Genetics of medulloblastoma: clues for novel therapies

Human Adapted Prosomeric Model: A Future for Brainstem Tumor Classification

This study reevaluates the conventional understanding of midbrain anatomy and neuroanatomical nomenclature in the context of recent genetic and anatomical discoveries. The authors assert that the midbrain should be viewed as an integral part of the forebrain due to shared genetic determinants and evolutionary lineage. The isthmo-mesencephalic boundary is recognized as a significant organizer for both the caudal midbrain and the isthmo-cerebellar area. The article adopts the prosomeric model, redefining the whole brain as neuromeres, offering a more precise depiction of brain development, including processes like proliferation, neurogenesis, cell migration, and differentiation. This shift in understanding challenges traditional definitions of the midbrain based on external brain morphology. The study also delves into the historical context of neuroanatomical models, including the columnar model proposed by Herrick in 1910, which has influenced our understanding of brain structure. Furthermore, the study has clinical implications, affecting neuroanatomy, neurodevelopmental studies, and the diagnosis and treatment of brain disorders. It emphasizes the need to integrate molecular research into human neuroanatomical studies and advocates for updating neuroanatomical terminology to reflect modern genetic and molecular insights. The authors propose two key revisions. First, we suggest reclassifying the isthmo-cerebellar prepontine region as part of the hindbrain, due to its role in cerebellar development and distinct location caudal to the genetically-defined midbrain. Second, we recommend redefining the anterior boundary of the genetically-defined midbrain to align with genetic markers. In conclusion, the authors highlight the importance of harmonizing neuroanatomical nomenclature with current scientific knowledge, promoting a more precise and informed understanding of brain structure, which is crucial for both research and clinical applications related to the human brain.

Glioma is formed by active Akt1 alone and promoted by active Rac1 in transgenic zebrafish

BACKGROUND

Ongoing characterization of glioma has revealed that Akt signaling plays a crucial role in gliomagenesis. In mouse models, however, Akt alone was not sufficient to induce glioma.

METHODS

We established transgenic zebrafish that overexpressed dominant-active (DA) human Akt1 or Rac1(G12V) (DARac1) at ptf1a domain and investigated transgenic phenotypes and mechanisms leading to gliomagenesis.

RESULTS

Transgene expressions were spatiotemporally restricted without any developmental abnormality of embryos and persisted at cerebellum and medulla in adult zebrafish. DAAkt1 alone induced glioma (with visible bumps at the head), with incidences of 36.6% and 49% at 6 and 9 months, respectively. Histologically, gliomas showed various histologic grades, increased proliferation, and frequent invasion into the fourth ventricle. Preferential location of small tumors at periventricular area and coexpression of Her4 suggested that tumors originated from Ptf1a- and Her4-positive progenitor cells at ventricular zone. Gliomagenesis was principally mediated by activation of survival pathway through upregulation of survivin genes. Although DARac1 alone was incapable of gliomagenesis, when coexpressed with DAAkt1, gliomagenesis was accelerated, showing higher tumor incidences (62.0% and 73.3% at 6 and 9 months, respectively), advanced histologic grade, invasiveness, and shortened survival. DARac1 upregulated survivin2, cyclin D1, β-catenin, and snail1a but downregulated E-cadherin, indicating that DARac1 promotes gliomagenesis by enhancing proliferation, survival, and epithelial-to-mesenchymal transition. On pharmacologic tests, only Akt1/2 inhibitor effectively suppressed gliomagenesis, inhibited cellular proliferation, and induced apoptosis in established gliomas.

CONCLUSIONS

The zebrafish model reinforces the pivotal role of Akt signaling in gliomagenesis and suggests Rac1 as an important protein involved in progression.

Childhood medulloblastoma: the paradigm shift in molecular stratification and treatment profile

Medulloblastoma is the most common malignant brain tumor of childhood, accounting for nearly 25% to 30% of primary central nervous system tumors in children younger than 18 years of age. Risk stratification into low and high risk categories has been based on age of clinical presentation, extent of postsurgical residual tumor, and disease dissemination. The World Health Organization (WHO) in 2007 recognized 5 histological subtypes as classic, anaplastic, large cell, desmoplastic/nodular, and medulloblastoma with extensive nodularity. Recent work with gene expression profiling along with histological classification has generated a novel combined histopathological and molecular stratification scheme into 4 subgroups (Wnt, Shh, group 3, and group 4). This could now help to identify patients who might benefit from dose escalation and de-escalation of therapy. Restratification brings optimism in treating these patients as scholars now have the ability to profile a more targeted therapy approach. This review discusses the literature regarding this new research endeavor.

Cerebrospinal fluid top-down proteomics evidenced the potential biomarker role of LVV- and VV-hemorphin-7 in posterior cranial fossa pediatric brain tumors

Posterior cranial fossa is the most frequent location of pediatric brain tumors. Its diagnosis is currently performed by postsurgery histopathology and the identification of biomarkers in cerebrospinal fluid (CSF) could provide a less invasive tool. Patient CSF was collected during surgery before the tumor removal (PRE-CSF) and 6 days after the resection (POST-CSF) and analyzed by top down LC-MS proteomics for comparison. The PRE-CSFs generally exhibited a less complex LC-MS profile than the relative POST-CSFs suggesting a suppressive role of the tumor toward proteins and peptides production or release. Particularly, a panel of peptides, identified as alpha- and beta-hemoglobin chains fragments, were generally absent in the PRE-CSF and present in the POST ones independently from contaminant blood hemoglobin. Among them, the LVV- and VV-hemorphin-7 showed the most repeatable trend and with a few remarkable exceptions: their unusual absence in POST surgery CSF was in fact interestingly correlated to the presence of tumor in the patient despite surgery due to metastases or to subtotal resection. These results ascribed a relevant biological role to LVV- and VV-h7 peptides in the disease and a strong potential as biomarkers. Their analysis in POST surgery CSF could be used to predict patient prognosis.

