Pharmacological modulation of T cell immunity results in long-term remission of autoimmune arthritis

Chronic inflammatory diseases like rheumatoid arthritis are characterized by a deficit in fully functional regulatory T cells. DNA-methylation inhibitors have previously been shown to promote regulatory T cell responses and, in the present study, we evaluated their potential to ameliorate chronic and acute animal models of rheumatoid arthritis. Of the drugs tested, decitabine was the most effective, producing a sustained therapeutic effect that was dependent on indoleamine 2,3-dioxygenase (IDO) and was associated with expansion of induced regulatory T cells, particularly at the site of disease activity. Treatment with decitabine also caused apoptosis of Th1 and Th17 cells in active arthritis in a highly selective manner. The molecular basis for this selectivity was shown to be ENT1, a nucleoside transporter, which facilitates intracellular entry of the drug and is up-regulated on effector T cells during active arthritis. It was further shown that short-term treatment with decitabine resulted in the generation of a population of regulatory T cells that were able to suppress arthritis upon adoptive transfer. In summary, a therapeutic approach using an approved drug is described that treats active inflammatory disease effectively and generates robust regulatory T cells with the IDO-dependent capacity to maintain remission.

What is the role of CRP in glioblastoma?

BACKGROUND

Glioblastoma is the most common primary malignant brain tumor in adults. Previous studies have suggested that CRP (C-reactive protein) could serve as a biomarker candidate as well as a prognostic factor in glioblastoma patients, and we here further investigate its potential role.

MATERIALS AND METHODS

Publicly available datasets were used to compare gene expression between brain samples from glioblastoma patients and non-tumor tissue. The structure of CRP was compared between humans and rats. Glioblastoma cells from humans and rats were stained with anti-CRP. Fischer 344 rats were inoculated with syngeneic glioblastoma cells pre-coated with anti-CRP, and survival was monitored. CRP concentration in rats carrying glioblastoma was followed.

RESULTS

CRP was upregulated on one locus on gene level in glioblastoma tissue as compared to non-tumor brain tissue, but not in glioma stem cells as compared to neural stem cells. The structure of the CRP protein was a characteristic pentamer in both humans and rats. Both human and rat glioblastoma cells were clearly positive for anti-CRP staining. Pre-coating of glioblastoma cells with anti-CRP antibodies did not affect survival in rats with intracranial tumors. Serum levels of CRP increased during tumor progression but did not reach significantly different levels.

CONCLUSIONS

Both human and rat glioblastoma cells could be stained with anti-CRP antibodies in vitro. In a syngeneic glioblastoma rat model we could see an increase in serum CRP during tumor progression, but coating glioblastoma cells with anti-CRP antibodies did not provide any survival change for the animals.

Growth pattern of experimental glioblastoma

Glioblastoma multiforme (GBM) is an aggressive primary brain malignancy with a very poor prognosis. Researchers employ animal models to develop potential therapies. It is important that these models have clinical relevance. This means that old models, propagated for decades in cultures, should be questioned. Parameters to be evaluated include whether animals are immune competent or not, the infiltrative growth pattern of the tumor, tumor volume resulting in symptoms and growth rate. We here describe the growth pattern of an experimental glioblastoma model in detail with GFP positive glioblastoma cells in fully immune competent animals and study tumor growth rate and tumor mass as a function of time from inoculation. We were able to correlate findings made with classical immunohistochemistry and MR findings. The tumor growth rate was fitted by a Gompertz function. The model predicted the time until onset of symptoms for 5000 inoculated cells to 18.7±0.4 days, and the tumor mass at days 10 and 14, which are commonly used as the start of treatment in therapeutic studies, were 5.97±0.62 mg and 29.1±3.0 mg, respectively. We want to raise the question regarding the clinical relevance of the outline of glioblastoma experiments, where treatment is often initiated at a very early stage. The approach presented here could potentially be modified to gain information also from other tumor models.

Upregulation of C1-inhibitor in pancreatic cancer

Purpose

The complement system has recently sparked more interest in cancer research. The classical pathway is initiated by activation of the C1 complex, which irreversibly can be bound to and inhibited by C1-INH. We have previously shown that C1-INH is upregulated in human glioblastoma (astrocytoma grade IV) on both gene and protein level. We here examine whether the complement system seems to play a role also in pancreatic cancer.

Technique and results

We performed an expression analysis of complement associated genes in 36 pancreatic ductal adenocarcinoma tumors and matching normal pancreatic tissue samples from pancreatic cancer patients (data from the publicly available database GSE15471). C1-INH was significantly upregulated in the pancreatic cancer tissue. None of the downstream components of the cascade were significantly upregulated in the cancer samples as compared to the control samples, which is the same pattern as we found in glioblastoma. GO analysis showed that membrane attack complex came up as the second most significantly associated cellular component. Analyzing gene expression of C1-INH in the pancreatic cancer cell lines from primary tumors versus metastatic tumor revealed no difference for the two mRNA transcripts (GSE59357).

Interpretation

Analysis of gene expression of complement related genes shows an upregulation of C1-INH and a downregulation of downstream components. This could suggest that C1-INH plays a role also in pancreatic cancer.

Anti-C1-inactivator treatment of glioblastoma

Purpose

Glioblastoma multiforme (GBM) or astrocytoma grade IV is the most common type of primary brain tumor in adults. In the present study, we investigate the role of the complement system in the glioblastoma situation in an experimental model, since we have previously been able to show a blockade of this system in the glioblastoma setting.

Technique and results

A GFP-positive glioblastoma cell line was used to induce glioblastomas subcutaneously in rats (n=42). Antibodies against C1-Inactivator (C1-IA) were used to try to re-activate the complement system. We were able to demonstrate an increased survival in rats treated with anti-C1-IA with an intratumoral route, and we could establish the same the results in a second series. Serum analyses revealed decreased levels of IL-1b and GM-CSF in animals 24 days after tumor cell inoculation in the anti-C1-IA group when compared to controls. Immunohistochemistry revealed decreased expression of C1-IA following treatment.

Interpretation

These results are in line with our previous work showing an upregulation of C1-IA, which is able to block the classical complement pathway, in glioblastomas. Treatment with antibodies against C1-IA seems to be beneficial in the glioblastoma situation, and no side effects could be seen in our experiments.

