Analysis of antitumor activity of an interleukin-13 (IL-13) receptor-targeted cytotoxin composed of IL-13 antagonist and Pseudomonas exotoxin

Engineering the IL-4/IL-13 axis for targeted immune modulation

The structurally and functionally related interleukin-4 (IL-4) and IL-13 cytokines play pivotal roles in shaping immune activity. The IL-4/IL-13 axis is best known for its critical role in T helper 2 (Th2) cell-mediated Type 2 inflammation, which protects the host from large multicellular pathogens, such as parasitic helminth worms, and regulates immune responses to allergens. In addition, IL-4 and IL-13 stimulate a wide range of innate and adaptive immune cells, as well as non-hematopoietic cells, to coordinate various functions, including immune regulation, antibody production, and fibrosis. Due to its importance for a broad spectrum of physiological activities, the IL-4/IL-13 network has been targeted through a variety of molecular engineering and synthetic biology approaches to modulate immune behavior and develop novel therapeutics. Here, we review ongoing efforts to manipulate the IL-4/IL-13 axis, including cytokine engineering strategies, formulation of fusion proteins, antagonist development, cell engineering approaches, and biosensor design. We discuss how these strategies have been employed to dissect IL-4 and IL-13 pathways, as well as to discover new immunotherapies targeting allergy, autoimmune diseases, and cancer. Looking ahead, emerging bioengineering tools promise to continue advancing fundamental understanding of IL-4/IL-13 biology and enabling researchers to exploit these insights to develop effective interventions.

Targeting and Sensitization of Breast Cancer Cells to Killing with a Novel Interleukin-13 Receptor α2-Specific Hybrid Cytolytic Peptide

Highly metastatic breast cancers, such as triple-negative subtypes (TNBC), require the most effective treatments. Since interleukin-13 receptor (IL-13R)α2 is reportedly over-expressed in some cancers, we investigated here its expression and the feasibility of therapeutically targeting this receptor in breast cancer using a novel hybrid cytolytic peptide (Pep-1-Phor21) consisting of IL-13Rα2-binding (Pep-1) and cytolytic (Phor21) domains. This study demonstrates that particularly TNBC tissues and cells display the prominent expression of IL-13Rα2. Furthermore, Pep-1-Phor21 induced the rapid necrosis of tumor cells expressing cell-surface IL-13Rα2. Notably, IL-13Rα2 expression was found to be epigenetically regulated in breast cancer cells in that the inhibition of histone deacetylase (HDAC) or DNA methyltransferase (DNMT) upregulated IL-13Rα2 expression, thereby sensitizing them to Pep-1-Phor21. IL-13Rα2-negative non-malignant cells were refractory to these epigenetic effects. Consistent with its cytolytic activity, Pep-1-Phor21 readily destroyed IL-13Rα2-expressing breast cancer spheroids with HDAC or DNMT inhibition, further enhancing cytolytic activity. Therefore, the Pep-1-Phor21-mediated targeting of IL-13Rα2 is a potentially novel therapeutic strategy for TNBC. Given that tumor cells can be selectively sensitized to Pep-1-Phor21 via the epigenetic up-regulation of IL-13Rα2, a combined adjuvant approach involving Pep-1-Phor21 and epigenetic inhibitors may be an effective strategy.

Targeting of the Interleukin-13 Receptor (IL-13R)α2 Expressing Prostate Cancer by a Novel Hybrid Lytic Peptide

The IL-13Rα2 cell surface receptor is highly expressed in tumours such as prostate cancer. In this report, we evaluated the hypothesis that prostate cancer cells with enhanced IL-13Rα2 expression are a suitable target for the hybrid lytic peptide (Pep-1-Phor21) peptide, which is generated by fusing the IL-13Rα2 specific ligand (Pep-1) and a cell membrane disrupting lytic peptide (Phor21). The expression of IL-13Rα2 mRNA and protein in prostate cancer tissues and cell lines was assessed via real-time PCR (RT-PCR) and immunoblotting. The effect of Pep-1-Phor21 on the viability of prostate cancer cells grown in monolayers (2D) and microtissue spheroids (3D) was assessed via CellTox green cytotoxic assay. IL-13Rα2 expression and Pep-1-Phor21-mediated killing were also determined in the cells treated with epigenetic regulators (Trichostatin A (TSA) and 5-aza-2 deoxycytidine (5-Aza-dC)). The hybrid lytic peptide cytotoxic activity correlated with the expression of IL-13Rα2 in prostate cancer cell lines cultured as monolayers (2D) or 3D spheroids. In addition, TSA or 5-Aza-dC treatment of prostate cancer cells, particularly those with low expression of IL-13Rα2, enhanced the cells' sensitivity to the lytic peptide by increasing IL-13Rα2 expression. These results demonstrate that the Pep-1-Phor21 hybrid lytic peptide has potent and selective anticancer properties against IL-13Rα2-expressing prostate cancer cells.

Targeting Receptors on Cancer Cells with Protein Toxins

Cancer cells frequently upregulate surface receptors that promote growth and survival. These receptors constitute valid targets for intervention. One strategy involves the delivery of toxic payloads with the goal of killing those cancer cells with high receptor levels. Delivery can be accomplished by attaching a toxic payload to either a receptor-binding antibody or a receptor-binding ligand. Generally, the cell-binding domain of the toxin is replaced with a ligand or antibody that dictates a new binding specificity. The advantage of this “immunotoxin” approach lies in the potency of these chimeric molecules for killing cancer cells. However, receptor expression on normal tissue represents a significant obstacle to therapeutic intervention.

Nontyphoidal Salmonella: a potential anticancer agent

Use of bacteria in cancer therapy, despite being considered as a potent strategy, has not really picked up the way other methods of cancer therapies have evolved. However, in recent years, the interest on use of bacteria to kill cancer cells has renewed considerably. The standard and widely followed strategies of cancer treatment often fail either due to the complexity of tumour biology or because of the accompanying side effects. In contrast, these limitations can be easily overcome in a bacteria-mediated approach. Salmonella is a bacterium, which is known for its ability to colonize solid or semisolid tumours more efficiently than any other bacteria. Among more than 2500 serovars of Salmonella, S. Typhimurium has been widely studied for its antagonistic effects on cancer cells. Here in, we review the current status of the preclinical and the clinical studies with a focus on the mechanisms that attribute the anticancer properties to nontyphoidal Salmonella.

