Evaluation of immunologic parameters in canine glioma patients treated with an oncolytic herpes virus

AIM

To molecularly characterize the tumor microenvironment and evaluate immunologic parameters in canine glioma patients before and after treatment with oncolytic human IL-12-expressing herpes simplex virus (M032) and in treatment naïve canine gliomas.

METHODS

We assessed pet dogs with sporadically occurring gliomas enrolled in Stage 1 of a veterinary clinical trial that was designed to establish the safety of intratumoral oncoviral therapy with M032, a genetically modified oncolytic herpes simplex virus. Specimens from dogs in the trial and dogs not enrolled in the trial were evaluated with immunohistochemistry, NanoString, Luminex cytokine profiling, and multi-parameter flow cytometry.

RESULTS

Treatment-naive canine glioma microenvironment had enrichment of Iba1 positive macrophages and minimal numbers of T and B cells, consistent with previous studies identifying these tumors as immunologically "cold". NanoString mRNA profiling revealed enrichment for tumor intrinsic pathways consistent with suppression of tumor-specific immunity and support of tumor progression. Oncolytic viral treatment induced an intratumoral mRNA transcription signature of tumor-specific immune responses in 83% (5/6) of canine glioma patients. Changes included mRNA signatures corresponding with interferon signaling, lymphoid and myeloid cell activation, recruitment, and T and B cell immunity. Multiplexed protein analysis identified a subset of oligodendroglioma subjects with increased concentrations of IL-2, IL-7, IL-6, IL-10, IL-15, TNFα, GM-CSF between 14 and 28 days after treatment, with evidence of CD4⁺ T cell activation and modulation of IL-4 and IFNγ production in CD4⁺ and CD8⁺ T cells isolated from peripheral blood.

CONCLUSION

These findings indicate that M032 modulates the tumor-immune microenvironment in the canine glioma model.

γ₁34.5-deleted HSV-1-expressing human cytomegalovirus IRS1 gene kills human glioblastoma cells as efficiently as wild-type HSV-1 in normoxia or hypoxia

Pathophysiological hypoxia, which fosters the glioma stem-like cell (GSC) phenotype, is present in high-grade gliomas and has been linked to tumor development, invasiveness, and resistance to chemotherapy and radiation. Oncolytic virotherapy with engineered herpes simplex virus-1 (HSV-1) is a promising therapy for glioblastoma; however efficacy of γ₁34.5-deleted HSVs, which have been used in clinical trials, was diminished in hypoxia. We investigated the ability of a chimeric HCMV/HSV-1 virus, which expresses the human CMV PKR evasion gene IRS1 and is in preparation for clinical trials, to infect and kill adult and pediatric patient-derived glioblastoma xenografts in hypoxia and normoxia. Infectivity, cytotoxicity and viral recovery were significantly greater with the chimeric virus compared to the γ₁34.5-deleted virus, regardless of oxygen tension. The chimeric virus infected and killed CD133+ GSCs similarly to wild-type HSV-1. Increased activation of mitogen-activated protein kinase (MAPK) p38 and its substrate heat shock protein 27 (Hsp27) was seen after viral infection in normoxia compared to hypoxia. Hsp27 knockdown or p38 inhibition reduced virus recovery indicating that the p38 pathway plays a role in the reduced efficacy of the γ₁34.5-deleted virus in hypoxia. Together these findings demonstrate chimeric HCMV/HSV-1 efficiently targets both CD133+ GSCs and glioma cells in hypoxia.

Assessment of oncolytic HSV efficacy following increased entry-receptor expression in malignant peripheral nerve sheath tumor cell lines

Limited expression and distribution of nectin-1, the major herpes simplex virus (HSV) type-1 entry-receptor, within tumors has been proposed as an impediment to oncolytic HSV (oHSV) therapy. To determine whether resistance to oHSVs in malignant peripheral nerve sheath tumors (MPNSTs) was explained by this hypothesis, nectin-1 expression and oHSV viral yields were assessed in a panel of MPNST cell lines using γ134.5-attenuated (Δγ134.5) oHSVs and a γ134.5 wild-type (wt) virus for comparison. Although there was a correlation between nectin-1 levels and viral yields with the wt virus (R=0.75, P =0.03), there was no correlation for Δγ134.5 viruses (G207, R7020 or C101) and a modest trend for the second-generation oHSV C134 (R=0.62, P=0.10). Nectin-1 overexpression in resistant MPNST cell lines did not improve Δγ134.5 oHSV output. While multistep replication assays showed that nectin-1 overexpression improved Δγ134.5 oHSV cell-to-cell spread, it did not confer a sensitive phenotype to resistant cells. Finally, oHSV yields were not improved with increased nectin-1 in vivo. We conclude that nectin-1 expression is not the primary obstacle of productive infection for Δγ134.5 oHSVs in MPNST cell lines. In contrast, viruses that are competent in their ability to counter the antiviral response may derive benefit with higher nectin-1 expression.

Increased oncolytic efficacy for high-grade gliomas by optimal integration of ionizing radiation into the replicative cycle of HSV-1

Oncolytic viruses have been combined with standard cancer therapies to increase therapeutic efficacy. Given the sequential activation of herpes viral genes (herpes simplex virus-1, HSV-1) and the temporal cellular changes induced by ionizing radiation, we hypothesized an optimal temporal sequence existed in combining oncolytic HSV-1 with ionizing radiation. Murine U-87 glioma xenografts were injected with luciferase encoding HSV-1, and ionizing radiation (IR) was given at times before or after viral injection. HSV-1 replication and tumor-volume response were followed. Radiation given 6-9 h after HSV-1 injection resulted in maximal viral luciferase expression and infectious viral production in tumor xenografts. The greatest xenograft regression was also seen with radiation given 6 h after viral injection. We then tested if HSV-1 replication had a dose response to ionizing radiation. HSV-1 luciferase expression exhibited a dose response as xenografts were irradiated from 0 to 5 Gy. There was no difference in viral luciferase expression as IR dose increased from 5 Gy up to 20 Gy. These results suggest that the interaction of IR with the HSV-1 lytic cycle can be manipulated for therapeutic gain by delivering IR at a specific time within viral replicative cycle.