Evaluating vacquinol-1 in rats carrying glioblastoma models RG2 and NS1

Glioblastoma multiforme (GBM) is the most common malignant primary brain tumor, and available experimental and routine therapies result in limited survival benefits. A vulnerability of GBM cells to catastrophic vacuolization and cell death, a process termed methuosis, induced by Vacquinol-1 (VQ-1) has been described earlier. In the present study, we investigate the efficacy of VQ-1 treatment in two syngeneic rat GBM models, RG2 and NS1. VQ-1 treatment affected growth of both RG2 and NS1 cells in vitro. Intracranially, significant reduction in RG2 tumor size was observed, although no effect was seen on overall survival. No survival advantage or effect on tumor size was seen in animals carrying the NS1 models compared to untreated controls. Furthermore, immunological staining of FOXP3, CD4 and CD8 showed no marked difference in immune cell infiltrate in tumor environment following treatment. Taken together, a survival advantage of VQ-1 treatment alone could not be demonstrated here, even though some effect upon tumor size was seen. Staining for immune cell markers did not indicate that VQ-1 either reduced or increased host anti-tumor immune response.

Zebularine induces long-term survival of pancreatic islet allotransplants in streptozotocin treated diabetic rats

BACKGROUND

Coping with the immune rejection of allotransplants or autologous cells in patients with an active sensitization towards their autoantigens and autoimmunity presently necessitates life-long immune suppressive therapy acting on the immune system as a whole, which makes the patients vulnerable to infections and increases their risk of developing cancer. New technologies to induce antigen selective long-lasting immunosuppression or immune tolerance are therefore much needed.

METHODOLOGY/PRINCIPAL FINDINGS

The DNA demethylating agent Zebularine, previously demonstrated to induce expression of the genes for the immunosuppressive enzymes indolamine-2,3-deoxygenase-1 (IDO1) and kynureninase of the kynurenine pathway, is tested for capacity to suppress rejection of allotransplants. Allogeneic pancreatic islets from Lewis rats were transplanted under the kidney capsule of Fischer rats previously made diabetic by a streptozotocin injection (40 mg/kg). One group was treated with Zebularine (225 mg/kg) daily for 14 days from day 6 or 8 after transplantation, and a control group received no further treatment. Survival of the transplants was monitored by blood sugar measurements. Rats, normoglycemic for 90 days after allografting, were subjected to transplant removal by nephrectomy to confirm whether normoglycemia was indeed due to a surviving insulin producing transplant, or alternatively was a result of recovery of pancreatic insulin production in some toxin-treated rats. Of 9 Zebularine treated rats, 4 were still normoglycemic after 90 days and became hyperglycemic after nephrectomy. The mean length of normoglycemia in the Zebularine group was 67±8 days as compared to 14±3 days in 9 controls. Seven rats (2 controls and 5 Zebularine treated) were normoglycemic at 90 days due to pancreatic recovery as demonstrated by failure of nephrectomy to induce hyperglycemia.

CONCLUSIONS/SIGNIFICANCE

Zebularine treatment in vivo induces a long-lasting suppression of the immune destruction of allogeneic pancreatic islets resulting in protection of allograft function for more than 10 weeks after end of treatment.

Better prognosis of patients with glioma expressing FGF2-dependent PDGFRA irrespective of morphological diagnosis

Signaling of platelet derived growth factor receptor alpha (PDGFRA) is critically involved in the development of gliomas. However, the clinical relevance of PDGFRA expression in glioma subtypes and the mechanisms of PDGFRA expression in gliomas have been controversial. Under the supervision of morphological diagnosis, analysis of the GSE16011 and the Repository of Molecular Brain Neoplasia Data (Rembrandt) set revealed enriched PDGFRA expression in low-grade gliomas. However, gliomas with the top 25% of PDGFRA expression levels contained nearly all morphological subtypes, which was associated with frequent IDH1 mutation, 1p LOH, 19q LOH, less EGFR amplification, younger age at disease onset and better survival compared to those gliomas with lower levels of PDGFRA expression. SNP analysis in Rembrandt data set and FISH analysis in eleven low passage glioma cell lines showed infrequent amplification of PDGFRA. Using in vitro culture of these low passage glioma cells, we tested the hypothesis of gliogenic factor dependent expression of PDGFRA in glioma cells. Fibroblast growth factor 2 (FGF2) was able to maintain PDGFRA expression in glioma cells. FGF2 also induced PDGFRA expression in glioma cells with low or non-detectable PDGFRA expression. FGF2-dependent maintenance of PDGFRA expression was concordant with the maintenance of a subset of gliogenic genes and higher rates of cell proliferation. Further, concordant expression patterns of FGF2 and PDGFRA were detected in glioma samples by immunohistochemical staining. Our findings suggest a role of FGF2 in regulating PDGFRA expression in the subset of gliomas with younger age at disease onset and longer patient survival regardless of their morphological diagnosis.

Photon activation therapy of RG2 glioma carrying Fischer rats using stable thallium and monochromatic synchrotron radiation

75 RG2 glioma-carrying Fischer rats were treated by photon activation therapy (PAT) with monochromatic synchrotron radiation and stable thallium. Three groups were treated with thallium in combination with radiation at different energy; immediately below and above the thallium K-edge, and at 50 keV. Three control groups were given irradiation only, thallium only, or no treatment at all. For animals receiving thallium in combination with radiation to 15 Gy at 50 keV, the median survival time was 30 days, which was 67% longer than for the untreated controls (p = 0.0020) and 36% longer than for the group treated with radiation alone (not significant). Treatment with thallium and radiation at the higher energy levels were not effective at the given absorbed dose and thallium concentration. In the groups treated at 50 keV and above the K-edge, several animals exhibited extensive and sometimes contra-lateral edema, neuronal death and frank tissue necrosis. No such marked changes were seen in the other groups. The results were discussed with reference to Monte Carlo calculated electron energy spectra and dose enhancement factors.

Rat multipotent mesenchymal stromal cells lack long-distance tropism to 3 different rat glioma models

BACKGROUND

Viral gene therapy of malignant brain tumors has been restricted by the limited vector distribution within the tumors. Multipotent mesenchymal stromal cells (MSCs) and other precursor cells have shown tropism for gliomas, and these cells are currently being explored as potential vehicles for gene delivery in glioma gene therapy.

OBJECTIVE

To investigate MSC migration in detail after intratumoral and extratumoral implantation through syngeneic and orthotopic glioma models.

METHODS

Adult rat bone marrow-derived MSCs were transduced to express enhanced green fluorescent protein and implanted either directly into or at a distance from rat gliomas.

