P14.11 Severe treatment-induced myelosuppression is more frequent in female malignant glioma patients and associated with reduced overall survival

BACKGROUND

An association of treatment-related myelotoxicity with female gender has been previously suggested. However, a systematic analysis of the prognostic relevance of radiochemotherapy-related cytopenia involving the different blood cell lineages is lacking.

MATERIAL AND METHODS

We retrospectively analyzed cytopenia during temozolomide-based concomitant radiochemotherapy (RCT) in 493 glioma patients. Histological grading, molecular pathology, surgical procedures and median overall survival (OS) were recorded. The extent of cytopenia was correlated with gender and outcome.

RESULTS

Treatment-induced severe cytopenia (leuko-, lympho-, neutro- and thrombocytopenia) occurred much more often in female than in male glioma patients (40.8 vs. 13.9%, p-value <0.0001). In female patients with IDH-wildtype high-grade astrocytomas there was a negative correlation of severe leuko-, lympho- and thrombocytopenia during temozolomide RCT with OS (36 vs. 54, 37 vs. 54 and 36 vs. 57 weeks, respectively; all p-values <0.05). In male patients there was also a trend for this unfavorable effect. Additionally, severe cytopenia correlated with reduced temozolomide dose exposure during RCT (all p-values <0.05 in total cohort) and reduced dose exposure was independently associated with worse OS (p-values <0.05 in the total and female cohort).

CONCLUSION

Our data confirm that women are at higher risk for treatment-induced cytopenia during RCT which is associated with a significant decrease in OS. From our data, it appears plausible that reduced temozolomide dose exposure during RCT is at least in part responsible for this finding. Immunosuppression of patients with severe cytopenia may be an independent contributor to adverse outcome.

OS12.6.A Combination therapy of CAR-NK-cells and anti-PD-1 results in high efficacy against advanced-stage glioblastoma in a syngeneic mouse model and induces protective anti-tumor immunity in vivo

INTRODUCTION

Checkpoint inhibitors as well as adoptive cell therapy hold promise for cancer therapy and encouraging treatment responses have already been demonstrated in different cancer indications. Glioblastoma (GB) is the most common and aggressive primary brain tumor. Standard therapy has very limited efficacy in the majority of patients. Analysis of the GB microenvironment (TME) has shown prominent immunosuppressive features, including expression of PD-L1 on tumor cells and increased frequency of FOXP3-positive regulatory T cells. While the surrounding brain is HER2-negative, GB are frequently HER2-positive, suggesting HER2 as a promising target for adoptive immunotherapy. Previous results from mouse glioma models showed efficacy of CAR-NK cells (NK-92/5.28.z) targeted against HER2 as monotherapy with early stage but not with advanced-stage tumors.

MATERIALS AND METHODS

The murine glioma cell line GL261 was transfected with human HER2. Tumor cells were implanted either subcutaneously or orthotopically into C57BL/6 mice and treated either with HER2-specific NK-92/5.28.z cells alone or in combination with an anti-PD-1 antibody. Effects on tumor growth and survival were determined. Lymphocyte infiltration and immunosuppressive TME were characterized via highplex multi-color flow cytometry (FACS Symphony) and IHC (Phenoptics). Furthermore, gene expression profiles of tumor-infiltrating cells were determined via bulk RNAseq (NanoString).

RESULTS

Combined treatment with NK-92/5.28.z cells and anti-PD-1 checkpoint blockade resulted in synergistic effects, with tumor regression and long-term survival observed even in advanced-stage tumor bearing mice. Analysis of the TME showed changes in lymphocyte infiltration and increased expression of exhaustion markers in tumor and immune upon combined treatment with NK-92/5.28.z cells and anti-PD-1 antibody resulting in an altered TME. Both, PD-1 and Lag-3 expression are highly upregulated on tumor infiltrating T cells. Total infiltrating lymphocytes show a rather cytotoxic phenotype up combination treatment with NK-92/5.28.z cells and anti-PD-1 antibody

CONCLUSION

Our data demonstrate that efficacy of NK-92/5.28.z cells can be enhanced by combination with checkpoint blockade, resulting in successful treatment of advanced tumors refractory to NK-92/5.28.z monotherapy. Furthermore, the combination therapy induced a cytotoxic rather than immunosuppressive TME, leading to a primed immune system. To translate the concept of CAR-NK-cell therapy plus checkpoint inhibition to a clinical setting, we are adding a combination therapy cohort to our ongoing phase I clinical study (CAR2BRAIN; NCT03383978).

