Pathologic correlates of primary central nervous system lymphoma defined in an orthotopic xenograft model

PURPOSE

The prospect for advances in the treatment of patients with primary central nervous system lymphoma (PCNSL) is likely dependent on the systematic evaluation of its pathobiology. Animal models of PCNSL are needed to facilitate the analysis of its molecular pathogenesis and for the efficient evaluation of novel therapeutics.

EXPERIMENTAL DESIGN

We characterized the molecular pathology of CNS lymphoma tumors generated by the intracerebral implantation of Raji B lymphoma cells in athymic mice. Lymphoma cells were modified for bioluminescence imaging to facilitate monitoring of tumor growth and response to therapy. In parallel, we identified molecular features of lymphoma xenograft histopathology that are evident in human PCNSL specimens.

RESULTS

Intracerebral Raji tumors were determined to faithfully reflect the molecular pathogenesis of PCNSL, including the predominant immunophenotypic state of differentiation of lymphoma cells and their reactive microenvironment. We show the expression of interleukin-4 by Raji and other B lymphoma cell lines in vitro and by Raji tumors in vivo and provide evidence for a role of this cytokine in the M2 polarization of lymphoma macrophages both in the murine model and in diagnostic specimens of human PCNSL.

CONCLUSION

Intracerebral implantation of Raji cells results in a reproducible and invasive xenograft model, which recapitulates the histopathology and molecular features of PCNSL, and is suitable for preclinical testing of novel agents. We also show for the first time the feasibility and accuracy of tumor bioluminescence in the monitoring of a highly infiltrative brain tumor.

EGFR signals to mTOR through PKC and independently of Akt in glioma

Amplification of the gene encoding the epidermal growth factor (EGF) receptor (EGFR) occurs commonly in glioblastoma, leading to activation of downstream kinases including phosphatidylinositol 3'-kinase (PI3K), Akt, and mammalian target of rapamycin (mTOR). Here, we show that phosphorylation of mTOR and its downstream substrate rpS6 (ribosomal protein S6) are robust biomarkers for the antiproliferative effect of EGFR inhibitors. Inhibition of EGFR signaling correlated with decreased abundance of phosphorylated mTOR (p-mTOR) and rpS6 (p-rpS6) in cells wild type for the gene encoding PTEN (phosphatase and tensin homolog on chromosome 10), a negative regulator of PI3K. In contrast, inhibition of EGFR signaling failed to affect p-mTOR or p-rpS6 in cells mutant for PTEN, which are resistant to EGFR inhibitors. Although the abundance of phosphorylated Akt (p-Akt) decreased in response to inhibition of EGFR signaling, Akt was dispensable for signaling between EGFR and mTOR. We identified an Akt-independent pathway linking EGFR to mTOR that was critically dependent on protein kinase C (PKC). Consistent with these observations, the abundance of EGFR generally correlated with phosphorylation of rpS6 and PKC in primary human glioblastoma tumors, and correlated poorly with phosphorylation of Akt. Inhibition of PKC led to decreased viability of glioma cells regardless of PTEN or EGFR status, suggesting that PKC inhibitors should be tested in glioma. These findings underline the importance of signaling between EGFR and mTOR in glioma, identify PKCalpha as essential to this network, and question the necessity of Akt as a critical intermediate coupling EGFR and mTOR in glioma.

p53 Small-molecule inhibitor enhances temozolomide cytotoxic activity against intracranial glioblastoma xenografts

In this study, we investigated the precursor and active forms of a p53 small-molecule inhibitor for their effects on temozolomide (TMZ) antitumor activity against glioblastoma (GBM), using both in vitro and in vivo experimental approaches. Results from in vitro cell viability analysis showed that the cytotoxic activity of TMZ was substantially increased when p53 wild-type (p53(wt)) GBMs were cotreated with the active form of p53 inhibitor, and this heightened cytotoxic response was accompanied by increased poly(ADP-ribose) polymerase cleavage as well as elevated cellular phospho-H2AX. Analysis of the same series of GBMs, as intracranial xenografts in athymic mice, and administering corresponding p53 inhibitor precursor, which is converted to the active compound in vivo, yielded results consistent with the in vitro analyses: TMZ + p53 inhibitor precursor cotreatment of three distinct p53(wt) GBM xenografts resulted in significant enhancement of TMZ antitumor effect relative to treatment with TMZ alone, as indicated by serial bioluminescence monitoring as well as survival analysis (P < 0.001 for cotreatment survival benefit in each case). Mice receiving intracranial injection with p53(null) GBM showed similar survival benefit from TMZ treatment regardless of the presence or absence of p53 inhibitor precursor. In total, our results indicate that the p53 active and precursor inhibitor pair enhances TMZ cytotoxicity in vitro and in vivo, respectively, and do so in a p53-dependent manner.

Comparative analyses of gene copy number and mRNA expression in glioblastoma multiforme tumors and xenografts

Development of model systems that recapitulate the molecular heterogeneity observed among glioblastoma multiforme (GBM) tumors will expedite the testing of targeted molecular therapeutic strategies for GBM treatment. In this study, we profiled DNA copy number and mRNA expression in 21 independent GBM tumor lines maintained as subcutaneous xenografts (GBMX), and compared GBMX molecular signatures to those observed in GBM clinical specimens derived from the Cancer Genome Atlas (TCGA). The predominant copy number signature in both tumor groups was defined by chromosome-7 gain/chromosome-10 loss, a poor-prognosis genetic signature. We also observed, at frequencies similar to that detected in TCGA GBM tumors, genomic amplification and overexpression of known GBM oncogenes, such as EGFR, MDM2, CDK6, and MYCN, and novel genes, including NUP107, SLC35E3, MMP1, MMP13, and DDX1. The transcriptional signature of GBMX tumors, which was stable over multiple subcutaneous passages, was defined by overexpression of genes involved in M phase, DNA replication, and chromosome organization (MRC) and was highly similar to the poor-prognosis mitosis and cell-cycle module (MCM) in GBM. Assessment of gene expression in TCGA-derived GBMs revealed overexpression of MRC cancer genes AURKB, BIRC5, CCNB1, CCNB2, CDC2, CDK2, and FOXM1, which form a transcriptional network important for G2/M progression and/or checkpoint activation. Our study supports propagation of GBM tumors as subcutaneous xenografts as a useful approach for sustaining key molecular characteristics of patient tumors, and highlights therapeutic opportunities conferred by this GBMX tumor panel for testing targeted therapeutic strategies for GBM treatment.

Phase II study of erlotinib plus temozolomide during and after radiation therapy in patients with newly diagnosed glioblastoma multiforme or gliosarcoma

PURPOSE

This open-label, prospective, single-arm, phase II study combined erlotinib with radiation therapy (XRT) and temozolomide to treat glioblastoma multiforme (GBM) and gliosarcoma. The objectives were to determine efficacy of this treatment as measured by survival and to explore the relationship between molecular markers and treatment response.

PATIENTS AND METHODS

Sixty-five eligible adults with newly diagnosed GBM or gliosarcoma were enrolled. We intended to treat patients not currently treated with enzyme-inducing antiepileptic drugs (EIAEDs) with 100 mg/d of erlotinib during XRT and 150 mg/d after XRT. Patients receiving EIAEDs were to receive 200 mg/d of erlotinib during XRT and 300 mg/d after XRT. After XRT, the erlotinib dose was escalated until patients developed tolerable grade 2 rash or until the maximum allowed dose was reached. All patients received temozolomide during and after XRT. Molecular markers of epidermal growth factor receptor (EGFR), EGFRvIII, phosphatase and tensin homolog (PTEN), and methylation status of the promotor region of the MGMT gene were analyzed from tumor tissue. Survival was compared with outcomes from two historical phase II trials.

RESULTS

Median survival was 19.3 months in the current study and 14.1 months in the combined historical control studies, with a hazard ratio for survival (treated/control) of 0.64 (95% CI, 0.45 to 0.91). Treatment was well tolerated. There was a strong positive correlation between MGMT promotor methylation and survival, as well as an association between MGMT promotor-methylated tumors and PTEN positivity shown by immunohistochemistry with improved survival.

CONCLUSION

Patients treated with the combination of erlotinib and temozolomide during and following radiotherapy had better survival than historical controls. Additional studies are warranted.

