Nakamura, Takafumi

Abstract Effective cancer therapy with a minimum of undesired side effects in multiple myeloma (MM) requires specifity of the therapeutic agent against the neoplastic cells. One approach to reach this aim is virotherapy using oncolytic measles virus. Attenuated replication-competent Edmonston lineage strains of measles virus (MV-Edm) have proven anti-tumor activity against xenograft models of human multiple myeloma, ovarian cancer, lymphoma and glioma. The virus is selectively oncolytic, causing extensive lethal cell to cell fusion via CD46, which is more highly expressed on tumor cells than on normal cells. However, MV-Edm retains the capacity to infect a variety of nontransformed cell types via its native receptors, CD46 and SLAM which are present on many different cell types. One approach to avoid this risk is to engineer the viral attachment protein to ablate its natural tropisms and at the same time, redirect its specificity to interact with alternative tumor specific receptors. The native measles Hemagglutinin (H) protein recognizes CD46 or SLAM resulting in membrane fusion and syncytia formation of cells. In this work the H protein was engineered to restrict and retarget membrane fusion through the display of a single-chain antibody (scFv) recognizing the Wue-1-antigen known to be highly specific for MM cells and abrogation of native measles binding domains for CD46 and SLAM by mutation. This modified H protein (chimeric H) was cloned in a full-length viral backbone including EGFP enabling to detect infected cells and syncytia formation under the UV light emitting green fluorescence (EGFP). On the basis of the parental measles virus expressing EGFP (MV-GFP) two different viruses were generated: non-ablated virus expressing the chimeric H protein including the scFv Wue-1 still competent to infect cells expressing CD46 and SLAM (MV-W1) with the chimeric H protein but ablated for the interactions with CD46 and SLAM (MV-W2). The genetically modified viruses propagated as recently described (Nat. Biotech., Vol.23, Nr.2, Feb.2005, pp.209–214.). To determine if the fully retargeted MV-Edm would be able to infect MM cell lines selectively a first array of infection assays was performed using the MM cell lines RPMI 8226 and ARH-77 expressing the Wue-1 antigen as expected targets and K562 and healthy CD40L activated CD19 positive B cells as controls. 24 to 96 hours after infection with MV-GFP, MV-W1 and MV-W2 we observed syncytia formation and expression of EGFP with MV-GFP and MV-W1 in all cells indicating that the modification of the virus with the scFv-Wue-1 doesn’t alter the potential to infect and kill cells compared to the parental virus. In contrast MV-W2 was able to form only EGFP positive plaques with the Wue-1 antigen positive cells RPMI 8226 and ARH-77 but did not infect K562 or CD19 positve B cells both negative for Wue-1 antigen. These results indicate that the measles virus vaccine strain Edmonston B can be modified to express a scFv recognizing the Wue-1 antigen. In addition the native H protein can be mutated resulting in ablation of the natural tropism towards CD46 and SLAM positive cells. Viruses with these modifications can be rescued and propagated in vitro and selectively infected Multiple Myeloma cells without causing damage to normal B-cell progenitors.

Abstract Multiple Myeloma (MM) is a disseminated plasma cell malignancy with approximately 14,600 new cases diagnosed in the USA annually. Despite recent progress in current therapeutical options the median survival is 3 to 5 years and cure is extremely rare. Therefore the evaluation of new treatment modalities for MM is highly warranted. An attractive approach to treat Myeloma with a minimum of undesired side effects is the use of a tumour antigen specific for MM cells. Wue-1, a monoclonal antibody binds very selectively normal and malignant plasma cells (50 of 51 MM samples, 14 of 15 immunocytoma and 13 of 13 MALT type lymphomas with plasma cell differentiation were Wue-1 positive, normal tissue including hematopoietic cells were negative) and offers the possibility to define MM cells as targets. The tool for selective killing of MM cells recognized by Wue-1 monoclonal antibody is in this study the measles virus vaccine strain Edmonston B in an ablated variant (MV-Wue) which no longer binds the usual measles receptors CD46 and CD150 (SLAM) expressed on almost every human cell type displaying a single-chain antibody (scFv) derived from the monoclonal Wue-1-antibody which has been tethered to the C-terminus of the H protein to restrict and retarget its interaction to malignant plasma cells especially MM cells. In addition, MV-Wue encodes EGFP facilitating the read out of infected cells. To determine if the fully retargeted MV-Wue would be able to infect MM cell lines and primary MM cells selectively an array of infection assays were performed using the MM cell lines U266 as well as primary CD138 positive MM cells expressing the Wue-1 antigen as expected targets and CD138 negative cells and normal B cells as controls negative for Wue-1. In these experiments selective infections of the MM cell line and primary MM cells were observed whereas the control cells were not infected with MV-Wue. In all cell types GFP expression indicating replicative infection correlated with the expression of the Wue-1 antigen determined by FACS. Infection experiments performed in the presence of monoclonal Wue-1 antibody showed a decreased GFP expression of about 78% in CD138 positive MM cells demonstrating specificity of the infection by MV-Wue. These results indicate that the engineered virus can be a safe and potential curative oncolytic agent to face the main problem in Multiple Myeloma which is responsible for frequent relapses, the minimal residual disease (MRD).

