Phase I study of temsirolimus in combination with EKB-569 in patients with advanced solid tumors

Purpose Activation of EGFR can stimulate proliferative and survival signaling through mTOR. Preclinical data demonstrates synergistic activity of combined EGFR and mTOR inhibition. We undertook a phase I trial of temsirolimus (T, an mTOR inhibitor) and EKB-569 (E, an EGFR inhibitor) to determine the safety and tolerability. Methods The primary aim was to determine the maximally tolerated dose (MTD) of this combination in adults with solid tumors. Following the dose-escalation phase, (Cohort A), two subsequent cohorts were used to assess any pharmacokinetic (PK) interaction between the agents. Results Forty eight patients were enrolled. The MTD of this combination was E, 35 mg daily and T, 30 mg on days 1-3 and 15-17 using a 28-day cycle. The most common toxicities were nausea, diarrhea, fatigue, anorexia, stomatitis, rash, anemia, neutropenia, thrombocytopenia, and hypertriglyceridemia. Sixteen patients (36%) had at least one grade 3 toxicity. The most frequent grade 3/4 toxicities were diarrhea, dehydration, and nausea and vomiting (19% each). No grade 5 events were seen. Four patients had a partial response and 15 had stable disease. Clinical benefit was seen across a range of tumor types and in all cohorts. PK analysis revealed no significant interaction between E and T. Conclusions This combination of agents is associated with tolerable toxicities at doses that induced responses. PK studies revealed no interaction between the drugs. Further investigations of this targeting strategy may be attractive in renal cell carcinoma, non-small cell lung cancer, alveolar sarcoma, and carcinoid tumor.

Mutational inactivation of STAG2 causes aneuploidy in human cancer

Most cancer cells are characterized by aneuploidy, an abnormal number of chromosomes. We have identified a clue to the mechanistic origins of aneuploidy through integrative genomic analyses of human tumors. A diverse range of tumor types were found to harbor deletions or inactivating mutations of STAG2, a gene encoding a subunit of the cohesin complex, which regulates the separation of sister chromatids during cell division. Because STAG2 is on the X chromosome, its inactivation requires only a single mutational event. Studying a near-diploid human cell line with a stable karyotype, we found that targeted inactivation of STAG2 led to chromatid cohesion defects and aneuploidy, whereas in two aneuploid human glioblastoma cell lines, targeted correction of the endogenous mutant alleles of STAG2 led to enhanced chromosomal stability. Thus, genetic disruption of cohesin is a cause of aneuploidy in human cancer.

Do doctors under-provide, over-provide or do both? Exploring the quality of medical treatment in the Philippines

OBJECTIVE

To assess the quality of medical treatment by disaggregating quality into components that distinguish between insufficient and unnecessary care.

DESIGN

Randomly selected doctors were asked how they would treat a sick child. Their responses were disaggregated into how much of an evidence-based essential treatment plan was completed and the number of additional non-essential treatments that were given. Key variables included the expected cost, the health consequences of insufficient and unnecessary care and comparisons between public and private physicians. Responses to 160 clinical performance vignettes (CPVs) were analysed.

SETTING

Philippines.

PARTICIPANTS

One hundred and forty-three public and private physicians in the Philippines, collected in November 2003-December 2004 and September 2006-June 2007.

INTERVENTIONS

CPVs administered to physicians.

MAIN OUTCOME MEASURES

Process quality measures (accounting for the possibility of both over-treatment and under-treatment).

RESULTS

Based on CPVs, doctors gave both insufficient and unnecessary treatment to under-five children in 69% of cases. Doctors who provided the least sufficient care were also the most likely to give costly or harmful unnecessary care. Insufficient care typically had potentially worse health consequences for the patient than unnecessary care, though unnecessary care remains a concern because of overuse of antibiotics (47%) and unnecessary hospitalization (34%).

CONCLUSIONS

Quality of care is complex, but over- and under-treatment coexist and, in our analysis physicians that were more likely to under-treat a sick child were also those more likely to over-treat.