RESULTS

We found no evidence of long-distance MSC migration through the intact striatum toward syngeneic D74(RG2), N32, and N29 gliomas in the ipsilateral hemisphere or across the corpus callosum to gliomas located in the contralateral hemisphere. After intratumoral injection, MSCs migrated extensively, specifically within N32 gliomas. The MSCs did not proliferate within tumors, suggesting a low risk of malignant transformation of in vivo grafted cell vectors. Using a model for surgical glioma resection, we found that intratumorally grafted MSCs migrate efficiently within glioma remnants after partial surgical resection.

CONCLUSION

The findings point to limitations for the use of MSCs as vectors in glioma gene therapy, although intratumoral MSC implantation provides a dense and tumor-specific vector distribution.

An epigenetic mechanism for high, synergistic expression of indoleamine 2,3-dioxygenase 1 (IDO1) by combined treatment with zebularine and IFN-γ: potential therapeutic use in autoimmune diseases

IDO1 can be induced by interferon gamma (IFN-γ) in multiple cell types. We have earlier described that the DNA methyltransferase inhibitor zebularine also induces IDO1 in several rat cell clones. We now describe a synergistic induction of IDO1 expression by IFN-γ and zebularine. To elucidate the mechanism of the IDO1 induction we have studied the methylation status in the promoter region of the IDO1 gene from both human monocytic THP-1 cells and H1D2 rat colon cancer cells. Interestingly, the IDO1 promoter is hypermethylated and IFN-γ is shown to induce a significant demethylation. The synergism in effect of zebularine and IFN-γ on IDO1 expression is paralleled by a similar synergistic effect on expression of two other IFN-γ-responsive genes, the transcription factors STAT1 and IRF1 with binding sites in the IDO1 promoter region. The demonstrated synergistic activation of IDO1 expression has implications in relation to therapeutic induction of immunosuppression in autoimmunity and chronic inflammation.

Distribution, cellular localization, and therapeutic potential of the tumor-associated antigen Ku70/80 in glioblastoma multiforme

Antibodies specifically targeting tumor-associated antigens have proved to be important tools in the treatment of human cancer. A desirable target antigen should be unique to tumor cells, abundantly expressed, and readily available for antibody binding. The Ku70/80 DNA-repair protein is expressed in the nucleus of most cells; it is, however, also present on the cell surface of tumor cell lines, and antibodies binding Ku70/80 at the cell surface were recently shown to internalize into tumor cells. To evaluate the potential of Ku70/80-antigen as a therapeutic target for immunotoxins in glioblastoma multiforme, we investigated binding and localization of Ku70/80-specific antibodies in tissue samples from glioblastomas and normal human brains, and in glioma cell cultures. Furthermore, the internalization and drug-delivery capacity were evaluated by use of immunotoxicity studies. We demonstrate that Ku70/80 is localized on the cell plasma membrane of glioma cell lines, and is specifically present in human glioblastoma tissue. Antibodies bound to the Ku70/80 antigen on the cell surface of glioma cells were found to internalize via endocytosis, and shown to efficiently deliver toxins into glioblastoma cells. The data further imply that different antibodies directed against Ku70/80 possess different abilities to target the antigen, in relation to its presentation on the cell surface or intracellular localization. We conclude that Ku70/80 antigen is uniquely presented on the plasma membrane in glioblastomas, and that antibodies specific against the antigen have the capacity to selectively bind, internalize, and deliver toxins into tumor cells. These results imply that Ku70/80 is a potential target for immunotherapy of glioblastoma multiforme.

Increased blood-brain barrier permeability in mammalian brain 7 days after exposure to the radiation from a GSM-900 mobile phone

Microwaves were for the first time produced by humans in 1886 when radio waves were broadcasted and received. Until then microwaves had only existed as a part of the cosmic background radiation since the birth of universe. By the following utilization of microwaves in telegraph communication, radars, television and above all, in the modern mobile phone technology, mankind is today exposed to microwaves at a level up to 10(20) times the original background radiation since the birth of universe. Our group has earlier shown that the electromagnetic radiation emitted by mobile phones alters the permeability of the blood-brain barrier (BBB), resulting in albumin extravasation immediately and 14 days after 2h of exposure. In the background section of this report, we present a thorough review of the literature on the demonstrated effects (or lack of effects) of microwave exposure upon the BBB. Furthermore, we have continued our own studies by investigating the effects of GSM mobile phone radiation upon the blood-brain barrier permeability of rats 7 days after one occasion of 2h of exposure. Forty-eight rats were exposed in TEM-cells for 2h at non-thermal specific absorption rates (SARs) of 0mW/kg, 0.12mW/kg, 1.2mW/kg, 12mW/kg and 120mW/kg. Albumin extravasation over the BBB, neuronal albumin uptake and neuronal damage were assessed. Albumin extravasation was enhanced in the mobile phone exposed rats as compared to sham controls after this 7-day recovery period (Fisher's exact probability test, p=0.04 and Kruskal-Wallis, p=0.012), at the SAR-value of 12mW/kg (Mann-Whitney, p=0.007) and with a trend of increased albumin extravasation also at the SAR-values of 0.12mW/kg and 120mW/kg. There was a low, but significant correlation between the exposure level (SAR-value) and occurrence of focal albumin extravasation (r(s)=0.33; p=0.04). The present findings are in agreement with our earlier studies where we have seen increased BBB permeability immediately and 14 days after exposure. We here discuss the present findings as well as the previous results of altered BBB permeability from our and other laboratories.

Blood-brain barrier permeability and nerve cell damage in rat brain 14 and 28 days after exposure to microwaves from GSM mobile phones

We investigated the effects of global system for mobile communication (GSM) microwave exposure on the permeability of the blood-brain barrier and signs of neuronal damage in rats using a real GSM programmable mobile phone in the 900 MHz band. Ninety-six non-anaesthetized rats were either exposed to microwaves or sham exposed in TEM-cells for 2 h at specific absorption rates of average whole-body Specific Absorption Rates (SAR) of 0.12, 1.2, 12, or 120 mW/kg. The rats were sacrificed after a recovery time of either 14 or 28 d, following exposure and the extravazation of albumin, its uptake into neurons, and occurrence of damaged neurons was assessed. Albumin extravazation and also its uptake into neurons was seen to be enhanced after 14 d (Kruskal Wallis test: p = 0.02 and 0.002, respectively), but not after a 28 d recovery period. The occurrence of dark neurons in the rat brains, on the other hand, was enhanced later, after 28 d (p = 0.02). Furthermore, in the 28-d brain samples, neuronal albumin uptake was significantly correlated to occurrence of damaged neurons (Spearman r = 0.41; p < 0.01).

