Tumor-specific targeting with modified Sindbis viral vectors: evaluation with optical imaging and positron emission tomography in vivo.

PURPOSE: Sindbis virus (SINV) infect tumor cells specifically and systemically throughout the body. Sindbis vectors are capable of expressing high levels of transduced suicide genes and thus efficiently produce enzymes for prodrug conversion in infected tumor cells. The ability to monitor suicide gene expression levels and viral load in patients, after administration of the vectors, would significantly enhance this tumor-specific therapeutic option. PROCEDURES: The tumor specificity of SINV is mediated by the 67-kDa laminin receptor (LR). We probed different cancer cell lines for their LR expression and, to determine the specific role of LR-expression in the infection cycle, used different molecular imaging strategies, such as bioluminescence, fluorescence molecular tomography, and positron emission tomography, to evaluate SINV-mediated infection in vitro and in vivo. RESULTS: All cancer cell lines showed a marked expression of LR. The infection rates of the SINV particles, however, differed significantly among the cell lines. CONCLUSION: We used novel molecular imaging techniques to visualize vector delivery to different neoplatic cells. SINV infection rates proofed to be not solely dependent on cellular LR expression. Further studies need to evaluate the herein discussed ways of cellular infection and viral replication.

Tumor-specific in vivo transfection with HSV-1 thymidine kinase gene using a Sindbis viral vector as a basis for prodrug ganciclovir activation and PET.

UNLABELLED: One type of gene therapy of tumors, gene-directed enzyme-prodrug therapy (GDEPT), holds considerable promise, although practical considerations limit its clinical applicability. These include the lack of acceptable noninvasive methods that are adaptable to humans for selective tumor targeting of the therapeutic genetic material. Sindbis virus is an oncolytic, alpha-virus that selectively targets tumors through the 67-kDa laminin receptor (LAMR). In this report we describe a novel approach that permits tumor-selective tumor targeting and quantitative in vivo monitoring using PET of a commonly applied GDEPT, based on herpes simplex virus thymidine kinase type 1 (HSVtk) and ganciclovir (GCV). METHODS: Sindbis/tk vectors were harvested from the supernatant of in vitro cultures of a packaging cell produced by electroporation of both replicon RNA (SinRep5/tk) and helper RNA (DH-BB) into baby hamster kidney (BHK) cells. The therapeutic effect of GCV was determined by incubation of transfected tumor cells with increasing concentrations of GCV. BHK tumors growing as xenografts in severe combined immunodeficiency disease (SCID) mice were transfected by parenteral administration of the vector. Imaging was performed using small-animal PET at 2 h after injection of 18F fluoro-ethyl-arabinosyluridine (18F-FEAU) and 24 h after the final parenteral injection of Sindbis/tk viral vector. RESULTS: The vector efficiently expresses the HSVtk enzyme in infected tumor cells, both in vitro and in vivo. High levels of HSVtk expression ensure sufficient prodrug GCV conversion and activation for bystander effects that kill the surrounding untransduced tumor cells. Tumor localization of intravenously administered 18F-FEAU after 2 and 3 parenteral vector treatments of Sindbis/tk demonstrated uptake of 1.7 and 3.1 %ID/g (percentage injected dose per gram), respectively. CONCLUSION: The vector efficiently targets the HSVtk enzyme gene into Sindbis-infected tumor cells. High levels of HSVtk expression ensure sufficient prodrug GCV conversion and activation for bystander effects that killed many surrounding untransduced tumor cells. In addition, the HSVtk activities in tumors can be noninvasively monitored using PET after systemic Sindbis/tk treatments as a basis for determining the levels and tissue distribution of vector, noninvasively in living animals, and for optimizing in vivo transfection rates of tumor.

Identification of amino acids of Sindbis virus E2 protein involved in targeting tumor metastases in vivo.

Previous studies conducted in our laboratory with Sindbis viral vectors in animal models demonstrated excellent in vivo targeting of tumor cells and significant reduction of metastatic implant size. To explore the influence of Sindbis strain on these factors, we constructed new plasmids from the wild-type Ar-339 Sindbis virus strain and compared their sequences. We found differences in the replicase and envelope proteins between JT, HRSP, and Ar-339 sequences. We made chimeras combining both strains and studied their efficiency in SCID mice bearing tumor xenograft using IVIS in vivo imaging techniques. We found that JT envelope proteins targeted tumors more efficiently than those of Ar-339, while the Ar-339 replicase showed increased efficacy in tumor reduction. To determine which residues are responsible for tumor targeting, we made mutants of Ar-339 E2 envelope protein and tested them by IVIS imaging in ES-2 tumor-bearing and tumor-free mice. The change of only one amino acid from E70 to K70 in Ar-339 E2 suppressed the ability to target metastatic tumor implants in mice. A K70 and V251 double E2 mutant did not reverse the loss of targeting capability. Only the mutant with JT E2 and Ar-339 helper targeted tumor, though with less intensity.

