Photodynamic therapy in neurosurgery: a review

Systematic Review of Photodynamic Therapy in Gliomas

Over the last 20 years, gliomas have made up over 89% of malignant CNS tumor cases in the American population (NIH SEER). Within this, glioblastoma is the most common subtype, comprising 57% of all glioma cases. Being highly aggressive, this deadly disease is known for its high genetic and phenotypic heterogeneity, rendering a complicated disease course. The current standard of care consists of maximally safe tumor resection concurrent with chemoradiotherapy. However, despite advances in technology and therapeutic modalities, rates of disease recurrence are still high and survivability remains low. Given the delicate nature of the tumor location, remaining margins following resection often initiate disease recurrence. Photodynamic therapy (PDT) is a therapeutic modality that, following the administration of a non-toxic photosensitizer, induces tumor-specific anti-cancer effects after localized, wavelength-specific illumination. Its effect against malignant glioma has been studied extensively over the last 30 years, in pre-clinical and clinical trials. Here, we provide a comprehensive review of the three generations of photosensitizers alongside their mechanisms of action, limitations, and future directions.

Metronomic Photodynamic Therapy with Conjugated Polymer Nanoparticles in Glioblastoma Tumor Microenvironment

Alternative therapies such as photodynamic therapy (PDT) that combine light, oxygen and photosensitizers (PSs) have been proposed for glioblastoma (GBM) management to overcome conventional treatment issues. An important disadvantage of PDT using a high light irradiance (fluence rate) (cPDT) is the abrupt oxygen consumption that leads to resistance to the treatment. PDT metronomic regimens (mPDT) involving administering light at a low irradiation intensity over a relatively long period of time could be an alternative to circumvent the limitations of conventional PDT protocols. The main objective of the present work was to compare the effectiveness of PDT with an advanced PS based on conjugated polymer nanoparticles (CPN) developed by our group in two irradiation modalities: cPDT and mPDT. The in vitro evaluation was carried out based on cell viability, the impact on the macrophage population of the tumor microenvironment in co-culture conditions and the modulation of HIF-1α as an indirect indicator of oxygen consumption. mPDT regimens with CPNs resulted in more effective cell death, a lower activation of molecular pathways of therapeutic resistance and macrophage polarization towards an antitumoral phenotype. Additionally, mPDT was tested in a GBM heterotopic mouse model, confirming its good performance with promising tumor growth inhibition and apoptotic cell death induction.

Nanoscintillator-Based X-Ray-Induced Photodynamic Therapy

Photodynamic therapy (PDT) is an emerging treatment option for cancer. In PDT, photosensitizers are delivered to tumors and stimulated by light to generate reactive oxygen species (ROS)-most importantly singlet oxygen (¹O₂)-to damage tumor cells or induce tissue ischemia. PDT is associated with a low level of systemic toxicity because photosensitizers are usually pharmaceutically inactive in the dark and photoirradiation is applied only to tumor areas in the procedure. Additionally, PDT can be applied repeatedly without cumulative toxicity or incurring resistance, and may stimulate systemic anti-tumor immunity. However, PDT's clinical use has been restricted due to the limited penetration of visible light through tissues. X-rays possess superior tissue penetration capability and are exploited in X-ray-induced photodynamic therapy to overcome this limitation. Herein we have demonstrated this principle with a novel LiGa₅O₈:Cr (LGO:Cr)-based nanoscintillator which emits near-infrared X-ray luminescence to both guide external beam therapy and induce PDT with the photosensitizer (2,3-naphthalocyanine) encapsulated in a mesoporous silica shell of the nanoscintillator.

A systematic review and meta-analysis of fluorescent-guided resection and therapy-based photodynamics on the survival of patients with glioma

Glioma is the most common primary central nervous system tumor; many methods are currently being used to research and treat glioma. In recent years, fluorescent-guided resection (FGR) and photodynamic therapy (PDT) have become hot spots in the treatment of glioma. Based on the existing literatures regarding the FGR enhancing resection rate and regarding efficacy of PDT for the treatment of glioma, this paper made a systematic review of FGR for gross total resection of patients and the PDT for the survival of patients with glioma. Meta-analysis of eligible studies was performed to derive precise estimation of PDT on the prognosis of patients with glioma by searching all related literatures in PubMed, EMBASE, Cochrane, and Web of Science databases, and further to evaluate (GTR) under FGR and the efficacy of PDT therapy, including 1-year and 2-year survival rates, overall survival (OS), and progression-free survival (PFS). According to the inclusion and exclusion criteria, a total of 1294 patients with glioma were included in the final analysis of 31 articles, among which a 73.00% (95% CI, 68.00 ~ 79.00%, P < 0.01) rate of GTR in 27 groups included in 23 articles was reported for those receiving FGR. The OS was 17.78 months (95% CI, 8.89 ~ 26.67, P < 0.01) in 5 articles on PDT-treated patients with glioma, and the mean difference of OS was 6.18 (95% CI, 3.3 ~ 9.06, P < 0.01) between PDT treatment and conventional glioma surgery, showing a statistically significant difference (P < 0.01). The PFS was 10.82 months (95% CI, 7.04 ~ 14.61, P < 0.01) in 5 articles on PDT-treated patients with glioma. A 1-year survival rate of 59.00% (95% CI, 38.00 ~ 77.00%, P < 0.01) in 10 groups included in 8 articles and 2-year survival rate of 25.00% (95% CI, 15.00 ~ 36.00%, P < 0.01) in 7 groups included in 6 articles were reported for those with PDT. FGR and PDT are feasible for treatment of patients with glioma, because FGR can effectively increase the resection rate, at the same time, PDT can prolong the survival time. However, due to the limitation of small sample size in the existing studies, larger samples and randomized controlled clinical trials are needed to analyze the resection under FGR and efficacy of PDT in patients with glioma.

