Photodynamic therapy of intracranial tissues: a preclinical comparative study of four different photosensitizers

Glucocorticoid receptor mediated sensitization of colon cancer to photodynamic therapy induced cell death

Photodynamic therapy (PDT) is a clinically approved, non-invasive alternate cancer therapy. A synthetic glucocorticoid (GC), dexamethasone (Dex) has previously been demonstrated to sensitize cancer cells to chemotherapy. However, to the best of our knowledge, the sensitization effect of GCs on PDT has not yet been investigated. We hypothesized that glucocorticoid receptor (GR) targeting can selectively make cancer cells more sensitive to PDT treatment, as PDT induces hypoxia wherein GR-activity gets enhanced. In addition, Dex was reported to act against the PDT-induced cell survival pathways like HIF-1α, NRF2, NF-κB, STAT3 etc. Thus, both the treatments can complement each other and may result in increasing the effectiveness of combination therapy. Hence, in this study, we developed liposomal formulations of our previously reported PDT agent P-Nap, either alone (D1P-Nap) or in combination with Dex (D1XP-Nap) to elucidate the sensitization effect. Interestingly, our RT-PCR results in hypoxic conditions showed down-regulation of HIF-1α and over expression of GR-activated genes for glucose-6-phosphatase (G6Pase) and PEPCK enzymes, indicating prominent GR-transactivation. We also observed higher phototoxicity in CT26.WT cells treated with D1XP-Nap PDT under hypoxic conditions as compared to normoxic conditions. These effects were reversed when cells were pre-treated with RU486, a competitive inhibitor of GCs. Moreover, our in vivo findings of subcutaneous tumor model of Balb/C mice for colon cancer revealed a significant decrease in tumor volume as well as considerable enhancement in the survivability of PDT treated tumor-bearing mice when Dex was present in the formulation. A high Bax/Bcl-xL ratio, high p53 expression, enhanced E-cadherin expression and down-regulation of pro-tumorigenic transcription factors NF-κB and c-Myc were found in tumor lysates from mice treated with D1XP-Nap under PDT, indicating GR-mediated sensitization of the tumor to PDT-induced cell death and enhancement of life-span for tumor bearing mice.

Simulating photodynamic therapy for the treatment of glioblastoma using Monte Carlo radiative transport

Significance

Glioblastoma (GBM) is a rare but deadly form of brain tumor with a low median survival rate of 14.6 months, due to its resistance to treatment. An independent simulation of the INtraoperative photoDYnamic therapy for GliOblastoma (INDYGO) trial, a clinical trial aiming to treat the GBM resection cavity with photodynamic therapy (PDT) via a laser coupled balloon device, is demonstrated.

Aim

To develop a framework providing increased understanding for the PDT treatment, its parameters, and their impact on the clinical outcome.

Approach

We use Monte Carlo radiative transport techniques within a computational brain model containing a GBM to simulate light path and PDT effects. Treatment parameters (laser power, photosensitizer concentration, and irradiation time) are considered, as well as PDT's impact on brain tissue temperature.

Results

The simulation suggests that 39% of post-resection GBM cells are killed at the end of treatment when using the standard INDYGO trial protocol (light fluence = 200    J / cm 2 at balloon wall) and assuming an initial photosensitizer concentration of 5    μ M . Increases in treatment time and light power (light fluence = 400    J / cm 2 at balloon wall) result in further cell kill but increase brain cell temperature, which potentially affects treatment safety. Increasing the p hotosensitizer concentration produces the most significant increase in cell kill, with 61% of GBM cells killed when doubling concentration to 10    μ M and keeping the treatment time and power the same. According to these simulations, the standard trial protocol is reasonably well optimized with improvements in cell kill difficult to achieve without potentially dangerous increases in temperature. To improve treatment outcome, focus should be placed on improving the photosensitizer.

Conclusions

With further development and optimization, the simulation could have potential clinical benefit and be used to help plan and optimize intraoperative PDT treatment for GBM.

Investigations on correlations between changes of optical tissue properties and NMR relaxation times

BACKGROUND

Accurate light dosimetry is a complex remaining challenge in interstitial photodynamic therapy (iPDT) for malignant gliomas. The light dosimetry should ideally be based on the tissue morphology and the individual optical tissue properties of each tissue type in the target region. First investigations are reported on using NMR information to estimate changes of individual optical tissue properties.

METHODS

Porcine brain tissue and optical tissue phantoms were investigated. To the porcine brain, supplements were added to simulate an edema or high blood content. The tissue phantoms were based on agar, Lipoveneous, ink, blood and gadobutrol (Gd-based MRI contrast agent). The concentrations of phantom ingredients and tissue additives are varied to compare concentration-dependent effects on optical and NMR properties. A 3-tesla whole-body MRI system was used to determine T1 and T2 relaxation times. Optical tissue properties, i.e., the spectrally resolved absorption and reduced scattering coefficient, were obtained using a single integrating sphere setup. The observed changes of NMR and optical properties were compared to each other.

RESULTS

By adjusting the NMR relaxation times and optical tissue properties of the tissue phantoms to literature values, recipes for human brain tumor, white matter and grey matter tissue phantoms were obtained that mimic these brain tissues simultaneously in both properties. For porcine brain tissue, it was observed that with increasing water concentration in the tissue, both NMR-relaxation times increased, while µa decreased and µs' increased at 635 nm. The addition of blood to porcine brain samples showed a constant T1, while T2 shortened and the absorption coefficient at 635 nm increased.

CONCLUSIONS

In this investigation, by changing sample contents, notable changes of both NMR relaxation times and optical tissue properties have been observed and their relations examined. The developed dual NMR/optical tissue phantoms can be used in iPDT research, clinical training and demonstrations.

