Characterization of Ablation Thresholds for 3D-Cultured Patient-Derived Glioma Stem Cells in Response to High-Frequency Irreversible Electroporation.

High-frequency irreversible electroporation (H-FIRE) is a technique that uses pulsed electric fields that have been shown to ablate malignant cells. In order to evaluate the clinical potential of H-FIRE to treat glioblastoma (GBM), a primary brain tumor, we have studied the effects of high-frequency waveforms on therapy-resistant glioma stem-like cell (GSC) populations. We demonstrate that patient-derived GSCs are more susceptible to H-FIRE damage than primary normal astrocytes. This selectivity presents an opportunity for a degree of malignant cell targeting as bulk tumor cells and tumor stem cells are seen to exhibit similar lethal electric field thresholds, significantly lower than that of healthy astrocytes. However, neural stem cell (NSC) populations also exhibit a similar sensitivity to these pulses. This observation may suggest that different considerations be taken when applying these therapies in younger versus older patients, where the importance of preserving NSC populations may impose different restrictions on use. We also demonstrate variability in threshold among the three patient-derived GSC lines studied, suggesting the need for personalized cell-specific characterization in the development of potential clinical procedures. Future work may provide further useful insights regarding this patient-dependent variability observed that could inform targeted and personalized treatment.

Hybrid mathematical model of glioma progression.

OBJECTIVES: Gliomas are an important form of brain cancer, with high mortality rate. Mathematical models are often used to understand and predict their behaviour. However, using current modeling techniques one must choose between simulating individual cell behaviour and modeling tumours of clinically significant size. MATERIALS AND METHODS: We propose a hybrid compartment-continuum-discrete model to simulate glioma growth and malignant cell invasion. The discrete portion of the model is capable of capturing intercellular interactions, including cell migration, intercellular communication, spatial cell population heterogeneity, phenotype differentiation, epigenetic events, proliferation, and apoptosis. Combining this with a compartment and continuum model allows clinically significant tumour sizes to be evaluated. RESULTS AND CONCLUSIONS: This model is used to perform multiple simulations to determine sensitivity to changes in important model parameters, specifically, the fundamental length parameter, necrotic cell degradation rate, rate of cell migration, and rate of phenotype transformation. Using these values, the model is able to simulate tumour growth and invasion behaviour, observed clinically. This mathematical model provides a means to simulate various tumour development scenarios, which may lead to a better understanding of how altering fundamental parameters can influence neoplastic progression.

Soluble monomeric EphrinA1 is released from tumor cells and is a functional ligand for the EphA2 receptor.

The ephrinA1 ligand exerts antioncogenic effects in tumor cells through activation and downregulation of the EphA2 receptor and has been described as a membrane-anchored protein requiring clustering for function. However, while investigating the ephrinA1/EphA2 system in the pathobiology of glioblastoma multiforme (GBM), we uncovered that ephrinA1 is released from GBM and breast adenocarcinoma cells as a soluble, monomeric protein and is a functional form of the ligand in this state. Conditioned media containing a soluble monomer of ephrinA1 caused EphA2 internalization and downregulation, dramatic alteration of cell morphology and suppression of the Ras-MAPK pathway. Moreover, soluble monomeric ephrinA1 was functional in a physiological context, eliciting collapse of embryonic neuronal growth cones. We also found that ephrinA1 is cleaved from the plasma membrane of GBM cells, an event which involves the action of a metalloprotease. Thus, the ephrinA1 ligand can, indeed, function as a soluble monomer and may act in a paracrine manner on the EphA2 receptor without the need for juxtacrine interactions. These findings have important implications for further deciphering the function of these proteins in pathology and physiology, as well as for the design of ephrinA1-based EphA2-targeted antitumor therapeutics.

Molecular targeting of malignant gliomas with novel multiply-mutated interleukin 13-based cytotoxins.

