Kinetics of porphyrin fluorescence accumulation in pediatric brain tumor cells incubated in 5-aminolevulinic acid

Past, present and future of Focused Ultrasound as an adjunct or complement to DIPG/DMG therapy: A consensus of the 2021 FUSF DIPG meeting

Diffuse Intrinsic Pontine Glioma (DIPG), now known as Diffuse Midline Glioma (DMG) is a devastating pediatric brain tumor with limited treatment options and a very poor prognosis. Despite more than 250 clinical trials aimed to treat children diagnosed with DMG, no curative therapies currently exist for this patient population. A major obstacle has been the intact blood brain barrier (BBB) which prevents most therapeutics from crossing into the tumor bed. Focused Ultrasound (FUS) is an emerging, noninvasive medical technology which has been shown in both preclinical and clinical research to disrupt the blood brain barrier safely and temporarily. FUS blood brain barrier opening has been studied in combination with chemotherapies in preclinical DMG models, and this technology is now being investigated in clinical trials for the treatment of pediatric brain tumors. Focused ultrasound has additional mechanisms of action, including sonodynamic therapy and radiation sensitization, that hold promise as future DMG therapies as well. This paper, largely based off the proceedings from a workshop held by the Focused Ultrasound Foundation in October of 2021, summarizes the current state of the field of focused ultrasound for DIPG/DMG, including preclinical, technical, and clinical summaries in addition to recommended next steps for continued advancement of the game changing technology of Focused Ultrasound.

5-Aminolevulinic acid for enhanced surgical visualization of high-grade gliomas: a prospective, multicenter study

OBJECTIVE

Greater extent of resection (EOR) is associated with longer overall survival in patients with high-grade gliomas (HGGs). 5-Aminolevulinic acid (5-ALA) can increase EOR by improving intraoperative visualization of contrast-enhancing tumor during fluorescence-guided surgery (FGS). When administered orally, 5-ALA is converted by glioma cells into protoporphyrin IX (PPIX), which fluoresces under blue 400-nm light. 5-ALA has been available for use in Europe since 2010, but only recently gained FDA approval as an intraoperative imaging agent for HGG tissue. In this first-ever, to the authors' knowledge, multicenter 5-ALA FGS study conducted in the United States, the primary objectives were the following: 1) assess the diagnostic accuracy of 5-ALA-induced PPIX fluorescence for HGG histopathology across diverse centers and surgeons; and 2) assess the safety profile of 5-ALA FGS, with particular attention to neurological morbidity.

METHODS

This single-arm, multicenter, prospective study included adults aged 18-80 years with Karnofsky Performance Status (KPS) score > 60 and an MRI diagnosis of suspected new or recurrent resectable HGG. Intraoperatively, 3-5 samples per tumor were taken and their fluorescence status was recorded by the surgeon. Specimens were submitted for histopathological analysis. Patients were followed for 6 weeks postoperatively for adverse events, changes in the neurological exam, and KPS score. Multivariate analyses were performed of the outcomes of KPS decline, EOR, and residual enhancing tumor volume to identify predictive patient and intraoperative variables.

RESULTS

Sixty-nine patients underwent 5-ALA FGS, providing 275 tumor samples for analysis. PPIX fluorescence had a sensitivity of 96.5%, specificity of 29.4%, positive predictive value (PPV) for HGG histopathology of 95.4%, and diagnostic accuracy of 92.4%. Drug-related adverse events occurred at a rate of 22%. Serious adverse events due to intraoperative neurological injury, which may have resulted from FGS, occurred at a rate of 4.3%. There were 2 deaths unrelated to FGS. Compared to preoperative KPS scores, postoperative KPS scores were significantly lower at 48 hours and 2 weeks but were not different at 6 weeks postoperatively. Complete resection of enhancing tumor occurred in 51.9% of patients. Smaller preoperative tumor volume and use of intraoperative MRI predicted lower residual tumor volume.

CONCLUSIONS

PPIX fluorescence, as judged by the surgeon, has a high sensitivity and PPV for HGG. 5-ALA was well tolerated in terms of drug-related adverse events, and its application by trained surgeons in FGS for HGGs was not associated with any excess neurological morbidity.

