Specific intensity imaging for glioblastoma and neural cell cultures with 5-aminolevulinic acid-derived protoporphyrin IX

Localization of protoporphyrin IX during glioma-resection surgery via paired stimulated Raman histology and fluorescence microscopy

The most widely used fluorophore in glioma-resection surgery, 5-aminolevulinic acid (5-ALA), is thought to cause the selective accumulation of fluorescent protoporphyrin IX (PpIX) in tumour cells. Here we show that the clinical detection of PpIX can be improved via a microscope that performs paired stimulated Raman histology and two-photon excitation fluorescence microscopy (TPEF). We validated the technique in fresh tumour specimens from 115 patients with high-grade gliomas across four medical institutions. We found a weak negative correlation between tissue cellularity and the fluorescence intensity of PpIX across all imaged specimens. Semi-supervised clustering of the TPEF images revealed five distinct patterns of PpIX fluorescence, and spatial transcriptomic analyses of the imaged tissue showed that myeloid cells predominate in areas where PpIX accumulates in the intracellular space. Further analysis of external spatially resolved metabolomics, transcriptomics and RNA-sequencing datasets from glioblastoma specimens confirmed that myeloid cells preferentially accumulate and metabolize PpIX. Our findings question 5-ALA-induced fluorescence in glioma cells and show how 5-ALA and TPEF imaging can provide a window into the immune microenvironment of gliomas.

Glioblastoma Multiforme: The Latest Diagnostics and Treatment Techniques

BACKGROUND

Glioblastoma multiforme (GBM) is a WHO grade 4 glioma and the most common malignant primary brain tumour. Recently, there has been outstanding progress in the treatment of GBM. In addition to the newest form of GBM removal using fluorescence, three-dimensional (3D) imaging, tomoradiotherapy, moderate electro-hyperthermia, and adjuvant temozolomide (post-operative chemotherapy), new developments have been made in the fields of immunology, molecular biology, and virotherapy. An unusual and modern treatment has been created, especially for stage 4 GBM, using the latest therapeutic techniques, including immunotherapy and virotherapy. Modern oncological medicine is producing extraordinary and progressive therapeutic methods. Oncological therapy includes individual analysis of the properties of a tumour and targeted therapy using small-molecule inhibitors. Individualised medicine covers the entire patient (tumour and host) in the context of immunotherapy. An example is individualised multimodal immunotherapy (IMI), which relies on individual immunological tumour-host interactions. In addition, IMI is based on the concept of oncolytic virus-induced immunogenic tumour cell death.

SUMMARY

In this review, we outline current knowledge of the various available treatment options used in the therapy of GBM including both traditional therapeutic strategy and modern therapies, such as tomotherapy, electro-hyperthermia, and oncolytic virotherapy, which are promising treatment strategies with the potential to improve prognosis in patients with GBM.

KEY MESSAGES

This newest therapy, immunotherapy combined with virotherapy (oncolytic viruses and cancer vaccines), is displaying encouraging signs for combating GBM. Additionally, the latest 3D imaging is compared to conventional two-dimensional imaging.

A review on surgical treatment options in gliomas

Gliomas are one of the most common primary central nervous system tumors, and surgical treatment remains the principal role in the management of any grade of gliomas. In this study, based on the introduction of gliomas, we review the novel surgical techniques and technologies in support of the extent of resection to achieve long-term disease control and summarize the findings on how to keep the balance between cytoreduction and neurological morbidity from a list of literature searched. With modern neurosurgical techniques, gliomas resection can be safely performed with low morbidity and extraordinary long-term functional outcomes.

Utility of 5-ALA for resection of CNS tumours other than high-grade gliomas: a protocol for a systematic review

INTRODUCTION

5-aminolevulinic acid (5-ALA) is a proagent developed for fluorescent-guided surgery for high-grade glioma patients associated with a significant increase in resection conferring survival. 5-ALA was shown to penetrate the blood-brain barrier accumulating in malignant glioma cells with high selectivity, sensitivity and positive predictive value. However, those have yet to be explored aiding diagnosis for tumours of the central nervous system (CNS) other than high-grade gliomas (HGG). No up-to-date systematic review exists reporting the major surgical outcomes and diagnostic accuracy. We sought to conduct a systematic review of the literature summarising surgical outcomes, evaluate the quality of diagnostic accuracy reported in the literature and qualitatively assess the evidence to inform future studies.