OS06.2A Local immunotherapy of glioblastoma via AAV-mediated gene transfer of checkpoint inhibitors in combination with CAR-NK cells

BACKGROUND

Glioblastoma (GB) is the most common primary brain tumor which is characterized by low immunogenicity of tumor cells and prevalent immunosuppression in the tumor microenvironment (TME). Since expression of PD-L1 on GB cells has been described, immunotherapy with checkpoint inhibitors (CIs) may be a promising approach for GB treatment. However, systemic administration of CIs bears the risk of autoimmune-like side effects, while the intratumoral drug concentration reached may not be sufficient.

METHODS

We studied delivery of CIs through targeted Adeno-associated viral vectors (AAVs) encoding an anti PD-1 immunoadhesin (aPD-1) as a novel approach towards local immunotherapy in the syngeneic GL261-HER2 glioma model. Tumor cell-specific delivery was achieved by targeting HER2 via a specific designed ankyrin repeat protein (DARPin). We investigated the effects of this strategy alone and in combination with local injection of HER2-specific CAR-NK cells (NK-92/5.28.z), which have already shown efficacy in preclinical GB models and are currently under investigation in the CAR2BRAIN phase I clinical trial. Furthermore, aPD-1 functionality and cellular response to viral transduction as well as compatibility of both therapy approaches has been evaluated in various in vitro models.

RESULTS

HER2-AAV transduction efficacy of GB cells correlated with HER2 expression level, while target cells did not show anti-viral responses upon transduction. After transduction with aPD-1 HER2-AAVs, aPD-1 immunoadhesin was secreted in a time-dependent manner, bound its target on PD-1-expressing cells and was able to re-activate T-cells due to PD-1 blockade. AAV-transduction did not interfere with CAR-NK cell mediated tumor cell lysis. Biodistribution studies in mice revealed the presence of aPD-1 up to 10 days after a single HER2-AAV injection. In subcutaneous GL261-HER2 tumors, local treatment with HER2-AAVaPD-1 or HER2-AAVIgG-Fc+ NK-92/5.28.z therapy had no significant effect, whereas combination therapy profoundly delayed tumor growth.

CONCLUSIONS

Local therapy with aPD-1 encoding HER2-AAVs in combination with NK-92/5.28.z cells is a promising novel strategy for GB immunotherapy with the potential to enhance efficacy and reduce side effects.

OS05.9.A Short-term fasting in glioma patients - Analysis of diet diaries and metabolic parameters of the ERGO2 trial

BACKGROUND

The prospective, randomized ERGO2 trial investigated the effect of fasting / calorie restricted ketogenic diet (KD-IF) on re-irradiation for recurrent brain tumors (Clinicaltrials.gov number: NCT01754350). The study did not meet its primary endpoint of improved progression-free survival in comparison to a standard diet (SD). We here report the results of the quality of life questionnaire, neurocognition testing, detailed analysis of the diet diaries and the alterations of metabolic parameters.

MATERIAL AND METHODS

50 Patients were randomized 1:1 to re-irradiation combined with either SD or KD-IF. The KD-IF schedule included 3 days of ketogenic diet (KD: 21–23 kcal/kg/d, carbohydrate intake limited to 50 g/d), followed by 3 days of fasting and again 3 days of KD. Follow-up included examination of cognition, quality of life and serum samples.

RESULTS

The 20 patients who completed KD-IF met the prespecified goals for calorie and carbohydrate restriction. In these, a decrease in leptin and insulin and an increase in uric acid was observed. The SD group had a lower calorie intake of 21 kcal/kg/d than the expected 30 kcal/kg/d. Neither quality of life nor cognition were affected by the diet. Low glucose emerged as a significant prognostic parameter in a best responder analysis.

CONCLUSION

The strict caloric goals of the ERGO2 trial could be achieved by patients with recurrent brain tumor. The unexpected lower calorie intake of the SD group might have hampered the interpretation of the trial. However, the short diet schedule already led to significant metabolic alterations, suggesting that short-term dietary interventions might be therapeutically useful, possibly combined with other modalities.

Lower Lactate Levels and Lower Intracellular pH in Patients with IDH-Mutant versus Wild-Type Gliomas

BACKGROUND AND PURPOSE

Preclinical evidence points toward a metabolic reprogramming in isocitrate dehydrogenase (IDH) mutated tumor cells with down-regulation of the expression of genes that encode for glycolytic metabolism. We noninvasively investigated lactate and Cr concentrations, as well as intracellular pH using ¹H/phosphorus 31 (³¹P) MR spectroscopy in a cohort of patients with gliomas.