5-Aminolevulinic Acid-Shedding Light on Where to Focus

BACKGROUND

Surgical management of gliomas is predicated on "safe maximal resection" across all histopathologic grades because progression-free survival and overall survival are positively affected by the increasing extent of resection. Administration of the prodrug 5-aminolevulinic acid (5-ALA) induces tumor fluorescence with high specificity and sensitivity for malignant high-grade glioma (HGG). Fluorescence-guided surgery (FGS) using 5-ALA improves the extent of resection in the contrast-enhancing and nonenhancing tumor components in HGG. It has also shown preliminary usefulness in other central nervous system tumors, but with certain limitations.

METHODS

We review and discuss the state of 5-ALA FGS for central nervous system tumors and identify the limitations in its use as a guide for future clinical optimization.

RESULTS

5-ALA FGS provides maximum clinical benefits in the treatment of newly diagnosed glioblastoma. 5-ALA fluorescence specificity is limited in low-grade glioma, recurrent HGG, and non-glial tumors. Several promising intraoperative adjuncts to 5-ALA FGS have been developed to expand its indications and improve the clinical efficacy and usefulness of 5-ALA FGS.

CONCLUSIONS

5-ALA FGS improves the clinical outcomes in HGG. However, further optimization of the diagnostic performance and clinical use of 5-ALA FGS is necessary for low-grade glioma and recurrent HGG tumors. Neurosurgical oncology will benefit from the novel use of advanced technologies and intraoperative visualization techniques outlined in this review, such as machine learning, hand-held fibe-optic probes, augmented reality, and three-dimensional exoscope assistance, to optimize the clinical usefulness and operative outcomes of 5-ALA FGS.

The Neurosurgeon's Armamentarium for Gliomas: An Update on Intraoperative Technologies to Improve Extent of Resection

Maximal safe resection is the standard of care in the neurosurgical treatment of high-grade gliomas. To aid surgeons in the operating room, adjuvant techniques and technologies centered around improving intraoperative visualization of tumor tissue have been developed. In this review, we will discuss the most advanced technologies, specifically fluorescence-guided surgery, intraoperative imaging, neuromonitoring modalities, and microscopic imaging techniques. The goal of these technologies is to improve detection of tumor tissue beyond what conventional microsurgery has permitted. We describe the various advances, the current state of the literature that have tested the utility of the different adjuvants in clinical practice, and future directions for improving intraoperative technologies.

5-aminolevulinic acid-guided surgery for focal pediatric brainstem gliomas: A preliminary study

Background:

There is a growing body of literature supporting the use of 5-aminolevulinic acid (5-ALA) in the pediatric population, however, its use is still considered “off label” in this setting. In this retrospective study, we report our experience using 5-ALA in pediatric patients with focal brainstem gliomas (BSGs).

Methods:

Patients younger than 16 years presenting with a newly diagnosed BSG that was focal in nature were considered suitable for treatment with 5-ALA-assisted surgery. Exclusion criteria included MRI features suggestive of a diffuse intrinsic pontine glioma. A single dose of 5-ALA was administered preoperatively. Intraoperative fluorescence was recorded as “solid,” “vague,” or “none.” The effectiveness of the fluorescence was graded as “helpful” or “unhelpful.”

Results:

Eight patients underwent 5-ALA-assisted surgery. There were four tumors located in the pons, two midbrain tumors, and two cervicomedullary tumors. Histological analysis demonstrated three diffuse astrocytomas, three pilocytic astrocytomas, and two anaplastic astrocytomas. Solid fluorescence was found in three of the eight cases, vague fluorescence was found in two cases, and no fluorescence was found in three cases. Fluorescence was useful in 3 (37%) cases. No patients experienced any complications attributable to the administration of the 5-ALA.

Conclusion:

With a total fluorescence rate of 62.5% but a subjectively assessed “usefulness” rate of only 37.5%, the role of 5-ALA in BSG surgery is limited. Given the toxicological safety, however, of the agent, caution is perhaps needed before dismissing the use of 5-ALA entirely.

Image-Guided Brain Surgery

In neurosurgery, the extent of resection plays a critical role, especially in the management of malignant gliomas. These tumors are characterized through a diffuse infiltration into the surrounding brain parenchyma. Delineation between tumor and normal brain parenchyma can therefore often be challenging. During the recent years, several techniques, aiming at better intraoperative tumor visualization, have been developed and implemented in the field of brain tumor surgery. In this chapter, we discuss current strategies for intraoperative imaging in brain tumor surgery, comprising conventional techniques such as neuronavigation, techniques using fluorescence-guided surgery, and further highly precise developments such as targeted fluorescence spectroscopy or Raman spectroscopy.

