An indwelling brachytherapy balloon catheter: potential use as an intracranial light applicator for photodynamic therapy

Photodynamic therapy mediated immune therapy of brain tumors

Photodynamic therapy of tumors requires the topical, systemic or oral administration of a photosensitizing compound, illumination of the tumor area by light of a specific wavelength and the presence of oxygen. Light activation of the photosensitizer transfers energy to molecular oxygen creating singlet oxygen, a highly reactive and toxic species that rapidly reacts with cellular components causing oxidative damage, ultimately leading to cell death. Tumor destruction caused by photodynamic therapy is not only a result of direct tumor cell toxicity via the generation of reactive oxygen species but there is also an immunological and vascular component involved. The immune response to photodynamic therapy has been demonstrated to significantly enhance its efficacy. Depending on a number of factors, including type of photosensitizer, light dose and dose rate, photodynamic therapy has been shown to induce cell death via apoptosis, necrosis, autophagy and in particular immunogenic cell death. It is the purpose of this review to focus mainly on the role photodynamic therapy could play in the generation of specific anti-tumor immunity and vaccines for the treatment of brain tumors.

The physics, biophysics and technology of photodynamic therapy

Photodynamic therapy (PDT) uses light-activated drugs to treat diseases ranging from cancer to age-related macular degeneration and antibiotic-resistant infections. This paper reviews the current status of PDT with an emphasis on the contributions of physics, biophysics and technology, and the challenges remaining in the optimization and adoption of this treatment modality. A theme of the review is the complexity of PDT dosimetry due to the dynamic nature of the three essential components -- light, photosensitizer and oxygen. Considerable progress has been made in understanding the problem and in developing instruments to measure all three, so that optimization of individual PDT treatments is becoming a feasible target. The final section of the review introduces some new frontiers of research including low dose rate (metronomic) PDT, two-photon PDT, activatable PDT molecular beacons and nanoparticle-based PDT.

Repetitive 5-aminolevulinic acid-mediated photodynamic therapy on human glioma spheroids

The response of human glioma spheroids to repetitive 5-aminolevulinic acid-mediated photodynamic therapy (PDT) was investigated. In all cases, light fluences were kept below toxic thresholds to simulate conditions typically found at 1-2 cm depths in brain adjacent to tumor. Significant inhibition of spheroid growth was observed following multiple PDT treatments at sub-threshold light fluences. The effect appears to be insensitive to the treatment intervals investigated (weekly or bi-monthly). In all cases, suppression of growth was observed for the duration of treatment. Low fluence rates (< or = 5 mW cm(-2)) appear to be more effective than high fluence rates (25 mW cm(-2)). No evidence of PDT resistance was found in this investigation.

Development of a novel indwelling balloon applicator for optimizing light delivery in photodynamic therapy

BACKGROUND AND OBJECTIVE

A human glioma spheroid model is used to investigate the efficacy of different light delivery schemes in 5-aminolevulinic acid (ALA)--mediated photodynamic therapy (PDT). The results provide the rationale for the development of an indwelling balloon applicator for optimizing light delivery.

STUDY DESIGN/MATERIALS AND METHODS

Human glioma spheroids were incubated in ALA (100 or 1000 microg /ml-1) for 4 hours and subjected to various light irradiation schemes. In one set of experiments, spheroid survival was monitored as a function of light fluence rate (5-200 mW cm-2). In all cases, spheroids were exposed to fluences of either 25 or 50 J cm-2. In a second study, the effects of repeated weekly PDT treatments, using sub-threshold fluences, were investigated. One group of spheroids was subjected to three treatments using fluences of 12, 12, and 25 J cm-2. Results were compared to spheroids receiving single treatments of either 12 or 25 J cm-2. A fluence rate of 25 mW cm-2 was used for all three groups of spheroids. In all cases, the effect of a given irradiation scheme was evaluated by monitoring spheroid growth.