MATERIALS AND METHODS

Thirty prospectively enrolled, mostly untreated patients with gliomas met the spectral quality criteria (World Health Organization II [n = 7], III [n = 16], IV [n = 7]; IDH-mutant [n = 23]; IDH wild-type [n = 7]; 1p/19q codeletion [n = 9]). MR imaging protocol included 3D ³¹P chemical shift imaging and ¹H single-voxel spectroscopy (point-resolved spectroscopy sequence at TE = 30 ms and TE = 97 ms with optimized echo spacing for detection of 2-hydroxyglutarate) from the tumor area. Values for absolute metabolite concentrations were calculated (phantom replacement method). Intracellular pH was determined from ³¹P chemical shift imaging.

RESULTS

At TE = 97 ms, lactate peaks can be fitted with little impact of lipid/macromolecule contamination. We found a significant difference in lactate concentrations, lactate/Cr ratios, and intracellular pH when comparing tumor voxels of patients with IDH-mutant with those of patients with IDH wild-type gliomas, with reduced lactate levels and near-normal intracellular pH in patients with IDH-mutant gliomas. We additionally found evidence for codependent effects of 1p/19q codeletion and IDH mutations with regard to lactate concentrations for World Health Organization tumor grades II and III, with lower lactate levels in patients exhibiting the codeletion. There was no statistical significance when comparing lactate concentrations between IDH-mutant World Health Organization II and III gliomas.

CONCLUSIONS

We found indirect evidence for metabolic reprogramming in IDH-mutant tumors with significantly lower lactate concentrations compared with IDH wild-type tumors and a near-normal intracellular pH.

P14.96 Gliomatosis cerebri imaging pattern: a treatment-independent marker for worse overall survival in WHO grade II and III gliomas

BACKGROUND

The term gliomatosis cerebri (GC) refers to glial brain tumors with widespread tumor expansion affecting three or more cerebral lobes. Formerly considered a distinct tumor entity, recent studies found no difference in the mutational profile of glial tumors with GC growth pattern compared to non-GC gliomas. Thus, in the new WHO classification of brain tumors, GC is no longer included as a separate diagnosis. While the presence of gliomas with GC growth pattern is associated with worse overall survival (OS), the underlying factors remain to be identified. Here, we asked whether differing therapeutic strategies in first line treatment could account for the worse outcome of patients with GC growth pattern and grade II and III histology.

MATERIAL AND METHODS

From the patient data bank of the University Cancer Center (UCT) Frankfurt, 47 patients with histological diagnosis of WHO grade II or III glioma, and with record of GC imaging pattern were identified. GC tumor expansion was confirmed by review of MRI scans prior to treatment initiation. Patients with WHO grade II or III glioma without GC growth pattern served as control cohort (n=379). IDH mutational status was available for 75% of GC tumors (IDH R132H mutated 32%; non-mutated 43%) and 69% of non-GC tumors (IDH R132H mutated 57%; non-mutated 12%).

RESULTS

Within the GC patient cohort, patients with tumors without contrast enhancement, lower WHO grade and mutated IDH status showed better OS. Compared to the control cohort, patients with GC had significantly shorter OS. This was independent of histological diagnosis or IDH mutation status. Patients with GC more frequently underwent radiochemotherapy (17% vs. 9% in the non-GC cohort), and drastically more often received chemotherapy alone (51% vs. 5%). We then analyzed OS in GC and non-GC patients that had received the same first line treatments. For radiochemotherapy in GC versus non-GC patients, OS was 1.1 years vs. 12.7 years (p =0.0075, log-rank test). For upfront chemotherapy alone, OS was significantly shorter in the GC cohort than in the non-GC cohort (3,6 years vs. undefined, p =0.0016, log-rank test).

CONCLUSION

Differences in first-line treatment cannot account for the worse prognosis of patients with GC imaging pattern. Further studies are needed to pinpoint biological or clinical factors that might influence responsiveness to therapy and prognosis of GC tumors.

P12.04 Synergistic effects of combination therapy of CAR-NK cells and anti-PD-1 antibody result in high efficacy against advanced stage orthotopic glioblastoma grafts in a syngeneic mouse model and induce protective anti-tumor immunity in vivo

BACKGROUND

Checkpoint inhibitors as well as adoptive cell therapy hold great promise for cancer treatment and encouraging treatment responses have already been demonstrated in different cancer indications. Glioblastoma (GB) is the most common and aggressive primary brain tumor. Standard therapy has very limited efficacy in the majority of patients. Analysis of the GB tumor microenvironment (TME) has shown prominent immunosuppressive features including expression of PD-L1 on tumor cells and increased frequency of FOX-P3 positive regulatory T cells. While the surrounding brain is HER2-negative, GB tumors are frequently HER2-positive, suggesting HER2 as a promising target for adoptive immunotherapy.

