Zeng B. Zhu

Mesenchymal stem cells as a vehicle for targeted delivery of CRAds to lung metastases of breast carcinoma

PurposeAlternative and complementary therapeutic strategies need to be developed for metastatic breast cancer. Virotherapy is a novel therapeutic approach for the treatment of cancer in which the replicating virus itself is the anticancer agent. However, the success of virotherapy has been limited due to inefficient virus delivery to the tumor site. The present study addresses the utility of human mesenchymal stem cells (hMSCs) as intermediate carriers for conditionally replicating adenoviruses (CRAds) to target metastatic breast cancer in vivo.Experimental designHMSC were transduced with CRAds. We used a SCID mouse xenograft model to examine the effects of systemically injected CRAd loaded hMSC or CRAd alone on the growth of MDA-MB-231 derived pulmonary metastases (experimental metastases model) in vivo and on overall survival.ResultsIntravenous injection of CRAd loaded hMSCs into mice with established MDA-MB-231 pulmonary metastatic disease homed to the tumor site and led to extended mouse survival compared to mice treated with CRAd alone.ConclusionInjected hMSCs transduced with CRAds suppressed the growth of pulmonary metastases, presumably through viral amplification in the hMSCs. Thus, hMSCs may be an effective platform for the targeted delivery of CRAds to distant cancer sites such as metastatic breast cancer.

Transcriptional targeting of tumors with a novel tumor-specific survivin promoter

It has been demonstrated that survivin, a novel member of the inhibitor of apoptosis (IAP) protein family, is expressed in human cancers but is undetectable in normal differentiated tissues. We employed a recombinant adenoviral vector (reAdGL3BSurvivin) in which a tumor-specific survivin promoter and a luciferase reporter gene were inserted into the E1-deleted region of adenovirus vector. Luciferase activity was measured in both multiple tumor cell lines and two primary melanoma cells infected with reAdGL3BSurvivin. Human fibroblast and mammary epithelial cell lines were used as negative controls. A reAdGL3CMV, containing the CMV promoter and luciferase gene, was used as a positive control to normalize the luciferase activity generated by the survivin promoter. Our data revealed that the survivin promoter showed high activity in both established tumor cell lines and the primary melanoma cells. In contrast, the in vivo studies indicated that the activities of survivin promoter were extremely low in the major mouse organs. The survivin promoter appears to be a promising tumor-specific promoter exhibiting a “tumor on” and “liver off” profile, and therefore, it may prove to be a good candidate for transcriptional targeting of cancer gene therapy in a wide variety of tumors.

Low-Dose Radiation Enhances Survivin-Mediated Virotherapy against Malignant Glioma Stem Cells

To improve the efficacy and selectivity of virotherapy for malignant glioma, we designed a strategy to amplify adenoviral replication in conjunction with radiotherapy using a radioinducible promoter. First, we compared the radiation-inducible activity of FLT-1, vascular endothelial growth factor, DR5, Cox2, and survivin. We then examined the capacity of the optimal promoter to modulate transgene expression followed by E1A activity in vitro and in vivo in a glioma stem cell model. In the presence of radiation, survivin mRNA activity increased 10-fold. Luciferase transgene expression was dose dependent and optimal at 2 Gy. A novel oncolytic adenovirus, CRAd-Survivin-pk7, showed significant toxicity and replication against a panel of passaged and primary CD133(+) glioma stem cells. On delivery of radiation, the toxicity associated with CRAd-Survivin-pk7 increased by 20% to 50% (P < 0.05). At the same time, the level of E1A activity increased 3- to 10-fold. In vivo, treatment of U373MG CD133(+) stem cells with CRAd-Survivin-pk7 and radiation significantly inhibited tumor growth (P < 0.05). At the same time, the level of E1A activity was 100-fold increased versus CRAd-Survivin-pk7 alone. Selected genes linked to radioinducible promoters whose expression can be regulated by ionizing radiation may improve the therapeutic ratio of virotherapy. In this study, we have identified a new radioinducible promoter, survivin, which greatly enhances the activity of an oncolytic adenovirus in the presence of low-dose radiotherapy.

Fiber‐knob modifications enhance adenoviral tropism and gene transfer in malignant glioma

Malignant gliomas remain refractory to Ad5‐mediated gene therapy due to deficiency of the coxsackie adenovirus receptor on tumor cells. The purpose of this study was to evaluate whether changes in adenoviral tropism can enhance gene transfer in the context of malignant glioma.