Analysis of the cancer genome atlas (TCGA) database identifies an inverse relationship between interleukin-13 receptor α1 and α2 gene expression and poor prognosis and drug resistance in subjects with glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults. A variety of targeted agents are being tested in the clinic including cancer vaccines, immunotoxins, antibodies and T cell immunotherapy for GBM. We have previously reported that IL-13 receptor subunits α1 and α2 of IL-13R complex are overexpressed in GBM. We are investigating the significance of IL-13Rα1 and α2 expression in GBM tumors. In order to elucidate a possible relationship between IL-13Rα1 and α2 expression with severity and prognoses of subjects with GBM, we analyzed gene expression (by microarray) and clinical data available at the public The Cancer Genome Atlas (TCGA) database (Currently known as Global Data Commons). More than 40% of GBM samples were highly positive for IL-13Rα2 mRNA (Log2 ≥ 2) while only less than 16% samples were highly positive for IL-13Rα1 mRNA. Subjects with high IL-13Rα1 and α2 mRNA expressing tumors were associated with a significantly lower survival rate irrespective of their treatment compared to subjects with IL-13Rα1 and α2 mRNA negative tumors. We further observed that IL-13Rα2 gene expression is associated with GBM resistance to temozolomide (TMZ) chemotherapy. The expression of IL-13Rα2 gene did not seem to correlate with the expression of genes for other chains involved in the formation of IL-13R complex (IL-13Rα1 or IL-4Rα) in GBM. However, a positive correlation was observed between IL-4Rα and IL-13Rα1 gene expression. The microarray data of IL-13Rα2 gene expression was verified by RNA-Seq data. In depth analysis of TCGA data revealed that immunosuppressive genes (such as FMOD, CCL2, OSM, etc.) were highly expressed in IL-13Rα2 positive tumors, but not in IL-13Rα2 negative tumors. These results indicate a direct correlation between high level of IL-13R mRNA expression and poor patient prognosis and that immunosuppressive genes associated with IL-13Rα2 may play a role in tumor progression. These findings have important implications in understanding the role of IL-13R in the pathogenesis of GBM and potentially other cancers.

Recombinant Immunotoxin Therapy of Glioblastoma: Smart Design, Key Findings, and Specific Challenges

Recombinant immunotoxins (RITs) refer to a group of recombinant protein-based therapeutics, which consists of two components: an antibody variable fragment or a specific ligand that allows RITs to bind specifically to target cells and an engineered toxin fragment that kills the target cells upon internalization. To date, over 1,000 RITs have been generated and significant success has been achieved in the therapy of hematological malignancies. However, the immunogenicity and off-target toxicities of RITs remain as significant barriers for their application to solid tumor therapy. A group of RITs have also been generated for the treatment of glioblastoma multiforme, and some have demonstrated evidence of tumor response and an acceptable profile of toxicity and safety in early clinical trials. Different from other solid tumors, how to efficiently deliver the RITs to intracranial tumors is more critical and needs to be solved urgently. In this article, we first review the design and expression of RITs, then summarize the key findings in the preclinical and clinical development of RIT therapy of glioblastoma multiforme, and lastly discuss the specific issues that still remain to forward RIT therapy to clinical practice.

Biomarkers and Immunotherapeutic Targets in Glioblastoma

Glioblastoma (GBM) is an aggressive central nervous system cancer with poor prognosis despite maximal therapy. The recent advent of immunotherapy holds great promise for improving GBM survival and has already made great strides toward changing management strategies. A diverse set of biomarkers have been implicated as immunotherapeutic targets and prognostic indicators in other cancers. Some of the more extensively studied examples include cytokines (IL-4, IL-13, and TGF-β), checkpoint molecules (PD-1, CTLA-4, TIM-3, LAG-3, CD137, GITR, OX40), and growth/angiogenesis proteins (endoglin and EGFR). Emerging theories involving the tumor mutational landscape and microbiome have also been explored in relation to cancer treatment. Although identification of novel biomarkers may improve and help direct treatment of patients with GBM, the next step is to explore the role of biomarkers in precision medicine and selection of specific immunotherapeutic drugs in an individualized manner.

Significance of interleukin-13 receptor alpha 2-targeted glioblastoma therapy

Glioblastoma multiforme (GBM) remains one of the most lethal primary brain tumors despite surgical and therapeutic advancements. Targeted therapies of neoplastic diseases, including GBM, have received a great deal of interest in recent years. A highly studied target of GBM is interleukin-13 receptor α chain variant 2 (IL13Rα2). Targeted therapies against IL13Rα2 in GBM include fusion chimera proteins of IL-13 and bacterial toxins, nanoparticles, and oncolytic viruses. In addition, immunotherapies have been developed using monoclonal antibodies and cell-based strategies such as IL13Rα2-pulsed dendritic cells and IL13Rα2-targeted chimeric antigen receptor-modified T cells. Advanced therapeutic development has led to the completion of phase I clinical trials for chimeric antigen receptor-modified T cells and phase III clinical trials for IL-13-conjugated bacterial toxin, with promising outcomes. Selective expression of IL13Rα2 on tumor cells, while absent in the surrounding normal brain tissue, has motivated continued study of IL13Rα2 as an important candidate for targeted glioma therapy. Here, we review the preclinical and clinical studies targeting IL13Rα2 in GBM and discuss new advances and promising applications.

Tumor immunology, immunomics and targeted immunotherapy for central nervous system malignancies

Although the brain was traditionally considered as 'immunologically privileged', recent findings have implied an involvement of immune mechanisms in neurological disease and illness, including central nervous system (CNS) malignancies. In this review, we initially focus on aspects of the immune system critical for effective antitumor immunity, as an understanding of normal immunological functions and how they relate to tumor immunology will set a foundation for understanding the unique challenges facing the integration of neuro-oncology and neuroimmunology. We summarize current knowledge of immune responses in the 'immunologically quiescent' brain and its role in tumor immunology. We will then discuss the emerging field of 'immunomics' and recent advances in molecular technologies, such as DNA microarray, which are being applied to brain tumor antigen epitope discovery and patient stratification for brain cancer immunotherapy. This, in turn, should have significant importance for ultimately designing and developing efficient and focused strategies for anticancer immunotherapy. Finally, the current state of immune-based treatment paradigms and future directions will be discussed, paying particular attention to targeted antibody strategies, adoptive cellular immunotherapy, and tumor vaccine approaches that have been studied in clinical trials for CNS neoplasms.