MATERIALS AND METHODS

The murine glioma cell line GL261 was transfected with HER2. Tumor cells were orthotopically implanted into C57BL/6 mice and treated either with HER2-specific NK-92/5.28.z cells alone or in combination with an anti-PD-1 antibody. Effects on tumor growth and survival were determined, lymphocyte infiltration and immunosuppressive TME were characterized.

RESULTS

Combined treatment with NK-92/5.28.z cells and anti-PD-1 antibody resulted in synergistic tumor regression and long-term survival of advanced-stage tumor bearing mice. Analysis of TME showed enhanced cytotoxic lymphocyte infiltration and altered profiles of exhaustion markers in tumor and immune cells.

CONCLUSION

These data demonstrate that efficacy of NK-92/5.28.z cells can be enhanced by co-therapy with checkpoint inhibitors, resulting in successful treatment of advanced tumors refractory to mono-therapy. Furthermore, this combination therapy induces a cytotoxic rather than immunosuppressive TME, leading to a primed immune system. To address this question in a clinical setting, we are planning a phase I clinical study (CAR2BRAIN-CHECK).

OS6.5 ERGO2: A prospective randomized trial of a 9-day schedule of calorically restricted ketogenic diet and fasting or standard diet in addition to re-irradiation for malignant glioma

BACKGROUND

Ketogenic diet (KD) and fasting have anticancer effects in tumor models, possibly due to a differential stress response with sensitization of tumor cells and protection of normal tissue. We therefore set up ERGO2 (NCT01754350), the first randomized clinical trial of calorically-restricted KD and intermittent fasting (KD-IF) in addition to re-irradiation for recurrent malignant gliomas.

MATERIAL AND METHODS

Patients were randomized 1:1 to re-irradiation combined with either calorically unrestricted diet (standard diet, SD) or KD-IF. The KD-IF schedule included 3 days of KD (21–23 kcal/kg/d), followed by 3 days of fasting and again 3 days of KD. The primary endpoint was progression-free survival (PFS) rate at 6 months (PFS6). Secondary endpoints were PFS, local control, overall survival (OS), frequency of epileptic seizures, rate of ketosis and quality of life.

RESULTS

50 patients were included. Four patients quit the trial before treatment and three patients stopped KD-IF prematurely. Of the 20 patients who completed KD-IF, 17 patients developed ketosis at day 6, and glucose levels declined significantly. KD-IF was well-tolerated with a modest weight loss of -2.1±1.8 kg. No severe adverse events attributable to the diet occurred. There was no difference in PFS6 between the two groups (KD-IF: 20%, SD: 16%). Similarly, no difference in PFS, local PFS6 and OS were observable. Explorative analysis revealed that among patients of the KD-IF group, those who achieved ketosis of at least 1.5 mmol/l had significantly longer PFS compared to those with lesser or no ketosis.

CONCLUSION

KD-IF is feasible and effective in inducing ketosis in heavily pretreated patients with recurrent glioblastoma. However, the short schedule reported here failed to increase the efficacy of re-irradiation.

CD74 regulates complexity of tumor cell HLA class II peptidome in brain metastasis and is a positive prognostic marker for patient survival

Despite multidisciplinary local and systemic therapeutic approaches, the prognosis for most patients with brain metastases is still dismal. The role of adaptive and innate anti-tumor response including the Human Leukocyte Antigen (HLA) machinery of antigen presentation is still unclear. We present data on the HLA class II-chaperone molecule CD74 in brain metastases and its impact on the HLA peptidome complexity.We analyzed CD74 and HLA class II expression on tumor cells in a subset of 236 human brain metastases, primary tumors and peripheral metastases of different entities in association with clinical data including overall survival. Additionally, we assessed whole DNA methylome profiles including CD74 promoter methylation and differential methylation in 21 brain metastases. We analyzed the effects of a siRNA mediated CD74 knockdown on HLA-expression and HLA peptidome composition in a brain metastatic melanoma cell line.We observed that CD74 expression on tumor cells is a strong positive prognostic marker in brain metastasis patients and positively associated with tumor-infiltrating T-lymphocytes (TILs). Whole DNA methylome analysis suggested that CD74 tumor cell expression might be regulated epigenetically via CD74 promoter methylation. CD74high and TILhigh tumors displayed a differential DNA methylation pattern with highest enrichment scores for antigen processing and presentation. Furthermore, CD74 knockdown in vitro lead to a reduction of HLA class II peptidome complexity, while HLA class I peptidome remained unaffected.In summary, our results demonstrate that a functional HLA class II processing machinery in brain metastatic tumor cells, reflected by a high expression of CD74 and a complex tumor cell HLA peptidome, seems to be crucial for better patient prognosis.