High-resolution longitudinal assessment of flow and permeability in mouse glioma vasculature: Sequential small molecule and SPIO dynamic contrast agent MRI

The poor prognosis associated with malignant glioma is largely attributable to its invasiveness and robust angiogenesis. Angiogenesis involves host-tumor interaction and requires in vivo evaluation. Despite their versatility, few studies have used mouse glioma models with perfusion MRI approaches, and generally lack longitudinal study design. Using a micro-MRI system (8.5 Tesla), a novel dual bolus-tracking perfusion MRI strategy was implemented. Using the small molecule contrast agent Magnevist, dynamic contrast enhanced MRI was implemented in the intracranial 4C8 mouse glioma model to determine K(trans) and v(e), indices of tumor vascular permeability and cellularity, respectively. Dynamic susceptibility contrast MRI was subsequently implemented to assess both cerebral blood flow and volume, using the macromolecular superparamagnetic iron oxide, Feridex, which circumvented tumor bolus susceptibility curve distortions from first-pass extravasation. The high-resolution parametric maps obtained over 4 weeks, indicated a progression of tumor vascularization, permeability, and decreased cellularity with tumor growth. In conclusion, a comprehensive array of key parameters were reliably quantified in a longitudinal mouse glioma study. The syngeneic 4C8 intracerebral mouse tumor model has excellent characteristics for studies of glioma angiogenesis. This approach provides a useful platform for noninvasive and highly diagnostic longitudinal investigations of anti-angiogenesis strategies in a relevant orthotopic animal model.

Treatment of recurrent malignant glioma with G207, a genetically engineered herpes simplex virus-1, followed by irradiation: Phase I study results

2042

Background: G207 is a doubly mutated (deletion of both γ134.5 loci, insertional inactivation of UL39) herpes simplex virus (HSV)-1. Safety and efficacy of intracerebral inoculations of G207 to patients suffering from recurrent malignant gliomas have been demonstrated in previous clinical trials. Methods: In this phase I clinical trial, a total of 1 x 109 plaque forming units (pfu) G207 were administered by five stereotactic injections of 0.2 mL each into regions of recurrent malignant glioma defined by MRI, followed by focal radiation therapy 24 hours post injection. Included patients suffered from inoperable pathologically proven recurrent glioblastoma multiforme (GBM) or anaplastic astrocytoma (AA) which was progressive despite radiotherapy or chemotherapy and failed external beam radiotherapy > 5 Gray prior to study enrolment. Results: 9 patients were treated in this phase I study. 5 patients were suffering from relapsed GBM, 4 patients were suffering from relapsed AA. 1 month after treatment, 3 patients (3xGBM) showed SD, 2 patients (1xGBM, 1xAA) PR, and 4 patients (1xGBM, 3xAA) PD. The 2 patients with initial PR (1xGBM, 1xAA) were re-treated with G207/Irradiation at time point of tumor recurrence, showing PR one month after re-treatment again. Median overall survival time for all 9 patients was 229 days (7.6 months), with one patient still alive at time of abstract submission. In patients suffering from relapsed GBM, mOS was 7.4 months, in patients suffering from relapsed AA, mOS was 9.25 months. 20 serious adverse events occurred in this study, only 3 were possible/probable related to G207/irradiation. Within persistent areas of tumor, HSV staining was present by using a polyclonal antibody for HSV, indicating intratumoral G207 replication (proof of concept). Conclusions: In 9 patients suffering from relapsed GBM or AA, stereotactic intracerebral G207 inoculation followed by radiation therapy was feasible, safe, and induced clinically relevant responses. G207/Irradiation re-treatment was possible and induced anew clinical responses. Median overall survival is superior to published data in this patient population. Therefore, further clinical development of G207 in GBM is medically reasonable.

[Table: see text]

A phase I study of ABT 510 and concurrent temozolamide and radiotherapy for patients with newly diagnosed glioblastoma multiforme

2023

Background: ABT-510 (Abbott Laboratories, Abbott Park, IL, USA) is a Thrombospondin-1 (TSP-1) mimetic drug with anti-angiogenic properties. This phase I dose escalation trial was designed to study the maximum tolerated dose (MTD) of ABT 510 when used concurrently with temozolomide (TMZ) and radiotherapy (RT) in patients with newly diagnosed glioblastoma multiforme (GBM). Methods: A total of 23 patients with newly diagnosed, histologically verified GBM were enrolled between April 2005 and January 2007, after obtaining written consent. The study was approved by the University of Alabama at Birmingham (UAB) Institutional Review Board. Four cohorts with three patients in each, receiving subcutaneous ABT 510 injection at doses of 20, 50, 100, and 200 mg/day were studied. The starting dose was primarily based on preclinical findings from animal studies and phase I studies on healthy subjects and cancer patients. Treatment plan included 10 weeks of induction phase (TMZ and RT with ABT 510) followed by a maintenance phase (ABT 510 and TMZ) of 14 cycles each consisting of 28 days. Patients were monitored with brain MRI along with laboratory values for dose limiting toxicities (DLT) defined as grades 3–4 non-hematological toxicities and grade 4 hematological toxicities (neutropenia or thrombocytopenia). In the absence of a DLT in at least two of the three patients, the dose was increased by 50% in the next cohort of patients. Therapy was discontinued if 14 maintenance cycles were completed, disease progression occurred, or if the patient requested withdrawal. Disease progression and survival statistics were analyzed. Results: During this trial, grade 3/4 DLT were not observed even after the dose was increased to 200 mg/day, hence, the last cohort was expanded to include 14 patients. A MTD was not defined. The median time to tumor progression (TTP) was 220 days and the median overall survival was 422 days. Gene expression analysis of the tumor pathology will be performed to evaluate the relationship between the expression of TSP-1, TSP-2, and patient response to the drug. Conclusions: ABT 510, at subcutaneous doses up to 200 mg/day, is tolerated well with concurrent TMZ and RT in patients with newly diagnosed GBM.

No significant financial relationships to disclose.

