Neuroendocrine tumors in the brain

Paraneoplastic neurologic manifestations of neuroendocrine tumors

Neuroendocrine neoplasms (NENs) are a heterogeneous group of tumors arising from the transformation of neuroendocrine cells in several organs, most notably the gastro-entero-pancreatic system and respiratory tract. The classification was recently revised in the 5th Edition of the WHO Classification of Endocrine and Neuroendocrine Tumors. NENs can rarely spread to the central or peripheral nervous systems. Neurologic involvement is determined by the rare development of paraneoplastic syndromes, which are remote effects of cancer. Mechanisms depend on immunologic response to a tumor, leading to the immune attack on the nervous system or the production of biologically active ("functioning") substances, which can determine humoral (endocrine) effects with neurologic manifestations. Paraneoplastic neurologic syndromes (PNS) are immunologically mediated and frequently detected in small cell lung cancer but rarely seen in other forms of NEN. PNS and Merkel cell carcinoma is increasingly reported, especially with Lambert Eaton myasthenic syndrome. Endocrine manifestations are found in a wide spectrum of NENs. They can develop at any stage of the diseases and determine neurologic manifestations. Patient outcomes are influenced by tumor prognosis, neurologic complications, and the severity of endocrine effects.

Decoding meningioma heterogeneity and neoplastic cell-macrophage interaction through single-cell transcriptome profiling across pathological grades

BACKGROUND

Analyzing meningioma of distinct pathological types at the single-cell level can provide new and valuable insights into the specific biological mechanisms of each cellular subpopulation, as well as their vital interplay within the tumor microenvironment.

METHODS

We recruited patients diagnosed with four distinct types of meningioma and performed single-cell RNA sequencing on their tumor samples, concurrently analyzing a publicly available dataset for comparison. Next, we separated the cells into discrete clusters and identified their unique identities. Using pseudotime analysis, we demonstrated cellular differentiation and dynamics. To investigate biological function, we employed weighted gene co-expression network analysis, gene regulatory network, and gene set enrichment analysis. Additionally, we conducted cell-cell communication analyses to characterize interactions among different clusters and validated a crucial interaction using multiple immunofluorescence staining.

RESULTS

The single-cell transcriptomic profiles for five meningioma of different pathological types demonstrated that neoplastic cells exhibited high inter-sample heterogeneity and diverse biological functions featured by metabolic regulation. A small cluster of neoplastic cells (N5 cluster, < 3%) was most proliferative, indicated by high expression of MKI67 and TOP2A. They were primarily observed in our atypical and transitional meningioma samples and located at the beginning of the pseudotime differentiation branch for neoplastic cells. Macrophages, the most abundant immune cells present, showed two distinct developmental trajectories, one promoting and the other suppressing meningioma growth, with the MIF-CD74 interaction serving as the primary signaling pathway for MIF signals in the tumor environment. Unexpectedly, despite its small cluster size, the N5 cluster demonstrated a significant contribution in this interaction. By staining pathological sections of more samples, we found that this interaction was widely present in different types of meningiomas.

CONCLUSIONS

Meningioma neoplastic cells' diverse types cause inter-sample heterogeneity and a wide range of functions. Some proliferative neoplastic cell may educate macrophages, which promotes tumorigenesis possibly through the MIF-CD74 interaction. It provides novel clues for future potential therapeutic avenues.

Somatostatin Receptor Splicing Variant sst5TMD4 Overexpression in Glioblastoma Is Associated with Poor Survival, Increased Aggressiveness Features, and Somatostatin Analogs Resistance

Glioblastoma (GBM) is the most malignant and lethal brain tumor. Current standard treatment consists of surgery followed by radiotherapy/chemotherapy; however, this is only a palliative approach with a mean post-operative survival of scarcely ~12-15 months. Thus, the identification of novel therapeutic targets to treat this devastating pathology is urgently needed. In this context, the truncated splicing variant of the somatostatin receptor subtype 5 (sst5TMD4), which is produced by aberrant alternative splicing, has been demonstrated to be overexpressed and associated with increased aggressiveness features in several tumors. However, the presence, functional role, and associated molecular mechanisms of sst5TMD4 in GBM have not been yet explored. Therefore, we performed a comprehensive analysis to characterize the expression and pathophysiological role of sst5TMD4 in human GBM. sst5TMD4 was significantly overexpressed (at mRNA and protein levels) in human GBM tissue compared to non-tumor (control) brain tissue. Remarkably, sst5TMD4 expression was significantly associated with poor overall survival and recurrent tumors in GBM patients. Moreover, in vitro sst5TMD4 overexpression (by specific plasmid) increased, whereas sst5TMD4 silencing (by specific siRNA) decreased, key malignant features (i.e., proliferation and migration capacity) of GBM cells (U-87 MG/U-118 MG models). Furthermore, sst5TMD4 overexpression in GBM cells altered the activity of multiple key signaling pathways associated with tumor aggressiveness/progression (AKT/JAK-STAT/NF-κB/TGF-β), and its silencing sensitized GBM cells to the antitumor effect of pasireotide (a somatostatin analog). Altogether, these results demonstrate that sst5TMD4 is overexpressed and associated with enhanced malignancy features in human GBMs and reveal its potential utility as a novel diagnostic/prognostic biomarker and putative therapeutic target in GBMs.