Photodynamic Priming Modulates Endothelial Cell-Cell Junction Phenotype for Light-activated Remote Control of Drug Delivery

The blood-brain barrier (BBB) remains a major obstacle for drug delivery to the central nervous system. In particular, the tight and adherens junctions that join the brain capillary endothelial cells limit the diffusion of various molecules from the bloodstream into the brain. Photodynamic priming (PDP) is a non-cytotoxic modality that involves light activation of photosensitizers to photochemically modulate nearby molecules without killing the cells. Here we investigate the effects of sub-lethal photochemistry on junction phenotype (i.e., continuous, punctate, or perpendicular), as well as the BBB permeability in a transwell model of human brain microvascular endothelial cells (HBMECs). We showed that PDP decreases the continuous junction architecture by ~20%, increases the perpendicular junction architecture by ~40%, and has minimal impact on cell morphology in HBMECs. Furthermore, transwell permeability assay revealed that PDP improves the HBMEC permeability to dextran or nanoliposomes by up to 30-fold for 6-9 days. These results suggest that PDP could safely reverse the mature brain endothelial junctions without killing the HBMECs. This study not only emphasizes the critical roles of PDP in the modulation junction phenotype, but also highlights the opportunity to further develop PDP-based combinations that opens the cerebrum endothelium for enhanced drug transporter across the BBB.

Predictors and Limitations of the Penetration Depth of Photodynamic Effects in the Rodent Brain

Fluorescence-guided surgery (FGS) is routinely utilized in clinical centers around the world, whereas the combination of FGS and photodynamic therapy (PDT) has yet to reach clinical implementation and remains an active area of translational investigations. Two significant challenges to the clinical translation of PDT for brain cancer are as follows: (1) Limited light penetration depth in brain tissues and (2) Poor selectivity and delivery of the appropriate photosensitizers. To address these shortcomings, we developed nanoliposomal protoporphyrin IX (Nal-PpIX) and nanoliposomal benzoporphyrin derivative (Nal-BPD) and then evaluated their photodynamic effects as a function of depth in tissue and light fluence using rat brains. Although red light penetration depth (defined as the depth at which the incident optical energy drops to 1/e, ~37%) is typically a few millimeters in tissues, we demonstrated that the remaining optical energy could induce PDT effects up to 2 cm within brain tissues. Photobleaching and singlet oxygen yield studies between Nal-BPD and Nal-PpIX suggest that deep-tissue PDT (>1 cm) is more effective when using Nal-BPD. These findings indicate that Nal-BPD-PDT is more likely to generate cytotoxic effects deep within the brain and allow for the treatment of brain invading tumor cells centimeters away from the main, resectable tumor mass.

Intracavitary radioimmunotherapy of high-grade gliomas: present status and future developments

There is a distinct need for new and second-line therapies to delay or prevent local tumor regrowth after current standard of care therapy. Intracavitary radioimmunotherapy, in combination with radiotherapy, is discussed in the present review as a therapeutic strategy of high potential. We performed a systematic literature search following the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA). The available body of literature on intracavitary radioimmunotherapy (iRIT) in glioblastoma and anaplastic astrocytomas is presented. Several past and current phase I and II clinical trials, using mostly an anti-tenascin monoclonal antibody labeled with I-131, have shown median overall survival of 19-25 months in glioblastoma, while adverse events remain low. Tenascin, followed by EGFR and variants, or smaller peptides have been used as targets, and most clinical studies were performed with I-131 or Y-90 as radionuclides while only recently Re-188, I-125, and Bi-213 were applied. The pharmacokinetics of iRIT, as well as the challenges encountered with this therapy, is comprehensively discussed. This promising approach deserves further exploration in future studies by incorporating several innovative modifications.

Nanoparticles to mediate X-ray-induced photodynamic therapy and Cherenkov radiation photodynamic therapy

Photodynamic therapy (PDT) has emerged as an attractive option for cancer treatment. However, conventional PDT is activated by light that has poor tissue penetration depths, limiting its applicability in the clinic. Recently the idea of using X-ray sources to activate PDT and overcome the shallow penetration issue has garnered significant interest. This can be achieved by external beam irradiation and using a nanoparticle scintillator as transducer. Alternatively, research on exploiting Cherenkov radiation from radioisotopes to activate PDT has also begun to flourish. In either approach, the most auspicious success is achieved using nanoparticles as either a scintillator or a photosensitizer to mediate energy transfer and radical production. Both X-ray induced PDT (X-PDT) and Cherenkov radiation PDT (CR-PDT) contain a significant radiation therapy (RT) component and are essentially PDT and RT combination. Unlike the conventional combination, however, in X-PDT and CR-PDT, one energy source simultaneously activates both processes, making the combination always in synchronism and the synergy potential maximized. While still in early stage of development, X-PDT and CR-PDT address important issues in the clinic and hold great potential in translation. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Assessment of safety of 5-aminolevulinic acid-mediated photodynamic therapy in rat brain

BACKGROUND

Oral 5-aminolevulinic acid (ALA) induces biosynthesis/accumulation of the natural photo-sensitizer protoporphyrin IX (PpIX) in cancer cells. ALA is used widely in photodynamic diagnosis (PDD) and therapy (PDT) during malignant glioma surgery, but few studies have examined the effects of photodynamics plus ALA on normal brain tissue in vivo. We investigated the effects of ALA-mediated PDD and PDT on normal brain tissue.