Mutation of Escherichia coli cytosine deaminase significantly enhances molecular chemotherapy of human glioma

Combined treatment using adenoviral (Ad)-directed enzyme/prodrug therapy and radiation therapy has the potential to become a powerful method of cancer therapy. We have developed an Ad vector encoding a mutant bacterial cytosine deaminase (bCD) gene (AdbCD-D314A), which has a higher affinity for cytosine than wild-type bCD (bCDwt). The purpose of this study was to evaluate cytotoxicity in vitro and therapeutic efficacy in vivo of the combination of AdbCD-D314A with the prodrug 5-fluorocytosine (5-FC) and ionizing radiation against human glioma. The present study demonstrates that AdbCD-D314A infection resulted in increased 5-FC-mediated cell killing, compared with AdbCDwt. Furthermore, a significant increase in cytotoxicity following AdbCD-D314A and radiation treatment of glioma cells in vitro was demonstrated as compared to AdbCDwt. Animal studies showed significant inhibition of subcutaneous or intracranial tumor growth of D54MG glioma xenografts by the combination of AdbCD-D314A/5-FC with ionizing radiation as compared with either agent alone, and with AdbCDwt/5-FC plus radiation. The results suggest that the combination of AdbCD-D314A/5-FC with radiation produces markedly increased cytotoxic effects in cancer cells in vitro and in vivo. These data indicate that combined treatment with this novel mutant enzyme/prodrug therapy and radiotherapy provides a promising approach for cancer therapy.

Enhanced antiglioma activity of chimeric HCMV/HSV-1 oncolytic viruses

Oncolytic herpes simplex virus (HSV)-1 gamma(1)34.5-deletion mutants (Deltagamma(1)34.5 HSV) are promising agents for tumor therapy. The attenuating mutation renders the virus aneurovirulent but also limits late viral protein synthesis and efficient replication in many tumors. We tested whether one function of gamma(1)34.5 gene, which mediates late viral protein synthesis through host protein kinase R (PKR) antiviral response evasion, could be restored, without restoring the neurovirulence. We have previously reported the construction of two chimeric Deltagamma(1)34.5 HSV vectors (chimeric HSV), C130 and C134, which express the human cytomegalovirus (HCMV) PKR-evasion genes TRS1 and IRS1, respectively. We now demonstrate the following. The HCMV/HSV-1 chimeric viruses (i) maintain late viral protein synthesis in the human malignant glioma cells tested (D54-MG, U87-MG and U251-MG); (ii) replicate to higher titers than Deltagamma(1)34.5 HSV in malignant glioma cells in vitro and in vivo; (iii) are aneurovirulent; and (iv) are superior to other Deltagamma(1)34.5 HSV with both improved reduction of tumor volumes in vivo, and improved survival in two experimental murine brain tumor models. These findings demonstrate that transfer of HCMV IRS1 or TRS1 gene into Deltagamma(1)34.5 HSV significantly improves replication in malignant gliomas without restoring wild-type neurovirulence, resulting in enhanced tumor reduction and prolonged survival.

Directing adenovirus across the blood–brain barrier via melanotransferrin (P97) transcytosis pathway in an in vitro model

Adenovirus serotype 5 (Ad5) is widely used in the development of gene therapy protocols. However, current gene therapy strategies involving brain are mostly based on intra-cranial injection. A major obstacle for systemically administered vectors to infect brain tissue is the blood-brain barrier (BBB). One strategy to cross the BBB is transcytosis, a transcellular transport process that shuttles a molecule from one side of the cell to the other side. Recently, melanotransferrin (MTf)/P97 was found to be able to cross the BBB and accumulate in brain. We thus hypothesize that re-directing Ad5 vectors to the MTf transcytosis pathway may facilitate Ad5 vectors to cross the BBB. To test this hypothesis, we constructed a bi-specific adaptor protein containing the extracellular domain of the coxsackie-adenovirus receptor (CAR) and the full-length melanotransferrin (sCAR-MTf), and investigated its ability to re-direct Ad5 vectors to the MTf transcytosis pathway. We found this adaptor protein could re-direct Ad5 to the MTf transcytosis pathway in an in vitro BBB model, and the transcytosed Ad5 viral particles retained their native infectivity. The sCAR-MTf-mediated Ad5 transcytosis was temperature- and dose dependent. In addition, we examined the directionality of sCAR-MTf-mediated Ad5 transcytosis, and found the efficiency of apical-to-basal transcytosis was much higher than that of basal-to-apical direction, supporting a role of this strategy in transporting Ad5 vectors towards the brain. Taken together, our study demonstrated that re-directing Ad5 to the MTf transcytosis pathway could facilitate gene delivery across the BBB.

Engineered herpes simplex virus expressing bacterial cytosine deaminase for experimental therapy of brain tumors

Lack of effective therapy of primary brain tumors has promoted the development of novel experimental approaches utilizing oncolytic viruses combined with gene therapy. Towards this end, we have assessed a conditionally replication-competent, gamma(1)34.5-deleted herpes simplex virus type 1 (HSV-1) expressing cytosine deaminase (CD) for treatment of malignant brain tumors. Our results are summarized as follows: (i) a recombinant HSV (M012) was constructed in which both copies of the gamma(1)34.5 gene were replaced with the bacterial CD gene, under the control of the cellular promoter Egr-1; (ii) M012-infected cells in vitro efficiently convert 5-fluorocytosine (5-FC) to 5-fluorouracil, thereby enhancing cytotoxicity of neighboring, uninfected cells; (iii) both direct and bystander cytotoxicity of murine neuroblastoma and human glioma cell lines after infection with M012 were demonstrated; (iv) direct intracerebral inoculation of A/J mice demonstrated lack of neurotoxicity at doses similar to G207, a gamma(1)34.5-deleted HSV with demonstrated safety in human patient trials and (v) intratumoral injection of M012 into Neuro-2a flank tumors in combination with 5-FC administration significantly reduced tumor growth versus tumors treated with R3659 combined with 5-FC, or treated with M012 alone. Thus, M012 is a promising new oncolytic HSV vector with an enhanced prodrug-mediated, antineoplastic effect that is safe for intracranial administration.