[Personalized neurooncology]

The treatment of patients with intrinsic brain tumors is radically changing. This change is currently not (yet) signified by the use of targeted therapy in clinical practice but more by the definition of molecular markers as predictors for response to therapy which have been used for a long time. While in the past the choice of treatment has been based solely on the tumor entity and its degree of malignancy derived from histological analyses, large randomized trials have now provided a solid basis for personalized molecular-guided treatment decisions. For instance, in the German NOA-08 trial a benefit of chemotherapy with temozolomide alone was only demonstrated in a subgroup of elderly patients with malignant gliomas displaying promoter hypermethylation of the DNA repair enzyme MGMT. This is only one of several examples where molecular analysis of tumor tissue becomes clinically relevant as these analyses can and should be taken into account for treatment decisions and not, as previously, just as an additional parameter for estimating prognosis. This article illustrates the current developments in the area of personalized neurooncology and critically reviews the impact on clinical decision-making in daily practice.

PAX2 is an antiapoptotic molecule with deregulated expression in medulloblastoma

PAX2 is a paired box transcription factor possessing a fundamental role in the embryogenesis of hindbrain and urinary tract. PAX genes are proto-oncogenes, PAX2 expression may contribute to the pathogenesis of renal cell carcinoma. Because of the expression of PAX2 in the developing hindbrain and its essential role in cerebellar development, it has been hypothesized that PAX2 may also be involved in medulloblastoma tumorigenesis. We investigated the expression pattern of PAX2 and various genes of the neuronal lineage in medulloblastoma and glioma cell lines. We found high expression of PAX2 mRNA and PAX2 protein in medulloblastoma cells and some glioma cell lines independent of their neuronal lineage gene expression signature. Gene suppression of PAX2 decreased the expression of the PAX2 transcriptional target GDNF in Daoy cells and had a profound cytotoxic effect in vitro on Daoy medulloblastoma and T98G glioma cells. Expression of PAX2 was then assessed in two separate medulloblastoma tissue microarrays with a total of 61 patient samples by immunohistochemistry. PAX2 expression was detected in the majority of medulloblastoma samples and correlated with less differentiated histology. Therefore, PAX2 is a biomarker for a more aggressive medulloblastoma phenotype and may represent a novel therapeutic target.

Complementary therapy use in patients with glioma: an observational study

OBJECTIVE

Despite novel multimodal therapeutic approaches, the vast majority of glial tumors are not curable. Patients may search for complementary therapies in order to contribute to the fight against their disease or to relieve symptoms induced by their brain tumor. The extent of the use of complementary or alternative therapies, the patients' rationale behind it, and the cost of complementary therapy for gliomas are not known. We used a questionnaire and the database of the German Glioma Network to evaluate these questions.

METHODS

A total of 621 questionnaires were available for evaluation from patients with glial tumors of WHO grades II to grade IV. The patients were recruited from 6 neuro-oncologic centers in Germany. Complementary therapy was defined as methods or compounds not used in routine clinical practice and not scientifically evaluated.

RESULTS

Forty percent of the responding patients reported the use of complementary therapies. Significant differences between the group of complementary therapy users and nonusers were seen with respect to age (younger > older), gender (female > male), and education (high education level > low education level). The motivation for complementary therapy use was not driven by unsatisfactory clinical care by the neuro-oncologists, but by the wish to add something beneficial to the standard of care.

CONCLUSIONS

In clinical practice, patients' use of complementary therapies may be largely overseen and underestimated. The major motivation is not distrust in conventional therapies. Neuro-oncologists should be aware of this phenomenon and encourage an open but critical dialogue with their patients.

