siRNA: novel therapeutics from functional genomics.

Long-term research on RNA interference led to an unfathomed understanding of the mechanism of siRNA-mediated silencing and finally siRNA has emerged as a powerful therapeutic tool. With siRNAs virtually every gene in the human genome contributing to a disease becomes amenable to regulation, thus opening unprecedented opportunities for drug discovery. siRNA has a well-established role as a tool for in vitro target screening and validation, besides these recent progresses of siRNA delivery in vivo, this has raised more expectations for siRNA-based drugs as the up-and-coming 'magic bullet'. Although a plethora of articles have been published with siRNA, the fundamentals of siRNA-mediated gene silencing and transforming the functional genomics to novel therapeutics are reviewed in this article with consideration to present hurdles as a new generation challenge.

The tumor suppressor Caliban regulates DNA damage-induced apoptosis through p53-dependent and -independent activity.

We previously identified Caliban (Clbn) as the Drosophila homolog of human Serologically defined colon cancer antigen 1 gene and demonstrated that it could function as a tumor suppressor in human non-small-cell lung cancer (NSCLC) cells, although its mode of action was unknown. Herein, we identify roles for Clbn in DNA damage response. We generate clbn knockout flies using homologous recombination and demonstrate that they have a heightened sensitivity to irradiation. We show that normal Clbn function facilitates both p53-dependent and -independent DNA damage-induced apoptosis. Clbn coordinates different apoptosis pathways, showing a two-stage upregulation following DNA damage. Clbn has proapoptotic functions, working with both caspase and the proapoptotic gene Hid. Finally, ecotopic expression of clbn(+) in NSCLC cells suppresses tumor formation in athymic nude mice. We conclude that Caliban is a regulator of DNA damage-induced apoptosis, functioning as a tumor suppressor in both p53-dependent and -independent pathways.

IL-4 receptors on human medulloblastoma tumours serve as a sensitive target for a circular permuted IL-4-Pseudomonas exotoxin fusion protein.

Cytotoxins directed to interleukin-4 receptors have shown to mediate relatively selective cytotoxicity against a variety of human cancer cells in vitro and in vivo. In an ongoing Phase I clinical trial, a recombinant protein comprised of circularly permuted IL-4 fused to a mutated form of Pseudomonas exotoxin (the fusion protein termed IL-4(38-37)-PE38KDEL or cpIL4-PE) has shown antitumour activity against malignant glioma. Human medulloblastomas are neuroectodermal tumours that occur in children and have a poor prognosis. The goal of this study was to determine whether human medulloblastoma derived cell lines express interleukin-4 receptor and whether interleukin-4 receptor expression is accompanied by sensitivity to cpIL4-PE. Medulloblastoma cell lines express interleukin-4 receptor at the protein and mRNA levels as determined by binding, indirect immunofluorescence and RT--PCR studies. These cells expressed IL-4Ralpha (also known as IL-4Rbeta) and IL-13Ralpha1 (also known as IL-13Ralpha') chains, however common gamma(c), a component of the interleukin-4 receptor system in immune cells was not detected. Consistent with the expression of IL-4R, cpIL4-PE was found to be highly and specifically cytotoxic to four of five medulloblastoma cell lines. Susceptibility of medulloblastoma cell lines to cpIL4-PE seemed to correlate closely to the functional IL-4 binding sites in general as demonstrated by 125I-IL-4 binding, but did not seem to correlate with mRNA or cell surface immunoreactive receptor protein expression. The sensitivity of medulloblastoma cells to cpIL4-PE could be eliminated by concurrent incubation with IL-4 or IL-13, but not with IL-2. None of these cell lines showed any change in proliferation upon treatment with exogenous IL-4. These studies establish the interleukin-4 receptor as a medulloblastoma-associated target for possible tumour-directed cancer therapy. Further studies are warranted to investigate interleukin-4 receptor expression in primary medulloblastoma tumours and sensitivity to cpIL-4PE in vitro and in vivo.

IL-13 fusion cytotoxin ameliorates chronic fungal-induced allergic airway disease in mice.