A New Treatment Opportunity for DIPG and Diffuse Midline Gliomas: 5-ALA Augmented Irradiation, the 5aai Regimen

Prognosis for diffuse intrinsic pontine glioma (DIPG) and generally for diffuse midline gliomas (DMG) has only marginally improved over the last ~40 years despite dozens of chemotherapy and other therapeutic trials. The prognosis remains invariably fatal. We present here the rationale for a planned study of adding 5-aminolevulinic acid (5-ALA) to the current irradiation of DIPG or DMG: the 5aai regimen. In a series of recent papers, oral 5-ALA was shown to enhance standard therapeutic ionizing irradiation. 5-ALA is currently used in glioblastoma surgery to enable demarcation of overt tumor margins by virtue of selective uptake of 5-ALA by neoplastic cells and selective conversion to protoporphyrin IX (PpIX), which fluoresces after excitation by 410 nm (blue) light. 5-ALA is also useful in treating glioblastomas by virtue of PpIX's transfer of energy to O₂ molecules, producing a singlet oxygen that in turn oxidizes intracellular DNA, lipids, and proteins, resulting in selective malignant cell cytotoxicity. This is called photodynamic treatment (PDT). Shallow penetration of light required for PpIX excitation and resultant energy transfer to O₂ and cytotoxicity results in the inaccessibility of central structures like the pons or thalamus to sufficient light. The recent demonstration that keV and MeV photons can also excite PpIX and generate singlet O₂ allows for reconsideration of 5-ALA PDT for treating DMG and DIPG. 5-ALA has an eminently benign side effect profile in adults and children. A pilot study in DIPG/DMG of slow uptitration of 5-ALA prior to each standard irradiation session-the 5aai regimen-is warranted.

Spectroscopic measurement of 5-ALA-induced intracellular protoporphyrin IX in pediatric brain tumors

OBJECTIVE

5-Aminolevulinic acid (5-ALA)-guided resection of gliomas in adults enables better delineation between tumor and normal brain, allowing improved resection and improved patients' outcome. Recently, several reports were published regarding 5-ALA for resection of pediatric brain tumors. The aim of the study was to determine the intracellular fluorescence of protoporphyrin IX (PPIX) in pediatric brain tumors by hyperspectral imaging and to compare it with visually observed intraoperative fluorescence.

METHODS

5-ALA was administered orally 4 h prior to surgery. During tumor resection, the surgeon assessed the fluorescence signal to be strong, weak, or absent. Subsequently, fluorescence intensity of tumor samples was measured via spectroscopy. In addition, clinical data, imaging, and laboratory data were analyzed.

RESULTS

Eleven children (1-16 years) were operated. Tumor entities included three (n = 3) medulloblastomas, two (n = 2) pilocytic astrocytomas (PA), two (n = 2) anaplastic ependymomas and one (n = 1) diffuse astrocytoma, anaplastic astrocytoma (n = 1), pilomyxoid astrocytoma (n = 1) and anaplastic pleomorphic xanthoastrocytoma (n = 1). Strong fluorescence was visible in all anaplastic tumors and one PA; one PA demonstrated weak fluorescence. Visible fluorescence was strongly associated with intracellular fluorescence intensity and PPIX concentration (P < 0.05). Within all tumors with visible fluorescence, the intracellular PPIX concentration was greater than 4 μg/ml. Except for moderate and transient elevation of liver enzymes, no 5-ALA related adverse events were reported.

CONCLUSION

We demonstrate a strong association between intraoperative observations and spectrometric measurements of PPIX fluorescence in tumor tissue. As in former studies, fluorescence signal was more commonly observed in malignant glial tumors. Further prospective controlled trials should be conducted to investigate the feasibility of 5-ALA-guided resection of pediatric brain tumors.