Photobac derived from bacteriochlorophyll-a shows potential for treating brain tumor in animal models by photodynamic therapy with desired pharmacokinetics and limited toxicity in rats and dogs

Photobac is a near infrared photosensitizer (PS) derived from naturally occurring bacteriochlorophyll- a, with a potential for treating a variety of cancer types (U87, F98 and C6 tumor cells in vitro). The main objective of the studies presented herein was to evaluate the efficacy, toxicity and pharmacokinetic profile of Photobac in animals (mice, rats and dogs) and submit these results to the United States Food and Drug Administration (US FDA) for its approval to initiate Phase I human clinical trials of glioblastoma, a deadly cancer disease with no long term cure. The photodynamic therapy (PDT) efficacy of Photobac was evaluated in mice subcutaneously implanted with U87 tumors, and in rats bearing C6 tumors implanted in brain. In both tumor types, the Photobac-PDT was quite effective. The long-term cure in rats was monitored by magnetic resonance imaging (MRI) and histopathology analysis. A detailed pharmacology, pharmacokinetics and toxicokinetic study of Photobac was investigated in both non-GLP and GLP facilities at variable doses following the US FDA parameters. Safety Pharmacology studies suggest that there is no phototoxicity, cerebral or retinal toxicity with Photobac. No metabolites of Photobac were observed following incubation in rat, dog, mini-pig and human hepatocytes. Based on current biological data, Photobac-IND received the approval for Phase-I human clinical trials to treat Glioblastoma (brain cancer), which is currently underway at our institute. Photobac has also received an orphan drug status from the US FDA, because of its potential for treating Glioblastoma as no effective treatment is currently available for this deadly disease.

5-Aminolevulinic acid increases boronophenylalanine uptake into glioma stem cells and may sensitize malignant glioma to boron neutron capture therapy

Boron neutron capture therapy (BNCT) is a high-LET particle radiotherapy clinically tested for treating malignant gliomas. Boronophenylalanine (BPA), a boron-containing phenylalanine derivative, is selectively transported into tumor cells by amino acid transporters, making it an ideal agent for BNCT. In this study, we investigated whether the amino acid 5-aminolevulinic acid (ALA) could sensitize glioma stem cells (GSCs) to BNCT by enhancing the uptake of BPA. Using human and mouse GSC lines, pre-incubation with ALA increased the intracellular accumulation of BPA dose-dependent. We also conducted in vivo experiments by intracerebrally implanting HGG13 cells in mice and administering ALA orally 24 h before BPA administration (ALA + BPA-BNCT). The ALA preloading group increased the tumor boron concentration and improved the tumor/blood boron concentration ratio, resulting in improved survival compared to the BPA-BNCT group. Furthermore, we found that the expression of amino acid transporters was upregulated following ALA treatment both in vitro and in vivo, particularly for ATB0,+. This suggests that ALA may sensitize GSCs to BNCT by upregulating the expression of amino acid transporters, thereby enhancing the uptake of BPA and improving the effectiveness of BNCT. These findings have important implications for strategies to improve the sensitivity of malignant gliomas to BPA-BNCT.

Integrating clinical access limitations into iPDT treatment planning with PDT-SPACE

PDT-SPACE is an open-source software tool that automates interstitial photodynamic therapy treatment planning by providing patient-specific placement of light sources to destroy a tumor while minimizing healthy tissue damage. This work extends PDT-SPACE in two ways. The first enhancement allows specification of clinical access constraints on light source insertion to avoid penetrating critical structures and to minimize surgical complexity. Constraining fiber access to a single burr hole of adequate size increases healthy tissue damage by 10%. The second enhancement generates an initial placement of light sources as a starting point for refinement, rather than requiring entry of a starting solution by the clinician. This feature improves productivity and also leads to solutions with 4.5% less healthy tissue damage. The two features are used in concert to perform simulations of various surgery options of virtual glioblastoma multiforme brain tumors.

Machine learning for real-time optical property recovery in interstitial photodynamic therapy: a stimulation-based study

With the continued development of non-toxic photosensitizer drugs, interstitial photodynamic therapy (iPDT) is showing more favorable outcomes in recent clinical trials. IPDT planning is crucial to further increase the treatment efficacy. However, it remains a major challenge to generate a high-quality, patient-specific plan due to uncertainty in tissue optical properties (OPs), µ _a and µ _s . These parameters govern how light propagates inside tissues, and any deviation from the planning-assumed values during treatment could significantly affect the treatment outcome. In this work, we increase the robustness of iPDT against OP variations by using machine learning models to recover the patient-specific OPs from light dosimetry measurements and then re-optimizing the diffusers' optical powers to adapt to these OPs in real time. Simulations on virtual brain tumor models show that reoptimizing the power allocation with the recovered OPs significantly reduces uncertainty in the predicted light dosimetry for all tissues involved.

Determination of Optical Properties and Photodynamic Threshold of Lung Tissue for Treatment Planning of In Vivo Lung Perfusion Assisted Photodynamic Therapy

BACKGROUND

Isolated lung metastases in sarcoma and colorectal cancer patients are inadequately treated with current standard therapies. In Vivo Lung Perfusion, a novel platform, could overcome limitations to photodynamic therapy treatment volumes by using low cellular perfusate, removing blood, theoretically allowing greater light penetration. To develop personalized photodynamic therapy protocols requires in silico light propagation simulations based on optical properties and maximal permissible photodynamic threshold dose of lung tissue. This study presents quantification of optical properties for two perfusates and the photodynamic threshold for 5-ALA and Chlorin e6.

METHODS

Porcine and human lungs were placed on Ex Vivo Lung Perfusion, and perfused with acellular solution or blood. Isotropic diffusers were placed within bronchi and on lung surface for light transmission measurements, from which absorption and light scattering properties were calculated at multiple wavelengths. Separately, pigs were injected with 5-ALA or Chlorin e6, and lung tissue was irradiated at increasing doses. Resultant lesion sizes were measured by CT and histology to quantify the photodynamic threshold.

RESULTS

Low cellular perfusate reduced the tissue absorption coefficient significantly, increasing penetration depth of light by 3.3 mm and treatment volumes 3-fold. The photodynamic threshold for lung exposed to 5-ALA was consistent with other malignancies. Chlorin e6 levels were undetectable in lung tissue and did not demonstrate photodynamic-induced necrosis.

CONCLUSIONS

Light penetration with low cellular perfusate is significantly greater and could enable treatments for diffuse disease. This data aids photodynamic treatment planning and will guide clinical translation of photodynamic therapy protocols in the lung, especially during lung perfusion.