Using sindbis viral vectors for specific detection and suppression of advanced ovarian cancer in animal models.

We studied the therapeutic value of Sindbis vectors for advanced metastatic ovarian cancer by using two highly reproducible and clinically accurate mouse models: a SCID xenograft model, established by i.p. inoculation of human ES-2 ovarian cancer cells, and a syngenic C57BL/6 model, established by i.p. inoculation of mouse MOSEC ovarian cancer cells. We demonstrate through imaging, histologic, and molecular data that Sindbis vectors systemically and specifically infect/detect and kill metastasized tumors in the peritoneal cavity, leading to significant suppression of the carcinomatosis in both animal models. Use of two different bioluminescent genetic markers for the IVIS Imaging System permitted demonstration, for the first time, of an excellent correlation between vector delivery and metastatic locations in vivo. Sindbis vector infection and growth suppression of murine MOSEC tumor cells indicate that Sindbis tumor specificity is not attributable to a species difference between human tumor and mouse normal cells. Sindbis virus is known to infect mammalian cells using the Mr 67,000 laminin receptor. Immunohistochemical staining of tumor cells indicates that laminin receptor is elevated in tumor versus normal cells. Down-regulated expression of laminin receptor with small interfering RNA significantly reduces the infectivity of Sindbis vectors. Tumor overexpression of the laminin receptor may explain the specificity and efficacy that Sindbis vectors demonstrate for tumor cells in vivo. We show that incorporation of antitumor cytokine genes such as interleukin-12 and interleukin-15 genes enhances the efficacy of the vector. These results suggest that Sindbis viral vectors may be promising agents for both specific detection and growth suppression of metastatic ovarian cancer.

Systemic tumor targeting and killing by Sindbis viral vectors.

Successful cancer gene therapy requires a vector that systemically and specifically targets tumor cells throughout the body. Although several vectors have been developed to express cytotoxic genes via tumor-specific promoters or to selectively replicate in tumor cells, most are taken up and expressed by just a few targeted tumor cells. By contrast, we show here that blood-borne Sindbis viral vectors systemically and specifically infect tumor cells. A single intraperitoneal treatment allows the vectors to target most tumor cells, as demonstrated by immunohistochemistry, without infecting normal cells. Further, Sindbis infection is sufficient to induce complete tumor regression. We demonstrate systemic vector targeting of tumors growing subcutaneously, intrapancreatically, intraperitoneally and in the lungs. The vectors can also target syngeneic and spontaneous tumors in immune-competent mice. We document the anti-tumor specificity of a vector that systemically targets and eradicates tumor cells throughout the body without adverse effects.

In vivo antitumor activity of Sindbis viral vectors.

BACKGROUND: Sindbis virus, a blood-borne virus transmitted by mosquitoes, has been used as a vector to efficiently express exogenous genes in vitro and in vivo and to induce apoptosis. Because Sindbis virus infects mammalian cells by interacting with the high-affinity laminin receptors, which are expressed at higher levels in several human cancers than in normal cells, we determined whether a Sindbis viral vector could be used to target cancers in vivo. METHODS: C.B-17-SCID mice with established xenografts were given daily intraperitoneal injections of the Sindbis viral vector SinRep/LacZ containing the bacterial beta-galactosidase gene. Control mice were untreated or received injections with phosphate-buffered saline. Tumor size was measured daily. Expression of beta-galactosidase and Factor VIII (a marker for endothelial cells) was determined by immunohistochemical staining of tumor sections. Apoptosis was analyzed by TUNEL (terminal deoxynucleotidyl transferase [TdT]-mediated dUTP nick end labeling) staining. C.B-17-SCID beige mice, which lack natural killer (NK) cells, were used to assess the importance of NK cells in antitumor efficacy of Sindbis viral vectors. RESULTS: Tumors from mice treated with SinRep/LacZ were statistically significantly smaller than tumors from control mice. This effect was observed for tumor xenografts derived from BHK (kidney, hamster), LS174T (colon, human), HT29 (colon, human), and CFPAC (pancreas, human) cells. Expression of beta-galactosidase co-localized with that of Factor VIII in tumor sections. Tumors from SinRep/LacZ-treated mice contained more apoptotic cells than tumors from control mice. Complete tumor regression was observed in three of five C.B-17-SCID mice but in none of five C.B-17-SCID beige mice treated with SinRep/LacZ. CONCLUSION: Sindbis viral vectors efficiently targeted tumors in vivo, were apparently delivered through the circulation, and were more effective in the presence of NK cells.