IL-13 has emerged as a major contributor to allergic and asthmatic responses, and as such it represents an attractive target in these diseases. In this study, IL-13-responsive cells in the lung were targeted via the intranasal administration of IL-13-PE38QQR (IL-13-PE), comprised of human IL-13 and a derivative of Pseudomonas exotoxin, to Aspergillus fumigatus-sensitized mice challenged with A. fumigatus spores, or conidia. Mice received 50, 100, or 200 ng of IL-13-PE or diluent alone (i.e., control group) on alternate days from day 14 to day 28 after the conidia challenge. The control group of mice exhibited significant airway hyperreactivity, goblet cell hyperplasia, and peribronchial fibrosis at day 28 after conidia. Although the two lower doses of IL-13-PE had limited therapeutic effects in mice with fungal-induced allergic airway disease, the highest dose of IL-13-PE tested significantly reduced all features of airway disease compared with the control group. Whole lung mRNA expression of IL-4Ralpha and IL-13Ralpha1 was markedly reduced, whereas bronchoalveolar lavage and whole lung levels of IFN-gamma were significantly elevated in mice treated with 200 ng of IL-13-PE compared with the control group. This study demonstrates that a therapy designed to target IL-13-responsive cells in the lung ameliorates established fungal-induced allergic airway disease in mice.

In situ expression of interleukin-4 (IL-4) receptors in human brain tumors and cytotoxicity of a recombinant IL-4 cytotoxin in primary glioblastoma cell cultures.

We have reported that human malignant glioma cell lines express high levels of plasma membrane interleukin-4 receptors (IL-4R). We have also reported that biopsy/surgical samples or primary explant cell cultures from brain tumors express mRNA and protein for the IL-4Ralpha chain, a primary IL-4-binding protein. However, whether IL-4R are expressed in brain tumors in situ has not been resolved. In addition, expression of IL-4R on the cell surface of various normal brain tissues is not known. We examined the expression of IL-4R by using a monoclonal antibody to the IL-4Ralpha chain (also known as IL-4R beta) in surgical/biopsy samples of brain tumor tissues by immunohistochemistry. Our data indicate that 15 of 18 glioblastoma multiforme (GBMs) tumors obtained from two different institutions and 12 other brain tumor samples are moderately to intensely positive for IL-4Ralpha. In contrast, although IL-4Ralpha mRNA was expressed, no IL-4R protein was detectable in two adult and one pediatric brain tissue specimens. In addition, a commercially available human neural tissue grid containing fixed tissues from various areas of brain showed no positive staining for the IL-4Ralpha chain. IL-4Ralpha expression was also demonstrated on astrocytoma grades I, II, and III. Because IL-4 cytotoxin comprised of a circularly permutated IL-4 and a mutated form of Pseudomonas exotoxin [IL4(38-37)-PE38KDEL] is cytotoxic to IL-4R-expressing cells, we tested whether primary GBM explant cell cultures are sensitive to IL-4 cytotoxin. Our data indicate that 13 of 15 GBM cell cultures were 25-74 times more sensitive to IL-4 cytotoxin compared with normal human astrocytes or the NT2 neuronal cell line. These observations indicate that human brain tumors in situ overexpress IL-4R compared with normal brain tissues, thus confirming our previous conclusions that IL-4R in brain tumors may serve as an attractive target for anticancer therapy.

Interleukin-13 receptor-targeted cancer therapy in an immunodeficient animal model of human head and neck cancer.

Although interleukin-13 receptors (IL-13R) are overexpressed on several head and neck cancer cell lines, a majority of cell lines express only low levels of IL-13R. We have found that the primary interleukin-13-binding protein IL-13Ralpha2 chain plays an important role in ligand binding and internalization. We showed that the gene transfer of IL-13Ralpha2 chain into various solid tumor cell lines that express few IL-13Rs can dramatically sensitize cells to the cytotoxic effect of a recombinant chimeric protein composed of interleukin-13 and a mutated form of Pseudomonas exotoxin A, IL13-PE38QQR. Based on the expression of IL-13R, we have classified five head and neck cancer cell lines into two groups: (a) IL-13Ralpha2 chain-positive cell lines (SCC-25 and KCCT873); and (b) IL-13Ralpha2 chain-negative cell lines (A253, YCUT891, and KCCT871). By plasmid-mediated stable gene transfer, we demonstrate that not only IL-13Ralpha2 chain-positive head and neck cancer cell lines but also IL-13Ralpha2 chain-negative cell lines can dramatically increase sensitivity to IL-13 toxin by 520-1000-fold compared with mock-transfected control cells after genetic alteration to express high levels of the IL-13Ralpha2 chain. In animal studies, i.p. or intratumoral administration of IL13-PE38QQR given daily or on alternate days for 3-5 days showed dramatic tumor response with complete remission in intratumorally injected tumors in both IL-13Ralpha2 chain-positive and -negative but transfected with IL-13Ralpha2 chain head and neck tumor implanted s.c. in nude mice. These results demonstrate that by using a combination approach of gene transfer and systemic or locoregional cytotoxin therapy, the IL-13R represents a new potent target for head and neck cancer therapy.