RESULTS

Low fluence rates produce greater cell kill than high fluence rates. The minimum effective fluence rate in human glioma spheroids is approximately 10 mW cm-2. Repeated weekly PDT treatments with sub-threshold fluences result in significant cell kill. In spheroids surviving the PDT treatments, growth is suppressed for the duration of the treatment period.

CONCLUSION

The results of the in vitro studies support the development of an indwelling balloon applicator for the delivery of light doses in long term multi-fractionated PDT regimens.

The Brain Tumor Cooperative Group NIH Trial 87-01: A Randomized Comparison of Surgery, External Radiotherapy, and Carmustine versus Surgery, Interstitial Radiotherapy Boost, External Radiation Therapy, and Carmustine

OBJECTIVE

The objective of the Brain Tumor Cooperative Group NIH Trial 87-01 trial was to investigate the effect of additional implanted radiation therapy in newly diagnosed patients with pathologically confirmed malignant gliomas.

METHODS

The study involved a randomized comparison of surgery, external beam radiotherapy, and carmustine (BCNU) versus surgery, external beam therapy, interstitial radiotherapy boost, and BCNU in newly diagnosed malignant gliomas. 125I was chosen as best suited for this effort because it allowed preimplantation planning and postimplantation quality assurance review. Two hundred ninety-nine patients met the eligibility criteria and were randomized into the two arms of the study between December 1987 and April 1994. Follow-up continued for an additional 3 years. Twenty-nine patients were identified as having committed protocol violations and were excluded, resulting in 270 subjects in the Valid Study Group. One hundred thirty-seven patients received external beam radiation and BCNU, and 133 underwent the 125I implantation plus external beam radiation and BCNU therapy.

RESULTS

The overall median survival for the Valid Study Group was 64.3 weeks. The median survival for patients receiving additional therapy of 125I was 68.1 weeks, and median survival for those receiving only external beam radiation and BCNU was 58.8 weeks. The cumulative proportion surviving between the two treatment groups was not statistically significantly different (log-rank test, P = 0.101). As in other studies in the literature, age, Karnofsky score, and pathology were predictors of mortality. Additional analyses incorporating an adjustment for these prognostic variables, either in a stratified analysis or Cox proportional hazards model, did not result in statistically significant differences in the cumulative proportion of patients surviving between the two treatment groups.

CONCLUSION

We conclude that there is no long-term survival advantage of increased radiation dose with 125I seeds in newly diagnosed glioma patients.

ALA- and ALA-ester-mediated photodynamic therapy of human glioma spheroids

The effects of photodynamic therapy (PDT) in human glioma spheroids incubated in 5-aminolevulinic acid (ALA), or ALA esters, are investigated. Spheroid survival and growth are monitored following PDT at representative drug concentrations, light doses, and dose rates. The primary finding of this study is that the response of human glioma spheroids to PDT with lipophilic ester derivatives, such as benzyl-ALA and hexyl-ALA, is equivalent to that observed with ALA, however, this equivalency is obtained for ester concentrations 10-20 times lower than the parent compound. The enhanced efficiency of the esters is likely due to their increased membrane penetrance. Potential clinical advantages of using lipophilic esters in PDT of gliomas are discussed.

Photodynamic therapy of human glioma spheroids using 5-aminolevulinic acid

The response of human glioma spheroids to 5-aminolevulinic acid (ALA)-mediated photodynamic therapy (PDT) is investigated. A two-photon fluorescence microscopy technique is used to show that human glioma cells readily convert ALA to protoporphyrin IX throughout the entire spheroid volume. The central finding of this study is that the response of human glioma spheroids to ALA-mediated PDT depends not only on the total fluence, but also on the rate at which the fluence is delivered. At low fluences (< or = 50 J cm-2), lower fluence rates are more effective. At a fluence of 50 J cm-2, near-total spheroid kill is observed at fluence rates of as low as 10 mW cm-2. The fluence rate effect is not as pronounced at higher fluences (> 50 J cm-2), where a favorable response is observed throughout the range of fluence rates investigated. The clinical implications of these findings are discussed.