Abnormal DNA methylation of CD133 in colorectal and glioblastoma tumors

Much recent effort has focused on identifying and characterizing cellular markers that distinguish tumor propagating cells (TPC) from more differentiated progeny. We report here an unusual promoter DNA methylation pattern for one such marker, the cell surface antigen CD133 (Prominin 1). This protein has been extensively used to enrich putative cancer propagating stem-like cell populations in epithelial tumors and, especially, glioblastomas. We find that, within individual cell lines of cultured colon cancers and glioblastomas, the promoter CpG island of CD133 is DNA methylated, primarily, in cells with absent or low expression of the marker protein, whereas lack of such methylation is evident in purely CD133+ cells. Differential histone modification marks of active versus repressed genes accompany these DNA methylation changes. This heterogeneous CpG island DNA methylation status in the tumors is unusual in that other DNA hypermethylated genes tested in such cultures preserve their methylation patterns between separated CD133+ and CD133- cell populations. Furthermore, the CD133 DNA methylation seems to constitute an abnormal promoter signature because it is not found in normal brain and colon but only in cultured and primary tumors. Thus, the DNA methylation is imposed on the transition between the active versus repressed transcription state for CD133 only in tumors. Our findings provide additional insight for the dynamics of aberrant DNA methylation associated with aberrant gene silencing in human tumors.

Induction of MGMT expression is associated with temozolomide resistance in glioblastoma xenografts

Temozolomide (TMZ)-based therapy is the standard of care for patients with glioblastoma multiforme (GBM), and resistance to this drug in GBM is modulated by the DNA repair protein O(6)-methylguanine-DNA methyltransferase (MGMT). Expression of MGMT is silenced by promoter methylation in approximately half of GBM tumors, and clinical studies have shown that elevated MGMT protein levels or lack of MGMT promoter methylation is associated with TMZ resistance in some, but not all, GBM tumors. In this study, the relationship between MGMT protein expression and tumor response to TMZ was evaluated in four GBM xenograft lines that had been established from patient specimens and maintained by serial subcutaneous passaging in nude mice. Three MGMT unmethylated tumors displayed elevated basal MGMT protein expression, but only two of these were resistant to TMZ therapy (tumors GBM43 and GBM44), while the other (GBM14) displayed a level of TMZ sensitivity that was similar in extent to that seen in a single MGMT hypermethylated line (GBM12). In tissue culture and animal studies, TMZ treatment resulted in robust and prolonged induction of MGMT expression in the resistant GBM43 and GBM44 xenograft lines, while MGMT induction was blunted and abbreviated in GBM14. Consistent with a functional significance of MGMT induction, treatment of GBM43 with a protracted low-dose TMZ regimen was significantly less effective than a shorter high-dose regimen, while survival for GBM14 was improved with the protracted dosing regimen. In conclusion, MGMT expression is dynamically regulated in some MGMT nonmethylated tumors, and in these tumors, protracted dosing regimens may not be effective.

PTEN loss does not predict for response to RAD001 (Everolimus) in a glioblastoma orthotopic xenograft test panel

PURPOSE

Hyperactivation of the phosphatidylinositol 3-kinase/Akt signaling through disruption of PTEN function is common in glioblastoma multiforme, and these genetic changes are predicted to enhance sensitivity to mammalian target of rapamycin (mTOR) inhibitors such as RAD001 (everolimus).

EXPERIMENTAL DESIGN

To test whether PTEN loss could be used as a predictive marker for mTOR inhibitor sensitivity, the response of 17 serially transplantable glioblastoma multiforme xenografts was evaluated in an orthotopic therapy evaluation model. Of these 17 xenograft lines, 7 have either genomic deletion or mutation of PTEN.

RESULTS

Consistent with activation of Akt signaling, there was a good correlation between loss of PTEN function and elevated levels of Akt phosphorylation. However, of the 7 lines with disrupted PTEN function, only 1 tumor line (GBM10) was significantly sensitive to RAD001 therapy (25% prolongation in median survival), whereas 1 of 10 xenograft lines with wild-type PTEN was significantly sensitive to RAD001 (GS22; 34% prolongation in survival). Relative to placebo, 5 days of RAD001 treatment was associated with a marked 66% reduction in the MIB1 proliferation index in the sensitive GBM10 line (deleted PTEN) compared with a 25% and 7% reduction in MIB1 labeling index in the insensitive GBM14 (mutant PTEN) and GBM15 (wild-type PTEN) lines, respectively. Consistent with a cytostatic antitumor effect, bioluminescent imaging of luciferase-transduced intracranial GBM10 xenografts showed slowed tumor growth without significant tumor regression during RAD001 therapy.

CONCLUSION

These data suggest that loss of PTEN function is insufficient to adequately predict responsiveness to mTOR inhibitors in glioblastoma multiforme.

Disabled-1 is a large common fragile site gene, inactivated in multiple cancers

Common fragile sites (CFS) are large, genomically unstable regions, which are hot-spots for deletions and other alterations, especially in cancer cells. Several have been shown to contain genes that span large genomic regions, such as FHIT (1.5 Mb), WWOX (1.0 Mb), GRID2 (1.36 Mb), PARK2 (1.3 Mb), and RORA (730 kb). These genes are frequently inactivated in multiple different cancers, and FHIT and WWOX are shown to function as tumor suppressors. The disabled-1 gene (DAB1) is one of the human homologs of the Drosophila disabled locus, which in mammals is involved in neuronal migration and lamination in the developing cerebral cortex. Mice DAB1 inactivation results in the neurological mutant Scrambler, having similarities to mice with the inactivation of PARK2 (Quaker), GRID2 (Lurcher), and RORA (Staggerer). We were interested in whether DAB1 was another large CFS gene that could have cancer development importance. We demonstrated here that the human DAB1 gene (spanning 1.25 Mb) mapped within FRA1B CFS region on chromosomal band 1p32.2. Real-time RT-PCR analysis revealed that the expression level of DAB1 was decreased in many human cancer samples, including primary tumor tissues and cancer-derived cell lines, from several different cancers, especially in brain and endometrial cancer. Additionally, the introduction of an over-expression DAB1 plasmid into two different cell lines, having insignificant endogenous DAB1 expression, resulted in decreased cell growth. In summary, DAB1 is another gene that resides within an unstable CFS region and might play a role in human tumorigenesis. These data may provide further linkage between neurological development and cancer.

Mechanisms of chemoresistance to alkylating agents in malignant glioma

Intrinsic or acquired chemoresistance to alkylating agents is a major cause of treatment failure in patients with malignant brain tumors. Alkylating agents, the mainstay of treatment for brain tumors, damage the DNA and induce apoptosis, but the cytotoxic activity of these agents is dependent on DNA repair pathways. For example, O6-methylguanine DNA adducts can cause double-strand breaks, but this is dependent on a functional mismatch repair pathway. Thus, tumor cell lines deficient in mismatch repair are resistant to alkylating agents. Perhaps the most important mechanism of resistance to alkylating agents is the DNA repair enzyme O6-methylguanine methyltransferase, which can eliminate the cytotoxic O6-methylguanine DNA adduct before it causes harm. Another mechanism of resistance to alkylating agents is the base excision repair (BER) pathway. Consequently, efforts are ongoing to develop effective inhibitors of BER. Poly(ADP-ribose)polymerase plays a pivotal role in BER and is an important therapeutic target. Developing effective strategies to overcome chemoresistance requires the identification of reliable preclinical models that recapitulate human disease and which can be used to facilitate drug development. This article describes the diverse mechanisms of chemoresistance operating in malignant glioma and efforts to develop reliable preclinical models and novel pharmacologic approaches to overcome resistance to alkylating agents.

miR-124 and miR-137 inhibit proliferation of glioblastoma multiforme cells and induce differentiation of brain tumor stem cells

BACKGROUND

Glioblastoma multiforme (GBM) is an invariably fatal central nervous system tumor despite treatment with surgery, radiation, and chemotherapy. Further insights into the molecular and cellular mechanisms that drive GBM formation are required to improve patient outcome. MicroRNAs are emerging as important regulators of cellular differentiation and proliferation, and have been implicated in the etiology of a variety of cancers, yet the role of microRNAs in GBM remains poorly understood. In this study, we investigated the role of microRNAs in regulating the differentiation and proliferation of neural stem cells and glioblastoma-multiforme tumor cells.

METHODS

We used quantitative RT-PCR to assess microRNA expression in high-grade astrocytomas and adult mouse neural stem cells. To assess the function of candidate microRNAs in high-grade astrocytomas, we transfected miR mimics to cultured-mouse neural stem cells, -mouse oligodendroglioma-derived stem cells, -human glioblastoma multiforme-derived stem cells and -glioblastoma multiforme cell lines. Cellular differentiation was assessed by immunostaining, and cellular proliferation was determined using fluorescence-activated cell sorting.