METHODS AND ANALYSIS

We will search electronic databases (Medline, Embase) with subsequent interrogation of references lists of articles reporting the use of 5-ALA for brain tumours other than high-grade glioma adult patients, which also report the extent of resection and/or survival. Prospective and retrospective cohort and case-control studies with more than five patients will be included. Two independent reviewers will screen the abstracts and full articles, with a third reviewer resolving any conflicts. The data will be extracted in a standardised template and outcomes will be reported using descriptive statists. The quality of non-randomised studies will be appraised.

ETHICS AND DISSEMINATION

The study will summarise the available evidence on the effect of the clinical utility of 5-ALA in achieving resection and improving survival and its diagnostic accuracy for tumours of the CNS other than HGG. The data will be presented nationally and internationally and the manuscript will be published in a peer-reviewed journal. No ethical approvals were needed. The aim is to inform prospective studies minimising reporting bias allowing for more reliable, reproducible and generalisable results. The study has been registered in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.PROSPERO registration numberCRD42021260542.

The Evolution of 5-Aminolevulinic Acid Fluorescence Visualization: Time for a Headlamp/Loupe Combination

BACKGROUND

The use of 5-ALA for intraoperative protoporphyrin IX (PpIX) fluorescent imaging in the resection of malignant gliomas has been demonstrated to improve tumor visualization, increase extent of resection, and extend progression-free survival. The current technique for visualization of 5-ALA consists of excitation and emission filters built into the operating microscope. However, there are notable limitations to this process, including low quantum yield, expense, and masking of surrounding anatomy.

METHODS

We present three cases in which three separate methods were employed for visualizing fluorescence. The devices reported are 1) a low-cost blue light flashlight and 2) a low-cost headlamp, and 3) the first reported case of the new Design for Vision® REVEAL™ FGS (Fluorescence Guided Surgery) 5-ALA fluorescent headlight and loupes. The aim of the study is to provide confirmation that tumor fluorescence can be observed using commercially-available products other than the microscope.

RESULTS

We demonstrate through three intraoperative cases that a variety of devices can produce visible fluorescence of the high-grade tumor and allow for simultaneous real-time visualization of the adjacent brain parenchyma and vasculature. The REVEAL™ FGS system appears to offer increased fluorescence emission compared to all other methods, including the microscope.

CONCLUSIONS

Our study demonstrates the feasibility of using blue/ultraviolet light supplied by a commercially available, inexpensive flashlight or headlamp to visualize 5-ALA fluorescence in high-grade gliomas. We also provide the first documentation of intraoperative use of the new Design for Vision® REVEAL™ FGS 5-ALA fluorescent headlight and loupes and report on the experience. Lack of an operative microscope capable of fluorescent illumination should not be a limiting factor in performing fluorescent-guided glioma resection.

Association of 5-aminolevulinic acid with intraoperative hypotension in malignant glioma surgery

BACKGROUND

Use of 5-aminolevulinic acid for photodynamic malignant tumor diagnosis reportedly causes intraoperative hypotension (systolic blood pressure < 70 mmHg) during urologic surgery. However, its association with intraoperative hypotension in malignant glioma surgery and underlying mechanisms has not yet been elucidated.. This study aimed to investigate whether 5-aminolevulinic acid administration is associated with intraoperative hypotension in malignant glioma surgery and explore the mechanisms of 5-aminolevulinic acid-induced hypotension in vitro.

METHODS

In this retrospective multicenter cohort study, we investigated intracellular nitric oxide as a candidate mediator of hypotension in response to 5-aminolevulinic acid in vitro in human umbilical vein endothelial cell cultures.

RESULTS

Of 142 patients, 94 underwent 5-aminolevulinic acid-guided surgery. Systolic blood pressure was significantly lower throughout surgery with 5-aminolevulinic acid administration. 5-Aminolevulinic acid administration was an independent risk factor for intraoperative hypotension according to multivariable logistic regression analysis (89% vs. 56%; odds ratio = 6.72, 95% confidence interval [2.05-22.1], P = 002). In subgroup analysis of the 5-aminolevulinic acid group, increasing age and use of renin-angiotensin system inhibitors had a synergistic effect with 5-aminolevulinic acid on decreased blood pressure. In the vascular endothelial cell culture study, 5-aminolevulinic acid induced a significant increase in intracellular nitric oxide generation.

CONCLUSIONS

5-Aminolevulinic acid administration was associated with intraoperative hypotension in malignant glioma surgery, with increasing age and use of renin-angiotensin system inhibitors boosting the blood pressure-lowering effect of 5-aminolevulinic acid. According to in vitro results, the low blood pressure induced by 5-aminolevulinic acid may be mediated by a nitric oxide increase in vascular endothelial cells.