A vast majority of high-grade gliomas over-express a receptor for interleukin 13 (IL13). This glioma-associated receptor for IL13 is interleukin 4 (IL4)-independent. This is in contrast to the physiological and IL4-shared receptor for the IL13, IL13/4 receptor, which is found on many normal organs. IL13-based Pseudomonas exotoxin (PE)-containing cytotoxic fusion proteins have been shown to be very potent anti-glioma agents. However, native IL13-based cytotoxins interact with both forms of the IL13 receptor. Therefore, mutations in IL13 were made in order to diminish/eliminate IL13's interaction with the shared IL13/4 receptor of normal tissue. These mutations encompassed amino acids located on alpha-helix A and C of IL13. We have engineered double or triple mutants of IL13 linked to various forms of PE. We found that these mutations could be successfully incorporated into IL13 without the loss of the protein's ability to selectively deliver the toxin to glioma cells while reducing their toxicity.

VEGF-D is an X-linked/AP-1 regulated putative onco-angiogen in human glioblastoma multiforme.

BACKGROUND: Glioblastoma multiforme (GBM) is a hypervascularized and locally infiltrating brain tumor of astroglial origin with a very poor prognosis. An X-linked c-fos oncogene-inducible mitogenic, morphogenic, and angiogenic factor, endothelial growth factor-D (VEGF-D), is the newest mammalian member of VEGF family. We analyzed VEGF-D in GBM because of its high angiogenic potential and its linkage to the X chromosome. MATERIALS AND METHODS: Nonmalignant brain and GBM tissue sections as well as GBM cell lines were analyzed by immunofluorescence for the expression of VEGF-D, factor VIII (endothelial cell marker), glial-fibrillary acidic protein (GFAP) (astrocytic cell lineage cytoplasmic marker), and several Fos family transcription factors, including c-Fos and Fra-1. The proteins were also detected by Western blots. The differences between genotypes of normal brain and GBM cells were examined by cDNA microarrays. RESULTS AND CONCLUSIONS: GBM expressed ubiquitously VEGF-D, which colocalized with GFAP. Contrary to our expectations, low levels of c-Fos were detected in GBM cells. However, we identified another Fos family member, Fra-1, together with its transcriptional activation partner, c-Jun, as being stably up-regulated in GBM cells. Furthermore, we demonstrated that a fra-1 transgene induced VEGF-D expression in cultured cells and GBM cell stimulation evoked a sustained increase in both Fra-1 and VEGF-D levels. This study reveals that an up-regulation of AP-1 factors may be a hallmark of GBM. Because VEGF-D activates VEGF receptor 2 and 3, receptors important for tumor angiogenesis, it may represent an X-linked/AP-1-regulated onco-angiogen in human GBM. The VEGF-D system and AP-1 activity appear to be very attractive targets for new molecular diagnostics and rational molecular anti-cancer therapies.

Expression of a restrictive receptor for interleukin 13 is associated with glial transformation.

We have previously documented that the vast majority of high-grade gliomas over-express binding sites for interleukin 13 (IL13) in situ. We now extend this analysis to evaluate the distribution of the binding of IL13 among other brain tumors. Tumor specimens from patients with low-grade gliomas, oligodendrogliomas, ependymomas, pilocytic astrocytomas, gliosarcomas, medulloblastomas, meningiomas, and metastases to the brain were analyzed and compared to a new series of glioblastoma multiforme (GBM) samples. Serial tumor tissue sections were incubated with 125I-labeled (i) IL13, (ii) antibody against transferrin (Tf) receptor, and (iii) epidermal growth factor (EGF). Most (17/18) GBMs stained specifically for IL13 binding sites while sections from 3/11 low-grade gliomas, 5/5 high-grade gliomas (grade III), 3/5 oligodendrogliomas (all three were anaplastic), and 1/2 gliosarcomas also showed specific binding for IL13. We did not detect IL13 binding sites in medulloblastomas (0/4) and found them only in 2/20 meningiomas. Metastases to the brain (4/12, i.e., lung adenocarcinomas and renal cell carcinoma) showed some binding of 125I-IL13. The presence of receptors for Tf was ubiquitous among all studied tumors while EGF receptor expression was much more variable. Since it appears that primarily the least differentiated forms of gliomas possess IL13 binding sites in abundance, it is plausible that IL 13 receptor expressed in low-grade gliomas might be a prognostically significant marker associated with their progression to high-grade gliomas. Finally, we demonstrate that the glioma-associated IL13 receptor is truly more restrictive in nature also due to its selective representation among brain tumors of glial origin.

