The Role of 5-ALA in Low-Grade Gliomas and the Influence of Antiepileptic Drugs on Intraoperative Fluorescence

Fluorescence-Guided Surgical Techniques in Adult Diffuse Low-Grade Gliomas: State-of-the-Art and Emerging Techniques: A Systematic Review

Diffuse low-grade gliomas are infiltrative tumors whose margins are not distinguishable from the adjacent healthy brain parenchyma. The aim was to precisely examine the results provided by the intraoperative use of macroscopic fluorescence in diffuse low-grade gliomas and to describe the new fluorescence-based techniques capable of guiding the resection of low-grade gliomas. Only about 20% and 50% of low-grade gliomas are macroscopically fluorescent after 5-amino-levulinic acid (5-ALA) or fluorescein sodium intake, respectively. However, 5-ALA is helpful for detecting anaplastic foci, and thus choosing the best biopsy targets in diffuse gliomas. Spectroscopic detection of 5-ALA-induced fluorescence can detect very low and non-macroscopically visible concentrations of protoporphyrin IX, a 5-ALA metabolite, and, consequently, has excellent performances for the detection of low-grade gliomas. Moreover, these tumors have a specific spectroscopic signature with two fluorescence emission peaks, which is useful for distinguishing them not only from healthy brain but also from high-grade gliomas. Confocal laser endomicroscopy can generate intraoperative optic biopsies, but its sensitivity remains limited. In the future, the coupled measurement of autofluorescence and induced fluorescence, and the introduction of fluorescence detection technologies providing a wider field of view could result in the development of operator-friendly tools implementable in the operative routine.

Mechanical characteristics of glioblastoma and peritumoral tumor-free human brain tissue

BACKGROUND

The diagnosis of brain tumor is a serious event for the affected patient. Surgical resection is a crucial part in the treatment of brain tumors. However, the distinction between tumor and brain tissue can be difficult, even for experienced neurosurgeons. This is especially true in the case of gliomas. In this project we examined whether the biomechanical parameters elasticity and stress relaxation behavior are suitable as additional differentiation criteria between tumorous (glioblastoma multiforme; glioblastoma, IDH-wildtype; GBM) and non-tumorous, peritumoral tissue.

METHODS

Indentation measurements were used to examine non-tumorous human brain tissue and GBM samples for the biomechanical properties of elasticity and stress-relaxation behavior. The results of these measurements were then used in a classification algorithm (Logistic Regression) to distinguish between tumor and non-tumor.

RESULTS

Differences could be found in elasticity spread and relaxation behavior between tumorous and non-tumorous tissue. Classification was successful with a sensitivity/recall of 83% (sd = 12%) and a precision of 85% (sd = 9%) for detecting tumorous tissue.

CONCLUSION

The findings imply that the data on mechanical characteristics, with particular attention to stress relaxation behavior, can serve as an extra element in differentiating tumorous brain tissue from non-tumorous brain tissue.

Intraoperative Fluorophores: An Update on 5-Aminolevulinic Acid and Sodium Fluorescein in Resection of Tumors of the Central Nervous System and Metastatic Lesions-A Systematic Review and Meta-Analysis

INTRODUCTION

Recent advances in tumor visualization have improved the extent of resection (EOR) of primary and secondary tumors of the central nervous system, while limiting the morbidity and mortality of the surgery. One area of recent interest has been the use of intraoperative fluorophores for tumor visualization such as 5-aminolevulinic acid (5-ala) and sodium fluorescein. We performed a systematic review and meta-analysis on the utility of fluorophore administration and EOR with each fluorophore to update the current literature.

METHODS

We conducted a systematic review and meta-analysis on the use of intraoperative 5-ala or fluorescein between 2021 and 2023 using the PubMed, SCOPUS, and WOS databases. The initial search yielded 8688 results. After inclusion and exclusion criteria were met, 44 studies remained for review. A meta-analysis was performed to compare the EOR between studies for each fluorophore and to compare the presence of intraoperative fluorescence by tumor type. Odds ratios (OR) were calculated for gross total resection (GTR), and two-way ANOVA tests were performed to compare rates of intraoperative fluorescence by fluorophore and tumor type.

RESULTS

In all groups except low-grade glioma, fluorescence was present after 5-ala administration; fluorescence was present for all groups after fluorescein administration. Two-way ANOVA analysis for both fluorophores demonstrated no statistically significant difference in presence of fluorescence between type of tumor resected. Meta-analysis of EOR did show a higher, but not significant, rate of GTR in the 5-ala group compared to controls (OR = 1.29, 95% CI = 0.49; 3.37). In the fluorescein group, there were statistically significant higher odds of GTR compared to the control group (OR = 2.10, 95% CI = 1.43; 3.10, I2 = 0%).

CONCLUSIONS

Both 5-ala and sodium fluorescein demonstrated intraoperative fluorescence among various tumor types in both cranial and spinal tumors, as well as efficacy in improving EOR. Both fluorophores merit further investigation for use in surgery of CNS tumors.

How Reliable Is Fluorescence-Guided Surgery in Low-Grade Gliomas? A Systematic Review Concerning Different Fluorophores

BACKGROUND

Fluorescence-guided surgery has been increasingly used to support glioma surgery with the purpose of obtaining a maximal safe resection, in particular in high-grade gliomas, while its role is less definitely assessed in low-grade gliomas.

METHODS

A systematic review was conducted. 5-aminolevulinic acid, sodium fluorescein, indocyanine green and tozuleristide were taken into account. The main considered outcome was the fluorescence rate, defined as the number of patients in whom positive fluorescence was detected out of the total number of patients. Only low-grade gliomas were considered, and data were grouped according to single fluorophores.

RESULTS

16 papers about 5-aminolevulinic acid, 4 about sodium fluorescein, 2 about indocyanine green and 1 about tozuleristide were included in the systematic review. Regarding 5-aminolevulinic acid, a total of 467 low-grade glioma patients were included, and fluorescence positivity was detected in 34 out of 451 Grade II tumors (7.3%); while in Grade I tumors, fluorescence positivity was detected in 9 out of 16 cases. In 16 sodium fluorescein patients, seven positive fluorescent cases were detected. As far as indocyanine is concerned, two studies accounting for six patients (three positive) were included, while for tozuleristide, a single clinical trial with eight patients (two positive) was retrieved.

CONCLUSIONS

The current evidence does not support the routine use of 5-aminolevulinic acid or sodium fluorescein with a standard operating microscope because of the low fluorescence rates. New molecules, including tozuleristide, and new techniques for fluorescence detection have shown promising results; however, their use still needs to be clinically validated on a large scale.

Combined Effects of Focused Ultrasound and Photodynamic Treatment for Malignant Brain Tumors Using C6 Glioma Rat Model

PURPOSE

Glioblastoma (GBM) is an intractable disease for which various treatments have been attempted, but with little effect. This study aimed to measure the effect of photodynamic therapy (PDT) and sonodynamic therapy (SDT), which are currently being used to treat brain tumors, as well as sono-photodynamic therapy (SPDT), which is the combination of these two.

MATERIALS AND METHODS

Four groups of Sprague-Dawley rats were injected with C6 glioma cells in a cortical region and treated with PDT, SDT, and SPDT. Gd-MRI was monitored weekly and 18F-FDG-PET the day before and 1 week after the treatment. The acoustic power used during sonication was 5.5 W/cm² using a 0.5-MHz single-element transducer. The 633-nm laser was illuminated at 100 J/cm². Oxidative stress and apoptosis markers were evaluated 3 days after treatment using immunohistochemistry (IHC): 4-HNE, 8-OhdG, and Caspase-3.