RESULTS

Our studies revealed that expression levels of microRNA-124 and microRNA-137 were significantly decreased in anaplastic astrocytomas (World Health Organization grade III) and glioblastoma multiforme (World Health Organization grade IV) relative to non-neoplastic brain tissue (P < 0.01), and were increased 8- to 20-fold during differentiation of cultured mouse neural stem cells following growth factor withdrawal. Expression of microRNA-137 was increased 3- to 12-fold in glioblastoma multiforme cell lines U87 and U251 following inhibition of DNA methylation with 5-aza-2'-deoxycytidine (5-aza-dC). Transfection of microRNA-124 or microRNA-137 induced morphological changes and marker expressions consistent with neuronal differentiation in mouse neural stem cells, mouse oligodendroglioma-derived stem cells derived from S100 beta-v-erbB tumors and cluster of differentiation 133+ human glioblastoma multiforme-derived stem cells (SF6969). Transfection of microRNA-124 or microRNA-137 also induced G1 cell cycle arrest in U251 and SF6969 glioblastoma multiforme cells, which was associated with decreased expression of cyclin-dependent kinase 6 and phosphorylated retinoblastoma (pSer 807/811) proteins.

CONCLUSION

microRNA-124 and microRNA-137 induce differentiation of adult mouse neural stem cells, mouse oligodendroglioma-derived stem cells and human glioblastoma multiforme-derived stem cells and induce glioblastoma multiforme cell cycle arrest. These results suggest that targeted delivery of microRNA-124 and/or microRNA-137 to glioblastoma multiforme tumor cells may be therapeutically efficacious for the treatment of this disease.

Increased expression of the glioma-associated antigen ARF4L after loss of the tumor suppressor PTEN. Laboratory investigation

OBJECT

Despite recent advances in cancer immunotherapy, cellular mechanisms controlling expression of tumor-associated antigens are poorly understood. Mutations in cancer cells, such as loss of PTEN, may increase expression of tumor-associated antigens. The authors investigated the relationship between PTEN status and the expression of a glioma-associated antigen, adenosine diphosphate-ribosylation factor 4-like (ARF4L) protein.

METHODS

Human glioma cell lines with confirmed PTEN status were examined by Northern blot analysis and quantitative polymerase chain reaction. Western blot analysis was used to measure ARF4L protein levels across multiple cell lines.

RESULTS

The loss of PTEN was shown to lead to increased levels of ARF4L protein but no change in transcript levels. Cell lines with serial mutations, including activation of Ras and Akt pathways, also demonstrated increased levels of ARF4L protein, which decreased after treatment with rapamycin. The ARF4L transcript preferentially localized to the polysomal compartment after PTEN loss in glioma or activation of Akt in human astrocytes.

CONCLUSIONS

Expression of ARF4L is controlled by the activated Akt/mTOR pathway, which is a downstream effect of the loss of PTEN function. Mutations leading to oncogenesis may impact the regulation and expression of tumor specific antigens. Screening of mutation status in glioma may be helpful in selecting patients for immunotherapy trials in the future.

DMD and IL1RAPL1: two large adjacent genes localized within a common fragile site (FRAXC) have reduced expression in cultured brain tumors

Common fragile sites (CFSs) are large regions of profound genomic instability found in all individuals. Spanning the center of the two most frequently expressed CFS regions, FRA3B (3p14.3) and FRA16D (16q23.2), are the 1.5 Mb FHIT gene and the 1.0 Mb WWOX gene. These genes are frequently deleted and/or altered in many different cancers. Both FHIT and WWOX have been demonstrated to function as tumor suppressors, both in vitro and in vivo. A number of other large CFS genes have been identified and are also frequently inactivated in multiple cancers. Based on these data, several additional very large genes were tested to determine if they were derived from within CFS regions, but DCC and RAD51L1 were not. However, the 2.0 Mb DMD gene and its immediately distal neighbor, the 1.8 Mb IL1RAPL1 gene are CFS genes contained within the FRAXC CFS region (Xp21.2-->p21.1). They are abundantly expressed in normal brain but were dramatically underexpressed in every brain tumor cell line and xenograft (derived from an intracranial model of glioblastoma multiforme) examined. We studied the expression of eleven other large CFS genes in the same panel of brain tumor cell lines and xenografts and found reduced expression of multiple large CFS genes in these samples. In this report we show that there is selective loss of specific large CFS genes in different cancers that does not appear to be mediated by the relative instability within different CFS regions. Further, the inactivation of multiple large CFS genes in xenografts and brain tumor cell lines may help to explain why this type of cancer is highly aggressive and associated with a poor clinical outcome.

An orthotopic skull base model of malignant meningioma

Meningioma tumor growth involves the subarachnoid space that contains the cerebrospinal fluid. Modeling tumor growth in this microenvironment has been associated with widespread leptomeningeal dissemination, which is uncharacteristic of human meningiomas. Consequently, survival times and tumor properties are varied, limiting their utility in testing experimental therapies. We report the development and characterization of a reproducible orthotopic skull-base meningioma model in athymic mice using the IOMM-Lee cell line. Localized tumor growth was obtained by using optimal cell densities and matrigel as the implantation medium. Survival times were within a narrow range of 17-21 days. The xenografts grew locally compressing surrounding brain tissue. These tumors had histopathologic characteristics of anaplastic meningiomas including high cellularity, nuclear pleomorphism, cellular pattern loss, necrosis and conspicuous mitosis. Similar to human meningiomas, considerable invasion of the dura and skull and some invasion of adjacent brain along perivascular tracts were observed. The pattern of hypoxia was also similar to human malignant meningiomas. We use bioluminescent imaging to non-invasively monitor the growth of the xenografts and determine the survival benefit from temozolomide treatment. Thus, we describe a malignant meningioma model system that will be useful for investigating the biology of meningiomas and for preclinical assessment of therapeutic agents.

Non-random inactivation of large common fragile site genes in different cancers

The common fragile sites are regions of profound genomic instability found in all individuals. The full size of each region of instability ranges from under one megabase (Mb) to greater than 10 Mbs. At least half of the CFS regions have been found to span extremely large genes that spanned from 600 kb to greater than 2.0 Mbs. The large CFS genes are also very interesting from a cancer perspective as several of them, including FHIT and WWOX, have already demonstrated the capacity to function as tumor suppressor genes, both in vitro and in vivo. We estimate that there may be 40-50 large genes localized in CFS regions. The expression of a number of the large CFS genes has been previously shown to be lost in many different cancers and this is frequently associated with a worse clinical outcome for patients. To determine if there was selection for the inactivation of different large CFS genes in different cancers, we examined the expression of 13 of the 20 known large CFS genes: FHIT, WWOX, PARK2, GRID2, NBEA, DLG2, RORA isoforms 1 and 4, DAB1, CNTNAP2, DMD, IL1RAPL1, IMMP2L and LARGE in breast, ovarian, endometrial and brain cancers using real-time RT-PCR analysis. Each cancer had a distinct profile of different large CFS genes that were inactivated. Interestingly, in breast, ovarian and endometrial cancers there were some cancers that had inactivation of expression of none or only one of the tested genes, while in other specimens there was inactivation of multiple tested genes. Brain cancers had inactivation of many of the tested genes, a number of which function in normal neurological development. We find that there is no relationship between the frequency that any specific CFS is expressed and the frequency that the gene from that region is inactivated in different cancers. Instead, it appears that different cancers select for the inactivation of different large CFS genes.

Bioluminescence monitoring of intracranial glioblastoma xenograft: response to primary and salvage temozolomide therapy

OBJECT

Bioluminescence imaging (BLI) offers a rapid and accurate means for longitudinal study of tumor cell growth and response to therapy in rodent models. Because this technology has only recently come into use in the field of small animal imaging, applications in this area have been limited. In the current study we have applied BLI to the analysis of clinically relevant issues involving use of the DNA methylating agent temozolomide (TMZ) in a mouse model.

METHODS

An invasive glioblastoma multiforme xenograft was modified for BLI via transduction with a luciferase-encoding lentivirus. Supratentorial tumors were established in athymic nude mice that were subsequently assigned randomly to control and TMZ treatment groups, and the extent of intracranial tumor was monitored using BLI.