METHODS

We established a rat model in which the brain surface was irradiated through the skull by light-emitting diode (635 nm) after ALA administration. Using this model, we investigated the effects of various amounts of light irradiation with various ALA doses on brain tissue.

RESULTS

Neurological symptoms developed with administration of ALA at 240 or 120 mg/kg accompanied by irradiation at 100 or 400 J/cm², respectively. Dye leakage occurred due to disruption of the blood-brain barrier (BBB) at 90 mg/kg and 100 J/cm², respectively. Thickness of the cortex increased significantly at 240 mg/kg and 400 J/cm², respectively. The number of neurons appeared to decrease at 200 mg/kg plus 400 J/cm², respectively, and there was an increase in the number of cells that were positive for terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling (TUNEL) staining.

CONCLUSIONS

ALA-mediated PDT is safe at doses of 90 mg/kg or less followed by light irradiation of 100 J/cm² in rat brains. At doses above this threshold, ALA-PDT led to irreversible BBB and brain damage in rats.

Efficient cell death induction in human glioblastoma cells by photodynamic treatment with Tetrahydroporphyrin-Tetratosylat (THPTS) and ionizing irradiation

Background

So far, glioblastomas cannot be cured by standard therapy and have an extremely poor median survival of about 15 months. The photodynamic therapy (PDT) with next generation photosensitizers, reaching a higher therapeutic depth, might offer a new, adjuvant treatment strategy in brain cancer therapy. Here, we investigated the effect of THPTS-PDT combined with ionizing irradiation (IR) on glioblastoma cells in vitro and in vivo.

Results

THPTS colocalized to mitochondria and was not found in the nucleus. THPTS (2–20 μg/ml)-PDT significantly reduced the proliferation, metabolic activity and clonogenic survival and induced cell death mainly through apoptosis and autophagy. THPTS-PDT combined with IR decreased the clonogenicity significantly compared to single treatments. THPTS (≤ 300 μg/ml) alone showed no dark toxicity. The maximum therapeutic depth of THPTS-PDT in C6 glioblastomas was 13 mm.

Materials and Methods

Three human glioblastoma cell lines (U-87 MG, A-172, DBTRG-05MG) were incubated with THPTS (1–300 μg/ml) 3–24 hours before laser treatment (760 nm, 30 J/cm²). THPTS localization and effects on metabolic activity, proliferation, cell death mechanisms and long-term reproductive survival were assessed. IR was conducted on an X-ray unit (0.813 Gy/min). Results were verified in vivo on a subcutaneous C6 glioblastoma model in Wistar rats.

Conclusions

This study demonstrated efficient THPTS-PDT in glioblastoma cells, in vitro and in vivo. The combinatorial effects of THPTS-PDT and IR are of specific clinical interest as enhanced eradication of infiltrating glioblastoma cells in the tumor surrounding tissue might possibly reduce the commonly occurring local relapses.

PLGA nanoparticle encapsulation reduces toxicity while retaining the therapeutic efficacy of EtNBS-PDT in vitro

Photodynamic therapy regimens, which use light-activated molecules known as photosensitizers, are highly selective against many malignancies and can bypass certain challenging therapeutic resistance mechanisms. Photosensitizers such as the small cationic molecule EtNBS (5-ethylamino-9-diethyl-aminobenzo[a]phenothiazinium chloride) have proven potent against cancer cells that reside within acidic and hypoxic tumour microenvironments. At higher doses, however, these photosensitizers induce "dark toxicity" through light-independent mechanisms. In this study, we evaluated the use of nanoparticle encapsulation to overcome this limitation. Interestingly, encapsulation of the compound within poly(lactic-co-glycolic acid) (PLGA) nanoparticles (PLGA-EtNBS) was found to significantly reduce EtNBS dark toxicity while completely retaining the molecule's cytotoxicity in both normoxic and hypoxic conditions. This dual effect can be attributed to the mechanism of release: EtNBS remains encapsulated until external light irradiation, which stimulates an oxygen-independent, radical-mediated process that degrades the PLGA nanoparticles and releases the molecule. As these PLGA-encapsulated EtNBS nanoparticles are capable of penetrating deeply into the hypoxic and acidic cores of 3D spheroid cultures, they may enable the safe and efficacious treatment of otherwise unresponsive tumour regions.

