Long-term immunological memory in the resistance of rats to transplanted intracerebral 9L gliosarcoma (9LGS) following subcutaneous immunization with 9LGS cells

Brainstem glioma progression in juvenile and adult rats

OBJECT

Brainstem gliomas are common in children and have the worst prognosis of any brain tumor in this age group. On the other hand, brainstem gliomas are rare in adults, and the authors of some clinical studies have suggested that this lesion behaves differently in adults than in children. In the present study, the authors test an orthotopic C6 brainstem glioma model in juvenile and adult rats, and investigate the biological behavior of this lesion in the 2 age groups.

METHODS

The C6 glioma cells were stereotactically implanted into the pons of juvenile or adult male rats. Neurological presentation and survival time were recorded. Tumor proliferation and the number of apoptotic cells in brainstem gliomas of young and adult rats were determined by immunohistochemical staining with Ki 67 and terminal deoxynucleotidyl transferase 2'-deoxyuridine 5'-triphosphate-mediated nick-end labeling assay.

RESULTS

Striking differences in the onset of neurological signs, duration of symptoms, survival time, tumor growth pattern, tumor proliferation, and number of apoptotic cells were found between the gliomas in the 2 groups of rats. The lesions were relatively focal in adult rats but more diffuse in young rats. Furthermore, brainstem gliomas in adult rats were less proliferative and had more apoptotic cells than those in young rats.

CONCLUSIONS

The authors found that the C6 brainstem glioma model in young and adult rats closely imitates the course of brainstem glioma in humans both in neurological findings and histopathological characteristics. Their findings also suggest that the different growth pattern and invasiveness of these lesions in children compared with that in adults could be due to different cellular environments in the 2 age groups, and warrants further investigation into the difference in the host response to brainstem gliomas in children and adults.

Orthotopic transplantation of v-src–expressing glioma cell lines into immunocompetent mice: establishment of a new transplantable in vivo model for malignant glioma

Object

The aim of this study was to develop and characterize a new orthotopic, syngeneic, transplantable mouse brain tumor model by using the cell lines Tu-9648 and Tu-2449, which were previously isolated from tumors that arose spontaneously in glial fibrillary acidic protein (GFAP)-v-src transgenic mice.

Methods

Striatal implantation of a 1-μl suspension of 5000 to 10,000 cells from either clone into syngeneic B6C3F1 mice resulted in tumors that were histologically identified as malignant gliomas. Prior subcutaneous inoculations with irradiated autologous cells inhibited the otherwise robust development of a microscopically infiltrating malignant glioma. Untreated mice with implanted tumor cells were killed 12 days later, when the resultant gliomas were several millimeters in diameter. Immunohistochemically, the gliomas displayed both the astroglial marker GFAP and the oncogenic form of signal transducer and activator of transcription–3 (Stat3). This form is called tyrosine-705 phosphorylated Stat3, and is found in many malignant entities, including human gliomas. Phosphorylated Stat3 was particularly prominent, not only in the nucleus but also in the plasma membrane of peripherally infiltrating glioma cells, reflecting persistent overactivation of the Janus kinase/Stat3 signal transduction pathway. The Tu-2449 cells exhibited three non-random structural chromosomal aberrations, including a deletion of the long arm of chromosome 2 and an apparently balanced translocation between chromosomes 1 and 3. The GFAP-v-src transgene was mapped to the pericentromeric region of chromosome 18.

Conclusions

The high rate of engraftment, the similarity to the high-grade malignant glioma of origin, and the rapid, locally invasive growth of these tumors should make this murine model useful in testing novel therapies for human malignant gliomas.

Evaluation of particulate systems supporting tumor cell fractions in a preventive vaccination against intracranial rat glioma

Object

Irradiated autologous tumor cells are commonly used as a source of antigens in antiglioma vaccinations to activate the immune system. As cell number is often a limiting factor in these cells’ preparation, the aim of the present study was to find a means that can lower the amount of cells required. Among strategies currently developed, adjuvant particulate systems offer a promising means to improve the antitumor immune response. In this study, the authors were interested in evaluating the role of particulate systems containing biodegradable microspheres that carry tumor cell fractions on their surfaces in the induction of a protective immunity in the 9L/Fischer 344 rat glioma model. The efficiency of these particulate systems was compared to that of irradiated 9L cells.

Methods

Particulate systems composed of poly(d,l-lactide-co-glycolide) (PLGA) microspheres that support 9L cell fractions on their surfaces (cell lysates or plasma membranes) or irradiated 9L cells alone were injected subcutaneously into the flanks of syngeneic Fischer 344 rats. Eighteen days later, the rats were intracranially injected with nonirradiated 9L cells. A study of survival in these animals and an analysis of the resulting immune response were then conducted.