Medical management of meningiomas

Meningiomas are the most frequently occurring primary brain tumors in adults, representing almost one-third of all primary central nervous system tumors. Several factors have been suggested as an underlying cause in the development of meningiomas, such as ionizing radiation (therapeutic or other incidental exposure), hormonal factors, and genetic predisposition syndromes. Other established factors associated with meningiomas include age, female gender, and those from non-Hispanic Black backgrounds. Though the 2016 World Health Organization Classification of Brain Tumors largely preserves the existing grading scheme for organization of meningioma, there is increasing understanding of the molecular factors underlying the development of meningioma, some of which now form the basis for active clinical investigation. The mainstay of treatment has been the combination of radiation therapy and surgery, with a limited role for systemic therapy due to low efficacy, short duration of treatment response, and lack of uniform response criteria. Similar to other primary and metastatic brain tumors, immune-based therapies hold promise and are still under investigation.

In vivo CART cell imaging: Paving the way for success in CART cell therapy

Chimeric antigen receptor T (CART) cells are a promising immunotherapy that has induced dramatic anti-tumor responses in certain B cell malignancies. However, CART cell expansion and trafficking are often insufficient to yield long-term remissions, and serious toxicities can arise after CART cell administration. Visualizing CART cell expansion and trafficking in patients can detect an inadequate CART cell response or serve as an early warning for toxicity development, allowing CART cell treatment to be tailored accordingly to maximize therapeutic benefits. To this end, various imaging platforms are being developed to track CART cells in vivo, including nonspecific strategies to image activated T cells and reporter systems to specifically detect engineered T cells. Many of these platforms are clinically applicable and hold promise to provide valuable information and guide improved CART cell treatment.

Emerging Medical Treatments for Meningioma in the Molecular Era

Meningiomas are the most common type of primary central nervous system tumors. Approximately, 80% of meningiomas are classified by the World Health Organization (WHO) as grade I, and 20% of these tumors are grade II and III, considered high-grade meningiomas (HGMs). Clinical control of HGMs, as well as meningiomas that relapse after surgery, and radiation therapy is difficult, and novel therapeutic approaches are necessary. However, traditional chemotherapies, interferons, hormonal therapies, and other targeted therapies have so far failed to provide clinical benefit. During the last several years, next generation sequencing has dissected the genetic heterogeneity of meningioma and enriched our knowledge about distinct oncogenic pathways driving different subtypes of meningiomas, opening up a door to new personalized targeted therapies. Molecular classification of meningioma allows a new design of clinical trials that assign patients to corresponding targeted agents based on the tumor genetic subtypes. In this review, we will shed light on emerging medical treatments of meningiomas with a particular focus on the new targets identified with genomic sequencing that have led to clinical trials testing novel compounds. Moreover, we present recent development of patient-derived preclinical models that provide platforms for assessing targeted therapies as well as strategies with novel mechanism of action such as oncolytic viruses.

Anti-SSTR2 peptide based targeted delivery of potent PLGA encapsulated 3,3'-diindolylmethane nanoparticles through blood brain barrier prevents glioma progression

Current therapy for Glioblastoma is insufficient because of the presence of blood brain barrier. It limits the transport of essential drugs to the tumor sites. To overcome this limitation we strategized the delivery of an anticancer compound 3,3’-diindolylmethane by encapsulation in poly (lactic-co-glycolic acid) nanoparticles. These nanoparticles were tagged with a novel peptide against somatostatin receptor 2 (SSTR2), a potential target in glioma. The nanoformulation (27-87nm) had loading and encapsulation efficiency of 7.2% and 70% respectively. It was successfully internalized inside the glioma cells resulting in apoptosis. Furthermore, an in vivo bio-distribution study revealed the selective accumulation of the nanoformulation into rat brain tumor sites by crossing the blood brain barrier. This resulted in abrogation of epidermal growth factor receptor pathway activation in glioma cells. Our novel nanopreparation therefore shows great promise to serve as a template for targeted delivery of other therapeutics in treating GBM.