Detection of early response to temozolomide treatment in brain tumors using hyperpolarized 13C MR metabolic imaging

PURPOSE

To demonstrate the feasibility of using DNP hyperpolarized [1-(13)C]-pyruvate to measure early response to temozolomide (TMZ) therapy using an orthotopic human glioblastoma xenograft model.

MATERIALS AND METHODS

Twenty athymic rats with intracranial implantation of human glioblastoma cells were divided into two groups: one group received an oral administration of 100 mg/kg TMZ (n = 10) and the control group received vehicle only (n = 10). (13)C 3D magnetic resonance spectroscopic imaging (MRSI) data were acquired following injection of 2.5 mL (100 mM) hyperpolarized [1-(13)C]-pyruvate using a 3T scanner prior to treatment (day D0), at D1 (days from treatment) or D2.

RESULTS

Tumor metabolism as assessed by the ratio of lactate to pyruvate (Lac/Pyr) was significantly altered at D1 for the TMZ-treated group but tumor volume did not show a reduction until D5 to D7. The percent change in Lac/Pyr from baseline was statistically different between the two groups at D1 and D2 (P < 0.008), while percent tumor volume was not (P > 0.2).

CONCLUSION

The results from this study suggest that metabolic imaging with hyperpolarized [1-(13)C]-pyruvate may provide a unique tool that clinical neuro-oncologists can use in the future to monitor tumor response to therapy for patients with brain tumors.

Inhibition of PI3K/mTOR pathways in glioblastoma and implications for combination therapy with temozolomide

Due to its molecular heterogeneity and infiltrative nature, glioblastoma multiforme (GBM) is notoriously resistant to traditional and experimental therapeutics. To overcome these hurdles, targeted agents have been combined with conventional therapy. We evaluated the preclinical potential of a novel, orally bioavailable PI3K/mTOR dual inhibitor (XL765) in in vitro and in vivo studies. In vivo serially passaged human GBM xenografts that are more genetically stable than GBM cell lines in culture were used for all experiments. Biochemical downstream changes were evaluated by immunoblot and cytotoxicity by colorimetric ATP-based assay. For in vivo experiments, human xenograft GBM 39 grown intracranially in nude mice was altered to express luciferase to monitor tumor burden by optical imaging. XL765 resulted in concentration-dependent decreases in cell viability in vitro. Cytotoxic doses resulted in specific inhibition of PI3K signaling. Combining XL765 with temozolomide (TMZ) resulted in additive toxicity in 4 of 5 xenografts. In vivo, XL765 administered by oral gavage resulted in greater than 12-fold reduction in median tumor bioluminescence compared with control (Mann-Whitney test p = 0.001) and improvement in median survival (logrank p = 0.05). TMZ alone showed a 30-fold decrease in median bioluminescence, but the combination XL765 + TMZ yielded a 140-fold reduction in median bioluminescence (Mann-Whitney test p = 0.05) with a trend toward improvement in median survival (logrank p = 0.09) compared with TMZ alone. XL765 shows activity as monotherapy and in combination with conventional therapeutics in a range of genetically diverse GBM xenografts.

Akt and autophagy cooperate to promote survival of drug-resistant glioma

Although the phosphatidylinositol 3-kinase to Akt to mammalian target of rapamycin (PI3K-Akt-mTOR) pathway promotes survival signaling, inhibitors of PI3K and mTOR induce minimal cell death in PTEN (phosphatase and tensin homolog deleted from chromosome 10) mutant glioma. Here, we show that the dual PI3K-mTOR inhibitor PI-103 induces autophagy in a form of glioma that is resistant to therapy. Inhibitors of autophagosome maturation cooperated with PI-103 to induce apoptosis through the mitochondrial pathway, indicating that the cellular self-digestion process of autophagy acted as a survival signal in this setting. Not all inhibitors of mTOR synergized with inhibitors of autophagy. Rapamycin delivered alone induced autophagy, yet cells survived inhibition of autophagosome maturation because of rapamycin-mediated activation of Akt. In contrast, adenosine 5'-triphosphate-competitive inhibitors of mTOR stimulated autophagy more potently than did rapamycin, with inhibition of mTOR complexes 1 and 2 contributing independently to induction of autophagy. We show that combined inhibition of PI3K and mTOR, which activates autophagy without activating Akt, cooperated with inhibition of autophagy to cause glioma cells to undergo apoptosis. Moreover, the PI3K-mTOR inhibitor NVP-BEZ235, which is in clinical use, synergized with the lysosomotropic inhibitor of autophagy, chloroquine, another agent in clinical use, to induce apoptosis in glioma xenografts in vivo, providing a therapeutic approach potentially translatable to humans.