RESULTS

A decrease in tumor volume was observed in MRI imaging 12 days after the treatment in the PDT group (p<0.05), but the SDT group showed a slight increase compared to the 5-Ala group. The high expression rates of reactive oxygen species-related factors, such as 8-OhdG (p<0.001) and Caspase-3 (p<0.001), were observed in the SPDT group compared to other groups in IHC.

CONCLUSION

Our findings show that light with sensitizers can inhibit GBM growth, but not ultrasound. Although SPDT did not show the combined effect in MRI, high oxidative stress was observed in IHC. Further studies are needed to investigate the safety parameters to apply ultrasound in GBM.

Serine hydroxymethyltransferase 1 promotes low-grade glioma progression by activating mTORC1 signaling

OBJECTIVES

This research aimed to explore the role and potential mechanism of serine hydroxymethyltransferase 1 (SHMT1) involvement in low-grade glioma (LGG).

METHODS

GEPIA were employed to analyze the expression and the correlation of LGG patient survival with the levels of SHMT1 in LGG based on the The Cancer Genome Atlas (TCGA) database. qRT-PCR and western blot were used to detect the expression of SHMT1 in LGG cells. Clone formation, EdU staining, MTT, Transwell and wound healing assays were conducted to analyze the proliferation, cell activity, migration and invasion of LGG cells. KEEG analysis was performed for enrichment pathways of SHMT1 in LGG.

RESULTS

SHMT1 was up-regulated in LGG tissues and cells, and SHMT1 level was negatively correlated with survival of patients with LGG. SHMT1 overexpression evidently promoted cell proliferation, migration and invasion, whereas SHMT1 silence obtained the opposite results. Next, KEEG analysis revealed that SHMT1 activated the mTORC1 pathway in LGG. SHMT1 overexpression significantly promoted the phosphorylation of downstream proteins (P70SK6 and S6) in LGG cells. Further, inhibition of the mTORC1 signaling pathway partially abolished the promotion of LGG progression by SHMT1 overexpression.

CONCLUSION

SHMT1 promoted proliferation, invasion and migration of LGG cells via activating mTORC1 signaling pathway. This provided a novel perspective for the treatment of LGG.

Circumferential sulcus-guided resection technique for improved outcomes of low-grade gliomas

OBJECTIVE

Many neurosurgeons resect nonenhancing low-grade gliomas (LGGs) by using an inside-out piecemeal resection (PMR) technique. At the authors' institution they have increasingly used a circumferential, perilesional, sulcus-guided resection (SGR) technique. This technique has not been well described and there are limited data on its effectiveness. The authors describe the SGR technique and assess the extent to which SGR correlates with extent of resection and neurological outcome.

METHODS

The authors identified all patients with newly diagnosed LGGs who underwent resection at their institution over a 22-year period. Demographics, presenting symptoms, intraoperative data, method of resection (SGR or PMR), volumetric imaging data, and postoperative outcomes were obtained. Univariate analyses used ANOVA and Fisher's exact test. Multivariate analyses were performed using multivariate logistic regression.

RESULTS

Newly diagnosed LGGs were resected in 519 patients, 208 (40%) using an SGR technique and 311 (60%) using a PMR technique. The median extent of resection in the SGR group was 84%, compared with 77% in the PMR group (p = 0.019). In multivariate analysis, SGR was independently associated with a higher rate of complete (100%) resection (27% vs 18%) (OR 1.7, 95% CI 1.1-2.6; p = 0.03). SGR was also associated with a statistical trend toward lower rates of postoperative neurological complications (11% vs 16%, p = 0.09). A subset analysis of tumors located specifically in eloquent brain demonstrated SGR to be as safe as PMR.

CONCLUSIONS

The authors describe the SGR technique used to resect LGGs and show that SGR is independently associated with statistically significantly higher rates of complete resection, without an increase in neurological complications, than with PMR. SGR technique should be considered when resecting LGGs.

5-ALA-guided tumor resection during awake speech mapping in gliomas located in eloquent speech areas: Single-center experience

Background

Achieving maximal functionally safe resection of gliomas located within the eloquent speech areas is challenging, and there is a lack of literature on the combined use of 5-aminolevulinic acid (5-ALA) guidance and awake craniotomy.

Objective

The aim of this study was to describe our experience with the simultaneous use of 5-ALA fluorescence and awake speech mapping in patients with left frontal gliomas located within the vicinity of eloquent speech areas.

Materials and methods

A prospectively collected database of patients was reviewed. 5-ALA was administered at a dose of 20 mg/kg 2 h prior to operation, and an operating microscope in BLUE400 mode was used to visualize fluorescence. All patients underwent surgery using the "asleep-awake-asleep" protocol with monopolar and bipolar electrical stimulation to identify the proximity of eloquent cortex and white matter tracts and to guide safe limits of resection along with fluorescence guidance. Speech function was assessed by a trained neuropsychologist before, during, and after surgery.

Results

In 28 patients operated with cortical mapping and 5-ALA guidance (12 Grade 4, 6 Grade 3, and 10 Grade 2 gliomas), Broca's area was identified in 23 cases and Wernicke's area was identified in 5 cases. Fluorescence was present in 14 cases. Six tumors had residual fluorescence due to the positive speech mapping in the tumor bed. Transient aphasia developed in 14 patients, and permanent aphasia developed in 4 patients. In 6 patients operated with cortical and subcortical speech mapping and 5-ALA guidance (4 Grade 4, 1 Grade 3, and 1 Grade 2 gliomas), cortical speech areas were mapped in 5 patients and subcortical tracts were encountered in all cases. In all cases, resection was stopped despite the presence of residual fluorescence due to speech mapping findings. Transient aphasia developed in 6 patients and permanent aphasia developed in 4 patients. In patients with Grade 2-3 gliomas, targeted biopsy of focal fluorescence areas led to upgrading the grade and thus more accurate diagnosis.

Conclusion

5-ALA guidance during awake speech mapping is useful in augmenting the extent of resection for infiltrative high-grade gliomas and identifying foci of anaplasia in non-enhancing gliomas, while maintaining safe limits of functional resection based on speech mapping. Positive 5-ALA fluorescence in diffuse Grade 2 gliomas may be predictive of a more aggressive disease course.

CD34 microvascularity in low-grade glioma: correlation with 5-aminolevulinic acid fluorescence and patient prognosis in a multicenter study at three specialized centers

OBJECTIVE

Early markers are urgently needed in low-grade glioma (LGG) evaluation to rapidly estimate the individual patient's prognosis and to determine the optimal postoperative management. Generally, visible 5-aminolevulinic acid (5-ALA) fluorescence is present in only a few LGGs. Recently, the authors identified visible 5-ALA fluorescence as a powerful intraoperative marker for unfavorable outcome in LGG treatment. However, its precise histopathological correlate is unclear. Neoangiogenesis represents a crucial event in tumor evolution, and CD34 is an established marker for vascular endothelial progenitors potentially indicating tumor progression. The aim of this study was thus to correlate 5-ALA fluorescence and CD34 microvascularity as well as to investigate the prognostic value of CD34 in a large series of LGGs.

METHODS

In this retrospective study including 3 specialized centers, patients with histopathologically confirmed isocitrate dehydrogenase-mutated LGGs (WHO grade II) receiving 5-ALA prior to resection were included. During surgery, the presence of visible fluorescence was analyzed and one representative tumor sample from the area with the maximum fluorescence effect (tumor with focal fluorescence or nonfluorescing tumor) was selected for each LGG. All fluorescing or nonfluorescing tumor samples were stained for CD34 and semiquantitatively analyzed for microvascular proliferation patterns (physiological vessels, branching capillaries, or microvessel clusters) as well as automatically quantified for CD34 microvessel density (MVD) by standardized histomorphometry software. These semiquantitative/quantitative CD34 data were correlated to the fluorescence status and patient outcome including progression-free survival (PFS), malignant transformation-free survival (MTFS), and overall survival (OS).