Histopathological examinations of rat brains after long-term exposure to GSM-900 mobile phone radiation

In order to mimic the real life situation, with often life-long exposure to the electromagnetic fields emitted by mobile phones, we have investigated in a rat model the effects of repeated exposures under a long period to Global System for Mobile Communication-900 MHz (GSM-900) radiation. Out of a total of 56 rats, 32 were exposed once weekly in a 2-h period, for totally 55 weeks, at different average whole-body specific absorption rates (SAR) (of in average 0.6 and 60 mW/kg at the initiation of the experimental period). The animals were exposed in a transverse electromagnetic transmission line chamber (TEM-cell) to radiation emitted by a GSM-900 test phone. Sixteen animals were sham exposed and eight animals were cage controls, which never left the animal house. After behavioural tests, 5-7 weeks after the last exposure, the brains were evaluated for histopathological alterations such as albumin extravasation, dark neurons, lipofuscin aggregation and signs of cytoskeletal and neuritic neuronal changes of the type seen in human ageing. In this study, no significant alteration of any these histopathological parameters was found, when comparing the GSM exposed animals to the sham exposed controls.

Radiofrequency and extremely low-frequency electromagnetic field effects on the blood-brain barrier

During the last century, mankind has introduced electricity and during the very last decades, the microwaves of the modern communication society have spread a totally new entity--the radiofrequency fields--around the world. How does this affect biology on Earth? The mammalian brain is protected by the blood-brain barrier, which prevents harmful substances from reaching the brain tissue. There is evidence that exposure to electromagnetic fields at non thermal levels disrupts this barrier. In this review, the scientific findings in this field are presented. The result is a complex picture, where some studies show effects on the blood-brain barrier, whereas others do not. Possible mechanisms for the interactions between electromagnetic fields and the living organisms are discussed. Demonstrated effects on the blood-brain barrier, as well as a series of other effects upon biology, have caused societal anxiety. Continued research is needed to come to an understanding of how these possible effects can be neutralized, or at least reduced. Furthermore, it should be kept in mind that proven effects on biology also should have positive potentials, e.g., for medical use.

Cognitive impairment in rats after long-term exposure to GSM-900 mobile phone radiation

Considering the frequent use of mobile phones, we have directed attention to possible implications on cognitive functions. In this study we investigated in a rat model the long-term effects of protracted exposure to Global System for Mobile Communication-900 MHz (GSM-900) radiation. Out of a total of 56 rats, 32 were exposed for 2 h each week for 55 weeks to radio-frequency electromagnetic radiation at different SAR levels (0.6 and 60 mW/kg at the initiation of the experimental period) emitted by a (GSM-900) test phone. Sixteen animals were sham exposed and eight animals were cage controls, which never left the animal house. After this protracted exposure, GSM-900 exposed rats were compared to sham exposed controls. Effects on exploratory behaviour were evaluated in the open-field test, in which no difference was seen. Effects on cognitive functions were evaluated in the episodic-like memory test. In our study, GSM exposed rats had impaired memory for objects and their temporal order of presentation, compared to sham exposed controls (P = 0.02). Detecting the place in which an object was presented was not affected by GSM exposure. Our results suggest significantly reduced memory functions in rats after GSM microwave exposure (P = 0.02).

Neuroblastomas and medulloblastomas exhibit more Coxsackie adenovirus receptor expression than gliomas and other brain tumors

Adenoviral vector-mediated treatment is a potential therapy for tumors of the central nervous system. To obtain a significant therapeutic effect by adenoviral vectors, a sufficient infection is required, the power of which depends predominantly on the level of Coxsackie adenovirus receptors. We stained surgical biopsies of central nervous system tumors and neuroblastomas for Coxsackie adenovirus receptors. For gliomas, the level of the receptor was low and markedly variable among individual tumors. By contrast, neuroblastomas and medulloblastomas exhibited a higher degree of Coxsackie adenovirus receptor expression than gliomas and other brain tumors. We conclude that neuroblastomas and medulloblastomas could be suitable for adenovirus-mediated gene therapy. Adverse effects of the treatment, however, must be considered because neurons and reactive astrocytes also express a significant amount of the receptor.

Genetic intratumour heterogeneity in high-grade brain tumours is associated with telomere-dependent mitotic instability

Glioblastoma multiforme (GBM) and other high-grade brain tumours are typically characterized by complex chromosome abnormalities and extensive intratumour cytogenetic heterogeneity. The mechanisms behind this diversity have been little explored. In this study, we analysed the pattern of chromosome segregation at mitosis in 20 brain tumours. We found an abnormal segregation of chromatids at mitosis through anaphase bridging (10-25% of anaphase cells) in all 10 GBMs. Anaphase bridging was also found in two medulloblastomas (7-15%), one anaplastic astrocytoma (17%) and one oligodendroglioma (6%). These tumours showed a relatively high degree of cytogenetic complexity and heterogeneity. In contrast, cell division abnormalities were not found in low-grade brain tumours with less complex karyotypes, including two pilocytic astrocytomas and two ependymomas. Further analysis of two GBMs by fluorescence in situ hybridization with telomeric repeat probes revealed excessive shortening of TTAGGG repeats, indicating dysfunctional protection of chromosome ends. In xenografts established from these GBMs, there was a gradual reduction in cytogenetic heterogeneity through successive passages as the proportion of abnormally short telomeres was reduced and the frequency of anaphase bridges decreased from >25% to 0. However, bridging could be reintroduced in late-passage xenograft cells by pharmacological induction of telomere shortening, using a small-molecule telomerase inhibitor. Telomere-dependent abnormal segregation of chromosomes at mitosis is thus a common phenomenon in high-grade brain tumours and may be one important factor behind cytogenetic intratumour diversity in GBM.

Postimmunization with IFN-γ-Secreting Glioma Cells Combined with the Inducible Nitric Oxide Synthase Inhibitor Mercaptoethylguanidine Prolongs Survival of Rats with Intracerebral Tumors

High-grade gliomas are one of the most aggressive human tumors with <1% of patients surviving 5 years after surgery. Immunotherapy could offer a possibility to eradicate remnant tumor cells after conventional therapy. Experimental immunotherapy can induce partial cure of established intracerebral tumors in several rodent models. One reason for the limited therapeutic effects could be immunosuppression induced by both the growing tumor and the induced immune reaction. NO has been implicated in tumor-derived immune suppression in tumor-bearing hosts, and unspecific inhibitors of NO synthase have been shown to boost antitumor immunity. In this study, we show that the inducible NO synthase (iNOS)-specific inhibitor mercaptoethylguanidine (MEG) superiorly enhanced lymphocyte reactivity after polyclonal stimulation compared with the iNOS-specific inhibitor L-NIL and the unspecific NO synthase inhibitor L-NAME. Both iNOS inhibitors increased the number and proliferation of T cells but not of B cells. When combined during postimmunization with IFN-gamma-secreting N32 rat glioma cells of rats harboring intracerebral tumors, only MEG increased the cure rate. However, this was only achieved when MEG was administered after immunizations. These findings implicate that NO has both enhancing and suppressive effects after active immunotherapy.