Molecular expression analysis of restrictive receptor for interleukin 13, a brain tumor-associated cancer/testis antigen.

BACKGROUND: The vast majority of patients with high-grade gliomas (HGG) over-express interleukin 4 (IL4)-independent binding sites for IL13 in situ. In addition, mutated IL13-based cytotoxins directed specifically toward glioma-associated sites are arguably the most active anti-glioma agents. Two IL13 receptor (R) proteins were identified: (1) IL13R alpha', a component of the signaling, heterodimeric high-affinity receptor for IL13 that is shared with IL4, and (2) IL13R alpha, a monomeric, IL4-independent receptor. MATERIALS AND METHODS: We analyzed gene expression of IL13R alpha, IL13R alpha' and that of IL4Rbeta, which is the other subunit of the shared IL13/4 receptor. The study was conducted with 40 human normal adult tissues, 20 discrete regions of the central nervous system (CNS), 7 fetal tissues, several cultured cell lines, and surgical CNS specimens. RESULTS: The most striking feature of the IL13R alpha gene expression was the virtual lack of its transcripts within the CNS. Furthermore, only the testes exhibited a prominent presence of the mRNA for IL13R alpha among peripheral organs. In contrast, the components of the shared IL13/4 receptor were readily detected both in the CNS and in vital organs, such as liver, heart, lungs, and gastrointestinal tract. CONCLUSIONS: The results strongly support a need to redirect IL13 towards its more restrictive, IL4-independent, receptor for glioma diagnosis and therapies. Moreover, the gene for IL13R alpha resides on chromosome X. Since IL13R alpha is (1) a cancer-associated protein, (2) virtually restricted to testes among normal tissues, and (3) its gene is on chromosome X, IL13R alpha is unexpectedly categorized as a cancer/testis antigen. Our findings make IL13R alpha even more attractive as a target for variety of approaches in glioma molecular management.

Cancer genetics/epigenetics and the X chromosome: possible new links for malignant glioma pathogenesis and immune-based therapies.

Human high-grade gliomas (HGGs) are rapidly progressing heterogeneous brain tumors of unknown etiology and there are no effective treatment modalities available. The recent discovery of cancer-specific antigens has opened new doors for specific tumor-targeted treatments using passive and active immunotherapeutic strategies. In particular, SEREX (serological analysis of recombinant cDNA expression libraries) has aided in the discovery of numerous new tumor antigens. These specific tumor antigens are located on chromosome X and are expressed predominantly in the testes among normal organs, and hence termed Cancer/Testis Antigens (CTAs). We found that the vast majority of HGG patients overexpress a receptor for an immune regulatory cytokine, interleukin 13 (IL-13), which differs from the normal tissue physiological receptor. Interestingly, the HGG-associated receptor protein, IL-13R alpha, is expressed solely in the testes and its gene is localized to chromosome X, which mirror the expression pattern and genomic localization of CTAs. There is little evidence for frequent gross structural abnormalities on chromosome X in HGG. Although the mechanism that causes X chromosome-linked CTAs to be aberrantly expressed in tumors is not fully understood, evidence is beginning to point toward the DNA methylation dysregulation that occurs in tumor cells as being implicit in this process and perhaps in the oncogenic process as well. Therefore, further study of the phenomenon of CTAs may bring the dual benefit of better understanding tumorigenesis and providing new molecular tools for better management of HGGs. Also, we propose that the X chromosome may in fact be an important player in HGG oncogenesis.

Retargeting interleukin 13 for radioimmunodetection and radioimmunotherapy of human high-grade gliomas.