Comparative evaluation of survivin, midkine, and CXCR4 promoters for transcriptional targeting of glioma gene therapy

Objective: Transcriptional targeting is a key strategy to enhance therapeutic efficacy of gene therapy applications. In the context of oncolytic virotherapy, transcriptional promoter elements are used from genes that are over expressed in a variety of malignant cancers. In the present study, we examined the feasibility of transcriptional targeting to glioma cells by comparing the activity of survivin, midkine, and CXCR4 tumor-specific promoters. Methods: To evaluate the expression level of several glioma related genes, we performed quantitative PCR analyses on samples obtained from cell lines and patients. To determine specific level of gene expression mediated by selective promoter elements, we measured luciferase expression in glioma samples transduced with replication deficient adenoviral vectors. Finally, we incorporated the optimal promoters into a conditionally replicative adenoviral vector, CRAd-5/3, and examined the cytopathic effect in vitro. Results: The survivin promoter demonstrated the highest level of mRNA expression in primary tumor samples and cell lines. Transcriptional targeting was confirmed by infection of glioma cells with an adenovirus expression vector containing a survivin-driven luciferase reporter gene. Of the tested promoters, minimal level of survivin activity was detected in normal human liver and brain. A novel vector, CRAd-5/3, with E1a under the control of the survivin promoter, exhibited enhanced cytopathic effect in vitro. Conclusions: Our data demonstrate that the survivin promoter element is very active in glioma samples and has low activity in normal human brain and liver. A novel oncolytic virus, CRAd-survivin-5/3, was effective against a panel of glioma cell lines in vitro. Our results suggest that employing the survivin promoter element in the context of CRAd-5/3 may present a new opportunity for the development of glioma specific oncolytic vectors.

Gene transfer to carcinoma of the breast with fiber-modified adenoviral vectors in a tissue slice model system

Successful adenoviral (Ad) vector-mediated strategies for breast cancer gene therapy and virotherapy have heretofore been hindered by low transduction efficiency. This has recently been understood to result from a relative paucity of expression of the primary adenovirus receptor, coxsackie-adenovirus-receptor (CAR), on primary tumor cells. To further investigate this issue, we evaluated the expression of CAR on breast cancer cell lines as well as primary breast cancer cells. With the exception of one patient sample, CAR expression was notably higher in the tumor cells from patients compared to CAR expression in the tumor cell lines. Furthermore, we explored CAR-independent targeting strategies to breast cancer tissue by exploring a panel of infectivity-enhanced Ad vectors, which contain CAR-independent targeting motifs for their utility in breast cancer gene therapy and virotherapy. These targeting motifs included Ad 3 knob (Ad5/3), canine Ad serotype 2 knob (Ad5CAV-2), RGD (Ad5.RGD), polylysine (Ad5.pK7), or both RGD and polylysine (Ad5.RGD.pK7), and were tested using the breast cancer tissue slice model, which is the most stringent substrate system available. Of all the tested tropism modified Ad vectors, Ad5/3 exhibited the highest transductional efficiency in breast cancer. These preclinical results suggest that Ad5/3 is the most useful modification to achieve higher clinical efficacy of breast cancer gene therapy and virotherapy.

Targeting Mesothelioma Using an Infectivity Enhanced Survivin-Conditionally Replicative Adenoviruses

Mesothelioma is a highly malignant neoplasm with no effective treatment. Conditionally replicative adenoviruses (CRAds) represent a promising new modality for the treatment of cancer in general. A key contribution in this regard is the introduction of tumor-selective viral replication for amplification of the initial inoculum in the neoplastic cell population. Under ideal conditions following cellular infection, the viruses replicate selectively in the infected tumor cells and kill the cells by cytolysis, leaving normal cells unaffected. However, to date there have been two limitations to clinical application of these CRAd agents; viral infectivity and tumor specificity have been poor. Herein we report on two CRAd agents, CRAd-S.RGD and CRAd-S.F5/3, in which the tumor specificity is regulated by a tumor-specific promoter, the survivin promoter, and the viral infectivity is enhanced by incorporating a capsid modification (RGD or F5/3) in the adenovirus fiber region. These CRAd agents effectively target human mesothelioma cell lines, induce strong cytoxicity in these cells in vitro, and viral replication in a H226 murine xenograft model in vivo. In addition, the survivin promoter has extremely low activity both in the non-transformed cell line, HMEC, and in human liver tissue. Our results suggest that the survivin-based CRAds are promising agents for targeting mesothelioma with low host toxicity. These agents should provide important insights into the identification of novel therapeutic strategies for mesothelioma.