Low dose Zebularine treatment enhances immunogenicity of tumor cells

STRATEGY

We have investigated how alterations in gene expression induced by the demethylating drug Zebularine affect the immune response tumor cells elicit. The rational has been to treat syngeneic rat colon cancer cells with Zebularine at different concentrations and then use these cells to study gene expression of different genes involved in cancer immunogenicity. Gene expressions were monitored by semi-quantitative PCR and real-time PCR.

RESULTS

Intriguingly there was a large increase in the production of indoleamine 2,3-dioxygenase (IDO) after treatment with 100 microM Zebularine as compared with untreated tumor cells, whereas treatment with 20 microM Zebularine caused a significant decrease of the IDO production. After immunization with syngeneic tumor cells, spleen cells were isolated and restimulated in vitro with irradiated tumor cells. Immune reactivity was measured by proliferation, and production of interferon gamma and interleukin10. The immunogenicity of tumor cells treated in vitro with a low dose of Zebularine increased, whereas it decreased after high dose exposure. The inhibition of immunogenicity by 100 microM Zebularine was shown to be counteracted by the IDO inhibitor 1-methyl-tryptophan (1 MT), confirming that this effect of Zebularine is mainly caused by IDO induction. Differences using Zebularine-treated or non-treated cells for in vitro restimulation were marginal.

CONCLUSION

Low dose treatment with Zebularine (20 microM) decreases the production of the immunosuppressive IDO from rat colon cancer cells and enhances their immunogenicity, whereas high dose Zebularine treatment (100 microM) enhances the IDO production from the cancer cells and suppresses their immunogenicity. This immunosuppression should be considered when cancer is treated with Zebularine or drugs acting in a similar way.

Lentiviral vector mediated siRNA knock-down of hTERT results in diminished capacity in invasiveness and in vivo growth of human glioma cells in a telomere length-independent manner

Glioma cells are characterized by their invasiveness and resistance against conventional therapeutics. Telomerase activity has been suggested to be an important target for glioma treatment. Here we assessed the anticancer effects and its potential mechanisms of lentiviral vector mediated siRNA knock-down of the human telomerase reverse transcriptase (hTERT) in U87MG human glioblastoma cells. Stable expression of anti-hTERT siRNA reduced the hTERT expression and TRAP assay telomerase activity to barely detectable levels. Injection of lentiviral vectors encoding anti-hTERT siRNA significantly inhibited the growth of pre-established macroscopic xenograft tumors, which was in contrast to the finding that no obvious effects on cell growth, cell cycle progression and telomere length were observed in anti-hTERT siRNA expressing U87MG cells during short-term in vitro cultures. The in vivo glioma growth inhibition effect was already evident in the period coincided with no detectable telomere length changes, suggesting that hTERT inhibition may hinder glioma cell growth in a telomere length-independent manner. Importantly, transwell migration assay showed profound inhibitory effect on the invasive capacity of U87MG cells following short-term anti-hTERT siRNA expression. Thus, efficient knock-down of hTERT can inhibit glioma cell proliferation and migration prior to its effect on telomere length.

Microarray analysis of gliomas reveals chromosomal position-associated gene expression patterns and identifies potential immunotherapy targets

Gliomas are among the most aggressive malignant tumors and the most refractory to therapy, in part due to the propensity for malignant cells to disseminate diffusely throughout the brain. Here, we have used 27 K cDNA microarrays to investigate global gene expression changes between normal brain and high-grade glioma (glioblastoma multiforme) to try and better understand gliomagenesis and to identify new therapeutic targets. We have also included smaller groups of grade II and grade III tumors of mixed astrocytic and oligodendroglial origin as comparison. We found that the expression of hundreds of genes was significantly correlated to each group, and employed a naïve Bayesian classifier with leave-one-out cross-validation to accurately classify the samples. We developed a novel algorithm to analyze the gene expression data from the perspective of chromosomal position, and identified distinct regions of the genome that displayed coordinated expression patterns that correlated significantly to tumor grade. The regions identified corresponded to previously known genetic copy number changes in glioma (e.g. 10q23, 10q25, 7q, 7p) as well as regions not previously associated significantly with glioma (e.g. 1p13, 6p22). Furthermore, to enrich for more suitable targets for therapy, we took a bioinformatics approach and annotated our signatures with two published datasets that identified membrane/secreted genes from cytosolic genes. The resulting focused list of 31 genes included interesting novel potential targets as well as several proteins already being investigated for immunotherapy (e.g. CD44 and tenascin-C). Software for the chromosome analysis was developed and is freely available at http://base.thep.lu.se.

Inhibition of inducible nitric oxide synthase enhances anti-tumour immune responses in rats immunized with IFN-gamma-secreting glioma cells

Interferon gamma (IFN-gamma) has successfully been used in immunotherapy of different experimental tumours. Mechanistically, IFN-gamma has extensive effects on the immune system including release of nitric oxide (NO) by upregulation of the inducible nitric oxide synthase (iNOS). NO has putative immunosuppressive effects but could also play a role in killing of tumour cells. Therefore, the aim of the present study was to clarify whether inhibition of iNOS in rats immunized with glioma cells (N32) producing IFN-gamma (N32-IFN-gamma), could enhance the anti-tumour immune response. Initially, both a selective iNOS, l-N(6)-(1-Iminoethyl)-l-lysine (l-NIL), and non-selective, N-nitro-l-arginine methyl ester (l-NAME), inhibitor of NOS were tested in vitro. After polyclonal stimulation with LPS and SEA, both l-NIL and l-NAME enhanced proliferation and production of IFN-gamma from activated rat splenocytes and this effect was inversely correlated to the production of NO. However, l-NIL had a broader window of efficacy and a lower minimal effective dose. When rats were immunized with N32-IFN-gamma, and administered NOS inhibitors by intraperitoneal (i.p.) mini-osmotic pumps, only splenocytes of rats treated with l-NIL, but not l-NAME, displayed an enhanced proliferation and production of IFN-gamma when re-stimulated with N32 tumour cells. Based on these findings, l-NIL was administered concurrently with N32-IFN-gamma cells to rats with intracerebral (i.c.) tumours resulting in a prolonged survival. These results show that inhibition of iNOS can enhance an IFN-gamma-based immunotherapy of experimental i.c. tumours implying that NO released after immunization has mainly immunosuppressive net effects.