Tetrakis(p-Carboranylthio-Tetrafluorophenyl)Chlorin (TPFC): Application for Photodynamic Therapy and Boron Neutron Capture Therapy

Carboranyl-containing chlorins have emerged as promising dual sensitizers for use in both photodynamic therapy (PDT) and boron neutron capture therapy (BNCT), by virtue of their known tumor affinity, low cytotoxicity in dark conditions, and their strong absorptions in the red region of the optical spectrum. Tetrakis(p-carboranylthio-tetrafluorophenyl)chlorin (TPFC) is a new synthetic carboranyl-containing chlorin of high boron content (24% by weight). To evaluate TPFC's applicability as sensitizer for both PDT and BNCT, we performed an in vitro and in vivo study using F98 rat glioma cells and F98 rat glioma-bearing brain tumor models. For the in vivo BNCT study, we used boronophenylalanine (BPA), which is currently used in clinical BNCT studies, via intravenous administration (i.v.) and/or used TPFC via convection-enhanced delivery (CED), a method for local drug infusion directly into the brain. In the in vitro PDT study, the cell surviving fraction following laser irradiation (9J/cm²) was 0.035 whereas in the in vitro BNCT study, the cell surviving fraction following neutron irradiation (thermal neutron=1.73×10¹² n/cm²) was 0.04. In the in vivo BNCT study, the median survival time following concomitant administration of BPA (i.v.) and TPFC (CED) was 42days (95% confidence interval; 37-43days). © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association.

Concomitant treatment with temozolomide enhances apoptotic cell death in glioma cells induced by photodynamic therapy with talaporfin sodium

BACKGROUND

Photodynamic therapy (PDT) induces selective cell death of neoplastic tissue and connecting vasculature by combining photosensitizers with light. We have previously reported that PDT induces apoptotic cell death in glioma cells when the photosensitizer talaporfin sodium (NPe6) is used. Here, we investigated the combined effect of NPe6-PDT with temozolomide, a DNA-alkylating drug used in glioma therapy.

METHODS

Human glioblastoma T98G cells and human glioma U251 cells were used as glioma cells. Cell viability was evaluated by WST-8 assay. Apoptosis was evaluated by measurement of caspase-3 activity and DNA-fragmentation. Intracellular reactive oxygen species were evaluated by dihydrorhodamine assay.

RESULTS

While the degree of NPe6-PDT induced cell death unchanged in T98G and U251 cells when temozolomide treatment was adjuvant, it was dose-dependently increased by concomitant treatment with temozolomide. Further, concomitantly administered temozolomide dose-dependently increased caspase-3 activity and DNA-fragmentation, while adjuvant-temozolomide did not. These results are suggesting that concomitantly administered temozolomide potentiates the effect of NPe6-PDT to facilitate apoptotic cell death. Additionally, concomitantly administered temozolomide increased intracellular NPe6-fluorescence and reactive oxygen species, suggesting that the augmentation effect of combined treatment may be due to increased intracellular accumulation of NPe6.

CONCLUSION

These results suggest that concomitant treatment with NPe6-PDT and temozolomide is a potentially useful therapy for glioma.

Photosensitizers in clinical PDT

Photosensitizers in photodynamic therapy allow for the transfer and translation of light energy into a type II chemical reaction. In clinical practice, photosensitizers arise from three families-porphyrins, chlorophylls, and dyes. All clinically successful photosensitizers have the ability to a greater or lesser degree, to target specific tissues or their vasculature to achieve ablation. Each photosensitizer needs to reliably activate at a high enough light wavelength useful for therapy. Their ability to fluoresce and visualize the lesion is a bonus. Photosensitizers developed from each family have unique properties that have so far been minimally clinically exploited. This review looks at the potential benefits and consequences of each major photosensitizer that has been tried in a clinical setting.

Tetra-sulfonate phthalocyanine zinc-bovine serum albumin conjugate-mediated photodynamic therapy of human glioma

Background

Glioma is the most common brain malignancy with poor prognosis. The current treatments for gliomas are mainly based on surgery, chemotherapy, and radiotherapy, which exhibit limited efficacy. Photodynamic therapy (PDT) using photosensitizers has been applied to glioma therapy. However, different photosensitizers usually lead to different therapeutic effects and adverse reactions.

Objective

This study investigates the anti-tumor effect of photosensitizer ZnPcS4-BSA in xenograft glioma tumors.

Methods

The xenograft glioma tumor model was established by inoculating nude mice with U251 cells. Tumor growth was evaluated by tumor volume, weight, and inhibition rate. Cell apoptosis was evaluated using TUNEL staining. Vascular endothelial growth factor (VEGF) expression and microvessel density were measured by immunohistochemistry.

Results

Significant decreases in tumor volume and weight as well as significant increases in tumor inhibition rate, cell apoptosis, VEGF expression, and microvessel density were observed in mice in the low- and high-dose PDT groups compared to the control, irradiation alone, and photosensitizer alone groups. No significant difference in cytotoxicity was observed between control group and photosensitizer alone group. Photosensitizer ZnPcS4-BSA significantly inhibited xenograft glioma tumor growth through induction of apoptosis.

Conclusion

PDT using ZnPcS4-BSA may be effective for the therapy of gliomas.

Experimental study of combined therapy for malignant glioma

The efficiency of photodynamic therapy with photosensitizer Tiosens (Russia) was evaluated in mono- and combined therapy of rats with malignant gliomas (glioblastoma 101/8, oligodendroglioma 14-4-9, and C6 glioma). The efficiency of photodynamic monotherapy was not high: the animals died from brain edema developing in tumor tissue and in the adjacent normal cerebral tissue. Pathomorphological studies of tumor tissue detected necrosis and apoptosis, destruction of vessels with hemorrhages, and vascular thrombosis. Combined therapy for malignant gliomas including Tiosens photodynamic therapy and subsequent temodal or lysomustine chemotherapy, was the most effective. In glioblastoma 101/8, combined therapy with lysomustine or temodal led to prolongation of the lifespan by 127 %; 62.5 and 50 % rats were cured, respectively; in oligodendroglioma 14-4-9, animal lifespan was prolonged by 80 and 60 %, with 43 and 45 % rats cured, respectively. Glioma C6 was least sensitive to therapy.