Characteristics of Fluorescent Intraoperative Dyes Helpful in Gross Total Resection of High-Grade Gliomas-A Systematic Review

Background: A very important aspect in the treatment of high-grade glioma is gross total resection to reduce the risk of tumor recurrence. One of the methods to facilitate this task is intraoperative fluorescence navigation. The aim of the study was to compare the dyes used in this technique fluorescent intraoperative navigation in terms of the mechanism of action and influence on the treatment of patients. Methods: The review was carried out on the basis of articles found in PubMed, Google Scholar, and BMC search engines, as well as those identified by searched bibliographies and suggested by experts during the preparation of the article. The database analysis was performed for the following phrases: "glioma", "glioblastoma", "ALA", "5ALA", "5-ALA", "aminolevulinic acid", "levulinic acid", "fluorescein", "ICG", "indocyanine green", and "fluorescence navigation". Results: After analyzing 913 citations identified on the basis of the search criteria, we included 36 studies in the review. On the basis of the analyzed articles, we found that 5-aminolevulinic acid and fluorescein are highly effective in improving the percentage of gross total resection achieved in high-grade glioma surgery. At the same time, the limitations resulting from the use of these methods are marked-higher costs of the procedure and the need to have neurosurgical microscope in combination with a special light filter in the case of 5-aminolevulinic acid (5-ALA), and low specificity for neoplastic cells and the dependence on the degree of damage to the blood-brain barrier in the intensity of fluorescence in the case of fluorescein. The use of indocyanine green in the visualization of glioma cells is relatively unknown, but some researchers have suggested its utility and the benefits of using it simultaneously with other dyes. Conclusion: The use of intraoperative fluorescence navigation with the use of 5-aminolevulinic acid and fluorescein allows the range of high-grade glioma resection to be increased.

Mathematical morphology-based imaging of gastrointestinal cancer cell motility and 5-aminolevulinic acid-induced fluorescence

The aim of this study was the quantitative evaluation of gastrointestinal cancer cell motility and 5-aminolevulinic acid (5-ALA)-induced fluorescence in vitro using mathematical morphology and structural analysis methods. The results of our study showed that MKN28 cells derived from the lymph node have the highest motility compared with AGS or HCT116 cells derived from primary tumors. Regions of single cells were characterized as most moving, and "tightly packed" cell colonies as nearly immobile. We determined the reduction of cell motility in late passage compared to early passage. Application of 5-ALA caused fluorescence in all investigated cells, and the fluorescence was different with regard to the cell type and application time. We observed higher fluorescence in MKN28 cells. Comprehensive image analysis did not reveal any statistically significant difference in fluorescence intensity between "tightly packed" cell regions, where nearly no motility was registered and loosely distributed cells, where the highest cell motility was registered. In conclusions, our study revealed that MKN28 cells derived from the lymph node have higher motility and 5-ALA-induced fluorescence than AGS or HCT116 derived from primary tumors. Moreover, image analysis based on a large amount of processed data is an important tool to study these tumor cell properties.

Toward Quantitative Neurosurgical Guidance With High-Resolution Microscopy of 5-Aminolevulinic Acid-Induced Protoporphyrin IX

Low-power fluorescence microscopy of 5-ALA-induced PpIX has emerged as a valuable intraoperative imaging technology for improving the resection of malignant gliomas. However, current fluorescence imaging tools are not highly sensitive nor quantitative, which limits their effectiveness for optimizing operative decisions near the surgical margins of gliomas, in particular non-enhancing low-grade gliomas. Intraoperative high-resolution optical-sectioning microscopy can potentially serve as a valuable complement to low-power fluorescence microscopy by providing reproducible quantification of tumor parameters at the infiltrative margins of diffuse gliomas. In this forward-looking perspective article, we provide a brief discussion of recent technical advancements, pilot clinical studies, and our vision of the future adoption of handheld optical-sectioning microscopy at the final stages of glioma surgeries to enhance the extent of resection. We list a number of challenges for clinical acceptance, as well as potential strategies to overcome such obstacles for the surgical implementation of these in vivo microscopy techniques.

How to Build a Neurosurgical Oncology Practice Specializing in Gliomas

For the neurosurgical oncologist, a specialty practice in gliomas represents an intersection of tailored surgical approaches, emerging intraoperative technologies, expanding surgical trial portfolios, and new paradigms in glioma biology. Assembling these disparate pieces into a cohesive career trajectory is a difficult task but ultimately enables the subspecialist to navigate all domains relevant to improving glioma patient outcomes. Within the larger clinical and basic science community, thoughtful integration and intensive collaborations are essential mechanisms when building a multidisciplinary glioma program.