A vast majority of patients with glioblastoma multiforme (GBM), a high-grade glioma, overexpress abundant amounts of a receptor for interleukin (IL)-13 in situ. This receptor is more restrictive because it is IL-4-independent and therefore differs from the IL-13/4 signaling receptor of normal tissue that is shared with IL-4. We previously identified one of the sites on the human IL (hIL)-13 molecule that is important for its interaction with the IL-13/4 receptor, a residue of glutamic acid at position 13. In this study, we mutated the cytokine and produced hIL-13.E13Y, in which the glutamic acid was substituted by tyrosine. This additional tyrosine residue was therefore strategically located within the region of IL-13 interaction with the signaling physiological receptor. hIL-13.E13Y did not transduce signals through the IL-13/4 receptor, whereas its interaction with the more restrictive, GBM-associated receptor remained intact. The mutated hIL-13 could be readily radiolabeled. Radiolabeled hIL-13.E13Y produced specific autoradiographic images of human GBM specimens. We demonstrate an effective way to redirect hIL-13 to its more restrictive receptor found in high-grade gliomas by mutagenizing the cytokine, and, concomitantly, we equipped hIL-13 with an additional tyrosine residue for higher specific activity radiolabeling.

Mutants of interleukin 13 with altered reactivity toward interleukin 13 receptors.

Interleukin 13 (IL13) belongs to a family of cytokines whose members exhibit structural homology, despite amino acid sequence dissimilarity. For example, while of limited sequence homology, IL13 and IL4 share a signaling receptor, IL13/4 receptor, on a variety of human normal cells. However, a subclass of IL4-independent IL13 receptors is overexpressed on certain transformed cells, including human malignant gliomas. We introduced mutations into human (h) IL13 to determine the site(s) involved in interaction with the shared receptor and/or the glioma-associated receptor. This analysis identified at least three protein regions that are needed for signaling through the shared receptor. These regions were localized to alpha-helices A, C, and D and were mainly separate from the region(s) needed to interact with the glioma-associated receptor. Glutamic acids at positions 13 and 16 in hIL13 alpha-helix A, arginine and serine at positions 66 and 69 in helix C, and arginine at position 109 in helix D were found to be important in inducing biological signaling since their specific mutation resulted in loss and/or gain of function phenomena. We demonstrate that the molecular requirements of hIL13 to interact with its respective receptors are generally distinct and can be controlled by mutagenesis of the cytokine.

Receptor for interleukin 13 is abundantly and specifically over-expressed in patients with glioblastoma multiforme.

We have recently documented that the vast majority of patients with glioblastoma multiforme (GBM) over-express a receptor (R) for interleukin 13 (IL13) in situ. We have now evaluated further the degree of relative specificity of the binding of IL13 to GBM when compared with other growth factor receptors. Tumor samples of 11 patients with GBM, 7 various normal brain samples, and several cell lines in culture were examined. Same patient tissue sections were incubated with 125I-labeled: IL13, monoclonal antibody HB21 against human transferrin (Tf) receptor, epidermal growth factor (EGF), and an IL4 antagonist, IL4.Y124D. All 11 GBMs stained specifically, densely, and relatively homogeneously for both IL13R and TfR. Seven GBM specimens showed specific binding for 125I-EGF, but it was less homogeneous when compared with IL13R or TfR. Two of the GBMs studied demonstrated extremely high density of the EGFR. Furthermore, we did not detect significant presence of the IL4R in the studied GBM specimens in situ. All sections of non-malignant brain tissues examined showed avid binding by the TfR with lack of consistent and specific binding of 125I-IL13 or -EGF. Thus, it appears that the GBM-associated IL13R is considerably more specific to GBM that the one for Tf and more frequently and homogeneously expressed than the EGFR. These results render further support for the hIL13R being a new unique candidate for delivery of variety of anti-GBM therapies.

Receptor for interleukin 13 is a marker and therapeutic target for human high-grade gliomas.