5-ALA fluorescence-guided surgery in pediatric brain tumors-a systematic review

BACKGROUND

5-Aminolevulinic acid (5-ALA)-guided resection of gliomas in adults enables better differentiation between tumor and normal brain tissue, allowing a higher degree of resection, and improves patient outcomes. In recent years, several reports have emerged regarding the use of 5-ALA in other brain tumor entities, including pediatric brains tumors. Since gross total resection (GTR) of many brain tumors in children is crucial and the role of 5-ALA-guided resection of these tumors is not clear, we sought to perform a comprehensive literature review on this topic.

METHODS

A systematic literature review of EMBASE and MEDLINE/PubMed databases revealed 19 eligible publications encompassing 175 5-ALA-guided operations on pediatric brain tumors. To prevent bias, publications were revised independently by two authors.

RESULTS

We found that 5-ALA-guided resection enabled the surgeons to identify the tumor more easily and was considered helpful mainly in cases of glioblastoma (GBM, 21/27, 78%), anaplastic ependymoma WHO grade III (10/14, 71%), and anaplastic astrocytoma (4/6, 67%). In contrast, cases of pilocytic astrocytomas (PAs) and medulloblastomas 5-ALA-guided surgery did not show consistent fluorescent signals and 5-ALA was considered helpful only in 12% and 22% of cases, respectively. Accumulation of fluorescent porphyrins seems to depend on WHO tumor grading. One important finding is that when 5-ALA-guided resections were considered helpful, the degree of resection was higher than is cases where it was not helpful. The rate of adverse events related to 5-ALA was negligible, especially new postoperative sequelae.

CONCLUSION

5-ALA could play a role in resection of pediatric brain tumors. However, further prospective clinical trials are needed.

The impact of fluorescein-guided technique in the surgical removal of CNS tumors in a pediatric population: results from a multicentric observational study

BACKGROUND

Surgery has a fundamental role in central nervous system (CNS) tumors in the pediatric population, as aggressive resection correlates with prognosis. Due to its accumulation in areas with damaged blood brain barrier, sodium fluorescein (SF) could be a valid tool to improve the extent of resection in tumors enhancing at preoperative MRI. This study is aimed to systematically assess the utility of SF in a pediatric population.

METHODS

Patient data were collected in two centers, one in Italy and the other in Germany. At the induction of anesthesia, SF was administered intravenously (5 mg/kg). Surgery was performed using a YELLOW560 filter. Fluorescence intensity was graduated as bright, moderate or absent based on surgeon's opinion; furthermore, SF use was judged as "helpful," "not helpful" or "not essential" in tumor removal.

RESULTS

Twenty-four patients for 27 surgical procedures were identified. In 21 of 27 (77.8%) procedures fluorescence was reported as bright or moderate, in two of 27 (7.4%) absent and in four of 27 (14.8%) data were unavailable. Intraoperative fluorescence was reported in 21 of 25 (84%) surgeries whose corresponding preoperative MRI had shown contrast enhancement. In 14 of 27 (51.8%) surgical procedures SF was considered "helpful"; in two of 27 (7.4%) not "helpful"; in seven of 27 (25.9%) "not essential." In four of 27 (14.8%) data were unavailable. No adverse effect to SF was registered.

CONCLUSIONS

SF could be considered a valid and safe tool to improve visualization of tumors enhancing at preoperative MRI also in pediatric patients. Future prospective studies are needed to confirm these preliminary data.

Indocyanine-Green for Fluorescence-Guided Surgery of Brain Tumors: Evidence, Techniques, and Practical Experience

