Intratumoral heterogeneity: pathways to treatment resistance and relapse in human glioblastoma

Intratumoral heterogeneity (ITH) has increasingly being described for multiple cancers as the root cause of therapy resistance. Recent studies have started to explore the scope of ITH in glioblastoma (GBM), a highly aggressive and fatal form of brain tumor, to explain its inevitable therapy resistance and disease relapse. In this review, we detail the emerging data that explores the extensive genetic, cellular and functional ITH present in GBM. We discuss current experimental models of human GBM recurrence and suggest harnessing new technologies (CRISPR-Cas9 screening, CyTOF, cellular barcoding, single cell analysis) to delineate GBM ITH and identify treatment-refractory cell populations, thus opening new therapeutic windows. We will also explore why current therapeutics have failed in clinical trials and how ITH can inform us on developing empiric therapies for the treatment of recurrent GBM.     

Understanding the role of tumor stem cells in glioblastoma multiforme: a review article

It has been hypothesized that cancer stem cells (CSC) may account for the pathogenesis underlying various tumors, including GBM. Markers of these CSCs can be potentially used as therapeutic targets. In this review, we discuss the most recent information regarding CSCs, their molecular biology and their potential role in GBM.     

Heterogeneity maintenance in glioblastoma: a social network

Glioblastoma multiforme (GBM), the most common intracranial tumor in adults, is characterized by extensive heterogeneity at the cellular and molecular levels. This insidious feature arises inevitably in almost all cancers and has great significance for the general outcome of the malignancy, because it confounds our understanding of the disease and also intrinsically contributes to the tumor's aggressiveness and poses an obstacle to the design of effective therapies. The classic view that heterogeneity arises as the result of a tumor's "genetic chaos" and the more contemporary cancer stem cell (CSC) hypothesis tend to identify a single cell population as the therapeutic target: the prevailing clone over time in the first case and the CSC in the latter. However, there is growing evidence that the different tumor cell populations may not be simple bystanders. Rather, they can establish a complex network of interactions between each other and with the tumor microenvironment that eventually strengthens tumor growth and increases chances to escape therapy. These differing but complementary ideas about the origin and maintenance of tumor heterogeneity and its importance in GBM are reviewed here.     

Molecular and genetic bases of neuroblastoma

Neuroblastoma, which is derived from the sympathetic nervous system, is the second most common pediatric solid malignant tumor. This pediatric tumor has a heterogeneous course, ranging from spontaneous regression to inexorable progression and death, depending on the biological features of the tumor. Identification of risk groups on the basis of clinical and molecular prognostic variables has allowed tailor-made therapy to improve outcomes and minimize the risk of deleterious consequences of therapy. In Japan, current therapeutic stratification of patients with neuroblastoma is based on risk assessment according to combinations of age, tumor stage, MYCN status, DNA ploidy status, and histopathology; however, unfavorable neuroblastoma is still one of the most difficult tumors to cure, with only 40?% long-term survival despite intensive multimodal therapy. Further refined therapeutic stratification based on newly identified prognostic factors will be required to improve the outcome of patients with unfavorable neuroblastoma and reduce the side effects of therapies for patients with favorable neuroblastoma. In the present review, we describe recent topics on the molecular and genetic bases of neuroblastoma; we hope this review will be helpful for understanding the mechanism of neuroblastoma tumorigenesis and aggressiveness and for developing a new therapeutic stratification and new protocols for neuroblastoma treatments.     

Pediatric High-grade Glioma: Molecular Genetic Clues for Innovative Therapeutic Approaches

Summary High grade glioma remains the most intractable childhood tumor of the central nervous system. The molecular genetics of childhood high grade glioma remain largely unknown in comparison to that of their adult counterparts. In an era of molecularly targeted therapies, this dearth of knowledge will present particular challenges to those who must design and implement the next generation of therapeutic trials with these new agents. In this review, we discuss the current understanding of the molecular genetics of childhood high grade glioma and compare/contrast it to that of the adult tumors bearing the same classification for the purpose of beginning to identify the most promising therapeutic targets.     