Unresectable Recurrent Multiple Meningioma: A Case Report with Radiological Response to Somatostatin Analogues

Medical treatment of meningiomas is reserved for cases in which surgery and radiotherapy have failed. Given that a high percentage of meningiomas express somatostatin receptors, treatment with somatostatin analogues has been proposed. In addition, these medications have been shown to have an antiproliferative and antiangiogenic effect in vitro. To date, very few cases with clinical response and none with radiological response have been described. The case described here is the first to report a radiological response. A 76-year-old Caucasian male was first diagnosed with unresectable meningioma at age 47. The patient experienced multiple recurrences and underwent three surgeries and radiotherapy over the years from the initial diagnosis. Despite treatment, the disease continued its progression. Based on an Octreoscan positive for tumour uptake, therapy with extended-release somatostatin analogues was started. Although no clinical neurological improvement was observed, magnetic resonance imaging scans revealed a discreet but continuous radiological response over time. After >2 years of continuous administration of lanreotide, the patient remains progression free. In highly selected cases, somatostatin analogue treatment for meningioma may be beneficial. Based on our findings, treatment with somatostatin analogues should be maintained longer than previously described before evaluating treatment response.

Radio-guided surgery and postoperative PET/CT scan of a surgical specimen of an intraosseous meningioma in a patient with neuroendocrine tumor of the pancreas

A 63-year-old man with a previously resected neuroendocrine tumor of the pancreas underwent Ga DOTATOC PET/CT, which showed intense Ga DOTATOC uptake in the left calvarium. Radio-guided surgery and subsequent histology revealed an intraosseous meningioma. Complete removal was proven by a PET/CT scan of the surgical specimen.

Novel therapies for meningiomas

Although advances in surgery, radiation therapy and stereotactic radiosurgery have significantly improved the treatment of meningiomas, there remains an important subset of patients who remain refractory to conventional therapy. Treatment with chemotherapeutic agents such as hydroxyurea and alpha-interferon has provided minimal benefit. In this review, the role of newly emerging novel therapies for meningiomas, with a focus on targeted molecular agents, will be discussed.

Medical therapies for meningiomas

Meningiomas are the most common primary brain tumor in adults. Although the majority of these tumors can be effectively treated with surgery and radiation therapy, an important subset of patients have inoperable tumors, or develop recurrent disease after surgery and radiotherapy, and require some form of medical therapy. There are increasing numbers of studies evaluating various medical therapies but the results remain disappointing. Chemotherapies and hormonal therapies have been generally ineffective, although somatostatin analogues may have therapeutic potential. There is also increasing interest in targeted molecular therapies. Agents inhibiting platelet derived growth factor receptors and epidermal growth factor receptors have shown little efficacy, but molecular agents inhibiting vascular endothelial growth factor receptors appear to have some promise. As with other tumors, advances in the medical therapies for meningiomas will require improved understanding of the molecular pathogenesis of these tumors, more predictive preclinical models, and efficient mechanisms for conducting clinical trials, given the small population of eligible patients.

Detection of amino-terminal extracellular domain of somatostatin receptor 2 by specific monoclonal antibodies and quantification of receptor density in medulloblastoma

Somatostatin receptor 2 (SSTR2) is expressed by most medulloblastomas (MEDs). We isolated monoclonal antibodies (MAbs) to the 12-mer (33)QTEPYYDLTSNA(44), which resides in the extracellular domain of the SSTR2 amino terminus, screened the peptide-bound MAbs by fluorescence microassay on D341 and D283 MED cells, and demonstrated homogeneous cell-surface binding, indicating that all cells expressed cell surface-detectable epitopes. Five radiolabeled MAbs were tested for immunoreactive fraction (IRF), affinity (KA) (Scatchard analysis vs. D341 MED cells), and internalization by MED cells. One IgG(3) MAb exhibited a 50-100% IRF, but low KA. Four IgG(2a) MAbs had 46-94% IRFs and modest KAs versus intact cells (0.21-1.2 x 10(8) M(-1)). Following binding of radiolabeled MAbs to D341 MED at 4 degrees C, no significant internalization was observed, which is consistent with results obtained in the absence of ligand. However, all MAbs exhibited long-term association with the cells; binding at 37 degrees C after 2 h was 65-66%, and after 24 h, 52-64%. In tests with MAbs C10 and H5, the number of cell surface receptors per cell, estimated by Scatchard and quantitative FACS analyses, was 3.9 x 10(4) for the "glial" phenotype DAOY MED cell line and 0.6-8.8 x 10(5) for four neuronal phenotype MED cell lines. Our results indicate a potential immunotherapeutic application for these MAbs.

