Tumors of the central nervous system: clinical aspects, molecular mechanisms, unanswered questions, and future research directions

Characterization of the blood brain barrier in pediatric central nervous system neoplasms

Objective

The normal blood–brain barrier (BBB) is composed of tight junctions between endothelial cells and surrounding astrocyte foot processes. Breakdown of the physiological astrocyte-endothelial cell relationship occurs in adult metastatic and primary brain tumors. However, the astrocyte-endothelial cell relationship has not been studied in pediatric tumors.

Materials and Methods

Utilizing specimens from cases of pilocytic astrocytoma (n = 5), medulloblastoma (n = 5), and low-grade diffuse astrocytoma (n = 1), immunofluorescence were performed using primary antibodies against CD31, glial fibrillary acidic protein (GFAP), and aquaporin 4 (AQ4). Clinical, magnetic resonance imaging, operative, and histopathological findings were analyzed.

Results

Strongly-enhancing areas of medulloblastoma exhibited complete BBB breakdown with sparse GFAP and AQ4 staining around CD31-positive vessels. Moderately enhancing regions of pilocytic astrocytomas exhibited regions of intact BBB and vasculature surrounded by dense GFAP staining but reduced and disorganized AQ4 staining, suggesting tumor cells could not fulfill physiological BBB support. Non-enhancing low-grade diffuse astrocytoma demonstrated intact BBB with intense peri-microvasculature GFAP and AQ4 staining. AQ4 stained so strongly that AQ4 visualization alone delineated CD31-positive vessels.

Conclusion

Taken together, BBB breakdown in pediatric tumors corresponds to a loss of normal endothelial cell-astrocyte foot process relationships. Further development of pharmaceutical agents capitalizing on this disrupted BBB is warranted in medulloblastoma and pilocytic astrocytoma. However, BBB integrity remains a challenge in treating low-grade diffuse astrocytoma before progression toward secondary glioblastoma.

Efficacy of cabazitaxel in mouse models of pediatric brain tumors

BACKGROUND

There is an unmet need in the treatment of pediatric brain tumors for chemotherapy that is efficacious, avoids damage to the developing brain, and crosses the blood-brain barrier. These experiments evaluated the efficacy of cabazitaxel in mouse models of pediatric brain tumors.

METHODS

The antitumor activity of cabazitaxel and docetaxel were compared in flank and orthotopic xenograft models of patient-derived atypical teratoid rhabdoid tumor (ATRT), medulloblastoma, and central nervous system primitive neuroectodermal tumor (CNS-PNET). Efficacy of cabazitaxel and docetaxel were also assessed in the Smo/Smo spontaneous mouse medulloblastoma tumor model.

RESULTS

This study observed significant tumor growth inhibition in pediatric patient-derived flank xenograft tumor models of ATRT, medulloblastoma, and CNS-PNET after treatment with either cabazitaxel or docetaxel. Cabazitaxel, but not docetaxel, treatment resulted in sustained tumor growth inhibition in the ATRT and medulloblastoma flank xenograft models. Patient-derived orthotopic xenograft models of ATRT, medulloblastoma, and CNS-PNET showed significantly improved survival with treatment of cabazitaxel.

CONCLUSION

These data support further testing of cabazitaxel as a therapy for treating human pediatric brain tumors.

The ABCG2 transporter is a key molecular determinant of the efficacy of sonodynamic therapy with Photofrin in glioma stem-like cells

We aimed to investigate the role of the ABCG2 transporter in the efficacy of sonodynamic therapy (SDT) with Photofrin in the glioma stem-like cells (GSCs) isolated and cultured from U251 glioma cells. Immunocytochemistry and flow cytometry analyses showed that ABCG2 was overexpressed in GSCs, and the percentage of ABCG2-positive GSCs was approximately 100%. The effect of ABCG2 on Photofrin extrusion in the absence or presence of a specific inhibitor of ABCG2 (fumitremorgin C; FTC) was investigated by determining the intracellular concentration of Photofrin in GSCs incubated with 20μg/ml Photofrin. Extrusion of Photofrin by ABCG2 was inhibited by 10μM FTC, which significantly increased the intracellular Photofrin concentration (p<0.05) from 0.32±0.11μg/10(6) cells to 0.89±0.13μg/10(6) cells. MTT and TUNEL assays showed that the antitumor effect of SDT (incubation of GSCs with 20μg/ml Photofrin for 6h in the dark and ultrasonic activation at 1.0MHz and 0.5W/cm(2) for 2min) was significantly improved by FTC pretreatment (p<0.05). Moreover, incubation of GSCs with FTC significantly increased the relative production of ROS in response to SDT. The overexpression of ABCG2 in GSCs results in efflux of Photofrin, indicating that the antitumor effect of SDT with Photofrin may be reduced in GSCs overexpressing ABCG2. However, since FTC improves the efficacy of SDT in GSCs by inhibiting ABCG2-mediated efflux of Photofrin, FTC may be useful in SDT treatment of ABCG2-expressing cancer cells.

Pediatric brain tumor treatment: growth consequences and their management

Tumors of the central nervous system, the most common solid tumors of childhood, are a major source of cancer-related morbidity and mortality in children. Survival rates have improved significantly following treatment for childhood brain tumors, with this growing cohort of survivors at high risk of adverse medical and late effects. Endocrine morbidities are the most prominent disorder among the spectrum of longterm conditions, with growth hormone deficiency the most common endocrinopathy noted, either from tumor location or after cranial irradiation and treatment effects on the hypothalamic/pituitary unit. Deficiency of other anterior pituitary hormones can contribute to negative effects on growth, body image and composition, sexual function, skeletal health, and quality of life. Pediatric and adult endocrinologists often provide medical care to this increasing population. Therefore, a thorough understanding of the epidemiology and pathophysiology of growth failure as a consequence of childhood brain tumor, both during and after treatment, is necessary and the main focus of this review.