Current status of local therapy in malignant gliomas--a clinical review of three selected approaches

Malignant gliomas are the most frequently occurring, devastating primary brain tumors, and are coupled with a poor survival rate. Despite the fact that complete neurosurgical resection of these tumors is impossible in consideration of their infiltrating nature, surgical resection followed by adjuvant therapeutics, including radiation therapy and chemotherapy, is still the current standard therapy. Systemic chemotherapy is restricted by the blood-brain barrier, while methods of local delivery, such as with drug-impregnated wafers, convection-enhanced drug delivery, or direct perilesional injections, present attractive ways to circumvent these barriers. These methods are promising ways for direct delivery of either standard chemotherapeutic or new anti-cancer agents. Several clinical trials showed controversial results relating to the influence of a local delivery of chemotherapy on the survival of patients with both recurrent and newly diagnosed malignant gliomas. Our article will review the development of the drug-impregnated release, as well as convection-enhanced delivery and the direct injection into brain tissue, which has been used predominantly in gene-therapy trials. Further, it will focus on the use of convection-enhanced delivery in the treatment of patients with malignant gliomas, placing special emphasis on potential shortcomings in past clinical trials. Although there is a strong need for new or additional therapeutic strategies in the treatment of malignant gliomas, and although local delivery of chemotherapy in those tumors might be a powerful tool, local therapy is used only sporadically nowadays. Thus, we have to learn from our mistakes in the past and we strongly encourage future developments in this field.

Targeting of interleukin-13 receptor α2 for treatment of head and neck squamous cell carcinoma induced by conditional deletion of TGF-β and PTEN signaling

Background

The sixth leading class of cancer worldwide is head and neck cancer, which typically arise within the squamous epithelium of the oral mucosa. Human head and neck squamous cell carcinoma (HNSCC) is known to be difficult to treat and has only a 50% five-year survival rate. With HNSCC, novel therapeutics are needed along with a means of rapidly screening anti-cancer agents in vivo, such as mouse models.

Methods

In order to develop new animal models of cancer to test safety and efficacy of novel therapeutic agents for human HNSCC, tumors resembling clinical cases of human HNSCC were induced in the head and neck epithelium of a genetically engineered mouse model. This mouse model was generated by conditional deletion of two tumor suppressors, Transforming Growth Factor-β Receptor 1 (TGFβRI) and Phosphatase and Tensin homolog (PTEN), in the oral epithelium. We discovered that the tumors derived from these Tgfbr1/Pten double conditional knockout (2cKO) mice over-expressed IL-13Rα2, a high affinity receptor for IL-13 that can function as a tumor antigen. To demonstrate a proof-of-concept that targeted therapy against IL-13Rα2 expression would have any antitumor efficacy in this spontaneous tumor model, these mice were treated systemically with IL-13-PE, a recombinant immunotoxin consisting of IL-13 fused to the Pseudomonas exotoxin A.

Results

Tgfbr1/Pten 2cKO mice when treated with IL-13-PE displayed significantly increased survival when compared to the untreated control mice. The untreated mice exhibited weight loss, particularly with the rapid onset of tongue tumors, but the treated mice gained weight while on IL-13-PE therapy and showed no clinical signs of toxicity due to the immunotoxin. Expression of IL-13Rα2 in tumors was significantly decreased with IL-13-PE treatment as compared to the controls and the number of myeloid-derived suppressor cells (MDSC) was also significantly reduced in the spleens of the IL-13-PE treated mice.

Conclusions

Our study demonstrates that the Tgfbr1/Pten 2cKO mouse model of human HNSCC is a useful model for assessing antitumor activity of new cancer therapeutic agents, and that IL-13-PE has therapeutic potential to treat human head and neck cancer.

Specific targeting of human interleukin (IL)-13 receptor α2-positive cells with lentiviral vectors displaying IL-13

The ability to selectively and efficiently target transgene delivery to specific cell types in vitro and in vivo remains one of the formidable challenges in gene therapy. Lentiviral vectors have several advantages that make them attractive as gene delivery vehicles and their tropism can be altered through pseudotyping, allowing transgene delivery to specific populations of cells. The human interleukin-13 receptor α2 (IL-13Rα2) is uniquely overexpressed in many different human tumors, making it an attractive target for cancer therapy. In this study, we examined whether IL-13Rα2-positive tumor cells can be specifically targeted with lentiviral vector pseudotypes containing a truncated fusion (F) protein derived from measles virus (MV) and a tail-truncated and receptor-blind MV hemagglutinin (H) protein bearing IL-13 at the C terminus. The retargeted lentiviral vector efficiently transduced cells that express high levels of IL-13Rα2, but not cells expressing low levels of IL-13Rα2 in vitro. In vivo, it specifically targeted IL-13Rα2-positive glioma cell xenografts in immunodeficient mice in the context of subcutaneous and intracranial glioma models. Similar lentiviral vectors may be developed for targeting other tumors expressing specific cell surface receptors.

Convection-enhanced delivery catheter placements for high-grade gliomas: complications and pitfalls

Convection-enhanced delivery (CED) of compounds into brain tumors reportedly circumvents the blood brain barrier. CED intends to increase drug delivery to malignant cells, reaching high local therapeutic concentration and decreasing or eliminating systemic side effects. Clinical experience and published data on catheter placement (CP) surgery are scarce. We propose practical and technical guidelines for planning CED based on our experience. We retrospectively analyzed the medical charts and relevant neuroimages of 25 patients following the insertion of 64 CED catheters. The patients were enrolled in at least one of four clinical trials using CED for treating recurrent glioblastoma multiforme in our institution between 2003-2006. Intra- and postoperative complications related to CP surgery and the difficulties and pitfalls of planning were evaluated. There were 29 CP surgeries. Forty-four peritumoral brain tissue catheters were inserted in 16 CP surgeries following tumor resection in 16 patients, and 20 catheters were placed into the tumor in 13 procedures in 10 patients. The lesions were in or near eloquent brain tissue areas in 13 of all CP surgeries. Complications included increased edema (31%), infection (6.9%), bleeding (6.9%) and seizures (13.8%). Significant neurological deterioration occurred in 4 patients (13.8%). Difficulties in adhering to CP surgery guidelines included lesion site (superficial, mesial temporal lobe, proximity to CSF spaces), proximity to eloquent cortical areas, tissue density that interfered with the trajectory, and technical limitations of stereotactic instruments. CED procedures for high-grade gliomas may be associated with surgical morbidity. Adherence to guidelines might be difficult because of lesion site and complicated by brain and tumor tissue characteristics. This should be considered while planning clinical trials that use convection-based technology.