Ex vivo activation and expansion of γδ T cells for immunotherapy of glioblastoma

2553

Background: Activated γδ T cells will efficiently kill established glioblastoma (GBM) cell lines in vitro. However, their potential for cell therapy has been limited by their relatively small numbers in the peripheral blood and their sensitivity to activation induced cell death (AICD) during ex vivo expansion. Our laboratory developed a method whereby γδ T cells, when stimulated by IFN-γ, IL- 12, and anti-CD2, acquire resistance to AICD and can be expanded in culture with anti-CD3 and IL-2. The γδ T cells expanded by this method are highly cytotoxic to GBM. We have now sought to adapt the laboratory method for human use. Methods: The laboratory method and selection procedure were modified to employ pharmaceutical-grade reagents. Peripheral blood mononuclear cells (1.0 × 106/ml) were stimulated overnight with media containing cGMP grade human serum, IFN-γ, IL-12, and anti-CD2. Media containing human serum, IL-2 and anti-CD3 was then added (1 v/v) and refreshed 1 v/v 3× weekly. The cultures were harvested after two weeks followed by depletion of CD4+ and CD8+ T cells, thereby enriching γδ T cells. Cytotoxicity of expanded of γδ T cells was evaluated against GBM primary tumor cultures, established GBM cell lines, and cultured astrocytes using a commercial flow cytometric method. Results: After two weeks in culture, γδ T cells expanded up to 1000 fold (usually 200–400 fold), consistent with results from our previous research-scale method. Positive selection yielded a γδ T cell product with >80% purity and >70% recovery. The cell products exhibited incremental cytotoxicity against several primary GBM cultures and established GBM cell lines. Astrocytoma cells were not killed. Conclusions: Apoptosis-resistant γδ T cells can be expanded and selected using clinically approvable reagents and in numbers sufficient for immunotherapy of malignant brain tumors. Initial data show that expanded γδ T cells retain cytotoxicity against the GBM primary cultures and spare normal astrocytes.

No significant financial relationships to disclose.

The use of a genetically engineered herpes simplex virus (R7020) with ionizing radiation for experimental hepatoma

The herpes simplex virus (HSV) recombinant virus R7020 is an attenuated virus designed as a candidate for immunization against both HSV-1 and HSV-2 infections. It was extensively tested in an experimental animal system and in a healthy human adult population without significant untoward effects. We report on the use of R7020 with ionizing radiation as an oncolytic agent for hepatomas. Two hepatoma cell lines were studied, Hep3B and Huh7. R7020 replicated to higher titers in Hep3B cells than in Huh7 cells. Tissue culture studies correlated with hepatoma xenograft responses to R7020. R7020 was more effective in mediating Hep3B tumor xenograft regression compared with Huh7. Ionizing radiation combined with R7020 also showed differential results in antitumor efficacy between the two cell lines in tumor xenografts. Ionizing radiation enhanced the replication of R7020 in Hep3B xenografts. Moreover, the combination of ionizing radiation and virus caused a greater regression of xenograft volume than either R7020 or radiation alone. Ionizing radiation had no effect on the replication of R7020 virus in Huh7 xenografts. These results indicate that a regimen involving infection with an appropriate herpesvirus such as R7020 in combination with ionizing radiation can be highly effective in eradicating certain tumor xenografts.

RNA replicons derived from poliovirus are directly oncolytic for human tumor cells of diverse origins

The failure and/or toxicity of conventional therapies for many types of human cancers underscore the need for development of safe and effective alternative treatments. Toward this goal, we describe the direct oncolytic activity of RNA-based vectors derived from poliovirus, termed replicons, which are genetically incapable of producing infectious virus. These replicons are cytopathic in vitro for human tumor cells originating from brain, breast, lung, ovary, and skin (melanoma). The cytopathic effects in a malignant glioma cell line were associated with nuclear DNA condensation, indicative of cells undergoing apoptosis. Injection of replicons into established xenograft flank tumors in scid mice resulted in oncolytic activity and extended survival. Inoculation of replicons into established intracranial xenograft tumors in scid mice resulted in tumor infection within 8 h and extended survival. Histological analysis revealed that replicons had infected tumor cells at the site of inoculation and, most importantly, diffused to infect tumor cells that had metastasized from the initial site of implantation. The wide spectrum of cytopathic activity for human tumors combined with effective distribution after in vivo inoculation establishes the therapeutic potential of poliovirus replicons for a variety of cancers.

pH alterations "reset" Ca2+ sensitivity of brain Na+ channel 2, a degenerin/epithelial Na+ ion channel, in planar lipid bilayers

Members of the degenerin/epithelial Na(+) channel superfamily of ion channels subserve many functions, ranging from whole body sodium handling to mechanoelectrical transduction. We studied brain Na(+) channel 2 (BNaC-2) in planar lipid bilayers to examine its single channel properties and regulation by Ca(2+). Upon incorporation of vesicles made from membranes of oocytes expressing either wild-type (WT) BNaC-2 or BNaC-2 with a gain-of-function (GF) point mutation (G433F), functional channels with different properties were obtained. WT BNaC-2 resided in a closed state with short openings, whereas GF BNaC-2 was constitutively activated; a decrease in the pH in the trans compartment of the bilayer activated WT BNaC-2 and decreased its permeability for Na(+) over K(+). Moreover, these maneuvers made the WT channel more resistant to amiloride. In contrast, GF BNaC-2 did not respond to a decrease in pH, and its amiloride sensitivity and selectivity for Na(+) over K(+) were unaffected by this pH change. Buffering the bathing solutions with EGTA to reduce the free [Ca(2+)] to <10 nm increased WT single channel open probability 10-fold, but not that of GF BNaC-2. Ca(2+) blocked both WT and GF BNaC-2 in a dose- and voltage-dependent fashion; single channel conductances were unchanged. A drop in pH reduced the ability of Ca(2+) to inhibit these channels. These results show that BNaC-2 is an amiloride-sensitive sodium channel and suggest that pH activation of these channels could be, in part, a consequence of H(+) "interference" with channel regulation by Ca(2+).

Evidence for peroxynitrite-mediated modifications to p53 in human gliomas: possible functional consequences

Based on previous findings of increased nitric oxide synthase (NOS) expression in human gliomas (4), we hypothesized that peroxynitrite, a highly reactive metabolite of nitric oxide (NO) and superoxide (O(*-)(2)), might be increased in these tumors in vivo. Here we demonstrate that nitrotyrosine (a footprint of peroxynitrite protein modification) is present in human malignant gliomas. Furthermore, we show that p53, a key tumor suppressor protein, has evidence of peroxynitrite-mediated modifications in gliomas in vivo. Experiments in vitro demonstrate that peroxynitrite treatment of recombinant wild-type p53 at physiological concentrations results in formation of higher molecular weight aggregates, tyrosine nitration, and loss of specific DNA binding. Peroxynitrite treatment of human glioma cell lysates similarly resulted in selective tyrosine nitration of p53 and was also associated with loss of p53 DNA binding ability. These data indicate that tyrosine nitration of proteins occurs in human gliomas in vivo, that p53 may be a target of peroxynitrite in these tumors, and that physiological concentrations of peroxynitrite can result in a loss of p53 DNA binding ability in vitro. These findings raise the possibility that peroxynitrite may contribute to loss of wild-type p53 functional activity in gliomas by posttranslational protein modifications.