Optical-sectioning microscopy of protoporphyrin IX fluorescence in human gliomas: standardization and quantitative comparison with histology

Systemic delivery of 5-aminolevulinic acid leads to enhanced fluorescence image contrast in many tumors due to the increased accumulation of protoporphyrin IX (PpIX), a fluorescent porphyrin that is associated with tumor burden and proliferation. The value of PpIX-guided resection of malignant gliomas has been demonstrated in prospective randomized clinical studies in which a twofold greater extent of resection and improved progression-free survival have been observed. In low-grade gliomas and at the diffuse infiltrative margins of all gliomas, PpIX fluorescence is often too weak to be detected with current low-resolution surgical microscopes that are used in operating rooms. However, it has been demonstrated that high-resolution optical-sectioning microscopes are capable of detecting the sparse and punctate accumulations of PpIX that are undetectable via conventional low-power surgical fluorescence microscopes. To standardize the performance of high-resolution optical-sectioning devices for future clinical use, we have developed an imaging phantom and methods to ensure that the imaging of PpIX-expressing brain tissues can be performed reproducibly. Ex vivo imaging studies with a dual-axis confocal microscope demonstrate that these methods enable the acquisition of images from unsectioned human brain tissues that quantitatively and consistently correlate with images of histologically processed tissue sections.

What is the Surgical Benefit of Utilizing 5-Aminolevulinic Acid for Fluorescence-Guided Surgery of Malignant Gliomas?

The current neurosurgical goal for patients with malignant gliomas is maximal safe resection of the contrast-enhancing tumor. However, a complete resection of the contrast-enhancing tumor is achieved only in a minority of patients. One reason for this limitation is the difficulty in distinguishing viable tumor from normal adjacent brain during surgery at the tumor margin using conventional white-light microscopy. To overcome this limitation, fluorescence-guided surgery (FGS) using 5-aminolevulinic acid (5-ALA) has been introduced in the treatment of malignant gliomas. FGS permits the intraoperative visualization of malignant glioma tissue and supports the neurosurgeon with real-time guidance for differentiating tumor from normal brain that is independent of neuronavigation and brain shift. Tissue fluorescence after oral administration of 5-ALA is associated with unprecedented high sensitivity, specificity, and positive predictive values for identifying malignant glioma tumor tissue. 5-ALA-induced tumor fluorescence in diffusely infiltrating gliomas with non-significant magnetic resonance imaging contrast-enhancement permits intraoperative identification of anaplastic foci and establishment of an accurate histopathological diagnosis for proper adjuvant treatment. 5-ALA FGS has enabled surgeons to achieve a significantly higher rate of complete resections of malignant gliomas in comparison with conventional white-light resections. Consequently, 5-ALA FGS has become an indispensable surgical technique and standard of care at many neurosurgical departments around the world. We conducted an extensive literature review concerning the surgical benefit of using 5-ALA for FGS of malignant gliomas. According to the literature, there are a number of reasons for the neurosurgeon to perform 5-ALA FGS, which will be discussed in detail in the current review.

The role of 5-aminolevulinic acid in enhancing surgery for high-grade glioma, its current boundaries, and future perspectives: A systematic review

5-Aminolevulinic acid (5-ALA) has been approved as an intraoperative adjunct in glioma surgery in Europe, but not North America. A systematic review was conducted to assess the evidence regarding 5-ALA as a surgical adjunct. The MEDLINE, EMBASE, and CENTRAL databases were searched, using terms relevant to "5-ALA" and "high-grade gliomas." Included studies were based on adults aged ≥18 years who underwent surgical resection/biopsy. No language or date limitations were used. Forty-three studies (1830 patients) were identified. Thirty-six were coordinated by European countries, 2 were in the United States, and none were in Canada. One was randomized, 28 were prospective, and 14 were retrospective. Twenty-six studies assessed the utility of 5-ALA as a diagnostic tool, 24 assessed its influence on the extent of resection (EOR), 9 assessed survival, and 22 reported adverse events. 5-ALA had high sensitivity and positive predictive value, whereas its specificity increased with additional adjuncts. The EOR increased with 5-ALA, but only progression-free survival was significantly influenced. Reporting of adverse events was not systematic. The use of 5-ALA improved tumor visualization and thus enabled a greater EOR and perhaps increased survival. However, additional adjuncts may be necessary for maximizing the specificity of resection and patient safety. Additional parameters, such as patient quality of life and health economic analyses, would be informative. Thus, additional systematic collection of prospective evidence may be necessary for the global incorporation of this potentially valuable surgical adjunct into routine practice. Cancer 2016;122:2469-78. © 2016 American Cancer Society.