Systemic and local drug delivery for treating diseases of the central nervous system in rodent models

Thorough preclinical testing of central nervous system (CNS) therapeutics includes a consideration of routes of administration and agent biodistribution in assessing therapeutic efficacy. Between the two major classifications of administration, local vs. systemic, systemic delivery approaches are often preferred due to ease of administration. However, systemic delivery may result in suboptimal drug concentration being achieved in the CNS, and lead to erroneous conclusions regarding agent efficacy. Local drug delivery methods are more invasive, but may be necessary to achieve therapeutic CNS drug levels. Here, we demonstrate proper technique for three routes of systemic drug delivery: intravenous injection, intraperitoneal injection, and oral gavage. In addition, we show a method for local delivery to the brain: convection-enhanced delivery (CED). The use of fluorescently-labeled compounds is included for in vivo imaging and verification of proper drug administration. The methods are presented using murine models, but can easily be adapted for use in rats.

Establishing intracranial brain tumor xenografts with subsequent analysis of tumor growth and response to therapy using bioluminescence imaging

Transplantation models using human brain tumor cells have served an essential function in neuro-oncology research for many years. In the past, the most commonly used procedure for human tumor xenograft establishment consisted of the collection of cells from culture flasks, followed by the subcutaneous injection of the collected cells in immunocompromised mice. Whereas this approach still sees frequent use in many laboratories, there has been a significant shift in emphasis over the past decade towards orthotopic xenograft establishment, which, in the instance of brain tumors, requires tumor cell injection into appropriate neuroanatomical structures. Because intracranial xenograft establishment eliminates the ability to monitor tumor growth through direct measurement, such as by use of calipers, the shift in emphasis towards orthotopic brain tumor xenograft models has necessitated the utilization of non-invasive imaging for assessing tumor burden in host animals. Of the currently available imaging methods, bioluminescence monitoring is generally considered to offer the best combination of sensitivity, expediency, and cost. Here, we will demonstrate procedures for orthotopic brain tumor establishment, and for monitoring tumor growth and response to treatment when testing experimental therapies.

Identification of internalizing human single-chain antibodies targeting brain tumor sphere cells

Glioblastoma multiforme (GBM) is the most common and aggressive form of primary brain tumor for which there is no curative treatment to date. Resistance to conventional therapies and tumor recurrence pose major challenges to treatment and management of this disease, and therefore new therapeutic strategies need to be developed. Previous studies by other investigators have shown that a subpopulation of GBM cells can grow as neurosphere-like cells when cultured in restrictive medium and exhibits enhanced tumor-initiating ability and resistance to therapy. We report here the identification of internalizing human single-chain antibodies (scFv) targeting GBM tumor sphere cells. We selected a large naive phage antibody display library on the glycosylation-dependent CD133 epitope-positive subpopulation of GBM cells grown as tumor spheres and identified internalizing scFvs that target tumor sphere cells broadly, as well as scFvs that target the CD133-positive subpopulation. These scFvs were found to be efficiently internalized by GBM tumor sphere cells. One scFv GC4 inhibited self-renewal of GBM tumor sphere cells in vitro. We have further developed a full-length human IgG1 based on this scFv, and found that it potently inhibits proliferation of GBM tumor sphere cells and GBM cells grown in regular nonselective medium. Taken together, these results show that internalizing human scFvs targeting brain tumor sphere cells can be readily identified from a phage antibody display library, which could be useful for further development of novel therapies that target subpopulations of GBM cells to combat recurrence and resistance to treatment.