RESULTS

In an experiment designed to compare the extent of antitumor effect between a single high-dose TMZ treatment and a protracted low-dose TMZ regimen, BLI revealed the protracted regimen as having superior antitumor effect, and this interpretation was consistent with results from a survival comparison between the two TMZ treatment groups. In a second experiment designed to assess the utility of BLI for testing therapies against recurrent glioblastoma multiforme, mice with intracranial tumors were retreated with TMZ at a time when BLI monitoring revealed tumor regrowth following initial TMZ treatment, and retreatment was successful in providing additional survival benefit.

CONCLUSIONS

The results of these experiments indicate that BLI monitoring can be used as a surrogate for predicting survival benefit from TMZ treatment, permits early determination of relative survival benefit associated with distinct TMZ therapeutic regimens, and offers a means of investigating secondary/salvage therapy efficacy following tumor regrowth from initial therapy.

Loss of genetic information in cancer

The determination and comparison of genotypic combinations at genomic loci in normal and tumour tissues from patients with various types of cancer have defined the chromosomal locations of loci at which recessive mutations play a role in disease. The predisposing nature of some of these mutant alleles is exemplified in studies of retinoblastoma and osteogenic sarcoma. These two clinically associated diseases share a pathogenetically causal predisposition that maps to chromosome position 13q14. A similar mechanism at 11p15.5 is involved in the development of the embryonal variant of rhabdomyo-sarcoma, Wilms' tumour and hepatoblastoma. Finally, genomic alteration of chromosome 10 is apparent in glioblastomas and mixed tumours of glioblastoma/astrocytoma grade III but not in homogenous astrocytoma grades II or III, suggesting the definition of a locus involved in tumour progression and, perhaps, an approach to molecular genetic staging of tumours.

Identification of molecular characteristics correlated with glioblastoma sensitivity to EGFR kinase inhibition through use of an intracranial xenograft test panel

In the current study, we examined a panel of serially passaged glioblastoma xenografts, in the context of an intracranial tumor therapy response model, to identify associations between glioblastoma molecular characteristics and tumor sensitivity to the epidermal growth factor receptor (EGFR) kinase inhibitor erlotinib. From an initial evaluation of 11 distinct glioblastoma xenografts, two erlotinib-sensitive tumors were identified, each having amplified EGFR and expressing wild-type PTEN. One of these tumors expressed truncated EGFRvIII, whereas the other expressed full-length EGFR. Subsequent cDNA sequence analysis revealed the latter tumor as expressing an EGFR sequence variant with arginine, rather than leucine, at amino acid position 62; this was the only EGFR sequence variant identified among the 11 xenografts, other than the aforementioned vIII sequence variant. EGFR cDNAs were then examined from 12 more xenografts to determine whether additional missense sequence alterations were evident, and this analysis revealed one such case, expressing threonine, rather than alanine, at amino acid position 289 of the extracellular domain. This glioblastoma was also amplified for EGFR, but did not display significant erlotinib sensitivity, presumably due to its lacking PTEN expression. In total, our study identified two erlotinib-sensitive glioblastoma xenografts, with the common molecular characteristics shared by each being the expression of wild-type PTEN in combination with the expression of amplified and aberrant EGFR.

Epidermal growth factor receptor variant III status defines clinically distinct subtypes of glioblastoma

PURPOSE

The clinical significance of epidermal growth factor receptor variant III (EGFRvIII) expression in glioblastoma multiforme (GBM) and its relationship with other key molecular markers are not clear. We sought to evaluate the clinical significance of GBM subtypes as defined by EGFRvIII status.

PATIENTS AND METHODS

The expression of EGFRvIII was assessed by immunohistochemistry in 649 patients with newly diagnosed GBM. These data were then examined in conjunction with the expression of phospho-intermediates (in a subset of these patients) of downstream AKT and Ras pathways and YKL-40 as well as with known clinical risk factors, including the Radiation Therapy Oncology Group's recursive partitioning analysis (RTOG-RPA) class.

RESULTS

The RTOG-RPA class was highly predictive of survival in EGFRvIII-negative patients but much less predictive in EGFRvIII-positive patients. These findings were seen in both an initial test set (n = 268) and a larger validation set (n = 381). Similarly, activation of the AKT/MAPK pathways and YKL-40 positivity were predictive of poor outcome in EGFRvIII-negative patients but not in EGFRvIII-positive patients. Pair-wise combinations of markers identified EGFRvIII and YKL-40 as prognostically important. In particular, outcome in patients with EGFRvIII-negative/YKL-40-negative tumors was significantly better than the outcome in patients with the other three combinations of these two markers.

CONCLUSION

Established prognostic factors in GBM were not predictive of outcome in the EGFRvIII-positive subset, although this requires confirmation in independent data sets. GBMs negative for both EGFRvIII and YKL-40 show less aggressive behavior.

Rarity of PTEN deletions and EGFR amplification in malignant gliomas of childhood: results from the Children's Cancer Group 945 cohort

OBJECT

In reporting on molecular studies involving malignant gliomas in adults, authors have noted that deletions of PTEN and amplification of EGFR are common and may contribute to tumor development, providing a rationale for a number of therapies aimed at these molecular targets. The frequency of comparable abnormalities has not been defined in a sizable pediatric cohort. To address this issue, we examined tumor samples from the Children's Cancer Group 945 study, a large randomized trial of treatment for childhood malignant gliomas.

METHODS

Tissue sections in 62 evaluable cases were examined, and the tumors were isolated by microdissection. Polymerase chain reaction amplification was used to detect PTEN mutations. Deletions of PTEN were also assessed by fluorescence in situ hybridization (FISH) in 27 cases and loss of heterozygosity analysis in 54; EGFR was assessed using immunohistochemistry to identify areas with maximal EGFR expression, followed by FISH to determine EGFR amplification. Alteration of the PTEN sequence was detected in just one of 62 tumors, in conjunction with loss of chromosome 10; PTEN deletions without mutation were evident in seven additional tumors. The PTEN alterations were more common in glioblastoma multiforme (seven of 25 tumors) than other tumor subgroups (one of 37 tumors) (p = 0.0056). Although 14 of 38 evaluable tumors had increased EGFR expression compared to normal tissue, only one tumor exhibited amplification of EGFR.

CONCLUSIONS

Alterations in PTEN and amplification of EGFR are uncommon in pediatric malignant gliomas, in contrast to adult malignant gliomas. From this one can infer that the pediatric and adult tumors involve distinct molecular causes. The results of this study have important implications for the adaptation of glioma therapies aimed at molecular targets in adults to the treatment of childhood gliomas, and highlight the need for investigations of therapies specifically directed toward childhood tumors.

Epidermal growth factor receptor (EGFR)-retargeted measles virus strains effectively target EGFR- or EGFRvIII expressing gliomas

A retargeted measles virus strain MV-GFP-H(AA)-scEGFR was generated by engineering the MV-NSe Edmonston vaccine strain to incorporate both CD46 (Y481A) and signaling lymphocyte activation molecule (SLAM) (R533A) ablating mutations in the hemagglutinin protein in combination with the display of a single-chain antibody against epidermal growth factor receptor (EGFR) at the C terminus of hemagglutinin. The unmodified MV-GFP virus was used as a positive control. Specificity of the EGFR retargeted virus was demonstrated in non-permissive Chinese hamster ovary (CHO) cells stably transfected to express either the natural receptors CD46 or SLAM or the target receptors EGFR and EGFRvIII. In vitro, the retargeted virus had potent antitumor activity against EGFR- or EGFRvIII-overexpressing primary glioblastoma multi-forme (GBM) cell lines that was comparable to the activity of the unmodified MV-GFP virus. Intratumoral administration of MV-GFP-H(AA)-scEGFRvIII in orthotopic GBM12 xenografts resulted in tumor regression, as demonstrated by bioluminescence imaging and significant prolongation of survival, that was comparable to the effect of the unmodified strain. In contrast to MV-GFP, central nervous system administration of the targeted MV-GFP-H(AA)-scEGFR virus in measles replication-permissive Ifnar(ko) CD46 transgenic mice resulted in no neurotoxicity. In conclusion, EGFR-retargeted measles virus strains have comparable therapeutic efficacy to the unmodified virus in glioma cells overexpressing EGFR or EGFRvIII in vivo and in vitro, and improved therapeutic index, a finding with potential translational implications in glioma virotherapy.