RESULTS

In a total of 86 LGGs, visible fluorescence was found during surgery in 13 (15%) cases. First, the semiquantitative CD34 score significantly correlated with intraoperative fluorescence (p = 0.049). Accordingly, the quantitative CD34 MVD was significantly higher in tumors showing fluorescence (p = 0.03). Altogether, the semiquantitative CD34 score showed a strong correlation with quantitative CD34 MVD (p < 0.001). At a mean follow-up of 5.4 ± 2.6 years, microvessel clusters in semiquantitative analysis were a prognostic marker for poor PFS (p = 0.01) and MTFS (p = 0.006), but not OS (p = 0.28). Finally, quantitative CD34 MVD > 10 vessels/mm2 was a prognostic marker for poor PFS (p = 0.01), MTFS (p = 0.008), and OS (p = 0.049).

CONCLUSIONS

The data indicate that CD34 microvascularity is associated with intraoperative 5-ALA fluorescence and outcomes in patients with LGG. Thus, visible fluorescence in LGGs might indicate increased CD34 microvascularity, serving as an early prognostic marker for unfavorable patient outcome that is already available during surgery.

Specular Reflection Suppression through the Adjustment of Linear Polarization for Tumor Diagnosis Using Fluorescein Sodium

In tumor surgery, the edges of the tumor can be visually observed using a fluorescent contrast agent and a fluorescent imaging device. By distinguishing it from normal tissues and blood vessels, it is possible to objectively judge the extent of resection while visually observing it during surgery, and it guarantees safe tumor resection based on more information. However, the main problem of such an imaging device is the specular reflection phenomenon. If specular reflection overlaps with important lesion locations, they are a major factor leading to diagnostic errors. Here, we propose a method to reduce specular reflection that occurs during tumor diagnosis using a linear polarization filter and fluorescent contrast agent. To confirm the effect of removing specular reflection, a self-made fluorescein sodium vial phantom was used, and the reliability of the results was increased using a large animal (pig) test. As a result of the experiment, it was possible to obtain an image in which specular reflection was removed by controlling the rotation angle of the filter by 90° and 270°, and the same results were confirmed in the phantom experiment and the animal experiment.

5-Aminolevulinic acid fluorescence in brain non-neoplastic lesions: a systematic review and case series

Fluorescence-guided surgery with 5-aminolevulinic acid (5-ALA) is used to assist brain tumor resection, especially for high-grade gliomas but also for low-grade gliomas, metastasis, and meningiomas. With the increasing use of this technique, even to assist biopsies, high-grade glioma-mimicking lesions had misled diagnosis by showing 5-ALA fluorescence in non-neoplastic lesions such as radiation necrosis and inflammatory or infectious disease. Since only isolated reports have been published, we systematically review papers reporting non-neoplastic lesion cases with 5-ALA according with the PRISMA guidelines, present our series, and discuss its pathophysiology. In total, 245 articles were identified and 12 were extracted according to our inclusion criteria. Analyzing 27 patients, high-grade glioma was postulated as preoperative diagnosis in 48% of the cases. Microsurgical resection was performed in 19 cases (70%), while 8 patients were submitted to biopsy (30%). We found 4 positive cases in demyelinating disease (50%), 4 in brain abscess (80%), 1 in neurocysticercosis (33%), 1 in neurotoxoplasmosis, infarction, and hematoma (100%), 4 in inflammatory disease (80%), and 3 in cortical dysplasia (100%). New indications are being considered especially in benign lesion biopsies with assistance of 5-ALA. Using fluorescence as an aid in biopsies may improve procedure time, number of samples, and necessity of intraoperative pathology. Further studies should include this technology to encourage more beneficial uses.

Reduction of Specular Reflection Based on Linear Polarization Control for Fluorescence-Induced Diagnostic Evaluation

The primary goal of cancer surgery is to completely eliminate tumors. A real-time diagnostic method uses a fluorescence contrast agent and a surgical microscope to assess the status of tumor resection and the patient’s blood circulation. The biggest problem in imaging diagnostics using a microscope is the specular reflection phenomenon. While observing a lesion, the observation field may be obstructed due to specular reflection, making it difficult to obtain accurate results during the diagnostic process. Herein we propose a method to reduce specular reflection during tumor diagnosis by introducing a linearly polarized filter for a surgical microscope system. The method of angular direction adjustment of the filter ensures that only the horizontally polarized light passes through it, thereby obstructing the specular reflection. As a result of removing specular reflection, clear images were obtained at 90° and 270°. This experiment was conducted using phantoms and animals. Our results prove that the proposed method can be applied to imaging cameras used in internal medicine, surgery, and radiology for diagnosis.

Evolutionary Trend Analysis of Research on 5-ALA Delivery and Theranostic Applications Based on a Scientometrics Study

5-aminolevulinic acid (5-ALA) has been extensively studied for its sustainability and broad-spectrum applications in medical research and theranostics, as well as other areas. It’s a precursor of protoporphyrin IX (PpIX), a sustainable endogenous and naturally-existing photosensitizer. However, to the best of our knowledge, a scientometrics study based on the scientific knowledge assay of the overall situation on 5-ALA research has not been reported so far, which would be of major importance to the relevant researchers. In this study, we collected all the research articles published in the last two decades from the Web of Science Core Collection database and employed bibliometric methods to comprehensively analyze the dataset from different perspectives using CiteSpace. A total of 1595 articles were identified. The analysis results showed that China published the largest number of articles, and SBI Pharmaceuticals Co., Ltd. was the most productive institution that sponsored several of the most productive authors. The cluster analysis and burst detections indicated that the improvement of photodynamic efficacy theranostics is the up-to-date key direction in 5-ALA research. Furthermore, we emphatically studied nanotechnology involvement in 5-ALA delivery and theranostics research. We envision that our results will be beneficial for researchers to have a panorama of and deep insights into this area, thus inspiring further exploitations, especially of the nanomaterial-based systems for 5-ALA delivery and theranostic applications.

Impact of Levetiracetam Treatment on 5-Aminolevulinic Acid Fluorescence Expression in IDH1 Wild-Type Glioblastoma

Simple Summary

The amino acid 5-aminolevulinic acid (5-ALA) is the benchmark regarding intraoperative imaging tools for glioblastoma (GB) surgery, and is known to facilitate the extent of resection, which results in an enhanced 6 month progression-free survival rate. Recent in vitro studies suggest that antiepileptic drugs (AEDs) result in a reduction in the fluorescence quality in gliomas. To date, there is no large clinical series investigating this issue in a homogeneous cohort. Approximately 25% of all GB patients have a symptomatic epilepsy as the initial symptom at presentation. Hence, this potential dilemma is of paramount importance. We found that the preoperative intake of levetiracetam is a significant risk factor for reduced intraoperative fluorescence in IDH1 wild-type GBs. We believe that this issue must be considered in future external validations, and physicians must carefully evaluate the indication of levetiracetam and avoid a prophylactic levetiracetam treatment in terms of the suspected diagnosis of glioblastoma.