Glioblastoma multiforme (GBM) is an incurable brain tumor. Due to the striking heterogeneity that characterizes GBM, there is no known tumor-specific antigen or receptor that is expressed by a majority of GBM patients. We found that virtually all studied human GBM specimens (23 samples) abundantly expressed a receptor for interleukin (IL)-13 in situ, whereas normal human brain had few, if any, IL-13-binding sites. The GBM-associated IL-13 receptor was both quantitatively and qualitatively different from and, thus, more restrictive than the shared signaling receptor of normal tissue: it was IL-4 independent. The receptor for IL-13 was overexpressed by a majority of cancer cells in situ. Furthermore, cytotoxins targeted to this more restrictive IL-13R produced cures in animals bearing xenografts of human high-grade gliomas. Thus, unexpectedly, the receptor for an immune regulatory cytokine may be a long sought marker and, concomitantly, a unique imaging site and therapeutic target for GBM, the most malignant and the most heterogeneous of brain tumors.

Pancreatic cancer cells express interleukin-13 and -4 receptors, and their growth is inhibited by Pseudomonas exotoxin coupled to interleukin-13 and -4.

BACKGROUND: Interleukin (IL)-13 and -4 are multifunctional cytokines that bind to specific cell-surface receptors. The aim of this study was to determine whether pancreatic cancer cells express either receptor, and to assess the growth suppressive effects of chimeric proteins composed of a Pseudomonas exotoxin (PE) A mutant (PE38QQR) fused to IL-13 (IL-13-PE38QQR) or IL-4 (IL-4-PE38QQR) in these cells. MATERIALS AND METHODS: Northern and Western blot analysis were used to analyze the expression of IL-4/-13 receptors and the common gamma chain (gamma c) in pancreatic cancer cell lines. MTT growth assays were carried out to assess the effects of IL-4/-13 and IL-4/-13-PE38QQR on cell growth. RESULTS: All 6 pancreatic cancer cell lines examined expressed IL-13R alpha 1 and IL-4R alpha, one cell line expressed IL-13R alpha 2, and 5 pancreatic cancer cell lines expressed gamma c. IL-13 (5 nM) significantly enhanced the growth of 3 cell lines, whereas IL-4 (5 nM) enhanced the growth of 1 cell line. In contrast, IL-13-PE38QQR and IL-4-PE38QQR inhibited the growth of all 6 tested cell lines. There were large variations in the individual sensitivity of the cells, with LD50 values ranging from 100 ng/ml to 5 micrograms/ml for IL-13-PE38QQR and from 20 ng/ml to 10 micrograms/ml for IL-4-PE38QQR. IL-13 and -4 antagonized these inhibitory activities in some, but not all, of the cell lines. CONCLUSIONS: IL-13 and -4 may act as mitogens toward pancreatic cancer cells by activating IL-4- and IL-13-receptors and IL-13- and IL-4-coupled toxins may ultimately have a role in the treatment of pancreatic cancer.

Characterization and distribution of ferritin binding sites in the adult mouse brain.

Studies on iron uptake into the brain have traditionally focused on transport by transferrin. However, transferrin receptors are not found in all brain regions and are especially low in white matter tracts where high iron concentrations have been reported. Several lines of research suggest that a receptor for ferritin, the intracellular storage protein for iron, may exist. We present, herein, evidence for ferritin binding sites in the brains of adult mice. Autoradiographic studies using 125I-recombinant human ferritin demonstrate that ferritin binding sites in brain are predominantly in white matter. Saturation binding analyses revealed a single class of binding sites with a dissociation constant (K(D)) of 4.65 x 10(-9) M and a binding site density (Bmax of 17.9 fmol bound/microg of protein. Binding of radiolabeled ferritin can be competitively displaced by an excess of ferritin but not transferrin. Ferritin has previously been shown to affect cellular proliferation, protect cells from oxidative damage, and deliver iron. The significance of a cellular ferritin receptor is that ferritin is capable of delivering 2,000 times more iron per mole of protein than transferrin. The distribution of ferritin binding sites in brain vis-à-vis transferrin receptor distribution suggests distinct methods for iron delivery between gray and white matter.

Novel way to increase targeting specificity to a human glioblastoma-associated receptor for interleukin 13.