Genetic and hypoxic regulation of angiogenesis in gliomas

Infiltrative astrocytic neoplasms are by far the most common malignant brain tumors in adults. Clinically, they are highly problematic due to their widely invasive nature which makes a complete resection almost impossible. Biologic progression of these tumors is inevitable and adjuvant therapies are only moderately effective in prolonging survival. Glioblastoma multiforme (GBM WHO grade IV), the most malignant form of infiltrating astrocytoma, can evolve from a lower grade precursor tumor (secondary GBM) or can present as high grade lesion from the outset, so-called de novoGBM. Molecular genetic investigations suggest that GBMs are comprised of multiple molecular genetic subsets. Notwithstanding the diversity of genetic alterations leading to the GBM phenotype, the vascular changes that evolve in this disease, presumably favoring further growth, are remarkably similar. Underlying genetic alterations in GBM may tilt the balance in favor of an angiogenic phenotype by upregulation of pro-angiogenic factors and down-regulation of angiogenesis inhibitors. Increased vascularity and endothelial cell proliferation in GBMs are also driven by hypoxia-induced expression of pro-angiogenic cytokines, such vascular endothelial growth factor (VEGF). Understanding the contribution of genetic alterations and hypoxia in angiogenic dysregulation in astrocytic neoplasms will lead to the development of better anti-angiogenic therapies for this disease. This review will summarize the properties of angiogenic dysregulation that lead to the highly vascularized nature of these tumors.     

Searching for a cure: gene therapy for glioblastoma

Glioblastoma multiforme (GBM) is an invariably fatal malignancy. The lethality of GBM has been linked to the highly invasive nature of GBM cells, their escape from immune cell oversight and their high degree of resistance to multiple established therapeutic modalities. The resistance of GBM cells to undergo death processes has, in part, been associated with mutations of specific oncogenes and altered expression of other signaling molecules that lead to reduced capacities to activate multiple apoptosis pathways as well as altered rates of DNA repair and autophagy in response to cytotoxic drugs and cellular stresses. This review will examine how gene therapeutic approaches have been used in the past and are continuing to be used alongside cell signaling modulators and DNA damaging agents as clinical tools to treat GBM. The concerted use of established and novel signal transduction modulatory agents on GBM survival may have potential to lower the apoptotic threshold and facilitate killing in this lethal malignancy.     

The evolution of the cancer stem cell state in glioblastoma: emerging insights into the next generation of functional interactions

Cellular heterogeneity is a hallmark of advanced cancers and has been ascribed in part to a population of self-renewing, therapeutically resistant cancer stem cells (CSCs). Glioblastoma (GBM), the most common primary malignant brain tumor, has served as a platform for the study of CSCs. In addition to illustrating the complexities of CSC biology, these investigations have led to a deeper understanding of GBM pathogenesis, revealed novel therapeutic targets, and driven innovation towards the development of next-generation therapies. While there continues to be an expansion in our knowledge of how CSCs contribute to GBM progression, opportunities have emerged to revisit this conceptual framework. In this review, we will summarize the current state of CSCs in GBM using key concepts of evolution as a paradigm (variation, inheritance, selection, and time) to describe how the CSC state is subject to alterations of cell intrinsic and extrinsic interactions that shape their evolutionarily trajectory. We identify emerging areas for future consideration, including appreciating CSCs as a cell state that is subject to plasticity, as opposed to a discrete population. These future considerations will not only have an impact on our understanding of this ever-expanding field but will also provide an opportunity to inform future therapies to effectively treat this complex and devastating disease.     

Molecular heterogeneity in glioblastoma: therapeutic opportunities and challenges

Glioblastoma (GBM) has been recognized as a clinical and pathologic entity for more than a century. Throughout its history, its cells of origin have been in question. Its behavior is aggressive and despite decades of effort, median survival is just beginning to improve. Surgical techniques and radiotherapy schemas continue to be refined, but the most recent progress has been achieved through improved medical therapies. These are the result of both pharmacological advances and a deeper understanding of the biological characteristics of GBM. Due to a combination of its complex phenotype and organ-specific clinical manifestations, efforts to refine GBM treatment with targeted therapies largely have been frustrated. In this review, we discuss recent attempts to exploit new molecular insights, consider the reasons for slow progress in developing better treatments, and examine future therapeutic options.     