Interleukin-13 receptor as a unique target for anti-glioblastoma therapy.

Surgery, radiotherapy and chemotherapy have minimally altered survival of glioblastoma patients. We explored a specific approach for glioblastoma therapy in which cellular interleukin-13 (IL-13) receptors were targeted by an IL-13 cytotoxin. A wide array of human glioblastoma cell lines expressing the receptor for IL-13 were effectively killed by an IL-13 cytotoxin, a chimeric protein composed of human IL-13 and a mutated form of Pseudomonas exotoxin (termed IL13-PE38QQR or IL-13 toxin). Daily (qd) intratumoral injections of IL-13 toxin (50 and 100 microg/kg/day) for 5 consecutive days into subcutaneous human U251 glioblastoma tumors (approx. 30 mm(2)) in nude mice resulted in complete regression of tumors in 4/5 and 5/5 mice, respectively. Tumor regression persisted for at least 221 days postimplantation. Three alternate day injections (qod) of IL-13 toxin (250 microg/kg/day) into other subcutaneous U87 glioblastoma tumors also produced durable complete responses (CR) in all 5 mice. Twice daily (bid) intraperitoneal injections of IL-13 toxin at 25 or 50 microg/kg/dose for 5 days (total doses = 10) regressed U251 tumors by 45% and 58% with 1/5 and 2/5 CRs, respectively, on day 54. Intraperitoneal administration of IL-13 toxin with an identical schedule at a dose of 50 microg/kg injected into mice bearing U87 xenografts reduced tumor burden by one-half on day 36. Similar doses (25 or 50 microg/kg) with a daily schedule (qd x 5) by the intravenous route also suppressed growth of U251 subcutaneous tumors by 75% and 81% with 1/6 CR in either group by day 34. All mice tolerated therapy well without any visible signs of toxicity. On the basis of these studies, we have initiated a Phase I clinical trial using IL13-PE38QQR in patients with recurrent glioblastoma. Published 2001 Wiley-Liss, Inc.

Sensitization of cancer cells to interleukin 13-pseudomonas exotoxin-induced cell death by gene transfer of interleukin 13 receptor alpha chain.

We have demonstrated that primary interleukin 13 (IL-13) binding protein IL-13 receptor (IL-13R) alpha chain plays an important role in IL-13 binding and internalization in the IL-13R system. Although IL-13R alpha chain is expressed on many cancer cell lines, some cancer types do not express or express low levels of this receptor chain. Consequently, these cells show no or low sensitivity to the cytotoxic effect of a recombinant chimeric protein composed of IL-13 and a mutated form of a Pseudomonas exotoxin, IL13-PE38QQR. Here we demonstrate that pancreatic cancer, renal cell carcinoma, head and neck cancer, and glioblastoma cell lines that were genetically altered to express high levels of IL-13R alpha chain increase their binding affinity for IL-13, and increase their sensitivity to IL13-PE38QQR by at least 6-fold to 1000-fold compared with mock-transfected control cells. This observation was made by protein synthesis inhibition assay and confirmed by clonogenic assay. Our studies provide a proof of principle for a novel strategy for cancer therapy that combines gene transfer and targeted cytotoxin therapy.

Conversion of interleukin-13 into a high affinity agonist by a single amino acid substitution.