Investigation of non-uniformly emitting optical fiber diffusers on the light distribution in tissue

The influence of inhomogeneities in the emission characteristics of optical fiber diffusers on the light distribution within biological tissue was evaluated by Monte Carlo (MC) simulations and by experiments on optical phantoms. Due to the strong scattering of light within biological tissue, inhomogeneities in the emission profile become blurred within a short light propagation distance, so that the light distribution within the tissue approaches that of a homogeneous diffuser. The degree of feature vanishing in the light distribution is mainly determined by the width of the inhomogeneities. It was shown that the influence of local inhomogeneities on top of a homogeneous light distribution fades away very effectively within 1 mm of tissue depth, which results in a light distribution very close to that for a homogeneously emitting diffuser. Emission profiles composed of multiple narrow peaks distributed over the full diffuser length with a peak-to-peak distance of less than 2 mm result in an almost homogeneous light distribution after approximately 1 mm of tissue depth. While this article is focused on the impact of diffuser inhomogeneities on the light distribution within the tissue, the importance of further investigations on the related thermal effects is also discussed.

Fluorescence and Treatment Light Monitoring for Interstitial Photodynamic Therapy

In interstitial photodynamic therapy, light is distributed to the tumor via light diffusers. The light dose and the related phototoxic effect achieved throughout the target volume critically depend on absorption, scattering and diffuser positioning. Using liquid tissue phantoms, we investigated the dependencies of treatment light transmission and protoporphyrin IX (PpIX) fluorescence on these parameters. This enabled monitoring hemoglobin oxygenation and methemoglobin formation during irradiation (635 nm, 200 mW cm^-1 diffuser length). Starting with two parallel cylindrical diffusers at 10 mm radial separation, the light transmitted between the fibers was largely determined by the minimal distance between the diffusers, but rather insensitive to an additional axial displacement or tilting of one fiber with respect to the other. For fixed distance between the diffusor centers, however, tilting up to direct contact resulted in a 10-fold signal increase. For hemoglobin within erythrocytes, irradiation leads to photobleaching of PpIX without marked change in hemoglobin oxygenation until hemolysis occurs. Afterward, hemoglobin is rapidly deoxygenized and methemoglobin is formed, leading to a dramatic increase in absorption. For lysed blood, these effects start immediately. A comparison of intraoperative monitoring of the signals with the experimental results might help prevent insufficient treatment by reconsidering treatment planning or prolonging irradiation.

Singlet oxygen model evaluation of interstitial photodynamic therapy with 5-aminolevulinic acid for malignant brain tumor

Interstitial photodynamic therapy (iPDT) with 5-aminolevulinic acid (ALA) is a possible alternative treatment for malignant brain tumors. Further evaluation is, however, required before it can be clinically applied. Computational simulation of the photophysical process in ALA-iPDT can offer a quantitative tool for understanding treatment outcomes, which depend on various variables related to clinical treatment conditions. We propose a clinical simulation method of ALA-iPDT for malignant brain tumors using a singlet oxygen (O1₂) model and O1₂ threshold to induce cell death. In this method, the amount of O1₂ generated is calculated using a photosensitizer photobleaching coefficient and O1₂ quantum yield, which have been measured in several previous studies. Results of the simulation using clinical magnetic resonance imaging data show the need to specify the insertion positions of cylindrical light diffusers and the level of light fluence. Detailed analysis with a numerical brain tumor model demonstrates that ALA-iPDT treatment outcomes depend on combinations of photobleaching and threshold values. These results indicate that individual medical procedures, including pretreatment planning and treatment monitoring, will greatly benefit from simulation of ALA-iPDT outcomes.

Efficacy of ruthenium coordination complex-based Rutherrin in a preclinical rat glioblastoma model

Background

Glioblastoma is an aggressive brain cancer in adults with a grave prognosis, aggressive radio and chemotherapy provide only a 15 months median survival.

Methods

We evaluated the tolerability and efficacy of the Ruthenium-based photosensitizer TLD-1433 with apo-Transferrin (Rutherrin) in the rat glioma 2 (RG-2) model. The specific tumor uptake ratio and photodynamic therapy (PDT) threshold of the rat glioblastoma and normal brain were determined, survival and CD8⁺T-cell infiltration post-therapy were analyzed. Results were compared with those obtained for 5-aminolevulinic acid (ALA)-induced Protoporphyrin IX (PpIX)-mediated photodynamic therapy in the same animal model. As both photosensitizers have different photophysical properties, the number of absorbed photons required to achieve an equal cell kill was determined for in vitro and in vivo studies.

Results

A significantly lower absorbed energy was sufficient to achieve LD₅₀ with Rutherrin versus PpIX-mediated PDT. Rutherrin provides a higher specific uptake ratio (SUR) >20 in tumors versus normal brain, whereas the SUR for ALA-induced PpIX was 10.6. To evaluate the short-term tissue response in vivo, enhanced T2-weighted magnetic resonance imaging (MRI) provided the spatial extent of edema, post PpIX-PDT at twice the cross-section versus Rutherrin-PDT suggesting reduced nonspecific damage, typically associated with a secondary wave of neuronal damage. Following a single therapy, a significant survival increase was observed in rats bearing glioma for PDT mediated by Rutherrin versus PpIX for the selected treatment conditions. Rutherrin-PDT also demonstrated an increased CD8+T-cell infiltration in the tumors.

Conclusion

Rutherrin-PDT was well tolerated providing a safe and effective treatment of RG-2 glioma.

Optimizing interstitial photodynamic therapy with custom cylindrical diffusers

Interstitial photodynamic therapy (iPDT) has shown promise recently as a minimally invasive cancer treatment, partially due to the development of non-toxic photosensitizers in the absence of activation light. However, a major challenge in iPDT is the pre-treatment planning process that specifies the number of diffusers needed, along with their positions and allocated powers, to confine the light distribution to the target volume as much as possible. In this work, a new power allocation algorithm for cylindrical light diffusers including those that can produce customized longitudinal (tailored) emission profiles is introduced. The proposed formulation is convex to guarantee the minimum over-dose possible on the surrounding organs-at-risk. The impact of varying the diffuser lengths and penetration angles on the quality of the plan is evaluated. The results of this study are demonstrated for different photosensitizers activated at different wavelengths and simulated on virtual tumors modeling virtual glioblastoma multiforme cases. Results show that manufacturable cylindrical diffusers with tailored emission profiles can significantly outperform those with conventional flat profiles with an average damage reduction on white matter of 15% to 55% and on gray matter of 23% to 58%.