99mTc-DTPA Uptake and Electrical Impedance Measurements in Verification ofIn VivoElectropermeabilization Efficiency in Rat Muscle

OBJECTIVE

In vivo electropermeabilization of cell membranes in rat muscle tissue cause a significant decrease of the electrical impedance, in the frequency region of 1-10 kHz. We aimed to study how the 99mTc-DTPA uptake in the electropermeabilized region correlates to the change of admittance Y = 1/absZ, where Z is the measured impedance.

METHODS

The electropermeabilization was performed in vivo by applying high-voltage (0.5-2 kV) short (0.1-2 ms) pulses through gold-plated needle electrodes in skeletal muscle. The impedance was measured before and after each electropermeabilization pulse. The uptake of 99mTc-DTPA uptake in the electropermeabilized region was measured after 6 and 24 hours with a gamma camera.

RESULTS

The pulse shape (square and exponential), duration, and amplitude of the applied electric field were varied, and electropermeabilization efficiency was evaluated using the various measurement modalities. Good correlations were found (correlation coefficient approximately 0.9) between the 99mTc-DTPA uptake in the electropermeabilized and control "region of interest" the admittance ratio Y (post-treatment)/Y (pretreatment), and charge displacement parameter Q.

CONCLUSION

The electrical impedance measurements method can be utilized in clinical settings to verify the efficiency of electropermeabilization applied to chemotherapy and to power RNAi (RNA-interference) and DNA-plasmid transfection in vaccination, immunization, and gene-therapy.

Dynamic susceptibility contrast-enhanced perfusion magnetic resonance (MR) imaging combined with contrast-enhanced MR imaging in the follow-up of immunogene-treated glioblastoma multiforme

PURPOSE

To assess the value of the combined use of dynamic susceptibility contrast-enhanced perfusion magnetic resonance imaging (MRI) and conventional contrast-enhanced MRI for the follow-up of treatment of glioblastoma multiforme (GBM).

MATERIAL AND METHODS

79 examinations were performed in six surgically and immunogene-treated patients and two surgically treated patients. Ratios of the relative cerebral blood volume (rCBV) in lesions and in the contralateral normal-appearing white matter were calculated. The regions with elevated rCBV were compared with those with contrast enhancement. Tissue specimens from surgical biopsies and autopsies were studied histopathologically.

RESULTS

The lesion-to-normal rCBV ratios were high in the tumors prior to operation (7.3 to 18.2) as well as in the recurrent tumors (1.6 to 13.2). The volumes of the regions with elevated rCBV were similar to those with contrast enhancement in 63 of the 79 examinations. However, in 11 of 79 examinations, the regions with high rCBV were smaller than the regions with contrast enhancement ("mismatch"). In two samples from the immunogene-treated patients this was correlated with the histopathological finding of malignant tumor with numerous proliferating GBM vessels with multiple minimal lumina, sometimes thrombotized or ruptured. These vessels may have increased permeability with contrast enhancement not accompanied by increased microvascular volume.

CONCLUSION

1) Elevated rCBV on perfusion MRI corresponding to the contrast-enhancing lesion supports the diagnosis of recurrent malignant tumor. 2) A mismatch showing a volume of rCBV elevation smaller than that of contrast enhancement can be seen in particularly aggressive tumor growth and is thus not always a sign of reactive non-tumor changes. 3) The combination of perfusion MRI and conventional contrast MRI provides useful information in the follow-up of glioblastoma multiforme treatment.

Coxsackievirus and adenovirus receptor expression in non-malignant lung tissues and clinical lung cancers

Adenoviral vector mediated gene delivery has been applied in clinical trials and mechanistic studies to explore new treatment approaches for lung cancers. The expression of coxsackievirus adenovirus receptor (CAR), the primary receptor for the most commonly used adenovirus serotype 5 (Ad5)-based vectors, predominantly determines the permissiveness of lung cancer cells. CAR expression is also suggested to modulate tumor cell proliferation capacity. Here, we studied CAR expression in archival lung cancer specimens by using well-characterized CAR 72 antibodies. High levels of CAR expression were observed in most of the 32 cases of squamous cell carcinoma lung cancers and in all the five cases of small cell lung cancers investigated. In contrast, high levels of CAR expression were detected only in 6 of 22 adenocarcinoma lung cancers. The relative levels of CAR expression did not correlate with the pathologic grade in lung cancers, and was thus inconsistent with a role of modulating cancer cell proliferation. Of note, CAR expression was not detected in non-malignant alveolar cells. Our data suggest a preferred utility of Ad5 vector mediated gene delivery to squamous cell carcinoma lung cancers, small cell lung cancers, but not to the majority of adenocarcinoma lung cancers.

Human short-term repopulating cells have enhanced telomerase reverse transcriptase expression

Telomerase activity has been suggested to be critically involved in hematopoietic stem cell (HSC) self-renewal. However, it has been unclear whether human HSCs have telomerase activity and how telomerase activity is regulated within the HSC and progenitor pool. Here, we isolated living cord-blood (CB) CD34+ cells with up-regulated human telomerase reverse transcriptase (hTERT) expression by using an hTERT-reporting adenoviral vector encoding destabilized green fluorescent protein (dGFP) driven by the hTERT promoter, and functionally characterized them in comparison with control vector–transduced CD34+ cells expressing GFP. Following a 2-day serum-free transduction protocol, cells were sorted into a dGFP+ and a GFP+ fraction. Cell-cycle analysis revealed that the dGFP+ cells had a greater proportion of cells in S/G2/M phase compared with the GFP+ cells, (56% ± 1.8% vs 35% ± 4.3%; P < .001) and fewer cells in G0 phase (8.1% ± 3.0% vs 20% ± 4.7%; P < .01) However, the colony-forming and short-term nonobese diabetic/severe combined immunodeficient (NOD/SCID) B2m–/– mice bone marrow–repopulating capacities were similar between the dGFP+ and the GFP+ cells. Interestingly, the dGFP+ cells had a 6-fold lower repopulating capacity in NOD/SCID mice compared with the GFP+ cells and lacked secondary NOD/SCID B2m–/– mice bone marrow–repopulating capacity. Thus, up-regulation of hTERT expression within the CB HSC pool is accompanied by decreased self-renewal capacity.