We created a novel mutated form of human interleukin-13 (IL-13) in which a positively charged arginine (R) at position 112 was substituted to a negatively charged aspartic acid (D). This mutant, termed IL-13R112D, was expressed in Escherichia coli and purified to near homogeneity. IL-13R112D was found to be a potent IL-13 agonist with 5-10-fold improved binding affinity to IL-13 receptors compared with wild-type IL-13 (wtIL-13). The conclusion of IL-13 agonist activity was drawn on the basis of approximately 10-fold improved activity over wtIL-13 in several assays: (a) inhibition of CD14 expression in primary monocytes; (b) proliferation of TF-1 and B9 cell lines; and (c) activation of STAT6 in Epstein-Barr virus-immortalized B cells, primary monocytes, and THP-1 monocytic cell line. Furthermore, mutant IL-13R112D neutralized the cytotoxic activity of a chimeric fusion protein composed of wtIL-13 and a Pseudomonas exotoxin A (IL-13-PE38) approximately 10 times better than wtIL-13. Based on these results, it was concluded that IL-13R112D interacts with much stronger affinity than wtIL-13 on all cell types tested and that Arg-112 plays an important role in the interaction with its receptors (IL-13R). Thus, these results suggest that IL-13R112D may be a useful ligand for the study of IL-13 interaction with its receptors or, alternatively, in designing specific targeted agents for IL-13R-positive malignancies.

Interleukin-13 receptor alpha chain: a novel tumor-associated transmembrane protein in primary explants of human malignant gliomas.

Human malignant glioma cell lines express high levels of interleukin-13 receptor (IL-13R). However, the subunit structure of this receptor in primary brain tumor cells is not known. Herein, we examined the subunit composition of IL-13R by analyzing the expression of four different putative subunits of IL-13R complex in 25 primary explants of malignant brain tumors. Reverse transcription-PCR (RT-PCR) of RNA from these tumor cells, normal astrocytes, and normal brain tissue showed that transcripts of IL-13R alpha chain were present in greater abundance in malignant glioma cells compared with normal astrocytes or normal brain tissues. The transcripts for two other chains (e.g., IL-13Ralpha' and IL-4Rbeta), on the other hand, yielded similar PCR positivity in brain tumors as well as in normal samples, whereas transcripts for gammac chain were absent in all brain tumor cells and normal tissues. The specificity of RT-PCR products for these genes was confirmed by oligo liquid hybridization analysis using a radiolabeled sequence-specific internal probe. Indirect immunofluorescence studies for different receptor chains confirmed the RT-PCR results and demonstrated a striking difference in the level of expression of IL-13Ralpha protein between normal astrocytes and malignant astrocytoma cells. These studies establish the IL-13Ralpha subunit as a novel tumor-specific protein that may be useful as a tumor marker, a target for cytotoxin/immunotoxin, or alternatively, a tumor-associated antigen for active, specific immunotherapy.

Preclinical studies with IL-13PE38QQR for therapy of malignant glioma.

To develop novel therapeutic agents for the treatment of brain tumors, we have been investigating the expression of unique tumor-associated receptors or antigens on the tumor cell surface. About six years ago, we discovered that human solid tumor cell lines, including human malignant glioma, express high- to intermediate-affinity receptors (R) for a Th2 cell-derived cytokine, interleukin-13 (IL-13). Analysis of the subunit composition of IL-13R in primary explants of malignant glioma cells has demonstrated that IL-13R is composed of three different chains (IL-13R alpha 1, IL-13R alpha 2 and IL-4R alpha, also known as IL-13R alpha', alpha and IL-4R beta, respectively) and that IL-13R alpha 2 chain is overexpressed on these cells. Normal brain tissues express IL-13R alpha 1 and IL-4R alpha chains, but show only marginal expression of IL-13R alpha 2 chain. Thus IL-13R alpha 2 chain appears to be overexpressed on glioma cells and may serve as a novel tumor biomarker or a target for receptor-directed therapeutic agents for brain tumors. To target IL-13 receptors, we have produced a recombinant fusion protein composed of IL-13 and a mutated form of Pseudomonas exotoxin (PE). This cytotoxin, termed IL-13PE38QQR or IL-13 cytotoxin, is highly and specifically cytotoxic to a spectrum of human glioma cell lines. In preclinical models of human glioblastoma tumors growing subcutaneously in immunodeficient mice, IL-13 cytotoxin has been found to have remarkable antitumor activity. The data that emerged from these studies reveal that localized or systemic administration of IL-13 cytotoxin can produce nontoxic drug levels and that IL-13 cytotoxin is potently effective against established glioblastoma tumors. On the basis of these and other preclinical studies, we have begun a phase I clinical trial using IL-13PE38QQR for therapy of recurrent malignant glioma.

The human immunodeficiency virus type 1 Tat protein potentiates zidovudine-induced cellular toxicity in transgenic mice.