Silencing IL-13Rα2 promotes glioblastoma cell death via endogenous signaling

Glioblastoma multiforme (GBM) is one of the most lethal forms of cancer, with a survival rate of only 13% to 27% within 2 years of diagnosis despite optimal medical treatment. We hypothesize that the presence of a unique IL-13Rα2 decoy receptor prevents GBM apoptosis. This receptor has a high affinity for interleukin-13 (IL-13), binds the cytokine, and competitively inhibits the intracellular signaling cascade initiated by IL-13. In cells lacking the IL-13Rα2 decoy receptor, IL-13 initiates the production of 15-lipoxygenase-1 (15-LOX-1), which has been implicated in cellular apoptosis. Our group and others have shown that induction of 15-LOX-1 correlates with tumor cell death in colorectal, pancreatic, and prostate cancer. How 15-LOX-1 induces apoptosis remains unclear. Preliminary evidence in GBM cells implicates an apoptotic process mediated by PPARγ. 15-LOX-1 metabolites can modulate PPARγ and activation of PPARγ can suppress tumor growth. We hypothesize that in GBM, IL-13 can induce 15-LOX-1, which regulates cell apoptosis via signaling through PPARγ and that expression of IL-13Rα2 prevents apoptosis and contributes to tumor growth. Our in vitro and in vivo data support this. Knocking down IL-13Rα2 with short interfering RNA dramatically induces 15-LOX-1 expression, promotes apoptosis, and reduces GBM tumor growth in vivo. These findings identify a mechanism for eliminating the blockade of endogenous IL-13 signaling and for promotion of apoptosis, and characterize a role for 15-LOX-1 in GBM apoptosis. Identifying a mechanistic pathway that can be targeted for pharmacologic intervention will have applied implications to developing novel and effective treatments of GBM.

Interleukin 13 mediates signal transduction through interleukin 13 receptor alpha2 in pancreatic ductal adenocarcinoma: role of IL-13 Pseudomonas exotoxin in pancreatic cancer therapy

PURPOSE

Interleukin-13 receptor alpha2 (IL-13Ralpha2) is a tumor antigen that is overexpressed in certain human tumors. However, its significance and expression in pancreatic cancer is not known. It is also not known whether IL-13 can signal through IL-13Ralpha2 in cancer.

EXPERIMENTAL DESIGN

The expression of IL-13Ralpha2 was assessed in pancreatic cancer samples by immunohistochemistry and in cell lines by flow cytometry and reverse transcription-PCR. The role of IL-13Ralpha2 was examined by IL-13-induced signaling in pancreatic cancer cell lines. IL-13Ralpha2-positive tumors were targeted by IL-13PE cytotoxin in vitro and in vivo in an orthotopic murine model of human pancreatic cancer.

RESULTS

Of the pancreatic tumor samples 71% overexpressed moderate to high-density IL-13Ralpha2 chain compared with normal pancreatic samples. IL-13 induced transforming growth factor-beta1 promoter activity in IL-13Ralpha2-positive tumor cells and in cells engineered to express IL-13Ralpha2 but not in IL-13Ralpha2-negative or RNA interference knockdown cells. c-Jun and c-Fos of the AP-1 family of nuclear factors were activated by IL-13 only in IL-13Ralpha2-positive cells. In the orthotopic mouse model, IL13-PE significantly decreased tumor growth when assessed by whole-body imaging and prolonged the mean survival time. Similar results were observed in mice xenografted with a surgically resected human pancreatic tumor sample.

CONCLUSIONS

These results indicate that IL-13Ralpha2 is a functional receptor as IL-13 mediates signaling in human pancreatic cancer cell lines. IL-13 causes transforming growth factor-beta activation via AP-1 pathway, which may cause tumor induced immunosuppression in the host. In addition, IL13-PE cytotoxin may be an effective therapeutic agent for the treatment of pancreatic cancer.

Therapeutic efficacy of Cintredekin Besudotox (IL13-PE38QQR) in murine lung fibrosis is unaffected by immunity to Pseudomonas aeruginosa exotoxin A

BACKGROUND

We have previously explored a therapeutic strategy for specifically targeting the profibrotic activity of IL-13 during experimental pulmonary fibrosis using a fusion protein comprised of human IL-13 and a mutated form of Pseudomonas aeruginosa exotoxin A (IL13-PE) and observed that the intranasal delivery of IL13-PE reduced bleomycin-induced pulmonary fibrosis through its elimination of IL-13-responsive cells in the lung. The aim of the present study was to determine whether the presence of an immune response to P. aeruginosa and/or its exotoxin A (PE) would diminish the anti-fibrotic properties of IL13-PE.

METHODOLOGY/PRINCIPAL FINDINGS

Fourteen days after P. aeruginosa infection, C57BL/6 mice were injected with bleomycin via the intratracheal route. Other groups of mice received 4 doses of saline or IL13-PE by either intranasal or intraperitoneal application, and were challenged i.t. with bleomycin 28 days later. At day 21 after bleomycin, all mice received either saline vehicle or IL13-PE by the intranasal route and histopatological analyses of whole lung samples were performed at day 28 after bleomycin. Intrapulmonary P. aeruginosa infection promoted a neutralizing IgG2A and IgA antibody response in BALF and serum. Surprisingly, histological analysis showed that a prior P. aeruginosa infection attenuated the development of bleomycin-induced pulmonary fibrosis, which was modestly further attenuated by the intranasal administration of IL13-PE. Although prior intranasal administration of IL13-PE failed to elicit an antibody response, the systemic administration of IL13-PE induced a strong neutralizing antibody response. However, the prior systemic sensitization of mice with IL13-PE did not inhibit the anti-fibrotic effect of IL13-PE in fibrotic mice.

CONCLUSIONS

Thus, IL13-PE therapy in pulmonary fibrosis works regardless of the presence of a humoral immune response to Pseudomonas exotoxin A. Interestingly, a prior infection with P. aeruginosa markedly attenuated the pulmonary fibrotic response suggesting that the immune elicitation by this pathogen exerts anti-fibrotic effects.