Abstract

The amino acid 5-aminolevulinic acid (5-ALA) is the most established neurosurgical fluorescent dye and facilitates the achievement of gross total resection. In vitro studies raised concerns that antiepileptic drugs (AED) reduce the quality of fluorescence. Between 2013 and 2018, 175 IDH1 wild-type glioblastoma (GB) patients underwent 5-ALA guided surgery. Patients’ data were retrospectively reviewed regarding demographics, comorbidities, medications, tumor morphology, neuropathological characteristics, and their association with intraoperative 5-ALA fluorescence. The fluorescence of 5-ALA was graded in a three point scaling system (grade 0 = no; grade 1 = weak; grade 2 = strong). Univariable analysis shows that the intake of dexamethasone or levetiracetam, and larger preoperative tumor area significantly reduce the intraoperative fluorescence activity (fluorescence grade: 0 + 1). Multivariable binary logistic regression analysis demonstrates the preoperative intake of levetiracetam (adjusted odds ratio: 12.05, 95% confidence interval: 3.91–37.16, p = 0.001) as the only independent and significant risk factor for reduced fluorescence quality. Preoperative levetiracetam intake significantly reduced intraoperative fluorescence. The indication for levetiracetam in suspected GB should be carefully reviewed and prophylactic treatment avoided for this tumor entity. Future comparative trials of neurosurgical fluorescent dyes need a special focus on the influence of levetiracetam on fluorescence intensity. Further trials must validate our findings.

Correlation of Intraoperative 5-ALA-Induced Fluorescence Intensity and Preoperative 11C-Methionine PET Uptake in Glioma Surgery

Simple Summary

In malignant brain tumor surgery, precise identification of the tumor is essential. 5-Aminolevulinic acid (5-ALA) labels tumor cells with red fluorescence to facilitate tumor resection. On the other hand, the nuclear medicine imaging technique, positron emission tomography with ¹¹C-methionine (MET-PET), can delineate tumors precisely but is not widely available. This study aimed to determine the correlation between intraoperative 5-ALA-induced fluorescence and preoperative MET-PET signals of gliomas. We quantitatively measured the fluorescence intensity from tumor samples and calculated the MET-PET uptake by the tumor. Our study showed that strong tumor fluorescence correlated with high MET-PET uptake and cellular proliferation. Our findings might be valuable to rapidly provide information on tumor biology at the time of surgery in circumstances where MET-PET is inaccessible.

Abstract

Background: 5-Aminolevulinic acid (5-ALA) is widely employed to assist fluorescence-guided surgery for malignant brain tumors. Positron emission tomography with ¹¹C-methionine (MET-PET) represents the activity of brain tumors with precise boundaries but is not readily available. We hypothesized that quantitative 5-ALA-induced fluorescence intensity might correlate with MET-PET uptake in gliomas. Methods: Adult patients with supratentorial astrocytic gliomas who underwent preoperative MET-PET and surgical tumor resection using 5-ALA were enrolled in this prospective study. The regional tumor uptake of MET-PET was expressed as the ratio of standardized uptake volume max to that of the normal contralateral frontal lobe. A spectrometric fluorescence detection system measured tumor specimens’ ex vivo fluorescence intensity at 635 nm. Ki-67 index and IDH mutation status were assessed by histopathological analysis. Use of an antiepileptic drug (AED) and contrast enhancement pattern on MRI were also investigated. Results: Thirty-two patients, mostly with Glioblastoma IDH wild type (46.9%) and anaplastic astrocytoma IDH mutant (21.9%), were analyzed. When the fluorescence intensity was ranked into four groups, the strongest fluorescence group exhibited the highest mean MET-PET uptake and Ki-67 index values. When rearranged into fluorescence Visible or Non-visible groups, the Visible group had significantly higher MET-PET uptake and Ki-67 index compared to the Non-visible group. Contrast enhancement on MRI and IDH wild type tumors were more frequent among the Visible group. AED use did not correlate with 5-ALA-induced fluorescence intensity. Conclusions: In astrocytic glioma surgery, visible 5-ALA-induced fluorescence correlated with high MET-PET uptake, along with a high Ki-67 index.

The Combined Use of 5-ALA and Chlorin e6 Photosensitizers for Fluorescence-Guided Resection and Photodynamic Therapy under Neurophysiological Control for Recurrent Glioblastoma in the Functional Motor Area after Ineffective Use of 5-ALA: Preliminary Results

The treatment of glial brain tumors is an unresolved problem in neurooncology, and all existing methods (tumor resection, chemotherapy, radiotherapy, radiosurgery, fluorescence diagnostics, photodynamic therapy, etc.) are directed toward increasing progression-free survival for patients. Fluorescence diagnostics and photodynamic therapy are promising methods for achieving gross total resection and additional treatment of residual parts of the tumor. However, sometimes the use of one photosensitizer for photodynamic therapy does not help, and the time until tumor relapse barely increases. This translational case report describes the preliminary results of the first combined use of 5-ALA and chlorin e6 photosensitizers for fluorescence-guided resection and photodynamic therapy of glioblastoma, which allowed us to perform total resection of tumor tissue according to magnetic resonance and computed tomography images, remove additional tissue with increased fluorescence intensity without neurophysiological consequences, and perform additional therapy. Two months after surgery, no recurrent tumor and no contrast uptake in the tumor bed were detected. Additionally, the patient had ischemic changes in the access zone and along the periphery and cystic-glial changes in the left parietal lobe.

Analysis of corticosteroid and antiepileptic drug treatment effects on heme biosynthesis mRNA expression in lower-grade gliomas: potential implications for 5-ALA metabolization

OBJECTIVES

Intraoperative visualization of gliomas with 5-aminolevulinic acid (5-ALA) induced fluorescence constitutes a powerful technique. While visible fluorescence is typically observed in high-grade gliomas, fluorescence is considerably less common in lower-grade gliomas (LGGs) WHO grade II&III. Whereas the exact mechanisms determining fluorescence in LGGs are not fully understood, metabolization of non-fluorescent 5-ALA to fluorescent Protoporphyrin IX by specific heme biosynthesis enzymes/transporters has been identified as relevant mechanism influencing fluorescence behavior. Furthermore, recent in-vitro studies have suggested preoperative treatment with corticosteroids and anti-epileptic drugs (AED) as potential factors influencing 5-ALA induced fluorescence.

METHODS

The goal of this study was thus to investigate the effect of preoperative corticosteroid/AED treatment on heme biosynthesis mRNA expression in a clinically relevant patient population. For this purpose, we analyzed the mRNA expression levels of specific heme biosynthesis factors including ALAD, HMBS, UROS, UROD, CPOX, PPOX, FECH, ABCB6, ACG2, SLC15A1 and SLC15A2, ABCB1, ABCB10 in a cohort of LGGs from "The Cancer Genome Atlas".

RESULTS

Altogether, 403 patients with available data on preoperative corticosteroid/AED treatment and heme biosynthesis mRNA expression were identified. Regarding corticosteroid treatment, no significant differences in expression of any of the 11 investigated heme biosynthesis factors were found. In contrast, a marginal yet statistically significant increase in SLC15A1 levels and decrease in ABCB6 levels were observed in patients with preoperative AED treatment.

CONCLUSION

While no significant differences in heme biosynthesis mRNA expression were observed according to preoperative corticosteroid treatment, changes in SLC15A1 as well as ABCB6 expression were detected in patients treated with AED. However, since these alterations were minor and have opposing effects on 5-ALA metabolization, our findings do not support a distinct effect of AED and corticosteroid treatment on heme biosynthesis regulation in LGGs.

Fluorescent diagnostics with chlorin e6 in surgery of low-grade glioma

Intraoperative fluorescence diagnostics of high-grade gliomas is widely used in neurosurgical practice. This work analyzes the possibilities of fluorescence diagnostics for low-grade gliomas (LGG) using chlorin e6 photosensitizer. The study included patients with newly diagnosed LGG, for whom chlorin e6 was used for intraoperative fluorescence control at a dose of 1 mg/kg. During the operation, the fluorescence intensity of various areas of the putative tumor tissue was analyzed using the RSS Cam – Endo 1.4.313 software. Tissue samples with various degrees of fluorescence intensity were compared with the results of their histopathological analysis (WHO tumor diagnosis, Ki-67 index, P53, VEGF). Fluorescence was detected in more than half of the cases, but in most cases had a focal character and low fluorescence intensity. The fluorescence intensity directly correlated with the data of histopathological examination of tumor tissues (Ki-67 index (p=0.002), expression of P53 (p=0.0015) and VEGF (p=0.001)). The sensitivity of the method for LGG surgery was 72%, the specificity was 56,7%. Intraoperative fluorescence diagnostics with chlorin e6 can be used in LGG surgery, especially to visualize intratumoral areas with a higher degree of anaplasia.