Very late relapses in glioblastoma long-term survivors

e13017

Background: Long-term survival of patients with histologically confirmed glioblastoma is a rare event with figures in the range of 2–3% for 5-year survival. Prognosis and further clinical course of these patients beyond 5 years after diagnosis are in essence unknown with only anecdotal reports of patients surviving for 10 years or more. Methods: We here report on the extended follow-up (mean, 139.4 months) of a cohort of 10 glioblastoma long-term survivors. Retrospective central histology, clinical monitoring, and regular magnetic resonance imaging were done. Results: A total of 5 patients of the 9 patients alive at a previous analysis have died during the extended follow-up. Four of these patients died from recurrent tumor. One patient died from leukoencephalopathy-associated complications without evidence of tumor progression. Details concerning the occurrence of relapses and their treatment are displayed in table 1. Notably, very late relapses occurred in three patients after 118, 124, and 126 months of progression-free survival. Thus, from the original cohort of 10 patients only 3 remain free from recurrence after the extended follow up of more than 10 years. Conclusions: Very late relapses pose a serious threat for glioblastoma long-term survivors and call for continuous vigilance. The maintenance of a tight control schedule even in patients surviving for more than 10 years should be considered.

[Table: see text]

No significant financial relationships to disclose.

Surviving glioblastoma for more than 5 years: The patient's perspective

The authors performed a comprehensive analysis of the functional outcome of 10 patients who had survived 5 years from a diagnosis of glioblastoma. Neurologic deficits were mild in most patients, but neuropsychological testing demonstrated cognitive deficits in all patients. Depression and anxiety were common. Although most patients thought that their social functioning and work ability were impaired, little reduction in overall quality of life was perceived.

One week on/one week off: A novel active regimen of temozolomide for recurrent glioblastoma

Twenty-one patients with recurrent or progressive glioblastoma were enrolled in a prospective phase II trial to determine the safety and efficacy of a 1-week on/1-week off regimen of temozolomide administered at 150 mg/m2 on days 1 to 7 and days 15 to 21 of 28-day treatment cycles. Two patients achieved a partial response (10%), and 17 patients (81%) had stable disease. The median progression-free survival was 5 months. The progression-free survival at 6 months was 48%.

Hypoxia-induced cell death in human malignant glioma cells: energy deprivation promotes decoupling of mitochondrial cytochrome c release from caspase processing and necrotic cell death

Hypoxia induces apoptosis in primary and transformed cells and in various tumor cell lines in vitro. In contrast, there is little apoptosis and predominant necrosis despite extensive hypoxia in human glioblastomas in vivo. We here characterize ultrastructural and biochemical features of cell death in LN-229, LN-18 and U87MG malignant glioma cells in a paradigm of hypoxia with partial glucose deprivation in vitro. Electron microscopic analysis of hypoxia-challenged glioma cells demonstrated early stages of apoptosis but predominant necrosis. ATP levels declined during hypoxia, but recovered with re-exposure to normoxic conditions unless hypoxia exceeded 8 h. Longer hypoxic exposure resulted in irreversible ATP depletion and delayed cell death. Hypoxia induced mitochondrial release of cytochrome c, but there was no cleavage of caspases 3, 7, 8 or 9, and no DNA fragmentation. Ectopic expression of BCL-XL conferred protection from hypoxia-induced cell death, whereas the overexpression of the antiapoptotic proteins X-linked-inhibitor-of-apoptosis-protein and cytokine response modifier-A had no effect. These findings suggest that glioma cells resist adverse effects of hypoxia until energy stores are depleted and then undergo necrosis rather than apoptosis because of energy deprivation.

Identification by suppression subtractive hybridization of p21 as a radio-inducible gene in human glioma cells

BACKGROUND

Radio-gene therapy involves the delivery, to tumor cells, of a therapeutic transgene whose expression is controlled by irradiation.

MATERIALS AND METHODS

Here, we sought to identify novel radio-inducible transcripts in U87MG human malignant glioma cells using suppression subtractive hybridization (SSH).

RESULTS

Of 998 clones from a subtracted library of irradiated U87MG cells, 24 candidate clones were identified by dot blot and 3 clones were confirmed as having been induced by irradiation by Northern blot analysis. All three clones showed 99-100% homology to the cyclin-dependent kinase (cdk) inhibitor, p21(Waf/Cip1). A screening of 12 human malignant glioma cell lines revealed that irradiation increased p21 mRNA expression and p21 protein levels levels in all of the five cell lines retaining p53 wild-type activity in a p53 reporter assay, but in none of seven p53 reporter-negative cell lines.

CONCLUSION

Irradiation induces p21 mRNA expression in a strictly p53-dependent manner and may only enhance the expression of a limited number of genes in glioma cells. We conclude that the identification of radio-inducible genomic sequences suitable for radio-gene therapy may turn out to be difficult.