Expression of IL-13Ralpha2 in liver cancer cells and its effect on targeted therapy of liver cancer

PURPOSE

Liver cancer is the third leading cause of cancer-related deaths globally. The number of liver cancers diagnosed in the world is increasing at an alarming rate. It is of great significance to find the new targets of the tumor cells and specific medicine. This research investigated the expression of interleukin-13 receptor alpha2 (IL-13Ralpha2) in different liver cancer cell lines and liver cancer tissues, and assessed the cytotoxin DT389-hIL13-13E13K (IL-13 and diphtheria toxin fusion protein) targeted killing effect on liver cancer cells. Based on study above, we further analyzed the function of IL-13Ralpha2 on the targeted liver cancer therapy. The results will provide a novel strategy and an alternative way for liver cancer therapy.

METHODS

The expression of IL-13Ralpha2 in different liver cancer cell lines and tissues were analyzed by RT-PCR and immunohistochemistry. Cytotoxicity assay of DT389-hIL13-13E13K was performed in eight different concentrations in liver cancer cell lines in vitro. At the same time, siRNA-mediated knockdown was introduced to assess the role of IL-13Ralpha2 in liver cancer therapy.

RESULTS

Two out of four tested liver cancer cell lines and 27 out of 33 (81.82%) liver tissues expressed the IL-13Ralpha2. The fusion protein DT(389)-hIL13-13E13K showed a moderate cytotoxicity to the cancer cell line BEL-7402 in vitro, which 50% inhibition (IC(50)) concentration occurred at 1.4 x 10(-5 )M. Besides, the sensitivity to fusion protein DT(389)-hIL13-13E13K was decreased in siRNA-transfected liver cells compared with control ones. These results suggest that IL-13Ralpha2 chain is a specific target for IL-13-directed fusion protein.

CONCLUSIONS

We reported the expression of IL-13Ralpha2 in liver cancer cell lines and tissues as well as investigated the cytotoxin (DT389-hIL13-13E13K) targeted killing efficiency of liver cancer cells and potential role of IL-13Ralpha2 in the cancer treatment.

IL-13 cytotoxin has potent antitumor activity and synergizes with paclitaxel in a mouse model of oral squamous cell carcinoma

Interleukin-13 receptor-targeted cytotoxin (IL13-PE38) is highly cytotoxic to certain types of human cancers expressing abundant levels of IL-13Ralpha2 chain. Although IL13-PE38 is being tested in a Phase III clinical trial in brain tumors, the activity of IL13-PE38 alone or when combined with taxane, a chemotherapeutic drug for oral squamous cell carcinoma (OSCC), has not been investigated. Here, we show that approximately 40% of OSCCs (n = 50) in a tissue array are strongly positive for IL-13Ralpha2, whereas normal oral mucosa (n = 10) expresses very low or undetectable levels evaluated by immunohistochemistry. IL13-PE38 was highly cytotoxic to OSCC cell lines, but not cytotoxic to normal oral fibroblasts. IL13-PE38 mediated a synergistic antitumor effect with paclitaxel in OSC-19 in vitro and in vivo in the orthotopic OSCC tongue tumor model. Real-time tumor growth was monitored by optical imaging using a Xenogen-IVIS imaging system. Treated animals showed significant (p < 0.05) improvement in survival, which correlated with in vivo imaging of tumor response without evidence of visible toxicity. Gene transfer of IL-13Ralpha2 in oral cancer cells increased sensitivity of OSCC cell line to IL13-PE38 in vitro. Retrovirus-mediated gene-transfer of IL-13Ralpha2 in HSC-3 into tongue tumors in vivo dramatically enhanced the antitumor activity of IL13-PE38, providing complete elimination of established tumors and prolonging survival of these animals. These results indicate that IL13-PE38 in combination with paclitaxel acting via different mechanisms may be a potential treatment option for IL-13Ralpha2 expressing OSCC or for the treatment of non-IL-13Ralpha2 expressing OSCC combined with gene transfer of IL-13Ralpha2.

Targeting IL-13Ralpha2-positive cancer with a novel recombinant immunotoxin composed of a single-chain antibody and mutated Pseudomonas exotoxin

We have shown previously that high-affinity receptors for interleukin-13 (IL-13Ralpha2) are overexpressed on a variety of solid cancer cells, diseased fibroblasts, and other cells, and a chimeric fusion protein composed of human IL-13 and mutated Pseudomonas exotoxin (IL-13-PE38) is highly and specifically cytotoxic to these cells in vitro and in vivo. To improve the specificity for the target, we isolated specific antibodies against IL-13Ralpha2 from human single-chain Fv (scFv) antibody phage library and developed immunotoxin by selecting two high-affinity clones of scFv and fused to PE. The fusion chimeric gene was expressed in Escherichia coli, and highly purified IL-13R-specific immunotoxin, termed anti-IL-13Ralpha2(scFv)-PE38, was tested for its cytotoxicity. This molecule was highly cytotoxic to U251 glioma and PM-RCC renal cell carcinoma cell lines in vitro. The cytotoxic activity was neutralized by purified extracellular domain of IL-13Ralpha2 but not by IL-13, indicating that cytotoxic activity is specific. Anti-IL-13Ralpha2(scFv)-PE38 showed significant antitumor activity in immunodeficient mice with s.c. glioma tumors. Both i.p. and i.t. routes of administration showed antitumor activity in a dose-dependent manner. The maximum tolerated dose of anti-IL-13Ralpha2(scFv)-PE38 was 200 microg/kg i.p. twice daily for 5 days. These results indicate that anti-IL-13Ralpha2(scFv)-PE38 is a highly selective therapeutic agent for cancer therapy and should be further tested in animal models of human cancer.

Interleukin-13 displaying retargeted oncolytic measles virus strains have significant activity against gliomas with improved specificity

The majority of glioblastoma multiforme (GBM) tumors (80%) overexpress interleukin-13 receptor alpha2 (IL-13Ralpha2), but there is no expression of IL-13Ralpha2 in normal brain. Vaccine strains of measles virus have significant antitumor activity against gliomas. We tested the hypothesis that measles virus entry could be retargeted via the IL-13Ralpha2. MV-GFP-H(AA)-IL-13 was generated from the Edmonston-NSe vaccine strain, by displaying human IL-13 at the C-terminus of the H protein, and introducing CD46 and signaling lymphocyte activation molecule (SLAM)-ablating mutations in H. The IL-13 retargeted virus showed significant cytopathic effect (CPE) against IL-13Ralpha2 overexpressing glioma lines, and lack of CPE/viral replication in normal human astrocytes and normal human fibroblasts not expressing IL-13Ralpha2. In vivo treatment of orthotopically implanted GBM12 xenografts demonstrated significant prolongation of survival in mice treated with the retargeted strain (P < 0.0001), and comparable activity between the IL-13R retargeted strain and MV-GFP (P = 0.6377). In contrast to MV-GFP-treated mice, administration of the retargeted strain in the central nervous system of measles replication-permissive Ifnar(ko) CD46 Ge mice resulted in lack of neurotoxicity. Strains of measles virus retargeted against the glioma-specific IL-13Ralpha2 receptor have comparable therapeutic efficacy, and improved specificity as compared with the unmodified measles virus strain MV-GFP in vitro and in vivo.