For the same amount of protein (50 μg) injected, irradiated 9L cells provided long-term survival in 30% of animals, whereas 9L plasma membranes adsorbed onto PLGA microspheres provided long-term survival in 10% of animals and cell lysates adsorbed onto microspheres provided long-term survival in 0%. Accordingly, particulate systems induced a lower T helper cell Type 1 (Th1) peripheral immune response than irradiated 9L cells. However, greater secretion of Th1 cytokines was observed when particulate systems were used than when cell fractions separated from microspheres were used, indicating the adjuvant property of these particulate systems.

Conclusions

Particulate systems have adjuvant properties but are still less efficient than irradiated whole tumor cells for vaccinations. Encapsulation of an activating molecule in the microsphere will be the next developmental step in the search for efficient antiglioma vaccinations.

Detailed characterization of the mouse glioma 261 tumor model for experimental glioblastoma therapy

Mouse glioma 261 (Gl261) cells are used frequently in experimental glioblastoma therapy; however, no detailed description of the Gl261 tumor model is available. Here we present that Gl261 cells carry point mutations in the K-ras and p53 genes. Basal major histocompatibility complex (MHC)I, but not MHCII, expression was detected in Gl261 cells. The introduction of interferon-gamma-encoding genes increased expression of both MHCI and MHCII. A low amount of B7-1 and B7-2 RNA was detected in wild-type cells, but cytokine production did not change expression levels. Gl261 cells were transduced efficiently by adenoviral vectors; the infectivity of retroviral vectors was limited. Low numbers of transplanted Gl261 cells formed both subcutaneous and intracranial tumors in C57BL/6 mice. The cells were moderately immunogenic: prevaccination of mice with irradiated tumor cells 7 days before intracranial tumor challenge prevented tumor formation in approximately 90% of mice. When vaccination was carried out on the day or 3 days after tumor challenge, no surviving animals could be found. In vitro-growing cells were radiosensitive: less than 2 Gy was required to achieve 50% cell mortality. Local tumor irradiation with 4 Gy X-rays in brain tumor-bearing mice slowed down tumor progression, but none of the mice were cured off the tumor. In conclusion, the Gl261 brain tumor model might be efficiently used to study the antitumor effects of various therapeutic modalities, but the moderate immunogenicity of the cells should be considered.

Synergy of gene-mediated immunoprophylaxis and microbeam radiation therapy for advanced intracerebral rat 9L gliosarcomas

PURPOSE

Microbeam radiation therapy (MRT), a novel experimental radiosurgery that largely spares the developing CNS and other normal tissues, is tolerated well by developing animals and palliates advanced 9LGS tumors. This report, to our knowledge, is the first demonstration that gene-mediated immunotherapy (GMIMPR) enhances the efficacy of MRT for advanced 9LGS tumors.

METHODS

Seventy-six male Fischer 344 rats were implanted ic with 10(4)9LGS cells on d0. By d14, the cells had generated approximately approximately 40 mm3 ic 9LGS tumours, experimental models for therapy of moderately aggressive human malignant astrocytomas. Each of the 14 untreated (control) rats died from a large (>100 mg) ic tumor before d29 (median, d21). On d14, the remaining 62 rats were given deliberately suboptimal microbeam radiation therapy (MRT) by a single lateral exposure of the tumor-bearing zone of the head to a 10.1 mm-wide, approximately approximately 11 mm-high array of 20-39 microm-wide, nearly parallel beams of synchrotron wiggler-generated radiation (mainly approximately 50-150 keV X-rays) that delivered 625 Gy peak skin doses at approximately approximately 211 microm ctc intervals in approximately approximately 300 ms either without additional treatments (MRT-only, 25 rats), with post-MRT GMIMPR (MRT+GMIMPR, 23 rats: multiple sc injections of irradiated (clonogenically-disabled) GM-CSF gene-transfected 9LGS cells), or with post-MRT IMPR (MRT+IMPR, 14 rats: multiple sc injections of irradiated (clonogenically-disabled) 9LGS cells.

RESULTS

The median post-implantation survivals of rats in the MRT-only, MRT+GMIMPR and MRT+IMPR groups were over twice that of controls; further, approximately approximately 20% of rats in MRT-only and MRT+IMPR groups survived >1 yr with no obvious disabilities. Moreover, over 40% of MRT+GMIMPR rats survived >1 yr with no obvious disabilities, a significant (P<0.04) increase over the MRT-only and MRT+IMPR groups.