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.

Fas-induced expression of chemokines in human glioma cells: involvement of extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase

Fas transduces not only apoptotic signals through various pathways but also angiogenic and proinflammatory responses in vivo. Human glioma cells express Fas although sensitivity to Fas-mediated cell death is variable, suggesting that Fas may have functions other than apoptosis in these cells. In this study, we addressed alternative functions of Fas expressed on human gliomas by Fas ligation in three human glioma cell lines, CRT-MG, U373-MG, and U87-MG, and the in vivo expression of Fas and chemokines in human glioblastoma multiforme (GBM). Herein, we demonstrate that: (a) stimulation with agonistic anti-Fas monoclonal antibody CH-11 and human recombinant soluble Fas ligand induces expression of the CC chemokine MCP-1 and the CXC chemokine interleukin-8 by human glioma cell lines at the mRNA and protein levels in a dose- and time-dependent manner; (b) selective pharmacological inhibitors of MEK1 (U0126 and PD98059) and p38 mitogen-activated protein kinase (MAPK) (SB202190) suppress Fas-mediated chemokine expression in a dose-dependent manner; (c) Fas ligation on human glioma cells leads to activation of both extracellular signal-regulated kinases ERK1/ERK2 and p38 MAPK; and (d) GBM samples express higher levels of Fas compared with normal control brain, which correlates with increased interleukin 8 expression. These findings indicate that Fas ligation on human glioma cells leads to the selective induction of chemokine expression, which involves the ERK1/ERK2 and p38 MAPK signaling pathways. Therefore, the Fas-Fas ligand system in human brain tumors may be involved not only in apoptotic processes but also in the provocation of angiogenic and proinflammatory responses.

Genetically engineered human herpes simplex virus in the treatment of brain tumours

Central nervous system malignancies--particularly glioblastoma multiforme--pose significant problems for the development of novel therapeutics. In the absence of advances with standard surgical and chemotherapeutic approaches, the utilization of genetically engineered viruses--both as direct oncolytic agents (virus therapy) and for the delivery of foreign proteins (gene therapy)--represents a significant advance in the experimental approach to the management of patients with incurable tumours. Among other viruses, herpes simplex virus (HSV) offers an opportunity to influence the replication of tumour cells directly within the central nervous system. The propensity for HSV to replicate in tumour cells, and its large coding capacity, provide an experimental model for the development of novel therapeutics. The status of these experimental approaches and Phase I studies are summarized.

HuR, a RNA stability factor, is expressed in malignant brain tumors and binds to adenine- and uridine-rich elements within the 3' untranslated regions of cytokine and angiogenic factor mRNAs

Tumors of the central nervous system (CNS) often have sustained expression of labile genes, including angiogenic growth factors and immunosuppressive cytokines, which promote tumor progression. Stabilization of the RNA transcripts for these genes, such as vascular endothelial growth factor (VEGF), is an important molecular pathway for this up-regulation. HuR, a member of the Elav family of RNA-binding proteins, has been implicated in this pathway through its binding to adenine and uridine (AU)-rich stability elements (ARE) located in the 3' untranslated regions (3'-UTRs) of the mRNA. Whereas three of the Elav family members (Hel-N1, HuC, and HuD) are restricted to young and mature neurons, HuR is more broadly expressed, including proliferating cells of the developing CNS. Because RNA stabilization of labile genes may promote tumor growth, we analyzed and compared the expression pattern of HuR in 35 freshly resected and cultured CNS tumors to determine whether there was any correlation with tumor grade or histological type. We found that HuR mRNA was consistently expressed in all of the tumors, regardless of cell origin or degree of malignancy. Using a novel HuR-specific polyclonal antibody, we found that strong HuR protein expression was limited to high-grade malignancies (glioblastoma multiforme and medulloblastoma). Within the glioblastoma multiforme, prominent HuR expression was also detected in perinecrotic areas in which angiogenic growth factors are up-regulated. To further define its role as a potential RNA stabilizer, we analyzed whether HuR could bind to the stability motifs within the 3'-UTRs of cytokines and growth factors linked to brain tumor progression. We used a novel ELISA-based RNA binding assay and focused on the 3'-UTRs of angiogenic factors VEGF, COX-2, and (interleukin) IL-8 as well as the immunomodulating factors IL-6, transforming growth factor (TGF)-beta and tumor necrosis factor (TNF)-alpha as potential RNA ligands. Our results indicated overall a very high binding affinity to these RNA targets. A comparison of these ligands revealed a hierarchy of binding affinities with the angiogenic factors, and TGF-beta showing the highest (Kd of 1.8-3.4 nM), and TNF-alpha the lowest (Kd of 18.3 nM). The expression pattern of HuR, coupled with the RNA binding data, strongly suggests a role for this protein in the posttranscriptional regulation of these genes in CNS tumors.

Human malignant glioma therapy using anti-alpha(v)beta3 integrin agents

Glioblastoma multiforme (GBM) is the most frequent malignant brain tumor in adults and is invariably fatal. We have investigated the effect of cyclo-(Arg-Gly-Asp-D-Phe-Val) (cRGDfV) peptide on survival of human malignant glioma cells in vitro and in vivo. Immunofluorescent analyses revealed the presence of alpha(v)beta3 integrin on U-87MG and U-373MG cells, but minimal expression on U-251MG cells. Treatment of U-87MG and U-373MG cells in vitro with cRGDfV (20 microg/ml), but not the linear peptide, resulted in the appearance of rounded and loosely attached cells with subsequent cell death. By comparison, neither this cyclic peptide nor its linear homolog had any significant effect on growth and morphology of U-251MG cells. The death of cRGDfV-treated (20 microg/ml) glioma cells was blocked by pretreatment (10 microM) of cells with DEVD-FMK and LEHD-FMK, inhibitors of caspase-3 and caspase-9, respectively. Moreover, when glioma cells grown as spheroids were treated with cRGDfV (50 microg/ml), spheroid formation was markedly reduced. Further, treatment of intracranial U-87MG tumors in scid mice with cyclic peptide significantly (p < 0.001) prolonged their survival. These results indicated (i) that cRGDfV induced apoptosis of human glioma cells by binding alpha(v)beta3 integrin expressed on their cell surfaces and (ii) that cRGDfV may be an effective and non-toxic direct anti-tumor therapy for alpha(v)beta3-expressing GBMs.