Pleiotropic role for MYCN in medulloblastoma

Medulloblastoma (MB) is the most common malignant brain tumor of childhood. Sonic Hedgehog (SHH) signaling drives a minority of MB, correlating with desmoplastic pathology and favorable outcome. The majority, however, arises independently of SHH and displays classic or large cell anaplastic (LCA) pathology and poor prognosis. To identify common signaling abnormalities, we profiled mRNA, demonstrating misexpression of MYCN in the majority of human MB and negligible expression in normal cerebella. We clarified a role in pathogenesis by targeting MYCN (and luciferase) to cerebella of transgenic mice. MYCN-driven MB showed either classic or LCA pathologies, with Shh signaling activated in approximately 5% of tumors, demonstrating that MYCN can drive MB independently of Shh. MB arose at high penetrance, consistent with a role for MYCN in initiation. Tumor burden correlated with bioluminescence, with rare metastatic spread to the leptomeninges, suggesting roles for MYCN in both progression and metastasis. Transient pharmacological down-regulation of MYCN led to both clearance and senescence of tumor cells, and improved survival. Targeted expression of MYCN thus contributes to initiation, progression, and maintenance of MB, suggesting a central role for MYCN in pathogenesis.

Phase II evaluation of gefitinib in patients with newly diagnosed Grade 4 astrocytoma: Mayo/North Central Cancer Treatment Group Study N0074

PURPOSE

Amplification of the epidermal growth factor receptor (EGFR) gene represents one of the most frequent gene alterations in glioblastoma (GBM). In the current study, we evaluated gefitinib, a potent EGFR inhibitor, in the treatment of adults with newly diagnosed GBM.

METHODS AND MATERIALS

Ninety-eight patients (96 evaluable) were accrued between May 18, 2001, and August 2, 2002. All were newly diagnosed GBM patients who were clinically and radiographically stable/improved after radiation treatment (enrollment within 5 weeks of radiation completion). No prior chemotherapy was permitted. EGFR amplification/mutation, as assessed by fluorescence in situ hybridization and immunohistochemistry, was not required for treatment with gefitinib but was studied when tissues were available. Gefitinib was administered at 500 mg each day; for patients receiving dexamethasone or enzyme-inducing (CYP3A4) agents, dose was escalated to a maximum of 1,000 mg QD. Treatment cycles were repeated at 4-week intervals with brain magnetic resonance imaging at 8-week intervals.

RESULTS

Overall survival (OS; calculated from time of initial surgery) at 1 year (primary end point) with gefitinib was 54.2%, which was not statistically different compared with that of historical control population (48.9%, data from three previous Phase III North Central Cancer Treatment Group studies of newly diagnosed GBM patients). Progression-free survival (PFS) at 1 year post-RT (16.7%) was also not significantly different to that of historical controls (30.3%). Clinical outcome was not affected by EGFR status (amplification or vIII mutation). Fatigue (41%), rash (62%), and loose stools (58%) constituted the most frequent adverse events, the majority of these being limited to Grade 1/2. Of note, the occurrence of drug-related adverse effects, such as loose stools was associated with improved OS.

CONCLUSIONS

In our evaluation of nearly 100 patients with newly diagnosed GBM, treatment with adjuvant gefitinib post-radiation was not associated with significant improvement in OS or PFS. However, patients who experienced gefitinib-associated adverse effects (rash/diarrhea) did demonstrate improved OS.