PIK3CA gene mutations in pediatric and adult glioblastoma multiforme

The phosphatidylinositol 3-kinases (PI3K) are a family of enzymes that relay important cellular growth control signals. Recently, a large-scale mutational analysis of eight PI3K and eight PI3K-like genes revealed somatic mutations in PIK3CA, which encodes the p110alpha catalytic subunit of class IA PI3K, in several types of cancer, including glioblastoma multiforme. In that report, 4 of 15 (27%) glioblastomas contained potentially oncogenic PIK3CA mutations. Subsequent studies, however, showed a significantly lower mutation rate ranging from 0% to 7%. Given this disparity and to address the relation of patient age to mutation frequency, we examined 10 exons of PIK3CA in 73 glioblastoma samples by PCR amplification followed by direct DNA sequencing. Overall, PIK3CA mutations were found in 11 (15%) samples, including several novel mutations. PIK3CA mutations were distributed in all sample types, with 18%, 9%, and 13% of primary tumors, xenografts, and cell lines containing mutations, respectively. Of the primary tumors, PIK3CA mutations were identified in 21% and 17% of pediatric and adult samples, respectively. No evidence of PIK3CA gene amplification was detected by quantitative real-time PCR in any of the samples. This study confirms that PIK3CA mutations occur in a significant number of human glioblastomas, further indicating that therapeutic targeting of this pathway in glioblastomas is of value. Moreover, this is the first study showing PIK3CA mutations in pediatric glioblastomas, thus providing a molecular target in this important pediatric malignancy.

Retargeted oncolytic measles strains entering via the EGFRvIII receptor maintain significant antitumor activity against gliomas with increased tumor specificity

Among the best-characterized genetic alterations in gliomas is the amplification of the epidermal growth factor receptor (EGFR) gene, present in approximately 40% of glioblastoma multiforme, and frequently associated with the EGFRvIII gene rearrangement. We have previously shown that attenuated vaccine strains of measles virus have potent antitumor activity against gliomas, and identified H protein mutations, which ablate recognition of the natural measles virus receptors CD46 and SLAM. Retargeted recombinant viruses were generated from the measles Edmonston-NSe vaccine strain displaying a single-chain antibody against EGFRvIII at the COOH terminus of H and containing the marker green fluorescent protein (GFP) gene in position 1. Two different H mutants were employed: H(SNS) (V451S, Y481N, and A527S)-CD46 blind, and H(AA) (Y481A and R533A)-CD46 and SLAM blind. MV-GFP virus was used as a positive control. Both EGFRvIII-retargeted viruses had significant antitumor activity against EGFRvIII-expressing glioblastoma multiforme but no cytopathic effect against normal cells. In an orthotopic model of EGFRvIII-expressing GBM39 xenografts, there was comparable therapeutic efficacy between retargeted strains and unmodified MV-GFP and statistically significant prolongation of survival in treated animals compared with the control group (P = 0.001). Formation of syncytia was observed in tumors treated with retargeted viruses, with a surrounding infiltrate consisting of macrophages and natural killer cells. In summary, EGFRvIII-retargeted oncolytic measles virus strains have comparable therapeutic efficacy with the unmodified MV-GFP strain against EGFRvIII-expressing glioma lines and xenografts with improved therapeutic index, a finding with potential translational implications in glioma virotherapy.

Use of an orthotopic xenograft model for assessing the effect of epidermal growth factor receptor amplification on glioblastoma radiation response

PURPOSE

The influence of epidermal growth factor receptor (EGFR) amplification on glioblastoma patient prognosis following definitive radiotherapy has been extensively investigated in clinical studies, and yet the relationship between EGFR status and radiation response remains unclear. The intent of the current study was to address this relationship using several EGFR-amplified glioblastoma xenografts in an orthotopic athymic mouse model.

EXPERIMENTAL DESIGN

We examined the effect of radiation on the survival of nude mice with intracranial xenografts derived from 13 distinct patient tumors, 7 of which have amplified EGFR. Mice with established intracranial tumors were randomized to sham treatment or 12-Gy radiation in six fractions delivered over 12 days.

RESULTS

For six of the xenografts, radiation of mice with intracranial tumor significantly extended survival, and four of these xenografts had EGFR amplification. For seven other xenografts, radiation treatment did not significantly extend survival, and three of these, including GBM12, had EGFR amplification. Similar to EGFR, the tumor genetic status of p53 or PTEN did not show preferential association with radiation-sensitive or radiation-resistant xenografts whereas hyperphosphorylation of Akt on Ser(473) was associated with increased radioresistance. To specifically investigate whether inhibition of EGFR kinase activity influences radiation response, we examined combined radiation and EGFR inhibitor treatment in mice with intracranial GBM12. The combination of oral erlotinib administered concurrently with radiation resulted only in additive survival benefit relative to either agent alone.

CONCLUSIONS

Our results indicate that EGFR amplification, as a biomarker, is not singularly predictive of glioblastoma response to radiation therapy, nor does the inhibition of EGFR enhance the intrinsic radiation responsiveness of glioblastoma tumors. However, efficacious EGFR inhibitor and radiation monotherapy regimens can be used in combination to achieve additive antitumor effect against a subset of glioblastoma.

Tumor suppressor p16 methylation in multiple myeloma: biological and clinical implications

The biological and clinical implications of p16 gene methylation in multiple myeloma (MM) are still unclear despite previous studies. In this comprehensive study, using methylation-specific PCR (MS-PCR), we show that p16 methylation is relatively common and occurs in monoclonal gammopathy of undetermined significance (MGUS; n=17), smoldering multiple myeloma (SMM; n=40), and MM (n=522) at a prevalence of 24%, 28%, and 34%, respectively. However, p16 methylation does not appear to affect gene expression level. In a large cohort of patients with long-term follow-up information (n=439), there was no difference in overall survival between patients with or without p16 methylation. We also found no association between p16 methylation and the main cytogenetic categories, although it was more common among patients with 17p13.1 deletions (p53 locus), a genetic progression event in MM. In addition, p16 methylation has no apparent effect on the cycle because there was also no difference in the plasma cell labeling index (a direct measurement of proliferation) between patients with and without p16 methylation. Our results question a major role for p16 methylation in the oncogenesis of the PC neoplasm, and we now believe p16 methylation may be a marker for overall epigenetic changes associated with disease progression, with no obvious direct biological or clinical consequences.

Disruption of parallel and converging signaling pathways contributes to the synergistic antitumor effects of simultaneous mTOR and EGFR inhibition in GBM cells

Elevated epidermal growth factor receptor (EGFR) and mammalian target of rapamycin (mTOR) signaling are known to contribute to the malignant properties of glioblastoma multiforme (GBM), which include uncontrolled cell proliferation and evasion of apoptosis. Small molecule inhibitors that target these protein kinases have been evaluated in multiple clinical trials for cancer patients, including those with GBM. Here we have examined the cellular and molecular effects of a combined kinase inhibition of mTOR (rapamycin) and EGFR (EKI-785) in U87 and U251 GBM cells. Simultaneous treatment with rapamycin and EKI-785 results in synergistic antiproliferative as well as proapoptotic effects. At a molecular level, rapamycin alone significantly decreases S6 phosphorylation, whereas EKI-785 alone promotes substantially reduced signal transducer and activator of transcription (STAT3) phosphorylation. Treatment with rapamycin alone also increases Akt phosphorylation on Ser-473, but this effect is blocked by a simultaneous administration of EKI-785. Individually, EKI-785 diminishes while rapamycin promotes the binding of the translation inhibitor eukaryotic initiation factor 4E binding protein (4EBP1) to the eukaryotic translation initiation factor 4E (eIF4E). In spite of these opposing effects, the highest level of 4EBP1-eIF4E binding occurs with the combination of the two inhibitors. These results indicate that the inhibition of EGFR and mTOR has distinct as well as common signaling consequences and provides a molecular rationale for the synergistic antitumor effects of EKI-785 and rapamycin administration.