The primary treatment for brain tumors often involves surgical resection for diagnosis, relief of mass effect, and prolonged survival. In neurosurgery, it is of utmost importance to achieve maximal safe resection while minimizing iatrogenic neurologic deficit. Thus, neurosurgeons often rely on extra tools in the operating room, such as neuronavigation, intraoperative magnetic resonance imaging, and/or intraoperative rapid pathology. However, these tools can be expensive, not readily available, time-consuming, and/or inaccurate. Recently, fluorescence-guided surgery has emerged as a cost-effective method to accurately visualize neoplastic areas in real-time to guide resection. Currently, 5-aminolevulinic-acid (5-ALA) remains the only fluorophore that has been approved specifically for fluorescence-guided tumor resection. Its use has demonstrated improved resection rates and prolonged progression-free survival. However, protoporphyrin-IX, the metabolic product of 5-ALA that accumulates in neoplastic cells, fluoresces in the visible-light range, which suffers from limited tissue penetration and significant auto-fluorescence. Near-infrared fluorescence, on the other hand, overcomes these problems with ease. Since 2012, researchers at our institution have developed a novel technique using indocyanine-green, which is a well-known near-infrared fluorophore used traditionally for angiography. This Second-Window-ICG (SWIG) technique takes advantage of the increased endothelial permeability in peritumoral tissue, which allows indocyanine-green to accumulate in these areas for intraoperative visualization of the tumor. SWIG has demonstrated utility in gliomas, meningiomas, metastases, pituitary adenomas, chordomas, and craniopharyngiomas. The main benefits of SWIG stem from its highly sensitive detection of neoplastic tissue in a wide variety of intracranial pathologies in real-time, which can help neurosurgeons both during surgical resections and in stereotactic biopsies. In this review of this novel technique, we summarize the development and mechanism of action of SWIG, provide evidence for its benefits, and discuss its limitations. Finally, for those interested in near-infrared fluorescence-guided surgery, we provide suggestions for maximizing the benefits while minimizing the limitations of SWIG based on our own experience thus far.

In-Vitro Use of 5-ALA for Photodynamic Therapy in Pediatric Brain Tumors

BACKGROUND

Light irradiation (635 nm) of cells containing protoporphyrin IX (PPIX) after 5- aminolevulinic acid (5-ALA) pretreatment causes cell death via different pathways including apoptosis and necrosis, as previously demonstrated for malignant glioma cells.

OBJECTIVE

To elucidate whether various malignant pediatric brain tumors, which have been shown to accumulate PPIX, would also be susceptible to photodynamic therapy (PDT).

METHODS

Medulloblastoma (DAOY, UW228), pNET (PFSK-1), and rhabdoid tumor (BT16) cell lines were incubated with 5-ALA in variable concentrations for 4 h. Consequently, cells were irradiated by 635 nm diode laser light. After 12 h, cell viability was measured by WST-1 testing and these results were compared to control cells incubated with 5-ALA without irradiation or irradiation only without prior incubation with 5-ALA.

RESULTS

We demonstrated significant cell death in malignant pediatric tumor cells after incubation with 5-ALA and laser irradiation in comparison to control groups. In all cell lines, we noticed significant cell death above a 5-ALA concentration of 50 μg/ml (P < .05). Neither 5-ALA incubation alone nor irradiation alone caused cell death. DAOY and PFSK cell lines were more susceptible than UW228 and BT16 cells.

CONCLUSION

We conclude that PDT causes cell death with higher PPIX concentrations after exposure to 5-ALA in vitro in accordance to similar studies with glioma cells. This indicates that PDT might be feasible for eliminating brain tumor cells in malignant pediatric brain tumors. Additionally, we noticed a dependency between fluorescence intensity and death rates.

Accumulation of protoporphyrin IX in medulloblastoma cell lines and sensitivity to subsequent photodynamic treatment

BACKGROUND

Medulloblastoma (MB) is the most common malignant primary brain tumor of childhood. High risk patients still have a poor outcome, and especially young patients suffer from standard therapy induced sequelae. Therefore, other therapeutic options need to be explored. In glioblastoma (GBM), application of 5-aminolaevulinic acid (5-ALA) results in selective accumulation of protoporphyrin IX (PPIX) in the tumor cells, which can be exploited during fluorescence-guided surgery to increase the extent of resection or for photodynamic therapy (PDT) induced phototoxicity. It is not entirely clear, whether MB cells accumulate PPIX and are sensitive to PDT.

METHODS

Human MYC-amplified (Med8A and D283) and non-amplified (UW228-2 and ONS76) MB cell lines were incubated for 2, 4 or 6 h with increasing doses (0-100 μg/ml) of 5-ALA, and PPIX accumulation was determined by flow cytometry. To assess sensitivity to 5-ALA/PDT, cells were incubated with 5-ALA and subsequently exposed to laser light of 635 nm wavelength (18.75 J/cm²). After an additional 24 h culture period, viability of cells was quantified using the WST-1 assay. Expression of ferrochelatase was detected by reverse transcription and quantitative polymerase chain reaction. Ferrochelatase activity was quantified by measuring the enzymatic conversion of PPIX to zinc-protoporphyrin. Expression of the ABCG2 transporter protein CD338 was detected by flow cytometry.