Differential gene expression profiling in human brain tumors

Gene expression profiling of three human temporal lobe brain tissue samples (normal) and four primary glioblastoma multiforme (GBM) tumors using oligonucleotide microarrays was done. Moreover, confirmation of altered expression was performed by whole cell patch clamp, immunohistochemical staining, and RT-PCR. Our results identified several ion and solute transport-related genes, such as N-methyl-d-aspartate (NMDA) receptors, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)-2 receptors, GABA(A) receptor subunits alpha3, beta1, beta2, and beta3, the glutamate transporter, the glutamate/aspartate transporter II, the potassium channel K(V)2.1, hK(V)beta3, and the sodium/proton exchanger 1 (NHE-1), that are all downregulated in the tumors compared with the normal tissues. In contrast, aquaporin-1, possibly aquaporins-3 and -5, and GLUT-3 message appeared upregulated in the tumors. Our results also confirmed previous work showing that osteopontin, nicotinamide N-methyltransferase, murine double minute 2 (MDM2), and epithelin (granulin) are upregulated in GBMs. We also demonstrate for the first time that the cytokine and p53 binding protein, macrophage migration inhibitory factor (MIF), appears upregulated in GBMs. These results indicate that the modulation of ion and solute transport genes and heretofore unsuspected cytokines (i.e., MIF) may have profound implications for brain tumor cell biology and thus may identify potential useful therapeutic targets in GBMs.

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.

Conditionally replicating herpes simplex virus mutant, G207 for the treatment of malignant glioma: results of a phase I trial

G207 is a conditionally replicating derivative of herpes simplex virus (HSV) type-1 strain F engineered with deletions of both gamma(1)34.5 loci and a lacZ insertion disabling the UL39 gene. We have demonstrated the efficacy of G207 in treating malignant glial tumors in athymic mice, as well as the safety of intracerebral G207 inoculation in mice and in Aotus nancymai. We sought to determine the safety of G207 inoculation into cerebral malignant glial tumors in humans. Criteria for inclusion into this dose-escalation study were the diagnosis of histologically proven malignant glioma, Karnofsky score > or = 70, recurrence despite surgery and radiation therapy, and an enhancing lesion greater than 1 cm in diameter. Serial magnetic resonance images were obtained for volumetric analysis. The trial commenced at a dose of 10(6) plaque forming units (p.f.u.) inoculated at a single enhancing site and was completed when the 21st patient was inoculated with 3x10(9) p.f.u. at five sites. While adverse events were noted in some patients, no toxicity or serious adverse events could unequivocally be ascribed to G207. No patient developed HSV encephalitis. We found radiographic and neuropathologic evidence suggestive of anti-tumor activity and long-term presence of viral DNA in some cases.

Targeted foreign gene expression in spinal cord neurons using poliovirus replicons

A hallmark of poliovirus is the propensity to infect and replicate in spinal cord neurons of the central nervous system. Previously, we characterized a poliovirus self-replicating RNA genome (replicon), which encodes firefly luciferase in place of the capsid genes. This replicon is encapsidated into an authentic poliovirion by providing the poliovirus capsid protein in trans. The amount of enzymatically active luciferase in cells infected with this replicon correlated with the infectious dose. To begin to characterize the in vivo infectious potential of replicons, we have inoculated mice transgenic for the human receptor for poliovirus (PVR), either intracranially or intraspinally, with the replicon encoding luciferase. Wild-type poliovirus delivered to PVR mice via intracranial or intraspinal routes resulted in paralysis and death. Replicon preparations were shown by a sensitive biological assay to be free of infectious poliovirus. Neither intracranial nor intraspinal inoculation of the replicon encoding luciferase resulted in any obvious paralysis or disease symptoms. Following intraspinal inoculation with replicons encoding luciferase, luciferase enzyme activity was detected at 4 h post-inoculation, with peak activity at approximately 8 h post-inoculation; by 48 - 72 h, the luciferase activity had returned to background levels. Luciferase activity was detected in spinal cord predominantly near the site of inoculation, although activity was detected anterior and posterior to the site of inoculation, indicating that replicons undergo limited movement within the CNS presumably via the cerebrospinal fluid. In stark contrast to poliovirus though, inoculation of replicons into the spinal cords of PVR mice did not result in noticeable pathogenesis. Using immunofluorescence with antibodies to double-stain for replicons and neurons, we determined that replicons exclusively infect the neurons of the spinal cord, with the expression of the luciferase and replicon proteins confined to the cytoplasm of the infected cells. Replicons, then, possess the identical capacity for infection of spinal cord neurons in vivo as poliovirus. The lack of discernible neuronal destruction following replicon inoculation into the spinal cord suggests that some of the pathogenesis observed during a poliovirus infection might not be due entirely to primary infection of neurons. Finally, the results of this study point to future use of replicons as a means to target recombinant protein expression to neurons in the spinal cord.

Immunotherapy of a murine T cell lymphoma localized to the brain

Mouse YC8 T cell lymphoma was used as a model to determine whether an effective immunotherapy procedure could be devised for the treatment of lymphoma localized to the brain. Implantation of 5 x 10(4) YC8 cells into the left cerebral hemisphere induced rapid loss of the animal's body weight. Severe loss of weight and early deaths were observed in the untreated control group. Although resistance can be conferred to the brain by immunization of naive BALB/c mice, adoptive chemoimmunotherapy procedures were surprisingly not effective in inducing remissions in animals with lymphoma confined to the brain. Even passive transfer of effector cells from immunized, tumor resistant donor animals combined with systemic IL-2 treatment did not impart resistance to recipients with brain tumors. However, regression of the intracranial tumor and apparent cures could be accomplished, when ex vivo cultured effector cells were transferred intravenously.