Fatty acid synthase is a predictive marker for aggressiveness in meningiomas

Meningiomas are the most frequent intracranial tumors. Although most are benign WHO grade I tumors, grade II and III tumors are aggressive and survival is poor. Treatment options for grade II and III meningiomas are limited, and molecular targets are few. The re-programming of metabolic pathways including glycolysis, lipogenesis, and nucleotide synthesis is a hallmark of the physiological changes in cancer cells. Because fatty acid synthase (FAS), the enzyme responsible for the de-novo synthesis of fatty acids, has emerged as a potential therapeutic target for several cancers, we investigated its involvement in meningiomas. We subjected 92 paraffin-embedded samples from 57 patients with grade I, 18 with grade II and III, and six with radiation-induced tumors to immunohistochemical study of FAS. Whereas its expression was increased in grade II and III meningiomas (62.9 %) compared with grade I tumors (29.8 %) (chi-squared test: p < 0.001), FAS was expressed in grade I tumors with a high MIB-1 index and infiltration into surrounded tissues. All radiation-induced meningiomas expressed FAS and its expression was positively correlated with the MIB-1 index (p < 0.005). Our findings suggest that increased FAS expression reflects the aggressiveness of meningiomas and that it may be a novel therapeutic target for treatment of unresectable or malignant tumors.     

Recurrent glioblastoma: a fresh look at current therapies and emerging novel approaches

Despite international efforts, the treatment of recurrent glioblastoma (GBM) remains challenging. Although advances in surgical resection, the use of radiotherapy, and, predominantly, improved medical therapies have led to incremental improvements in median survival, few options exist for the management of recurrent or resistant disease. Insight into the molecular pathogenesis of GBM has led to the recent development of targeted therapeutic strategies aimed at the interruption of key molecular signaling pathways. However, due to the complex and redundant activation of the signaling mechanisms in GBM tumors, the evaluation of targeted agents in clinical trials has been largely limited. The ongoing effort to identify effective strategies for the treatment of recurrent GBM includes combination strategies with agents that target complementary or redundant pathways. Incorporation of novel trial designs that permit simultaneous evaluation of several agent combinations and allow for rapid discontinuation of ineffective regimens can accelerate the clinical evaluation of such candidate regimens. This review discusses strategies and outcomes of existing and emerging treatment approaches, and the challenges associated with the integration of novel therapies into clinical practice.     

Emerging Variants of Castration-Resistant Prostate Cancer

Metastatic castration-resistant prostate cancer (CRPC) is associated with substantial clinical, pathologic, and molecular heterogeneity. Most tumors remain driven by androgen receptor (AR) signaling, which has clinical implications for patient selection for AR-directed approaches. However, histologic and clinical resistance phenotypes can emerge after AR inhibition, in which the tumors become less dependent on the AR. In this review, we discuss prostate cancer variants including neuroendocrine (NEPC) and aggressive variant (AVPC) prostate cancers and their clinical implications. Improvements in the understanding of the biologic mechanisms and molecular features underlying prostate cancer variants may help prognostication and facilitate the development of novel therapeutic approaches for subclasses of patient with CRPC.     

Current clinical development of PI3K pathway inhibitors in glioblastoma

Glioblastoma (GBM) is the most common and lethal primary malignant tumor of the central nervous system, and effective therapeutic options are lacking. The phosphatidylinositol 3-kinase (PI3K) pathway is frequently dysregulated in many human cancers, including GBM. Agents inhibiting PI3K and its effectors have demonstrated preliminary activity in various tumor types and have the potential to change the clinical treatment landscape of patients with solid tumors. In this review, we describe the activation of the PI3K pathway in GBM, explore why inhibition of this pathway may be a compelling therapeutic target for this disease, and provide an update of the data on PI3K inhibitors in clinical trials and from earlier investigation.     