3'-Azido-2',3'-dideoxythymidine (AZT, zidovudine) is the principal antiretroviral agent in the treatment of AIDS. Although beneficial, AZT remains restricted for human usage because of its severe toxic effects. We examined the AZT sensitivity in transgenic mice expressing HIV-1 one-exon-encoded 72 amino acid Tat (Tat72) and full-length 86 amino acid Tat (Tat86) proteins. Administration of AZT (1 mg/ml) in drinking water for 1 week resulted in a three- to fourfold decrease in hematopoietic progenitors from bone marrow in Tat mice compared to AZT-treated nontransgenic controls as determined by erythroid and granulocyte/macrophage colony-forming unit assays. In liver and thymus, two of the tissues examined, AZT treatment of Tat mice resulted in as much as 80-90% suppression of Mn-superoxide dismutase (Mn-SOD) activity. Other parameters associated with loss of Mn-SOD such as increase in carbonyl proteins and decrease of sulfhydryl content were also significantly enhanced by AZT in Tat mice. Our in vivo study suggests that AZT therapy is associated with oxidative damage affecting cellular functions in several tissues and that Tat is one of the contributory factors in AZT-induced toxicities. The findings of AZT-induced oxidative damage may help to improve the therapeutic index of AZT and other related drugs in AIDS patients.

Analysis of live, oral poliovirus vaccine monopools for human immunodeficiency virus type 1 and simian immunodeficiency virus.

Although there is no evidence for transmission of mammalian retroviruses to humans via vaccine immunization, the allegations of contamination of oral poliovirus vaccines with human immunodeficiency virus (HIV) type 1 or a hypothetical progenitor virus from monkeys has created controversy and dispute regarding the origin of AIDS in humans. Twelve monovalent lots of live, attenuated oral poliovirus vaccine types 1, 2, and 3, which were released for use by a North American manufacturer between 1976-1989, were tested for the presence of HIV-1 and simian immunodeficiency virus (SIV). HIV/SIV were not detected in these monovalent poliovirus vaccine lots with the reverse transcriptase assay, a general detection assay, and highly sensitive and specific polymerase chain reaction assays.

Efficacy of serum lactate dehydrogenase and its isozymes in monitoring the therapy in patients with acute leukemia.

The pretreatment levels of serum Lactate Dehydrogenase (LDH) and its isozymes are measured in 12 cases of Acute Lymphoid Leukemia (ALL) and 8 cases of Acute Myeloid Leukemia (AML) and compared with 14 matched healthy controls. Patients showed only first three bands of LDH while normal sera exhibited five bands. A significant increase in total LDH activity was observed in patients of both the groups as compared to controls at the time of admission. The patients were treated with chemotherapy and were followed at 72 hrs. and after 4 weeks. The patients who successfully responded to the therapy showed increased levels of total LDH and LDH2 and LDH3 isoenzymes as early as 72 hrs. after commencement of the therapy. The nonresponders, on the other hand, circulated, decreased or unaltered values of isozymes during this interval. Following them up for a month, ALL responders showed decreased values of total LDH activity, LDH2 and LDH3 activities when compared with their 72 hour values except LDH1. Non responders of this group had practically unaltered values of these isozymes. AML responders circulated decreased values of all the isozymes while AML non responders "showed significant increases in total LDH, and all its isozymes as compared with their 72 hour values. The determination of total enzyme and its isozyme levels at pre, mid and end of treatment seems to be a promising biochemical parameter to predict the early response to chemotherapy administered.

Efficacy of serum sialoglycoproteins as a biomarker of the disease activity & treatment monitoring in patients with base tongue malignancy.

Serum levels of sialoglycoprotein constituents i.e., sialic acid, seromucoid hexoses, and mucoid proteins were determined in 34 patients with base tongue malignancy and 15 controls matched for age and sex. All three constituents were found to be significantly raised; however, only sialic acid levels increased with the severity of the disease. More than 92 per cent of the patients in each clinical stage showed abnormal values of hexoses and mucoid proteins in seromucoids. Electrophoretic separation showed a split in alpha-2-glycoprotein at pretreatment time in 67.6 per cent of the patients. On administration of radiotherapy, all three fractions decreased while alpha-2- split disappeared in 61.8 per cent patients and gamma glycoprotein peak emerged at the end of the protocol with a parallel decrease in these three constituents. It may be concluded from the data that serum sialoglycoproteins can be useful to monitor therapy in base tongue malignancy patients.