Engineered herpes simplex virus expressing IL-12 in the treatment of experimental murine brain tumors

Genetically engineered, neuroattenuated herpes simplex viruses (HSVs) expressing various cytokines can improve survival when used in the treatment of experimental brain tumors. These attenuated viruses have both copies of gamma(1)34.5 deleted. Recently, we demonstrated increased survival of C57BL/6 mice bearing syngeneic GL-261 gliomas when treated with an engineered HSV expressing IL-4, as compared with treatment with the parent construct (gamma(1)34. 5(-)) alone or with a virus expressing IL-10. Herein, we report construction of a conditionally replication-competent mutant expressing both subunits of mIL-12 (M002) and its evaluation in a syngeneic neuroblastoma murine model. IL-12 induces a helper T cell subset type 1 response, which may induce more durable antitumor effects. In vitro studies showed that, when infected with M002, both Vero cells and murine Neuro-2a neuroblastoma cells produced physiologically relevant levels of IL-12 heterodimers, as determined by ELISA. M002 was cytotoxic for Neuro-2a cells and human glioma cell lines U251MG and D54MG. Neurotoxicity studies, as defined by plaque-forming units/LD(50), performed in HSV-1-sensitive A/J strain mice found that M002 was not toxic even at high doses. When evaluated in an intracranial syngeneic neuroblastoma murine model, median survival of M002-treated animals was significantly longer than the median survival of animals treated with R3659, the parent gamma(1)34.5(-) mutant lacking any cytokine gene insert. Immunohistochemical analysis of M002-treated tumors identified a pronounced influx of CD4(+) T cells and macrophages as well as CD8(+) cells when compared with an analysis of R3659-treated tumors. We conclude that M002 produced a survival benefit via oncolytic effects combined with immunologic effects meditated by helper T cells of subset type 1.

Genetically engineered HSV in the treatment of glioma: a review

Central nervous system malignancies, particularly glioblastoma multiforme, pose significant problems for the development of novel therapeutics. In the absence of advances with standard surgical and chemotherapeutic approaches, the utilisation of genetically engineered viruses, both as direct oncolytic agents as well as for the delivery of foreign proteins, represents a significant advance in the experimental approach to management of patients with these incurable tumours. Among other viruses, HSV offers an opportunity to directly influence the replication of tumour cells within the central nervous system. Because of its propensity to replicate in neuronal tissue as well as its large coding capacity, it provides an experimental model for the development of novel therapeutics. The status of these experimental approaches will be summarised in this review.

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.

Ionizing radiation improves survival in mice bearing intracranial high-grade gliomas injected with genetically modified herpes simplex virus

Malignant gliomas remain incurable with current interventions. Encouraging investigational approaches include the use of genetically modified herpes simplex-1 (HSV-1) viruses as direct cytotoxic agents. Combining attenuated HSV-1 with standard therapy, human U-87 malignant glioma xenografts grown in the hind limb or intracranially in athymic nude mice were exposed to ionizing radiation, inoculated with genetically modified HSV R3616, or received both virus and radiation. The combination of virus with fractionated ionizing radiation suggests a synergistic action and results in reduced tumor volumes and longer survivals when compared with treatment with either modality alone.

Malignant human gliomas express an amiloride-sensitive Na+ conductance

Human astrocytoma cells were studied using whole cell patch-clamp recording. An inward, amiloride-sensitive Na+ current was identified in four continuous cell lines originally derived from human glioblastoma cells (CH235, CRT, SKMG-1, and U251-MG) and in three primary cultures of cells obtained from glioblastoma multiforme tumors (up to 4 passages). In addition, cells freshly isolated from a resected medulloblastoma tumor displayed this same characteristic inward current. In contrast, amiloride-sensitive currents were not observed in normal human astrocytes, low-grade astrocytomas, or juvenile pilocytic astrocytomas. The only amiloride-sensitive Na+ channels thus far molecularly identified in brain are the brain Na+ channels (BNaCs). RT-PCR analyses demonstrated the presence of mRNA for either BNaC1 or BNaC2 in these tumors and in normal astrocytes. These results indicate that the functional expression of amiloride-sensitive Na+ currents is a characteristic feature of malignant brain tumor cells and that this pathway may be a potentially useful target for therapeutic intervention.

Glioma migration can be blocked by nontoxic inhibitors of myosin II

Anaplastic gliomas are infiltrative tumors, and their ability to migrate through normal brain contributes to their highly malignant behavior. Invasion of brain requires cell motility, which in turn depends on the activity of the cytoskeleton. A cytoskeletal component central to this process is myosin II, the cytoplasmic analogue of smooth and skeletal muscle myosin. Myosin II activity is regulated by the enzyme myosin light chain kinase, which activates myosin II by phosphorylating it on its regulatory light chain. We have investigated the role of myosin II in glioma motility and invasiveness by examining the effects of two inhibitors of myosin light chain kinase, ML7 and KT5926. Both drugs are potent inhibitors of both glioma motility, as measured by a scrape motility assay, and an in vitro haptotaxis assay. The inhibition of in vitro haptotaxis follows the dose-response relationship expected for competitive inhibition of myosin light chain kinase by these drugs and is seen at drug concentrations that are nontoxic. These results highlight the important role that myosin II contributes to glioma invasiveness and suggest that it may serve as a target in future strategies at blocking invasion by these tumors.

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.

Replication-competent, nonneuroinvasive genetically engineered herpes virus is highly effective in the treatment of therapy-resistant experimental human tumors

A genetically engineered, nonneurotropic herpes simplex virus (R7020) with a proven safety profile in both animals and humans was found effective in the treatment of large xenotransplanted tumors arising from a radiation- and chemotherapy-resistant human epidermoid carcinoma and a hormone-refractory prostate adenocarcinoma. R7020 replicated to high titer and caused rapid regression of the human tumor xenografts. Tumor destruction was accelerated in animals given both R7020 and fractionated ionizing radiation. Tumors arising from cells surviving one treatment with R7020 were fully susceptible to a second dose of virus. We conclude R7020 is an effective antitumor agent for non-central nervous system tumor xenografts with an excellent safety profile.

Gene therapy of cancer: activation of nucleoside prodrugs with E. coli purine nucleoside phosphorylase

During the last few years, many gene therapy strategies have been developed for various disease targets. The development of anticancer gene therapy strategies to selectively generate cytotoxic nucleoside or nucleotide analogs is an attractive goal. One such approach involves the delivery of herpes simplex virus thymidine kinase followed by the acyclic nucleoside analog ganciclovir. We have developed another gene therapy methodology for the treatment of cancer that has several significant attributes. Specifically, our approach involves the delivery of E. coli purine nucleoside phosphorylase, followed by treatment with a relatively non-toxic nucleoside prodrug that is cleaved by the enzyme to a toxic compound. This presentation describes the concept, details our search for suitable prodrugs, and summarizes the current biological data.