AlPcS4-PDT for gastric cancer therapy using gold nanorod, cationic liposome, and Pluronic® F127 nanomicellar drug carriers

Purpose

As a promising photodynamic therapy (PDT) agent, Al(III) phthalocyanine chloride tetrasulfonic acid (AlPcS₄) provides deep penetration into tissue, high quantum yields, good photostability, and low photobleaching. However, its low delivery efficiency and high binding affinity to serum albumin cause its low penetration into cancer cells, further limiting its PDT effect on gastric cancer. In order to improve AlPcS₄/PDT effect, the AlPcS₄ delivery sys tems with different drug carriers were synthesized and investigated.

Materials and methods

Gold nanorods, cationic liposomes, and Pluronic^® F127 nanomicellars were used to formulate the AlPcS₄ delivery systems. The anticancer effect was evaluated by CCK-8 assay and colony formation assay. The delivery efficiency of AlPcS₄ and the binding affinity to serum proteins were determined by fluorescence intensity assay. The apoptosis and necrosis ability, reactive oxygen species and singlet oxygen generation, mitochondrial transmembrane potential and ([Ca²⁺]_i) concentration were further measured to evaluate the mechanism of cell death.

Results

The series of synthesized AlPcS₄ delivery systems with different drug carriers improve the limited PDT effect in varying degrees. In contrast, AlPcS₄ complex with gold nanorods has significant anticancer effects because gold nanorods are not only suitable for AlPcS₄ delivery, but also exhibit enhanced singlet oxygen generation effect and photothermal effect to induce cell death directly. Moreover, AlPcS₄ complex with cationic liposomes shows the potent inhibition effect because of its optimal AlPcS₄ delivery efficiency and ability to block serum albumin. In addition, AlPcS₄ complex with Pluronic F127 exhibits inferior PDT effect but presents lower cytotoxicity, slower dissociation rate, and longer retention time of incorporated drugs; thus, F127–AlPcS₄ is used for prolonged gastric cancer therapy.

Conclusion

The described AlPcS₄ drug delivery systems provide promising agents for gastric cancer therapy.

Automatic interstitial photodynamic therapy planning via convex optimization

Finding a high-quality treatment plan is an essential, yet difficult, stage of Photodynamic therapy (PDT) as it will determine the therapeutic efficacy in eradicating malignant tumors. A high-quality plan is patient-specific, and provides clinicians with the number of fiber-based spherical diffusers, their powers, and their interstitial locations to deliver the required light dose to destroy the tumor while minimizing the damage to surrounding healthy tissues. In this work, we propose a general convex light source power allocation algorithm that, given light source locations, guarantees optimality of the resulting solution in minimizing the over/under-dosage of volumes of interest. Furthermore, we provide an efficient framework for source selection with concomitant power reallocation to achieve treatment plans with a clinically feasible number of sources and comparable quality. We demonstrate our algorithms on virtual test cases that model glioblastoma multiforme tumors, and evaluate the performance of four different photosensitizers with different activation wavelengths and specific tissue uptake ratios. Results show an average reduction of the damage to organs-at-risk (OAR) by 29% to 31% with comparable runtime to existing power allocation techniques.

Delineation of Tumor Habitats based on Dynamic Contrast Enhanced MRI

Tumor heterogeneity can be elucidated by mapping subregions of the lesion with differential imaging characteristics, called habitats. Dynamic Contrast Enhanced (DCE-)MRI can depict the tumor microenvironments by identifying areas with variable perfusion and vascular permeability, since individual tumor habitats vary in the rate and magnitude of the contrast uptake and washout. Of particular interest is identifying areas of hypoxia, characterized by inadequate perfusion and hyper-permeable vasculature. An automatic procedure for delineation of tumor habitats from DCE-MRI was developed as a two-part process involving: (1) statistical testing in order to determine the number of the underlying habitats; and (2) an unsupervised pattern recognition technique to recover the temporal contrast patterns and locations of the associated habitats. The technique is examined on simulated data and DCE-MRI, obtained from prostate and brain pre-clinical cancer models, as well as clinical data from sarcoma and prostate cancer patients. The procedure successfully identified habitats previously associated with well-perfused, hypoxic and/or necrotic tumor compartments. Given the association of tumor hypoxia with more aggressive tumor phenotypes, the obtained in vivo information could impact management of cancer patients considerably.

ALA-PpIX mediated photodynamic therapy of malignant gliomas augmented by hypothermia

Background

Malignant gliomas are highly invasive, difficult to treat, and account for 2% of cancer deaths worldwide. Glioblastoma Multiforme (GBM) comprises the most common and aggressive intracranial tumor. The study hypothesis is to investigate the modification of Photodynamic Therapy (PDT) efficacy by mild hypothermia leads to increased glioma cell kill while protecting normal neuronal structures.

Methods

Photosensitizer accumulation and PDT efficacy in vitro were quantified in various glioma cell lines, primary rat neurons, and astrocytes. In vivo studies were carried out in healthy brain and RG2 glioma of naïve Fischer rats. Hypothermia was induced at 1 hour pre- to 2 hours post-PDT, with ALA-PpIX accumulation and PDT treatments effects on tumor and normal brain PDT quantified using optical spectroscopy, histology, immunohistochemistry, MRI, and survival studies, respectively.

Findings

In vitro studies demonstrated significantly improved post-PDT survival in primary rat neuronal cells. Rat in vivo studies confirmed a neuroprotective effect to hypothermia following PpIX mediated PDT by T₂ mapping at day 10, reflecting edema/inflammation volume reduction. Mild hypothermia increased PpIX fluorescence in tumors five-fold, and the median post-PDT rat survival time (8.5 days normothermia; 14 days hypothermia). Histology and immunohistochemistry show close to complete cellular protection in normal brain structures under hypothermia.

Conclusions

The benefits of hypothermia on both normal neuronal tissue as well as increased PpIX fluorescence and RG2 induced rat survival strongly suggest a role for hypothermia in photonics-based surgical techniques, and that a hypothermic intervention could lead to considerable patient outcome improvements.