Pharmacologic inhibition of cyclin-dependent kinases 4 and 6 arrests the growth of glioblastoma multiforme intracranial xenografts

Activation of cyclin-dependent kinases 4 and 6 (cdk4/6) occurs in the majority of glioblastoma multiforme (GBM) tumors, and represents a promising molecular target for the development of small molecule inhibitors. In the current study, we investigated the molecular determinants and in vivo response of diverse GBM cell lines and xenografts to PD-0332991, a cdk4/6-specific inhibitor. In vitro testing of PD-0332991 against a panel of GBM cell lines revealed a potent G(1) cell cycle arrest and induction of senescence in each of 16 retinoblastoma protein (Rb)-proficient cell lines regardless of other genetic lesions, whereas 5 cell lines with homozygous inactivation of Rb were completely resistant to treatment. Short hairpin RNA depletion of Rb expression conferred resistance of GBM cells to PD-0332991, further demonstrating a requirement of Rb for sensitivity to cdk4/6 inhibition. PD-0332991 was found to efficiently cross the blood-brain barrier and proved highly effective in suppressing the growth of intracranial GBM xenograft tumors, including those that had recurred after initial therapy with temozolomide. Remarkably, no mice receiving PD-0332991 died as a result of disease progression while on therapy. Additionally, the combination of PD-0332991 and radiation therapy resulted in significantly increased survival benefit compared with either therapy alone. In total, our results support clinical trial evaluation of PD-0332991 against newly diagnosed as well as recurrent GBM, and indicate that Rb status is the primary determinant of potential benefit from this therapy.

A hierarchy of self-renewing tumor-initiating cell types in glioblastoma

The neural stem cell marker CD133 is reported to identify cells within glioblastoma (GBM) that can initiate neurosphere growth and tumor formation; however, instances of CD133(-) cells exhibiting similar properties have also been reported. Here, we show that some PTEN-deficient GBM tumors produce a series of CD133(+) and CD133(-) self-renewing tumor-initiating cell types and provide evidence that these cell types constitute a lineage hierarchy. Our results show that the capacities for self-renewal and tumor initiation in GBM need not be restricted to a uniform population of stemlike cells, but can be shared by a lineage of self-renewing cell types expressing a range of markers of forebrain lineage.

Noninvasive detection of target modulation following phosphatidylinositol 3-kinase inhibition using hyperpolarized 13C magnetic resonance spectroscopy

Numerous mechanism-based anticancer drugs that target the phosphatidylinositol 3-kinase (PI3K) pathway are in clinical trials. However, it remains challenging to assess responses by traditional imaging methods. Here, we show for the first time the efficacy of hyperpolarized (13)C magnetic resonance spectroscopy (MRS) in detecting the effect of PI3K inhibition by monitoring hyperpolarized [1-(13)C]lactate levels produced from hyperpolarized [1-(13)C]pyruvate through lactate dehydrogenase (LDH) activity. In GS-2 glioblastoma cells, PI3K inhibition by LY294002 or everolimus caused hyperpolarized lactate to drop to 42 +/- 12% and to 76 +/- 5%, respectively. In MDA-MB-231 breast cancer cells, hyperpolarized lactate dropped to 71 +/- 15% after treatment with LY294002. These reductions were correlated with reductions in LDH activity to 48 +/- 4%, 63 +/- 4%, and 69 +/- 12%, respectively, and were associated with a drop in levels of LDHA mRNA and LDHA and hypoxia-inducible factor-1alpha proteins. Supporting these findings, tumor growth inhibition achieved by everolimus in murine GS-2 xenografts was associated with a drop in the hyperpolarized lactate-to-pyruvate ratio detected by in vivo MRS imaging, whereas an increase in this ratio occurred with tumor growth in control animals. Taken together, our findings illustrate the application of hyperpolarized (13)C MRS of pyruvate to monitor alterations in LDHA activity and expression caused by PI3K pathway inhibition, showing the potential of this method for noninvasive imaging of drug target modulation.