Differential susceptibility of primary and established human glioma cells to adenovirus infection: targeting via the epidermal growth factor receptor achieves fiber receptor-independent gene transfer

Adenovirus (Ad) vectors are promising for gene therapy of glioma due to their ability to achieve efficient gene transfer upon intratumoral administration. Yet in this context, Ad mediates widespread gene transfer to both tumor and surrounding parenchyma. Ad entry is dependent upon the expression of fiber receptors, such as coxsackie/adenovirus receptor, and alpha(v) integrins on the target cells for binding and internalization, respectively. We hypothesized that the susceptibility of human gliomas to Ad would likely be heterogeneous due to variable expression of these receptors. It was found that established human glioma cell lines exhibited differential susceptibility to Ad-mediated gene transfer, which correlated directly with the level of radiolabeled Ad binding and with the expression of coxsackie/adenovirus receptor but not with the expression of alpha(v) integrins. To circumvent the lack of fiber receptors and to target Ad gene transfer specifically to tumor cells, we used a bispecific antibody conjugate to ablate Ad binding to fiber receptors and retarget binding to the epidermal growth factor receptor (EGFR), a tumor-associated marker negligibly expressed in normal, mitotically quiescent neural tissues. The results demonstrate that EGFR-targeted Ad gene transfer was EGFR specific and independent of fiber-fiber receptor interactions. Furthermore, EGFR targeting significantly enhanced Ad gene delivery to 7 of 12 established glioma cell lines and to 6 of 8 cultured primary gliomas. Interestingly, EGFR-targeted Ad gene transfer did not correlate with EGFR expression across cell lines, suggesting the importance of other factors. This study establishes that fiber receptor expression limits the utility of Ad vectors for gene transfer to glioma cells and suggests that targeting Ad via EGFR may prove valuable for tumor-specific gene transfer to high-grade gliomas. These findings have key relevance in the context of Ad vector-based approaches for glioma gene therapy.

Paracrine expression of a native soluble vascular endothelial growth factor receptor inhibits tumor growth, metastasis, and mortality rate

Vascular endothelial growth factor (VEGF) is a potent and selective vascular endothelial cell mitogen and angiogenic factor. VEGF expression is elevated in a wide variety of solid tumors and is thought to support their growth by enhancing tumor neovascularization. To block VEGF-dependent angiogenesis, tumor cells were transfected with cDNA encoding the native soluble FLT-1 (sFLT-1) truncated VEGF receptor which can function both by sequestering VEGF and, in a dominant negative fashion, by forming inactive heterodimers with membrane-spanning VEGF receptors. Transient transfection of HT-1080 human fibrosarcoma cells with a gene encoding sFLT-1 significantly inhibited their implantation and growth in the lungs of nude mice following i.v. injection and their growth as nodules from cells injected s.c. High sFLT-1 expressing stably transfected HT-1080 clones grew even slower as s.c. tumors. Finally, survival was significantly prolonged in mice injected intracranially with human glioblastoma cells stably transfected with the sflt-1 gene. The ability of sFLT-1 protein to inhibit tumor growth is presumably attributable to its paracrine inhibition of tumor angiogenesis in vivo, since it did not affect tumor cell mitogenesis in vitro. These results not only support VEGF receptors as antiangiogenic targets but also demonstrate that sflt-1 gene therapy might be a feasible approach for inhibiting tumor angiogenesis and growth.

Metabolism and metabolic actions of 6-methylpurine and 2-fluoroadenine in human cells

Activation of purine nucleoside analogs by Escherichia coli purine nucleoside phosphorylase (PNP) is being evaluated as a suicide gene therapy strategy for the treatment of cancer. Because the mechanisms of action of two toxic purine bases, 6-methylpurine (MeP) and 2-fluoroadenine (F-Ade), that are generated by this approach are poorly understood, mechanistic studies were initiated to learn how these compounds differ from agents that are being used currently. The concentration of F-Ade, MeP, or 5-fluorouracil required to inhibit CEM cell growth by 50% after a 4-hr incubation was 0.15, 9, or 120 microM, respectively. F-Ade and MeP were also toxic to quiescent MRC-5, CEM, and Balb 3T3 cells. Treatment of CEM, MRC-5, or Balb 3T3 cells with either F-Ade or MeP resulted in the inhibition of protein, RNA, and DNA syntheses. CEM cells converted F-Ade and MeP to F-ATP and MeP-ribonucleoside triphosphate (MeP-R-TP), respectively. The half-life for disappearance of HeP-ribonucleoside triphosphate from CEM cells was approximately 48 hr, whereas the half-lives of F-ATP and ATP were approximately 5 hr. Both MeP and F-Ade were incorporated into the RNA and DNA of CEM cells. These studies indicated that the mechanisms of action of F-Ade and MeP were quite different from those of other anticancer agents, and suggested that the generation of these agents in tumor cells by E. coli PNP could result in significant advantages over those generated by either herpes simplex virus thymidine kinase or E. coli cytosine deaminase. These advantages include a novel mechanism of action resulting in toxicity to nonproliferating and proliferating tumor cells and the high potency of these agents during short-term treatment.

Intracellular expression of a single-chain antibody directed against human papillomavirus type 16 E7 oncoprotein achieves targeted antineoplastic effects

Human papillomavirus type 16 (HPV16) E7 is a viral oncoprotein that is believed to play a major role in cervical neoplasia. Anti-HPV16 E7 intracellular single-chain antibodies (scFvs) were constructed to down-regulate HPV16 E7 oncoprotein in HPV DNA-containing cell lines. In these studies, we transfected anti-E7 scFvs into the HPV16-positive human cervical carcinoma cell lines CaSki and SiHa and tested them for their ability to inhibit cell proliferation and alter the level of HPV16 E7 oncoprotein. Our results showed that anti-HPV16 E7 scFvs inhibited cell proliferation by >85% in CaSki cells and by 95% in SiHa cells. E7 oncoprotein was down-regulated by anti-HPV16 E7 scFv, and its expression was inversely related to the amount of scFv transfected. However, there were no effects of transfecting scFvs alone in HPV-negative cell lines. These results imply that anti-HPV16 E7 scFvs only have specific anti-HPV16 E7 effects on cell proliferation and on the synthesis of virally encoded proteins in HPV-positive cell lines. Thus, transfection of HPV16 E7-positive tumors with antigen-specific scFvs may be a viable strategy for cervical cancer gene therapy.