A Pilot Study of Fluorescence-Guided Resection of Pituitary Adenomas with Chlorin e6 Photosensitizer

Fluorescence diagnostics is one of the promising methods for intraoperative detection of brain tumor boundaries and helps in maximizing the extent of resection. This paper presents the results of a pilot study on the first use of the chlorin e6 photosensitizer and a two-channel video system for fluorescence-guided resection of pituitary adenomas. The study’s clinical part involved two patients diagnosed with hormonally inactive pituitary macroadenomas and one patient with a hormonally active one. All neoplasms had different sizes and growth patterns. The data showed accumulation of chlorin e6 in tumor tissues in high concentrations: Patient 1: 2 mg/kg, Patient 2: 5 mg/kg, and Patient 3: 4 mg/kg. For Patient 1, the residual part of the tumor was not resected since it was intimately attached to the anterior genu of the internal carotid artery. For Patients 2 and 3, no regions of increased Ce6 accumulation were detected in the tumor foci after resection. Therefore, the use of the Ce6 and a two-channel video system helped to achieve a high degree of tumor resection in each case.

Advanced Optical Imaging-Guided Nanotheranostics towards Personalized Cancer Drug Delivery

Nanomedicine involves the use of nanotechnology for clinical applications and holds promise to improve treatments. Recent developments offer new hope for cancer detection, prevention and treatment; however, being a heterogenous disorder, cancer calls for a more targeted treatment approach. Personalized Medicine (PM) aims to revolutionize cancer therapy by matching the most effective treatment to individual patients. Nanotheranostics comprise a combination of therapy and diagnostic imaging incorporated in a nanosystem and are developed to fulfill the promise of PM by helping in the selection of treatments, the objective monitoring of response and the planning of follow-up therapy. Although well-established imaging techniques, such as Magnetic Resonance Imaging (MRI), Computed Tomography (CT), Positron Emission Tomography (PET) and Single-Photon Emission Computed Tomography (SPECT), are primarily used in the development of theranostics, Optical Imaging (OI) offers some advantages, such as high sensitivity, spatial and temporal resolution and less invasiveness. Additionally, it allows for multiplexing, using multi-color imaging and DNA barcoding, which further aids in the development of personalized treatments. Recent advances have also given rise to techniques permitting better penetration, opening new doors for OI-guided nanotheranostics. In this review, we describe in detail these recent advances that may be used to design and develop efficient and specific nanotheranostics for personalized cancer drug delivery.

Analysis of Factors Affecting 5-ALA Fluorescence Intensity in Visualizing Glial Tumor Cells-Literature Review

Glial tumors are one of the most common lesions of the central nervous system. Despite the implementation of appropriate treatment, the prognosis is not successful. As shown in the literature, maximal tumor resection is a key element in improving therapeutic outcome. One of the methods to achieve it is the use of fluorescent intraoperative navigation with 5-aminolevulinic acid. Unfortunately, often the level of fluorescence emitted is not satisfactory, resulting in difficulties in the course of surgery. This article summarizes currently available knowledge regarding differences in the level of emitted fluorescence. It may depend on both the histological type and the genetic profile of the tumor, which is reflected in the activity and expression of enzymes involved in the intracellular metabolism of fluorescent dyes, such as PBGD, FECH, UROS, and ALAS. The transport of 5-aminolevulinic acid and its metabolites across the blood–brain barrier and cell membranes mediated by transporters, such as ABCB6 and ABCG2, is also important. Accompanying therapies, such as antiepileptic drugs or steroids, also have an impact on light emission by tumor cells. Accurate determination of the factors influencing the fluorescence of 5-aminolevulinic acid-treated cells may contribute to the improvement of fluorescence navigation in patients with highly malignant gliomas.

Nanoparticles for Diagnosis and Target Therapy in Pediatric Brain Cancers

Pediatric brain tumors represent the most common types of childhood cancer and novel diagnostic and therapeutic solutions are urgently needed. The gold standard treatment option for brain cancers in children, as in adults, is tumor resection followed by radio- and chemotherapy, but with discouraging therapeutic results. In particular, the last two treatments are often associated to significant neurotoxicity in the developing brain of a child, with resulting disabilities such as cognitive problems, neuroendocrine, and neurosensory dysfunctions/deficits. Nanoparticles have been increasingly and thoroughly investigated as they show great promises as diagnostic tools and vectors for gene/drug therapy for pediatric brain cancer due to their ability to cross the blood–brain barrier. In this review we will discuss the developments of nanoparticle-based strategies as novel precision nanomedicine tools for diagnosis and therapy in pediatric brain cancers, with a particular focus on targeting strategies to overcome the main physiological obstacles that are represented by blood–brain barrier.

5-ALA in Suspected Low-Grade Gliomas: Current Role, Limitations, and New Approaches

Radiologically suspected low-grade gliomas (LGG) represent a special challenge for the neurosurgeon during surgery due to their histopathological heterogeneity and indefinite tumor margin. Therefore, new techniques are required to overcome these current surgical drawbacks. Intraoperative visualization of brain tumors with assistance of 5-aminolevulinic acid (5-ALA) induced protoporphyrin IX (PpIX) fluorescence is one of the major advancements in the neurosurgical field in the last decades. Initially, this technique was exclusively applied for fluorescence-guided surgery of high-grade glioma (HGG). In the last years, the use of 5-ALA was also extended to other indications such as radiologically suspected LGG. Here, we discuss the current role of 5-ALA for intraoperative visualization of focal malignant transformation within suspected LGG. Furthermore, we discuss the current limitations of the 5-ALA technology in pure LGG which usually cannot be visualized by visible fluorescence. Finally, we introduce new approaches based on fluorescence technology for improved detection of pure LGG tissue such as spectroscopic PpIX quantification fluorescence lifetime imaging of PpIX and confocal microscopy to optimize surgery.

Prediction of Intraoperative Fluorescence of Brain Gliomas: Correlation between Tumor Blood Flow and the Fluorescence

INTRODUCTION

The prediction of the fluorescent effect of 5-aminolevulinic acid (5-ALA) in patients with diffuse gliomas can improve the selection of patients. The degree of enhancement of gliomas has been reported to predict 5-ALA fluorescence, while, at the same time, rarer cases of fluorescence have been described in non-enhancing gliomas. Perfusion studies, in particular arterial spin labeling perfusion, have demonstrated high efficiency in determining the degree of malignancy of brain gliomas and may be better for predicting fluorescence than contrast enhancement. The aim of the study was to investigate the relationship between tumor blood flow, measured by ASL, and intraoperative fluorescent glow of gliomas of different grades.

MATERIALS AND METHODS

Tumoral blood flow was assessed in 75 patients by pCASL (pseudo-continuous arterial spin labeling) within 1 week prior to surgery. In all cases of tumor removal, 5-ALA had been administered preoperatively. Maximum values of tumoral blood flow (TBF max) were measured, and normalized tumor blood flow (nTBF) was calculated.

RESULTS

A total of 76% of patients had significant contrast enhancement, while 24% were non-enhancing. The histopathology revealed 17 WHO grade II gliomas, 12 WHO grade III gliomas and 46 glioblastomas. Overall, there was a relationship between the degree of intraoperative tumor fluorescence and ASL-TBF (R_s = 0.28, p = 0.02 or the TBF; R_s = 0.34, p = 0.003 for nTBF). Non-enhancing gliomas were fluorescent in 9/18 patients, with nTBF in fluorescent gliomas being 54.58 ± 32.34 mL/100 mg/s and in non-fluorescent gliomas being 52.99 ± 53.61 mL/100 g/s (p > 0.05). Enhancing gliomas were fluorescent in 53/57 patients, with nTBF being 170.17 ± 107.65 mL/100 g/s in fluorescent and 165.52 ± 141.71 in non-fluorescent gliomas (p > 0.05).