SIGNIFICANCE

These data suggest that the combination of MRT+GMIMPR might be better than MRT only for unifocal CNS tumors, particularly in infants and young children.

Effects of syngeneic cellular vaccinations alone or in combination with GM-CSF on the weakly immunogenic F98 glioma model

Cancer vaccines are one approach for the treatment of brain tumors. Most experimental studies are performed on so-called "immunogenic" brain tumor models such as the rat 9L glioma which does not reflect characteristics of human glioblastoma. In the present study, we tested syngeneic cellular vaccinations alone or in combination with granulocyte-macrophage colony-stimulating factor (GM-CSF) on the weakly immunogenic F98 glioma model. Previous studies have shown the efficacy of this treatment on the 9L glioma model. Fisher rats received an intracerebral implantation of F98 cells. Three days later, two subcutaneous vaccinations with irradiated F98 cells were realized in presence or absence of GM-CSF. This scheme of vaccination induced a systemic cellular and humoral immune response capable of in vitro cytolytic activity against F98 cells. However, no significant differences in survival times were noted between vaccinated and untreated animals. Animals vaccinated with GM-CSF or without GM-CSF had respectively a survival time of 26 +/- 2.1 and 25 +/- 4.4 days following tumor challenge versus 26.5 +/- 2.4 days for untreated rats. Fourteen days after the intracerebral tumor implantation, the tumors of vaccinated animals showed a robust infiltration by T lymphocytes, NK cells, dendritic cells, granulocytes and CD11b/c+ myeloid cells. This infiltration was nearly absent in untreated animals except for CD11b/c+ myeloid cells. This study shows that, contrary to the 9L glioma model, the F98 glioma model is resistant to syngeneic cellular vaccinations although a strong peripheral and intratumoral immune response can be induced. These results suggest that the F98 glioma is an attractive model to understand the mechanisms of glioma immunotherapy resistance.

Opposite role of Bax and BCL-2 in the anti-tumoral responses of the immune system

Background

The relative role of anti apoptotic (i.e. Bcl-2) or pro-apoptotic (e.g. Bax) proteins in tumor progression is still not completely understood.

Methods

The rat glioma cell line A15A5 was stably transfected with human Bcl-2 and Bax transgenes and the viability of theses cell lines was analyzed in vitro and in vivo.

Results

In vitro, the transfected cell lines (huBax A15A5 and huBcl-2 A15A5) exhibited different sensitivities toward apoptotic stimuli. huBax A15A5 cells were more sensitive and huBcl-2 A15A5 cells more resistant to apoptosis than mock-transfected A15A5 cells (pCMV A15A5). However, in vivo, in syngenic rat BDIX, these cell lines behaved differently, as no tumor growth was observed with huBax A15A5 cells while huBcl-2 A15A5 cells formed large tumors. The immune system appeared to be involved in the rejection of huBax A15A5 cells since i) huBax A15A5 cells were tumorogenic in nude mice, ii) an accumulation of CD8+ T-lymphocytes was observed at the site of injection of huBax A15A5 cells and iii) BDIX rats, which had received huBax A15A5 cells developed an immune protection against pCMV A15A5 and huBcl-2 A15A5 cells.

Conclusions

We show that the expression of Bax and Bcl-2 controls the sensitivity of the cancer cells toward the immune system. This sensitization is most likely to be due to an increase in immune induced cell death and/or the amplification of an anti tumour immune response

Rat brain tumor models to assess the efficacy of boron neutron capture therapy: a critical evaluation