Hyperpolarized 13C magnetic resonance metabolic imaging: application to brain tumors

In order to compare in vivo metabolism between malignant gliomas and normal brain, (13)C magnetic resonance (MR) spectroscopic imaging data were acquired from rats with human glioblastoma xenografts (U-251 MG and U-87 MG) and normal rats, following injection of hyperpolarized [1-(13)C]-pyruvate. The median signal-to-noise ratio (SNR) of lactate, pyruvate, and total observed carbon-13 resonances, as well as their relative ratios, were calculated from voxels containing Gadolinium-enhanced tissue in T(1) postcontrast images for rats with tumors and from normal brain tissue for control rats. [1-(13)C]-labeled pyruvate and its metabolic product, [1-(13)C]-lactate, demonstrated significantly higher SNR in the tumor compared with normal brain tissue. Statistical tests showed significant differences in all parameters (P < .0004) between the malignant glioma tissue and normal brain. The SNR of lactate, pyruvate, and total carbon was observed to be different between the U-251 MG and U-87 MG models, which is consistent with inherent differences in the molecular characteristics of these tumors. These results suggest that hyperpolarized MR metabolic imaging may be valuable for assessing prognosis and monitoring response to therapy for patients with brain tumors.

Integrated genomic analysis identifies clinically relevant subtypes of glioblastoma characterized by abnormalities in PDGFRA, IDH1, EGFR, and NF1

The Cancer Genome Atlas Network recently cataloged recurrent genomic abnormalities in glioblastoma multiforme (GBM). We describe a robust gene expression-based molecular classification of GBM into Proneural, Neural, Classical, and Mesenchymal subtypes and integrate multidimensional genomic data to establish patterns of somatic mutations and DNA copy number. Aberrations and gene expression of EGFR, NF1, and PDGFRA/IDH1 each define the Classical, Mesenchymal, and Proneural subtypes, respectively. Gene signatures of normal brain cell types show a strong relationship between subtypes and different neural lineages. Additionally, response to aggressive therapy differs by subtype, with the greatest benefit in the Classical subtype and no benefit in the Proneural subtype. We provide a framework that unifies transcriptomic and genomic dimensions for GBM molecular stratification with important implications for future studies.

Reversing HOXA9 oncogene activation by PI3K inhibition: epigenetic mechanism and prognostic significance in human glioblastoma

HOXA genes encode critical transcriptional regulators of embryonic development that have been implicated in cancer. In this study, we documented functional relevance and mechanism of activation of HOXA9 in glioblastoma (GBM), the most common malignant brain tumor. Expression of HOXA genes was investigated using reverse transcription-PCR in primary gliomas and glioblastoma cell lines and was validated in two sets of expression array data. In a subset of GBM, HOXA genes are aberrently activated within confined chromosomal domains. Transcriptional activation of the HOXA cluster was reversible by a phosphoinostide 3-kinase (PI3K) inhibitor through an epigenetic mechanism involving histone H3K27 trimethylation. Functional studies of HOXA9 showed its capacity to decrease apoptosis and increase cellular proliferation along with tumor necrosis factor-related apoptosis-including ligand resistance. Notably, aberrant expression of HOXA9 was independently predictive of shorter overall and progression-free survival in two GBM patient sets and improved survival prediction by MGMT promoter methylation. Thus, HOXA9 activation is a novel, independent, and negative prognostic marker in GBM that is reversible through a PI3K-associated epigenetic mechanism. Our findings suggest a transcriptional pathway through which PI3K activates oncogenic HOXA expression with implications for mTOR or PI3K targeted therapies.

Oncogenic BRAF mutation with CDKN2A inactivation is characteristic of a subset of pediatric malignant astrocytomas

Malignant astrocytomas are a deadly solid tumor in children. Limited understanding of their underlying genetic basis has contributed to modest progress in developing more effective therapies. In an effort to identify such alterations, we performed a genome-wide search for DNA copy number aberrations (CNA) in a panel of 33 tumors encompassing grade 1 through grade 4 tumors. Genomic amplifications of 10-fold or greater were restricted to grade 3 and 4 astrocytomas and included the MDM4 (1q32), PDGFRA (4q12), MET (7q21), CMYC (8q24), PVT1 (8q24), WNT5B (12p13), and IGF1R (15q26) genes. Homozygous deletions of CDKN2A (9p21), PTEN (10q26), and TP53 (17p3.1) were evident among grade 2 to 4 tumors. BRAF gene rearrangements that were indicated in three tumors prompted the discovery of KIAA1549-BRAF fusion transcripts expressed in 10 of 10 grade 1 astrocytomas and in none of the grade 2 to 4 tumors. In contrast, an oncogenic missense BRAF mutation (BRAF(V600E)) was detected in 7 of 31 grade 2 to 4 tumors but in none of the grade 1 tumors. BRAF(V600E) mutation seems to define a subset of malignant astrocytomas in children, in which there is frequent concomitant homozygous deletion of CDKN2A (five of seven cases). Taken together, these findings highlight BRAF as a frequent mutation target in pediatric astrocytomas, with distinct types of BRAF alteration occurring in grade 1 versus grade 2 to 4 tumors.