[Examination of somatostatin receptor expression in recurrent childhood medulloblastomas]

Medulloblastoma is the most common malignant pediatric central nervous system tumor. Despite the adequate therapy the tumor often recurs. The primary medulloblastoma expresses somatostatin receptor-2 (SSTR-2), but so far we had no experience about the receptor status in recurrent tumors. The presence of SSTR-2 may have an important role in the early detection and treatment of recurrent medulloblastomas. Our aim was to examine the state of SSTR-2 expression in recurrent childhood medulloblastomas. We examined SSTR-2 expression by immunohistochemistry in primary and recurrent medulloblastoma samples of ten children treated with recurrent medulloblastoma at Semmelweis University, Departments of Pediatrics, between 1998 and 2004. All primary and recurrent tumors have been operated at the National Institute of Neurosurgery. We examined the intensity and the percentage of SSTR-2-positive tumor cells in the primary and recurrent tumor samples. All primary tumors were receptor-positive and SSTR-2 was also expressed in all recurrent medulloblastomas. In our samples the percentage of SSTR-2-positive tumor cells was 30-90%. As a positive in vivo control Octreoscan images were available in two cases. In these cases the results of immunohistochemistry and Octreoscan imaging seemed to correlate. As a conclusion, SSTR-2-positive recurrent tumors can be detected early by Octreoscan imaging, and the presence of SSTR-2 establishes the opportunity of applying somatostatin analogues (octreotide) in the treatment of recurrent childhood medulloblastoma.

Targeted drug therapy for meningiomas

✓ Although advances in surgery, radiation therapy, and stereotactic radiosurgery have significantly improved the treatment of meningiomas, there remains an important subset of patients whose tumors are refractory to conventional therapy. Treatment with traditional chemotherapeutic agents has provided minimal benefit. In this review, the role of targeted molecular therapies for recurrent or progressive meningiomas is discussed.

Multiple Meningiomas

A 57-year-old woman with hyperthyroid ophthalmopathy underwent somatostatin receptor scintigraphy with In-111 pentetreotide. She also reported migraine-type headaches over the previous 3 months, without any other obvious neurologic symptoms and signs. The study revealed an increased uptake of the radiopharmaceutical in both periorbital areas and the right lobe of the thyroid gland. Multiple foci of marked tracer uptake were also detected in the right half of the head. A brain MRI scan subsequently revealed multiple lesions consistent with meningiomas on the surface of the right cerebral hemisphere.

Acromegaly due to a growth hormone-releasing hormone-secreting intracranial gangliocytoma

In more than 95% of cases acromegaly is due to GH hypersecretion by a pituitary adenoma. GHRH hypersecretion accounts for about 0.5% of cases of acromegaly. Intracranial GHRH-secreting tumors are extremely rare and only a few well-documented cases have been reported. The clinical features of acromegaly due to intracranial GHRH-secreting tumor are indistinguishable from those of other patients with "classical acromegaly". In cases of intrasellar gangliocytomas, not even radiological findings help to make the correct diagnosis, which can only be made with the hystological study. We present the case of a woman with acromegaly; the magnetic resonance demonstrated a 2x1.8x1.2 cm mass in the jugum sphenoidalis region, associated with a partial empty sella. There was a partial response to high-dose lanreotide therapy, so surgical treatment was decided, although only part of the tumor could be removed. Histopathological diagnosis was consistent with gangliocytoma, and immunostaining in the ganglionic cells was positive for GHRH. After surgery, hormone hypersecretion persisted, so medical treatment was reintroduced. In summary, we report a well-documented case of an intracranial GHRH-secreting gangliocytoma, an exceedingly rare cause of acromegaly. Clinical and biochemical data did not allow to make the correct diagnosis, which was only made on the pathological study. This case underscores that acromegaly can be due to causes other than a GH-secreting adenoma, and underlines that finding an image not typical of a pituitary adenoma should raise the suspicion that an unusual cause subsides the acromegaly.

Ligand liposomes and boron neutron capture therapy

Boron neutron capture therapy (BNCT) has been used both experimentally and clinically for the treatment of gliomas and melanomas, with varying results. However, the therapeutic effects on micro-invasive tumor cells are not clear. The two drugs that have been used clinically, p-boronophenylalanine, (BPA), and the sulfhydryl borane, (BSH), seem to be taken up preferentially in solid tumor areas but it is uncertain whether enough boron is taken up by micro-invasive tumor cells. To increase the selective uptake of boron by such cells, would be to exploit tumor transformation related cellular changes such as over-expression of growth factor receptors. However, the number of receptors varies from small to large and the uptake of large amounts of boron for each receptor interaction is necessary in order to deliver sufficient amounts of boron. Therefore, each targeting moiety must deliver large number of boron atoms. One possible way to meet these requirements would be to use receptor-targeting ligand liposomes, containing large number of boron atoms. This will be the subject of this review and studies of boron containing liposomes, with or without ligand, will be discussed. Two recent examples from the literature are ligand liposomes targeting either folate or epidermal growth factor (EGF) receptors on tumor cells. Other potential receptors on gliomas include PDGFR and EGFRvIII. Besides the appropriate choice of target receptor, it is also important to consider delivery of the ligand liposomes, their pharmacodynamics and pharmacokinetics and cellular processing, subjects that also will be discussed in this review.