The applicability of cytoreductive treatment of malignant diseases using recombinant viruses strongly depends on specific recognition of surface receptors to target exclusively neoplastic cells. A recently generated monoclonal antibody (mAb), Wue-1, specifically detects CD138+ multiple myeloma (MM) cells. In this study, a haemagglutinin (H) protein that was receptor-blinded (i.e. did not bind to CD46 and CD150) was genetically re-engineered by fusing it to a single-chain antibody fragment (scFv) derived from the Wue-1 mAb open reading frame (scFv-Wue), resulting in the recombinant retargeted measles virus (MV)-Wue. MV-Wue efficiently targeted and fully replicated in primary MM cells, reaching titres similar to those seen with non-retargeted viruses. In agreement with its altered receptor specificity, infection of target cells was no longer dependent on CD150 or CD46, but was restricted to cells that had been labelled with Wue-1 mAb. Importantly, infection with MV-Wue rapidly induced apoptosis in CD138+ malignant plasma cell targets. MV-Wue is the first fully retargeted MV using the restricted interaction between Wue-1 mAb and primary MM cells specifically to infect, replicate in and deplete malignant plasma cells.

Abstract Oncolytic measles virus (MV) induces cell fusion and cytotoxicity in a CD46-dependent manner. Development of fully retargeted oncolytic MVs would improve tumor selectivity. The urokinase-type plasminogen activator receptor (uPAR) is a tumor and stromal target overexpressed in multiple malignancies. MV-H glycoproteins fully retargeted to either human or murine uPAR were engineered and their fusogenic activity was determined. Recombinant human (MV-h-uPA) and murine (MV-m-uPA) uPAR–retargeted MVs expressing enhanced green fluorescent protein (eGFP) were rescued and characterized. Viral expression of chimeric MV-H was shown by reverse transcription-PCR and Western blot. In vitro viral replication was comparable to MV-GFP control. The receptor and species specificity of MV-uPAs was shown in human and murine cells with different levels of uPAR expression. Removal of the NH2-terminal fragment ligand from MV-uPA by factor X(a) treatment ablated the MV-uPA functional activity. Cytotoxicity was shown in uPAR-expressing human and murine cells. MV-h-uPA efficiently infected human endothelial cells and capillary tubes in vitro. I.v. administration of MV-h-uPA delayed tumor growth and prolonged survival in the MDA-MB-231 breast cancer xenograft model. Viral tumor targeting was confirmed by immunohistochemistry. MV-m-uPA transduced murine mammary tumors (4T1) in vivo after intratumor administration. MV-m-uPA targeted murine tumor vasculature after systemic administration, as shown by dual (CD31 and MV-N) staining of tumor capillaries in the MDA-MB-231 model. In conclusion, MV-uPA is a novel oncolytic MV associated with potent and specific antitumor effects and tumor vascular targeting. This is the first retargeted oncolytic MV able to replicate in murine cells and target tumor vasculature in a uPAR-dependent manner. [Cancer Res 2009;69(4):1459–68]

ABSTRACT Enveloped viruses trigger membrane fusion to gain entry into cells. The receptor affinities of their attachment proteins vary greatly, from 10 −4 M to 10 −9 M, but the significance of this is unknown. Using six retargeted measles viruses that bind to Her-2/neu with a 5-log range in affinity, we show that receptor affinity has little impact on viral attachment but is nevertheless a key determinant of infectivity and intercellular fusion. For a given cell surface receptor density, there is an affinity threshold above which cell-cell fusion proceeds efficiently. Suprathreshold affinities do not further enhance the efficiency of membrane fusion.