Revisiting photodynamic therapy dosimetry: reductionist & surrogate approaches to facilitate clinical success

Photodynamic therapy (PDT) can be a highly complex treatment, with many parameters influencing treatment efficacy. The extent to which dosimetry is used to monitor and standardize treatment delivery varies widely, ranging from measurement of a single surrogate marker to comprehensive approaches that aim to measure or estimate as many relevant parameters as possible. Today, most clinical PDT treatments are still administered with little more than application of a prescribed drug dose and timed light delivery, and thus the role of patient-specific dosimetry has not reached widespread clinical adoption. This disconnect is at least partly due to the inherent conflict between the need to measure and understand multiple parameters in vivo in order to optimize treatment, and the need for expedience in the clinic and in the regulatory and commercialization process. Thus, a methodical approach to selecting primary dosimetry metrics is required at each stage of translation of a treatment procedure, moving from complex measurements to understand PDT mechanisms in pre-clinical and early phase I trials, towards the identification and application of essential dose-limiting and/or surrogate measurements in phase II/III trials. If successful, identifying the essential and/or reliable surrogate dosimetry measurements should help facilitate increased adoption of clinical PDT. In this paper, examples of essential dosimetry points and surrogate dosimetry tools that may be implemented in phase II/III trials are discussed. For example, the treatment efficacy as limited by light penetration in interstitial PDT may be predicted by the amount of contrast uptake in CT, and so this could be utilized as a surrogate dosimetry measurement to prescribe light doses based upon pre-treatment contrast. Success of clinical ALA-based skin lesion treatment is predicted almost uniquely by the explicit or implicit measurements of photosensitizer and photobleaching, yet the individualization of treatment based upon each patients measured bleaching needs to be attempted. In the case of ALA, lack of PpIX is more likely an indicator that alternative PpIX production methods must be implemented. Parsimonious dosimetry, using surrogate measurements that are clinically acceptable, might strategically help to advance PDT in a medical world that is increasingly cost and time sensitive. Careful attention to methodologies that can identify and advance the most critical dosimetric measurements, either direct or surrogate, are needed to ensure successful incorporation of PDT into niche clinical procedures.

Drug Carrier for Photodynamic Cancer Therapy

Photodynamic therapy (PDT) is a non-invasive combinatorial therapeutic modality using light, photosensitizer (PS), and oxygen used for the treatment of cancer and other diseases. When PSs in cells are exposed to specific wavelengths of light, they are transformed from the singlet ground state (S₀) to an excited singlet state (S₁-Sn), followed by intersystem crossing to an excited triplet state (T₁). The energy transferred from T₁ to biological substrates and molecular oxygen, via type I and II reactions, generates reactive oxygen species, (¹O₂, H₂O₂, O₂*, HO*), which causes cellular damage that leads to tumor cell death through necrosis or apoptosis. The solubility, selectivity, and targeting of photosensitizers are important factors that must be considered in PDT. Nano-formulating PSs with organic and inorganic nanoparticles poses as potential strategy to satisfy the requirements of an ideal PDT system. In this review, we summarize several organic and inorganic PS carriers that have been studied to enhance the efficacy of photodynamic therapy against cancer.

Efficacy and safety of continuous low-irradiance photodynamic therapy in the treatment of chest wall progression of breast cancer

BACKGROUND

Photodynamic therapy (PDT) is a binary therapy using a drug and high-energy light source. PDT is approved for several premalignant and malignant conditions. Recent in-vitro and animal data suggest that enhanced tumor-specific cytotoxicity can be achieved with far less collateral damage to normal surrounding tissues if PDT is administered continuously at a lower dose rate for extended periods of time. Based on these promising preclinical data, we conducted a Phase I clinical trial of continuous low-irradiance photodynamic therapy (CLIPT) using 630 nm laser energy and intravenously administered porforin sodium as the photosensitizer. We determined the maximum tolerated dose (MTD) of CLIPT on skin and tumor response in subjects with cutaneous and subcutaneous metastatic nodules who had failed radiation and surgery.

METHODS

Patients with cutaneous and/or subcutaneous metastatic nodules that had failed radiation and surgery were offered enrollment into the trial. The initial study design planned for sequential cohorts of six subjects to be treated at increasing laser intensity, starting at 100 J/cm(2) administered continuously over 24 h (10(-2) dose rate compared with standard PDT). Dose-limiting toxicity was defined as partial or full-thickness necrosis of the surrounding tumor-free, previously irradiated skin. The MTD was defined as the highest laser energy at which ≤33% of subjects experienced the dose-limiting toxicity. Subjects received intravenous porfirmer sodium 0.8 mg/kg 48 h before commencing CLIPT. Response rates and quality of life measures were assessed.

RESULTS

Nine subjects were enrolled with chest wall progression of breast cancer following mastectomy. All had failed prior surgery and electron-beam radiation therapy. The initial two subjects were treated at 100 J/cm(2) and developed partial thickness skin necrosis. Dose reduction was therefore instituted, and the next cohort was treated at 50 J/cm(2). None of the subsequent seven subjects suffered partial or full thickness necrosis, thus establishing the MTD at 50 J/cm(2) over 24 h (0.5 mW irradiance). Six of the nine subjects (67%) had either a complete or partial clinical response. Of note, two subjects had significant regression of tumor nodules distant from the treatment field. Of the eight subjects whose terminal deoxynucleotidyl transferase dUTP nick end labeling assay results were available, 8 (100%) demonstrated histologic response to treatment as evidenced by either tumor apoptosis or regression. Quality of life measures were improved following treatment-particularly bleeding and pain from the tumor nodules.

CONCLUSIONS

The MTD of CLIPT was established at 50 J/cm(2) administered continuously over 24 h. These preliminary data suggest CLIPT may be an effective, low-morbidity therapeutic modality in the treatment of cutaneous and subcutaneous metastases of breast cancer following mastectomy. Further evaluation in a larger cohort is warranted to better assess efficacy and optimize the intervention.

Modulation of PPIX synthesis and accumulation in various normal and glioma cell lines by modification of the cellular signaling and temperature

Effective therapies for malignant gliomas are still elusive and limited survival improvements are provided only by Temozolomide or fluorescence guided resection. The efficacy of photodynamic therapy (PDT) in this indication is limited by the higher sensitivity of normal brain structures compared to glioma necessitating a modulation of its sensitivity. We evaluate the influence of hypothermia and the tyrosine kinase inhibitor Erlotinib on cell's ability to synthesize PPIX following the administration of ALA which was not previously investigated. We demonstrate that both hypothermia and Erlotinib are favorable in PPIX selectivity as only glioma cell lines demonstrate an increased PPIX synthesis, whereas the neuronal and astrocytic synthesis is remaining unaffected. The results are encouraging to consider hypothermia and Erlotinib as adjuvant therapies to increase the PDT therapeutic index between GBM and normal intracranial tissues, as well as to improve contrast in fluorescence guided resection.

