy in posterior fossa brain tumors. A preclinical study in a canine glioma model.

Photodynamic therapy was studied in dogs with and without posterior fossa glioblastomas. This mode of therapy consisted of intravenous administration of Photofrin-II at doses ranging from 0.75 to 4 mg/kg 24 hours prior to laser light irradiation in the posterior fossa. Tissue levels of Photofrin-II were four times greater in the tumor than in the surrounding normal brain. Irradiation was performed using 1 hour of 500 mW laser light at a wavelength of 630 nm delivered through a fiberoptic catheter directly into the tumor bed via a burr hole. All animals receiving a high dose (4 or 2 mg/kg) of Photofrin-II developed serious brain-stem neurotoxicity resulting in death or significant residual neurological deficits. A lower dose (0.75 mg/kg) of Photofrin-II produced tumor kill without significant permanent brain-stem toxicity in either the control animals or the animals with cerebellar brain tumors receiving photodynamic therapy.

Intracellular growth factor metabolism in proliferation of a brain tumor cell line. Intracellular growth factors and brain tumor proliferation.

Brain tumor cells secrete platelet-derived growth factor (PDGF) and transforming growth factor beta (TGF-beta), and through local production of these growth factors, brain tumor cells may stimulate their own proliferation. Previously we have shown that several different clones of canine glioma cells secrete varying amounts of PDGF and TGF-beta which correlate with in vitro cloning efficiency and in vivo tumorigenicity. In this study, intracellular trafficking of PDGF and TGF-beta was assessed by treatment of each clone with agents preventing vesicular degradation and secretion of growth factors. Clone 2 was more sensitive to these agents (chloroquine and monensin) than clone 5, resulting in retention of intracellular 125I-PDGF and 125I-TGF-beta. Furthermore, exogenous TGF-beta inhibited DNA-synthesis dramatically in clone 2 (compared with clone 5), presumably by interfering with intracellular growth factor receptor availability. This is supported by the fact that exogenous TGF-beta increased the number of its receptors on clone 2 cells, whereas surface receptors decreased on clone 5 cells treated with TGF-beta. These results illustrate the potential for autocrine growth factors to interact with their receptors intracellularly during neoplastic cell proliferation.