Abstract Among the best-characterized genetic alterations in gliomas is the amplification of the epidermal growth factor receptor (EGFR) gene, present in ∼40% of glioblastoma multiforme, and frequently associated with the EGFRvIII gene rearrangement. We have previously shown that attenuated vaccine strains of measles virus have potent antitumor activity against gliomas, and identified H protein mutations, which ablate recognition of the natural measles virus receptors CD46 and SLAM. Retargeted recombinant viruses were generated from the measles Edmonston-NSe vaccine strain displaying a single-chain antibody against EGFRvIII at the COOH terminus of H and containing the marker green fluorescent protein (GFP) gene in position 1. Two different H mutants were employed: HSNS (V451S, Y481N, and A527S)-CD46 blind, and HAA (Y481A and R533A)-CD46 and SLAM blind. MV-GFP virus was used as a positive control. Both EGFRvIII-retargeted viruses had significant antitumor activity against EGFRvIII-expressing glioblastoma multiforme but no cytopathic effect against normal cells. In an orthotopic model of EGFRvIII-expressing GBM39 xenografts, there was comparable therapeutic efficacy between retargeted strains and unmodified MV-GFP and statistically significant prolongation of survival in treated animals compared with the control group (P = 0.001). Formation of syncytia was observed in tumors treated with retargeted viruses, with a surrounding infiltrate consisting of macrophages and natural killer cells. In summary, EGFRvIII-retargeted oncolytic measles virus strains have comparable therapeutic efficacy with the unmodified MV-GFP strain against EGFRvIII-expressing glioma lines and xenografts with improved therapeutic index, a finding with potential translational implications in glioma virotherapy. (Cancer Res 2006; 66(24): 11840-50)

Abstract Purpose: Attenuated measles viruses are promising experimental anticancer agents currently being evaluated in a phase I dose escalation trial for ovarian cancer patients. Virus attachment, entry, and subsequent intercellular fusion between infected and uninfected neighboring cells are mediated via the two measles receptors (CD46 and SLAM). To minimize potential toxicity due to measles virus–associated immunosuppression and infection of nontarget tissues, we sought to develop an ovarian cancer exclusive fully retargeted measles virus. Experimental Design and Results: Interactions of measles virus with its natural receptors were ablated, and a single-chain antibody (scFv) specific for α-folate receptor (FRα), a target overexpressed on 90% of nonmucinous ovarian cancer, was genetically engineered on the viral attachment protein (MV-αFR). Specificity of virus tropism was tested on tumor and normal cells. Biodistribution of measles virus infection was evaluated in measles-susceptible CD46 transgenic mice, whereas antitumor activity was monitored noninvasively by bioluminescence imaging in xenograft models. Tropism and fusogenic activity of MV-αFR was redirected exclusively to FRα without compromise to virus infectivity. In contrast to the parental virus, MV-αFR has no background infectivity on normal human cells. The antitumor activity of MV-αFR, as assessed by tumor volume reduction and overall survival increase, was equal to the parental virus in two models of human ovarian cancer (s.c. and i.p.). Conclusions: A FR-exclusive ovarian cancer targeted oncolytic virus was generated and shown to be therapeutically effective, thus introducing a new modality for FR targeting and a candidate measles virus for clinical testing.

AbstractLive attenuated Edmonston B strain of measles virus (MV-Edm) is a potent and specific oncolytic agent, but the mechanism underlying its tumor selectivity is unknown. The virus causes cytopathic effects (CPEs) of extensive syncytial formation in tumor cells but minimal damage or cell killing in normal cells. The CPE is dependent on expression of viral proteins and the presence of CD46, the major cellular receptor of MV-Edm. Using a virally encoded soluble marker peptide to provide a quantitative readout of the level of viral gene expression, we determined that tumor cells and normal cells expressed comparable levels of viral proteins. CD46 mediates virus attachment, entry, and virus-induced cell-to-cell fusion. Using engineered cells expressing a range of CD46 densities, we determined that whereas virus entry increased progressively with CD46 density, cell fusion was minimal at low receptor densities but increased dramatically above a threshold density of CD46 receptors. It is well established that tumor cells express abundant CD46 receptors on their surfaces compared with their normal counterparts. Thus, at low CD46 densities typical of normal cells, infection occurs, but intercellular fusion is negligible. At higher densities typical of tumor cells, infection leads to extensive cell fusion. Intercellular fusion also results in enhancement of viral gene expression through recruitment of neighboring uninfected cells into the syncytium, further amplifying the CPE. Discrimination between high and low CD46 receptor density provides a compelling basis for the oncolytic specificity of MV-Edm and establishes MV-Edm as a promising CD46-targeted cancer therapeutic agent.