Human brain cancers (gliomas) overexpress large numbers of a receptor for interleukin 13 (IL13), making this receptor an attractive target for anti-glioma therapies. We have recently proposed that the glioma-associated IL13 receptor is different from the one expressed on some hemopoietic and somatic cells. In an attempt to identify an even more glioma-specific target, we have used an antagonist of a related cytokine, IL4, which neutralizes the physiological effects of both IL13 and IL4 on normal cells. Here we demonstrate that the IL4 antagonist also counteracts the action of cytotoxins targeted to the IL13 receptor on normal human cells. Importantly, the IL4 antagonist does not inhibit IL13-based cytotoxins on glioma cells at all. Thus, the IL13 receptor on glioma cells can be categorized as tumor-specific in the presence of an IL4 antagonist. We conclude that IL13 receptor-directed cytotoxins can be delivered to glioma cells without being cytotoxic to normal cells.

Novel anti-brain tumor cytotoxins specific for cancer cells.

The vast majority of brain cancers (gliomas) express a receptor (R) for interleukin 13 (IL13). In order to achieve specific targeting of the IL13R in gliomas, we have mutagenized human (h) IL13. The mutation was made to alter IL13 interaction with the shared functional IL13/4 normal tissue receptor, but not with the glioma-associated receptor. We have thus produced hIL13.E13K (glutamic acid at position 13 changed to lysine) and fused it to derivatives of Pseudomonas exotoxin A. The hIL13.E13K-based cytotoxins are less active on normal cells and thus less toxic, and are better antitumor agents compared with the cytotoxins containing nonmutagenized hIL13.

An immune regulatory cytokine receptor and glioblastoma multiforme: an unexpected link.

Human high-grade gliomas (HGG) are one of the most devastating human malignancies. They are rapidly progressing heterogenous tumors for which no curable treatment is available. Although these tumors are believed to be of glial cell origin, known tumor-specific markers do not characterize them. The specific environmental conditions that cause or promote the development of HGG are not known. The pathomechanism of HGG is yet to be revealed, although more specific genetic alterations are assigned to HGG. Recently, we have found that HGG overexpress a receptor for an immune regulatory cytokine, interleukin-13 (IL-13). In fact, it appears that all patients with glioblastoma multiforme may possess this receptor. IL-13 is an antiinflammatory cytokine with many overlapping functions to its homologue, IL-4. There is a high degree of specificity of the overexpression of the IL-13 receptor in HGG. This receptor is not only quantitatively but also qualitatively different from the only known functional signaling receptor for IL-13 of normal tissue. It is not shared with IL-4. The more restrictive receptor for IL-13 thus may represent a new factor specific for a disease as heterogenous as HGG.

Interleukin-13 receptors on human prostate carcinoma cell lines represent a novel target for a chimeric protein composed of IL-13 and a mutated form of Pseudomonas exotoxin.

We have discovered a new cell surface protein in the form of interleukin-13 receptor on several solid tumor cells, including human renal cell carcinoma cells (Obiri et al., 1995; Debinski et al., 1995). This study reports that human prostate cancer cell lines also express high affinity IL-13 receptors (Kd = 159 pM). These receptors are functional because IL-13 surprisingly increased proliferation of all three prostate cancer cell lines studied as determined by thymidine uptake and clonogenic assays. IL-13 receptors on prostate cancer cell lines were targeted using a chimeric protein composed of IL-13 and a mutated form of Pseudomonas exotoxin (PE38QQR). This molecule, termed IL13-PE38QQR, has been found cytotoxic to all three prostate cancer cell lines as determined by the inhibition of protein synthesis. The IC50 ranged between 1 nmol/l, to 15 nmol/l. These data were confirmed by clonogenic assays in which IL13-PE38QQR almost completely inhibited colony formation at 10 nmol/l. IL13-PE38QQR was not cytotoxic to cells that express little or no IL-13R. Heat inactivated IL13-PE38QQR was not cytotoxic to prostate cancer cells indicating specificity. IL13-PE38QQR was also cytotoxic to colonies when they were allowed to form first for several days before the addition of toxins. Our data suggest that additional studies should be performed to target IL-13 receptor bearing prostate cancer.