Molecular analysis of anaplastic oligodendroglial tumors in a prospective randomized study: A report from EORTC study 26951

Recent studies have shown that the clinical outcome of anaplastic oligodendroglial tumors is variable, but also that the histological diagnosis is subject to interobserver variation. We investigated whether the assessment of 1p/19q codeletion, polysomy of chromosome 7, epidermal growth factor receptor (EGFR) gene amplification (EGFR^amp), and loss of chromosome 10 or 10q offers additional prognostic information to the histological diagnosis and would allow molecular subtyping. For this study, we used the clinical data and tumor samples of the patients included in multicenter prospective phase III European Organisation for Research and Treatment of Cancer (EORTC) study 26951 on the effects of adjuvant procarbazine, chloroethyl cyclohexylnitrosourea (lomustine), and vincristine chemotherapy in anaplastic oligodendroglial tumors. Fluorescence in situ hybridization was used to assess copy number aberrations of chromosome 1p, 19q, 7, 10, and 10q and EGFR. Three different analyses were performed: on all included patients based on local pathology diagnosis, on the patients with confirmed anaplastic oligodendroglial tumors on central pathology review, and on this latter group but after excluding anaplastic oligoastrocytoma (AOA) with necrosis. As a reference set for glioblastoma multiforme (GBM), patients from the prospective randomized phase III study on GBM (EORTC 26981) were used as a benchmark. In 257 of 368 patients, central pathology review confirmed the presence of an anaplastic oligodendroglial tumor. Tumors with combined 1p and 19q loss (1p^loss19q^loss) were histopathologically diagnosed as anaplastic oligodendroglioma, were more frequently located in the frontal lobe, and had a better outcome. Anaplastic oligodendroglial tumors with EGFR^amp were more frequently AOA, were more often localized outside the frontal lobe, and had a survival similar to that for GBM. Survival of patients with AOA harboring necrosis was in a similar range as for GBM, while patients with AOA with only endothelial proliferation had better overall survival. In univariate analyses, all molecular factors except loss of 10q were of prognostic significance, but on multivariate analysis a histopathological diagnosis of AOA, necrosis, and 1p^loss19q^loss remained independent prognostic factors. AOA tumors with necrosis are to be considered WHO grade IV tumors (GBM). Of all molecular markers analyzed in this study, especially loss of 1p/19q carried prognostic significance, while the others contributed little prognostic value to classical histology.     

乳腺癌肿瘤内异质性的驱动因素及临床研究进展

乳腺癌是第一种根据患者肿瘤的分子特征指导临床选择治疗策略的恶性肿瘤。然而,无论是基于免疫组织化学的分子分型还是基于基因组分析的固有分型,均存在一定的缺陷,二者不能完全解释乳腺癌预后和治疗的临床异质性。肿瘤内异质性（intratumoral heterogeneity,ITH）理论与乳腺癌的分型理论不同,异质性理论是指在同一肿瘤中存在多个不同亚型（空间异质性）,并且肿瘤在不同时期不同表型间可相互转化（时间异质性）。这些异质性是由肿瘤细胞状态异质性和克隆进化驱动,同时受肿瘤微环境、代谢重编程的协同影响。对肿瘤内异质性ITH的研究可进一步解释乳腺癌转移和耐药机制,有望成为潜在的新型治疗靶点。本文将对乳腺癌ITH的驱动因素和临床意义的研究进展进行综述。      

Comparative genomic and genetic analysis of glioblastoma-derived brain tumor-initiating cells and their parent tumors

Background

Glioblastoma (GBM) is a fatal cancer that has eluded major therapeutic advances. Failure to make progress may reflect the absence of a human GBM model that could be used to test compounds for anti-GBM activity. In this respect, the development of brain tumor-initiating cell (BTIC) cultures is a step forward because BTICs appear to capture the molecular diversity of GBM better than traditional glioma cell lines. Here, we perform a comparative genomic and genetic analysis of BTICs and their parent tumors as preliminary evaluation of the BTIC model.

Methods

We assessed single nucleotide polymorphisms (SNPs), genome-wide copy number variations (CNVs), gene expression patterns, and molecular subtypes of 11 established BTIC lines and matched parent tumors.

Results

Although CNV differences were noted, BTICs retained the major genomic alterations characteristic of GBM. SNP patterns were similar between BTICs and tumors. Importantly, recurring SNP or CNV alterations specific to BTICs were not seen. Comparative gene expression analysis and molecular subtyping revealed differences between BTICs and GBMs. These differences formed the basis of a 63-gene expression signature that distinguished cells from tumors; differentially expressed genes primarily involved metabolic processes. We also derived a set of 73 similarly expressed genes; these genes were not associated with specific biological functions.

Conclusions

Although not identical, established BTIC lines preserve the core molecular alterations seen in their parent tumors, as well as the genomic hallmarks of GBM, without acquiring recurring BTIC-specific changes.