Intraoperative Spectroscopy with Ultrahigh Sensitivity for Image-Guided Surgery of Malignant Brain Tumors

Intraoperative cancer imaging and fluorescence-guided surgery have attracted considerable interest because fluorescence signals can provide real-time guidance to assist a surgeon in differentiating cancerous and normal tissues. Recent advances have led to the clinical use of a natural fluorophore called protoporphyrin IX (PpIX) for image-guided surgical resection of high-grade brain tumors (glioblastomas). However, traditional fluorescence imaging methods have only limited detection sensitivity and identification accuracy and are unable to detect low-grade or diffuse infiltrating gliomas (DIGs). Here we report a low-cost hand-held spectroscopic device that is capable of ultrasensitive detection of protoporphyrin IX fluorescence in vivo, together with intraoperative spectroscopic data obtained from both animal xenografts and human brain tumor specimens. The results indicate that intraoperative spectroscopy is at least 3 orders of magnitude more sensitive than the current surgical microscopes, allowing ultrasensitive detection of as few as 1000 tumor cells. For detection specificity, intraoperative spectroscopy allows the differentiation of brain tumor cells from normal brain cells with a contrast signal ratio over 100. In vivo animal studies reveal that protoporphyrin IX fluorescence is strongly correlated with both MRI and histological staining, confirming that the fluorescence signals are highly specific to tumor cells. Furthermore, ex vivo spectroscopic studies of excised brain tissues demonstrate that the hand-held spectroscopic device is capable of detecting diffuse tumor margins with low fluorescence contrast that are not detectable with current systems in the operating room. These results open new opportunities for intraoperative detection and fluorescence-guided resection of microscopic and low-grade glioma brain tumors with invasive or diffusive margins.

Trends in fluorescence image-guided surgery for gliomas

Mounting evidence suggests that a more extensive surgical resection is associated with an improved life expectancy for both low-grade and high-grade glioma patients. However, radiographically complete resections are not often achieved in many cases because of the lack of sensitivity and specificity of current neurosurgical guidance techniques at the margins of diffuse infiltrative gliomas. Intraoperative fluorescence imaging offers the potential to improve the extent of resection and to investigate the possible benefits of resecting beyond the radiographic margins. Here, we provide a review of wide-field and high-resolution fluorescence-imaging strategies that are being developed for neurosurgical guidance, with a focus on emerging imaging technologies and clinically viable contrast agents. The strengths and weaknesses of these approaches will be discussed, as well as issues that are being addressed to translate these technologies into the standard of care.

Comparing high-resolution microscopy techniques for potential intraoperative use in guiding low-grade glioma resections

BACKGROUND AND OBJECTIVES

Fluorescence image-guided surgery (FIGS), with contrast provided by 5-ALA-induced PpIX, has been shown to enable a higher extent of resection of high-grade gliomas. However, conventional FIGS with low-power microscopy lacks the sensitivity to aid in low-grade glioma (LGG) resection because PpIX signal is weak and sparse in such tissues. Intraoperative high-resolution microscopy of PpIX fluorescence has been proposed as a method to guide LGG resection, where sub-cellular resolution allows for the visualization of sparse and punctate mitochondrial PpIX production in tumor cells. Here, we assess the performance of three potentially portable high-resolution microscopy techniques that may be used for the intraoperative imaging of human LGG tissue samples with PpIX contrast: high-resolution fiber-optic microscopy (HRFM), high-resolution wide-field microscopy (WFM), and dual-axis confocal (DAC) microscopy.

MATERIALS AND METHODS

Thick unsectioned human LGG tissue samples (n = 7) with 5-ALA-induced PpIX contrast were imaged using three imaging techniques (HRFM, WFM, DAC). The average signal-to-background ratio (SBR) was then calculated for each imaging modality (5 images per tissue, per modality).

RESULTS

HRFM provides the ease of use and portability of a flexible fiber bundle, and is simple and inexpensive to build. However, in most cases (6/7), HRFM is not capable of detecting PpIX signal from LGGs due to high autofluorescence, generated by the fiber bundle under laser illumination at 405 nm, which overwhelms the PpIX signal and impedes its visualization. WFM is a camera-based method possessing high lateral resolution but poor axial resolution, resulting in sub-optimal image contrast.

CONCLUSIONS

Consistent successful detection of PpIX signal throughout our human LGG tissue samples (n = 7), with an acceptable image contrast (SBR >2), was only achieved using DAC microscopy, which offers superior image resolution and contrast that is comparable to histology, but requires a laser-scanning mechanism to achieve optical sectioning.

