Biomedical subjects

Brian C Wilson

Publications and source records attributed to Brian C Wilson.

44 records · Page 3Linked to original sources

PubMed2002

Direct near-infrared luminescence detection of singlet oxygen generated by photodynamic therapy in cells in vitro and tissues in vivo.

Singlet oxygen (1O2) is believed to be the major cytotoxic agent involved in photodynamic therapy (PDT). Measurement of 1O2 near-infrared (NIR) luminescence at 1270 nm in biological environments is confounded by the strongly reduced 1O2 lifetime and probably has never been achieved. We present evidence that this is now possible, using a new NIR-sensitive photomultiplier tube. Time-resolved 1O2 luminescence measurements were made in various solutions of aluminum tetrasulphonated phthalocyanine (AlS4Pc) and Photofrin. Measurements were also performed on suspensions of leukemia cells incubated with AlS4Pc, and a true intracellular component of the 1O2 signal was clearly identified. Time-resolved analysis showed a strongly reduced 1O2 lifetime and an increased photosensitizer triplet-state lifetime in the intracellular component. In vivo measurements were performed on normal skin and liver of Wistar rats sensitized with 50 mg/kg AlS4Pc. In each case, a small but statistically significant spectral peak was observed at 1270 nm. The 1O2 lifetime based on photon count rate measurements at 1270 nm was 0.03-0.18 micros, consistent with published upper limits. We believe that these are the first direct observations of PDT-generated intracellular and in vivo 102. The detector technology provides a new tool for PDT research and possibly clinical use.

Animals↗

PubMed2002

Preclinical studies in normal canine prostate of a novel palladium-bacteriopheophorbide (WST09) photosensitizer for photodynamic therapy of prostate cancers.

Photodynamic therapy (PDT) uses light to activate a photosensitizer to achieve localized tumor control. In this study, PDT mediated by a second-generation photosensitizer, palladium-bacteriopheophorbide WST09 (Tookad) was investigated as an alternative therapy for prostate cancer. Normal canine prostate was used as the animal model. PDT was performed by irradiating the surgically exposed prostate superficially or interstitially at 763 nm to different total fluences (100 or 200 J/cm2; 50, 100 or 200 J/cm) at 5 or 15 min after intravenous administration of the drug (2 mg/kg). Areas on the bladder and colon were also irradiated. The local light fluence rate and temperature were monitored by interstitial probes in the prostate. All animals recovered well, without urethral complications. During the 1 week to 3 month post-treatment period, the prostates were harvested for histopathological examination. The PDT-induced lesions showed uniform hemorrhagic necrosis and atrophy, were well delineated from the adjacent normal tissue and increased linearly in diameter with the logarithm of the delivered light fluence. A maximum PDT-induced lesion size of over 3 cm diameter could be achieved with a single interstitial treatment. There was no damage to the bladder or rectum caused by scattered light from the prostate. The bladder and rectum were also directly irradiated with PDT. At 80 J/cm2, a full-depth necrosis was observed but resulted in no perforation. At 40 J/cm2, PDT produced minimal damage to the bladder or rectum. On the basis of optical dosimetry, we have estimated that 20 J/cm2 is the fluence required to produce prostatic necrosis. Thus, the normal structure adjacent to the prostate can be safely preserved with careful dosimetry. At therapeutic PDT levels, there was no structural or functional urethral damage even when the urethra was within the treated region. Hence, Tookad-PDT appears to be a promising candidate for prostate ablation in patients with recurrent, or possibly even primary, prostate cancer.

Animals↗

PubMedDate not supplied

Bioluminescence imaging of the response of rat gliosarcoma to ALA-PpIX-mediated photodynamic therapy.

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 bioluminescence 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. Furthermore, 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 intracranial brain tumor responses after PDT and may serve as a valuable response-endpoint measure.

Aminolevulinic Acid↗

PubMedDate not supplied

Metronomic photodynamic therapy as a new paradigm for photodynamic therapy: rationale and preclinical evaluation of technical feasibility for treating malignant brain tumors.

The concept of metronomic photodynamic therapy (mPDT) is presented, in which both the photosensitizer and light are delivered continuously at low rates for extended periods of time to increase selective tumor cell kill through apoptosis. The focus of the present preclinical study is on mPDT treatment of malignant brain tumors, in which selectivity tumor cell killing versus damage to normal brain is critical. Previous studies have shown that low-dose PDT using 5-aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) can induce apoptosis in tumor cells without causing necrosis in either tumor or normal brain tissue or apoptosis in the latter. On the basis of the levels of apoptosis achieved and model calculations of brain tumor growth rates, metronomic delivery or multiple PDT treatments, such as hyperfractionation, are likely required to produce enough tumor cell kill to be an effective therapy. In vitro studies confirm that ALA-mPDT induces a higher incidence of apoptotic (terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate, sodium salt nick-end labeling positive) cells as compared with an acute, high-dose regimen (ALA-aPDT). In vivo, mPDT poses two substantial technical challenges: extended delivery of ALA and implantation of devices for extended light delivery while allowing unencumbered movement. In rat models, ALA administration via the drinking water has been accomplished at very high doses (up to 10 times therapeutic dose) for up to 10 days, and ex vivo spectrofluorimetry of tumor (9L gliosarcoma) and normal brain demonstrates a 3-4 fold increase in the tumor-to-brain ratio of PpIX concentration, without evidence of toxicity. After mPDT treatment, histological staining reveals extensive apoptosis within the tumor periphery and surrounding microinvading colonies that is not evident in normal brain or tumor before treatment. Prototype light sources and delivery devices were found to be practical, either using a laser diode or light-emitting diode (LED) coupled to an implanted optical fiber in the rat model or a directly implanted LED using a rabbit model. The combined delivery of both drug and light during an extended period, without compromising survival of the animals, is demonstrated. Preliminary evidence of selective apoptosis of tumor under these conditions is presented.