Protoporphyrin IX fluorescence and photobleaching during interstitial photodynamic therapy of malignant gliomas for early treatment prognosis

BACKGROUND AND OBJECTIVE

Interstitial photodynamic therapy (iPDT) of non-resectable recurrent glioblastoma using 5-aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) has shown a promising outcome. It remained unclear, however, to what extent inter- and intra-tumoural differences of PpIX concentrations influence the efficacy of iPDT. In the current pilot study, we analysed PpIX concentrations quantitatively and assessed PpIX induced fluorescence and photobleaching intraoperatively.

MATERIALS AND METHODS

Five patients harbouring non-resectable glioblastomas were included. ALA (20 or 30 mg/kg body weight) was given 5-8 hours before treatment. Stereotactic biopsies were taken throughout the tumour volume for both histological analysis and determination of PpIX concentrations, which were measured by chemical extraction. Cylindrical light diffusors were stereotactically implanted. Prior to and after irradiation, fluorescence measurements were performed. Outcome measurement was based on clinical and neuro-radiological follow up.

RESULTS

In three patients, a strong PpIX fluorescence was seen before treatment, which was completely photobleached after iPDT. High concentrations of PpIX could be detected in viable tumour parts of these patients (mean PpIX uptake per tumour: 1.4-3.0 µM). In the other two patients, however, no or only low PpIX uptake (0-0.6 µM) could be detected. The patients with strong PpIX uptake showed treatment response and long-term clinical stabilisation (no progression in 29, 30 and 36 months), early treatment failure was seen in the remaining two patients (death after 3 and 9 months).

CONCLUSIONS

Intra-tumoural PpIX concentrations exhibited pronounced inter- and intra-tumoural variations in glioblastoma, which are directly linked to variable degrees of fluorescence intensity. High intra-tumoural PpIX concentrations with strong fluorescence intensity and complete photobleaching after iPDT seem to be associated with favourable outcome. Real-time monitoring of PpIX fluorescence intensity and photobleaching turned out to be feasible and safe and might be employed for early treatment prognosis of iPDT.

Photodynamic therapy in combination with talaporfin sodium induces mitochondrial apoptotic cell death accompanied with necrosis in glioma cells

Photodynamic therapy (PDT) induces selective cell death of neoplastic tissue and connecting vasculature by combining photosensitizers with light. Here we clarified the types of cell death induced by PDT in combination with the photosensitizer talaporfin sodium (mono-L-aspartyl chlorine e6, NPe6) in order to evaluate the potential of this therapy as a treatment for glioma. PDT with NPe6 (NPe6-PDT) induces dose-dependent cell death in human glioblastoma T98G cells. Specifically, cell death modalities were observed in NPe6-PDT treated T98G cells, including signs of apoptosis (activation of caspase-3, expression of phosphatidylserine, and DNA fragmentation) and necrosis (stainability of propidium iodide). In addition, high doses of NPe6-PDT decreased the proportion of apoptotic cell death, while increasing necrosis. Closer examination of apoptotic characteristics revealed release of cytochrome-c from mitochondria as well as activation of both caspse-9 and caspase-3 in cells treated with low doses of NPe6-PDT. Benziloxycarbonyl-Leu-Gln(OMe)-His-Asp(OMe)-fluoromethyl-ketone (Z-LEHD-fmk), a caspase-9 specific inhibitor, and benziloxycarbonyl-Asp(OMe)-Gln-Met-Asp(OMe)-fluoromethyl-ketone (Z-DQMD-fmk), a caspase-3 specific inhibitor, showed dose-dependent prevention of cell death in NPe6-PDT treated cells, indicating that mitochondrial apoptotic pathway was a factor in the observed cell death. Further, the cell morphology was observed after PDT. Time- and NPe6-dose dependent necrotic features were increased in NPe6-PDT treated cells. These results suggest that NPe6-PDT could be an effective treatment for glioma if used in mild doses to avoid the increased necrosis that may induce undesirable obstacles.

Image-Based Quantification of Benzoporphyrin Derivative Uptake, Localization, and Photobleaching in 3D Tumor Models, for Optimization of PDT Parameters

Photodynamic therapy (PDT) is a light-based treatment modality in which wavelength specific activation of a photosensitizer (PS) generates cytotoxic response in the irradiated region. PDT response is critically dependent on several parameters including light dose, PS dose, uptake time, fluence rate, and the mode of light delivery. While the systematic optimization of these treatment parameters can be complex, it also provides multiple avenues for enhancement of PDT efficacy under diverse treatment conditions, provided that a rational framework is established to quantify the impact of parameter selection upon treatment response. Here we present a theranostic technique, combining the inherent ability of the PS to serve simultaneously as a therapeutic and imaging agent, with the use of image-based treatment assessment in three dimensional (3D) in vitro tumor models, to comprise a platform to evaluate the impact of PDT parameters on treatment outcomes. We use this approach to visualize and quantify the uptake, localization, and photobleaching of the PS benzoporphyrin derivative monoacid ring-A (BPD) in a range of treatment conditions with varying uptake times as well as continuous and fractionated light delivery regimens in 3D cultures of AsPC-1 and PANC-1 cells. Informed by photobleaching patterns and correlation with cytotoxic response, asymmetric fractionated light delivery at 4 hours BPD uptake was found to be the most effective regimen assessed. Quantification of the spatial profile of cell killing within multicellular nodules revealed that these conditions also achieve the highest depth of cytotoxicity along the radial axis of 3D nodules. The framework introduced here provides a means for systematic assessment of PDT treatment parameters in biologically relevant 3D tumor models with potential for broader application to other systems.