Intraoperative 5-aminolevulinic acid-induced fluorescence in primary central nervous system lymphoma

The authors report a case of primary CNS lymphoma located in the floor of the fourth ventricle that showed intense fluorescence after preoperative administration of 5-aminolevulinic acid. The authors believe that this is the first demonstration of a 5-aminolevulinic acid-induced fluorescence pattern in primary CNS lymphoma.

Intraoperative fluorescence-guided resection of high-grade malignant gliomas using 5-aminolevulinic acid-induced porphyrins: a systematic review and meta-analysis of prospective studies

Background

We performed a systematic review and meta-analysis to address the (added) value of intraoperative 5-aminolevulinic acid (5-ALA)-guided resection of high-grade malignant gliomas compared with conventional neuronavigation-guided resection, with respect to diagnostic accuracy, extent of tumor resection, safety, and survival.

Methods and Findings

An electronic database search of Medline, Embase, and the Cochrane Library was undertaken. The review process followed the guidelines of the Cochrane Collaboration. 10 studies matched all selection criteria, and were thus used for qualitative synthesis. 5-ALA-guided resection demonstrated an overall sensitivity of 0.87 (95% confidence interval [CI], 0.81–0.92), specificity of 0.89 (95% CI, 0.79–0.94), positive likelihood ratio (LR) of 7.62 (95% CI, 3.87–15.01), negative LR of 0.14 (95% CI, 0.09–0.23), and diagnostic odds ratio (OR) of 53.06 (95% CI, 18.70–150.51). Summary receiver operating characteristic curves (SROC) showed an area under curve (AUC) of 94%. Contrast-enhancing tumor was completely resected in patients assigned 5-ALA as compared with patients assigned white light. Patients in the 5-ALA group had higher 6-month progression free survival and overall survival than those in the white light group.

Conclusion

Based on available literature, there is level 2 evidence that 5-ALA-guided surgery is more effective than conventional neuronavigation-guided surgery in increasing diagnostic accuracy and extent of tumor resection, enhancing quality of life, or prolonging survival in patients with high-grade malignant gliomas.

Emerging operative strategies in neurosurgical oncology

PURPOSE OF REVIEW

In recent years, the safety and efficacy of neurosurgical intervention has rapidly improved for brain tumor patients. Technological advances, combined with refined intraoperative techniques, now enable well tolerated surgical access to any region of the human brain. For patients with gliomas, these improvements have redefined the clinical possibilities, and here we review several emerging operative strategies that are essential for next-generation neurosurgical oncologists and major brain tumor centers.

RECENT FINDINGS

The value of glioma extent of resection remains controversial, but review of the modern literature reveals important opportunities for early neurosurgical intervention. Although microsurgical resection must be balanced by the risk of neurological compromise, improvements in intraoperative stimulation techniques now enable resection of highly eloquent tumors with minimal morbidity. Additionally, the emergence of fluorescence-guided surgery as a new operative paradigm provides a unique opportunity to resect tumors to the margins of microscopic infiltration.

SUMMARY

Neurosurgical intervention remains the first step in effective glioma management. With intraoperative mapping techniques, aggressive microsurgical resection can be safely pursued even when tumors occupy essential functional pathways. With the development of tumor-specific fluorophores, such as 5-aminolevulinic acid, real-time microscopic visualization of tumor infiltration can be surgically targeted prior to adjuvant therapy.

¹¹C-methionine uptake and intraoperative 5-aminolevulinic acid-induced fluorescence as separate index markers of cell density in glioma: a stereotactic image-histological analysis

BACKGROUND

The extent of tumor resection is acknowledged as 1 of the prognostic factors for glioma. 5-Aminolevulinic acid (5-ALA)-induced fluorescence guidance and neuronavigation integrated with (11) C-methionine positron emission tomography (PET) are widely utilized under the expectation of improving the extent of resection. These 2 novel approaches are beneficial for glioma resections, and the combination of these approaches appears rational. However, biological characteristics reflecting 5-ALA-induced fluorescence and (11) C-methionine uptake have not been clearly elucidated, and studies about the relationship between 5-ALA-induced fluorescence and (11) C-methionine uptake have been limited. The present study aimed to clarify this issue.

METHODS

Data from 11 consecutive patients harboring astrocytic tumors were analyzed: 2 grade II and 2 grade III, and 7 grade IV tumors were included. Thirty samples from these patients were obtained from the relative periphery of each tumor. Relationships among histology, 5-ALA-induced fluorescence and (11) C-methionine uptake were analyzed by stereotactic sampling and image analysis.