Overexpression of Pax5 is not sufficient for neoplastic transformation of mouse neuroectoderm

The developmental control genes of the Pax family are essential for brain development. Several Pax genes are also involved in chromosomal translocations causing malignancies in humans, and Pax5 expression is deregulated in medulloblastomas. We have investigated whether Pax5 can induce tumors in the developing mouse brain. Primary mouse embryonic neuroectodermal cells were retrovirally transduced with mouse Pax5 and transplanted into the brain of syngeneic host mice. No tumors developed in 36 transplants after one year, and there were no alterations in the differentiation pattern of the neural transplants. We then generated transgenic mice expressing human Pax5 under control of the Engrailed-2 promoter, which is expressed in the cerebellar external granule cell layer and in medulloblastomas. Sustained expression was achieved in the cerebellum of transgenic animals throughout lifetime. Expression levels were similar to those observed in human medulloblastomas. Again, cerebellar morphogenesis was undisturbed, and no tumors arose. These results strongly argue against a dominant transforming activity of PAX5 in NEC and in cerebellar granule cell precursors of mice, and underline the restricted tissue-specificity of PAX5 related oncogenesis.

Distinct phases of cryogenic tissue damage in the cerebral cortex of wild-type and c-fos deficient mice

To characterize the development of tissue damage following cryogenic injury to the mouse cortex, the time course of histopathological changes, transcriptional responses and DNA strand breaks following application of a liquid nitrogen-cooled probe to the surface of the parietal bone were assessed. Distinct phases of tissue damage were observed: after 30 min, there was demarcation of a core lesion followed by mainly necrotic cell death starting 2 h after injury. At 12 hours, progressive apoptotic death of scattered cells in the periphery of the core lesion was detected, resembling the penumbra observed in ischaemic stroke. In situ hybridization for c-fos revealed an absence of expression in the core region, suggesting early cessation of transcription. There was strong induction of c-fos in the penumbra 30 min after the lesion, which had spread over the ipsilateral hemisphere at 2 h, possibly caused by peri-infarction depolarization. At later time points, sustained expression of c-fos was observed in some cells in the penumbra. Since a role for c-fos has been postulated in the initiation or execution of apoptotic pathways, the susceptibility of c-fos deficient mice was explored (n=4) in this model. Cryoinjury-induced tissue injury was markedly attenuated in c-fos deficient mice. A model of the phases and mechanisms of cryogenic injury is proposed, which discriminates an early phase characterized by physical changes caused by hypothermia and their immediate consequences (i.e. transcriptional block), an intermediate phase where secondary changes lead to necrosis in the core region, and a final phase of delayed apoptotic cell death in the penumbra.

Characterization of Tu-2449, a glioma cell line derived from a spontaneous tumor in GFAP-v-src-transgenic mice: comparison with established murine glioma cell lines

Glial fibrillary acidic protein (GFAP)-v-src transgenic mice develop spontaneous gliomas with a high incidence of malignant progression. We characterize the first glial cell line derived from v-src transgenic mice, Tu-2449 in comparison with a virally induced murine glioma, SRB-10, and a spontaneous murine glioma, P497. Doubling times were lowest, as clonogenicity in soft agar was highest for Tu-2449, and to a lesser degree, Tu-2449 cells formed spheroids and showed migratory behaviour and invaded fetal rat brain aggregates. BCL-2 and BAX expression were lower in Tu-2449 and P497 than in SRB-10 cells. Only Tu-2449 cells accumulated p53 protein in response to genotoxic stress. Tu-2449 and SRB-10 cells that showed low CD95 expression were resistant to CD95 ligand (CD95L)-induced apoptosis unless coexposed to CD95L and inhibitors of RNA or protein synthesis. A chemosensitivity profile revealed Tu-2449 to be rather chemoresistant. Tu-2449 thus displays growth characteristics and patterns of resistance to apoptosis similar to those of other mouse and human glioma cell lines and may therefore become a valuable tool to evaluate new therapies for malignant gliomas in vitro and in vivo.

Hypersensitivity to seizures in beta-amyloid precursor protein deficient mice

Secreted forms of the beta-amyloid precursor protein (beta-APP) have neuroprotective properties in vitro and may be involved in the containment of neuronal excitation. To test whether loss of secreted forms of beta-APP (sAPPs) may enhance excitotoxic responses, we injected mice homozygous for a targeted mutation of the beta-APP gene (beta-APPDelta/Delta) intraperitoneally with kainic acid. We found that in these mice, kainic acid induced seizures initiated earlier, and acute mortality was enhanced compared to isogenic wild-type mice independently from the callosal agenesis phenotype observed to occur at increased frequency in APP mutant mice. Expression of c-fos in cortex and cingulate gyrus was enhanced in beta-APPDelta/Delta mice, although the amount of structural damage and apoptosis in the hippocampal pyramidal cell layer and cortex was similar to that of controls. When cerebellar granule cell cultures and cortical neuronal cultures were challenged with glutamate receptor agonists, the rates of cell death and apoptosis of beta-APPDelta/Delta mice were indistinguishable from those of controls. Therefore, deficiency of sAPPs causes facilitation of seizure activity in the absence of enhanced cell death. Since enhanced seizures were observed also in mice homozygous for a deletion of the entire beta-APP gene, this phenotype results from a loss of APP rather than from a dominant effect of APPDelta.