Unique aspects of mda-7/IL-24 antitumor bystander activity: establishing a role for secretion of MDA-7/IL-24 protein by normal cells

Melanoma differentiation associated gene-7 (mda-7) was cloned using subtraction hybridization from terminally differentiated human melanoma cells. Based on structural and functional properties, mda-7 is now recognized as interleukin-24 (IL-24), a new member of the expanding IL-10 gene family. Unique properties of mda-7/IL-24 include its ability to selectively induce growth suppression, apoptosis and radiosensitization in diverse human cancer cells, without causing similar effects in normal cells. The utility of mda-7/IL-24, administered by means of a replication-incompetent adenovirus, as a gene therapy for cancer has recently received validation in patients, highlighting an important phenomenon initially observed in pancreatic tumor cells, namely a 'potent bystander apoptosis-inducing effect' in adjacent tumor cells not initially receiving this gene product. We presently investigated the contribution of mda-7/IL-24 secreted by normal cells in mediating this 'bystander effect', and document that normal cells induced to produce mda-7/IL-24 following infection with recombinant adenoviruses expressing this cytokine secrete mda-7/IL-24, which modifies the anchorage-independent growth, invasiveness, survival and sensitivity to radiation of cancer cells that contain functional IL-20/IL-22 receptors, but not in cancer cells that lack a complete set of receptors. Moreover, the combination of secreted mda-7/IL-24 and radiation engenders a 'bystander antitumor effect' not only in inherently mda-7/IL-24 or radiation-sensitive cancer cells, but also in tumor cells overexpressing the antiapoptotic proteins bcl-2 or bcl-x(L) and displaying resistance to either treatment alone. The present studies provide definitive evidence that secreted mda-7/IL-24 from normal cells can induce direct antitumor and radiation-enhancing effects that are dependent on the presence of canonical receptors for this cytokine on tumor cells. Moreover, we now describe a novel means of enhancing mda-7/IL-24's therapeutic potential by targeting normal cells to produce and release this cancer-specific apoptosis-inducing cytokine, a strategy that could be employed as an innovative way of using this unique gene product for treating metastatic disease.

mTOR controls FLIPS translation and TRAIL sensitivity in glioblastoma multiforme cells

The tumor-selective, proapoptotic, death receptor ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a mediator of antitumor drug activity and in itself is a promising agent for the treatment of human malignancies. Like many tumors, however, glioblastoma multiforme (GBM), the most fatal form of glioma, exhibits a range of TRAIL sensitivity, and only a small percentage of GBM tumors undergo TRAIL-induced apoptosis. We here show that TRAIL resistance in GBM is a consequence of overexpression of the short isoform of the caspase-8 inhibitor, c-FLICE inhibitory protein (FLIP(S)), and that FLIP(S) expression is in turn translationally enhanced by activation of the Akt-mammalian target of rapamycin (mTOR)-p70 S6 kinase 1 (S6K1) pathway. Conversely, pharmacologic or genetic inhibition of mTOR, or the mTOR target S6K1, suppresses polyribosomal accumulation of FLIP(S) mRNA, FLIP(S) protein expression, and TRAIL resistance. In archived material from 12 human GBM tumors, PTEN status was a predictor of activation of the Akt-mTOR-S6K1 pathway and of FLIP(S) levels, while in xenografted human GBM, activation status of the PTEN-Akt-mTOR pathway distinguished the tumors inherently sensitive to TRAIL from those which could be sensitized by the mTOR inhibitor rapamycin. These results define the mTOR pathway as a key limiter of tumor elimination by TRAIL-mediated mechanisms, provide a means by which the TRAIL-sensitive subset of GBM can be identified, and provide rationale for the combined use of TRAIL with mTOR inhibitors in the treatment of human cancers.

Patient tumor EGFR and PDGFRA gene amplifications retained in an invasive intracranial xenograft model of glioblastoma multiforme

We have previously described a panel of serially transplantable glioblastoma multiforme xenograft lines established by direct subcutaneous injection of patient tumor tissue in the flanks of nude mice. Here we report the characterization of four of these lines with respect to their histopathologic, genetic, and growth properties following heterotopic-to-orthotopic (flank-to-intracranial) transfer. Cells from short-term cultures, established from excised flank xenografts, were harvested and injected into the brains of nude mice (10(6) cells per injection). The intracranial tumors generated from these injections were all highly mitotic as well as highly invasive, but they lacked necrotic features in most instances and failed to show endothelial cell proliferation in all instances. For mice receiving injections from a common explant culture, tumor intracranial growth rate was consistent, as indicated by relatively narrow ranges in survival time. In contrast to the loss of epidermal growth factor receptor gene (EGFR) amplification in cell culture, high-level amplification and overexpression of EGFR were retained in intracranial tumors established from two EGFR-amplified flank tumors. A third intracranial tumor retained patient tumor amplification and high-level expression of platelet-derived growth factor receptor alpha gene. Because the heterotopic-to-orthotopic transfer and propagation of glioblastoma multiforme preserves the receptor tyrosine kinase (RTK) gene amplification of patient tumors, this approach should facilitate investigations for determining the extent to which RTK amplification status influences tumor response to RTK-directed therapies. The fact that such studies were carried out by using an invasive tumor model in an anatomically appropriate context should ensure a rigorous preclinical assessment of agent efficacy.

ECop (EGFR-coamplified and overexpressed protein), a novel protein, regulates NF-kappaB transcriptional activity and associated apoptotic response in an IkappaBalpha-dependent manner

In the present study, we describe the function of a novel protein, ECop (EGFR-Coamplified and overexpressed protein), in the regulation of NF-kappaB activity. Ectopic expression of ECop increases NF-kappaB transcriptional activity by promoting nuclear translocation and DNA binding of NF-kappaB, and ECop-induced NF-kappaB activation confers cellular resistance to apoptotic challenge. In ECop knockdown cells, NF-kappaB transcriptional activity is suppressed due to delayed IkappaBalpha degradation, which results in a delayed nuclear translocation as well as decreased DNA binding of NF-kappaB. Suppression of NF-kappaB activation by ECop knockdown increases cellular susceptibility to apoptosis. These results suggest that ECop is a key regulator of NF-kappaB signaling, and that high-level, amplification-mediated ECop expression, such as that occurring in tumors with amplified EGFR, could contribute to resistance to apoptosis.

Altered molecular pathways in gliomas: An overview of clinically relevant issues

Primary central nervous system (CNS) tumors constitute a small fraction of the overall incidence of human cancer, but they represent a major source of cancer-related morbidity and mortality. The most common CNS tumor subtype in adults, high-grade astrocytoma, confers a dismal prognosis with a median survival of only 1 to 2 years. Other common adult CNS tumors, ie, low-grade astrocytomas and oligodendrogliomas, carry a less ominous, yet still poor prognosis. Unfortunately, there has been little progress in extending the survival or quality of life for glioma patients, despite nearly four decades of extensive research. This research has, however, greatly increased our understanding of the underlying molecular biology of these tumors, examples of which include the determination of elevated epidermal growth factor receptor (EGFR) as well as platelet-derived growth factor receptor (PDGF) signaling, and the inactivation of p53 , p16 , and PTEN tumor-suppressor genes (TSGs) that negatively regulate specific enzymatic activities in normal glial cells. Such observations have greatly improved our understanding of the pathogenesis of these tumors and have potential diagnostic as well as therapeutic relevance. With respect to the latter of these two issues, the identification of aberrant enzymatic activities in gliomas has promoted the development of novel therapeutic agents that target specific signaling effectors, and whose inhibition should, in theory, prove to be cytostatic, if not cytotoxic, to tumor cells. Several clinical trials are currently underway for testing these therapeutic agents in patients with primary brain tumors, and it is hoped that the targeting of pro-tumorigenic enzymatic activities will lead to better patient outcomes. In this review, we will describe the most pertinent genetic and signaling pathway alterations that are clinically relevant to the management of glial tumors.

Immunohistochemical detection of EGFRvIII in high malignancy grade astrocytomas and evaluation of prognostic significance

The purpose of this study was to establish an accurate and accessible immunohistochemical (IHC) method for detecting vIII Egf receptor and to assess the prognostic significance of the method as applied to the detection of vIII in malignant astrocytomas. The accuracy of the method was determined by comparing vIII immunoreactivity in formalin-fixed and paraffin-embedded tumor sections versus RT-PCR results from the analysis of RNA extracted from corresponding frozen specimens. RT-PCR revealed vIII transcript in 18 of 44 cases in this series, and IHC analysis of matched formalin-fixed and paraffin-embedded sections showed EGFRvIII reactivity in each of these 18 tumors, as well as 1 additional tumor that was negative for vIII transcript. EGFR amplification was evident in all tumors expressing vIII; none of the 15 tumors lacking amplified EGFR were positive for vIII transcript or vIII protein. IHC analysis for vill expression was next applied to a large series of anaplastic astrocytomas (AAs) and glioblastoma multiforme (GBMs) from clinical trial patients with complete follow-up and that had been previously examined by FISH for amplified EGFR. Among the GBMs, vIII detection by IHC was determined in 19 of 46 cases (41.3%) with EGFR amplification, and in only 3 of 59 tumors lacking amplified EGFR (5.1%). Among the AAs, vIII expression was observed in 3 of 14 cases with amplified EGFR (21.4%) and in 6 of 49 cases without EGFR amplification (12.2%). GBM and AA patient survival analysis as a function of vIII expression showed contrasting results, with vIII positivity having no association with survival among GBM patients (p = 0.84), but being highly associated with reduced survival among AA patients (p = 0.0016). This latter finding, though quite possibly a result of vIII's association with increasing AA patient age, suggests that vIII IHC will be useful for identifying and/or confirming the identity of malignant astrocytomas whose clinical behavior is consistent with that of GBM.