Detection of cell cycle- and differentiation stage-dependent human telomerase reverse transcriptase expression in single living cancer cells

Elevated telomerase activity is an important molecular signature of cancer cells and primitive cells in regenerative tissues. However, isolation of single living cells with endogenous telomerase activity has not yet been possible. Here, we developed adenovirus serotype 35 tropism-based vectors encoding destabilized enhanced green fluorescence protein with a half-life of 2 h (d2EGFP) driven by the human telomerase reverse transcriptase (hTERT) promoter. As assessed in telomerase-positive or -negative cell lines, the d2EGFP expression positively correlated with hTERT transcript content and telomerase activity. In retinoic acid-induced differentiating HL-60 cells, the d2EGFP expression is diminished in the same manner as the hTERT expression. Individual cells from HeLa and HL-60 cell lines exhibited heterogeneous d2EGFP expression, which was cell cycle dependent, as the sorted d2EGFP+ HL-60 cells contained twice as many cells in S/G2/M phase of the cell cycle compared with the d2EGFP- HL-60 cells. However, both cell populations exhibited the same proliferation and regeneration capacities. Heterogeneous d2EGFP expression was also detected in xenograft glioblastoma multiforme cells with tumor formation capacity. Thus, d2EGFP expression reported cell cycle- and differentiation stage-dependent hTERT expression. Our study facilitates isolation and characterization of single living cells with telomerase activity.

Glioma stem cells: evidence and limitation

Gliomas, in particular the high-grade anaplastic glioma and glioblastoma multiforme (GBM), are manifested by morphological, genetic and phenotypic heterogeneity. Most of the studies hitherto have been performed on bulk glioma cells, with limited understanding on the origin and the relative contribution of particular glioma cell populations to glioma growth and progression. Recent studies have demonstrated the existence of a small fraction of glioma cells endowed with features of primitive neural progenitor cells and tumor-initiating function. Such cells have been defined as glioma stem cells. However, questions remain as to whether the currently identified glioma stem cells are the cell-of-origin for glioma initiation and progression, or the results of such processes. In this review, we discuss the current evidence and limitation in identifying glioma stem cells and the potential origin of glioma stem cells in the context of post-natal neural cell regeneration and their transformation mechanisms. The implication of these findings for glioma diagnosis and treatment will also be reviewed.

Exposure of rat brain to 915 MHz GSM microwaves induces changes in gene expression but not double stranded DNA breaks or effects on chromatin conformation

We investigated whether exposure of rat brain to microwaves (MWs) of global system for mobile communication (GSM) induces DNA breaks, changes in chromatin conformation and in gene expression. An exposure installation was used based on a test mobile phone employing a GSM signal at 915 MHz, all standard modulations included, output power level in pulses 2 W, specific absorption rate (SAR) 0.4 mW/g. Rats were exposed or sham exposed to MWs during 2 h. After exposure, cell suspensions were prepared from brain samples, as well as from spleen and thymus. For analysis of gene expression patterns, total RNA was extracted from cerebellum. Changes in chromatin conformation, which are indicative of stress response and genotoxic effects, were measured by the method of anomalous viscosity time dependencies (AVTD). DNA double strand breaks (DSBs) were analyzed by pulsed-field gel electrophoresis (PFGE). Effects of MW exposure were observed on neither conformation of chromatin nor DNA DSBs. Gene expression profiles were obtained by Affymetrix U34 GeneChips representing 8800 rat genes and analyzed with the Affymetrix Microarray Suite (MAS) 5.0 software. In cerebellum from all exposed animals, 11 genes were upregulated in a range of 1.34-2.74 fold and one gene was downregulated 0.48-fold (P < .0025). The induced genes encode proteins with diverse functions including neurotransmitter regulation, blood-brain barrier (BBB), and melatonin production. The data shows that GSM MWs at 915 MHz did not induce PFGE-detectable DNA double stranded breaks or changes in chromatin conformation, but affected expression of genes in rat brain cells.

Activation of purified allogeneic CD4+ T cells by rat bone marrow-derived dendritic cells induces concurrent secretion of IFN-γ, IL-4, and IL-10

Dendritic cells (DCs) are highly specialized antigen-presenting cells that play a key role in the initiation and regulation of immune responses. The ability of DCs to process antigens and the outcome of their interaction with T cells are largely dependent on phenotype as well as maturation state of DCs. In this study, we generated DCs from rat bone marrow precursors. Bone marrow cells cultured in the presence of granulocyte macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-4, and Flt-3 ligand (FL) produced immature DCs that expressed intermediate levels of major histocompatibility complex (MHC) class II, low levels of CD80 and CD86 molecules and displayed a high capacity of endocytosis. Bone marrow-derived DCs (BMDCs) matured in the presence of lipopolysaccharide (LPS) upregulated expression of MHC class II, CD80 and CD86, while their phagocytic capacity was dramatically reduced. Mature BMDCs stimulated vigorous proliferation of purified allogeneic CD4(+) T cells in a primary mixed leukocyte reaction (MLR) and elicited a mixed cytokine profile in allogeneic CD4(+) T cells: DCs activated CD4(+) T cells to produce interferon (IFN)-gamma, IL-4, and IL-10. Thus, rat BMDCs effectively internalize antigens and stimulate T cell proliferation but fail to induce an unidirectional polarization of T helper (T(H)) cells and in this respect differ from both human and mouse DCs.

Immunotreatment in patients with glioblastoma multiforme--a histopathological evaluation of reactive and inflammatory changes

Glioblastoma multiforme (GBM) is the most common highly malignant brain tumor and is also one among the most therapy-resistant human neoplasias. At the University Hospital in Lund, a group of patients with GBM were treated with a new therapy form attempting immunization by glioma cells transfected to produce interferon-gamma. The purpose of this report was to evaluate tumor material from the first nine patients treated with this therapy, assessing the levels of inflammatory/reactive cells (lymphocytes and macrophages). Tumor biopsies from surgery performed at different time points during treatment were analyzed with conventional histotechnical methods and immunohistochemistry. A post-mortem neuropathological investigation with a whole brain assessment was achieved in 5 immunized patients. The results show that cytotoxic T lymphocytes exhibited a mild increase during immunotreatment. This increase indicates an invoked stimulation of a cytotoxic T cell reaction, which may prove beneficial when immunization is adequately manipulated in dosage and timing.