Cintredekin besudotox in treatment of malignant glioma

BACKGROUND

Interleukin-13 (IL-13) receptors are overexpressed in glioblastoma multiforme (GBM). The presence of IL-13 binding sites in GBM and their absence in normal brain tissue validates IL-13 receptor as an important target in human GBM.

OBJECTIVE

This review discusses the bench-to-bedside experience with a recombinant cytotoxin composed of human IL-13 and a truncated form of Pseudomonas exotoxin A (PE38QQR), delivered via convection-enhanced delivery (CED), in GBM treatment.

METHODS

The authors review publications regarding the laboratory research and clinical development of IL-13-directed therapies and summarize the future of IL-13-targeted cytotoxin.

CONCLUSION

The IL-13 receptor remains an important potential target in GBM, and preliminary experience with the IL-13-PE38QQR cytotoxin (also called cintredekin besudotox) has helped to pave the way for study of CED as an important means of drug delivery to malignant gliomas. Ongoing analysis of recently completed clinical trials will determine the future of this agent and its potential therapeutic targets.

Role of interleukin-13 in cancer, pulmonary fibrosis, and other T(H)2-type diseases

Interleukin (IL)-13 plays a major role in various inflammatory diseases including cancer, asthma, and allergy. It mediates a variety of different effects on various cell types including B cells, monocytes, natural killer cells, endothelial cells, and fibroblasts. IL-13 binds to two primary receptor chains IL-13Ralpha1 and IL-13Ralpha2. The IL-13Ralpha2 but not IL-13Ralpha1 chain binds IL-13 with high affinity and is overexpressed in a variety of human cancer cells derived from glioma, squamous cell carcinoma of head and neck, and AIDS-associated Kaposi's sarcoma. We have also demonstrated that IL-13Ralpha2 expression is greatly increased in lung cells when mice were challenged intranasally with bleomycin or Aspergillus fumigatus. In addition, IL-13Ralpha2 increased in surgical lung biopsies from patients with usual interstitial pneumonia, nonspecific interstitial pneumonia, and respiratory bronchiolitic interstitial pneumonia of unknown origin. Based on various studies, it is concluded that IL-13Ralpha2-expressing cells are involved in various pulmonary pathological conditions. In contrast, normal tissues such as brain, lung, endothelial cells, and head and neck tissues express IL-13Ralpha1 chain, but show only marginal expression of IL-13Ralpha2 chain. Thus, IL-13Ralpha2 chain may serve as a novel biomarker for diseased cells such as cancer or fibrosis and a target for receptor-directed therapeutic agents. To target IL-13R, a recombinant fusion protein composed of IL-13 and a derivative of Pseudomonas exotoxin (PE) has been produced. This cytotoxin termed as IL-13PE38QQR or IL-13PE38, or IL-13PE is highly and specifically cytotoxic to a variety of human tumor cell lines. In preclinical models of human glioblastoma, head and neck and AIDS-associated Kaposi's cancer, IL-13PE has been found to have significant antitumor activity at a tolerated dose. Several phase I clinical trials have been completed in patients with recurrent malignant glioma. Recently a phase III clinical trial (PRECISE) in patients with recurrent malignant glioma has been completed recruiting a total of 294 patients. IL-13PE cytotoxin has also shown a significant therapeutic effect in preclinical bleomycin or A. fumigatus or Schistosoma mansoni-induced pulmonary pathology including granulomatous fibrosis in mouse models. A clinical study in these diseases has yet to be initiated.

Interleukin-13 receptor alpha2 chain: a potential biomarker and molecular target for ovarian cancer therapy

BACKGROUND

Epithelial ovarian cancer demonstrates high mortality due to diagnosis at an advanced stage. In the search for a biomarker for early diagnosis and a target for therapy, the issue of whether interleukin-13 receptor (IL-13R), shown to be expressed on a variety of human cancers, is expressed in ovarian tumor samples was explored. In addition, whether this receptor serves as a biomarker and can be targeted by IL-13 cytotoxin was examined.

METHODS

IL-13R expression in 15 normal and 68 ovarian tumor tissue samples was determined by immunohistochemistry. Correlation between clinicopathologic features and IL-13R expression was analyzed. The efficacy of IL-13R-directed cytotoxin was determined in mice with subcutaneous, orthotopic, and peritoneal metastatic ovarian cancer.

RESULTS

Immunohistochemical analyses revealed that 83% of ovarian cancer specimens express IL-13Ralpha2, a high-affinity IL-13R subunit chain, whereas normal ovary samples expressed none or very low levels. The majority of clear cell ovarian carcinomas with the worst prognosis showed strong staining for IL-13Ralpha2. IL-13 cytotoxin was highly cytotoxic to the IGROV-1 ovarian cancer cell line in vitro, and it mediated significant antitumor activity against a xenografted tumor model. The antitumor effects were confirmed by treating orthotopically implanted or peritoneal metastatic ovarian tumors, which showed significant extension of survival in immunodeficient mice. IL-13 cytotoxin also prevented cachexia in treated mice. The soluble form of IL-13Ralpha2 was detected in the serum of mice with peritoneal metastasis, and the level decreased to baseline in the treated group.

CONCLUSIONS

IL-13Ralpha2 is a promising target for ovarian cancer therapy, and the soluble form of IL-13R may be a possible surrogate marker for disease monitoring.