RESULTS

All MB cell lines showed a time- and dose-dependent accumulation of PPIX after exposure to exogenous 5-ALA and became sensitive to 5-ALA/PDT-induced phototoxicity. PPIX accumulation was reduced compared to U373 GBM cells at shorter incubation periods and limiting 5-ALA doses. Moreover, not all MB cells became PPIX positive and overall phototoxicity was lower in the MB cell lines. Notably, the MYC-amplified MB cells demonstrated a more pronounced photosensitivity compared to their non-amplified counterparts. There was no difference in expression of ferrochelatase, but enzymatic activity appeared to be reduced in the MB cells compared to U373 GBM cells, whereas CD338 was expressed on the MB cells only.

CONCLUSION

Medulloblastoma cell lines accumulate PPIX after application of 5-ALA and become sensitive to PDT, associated with low ferrochelatase expression and activity. Photosensitivity is more pronounced in MYC-amplified cell lines. In contrast to GBM cells, however, PPIX accumulation appears to be reduced, restricted to a subset of cells and associated with lower photosensitivity of the MB cell lines, possibly due to expression of the ABCG2 transporter protein CD338 on MB cells.

Randomized, Prospective Double-Blinded Study Comparing 3 Different Doses of 5-Aminolevulinic Acid for Fluorescence-Guided Resections of Malignant Gliomas

BACKGROUND

Five-aminolevulinic acid (5-ALA) is used for fluorescence-guided resections of malignant glioma at a dose of 20 mg/kg; yet, it is unknown whether lower doses may also provide efficacy.

OBJECTIVE

To perform a double-blinded randomized study comparing 3 different doses of 5-ALA.

METHODS

Twenty-one patients with suspected malignant glioma were randomly assigned to 0.2, 2, or 20 mg/kg 5-ALA. Investigators were unaware of dose. Intraoperatively, regions of interest were first defined in tumor core, margin, and adjacent white matter under white light. Under violet-blue illumination, the surgeon's impression of fluorescence was recorded per region, followed by spectrometry and biopsy. Plasma was collected after administration and analyzed for 5-ALA and protoporphyrin IX (PPIX) content.

RESULTS

The positive predictive value of fluorescence was 100%. Visual and spectrometric fluorescence assessment showed 20 mg/kg to elicit the strongest fluorescence in tumor core and margins, which correlated with cell density. Spectrometric and visual fluorescence correlated significantly. A 10-fold increase in 5-ALA dose (2-20 mg/kg) resulted in a 4-fold increase of fluorescence contrast between marginal tumor and adjacent brain. t max for 5-ALA was 0.94 h for 20 mg/kg (0.2 kg: 0.50 h, 2 mg/kg: 0.61 h). Integrated PPIX plasma levels were 255.8 and 779.9 mcg*h/l (2 vs 20 mg/kg). Peak plasma concentrations were observed at 1.89 ± 0.71 and 7.83 ± 0.68 h (2 vs 20 mg/kg; average ± Standard Error of Mean [SEM]).

CONCLUSION

The highest visible and measurable fluorescence was yielded by 20 mg/kg. No fluorescence was elicited at 0.2 mg/kg. Increasing 5-ALA doses did not result in proportional increases in tissue fluorescence or PPIX accumulation in plasma, indicating that doses higher than 20 mg/kg will not elicit useful increases in fluorescence.

Epithelial growth factor receptor expression influences 5-ALA induced glioblastoma fluorescence