Characterization of infectivity of knob-modified adenoviral vectors in glioma

Malignant gliomas have been a major target for gene therapy and virotherapy, because of their current lack of effective treatment. These approaches remain hampered by lack of significant infectivity of glioma cells by viral vectors, in particular for vectors derived from serotype 5 adenoviruses (Ad5). This has been shown to result from a relative paucity of cell surface expression of the native adenovirus receptor, coxsackie-adenovirus-receptor (CAR), on primary tumor cells. Thus, targeting strategies applying adenovirus capsid modifications to enhance viral infectivity via CAR-independent pathways have been developed. All these capsid modifications (such as RGD, polylysine fiber modification……) have previously been shown to enhance viral infectivity (to different levels) in a variety of tumor types, including human glioma. Recently, we extended these infectivity enhancements to the development of “xenotype” knobs, whereby canine adenovirus types 1 and 2 knobs were switched with adenovirus type 5 knob to achieve enhanced transduction in low-CAR containing human tumors. In this study, we tested human adenoviral vectors that carry a luciferase reporter gene (driven by the CMV promoter) with five different xenotype Ad knobs, including those derived from murine, ovine, porcine and canine species, in four human glioma cell lines (U87MG, U118MG, U251MG and D65MG) and in primary glioma tumor cells from four different patients. Adenovirus vectors carrying either canine type 1 or porcine knob had the highest luciferase levels in both tumor cell lines and primary tumor cells. The correlation between the viral infectivity of modified adenovirus vectors and expression of human CAR and CD46 (an adenovirus type B receptor) on the surfaces of tumor cells was also analyzed. Taken together, human adenovirus vectors modified with either canine type 1 or porcine knob should be excellent candidates to target human glioma as they demonstrate enhanced viral infectivity at the transductional level.

The natural history of a novel, systemic, disseminated model of syngeneic mouse B-cell lymphoma.

Lymphomas and leukemias, neoplasms of hematopoetic lineage, pose unique challenges that require novel treatment paradigms. The inter-relationship between the immune system and the neoplastic lesion in these diseases dictates that, to evaluate novel therapies, models are needed that mimic human disease in an immunocompetent host. In the present study, we describe a disseminated, syngeneic model of B-cell lymphoma in the Balb/c mouse based upon the A20 cell line. This model mimics aspects of diffuse large B-cell lymphomas in humans, and recapitulates para-spinous tumor growth, bone destruction and nerve root compression, which may complicate disseminated disease. Furthermore, this tumor expresses a key marker of interest, CD40, which is a candidate for tumor-specific vector targeting via current modalities. The present study therefore describes a high-fidelity model of disseminated lymphoma with implications for novel targeted therapeutics. Lymphomas and leukemias, neoplasms of hematopoetic lineage, pose unique challenges that require novel treatment paradigms. The inter-relationship between the immune system and the neoplastic lesion in these diseases dictates that, to evaluate novel therapies, models are needed that mimic human disease in an immunocompetent host. In the present study, we describe a disseminated, syngeneic model of B-cell lymphoma in the Balb/c mouse based upon the A20 cell line. This model mimics aspects of diffuse large B-cell lymphomas in humans, and recapitulates para-spinous tumor growth, bone destruction and nerve root compression, which may complicate disseminated disease. Furthermore, this tumor expresses a key marker of interest, CD40, which is a candidate for tumor-specific vector targeting via current modalities. The present study therefore describes a high-fidelity model of disseminated lymphoma with implications for novel targeted therapeutics.

Novel infectivity-enhanced oncolytic adenovirus With a capsid-incorporated dual-imaging moiety for monitoring virotherapy in ovarian cancer

We sought to develop a cancer-targeted, infectivity-enhanced oncolytic adenovirus that embodies a capsid-labeling fusion for non-invasive dual-modality imaging of ovarian cancer virotherapy. A functional fusion protein composed of fluorescent and nuclear imaging tags was genetically incorporated into the capsid of an infectivity-enhanced conditionally replicative adenovirus. Incorporation of herpes simplex virus thymidine kinase (HSV-tk) and monomeric red fluorescent protein 1 (mRFP1) into the viral capsid and its genomic stability were verified by molecular analyses. Replication and oncolysis were evaluated in ovarian cancer cells. Fusion functionality was confirmed by in vitro gamma camera and fluorescent microscopy imaging. Comparison of tk-mRFP virus to single-modality controls revealed similar replication efficiency and oncolytic potency. Molecular fusion did not abolish enzymatic activity of HSV-tk as the virus effectively phosphorylated thymidine both ex vivo and in vitro. In vitro fluorescence imaging demonstrated a strong correlation between the intensity of fluorescent signal and cytopathic effect in infected ovarian cancer cells, suggesting that fluorescence can be used to monitor viral replication. We have in vitro validated a new infectivity-enhanced oncolytic adenovirus with a dual-imaging modality-labeled capsid, optimized for ovarian cancer virotherapy. The new agent could provide incremental gains toward climbing the barriers for achieving conditionally replicated adenovirus efficacy in human trials.