Application of a novel boronated porphyrin (H₂OCP) as a dual sensitizer for both PDT and BNCT

BACKGROUND AND OBJECTIVE

Boronated porphyrins have emerged as promising dual sensitizers for use in both photodynamic therapy (PDT) and boron neutron capture therapy (BNCT), by virtue of their known tumor affinity, low cytotoxicity in dark conditions, and easy synthesis with high boron content. Octa-anionic 5,10,15,20-tetra[3,5-(nido-carboranylmethyl)phenyl] porphyrin (H₂OCP) is a boronated porphyrin having eight boron clusters linked to the porphyrin ring. To evaluate H₂OCP's applicability to both PDT and BNCT, we performed an in vitro and ex vivo study using F98 rat glioma cells.

MATERIALS AND METHODS

We examined the time-dependent cellular uptake of H₂OCP by measuring the boron concentration over time, and compared the cellular uptake/clearance of boron after exposure to H₂OCP in conjunction with boronophenylalanine (BPA) and sodium borocaptate (BSH), both of which are currently used in clinical BNCT studies. We evaluated the cytotoxicity of H₂OCP-mediated PDT using a colony-forming assay and assessed the tumorigenicity of the implantation of pre-treated cells using Kaplan-Meier survival curves. Fluorescence microscopy was also performed to evaluate the cellular uptake of H₂OCP.

RESULTS

H₂OCP accumulated within cells to a greater extent than BPA/BSH, and H₂OCP was retained inside the cells to approximately the same extent as BSH. The cell-surviving fraction following laser irradiation (8 J/cm², 18 hours after exposure to 10 µg B/ml H₂OCP) was <0.05. The median survival times of the pre-treated cell-implanted rats were longer than those of the untreated group (P < 0.05). The fluorescence of H₂OCP was clearly demonstrated within the tumor cells by fluorescence microscopy.

CONCLUSIONS

H₂OCP has been proven to be a promising photosensitizer for PDT. H₂OCP has also been proposed as a potentially effective replacement of BPA or BSH, or as a replacement of both BPA/BSH. Our study provides more evidence that H₂OCP could be an effective novel dual sensitizing agent for use in both PDT and BNCT.

Silencing of ferrochelatase enhances 5-aminolevulinic acid-based fluorescence and photodynamic therapy efficacy

Background:

Recurrence of glioma frequently occurs within the marginal area of the surgical cavity due to invading residual cells. 5-Aminolevulinic acid (5-ALA) fluorescence-guided resection has been used as effective therapeutic modalities to improve discrimination of brain tumour margins and patient prognosis. However, the marginal areas of glioma usually show vague fluorescence, which makes tumour identification difficult, and the applicability of 5-ALA-based photodynamic therapy (PDT) is hampered by insufficient therapeutic efficacy in glioma tissues.

Methods:

To overcome these issues, we assessed the expression of ferrochelatase (FECH) gene, which encodes a key enzyme that catalyses the conversion of protoporphyrin IX (PpIX) to heme, in glioma surgical specimens and manipulated FECH in human glioma cell lines.

Results:

Prominent downregulation of FECH mRNA expression was found in glioblastoma tissues compared with normal brain tissues, suggesting that FECH is responsible for PpIX accumulation in glioblastoma cells. Depletion of FECH by small interference RNA enhanced PpIX fluorescence after exposure to 5-ALA concomitant with increased intracellular PpIX accumulation in glioma cells. Silencing of FECH caused marked growth inhibition and apoptosis induction by PDT in glioma cells.

Conclusion:

These results suggest that knockdown of FECH is a potential approach to enhance PpIX fluorescent quality for optimising the subjective discrimination of vague fluorescence and improving the effect of 5-ALA-PDT.

Therapeutic options for recurrent malignant glioma

BACKGROUND AND PURPOSE

Despite the given advances in neuro-oncology most patients with high grade malignant glioma ultimately fail locally or locoregionally. In parallel with improvements of initial treatment options, several salvage strategies have been elucidated and already entered clinical practice. Aim of this article is to review the current status of salvage strategies in recurrent high grade glioma.

MATERIAL AND METHODS

Using the following MESH headings and combinations of these terms the pubmed database was searched: "Glioma", "Recurrence", "Neoplasm Recurrence, Local", "Radiosurgery", "Brachytherapy", "Neurosurgical Procedures" and "Drug Therapy". For citation crosscheck the ISI web of science database was used employing the same search terms. In parallel, the abstracts of ASCO 2008-2009 were analyzed accordingly.