RESULTS

Uptake of (11) C-methionine correlated with cell density (R(2) = 0.322, P = .0059). Cell density was higher in fluorescence-positive areas than in negative areas (2760 ± 1080 vs 1450 ± 1380/mm(2) , P = .0132). Although both (11) C-methionine uptake and fluorescence seemed to correlate with cell density, no significant difference in (11) C-methionine uptake was seen between fluorescence-positive and -negative areas (P = .367). Multiple linear regression analysis revealed (11) C-methionine uptake and 5-ALA-induced fluorescence as independent indices for tumor cell density.

CONCLUSIONS

These results indicate that 5-ALA fluorescence and (11) C-methionine PET image are separate index markers for cytoreduction surgery of gliomas.

Intraoperative confocal microscopy in the visualization of 5-aminolevulinic acid fluorescence in low-grade gliomas

OBJECT

Greater extent of resection (EOR) for patients with low-grade glioma (LGG) corresponds with improved clinical outcome, yet remains a central challenge to the neurosurgical oncologist. Although 5-aminolevulinic acid (5-ALA)-induced tumor fluorescence is a strategy that can improve EOR in gliomas, only glioblastomas routinely fluoresce following 5-ALA administration. Intraoperative confocal microscopy adapts conventional confocal technology to a handheld probe that provides real-time fluorescent imaging at up to 1000× magnification. The authors report a combined approach in which intraoperative confocal microscopy is used to visualize 5-ALA tumor fluorescence in LGGs during the course of microsurgical resection.

METHODS

Following 5-ALA administration, patients with newly diagnosed LGG underwent microsurgical resection. Intraoperative confocal microscopy was conducted at the following points: 1) initial encounter with the tumor; 2) the midpoint of tumor resection; and 3) the presumed brain-tumor interface. Histopathological analysis of these sites correlated tumor infiltration with intraoperative cellular tumor fluorescence.

RESULTS

Ten consecutive patients with WHO Grades I and II gliomas underwent microsurgical resection with 5-ALA and intraoperative confocal microscopy. Macroscopic tumor fluorescence was not evident in any patient. However, in each case, intraoperative confocal microscopy identified tumor fluorescence at a cellular level, a finding that corresponded to tumor infiltration on matched histological analyses.

CONCLUSIONS

Intraoperative confocal microscopy can visualize cellular 5-ALA-induced tumor fluorescence within LGGs and at the brain-tumor interface. To assess the clinical value of 5-ALA for high-grade gliomas in conjunction with neuronavigation, and for LGGs in combination with intraoperative confocal microscopy and neuronavigation, a Phase IIIa randomized placebo-controlled trial (BALANCE) is underway at the authors' institution.

Intraoperative 5-aminolevulinic-acid-induced fluorescence in meningiomas

OBJECT

5-aminolevulinic acid (5-ALA) has gained importance as an intraoperative photodynamic diagnostic agent for the extirpation of malignant gliomas. The application of this technique for resection of meningiomas has barely been explored. The aim of this study was to evaluate the utility of 5-ALA-induced fluorescence as a visual tool in meningioma resection and its correlation with histological findings.

METHODS

A total of 33 consecutive patients undergoing resection of intracranial meningiomas from December 2007 to August 2009 were included in this study. After confirmation of normal liver function, 5-ALA was administered orally (20 mg/kg) within 3-5 h prior to skin incision. All cases were operated on using standard microsurgical and neuronavigation-guided techniques. Intraoperative 440 nm fluorescence was applied periodically during and at the end of resection in order to detect tumor-infiltrated sites. The fluorescence of the tumor was evaluated intraoperatively by the surgeon and confirmed by subsequent video analysis.

RESULTS

A total of 32 (97%) patients presented with benign meningiomas (WHO I-II). In 1 (3%) patient, histological anaplastic signs (WHO III) could be demonstrated. 5-ALA-induced fluorescence of the tumor was confirmed in a total of 31 (94%) patients. The fluorescence did not correlate with the histological findings (n = 30 WHO I-II, n = 1 WHO grade III) or with preoperative brain edema and administration of steroids. A total resection could be postoperatively demonstrated in 25 (76%) patients. No adverse effects attributable to 5-ALA occurred.

CONCLUSIONS

5-ALA-induced fluorescence is a useful and promising intraoperative tool for the visualization of meningioma tissue. The novel findings demonstrated in this study in terms of high fluorescence and poor correlation with histological findings highlight the usefulness of this technique as a routine visual tool to achieve optimal resection of meningiomas.