The extent of 5-aminolevulinic acid (5-ALA) guided tumor resection has a determining impact in high-grade glioma and glioblastoma surgery. Yet the intensity of the 5-ALA induced fluorescence may vary within the tumor. We aimed to correlate 5-ALA induced fluorescence with the expression of epithelial growth factor receptor (EGFR) and its constitutively active version EGFRvIII in different glioblastoma (GBM) cell lines. To elucidate the role of EGFR in the metabolism of 5-ALA in GBM cell lines with variable EGFR expression status, we analyzed the activation of EGFR by its primary ligand EGF, and its downstream effect on Heme oxygenase-1 (HO-1), a key enzyme regulating the metabolism of Protoporphyrin IX (PpIX), the fluorescent metabolite of 5-ALA. Effects of direct pharmacological inhibition by Tin(IV)-Protoporphyrin (SnPP) or gene knockdown by small interfering RNA (siRNA) on HO-1 enzyme were analyzed in respect to 5-ALA induced fluorescence. Furthermore, inhibition of EGFR by Gefitinib was tested. A significant difference in 5-ALA induced fluorescence was obtained in U87MG (low EGFR expression) and LN229EGFR cells (EGFR overexpression) compared to BS153 (EGFR overexpression/EGFRvIII+). Treatment of U87MG and LN229EGFR cells with EGF significantly reduced cellular fluorescence, by promoting HO-1 transcription and expression in a concentration-dependent manner. This effect could be reversed by EGFR-specific siRNA treatment, which reduced protein expression of about 80% in U87MG. Remarkably, inhibition of HO-1 activity by SnPP or reduction of HO-1 protein levels by siHO-1 treatment restored fluorescence in all cell lines, independently of EGFR quantitative and qualitative expression. Gefitinib treatment was able to restore fluorescence after EGF stimulation in U87MG cells but not in BS153 cells, overexpressing EGFR/EGFRvIII. In GBM cell lines, 5-ALA induced fluorescence is variable and influenced by EGF-induced downstream activation of HO-1. HO-1 protein expression was identified as a negative regulator of 5-ALA induced fluorescence in GBM cells. We further propose that co-expression of EGFRvIII but not quantitative EGFR expression influence HO-1 activity and therefore cellular fluorescence.

Fluorescence in neurosurgery: Its diagnostic and therapeutic use. Review of the literature

Fluorescent agents, e.g. 5-aminolevulinic acid (5-ALA), fluorescein and indocyanine green (ICG) are in common use in neurosurgery for tumor resection and neurovascular surgery. Protoporphyrine IX (PPIX) as major metabolite of 5-ALA is a strong fluorescent substance accumulated within malignant glioma tissue and a very sensitive and specific tool for visualizing high grade glioma tissue during surgery. Furthermore, 5-ALA or rather PPIX also offers an intratumoral therapeutic option stimulated by laser light in specific wavelength. Fluorescein was demonstrated to show similar fluorescent reactions in neurosurgery, but is controversial in its use, especially in high grade tumor surgery. Intraoperative angiography during resection of arterio-venous malformations, extracranial-intracranial-bypass or aneurysm surgery is supported by ICG fluorescence. Generally ICG will provide beneficial information for both, exposure of the pathology and illustration of healthy structures. This manuscript shows an overview of the literature focussing fluorescence in neurosurgery.

Predicting the "usefulness" of 5-ALA-derived tumor fluorescence for fluorescence-guided resections in pediatric brain tumors: a European survey

BACKGROUND

Five-aminolevulinic acid (Gliolan, medac, Wedel, Germany, 5-ALA) is approved for fluorescence-guided resections of adult malignant gliomas. Case reports indicate that 5-ALA can be used for children, yet no prospective study has been conducted as of yet. As a basis for a study, we conducted a survey among certified European Gliolan users to collect data on their experiences with children.

METHODS

Information on patient characteristics, MRI characteristics of tumors, histology, fluorescence qualities, and outcomes were requested. Surgeons were further asked to indicate whether fluorescence was "useful", i.e., leading to changes in surgical strategy or identification of residual tumor. Recursive partitioning analysis (RPA) was used for defining cohorts with high or low likelihoods for useful fluorescence.

RESULTS

Data on 78 patients <18 years of age were submitted by 20 centers. Fluorescence was found useful in 12 of 14 glioblastomas (85 %), four of five anaplastic astrocytomas (60 %), and eight of ten ependymomas grades II and III (80 %). Fluorescence was found inconsistently useful in PNETs (three of seven; 43 %), gangliogliomas (two of five; 40 %), medulloblastomas (two of eight, 25 %) and pilocytic astrocytomas (two of 13; 15 %). RPA of pre-operative factors showed tumors with supratentorial location, strong contrast enhancement and first operation to have a likelihood of useful fluorescence of 64.3 %, as opposed to infratentorial tumors with first surgery (23.1 %).

CONCLUSIONS

Our survey demonstrates 5-ALA as being used in pediatric brain tumors. 5-ALA may be especially useful for contrast-enhancing supratentorial tumors. These data indicate controlled studies to be necessary and also provide a basis for planning such a study.