N-linked glycosylation of IL-13R alpha2 is essential for optimal IL-13 inhibitory activity

A high-affinity receptor for interleukin (IL)-13 (interleukin-13R alpha 2) is over-expressed in disease-related fibroblasts and neoplastic cells and is involved in cancer, allergic, and inflammatory diseases. The extracellular domain of IL-13R alpha2 (ECD alpha2) could be cleaved, which serves as a decoy receptor. We have expressed and purified ECD alpha2 in both Escherichia coli (E. coli) and mammalian systems as a soluble fragment and studied its biological activities. Although both products of ECD alpha2 showed IL-13 inhibitory activities, mammalian cell-derived ECD alpha2 appeared to be superior compared with purified protein from E. coli. When expressed in E. coli, ECD alpha2 appeared to be a monomer of 42 but a 60 kDa protein when purified from mammalian cells due to heavy glycosylation. The purified glycosylated ECD alpha2 efficiently inhibited IL-13-induced STAT6 phosphorylation in immune and Hodgkin's lymphoma cell lines, IL-13 binding, and cytotoxicity of IL-13 cytotoxin in various cancer cell lines. The improved potency of mammalian cell-derived ECD alpha2 was shown over ECD alpha2/Fc fusion protein. The N-linked glycosylation of ECD alpha2 was found to be essential for optimal IL-13 inhibitory activity as deglycosylation by PNGase F showed lower activity. ECD alpha2 did not inhibit IL-4-induced STAT6 phosphorylation, indicating that inhibitory effects of ECD alpha2 are receptor specific. These results indicate that glycosylated ECD alpha2 can serve as a potent inhibitor of IL-13 in a variety of conditions in which IL-13 is a key mediator, e.g., pulmonary, allergic, fibrotic, and neoplastic diseases.

Convection-enhanced delivery of interleukin-13 receptor-directed cytotoxin for malignant glioma therapy

The treatment of patients with malignant brain tumors, in particular glioblastoma multiforme (GBM) is very challenging because of their diffuse infiltrative nature and the cytological heterogeneity. The median survival of patients with newly diagnosed GBM is only 12-15 months, and only 8-12% of them survive for two years. Novel approaches for brain tumor therapy are needed. Recently, targeted therapies have emerged as promising modality for cancer targeting. We have discovered that high affinity plasma membrane receptor for interleukin-13 (IL-13), an immune regulatory cytokine, is over-expressed in 60-80% of malignant brain tumors. To target these IL-13R, we generated a chimeric fusion protein, composed of human IL-13 and mutated Pseudomonas exotoxin (PE), termed IL-13 cytotoxin (IL13-PE), and tested its cytotoxicity to IL-13R-expressing GBM cells. IL-13 cytotoxin was highly potent and selective in killing IL-13R-expressing GBM cells. In contrast, normal cells including brain, immune, and endothelial cells were generally not affected by this cytotoxin due to no or low expression of IL-13R. In vivo pre-clinical studies for safety and toxicity were also performed in mice, rats, and monkeys, and IL-13 cytotoxin was found to be well tolerated by both systemic and intracerebral administrations. IL-13 cytotoxin was found to mediate remarkable efficacy in animal models of human brain tumors. Encouraged by these pre-clinical studies, four Phase 1/2 clinical trials in adult patients with recurrent malignant glioma have been completed. These clinical trials involved convection-enhanced delivery (CED) of IL-13 cytotoxin either intratumoral or intraparenchymal after resection of tumor. CED is a novel loco-regional drug delivery method for intracranial tumors that relies on a continuous pressure gradient to distribute drug into interstitial space. This route of IL-13 cytotoxin administration appears to be very well tolerated and have a good risk-benefit profile. Most recently, a randomized controlled Phase 3 clinical trial (PRECISE) with intraparenchymal IL-13 cytotoxin administration was completed and subjects are being monitored for safety and survival.

Intratumoral Therapy with IL13-PE38 Results in Effective CTL-Mediated Suppression of IL-13Rα2-Expressing Contralateral Tumors

PURPOSE

IL13-PE38, a targeted cytotoxin comprised of interleukin 13 (IL-13) and a mutated form of Pseudomonas exotoxin, induces specific killing of tumor cells expressing abundant levels of the IL-13Ralpha2 chain. We hypothesized that tumor cells killed by the cytotoxin may release antigens and/or apoptotic bodies when cells are dying, which then induce adoptive immunity, and that the PE38 portion of IL13-PE38 may act as a stimulant for the induction of a CTL response.

EXPERIMENTAL DESIGN

To test this hypothesis, we established D5 melanoma tumors with or without expression of the IL-13Ralpha2 chain in both flanks of C57BL/6 mice, and then IL13-PE38 was injected in the right flank tumors only.

RESULTS AND CONCLUSIONS

When animals with IL-13Ralpha2-expressing D5 tumor (right) were injected with IL13-PE38, right flank tumors expressing the IL-13Ralpha2 chain not only showed dramatic regression but contralateral tumors (left flank) also showed tumor regression. Cell depletion experiments in tumor-bearing animals indicated that both CD8(+) and CD4(+) T cells contribute to the regression of contralateral tumors through CTL activation in the periphery and cellular infiltration into tumors. In addition, intratumoral treatment into s.c. tumors of mice bearing metastatic lung tumors with IL13-PE38 showed not only the reduction of treated s.c. tumor but also the reduction of lung metastasis. Thus, IL13-PE38 mediates an antitumor effect not only directly but also indirectly by inducing a host CD8(+) T cell immune response. Accordingly, targeted cytotoxins may be used to treat local disease even if they cannot be administered systemically, and yet may still induce a reasonable systemic antitumor response.

SV40 Pseudovirion gene delivery of a toxin to treat human adenocarcinomas in mice

SV40 vectors packaged in vitro (pseudovirions) are an efficient delivery system for plasmids up to 17.7 kb, with or without SV40 sequences. A truncated Pseudomonas exotoxin gene (PE38) was delivered into various human cells (HeLa, KB-3-1, human lymphoblastoids, and erythroleukemia cells), in vitro using pseudovirions. The number of viable cells was reduced significantly in the PE38-transduced cells. Human KB adenocarcinomas growing in mice were treated with intratumoral injection of PE38 packaged in vitro, and tumor size decreased significantly. Intraperitoneal treatments were as effective in reducing tumor size as intratumoral treatments. To check the viability of mock- or PE38-treated mice, every 4 days they were weighed, their blood was tested, and various tissues were screened for pathology. All parameters showed that the in vitro-packaged vectors, injected into tumors or intraperitoneally, caused no abnormalities in mice. The combined treatment of doxorubicin with in vitro-packaged PE38 reduced tumor size slightly more than each of the treatments separately. However, the combined treatment did not cause the weight loss seen with doxorubicin alone. These results indicate that SV40 in vitro packaging is an effective system for cancer gene delivery using two different routes of injection and in combination with chemotherapy.