RESULTS

Currently the following options for salvage entered clinical practice: re-resection, re-irradiation (stereotactic radiosurgery, (hypo-)fractionated (stereotactic) radiotherapy, interstitial brachytherapy) or single/poly-chemotherapy schedules including new dose-intensified or alternative treatment protocols employing targeted drugs. Re-operation is associated with high morbidity and mortality, however, is an option in a highly selected patient cohort. Since toxicity has been overestimated, re-irradiation is an increasingly used option with precise fractionated radiotherapy being the most optimal technique. On average, time to secondary progression is in the range of several months. Conventional chemotherapy regimens also improve time to secondary progression; however the efficacy is only modest and treatment-related toxicities like myelo-suppression occur very frequently. Molecular targeted agents/kinases are undergoing clinical testing; however no final recommendations can be made.

CONCLUSIONS

Currently, several re-treatment options with only modest efficacy exist. The relative value of each approach compared to other options is unknown as well as it remains open which sequence of modalities should be chosen.

The role of porphyrin chemistry in tumor imaging and photodynamic therapy

In recent years several review articles and books have been published on the use of porphyrin-based compounds in photodynamic therapy (PDT). This critical review is focused on (i) the basic concept of PDT, (ii) advantages of long-wavelength absorbing photosensitizers (PS), (iii) a brief discussion on recent advances in developing PDT agents, and (iv) the various synthetic strategies designed at the Roswell Park Cancer Institute, Buffalo, for developing highly effective long-wavelength PDT agents and their utility in constructing the conjugates with tumor-imaging and therapeutic potential (Theranostics). The clinical status of certain selected PDT agents is also summarized (205 references).

Oncologic photodynamic therapy photosensitizers: a clinical review

A myriad of naturally occurring and synthetic structures are capable of transferring the energy of light. Few, however, allow for this energy transfer to enable a type II photochemical reaction which, as currently practiced, is a fundamental component of photodynamic therapy. Even fewer of these agents, aptly termed photosensitizers, have found success in the treatment of patients. This review will focus on the oncologic photosensitizers that have come to clinical trial with outcomes published in peer reviewed journals. Based on a clinical orientation the qualities of successful photosensitizers will be examined, how current drugs fare and potential future options explored.

Quantitative measurement of reactive oxygen species in vivo by utilizing a novel method: chemiluminescence with an internal fluorescence as reference

Reactive oxygen species (ROS) produced by photodynamic therapy (PDT) is recorded in vivo using a chemiluminescence (CL)-based gated optical system. A novel approach is developed to utilize the fluorescence (FL) of the CL probe as an internal fluorescence to calibrate the observed CL on pharmacokinetics of the probe in situ. The results show that during an in vivo PDT session, the intensity of CL decreases significantly and the decaying of CL is governed by fast and slow time components. By comparing the temporal profile of FL to that of the corresponding CL, it is found that the slow component is mainly attributed to the probe pharmacokinetics, whereas the fast component is likely due to rapid oxygen consumption as a result of PDT treatment. With carefully selected criteria, it is possible to minimize the effect of probe pharmacokinetics. This significantly improves the monitoring method for practical applications.

Photodynamic diagnosis and therapy and the brain

Photodynamic techniques such as photodynamic diagnosis (PDD), fluorescence-guided tumour resection (FGR) and photodynamic therapy (PDT) are currently undergoing intensive clinical investigations as adjuvant treatment for malignant brain tumours. The following chapter provides an overview on the current clinical data and trials of PDT as well as photosensitizers, technical developments and indications for photodynamic application in neurosurgery. Besides many clinical phase I/II trials for PDT for malignant brain tumours, there are only few controlled clinical trials following tumour resection. Variations in treatment protocols, variation of photosensitizers and light dose make the evaluation scientifically difficult; however there is a clear trend towards prolonging median survival after one single photodynamic treatment as compared to standard therapeutic regimens. According to the meta analysis the median survival after PDT for primary glioblastoma multiforme (WHO grade IV) was 22 months and for recurrent GBM was 9 months as compared to standard conventional treatment, in which it is 15 and 3 months, respectively. Fluorescence-guided resection of the tumour demonstrated significant greater reduction of tumour burden. The combination of PDD/ FGR and intraoperative PDT ("to see and to treat") offers an exciting approach to the treatment of malignant brain tumours. PDT was generally well tolerated and side effects consisted of occasionally increased intracranial pressure and prolonged skin sensitivity against direct sunlight.

Combination therapy with antiangiogenic treatment and photodynamic therapy for the nude mouse bearing U87 glioblastoma

The objective of this study was to evaluate the effects of combination therapy with photodynamic therapy (PDT) and a novel antiangiogenic regimen using monoclonal antibodies against both vascular endothelial growth factor receptors (VEGFR)-1 (MF1) and VEGFR-2 (DC101) on intracranial glioblastoma xenografts in nude mice. Nude mice bearing intracerebral U87 glioblastoma were treated with PDT and the antiangiogenic regimen (MF1 and DC101) either alone or in combination, while those left untreated served as tumor controls. Tumor volume and animal survival time were analyzed to evaluate the outcome of different treatment modalities. In addition, the immunohistochemical expression of VEGF in the brain adjacent to the tumor, von Willebrand factor (vWF), apoptotic, and proliferative markers in the tumor area were examined. PDT or MF1 + DC101 alone significantly reduced the tumor volume and prolonged the survival time of glioma-implanted animals. Combined therapy markedly reduced tumor volume and increased survival time with significantly better outcomes than both monotherapies. Both vWF and VEGF levels significantly increased after PDT while they both significantly decreased after antiangiogenic treatment, compared with no treatment. PDT plus antiangiogenic treatment led to significant decreases in both vWF and VEGF expression, compared with PDT alone. Either PDT or antiangiogenic treatment alone significantly increased tumor cell apoptosis compared with no treatment, while combination therapy resulted in further augmentation of apoptosis. Antiangiogenic treatment with or without PDT significantly decreased tumor cell proliferation, compared with either no treatment or PDT alone. In summary, we demonstrate both significant inhibition of tumor growth and extended survival of mice treated by the combination therapy with PDT and antiangiogenic agents, compared with each single treatment, suggesting that the combination therapy may be a promising strategy to improve clinical outcomes in glioblastoma.