MDA-7 regulates cell growth and radiosensitivity in vitro of primary (non-established) human glioma cells

We examined the impact of purified bacterially synthesized GST-MDA-7 (IL-24) and ionizing radiation on the proliferation and survival of nonestablished human glioblastoma multiforme (GBM) cells. Glioma cell types expressing mutated PTEN and p53 molecules, activated ERBB1VIII, overexpressing wild type ERBB1 or without receptor overexpression were selected. In MTT assays, GST-MDA-7 caused a dose-dependent reduction in the proliferation of nonestablished glioma cells; however only at higher concentrations did GST-MDA-7 reduce cell viability. The anti-proliferative and cytotoxic effects of GST-MDA-7 were enhanced by radiation in a greater than additive fashion that correlated with JNK1/2/3 activation. The reduction in cell growth and enhancement in cell killing by the combination of GST-MDA-7 and radiation were blocked by an ROS scavenger, N-acetyl cysteine (NAC), a JNK1/2/3 inhibitor SP600125, a pan-caspase inhibitor (zVAD) and by an inhibitor of caspase 9 (LEHD), but not by an inhibitor of caspase 8 (IETD). Low concentrations of either GST-MDA-7 or radiation reduced clonogenic survival, however colony formation ability was significantly further decreased when the two treatments were combined, which was also blocked by inhibition of caspase 9 function. In general agreement with activation of the intrinsic caspase pathway, cell death correlated with reduced BCL-XL expression and with increased levels of the pro-apoptotic proteins BAD and BAX. Inhibition of caspase 9 after combination treatment blunted neither JNK1/2/3 activation nor the enhanced expression of BAD and BAX, but did block caspase 3 cleavage, reduced expression of BCL-XL and inhibition of ERK1/2 activity. In contrast, incubation with NAC blocked JNK1/2/3 activation and cell killing, but not the increases in BAD and BAX expression. These findings argue that after combination treatment JNK1/2/3 activation is a primary pro-apoptotic event and loss of BCL-XL expression and ERK1/2 activity are secondary caspase-dependent processes. This data also argues that GST- MDA-7 induces two parallel pro-apoptotic pathways via ROS-dependent and -independent mechanisms. Infection of primary human astrocytes with a recombinant adenovirus to express MDA-7, Ad.mda-7, but not infection with either Ad.cmv or Ad.mda-7SP- lacking MDA-7 secretion, resulted in the suppression of GBM cell colony formation in soft agar overlay assays, an effect that was enhanced in a greater than additive fashion by radiation. Collectively, our findings demonstrate that MDA-7 reduces proliferation and enhances the radiosensitivity of nonestablished human GBM cells in vitro, and when grown in 3 dimensions, and that sensitization occurs independently of basal EGFR/ERK1/2/AKT activity or the functions of PTEN and p53.

Correlation of the response of recurrent malignant gliomas treated with interferon alpha with tumor interferon alpha gene content

Malignant gliomas are treated by combining surgery and radiation with chemotherapy. Cure is rare and utilizing information arising from our improved understanding of brain tumor biology may be of value. Interferon alpha (IFNalpha) treatment as restorative immunotherapy has been utilized in malignant gliomas in the past. Interferon alpha/beta gene presence is variable in these tumors. The relationship between response to IFNalpha therapy and gene status has not been assessed prospectively. Patients with recurrent malignant gliomas were treated with 8-week courses of IFNalpha. Clinical and laboratory toxicity was assessed and response determined by MRI scans. Tumor interferon alpha/beta gene content was measured. Toxicities included fourteen grade 3/4 neuro-motor events, and eleven grade 3 neuro-cortical events. Rapid tolerance developed and with dose reductions few doses were missed. Three individuals with glioblastoma multiforme demonstrated a partial response. Median time to progression was 24.6 (+/-17.6) weeks for all glioblastomas. The correlation between longer time to progression and lower tumor IFNalpha gene content as measured here was significant. A minority of patients with recurrent malignant gliomas will respond to IFNalpha therapy at starting doses of 20 Mu/m(2) and above. These doses are associated with significant toxicity. A relationship between the tumor IFNalpha gene status and tumor response to therapy may be present. With current improved understanding of IFNalpha toxicities and ability to measure tumor IFNalpha function, this therapy warrants further evaluation for identifying patients whose tumors are likely to be responsive to IFNalpha therapy.

Alosetron repeat dose pharmacokinetics, effects on enzyme activities, and influence of demographic factors

AIM

To assess the pharmacokinetics of alosetron, its effect on in vivo enzyme activities, and influence of demographic factors during repeated dosing.

METHODS

Thirty healthy men and women received 1 mg oral alosetron twice-daily for 29.5 days and a single oral dose of a metabolic probe cocktail before and on the last day of alosetron dosing. Serum alosetron concentrations were measured on days 1, 8, 15, 22 and 29. Probe-substrate and metabolite concentrations were measured after each cocktail dose.

RESULTS

Alosetron accumulation in serum was negligible. Exposure to alosetron did not alter probe-metabolite/substrate ratios associated with CYP2C19, 2E1, 2C9, or 3A4 activity, but modestly decreased those associated with CYP1A2 and N-acetyltransferase activity. Systemic exposure to alosetron was higher in women, positively correlated with age and body mass index, and negatively correlated with CYP1A2 activity. Incidence of constipation was higher in women, but not associated with alosetron concentration.

CONCLUSIONS

Single dose data can reliably predict the pharmacokinetics of alosetron after repeated doses. Alosetron exhibits limited potential for inhibition of cytochrome P450-mediated metabolism. Interindividual differences in alosetron pharmacokinetics associated with demographic factors may be related to strong dependence on metabolism by CYP1A2.

Contrasting in vivo and in vitro fates of glioblastoma cell subpopulations with amplified EGFR

Despite the high incidence of EGFR amplification in patient glioblastoma multiforme (GBM) tissues, only a single GBM cell line, of the many described in the literature, is known to contain and maintain amplified EGFR. Because EGFR mutations in GBM manifest primarily, if not exclusively, in amplified form, it follows that the availability of cell lines with mutation of endogenous EGFR would also be in short supply. In fact, there are no GBM cell lines harboring the common EGFR mutants described in patient GBMs. These observations suggest that in vivo environments select for EGFR amplification, whereas in vitro environments, specifically cell cultures, select against this gene alteration. To contrast directly the fates of EGFR amplification in vivo and in vitro, as well as to examine potential relationships between EGFR amplification and mutation, we have established and maintained GBM explants as xenografts by serial passaging in nude mice. Analysis of EGFR copy number and EGFR mutation status in 11 patient tumors and their corresponding xenografts, as well as the monitoring of EGFR copy number during the establishment of a GBM cell line from a xenograft with amplified EGFR, indicated that selection for EGFR amplification is an in vivo phenomenon. Furthermore, our data indicated that EGFR mutation occurs only in tumors with EGFR amplification and showed that the selection of amplified mutant EGFR over amplified wild-type EGFR as a xenograft occurred rapidly and completely during tumor propagation.

Molecular analysis of astrocytomas presenting after age 10 in individuals with NF1

BACKGROUND

Fifteen to 20% of children with neurofibromatosis type 1 (NF1) develop low-grade astrocytomas. Although brain tumors are less common in teenagers and adults with NF1, recent studies have suggested that patients with NF1 are at a significantly increased risk of developing astrocytomas.

OBJECTIVE

S: To investigate the genetic basis for astrocytoma development in patients with NF1 beyond the first decade of life.

METHODS

The authors performed molecular genetic analyses of 10 NF1-associated astrocytomas representing all World Health Organization (WHO) malignancy grades using fluorescence in situ hybridization, loss of heterozygosity, immunohistochemistry, and direct sequencing.

RESULTS

Later-onset NF1-associated astrocytomas, unlike histologically identical sporadic astrocytomas, exhibit NF1 inactivation, supporting a direct association with NF1 rather than a chance occurrence. Furthermore, some of these astrocytomas have homozygous NF1 deletion. In addition, genetic changes observed in high-grade sporadic astrocytomas, including TP53 mutation and CDKN2A/p16 deletion, are also seen in NF1-associated high-grade astrocytomas.