A strain-independent postnatal neurodegeneration in mice lacking the EGF receptor

Mice lacking the epidermal growth factor receptor (EGFR) exhibit strain-dependent phenotypes ranging from placental to postnatal skin, lung and brain defects. After birth, all mutant mice develop a progressive neurodegeneration in the frontal cortex, olfactory bulb and thalamus, characterized by massive apoptosis and upregulation of c-fos. These defects occur in a strain-independent manner, since neither rescue of the placental phenotype by aggregation of diploid 129/Sv EGFR mutant and tetraploid wild-type embryos, nor promotion of lung maturation by transplacental dexamethasone administration alters the course of neurodegeneration. VEGF is not induced during the degenerative process, excluding hypoxia and ischemia as causes of cell death. A migratory disorder is detected in the hippocampus with nests of ectopic neurons, which are also apoptotic. Cerebral cortices from EGFR mutants contain lower numbers of GFAP positive astrocytes, which display reduced proliferation in vitro. Since EGFR is expressed in the affected cell-types, these results define a specific function for EGFR in the proliferation and/or differentiation of astrocytes and in the survival of postmitotic neurons.

Development and malignant progression of astrocytomas in GFAP-v-src transgenic mice

We have generated a transgenic mouse model for astrocytoma by expressing the v-src kinase under control of the glial fibrillary acidic protein (GFAP) gene regulatory elements in astrocytes. Abnormal astrogliosis was observed in all transgenic animals already at 2 weeks postnatally, frequently followed by the development of dysplastic changes. Later, small proliferative foci arose, and overt astrocytoma developed in the brain and spinal cord in 14.4% of mice after a follow up time of 65 weeks. While early lesions were histologically consistent with low-grade astrocytoma, at later stages most tumors were highly mitotic and frankly malignant. Vascular endothelial growth factor (VEGF) was expressed by tumor cells already at early stages, suggesting induction by v-src, and it was most pronounced in pseudopalisading cells surrounding necrotic areas, implying additional upregulation by hypoxia. In larger lesions, mitotic activity and expression of flk-1, the cognate receptor of VEGF were induced in endothelial cells. Therefore, end-stage tumors mimicked the morphological and molecular characteristics of human glioblastoma multiforme. Time course and stochastic nature of the process indicate that v-src did not suffice for malignant transformation, and that astrocytomas were the result of a multistep process necessitating co-operation of additional genetic events.

The absence of c-fos prevents light-induced apoptotic cell death of photoreceptors in retinal degeneration in vivo

Apoptotic cell death in the retina was recently demonstrated in animal models of the hereditary human retinal dystrophy known as retinitis pigmentosa. Although recent evidence indicates that the proto-oncogene c-fos is a mediator of apoptosis, its precise role is unclear. In fact, under some conditions, c-fos may even protect against apoptotic cell death. In the retina, c-fos is physiologically expressed in a diurnal manner and is inducible by light. We previously observed a light-elicited, dose-dependent apoptotic response in rat photoreceptors. To determine whether c-fos is involved in the light-induced apoptotic pathway we have used control mice and mice lacking c-fos. We found that following dark adaptation and two hours of light exposure both groups of animals exhibited only a few apoptotic cells. However, at 12 and 24 additional hours after light exposure, apoptosis increased dramatically in controls but was virtually absent in those mice lacking c-fos. Therefore, c-fos is essential for light-induced apoptosis of photoreceptors. Notably, c-fos is continuously upregulated concomitant with apoptotic photoreceptor death in our system and in animal models of retinitis pigmentosa (Agarwal, N. et al., Invest. Ophthalmol. Vis.Sci. Suppl. 36, S638 and Rich, K.A. et al., Invest. Ophthalmol. Vis. Sci. Suppl. 35, 1833). Inhibition of c-fos expression might therefore represent a novel therapeutic strategy to retard the time course of retinal dystrophies and light-induced retinal degeneration.