Selective accumulation of hematoporphyrin derivative in glioma through proton-coupled folate transporter SLC46A1

The mechanism of tumor-specific porphyrin accumulation is not clear. We investigated the expression of proton-coupled folate transporter SLC46A1 in glioma and aimed to clarify the relationship between tumor fluorescence and SLC46A1 expression.We confirmed the expression of SLC46A1 in surgical specimens from 24 glioma patients by immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR). We also investigated SLC46A1 expression in glioma cell lines by RT-PCR. The cellular uptake of hematoporphyrin derivative in vitro was measured with a microplate reader and fluorescence microscope. In these experiments, we used three human malignant glioma cell lines: U87, U251 and T98G. Immunohistochemistry showed SLC46A1 positivity in the malignant tumor lesion of each specimen. Strong positive SLC46A1 expression was observed in 33% of grade IV, 22% of grade III and 17% of grade II gliomas. All four randomly obtained malignant glioma frozen sections expressed SLC46A1 mRNA by RT-PCR. In vitro, U87 showed the least SLC46A1 expression, U251 was intermediate, and T98G showed the most expression. The amount of hematoporphyrin derivative (HpD) cellular uptake correlated with SLC46A1 expression. These results suggest that the accumulation of HpD in glioma cells is related to SLC46A1 function and SLC46A1 is involved in the mechanism of glioma fluorescence.

Risk factors for developing oral 5-aminolevulinic acid-induced side effects in patients undergoing fluorescence guided resection

Oral 5 aminolevulinic acid (5-ALA) is used to assist surgical resection of malignant tumours in the brain and other locations. Hypotension and alteration of liver functions have been reported as potential adverse effects. This study was designed to assess the incidence and contributing factors that cause 5-ALA induced side effects in a cohort of 90 patients. Hypotension occurred in 11% of patients irrespective of 5-ALA dose. The only contributing factor was the presence of cardiovascular disease and antihypertensive drug therapy with an odd ratio of 17.7. Liver function were disturbed in 2% in patients who received 20mg or less/kg body weight compared to 4% in those who received a dose of >20mg/kg 5-ALA. The liver dysfunction was minor and was not clinically significant. We concluded that 5-ALA induced side effects were minimal and hypotension more likely to occur in patients receiving antihypertensive drug therapy.

Haematoporphyrin enhances the peroxidase activity of haemoglobin

The effect of haematoporphyrin, a component of some of the widely used anticancer drugs, on the peroxidase activity of haemoglobin has been studied. Haematoporphyrin increases the haemoglobin-catalysed hydrogen peroxide-mediated oxidation of o-dianisidine or NADH. Spectrophotometric study reveals that an interaction occurs between haemoglobin and haematoporphyrin which leads to a conformational change of the protein. The extent of enhanced peroxidase activity as well as conformational change of the protein vary in a positive manner with the stoichiometric ratio of haematoporphyrin/haemoglobin. An increase in the peroxidase activity of haemoglobin was also observed in the presence of superoxide dismutase, which catalysed the removal of superoxide anion generated during autoxidation of haemoglobin. Possible mechanisms underlying the relation between the conformational change of haemoglobin due to its interaction with haematoporphyrin and the enhanced peroxidase activity are discussed.

The hydroxypyridinone iron chelator CP94 can enhance PpIX-induced PDT of cultured human glioma cells

Photodynamic therapy (PDT) with the pro-drugs 5-aminolevulinic acid (ALA) or methyl aminolevulinate (MAL) utilizes the combined interaction of a photosensitizer, light and molecular oxygen to ablate tumor tissue. To potentially increase accumulation of the photosensitizer, protoporphyrin IX (PpIX), within tumor cells an iron chelator can be employed. This study analyzed the effects of ALA/MAL-induced PDT combined with the iron chelator 1, 2-diethyl-3-hydroxypyridin-4-one hydrochloride (CP94) on the accumulation of PpIX in human glioma cells in vitro. Cells were incubated for 0, 3 and 6h with various concentrations of ALA/MAL with or without CP94 and the resulting accumulations of PpIX, which naturally fluoresces, were quantified prior to and following light irradiation. In addition, counts of viable cells were recorded. The use of CP94 in combination with ALA/MAL produced significant enhancements of PpIX fluorescence in human glioma cells. At the highest concentrations of each prodrug, CP94 enhanced PpIX fluorescence significantly at 3h for ALA and by more than 50% at 6h for MAL. Cells subsequently treated with ALA/MAL-induced PDT in combination with CP94 produced the greatest cytotoxicity. It is therefore concluded that with further study CP94 may be a useful adjuvant to photodiagnosis and/or PpIX-induced PDT treatment of glioma.

Quantification of in vivo fluorescence decoupled from the effects of tissue optical properties using fiber-optic spectroscopy measurements

We present a method for tissue fluorescence quantification in situ using a handheld fiber optic probe that measures both the fluorescence and diffuse reflectance spectra. A simplified method to decouple the fluorescence spectrum from distorting effects of the tissue optical absorption and scattering is developed, with the objective of accurately quantifying the fluorescence in absolute units. The primary motivation is measurement of 5-aminolevulinic acid-induced protoporphyrin IX (ALA-PpIX) concentration in tissue during fluorescence-guided resection of malignant brain tumors. This technique is validated in phantoms and ex vivo mouse tissues, and tested in vivo in a rabbit brain tumor model using ALA-PpIX fluorescence contrast.

Site-specific opening of the blood-brain barrier

The blood-brain barrier (BBB) poses a significant impediment for the delivery of therapeutic drugs into the brain. This is particularly problematic for the treatment of malignant gliomas which are characterized by diffuse infiltration of tumor cells into normal brain where they are protected by a patent BBB. Selective disruption of the BBB, followed by administration of anti-cancer agents, represents a promising approach for the elimination of infiltrating glioma cells. A summary of the techniques (focused ultrasound, photodynamic therapy and photochemical internalization) for site-specific opening of the BBB will be discussed in this review. Each approach is capable of causing localized and transient opening of the BBB with minimal damage to surrounding normal brain as evidenced from magnetic resonance images and histology.

