Fluorescence-guided surgery for brain tumors

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

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

Creation of Non-Contact Device for Use in Metastatic Melanoma Margin Identification in ex vivo Mouse Brain

Because contemporary intraoperative tumor detection modalities, such as intraoperative MRI, are not ubiquitously available and can disrupt surgical workflow, there is an imperative for an accessible diagnostic device that can meet the surgeon's needs in identifying tissue types. The objective of this paper is to determine the efficacy of a novel non-contact tumor detection device for metastatic melanoma boundary identification in a tissue-mimicking phantom, evaluate the identification of metastatic melanoma boundaries in ex vivo mouse brain tissue, and find the error associated with identifying this boundary. To validate the spatial and fluorescence resolution of the device, tissue-mimicking phantoms were created with modifiable optical properties. Phantom tissue provided ground truth measurements for fluorophore concentration differences with respect to spatial dimensions. Modeling metastatic disease, ex vivo melanoma brain metastases were evaluated to detect differences in fluorescence between healthy and neoplastic tissue. This analysis includes determining required-to-observe fluorescence differences in tissue. H&E staining confirmed tumor presence in mouse tissue samples. The device detected a difference in normalized average fluorescence intensity in all three phantoms. There were differences in fluorescence with the presence and absence of melanin. The estimated tumor boundary of all tissue phantoms was within 0.30 mm of the ground truth tumor boundary for all boundaries. Likewise, when applied to the melanoma-bearing brains from ex vivo mice, a difference in normalized fluorescence intensity was successfully detected. The potential prediction window for the tumor boundary location is less than 1.5 mm for all ex vivo mouse brain tumors boundaries. We present a non-contact, laser-induced fluorescence device that can identify tumor boundaries based on changes in laser-induced fluorescence emission intensity. The device can identify phantom ground truth tumor boundaries within 0.30 mm using instantaneous rate of change of normalized fluorescence emission intensity and can detect endogenous fluorescence differences in melanoma brain metastases in ex vivo mouse tissue.

Stimulation and homogenization of the protoporphyrin IX endogenous production by photobiomodulation to increase the potency of photodynamic therapy

Protoporphyrin IX (PpIX) is produced in the mitochondria and used as fluorescent contrast agent or photosensitizer after exogenous 5-aminolevulinic acid (ALA) delivery in cancer photodynamic detection and therapy (PDT). Although routinely used in the clinics, the stimulated production of PpIX is often insufficient and/or heterogeneous within the lesions, thereby limiting the PDT performances. Since photobiomodulation, which is based on the illumination of the tissues with sub-thermal radiometric conditions in the red or near-infrared, is known to stimulate the cell metabolism, we have optimized these conditions in vitro. Some of them lead to the homogenization and strong stimulation of the PpIX endogenous production. Interestingly, combined sequentially, PBM enhanced significantly the potency of PpIX-based PDT in vitro and in vivo in tumors grown on the chicken embryo chorioallantoic membrane. These results are in excellent agreement with other assays based on measurements of the cell survival/death, the production of reactive oxygen species, including singlet oxygen, and the mitochondrial membrane potential.

Fluorescent Affibody Molecule Administered In Vivo at a Microdose Level Labels EGFR Expressing Glioma Tumor Regions

Purpose

Fluorescence guidance in surgical oncology provides the potential to realize enhanced molecular tumor contrast with dedicated targeted tracers, potentially with a microdose injection level. For most glioma tumors, the blood brain barrier is compromised allowing some exogenous drug/molecule delivery and accumulation for imaging. The aberrant overexpression and/or activation of epidermal growth factor receptor (EGFR) is associated with many types of cancers, including glioblastoma, and so the use of a near-infrared (NIR) fluorescent molecule targeted to the EGFR receptor provides the potential for improving tumor contrast during surgery. Fluorescently labeled affibody molecule (ABY-029) has high EGFR affinity and high potential specificity with reasonably fast plasma clearance. In this study, ABY-29 was evaluated in glioma versus normal brain uptake from intravenous injection at a range of doses, down to a microdose injection level.

Procedure

Nude rats were inoculated with the U251 human glioma cell line in the brain. Tumors were allowed to grow for 3–4 weeks. ABY-029 fluorescence ex vivo imaging of brain slices was acquired at different time points (1–48 h) and varying injection doses from 25 to 122 μg/kg (from human protein microdose equivalent to five times microdose levels).

Results

The tumor was most clearly visualized at 1-h post-injection with 8- to 16-fold average contrast relative to normal brain. However, the tumor still could be identified after 48 h. In all cases, the ABY-029 fluorescence appeared to localize preferentially in EGFR-positive regions. Increasing the injected dose from a microdose level to five times, a microdose level increased the signal by 10-fold, and the contrast was from 8 to 16, showing that there was value in doses slightly higher than the microdose restriction. Normal tissue uptake was found to be affected by the tumor size, indicating that edema was a likely factor affecting the expected tumor to normal tissue contrast.

Conclusion

These results suggest that the NIR-labeled affibody molecules provide an excellent potential to increase surgical visualization of EGFR-positive tumor regions.

Treatment of glioblastoma in elderly patients

Although glioblastoma occurs mostly in elderly patients, there is a paucity of trials addressing patients older than 70 years of age. Age, by itself, constitutes an unfavorable prognostic factor, which is probably due to unpropitious genetic features, but also due to iatrogenic defeatism. However, many retrospective studies report a survival benefit achieved by aggressive surgical resection seeking gross total removal of contrast-enhancing tumor according to preoperative MRI. Combined radiochemotherapy with concomitant and adjuvant temozolomide has not been investigated in prospective trials. Numerous retrospective studies and a meta-analysis suggest benefit from combined treatment. Prospective randomized trials only evaluated either temozolomide or radiotherapy. Single-treatment hypofractionated radiotherapy performed superior to conventional fractionation. In patients with methylated MGMT promoter, first-line dose-dense temozolomide facilitates prolonged survival. However, there is no comparison with combined radiochemotherapy as the standard-of-care in adult patients. Comorbidity is more frequent in elderly patients, but does not correlate with preterm termination of temozolomide treatment. This review article compiles data proposing a straightforward glioblastoma treatment, irrespective of age.