Morphologic and molecular characterization of ATRT xenografts adapted for orthotopic therapeutic testing

Atypical teratoid rhabdoid tumor (ATRT) is a malignant tumor of the central nervous system that most commonly arises in young children. The aggressive growth and propensity for early dissemination throughout the neuraxis confers a dismal prognosis. Large clinical trials that could test new therapeutic agents are difficult to conduct due to the low incidence of this cancer. For this reason, high throughput preclinical testing with suitable animal models for ATRT would serve a critical need for identifying the most efficacious treatments. In response to this need, we have adapted ATRT cell lines for bioluminescence imaging (BLI) of intracranial (orthotopic) xenografts established in athymic mice. Our results indicate that following supratentorial or infratentorial injection in athymic mice, ATRT cells produce rapidly growing tumors, often with intraventricular spread or neuraxis dissemination. When established as orthotopic xenografts, the tumors predominantly display cells with a rhabdoid-like cellular morphology that show a spectrum of immunophenotypes similar to primary ATRT tumors. To demonstrate the feasibility of this orthotopic ATRT xenograft model for therapeutic testing with correlation to biomarker analysis, we examined the responses of luciferase-modified ATRT cells to temozolomide (TMZ). These xenografts, which highly express MGMT, are resistant to TMZ treatment when compared with an orthotopic glioblastoma xenograft that is MGMT deficient and responsive to TMZ. These data suggest that an orthotopic ATRT xenograft model, in which BLI is used for monitoring tumor growth and response to therapy, should contribute to the identification of effective therapeutics and regimens for treating this highly aggressive pediatric brain tumor.

microRNAs in gliomas: small regulators of a big problem

Gliomas are the most common form of primary brain tumors and are associated with a poor clinical outcome. The molecular mechanisms that contribute to gliomagenesis have become increasingly clear in recent years, yet much remains to be learned. This is particularly true for the role of microRNAs in gliomagenesis, as an appreciation for the significance of aberrant miRNA expression in human cancer has only emerged in the last 5 years. It is now evident that microRNAs regulate a wide variety of tumorigenic processes including cellular proliferation, differentiation, angiogenesis, invasion, and apoptosis. Here we review the current state of knowledge related to the role of microRNAs in glial tumor development. This is a rapidly evolving field and it is likely that we have only begun to appreciate the involvement of microRNAs in relation to glioma formation, and the therapeutic potential of microRNAs to improve outcome for glioma patients.

Immunological considerations of modern animal models of malignant primary brain tumors

Recent advances in animal models of glioma have facilitated a better understanding of biological mechanisms underlying gliomagenesis and glioma progression. The limitations of existing therapy, including surgery, chemotherapy, and radiotherapy, have prompted numerous investigators to search for new therapeutic approaches to improve quantity and quality of survival from these aggressive lesions. One of these approaches involves triggering a tumor specific immune response. However, a difficulty in this approach is the the scarcity of animal models of primary CNS neoplasms which faithfully recapitulate these tumors and their interaction with the host's immune system. In this article, we review the existing methods utilized to date for modeling gliomas in rodents, with a focus on the known as well as potential immunological aspects of these models. As this review demonstrates, many of these models have inherent immune system limitations, and the impact of these limitations on studies on the influence of pre-clinical therapeutics testing warrants further attention.