Monitoring singlet oxygen in situ with delayed chemiluminescence to deduce the effect of photodynamic therapy

Singlet oxygen ((1)O(2)) is an important factor mediating cell killing in photodynamic therapy (PDT). We previously reported that chemiluminescence (CL) can be used to detect (1)O(2) production in PDT and linked the signal to the PDT-induced cytotoxicity in vitro. We develop a new CL detection apparatus to achieve in vivo measurements. The system utilizes a time-delayed CL signal to overcome the interference from scattered excitation light, thus greatly improving the accuracy of the detection. The system is tested on healthy skin of BALB/ca mouse for its feasibility and reliability. The CL measurement is made during a synchronized gating period of the irradiation light. After each PDT treatment and in situ CL measurement, the skin response is scored over a period of 2 weeks. A remarkable relationship is observed between the score and the CL, regardless of the PDT treatment protocol. Although there are many issues yet to be addressed, our results clearly demonstrate the feasibility of CL measurement during PDT and its potential for in vivo PDT dosimetry. This requires further investigations.

Interstitial photodynamic therapy of nonresectable malignant glioma recurrences using 5-aminolevulinic acid induced protoporphyrin IX

BACKGROUND AND OBJECTIVE

Limited knowledge of the light and temperature distribution within the target volume in combination with non-selective accumulation of the applied photosensitizers (PS) has hampered the clinical relevance of interstitial photodynamic therapy (iPDT) for treatment of malignant glioma patients. The current pilot study focused on the development and the clinical implementation of an accurate and reproducible irradiation scheme for iPDT using 5-aminolevulinic acid (5-ALA) induced protoporphyrin IX (PPIX) as a selectively working PS.

STUDY DESIGN/MATERIALS AND METHODS

Monte Carlo simulations of fluence rate and heat transport simulations were performed using the optical properties of normal brain tissue infiltrated by tumor cells (absorption coefficient micro(a) = 0.2 cm(-1), reduced scattering coefficient: micro'(s) = 20 cm(-1)). A modified 3-D treatment-planning software was used to calculate both, the treatment-volume and the exact position of the light diffusers within the lesion. The feasibility and the risk of iPDT were tested in 10 patients with small and circumscribed recurrent malignant gliomas.

RESULTS

The optimum distance between the implanted light diffusers was determined to be 9 mm with regard to both fluence rate and temperature distribution. For this distance a temperature increase above 42 degrees C was not expected to occur. Up to six cylindrical light diffusers were stereotactically implanted to achieve a complete irradiation of the tumor volume, which was possible in every single patient (mean tumor volume: 5.9 cm3). The total applied light fluence was between 4,320 J and 11,520 J. Side effects of iPDT were not observed. Median survival was 15 months.

CONCLUSION

5-ALA iPDT in combination with a 3-D treatment-planning (which was based on optical and thermal simulations) is a safe and feasible treatment modality. The clinical impact of these findings deserves further prospective evaluation.

Photodynamic effects of SIM01, a new sensitizer, on experimental brain tumors in rats

BACKGROUND

Glioblastomas are the third most common cause of cancer death in patients between 15 and 35 years old. Literature suggests that PDT could represent a promising treatment, providing that sensitizers could accumulate within the cancer tissues despite the blood-brain barrier.

METHODS

Distribution and PDT effect of SIM01, a promising photosensitizer, have been evaluated on orthotopic C6 tumor model in rats by comparison with HPD and m-THPC. Pharmacokinetics had been analyzed with fluorescence and ROS. Photodynamic treatment was done using a 630-nm light with an energy density of 100 J cm(-2) for HPD and a 652-nm light with an energy density of 20 J cm(-2) for m-THPC and SIM01.

RESULTS

The correlation between fluorescence and ROS dosimetry was found to be excellent. An optimal concentration was found after 12 hours for SIM01 (4 mg/kg), 24 hours for HPD (10 mg/kg), and 48 hours for m-THPC (4 mg/kg). The best normal tissue/cancer ratio of concentration had been found after 12 hours for SIM01 and 48 hours for HPD and m-THPC. Pathological examinations after PDT showed that the criteria for histology of glioblastic origin were absent in SIM01-treated rats 12 hours after injection but were present in 50% of rats treated 24 hours after injection and in all after a 48-hour delay. Mean survival of rats treated 12 or 24 hours after SIM01 injection was significantly improved compared with controls, HPD-, or m-THPC-treated groups. Survival of rats treated 12 or 24 hours after SIM01 injection reached 20 days but decreased for longer delays. On the contrary, survival reached 18 days at the maximum for rats treated 48 hours after m-THPC or HPD injection.

CONCLUSIONS

Our results confirm that PDT is a promising treatment for glioblastomas. SIM01 efficacy is as efficient as m-THPC but with much more favorable pharmacokinetics.