CONCLUSION

Tumoral blood flow levels measured by non-contrast ASL perfusion method predict the fluorescence by 5-ALA; however, the additional value beyond contrast enhancement is not clear. ASL is, however, useful in cases with contraindication to contrast.

Rationale and Clinical Implications of Fluorescein-Guided Supramarginal Resection in Newly Diagnosed High-Grade Glioma

Current standard of care for glioblastoma is surgical resection followed by temozolomide chemotherapy and radiation. Recent studies have demonstrated that >95% extent of resection is associated with better outcomes, including prolonged progression-free and overall survival. The diffusely infiltrative pattern of growth in gliomas results in microscopic extension of tumor cells into surrounding brain parenchyma that makes complete resection unattainable. The historical goal of surgical management has therefore been maximal safe resection, traditionally guided by MRI and defined as removal of all contrast-enhancing tumor. Optimization of surgical resection has led to the concept of supramarginal resection, or removal beyond the contrast-enhancing region on MRI. This strategy of extending the cytoreductive goal targets a tumor region thought to be important in the recurrence or progression of disease as well as resistance to systemic and local treatment. This approach must be balanced against the risk of impacting eloquent regions of brain and causing permanent neurologic deficit, an important factor affecting overall survival. Over the years, fluorescent agents such as fluorescein sodium have been explored as a means of more reliably delineating the boundary between tumor core, tumor-infiltrated brain, and surrounding cortex. Here we examine the rationale behind extending resection into the infiltrative tumor margins, review the current literature surrounding the use of fluorescein in supramarginal resection of gliomas, discuss the experience of our own institution in utilizing fluorescein to maximize glioma extent of resection, and assess the clinical implications of this treatment strategy.

5-ALA Fluorescence Is a Powerful Prognostic Marker during Surgery of Low-Grade Gliomas (WHO Grade II)-Experience at Two Specialized Centers

The prediction of the individual prognosis of low-grade glioma (LGG) patients is limited in routine clinical practice. Nowadays, 5-aminolevulinic acid (5-ALA) fluorescence is primarily applied for improved intraoperative visualization of high-grade gliomas. However, visible fluorescence is also observed in rare cases despite LGG histopathology and might be an indicator for aggressive tumor behavior. The aim of this study was thus to investigate the value of intraoperative 5-ALA fluorescence for prognosis in LGG patients. We performed a retrospective analysis of patients with newly diagnosed histopathologically confirmed LGG and preoperative 5-ALA administration at two independent specialized centers. In this cohort, we correlated the visible intraoperative fluorescence status with progression-free survival (PFS), malignant transformation-free survival (MTFS) and overall survival (OS). Altogether, visible fluorescence was detected in 7 (12%) of 59 included patients in focal intratumoral areas. At a mean follow-up time of 5.3 ± 2.9 years, patients with fluorescing LGG had significantly shorter PFS (2.3 ± 0.7 vs. 5.0 ± 0.4 years; p = 0.01), MTFS (3.9 ± 0.7 vs. 8.0 ± 0.6 years; p = 0.03), and OS (5.4 ± 1.0 vs. 10.3 ± 0.5 years; p = 0.01) than non-fluorescing tumors. Our data indicate that visible 5-ALA fluorescence during surgery of pure LGG might be an already intraoperatively available marker of unfavorable patient outcome and thus close imaging follow-up might be considered.

Molecular and Metabolic Mechanisms Underlying Selective 5-Aminolevulinic Acid-Induced Fluorescence in Gliomas

Simple Summary

5-aminolevulinic acid (5-ALA) is a medication that produces fluorescence in certain cancers, which enables surgeons to visualize tumor margins during surgery. Gliomas are brain tumors that can be difficult to fully resect due to their infiltrative nature. In this review we explored what is known about the mechanism of 5-ALA, recent discoveries that increase our understanding of that mechanism, and potential targets to increase fluorescence in lower grade gliomas.

Abstract

5-aminolevulinic acid (5-ALA) is a porphyrin precursor in the heme synthesis pathway. When supplied exogenously, certain cancers consume 5-ALA and convert it to the fluorogenic metabolite protoporphyrin IX (PpIX), causing tumor-specific tissue fluorescence. Preoperative administration of 5-ALA is used to aid neurosurgical resection of high-grade gliomas such as glioblastoma, allowing for increased extent of resection and progression free survival for these patients. A subset of gliomas, especially low-grade tumors, do not accumulate PpIX intracellularly or readily fluoresce upon 5-ALA administration, making gross total resection difficult to achieve in diffuse lesions. We review existing literature on 5-ALA metabolism and PpIX accumulation to explore potential mechanisms of 5-ALA-induced glioma tissue fluorescence. Targeting the heme synthesis pathway and understanding its dysregulation in malignant tissues could aid the development of adjunct therapies to increase intraoperative fluorescence after 5-ALA treatment.

Multicellular "hotspots" harbor high-grade potential in lower-grade gliomas

BACKGROUND

Lower-grade gliomas may be indolent for many years before developing malignant behavior. The mechanisms underlying malignant progression remain unclear.

METHODS

We collected blocks of live human brain tissue donated by people undergoing glioma resection. The tissue blocks extended through the peritumoral cortex and into the glioma. The living human brain tissue was cut into ex vivo brain slices and bathed in 5-aminolevulinic acid (5-ALA). High-grade glioma cells avidly take up 5-ALA and accumulate high levels of the fluorescent metabolite, Protoporphyrin IX (PpIX). We exploited the PpIX fluorescence emitted by higher-grade glioma cells to investigate the earliest stages of malignant progression in lower-grade gliomas.

RESULTS

We found sparsely distributed "hot-spots" of PpIX-positive cells in living lower-grade glioma tissue. Glioma cells and endothelial cells formed part of the PpIX hotspots. Glioma cells in PpIX hotspots were IDH1 mutant and expressed nestin suggesting they had acquired stem-like properties. Spatial analysis with 5-ALA-conjugated quantum dots indicated that these glioma cells replicated adjacent to blood vessels. PpIX hotspots were formed in the absence of angiogenesis.

CONCLUSION

Our data show that PpIX hotspots represent microdomains of cells with high-grade potential within lower-grade gliomas and identify locations where malignant progression could start.

Terahertz dielectric spectroscopy of human brain gliomas and intact tissues ex vivo: double-Debye and double-overdamped-oscillator models of dielectric response

Terahertz (THz) technology offers novel opportunities in the intraoperative neurodiagnosis. Recently, the significant progress was achieved in the study of brain gliomas and intact tissues, highlighting a potential for THz technology in the intraoperative delineation of tumor margins. However, a lack of physical models describing the THz dielectric permittivity of healthy and pathological brain tissues restrains the further progress in this field. In the present work, the ex vivo THz dielectric response of human brain tissues was analyzed using relaxation models of complex dielectric permittivity. Dielectric response of tissues was parametrized by a pair of the Debye relaxators and a pair of the overdamped-oscillators - namely, the double-Debye (DD) and double-overdamped-oscillator (DO) models. Both models accurately reproduce the experimental curves for the intact tissues and the WHO Grades I-IV gliomas. While the DD model is more common for THz biophotonics, the DO model is more physically rigorous, since it satisfies the sum rule. In this way, the DO model and the sum rule were, then, applied to estimate the content of water in intact tissues and gliomas ex vivo. The observed results agreed well with the earlier-reported data, justifying water as a main endogenous label of brain tumors in the THz range. The developed models can be used to describe completely the THz-wave - human brain tissues interactions in the frameworks of classical electrodynamics, being quite important for further research and developments in THz neurodiagnosis of tumors.