The effects of ultra low fluence rate single and repetitive photodynamic therapy on glioma spheroids

BACKGROUND AND OBJECTIVE

Achieving local control of gliomas with photodynamic therapy (PDT) requires the delivery of adequate light fluences to depths of 1-2 cm in the resection margin where the majority of local recurrences originate. This is clinically impractical with current single-shot, intraoperative PDT treatments due to the length of time required to deliver adequate fluences. Multiple or extended treatment protocols would therefore seem to be required. The response of human glioma spheroids to 5-aminolevulinic acid (ALA)-mediated PDT using single or, repetitive light delivery protocols was investigated at both low and ultra low fluence rates.

STUDY DESIGN/MATERIALS AND METHODS

Human glioma spheroids (400 microm diameter) were subjected to sub-threshold light fluence (1.5, 3, or 6 J cm(-2)) ALA-PDT consisting of four light delivery schemes: single treatment given over either 1 or 24 hours, repetitive treatment given either as four 1 hour light treatments separated by a 4 day interval, or 24 hours light delivery, consisting of four 24 hours treatments separated by a 3 day interval. Treatment efficacy was evaluated using a growth assay. In some cases, confocal microscopy was used to image cell viability.

RESULTS

The repetitive and single light treatment protocols were most effective when delivered at ultra low (microW cm(-2)) fluence rates. In all cases, growth inhibition was light dose-dependent. The repetitive ultra low fluence rate treatment (1.5 J cm(-2); irradiance = 17 microW cm(-2)) light delivery protocol was the most effective resulting in total growth inhibition during the 2-week observation period.

CONCLUSION

Ultra low light fluence rate ALA-PDT results in significant spheroid growth inhibition. Repeated administration of ALA was required during repetitive and/or protracted single PDT treatment protocols. The existence of a lower fluence rate limit, below which the efficacy of threshold light fluences diminish was not found in these studies. Lasers Surg. Med. 41:578-584, 2009. (c) 2009 Wiley-Liss, Inc.

Three-dimensional fluence rate measurement and data acquisition system for minimally invasive light therapies

Light based therapies such as photodynamic therapy are in need of advanced tools for light fluence rate dosimetry and monitoring within the context of therapy planning and light delivery to ensure maximum treatment efficacy. The use of a single, multisensor fiber-based fluorescent probe capable of performing spatially resolved fluence rate measurements along an axis was demonstrated. This work extends the previous technique and describes a fluence rate quantification system able to employ up to 12 multisensor probes to simultaneously measure fluence rate distribution throughout a 3D treatment volume. The system optoelectronics provides for sensor calibration, data acquisition, and weighted least-squares processing to extract localized fluence rate information in real-time. Core components include an integrating cylinder for source sensor calibration, a 2D back thin CCD detector for sensor signal detection from multiple probes, high-speed data acquisition card, and custom software for real-time extraction of fluence rate information from all sensors.

Interactive transport, subcellular relocation and enhanced phototoxicity of hypericin encapsulated in guanidinylated liposomes via molecular recognition

Hypericin (HYP), a photocytotoxic phenanthroperylenquinone was encapsulated in liposomes outfitted with guanidinium-bearing lipids to ensure efficient cell binding through molecular recognition with anionic groups resident on the plasma membrane. The uptake of HYP encapsulated in these liposomes by DU145 human prostate cancer cells, was studied employing fluorescence, versus nonguadinylated liposomes and free HYP. The subcellular localization was in all cases studied by confocal microscopy employing specific subcellular organelle probes. The photocytotoxicity of HYP was assessed, 24 h following irradiation with 15 mWcm(-2) light through a GG 495 Schott filter, by a standard tetrazolium to formazan assay (XTT). HYP uptake by DU145 cells was found to be profoundly enhanced by using guanidinylated liposomes. Also the distance of the guanidinium group from the liposomal surface was found to significantly affect HYP loading, subcellular localization and phototoxicity. The two different modes of liposome cell internalization observed, i.e. plasma membrane fusion and endocytosis, were found to greatly affect the phototoxicity of HYP. Molecular recognition was overall appraised as a promising, novel route for photodynamic therapy, profoundly enhancing its efficacy. HYP encapsulated in liposomes-bearing guanidinium groups was more efficiently taken up by cells, leading to enhanced phototoxicity, in contrast to HYP encapsulated in their nonguanidinylated counterparts.

Photodynamic therapy with intratumoral administration of Lipid-Based mTHPC in a model of breast cancer recurrence

BACKGROUND AND OBJECTIVES

Generalized skin sensitization is a main drawback of photodynamic therapy with systemic administration of photosensitizers. We have evaluated the potential use of an intratumoral injection of a liposomal formulation of mTHPC (Foslip) in a mouse model of local recurrence of breast cancer.

MATERIALS AND METHODS

Mice were directly injected into the tumor (IT) with 25 microl of a Foslip suspension (0.15 mg/ml) and illumination (652 nm, 20 J/cm(2)) was performed at different time points with pathological assessment after 48 hours. In a parallel mice series plasma samples were obtained at different endpoints after IT Foslip injection for HPLC analysis and the tumors were subjected in toto to macrofluorescence imaging. Fluorescence polarization measurements were conducted in vitro to estimate the rate of sensitizer redistribution from liposomes.

RESULTS

Optimal, albeit partial, cure rates were obtained at 24 hours post-sensitizer and uninistration. Inhomogeneous and weak fluorescence was observed at early time points and became maximal at 24 hours. Plasma levels of mTHPC increased until 15 hours. Fluorescence polarization measurements showed a slow sensitizer transfer from liposomes to model membranes.

DISCUSSION AND CONCLUSION

The weak intratumoral fluorescence at early time points could be explained by concentration quenching within the liposomes as evidenced from fluorescence polarization studies. Progressive mTHPC redistribution from liposomes and its further incorporation into tumor tissue resulted in fluorescence build-up over time with a maximum at 24 hours post-injection. This correlates perfectly with the best therapeutic effect at this time point. The absence of total cure can be attributed to inhomogeneous photosensitizer distribution. mTHPC is reabsorbed into the blood stream but the total administered amount is much reduced as opposed to systemic administration so that repeated PDT sessions might be favorable in terms of side effects and tumor response.