Oncostatin M signaling in human glioma cell lines

We have recently found that oncostatin M (OSM) is overexpressed in most human brain tumors. The effects of OSM are unclear with conflicting reports of growth stimulatory or inhibitory effects in various cell types. The aim of this study was to investigate the effects of OSM in 5 glioma cell lines and 7 short-term cultures of human gliomas and in normal cultured human astrocytes. None of the cell lines and short-term cultured tumor cells expressed OSM in vitro. OSM signals through a gp130 containing receptor complex over the JAK/STAT pathway. Immunofluorescence and RT-PCR analysis showed that the tumor cells express gp130 and the other receptor components, LIFRbeta and OSMRbeta. OSM treatment induced phosphorylation of STAT3 and STAT1 indicating presence of a functional JAK/STAT pathway. No OSM effect on proliferation was observed. OSM gave no protective effects against tumor necrosis factor-related apoptosis inducing ligand (TRAIL)-induced cytotoxicity.

Efficient internalization into low-passage glioma cell lines using adenoviruses other than type 5: an approach for improvement of gene delivery to brain tumours

There is a need for improvement of the commonly used adenovirus vectors based on serotype 5. This study was performed on three adenovirus serotypes with a CAR-binding motif (Ad4p, Ad5p and Ad17p) and three non-CAR-binding serotypes (Ad11p, Ad16p and Ad21p). The capacity of these alternative adenovirus vector candidates to deliver DNA into low-passage glioma cell lines from seven different donors was evaluated. The non-CAR-binding serotype Ad16p was the most efficient serotype with regard to import of its DNA, as well as initiation of hexon protein expression. Ad16p established hexon expression in 60–80 % of the cell population in gliomas from all donors tested. The other non-CAR-binding serotypes, Ad11p and Ad21p, showed hexon expression in 25–60 and 40–80 % of cells, respectively. The corresponding figure for the best CAR-binding serotype, Ad5p, was only 25–65 %, indicating greater variability between cells from different donors than serotype Ad16p had. The other CAR-binding serotypes, Ad4p and Ad17p, were refractory to some of the gliomas, giving a maximum of only 45 and 40 % hexon expression, respectively, in the most permissive cells. Interestingly, the transduction capacity of the CAR-binding serotypes was not correlated to the level of CAR expression on the cells.

Quality assurance of patient dosimetry in boron neutron capture therapy

The verification of the correctness of planned and executed treatments is imperative for safety in radiotherapy. The purpose of the present work is to describe and evaluate the quality assurance (QA) procedures for patient dosimetry implemented at the boron neutron capture therapy (BNCT) facility at Studsvik, Sweden. The dosimetric complexity of the mixed neutron-photon field during BNCT suggests a careful verification of routine procedures, specifically the treatment planning calculations. In the present study, two methods for QA of patient dosimetry are presented. The first is executed prior to radiotherapy and involves an independent check of the planned absorbed dose to be delivered to a point in the patient for each treatment field. The second QA procedure involves in vivo dosimetry measurements using post-treatment activation analysis. Absorbed dose conversion factors taking the difference in material composition and geometry of the patient and the PMMA phantom used for reference dosimetry were determined using the Monte Carlo method. The agreement of the QA procedure prior to radiotherapy reveals an acceptably small deviation for 60 treatment fields of +/-4.2% (1 SD), while the in vivo dosimetry method presented may benefit from improvements, as the deviations observed were quite substantial (+/- 12%, 1 SD), and were unlikely to be due to actual errors in the clinical dosimetry

A model for evaluating therapeutic response of combined cancer treatment modalities: applied to treatment of subcutaneously implanted brain tumors (N32 and N29) in Fischer rats with pulsed electric fields (PEF) and 60Co-gamma radiation (RT)

The aim of the present study is to develop a mathematical model for evaluating therapeutic response of combined treatment modalities. The study was performed in rats of the Fischer-344 strain with rat glioma N32 or N29 tumors implanted subcutaneously on the thigh of the hind leg. Pulsed electric fields, PEF, with 16 exponentially decaying pulses with a maximum electric field strength of 140 V/mm and t(1/e)= 1 ms were first applied to the tumors. Then within 5 min radiation therapy with (60)Co-gamma radiation, RT, was given in daily fractions of 5 Gy. The animals were arranged into one group of controls and 3 groups of different kind of treatments: PEF only, RT only or combination of PEF + RT. At about 4 weeks after inoculation, the tumors were given the treatment sessions during one week. In 2 experimental series with totally 52 rats with N32 tumors, of which 16 were controls, were given 4 sessions of PEF treatments and RT (totally 20 Gy). In a special experimental series with totally 56 rats with N32 tumors, of which 10 were controls, the different groups were given 1, 2, 3 or 4 treatment sessions respectively. Another strain of glioma tumor, N29 with 62 tumors of which 14 were controls was studied in 2 series given 4PEF + 4RT and 2PEF + 4RT respectively. Fitting the data obtained from consecutive measurements of tumor volume (TV) of each individual tumor to an exponential model TV = TV(0). exp[TGR.t] estimated the tumor growth rate (TGR % per day) after the first day of treatment (t = 0). The TGR of N32 tumors treated with the combination of 4PEF + 4RT are significantly decreased compared to the controls (p < 0.0001), compared to RT alone (p < 0.0001) and compared to PEF alone (p < 0.001). The combined treatment of N32 gives significant effect on the tumor growth rate after 2, 3 and 4 treatment session while RT alone seems to be most efficient after one treatment of 5 Gy and PEF alone is most efficient after 2 treatments at 2 consecutive days. The TGR of N29 tumors treated with the combination of 4PEF + 4RT are significantly decreased compared to the controls (p < 0.05) but the combination of 2PEF + 4RT was more effective (p < 0.005). The specific therapeutic effect STE is defined as the difference between the average tumor growth rates of controls and exposed tumors divided by the average tumor growth rate of the controls. With 4PEF treatments alone the average STE value was 0.32 for N32 tumors and 0 for N29; for 4RT alone the STE values were 0.29 and 0.42 respectively, and for combined treatments 4PEF + 4RT 0.67 and 0.17 respectively. For the N29 tumors treated with 2PEF + 4RT the STE value was 0.53. The therapeutic enhancement ratio, TER, value increase with the number of treatment sessions and the TER of the combined treatments is above 1 in two of the N32 series, which indicates a synergistic effect of 4PEF + 4RT. This work demonstrate the use of our model for analyzing the combination PEF + RT, but it can also be used for evaluation the therapeutic effects of combining RT with chemotherapy or immunogenetic therapy.