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.

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.

Photodynamic therapy, priming and optical imaging: Potential co-conspirators in treatment design and optimization - a Thomas Dougherty Award for Excellence in PDT paper

Photodynamic therapy is a photochemistry-based approach, approved for the treatment of several malignant and non-malignant pathologies. It relies on the use of a non-toxic, light activatable chemical, photosensitizer, which preferentially accumulates in tissues/cells and, upon irradiation with the appropriate wavelength of light, confers cytotoxicity by generation of reactive molecular species. The preferential accumulation however is not universal and, depending on the anatomical site, the ratio of tumor to normal tissue may be reversed in favor of normal tissue. Under such circumstances, control of the volume of light illumination provides a second handle of selectivity. Singlet oxygen is the putative favorite reactive molecular species although other entities such as nitric oxide have been credibly implicated. Typically, most photosensitizers in current clinical use have a finite quantum yield of fluorescence which is exploited for surgery guidance and can also be incorporated for monitoring and treatment design. In addition, the photodynamic process alters the cellular, stromal, and/or vascular microenvironment transiently in a process termed photodynamic priming, making it more receptive to subsequent additional therapies including chemo- and immunotherapy. Thus, photodynamic priming may be considered as an enabling technology for the more commonly used frontline treatments. Recently, there has been an increase in the exploitation of the theranostic potential of photodynamic therapy in different preclinical and clinical settings with the use of new photosensitizer formulations and combinatorial therapeutic options. The emergence of nanomedicine has further added to the repertoire of photodynamic therapy's potential and the convergence and co-evolution of these two exciting tools is expected to push the barriers of smart therapies, where such optical approaches might have a special niche. This review provides a perspective on current status of photodynamic therapy in anti-cancer and anti-microbial therapies and it suggests how evolving technologies combined with photochemically-initiated molecular processes may be exploited to become co-conspirators in optimization of treatment outcomes. We also project, at least for the short term, the direction that this modality may be taking in the near future.

Lighting Up the Tumor-Fluorescein-Guided Resection of Gangliogliomas

(1) Background: Gangliogliomas comprise a small number of brain tumors. They usually present as World Health Organization (WHO) grade I, and they delineate on gadolinium-enhanced MRI; the surgical goal is wide radical resection, and the course thereafter is usually benign. Fluorescein sodium (FL) tends to accumulate in areas with altered blood–brain barrier (BBB). Thus far, the results provided by prospective and retrospective studies show that the utilization of this fluorophore may be associated with better visualization and improvement of resection for several tumors of the central nervous system. In this study, we retrospectively studied the effect of fluorescein sodium on visualization and resection of gangliogliomas. (2) Methods: Surgical databases in three neurosurgical departments (Regensburg University Hospital; Besta Institute, Milano, Italy; and Liv Hospital, Istanbul, Turkey), with approval by the local ethics committee, were retrospectively reviewed to find gangliogliomas surgically removed by a fluorescein-guided technique by the aid of a dedicated filter on the surgical microscope from April 2014 to February 2020. Eighteen patients (13 women, 5 men; mean age 22.9 years, range 3 to 78 years) underwent surgical treatment for gangliogliomas during 19 operations. Fluorescein was intravenously injected (5 mg/kg) after general anesthesia induction. Tumors were removed using a microsurgical technique with the YELLOW 560 Filter (YE560) (KINEVO/PENTERO 900, Carl Zeiss Meditec, Oberkochen, Germany). (3) Results: No side effects related to fluorescein occurred. In all tumors, contrast enhancement on preoperative MRI correlated with bright yellow fluorescence during the surgical procedure (17 gangliogliomas WHO grade I, 1 ganglioglioma WHO grade II). Fluorescein was considered helpful by the operating surgeon in distinguishing tumors from viable tissue in all cases (100%). Biopsy was intended in two operations, and subtotal resection was intended in one operation. In all other operations considered preoperatively eligible, gross total resection (GTR) was achieved in 12 out of 16 (75%) instances. (4) Conclusions: The use of FL and YE560 is a readily available method for safe fluorescence-guided tumor resection, possibly visualizing tumor margins intraoperatively similar to contrast enhancement in T1-weighted MRI. Our data suggested a positive effect of fluorescein-guided surgery on intraoperative visualization and extent of resection during resection of gangliogliomas.

Blood-Brain Barrier, Blood-Brain Tumor Barrier, and Fluorescence-Guided Neurosurgical Oncology: Delivering Optical Labels to Brain Tumors

Recent advances in maximum safe glioma resection have included the introduction of a host of visualization techniques to complement intraoperative white-light imaging of tumors. However, barriers to the effective use of these techniques within the central nervous system remain. In the healthy brain, the blood-brain barrier ensures the stability of the sensitive internal environment of the brain by protecting the active functions of the central nervous system and preventing the invasion of microorganisms and toxins. Brain tumors, however, often cause degradation and dysfunction of this barrier, resulting in a heterogeneous increase in vascular permeability throughout the tumor mass and outside it. Thus, the characteristics of both the blood-brain and blood-brain tumor barriers hinder the vascular delivery of a variety of therapeutic substances to brain tumors. Recent developments in fluorescent visualization of brain tumors offer improvements in the extent of maximal safe resection, but many of these fluorescent agents must reach the tumor via the vasculature. As a result, these fluorescence-guided resection techniques are often limited by the extent of vascular permeability in tumor regions and by the failure to stain the full volume of tumor tissue. In this review, we describe the structure and function of both the blood-brain and blood-brain tumor barriers in the context of the current state of fluorescence-guided imaging of brain tumors. We discuss features of currently used techniques for fluorescence-guided brain tumor resection, with an emphasis on their interactions with the blood-brain and blood-tumor barriers. Finally, we discuss a selection of novel preclinical techniques that have the potential to enhance the delivery of therapeutics to brain tumors in spite of the barrier properties of the brain.

5-ALA fluorescence in a WHO grade I papillary glioneuronal tumour: a case report

5-ALA is proven to be effective in high-grade glioma operative resection. The use of 5-ALA in WHO grade I lesions is still controversial. A 49-year-old lady was diagnosed in 2004 with a left temporal lobe lesion as an incidental finding; she was followed up clinically and radiologically. In 2016, the lesion showed contrast enhancement and she was offered surgical resection but given she is asymptomatic, she refused. In 2018, the lesion showed signs of transformation with ring contrast enhancement, increased vasogenic oedema and perfusion; the patient accepted surgery at that point. She had preoperative mapping by navigated transcranial magnetic stimulation and she had operative resection with 5-ALA. The tumour was bright fluorescent under Blue 400 filter—Zeiss Pentero 900©(Carl Zeiss Meditec)—and both bright fluorescence and pale fluorescence were resected. Postoperative MRI showed complete resection and histopathology revealed WHO grade I papillary glioneuronal tumour, negative for BRAF V600 mutation. WHO grade I papillary glioneuronal tumour may present as 5-ALA fluorescent lesions. From a clinical perspective, 5-ALA can be used to achieve complete resections in these lesions which, in most cases, can be curative.