Development of any therapeutic modality can be facilitated by the use of the appropriate animal models to assess its efficacy. This report primarily will focus on our studies using the F98 and 9L rat glioma models to evaluate the effectiveness of boron neutron capture therapy (BNCT) of brain tumors. Following intracerebral implantation the biological behavior of each tumor resembles that of human high grade gliomas in a number of ways. In both models, glioma cells were implanted intracerebrally into syngeneic Fischer rats and approximately 10-14 days later BNCT was initiated at the Brookhaven National Laboratory Medical Research Reactor. Two low molecular weight (M(r) < 210Da) 10B-containing drugs, boronophenylalanine (BPA) and/or sodium borocaptate (BSH) were used as capture agents, either alone or in combination with each other. The 9L gliosarcoma, which has been difficult to cure by means of either chemo- or radiotherapy alone, was readily curable by BNCT. The best survival data were obtained using BPA at a dose of 1200 mg/kg (64.8mg 10B), administered intraperitoneally (i.p.), with a 100% survival rate at 8 months. In contrast, the F98 glioma has been refractory to all therapeutic modalities. Tumor bearing animals, which had received 500 mg/kg (27 mg 10B) of BPA, or an equivalent amount of BSH i.v., had mean survival time (MST) of 37 and 33 days, respectively, compared to 29 days for irradiated controls. The best survival data with the F98 glioma model were obtained using BPA + BSH in combination, administered intra-arterially via the internal carotid artery (i.c.) with hyperosmotic mannitol induced blood-brain barrier disruption (BBB-D). The MST was 140 days with a cure rate of 25%, compared to a MST of 73 days with a 5% cure rate without BBB-D, and 41 days following i.v. administration of both drugs. A modest but significant increase in MST also was observed in rats that received intracarotid (i.c.) BPA in combination with Cereport (RMP-7), which produced a pharmacologically mediated opening of the BBB. Studies also have been carried out with the F98 glioma to determine whether an X-ray boost could enhance the efficacy of BNCT, and it was shown that there was a significant therapeutic gain. Finally, molecular targeting of the epidermal growth factor receptor (EGFR) has been investigated using F98 glioma cells, which had been transfected with the gene encoding EGFR and, intratumoral injection of boronated EGF as the delivery agent, followed by BNCT. These studies demonstrated that there was specific targeting of EGFR and provided proof of principle for the use of high molecular weight, receptor targeting-boron delivery agents. Finally, a xenograft model for melanoma metastatic to the brain has been developed using a human melanoma (MRA27), stereotactically implanted into the brains of nude rats, and these studies demonstrated that BNCT either cured or significantly prolonged the survival of tumor-bearing rats. It remains to be determined, which, if any, of these experimental approaches will be translated into clinical studies. Be that as it may, rat brain tumor models already have made a significant contribution to the design of clinical BNCT protocols, and should continue to do so in the future.

The combination of X-ray-mediated radiosurgery and gene-mediated immunoprophylaxis for advanced intracerebral gliosarcomas in rats

Rats with advanced, imminently lethal, approximately 4 mm diameter, left-sided intracerebral 9L gliosarcoma (9LGS), a well characterized malignant tumor with some similarities to human high-grade astrocytomas, were used as a therapy model 14 days post-implantation of 10(4) cells. Such tumor-bearing rats die within two weeks (median, 6 days) thereafter if untreated. However, if these tumors are exposed on day 14 to 12-25 Gy of an electron-equilibrated 6 MV photon beam (radiosurgery), survival is extended about 5-6 fold to a median of 34 days, but long-term survival (> 1 year) is increased only to approximately 18%. Multiple subcutaneous inoculations of radiation-disabled 9LGS cells post-radiosurgery (immunoprophylaxis) extended lifespan and long-term (> 1 year) survival minimally (median, 37 days; 25%, respectively). In sharp contrast, radiosurgery followed by multiple subcutaneous inoculations of radiation-disabled 9LGS cells that had been transfected with granulocyte macrophage colony stimulating factor (GMCSF), a cytokine with demonstrated immune-enhancing properties (i.e. gene-mediated immunoprophylaxis, GMIMPR) increased long-term survival to approximately 67%. To our knowledge, these results are the first to show that the combination of photon radiosurgery and GMIMPR is effective for an advanced, imminently lethal brain tumor in a mammal. These data raise the possibility that GMIMPR following radiation therapy might prove effective for the treatment of some human malignant gliomas.

The combination of boron neutron-capture therapy and immunoprophylaxis for advanced intracerebral gliosarcomas in rats

Glioblastoma multiforme (GBM) is the most common primary human brain tumor. About 7000 new cases are diagnosed yearly in the USA and GBM is almost invariably fatal within a few years after it is diagnosed. Despite current neurosurgical and radiotherapeutic tumor cytoreduction methods, in most cases occult foci of tumor cells infiltrate surrounding brain tissues and cause recurrent disease. Therefore the combination of neurosurgical and radiotherapeutic debulking methods with therapies to inhibit occult GBM cells should improve prognosis. In this study we have combined boron neutron-capture therapy (BNCT), a novel binary radiotherapeutic treatment modality that selectively irradiates tumor tissue and largely spares normal brain tissue, with immunoprophylaxis, a form of active immunization initiated soon after BNCT treatment, to treat advanced, clinically relevantly-sized brain tumors in rats. Using a malignant rat glioma model of high immunogenicity, the 9L gliosarcoma, we have shown that about half of the rats that would have died after receiving BNCT debulking alone, survived after receiving BNCT plus immunoprophylaxis. Further, most of the surviving rats display immunological-based resistance to recurrent 9LGS growth six months or more after treatment. To our knowledge this study represents the first time BNCT and immunoprophylaxis have been combined to treat advanced brain tumors in rats.