Characterization of a novel human tumor antigen interleukin-13 receptor alpha2 chain

The interleukin (IL)-13 receptor alpha2 (IL-13Ralpha2) chain is a primary binding and internalization subunit for a Th2-derived immune regulatory cytokine, IL-13. Although extremely high levels of IL-13Ralpha2 chain are expressed on a variety of human tumor cells and specimens, its precise role in tumor immunology has not been defined. To investigate the role of IL-13Ralpha2 in tumor immunity, we used D5 melanoma cells stably transfected with the human IL-13Ralpha2 gene (D5alpha2) to assess the effect of an IL-13Ralpha2 DNA vaccine in immunocompetent animals. Prophylactic immunization of mice with the IL-13Ralpha2 DNA vaccine resulted in protection against D5alpha2 tumor development. In vivo depletion experiments in C57BL/6 and RAG-2 knockout mice indicated that both T and B cells, but not natural killer cells, were required for the tumor protection. In addition, antibody induced by the IL-13Ralpha2 DNA vaccine showed a modest but significant inhibitory effect on D5alpha2 cells in vitro, suggesting that the antibody is biologically functional. The IL-13Ralpha2 DNA vaccine also exhibited antitumor activity against established D5alpha2 tumors in mice. Histologic analysis of regressing tumors identified infiltration of CD4+ and CD8+ T cells and the expression of CXCL9 chemokine in tumors. Taken together, our results identify the human IL-13Ralpha2 chain as a novel tumor rejection antigen.

Treatment options for glioblastoma

Following the seminal trial conducted by the European Organisation for Research and Treatment of Cancer (EORTC) and the National Cancer Institute of Canada (NCIC), concurrent temozolomide and radiotherapy has become the new standard of care for patients with newly diagnosed glioblastoma multiforme (GBM). Investigation of emerging therapies (which are now used as salvage therapy) such as small-molecule inhibitors (for example, epidermal growth factor receptor inhibitors) and convection-enhanced delivery (CED) of targeted toxins (for example, interleukin-13/pseudomonas exotoxin) is likely to build on the EORTC/NCIC treatment platform and will, it is hoped, improve survival rates in patients with GBM. The majority of adjuvant Phase I and II trials being conducted by the brain tumor consortia are based on the EORTC/NCIC treatment platform and have added a targeted therapy in an effort to find a promising synergistic treatment. Furthermore, researchers in the consortia are continuing to explore treatments for recurrent GBM, not otherwise eligible for local therapies, such as CED. The treatments under study include novel cytotoxic chemotherapy as well as small-molecule inhibitors; these are being assessed in a variety of Phase I or II trials.

Evidence that IL-13R alpha2 chain in human glioma cells is responsible for the antitumor activity mediated by receptor-directed cytotoxin therapy

The interleukin-13 receptor alpha2 (IL-13R alpha2) chain is a primary IL-13 binding and internalization component of the IL-13R system. Previous studies have shown that human brain tumors, including glioblastoma multiforme (GBM), overexpress IL-13R alpha2 chain, while normal brain cells do not express this protein or express very low levels of it. To target IL-13R on brain tumor cells, the authors have developed an IL-13R-directed cytotoxin termed IL13-PE38QQR to induce specific cancer cell killing. To investigate the role of IL-13R alpha2 chain in GBM, cells were treated with antisense oligonucleotide or siRNA to IL-13R alpha2 chain, and cellular IL-13 binding and sensitivity to IL-13 cytotoxin were assessed. IL-13R alpha2 gene interference in GBM cells showed decreased ligand binding, and consequently IL-13 cytotoxin exhibited less cytotoxicity to these cells. The authors next evaluated the antitumor activity of IL-13 cytotoxin in native IL-13R-expressing tumors and after gene transfer of IL-13R alpha2 by injecting plasmid in U87MG tumors subcutaneously implanted in nude mice. These mice were then treated with IL-13 cytotoxin. Mean tumor size in mice receiving intraperitoneal or intratumoral IL-13 cytotoxin was significantly smaller in control tumors; however, tumor sizes were much smaller in IL-13R alpha2-transfected tumors. Furthermore, convection-enhanced delivery of IL-13R alpha2 cDNA in intracranially established U87MG glioma followed by IL-13 cytotoxin administration by the same route mediated tumor regression and prolonged survival of animals by 164% compared with control. These results indicate that IL-13R alpha2 chain in GBM cells is essential for IL-13 cytotoxin-induced cytotoxicity and that IL-13R alpha2 chain plays a critical biologic role in IL-13 cytotoxin-mediated therapy for GBM.

Combined effects of radiation and interleukin-13 receptor-targeted cytotoxin on glioblastoma cell lines

PURPOSE

Interleukin-13 receptor-targeted cytotoxin (IL13-PE38) is highly cytotoxic to human glioblastoma (GBM) cells. Although this molecule is being tested in a multicenter Phase III clinical trial (PRECISE Study) in patients with recurrent disease, the activity of IL13-PE38 when combined with radiation therapy has not been investigated.

METHODS AND MATERIALS

Cytotoxicity of IL13-PE38 to GBM cell lines was assessed by protein synthesis inhibition and clonogenic assays, and the growth of GBM cells receiving radiation was assessed by thymidine uptake assays. Expression of IL-13 receptor alpha2 (IL-13Ralpha2) messenger ribonucleic acid (mRNA) in GBM cells exposed to radiation was assessed by quantitative reverse transcriptase/polymerase chain reaction (RT-PCR) and IL-13R density by radiolabeled IL-13 binding assays.

RESULTS

Prior irradiation of GBM cell lines followed by IL13-PE38 treatment did not enhance cytotoxicity; however, concomitant 5 Gy irradiation and IL13-PE38 treatment was highly cytotoxic to T98G, M059K, A172, and LN-229 cell lines as determined by cell viability assays. There was a statistically significant decrease in number of viable cells in IL13-PE38 and irradiated cells compared with irradiated cells alone (p < 0.05) or IL13-PE38 treated cells alone (p < 0.05). In contrast, U251, SN19, and U87MG cell lines did not show any combined effect. These results were confirmed by clonogenic assays. Although three GBM cell lines-U251, SN19, and A172-showed 2.8- to 13.9-fold upregulation of IL-13Ralpha2 mRNA expression at 6-24 h after exposure to 5 Gy radiation, specific binding of radiolabeled IL-13 to these cell lines did not improve.

CONCLUSIONS

Our results suggest that concomitant radiation therapy and IL13-PE38 treatment may be beneficial for the treatment of patients with GBM. This strategy may be worth exploring in animal models of human glioma.