Corrigendum to "Protoporphyrin IX tracer fluorescence modulation for improved brain tumor cell lines visualization"

Fluorescence image guided surgical resection (FIGR) of high grade gliomas (HGGs) takes advantage of the accumulation of the tracer protoporphyrin IX (PpIX) in glioma cells following administration of 5-aminolevulinic acid (5-ALA). Occasionally, PpIX fluorescence intensity may be insufficient, thus compromising the efficacy and precision of the surgical intervention. The cause for the signal variation is unclear and strategies to improve the intensity of PpIX fluorescence are considered necessary. We have previously shown that differential expression of the epidermal growth factor receptor in glioblastoma cells affects PpIX fluorescence. Herein, we investigated other factors impairing PpIX accumulation and pharmacological treatments able to enhance PpIX fluorescence in glioblastoma cells displaying lower signal. In the present study we demonstrate that presence of serum in cell culture medium and differences in cellular confluence can negatively influence PpIX accumulation in U87 cell lines. We hypothesized that PpIX fluorescence intensity results from the interplay between the metabolic clearance of PpIX mediated by ferrochelatase (FECH) and heme oxygenase-1 (HO-1) and the cellular efflux of PpIX through the ATP-binding cassette subfamily G member 2 (ABCG2). Based on the availability of compounds targeting these proteins and inhibiting them, in this study we used modulators such as genistein, an isoflavone able to inhibit ABCG2; deferoxamine, which chelate iron ions impairing FECH activity and tin protoporphyrin IX (SnPP), the specific HO-1 inhibitor. Finally, we showed the efficacy of a precisely tuned pharmacological treatment in increasing PpIX accumulation and consequently fluorescence in glioblastoma cells. This strategy may translate in more sensitive tracing of tumor cells in-vivo and improved FIGR of HGGs and possibly low grade gliomas (LGGs).

[Intraoperative vascular fluorescence in cerebral glioblastomas and vascular histological features]

5-ALA intraoperative fluorescence is widely used in surgery of brain tumors for intraoperative demarcation of boundaries and more total resection because 5-ALA metabolites are not accumulated in the intact brain and vascular tissues. Given this fact, it was hypothesized that fluorescence of vessels in the immediate vicinity of a brain tumor may indicate their infiltration by tumor cells as a potential pathway for their dissemination and as a factor for continued tumor growth after surgery and adjuvant therapy.

PURPOSE

Identification of fluorescent vessels located near cerebral gliomas, with a histological description of their structure, relationships with the tumor, and potential invasion of the walls by tumor cells.

MATERIAL AND METHODS

A prospective cohort study included 14 patients with malignant supratentorial gliomas, aged 20 to 78 years. Five patients were operated on due to continued tumor growth. Two hours before surgery, all patients received 5-ALA orally. During surgery, a microscope (Carl Zeiss OPMI Pentero, Germany) with a fluorescent module (BLUE-400) was used. In all cases, molecular-genetic and immunohistochemical examinations of the tumor material were performed. During surgery, fluorescent vessels, after evaluating their functional significance, were also resected for histological examination.

RESULTS

Glioblastoma and anaplastic astrocytoma were verified in 10 and 4 patients, respectively. In 4 out of 10 glioblastoma cases, vessels with homogeneous or fragmentary fluorescent walls were detected in the tumor bed after resection of most of the tumor; in patients with anaplastic astrocytomas, vascular fluorescence was not observed. In the four vascular samples with intraoperatively detected wall fluorescence, tumor invasion into the vascular layers was revealed in all cases. These patients underwent an immunohistochemical examination with monoclonal antibodies to the glial GFAP marker, which clearly identified areas of ingrowth of tumor cells into the vascular wall.

CONCLUSION

5-ALA intraoperative fluorescence is a fundamentally new approach in the rapid diagnosis of tumor-infiltrated blood vessels. Invasion of tumor cells to intact vessels may be a mechanism of tumor progression and dissemination. Additional resection of fluorescent vessels may affect the radicalness of surgical treatment, but requires a mandatory assessment of their functional significance.

Protoporphyrin IX tracer fluorescence modulation for improved brain tumor cell lines visualization

Fluorescence image guided surgical resection (FIGR) of high grade gliomas (HGGs) takes advantage of the accumulation of the tracer protoporphyrin IX (PpIX) in glioma cells following administration of 5-aminolevulinic acid (5-ALA). Occasionally, PpIX fluorescence intensity may be insufficient, thus compromising the efficacy and precision of the surgical intervention. The cause for the signal variation is unclear and strategies to improve the intensity of PpIX fluorescence are considered necessary. We have previously shown that differential expression of the epidermal growth factor receptor in glioblastoma cells affects PpIX fluorescence. Herein, we investigated other factors impairing PpIX accumulation and pharmacological treatments able to enhance PpIX fluorescence in glioblastoma cells displaying lower signal. In the present study we demonstrate that presence of serum in cell culture medium and differences in cellular confluence can negatively influence PpIX accumulation in U87 cell lines. We hypothesized that PpIX fluorescence intensity results from the interplay between the metabolic clearance of PpIX mediated by ferrochelatase and heme oxygenase-1 and the cellular efflux of PpIX through the ATP-binding cassette subfamily G member 2 (ABCG2). Based on the availability of compounds targeting these proteins and inhibiting them, in this study we used modulators such as genistein, an isoflavone able to inhibit ABCG2; deferoxamine, which chelate iron ions impairing FECH activity and tin protoporphyrin IX (SnPP), the specific HO-1 inhibitor. Finally, we showed the efficacy of a precisely tuned pharmacological treatment in increasing PpIX accumulation and consequently fluorescence in glioblastoma cells. This strategy may translate in more sensitive tracing of tumor cells in-vivo and improved FIGR of HGGs and possibly low grade gliomas (LGGs).

Fluorescence Diagnosis in Neurooncology: Retrospective Analysis of 653 Cases

Objective: This study is to analyze fluorescence sensitivity in the diagnosis of brain and spinal cord tumors. Material and methods: The authors conducted a multicenter retrospective analysis of data on 653 cases in 641 patients: 553 of them had brain tumors and 88 spinal cord tumors. Brain tumor resection was performed in 523 patients, of whom 484 were adults and 39 children. The analyzed series was presented by 320 gliomas, 101 meningiomas, and 72 metastases. A stereotactic biopsy was performed in 20 patients and endoscopic surgery in 10 patients. In all cases, 20 mg/kg of 5-Aminolaevulinic acid was administered orally 2-h before surgery. All surgical interventions were performed with a microscope BLUE 400 to visualize fluorescence, while endoscopic surgery-with an endoscope equipped with a fluorescent module. Fluorescence spectroscopy was conducted in 20 cases of stereotactic biopsies and in 88 cases of spinal cord tumors. Results: Among adult brain tumors operated by microsurgical techniques, meningiomas showed the highest 5-ALA fluorescence sensitivity 94% (n = 95/101), brain metastases 84.7% (n = 61/72), low-grade gliomas 46.4% (n = 26/56), and high-grade gliomas 90.2% (n = 238/264). In children the highest 5-ALA visible fluorescence was observed in anaplastic astrocytomas 100% (n = 4/4) and in anaplastic ependymomas 100% (n = 4/4); in low-grade gliomas it made up 31.8% (n = 7/22). As for the spinal cord tumors in adults, the highest sensitivity was demonstrated by glioblastomas 100% (n = 4/4) and by meningiomas 100% (n = 4/4); Fluorescence was not found in gemangioblastomas (n = 0/6) and neurinomas (n = 0/4). Fluorescence intensity reached 60% (n = 6/10) in endoscopic surgery and 90% (n = 18/20) in stereotactic biopsy. Conclusion: 5-ALA fluorescence diagnosis proved to be most sensitive in surgery of HGG and meningioma (90.2 and 94.1%, respectively). Sensitivity in surgery of intracranial metastases and spinal cord tumors was slightly lower (84.7 and 63.6%, correspondingly). The lowest fluorescence sensitivity was marked in pediatric tumors and LGG (50 and 46.4%, correspondingly). Fluorescence diagnosis can also be used in transnasal endoscopic surgery of skull base tumors and in stereotactic biopsy.