Lapatinib and obatoclax kill tumor cells through blockade of ERBB1/3/4 and through inhibition of BCL-XL and MCL-1

Prior studies in breast cancer cells have shown that lapatinib and obatoclax interact in a greater than additive fashion to cause cell death and do so through a toxic form of autophagy. The present studies sought to extend our analyses to the central nervous system (CNS) tumor cells and to further define mechanisms of drug action. Lapatinib and obatoclax killed multiple CNS tumor isolates. Cells lacking PTEN (phosphatase and tensin homolog on chromosome 10) function were relatively resistant to drug combination lethality; expression of PTEN in PTEN-null cells restored drug sensitivity, and knockdown of PTEN promoted drug resistance. On the basis of knockdown of ERBB1-4 (erythroblastic leukemia viral oncogene homolog 1-4), we discovered that the inhibition of ERBB1/3/4 receptors were most important for enhancing obatoclax lethality rather than ERBB2. In parallel, we noted in CNS tumor cells that knockdown of BCL-xL (B-cell lymphoma-extra large)and MCL-1 (myeloid cell leukemia-1) interacted in an additive fashion to facilitate lapatinib lethality. Pretreatment of tumor cells with obatoclax enhanced the lethality of lapatinib to a greater extent than concomitant treatment. Treatment of animals carrying orthotopic CNS tumor isolates with lapatinib- and obatoclax-prolonged survival. Altogether, our data show that lapatinib and obatoclax therapy could be of use in the treatment of tumors located in the CNS.

Cellular redox modulator, ortho Mn(III) meso-tetrakis(N-n-hexylpyridinium-2-yl)porphyrin, MnTnHex-2-PyP(5+) in the treatment of brain tumors

Despite intensive efforts to improve multimodal treatment of brain tumor, survival remains limited. Current therapy consists of a combination of surgery, irradiation and chemotherapy with predisposition to long-term complications. Identifying novel targeted therapies is therefore at the forefront of brain tumor research. This study explores the utility of a manganese porphyrin in a brain tumor model. The compound used is ortho isomer, mangnese(III) meso-tetrakis(N-n-hexylpyridinium-2-yl)porphyrin, MnTnHex-2-PyP(5+). It is a powerful SOD mimic and peroxynitrite scavenger and a potent modulator of redox-based cellular transcriptional activity, able to suppress excessive immune and inflammatory responses and in turn proliferative pathways. It is further one of the most lipophilic compound among cationic Mn(III) N-alkylpyridylporphyrins, and thus accumulates predominantly in mitochondria relative to cytosol. In mitochondria, MnTnHex-2-PyP(5+) mimics our key antioxidant system, mitochondrial superoxide dismutase, MnSOD, whose overexpression has been widely shown to suppress tumor growth. Importantly, MnTnHex-2-PyP(5+) crosses blood brain barrier in sufficient amounts to demonstrate efficacy in treating CNS injuries. For those reasons we elected to test its effects in inhibiting brain tumor growth. This study is the first report of the antitumor properties of MnTnHex-2-PyP(5+) as a single agent in adult and pediatric glioblastoma multiforme (D-54 MG, D-245 MG, D-256 MG, D-456 MG) and pediatric medulloblastoma (D-341 MED), and is the first case where a redox-able metal complex has been used in glioma therapy. When given subcutaneously to mice bearing subcutaneous and intracranial xenografts, MnTnHex-2-PyP(5+) caused a significant (P ≤ 0.001) growth delay in D 245 MG, D-256 MG, D-341 MED, and D-456 MG tumors. Growth delay for mice bearing subcutaneous xenografts ranged from 3 days in D-54 MG to 34 days in D-341 MED. With mice bearing intracranial xenografts, MnTnHex-2-PyP(5+) increases median survival by 33% in adult glioblastoma multiforme (D-256 MG; p≤ 0.001) and 173% in pediatric medulloblastoma (D-341 MED, <0.001). The beneficial effects of MnTnHex-2-PyP(5+) are presumably achieved either (1) indirectly via elimination of signaling reactive oxygen and nitrogen species (in particular superoxide and peroxynitrite) which in turn would prevent activation of transcription factors; or (2) directly by coupling with cellular reductants and redox-sensitive signaling proteins. The former action is antioxidative while the latter action is presumably pro-oxidative in nature. Our findings suggest that the use of Mn porphyrin-based SOD mimics, and in particular lipophilic analogues such as MnTnHex-2-PyP(5+), is a promising approach for brain tumor therapy.

Prognostic significance of angiogenesis in relation to Ki-67, p-53, p-27, and bcl-2 expression in embryonal tumors

AIM

We investigated the angiogenesis and density of newly formed blood vessels in embryonal tumors in relation to Ki-67, bcl-2, p-53 and p-27 expression.

METHODS

Forty-five children with embryonal tumors were enrolled in the study. Forty patients had a medulloblastoma (MB) and 5 patients had atypical teratoid/rhabdoid tumor (AT/RT).

RESULTS

In MB, the 5-year PFS and OS was 62.5 and 70%, respectively. Patients with Ki-67 index >50%, bcl-2 index >30% and higher density of new vessels were associated with worse survival. In the multivariate analysis, Ki-67 index was identified as a factor with independent prognostic power. In AT/RTs, high density of new vessels (>25 HRF) was observed in 3 patients and Ki-67 index over 25% was found in 4 patients.

CONCLUSION

Increased Ki-67, bcl-2 and density of new vessels are of prognostic value for the disease outcome in MB.