Apoptosis↗

PubMedDate not supplied

Assessment of cutaneous photosensitivity of TOOKAD (WST09) in preclinical animal models and in patients.

TOOKAD (WST09) is a new, long-wavelength palladium bacteriopheophorbide photosensitizer that targets tissue vasculature. The cutaneous phototoxicity of TOOKAD was assessed in normal rat and pig animal models and in patients in a Phase-I trial of TOOKAD-mediated photodynamic therapy (PDT) for recurrent prostate cancer. Controlled skin exposures were administered using solar-simulated light at various times after drug administration. Two different spectral ranges were used. In the first, the UV portion of the spectrum was removed (UV(-)) because UV irradiation in nondrugged control animals produced an erythema response at incident energy densities (J/cm(2)) lower than those required to induce a PDT response. In the second, the full solar spectrum (UV(+)) was used, and the potentiation by the photosensitizer of the UV-mediated minimum erythema dose was assessed. Results showed that the PDT skin response was negligible at clinical drug doses of 2 mg/kg for any period after administration at light doses of 128 J/cm(2) in the animal models. In patients, there was no observed UV(-) skin response at doses of up to 2 mg/kg, drug-light intervals of 1-3 h or greater and light exposures up to 128 J/cm(2). At higher drug doses in the rat and pig models, the duration of skin phototoxicity was found to be approximately 3 h and less than 1 h, respectively. Using the full spectrum of solar-simulated light, the presence of TOOKAD did not measurably enhance the UV(+)-induced erythema in the rats, pigs or patients.

Animals↗

PubMedDate not supplied

Imaging of photodynamically generated singlet oxygen luminescence in vivo.

We describe a novel scanning-laser system for imaging type-II photodynamically generated singlet oxygen (1O2[1delta(g)]) luminescence and demonstrate it in vivo in an intradermal tumor model in mice. We verify the strong oxygen-dependence of the signal and show that the images are near the practical resolution limit.

Light↗

PubMedDate not supplied

Simultaneous two-photon excitation of photofrin in relation to photodynamic therapy.

Photodynamic therapy (PDT), the use of light-activated drugs (photosensitizers), is an emerging treatment modality for tumors as well as various nononcologic conditions. Single-photon (1-gamma) PDT is limited by low specificity of the photosensitizer, leading to damage to healthy tissue adjacent to the diseased target tissue. One solution is to use simultaneous two-photon (2-gamma) excitation with ultrafast pulses of near-IR light. Due to the nonlinear interaction mechanism, 2-gamma excitation with a focused beam is localized in three dimensions, allowing treatment volumes on the order of femtoliters. We propose that this will be valuable in PDT of age-related macular degeneration (AMD), which causes blindness due to abnormal choroidal neovasculature and which is currently treated by 1-gamma PDT. Here, Photofrin has been used as the photosensitizer to demonstrate proof-of-principle of 2-gamma killing of vascular endothelial cells in vitro. The 2-gamma absorption properties of Photofrin were investigated in the 750-900 nm excitation wavelength range. It was shown that 2-gamma excitation dominates over 1-gamma excitation above 800 nm. The 2-gamma absorption spectrum of Photofrin in the 800-900 nm excitation wavelength range was measured. The 2-gamma cross section decreased from about 10 GM (1 GM = 10(-50) cm4 s/photon) at 800 nm to 5 GM at 900 nm. Adherent YPEN-1 endothelial cells were then incubated with Photofrin for 24 h and then treated by PDT at 850 nm where the 1-gamma contribution was negligible. Cell death was monitored with the use of 2-gamma scanning laser microscopy. The light doses required for killing were high (6300 J cm(-2) for approximately 50% killing), but 2-gamma cytotoxicity was unequivocally demonstrated. Although Photofrin is, per se, not a good choice for 2-gamma PDT due to its low 2-gamma cross section, this work provides baseline data to guide the development of novel photosensitizers with much higher 2-gamma cross sections (>100 GM), which will be required for 2-gamma PDT of AMD (and other conditions) to be clinically practical.

Aging↗

PubMedDate not supplied

Singlet oxygen luminescence dosimetry (SOLD) for photodynamic therapy: current status, challenges and future prospects.

As photodynamic therapy (PDT) continues to develop and find new clinical indications, robust individualized dosimetry is warranted to achieve effective treatments. We posit that the most direct PDT dosimetry is achieved by monitoring singlet oxygen (1O2), the major cytotoxic species generated photochemically during PDT. Its detection and quantification during PDT have been long-term goals for PDT dosimetry and the development of techniques for this, based on detection of its near-infrared luminescence emission (1270 nm), is at a noteworthy stage of development. We begin by discussing the theory behind singlet-oxygen luminescence dosimetry (SOLD) and the seminal contributions that have brought SOLD to its current status. Subsequently, technology developments that could potentially improve SOLD are discussed, together with future areas of research, as well as the potential limitations of this method. We conclude by examining the major thrusts for future SOLD applications: as a tool for quantitative photobiological studies, a point of reference to evaluate other PDT dosimetry techniques, the optimal means to evaluate new photosensitizers and delivery methods and, potentially, a direct and robust clinical dosimetry system.

Animals↗