Motexafin gadolinium enhances the efficacy of aminolevulinic acid mediated-photodynamic therapy in human glioma spheroids

Photodynamic therapy (PDT) has been investigated as a postoperative treatment in patients with high grade gliomas. The purpose of this in vitro investigation was to determine whether motexafin gadolinium (MGd), a known radiation sensitizer, could potentiate the effects of 5-aminolevulinic acid (ALA)-PDT. Human glioma (ACBT) spheroids (250 microm diameter) were incubated in 5-aminolevulinic acid (ALA) with and without MGd and irradiated with 635 nm light for a total light fluence of 6, 12, or 18 J cm(-2) delivered at a fluence rate of 5 mW cm(-2). Spheroid growth was monitored for a period of 4 weeks following each treatment. In another set of experiments, 400-500 microm diameter ACBT spheroids were implanted into a gel collagen matrix and subjected to ALA-PDT (fluence: 3 or 6 J cm(-2)), MGd, or a combination of ALA-PDT and MGd. The migration distance of surviving glioma cells in each treatment group was recorded over a 5-day period. The results showed that MGd interacted with PDT in a synergistic manner resulting in greater cytotoxicity than that achievable with either treatment modality alone. The degree of synergism was shown to increase with increasing light fluence. At the highest light fluence investigated (18 J cm(-2)), the percentage of spheroids demonstrating growth 4 weeks following exposure to MGd, ALA-PDT, or MGd + ALA-PDT was 100%, 75%, and 15%, respectively. The results of cell migration studies revealed that the combination of PDT and MGd produced a significant inhibitory effect on glioma cell migration: the addition of MGd resulted in an approximately three times reduction in migration distance compared with PDT alone. Overall, the results suggest that MGd can potentiate both the cytotoxic and migration inhibitory effects of ALA-PDT and hence, this combined therapeutic approach has the potential to extend treatment volumes in patients with malignant gliomas.

A Ratiometric Fluorescence Imaging System for Surgical Guidance

A 3-chip CCD imaging system has been developed for quantitative in vivo fluorescence imaging. This incorporates a ratiometric algorithm to correct for the effects of tissue optical absorption and scattering, imaging “geometry” and tissue autofluorescence background. The performance was characterized, and the algorithm was validated in tissue-simulating optical phantoms for quantitative measurement of the fluorescent molecule protoporphyrin IX (PpIX). The technical feasibility to use this system for fluorescence-guided surgical resection of malignant brain tumor tissue was assessed in an animal model in which PpIX was induced exogenously in the tumor cells by systemic administration of aminolevulinic acid (ALA).

Photodynamic therapy of vertebral metastases: evaluating tumor-to-neural tissue uptake of BPD-MA and ALA-PpIX in a murine model of metastatic human breast carcinoma

Photodynamic therapy has been successfully applied to numerous cancers. Its potential to treat cancer metastases in the spine has been demonstrated previously in a preclinical animal model. The aim of this study was to test two photosensitizers, benzoporphyrin-derivative monoacid ring A (BPD-MA) and by 5-aminolevulinic acid (5-ALA)-induced protoporphyrin IX (PpIX), for their potential use to treat bony metastases. The difference in photosensitizer concentration in the spinal cord and the surrounding tumor-bearing vertebrae was of particular interest to assess the risk of potential collateral damage to the spinal cord. Vertebral metastases in a rat model were generated by intracardiac injection of human breast cancer cells. When tumor growth was confirmed, photosensitizers were injected systemically and the animals were euthanized at different time points. The following tissues were harvested: liver, kidney, ovaries, appendicular bone, spinal cord and lumbar vertebrae. Photosensitizer tissue concentration of BPD-MA or PpIX was determined by fluorescence spectrophotometry. In contrast to BPD-MA, ALA-PpIX did not demonstrate an appreciable difference in the uptake ratio in tumor-bearing vertebrae compared to spinal cord. The highest ratio for BPD-MA concentration was found 15 min after injection, which can be recommended for therapy in this model.

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.

Subclinical photodynamic therapy treatment modifies the brain microenvironment and promotes glioma growth

Photodynamic therapy (PDT) has been clinically investigated as an adjuvant local therapy for brain tumors. Therapeutic interventions intended to promote tumor cell death can also promote changes in the tumor microenvironment that could favor tumor growth. We have previously shown that PDT can activate pro-angiogenic factors in the normal rodent brain. This study seeks to further elucidate the effects of subtherapeutic doses of Photofrin-PDT on normal brain and to establish a mouse model for studying glioma progression in an environment modified by oxidative stress. Photofrin was administered to nude mice, and a defined intracranial area was illuminated with laser to deliver an optical dose equivalent to 80 J/cm(2). Three and 7 days after PDT, mice were sacrificed and brains were fixed and analyzed by immunohistochemistry. PDT treatment resulted in transient increase in cell proliferation, associated with a robust activation of astrocytes and microglia in the treated region, without causing substantial cell death. To test how this modified environment would affect glioma growth, human glioblastoma U87 cells were implanted in the PDT-treated hemisphere or in the control brain subjected to sham surgery. Significantly larger tumors were observed after 3 weeks in the PDT treated brains relative to control treatment. Our results indicate that subclinical Photofrin-PDT locally alters the brain homeostasis without inflicting significant disruption to the tissue architecture, providing a model to study the effects of the microenvironment on glioma growth, with implications for the optimization of the clinical use of PDT for brain tumors.

Interstitial in vivo ALA-PpIX mediated metronomic photodynamic therapy (mPDT) using the CNS-1 astrocytoma with bioluminescence monitoring

BACKGROUND

We report the first truly metronomic delivery of photodynamic therapy using the rat-derived CNS-1 astrocytoma, a model with close histopathology with human brain tumours.

METHODS

Metronomic PDT (mPDT) was delivered to CNS-1 bearing female Lewis rats. 5-Aminoluvelinic acid was delivered continuously through drinking water, while light was delivered via tetherless, light-weight, LED-based fiber coupled optical sources. Tumour burden before and after mPDT treatment was determined using bioluminescence imaging (BLI).

RESULTS

Preliminary studies demonstrated that 24h of continuous mPDT illumination was capable of destroying small tumours (7 days post-implant). The reduction or elimination of tumour was confirmed using BLI and corroborated by histology. Additional studies showed that 24 and 48h continuous mPDT illumination had the capability to delay tumour re-growth by a period corresponding to approximately two doubling times. Animals given 4-day mPDT did not show any signs of tumour re-growth via BLI at 26 days post-tumour implantation.

CONCLUSIONS

In summary, these results demonstrate the feasibility of delivering mPDT for extended periods, as well as its potential as a treatment for small brain tumours.