CONCLUSIONS

Neurofibromatosis type 1-associated astrocytomas occurring in patients older than 10 years exhibit genetic changes observed in sporadic high-grade astrocytomas. Patients with neurofibromatosis type 1 and germline NF1 deletions may be at risk for developing late-onset astrocytomas.

Genetic and signaling pathway alterations in glioblastoma: relevance to novel targeted therapies

Glioblastomas multiforme (GBM) is the most common malignant primary brain tumor in adults. GBM patients have a dismal prognosis, with a median survival of less than 1 year. During the past decade, significant advances have been made in our understanding of the molecular pathogenesis of these tumors. Specific genetic defects have been identified that appear to be important for the development, as well as maintenance of the malignant characteristics that are associated with GBM. Some of these genetic aberrations appear to have prognostic significance. However, even more exciting in this era of molecularly targeted therapy are the clues these gene alterations provide for identifying signaling mechanisms responsible for carcinogenesis, and for identifying potential therapeutic targets. Cancer drug therapy is currently undergoing a major transition with an attempt to move from the use of cytotoxic drugs towards the use of tumor mechanism-based drugs. Advances such as the decoding of the human genome, combinatorial chemistry, and gene expression profiling have led to an increase in the rate at which new drugs are being developed. In this review, we will describe the most common genetic and signaling pathway alterations that have relevance to new drug development for the treatment of GBM.

Lanthionine synthetase components C-like 2 increases cellular sensitivity to adriamycin by decreasing the expression of P-glycoprotein through a transcription-mediated mechanism

Although the coincidental amplification and accompanying overexpression of bystander genes that neighbor oncogene targets occur frequently during the development of human tumors, little has been done to investigate the functional or biological consequences of amplified bystander gene overexpression. LANCL2 (LANC-like 2) is a bystander gene that is coamplified and overexpressed with epidermal growth factor receptor in approximately 20% of all glioblastomas. This gene has also been designated as Testis Adriamycin Sensitivity Protein because it is most highly expressed in testis and its expression has been noted to increase cellular sensitivity to Adriamycin. Because of the latter association, we have examined potential relationships between LANCL2 and the expression of multidrug-resistance (MDR)1, as well as its cognate protein, P-glycoprotein (P-gp), because elevated expression of P-gp is known to increase cell resistance to many cytotoxic drugs, including Adriamycin. Using the Dx5 derivative of MES-SA cells in which P-gp is overexpressed, we show that the level of endogenous P-gp decreases with increased expression of exogenous LanCl-2 and that cells with reduced P-gp show increased sensitivity to Adriamycin. Results from reverse transcription-PCR and MDR1 promoter activity analyses suggest that LanCl-2 transcriptionally suppresses MDR1, and this interpretation of LanCl-2 function is consistent with results from immunofluorescence analysis, which shows that LanCl-2 resides in the nucleus, as well as at the plasma membrane. With respect to this study, our data indicate that LanCl-2 increases cellular sensitivity to Adriamycin by decreasing the expression of P-gp, but more generally, these results indicate that the identification of bystander gene amplification in human tumors can have clinical implications.

Combination of epidermal growth factor receptor targeted therapy with radiation therapy for malignant gliomas

Glioblastoma multiforme (GBM) are extremely aggressive brain tumors characterized by resistance to standard treatment modalities including surgery, radiation therapy and chemotherapy. While radiation therapy is the standard treatment after surgical resection, these tumors invariably recur and are associated with a uniformly dismal prognosis. Cytotoxic chemotherapy has failed to improve on the modest gains conferred by radiation therapy. Our understanding of the molecular events driving gliomagenesis has led to the recognition of frequent alterations in the epidermal growth factor receptor (EGFR) pathway, leading to increased aggressiveness and a poorer prognosis. Based on the importance of EGFR in the development of malignancy in multiple tumor types, several classes of novel therapeutic agents have been developed that specifically target EGFR. This review outlines the relevance of normal and aberrant EGFR signaling in the biology of gliomas, the strategies for inhibiting EGFR activity and the rationale for combining EGFR inhibitors with radiation therapy in the treatment of GBM.

Neuropathology of genetically engineered mice: consensus report and recommendations from an international forum

The Mouse Models of Cancer Consortium of the NCI sponsored a meeting of neuropathologists and veterinary pathologists in New York City in November of 2000. A rapidly growing number of genetically engineered mice (GEM) predisposed to tumors of the nervous system have led to a concomitant need for neuropathological evaluation and validation of these models. A panel of 13 pathologists reviewed material representing most of the available published and unpublished GEM models of medulloblastoma, primitive neuroectodermal tumor, astrocytoma, oligodendroglioma, mixed glioma, and tumors of the peripheral nerve. The GEM tumors were found to have many similarities and some distinct differences with respect to human disease. After review of the biology and pathology for all models presented, participants were split into groups reflective of clinical expertise in human pathology, tumor biology, neuroimaging, or treatment/intervention. Recommendations were made detailing an extensive and complete neuropathological characterization of animals. Importance was placed on including information on strains, tumor clonality, and examination for genetic mutation or altered gene expression characteristics of the corresponding human malignancy. Specific proposals were made to incorporate GEM models in emerging neuroradiological modalities. Recommendations were also made for preclinical validation of these models in cancer therapeutics, and for incorporation of surrogate markers of tumor burden to facilitate preclinical evaluation of new therapies.

Mucosa-associated lymphoid tissue lymphomas with t(11;18)(q21;q21) and mucosa-associated lymphoid tissue lymphomas with aneuploidy develop along different pathogenetic pathways

t(11;18)(q21;q21) and aneuploidy are recurrent chromosomal aberrations in mucosa-associated lymphoid tissue (MALT) lymphomas. To investigate their relationship and clinical significance, we developed a two-color fluorescence in situ hybridization (FISH) technique to detect t(11;18) and aneuploidy in nuclei isolated from paraffin-embedded tissue. Thirty-seven MALT lymphomas (all previously evaluated for t(11;18) by reverse transcriptase-polymerase chain reaction), 1 large cell lymphoma (LCL) arising subsequent to MALT lymphoma, and 16 controls were tested by FISH using the t(11;18) probe set and multiple centromeric probes. t(11;18)(q21;q21) was present by FISH in 11 of 12 polymerase chain reaction-positive MALT lymphomas (92%). The LCL and its clonally identical antecedent MALT lymphoma both showed t(11;18). The LCL had trisomy 12, and a small subset of MALT lymphoma cells had trisomy 3 and/or 12. Only one other MALT lymphoma with t(11;18) showed aneuploidy (trisomy 3) in a small clone, whereas 15 of 25 t(11;18)-negative MALT lymphomas (60%) showed trisomy of chromosomes 18 (n = 12), 3 (n = 8), 7 (n = 2), and/or 11 (n = 1). t(11;18) and aneuploidy are primarily mutually exclusive events, suggesting different pathogenetic pathways in the development of MALT lymphomas. Both t(11;18) and aneuploidy were seen disproportionately in lung, and both were associated with recurrent disease.

A chromosomal region 7p11.2 transcript map: its development and application to the study of EGFR amplicons in glioblastoma

Cumulative information available about the organization of amplified chromosomal regions in human tumors suggests that the amplification repeat units, or amplicons, can be of a simple or complex nature. For the former, amplified regions generally retain their native chromosomal configuration and involve a single amplification target sequence. For complex amplicons, amplified DNAs usually undergo substantial reorganization relative to the normal chromosomal regions from which they evolve, and the regions subject to amplification may contain multiple target sequences. Previous efforts to characterize the 7p11.2 epidermal growth factor receptor ) amplicon in glioblastoma have relied primarily on the use of markers positioned by linkage analysis and/or radiation hybrid mapping, both of which are known to have the potential for being inaccurate when attempting to order loci over relatively short (<1 Mb) chromosomal regions. Due to the limited resolution of genetic maps that have been established through the use of these approaches, we have constructed a 2-Mb bacterial and P1-derived artificial chromosome (BAC-PAC) contig for the EGFR region and have applied markers positioned on its associated physical map to the analysis of 7p11.2 amplifications in a series of glioblastomas. Our data indicate that EGFR is the sole amplification target within the mapped region, although there are several additional 7p11.2 genes that can be coamplified and overexpressed with EGFR. Furthermore, these results are consistent with EGFR amplicons retaining the same organization as the native chromosome 7p11.2 region from which they are derived.