Dawn M. Bajic

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.

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/cm2 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.

Medical applications of space light-emitting diode technology—space station and beyond

Space light-emitting diode (LED) technology has provided medicine with a new tool capable of delivering light deep into tissues of the body, at wavelengths which are biologically optimal for cancer treatment and wound healing. This LED technology has already flown on Space Shuttle missions. and shows promise for wound healing applications of benefit to Space Station astronauts. PHOTODYNAMIC THERAPY Photodynamic therapy (PDT) is a cancer treatment modality that recently has been applied as adjuvant therapy for brain tumors. PDT consists of intravenously injecting a photosensitizer, which preferentially accumulates in tumor cells, into a patient and then activating the photosensitizer with a light source. This results in free radical generation followed by cell death. The development of more effective light sources for PDT of brain tumors has been facilitated by applications of space light-emitting diode array technology; thus permitting deeper tumor penetration of light and use of better photosensitizers. Lutetium Texaphyrin (Lutex) is a new, second generation photosensitizer that can potentially improve PDT for brain tumors. Lutex has a major absorption peak at 730 nm, which gives it two distinct advantages. First, longer wavelengths of light penetrate brain tissue easily so that larger tumors could be treated, and second, the major absorption peak means that more of the drug is activated upon exposure to light. Tumoricidal effects of Lutex have been studied in vitro using canine glioma and human glioblastoma cell cultures. Using light emitting diodes (LED) with a peak emission of 728 nm as a light source, a greater than 50 percent cell kill was measured in both cell lines by tumor DNA synthesis reduction. The effectiveness of Lutex against tumor cells in vitro thus established, we have taken the first step toward determining its effectiveness in vivo by performing experiments to deten-nine the largest dose of both Lutex and light that can be administered to dogs before toxicity is seen i.e. the maximum tolerated dose (MTD). Using this dose allows us to effect maximum tumor cell destruction during in vivo studies. Based upon the MTD of Lutex in dogs, human trials are now anticipated.

Selective incorporation of111In-labeled PHOTOFRIN™ by glioma tissuein vivo

The use of PHOTOFRIN™ for photodynamic therapy of human gliomas has been studied by i.v. administration and laser photosensitization. Defining the uptake of PHOTOFRIN™ in the patients tumor in comparison with the surrounding normal brain tissue is highly desirable for patient selection and study ofin vivo kinetics. We utilized a non-invasive approach to the detection of PHOTOFRIN™ uptake in brain tumors with111In-oxine radiolabeled PHOTOFRIN™ and external imaging and quantitation using a gamma camera. Biodistribution of111In-labeled PHOTOFRIN™ in 13 organs was determined in four dogs and 15 mice with gliomas.99mTc-DTPA was used as a control for nonspecific uptake. The greatest concentration of111In-PHOTOFRIN™ in the brain tumor occurred at 24 hours post i.v. administration. The brain tumor PHOTOFRIN™ uptake was seven times greater than that of normal brain. The decreased blood background at 72 hours made this the optimum time for imaging. Specific tumor tissue uptake of111In-PHOTOFRIN™ occurred, well beyond that resulting from blood-brain-barrier (BBB) breakdown.

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.

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.

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-β), 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-β which correlate within vitro cloning efficiency andin vivo tumorigenicity. In this study, intracellular trafficking of PDGF and TGF-β 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 intracellular125I-PDGF and125I-TGF-β. Furthermore, exogenous TGF-β 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-β increased the number of its receptors on clone 2 cells, whereas surface receptors decreased on clone 5 cells treated with TGF-β. These results illustrate the potential for autocrine growth factors to interact with their receptors intracellularly during neoplastic cell proliferation.

The role of light‐emitting diodes for photodynamic therapy of brain tumors

The development of more effective light sources for Photodynamic Therapy (PDT) of brain tumors would be of benefit for both research and clinical application. In this study, the use of light‐emitting diode arrays for PDT of brain tumors with Photofrin® porfimer sodium was investigated. An inflatable balloon device with an LED tip was constructed. These light‐emitting diodes (LED’s) are based on the new semiconductor Aluminum Gallium Arsenide (AlGaAs). 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 to the absorption spectrum of Photofrin®. This analysis showed that of 27.5% of the LED light emission is absorbed by Photofrin® as compared to a 630 nm monochromatic laser light source. Thus, in order to achieve an...

Benzoporphyrin derivative and light-emitting diode for use in photodynamic therapy: Applications of space light-emitting diode technology

Photodynamic therapy (PDT) is a cancer treatment modality that recently has been applied as adjuvant therapy for brain tumors. PDT consists of intravenously injecting a photosensitizer, which preferentially accumulates in tumor cells, into a patient and then activating the photosensitizer with a light source. This results in free radical generation followed by cell death. The development of more effective light sources for PDT of brain tumors has been facilitated by applications of space light-emitting diode array technology; thus permitting deeper tumor penetration of light and use of better photosensitizers. Currently, the most commonly used photosensitizer for brain tumor PDT is Photofrin®. Photofrin® is a heterogeneous mixture of compounds derived from hematoporphyrin. Photofrin® is activated with a 630 nm laser light and does destroy tumor cells in animal models and humans. However, treatment failure does occur using this method. Most investigators attribute this failure to the limited penetration of...