Uptake and phototoxicity of meso-tetrahydroxyphenyl chlorine are highly variable in human biliary tract cancer cell lines and correlate with markers of differentiation and proliferation

Photodynamic therapy (PDT) using Photofrin and, recently, Foscan has gained broad acceptance for palliative treatment of non-resectable cholangiocarcinoma (CC). No information, however, is available whether the phenotype of CC tumour cells has an effect on the efficiency of the treatment. Using a well-characterised set of n = 9 biliary tract cancer cell lines this study investigated the uptake, phototoxicity, and release of meso-tetrahydroxyphenyl chlorine (mTHPC, Foscan) after incubation with 200 or 400 ng ml(-1) mTHPC. For uptake of mTHPC we found great variations between the individual cell lines (up to a factor 2), resulting in even more pronounced differences in phototoxicity. Based on statistical classification by hierarchical cluster analysis, two groups of cell lines can be distinguished which are characterised by either high or low susceptibility towards mTHPC-based photodynamic treatment. Correlation analysis with previously established immunochemical parameters showed that cells with a low cytokeratin-19 (ductal differentiation), high vimentin (mesenchymal marker), and high proliferative phenotype preferentially show higher uptake of mTHPC and subsequent phototoxicity. These results demonstrate high variability of biliary tract cancer cells when subjected to mTHPC-based photodynamic treatment and identify possible markers that could be used in the clinical setting in order to predict the efficiency of PDT and adjust the dose for complete tumour elimination.

Noninvasive measurement of aminolevulinic acid-induced protoporphyrin IX fluorescence allowing detection of murine glioma in vivo

Aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) fluorescence is studied as a contrast agent for noninvasive detection of murine glioma, using the fluorescence-to-transmission ratio measured through the cranium. Signals measured prior to administration of ALA are very similar between control animals, 9L-GFP, and U251 tumor-bearing animals. However, 2 h after ALA administration, the PpIX signal from both tumor-bearing groups is significantly higher than the control group (9L-GFP group p-value=0.016, and U251 group p-value=0.004, relative to the control group). The variance in signal from the 9L-GFP group is much larger than either the control group or the U251 group, which is consistent with higher intrinsic PpIX fluorescence heterogeneity as seen in situ at ex vivo analysis. Decreasing the skin PpIX fluorescence via intentional photobleaching using red light (635 nm) is examined as a tool for increasing PpIX contrast between the tumor-bearing and control groups. The red light bleaching is found to increase the ability to accurately quantify PpIX fluorescence in vivo, but decreases the specificity of detection between tumor-bearing and nontumor-bearing groups.

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).

Relation between intracellular location and photodynamic efficacy of 5-aminolevulinic acid-induced protoporphyrin IX in vitro. Comparison between human glioblastoma cells and other cancer cell lines

A promising clinical application of 5-aminolevulinic acid (5-ALA)-induced protoporphyrin IX (PP IX) is fluorescence detection and photodynamic treatment of residual tumour tissue during surgical resection of high grade malignant glioma. U373 MG human glioblastoma cells were used as a model system to study the relation between intracellular location and photodynamic efficacy of 5-ALA-induced PP IX in more detail. Therefore, ultra-sensitive fluorescence microscopy, using either optical excitation of whole cells or selective excitation of the plasma membrane by an evanescent electromagnetic field, was combined with quantitative measurements of intracellular porphyrin amount and phototoxicity. Glioblastoma cells accumulated PP IX to a moderate extent as compared to T47D breast cancer cells (high accumulation) or OV2774 ovarian cancer cells (low accumulation). Although photodynamic inactivation of the different cell lines (decreasing in the order T47D > U373 MG > OV2774) seemed to be directly related to PP IX accumulation, examination of the data in more detail revealed that photodynamic efficacy per photosensitizer molecule (PE) was about two times higher in glioblastoma and ovarian cancer cells as compared to breast cancer cells. The different photodynamic efficacy of PP IX was related to the different intracellular location. In contrast to breast cancer cells where PP IX fluorescence was localized in small granules, PP IX fluorescence in glioblastoma cells and ovarian cancer cells originated mainly from cellular membranes. Thus, the intracellular location of PP IX in a predominantly lipophilic environment, characterized by a comparably high photostability (probed by photobleaching and photoproduct formation) and a lower degree of porphyrin aggregation (probed previously by fluorescence decay kinetics), seems to be the key factor for high photodynamic efficacy of 5-ALA-induced PP IX. In the case of OV2774 ovarian cancer cells, however, a low PP IX accumulation limited cell inactivation upon irradiation, whereas the results obtained for glioblastoma cells are encouraging to develop PDT to an additional therapeutic option for the treatment of tumour margins in patients who underwent fluorescence-guided resection of high grade malignant glioma after 5-ALA administration.